gambit user guide

GAMBIT 2

Modeling Guide

Volume 1

December 2001

Licensee acknowledges that use of Fluent, Inc.’s products can only provide an imprecise estimation of possible future performance and that additional testing and analysis, independent of the Licensor’s products, must be conducted before any product can be finally developed or commercially introduced. As a result, Licensee agrees that it will not rely upon the results of any usage of Fluent, Inc.’s products in determining the final design, composition, or structure of any product.

© 2001 by Fluent, Incorporated

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GAMBIT Modeling Guide—Chapters

Volume Chapter Title

u 1 1 INTRODUCTION

2 CREATING THE GEOMETRY

2 3 MESHING THE MODEL

4 SPECIFYING ZONE TYPES

5 USING THE MODELING TOOLS

6 POSTPROCESSING RESULTS

A VIRTUAL GEOMETRY

iv

TABLE OF CONTENTS

1. INTRODUCTION ............................................................................... 1-1 1.1 Format and Font Conventions ......................................................................1-2

1.1.1 Format Conventions ............................................................................. 1-2 Graphic Format ................................................................................. 1-2 Layout Format................................................................................... 1-4

1.1.2 Fonts ................................................................................................... 1-6 1.2 Modeling Guide—Outline..............................................................................1-7

2. CREATING THE GEOMETRY ........................................................ 2-1 2.1 General Operations ........................................................................................2-2

2.1.1 Labeling Entities .................................................................................. 2-2 2.1.2 Specifying Entities ............................................................................... 2-4

Specifying Individual Entities........................................................... 2-4 Specifying Multiple Entities ............................................................. 2-4

2.1.3 Working with Coordinate Systems....................................................... 2-5 Specifying Reference Coordinate Systems ....................................... 2-5 Specifying Coordinate Parameters.................................................... 2-6

2.1.4 Moving, Copying, and Aligning Entities ............................................. 2-7 Moving an Entity .............................................................................. 2-8 Copying an Entity ........................................................................... 2-30 Aligning an Entity........................................................................... 2-33

2.2 Vertex Commands ........................................................................................2-43 2.2.1 Create Vertex ..................................................................................... 2-44

Create Real Vertex.......................................................................... 2-45 Create Vertex On Edge................................................................... 2-46 Create Vertex On Face.................................................................... 2-49 Create Virtual Vertex On Volume .................................................. 2-52 Create Vertices At Edge Intersections ............................................ 2-54

2.2.2 Slide Virtual Vertex ........................................................................... 2-57 Changing the Shape of Virtual Entities .......................................... 2-57 Sliding the Vertex ........................................................................... 2-57 Sliding Linked Vertices .................................................................. 2-57 Using the Slide Virtual Vertex Form.............................................. 2-58

2.2.3 Connect/Disconnect Vertices ............................................................. 2-60 Connect Vertices............................................................................. 2-61 Disconnect About Real Vertex ....................................................... 2-67

2.2.4 Modify Vertex Color/Label................................................................ 2-69 Modify Vertex Color ...................................................................... 2-70 Modify Vertex Label ...................................................................... 2-72

2.2.5 Move/Copy/Align Vertices ................................................................ 2-73 Move/Copy Vertices ....................................................................... 2-74

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Align Vertices ................................................................................. 2-75 2.2.6 Convert Vertices ................................................................................ 2-76

Using the Convert Vertices Form ................................................... 2-76 2.2.7 Summarize/Check/Query Vertices and Total Entities........................ 2-77

Summarize Vertices ........................................................................ 2-78 Check Vertices................................................................................ 2-79 Query Vertices ................................................................................ 2-81 Total Entities................................................................................... 2-83

2.2.8 Delete Vertices ................................................................................... 2-84 Deleting Virtual Vertices ................................................................ 2-84 Using the Delete Vertices Form...................................................... 2-84

2.3 Edge Commands...........................................................................................2-85 2.3.1 Create Edge ........................................................................................ 2-86

Create Straight Edge ....................................................................... 2-87 Create Real Circular Arc................................................................. 2-90 Create Real Full Circle ................................................................... 2-97 Create Real Elliptical Arc ............................................................. 2-100 Create Real Conic Arc .................................................................. 2-103 Create Real Fillet Arc ................................................................... 2-106 Create Real Edge From Vertices................................................... 2-115 Revolve Vertices........................................................................... 2-118 Project Edge On Face ................................................................... 2-120

2.3.2 Connect/Disconnect Edges............................................................... 2-123 Connect Edges .............................................................................. 2-124 Disconnect About Real Edge........................................................ 2-131

2.3.3 Modify Edge Color/Label ................................................................ 2-135 Modify Edge Color ....................................................................... 2-136 Modify Edge Label ....................................................................... 2-137

2.3.4 Move/Copy/Align Edges.................................................................. 2-138 Move/Copy Edges......................................................................... 2-139 Align Edges .................................................................................. 2-140

2.3.5 Split/Merge Edges............................................................................ 2-141 Split Edge...................................................................................... 2-142 Merge Edges (Virtual) .................................................................. 2-150

2.3.6 Convert Edges .................................................................................. 2-153 Using the Convert Edges Form..................................................... 2-153

2.3.7 Summarize/Check/Query Edges and Total Entities ......................... 2-154 Summarize Edges.......................................................................... 2-155 Check Edges ................................................................................. 2-156 Query Edges.................................................................................. 2-159 Total Entities................................................................................. 2-160

2.3.8 Delete Edges .................................................................................... 2-161 Retaining Edge Endpoint Vertices................................................ 2-161

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Deleting Associated Vertices........................................................ 2-161 Deleting Virtual Edges.................................................................. 2-161 Using the Delete Edges Form ....................................................... 2-162

2.4 Face Commands..........................................................................................2-163 2.4.1 Form Face ........................................................................................ 2-165

Create Face From Wireframe........................................................ 2-167 Create Real Parallelogram Face.................................................... 2-171 Create Real Polygon Face............................................................. 2-173 Create Real Circular Face From Vertices ..................................... 2-175 Create Real Elliptical Face From Vertices.................................... 2-178 Create Real Skin Surface Face...................................................... 2-181 Create Real Net Surface Face ....................................................... 2-183 Create Real Face From Vertex Rows............................................ 2-186 Revolve Edges .............................................................................. 2-190 Sweep Edges................................................................................. 2-193

2.4.2 Create Face....................................................................................... 2-208 Create Real Rectangular Face....................................................... 2-209 Create Real Circular Face ............................................................. 2-211 Create Real Elliptical Face............................................................ 2-213

2.4.3 Boolean Operations.......................................................................... 2-215 Unite Real Faces ........................................................................... 2-217 Subtract Real Faces....................................................................... 2-218 Intersect Real Faces ...................................................................... 2-219

2.4.4 Connect/Disconnect Faces ............................................................... 2-220 Connect Faces............................................................................... 2-221 Disconnect About Real Face ........................................................ 2-225

2.4.5 Modify Face Color/Label................................................................. 2-227 Modify Face Color........................................................................ 2-228 Modify Face Label........................................................................ 2-229

2.4.6 Move/Copy/Align Faces .................................................................. 2-230 Move/Copy Faces ......................................................................... 2-231 Align Faces ................................................................................... 2-232

2.4.7 Split/Merge/Collapse/Simplify Faces............................................... 2-233 Split Face ...................................................................................... 2-234 Merge Faces (Virtual)................................................................... 2-242 Collapse Face (Virtual)................................................................. 2-246 Simplify Faces .............................................................................. 2-250

2.4.8 Heal/Convert Faces .......................................................................... 2-252 Heal Real Faces ............................................................................ 2-253 Convert Faces ............................................................................... 2-258

2.4.9 Summarize/Check/Query Faces and Total Entities .......................... 2-259 Summarize Faces .......................................................................... 2-260 Check Faces .................................................................................. 2-261

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Query Faces .................................................................................. 2-264 Total Entities................................................................................. 2-265

2.4.10 Delete Faces ................................................................................... 2-266 Retaining Face Edges.................................................................... 2-266 Retaining and Deleting Associated Vertices................................. 2-266 Deleting Virtual Faces .................................................................. 2-266 Using the Delete Faces Form........................................................ 2-267

2.5 Volume Commands ....................................................................................2-268 2.5.1 Form Volume ................................................................................... 2-270

Stitch Faces................................................................................... 2-271 Sweep Real Faces ......................................................................... 2-273 Revolve Real Faces....................................................................... 2-286 Form Real Volume From Wireframe............................................ 2-291

2.5.2 Create Volume ................................................................................. 2-294 Create Real Brick.......................................................................... 2-295 Create Real Cylinder..................................................................... 2-298 Create Real Prism ......................................................................... 2-302 Create Real Pyramid ..................................................................... 2-307 Create Real Frustum ..................................................................... 2-311 Create Real Sphere ....................................................................... 2-315 Create Real Torus ......................................................................... 2-316

2.5.3 Boolean Operations.......................................................................... 2-318 Overview....................................................................................... 2-318 Unite Real Volumes...................................................................... 2-320 Subtract Real Volumes ................................................................. 2-321 Intersect Real Volumes................................................................. 2-322

2.5.4 Blend Volumes................................................................................. 2-323 Specifying Edge Blend Type ........................................................ 2-323 Specifying Vertex Blend Type...................................................... 2-331 Using the Blend Volumes Form ................................................... 2-333

2.5.5 Modify Volume Color/Label............................................................ 2-337 Modify Volume Color .................................................................. 2-338 Modify Volume Label................................................................... 2-339

2.5.6 Move/Copy/Align Volumes ............................................................. 2-340 Move/Copy Volumes .................................................................... 2-341 Align Volumes.............................................................................. 2-342

2.5.7 Split/Merge Volumes ....................................................................... 2-343 Split Volume................................................................................. 2-344 Merge Volumes............................................................................. 2-352

2.5.8 Heal/Convert Volumes..................................................................... 2-353 Heal Real Volume......................................................................... 2-354 Convert Volumes .......................................................................... 2-357

2.5.9 Summarize/Check/Query Volumes and Total Entities..................... 2-358

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Summarize Volumes ..................................................................... 2-359 Check Volumes............................................................................. 2-360 Query Volumes ............................................................................. 2-362 Total Entities................................................................................. 2-363

2.5.10 Delete Volumes.............................................................................. 2-364 Retaining Volume Faces ............................................................... 2-364 Deleting Associated Vertices........................................................ 2-364 Deleting Virtual Volumes ............................................................. 2-364 Using the Delete Volumes Form................................................... 2-365

2.6 Group Commands ......................................................................................2-366 2.6.1 Create Group.................................................................................... 2-367

Overview....................................................................................... 2-367 Including and Excluding Lower Topology ................................... 2-367 The Effect of Excluding Lower Topology.................................... 2-369 Using the Create Group Form....................................................... 2-369 Using Edit Lower Topology Forms .............................................. 2-371

2.6.2 Modify Group .................................................................................. 2-380 Using the Modify Group Form..................................................... 2-380

2.6.3 Modify Group Color/Label .............................................................. 2-382 Modify Group Color ..................................................................... 2-383 Modify Group Label ..................................................................... 2-384

2.6.4 Move/Copy/Align Groups................................................................ 2-385 Move/Copy Groups ...................................................................... 2-386 Align Groups ................................................................................ 2-387

2.6.5 Summarize/Check/Query Groups and Total Entities ....................... 2-388 Summarize Groups ....................................................................... 2-389 Check Groups ............................................................................... 2-390 Query Groups................................................................................ 2-392 Total Entities................................................................................. 2-393

2.6.6 Delete Groups .................................................................................. 2-394 Deleting Group Member Entities.................................................. 2-394 Deleting Virtual Groups ............................................................... 2-395 Using the Delete Groups Form..................................................... 2-395

VIRTUAL GEOMETRY Introduction

© Fluent Inc., Nov-01 A-1

A. VIRTUAL GEOMETRY

A.1 Introduction

GAMBIT geometry operations comprise a comprehensive assortment of tools that allow you to create and modify solid models. They involve three general types of entities:

• Real

• Virtual

• Faceted

Real entities possess their own geometrical descriptions—that is, they are defined by mathematical formulae that describe their locations and shapes. Virtual entities do not possess their own geometrical descriptions—instead, they derive their geometry by reference to one or more real entities. Faceted entities are defined in reference to an underlying mesh.

u NOTE: The GAMBIT GUI references only real and virtual geometry. To apply GAMBIT geometry operations to faceted geometry, you must treat the faceted geometry as if it were virtual.

The purpose of this appendix is to describe the fundamental differences between real and virtual geometry operations (Section A.2) and to outline the following characteristics of virtual geometry:

• Fundamentals (Section A.3)

• Operations (Section A.4)

• Applications (Section A.5)

Differences Between Real and Virtual Operations VIRTUAL GEOMETRY

A-2 © Fluent Inc., Nov-01

A.2 Differences Between Real and Virtual Operations

There are two basic types of GAMBIT geometry operations:

• Real

• Virtual

Real geometry operations employ only real entities and result in the creation or modification of real topological entities. Virtual geometry operations can employ any combination of real and/or virtual entities but result in the creation or modification of virtual entities only.

Table A-1 and Table A-2 list some of the basic tasks that are included in GAMBIT real and virtual geometry operations, respectively.

Table A-1: Real geometry operations

Category Tasks

Creation • Creation of real vertices at specified points in space

• Formation of real edges, faces, and volumes from existing real, lower-topology entities

• Creation of real primitive volume forms, such as cylinders and prisms

Modification • Splitting of edges, faces, and volumes

• Boolean operations—unite, subtract, and intersect—for faces and volumes

• Blending of volume edges and vertices

VIRTUAL GEOMETRY Differences Between Real and Virtual Operations


Table A-2: Virtual geometry operations

Category Tasks

Creation • Creation of virtual vertices at locations confined to existing real edges or faces

• Formation of virtual edges, faces, and volumes the shapes of which are defined by existing entities

Modification • Repositioning of virtual vertices hosted by an edge or face

• Splitting of real or virtual edges, faces, and volumes

• Merging of two real or virtual entities into a single virtual entity

• Collapsing of a real or virtual face between two neighboring faces

Chapter 2 of this guide describes the procedures and specifications required to create and/or modify real and virtual entities.

u NOTE: Throughout this appendix, the labels of topological entities reflect the GAMBIT default labeling conventions. That is, vertices, edges, faces, and vol-umes are labeled vertex.a, edge.b, face.c, and volume.d, respectively, where a, b, c, and d represent integer numbers—for example, vertex.5 or face.12. Virtual-entity labels are similar to real-entity labels but include the prefix “v_”—for example, v_edge.3 or v_volume.9.

Virtual Geometry Fundamentals VIRTUAL GEOMETRY


A.3 Virtual Geometry Fundamentals

A.3.1 Model Foreground and Background

To understand the basic purpose of virtual geometry operations, it is useful to think of a GAMBIT model as possessing two different logical domains:

• Foreground

• Background

The model foreground consists of topological entities that are observable upon direct examination of the model. Such entities reflect the outward appearance of the model both in shape and in structure. The model background consists of topological entities that are not directly observable but the mathematical defi-nitions of which define the overall shape and structure of the model.

The following sections describe and illustrate the differences between the fore-ground and background of GAMBIT models and the fundamental role of the model foreground in GAMBIT display and meshing operations.

Foreground vs. Background—Example

As an example of the difference between the foreground and background of a model, consider the simple, 2-D model shown in Figure A-1. The model con-sists of six real edges arranged in the form of an irregular, planar hexagon. Each edge shares its endpoint vertices with its neighboring edges and is, there-fore, “connected” to those edges. All six edges and vertices exist in the fore-ground of the model.

VIRTUAL GEOMETRY Virtual Geometry Fundamentals


edge.2 edge.3

edge.4

edge.6

edge.1

vertex.2

vertex.3

vertex.4

vertex.5vertex.1

edge.5

vertex.6

Figure A-1: Irregular hexagon—before merge operation

Each edge and vertex shown in Figure A-1 possesses its own geometrical description; the edges are defined as curves, and the vertices are defined as specific points in the modeling space. The combined definitions of all six edges and vertices constitutes the overall geometrical description of the model.

If you perform a virtual “merge” operation (see “Merge Operations,” below) that involves edge.1 and edge.2 in Figure A-1, GAMBIT replaces them in the model foreground with a single virtual edge, labeled v_edge.7 (see Figure A-2).



edge.3

edge.4

edge.6

v_edge.7

vertex.3

vertex.4

vertex.5

vertex.1

edge.5

vertex.6

Figure A-2: Irregular hexagon—after merge operation

The virtual edge, v_edge.7, does not possess its own geometrical description. Instead, its shape is defined only by reference to the geometrical descriptions of edge.1 and edge.2. In that sense, v_edge.7 constitutes an “overlay” entity that represents the specific set of edges to which it refers.

When GAMBIT performs the merge operation illustrated in Figure A-1 and Figure A-2, it shifts edge.1, edge.2, and their common vertex, vertex.2, to the background of the model and replaces them in the model foreground with the single virtual edge, v_edge.7. Consequently, the model display retains its origi-nal hexagonal shape but includes only five topological edges—one of which constitutes a virtual edge.

The following table summarizes the foreground and background components of the model before and after the merge operation illustrated in Figure A-1 and Figure A-2.



Stage Before After

Domain Foreground Background Foreground Background

Vertices vertex.1 vertex.2 vertex.3 vertex.4 vertex.5 vertex.6

None vertex.1 vertex.3 vertex.4 vertex.5 vertex.6

vertex.2

Edges edge.1 edge.2 edge.3 edge.4 edge.5 edge.6

None edge.3 edge.4 edge.5 edge.6

v_edge.7

edge.1 edge.2

Model Foreground in Display and Meshing Operations

The distinction between the model foreground and background is important to the GAMBIT user for the following reason:

GAMBIT display and meshing operations involve only those topologi-cal components that exist in the foreground of the model.

For example, if you mesh the curve represented by edge.1 and edge.2 in Figure A-1, you must apply mesh node grading schemes independently to each edge, because both edges exist in the foreground of the model. Because GAMBIT is constrained by its meshing rules to create mesh nodes at the endpoint vertices of meshed edges, it necessarily creates a mesh node at vertex.2—which consti-tutes the bending point in the curve (see Figure A-3(a)).



edge.2

edge.1

v_edge.7

vertex.2

(a) (b)

Figure A-3: Irregular hexagon—mesh node spacing

By contrast, if you mesh the curve as represented by the virtual edge, v_edge.7, GAMBIT allows you to apply a single grading scheme to the curve. Further-more, because v_edge.7 constitutes an individual topological entity, GAMBIT is not constrained to create a mesh node at the bending point in the curve (see Figure A-3(b)). Therefore, the existence of v_edge.7 in the foreground of the model GAMBIT imposes fewer overall constraints on mesh node placement than are imposed by the existence of edge.1 and edge.2.

The fundamental purpose of GAMBIT is to create arrays of mesh nodes the locations of which represent specific points in a physical model. In that sense, GAMBIT geometry operations represent only intermediate steps in the overall process of creating a usable model. Because GAMBIT meshing procedures involve only those components that exist in the foreground of the model, virtual geometry operations provide the user with a convenient and powerful means of controlling the shape and density of the mesh in localized regions of the model and, therefore, in the model as a whole.



A.3.2 Virtual Entity Categories

There are two general categories into which entities that participate in GAMBIT virtual geometry operations can be grouped:

• Relationship

• Class

The relationship category defines which specific real and/or virtual entities are associated with each other by means of a given virtual geometry operation. The class category describes the nature of the association—that is, the manner in which a given virtual entity is defined by one or more real entities to which it refers.

The following sections outline the general rules of nomenclature that are employed with respect to the categories listed above.

Relationship Category

The relationship category includes two general classifications:

• Host

• Guest

Host entities are real or virtual entities that are in some way referenced by one or more virtual entities. In most cases, they exist in the background of the model. Guest entities are virtual entities that reference one or more real or virtual entities. They exist in the foreground of the model (see NOTE below).

u NOTE: If a virtual entity serves as the host for another virtual entity, the host virtual entity exists in the model background.



Class Category

There are five basic classes of virtual entities, each of which is defined by the nature of the relationship between the virtual (guest) entity and its real (host) entity (or entities). The five classes of virtual entities are as follows:

• Superset

• Subset

• Interpolant

• Parasite

• Orphan

The following sections describe each of the entity classes listed above.

Superset Entities

A superset entity is a virtual entity that references two or more real entities. For example, the virtual edge, v_edge.7, shown in Figure A-2, above, consti-tutes a superset entity, because its shape is defined in reference to two real entities (edge.1 and edge.2 in Figure A-1). Superset entities occupy the fore-ground of the model, and the real entities that comprise the elements of their sets occupy the background of the model (see NOTE below).

u NOTE: If a superset entity constitutes one component of a higher superset entity, the lower superset entity occupies the model background. For example, if you merge edge.6 and v_edge.7 in Figure A-2 to create the superset entity v_edge.8, GAMBIT places v_edge.7 in the model background.



Subset Entities

A subset entity is a virtual entity that constitutes one element in a set of entities that reference a single host entity. As an example of a subset entity, consider the topological configuration shown in Figure A-4(a). The configuration con-sists of a straight real edge (edge.1) and its endpoint vertices (vertex.1 and vertex.2).

(a) (b)

Split point

edge.1

v_edge.2

v_edge.3

v_vertex.3

vertex.2

vertex.1

vertex.2

vertex.1

Figure A-4: Subset virtual entities—example

If you perform a virtual split operation (see “Split Operations,” below) on edge.1 using the split point indicated in Figure A-4(a), GAMBIT creates a virtual vertex (v_vertex.3) at the split point and replaces edge.1 with two virtual edges, v_edge.2 and v_edge.3 (see Figure A-4(b)). The virtual edges constitute subset entities, because they are each part of a set of entities that reference a single real entity—that is, edge.1.



Interpolant Entities

An interpolant entity is a virtual entity the geometrical description of which represents an average of two or more real entities to which it refers. As an example of an interpolant entity, consider the topological configuration shown in Figure A-5(a). The configuration consists of two real, NURBS edges and their respective endpoint vertices. The edges exist in a single plane and are located near to each other but are not connected to each other.

(a) (b)

y

x

vertex.1 vertex.3 v_vertex.5

vertex.2 vertex.4

edge.1

edge.2 v_edge.3

v_vertex.6

Figure A-5: Interpolant virtual entity—example

If you perform a virtual connect operation (see “Connect Operations,” below) that involves edge.1 and edge.2, GAMBIT replaces the edges with a single virtual edge, v_edge.3 (see Figure A-5(b)). The geometry of the virtual edge represents a composite average of the geometries of edge.1 and edge.2. Simi-larly, its endpoint vertices, v_vertex.5 and v_vertex.6, are located at points that represent the average positions of the vertex pairs [vertex.1, vertex.3] and [vertex.2, vertex.4], respectively.

The virtual edge, v_edge.3, in Figure A-5(b), constitutes an interpolant entity that references edge.1 and edge.2. Similarly, the virtual vertices, v_vertex.5 and v_vertex.6, constitute interpolant entities each of which references a distinct pair of real vertices.



Parasite Entities

A parasite entity is a virtual entity that references a single, higher-order host entity such that its geometry is defined by that of the host entity. The location of a parasite virtual vertex is defined by reference to a host edge or face; the shape and orientation of a parasite virtual edge is defined by reference to a host face.

The following examples illustrate the operations and properties that are associ-ated with the construction and modification of parasite vertices and edges.

Parasite Vertices

Constructing a Parasite Vertex

As an example of the construction of a parasite vertex, consider the topologi-cal configuration shown in Figure A-6(a). The configuration consists of a straight real edge that is identical in geometry to that shown in Figure A-4(a).

Constructionpoint

edge.1

v_vertex.3

vertex.2

vertex.1

vertex.2

vertex.1

edge.1

(a) (b)

Figure A-6: Parasite virtual vertex—example



If you perform a virtual construct operation (see “Construct Operations,” below) using the construction point indicated in Figure A-6(a), GAMBIT creates a parasite virtual vertex, v_vertex.3, at the construction point (see Figure A-6(b)). The virtual vertex, v_vertex.3, is constrained to lie on edge.1 but is not topologically connected to edge.1.

The configuration shown in Figure A-6(b) differs from that of Figure A-4(b) in that v_vertex.3 does not constitute an endpoint vertex for any virtual edge that derives its geometry from edge.1. Instead, v_vertex.3 exists as an independ-ent entity that directly references a higher-topology host entity—that is, edge.1.

Modifying a Parasite Vertex

You can modify the position of any parasite vertex by means of the GAMBIT Slide Virtual Vertex operation. The Slide Virtual Vertex operation allows you to relocate a parasite vertex anywhere along the curve or surface to which it refers. For example, GAMBIT allows you to reposition v_vertex.3 in Figure A-6(b) anywhere along the curve represented by edge.1. (For a description of the procedures and specifications required to modify the position of a virtual vertex, see “Slide Virtual Vertex” in Chapter 2 of this guide.)

Parasite Edges

Constructing a Parasite Edge

As an example of the construction of a parasite edge, consider the topological configuration shown in Figure A-7. The configuration consists of a real four-sided face (face.1) that possesses a curved, 3-D surface and is bounded by two straight real edges (edge.2 and edge.4), two curved real edges (edge.1 and edge.3).



edge.2

edge.4

edge.1

edge.3

vertex.2

vertex.3

vertex.4

vertex.1

face.1

Construction points

Figure A-7: Curved, four-sided face

If you construct virtual vertices at the two construction points indicated in Figure A-7, GAMBIT creates the two parasite vertices shown in Figure A-8. The parasite vertices are constrained to lie on the surface of face.1 but are not topologically connected to face.1.



v_vertex.6

v_vertex.5

Figure A-8: Curved, four-sided face with parasite virtual vertices

If you perform a virtual construct operation to create a virtual edge that employs v_vertex.5 and v_vertex.6 as its endpoints and face.1 as its host entity, GAMBIT creates the parasite virtual edge shown in Figure A-9.



v_edge.5

Figure A-9: Curved, four-sided face with parasite virtual edge

The parasite edge, v_edge.5, is constrained to lie along the surface of face.1 but is not topologically connected to face.1. The geometry of v_edge.5 represents the projection onto the surface of face.1 of a straight line drawn between v_vertex.5 and v_vertex.6.

Modifying the Geometry of a Parasite Edge

As noted above, the GAMBIT Slide Virtual Vertex operation allows you to reposition an existing parasite vertex under the constraint that it remains on its host entity. If you reposition a parasite vertex that constitutes one endpoint of a parasite virtual edge, GAMBIT redefines the geometry of the parasite edge when it repositions the parasite vertex (for example, see Figure A-10).



v_vertex.5 (old)

v_edge.5 (old)

v_vertex.5 (new)

v_edge.5 (new)

Figure A-10: Repositioned parasite vertex and edge

For a description of the procedures and specifications required to modify the position of a virtual vertex, see “Slide Virtual Vertex” in Chapter 2 of this guide.

Orphan Entities

An orphan entity is a virtual entity that does not reference any host entity. Orphan entities derive their geometries only from the lower-topology compo-nents that comprise their boundaries.

Constructing an Orphan Edge

As an example of an orphan entity, consider again the topological configura-tion shown in Figure A-8, above. The configuration consists of a curved, non-planar face upon which two parasite virtual vertices have been constructed.

If you perform a virtual construct operation to create a virtual edge that includes v_vertex.5 and v_vertex..6 as its endpoints of a virtual edge but do not specify a host entity for the edge, GAMBIT creates the orphan virtual edge, v_edge.5, shown in Figure A-11. Unlike the parasite edge shown in Figure A-9, the geometry of the orphan edge consists of a straight line drawn between its two endpoint vertices.



v_edge.5

Figure A-11: Curved, four-sided face with orphan virtual edge

Modifying the Geometry of an Orphan Edge

As noted above, the GAMBIT Slide Virtual Vertex operation allows you to reposition an existing parasite vertex under the constraint that it remains on its host entity. If you reposition a parasite vertex that constitutes one endpoint of an orphan virtual edge, GAMBIT redefines the geometry of the orphan edge when it repositions the parasite vertex.

For a complete description of the procedures and specifications required to reposition a virtual vertex, see “Slide Virtual Vertex” in Chapter 2 of this guide.

Constructing an Orphan Face

It is possible to construct an orphan virtual face from edges that constitute the boundaries of a real face. Although the orphan virtual face shares common edges with the real face, its surface may differ in shape from that of the real face. The difference is due to the fact that, while the surface of the real face possesses its own geometrical description, the surface of the orphan face rep-resents an interpolation based on the geometrical descriptions of its bounding edges.

Virtual Geometry Operations VIRTUAL GEOMETRY


A.4 Virtual Geometry Operations

There are two general types of GAMBIT virtual geometry operations:

• Low-level

• High-level

Low-level virtual operations are specialized operations that operate on individ-ual topological entities or on pairs of entities. High-level virtual operations consist of two or more low-level operations that are grouped according to spe-cific purposes.

The following sections describe the various low- and high-level virtual geome-try operations available in GAMBIT.

A.4.1 Low-Level Operations

GAMBIT provides the following types of low-level virtual operations.

Operation Description

Merge Replaces two connected entities with a single virtual (superset) entity.

Split Partitions an individual entity into two separate virtual (subset) entities.

Connect Combines two individual, unconnected entities into a single virtual (interpolant) entity.

Construct Creates independent virtual (parasite or orphan) entities.

The following sections describe the operations listed above.

VIRTUAL GEOMETRY Virtual Geometry Operations


Merge Operations

When you merge two entities, GAMBIT replaces the entities with a single virtual entity the geometry of which represents the combination of the geome-tries of the merged entities. The virtual (guest) entity constitutes a superset of the merged (host) entities.

The following examples illustrate the principles of GAMBIT merge operations as they apply to face and edge entities.

Merging Faces

As an example of a merge operation, consider the two four-sided faces (face.1 and face.2) shown in Figure A-12(a). The faces share a common edge (edge.1).

v_face.3

θ

face.1edge.1

face.2

θ

(a)

(b)

Figure A-12: Merging of two real faces

If you merge face.1 with face.2, GAMBIT replaces them in the model fore-ground with a single virtual face, v_face.3 (see Figure A-12(b)). The virtual face does not possess its own geometrical description but derives its geometry from the mathematical definitions of the surfaces that describe face.1 and face.2.



When you merge two entities, GAMBIT shifts both entities to the model back-ground and also shifts the entity by which they are connected. For example, if you perform the merge operation illustrated in Figure A-12, GAMBIT shifts face.1, face.2, and edge.1 to the model background.

The following table summarizes the entity populations of the model fore-ground and background before and after the merge operation illustrated in Figure A-12.

Stage Before After



None vertex.1 vertex.2 vertex.3 vertex.4 vertex.5 vertex.6

None

Edges edge.1 edge.2 edge.3 edge.4 edge.5 edge.6 edge.7

None edge.2 edge.3 edge.4 edge.5 edge.6 edge.7

edge.1

Faces face.1 face.2

None v_face.3 face.1 face.2



Merging Edges

As a second example of the merge operation, consider the topological configu-ration shown in Figure A-13(a). The configuration is identical to that shown in Figure A-12(b) but includes labels for each of the six real edges that circum-scribe the virtual face and for the two real vertices that exist at the outer bend-ing points of the virtual face.

edge.2edge.7

edge.4edge.5

edge.3

edge.6

vertex.4 vertex.3

edge.3

edge.6v_edge.8

v_edge.9

(a)

(b)

Figure A-13: Merge operation—merging of real edges

If you merge edge2. with edge.7 and edge.4 with edge.5, GAMBIT creates the topological configuration shown in Figure A-13(b). The merged configuration consists of a single virtual face (v_face.3) that is circumscribed by four edges. Two of the edges constitute straight, real edges (edge.3 and edge.6), and two constitute bent, virtual edges (v_edge.8 and v_edge.9). The virtual edges do not possess their own geometrical descriptions but derive their geometries from the mathematical definitions of the curves that describe the real edges to which they refer.

The following table summarizes the entity populations of the model fore-ground and background before and after the merge operation illustrated in Figure A-13.



Stage Before After



None vertex.1 vertex.2 vertex.5 vertex.6

vertex.3 vertex.4

Edges edge.2 edge.3 edge.4 edge.5 edge.6 edge.7

edge.1 edge.3 edge.6

v_edge.8 v_edge.9

edge.1 edge.2 edge.4 edge.5 edge.7

Faces v_face.3 face.1 face.2

v_face.3 face.1 face.2



Merge Operation Rules and Restrictions

GAMBIT virtual merge operations are subject to the following rules and restrictions.

1. Each merge operation must involve exactly two entities to be merged.

2. The topological orders of the entities to be merged must be identical to each other. For example, it is not possible to merge a vertex with an edge or to merge an edge with a volume.

3. The entities to be merged must be connected by means of a common lower-order entity. For example, if two edges do not share a common end-point vertex, they cannot be merged. Similarly, two faces can be merged only if they are connected by means of a common edge, and two volumes can be merged only if they are connected by means of a common face.

4. If you merge two entities that constitute subcomponents of a higher-order entity, GAMBIT replaces the higher-order entity with a virtual entity of the same order. For example, consider the five-sided, planar face shown in Figure A-14(a). If you merge edge.4 with edge.5, GAMBIT replaces them in the model foreground with v_edge.6 (see Figure A-14(b)). At the same time, however, GAMBIT replaces face.1 with v_face.2.

(a)

face.1

edge.1 edge.2

edge.3

edge.4

edge.5

vertex.1

vertex.2

vertex.3

vertex.4vertex.5

(b)

v_face.2

edge.1 edge.2

edge.3v_edge.6

vertex.1

vertex.2

vertex.3

vertex.4

Figure A-14: Merge operations—replacement of higher-order entities



5. You cannot merge two edges the common endpoint vertex of which is also shared by one or more other edges in the model. For example, consider the topological configuration shown in Figure A-15. GAMBIT does not allow you to merge edge.1 with edge.2, because their common endpoint vertex (vertex.1) is also shared by edge.3.

edge.1

edge.3

edge.2vertex.1

Figure A-15: Merge operations—common-endpoint restriction

Similar rules apply to faces and volumes. For example, you cannot merge two faces a common edge of which is shared by another face.



Split Operations

When you split an entity, GAMBIT replaces the entity with two virtual entities (for exceptions, see NOTE, below). The virtual (guest) entities that result from the split constitute subsets of the split (host) entity, and they are connected to each other by means of a common lower-order virtual entity.

To perform a virtual split operation, you must specify two parameters:

• The entity to be split

• The split tool

The entity to be split can be any real or virtual edge, face, or volume that cur-rently exists in the foreground of the model. The split tool constitutes the entity that defines the location of the split.

u NOTE: If the entity to be split is a real entity, GAMBIT allows you to perform either a real or virtual split operation involving the entity. Real and virtual split operations differ from each other as follows:

• If you perform a real split operation, GAMBIT replaces the real entity with two real entities and deletes the original real entity from the model.

• If you perform a virtual split operation, GAMBIT replaces the real entity in the model foreground with two virtual entities and shifts the original real entity to the model background.

For a complete description of real split operations, see Chapter 2 of this guide.

Splitting an Edge

As an example of a split operation, consider the topological configuration shown in Figure A-16(a). The configuration consists of a real, elliptical arc edge and two real endpoint vertices.



edge.1

6SOLW�SRLQW v_edge.2

v_edge.3

vertex.2

vertex.1

vertex.2

vertex.1

v_vertex.3

(a) (b)

Figure A-16: Virtual split operation—real, elliptical arc edge

If you split the edge (edge.1) at the split point indicated in Figure A-16(a), GAMBIT replaces the edge with two virtual edges and connects the virtual edges by means of a common virtual vertex (v_vertex.3) which is located at the split point (see Figure A-16(b)). The virtual edges do not possess geometrical descriptions of their own but are defined in reference to the mathematical defi-nition of the original edge.

The following table summarizes the foreground and background entity popula-tions before and after the virtual split operation illustrated in Figure A-16.

Stage Before After


Vertices vertex.1 vertex.2

None vertex.1 vertex.2

v_vertex.3

None

Edges edge.1 None v_edge.2 v_edge.3

edge.1



Splitting a Face

As a second example of a virtual split operation, consider the topological con-figuration shown in Figure A-17(a). The configuration consists of a real, planar, quadrilateral face that is bounded by four real edges and four real vertices.

face.1

edge.1

edge.4

edge.2

edge.3

vertex.1

vertex.4

vertex.3

vertex.2

(a)

v_vertex.5

v_vertex.6

(b)

v_edge.5

(c) (d)

v_face.2

v_face.3

v_edge.6 v_edge.7

v_edge.9

v_edge.8

Figure A-17: Virtual split operation—real, four-sided face

To split the face, you must first create and/or specify the split tool. Figure A-17 illustrates the procedure required to split the face vertically using an edge as the split tool. The procedure involves the following steps.

Step Description

1 Construct virtual parasite vertices (v_vertex.5 and v_vertex.6) on the top and bottom edges of the face (see Figure A-17(b)).

2 Construct a straight, virtual edge (v_edge.5) using the virtual vertices created in Step 1 (see Figure A-17(c)).

3 Split face.1, using v_edge.5 as the split tool.



When you split face.1 according to the procedure outlined above, GAMBIT replaces face.1 with v_face.2 and v_face.3 (see Figure A-17(d)). Note that, in the process of splitting the face.1, GAMBIT also splits edge.1 and edge.3 and replaces them with the virtual-edge pairs [v_edge.6, v_edge.7] and [v_edge.8, v_edge.9], respectively.

Split Operation Rules and Restrictions

GAMBIT virtual split operations are subject to the following rules and restric-tions.

1. Each virtual split operation must involve only one entity to be split and one split tool.

2. When you perform a virtual split operation, you must employ a split tool that is of lower order than the entity to be split. Specifically, the rules regarding the available split tools are as follows.

Entity to be Split Available Split Tools

Edge • A specified point on the edge

• A parasite vertex that exists along the curve that defines the edge

• A mesh node that exists on the edge

Face • A pair of vertices that exist on and are con-nected to the boundary of the face

• An edge the curve of which follows the sur-face of the face and the endpoints of which are connected to the boundary of the face

• A set of mesh nodes

Volume • An existing face that is connected to the volume

u NOTE: If you perform a real split operation on a face, GAMBIT allows you to use a separate face as the split tool.



Connect Operations

When you perform a virtual connect operation involving two entities, GAMBIT replaces the entities with a single virtual entity. The geometrical description of the virtual entity represents an average of the geometrical descriptions of the entities that are connected by means of the connect opera-tion. The virtual (guest) entity is an interpolant entity that references the con-nected (host) entities.

u NOTE: If the entities to be connected are both real entities, GAMBIT allows you to perform either a real or virtual connect operation. Real and virtual con-nect operations differ from each other as follows:

• If you perform a real connect operation, GAMBIT replaces the real entities with a single real entity and deletes the original entities from the model.

• If you perform a virtual connect operation, GAMBIT replaces the real entities with a single virtual entity and shifts the original entities to the model background.

Connecting Vertices

As an example of a virtual connect operation, consider the two real edges shown in Figure A-18(a). The endpoint vertices vertex.2 and vertex.3 are located in proximity to each other but are not connected to each other.



edge.2

edge.1

vertex.1

vertex.4

vertex.3

vertex.2

v_edge.4

v_edge.3

v_vertex.5

(a) (b)

Figure A-18: Virtual connect operation—two real vertices

If you perform a virtual connect operation that involves vertex.2 and vertex.3, GAMBIT replaces them in the model foreground with a single virtual vertex, v_vertex.5 (see Figure A-18(b)). In the process, GAMBIT replaces edge.1 and edge.2 with v_edge.3 and v_edge.4, respectively.

The following table summarizes the foreground and background entity popula-tions before and after the vertex connect operation illustrated in Figure A-18.

Stage Before After


Vertices vertex.1 vertex.2 vertex.3 vertex.4

None vertex.1 vertex.4

v_vertex.5

vertex.2 vertex.3

Edges edge.1 edge.2

None v_edge.3 v_edge.4

edge.1 edge.2



Connecting Edges

As a second example of a virtual connect operation, consider the two real, planar faces shown in Figure A-19. Each face is bounded by four real edges, three of which are straight and one of which is curved. The curved edges are located near each other but are not connected to each other.

vertex.1 edge.1

edge.8

edge.7

edge.6

edge.5

edge.2edge.4

edge.3

vertex.2 vertex.5

vertex.6

vertex.7vertex.4

vertex.3 vertex.8

face.1 face.2

Figure A-19: Virtual connect operation—two real, four-sided faces

If you perform a virtual connect operation that involves edge.2 and edge.8, GAMBIT replaces them in the model foreground with a single virtual edge, v_edge.9 (see Figure A-20). The virtual edge is bounded by the virtual end-point vertices v_vertex.9 and v_vertex.10. In the process of the connect opera-tion, GAMBIT also replaces face.1 and face.2 with two virtual faces (v_face.3 and v_face.4) that are connected to each other by means of their common virtual edge, v_edge.9.



v_edge.9

v_vertex.9

v_vertex.10

v_face.3 v_face.4

Figure A-20: Virtual connect operation—connected virtual faces

The following table summarizes the foreground and background entity popula-tions before and after the connect operation illustrated in Figure A-19 and Figure A-20.



Stage Before After


Vertices vertex.1 vertex.2 vertex.3 vertex.4 vertex.5 vertex.6 vertex.7 vertex.8

None vertex.1 vertex.4 vertex.6 vertex.7

v_vertex.9 v_vertex.10

vertex.2 vertex.3 vertex.5 vertex.8

Edges edge.1 edge.2 edge.3 edge.4 edge.5 edge.6 edge.7 edge.8

None v_edge.1 v_edge.3 edge.4

v_edge.5 edge.6

v_edge.7 v_edge.9

edge.1 edge.2 edge.3 edge.5 edge.7 edge.8

Faces face.1 face.2

None v_face.2 v_face.3

face.1 face.2



Construct Operations

When you perform a virtual construct operation, GAMBIT creates either of two types of entities:

• Parasite

• Orphan

If you specify a host entity for the construct operation, GAMBIT creates a parasite virtual entity. Parasite entities derive their geometries from the host entity but are not directly connected to such entities. If you do not specify a host entity, GAMBIT creates an orphan entity. Orphan entities derive their geometries only from the entities that comprise their boundaries.

For examples of the types of entities that result from GAMBIT virtual con-struct operations, see “Parasite Entities” and “Orphan Entities” in Section A.3.2, above.



A.4.2 High-Level Operations

GAMBIT provides the following types of high-level virtual operations.

Operation Description

Collapse Splits a face and merges the resulting pieces with two or more neighboring faces.

T-Connect Splits edges by vertices that exist within tolerance of the edges, then connects the split entities


Collapse Operations

When you perform a virtual collapse operation, GAMBIT overlays the col-lapsed face with two or more virtual faces that represent the merging of the collapsed face with its neighboring faces. Collapse operations require that the face to be collapsed is connected by means of a common edge to each of the other faces that are involved in the operation.

As an example of a collapse operation, consider the topological configuration shown in Figure A-21. The configuration consists of three square, real faces arranged in the shape of an “L”. The central face (face.2) is connected to each of its neighboring faces (face.1 and face.3) by means of two common edges—that is, edge.3 and edge.5, respectively.

If you perform a virtual collapse operation in which face.2 is collapsed between face.1 and face.3, GAMBIT performs the two-step process illustrated in Figure A-22. The process consists of the following steps.

1. Split face.2 along curve a to create two intermediate virtual faces, A and B (see Figure A-22(a)).

2. Merge face A with face.1 and face B with face.3 to create two virtual faces—that is, v_face.4 and v_face.5 (see Figure A-22(b)).



edge.1

face.2

face.1

edge.10

face.3

edge.4

edge.7

edge.3

edge.5

edge.2

edge.6

edge.8

edge.9

vertex.4

vertex.1 vertex.2

vertex.3

vertex.5

vertex.6 vertex.8

vertex.7

Figure A-21: Three square faces arranged in an “L” shape

face.1

face.3a B

A

v_face.4

v_face.5

v_edge.12

v_edge.13

v_edge.11

(a) (b)

Figure A-22: Virtual collapse operation—three square faces



T-Connect Operations

When you perform a virtual T-connect operation on an edge, GAMBIT per-forms the following operations:

• Split the edge using the projections of any vertices that exist near the edge to within a specified tolerance

• Connect the split entities

The following paragraphs illustrate the effect of T-connect operations on lone edges—that is, edges that do not constitute boundaries of a face—and bound-ary edges.

T-Connecting Lone Edges

As an example of a T-connect operation, consider the topological configura-tion shown in Figure A-23. The configuration consists of two edges, edge.1 and edge.2, neither of which constitutes a boundary edge for any higher-order entity. One of the endpoint vertices of edge.2 (vertex.3) is located near the curve that describes edge.1 to within a specified tolerance.

edge.1

edge.2

vertex.1

vertex.3

vertex.4

vertex.2

Figure A-23: Two perpendicular, unconnected edges



If you perform a virtual T-connect operation involving edge.1 and edge.2 in Figure A-23, GAMBIT executes the following steps (see Figure A-24).

1. Split edge.1 at Point a to create two intermediate virtual edges, A and B (see Figure A-24(a)). (NOTE: Point a represents the projection of vertex.3 onto edge.1.)

2. Connect the virtual vertex at Point a with vertex.3 to create a single vir-tual vertex (v_vertex.5) that constitutes the common endpoint for three virtual edges—v_edge.3, v_edge.4, and v_edge.5 (see Figure A-24(b)). (NOTE: The location of v_vertex.5 constitutes the average locations of the intermediate virtual vertex at Point a and vertex.3.)

A a B v_edge.3

v_vertex.5

v_edge.4

v_edge.5

(a) (b)

Figure A-24: Virtual T-connect operation—two perpendicular edges



The following table summarizes the foreground and background entity popula-tions before and after the T-connect operation illustrated in Figure A-24.

Stage Before After


Vertices vertex.1 vertex.2 vertex.3 vertex.4

None vertex.1 vertex.2 vertex.4

v_vertex.5

vertex.3

Edges edge.1 edge.2

None v_edge.3 v_edge.4 v_edge.5

edge.1 edge.2

u NOTE: If either edge constitutes part of a face, GAMBIT replaces the face in the model foreground with a virtual face. If the face constitutes part of a volume, GAMBIT creates a corresponding virtual volume.

T-Connecting Boundary Edges

If you perform a virtual T-connect operation that involves two edges each of which constitutes a boundary edge for an individual face, GAMBIT replaces the edges with virtual edges and replaces the faces with virtual faces. For example, consider the topological configuration shown in Figure A-25. The configuration includes two coplanar, rectangular faces (face.1 and face.2) the adjoining edges of which (edge.3 and edge.5) are offset slightly from each other.



edge.1

face.2

face.1edge.4

edge.7

edge.3

edge.5

edge.2

edge.6edge.8

vertex.4

vertex.1 vertex.2

vertex.3

vertex.5

vertex.6

vertex.8 vertex.7

Figure A-25: Two offset rectangular faces edges

If you perform a virtual connect operation that involves edge.3 and edge.5 and allow the formation of T-connections, GAMBIT splits both edges and con-nects them to each other such that they form three virtual edges (see Figure A-26). In the process of the connect operation, GAMBIT also replaces face.1 and face.2 with v_face.3 and v_face.4, respectively.



v_face.4

v_face.3

v_edge.9

v_vertex.10

v_vertex.9

v_edge.10 v_edge.11

Figure A-26: T-connected boundary edges

The following table summarizes the foreground and background entity popula-tions before and after the T-connect operation illustrated in Figure A-24.



Stage Before After


Vertices vertex.1 vertex.2 vertex.3 vertex.4 vertex.5 vertex.6 vertex.7 vertex.8

None vertex.1 vertex.2 vertex.4 vertex.6 vertex.7 vertex.8


vertex.3 vertex.5

Edges edge.1 edge.2 edge.3 edge.4 edge.5 edge.6 edge.7 edge.8

None edge.1 edge.2 edge.4 edge.6 edge.7 edge.8

v_edge.9 v_edge.10 v_edge.11

edge.3 edge.5

Faces face.1 face.2

None v_face.3 v_face.4

face.1 face.2

u NOTE: After you perform the connect operation illustrated in Figure A-26, above, you can merge v_face.2 and v_face.3 to create a single virtual face the geometry of which reflects the overall geometry of the original, unconnected faces—that is, face.1 and face.2. It is then possible to mesh the overall geome-try of the original faces by means of a single meshing operation.

VIRTUAL GEOMETRY Virtual Geometry Applications


A.5 Virtual Geometry Applications

The virtual geometry operations described in Section A.4 allow you to perform several important tasks that are related to GAMBIT modeling and meshing operations. The four primary tasks are as follows:

• Clean up imported geometry

• Simplify geometry

• Decompose geometry

• Adjust the mesh

The following table describes each of the tasks listed above.

Task Description

Clean up imported geometry

Correct problems that are due to imported geometry that is incomplete or inconsistent

Simplify geometry Modify the model to create meshable compo-nents; remove insignificant details from the model

Decompose geometry Break down complex geometry into small, meshable components

Modify the mesh Modify meshed geometry and thereby change the positions of existing mesh nodes

The following sections describe and illustrate the basic principles associated with each of the tasks listed above.

Virtual Geometry Applications VIRTUAL GEOMETRY


A.5.1 Cleaning Up Imported Geometry

Geometry that is created outside GAMBIT sometimes violates GAMBIT validity criteria. GAMBIT meshing operations do not apply to invalid geome-try; therefore, you must clean up such geometry before attempting to mesh an imported model.

GAMBIT Validity Criteria

To constitute valid GAMBIT geometry, the topological components of a model must satisfy two criteria:

• Consistency

• Completeness

Consistent geometry is that for which topological components of a given entity are coincident with each other and are correctly connected to each other. Complete geometry is that which includes surface shape definitions and for which connectivity information is available.

The following sections describe the conditions of consistency and complete-ness and outline the use of virtual geometry operations to correct imported geometry that is inconsistent or incomplete.

Consistency Criteria

As noted above, consistent geometry is that for which topological components of a given entity satisfy the following criteria:

• They are coincident with each other—that is, they are located within proximity of each other to within a specified tolerance.

• They are correctly connected to each other.

As an example of the criteria described above, consider the topological con-figurations shown in Figure A-27(a) and (b). Each configuration consists of a curved face and four edges that constitute the boundaries of the face.



(a)

(b)

Figure A-27: Consistent vs. inconsistent geometry

Although the numbers and general geometries of the components in both con-figurations are similar, the configurations differ with respect to whether or not they satisfy GAMBIT consistency criteria. Specifically, the configuration shown in Figure A-27(a) is not consistent; whereas the configuration shown in Figure A-27(b) is consistent.

The configuration shown in Figure A-27(a) is inconsistent for the following reasons.

• The curves that define the edges are not coincident with the surface of the face at its boundaries.

• The edges are not connected to the face.

• The edges are not connected to each other at their endpoint vertices.

Conversely, the configuration shown in Figure A-27(b) satisfies the GAMBIT consistency criteria for the following reasons.

• The curves that define the edges are coincident with the surface of the face at its boundaries.

• The edges are connected to the face.

• The edges are connected to each other at their endpoint vertices.



u NOTE: When you import geometry, GAMBIT automatically performs clean-up operations. Such operations create real geometry whenever possible and use virtual geometry operations where necessary.

Sources of Inconsistent Geometry

Computer automated design (CAD) programs often generate geometry data that is inconsistent with respect to GAMBIT operations. The inconsistencies arise due to the differences in tolerance values employed by the two types of programs. CAD programs are designed to create a set of mathematical descriptions that can be used to generate visual representations of geometry or to serve as a software blueprint for computer-aided manufacturing (CAM) operations. Consequently, their tolerance and consistency criteria are less strict than those employed by GAMBIT. GAMBIT operations are designed to employ geometry that is exact enough to be used for mathematical modeling operations. Therefore, they require that topological components of the model meet strict tolerance and consistency criteria.

Completeness Criteria

Model geometry is complete if it includes the following information:

• Connectivity

• Shape definitions

Connectivity information describes the relationship between, for example, the boundary edges of a given face or the endpoint vertices of a set of edges. Shape definitions describe curves or surfaces that are associated with the model edges or faces, respectively.



Example Application—Clean-up of Unconnected Edges

As an example of the use of GAMBIT virtual geometry operations to clean up geometry, consider the topological configuration shown in Figure A-28. The configuration includes 25 edges—only some of which are connected to others by means of common vertices. Although the configuration does not include any face entities, the edges are arranged such that they represent the general outline of a curved surface.

Figure A-28: Geometry clean-up example—unconnected edges

GAMBIT virtual geometry operations allow you to create a single, meshable face from the configuration shown in Figure A-28 without altering the under-lying topology. To do so, you must perform the following steps:

1. Connect the edges to each other such that they form a continuous, wireframe outline of a curved surface

2. Create virtual faces from the connected edges

3. Merge the virtual faces to create a single, meshable face



Step (1)—Connecting Edges

If you perform a virtual connect operation that involves all edges shown in Figure A-28 and allow the T-connect operation, GAMBIT creates a web of connected virtual edges that forms a general outline of a curved surface (see Figure A-30).

Figure A-29: Geometry clean-up example—connected edges

Most of the virtual edges that exist in the interior of the wireframe shown in Figure A-30 constitute interpolant entities.



Step (2)—Creating Virtual Faces

If you construct virtual faces from the edge loops that result from the connect operation of Step (1), GAMBIT creates a patchwork of virtual faces the com-bined geometries of which generally describe a single curved surface (see Figure A-30). Each of the faces constitutes an orphan entity and is connected to its neighboring faces by means of two or more common virtual edges.

v_face.1

v_face.3

v_face.4

v_face.5

v_face.6

v_face.2

v_face.7

Figure A-30: Geometry clean-up example—patchwork of connected faces



Step (3)—Merging Virtual Faces

If you perform a virtual merge operation involving the virtual faces shown in Figure A-30, GAMBIT constructs a single, virtual face, v_face.8, the surface of which represents the shape of the original arrangement of unconnected edges (see Figure A-31). Because v_face.8 exists as a single entity, you can apply a single set of mesh specifications to the face, thereby creating a smooth, unified mesh, such as that shown in Figure A-31.

v_face.8

Figure A-31: Geometry clean-up example—single meshed surface

u NOTE: It is possible to further simplify the geometry shown in Figure A-31 by merging the edges that comprise its boundaries. If you do so, GAMBIT elimi-nates the virtual vertices at the non-corner positions and thereby frees the meshing procedures from the constraint of having to locate mesh nodes at those vertices.



A.5.2 Simplifying the Geometry

Some models that represent detailed descriptions of real-world objects include details that complicate the process of creating a mesh. Such details may be important to processes that require an exact description of the object—such as computer-aided manufacturing (CAM) systems—but are often irrelevant to mathematical analyses for which a mesh is created. They include, but are not limited to, fillets and chamfered edges, sliver-shaped faces, holes, and small depressions or bumps on the surface of model faces.

There are two basic methods of simplifying complex geometry descriptions so that they can be used to create a mesh that is suitable for mathematical analy-ses. The two methods are as follows:

• Changing the existing real geometry itself

• Using virtual operations to overlay the existing real geometry with virtual counterparts

The process of changing the existing real geometry involves procedures that are often complicated and costly, such as the redefinition of curves and surfaces. The redefined geometry that results from the process often represents an approximation of the original geometry, thereby reducing the accuracy of the model. Furthermore, in some cases, the process itself is incapable of pro-ducing meshable geometry.

The process of using virtual operations, on the other hand, involves simple procedures that simplify the model without compromising or altering its underlying real geometry. Furthermore, virtual operations retain the exact geometrical descriptions of the original geometry, thereby circumventing the loss in accuracy that results from the process of changing the existing real geometry.

The following examples illustrate the use of virtual operations to simplify geometry and improve or enable GAMBIT meshing operations. Specifically, the examples illustrate the following operations.

Example Description

1 Simplifying a square surface

2 Removing a spherical bump

3 Simplifying a cube with a cutout corner



Example 1—Simplifying a Square Surface

As an example of the use of virtual geometry operations to simplify and/or improve meshing operations, consider the topological configuration shown in Figure A-32. The configuration consists of two triangular faces and one quad-rilateral face all of which are arranged such that they form a square, planar surface. The faces face.1 and face.2 are connected to each other by means of their common edge, edge.7, and face.2 and face.3 are connected to each other by means of edge.8.

face.1face.3

face.2

edge.1

edge.3

edge.4

edge.2

edge.6

edge.5

edge.7 edge.8

vertex.1 vertex.2 vertex.3

vertex.4

vertex.5vertex.6

Figure A-32: Three real faces arranged in the shape of a square

If you mesh each face separately by means of GAMBIT default meshing schemes and parameters, GAMBIT creates Tri Primitive meshes on the two tri-angular faces and a Quad-Map mesh on the quadrilateral face. (For a complete description of GAMBIT face-meshing schemes and parameters, see Chapter 3 of this guide.) The resulting mesh for the entire square surface is shown in Figure A-33.



Tri Primitive mesh schemes

Quad-Map mesh scheme

Figure A-33: Example mesh—three meshed faces

The mesh shown in Figure A-33 is highly irregular with respect to the square surface. Such irregularity is a consequence of the fact that each face is meshed separately and that GAMBIT meshing operations require the creation of mesh nodes on all edges, including those that are common to multiple faces that describe a single surface.

In order to create a mesh that is smooth and continuous across the square surface shown in Figure A-32, you must form a single face the surface of which represents a combination of the three faces that make up the square. GAMBIT merge operations applied to the faces and edges of the configuration allow you to form such a face. Specifically, the procedure required to form a single, square face is as follows:

1. Merge face.2 with face.3 to create v_face.4.

2. Merge v_face.4 with face.1 to create v_face.5.

3. Merge the edges of v_face.5 to remove intermediate vertices.

The resulting virtual face includes only four edges and four vertices in the model foreground, therefore, GAMBIT meshing operations produce a smooth Map mesh for the square surface (see Figure A-34).



v_face.5

(a) (b)

v_edge.9

v_edge.10

Figure A-34: Simplification of a square surface—Step 3



Example 2—Removing a Bump

As an example of the use of virtual geometry operations to remove irrelevant details and improve mesh quality, consider the topological configuration shown in Figure A-35. The configuration consists of two real faces one of which (face.2) constitutes a spherical bump in an otherwise planar, square surface.

face.1 face.2

Figure A-35: Planar square face with spherical bump

To mesh the entire surface represented by the two faces shown in Figure A-35, you must mesh each face separately. The configurations of the faces dictate that GAMBIT typically applies a Pave meshing scheme to each face. Figure A-36 shows the overall mesh grid that results from the GAMBIT meshing operations.



Figure A-36: Pave-mesh grids on square face with spherical bump

If you merge face.1 with face.2 by means of GAMBIT virtual geometry opera-tions, GAMBIT replaces them with a single, virtual face, v_face.3 (see Figure A-37). The geometry of the virtual face represents that of the combined real faces, but its lower-topology components include only the outer edges and vertices of face.2. As a result, v_face.3 constitutes a simple quadrilateral face and can be meshed according to the map meshing scheme shown in the figure.



v_face.3

Figure A-37: Map-mesh grids on square face with spherical bump

Note that the mesh node spacing is much more regular for the map meshing scheme shown in Figure A-37 than for the pave meshing schemes shown in Figure A-36. In addition, it is possible to employ a mapped mesh that is courser than a paved mesh of similar mesh quality.



Example 3—Simplifying a Cube with a Cutout Corner

As an example of the use of virtual geometry operations to enable meshing of a volume, consider the topological configuration shown in Figure A-38. The configuration consists of a regular cubic volume from which one corner has been removed. Each of the inside edges of the cutout section has been rounded by means of a volume blend operation, as has the vertex at which they intersect.

face.9

face.8

face.7

face.10

face.11

face.12

face.13

Figure A-38: Cube with cutout corner

Although each face of the volume is meshable on its own by means of a stan-dard GAMBIT face-meshing scheme, the volume itself cannot be meshed as a single entity by any standard volume-meshing scheme. It is possible, however, to simplify the volume by means of GAMBIT virtual geometry operations and, thereby, to render it meshable.

The steps involved in simplifying the volume are as follows:



1) Collapse the three curved faces that constitute the inside corners of the cutout. The following table lists each face in relation to the neighboring faces between which it is collapsed.

Face to be Collapsed Neighboring Faces

face.10 face.7 and face.8



When you perform the virtual collapse operations described in the table above, the volume appears as shown in Figure A-39.

v_face.16

v_face.15

v_face.14

Figure A-39: Simplifying a cube with cutout corner—Step 1



2) Collapse face.13 between v_face.14, v_face.15, and v_face.16.

The final form of the simplified volume consists of six rectangular faces and three L-shaped faces and can be meshed by means of the Submap volume meshing scheme (see Figure A-40).

Figure A-40: Simplifying a cube with cutout corner—Submap mesh



A.5.3 Decomposing the Geometry

It is sometimes necessary to decompose complex models into meshable sub-volumes. GAMBIT provides two general types of operations that allow you to perform such decompositions:

• Real Boolean operations

• Virtual split operations

Real Boolean operations and virtual split operations exhibit the following characteristics.

Operations Characteristics

Real Boolean • Alter the underlying topology of the model

• Often involve complex calculations

Virtual split • Do not affect the underlying structure of the model

• Are not computationally intensive

In addition to the characteristics noted above, virtual faces often constitute more usable split entities than do real faces, because their surfaces do not exhibit the high curvature that is sometimes characteristic of real faces formed from existing edges.



A.5.4 Adjusting the Mesh

In addition to the applications noted above, you can use virtual geometry operations to create “flexible” topology that can, in turn, be used to control the shape and density of an existing mesh. As an example of the use of such geometry, consider the topological configuration shown in Figure A-41. The configuration consists of a curved, 3-D surface identical to that shown in Figure A-7. Its surface is represented in the model foreground by two virtual faces (v_face.2 and v_face.3) that are connected by means of a common virtual parasite edge (v_edge.5). Two virtual parasite vertices (v_vertex.5 and v_vertex.6) comprise the endpoints of the parasite edge and are constrained to lie on edge.1 and edge.3, respectively.

v_face.2

v_face.3

v_edge.5

v_vertex.6

v_vertex.5

Figure A-41: Curved 3-D face with virtual parasite entities

The virtual faces shown in Figure A-41 are each meshed according to identical meshing parameters, and the virtual vertices that comprise the endpoints of their common edge are located at the midpoints of their respective edges.



As noted in Section A.2, above, GAMBIT allows you to reposition parasite vertices along or across their host edges or faces. Consequently, you can change the shape of the mesh shown in Figure A-41 simply by repositioning either or both of the parasite virtual vertices. When you do so, GAMBIT repo-sitions the parasite edge, thereby changing the shape of the two virtual faces that represent the surface. In the process, GAMBIT repositions any existing mesh nodes on each of the faces.

Figure A-42 shows an example mesh that results from repositioning both para-site vertices from their positions as shown in Figure A-41.

v_edge.5v_vertex.5 (new)

v_vertex.6 (new)

v_vertex.5 (old)

v_vertex.6 (old)

Figure A-42: Curved 3-D face—repositioned parasite vertices

Note that, although the sizes and shapes of individual mesh elements change when you reposition the virtual vertices, the connectivity of the mesh remains unchanged.

INTRODUCTION

© Fluent Inc., Nov-01 1-1

1. INTRODUCTION

The purpose of this guide is to categorize and describe the operations that are available by means of the GAMBIT GUI. The logical structure of the guide follows that of the Operation toolpad and its associated subpads. That is, the organization of the chapters, sections, and subsections reflects the hierarchy of command buttons on the GUI. For example, Chapters 2, 3, 4, 5, and 6 describe operations associated with the Geometry, Mesh, Zones, Tools, and Postprocessing command buttons, respectively—which reflects the order in which the command buttons appear on the on the Operation toolpad (see Figure 1-1). (NOTE: The postprocessing capabilities described in Chapter 6 are available only in the Fluent FlowLab software package—which is derived from the GAMBIT program. Consequently, they pertain only to the direct use of FlowLab and/or to the use of GAMBIT to create FlowLab templates.)

Figure 1-1: Operation toolpad

Similarly, the description of the Blend Volumes operation follows that of the Volume Boolean operations, because its toolpad command button is located immediately to the right of the Boolean command button on the Geometry/ Volume subpad (see Figure 1-2).

Figure 1-2: Geometry/Volume subpad

Format and Font Conventions INTRODUCTION

1-2 © Fluent Inc., Nov-01

1.1 Format and Font Conventions

Chapter 1 of the GAMBIT User’s Guide describes the basic format and font conventions that are employed throughout this guide. For convenience, the descriptions of format and font conventions are duplicated here.

1.1.1 Format Conventions

This guide employs two standard format types.

• Graphic format

• Layout format

The graphic format determines the types of symbols that are used to represent control elements and command buttons on the GAMBIT graphical user inter-face (GUI). The layout format determines the structure of the descriptions of GAMBIT specification forms.

Graphic Format

The GAMBIT GUI employs two basic types of components for user interac-tion.

• Control elements

• Toolpad command buttons

The following sections describe the conventions that are used throughout the documentation to describe the components listed above.

Control Elements

The GAMBIT GUI employs control elements such as command buttons, option buttons, and text boxes to allow you to perform operations such as exe-cuting actions, choosing from among sets of options, and inputting alphanu-meric data. The graphic format conventions used in this guide to represent the GAMBIT GUI control elements are as follows.

INTRODUCTION Format and Font Conventions


Control Element Example Graphic Format Function

Command button Command Executes the

command indicated on the button title

Option button

Option 1 q Option 2 …

Selects from a hidden menu of mutually exclusive options

Text box

Value Accepts alphanu-meric data from the keyboard

Form heading

Heading: Indicates the general function of button and selector groups

Radio button

l Option Selects from a dis-played menu of mutually exclusive options

Check box R Option Toggles on or off a

program option

Pick-list box

List ¬ Selects items from a pick list form

Scroll list

List o Displays scrollable lists

Slider bar

Parameter –��– Selects parameter values across a con-tinuous range

For a complete description of the function and operation of GUI control ele-ments, see Chapter 3 of the GAMBIT User’s Guide.



Toolpad Command Buttons

In addition to the control elements listed above, GAMBIT also employs tool-pad command buttons in the execution of its operations. Toolpad command buttons are used to perform operations such as opening other toolpads and specification forms and are also used to control the GUI display characteris-tics, such as the screen layout and the orientation of the model in the graphics window.

Toolpad command buttons appear on toolpads located on the upper and lower right portions of the GUI. Each toolpad command button contains a graphical symbol that represents the function of the button. For example, the Examine Mesh command button appears as follows:

.

In this guide, all toolpad command buttons are represented as push buttons containing the graphical symbol appropriate to the button.

Layout Format

Throughout this guide, descriptions of specification forms follow a layout format convention wherein paragraphs describing subgroups of control ele-ments are indented relative to their respective headings or groups. For example, the description of the Create Straight Edge form (see Section 2.3.1) appears as follows.

Using the Create Straight Edge Form

To open the Create Straight Edge form (see below), click the Create Straight Edge command button on the Geometry/Edge subpad.

The Create Straight Edge form includes the following specifications.

INTRODUCTION Format and Font Conventions


Vertices ¬ specifies the vertices that constitute the endpoints of the edges.

Type: —————————————————————————

l Real specifies the creation of a real edge.

l Virtual specifies the creation of a virtual edge. If you choose the Virtual option, you can also specify a host edge, face, or volume for the virtual edge.

R Host specifies that any created virtual edges are hosted by an existing volume, face, or edge.

Volume q Face Edge

specifies the host entity type.

Volume ¬ Face Edge

specifies the host entity name.

Label specifies a label for the new edge. (See Section 2.1.1.)

Note that the Real and Virtual radio button descriptions are indented relative to that of the Type: heading, because they constitute subcomponents of that heading.



1.1.2 Fonts

The following font conventions are used throughout this guide to represent user input data, the titles of forms and command buttons, and the names of modeling objects, such as topological entities and coordinate systems.

Font Description Example(s)

Courier New User keyboard input, such as command line arguments and file names

gambit value

Courier New, Italic Command line options filename vertex

Arial Narrow, Bold Titles of buttons, selectors, and form fields

Model Volume Vertex

Arial Narrow Titles of options and commands

Interval size Lower topology

Arial Narrow, Italic Names of GAMBIT topological entities, coordi-nate systems, and boundary layers

edge.1 vertex.1 c_sys.1 b_layer.1

INTRODUCTION Modeling Guide—Outline


1.2 Modeling Guide—Outline

The following table summarizes the content of this guide.

Chapter Title Description

1 Introduction A brief overview of this guide

2 Creating the Geometry Geometry operations, such as creating volumes and splitting or merging edges or faces

3 Meshing the Model Meshing operations, such as specifying boundary conditions and setting face vertex types

4 Specifying Zone Types Operations related to the specification of boundary and continuum types

5 Using the Modeling Tools Operations related to GAMBIT procedures, such as creating a coordinate system or activating a grid

6 Postprocessing Results Operations related to the display of simulation results

A Virtual Geometry An overview of “virtual” geometry operations

CREATING THE GEOMETRY

© Fluent Inc., Dec-01 2-1

2. CREATING THE GEOMETRY When you click the Geometry command button on the Operation toolpad, GAMBIT opens the Geometry subpad. The Geometry subpad contains com-mand buttons that allow you to create, move, copy, modify, summarize, and delete vertices, edges, faces, and volumes. The Geometry subpad also contains a command button that allows you to perform operations involving groups of topological entities.

The symbols associated with each of the Geometry subpad command sets are as follows.

Symbol Command Set

Vertex

Edge

Face

Volume

Group

The following sections of this chapter describe general operations related to building a GAMBIT model as well as the commands necessary to create and modify the topological entities listed above.

General Operations CREATING THE GEOMETRY

2-2 © Fluent Inc., Dec-01

2.1 General Operations

2.1.1 Labeling Entities

Each of the GAMBIT modeling forms that allow you to create a new entity also allow you to specify a label for the entity. For example, if you create a vertex using the Create Real Vertex form (Figure 2-1), you can specify a label for the vertex by entering a name in the Label text box at the bottom of the form.

Figure 2-1: Example Create Real Vertex form

If you create an entity or coordinate system without specifying a label, GAMBIT automatically assigns a label to the entity. The automatically assigned label consists of a name representing the entity type followed by a decimal point and an integer—for example, volume.6. Automatically assigned labels for virtual and faceted entities are preceded by the characters “v_” and “ f_”—for example, v_volume.6 and f_edge.12.

u NOTE: For a description of the differences between real, virtual, and faceted entities, see the Appendix of this guide.

CREATING THE GEOMETRY General Operations


GAMBIT uses the following names for automatically labeled entities and coordinate systems.

Item Real Entity Virtual Entity Faceted Entity

Vertex vertex v_vertex f_vertex

Edge edge v_edge f_edge

Face face v_face f_face

Volume volume v_volume f_volume

Group group N/A N/A

Coordinate System c_sys N/A N/A

The integer that GAMBIT assigns to automatically labeled entity names is equal to n+1, where n is the highest integer associated with any currently existing entity of the same type. The value of the assigned integer is independ-ent of whether or not the entity is real or virtual.

The following examples summarize the general rules that GAMBIT uses for automatically labeling new entities.

• If you create a real vertex in a model that already contains vertices labeled vertex.1, vertex.2, and vertex.3, the new vertex is named vertex.4.

• If you create real vertices vertex.1, vertex.2, and vertex.3, then delete vertex.3—so that the model only contains vertex.1 and vertex.2—the next automatically labeled real vertex is named vertex.3.

• If you create real vertices vertex.1, vertex.2, and vertex.3, then delete vertex.2—so that the model only contains vertex.1 and vertex.3, the next automatically labeled real vertex is named vertex.4.



2.1.2 Specifying Entities

Specifying Individual Entities

Many of the modeling forms require you to specify individual entities—such as vertices, edges, or faces—to which to apply the operations specified on the form. When a form requires you to specify one or more individual entities, it contains a list box titled with the entity type. For example, the Create Real Vertex form (see Figure 2-1) requires you to specify the coordinate system with respect to which the vertex is to be positioned; therefore, it contains a list box, titled Coordinate Sys.

Unless otherwise noted, you can specify an individual entity in one of three ways:

• Input the name of the entity in the list box.

• Click the pick-list button at the right side of the list box and select the entity by means of the pick-list form.

• Pick the entity from the model as displayed in the graphics window.

Specifying Multiple Entities

On some forms, GAMBIT provides a single list box for the specification of more than one entity. For example, on the Connect Faces form, GAMBIT pro-vides only one list box for the specification of both faces to be connected. When GAMBIT provides only one list box for the specification of multiple entities, you can specify the entities in one of three ways:

• Input the first entity name, press Enter; and clear the list box. Input the second entity name and press Enter again.

• Click the pick-list button located at the right side of the list box and select the entities by means of the pick-list form.

• Pick a vertex or edge associated with the first entity as displayed in the graphics window and Shift-right-click anywhere else in the graphics window to accept the selection. Then repeat the procedure for the second entity.

u NOTE: To select entities that share a common lower-topology entity, pick the lower-topology entity multiple times. For example, to pick three faces that share a common edge, pick the edge three times.



2.1.3 Working with Coordinate Systems

Some of the GAMBIT modeling forms require you to specify a location in space relative to a specified coordinate system. For example, the Create Real Vertex form shown in Figure 2-1 requires you to specify the three coordinates describing the point at which the vertex is to be created.

You can specify point coordinates with respect to either a global or local coor-dinate system. GAMBIT’s global coordinate system is named c_sys.1, and it cannot be deleted. As a result, it is always available for the specification of coordinates. To specify the coordinates of a point relative to a local coordinate system, you must first create the local system using the procedures outlined in Section 5.1.2 of this guide.

To specify the location of a point, you must specify the following information:

• The reference coordinate system (global or local)

• Three coordinate parameters that describe the point relative to the specified reference system

Specifying Reference Coordinate Systems

You can specify the reference coordinate system in one of three ways:

• Input the name of the coordinate system in the Coordinate Sys list box.

• Click the pick-list button located at the right side of the Coordinate Sys list box and select the system from the coordinate-system pick list.

• Pick the coordinate system (on one of its axes) in the graphics window.



Specifying Coordinate Parameters

To specify a point, you must input three parameters that define its location in space. GAMBIT allows you to specify the three parameters in terms of Carte-sian, cylindrical, or spherical coordinates—regardless of the reference coordi-nate system type. For example, you can specify parameters in terms of spheri-cal coordinates referenced to c_sys.1, which is defined as Cartesian, or in terms of Cartesian coordinates for any local system defined as cylindrical. GAMBIT modifies the titles on the Global and Local text boxes according to the specified location coordinate Type.

The required input parameters for each of the three types of coordinate sys-tems are as follows.

System Type Parameters GAMBIT Titles

Cartesian x y z, , x, y, z

Cylindrical r z, ,θ r, t, z

Spherical r, ,θ φ r, t, p

The angle parameters, θ and φ , must be specified in degrees. They are defined such that vectors are coincident with the x, y, and z axes of a Cartesian coor-dinate system when θ and φ , have the following values.

System Angle Parameter Axis Direction

Cylindrical θ = =0 0, z θ = � =90 0, z

x y

+x +y

Spherical θ φ= = �0 90, θ φ= � = �90 90,

z x

+z +x

When you input values for the coordinate parameters into the Global text boxes on any form, GAMBIT automatically updates the Local text box parameters to reflect the location definition relative to the local coordinate system. Likewise, when you input values into the Local text boxes, GAMBIT updates the Global text box parameters.



2.1.4 Moving, Copying, and Aligning Entities

You can change the position and/or orientation of an entity in one of two ways:

• Move or copy the entity, by means of a Move/Copy form

• Align the entity, by means of an Align form

When you move an entity, GAMBIT changes its position and/or orientation relative to a specified reference object. The reference object can be a coordi-nate system, an axis around which the entity is to be rotated, or a plane relative to which the entity is to be reflected.

When you copy an entity, GAMBIT creates a duplicate of the entity and locates it according to the position and orientation specified on the Move/Copy form. Each copy includes all lower topology associated with the “parent” entity. For example, if you create a single copy of an edge, GAMBIT dupli-cates the edge and the pair of vertices that constitute its endpoints. If you copy an edge that constitutes part of a face or volume, GAMBIT duplicates only the edge and its endpoint vertices and does not duplicate the face or volume of which it is a component.

When you align an entity, GAMBIT changes its position and/or orientation relative to vertices already existing in the model. The GAMBIT alignment procedure constitutes a convenient way to make vertices, edges, faces, or volumes coincide with each other.



Moving an Entity

GAMBIT provides the following options with respect to moving an entity:

• Translate—moves the entity by a specified amount relative to its current position

• Rotate—rotates the entity about a specified axis

• Reflect—reflects the entity relative to a specified reflection plane

• Scale—enlarges or reduces the size of an entity according to a speci-fied scaling factor

Each option is accessible by means of a Move/Copy form, such as that shown in Figure 2-2.

Figure 2-2: Example Move/Copy form

The following sections constitute a general description of each of the four options listed above.



Translating an Entity

When you translate an entity (see Figure 2-3), GAMBIT repositions the entity but does not change its orientation with respect to the reference coordinate system.

Initial position

Final position

A

B

C

D

A

B

C

D

Figure 2-3: Example Move/Copy Volumes:Translate operation

To translate an entity, you must specify the following information:

• The reference coordinate system

• The translation parameters that define the new position of the entity relative to its current position



Rotating an Entity

When you rotate an entity (see Figure 2-4), GAMBIT repositions and re-orients the entity by rotating its vertices and edges about a specified axis.

Initialposition

Finalposition

A

B

C

D

θ

A

B C

D

Rotationalaxis

Figure 2-4: Example Move/Copy Volumes:Rotate operation

To rotate an entity, you must specify the following information:

• The axis around which the entity is to be rotated

• The angle of rotation



Specifying the Axis of Rotation

To rotate an entity, you must specify a vector that defines the axis of rotation. For the purposes of defining an axis of rotation, the magnitude of the vector is unimportant. The direction of the vector, however, defines the direction of rotation that is associated with positive values of the rotational angle. The vector is defined as positive in the direction from the start endpoint to the end endpoint.

You can specify the rotational axis vector in any of the following ways:

• Specify a coordinate system axis

• Specify any two existing vertices

• Specify the locations of any two points in space

• Specify any existing edge, the endpoints of which constitute the end-points of the vector

GAMBIT constructs the vector according to the following conventions:

• If you specify a coordinate system axis, GAMBIT defines the rota-tional axis vector as a unit vector pointing in the direction of the axis.

• If you specify two existing vertices as the endpoints, GAMBIT con-structs the vector from the Start vertex to the End vertex.

• If you specify two points as vector endpoints, GAMBIT constructs the vector from Point 1 to Point 2.

• If you specify an existing edge to define the vector, GAMBIT con-structs the vector from the edge start vertex to the edge end vertex.

Each method listed above employs the Vector Definition form as means of defining the axis of rotation (see “Using the Vector Definition Form“, below). To open the Vector Definition form, click the Axis Define command button on the Move/Copy form. (NOTE: When you select the Rotate option, the Axis Define command button appears in the middle section of the Move/Copy form.)



Reflecting an Entity

When you reflect an entity (see Figure 2-5), GAMBIT repositions the entity so that its vertices are equidistant from but on opposite sides of a specified reflection plane.

Initial position

Final position

Reflection plane

AB

CD

A

BC

D

Figure 2-5: Example Move/Copy Volumes:Reflect operation

To reflect an entity, you must define the plane of reflection. To define the plane of reflection, you must specify a vector normal to the plane.

According to GAMBIT conventions, the start endpoint of the normal vector lies in the plane and, therefore, defines the location of the plane. The end end-point determines the direction of the vector and, therefore, the orientation of the plane.

To specify the endpoints of the normal vector that defines the plane of reflec-tion, you must employ the same procedure used to specify the axis of rotation by means of the Vector Definition form. (See “Using the Vector Definition Form,” below.)



Scaling an Entity

When you scale an entity (see Figure 2-6), GAMBIT changes the size of the entity according to a specified scaling factor. If you specify translation parameters in addition to a scaling factor, GAMBIT also repositions the scaled entity.

Initial volume

Final volume

Referencepoint

Factor = 2.0

Figure 2-6: Scaling of a rectangular brick

To scale an entity, you must specify the following information:

• Reference point

• Scaling factor

The reference point serves as the center projection point for the scaling opera-tion. The scaling factor specifies the magnitude of the change in entity size.



u NOTE: If you specify extreme values for the scaling factor, the scaling opera-tion may produce invalid geometry.

• If you specify very large scaling factors, the scaled geometry may contain gaps between entities that are coincident with tolerance in the unscaled geometry.

• If you specify very small scaling factors, the scaled geometry may be smaller than the minimum allowable value of 10−5.

Projecting the Geometry

When you scale an entity, GAMBIT projects each point associated with entity along a ray drawn from the reference point. For example, when GAMBIT scales a face such as that shown in Figure 2-7, it projects each point associated with the face, including its edges and vertices, away from the reference point.

Initial face

Final face

Referencepoint

L

2L

Factor = 2.0

Figure 2-7: GAMBIT face scaling operation



Specifying the Reference Point

To specify the reference point, you must specify a reference coordinate system (Global or Local) and three spatial coordinates that define the location of the reference point. If any point on the entity to be scaled is coincident with the reference point, the point does not change position as a result of the scaling operation. For example, in the scaling operation illustrated in Figure 2-6, one corner vertex of the rectangular brick volume to be scaled is exactly coincident with the reference point. As a result, the vertex itself does not change position when the brick is scaled.

If none of the vertices associated with the entity are coincident with the refer-ence point, the entire entity is translated during the scaling operation. For example, if the rectangular brick shown in Figure 2-6 is initially offset from the reference point, then all of the vertices, edges, and faces associated with the brick are shifted when the brick is scaled (see Figure 2-8). As a result, the entire brick moves away from the reference point.

Initial volume

Final volume

Referencepoint

Factor = 2.0

Figure 2-8: Scaling of a brick not coincident with the reference point



Moving Lower Topology

When you move an entity, GAMBIT also moves all lower topology associated with the entity. For example, if you move a rectangular brick volume using the Move/Copy Volumes form, GAMBIT translates, rotates, reflects, or scales all vertices, edges, and faces associated with the brick.

Moving Higher Topology and Connected Geometry

When you select the Move option on any Move/Copy form, GAMBIT displays the Connected Geometry option at the bottom of the form. The Connected Geometry option allows you to move entities that are connected to geometry of equal or higher topology. (NOTE: By default, GAMBIT does not move an entity if it is connected to geometry of equal or higher topology. For example, if you attempt to move a vertex that constitutes one corner of a rectangular brick volume, GAMBIT does not, by default, move the vertex, because the vertex is connected to the volume. Similarly, if you attempt to move an edge that is connected to another edge that is not specified for the move operation, GAMBIT does not, by default, move the specified edge.)

To move an entity that is connected to geometry of equal or higher topology, you must select the Connected Geometry option. When you select the Connected Geometry option and move an entity, GAMBIT moves all geometry of equal and higher topology geometry that is associated with the entity. For example, if you select the Connected Geometry option when attempting to move a vertex that constitutes one corner of a rectangular brick volume, GAMBIT moves the entire volume according to the specifications on the Move/Copy Vertices form.

Copying Mesh Information

If you select the Copy option on any Move/Copy form (other than the Move/ Copy Vertices form), GAMBIT displays two options at the bottom of the form:

• Copy mesh linked

• Copy mesh unlinked

Both options specify that any mesh information associated with the original entity is reproduced in the copied entity. The options differ from each other only with respect to whether or not the copied mesh is linked to the mesh on the original entity. For example, if you copy a meshed face and select the Copy mesh linked option, GAMBIT copies the face and its mesh and links the mesh on the copied face to that on the original face. If you select the Copy mesh unlinked option, GAMBIT copies the face and its mesh but does not link the original and copied meshes.



Using Move/Copy Forms

Move/Copy forms allow you to reposition, reorient, and/or create copies of vertices, edges, faces, volumes, or groups. Each type of entity is associated with its own Move/Copy form, but all Move/Copy forms are identical with respect to the types of specifications available on the form. Move/Copy forms differ from each other only with respect to the type of entity being moved or copied.

To open any Move/Copy form, click the Move/Copy command button on the Geometry subpad specific to the entity being moved or copied. For example, to open the Move/Copy Vertices form (Figure 2-9), click the Move/Copy command button on the Geometry/Vertex subpad.

Figure 2-9: Example Move/Copy form



All Move/Copy forms include the following specifications.

Entities ¬ specifies the entities to be moved or copied. The type of entities specified by means of the Entities list box is determined by the nature of the current Move/Copy form. For example, on the Move/Copy Vertices form, the Entities list box is titled “Vertices” and specifies the vertices to be moved or copied.

NOTE: On any Move/Copy form, you can move more than one entity of a given type by means of a single move/copy opera-tion.

All q Pick

• All specifies all entities of the specified type in the model.

• Pick specifies entities selected by means of the Entities list box. (NOTE: If you pick an entity in the graphics window or click in the Entities list box, GAMBIT automatically selects the Pick option.)

l Move specifies that the entities are to be moved.

l Copy specifies that the entities are to be copied. If you choose the Copy option, you must input the number of copies to be created in the text box at the right side of the Copy button.

Operation: —————————————————————————

l Translate specifies that the entities (or copies) are to be translated relative to a specified reference coordinate system. (See “Translating an Entity,” above.)

l Rotate specifies that the entities (or copies) are to be rotated about a specified axis. (See “Rotating an Entity,” above.)

l Reflect specifies that the entities (or copies) are to be reflected across a specified plane. (See “Reflecting an Entity,” above.)

l Scale specifies that the entities (or copies) are to be scaled according to a specified scaling factor. (See “Scaling an Entity,” above.)



R Connected Geometry

(Move option only) specifies that any connected geometry of equal or higher topology moves with the entity to be moved. (NOTE: If the entity to be moved is connected to geometry of equal or higher topology, and you do not specify the Connected Geometry option, GAMBIT does not move the entity.)

R Copy mesh linked

(Copy option only) specifies that any mesh information associated with the original entities is copied along with the entities and that the original and copied meshes are linked.

R Copy mesh unlinked

(Copy option only) specifies that any mesh information associated with the original entities is copied along with the entities and that the original and copied meshes are not linked.

The middle section of the Move/Copy form varies according to the type of operation selected. The following sections describe the specifications available for each operation.

Translation Specifications

When you specify the Translate operation, the middle section of the Move/Copy form appears as shown in Figure 2-9, above. Translate specifications are as follows.

Coordinate ¬ Sys

specifies the reference coordinate system to be used in translat-ing the entities. (See Section 2.1.3.)

Type —————————————————————————

Cartesian q Cylindrical Spherical

specifies the type of coordinate parameters to be used in translating the entities.

Global | Local specifies the translation parameters with respect to either the Global or Local system.



Rotation Specifications

When you specify the Rotate operation, the middle section of the Move/Copy form appears as shown in Figure 2-10.

Figure 2-10: Move/Copy form, Rotate specifications

Rotate specifications are as follows.

Angle specifies the angle of rotation.

Axis —————————————————————————

Define opens the Vector Definition form, which allows you to spec-ify a vector defining the axis of rotation. (See “Using the Vector Definition Form,” below.)

Active Coord. Sys. Vector

displays the endpoint coordinates of the vector that currently defines the axis of rotation. The displayed coordinates of the vector are always defined in terms of the active coordinate system.



Reflection Specifications

When you specify the Reflect operation, the middle section of the Move/Copy Vertices form appears as shown in Figure 2-11.

Figure 2-11: Move/Copy form, Reflect options

Reflect specifications are as follows.

Reflection Plane —————————————————————————

Define opens the Vector Definition form, which allows you to spec-ify a vector defining the plane of reflection. (See “Using the Vector Definition Form,” below.)

Active Coord. Sys. Vector

displays the endpoint coordinates of the vector that currently defines the plane of reflection. The displayed coordinates of the vector are always defined in terms of the active coordinate system.



Scaling Specifications

When you specify the Scale operation, the middle section of the Move/Copy Vertices form appears as shown in Figure 2-12.

Figure 2-12: Move/Copy form, Scale options

Scale specifications are as follows.

Factor specifies the scaling factor to be used in scaling and translating the entities.

Coordinate ¬ Sys

specifies the reference coordinate system to be used in scaling and translating the entities. (See Section 2.1.3.)

Type —————————————————————————


specifies the type of coordinate parameters to be used in translating the entities.

Global | Local specifies the parameters that define the scaling reference point.



Using the Vector Definition Form

The Vector Definition form (see below) allows you to define a vector for use in GAMBIT operations such as the specification of axes of rotation or model orientation (for example, see “Orient Model” in Section 3.4.2 of the GAMBIT User’s Guide). To define a vector, you must specify information regarding its magnitude and direction, as well as the location of its origin. GAMBIT provides several options for specifying such information.

The Vector Definition form includes the following specifications.

Active Coordinate System Vector

displays the coordinates of the origin (Start) and tip (End) for the current vector definition. (NOTE: The Start and End locations are always defined in terms of the active coordinate system.)



R Magnitude specifies the magnitude of the vector. (NOTE: If you input a negative value for the Magnitude parameter, GAMBIT reverses the direction of the vector relative to its Method-option definition but does not change the location of the vector origin.)

Method: —————————————————————————

Coord. Sys. Axis q Edge 2 Points 2 Vertices Screen View

specifies the method to be used for specifying the vector endpoints. The available options are as follows:

• Coord. Sys. Axis—defines the vector with respect to one of the coordinate axes

• Edge—defines the vector by means of the endpoints of an existing edge

• 2 Vertices—defines the vector by means of two existing vertices

• 2 Points—defines the vector by means of two specified locations (points) in space

• Screen View—defines the vector relative to the model orientation currently displayed in the graphics window

The specifications available in the lower section of the Vector Definition form vary according to Method option. The following subsections describe specifi-cations associated with each of the options listed above.



Specifying a Vector Defined by a Coordinate System Axis

When you select the Coord. Sys. Axis option, GAMBIT defines the vector with respect to a coordinate axis. To define the vector, you must specify the following information:

• The coordinate system to be used in defining the vector

• The axis and direction that defines the vector

For this option, the lower portion of the Vector Definition form appears as shown above and includes the following specifications.

Coordinate ¬ Sys.

specifies the reference coordinate system for the vector.

Direction: contains radio buttons that allow you to specify the axis and direction to be used in the vector definition. The available options are as follows:

• X—Positive or Negative

• Y—Positive or Negative

• Z—Positive or Negative

For example, if you specify c_sys.1 in the Coordinate Sys. list box and select the Z Negative orientation option, GAMBIT defines a vector that points in the negative direction along the z axis of c_sys.1 with an origin at the origin of c_sys.1.



Specifying a Vector Defined by a Model Edge

When you select the Edge option, GAMBIT defines the vector by means of the endpoint vertices of an existing edge. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specification.

Figure 2-13: Vector Definition form—Edge option specification

Edge ¬ specifies an edge the endpoints of which define the origin, magnitude, and direction of the vector.

The origin of the vector is located at the edge start endpoint vertex, and its tip is located at its end endpoint vertex. To reverse the direction of the vector, either middle-click the edge to reverse its sense or input a negative value for the Magnitude specification. (For a description of edge start and end vertices and the meaning of edge sense, see Section 2.3.1 of the GAMBIT Modeling Guide.)



Specifying a Vector Defined by Two Vertices

When you select the 2 Vertices option, GAMBIT defines the vector by means of the locations of two existing vertices. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specifications.

Figure 2-14: Vector Definition form—2 Vertices option specifications

Vertices: contains two list boxes that specify vertices defining the origin (Start) and tip (End) of the vector. (NOTE: To reverse the direction of the vector, either switch the Start and End vertex specifications or input a negative value for the Magnitude specification.)



Specifying a Vector Defined by Two Points

When you select the 2 Points option, GAMBIT defines the vector by means of two point locations. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specifications.

Figure 2-15: Vector Definition form—2 Points option specifications

Coordinate Values:

contains two radio buttons that specify the point associated with the values currently displayed in the lower part of the form. The options, Point 1 and Point 2, specify the positions of the vector origin and tip, respectively. (NOTE: To reverse the direction of the vector, either switch the specifications for the two points or input a negative value for the Magnitude specification.)

Coordinate ¬ Sys

specifies the coordinate system of reference for the points that define the vector.

Type ———————————————————————


specifies the type of coordinate system to be used in the current point specification.

Global | Local specifies the location of the point with respect to either the Global or Local system.



Specifying a Vector Defined by the Current Screen View

When you select the Screen View option, GAMBIT defines the vector relative to the current orientation of the model in the graphics window. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specifications.

Figure 2-16: Vector Definition form—Screen View option specifications

Direction: contains a group of paired radio buttons that allow you to specify the vector definition relative to the currently displayed orientation of the model in the graphics window. The six Direction options are as follows:

• Piercing—Out or In

• Horizontal—Right or Left

• Vertical—Up or Down

For example, if you select the Piercing—In option and left-click on a graphics window quadrant, GAMBIT defines a vector pointing directly into the screen with an origin located in the center of the quadrant.



Copying an Entity

To copy an entity, you must specify three types of information:

• The name of the entity to be copied (the “parent” entity)

• The number of copies to be created

• The manner in which the copies are to be repositioned and/or reori-ented relative to the parent entity

Creating a Single Copy of an Entity

When you create a single copy of an entity, GAMBIT duplicates all lower topology associated with the entity and locates the copy according to the specifications on the Move/Copy form. The final position and orientation of the copy is determined according to the same procedures employed when you move an entity. (See “Moving an Entity,” above.)

Creating Multiple Copies of an Entity

When you create multiple copies of an entity, GAMBIT positions, orients, and/or scales the first copy relative to the parent entity and positions, orients, and scales each subsequent copy relative to the previous copy created. For example, if you create two copies of a rectangular brick and specify that the copies are to be translated in the x, y, and z directions, GAMBIT translates the first copy relative to the parent brick and translates the second copy relative to the first copy (see Figure 2-17).



Parent

Copy 1

Copy 2

Figure 2-17: Two translated copies of a rectangular brick

Similarly, if you create two copies of a rectangular brick and specify a scaling factor of 1.5, GAMBIT creates one copy the edges of which are 1.5 times larger than those of the parent brick and another copy the edges of which are 2.25 (= 1.5 � 1.5) times larger than those of the parent brick (see Figure 2-18).

u NOTE: If the parent brick is offset from the scaling reference point, each copy of a multiple set of copies is displaced from the reference point according to the cumulative effect of the scaling factor. For example, if the parent brick shown in Figure 2-18 is offset by 1 unit from a reference point located at the center of the Global coordinate system, the first copy is offset by 1.5 units, and the second copy is offset by 2.25 units.



Parent

Copy 1

Copy 2

Factor = 1.5

Figure 2-18: Two scaled copies of a rectangular brick

Copying Mesh Characteristics

When you copy an entity, GAMBIT allows you to copy any mesh characteris-tics associated with the entity. For example, if you create two copies of an edge containing 10 equally spaced mesh nodes and specify the Copy Mesh option on the Move/Copy Edges form, GAMBIT creates two copies of the edge, and each copy contains 10 equally spaced mesh nodes.

Copying Lower Topology

When you copy an entity, GAMBIT also copies all lower topology associated with the entity. For example, if you copy a rectangular brick volume using the Move/Copy Volumes form, GAMBIT creates a copy of all vertices, edges, and faces associated with the brick.

Copying Higher Topology and Connected Geometry

When you copy an entity, GAMBIT does not copy higher topology or any geometry connected to the entity. For example, if you copy an edge that con-stitutes part of a rectangular brick volume, GAMBIT copies only the edge.



Aligning an Entity

To align an entity, you must specify two types of parameters:

• The entity type and name

• One, two, or three pairs of vertices that define the alignment

The entity type and name determine which entity is to be moved by means of the alignment procedure. The vertex-pair specifications define the extent of the movement in each of the three spherical coordinate directions.

General Three-Step Alignment Procedure

When GAMBIT aligns an entity, it performs the following three operations in sequence.

Step Operation Description

1 Translate Change the position of the entity without affect-ing its orientation relative to the global coordinate system

2 Rotate Change the orientation of the entity by rotating it so that vertices are collinear

3 Plane-align Change the orientation of the entity by rotating it about an axis vector the endpoints of which are defined by two existing vertices

Each step in the procedure is defined by a specified pair of existing vertices. The following example illustrates the overall alignment procedure and the effect of vertex-pair specification on the final position and orientation of an aligned face.



Alignment Example

Consider the two planar, nonaligned faces shown in Figure 2-19. Face face.1 is larger than face.2 and is parallel to the y-z coordinate plane. Face face.2 is not parallel to any coordinate plane.

face.1

face.2

vertex.1

vertex.2

vertex.3

vertex.4

vertex.5

vertex.6

vertex.7

vertex.8

Figure 2-19: Two nonaligned GAMBIT faces

There are several ways to align face.2 such that it is coincident with face.1. One possible procedure is as follows (see Figure 2-20):

1. Translate face.2 so that vertex.5 coincides with vertex.1 (Figure 2-20(a))

2. Rotate face.2 about vertex.1 so that a straight line drawn from vertex.1 to vertex.2 coincides with a straight line drawn from vertex.5 to vertex.6 (Figure 2-20(b))

3. Rotate (plane-align) face.2 about a straight line drawn from vertex.2 to vertex.1 so that a plane defined by vertex.5, vertex.6, and vertex.7 coin-cides with a plane defined by vertex.1, vertex.2, and vertex.3 (Figure 2-20(c))



(a) Translation (b) Rotation

(c) Plane alignment (d) Final configuration

Figure 2-20: GAMBIT face-alignment operations

To define an alignment procedure, such as that shown in Figure 2-20, you must specify vertex pairs that describe each step in the procedure. In GAMBIT, such vertex pairs are specified by means of Align forms (see below).



Align Form Specifications

Each type of entity is associated with its own Align form. For example, the Align Faces form shown in Figure 2-21 is used to align face entities. The Align Vertices, Align Edges, Align Faces, Align Volumes, and Align Groups forms differ from each other only with respect to the type of entity being aligned.

Figure 2-21: Example Align Faces form

The pairs of vertices that define the alignment are classified on each form as Translation, Rotation, and Plane Alignment vertex pairs. Each vertex pair con-sists of a Start vertex and an End vertex. The Start vertex corresponds to the position of the entity before it is aligned. The End vertex corresponds to the position or orientation of the entity after the alignment operation is complete.

For example, the operation illustrated in Figure 2-20 can be defined according to the following specifications on the Align Faces form.



Parameter Specification

Face face.2

Translation Vertex Pair: Start End

vertex.5 vertex.1

Rotation Vertex Pair: Start End

vertex.6 vertex.2

Plane Alignment Vertex Pair: Start End

vertex.8 vertex.4

In most cases, a given final configuration may be associated with more than one set of alignment specifications. For example, there are six different sets of alignment specifications that produce the final configuration shown in Figure 2-20(d). One set of specifications is that listed in the table above. Another set of specifications is as follows.

Parameter Specification


vertex.5 vertex.1


vertex.8 vertex.4

Plane Alignment Vertex Pair: Start End

vertex.6 vertex.2

Effect of Vertex-Pair Specification on Orientation

The final orientation of the aligned entities depends on which vertex pairs are used to define each of the three steps in the alignment procedure. As an exam-ple of the effect of vertex-pair specification on the final orientation, consider the two rectangular faces shown in Figure 2-22. The faces are identical in shape and orientation to those shown in Figure 2-19 but are labeled more gen-erally with respect to their vertices.



A

B

C

D

1

EF

HG

2

Figure 2-22: Two nonaligned rectangular faces

There are several configurations in which Face 2 may be considered to be fully aligned with Face 1. Four such configurations are shown in Figure 2-23. The following table lists one of the possible sets of vertex-pair specifications that result in each of the configurations shown in Figure 2-23.

Parameter (a) (b) (c) (d)


E A

G A

E A

G A


F B

H B

F D

H D

Plane Alignment Start Vertex Pair: End

H D

F D

H B

F B



A

EF

B

C

D

(a)

A

GH

B

C

D

(b)

G E

A

EBH

C

D

(c)

G

F

H F

A

GBF

C

DE

H

(d)

Figure 2-23: Example alignment configurations of two faces

Aligning Lower Topology

When you align an entity, GAMBIT also aligns all lower topology associated with the entity. For example, if you align a rectangular brick volume using the Align Volumes form, GAMBIT translates, rotates, and plane-aligns all vertices, edges, and faces associated with the brick.

Aligning Higher Topology and Connected Geometry

By default, GAMBIT does not align an entity if it constitutes part of higher topology or if it is connected, either directly or indirectly, to other geometry. For example, if a vertex specified on an Align Vertices form constitutes one corner of a rectangular brick volume, GAMBIT does not perform the align-ment operation specified on the form. Likewise, if a face specified on an Align Faces form is connected by means of one of its vertices to another face, GAMBIT does not perform the alignment operation.

To align an entity that constitutes part of higher topology or is connected to other geometry, select the Connected Geometry option on the Align form. When you select the Connected Geometry option, GAMBIT aligns the entity, all higher topology of which the entity is a part, and all geometry connected either to the entity or to any higher topology of which the entity is a part.



Scaling Aligned Entities

If the distances between the first two of the Start vertices differ from the cor-responding distances between the End vertices, GAMBIT activates the Scale option on the Align form. The Scale option allows you to resize the aligned entity to match the distances between the End vertices to which the entity is aligned. For example, if you select the Scale option for the procedure illus-trated in Figure 2-20, GAMBIT resizes face.2 so that the edge defined by vertex.5 and vertex.6 is identical in length to the corresponding edge on face.1.

Start Vertex and End Vertex Specifications

Start and End vertices specified on Align forms may exist independently of the entity or entities to be aligned. For instance, in the example presented above, the final position of face.2 does not depend on whether vertex.1, vertex.2, and vertex.3 exist separately from or constitute the corners of face.1.

If you specify a translation Start vertex that does not constitute part of the entity to be aligned, GAMBIT translates the entity relative to its current posi-tion according to the distance and direction defined by a vector drawn between the translation Start and End vertices. For instance, in the example presented above, if you specify vertex.1 as the translation Start vertex and vertex.2 as the translation End vertex—and do not specify rotation or plane-alignment vertices—GAMBIT translates face.2 as shown in Figure 2-24.

face.1face.2

Initial

Final

vertex.1 (Start vertex)

vertex.2 (End vertex)

Figure 2-24: Specifying Start and End vertices not connected to face.2



Using Align Forms

Align forms allow you to reposition and/or reorient vertices, edges, faces, vol-umes, or groups relative to vertices already existing in the model. Each type of entity is associated with its own Align form, but all Align forms are identical with respect to the types of specifications available. Align forms differ from each other only with respect to the type of entity being aligned.

To open any Align form, click the Align command button on the Geometry sub-pad specific to the entity being aligned. For example, to open the Align Vertices form (Figure 2-25), click the Align command button on the Geometry/Vertex subpad.

Figure 2-25: Example Align form

Each Align form includes the following specifications.

Entities ¬ specifies the entities to be aligned. The type of entities speci-fied by means of the Entity list box is determined by the nature of the current Align form. For example, on the Align Vertices form, the Entity list box is titled “Vertices” and specifies one or more vertices to be aligned.

Translation Vertex Pair:

specifies the translation Start and End vertices. (See “Start Vertex and End Vertex Specifications,” above.)



Rotation Vertex Pair:

specifies the rotation Start and End vertices. (See “Start Vertex and End Vertex Specifications,” above.)

Plane Alignment Vertex Pair:

specifies the plane-alignment Start and End vertices. (See “Start Vertex and End Vertex Specifications,” above.)

R Connected Geometry

specifies that all geometry connected to the vertex is to be aligned according to the specifications on the form. (See “Aligning Higher Topology and Connected Geometry,” above.)

R Scale specifies that all topology to which the vertex is connected is to be scaled to match the distances between the translation, rota-tion, and plane-alignment Start and End vertices. (See “Scaling Aligned Entities,” above.)

CREATING THE GEOMETRY Vertex Commands


2.2 Vertex Commands

The following commands are available on the Geometry/Vertex subpad.

Symbol Command Description

Create Vertex Creates a real vertex at any specified location, a real or virtual vertex on an edge or face, a virtual vertex associ-ated with a volume, or a real or virtual vertex at the intersection of two edges

Slide Virtual Vertex Changes the position of a virtual vertex along the edge or face upon which it was created

Connect Vertices Disconnect Vertices

Connects real and/or virtual vertices; disconnects vertices that are common to two or more entities

Modify Vertex Color Modify Vertex Label

Changes a vertex color; changes a vertex label

Move/Copy Vertices Align Vertices

Moves and/or copies vertices; aligns vertices and connected geometry

Convert Vertices Converts non-real vertices to real vertices

Summarize Vertices Check Vertices Query Vertices Total Entities

Displays vertex summary information; checks validity of vertex topology and geometry; opens a vertex query list; displays entity totals

Delete Vertices Deletes real or virtual vertices

The following sections describe the purpose and operation of each of the Vertex commands listed above.

Vertex Commands CREATING THE GEOMETRY


2.2.1 Create Vertex

The Create Vertex command button allows you to perform the following operations.


Create Real Vertex Creates a real vertex at any specified location

Create Vertex on Edge Creates a real or virtual vertex on an existing real edge

Create Vertex on Face Creates a real or virtual vertex on an existing real face

Create Virtual Vertex on Volume

Creates a virtual vertex associated with an existing real volume

Create Vertices At Edge Intersections

Creates real or virtual vertices at the intersections of two edges

The following sections describe the procedures and specifications required to execute the commands listed above.



Create Real Vertex

The Create Real Vertex command allows you to create a real vertex at any specified location.

Using the Create Real Vertex Form

To open the Create Real Vertex form (see below), click the Create Real Vertex command button on the Geometry/Vertex subpad.

The Create Real Vertex form includes the following specifications.

Coordinate ¬ Sys.

specifies the coordinate system with respect to which the vertex position is specified. (See Section 2.1.3.)

Type ————————————————————————


specifies the type of coordinate parameters to be used in creating the vertex.

Global | Local Specifies the location of the vertex with respect to either the Global or Local system.

Label specifies a label for the new vertex. (See Section 2.1.1).



Create Vertex On Edge

The Create Vertex On Edge command allows you to create a real or virtual vertex on any real edge.

Specifying the Position Parameter, u

When you create a vertex on an edge, GAMBIT associates a position parame-ter, u, with the vertex creation point. The position parameter represents the fraction of total edge length measured from the start endpoint of the edge. For example, if you locate the creation point at the exact center of the edge, the value of u is 0.5.

The default value of u depends on the method used to specify the edge upon which the vertex is created. There are two ways to specify the edge:

• By means of the Edge list box

• By means of the mouse—by picking the edge from the model as dis-played in the graphics window

If you specify the edge by means of the Edge list box, GAMBIT assigns a default value of 0.5 to the parameter u—thereby locating the creation point at the exact center of the edge. To reposition the creation point, you can either input a new value of u or directly input the coordinates of the creation point. If you input coordinates describing a point that does not coincide with the edge, GAMBIT “snaps” the vertex to the edge—that is, GAMBIT changes the coordinates so that the new vertex is projected onto the closest point on the specified edge.

If you specify the edge by means of the mouse, GAMBIT assigns a value of u corresponding to the exact point at which the edge was selected. For example, if you select the edge by picking a point 27.3% of the distance along the edge as measured from the start endpoint, GAMBIT assigns a value of u equal to 0.273. To reposition the vertex using the mouse, drag the vertex along the edge.



u NOTE: When you pick the edge on which the vertex is to be created and release the mouse button, GAMBIT fixes the position of the vertex creation point. If you release the mouse button before the creation point is at the desired position, you can reposition the creation point in one of three ways:

• Input its u value

• Input its coordinates

• Repick the with the middle mouse button and drag the vertex creation point to the desired position

Using the Create Vertex On Edge Form

To open the Create Vertex On Edge form (see below), click the Create Vertex On Edge command button on the Geometry/ Vertex subpad.

The Create Vertex On Edge form includes the following specifications.

Edge ¬ specifies the edge upon which the vertex is created.



Type: —————————————————————————

l Real specifies the creation of a real vertex.

l Virtual specifies the creation of a virtual vertex.

U Value specifies the value of the position parameter, u.

Coordinate ¬ Sys.


Type ————————————————————————




Label specifies a label for the new vertex. (See Section 2.1.1.)



Create Vertex On Face

The Create Vertex On Face command allows you to create a real or virtual vertex on any real face.

Specifying the Position Parameters, u and v

When you create a vertex on a face, GAMBIT associates two position parameters, u and v, with the vertex creation point. The position parameters represent coordinates for a two-dimensional mapping of the creation point. The default values of u and v depend on the method used to specify the face upon which the vertex is created. There are two ways to specify the face:

• By means of the Face list box

• By means of the mouse—by picking the face from the model as dis-played in the graphics window

If you specify the face by means of the Face list box, GAMBIT assigns default values to the parameters u and v that locate the creation point at the center of the face. To reposition the creation point, you can either input new values of u and v or directly input the coordinates of the creation point. If you input coordinates describing a point that does not lie on the specified face, GAMBIT “snaps” the vertex to the face—that is, GAMBIT changes the coordinates so that the new vertex is projected onto the closest point on the face.

If you specify the face by means of the mouse, GAMBIT assigns values of u and v corresponding to the point at which the face was selected. To reposition the vertex using the mouse, drag the vertex in any direction along the face.

u NOTE: When you pick the face on which the vertex is to be created and release the mouse button, GAMBIT fixes the position of the vertex creation point. If you release the mouse button before the creation point is at the desired position, you can reposition the creation point in one of three ways:

• Input its u and v values

• Input its coordinates

• Repick the with the middle mouse button and drag the vertex creation point to the desired position



Using the Create Vertex On Face Form

To open the Create Vertex On Face form (see below), click the Create Vertex On Face command button on the Geometry/ Vertex subpad.

The Create Vertex On Face form contains the following options.

Face ¬ specifies the face upon which the vertex is created.

Type: —————————————————————————

l Real specifies the creation of a real vertex.

l Virtual specifies the creation of a virtual vertex.

U Value specifies the value of the position parameter, u.

V Value specifies the value of the position parameter, v.

Coordinate ¬ Sys.




Type ————————————————————————







Create Virtual Vertex On Volume

The Create Virtual Vertex On Volume command allows you to create a virtual vertex associated with any real volume.

Regardless of whether you specify the volume by means of the Volume list box or by means of the mouse, GAMBIT locates the vertex creation point in the center of the volume by default. To reposition the creation point, you must input its location coordinates.

u NOTE: You cannot use the mouse to create or relocate a virtual vertex associ-ated with a volume.

GAMBIT does not require the new vertex to be located within the volume with which it is associated. Therefore, if you specify vertex coordinates that lie outside the volume, GAMBIT does not “snap” the vertex to the volume.

Using the Create Virtual Vertex On Volume Form

To open the Create Virtual Vertex On Volume form (see below), click the Create Virtual Vertex On Volume command button on the Geometry/Vertex subpad.

The Create Virtual Vertex On Volume form contains the following options.

Volume ¬ specifies the volume within which the vertex is created.



Coordinate ¬ Sys.


Type ————————————————————————







Create Vertices At Edge Intersections

The Create Vertices At Edge Intersections command creates real or virtual ver-tices at the points of intersection (or closest approach) between any two speci-fied edges. Vertices created by means of this command are not connected to either of the edges used to define the points of intersection.

The Create Vertices At Edge Intersections command requires the following input parameters:

• Two edges that define the points at which the vertices are to be created

• Tolerance value (optional)

• Vertex geometry type (optional)

Specifying the Edges

You can specify any combination of real and/or non-real edges to define the points of intersection (or closest approach) at which vertices are to be created. If you specify two edges that intersect or approach each other at more than one location, GAMBIT creates a separate vertex at each point of intersection or closest approach. The types of edges (real or non-real) used to define the points of intersection do not affect the types of vertices that result from the vertex creation operation (see below).

If you specify two edges that intersect or approach each other at or near the endpoint(s) of one of the edges, GAMBIT determines whether or not to create new vertices according to the following criteria (see Figure 2-26):

• If the endpoint of Edge 2 (as specified in the lower pick list on the Create Vertices At Edge Intersections form) lies on or near the body of Edge 1, GAMBIT creates a new vertex (see Figure 2-26(a)).

• If the endpoint of Edge 1 lies on or near the body of Edge 2, GAMBIT does not create a new vertex (see Figure 2-26(b)).



(a) Vertex created (b) Vertex not created

Edge 1

Edge 2

Edge 2

Edge 1

Figure 2-26: Create Vertices At Edge Intersections—Endpoint criteria

Specifying the Tolerance Value

GAMBIT allows you to create vertices at points at which the specified edges do not intersect to within the implicit distance tolerance (10-6). When you select the Tolerance option, GAMBIT creates vertices at the points of closest approach between the specified edges provided that the distance of closest approach is within the specified Tolerance value.

When you employ the Tolerance option and specify two edges that do not intersect to within the distance tolerance, GAMBIT locates the created vertices on Edge 1. For example, if you specify v_edge.5 and edge.17 in the Edge 1 and Edge 2 pick list boxes, respectively, and specify the Tolerance option, GAMBIT locates any created vertices on v_edge.5.

Specifying the Vertex Geometry Type

The Create Vertices At Edge Intersections command allows you to create real or virtual vertices regardless of whether the edges that define the points of intersection are, themselves, real or non-real. For example, it is possible to create a real vertex at the point of intersection between two virtual edges or between a real edge and a virtual edge.

• To create virtual vertices, select the Virtual option on the Create Vertices At Edge Intersections form.

• To create real vertices, deselect the Virtual option.



Using the Create Vertices At Edge Intersections Form

To open the Create Vertices At Edge Intersections form (see below), click the Create Vertices At Edge Intersections command button on the Geometry/Vertex subpad.

The Create Vertices At Edge Intersections form contains the following specifi-cations.

Edge 1 ¬ specifies the first of two edges the intersection point(s) of which locate(s) the position of the created vertex (or vertices).

Edge 2 ¬ specifies the second of two edges the intersection point(s) of which locate(s) the position of the created vertex (or vertices).

R Tolerance specifies that vertices are created at all points of closest approach between the specified edges provided that the distance of closest approach is within the specified Tolerance value.

R Virtual specifies that all created vertices are virtual vertices.

Label specifies a label for the created vertex. (See Section 2.1.1.)



2.2.2 Slide Virtual Vertex

The Slide Virtual Vertex command allows you to interactively move a virtual vertex that is hosted by an edge or face entity and/or to reposition a virtual vertex that is hosted by a volume entity. If you slide an edge- or face-hosted vertex, you cannot slide the vertex to any position that does not lie on its host edge or face, respectively. If you reposition a volume-hosted vertex, you can move the vertex to any location inside or outside the volume.

Changing the Shape of Virtual Entities

When you slide a virtual vertex, GAMBIT changes the shapes and positions of any higher-topology virtual entities connected to the vertex. For example, if you slide a virtual vertex that constitutes one apex of a virtual pyramid, GAMBIT changes the shape of the pyramid to reflect the new position of the vertex.

Sliding the Vertex

There are three ways to slide an edge- or face-hosted virtual vertex along the curve or surface of its host edge or face, respectively.

• Pick the vertex as displayed in the graphics window and drag it to its new position.

• Input values for the vertex position parameters, u and v.

• Input the coordinates of the new vertex location.

If you drag the vertex to its new position using the mouse, GAMBIT restricts its movement to the host entity to which it is attached. If you input values for the position parameters or coordinates that do not lie on the host entity, GAMBIT “snaps” the vertex to the host entity—that is, GAMBIT changes the coordinates so that the vertex moves to the closest point on the entity.

To move a volume-hosted vertex, you must select the vertex and input its new coordinates on the Slide Virtual Vertex form.

Sliding Linked Vertices

GAMBIT allows you to specify whether linked vertices are moved in conjunction with the selected vertex, by means of the Move with links option on the Slide Virtual Vertex form. If you select the Move with links option when sliding a vertex, GAMBIT slides all vertices the host edges of which are linked to the host edge of the selected vertex. If you unselect the Move with links option, GAMBIT moves only the selected vertex.



u NOTE: If you slide a vertex the host edge of which is periodically linked to another edge, GAMBIT moves the corresponding vertex on the linked edge regardless of whether or not you select the Move with links option. (For a description of edge linking operations, see Section 3.2.3 of this guide.)

Using the Slide Virtual Vertex Form

To open the Slide Virtual Vertex form (see below), click the Slide Virtual Vertex command button on the Geometry/Vertex subpad.

The Slide Virtual Vertex form includes the following specifications.

Vertex ¬ specifies the vertex to be moved.

U Value specifies the value of the position parameter, u (edges and faces).

V Value specifies the value of the position parameter, v (faces only).

Coordinate ¬ Sys.

specifies the reference coordinate system for coordinate input values. (See Section 2.1.3.)



Type ————————————————————————



Global | Local Specifies the new location of the vertex with respect to either the Global or Local system.

Label specifies a label for the vertex. (See Section 2.1.1.)

R Move with links moves all vertices that are linked to the selected vertex.



2.2.3 Connect/Disconnect Vertices

The Connect/Disconnect Vertices command button allows you to perform two operations.


Connect Vertices Connects coincident real vertices or creates virtual vertices that represent the connection of two or more existing vertices

Disconnect About Real Vertex

Disconnects edges, faces, and/or volumes that share a common real vertex

The following sections describe the procedures and specifications required to execute the operations listed above.

u NOTE: The Specify Color Mode command button on the Global Control tool-pad allows you to display model colors based on entity connectivity rather than topology. For a description of the use of the Specify Color Mode command button, see the GAMBIT User’s Guide, Section 3.4.2.



Connect Vertices

The Connect Vertices command allows you to connect two or more vertices.

To connect vertices, you must specify the following parameters:

• Two or more vertices to be connected

• The connection type

Specifying the Vertices to Be Connected

The vertices to be connected can be real or virtual, but they are subject to certain restrictions imposed by the connection type (see below).

Specifying the Connection Type

There are four types of vertex connection operations:

• Real

• Virtual (Forced)

• Virtual (Tolerance)

• Real and Virtual (Tolerance)

If you connect a set of vertices using a Virtual (Forced), Virtual (Tolerance), or Real and Virtual (Tolerance) operation, GAMBIT allows you to specify the loca-tion of the vertex resulting from the connect operation by means of the Preserve first vertex location option (see below).

The following sections describe the basic features of each connection type.

Specifying a Real Connection

The Real option allows you to connect coincident real vertices. When you con-nect real vertices and specify the Real option, GAMBIT deletes all but one of the specified vertices and connects the remaining real vertex to all higher topology associated with the deleted vertices.

u NOTE: For the purpose of connecting vertices, GAMBIT defines coincidence with respect to a global tolerance value of 10-6.

As an example of the Real connection operation, consider the configuration shown in Figure 2-27, in which two real, unconnected edges are located such that two of their endpoint vertices (vertex.2 and vertex.3) are coincident.



vertex.1

edge.1

vertex.2 and vertex.3 (coincident)

vertex.4

edge.2

(a) Before connection

vertex.1

edge.1

vertex.2

vertex.4

edge.2

(b) After connection

Figure 2-27: Connecting vertices, Real option

If you connect vertex.2 and vertex.3 by means of the Real connection operation, GAMBIT deletes vertex.3 and redefines edge.2 such that its endpoints are vertex.2 and vertex.4. As a result, edge.1 and edge.2 share a common end-point—that is, vertex.2—and are, therefore, connected.

Specifying a Virtual (Forced) Connection

The Virtual (Forced) option allows you to connect real or virtual vertices, regardless of their proximity to each other. When you connect vertices and specify the Virtual (Forced) option, GAMBIT replaces all of the specified verti-ces with a single virtual vertex. If a specified vertex constitutes the endpoint of an edge, GAMBIT overlays the edge with a virtual edge and positions the virtual edge according to the location of the new virtual vertex. If the edge is connected to a face and/or volume, GAMBIT overlays the face and/or volume with a corresponding virtual entity.



Specifying a Virtual (Tolerance) Connection

The Virtual (Tolerance) option allows you to specify that only those vertices that are near to each other to within a specified tolerance are connected. There are two ways to express the tolerance value:

• Tolerance

• Shortest Edge%

The Tolerance specification represents the tolerance value as expressed in absolute distance units. The Shortest Edge% specification represents the toler-ance value expressed as a percentage of the length of the shortest edge.

Specifying a Real and Virtual (Tolerance) Connection

When you specify the Real and Virtual (Tolerance) option, GAMBIT performs the following two operations in sequence:

1) Real connect operations for vertices that are coincident to within the global tolerance value

2) Virtual (Tolerance) connect operations for unconnected, specified verti-ces that are near to each other to within the user-specified tolerance

Preserving the First Vertex Location

If you connect a set of vertices using a Virtual (Forced), Virtual (Tolerance), or Real and Virtual (Tolerance) operation, you can specify the location of the resulting vertex by means of the Preserve first vertex location option. When you select the Preserve first vertex location option, GAMBIT places the vertex resulting from the connect operation at the location of the first vertex listed in the Vertices list.

As an example of the effect of the Preserve first vertex location option, consider the set of edges shown in Figure 2-28(a).



edge.1vertex.3

vertex.2vertex.1

edge.2

vertex.4(a) (b)

(c) (d)

v_edge.3

v_vertex.5

v_edge.4

v_edge.3v_vertex.5

v_edge.4

v_edge.3v_vertex.5

v_edge.4

Figure 2-28: Effect of Preserve first vertex location option

If you connect vertex.1 and vertex.3 by means of either the Virtual (Forced) or Virtual (Tolerance) operation, the location of the created vertex (v_vertex.5) and shapes of the created edges (v_edge.3 and v_edge.4) depend on which original vertex is listed first in the Vertices list.

• If vertex.1 is listed first, v_vertex.5 is created at the original location of vertex.1 (see Figure 2-28(b)).

• If vertex.3 is listed first, v_vertex.5 is created at the original location of vertex.3 (see Figure 2-28(c)).

If you do not select the Preserve first vertex location option when connecting the vertices, GAMBIT creates v_vertex.5 at a location intermediate to the original locations of vertex.1 and vertex.3 (see Figure 2-28(d)).



Using the Connect Vertices Form

To open the Connect Vertices form (see below), click the Connect command button on the Geometry/Vertex subpad.

The Connect Vertices form includes the following specifications.

Vertices ¬ specifies the vertices to be connected.

l Real specifies that the vertex that results from the connection of vertices is a real vertex. (NOTE: To obtain a real vertex from the connection of two or more real vertices, the specified vertices must be coincident.)

l Virtual (Forced) specifies the following characteristics for the vertex that results from the connection of vertices:

• The vertex is a virtual vertex

• The vertex is created regardless of the distance between the specified vertices

l Virtual (Tolerance) specifies the following characteristics for the vertex that results from the connection of vertices:

• The vertex is a virtual vertex

• The specified vertices are connected only if the dis-tance between them is less than a specified tolerance (see below)



l Real and Virtual (Tolerance)

specifies the following sequence of operations:

1) Real connect operations where possible

2) Virtual (Tolerance) connect operations for the remaining specified, unconnected vertices

Tolerance specifies the maximum allowable distance (absolute units) between vertices to be connected.

Shortest Edge % specifies the maximum allowable distance (percent of shortest edge) between vertices to be connected.

Highlight shortest edge highlights the shortest edge that exists in the current model.

R Preserve first vertex location

creates the new vertex at the location of the first vertex listed in the Vertices list.



Disconnect About Real Vertex

The Disconnect About Real Vertex command allows you to disconnect topo-logical entities that share a common vertex.

When you disconnect edges, faces, and/or volumes about a common vertex, GAMBIT creates a separate vertex for each entity to which the specified ver-tex is connected. As a result, the entities are disconnected and can be treated (for example, moved or aligned) independently with respect to each other.

As an example of the vertex disconnection procedure, consider the configura-tion shown in Figure 2-29, in which face.1 and edge.5 share a common vertex (vertex.4). If you disconnect the topology about vertex.4, GAMBIT creates a new vertex (vertex.6) that is coincident with vertex.4 and assigns it as an end-point of edge.5. As a result, face.1 and edge.5 are disconnected from each other.

vertex.1

vertex.3

vertex.4 (and vertex.6)

vertex.2

edge.5

edge.4

edge.3

edge.2

edge.1

face.1

vertex.5

Figure 2-29: Disconnecting entities about a common vertex

u NOTE: GAMBIT does not allow you to disconnect topology around a vertex that constitutes part of an individual face or volume. For example, you cannot disconnect edge.1 and edge.2 about vertex.1 in Figure 2-29, because vertex.1 constitutes one corner of a single topological entity—that is, face.1.



Using the Disconnect About Real Vertex Form

To open the Disconnect About Real Vertex form (see below), click the Disconnect command button on the Geometry/Vertex subpad.

The Disconnect About Real Vertex form includes only a list box that allows you to specify the vertex about which the topology is to be disconnected.



2.2.4 Modify Vertex Color/Label

The Modify Vertex Color/Label command button allows you to perform two operations.

Symbol Operation Description

Modify Vertex Color Changes the color of the geometry and/or mesh nodes associated with one or more vertices as displayed in the graphics window

Modify Vertex Label Changes a vertex label




Modify Vertex Color

The Modify Vertex Color command allows you to change the displayed color of the geometry and/or mesh associated with one or more vertices.

To modify the Geometry or Mesh color specification on the Modify Vertex Color form, click the color bar located immediately to the right of the Geometry or Mesh check box, respectively. When you do so, GAMBIT opens the Set Color form. The Set Color form allows you to select a color from a preset list of available colors. (See “Using the Set Color Form,” below.)

Using the Modify Vertex Color Form

To open the Modify Vertex Color form (see below), click the Modify Color command button on the Geometry/Vertex subpad.

The Modify Vertex Color form includes the following specifications.

Vertices ¬ specifies one or more vertices the color of which is to be modified.

Color: —————————————————————————

R Geometry specifies modifying the color of the picked vertices.

R Mesh specifies modifying the color of the mesh associated with the picked vertices.



Using the Set Color Form

To open the Set Color form (see below), click either the Geometry or Mesh color bar on the Modify Vertex Color form.

The Set Color form includes the following specifications.

Color name specifies the color by name.

Colors: o allows you to select a color from a list of available colors. GAMBIT displays the currently selected color as a color band located immediately above the Colors: scroll list.



Modify Vertex Label

The Modify Vertex Label command allows you to change the label associated with any vertex.

Using the Modify Vertex Label Form

To open the Modify Vertex Label form (see below), click the Modify Label command button on the Geometry/Vertex subpad.

The Modify Vertex Label form includes the following specifications.

Vertex ¬ specifies the vertex to be modified.

Label specifies a new label for the vertex. (See Section 2.1.1).



2.2.5 Move/Copy/Align Vertices

The Move/Copy/Align Vertices command button allows you to perform two operations.


Move/Copy Vertices Moves and copies vertices

Align Vertices Aligns vertices and connected geome-try with existing topological entities




Move/Copy Vertices

The Move/Copy Vertices command allows you to reposition one or more verti-ces or to create copies of vertices. For a description of the procedures and specifications required to move and/or copy entities, see “Moving an Entity“ and “Copying an Entity,” respectively, in Section 2.1.4.

Using the Move/Copy Vertices Form

To open the Move/Copy Vertices form (see below), click the Move/Copy command button on the Geometry/Vertex subpad.

For a complete description of the specifications available on the Move/Copy Vertices form, see “Using Move/Copy Forms“ in Section 2.1.4.



Align Vertices

The Align Vertices command allows you to reposition a vertex so that it coin-cides with another vertex. When you align a vertex, GAMBIT translates the vertex according to the specifications on the Align Vertices form. You cannot rotate or plane-align a vertex because vertices are zero-dimensional entities. (For a general description of the procedure and specifications required to align an entity, see “Aligning an Entity,” in Section 2.1.4.)

Using the Align Vertices Form

To open the Align Vertices form (see below), click the Align command button on the Geometry/Vertex subpad.

For a complete description of the specifications available on the Align Vertices form, see “Using Align Forms“ in Section 2.1.4.



2.2.6 Convert Vertices

The Convert Vertices command converts one or more non-real (faceted and/or virtual) vertices to real vertices. The topology and any existing mesh associ-ated with the converted vertices are preserved in the conversion process.

Using the Convert Vertices Form

To open the Convert Vertices form (see below), click the Convert Vertices command button on the Geometry/Vertex subpad.

The Convert Vertices form includes the following specifications.

Vertices ¬ specifies which non-real vertices are to be converted to real vertices.

All q Pick

• All specifies all vertices in the model.

• Pick specifies vertices selected by means of the Vertices list box. (NOTE: If you pick a vertex in the graphics window or click in the Vertices list box, GAMBIT automatically selects the Pick option.)



2.2.7 Summarize/Check/Query Vertices and Total Entities

The Summarize/Check/Query Vertices and Total Entities command button lets you perform the following operations.


Summarize Vertices Displays vertex summary information in the Transcript window

Check Vertices Checks the topological and geometric validity of model vertices

Query Vertices Opens the vertex query list

Total Entities Displays in the Transcript window the total number of entities of one or more specified types




Summarize Vertices

The Summarize Vertices command displays vertex summary information in the Transcript window. The summary information includes the vertex name, mesh status, and the coordinates of the vertex relative to the global coordinate system.

Using the Summarize Vertices Form

To open the Summarize Vertices form (see below), click the Summarize com-mand button on the Geometry/Vertex subpad.

The Summarize Vertices form includes the following specifications.

Vertices ¬ specifies one or more vertices for which information is to be summarized in the Transcript window.

All q Pick





Check Vertices

The Check Vertices command assesses the topological and/or geometric valid-ity of vertices in the model and summarizes the results in the Transcript window.

When you execute the Check Vertices command, GAMBIT checks the model to determine its validity with respect to either or both of the following types of characteristics:

• Topology

• Geometry

Topology refers to the spatial relationships between entities. Geometry refers to proximity and shape characteristics of the model.

u NOTE: Failure of the topology and/or geometry check for any vertex in the model constitutes a serious problem for the model as a whole. GAMBIT does not currently include any tools that allow you to repair problems that cause failures of topology or geometry checks for vertices.

Topology Check

Topological validity is an assessment of the underlying organization of the model—for example, the correct associations between a face entity and the edges that comprise its boundaries or between entities that are associated with each other by virtue of a virtual-geometry, guest-host relationship.

For a given vertex, the Check Vertices topology check operation examines the model to ensure that it meets the following criteria:

• Upper-topology edges associated with the vertex correctly reference the vertex.

• Any virtual entities that are guests of the vertex correctly reference the vertex as a host.



Geometry Check

Geometrical validity is an assessment of the model with respect to proximity and shape characteristics—such as the distances between connected edges and/or the mathematical continuity of model curves and surfaces. The Check Vertices geometry check criteria are as follows:

• All real vertices correctly reference the ACIS model.

• Any virtual-vertex hosts are of the correct type. For example, a virtual vertex formed by connecting two vertices must reference only the two vertices as hosts. Similarly, a virtual vertex defined on an edge, face, or volume must not be hosted by a vertex. (NOTE: The vertex geometry check operation also checks the validity of host geometry.)

Using the Check Vertices Form

To open the Check Vertices form (see below), click the Check command button on the Geometry/Vertex subpad.

The Check Vertices form includes the following specifications.

Vertices ¬ specifies the vertices to be included in the checking operations.

All q Pick



R Check Topology specifies a topology check on the selected vertices.

R Check Geometry specifies a geometry check on the selected vertices.



Query Vertices

The Query Vertices command allows you to identify the location and/or the names of specific vertices.

When you execute the Query Vertices command, GAMBIT opens the Query Vertices form, which lists all vertices currently existing in the model. The Query Vertices form allows you to identify individual vertices, one at a time, or subsets of vertices by means of a label filter.

Identifying Vertices

To identify the location of a vertex in the graphics window, highlight (left-click) its name in the query list. GAMBIT displays the vertex in red in the graphics window.

To identify the name of a vertex in the query list, pick the vertex in the graph-ics window. GAMBIT highlights the vertex name in the query list.

Specifying a Label Filter

GAMBIT allows you to identify subsets of vertices by means of the Filter text box on the Query Vertices form. To highlight a subset of vertices, input a string value common to all vertices in the subset. For example, if you specify the filter string, “vertex.2,” GAMBIT highlights vertex.2; vertex.20, vertex.21, . . ., vertex.29; vertex.200, vertex.201, . . ., vertex.299, and so on.



Using the Query Vertices Form

To open the Query Vertices form (see below), click the Query command button on the Geometry/Vertex subpad.

The Query Vertices form includes the following specifications.

Label Names o contains the names of all vertices currently existing in the model. Vertices corresponding to highlighted names are dis-played in red in the graphics window.

Filter specifies the filter text string.

R Label specifies that labels corresponding to highlighted vertex names are displayed in the graphics window.



Total Entities

The Total Entities command displays in the Transcript window the total number of geometry and/or mesh entities that currently exist in the model. For example, if you select the Geometry entities option on the Total Entities form and click Apply, GAMBIT displays in the Transcript window the total numbers of vertices, edges, faces, volumes, groups, and coordinate systems that currently exist in the model.

Using the Total Entities Form

To open the Total Entities form (see below), click the Total command button on the Geometry/Vertex subpad.

The Total Entities form includes two check boxes that allow you to specify the types of entities the totals of which are displayed in the Transcript window. It includes the following options.

• Geometry entities

• Mesh entities



2.2.8 Delete Vertices

The Delete Vertices command allows you to delete one or more vertices from the model.

The Delete Vertices operation is subject to the following restrictions:

• GAMBIT does not allow you to delete vertices that constitute parts of higher-topology entities. For example, you cannot delete a vertex that constitutes the endpoint of an edge or one corner of a volume.

• If you delete a virtual vertex that constitutes the connection of two or more real or virtual vertices, GAMBIT restores the real vertices when it deletes the specified vertex.

Deleting Virtual Vertices

If you delete a virtual vertex, GAMBIT deletes all virtual hierarchy that is associated with the vertex and is not associated with any other entities in the model.

Using the Delete Vertices Form

To open the Delete Vertices form (see below), click the Delete command button on the Geometry/Vertex subpad.

The Delete Vertices form includes the following specifications.

Vertices ¬ specifies one or more vertices to be deleted.

All q Pick



CREATING THE GEOMETRY Edge Commands


2.3 Edge Commands

The following commands are available on the Geometry/Edge subpad.


Create Edge Creates a real or virtual edge

Connect Edges Disconnect Edges

Connects real and/or virtual edges; disconnects edges that are common to two or more entities

Modify Edge Color Modify Edge Label

Changes an edge color; changes an edge label

Move/Copy Edges Align Edges

Moves and/or copies edges; aligns edges and connected geometry

Split Edge Merge Edges

Splits or merges edges

Convert Edges Converts non-real edges to real edges

Summarize Edges Check Edges Query Edges Total Entities

Displays edge summary information; checks validity of edge topology and geometry; opens an edge query list; displays entity totals

Delete Edges Deletes real or virtual edges

The following sections describe the purpose and operation of each of the Edge commands listed above.

Edge Commands CREATING THE GEOMETRY


2.3.1 Create Edge

The Create Edge command button allows you to perform the following opera-tions.


Create Straight Edge Creates one or more straight edges between two or more existing vertices

Create Real Circular Arc Creates a circular arc edge

Create Real Full Circle Creates a full circle edge

Create Real Elliptical Arc Creates an elliptical arc edge

Create Real Conic Arc Creates a conic arc edge

Create Real Fillet Arc Creates a fillet arc of a specified radius between two existing edges

Create Real Edge From Vertices

Creates a NURBS edge according to the specification of three or more existing vertices

Revolve Vertices Creates one or more circular arc edges by revolving existing vertices

Project Edge On Face Projects an existing edge onto an existing face to create a new edge that follows the contour of the face




Create Straight Edge

The Create Straight Edge command allows you to create one or more straight edges between any two or more existing vertices. The created edges can be real or virtual.

The Create Straight Edge command requires the following input parameters:

• Two or more vertices that comprise the endpoints of the edge(s) to be created

• Edge geometry type (real or virtual)

• Host entity (optional)

Specifying the Endpoint Vertices

Creating a Single Edge

To create an edge by means of the Create Straight Edge command, you must specify two vertices that comprise the endpoints of the edge. GAMBIT defines the sense of the edge based on the order in which the vertices are specified. The edge sense points from the first (start) vertex to the second (end) vertex (see Figure 2-30).

Start vertex End vertex

Sense

�

�

� �

Figure 2-30: Straight edge specifications

Creating Multiple Edges

If you specify more than two vertices on the Create Straight Edge form, GAMBIT creates multiple edges from a single operation. The order in which the vertices are specified determines the locations and connectivity of the created edges. For example, if you specify (in order) three vertices labeled vertex.1, vertex.7, and vertex.3 for a Create Straight Edge operation, GAMBIT creates two edges defined as follows.



Edge Start Vertex End Vertex

edge.1 vertex.1 vertex.7

edge.2 vertex.7 vertex.3

Note that the two edges defined in the table above are connected to each other by means of vertex.7.

Specifying the Geometry Type

The Create Straight Edge command allows you to create either real or virtual edges. The geometry type (real or virtual) of the created edge is subject to the following constraints for vertex specification:

• To create a real edge, you must specify two real endpoint vertices.

• To create a virtual edge, you can specify any combination of real or virtual endpoint vertices.

Specifying the Host Entity

If you create a virtual edge by means of the Create Straight Edge command, GAMBIT allows you to specify whether the virtual edge is hosted or unhosted. Hosted edges possess guest-host relationships with existing volumes, faces, or edges. Unhosted edges exist on their own and do not possess guest-host relationships with any other entities in the model.



Using the Create Straight Edge Form

To open the Create Straight Edge form (see below), click the Create Straight Edge command button on the Geometry/Edge subpad.

The Create Straight Edge form includes the following specifications.

Vertices ¬ specifies the vertices that constitute the endpoints of the edges.

Type: —————————————————————————

l Real specifies the creation of a real edge.

l Virtual specifies the creation of a virtual edge. If you choose the Virtual option, you can also specify a host edge, face, or vol-ume for the virtual edge.

R Host specifies that any created virtual edges are hosted by an existing volume, face, or edge.


specifies the host entity type.

Volume ¬ Face Edge

specifies the host entity name.




Create Real Circular Arc

The Create Real Circular Arc command allows you to create a real edge in the shape of a circular arc.

GAMBIT provides three methods for creating a circular arc edge. Two meth-ods require you to specify three existing vertices to define the size and location of the arc. The other method requires the specification of the arc radius, angle, center, and coordinate plane. The input parameters associated with each method are as follows:

Method Parameters

1 • One vertex that constitutes the center of the circle upon which the arc lies

• Two vertices that define the endpoints of the arc

2 • Three vertices that lie on the arc

3 • Arc radius

• Start and end angles

• Center of the arc sweep

• Coordinate plane in which the arc lies

The following sections describe the specifications required to create a circular arc edge by means of the methods listed above.



Method 1—Center Vertex and Two Endpoint Vertices

To create a circular arc edge by means of Method 1, you must specify one center vertex and two endpoint vertices. The endpoint vertices must be equi-distant from the center vertex (see Figure 2-31). You must also specify whether the edge is to be created along the longer or shorter of the two circu-lar arcs that can be constructed between the endpoint vertices.

Sense of longer arc

�

�

�

�Center

End-Points

rr

2

1

�

� �

� Sense of shorter arc

Figure 2-31: Circular arc edge specifications—Method 1



Method 2—Three Vertices on the Arc

To create a circular arc edge by means of Method 2, you must specify three vertices each of which lies on the circle that defines the size and shape of the arc. GAMBIT constructs the edge from the first specified vertex through the second specified vertex to the third specified vertex (see Figure 2-32). There-fore, the first and third specified vertices constitute the endpoints of the edge.

Sense

�

�

�

�

Vertices

2

1

�

� �

�

3




Method 3—Radius, Angle, Center, and Plane

To create a circular arc edge by means of Method 3, you must specify the fol-lowing parameters (see Figure 2-33):

• Radius

• Start Angle and End Angle that define the arc sweep

• Center vertex (optional)

• Plane in which the arc lies

Sense

Center

Start Angle

End Angle

Radius


The Radius, Start Angle, and End Angle specifications define the size and sweep of the arc. The Center vertex specification defines the global location of the arc. (NOTE: If you do not specify a Center vertex, GAMBIT locates the center of the arc at the center of the currently active coordinate system.) The Plane specification defines the coordinate plane in which the arc lies.



Using the Create Real Circular Arc Form

To open the Create Real Circular Arc form (see below), click the Create Real Circular Arc command button on the Geometry/Edge subpad.

The Create Real Circular Arc form includes the following specifications.

Method: contains three radio buttons that allow you to specify the method by which the arc is created. The methods are briefly described as follows:

• Method 1—Specify one vertex that constitutes the center of a circle containing the arc and two other verti-ces that constitute the endpoints of the arc

• Method 2—Specify three vertices that lie on the arc

• Method 3—Specify the arc radius, angle, center, and plane



The center section of the Create Real Circular Arc form varies according to the method selected to construct the arc edge. The specifications available on the center section of the form are as follows.

Method 1

Vertex: —————————————————————————

Center ¬ specifies the vertex that constitutes the center of the arc.

End-Points ¬ specifies the vertices that constitute the endpoints of the arc.

Arc: allows you to specify whether the created edge represents the shorter or longer arc between the endpoints.

Label (both methods) specifies a label for the new edge. (See Section 2.1.1.)

Method 2

When you specify Method 2 for the creation of a circular arc edge, the middle section of the Create Real Circular Arc form appears as shown below.

Vertices ¬ specifies the three vertices that lie on the arc.



Method 3

When you specify Method 3 for the creation of a circular arc edge, the middle section of the Create Real Circular Arc form appears as shown below.

Radius specifies the radius of the arc.

Start Angle specifies the start angle for the arc as measured from one of the two coordinate axes on the selected coordinate plane.

End Angle specifies the end angle for the arc.

R Center specifies that the center of the arc is defined by an existing vertex.

Center ¬ specifies the vertex that defines the center of the arc.

Plane —————————————————————————

XY q YZ ZX

specifies the coordinate plane in which the arc lies.



Create Real Full Circle

The Create Real Full Circle command allows you to create an edge in the shape of a full circle.

GAMBIT provides two methods for creating an edge in the shape of a full circle. Both methods require you to specify three existing vertices to define the size and location of the circle. The methods are defined as follows:

• Method 1—specifies one vertex that constitutes the center of the circle and two vertices that lie on the circle

• Method 2—specifies three vertices that lie on the circle

Method 1 (Figure 2-34(a)) requires that the two vertices that lie on the circle itself are equidistant from the vertex at the center of the circle. Method 2 (Figure 2-34(b)) requires only that the three specified vertices are not collinear.

a) Method 1 b) Method 2

rr

Center

End-Points

1

21

2

3

Sense Sense

Vertices

�

�

Figure 2-34: Full-circle edge specifications



Using the Create Real Full Circle Form

To open the Create Real Full Circle form (see below), click the Create Real Full Circle command button on the Geometry/Edge subpad.

The Create Real Full Circle form includes the following specifications.

Method: contains two radio buttons that allow you to specify the method by which the circle is created. For either method, you must specify three vertices. The two methods differ in their treatment of the vertices as follows:

• Method 1—One vertex constitutes the center of a circle containing the arc, and the other two vertices lie on the circle itself

• Method 2—All three vertices lie on the circle

The center section of the Create Real Full Circle form varies according to the method selected to construct the circle. The specifications available on the center section of the form are as follows.

Method 1

Vertices: —————————————————————————

Center ¬ specifies the vertex that constitutes the center of the circle.

End-Points ¬ specifies the vertices that lie on the circle.

Label (both methods) specifies a label for the new edge. (See Section 2.1.1.)



Method 2

When you specify Method 2 for the creation of a full circle, the middle section of the Create Real Full Circle form appears as shown below.

Vertices ¬ specifies the three vertices that lie on the circle.



Create Real Elliptical Arc

The Create Real Elliptical Arc command allows you to create an edge in the shape of an elliptical arc.

To create an elliptical arc edge, you must specify the following parameters (see Figure 2-35):

• Center vertex—located at the center of the ellipse

• Major vertex—defines the length of the major axis

• On Edge vertex—defines the dimensions of the ellipse

• Start angle and Stop angle for the edge—define the length and position of the edge along the elliptical arc

Sense

Center

Start�angle

Stop�angle

Major

On Edge

Figure 2-35: Elliptical arc edge specifications

The Center, Major, and On Edge vertices define the shape and size of the full ellipse of which the arc edge is a part. The Start angle and Stop angle define the length of the edge as well as its angular position relative to a reference vector constructed from the Center vertex to the Major vertex. (NOTE: The three vertices that define the ellipse must not be collinear.)



Using the Create Real Elliptical Arc Form

To open the Create Real Elliptical Arc form (see below), click the Create Real Elliptical Arc command button on the Geometry/Edge subpad.

The Create Real Elliptical Arc form includes the following specifications.

Vertex: —————————————————————————

Center ¬ specifies the vertex that constitutes the center of the ellipse.

Major ¬ specifies the vertex that defines the major axis of the ellipse.

On Edge ¬ specifies a vertex that lies on the edge of the full ellipse. If a vector drawn from the Center vertex to the On Edge vertex is at right angles to a vector drawn from the Center vertex to the Major vertex, then the distance between the Center vertex and the On Edge vertex exactly defines the length of the minor axis.



Angle: allows you to specify the angle encompassed by the elliptical edge. The zero-angle reference vector points from the Center vertex to the Major vertex.

Start specifies the start angle for the elliptical arc.

End specifies the end angle for the elliptical arc.




Create Real Conic Arc

The Create Real Conic Arc command allows you to create an edge in the shape of a conic arc.

To create a conic arc edge, you must specify the following parameters (see Figure 2-36):

• Start vertex—specifies the start endpoint

• Shoulder vertex—specifies the apex of the arc

• End vertex—specifies the end endpoint

• Shape Parameter—specifies the general shape of the arc (elliptical, parabolic, or hyperbolic)

Start

Shoulder

End

Hyperbolicr > 0.5

Ellipticalr < 0.5

Parabolicr = 0.5

r = Shape Parameter

Sense

Figure 2-36: Conic edge specifications



Specifying the Start, Shoulder, and End Vertices

The Start, Shoulder, and End vertices specify the location and sense of the conic arc edge. The sense of the edge points from the Start vertex to the End vertex.

The Shoulder vertex constitutes the apex of the conic arc, and its position of the Shoulder vertex determines whether or not the conic edge is symmetric with respect to the Start and End vertices. If the Shoulder vertex is equidistant from the Start and End vertices (as shown in Figure 2-36) then the conic arc edge is symmetric.

Specifying the Shape Parameter

The Shape Parameter specifies the shape of the conic arc edge. Its allowable values range from 0.01 to 0.99. The relationship between the Shape Parameter and the arc shape is as follows (see Figure 2-36).

Shape Parameter Arc Shape

0 01 050. .� <ρ Elliptical

ρ = 050. Parabolic

050 0 99. .< �ρ Hyperbolic



Using the Create Real Conic Arc Form

To open the Create Real Conic Arc form (see below), click the Create Real Conic Arc command button on the Geometry/Edge subpad.

The Create Real Conic Arc form includes the following specifications.

Vertex: —————————————————————————

Start ¬ specifies the vertex that constitutes the start endpoint of the edge.

Shoulder ¬ specifies the vertex that defines the apex of the conic edge.

End ¬ specifies the vertex that constitutes the end endpoint of the edge.

Shape Parameter

specifies the shape parameter for the arc (see above). NOTE: GAMBIT displays the name of the shape corresponding to the currently specified Shape Parameter.




Create Real Fillet Arc

The Create Real Fillet Arc command allows you to create a fillet edge between two existing edges.

To create a fillet edge, you must specify the following parameters:

• Two existing edges that define the fillet

• The edge selection points (u values)

• The fillet radius

• Whether or not the edges that are used to define the fillet are trimmed in the creation of the fillet edge

Specifying the Defining Edges

When you create a fillet edge, GAMBIT creates a circular arc edge between two existing edges that define the fillet. The defining edges may be straight or curved, but they must be coplanar. GAMBIT locates the fillet edge such that the circle that contains it is tangent to both edges. Furthermore, GAMBIT creates the fillet edge such that it constitutes the smaller of the two circular arcs that can be constructed between its endpoints (see Figure 2-37).

Fillet edge

�

�

Defining edgesFillet radius

Point of tangency

Point of tangency

Figure 2-37: Fillet edge definition



Specifying Edge Selection Points

When you create a fillet edge between two existing edges, you must specify a selection point (u value) for each edge. The selection point is a dimensionless length parameter that corresponds to the distance between the selection point and one of the endpoints on the selected edge.

If an edge pair provides more than one possible location for a fillet of a speci-fied radius, the selection points determine the location at which GAMBIT constructs the fillet edge. The effect of the selection point location varies according to whether or not the defining edges intersect each other. The gen-eral rules that apply to the effect of the selection point location are as follows.

Non-intersecting Edges

If a pair of edges does not intersect but does provide more than one possible location for a fillet, GAMBIT constructs the fillet edge nearest the selection point for one of the two edges. As an example, consider the two edges shown in Figure 2-38. In Figure 2-38(a), the selection points are both near the left-most ends of the defining edges, therefore GAMBIT locates the fillet edge on the left. Similarly, in Figure 2-38(b), the selection points are near the rightmost ends of the defining edges, therefore GAMBIT locates the fillet edge on the right. In Figure 2-38(c), one of the selection points is near the left end of one edge, and the other selection point is near the right end of the other. In such cases, the final location of the fillet edge depends on the orientations and shapes of the defining edges.



Selection points

Fillet edge(a)

(b)

(c)

�

�

Figure 2-38: Fillet location—non-intersecting edges



Intersecting Edges

When the edges that define the fillet intersect each other, the fillet location depends on the following two factors:

• The location of the selection points with respect to the edge endpoints

• The location of the selection points with respect to the point of inter-section between the edges

Figure 2-39 illustrates the general effect of selection point locations for two perpendicular straight edges.

Selection points

Point ofintersection

�

�

Figure 2-39: Fillet location—intersecting edges



Specifying the Fillet Radius

When you create a fillet edge, the location of the fillet depends, in part, on the fillet radius. Figure 2-40 shows the effect of fillet radius on the location of a fillet edge constructed between two curved edges. Note that both fillet edges shown in Figure 2-40 are located such that the circles that contain them are tangent to the defining edges at their points of intersection.

r

�

�

r2

Figure 2-40: The effect of fillet radius on fillet edge location

If you specify a fillet radius that is either too small or too large to result in points of tangency between the defining edges, GAMBIT does not create the fillet edge.



Trimming Edges

When you create a fillet edge, GAMBIT allows you to specify that both of the defining edges are trimmed when the fillet edge is created. If you select the trim-edges option, GAMBIT deletes two of the four edge segments that exist on either side of the fillet edge endpoints. Figure 2-41 shows the difference between trimmed and untrimmed edges when creating a fillet edge according to the specifications shown in Figure 2-37.

(a) Untrimmed

(b) Trimmed

�

�

Figure 2-41: Fillet edge—effect of trimming edges



The Effect of Selection Point on Trimmed Edges

When you specify that the defining edges are to be trimmed, GAMBIT uses the locations of the selection points to determine which edge segments to retain. As a general rule, GAMBIT retains the edge segments that contain the selection points.

Figure 2-42 shows the effect of edge trimming on two non-intersecting edges possessing shapes and orientations identical to those shown in Figure 2-38.

Selection points

Deleted edges

�

�

Figure 2-42: Fillet edge trimming—non-intersecting edges

Figure 2-43 shows the effect of edge trimming on two perpendicular intersect-ing edges identical to those shown in Figure 2-39.



Selection points

��

Deletededges

��

Figure 2-43: Fillet edge trimming—intersecting edges



Using the Create Real Fillet Arc Form

To open the Create Real Fillet Arc form (see below), click the Create Real Fillet Arc command button on the Geometry/Edge subpad.

The Create Real Fillet Arc form includes the following specifications.

Edge 1 ¬ specifies one of two edges that define the fillet.

Uval1 specifies the location of the selection point for Edge 1.

Edge 2 ¬ specifies the second of two edges that define the fillet.

Uval2 specifies the location of the selection point for Edge 2.

Radius specifies the fillet radius.

R Trim edges specifies that the defining edges are trimmed.

Label specifies a name for the new edge. (See Section 2.1.1.)



Create Real Edge From Vertices

The Create Real Edge From Vertices command allows you to create a NURBS edge the shape of which is defined by a set of vertices.

When you create an edge by means of the Create Real Edge From Vertices form, GAMBIT forms the edge in the shape of a general NURBS curve of degree n. A NURBS curve of degree n is a piecewise rational polynomial function wherein the numerator and denominator are non-periodic B-splines of degree n. By default, GAMBIT employs a value of n = 3 and applies natural boundary conditions at the endpoint vertices. That is, the NURBS curve is created such that its second derivative is zero at the endpoints.

To create a NURBS edge, you must specify the following parameters:

• Two or more real vertices to be used in constructing the edge

• The method by which the edge is to be constructed

Specifying Vertices

The Create Real Edge From Vertices operation is subject to the following rules and restrictions:

• All specified vertices must be real.

• The sequence in which you specify the vertices determines the shape of the edge. (NOTE: It is possible to create more than one edge shape from a single set of vertices.)

• When GAMBIT constructs a NURBS edge, the first and last specified vertices become the endpoint vertices of the edge. Therefore, when you delete a NURBS edge and specify the Lower Geometry option on the Delete Edges form, GAMBIT deletes only the endpoint vertices when it deletes the edge.



Specifying the Curve Construction Method

GAMBIT provides two methods for constructing a NURBS edge (see Figure 2-44):

• Interpolate

• Approximate

The Interpolate method forces the edge to pass through all specified vertices. The Approximate method creates an edge that passes near to all interior vertices to within a specified tolerance. In both cases, the new edge begins and ends at the first and last specified vertices. (NOTE: The Interpolate method is equiva-lent to the Approximate method with zero tolerance.)

Interpolate�method

Approximate�method

�

� �

�

1

8

7

65

4

3

210

9

Sense

Figure 2-44: NURBS curve methods



Using the Create Real Edge From Vertices Form

To open the Create Real Edge From Vertices form (see below), click the Create Real Edge From Vertices command button on the Geometry/Edge subpad.

The Create Real Edge From Vertices form includes the following specifica-tions.

Vertices ¬ specifies the vertices to be used in creation of the edge.

Method: —————————————————————————

l Interpolate (Real) specifies that the edge passes through all vertices.

l Approximate (Real) specifies that the edge passes near to all internal verti-ces to within the specified Tolerance value.

Tolerance specifies the maximum allowable distance between the NURBS curve and any of the internal vertices.




Revolve Vertices

The Revolve Vertices command allows you to create one or more real circular arc edges by revolving existing real and/or non-real vertices about a specified axis.

The Revolve Vertices command requires the following input parameters:

• One or more vertices to be revolved

• The axis of revolution

• The angle through which the vertices are revolved about the axis

Specifying Vertices to Be Revolved

When you create an edge by revolving a vertex, GAMBIT sweeps the vertex through the specified angle of revolution to create a circular arc edge (see Figure 2-45). (NOTE: If you revolve a non-real vertex, GAMBIT makes a real, in-place copy of the non-real vertex and revolves the real copy to create the edge.) The vertex specified for revolution (or real, in-place copy) consti-tutes the start endpoint of the created edge, and the edge sense points in the direction of revolution.

q

Angle of revolution

Vertex to be revolved

�

�

�

Axis of revolution

Edge sense

�

Figure 2-45: Revolve Vertices operation

You can specify any number of real and/or non-real vertices for the Revolve Vertices operation. As noted above, if you specify a non-real vertex, GAMBIT copies the virtual vertex to create a real vertex at the same location and revolves the real vertex to create a real edge. As a result, the Revolve Vertices



command always creates a real edge regardless of the geometry type of the specified vertex.

Specifying the Axis and Angle of Revolution

To specify the axis of revolution, you must define the axis by means of the Vector Definition form. For a description of the Vector Definition form and its operation, see “Using the Vector Definition Form“ in Section 2.1.4. The con-ventions regarding the angle of revolution for the Revolve Vertices operation are identical to those described in “Rotating an Entity“ in Section 2.1.4.

Using the Revolve Vertices Form

To open the Revolve Vertices form (see below), click the Revolve Vertices command button on the Geometry/Edge subpad.

The Revolve Vertices form includes the following specifications.

Vertices ¬ specifies one or more real vertices to be revolved.

Angle specifies the angle through which the vertices are revolved.

Axis: includes two components:

• A Define command button that allows you to define the axis around which the edge is to be revolved

• The coordinates of the start and end points for a vector defining the axis of revolution

Label specifies a label for the new face. (See Section 2.1.1.)



Project Edge On Face

The Project Edge On Face command allows you to create a real edge that rep-resents the projection of an existing real or virtual edge onto the surface of an existing real or virtual face.

Overview

When you execute the Project Edge On Face command, GAMBIT creates a real edge the shape of which represents the projection of the specified (projec-tion) edge onto the surface of a specified (target) face (see Figure 2-46). The shape of the created edge follows the contours of the projection face, but the created edge is not connected to or topologically associated with the face.

Projection edge

Target face

Created edge

Projectiondirection

�

�

Figure 2-46: Project Edge On Face—edge-project operation

If the projection of the edge in the direction of the face results in a curve that extends beyond the boundaries of the face, GAMBIT truncates the created edge at the face boundaries. In addition, if the projection of the edge crosses the face boundaries more than once, GAMBIT creates multiple edges from the Project Edge On Face operation (see Figure 2-47).



Projection faceCreated edges

Projectiondirection

�

�

Projection edge

Figure 2-47: Project Edge On Face—creation of multiple edges

Projection Specifications

The Project Edge On Face command includes the following specifications:

• The edge to be projected (projection edge)

• A face that constitutes the projection surface (target face)

• A vector that defines the direction of projection

Specifying the Projection Edge and Target Face

The projection edge and target face can represent any combination of real and/or virtual entities. For example, it is possible to project a real edge onto a virtual face or vice versa. Regardless of the geometry type(s) of the projection edge and face, however, the Project Edge On Face operation creates a real edge on the projection surface.



Specifying the Projection Direction

To specify the direction of projection, you must define the direction vector by means of the Vector Definition form. The Vector Definition form allows you to define the projection vector by means of either an existing edge, two points, two existing vertices, or a direction relative to any currently defined coordinate system. For a description of the Vector Definition form and its use, see “Using the Vector Definition Form“ in Section 2.1.4.

Using the Project Edge On Face Form

To open the Project Edge On Face form (see below), click the Project Edge On Face command button on the Geometry/Face subpad.

The Project Edge On Face form includes the following specifications.

Edge ¬ specifies the real or virtual edge to be projected.

Face ¬ specifies the real or virtual face that constitutes the projection surface.

Direction: includes two components:

• A Define command button that allows you to define the vector that describes the projection direction

• The coordinates of the start and end points for a vector defining projection path




2.3.2 Connect/Disconnect Edges

The Connect/Disconnect Edges command button allows you to perform the following operations.


Connect Edges Connects coincident real edges or creates virtual edges that represent the connection of one or more existing edges

Disconnect About Real Edge

Disconnects faces, and volumes that share a common real edge





Connect Edges

The Connect Edges command allows you to connect two or more edges. (NOTE: If you connect two or more meshed edges, and the numbers of mesh nodes on each edge are identical to each other, GAMBIT preserves the meshes when connecting the edges.)

To connect edges, you must specify the following parameters:

• Two or more edges to be connected


Specifying the Edges to Be Connected

The edges to be connected can be real or virtual, but they are subject to certain restrictions imposed by the connection type (see below).


GAMBIT allows the following types of edge-connect operations:

• Real




If you connect a set of edges using a Virtual (Forced), Virtual (Tolerance), or Real and Virtual (Tolerance) operation, GAMBIT allows you to specify the location and shape of the edge resulting from the connect operation by means of the Preserve first edge shape option (see below).



The Real option allows you to connect coincident real edges—that is, two or more real edges that possess identical orientations and the endpoint vertices of which are coincident to within a global tolerance value of 10-6. When you con-nect real edges and specify the Real option, GAMBIT deletes all but one of the specified edges and connects the remaining real edge to any and all faces to which the deleted edges were connected.




The Virtual (Forced) option allows you to connect real or virtual edges, regard-less of their proximity to each other. When you connect edges and specify the Virtual (Forced) option, GAMBIT replaces the specified edges with a virtual edge. If a specified edge constitutes part of a face, GAMBIT overlays the face with a virtual face and shapes the virtual face according to the position of the new virtual edge. If the face is connected to a volume—GAMBIT overlays the volume with a virtual volume.


The Virtual (Tolerance) option allows you to specify that only those real and/or virtual edges that are near to each other to within a specified tolerance are connected. There are two ways to express the tolerance value:

• Tolerance

• Shortest Edge%

The Tolerance specification represents the tolerance value as expressed in absolute distance units. The Shortest Edge% specification represents the toler-ance value expressed as a percentage of the length of the shortest edge in the model.

If you specify the Virtual (Tolerance) option, you can also specify the T-Junctions option. The T-Junctions option allows the creation of T-junctions during the edge connect operation (see “Specifying the T-Junctions Option,” below).



1) Real connect operations for edges that are coincident to within the global tolerance value

2) Virtual (Tolerance) connect operations (including the T-Junctions option) for unconnected, specified edges that are near to each other to within the user-specified tolerance



Specifying the T-Junctions Option

When you employ either the Virtual (Tolerance) or Real and Virtual (Tolerance) option to connect edges, GAMBIT allows you to select the T-Junctions option. If you specify the T-Junctions option, GAMBIT performs virtual T-connect operations where appropriate to connect edges the endpoints of which are near to the virtual edge to within a specified tolerance. (For a description of virtual T-connect operations, see Appendix A of this guide.)

As an example of the use of the T-Junctions option, consider the edges shown in Figure 2-48(a). If you specify the T-Junctions option when performing a Virtual (Tolerance) or Real and Virtual (Tolerance) connection operation involving edge.1 and edge.2, GAMBIT splits edge.1 and creates a T-connection at v_vertex.5 (see Figure 2-48(b)).

(a) Before connection

(b) After connection

edge.1

edge.2

v_vertex.5

Figure 2-48: Connecting edges—T-Junctions option



Preserving the First Edge Shape

If you connect a set of edges using a Virtual (Forced), Virtual (Tolerance), or Real and Virtual (Tolerance) operation, you can determine the shape of the resulting edge by means of the Preserve first edge shape option. When you select the Preserve first edge shape option, the edge that results from the connect opera-tion retains the shape of the first edge listed in the Edges list. If you do not select the Preserve first edge shape option when connecting the edges, the shape and location of the edge that results from the connect operation represents an average of the shapes and locations of the edges to be connected.

Preserving the Split Edge Shape in T-Connection Operations

When you perform a T-connection operation, GAMBIT allows you to specify the Preserve split-edge shape option. When you select the Preserve split-edge shape option, GAMBIT retains the shape of the edge to be split during the T-connection operation.

As an example of the effect of the Preserve split-edge shape option, consider the two edges (edge.1 and edge.2) shown in Figure 2-49(a).

• If you do not specify the Preserve split-edge shape option, GAMBIT creates the edges shown in Figure 2-49(b).

• If you do specify the Preserve split-edge shape option, GAMBIT retains the shape of edge.1 during the T-connect operation and creates the edges shown in Figure 2-49(c).



edge.1

edge.2

v_edge.3 v_edge.4

v_edge.5

v_edge.3 v_edge.4

v_edge.5

(a)

(b) (c)

Figure 2-49: Effect of Preserve split-edge shape option

u NOTE: The Preserve split-edge shape option takes precedence over the Preserve first edge shape option.



Using the Connect Edges Form

To open the Connect Edges form (see below), click the Connect command button on the Geometry/Edge subpad.

The Connect Edges form includes the following specifications.

Edges ¬ specifies the edges to be connected.

l Real specifies that the edge that results from the connection of edges is a real edge. (NOTE: To obtain a real edge from the connection of two or more real edges, the specified edges must be coincident.)

l Virtual (Forced) specifies the following characteristics for the edge that results from connection of edges:

• The edge is a virtual edge

• The edge is created regardless of the distance between the specified edges



l Virtual (Tolerance) specifies the following characteristics for the edge that results from connection of edges:

• The edge is a virtual edge

• The specified edges are connected only if the distance between them is less than a specified tolerance




2) Virtual (Tolerance) connect operations for the remaining specified, unconnected edges

Tolerance specifies the maximum allowable distance (absolute units) between edges to be connected.

Shortest Edge % specifies the maximum allowable distance (percent of shortest edge) between edges to be connected.


R Preserve first edge shape

preserves the shape of the first edge listed in the Edges list when performing the connect operation.

R T-Junctions specifies the creation of T-junctions where possible.

Vertices ¬ (All or Pick) specifies vertices subject to the T-junctions option.

R Preserve split-edge shape

preserves the shape of the edge to be split during T-junctions operations.



Disconnect About Real Edge

The Disconnect About Real Edge command allows you to disconnect topologi-cal entities that share a common real edge.

When you disconnect faces or volumes about a common real edge, GAMBIT creates new edges for all but one of the entities to which the specified edge is connected. For example, if the specified edge is shared by three faces, GAMBIT creates two new edges that are coincident with the specified edge and connects them to two of the three faces. The original edge is connected to the remaining face.

Specifying Endpoint Vertex Options

GAMBIT provides the following options with respect to the treatment of end-point vertices for the disconnected edge:

• Edge + Vertices

• Edge Only

• Edge + Select Vertex

The following table describes the effects associated with each option.

Option Description

Edge + Vertices GAMBIT disconnects the specified edge and its endpoint vertices. As a result, GAMBIT creates two new endpoint vertices for each new edge.

Edge Only GAMBIT disconnects the edge but not its endpoint vertices. Each new edge created in the disconnection process shares the endpoint vertices of the specified edge.

Edge + Select Vertex GAMBIT disconnects the edge and one of its two endpoint vertices (specified by the user). The other endpoint vertex is shared between all new edges.



As an example of the difference between the options described above, con-sider the configuration shown in Figure 2-50, in which two faces are con-nected by means of a common edge (edge.4) the endpoint vertices of which (vertex.3 and vertex.4) are also common to both faces.

face.1 face.2

vertex.3

vertex.4

edge.4

Figure 2-50: Two faces sharing a common edge

If you disconnect the faces about edge.4, GAMBIT creates a new edge that is coincident with edge.4 and connects it to one of the two faces—for example, face.2. The original edge (edge.4) remains connected to the other face (face.1).

The manner in which GAMBIT treats the endpoint vertices varies according to the option type as follows.



Option Description

Edge + Vertices GAMBIT disconnects vertex.3 and vertex.4 and des-ignates the vertices that result from the disconnection as the endpoints of the new edge.

Edge Only GAMBIT does not disconnect vertex.3 and vertex.4. The new edge shares endpoint vertices with edge.4; that is, vertex.3 and vertex.4 are common to both edges.

Edge + Select Vertex GAMBIT disconnects only one of the endpoint vertices of edge.4. The other vertex (vertex.3 or vertex.4) constitutes an endpoint of both the specified edge and the new edge.



Using the Disconnect About Real Edge Form

To open the Disconnect About Real Edge form (see below), click the Discon-nect About Real Edge command button on the Geometry/Edge subpad.

The Disconnect About Real Edge form includes the following specifications.

Edge ¬ specifies the edge about which geometry is to be disconnected.

Method: —————————————————————————

l Edge + Vertices

specifies that the endpoint vertices of the specified edge are to be disconnected along with the edge.

l Edge Only specifies that the endpoint vertices of the specified edge are to remain connected when the edge is disconnected.

l Edge + Select Vertex

specifies that only one of the two endpoint vertices for the specified edge is to be disconnected.

Vertex ¬ specifies the vertex that is to be disconnected in con-junction with the specified edge.



2.3.3 Modify Edge Color/Label

The Modify Edge Color/Label command button allows you to perform two operations.


Modify Edge Color Changes the color of the geometry and/or mesh nodes associated with one or more edges as displayed in the graphics window

Modify Edge Label Changes an edge label




Modify Edge Color

The Modify Edge Color command allows you to change the displayed color of the geometry and/or mesh nodes associated with one or more edges.

Using the Modify Edge Color Form

To open the Modify Edge Color form (see below), click the Modify Color com-mand button on the Geometry/Edge subpad.

The Modify Edge Color form includes the following specifications.

Edges ¬ specifies one or more edges for which the color is to be changed.

Color: —————————————————————————

R Geometry specifies modifying the color of the specified edge(s).

R Mesh specifies modifying the color of the mesh node(s) associ-ated with the specified edge(s)..

For specific instructions on setting the Geometry or Mesh colors, see Section 2.2.4.



Modify Edge Label

The Modify Edge Label command allows you to change the label associated with any edge.

Using the Modify Edge Label Form

To open the Modify Edge Label form (see below), click the Modify Label com-mand button on the Geometry/Edge subpad.

The Modify Edge Label form includes the following specifications.

Edge ¬ specifies the edge to be modified.

Label specifies a new label for the edge. (See Section 2.1.1).



2.3.4 Move/Copy/Align Edges

The Move/Copy/Align Edges command button allows you to perform two operations.


Move/Copy Edges Moves and copies edges

Align Edges Aligns edges and connected geometry with existing topological entities




Move/Copy Edges

The Move/Copy Edges command allows you to reposition and/or reorient one or more edges or to create copies of edges. For a general description of the procedures and specifications required to move and/or copy entities, see “Moving an Entity“ and “Copying an Entity,” respectively, in Section 2.1.4.

Using the Move/Copy Edges Form

To open the Move/Copy Edges form (see below), click the Move/Copy com-mand button on the Geometry/Edge subpad.

For a complete description of the specifications available on the Move/Copy Edges form, see “Using Move/Copy Forms“ in Section 2.1.4.



Align Edges

The Align Edges command allows you to reposition and/or reorient an edge so that it coincides with another edge or is aligned with a vector drawn between two vertices. You cannot plane-align an edge, because edges are one-dimen-sional entities. (For a general description of the procedure and specifications required to align an entity, see “Aligning an Entity“ in Section 2.1.4, above.)

Using the Align Edges Form

To open the Align Edges form (see below), click the Align command button on the Geometry/Edge subpad.

For a complete description of the specifications available on the Align Edges form, see “Using Align Forms“ in Section 2.1.4.



2.3.5 Split/Merge Edges

The Split/Merge Edges command button allows you to perform the following operations.


Split Edge Splits an existing edge into two real or virtual edges

Merge Edges (Virtual) Merges two or more existing edges into a virtual edge




Split Edge

The Split Edge command allows you to split an existing edge into two real or virtual edges. (NOTE: If you split an edge that is linked to one or more edges, GAMBIT splits every edge in the set of linked edges in addition to the specified edge.)

The Split Edge command includes the following input parameters:

• The edge to be split

• The split type

• The split tool

Specifying the Edge to Be Split

GAMBIT allows you to split real or non-real edges but places the following restrictions on the type of edges that can be created from the split:

• If you split a real edge, you can create two real or virtual edges.

• If you split a non-real edge, you must create two virtual edges.

Specifying the Split Type

There are three types of edge split operations:

• Real connected

• Real disconnected

• Virtual connected

When you split a real edge, you must specify whether the two edges that replace it are real or virtual. If you replace a real edge with two real edges, you must specify whether the resulting edges are connected (Real connected) or disconnected (Real disconnected) at the split point. If you replace an edge with two virtual edges, GAMBIT connects the edges at the split point by means of a virtual vertex (Virtual connected).

u NOTE: GAMBIT does not allow you to employ the Real disconnected option when splitting edges that are associated with higher-topology face or volume entities.



Specifying the Split Tool

When you split an edge, you must specify the location at which the edge is to be split. To do so, you must designate a split tool—that is, the means of locat-ing the split point. There are three types of split tools:

• Point

• Vertex

• Edge

Specifying a Point as the Split Tool

If you split a real or virtual edge using a point as the split tool, you must spec-ify a U Value parameter that identifies the location of the point on the edge. The U Value parameter represents the fraction of total edge length and is equivalent to the u value used when creating a vertex on an edge. (For a detailed description of the u value, see “Create Vertex On Edge,” in Section 2.2.1.)

When you specify the Point option and pick the edge from the graphics win-dow using the mouse, GAMBIT highlights the edge and shows the location of the split point. You can slide the split point along the edge until you release either the Shift key or the left mouse button—at which time GAMBIT fixes the position of the split point. To change the position of the split point, either re-pick (Shift-middle-click) the edge and move the point to another location, or input the desired u value in the U Value text box on the Split Edge form.

Specifying a Vertex as the Split Tool

If you split an edge using the Vertex option, you must specify an existing vertex that identifies the location of the split point. The rules governing the type of vertex that can be used to split an edge are as follows:

• To perform a real split operation, you must use a real vertex as the split tool.

• To perform a virtual split operation, you can use either a real or non-real vertex as the split tool.

If you specify the Virtual connected split-type option (see above) and specify a vertex as the split tool, you can specify a tolerance value that determines whether GAMBIT performs the split operation. If the split-tool vertex is coincident with the edge or near to the edge within the specified tolerance value, GAMBIT performs the split operation. The final shape and location of the split edge is determined by the Split-edge Position (see below).



Specifying the Split-edge Position

When you split an edge with a split-tool vertex that is not coincident with the edge, GAMBIT allows you to determine the final configuration of the edge shape and vertex location by means of the Split-edge Position specification. The Split-edge Position specification includes three options (see Figure 2-51):

• Interpolate

• Preserve vertex location

• Preserve edge shape

The Interpolate option (Figure 2-51(b)) shapes the edge split such that the split point (and connecting vertex between the split edges) is located at a point halfway between the split-tool vertex and the original edge. The Preserve vertex location option (Figure 2-51(c)) retains the location of the split-tool vertex and shapes the edge split so that the resulting edges meet at that point. The Preserve edge shape option (Figure 2-51(d)) retains the shape of the original edge and locates the split point by projecting the split-tool vertex onto the edge.

(b) Interpolate(a) Original configuration

(d) Preserve edge shape(c) Preserve vertex location

Split-tool vertex

Edge

Figure 2-51: Split-edge Position options



Specifying an Edge as the Split Tool

The Edge option allows you to split an edge at a location defined by the point(s) of intersection (or closest approach) between the specified (target) edge and an edge that serves as a split tool. If the target edge intersects or approaches the split-tool edge at more than one location, GAMBIT splits the target edge at each location.

GAMBIT provides three suboptions for the Edge split tool option:

• Retain

• Bidirectional

• Tolerance

The Retain suboption specifies that the split-tool edge is not deleted upon the completion of the Split Edge operation. (NOTE: If you do not select the Retain option, GAMBIT deletes the split-tool edge upon completion of the opera-tion.)

The Bidirectional suboption splits both the target edge and the split-tool edge at their point(s) of intersection or closest approach. The target edge and split-tool edge are joined together at the split location. That is, the vertices created at the edge split locations are connected after the split operation is complete.

The Tolerance suboption performs the split operation at points of near inter-section between the split-tool edge and the target edge. For the purposes of the edge-split operation, edges are considered to nearly intersect if they approach each other to within the user-specified Tolerance value on the Split Edge form.



Using the Split Edge Form

To open the Split Edge form (see below), click the Split command button on the Geometry/Edge subpad.

The Split Edge form includes the following specifications.

Edge ¬ specifies the edge to be split.

Type —————————————————————————

l Real connected

specifies that the edges that result from the edge-split operation are real and connected.

l Real dlisconnected

specifies that the edges that result from the edge-split operation are real and disconnected.

l Virtual connected

specifies that the edges that result from the edge-split operation are virtual and connected.



Split With —————————————————————————

Point q Vertex Edge

specifies the general nature of the split tool.

The lower section of the Split Edge form allows you to specify parameters related to the Split With option selected (Point, Vertex, or Edge).

Point Option

U Value specifies the u value position parameter.

Coordinate ¬ Sys.

specifies the coordinate system with respect to which the split-tool point is specified. (See Section 2.1.3.)

Type ————————————————————————


specifies the type of coordinate parameters to be used in locating the split point.

Global | Local Specifies the location of the point with respect to either the Global or Local system.



Vertex Option

When you specify the Split With:Vertex option, the middle section of the Split Edge form appears as shown below.

Vertex ¬ specifies the vertex to be used as the split tool.

Tolerance (Virtual connected split operations only) specifies that the vertex is to be used as a split-tool if it is located near the target edge to within the specified tolerance value.

Split-edge Position

(Virtual connected split operations only) —————————

l Interpolate shapes split edges such that the connecting vertex is located between the original edge and split-tool vertex.

l Preserve vertex location

shapes split edges such that the split-tool vertex is retained as the location of the connecting vertex between split edges.

l Preserve edge shape

retains the edge shape and projects the split-tool vertex onto the edge to be split.



Edge Option

When you specify the Split With:Edge option, the middle section of the Split Edge form appears as shown below.

Edge ¬ specifies the edge to be used as the split tool.

R Retain specifies that the split-tool edge is retained upon completion of the edge-split operation.

R Bidirectional specifies that the split-tool edge is retained and is split at the points of intersection upon completion of the edge-split opera-tion.

R Tolerance specifies that a given location is considered a point of intersec-tion if the target and split-tool edge approach to within the specified tolerance value.

Tolerance specifies the tolerance value.



Merge Edges (Virtual)

The Merge Edges (Virtual) command allows you to merge two or more real and/or virtual edges into a single virtual edge. (NOTE: If you merge edges that possess identical boundary-zone type specifications, GAMBIT assigns the specification to the edge that results from the merge operation.)

To merge edges by means of the Merge Edges (Virtual) command, you must specify the following parameters:

• The set of edges to be merged

• The merge type

Specifying the Edges to Be Merged

GAMBIT allows you to merge sets of two or more real and virtual edges but applies the following rules with respect to the set of edges to be merged (see Figure 2-52):

• Each edge in the set must be connected at one or both of its endpoints to another edge in the set

• None of the connected endpoints are allowed to be connected to more than two edges

(a) Allowed

(b) Not allowed

(c) Not allowed

edge.1

edge.3

edge.2

edge.1

edge.3

edge.2

edge.1

edge.3

edge.2

Figure 2-52: GAMBIT edge-merging rules



Specifying the Merge Type

When you merge edges, you must specify the merge type. There are two types of edge-merging operations:



When you specify a Virtual (Forced) merge, GAMBIT merges all of the edges in the specified set, regardless of their respective lengths or angles with respect to each other. When you specify a Virtual (Tolerance) merge, GAMBIT performs the merge operation only if all edges in the set meet specified tol-erance criteria.

Specifying Tolerance Criteria

There are two types of edge-merging tolerance criteria:

• Max. Edge Length

• Min. Angle

When you specify the Max Edge Length criterion, GAMBIT includes in the merge operation only those edges that are shorter than the specified length.

The Min Angle criterion is based on the internal angle between edge pairs. When you specify the Virtual (Tolerance) option, GAMBIT includes in the merge operation only those edge pairs the internal angles of which are greater than the specified angle.



Using the Merge Edges (Virtual) Form

To open the Merge Edges (Virtual) form (see below), click the Merge command button on the Geometry/Edge subpad.

The Merge Edges (Virtual) form includes the following specifications.

Edges ¬ specifies the set of edges to be merged.

Type: —————————————————————————

l Virtual (Forced) specifies that the edges in the set are to be merged regardless of their respective lengths or orientations to each other.

l Virtual (Tolerance) specifies that the edges in the set are to be merged only if all edges and orientations meet the tolerance criteria.

Max. Edge Length

specifies the maximum edge length tolerance criterion.

Min. Angle specifies the minimum angle tolerance criterion (in degrees).



2.3.6 Convert Edges

The Convert Edges command converts one or more non-real (faceted and/or virtual) edges to real edges. The conversion process preserves both the topo-logy and any existing mesh(es) associated with the converted edge(s). In addi-tion, all non-real vertices associated with the edge(s) are converted to real vertices.

u NOTE: To determine the shape of the converted edge, GAMBIT facets the edge using a user-specified number of points and fits the points with a spline. To specify the number of points used in the fitting procedure, open the Edit Defaults form and modify the variable “VIRTUAL_SAMPLING_POINTS” (see Chapter 4 of the GAMBIT User’s Guide).

Using the Convert Edges Form

To open the Convert Edges form (see below), click the Convert Edges com-mand button on the Geometry/Edge subpad.

The Convert Edges form includes the following specifications.

Edges ¬ specifies which non-real edges are to be converted to real edges.

All q Pick

• All specifies all edges in the model.

• Pick specifies edges selected by means of the Edges list box. (NOTE: If you pick an edge in the graphics window or click in the Edges list box, GAMBIT automatically selects the Pick option.)



2.3.7 Summarize/Check/Query Edges and Total Entities

The Summarize/Check/Query Edges and Total Entities command button allows you to perform the following operations.


Summarize Edges Displays edge summary information in the Transcript window

Check Edges Checks the topological and geometric validity of model edges

Query Edges Opens the edge query list





Summarize Edges

The Summarize Edges command displays edge summary information in the Transcript window.

Using the Summarize Edges Form

To open the Summarize Edges form (see below), click the Summarize com-mand button on the Geometry/Edge subpad.

The Summarize Edges form includes the following specifications.

Edges ¬ specifies one or more edges for which information is to be summarized in the Transcript window.

All q Pick





Check Edges

The Check Edges command assesses the topological and/or geometric validity of edges in the model and summarizes the results in the Transcript window.

When you execute the Check Edges command, GAMBIT checks the model to determine its validity with respect to either or both of the following types of characteristics:

• Topology

• Geometry


Topology Check


For a given edge, the Check Edges topology check operation examines the model to ensure that it meets the following criteria:

• Lower-topology vertices are visible and correctly reference the edge.

• Upper-topology faces correctly reference the edge.

• Upper-topology faces maintain correct sense information for the edge.

• Virtual guest entities correctly reference the edge as a host.

u NOTE: Failure of the topology check for any edge in the model constitutes a serious problem for the model as a whole. GAMBIT does not currently include any tools that allow you to repair problems that cause failures of topology checks.

Geometry Check

Geometrical validity is an assessment of the model with respect to proximity and shape characteristics—such as the distances between connected edges and/or the mathematical continuity of model curves and surfaces. The Check Edges geometry check criteria are as follows:



• All real edges correctly reference the ACIS model.

• No real edges exhibit problems related to continuity, self-intersection, or bad closure.

• Any virtual-edge hosts are of the correct type. For example, a virtual edge formed by connecting or merging two edges must reference only the two edges as hosts. Similarly, a virtual edge defined on a face or volume must not be hosted by an edge, and a virtual edge formed by splitting an edge must be hosted by the edge that is split. (NOTE: The edge geometry check operation also checks the validity of host geometry.)

u NOTE: Failure of the geometry check for a model edge does not necessarily constitute a serious problem for the model as a whole. It is sometimes possible to repair geometry errors for edges that belong to faces for which a Heal Real Faces (see Section 2.4.8) or Heal Real Volume (see Section 2.5.8) operation is attempted .



Using the Check Edges Form

To open the Check Edges form (see below), click the Check command button on the Geometry/Edge subpad.

The Check Edges form includes the following specifications.

Edges ¬ specifies the edges to be included in the checking operations.

All q Pick



R Check Topology specifies a topology check on the selected edges.

R Check Geometry specifies a geometry check on the selected edges.



Query Edges

The Query Edges command allows you to identify the location and/or the names of specific edges.

Using the Query Edges Form

To open the Query Edges form (see below), click the Query command button on the Geometry/Edge subpad.

For a general description of using the Query Edges form, see “Using the Query Vertices Form“ in Section 2.2.7, above.



Total Entities



For a description of the options available on the Total Entities form, see “Total Entities,” in Section 2.2.7.



2.3.8 Delete Edges

The Delete Edges command deletes one or more edges from the model subject to the following restrictions:

• GAMBIT does not allow you to delete edges that constitute parts of higher-topology entities. For example, you cannot delete an edge that constitutes the side of a face or one edge of a volume.

• If you delete a virtual edge that constitutes the connection of two or more real or virtual edges, GAMBIT restores those original edges to the model when it deletes the specified edge.

Retaining Edge Endpoint Vertices

By default, when you delete an edge, GAMBIT deletes the vertices that con-stitute the endpoints of the edge. To retain the endpoint vertices when the edge is deleted, unselect the Lower Geometry option at the bottom of the Delete Edges form.

Deleting Associated Vertices

When you delete an edge that constitutes a host entity for one or more virtual vertices, GAMBIT deletes the virtual vertices when it deletes the edge.

Deleting Virtual Edges

If you delete a virtual edge, GAMBIT deletes all lower topology and virtual hierarchy that is associated with the edge and is not associated with any other entities in the model.



Using the Delete Edges Form

To open the Delete Edges form (see below), click the Delete command button on the Geometry/Edge subpad.

The Delete Edges form includes the following specifications.

Edges ¬ specifies one or more edges to be deleted.

All q Pick



R Lower Geometry

specifies that all vertices associated with the specified edges are deleted.

CREATING THE GEOMETRY Face Commands


2.4 Face Commands

The following commands are available on the Geometry/Face subpad.


Form Face Creates a face from existing edges or vertices

Create Face Creates a face in one of three primitive shapes

Boolean Operations Unites, intersects, or subtracts faces

Connect Faces Disconnect Faces

Connects real and virtual faces; dis-connects faces shared between entities

Modify Face Color Modify Face Label

Changes a face color; changes a face label

Move/Copy Faces Align Faces

Moves and/or copies faces: aligns faces and connected geometry

Split Faces Merge Faces (Virtual) Collapse Face (Virtual) Simplify Faces

Splits faces about a face or vertices; merges faces; collapses a face; simplifies faces by removing dangling edges

Heal Real Faces Convert Faces

Heals real face geometry; converts non-real faces to real faces

Summarize Faces Check Faces Query Faces Total Entities

Displays face summary information; checks validity of topology and geometry; opens a face query list; displays entity totals

Face Commands CREATING THE GEOMETRY



Delete Faces Deletes real or virtual faces



2.4.1 Form Face

The Form Face command button allows you to perform the following opera-tions.


Create Face From Wireframe

Creates a face from existing edges

Create Real Parallelogram Face

Creates a parallelogram face from three existing vertices

Create Real Polygon Face Creates a polygonal face from a set of three or more existing vertices

Create Real Circular Face From Vertices

Creates a planar, circular face defined by a set of three vertices

Create Real Elliptical Face From Vertices

Creates a planar, elliptical face defined by a set of vertices and angles

Create Skin Surface Face Creates a skin-surface face from a specified set of existing edges

Create Net Surface Face Creates a net-surface face from a specified set of edges

Create Real Face From Vertex Rows

Creates a face from specified rows of existing vertices

Revolve Edges Creates a face by revolving an existing edge about an axis




Sweep Edges Creates a face by sweeping an existing edge a specified distance in a direction defined by a specified vector

The following sections describe the purpose and operation of each of the commands listed above.



Create Face From Wireframe

The Create Face From Wireframe command allows you to create a face from two or more existing edges. To create a face by means of the Create Face From Wireframe command, you must specify the following parameters:

• The edges that define the wireframe

• The face type—real or virtual

Specifying Edges of the Wireframe

GAMBIT employs the following rules for specifying edges used to create a face by means of the Create Face From Wireframe command.

• The sequence in which you specify the wireframe edges does not affect the final form of the face.

• The edges do not have to be connected to each other, but each edge must possess endpoint vertices that are coincident with the endpoint vertex of one other specified edge (see Figure 2-53).

(a) Allowed (b) Not allowed

Figure 2-53: Wireframe endpoint vertex requirements



Specifying the Face Type

GAMBIT allows you to create both real and virtual faces using the Create Face From Wireframe command. To create a real face, you must specify only real edges for the wireframe. To create a virtual face, you can specify any combination of real and/or virtual edges for the wireframe.

Creating a Real Face

The following rules apply to the creation of a real face.

• To construct a real face, you must specify only real edges for the wire-frame.

• If the specified edges are not coplanar, GAMBIT applies the following rules with respect to the creation of the face.

a) If you specify only two edges, GAMBIT attempts to construct a skin-surface face. (See “Create Real Skin Surface Face,” below.)

b) If you specify three or four edges, GAMBIT checks the orientation of the edges to determine whether the edges meet with tangent continuity at their endpoints. If the edges do not meet with tangent continuity, GAMBIT does not create the face.

Creating a Virtual Face

If you specify the creation of a virtual face, you can also specify a host face or volume.

• If you do not specify a host face or volume, GAMBIT creates an orphan face—the shape of which is defined only by means of its boundary edges.

• If you specify a host face or volume, GAMBIT creates a parasite face and employs the existing geometry (shape) of the host entity to define the shape of the virtual face.

If you specify a host face, GAMBIT allows you to determine the visibility of the host face by means of the Hide host option on the Create Face From Wireframe form. If you select the Hide host option, GAMBIT renders the host face invisible for all operations, including display operations executed by means of the Specify Display Attributes command (see Chapter 3 of the GAMBIT User’s Guide). To render the host face visible again, you must delete the hosted virtual face.



Specifying the Tolerance Value

If you specify a host face for the creation of a virtual face, GAMBIT allows you to specify a Tolerance value. The tolerance value constitutes the maximum allowable distance between the wireframe edges and the surface of the host face.

Using the Create Face From Wireframe Form

To open the Create Face From Wireframe form (see below), click the Create Face From Wireframe command button on the Geometry/Face subpad.

The Create Face From Wireframe form includes the following specifications.

Edges ¬ specifies the edges to be used in creating the face.

Type: —————————————————————————

l Real specifies creation of a real face.

l Virtual specifies creation of a virtual face.

R Host specifies that the virtual face is to be attached to a host face or volume.

Face q Volume

specifies whether the host entity is a face or a volume.

Face ¬ Volume

specifies the entity to be used as a host for the virtual face.



R Hide host renders the host entity invisible.

Tolerance specifies the maximum allowable distance between the wireframe edges and the host face.




Create Real Parallelogram Face

The Create Real Parallelogram Face command allows you to create a real, four-sided face in the shape of a parallelogram.

To create a face by means of the Create Real Parallelogram Face option, you must specify three existing real vertices that define the face. The vertices are designated as Origin, Incline, and Base and are defined as shown in Figure 2-54.

Origin

Incline

Base

Sense

Figure 2-54: Parallelogram-face vertex definitions

The edges formed in the creation of the face are defined such that their senses are from the Origin vertex to the Base vertex and from the Incline vertex to the Origin vertex. If you reverse the specifications regarding which vertices con-stitute the Base and Incline vertices, respectively, the shape of the resulting face does not change, but GAMBIT reverses the sense of each of its edges.



Using the Create Real Parallelogram Face Form

To open the Create Real Parallelogram Face form (see below), click the Create Real Parallelogram Face command button on the Geometry/Face subpad.

The Create Real Parallelogram Face form includes the following specifications.

Vertices: —————————————————————————

Origin ¬ specifies the vertex that constitutes a common endpoint for both the base edge and one of the inclined edges of the par-allelogram.

Incline ¬ specifies the vertex that constitutes the other endpoint of one of the inclined edges of the parallelogram.

Base ¬ specifies the vertex that constitutes the other endpoint of the base edge of the parallelogram.




Create Real Polygon Face

The Create Real Polygon Face command allows you to create a planar, polygo-nal face defined by a set of existing real vertices. (NOTE: If you specify a set of five or more vertices, all vertices in the set must be coplanar.)

To execute the Create Real Polygon Face command, you must specify a set of at least three vertices. To create the polygonal face, GAMBIT first creates a closed loop of edges that join the specified vertices then creates a face bounded by the closed loop.

The order in which the vertices are specified on the Create Real Polygon Face form determines the order in which the bounding edges are created—which, in turn, affects the shape of the created face. As an example of this effect, con-sider the set of six vertices shown in Figure 2-55(a).

vertex.1 vertex.2

vertex.6vertex.3

vertex.4

vertex.5(a)

(b) (c)

�

�

Figure 2-55: Effect of vertex specification sequence

Figure 2-55(b) and Figure 2-55(c) show two example faces created using the vertex specification sequences listed in the following table.



Figure 2-55(b) Figure 2-55(c)

vertex.1 vertex.2 vertex.3 vertex.4 vertex.5 vertex.6

vertex.1 vertex.2 vertex.4 vertex.3 vertex.5 vertex.6

Using the Create Real Polygon Face Form

To open the Create Real Polygon Face form (see below), click the Create Real Polygon Face command button on the Geometry/Face subpad.

The Create Real Polygon Face form includes the following specifications.

Vertices ¬ specifies the vertices that define the bounding region of the polygonal face.




Create Real Circular Face From Vertices

The Create Real Circular Face From Vertices command allows you to create a planar face in the shape of a full circle.

GAMBIT provides two methods for creating a face in the shape of a full circle. Both methods require you to specify three existing vertices to define the size and location of the circle. The methods are defined as follows:

• Method 1—specifies one vertex that constitutes the center of the circle and two vertices that lie on the circular edge that bounds the face

• Method 2—specifies three vertices that lie on the circular edge that bounds the face

Method 1 (Figure 2-56(a)) requires that the two vertices that lie on the circular bounding edge are equidistant from the vertex at the center of the circle. Method 2 (Figure 2-56(b)) requires only that the three specified vertices are not collinear.

(a) Method 1 (b) Method 2

rr

Center

End-Points

1

21

2

3

Vertices

Figure 2-56: Circular face specifications



Using the Create Real Circular Face From Vertices Form

To open the Create Real Circular Face From Vertices form (see below), click the Create Real Circular Face From Vertices command button on the Geometry/ Face subpad.

The Create Real Circular Face From Vertices form includes the following speci-fications.

Method: contains two radio buttons that allow you to specify the method by which the circular face is created. For either method, you must specify three vertices. The two methods differ in their treatment of the vertices as follows:

• Method 1—One vertex constitutes the center of the circle and the other two vertices lie on the bounding cir-cular edge

• Method 2—All three vertices lie on the bounding circu-lar edge

The center section of the Create Real Circular Face From Vertices form varies according to the method selected to construct the bounding circle. The specifi-cations available on the center section of the form are as follows.



Method 1

Vertices: —————————————————————————

Center ¬ specifies the vertex that constitutes the center of the circle.

End-Points ¬ specifies the vertices that lie on the bounding circular edge.

Label (both methods) specifies a label for the new face. (See Section 2.1.1.)

Method 2

When you specify Method 2 for the creation of a circular face, the middle section of the Create Real Circular Face From Vertices form appears as shown below.

Vertices ¬ specifies the three vertices that lie on the circular bounding edge.



Create Real Elliptical Face From Vertices

The Create Real Elliptical Face From Vertices command allows you to create a face that represents a section of a full ellipse.

To create an elliptical face, you must specify the following parameters (see Figure 2-57):

• Center vertex—located at the center of the full ellipse

• Major vertex—defines the length of the major axis

• On Edge vertex—defines the dimensions of the full ellipse

• Start Angle and Stop Angle—define the size and location of the elliptical section that bounds the face

Center

Start angle

Stop angle

Major

On Edge

Created face

Figure 2-57: Elliptical face specifications

The Center, Major, and On Edge vertices define the shape and size of the full ellipse of which the face constitutes a section. The Start Angle and Stop Angle define the size and position of the face relative to the Center vertex and major axis. (NOTE: The three vertices that define the ellipse must not be collinear.)



Using the Create Real Elliptical Face From Vertices Form

To open the Create Real Elliptical Face From Vertices form (see below), click the Create Real Elliptical Face From Vertices command button on the Geometry/ Face subpad.

The Create Real Elliptical Face From Vertices form includes the following specifications.

Center ¬ specifies the vertex that constitutes the center of the full ellipse.

Major ¬ specifies the vertex that defines the major axis of the full ellipse.

On Edge ¬ specifies a vertex that lies on the edge of the full ellipse. If a vector drawn from the Center vertex to the On Edge vertex is at right angles to a vector drawn from the Center vertex to the Major vertex, then the distance between the Center vertex and the On Edge vertex exactly defines the length of the minor axis of the ellipse.

Angle: specifies the size of the face relative to the region bounded by the full ellipse. The zero-angle reference vector points from the Center vertex to the Major vertex.

R Start Angle ————————————————————————

Start Angle specifies the start angle for the elliptical arc that defines the curved bounding edge for the face.



R End Angle ————————————————————————

End Angle specifies the end angle for the elliptical arc that defines the curved bounding edge for the face.




Create Real Skin Surface Face

The Create Real Skin Surface Face command allows you to create a real, four-sided face by specifying a series of edges that define its surface.

Specifying Edges for a Skin-Surface Face

To create a face by means of the Create Real Skin Surface Face option, you must specify two or more existing edges that define the face. The first and last edges that you specify comprise two of the four sides of the face. The other two sides consist of continuous curves fit through the start and end endpoint vertices of all specified edges. The surface of the created face constitutes an interpolation through all of the edges specified for the face.

As an example of edge specification for the Create Real Skin Surface Face operation, consider the four edges shown in Figure 2-58(a). If you use all four edges to create a face by means of the Create Real Skin Surface Face operation, GAMBIT creates a face such as that shown in Figure 2-58(b).

1

2

3

4

(a) (b)

6

5

Figure 2-58: Create Skin Surface Face edge specifications

The first and last edges specified (1 and 4, respectively) comprise two of the four boundary edges of the skin-surface face. The other two boundary edges (5 and 6) consist of continuous curves constructed through the endpoint vertices of the original four edges.



u NOTE (1): The order in which you specify edges determines the shape of the resulting face. For example, to create the face shown in Figure 2-58(b), you must specify the edges in the order (1, 2, 3, 4) or (4, 3, 2, 1), rather than (1, 4, 2, 3) or (3, 2, 1, 4).

u NOTE (2): GAMBIT ignores edge sense when creating a face by means of the Create Skin Surface Face operation. For example, the final shape of the face shown in Figure 2-58(b) is independent of the senses of the edges that define its surface.

Using the Create Real Skin Surface Face Form

To open the Create Real Skin Surface Face form (see below), click the Create Real Skin Surface Face command button on the Geometry/Face subpad.

The Create Real Skin Surface Face form includes the following specifications.

Edges ¬ specifies the existing edges that define the face.




Create Real Net Surface Face

The Create Real Net Surface Face command allows you to create a real, four-sided face by specifying two sets of logically parallel edges that define the boundaries and shape of its surface.

Specifying Edges for a Net-Surface Face

To create a face by means of the Create Real Net Surface Face option, you must specify two or more sets of existing edges that define the shape of the face. Each set must include at least two edges. The surface of the created face constitutes an interpolation through all of the edges specified for the face.

As an example of edge specification for the Create Real Net Surface Face operation, consider the edges shown in Figure 2-59(a). The figure consists of nine edges, four of which (designated by the letter u) are logically perpendicular to the other five (designated by the letter v).

(a) (b)

(c)

v5

v4

v3

v2

v1

u1

u2

u3

u4

Figure 2-59: Create Net Surface Face edge specifications

If you use all four edges in the u direction and all five edges in the v direction to create a net-surface face, GAMBIT creates a face such as that shown in Figure 2-59(b). If you specify edges in either direction the lengths of which exceed the boundary defined by the first or last edges specified in the other direction, GAMBIT truncates the created face. As an example of such trunca-



tion, consider the edges shown in Figure 2-59(a), above. If you specify edges 2, 3, and 4 in the u direction and edges 2, 3, 4, and 5 in the v direction, GAMBIT creates the net-surface face shown in Figure 2-59(c). Note that the final form of the net-surface face approximates the intersection of skin-surface faces created by means of edges 2, 3, and 4 in the u direction and edges 2, 3, 4, and 5 in the v direction.

u NOTE (1): To create a face by means of the Create Net Surface Face opera-tion, you must specify the edges monotonically in each direction with respect to their relative positions in defining the face. For example, to create the face shown in Figure 2-59(b), you must specify the u-direction edges in the order (1, 2, 3, 4) or (4, 3, 2, 1) and the v-direction edges in the order (1, 2, 3, 4, 5) or (5, 4, 3, 2, 1).

u NOTE (2): GAMBIT ignores edge sense when creating a face by means of the Create Net Surface Face operation. For example, the final shape of the face shown in Figure 2-59(b) is independent of the senses of the edges that define its surface.

Specifying the Tolerance Option

If the edges in the u direction do not exactly intersect the edges in the v direc-tion (or vice versa), you must select the Tolerance option and specify a toler-ance value. The tolerance value is the maximum allowable distance between any of the edges and the resulting face.



Using the Create Real Net Surface Face Form

To open the Create Real Net Surface Face form (see below), click the Create Real Net Surface Face command button on the Geometry/Face subpad.

The Create Real Net Surface Face form includes the following specifications.

U Dir. Edges ¬ specifies the edges that define the surface of the face with respect to the u direction (see Figure 2-59(a)).

V Dir. Edges ¬ specifies the edges that define the surface of the face with respect to the v direction (see Figure 2-59(a)).

R Tolerance specifies the allowable tolerance between any of the edges and the surface of the resulting face.

Tolerance specifies the tolerance value.




Create Real Face From Vertex Rows

The Create Real Face From Vertex Rows command allows you to create a four-sided face by specifying a series of vertex rows that define the surface of the face.

To create a face by means of the Create Real Face From Vertex Rows option, you must specify the following parameters:

• A sequence of vertices that define the face

• The number of rows of vertices to be used in defining the face

• The method used to fit curves through the vertices that define the face

The vertex locations define the overall shape of the face. The number of rows determines the shape and numbering of the edges created in the creation of the face.

Specifying the Vertex Sequence

When you specify vertices for the Create Real Face From Vertex Rows opera-tion, you must select the vertices in an ordered sequence that represents the position of each vertex in a sequential series of rows. That is, you must specify all the vertices that constitute the first row, then all the vertices that constitute the second row, and so on.

The first and last rows of vertices specified define edges that comprise two of the four sides of the face. The other two sides of the face consist of continuous curves fit through two sets of vertices defined as follows:

• The first vertex specified in each row

• The last vertex specified in each row

As an example of vertex specification for the Create Real Face From Vertex Rows operation, consider the face shown in Figure 2-60. The face is defined by four rows of three vertices each. The numbers associated with the vertices in the figure indicate the sequence in which the vertices are specified when creating the face.



1

5

4

3

2

9

8

7

612

11

10

edge.1

edge.3

edge.4

edge.2

Sense

Figure 2-60: Create Real Face From Vertex Rows specifications—4 rows

Specifying the Number of Vertex Rows

When you create a face by means of the Create Real Face From Vertex Rows operation, you must specify the number of rows represented by the specified vertices. The total number of vertices must represent an integer multiple of the number of vertex rows. For example, if you specify a total of 12 vertices, you must specify either 2, 3, 4, or 6 vertex rows. The number of vertices in each row is equal to the total number of vertices divided by the number of rows.

It is possible to create a face of a given shape using two different specifica-tions for the number of rows. For example, the face shown in Figure 2-61 rep-resents a face created from the same set of vertices employed to create the face in Figure 2-60. The face differs from the face in Figure 2-60 in that it is created by specifying three rows of four vertices each rather than four rows of three vertices each.



1

6

2

9

5

11

7

3

1012

8

4

edge.4

edge.2

edge.1

edge.3

Sense

Figure 2-61: Create Real Face From Vertex Rows specifications—3 rows

Although the shapes of the two faces are identical to each other, they differ in two respects:

• The sequence in which the vertices are specified

• The numbering of the edges created in the creation of the face

Specifying the Curve Fit Method

GAMBIT allows you to specify one of two methods by which curves are fit through the vertex rows to define the face. The two methods are as follows.

• Interpolate

• Approximate

If you select the Approximate method, you must also specify a Tolerance value. (For a description of the Interpolate and Approximate methods and the Tolerance value, see “Specifying the Curve Construction Method“ in Section 2.3.1, above.)



Using the Create Real Face From Vertex Rows Form

To open the Create Real Face From Vertex Rows form (see below), click the Create Real Face From Vertex Rows command button on the Geometry/ Face subpad.

The Create Real Face From Vertex Rows form includes the following specifica-tions.

Vertices ¬ specifies the vertices to be used in the creation of the face.

No. of Rows specifies the total number of vertex rows. (NOTE: The total number of vertices specified must be equal to an integer multi-ple of the number of vertex rows.)

Method: —————————————————————————

l Interpolate specifies that the face passes through all vertices.

l Approximate specifies that the face passes near to the internal vertices to within the specified Tolerance value.

Tolerance specifies the maximum allowable distance between the face and any of the internal vertices.




Revolve Edges

The Revolve Edges command allows you to create real, two-, three-, or four-sided faces by revolving existing edges about a specified axis.

To create a face by means of the Revolve Edges option, you must specify the following parameters:

• One or more real or non-real edges to be revolved

• The axis of rotation

• The angle through which the edges are revolved about the axis

When you create a face by revolving an edge, GAMBIT sweeps the edge through the specified angle of rotation (see Figure 2-62). One of the edges that GAMBIT creates in the process of creating the face is a duplicate of the edge to be revolved. The other two edges are circular arc edges centered at the axis of rotation. If the axis of rotation passes through either endpoint of an edge to be swept, GAMBIT does not execute the Revolve Edges operation.

q

Angle of revolution

edge.1

edge.3

edge.2edge.4

Edge to be revolved

�

��

�

Axis of revolution

Figure 2-62: Revolve Real Edge operation



Specifying Edges to Be Revolved

To create faces by means of the Revolve Edges form, you must specify one or more real or non-real edges to be revolved about the axis of rotation. GAMBIT creates a separate face corresponding to each specified edge. The specified edges can be straight or curved, and they do not have to be coplanar with the axis of rotation.

u NOTE: If you revolve a non-real edge to create a face, GAMBIT first creates a real copy of the non-real edge, then revolves the real copy to create the face.

Specifying the Axis and Angle of Rotation

To specify the axis of rotation, you must define the axis by means of the Vector Definition form. For a description of the Vector Definition form and its operation, see “Using the Vector Definition Form“ in Section 2.1.4. The con-ventions regarding the angle of rotation for the Revolve Edges operation are identical to those described in “Rotating an Entity“ in Section 2.1.4.



Using the Revolve Edges Form

To open the Revolve Edges form (see below), click the Revolve Edges com-mand button on the Geometry/Face subpad.

The Revolve Edges form includes the following specifications.

Edges ¬ specifies one or more edges to be revolved.

Angle specifies the angle through which the edges are revolved.

Axis: includes two components:


• The coordinates of the start and end points for a vector defining the rotational axis




Sweep Edges

The Sweep Edges command creates real faces by sweeping one or more edges along a specified path. If you sweep a non-real edge to create a face, GAMBIT first creates a real copy of the non-real edge, then sweeps the real copy to create the face.

To create a face by means of the Sweep Edges command, you must specify the following parameters.

• Profile

• Path

• Type

The profile consists of one or more edges to be swept. The path constitutes the trajectory of the sweep operation. The sweep type defines the final shape and orientation of the created face relative to those of the profile and path.

Specifying the Sweep Profile

When you create a face by sweeping an edge, you must specify a set of one or more edges that constitute the sweep profile. The edges that comprise the profile can be straight or curved, and they may or may not be connected to each other. Each type of sweep operation is governed by its own set of rules regarding whether or not an edge constitutes a valid profile component. In general, however, GAMBIT does not allow you to specify profile edges that are parallel to the sweep path.

Specifying the Sweep Path

You can define the sweep path by means of either of the following specifica-tions:

• Edge

• Vector

When you define the sweep path by specifying an edge, GAMBIT defines the path according to the shape, length, and sense of the specified edge. You can reverse the direction of the sweep path relative to the sense of the specified edge by means of the Reverse option on the Sweep Edges form.

When you define the sweep path by specifying a vector, GAMBIT defines the path as a straight line possessing the magnitude and direction of the vector. You must define the vector by means of the Vector Definition form (see “Using the Vector Definition Form“ in Section 2.1.4).



Specifying the Sweep Type

GAMBIT provides two general types of sweep operations:

• Rigid

• Perpendicular

When you specify a rigid sweep, GAMBIT sweeps the profile along the entire length of the specified path without altering the profile orientation. When you specify a perpendicular sweep, you can modify the orientation of the profile over the length of the path.

Performing a Rigid Sweep

When you perform a rigid sweep operation, GAMBIT projects the profile along the entire length of the specified path without altering the orientation of the profile. The shape and orientation of a face created by means of a rigid sweep operation depend on two factors:

• The shape of the profile and its orientation relative to the path

• The shape and direction of the path

The profile edge can be straight or curved and can be located anywhere in the model domain as long as it is not strictly parallel to the path. The shape and direction of the path depend, in part, on whether you specify an edge or a vector to define the path. If you specify an edge to define the path, the path can be straight or curved—depending on the shape of the edge. If you specify a vector to define the path, the path is straight by definition.

The following examples demonstrate the effects of the shapes and orientations of the profile and path on the final form of a face created by means of a simple rigid sweep operation.



Rigid Sweep—Profile Perpendicular to the Path

Figure 2-63 illustrates a rigid sweep operation in which the path and profile consist of straight edges oriented perpendicular to each other. In this case, the profile is aligned with the x coordinate axis, and the path lies in the y-z coordinate plane.

(a) Path and profile (b) Created face

Path

Profile

Endpoints

Projectedpaths

Projectedprofile

Figure 2-63: Rigid sweep—straight, perpendicular profile and path

To create a face by means of the rigid sweep operation, GAMBIT performs the following two-step procedure (see Figure 2-63(b)):

1. Project copies of the path onto the profile endpoints.

2. Project a copy of the profile, itself, to connect the upper endpoints of the projected paths.

The original profile edge and the three edges resulting from the copy-and-project operations constitute the boundary wireframe for the created face.



Rigid Sweep—Profile Not Perpendicular to the Path

The profile edges for a rigid sweep operation can be located anywhere in the model domain as long as they are not parallel to the path. For example, Figure 2-64 shows a rigid sweep operation similar to that shown in Figure 2-63 but in which the profile consists of a curved, circular arc edge that lies in the x-z plane. As in the previous example, the boundary edges of the created face consist of the original profile edge, a projected copy of the profile edge, and two edges that represent projected copies of the path.


Path

Profile

Endpoints

Projectedpaths

Projectedprofile

Figure 2-64: Rigid sweep—profile not perpendicular to the path



Rigid Sweep—Curved Path

The path used for a rigid sweep operation can be straight or curved. To employ a straight path, you can define the path by means of either a straight edge or a vector. To employ a curved path, you must define the path by means of a curved edge.

Figure 2-65 shows a rigid sweep operation similar to that shown in Figure 2-64 but for which the path consists of a circular arc edge that lies in the y-z plane. As in the two previous examples, the boundary edges of the created face consist of the original profile edge, a projected copy of the profile edge, and two edges that represent projected copies of the path.


Path

Profile

Endpoints

Projectedpaths

Projectedprofile

Figure 2-65: Rigid sweep—curved profile, curved path



Performing a Perpendicular Sweep

Overview

Perpendicular sweep operations differ from rigid sweep operations in that, for perpendicular sweeps, the initial orientation between the profile and path is maintained along the entire length of the sweep path. Rigid sweeps, by contrast, maintain the orientation of the profile with respect to the global coordinate system along the sweep path.

As an example of the difference between rigid and perpendicular sweep operations, consider the profile and path shown in Figure 2-66(a). In this case, the profile consists of a straight edge aligned with the y coordinate axis, and the path is defined by a circular arc edge that lies in the y-z plane.

(a) Path and profile (b) Rigid sweep

Path

Profile

(c) Perpendicular sweep

Constant angle betweenprofile and path

Figure 2-66: Example Rigid and Perpendicular sweep operations—curved path

The differences between the created faces can be summarized as follows.

• If you perform a rigid sweep using the path and profile shown in Figure 2-66(a), GAMBIT maintains the angle of the profile with respect to the global coordinate system, thereby creating the horn-shaped face shown in Figure 2-66(b).



• If you perform a perpendicular sweep with a zero draft angle (see below), GAMBIT maintains the angle between the path and profile and creates the face shown in Figure 2-66(c).

Perpendicular Sweep Options

Perpendicular sweep operations can be modified such that the boundary edges of the created face deviate from the projected sweep path by a specified angle. Such modifications are specified by means of the following options on the Sweep Edges form:

• Draft

• Twist

The Draft option specifies a fixed angle of deviation between the path and the swept surface that constitutes the created face. The Twist option revolves the profile through a specified angle along the length of the path.

Draft Option

To sweep a single profile edge—such as that shown in Figure 2-66, above—by means of the perpendicular draft operation, GAMBIT performs the following procedure (see Figure 2-67):

1. Project a copy of the path onto the start endpoint of the profile edge (Figure 2-67(a)).

2. Trace the end endpoint of the profile edge along the projected path, maintaining the original angle between the profile and projected path (Figure 2-67(b)).

3. Project a copy of the profile, itself, to connect the endpoints of the projected profile and traced end endpoint (Figure 2-67(c)).

The boundary edges of the created face (Figure 2-67(d)) consist of the original profile edge, the copy of the path projected to the profile start endpoint, an edge that represents the traced end endpoint of the profile edge, and the projected profile.

u NOTE: The procedure described above applies strictly only to sweep opera-tions that involve a zero draft angle. For a description of the effect of draft angle on faces resulting from perpendicular draft sweep operations, see “Effect of Draft Angle,” below.



(a) (b)

(c) (d)

Startendpoint

Endendpoint

Profileprojection

Figure 2-67: Perpendicular draft method—procedure

The characteristics of the face created from a perpendicular draft sweep operation depend, in part, on the following factors:

• Profile edge sense

• Draft angle

The direction (or sense) of the path relative to the sense and position of the profile can also strongly affect the shape of the created face, but such effects are difficult to generalize and depend strongly on the shapes, lengths, and orientations of the profiles and paths.

Effect of Profile Edge Sense

As noted above, when you sweep an edge by means of the perpendicular draft method and specify a zero draft angle, GAMBIT copies and projects the profile onto the start endpoint of the profile edge and maintains the angle between the profile and path along the entire length of the path. Consequently, the start and end endpoint designations (which determine the edge sense) influence the shape of the created face.



As an example of the dependence on edge sense described above, consider the path and profile shown in Figure 2-68(a). The path consists of a circular arc edge that lies in the y-z plane, and the profile consists of a single edge aligned with the y coordinate axis.

(a) (b)

Path

Profile

(c)

A

B

Pathprojections

Figure 2-68: Effect of profile sense on swept face

The characteristics of the face created by means of a perpendicular draft sweep of the profile shown in Figure 2-68(a) depend on the sense of the profile edge in the following manner.

• If the profile edge is defined such that vertex A constitutes its start endpoint, the sweep operation results in the face shown in Figure 2-68(b). To create the face shown in Figure 2-68(b), GAMBIT copies the path edge and projects it onto vertex A of the initial profile. In this case, the outer curved boundary edge of the face represents the copied projection of the sweep path.

• If the profile edge is defined such that vertex B constitutes its start endpoint, the sweep operation results in the face shown in Figure 2-68(c). To create the face shown in Figure 2-68(c), GAMBIT copies the path edge and projects it onto vertex B of the initial profile. In this case, the inner curved boundary edge of the face represents the copied projection of the sweep path.



u NOTE: If the profile edge shown in Figure 2-68(a) were aligned with the x coordinate axis, rather than the y coordinate axis, the characteristics of the face resulting from the sweep operation would be independent of the profile edge sense.

Effect of Draft Angle

When you perform a sweep operation by means of the draft method, GAMBIT allows you to specify a draft angle for the created face. The draft angle specifies the angle by which the boundary edges of the created face deviate from the projected path.

The effect of the draft angle specification depends strongly on the shapes and orientations of the profile and path relative to each other. Figure 2-69 shows the effect of draft angle for two simple profiles and paths similar to those shown above.

Draft Angle

+10º0º

-10º

Draft Angle

-5º

0º

-10º

(a) (b)

Figure 2-69: Effect of draft angle on swept face

In Figure 2-69(a), the path and profile consist, respectively, of a circular arc edge aligned with the y-z plane and a straight edge aligned with the y coordinate axis. In this case, the draft angle determines the angle by which the plane that contains the created face deviates from the y-z plane.



u NOTE (1): For the path and profile configuration shown in Figure 2-69(a), the perpendicular draft sweep operation always creates a planar face aligned with the y coordinate axis, regardless of draft angle.

NOTE (2): The projections of the three faces shown in Figure 2-69(a) onto the y-z coordinate plane are identical to each other in shape, size, and orientation.

In Figure 2-69(b), the path consists of a circular arc edge aligned with the y-z plane the profile edge is aligned with the x coordinate axis. In this case, the draft angle specification serves to increase or decrease the size of the swept arc represented by the created face.

Twist Option

When you perform a perpendicular sweep operation by means of the twist option, GAMBIT revolves the profile through a specified angle as it sweeps the profile along the length of the path. The profile and path can be either straight or curved, but curved paths require an additional restriction with respect to the orientation between the profile and path (see below).

Using a Straight Path

Figure 2-70 illustrates the effect of the perpendicular twist sweep operation for a configuration that involves a straight sweep path. In this case, the profile is defined by a circular arc edge that lies in the x-z plane, the path is defined by a straight edge that is similar in orientation to that shown in Figure 2-63, above, and the twist angle is specified as 360º.




Path

Profile

Twist Angle = +360º

Figure 2-70: Effect of perpendicular twist sweep operation—straight path

Using a Curved Path

Under certain circumstances, GAMBIT allows you to perform twist sweep operations using a curved path. Figure 2-71 illustrates the effect of the twist sweep operation for a configuration that involves a curved path. In this case, the path is defined by a circular arc edge similar in orientation to that shown in Figure 2-65. The profile consists of a single, straight edge one endpoint of which is connected to the start point of the path, and the twist angle is specified as 180º.




Path

Profile

Twist Angle = + 180º

Figure 2-71: Effect of perpendicular twist sweep operation—curved path



Using the Sweep Edges Form

To open the Sweep Edges form (see below), click the Sweep Edges command button on the Geometry/Face subpad.

The Sweep Edges form includes the following specifications.

Edges ¬ specifies one or more edges that constitute the sweep profile. (NOTE: GAMBIT creates a separate face for each specified edge.)

Path: —————————————————————————

l Edge specifies that the path is described by the length, orienta-tion, and sense of an existing edge.

Edge ¬ specifies the existing edge to be used as the sweep path.

Reverse reverses the direction of the path relative to the sense of the specified edge.



l Vector specifies that the path is described by a vector.

When you select the Vector option, GAMBIT displays a command button titled Define Vector. When you click the Define Vector command button, GAMBIT opens the Vector Definition form, which allows you to specify parameters that define the path vector. For instructions on using the Vector Definition form, see “Using the Vector Definition Form“ in Section 2.1.4.

Type: —————————————————————————

l Rigid specifies a rigid sweep operation.

l Perpendicular specifies a perpendicular sweep operation

Option: ——————————————————————

l Draft specifies the draft perpendicular sweep method.

l Twist specifies the twist perpendicular sweep method.

Angle specifies the draft angle or twist angle.




2.4.2 Create Face

The Create Face command button allows you to perform the following opera-tions.


Create Real Rectangular Face

Creates a real face in the shape of a rectangle

Create Real Circular Face Creates a real face in the shape of a circle

Create Real Elliptical Face Creates a real face in the shape of an ellipse




Create Real Rectangular Face

The Create Real Rectangular Face command creates a real planar face in the shape of a rectangle.

When you execute the Create Real Rectangular Face command, GAMBIT creates a real rectangular, planar face. GAMBIT orients and locates the face such that it is aligned with one of the coordinate planes of a specified refer-ence coordinate system. The Create Real Rectangular Face command includes the following input parameters:

• Width

• Height

• Coordinate Sys.

• Direction

The Width and Height parameters determine the dimensions of the rectangular face. (NOTE: If you do not specify the Height parameter, GAMBIT creates a square face with sides of the length specified by the Width parameter (and vice versa)). The Coordinate Sys. parameter specifies the reference coordinate system for the face creation operation. The Direction parameter specifies the orientation and location of the face relative to the reference coordinate system.

Using the Create Real Rectangular Face Form

To open the Create Real Rectangular Face form (see below), click the Create Real Rectangular Face command button on the Geometry/Face subpad.

The Create Real Rectangular Face form includes the following specifications.



Width specifies the width of the rectangular face. (NOTE: For faces created in the x-y, y-z, and z-x planes, the Width dimension is aligned with x, y, and z directions, respectively.)

Height specifies the height of the rectangular face. (NOTE: For faces created in the x-y, y-z, and z-x planes, the Height dimension is aligned with y, z, and x directions, respectively.)

Coordinate ¬ Sys.

specifies the reference coordinate system for the face creation operation (default = currently active coordinate system).

Direction —————————————————————————

+X +Y q +X -Y -X +Y -X -Y XY Centered +Y +Z +Y -Z -Y +Z -Y -Z YZ Centered +Z +X +Z -X -Z +X -Z -X ZX Centered

specifies the face orientation plane relative to the reference coordinate system and the region of the orientation plane in which the face is created.




Create Real Circular Face

The Create Real Circular Face command creates a real planar face in the shape of a circle.

When you execute the Create Real Circular Face command, GAMBIT creates a real circular, planar face. GAMBIT orients and locates the face such that it is aligned with one of the coordinate planes of a specified reference coordinate system. The Create Real Circular Face command includes the following input parameters:

• Radius

• Coordinate Sys.

• Plane

The Radius parameter determines the size of the circular face. The Coordinate Sys. parameter specifies the reference coordinate system for the face creation operation. The Plane parameter specifies the orientation of the face relative to the reference coordinate system. (NOTE: The created face is always centered at the origin of the reference coordinate system.)

Using the Create Real Circular Face Form

To open the Create Real Circular Face form (see below), click the Create Real Circular Face command button on the Geometry/Face subpad.

The Create Real Circular Face form includes the following specifications.



Radius specifies the radius of the circular face.

Coordinate ¬ Sys.


Plane —————————————————————————

XY q YZ ZX

specifies the face orientation plane relative to the reference coordinate system.




Create Real Elliptical Face

The Create Real Elliptical Face command creates a real planar face in the shape of an ellipse.

When you execute the Create Real Elliptical Face command, GAMBIT creates a real elliptical, planar face. GAMBIT orients and locates the face such that it is aligned with one of the coordinate planes of a specified reference coordinate system. The Create Real Elliptical Face command includes the following input parameters:

• Radius 1

• Radius 2

• Coordinate Sys.

• Plane

Radius 1 and Radius 2 represent the lengths of the major and minor axes of the ellipse. For the purposes of this command, the major and minor axes are always aligned with the coordinate axes of the plane in which the elliptical face is created. Either parameter, Radius 1 or Radius 2, can serve as the major or minor axis of the ellipse. (NOTE: If you do not specify Radius 2, GAMBIT creates a circular face of radius Radius 1.)

The Coordinate Sys. parameter specifies the reference coordinate system for the face creation operation. The Plane parameter specifies the orientation of the face relative to the reference coordinate system. (NOTE: The created face is always centered at the origin of the reference coordinate system.)



Using the Create Real Elliptical Face Form

To open the Create Real Elliptical Face form (see below), click the Create Real Elliptical Face command button on the Geometry/Face subpad.

The Create Real Elliptical Face form includes the following specifications.

Radius 1 specifies the length of the major or minor axis of the ellipse.

Radius 2 specifies the length of the minor or major axis of the ellipse.

Coordinate ¬ Sys.


Plane —————————————————————————

XY q YZ ZX

specifies the orientation plane for the face relative to the reference coordinate system.




2.4.3 Boolean Operations

The Boolean Operations command button allows you to perform the following operations.


Unite Real Faces Unites two or more real faces into one real face

Subtract Real Faces Subtracts the intersecting region(s) between two or more faces

Intersect Real Faces Creates a face representing the inter-section of two or more faces

Overview

Each of the commands listed above allows you to perform a Boolean operation involving two or more faces. The specified faces do not have to be planar, but they must be coincident in the intersecting region between them. (NOTE: For the lone exception to this rule, see “Unite Real Faces,” below.)

Figure 2-72 illustrates the general results of each of the Boolean face opera-tions on a coplanar circle and square.



face.1 face.2

(a) Specified faces (b) Unite

(d) Intersect(c) Subtract (face.2 from face.1)

�

�

Figure 2-72: Boolean face operations

Retaining the Specified Faces

Each Boolean operation form includes at least one Retain option. When you perform a Boolean operation involving a set of specified faces, GAMBIT replaces the specified faces with a single face that constitutes the result of the operation. If you select the Retain option, GAMBIT retains the original faces when it performs the Boolean operation.



Unite Real Faces

The Unite Real Faces command allows you to unite two or more overlapping faces into one or more real faces.

When you unite overlapping faces by means of the Unite Real Faces command, GAMBIT creates one real face that represents the union of the overlapping faces. If you specify a set of faces on the Unite Real Faces form such that the set consists of two or more subsets of faces that overlap each other but do not overlap the faces of any other subset, GAMBIT creates a separate real face for each subset.

Using the Unite Real Faces Form

To open the Unite Real Faces form (see below), click the Unite command button on the Geometry/Face subpad.

The Unite Real Faces form includes the following specifications.

Faces ¬ specifies the set of faces to be united.

R Retain specifies that all original specified faces are retained.



Subtract Real Faces

The Subtract Real Faces command allows you to perform a Boolean subtrac-tion involving two or more real faces.

Using the Subtract Real Faces Form

To open the Subtract Real Faces form (see below), click the Subtract command button on the Geometry/Face subpad.

The Subtract Real Faces form includes the following specifications.

Face ¬ specifies the target face from which overlapping regions are to be subtracted.

R Retain specifies that the target face is retained.

Subtract —————————————————————————

Faces ¬ specifies one or more faces that constitute subtraction tools.

R Retain specifies that all subtraction-tool faces are retained.



Intersect Real Faces

The Intersect Real Faces command allows you to perform a Boolean intersec-tion of two or more real faces.

Using the Intersect Real Faces Form

To open the Intersect Real Faces form (see below), click the Intersect com-mand button on the Geometry/Face subpad.

The Intersect Real Faces form includes the following specifications.

Faces ¬ specifies two or more faces for the intersection operation.

R Retain specifies that all original specified faces are retained.



2.4.4 Connect/Disconnect Faces

The Connect/Disconnect Faces command button allows you to perform two operations.


Connect Faces Connects coincident real faces or creates virtual faces that represent the connection of one or more existing faces

Disconnect About Real Face Disconnects volumes that share a common real face





Connect Faces

The Connect Faces command allows you to connect two or more faces. (NOTE: If you connect two or more meshed faces, and the meshes on each face are topologically identical to each other, GAMBIT preserves the meshes when connecting the faces.)

To connect faces, you must specify the following parameters:

• Two or more faces to be connected


Specifying the Faces to Be Connected

The faces to be connected can be real or virtual, but they are subject to certain restrictions imposed by the connection type (see below).


There are four types of face connection operations:

• Real






The Real option allows you to connect coincident real faces—that is, two or more real faces the edges of which are coincident. When you connect real faces and specify the Real option, GAMBIT deletes all but one of the specified faces and connects the remaining real face to any and all volumes of which the deleted faces were a part.




The Virtual (Forced) option allows you to connect real and/or virtual faces, regardless of their proximity to each other. When you connect faces and spec-ify the Virtual (Forced) option, GAMBIT replaces the specified faces with a vir-tual face. If a specified face constitutes part of a volume, GAMBIT overlays the volume with a virtual volume and forms the virtual volume according to the shape and position of the new virtual face.


The Virtual (Tolerance) option allows you to specify that only those real and/or virtual faces the edges of which are near to each other to within a specified tolerance are connected. There are two ways to express the tolerance value:

• Tolerance

• Shortest Edge%

The Tolerance specification represents the tolerance value as expressed in absolute distance units. The Shortest Edge% specification represents the toler-ance value expressed as a percentage of the length of the shortest edge.



1) Real connect operations for faces that are coincident to within the global tolerance value

2) Virtual (Tolerance) connect operations for unconnected, specified faces that are near to each other to within the user-specified tolerance

u NOTE: When you connect faces by means of a virtual face-connect operation, GAMBIT replaces the original faces with a single virtual face, the boundary edges of which are interpolations between the corresponding boundary edges of the original faces. If you mesh the created virtual face, GAMBIT locates the edge mesh nodes on the boundary edges of the face but projects the face mesh nodes onto the surface of the first face picked for the virtual face-connect operation—that is, the topmost face in the Faces pick list.



Using the Connect Faces Form

To open the Connect Faces form (see below), click the Connect command button on the Geometry/Face subpad.

The Connect Faces form includes the following specifications.

Faces ¬ specifies the faces to be connected.

l Real specifies that the face that results from the connection of faces is a real face. (NOTE: To obtain a real face from the connection of two or more real faces, the specified faces must be coincident.)

l Virtual (Forced) specifies the following characteristics for the face that results from connection of faces:

• The face is a virtual face

• The face is created irrespective of the distance between the specified faces

l Virtual (Tolerance) specifies the following characteristics for the face that results from connection of faces:

• The face is a virtual face

• The specified faces are connected only if the distance between them is less than a specified tolerance (see below)






2) Virtual (Tolerance) connect operations for the remaining specified, unconnected faces

Tolerance specifies the maximum allowable distance (absolute units) between faces to be connected.

Shortest Edge % specifies the maximum allowable distance (percent of shortest edge) between faces to be connected.




Disconnect About Real Face

The Disconnect About Real Face command allows you to disconnect indi-vidual real faces and/or volumes that share a common face.

When you disconnect faces, GAMBIT creates a new face for all but one of the entities to which the specified face is connected. For example, if the specified face is shared by three volumes, GAMBIT creates two new faces that are coincident with the specified face and connects them to two of the three volumes. The original face is connected to the remaining volume.

Specifying the Edge and Vertex Options

GAMBIT provides the following three options with respect to the treatment of endpoint vertices for the disconnected edges:

• Face + Edges/Vertices

• Face Only

• Face + Selected Edges

The following table describes the effects associated with each option.

Option Description

Face + Edges/Vertices GAMBIT disconnects the specified face and all of its component edges and vertices.

Face Only GAMBIT disconnects the face but not its edges. Each new face created in the discon-nection process shares the edges of the speci-fied face.

Face + Selected Edges GAMBIT disconnects the face and one or more of its edges (specified by the user). The remaining edges are shared between all new faces created in the disconnection process.



Using the Disconnect About Real Face Form

To open the Disconnect About Real Face form (see below), click the Discon-nect command button on the Geometry/Face subpad.

The Disconnect About Real Face form includes the following specifications.

Face ¬ specifies the face to be disconnected.

l Face + Edges/ Vertices

specifies that all edges and vertices that are components of the face are to be disconnected.

l Face Only specifies that only the face is to be disconnected and that any new faces created in the disconnection process share the edges and vertices of the specified face.

l Face + Selected Edges

specifies that one or more user-specified edges are to be disconnected along with the face. Any edges not specified are shared between the specified face and any new faces created in the disconnection process.

Edge ¬ specifies the edges to be disconnected in conjunction with the specified face.



2.4.5 Modify Face Color/Label

The Modify Face Color/Label command button allows you to perform two operations.


Modify Face Color Changes the color of the geometry and/or mesh associated with one or more faces as displayed in the graphics window

Modify Face Label Changes a face label




Modify Face Color

The Modify Face Color command allows you to change the displayed color of the geometry and/or mesh and/or shading associated with one or more faces.

Using the Modify Face Color Form

To open the Modify Face Color form (see below), click the Modify Color com-mand button on the Geometry/Face subpad.

The Modify Face Color form includes the following specifications.

Faces ¬ specifies one or more faces for which the color is to be changed.

Color: —————————————————————————

R Geometry specifies modifying the color of the face(s).

R Mesh specifies modifying the color of the mesh associated with the face(s).

R Shade specifies modifying the color of the shading associated with the face(s).

For specific instructions on setting colors, see “Using the Set Color Form“ in Section 2.2.4.



Modify Face Label

The Modify Face Label command allows you to change the label associated with any face.

Using the Modify Face Label Form

To open the Modify Face Label form (see below), click the Modify Label com-mand button on the Geometry/Face subpad.

The Modify Face Label form includes the following specifications.

Face ¬ specifies the face to be modified.

Label specifies a new label for the face. (See Section 2.1.1).



2.4.6 Move/Copy/Align Faces

The Move/Copy/Align Faces command button allows you to perform two operations.


Move/Copy Faces Moves and copies faces

Align Faces Aligns faces and connected geometry with existing topological entities




Move/Copy Faces

The Move/Copy Faces command allows you to reposition and/or reorient one or more faces or to create copies of faces. For a general description of the pro-cedures and specifications required to move and/or copy entities, see “Moving an Entity“ and “Copying an Entity,” respectively, in Section 2.1.4.

Using the Move/Copy Faces Form

To open the Move/Copy Faces form (see below), click the Move/Copy com-mand button on the Geometry/Face subpad.

For a complete description of the specifications available on the Move/Copy Faces form, see “Using Move/Copy Forms“ in Section 2.1.4.



Align Faces

The Align Faces command allows you to reposition and/or reorient a face so that it coincides with another face or is aligned with a plane defined by three vertices. (For a general description of the procedure and specifications required to align an entity, see “Aligning an Entity,” in Section 2.1.4, above.)

Using the Align Faces Form

To open the Align Faces form (see below), click the Align command button on the Geometry/Face subpad.

For a complete description of the specifications available on the Align Faces form, see “Using Align Forms“ in Section 2.1.4.



2.4.7 Split/Merge/Collapse/Simplify Faces

The Split/Merge/Collapse/Simplify Faces command button allows you to perform the following operations.


Split Face Splits an existing face into two real or virtual faces

Merge Faces (Virtual) Merges two or more existing faces into a virtual face

Collapse Face (Virtual) Collapses two or more real or virtual faces into a virtual edge or vertex

Simplify Faces Simplifies face geometry by removing dangling edges




Split Face

The Split Face command allows you to split an existing face into one or two real or virtual faces. (NOTE: If you split a face that is linked to one or more faces, GAMBIT splits every face in the set of linked face in addition to the specified face.)

To split a face by means of the Split Face command, you must specify the fol-lowing parameters:

• Target face

• Split type

The target face specifies the face to be split by the Split Face operation. The split type determines the type of split tool to be used for the split (face, edges, vertices) and type of geometry to be produced from the operation (real, virtual, or faceted).

Specifying the Target Face

GAMBIT allows you to split either real or virtual faces by means of the Split Face operation but places the following restrictions on the type of faces that can be created from the split:

• If you split a real face, GAMBIT can create real or non-real faces.

• If you split a non-real face, GAMBIT creates only non-real faces.


GAMBIT provides the following types of face-split options:

• Face (Real)

• Face (Faceted)

• Edges (Virtual)

• Vertices (Virtual)

Each option differs from the others with respect to the type of split tool used and the type of geometry created from the split operation. The following subsections describe the options listed above.



Specifying a Face (Real) Split Operation

The Face (Real) split option allows you to split a real target face using a real split-tool face. (NOTE: You cannot use the Face (Real) option to split a non-real face.) When you split a face using the Face (Real) split option, GAMBIT creates a set of real faces from the split operation.

The general rules that govern the relationship between the target and split-tool faces for a Face (Real) split operation are as follows:

• The split-tool face must fully or partially intersect the target face. The extent of intersection between the split-tool face and the target face determines the types of edges and faces created from the split opera-tion as follows (see Figure 2-73):

— If the split-tool face fully intersects the face to be split, GAMBIT creates two faces that share a common edge representing the curve of intersection (see Figure 2-73(a)).

— If the split-tool face partially intersects the face to be split, GAMBIT creates a single face that includes a dangling edge (see Figure 2-73(b)).

(a) Split with fully intersecting split-tool

Target

Split tool

(b) Split with partially intersecting split-tool

TargetSplit tool

Dangling edge

Figure 2-73: Effect of fully and partially intersecting split-tool faces



• If the face to be split is part of an existing volume, you must specify the Connected suboption (see below).

The Face (Real) split option includes two suboptions:

• Retain

• Connected

If you specify the Retain option, GAMBIT retains the split-tool face upon completion of the split operation. If you do not specify the Retain option, GAMBIT deletes the split-tool face.

If you specify the Connected option, GAMBIT connects the faces that result from the split operation along their common edge(s). If you do not specify the Connected option, the split operation creates disconnected faces.

Specifying a Face (Faceted) Split Operation

The Face (Faceted) split option allows you to split a faceted target face using a faceted split-tool face—that is, the Face (Faceted) split operation cannot be used to split real or virtual target faces or to split a faceted face with a real or virtual split-tool face.

The Face (Faceted) operation includes a Retain option. If you specify the Retain option, GAMBIT retains the split-tool face upon completion of the split operation. If you do not specify the Retain option, GAMBIT deletes the split-tool face.

Specifying an Edges (Virtual) Split Operation

The Edges (Virtual) split option allows you to split a real or non-real target face using a split-tool consisting of one or more real or non-real edges. Regardless of the type(s) of edge(s) used in the operation, the Edge (Virtual) split operation produces only connected, virtual faces.

The Edges (Virtual) split-tool can consist of either a single edge or of a chain of connected edges. In either case, the endpoints of the split-tool edge or outermost endpoints of the split-tool chain must comprise components of the boundary for the target face. If you specify a chain of connected edges as the split tool, GAMBIT transforms the chain into a single, virtual edge along which the faces that result from the split operation are connected.

The Edges (Virtual) split option includes a Tolerance suboption that allows you to specify an allowable tolerance between the split-tool edge or edge-chain and the surface of the target face.



Specifying a Vertices (Virtual) Split Operation

The Vertices (Virtual) split option allows you to split a real or non-real target face using a split-tool consisting of two or more real or non-real vertices. Regardless of the type(s) of vertices used in the operation, the Vertices (Virtual) split operation produces connected, virtual faces.

The Vertices (Virtual) split-tool can consist of either a pair of vertices or a series of vertices located on the surface of the face. In either case, the vertex pair or outermost endpoints of the vertex series must comprise components of the boundary for the target face. If you specify a series of vertices as the split tool, GAMBIT transforms the series into a chain of straight virtual edges that serves as the boundary between the faces resulting from the split operation.

The Vertices (Virtual) split option includes two suboptions:

• Tolerance

• Shaped Edge

The Tolerance suboption allows you to specify an allowable tolerance between vertices comprising components of a split-tool series and the surface of the target face.

The Shaped Edge suboption specifies that the edge resulting from the split operation is shaped such that it bisects the face boundary at its endpoints (see Figure 2-74).



(a) Shaped Edge off (b) Shaped Edge on

Split-tool vertices

Shaped edge

Figure 2-74: Effect of Shaped Edge option

u NOTE: The Shaped Edge option is available for the Vertices (Virtual) operation only when the face is split by two vertices. If you specify more than two vertices for the Vertices (Virtual) face split operation, GAMBIT creates a chain of straight virtual edges that serves as the boundary between the faces resulting from the split operation.



Using the Split Face Form

To open the Split Face form (see below), click the Split command button on the Geometry/Face subpad.

The specifications on the Split Face form are as follows.

Face ¬ specifies the face to be split.

Split with —————————————————————————

Face (Real) q Face (Faceted) Edges (Virtual) Vertices (Virtual)

specifies the split type.

The specifications available on the lower section of the Split Face form depend on the specified Split with option as follows.



Face (Real) Split Option

When you specify the Face (Real) option, the lower section of the Split Face form appears as shown above and includes the following specifications.

Face ¬ specifies the real face that constitutes the split tool.

R Retain specifies retaining the split-tool face at the conclusion of the split operation.

R Connected specifies connecting the edge(s) that constitute(s) the boundary between the faces resulting from the split operation.

Face (Faceted) Split Option

When you specify the Face (Faceted) option, the lower section of the Split Face form appears as shown below and includes the following specifications.

Face ¬ specifies the faceted face that constitutes the split tool.




Edges (Virtual) Split Option

When you specify the Edges (Virtual) option, the lower section of the Split Face form appears as shown below and includes the following specifications.

Edges ¬ specifies the real or non-real edge(s) that constitute(s) the split tool.

R Tolerance specifies that the split operation is performed if the split-tool edges are located in proximity to the face to within the specified tolerance value.

Vertices (Virtual) Split Option

When you specify the Vertices (Virtual) option, the lower section of the Split Face form appears as shown below and includes the following specifications.

Vertices ¬ specifies the real or non-real vertices that constitute the split tool.

R Tolerance specifies that the split operation is performed if the split-tool vertices are located in proximity to the face to within the specified tolerance value.

R Shaped Edge shapes the resulting splitting edge so that it is normal to the face boundary edges at its endpoints.



Merge Faces (Virtual)

The Merge Faces (Virtual) command allows you to merge two or more real and/or virtual faces into a single virtual face. (NOTE: If you merge faces that possess identical boundary-zone type specifications, GAMBIT retains the specification and assigns it to the face that results from the merge operation. If the faces differ with respect to their boundary-zone specifications, GAMBIT does not assign a specification to the resulting face.)

To merge faces by means of the Merge Faces (Virtual) command, you must specify the following parameters:

• The set of faces to be merged

• The merge type

• The Merge edges option

Specifying the Faces to Be Merged

GAMBIT allows you to merge two or more real and/or virtual faces into a single virtual face but applies the following rules with respect to the set of faces to be merged:

• Each face in the set must be connected by means of a common edge to at least one other face in the set

• None of the connected, common edges between faces are allowed to be connected to faces that are not in the set of faces to be merged

Specifying the Merge Type

When you merge faces, you must specify the merge type. There are two types of face-merge operations:



When you specify a Virtual (Forced) merge, GAMBIT merges all of the faces in the specified set, regardless of the lengths of their sides. (NOTE: GAMBIT does not allow you to merge faces oriented such that they form sharp angles. You can set the angle criteria by means of the Edit Defaults form (default = 90�).) When you specify a Virtual (Tolerance) merge, GAMBIT performs the merge operation only if all edges in the set meet specified tolerance criteria.



Virtual (Tolerance) Criteria

There are two types of face-merging Virtual (Tolerance) criteria:

• Max. Distance

• Min. Angle

The Max Distance criterion is based on a theoretical plane fit through all faces specified for the merge operation. When you specify the Virtual (Tolerance) option, GAMBIT includes in the merge operation only those faces that are located near the theoretical plane to within the specified distance.

The Min Angle criterion is based on the internal angles between pairs of neigh-boring faces. When you specify the Virtual (Tolerance) option, GAMBIT merges only those face pairs the internal angle of which is greater than the specified tolerance. For example, to merge two side faces of a regular, six-sided prism using the Virtual (Tolerance) option, you must specify a Min Angle value of 119°.

Specifying the Merge edges Option

When you specify the Merge edges option, GAMBIT merges the edges that result from the face-merge operation. As an example of the effect of the Merge edges option, consider the two square, coplanar faces shown in Figure 2-75, which are connected by means of edge.1.

• If you do not specify the Merge edges option when merging the square, coplanar faces, GAMBIT creates a four-sided face bounded by six edges (see Figure 2-76(a)).

• If you specify the Merge edges option, GAMBIT merges the pairs of edges that constitute the upper and lower sides of the four-sided face, thereby creating a face bounded by only four edges (see Figure 2-76 (b)).

u NOTE: Edges to be merged as a result of the Merge edges option on the Merge Faces (Virtual) command must satisfy the standard edge-merging criteria (see “Merge Edges (Virtual),” in Section 2.3.5, above).



edge.1

face.1 face.2

Figure 2-75: Face merge—effect of Merge edges option, original faces

(a) Merge edges option off

(b) Merge edges option on

Figure 2-76: Face merge—effect of Merge edges option, merged faces



Using the Merge Faces (Virtual) Form

To open the Merge Faces (Virtual) form (see below), click the Merge command button on the Geometry/Face subpad.

The Merge Faces (Virtual) form includes the following specifications.

Faces ¬ specifies the set of faces to be merged.

Type: —————————————————————————

l Virtual (Forced) specifies that the faces in the set are to be merged regard-less of their orientation to each other. (NOTE: None of the angles between faces in the set are allowed to be less than 90�.)

l Virtual (Tolerance) specifies that the edges in the set are to be merged only if their distances and orientations with respect to neighbor-ing faces meet specified tolerance criteria.

Max. Distance specifies the maximum allowable distance between any face and a theoretical plane fit through all faces to be merged.

Min. Angle specifies the minimum allowable angle between neigh-boring faces to be merged.

R Merge edges merges edges that result from the face-merge operation.



Collapse Face (Virtual)

The Collapse Face (Virtual) command allows you to collapse a real or virtual face that lies between two or more neighboring real and/or virtual faces.

When you collapse a face, GAMBIT performs the following operations:

1) Split the face into two or more faces of approximately equal size.

2) Merge the resulting faces with their specified neighboring faces.

Each of the neighboring faces specified for the collapse operation must be connected to the face to be collapsed by means of one or more common edges. The virtual faces that result from the collapse operation share the virtual edge or vertex that replaces the collapsed face.

The following sections illustrate the results of the face collapse operation for three different situations involving planar faces.

Three Coplanar Faces in a Line

In Figure 2-77, three square faces—labeled face.1, face.2, and face.3—are arranged in a line, and face.2 is connected to face.1 and face.3 at edge.4 and edge.8, respectively. The face-collapse operation replaces face.2 with a virtual edge (v_edge.11) and overlays two virtual faces (v_face.4 and v_face.5) onto face.1 and face.3.

(a) Before

(b) After

face.1 face.3face.2

edge.4 edge.8

v_face.4 v_face.5

v_edge.11

Figure 2-77: Face collapse—3 coplanar faces arranged in a line



Three Coplanar Faces at an Angle

In Figure 2-78, three square faces are arranged at an angle with respect to each other. As in the previous example, the face-collapse operation replaces face.1 with a virtual edge and overlays two virtual faces onto face.1 and face.3.

(a) Before (b) After

face.1 face.3

face.2 v_face.4

v_face.5

Figure 2-78: Face collapse—3 coplanar faces arranged at an angle



Four Non-coplanar Faces

In Figure 2-79, a triangular face is surrounded by three faces that are arranged at right angles with respect to each other. The face-collapse operation replaces face.4 with a virtual vertex (v_vertex.12), and overlays three virtual faces that share the vertex.

(a) Before (b) After

face.1face.3

face.2

face.4

v_face.5

v_face.6

v_face.7

v_vertex.12

Figure 2-79: Face collapse—4 non-coplanar faces

Face Collapse Specifications

To collapse a face by means of the Collapse Face (Virtual) form, you must specify the following parameters:

• The face to be collapsed

• The neighboring faces between which the face is to be collapsed

The following general rules govern the specifications of parameters for the face-collapse operation:

• You cannot collapse a face that constitutes part of a volume. For example, GAMBIT does not allow you to collapse one end of a prism.

• Each of the specified neighboring faces must be connected to the face to be collapsed by means of a common edge.



Using the Collapse Face (Virtual) Form

To open the Collapse Face (Virtual) form (see below), click the Collapse com-mand button on the Geometry/Face subpad.

The Collapse Face (Virtual) form includes the following specifications.

Face ¬ specifies the face to be collapsed.

Between —————————————————————————

Faces ¬ specifies the neighboring faces that define the collapse operation.



Simplify Faces

The Simplify Faces command removes (deletes) dangling edges from faces. Dangling edges are edges that are included in the list of edges that define a face but which do not constitute necessary parts of the closed edge loop that circumscribes the face. They most often result from face-split operations in which the split-tool face only partially intersects the target face (see “Split Face,” above).

Figure 2-80 shows two different types of dangling edges, both of which can be removed by means of the Simplify Faces command. In Figure 2-80(a), the dangling edge is connected to the boundary-edge loop of its associated face. In Figure 2-80(b), the dangling edge exists apart from and is not connected to the boundary even though it is included in the list of edges associated with the face.

(a) Connected dangling edge

Dangling edges

(b) Unconnected dangling edge

Figure 2-80: Faces that include dangling edges



Using the Simplify Faces Form

To open the Simplify Faces form (see below), click the Simplify command button on the Geometry/Face subpad.

The Simplify Faces form includes the following specification.

Faces ¬ specifies one or more faces for which dangling edges are to be removed.



2.4.8 Heal/Convert Faces

The Heal/Convert Faces command button allows you to perform the following operations.


Heal Real Faces Heals real face geometry

Convert Faces Converts non-real faces to real faces




Heal Real Faces

The Heal Real Faces command attempts to heal geometry and topology prob-lems that sometimes occur in sets of real faces.

Overview

GAMBIT real geometry operations employ ACIS modeling techniques. ACIS modeling algorithms require a high degree of precision and accuracy in the geometric data that describe the model. Such precision and accuracy manifests in the form of tight distance tolerances and completeness of connectivity information.

In most cases, model geometry data generated from within GAMBIT automatically meet the stringent integrity standards required by the ACIS modeler. However, several GAMBIT operations—for example, Boolean operations—can sometimes produce geometry that fails to meet the ACIS standards. In addition, geometry imported to GAMBIT from outside sources may not meet such standards due to any of the following factors:

• Inherent numerical limitations in the system used to generate the geometry

• Limitations of data transfer through neutral file formats

• Differences in tolerance settings between the model-generating pro-gram and GAMBIT

The Heal Real Faces command attempts to detect and repair geometry and topology problems that involve face entities. The healing operation is a three-step process that involves simplifying geometry, stitching together loose faces (if necessary), and building new geometry to repair geometry and topology problems.

u NOTE: The GAMBIT healing operations—Heal Real Faces and Heal Real Volume (see Section 2.5.8)—are not guaranteed to correct all geometry and topology problems in the model. In general, both operations should be used with caution, because they are not robust and sometimes produce peculiar model geometry.



Specifying the Heal Real Faces Options

As noted above, the healing operation involves three steps:

• Geometry simplification

• Stitching

• Geometry building

In the geometry simplification step, GAMBIT converts NURBS data to ana-lytic data, where possible, to within a specified tolerance. In the stitching step, GAMBIT attempts to connect edges and vertices within an iterated tolerance value. In the geometry building step, GAMBIT modifies surface and edge geometry to bring it within a specified tolerance (if possible).

GAMBIT allows you to control the geometry simplification and stitching steps by means of the Geometry simplification and Stitch faces options, respectively, on the Heal Real Faces form.

Geometry simplification Option

The Geometry simplification option allows you to specify whether or not GAMBIT employs geometry simplification when healing faces. If you select the Geometry simplification option, you can also specify a Tolerance value. The Tolerance value is used to determine whether or not NURBS surfaces can be approximated by analytic surfaces. If the Geometry simplification Tolerance is too loose, approximate analytic fits to NURBS geometry may be obtained. In such cases, the gaps between surfaces may increase, and healing in subsequent steps may be more difficult or may fail.

Stitch faces Option

The Stitch faces option allows you to specify whether or not GAMBIT stitches faces during the healing operation. If you select the Stitch faces option, you can also specify Minimum tolerance and Maximum tolerance values. The Minimum tolerance and Maximum tolerance values specify the range in which GAMBIT performs stitching between edges. GAMBIT begins stitching at the Minimum tolerance value and increases in steps toward the Maximum tolerance value.

At each step, GAMBIT stitches only those edges the lengths of which are greater than the current tolerance value. Consequently, the Minimum tolerance must be smaller than the length of the shortest edge in the model. The Maximum tolerance value represents the maximum gap size for which GAMBIT performs stitching.



Repairing Gaps Between Faces

One of the primary purposes of the Heal Real Faces command is to repair gaps between adjacent faces. If you perform the Heal Real Faces operation on a set of unconnected faces the bounding edges of which are located near to each other (see Figure 2-81(a)), GAMBIT stitches the faces together, connecting their adjacent boundary edges (see Figure 2-81(b)).

(a) Three unconnected faces (b) Connected faces

Figure 2-81: Heal Real Faces operation on faces with boundary edge gaps

If the set of connected faces resulting from the Heal Real Faces operation rep-resents a closed three-dimensional region, GAMBIT creates a volume bounded by the set of faces (see Figure 2-82).



(a) Six unconnected faces (b) Created volume

Figure 2-82: Heal Real Faces operation—volume creation

Using the Heal Real Faces Form

To open the Heal Real Faces form (see below), click the Heal command button on the Geometry/Face subpad.

The Heal Real Faces form includes the following specifications.



Faces ¬ specifies the faces for which GAMBIT attempts the heal opera-tion.

All q Pick

• All specifies all faces in the model.

• Pick specifies faces selected by means of the Faces list box. (NOTE: If you pick a face in the graphics window or click in the Faces list box, GAMBIT automatically selects the Pick option.)

R Geometry simplification

attempts to simplify geometry during the healing operation.

Tolerance specifies the tolerance value for simplification.

R Stitch faces attempts to stitch faces during the healing operation.

Minimum tolerance

specifies the minimum tolerance value for the stitching operation.

Maximum tolerance

specifies the maximum tolerance value for the stitching operation.



Convert Faces

The Convert Faces command converts one or more non-real (faceted and/or virtual) faces to real faces. The conversion process preserves both the topo-logy and any existing mesh(es) associated with the converted face(s). In addition, all non-real edges and vertices associated with the face(s) are converted to real edges and vertices.

u NOTE (1): Only non-real faces that include a mapped mesh can be converted to real faces.

u NOTE (2): Hidden entities that serve as hosts for virtual entities may become active (that is, visible) when their guest entities are converted to real geo-metry.

Using the Convert Faces Form

To open the Convert Faces form (see below), click the Convert Faces com-mand button on the Geometry/Face subpad.

The Convert Faces form includes the following specifications.

Faces ¬ specifies which non-real faces are to be converted to real faces.

All q Pick





2.4.9 Summarize/Check/Query Faces and Total Entities

The Summarize/Check/Query Faces and Total Entities command button allows you to perform two operations.


Summarize Faces Displays face summary information in the Transcript window

Check Faces Checks the topological and geometric validity of model faces

Query Faces Opens the face query list





Summarize Faces

The Summarize Faces command displays face summary information in the Transcript window.

Using the Summarize Faces Form

To open the Summarize Faces form (see below), click the Summarize com-mand button on the Geometry/Face subpad.

The Summarize Faces form includes the following specifications.

Faces ¬ specifies one or more faces for which information is to be summarized in the Transcript window.

All q Pick





Check Faces

The Check Faces command assesses the topological and/or geometric validity of faces in the model and summarizes the results in the Transcript window.

When you execute the Check Faces command, GAMBIT checks the model to determine its validity with respect to either or both of the following types of characteristics:

• Topology

• Geometry


Topology Check


For a given face, the Check Faces topology check operation examines the model to ensure that it meets the following criteria:

• Lower-topology edges are in separate loops.

• Lower-topology edges are visible and correctly reference the face.

• Sense information (in the form of co-edges) exists for all edges.

• Upper-topology volumes correctly reference the face.

• Upper-topology volumes maintain correct sense information for the face (in the form of co-faces).

• Virtual guest entities correctly reference the face as a host.

u NOTE: Failure of the topology check for any face in the model constitutes a serious problem for the model as a whole. GAMBIT does not currently include any tools that allow you to repair problems that cause failures of topology checks.



Geometry Check

Geometrical validity is an assessment of the model with respect to proximity and shape characteristics—such as the distances between connected edges and/or the mathematical continuity of model curves and surfaces. The Check Faces geometry check criteria are as follows:

• All real faces correctly reference the ACIS model.

• No real faces exhibit problems related to continuity, self-intersection, bad closure, degeneracies, or singularities.

• Any virtual-face hosts are of the correct type. For example, a virtual face formed by connecting or merging two faces must reference only the two faces as hosts. Similarly, a virtual face defined on a volume must not be hosted by a face, and a virtual face formed by splitting a face must be hosted by the face that is split. (NOTE: The face geome-try check operation also checks the validity of host geometry.)

u NOTE: Face-check errors may not represent a serious problem for certain geometry or meshing operations. For example, a face may be meshable even if other operations—such as Boolean operations—fail.

It is sometimes possible to repair geometry errors for faces by means of face- or volume-healing operations (see Sections 2.4.8 and 2.5.8, respectively). Healing processes operate on a set of faces (which may belong to a volume) by modifying geometry near edge and vertex boundaries so that the geometry is within tolerance. Healing operations do not modify regions distant from edge or vertex boundaries. When edges or vertices of different faces are located near to each other, healing operations attempt to modify the geometry in order to connect these edges or vertices.



Using the Check Faces Form

To open the Check Faces form (see below), click the Check command button on the Geometry/Face subpad.

The Check Faces form includes the following specifications.

Faces ¬ specifies the faces to be included in the checking operations.

All q Pick



R Check Topology specifies a topology check on the selected faces.

R Check Geometry specifies a geometry check on the selected faces.



Query Faces

The Query Faces command allows you to identify the locations and/or the names of specific faces.

Using the Query Faces Form

To open the Query Faces form (see below), click the Query command button on the Geometry/Face subpad.

For a general description of using the Query Faces form, see “Using the Query Vertices Form“ in Section 2.2.7, above.



Total Entities






2.4.10 Delete Faces

The Delete Faces command deletes one or more faces from the model.

The Delete Faces operation is subject to the following restrictions:

• GAMBIT does not allow you to delete faces that constitute parts of a volume.

• If you delete a virtual face that constitutes the connection of two or more real or virtual faces, GAMBIT restores those faces to the model when it deletes the specified face.

Retaining Face Edges

By default, when you delete a face, GAMBIT deletes the edges that constitute parts of the face as well as their endpoint vertices. To retain the edges and ver-tices when the face is deleted, unselect the Lower Geometry option at the bot-tom of the Delete Faces form. When you delete a face and retain its edges, the edges remained connected to each other by means of their common endpoint vertices.

Retaining and Deleting Associated Vertices

When you delete a face with associated vertices created by means of the Create Vertex On Face command, GAMBIT retains or deletes the vertices depending on whether they are real or virtual entities, respectively. For example, if you delete a face that is associated with one real vertex and one virtual vertex—both of which were created by means of the Create Vertex On Face command—GAMBIT retains the real vertex and deletes the virtual vertex. (The virtual vertex cannot exist without the host face.)

Deleting Virtual Faces

If you delete a virtual face, GAMBIT deletes all lower topology and virtual hierarchy that is associated with the face and is not associated with any other entities in the model.



Using the Delete Faces Form

To open the Delete Faces form (see below), click the Delete command button on the Geometry/Face subpad.

The Delete Faces form includes the following specifications.

Faces ¬ specifies one or more faces to be deleted.

All q Pick



R Lower Geometry

specifies that all edges and vertices that constitute parts of the faces are deleted.

Volume Commands CREATING THE GEOMETRY


2.5 Volume Commands

The following commands are available on the Geometry/Volume subpad.


Form Volume Creates a volume from existing faces or edges

Create Volume Creates a volume in one of several primitive shapes

Boolean Operations Unites, intersects, or subtracts volumes

Blend Volumes Rounds and/or trims volume edges

Modify Volume Color Modify Volume Label

Changes a volume color: changes a volume label

Move/Copy Volumes Align Volumes

Moves and/or copies volumes; aligns volumes and connected geometry

Split Volume Merge Volumes

Splits or merges volumes

Heal Real Volume Convert Volumes

Heals real volume geometry; converts non-real volumes to real volumes

Summarize Volumes Check Volumes Query Volumes Total Entities

Displays volume summary informa-tion; checks validity of topology and geometry; opens a volume query list; displays entity totals

CREATING THE GEOMETRY Volume Commands



Delete Volumes Deletes real or virtual volumes



2.5.1 Form Volume

The Form Volume command button allows you to perform the following operations.


Stitch Faces Creates a volume from a set of exist-ing faces

Sweep Real Faces Creates a volume by sweeping a face along a specified path

Revolve Real Faces Creates a volume by revolving a face through a specified angle

Form Real Volume From Wireframe

Creates a volume from a set of exist-ing edges




Stitch Faces

The Stitch Faces command allows you to form a volume from a set of existing faces.

To form a volume by means of the Stitch Faces command, you must specify the following information:

• A set of faces that comprise the sides of the volume

• The volume type

Specifying the Faces

To stitch faces to form a volume, you must specify a set of faces that constitute the sides of the volume. The faces do not have to be planar but must possess coincident edges such that the set defines a completely closed volume.

Specifying the Volume Type

GAMBIT allows you to form a real or virtual volume by means of the Stitch Faces command. To form a real volume, you must specify only real faces. To form a virtual volume, you can specify real and/or virtual faces.

If you specify the creation of a virtual volume, you can also specify a Tolerance value. The Tolerance value allows you to form a volume from a set of faces the edges of which are not exactly coincident with each other.



Using the Stitch Faces Form

To open the Stitch Faces form (see below), click the Stitch Faces command button on the Geometry/Volume subpad.

The Stitch Faces form includes the following specifications.

Faces ¬ specifies the faces to be used in forming the volume.

Type: —————————————————————————

l Real specifies the creation of a real volume.

l Virtual specifies the creation of a virtual volume.

Tolerance specifies the maximum allowable distance between “coinci-dent” boundary edges for the set of specified faces.

Label specifies a label for the new volume. (See Section 2.1.1.)



Sweep Real Faces

The Sweep Real Faces command allows you to form volumes by sweeping real faces along a specified path.

To create a volume by means of the Sweep Real Faces command, you must specify the following parameters.

• Profile

• Path

• Type

The profile consists of a set of one or more faces to be swept. The path represents the trajectory of the sweep operation. The type defines the shape and orientation of the created volume relative to those of the profile and path.

Specifying the Sweep Profile

The sweep profile consists of a set of one or more existing faces. GAMBIT creates a separate volume corresponding to each face in the profile. Each type of sweep operation possesses its own set of rules that govern whether or not a face constitutes a valid profile component. In general, however, GAMBIT does not allow you to specify profile faces that are parallel to the sweep path.

Specifying the Sweep Path

You can define the sweep path by means of either of the following specifications.

• Edge

• Vector

When you describe the sweep path by specifying an edge, GAMBIT defines the path according to the shape, length, and sense, respectively, of the speci-fied edge. You can reverse the direction of the sweep path relative to the sense of the specified edge by means of the Reverse option on the Sweep Real Faces form.

When you define the sweep path by specifying a vector, GAMBIT defines the path as a straight line possessing the magnitude and direction specified for the vector. You must define the vector by means of the Vector Definition form (see “Using the Vector Definition Form“ in Section 2.1.4).



Specifying the Sweep Type

GAMBIT provides two general types of sweep operations:

• Rigid

• Perpendicular

When you specify a rigid sweep, GAMBIT sweeps the profile along the entire length of the specified path without altering the profile orientation with respect to the global coordinate system. When you specify a perpendicular sweep, GAMBIT maintains a constant angle between the face and the sweep path along the entire length of the path.

Performing a Rigid Sweep

When you specify a rigid sweep operation, GAMBIT projects the profile along the entire length of the specified path without altering the size, shape, or orientation of the profile. The shape and orientation of any volume created by means of a rigid sweep operation depends on two factors:

• The shape of the profile face and its orientation relative to the path

• The shape and direction of the path

Specifying the Profile

The edges that bound the profile face(s) can be straight or curved, and the profile face does not have to be planar. However, GAMBIT imposes the following restrictions on profiles and paths employed in face-sweep opera-tions:

• None of the edges that bound the profile face can be parallel to the path

• The face normal cannot be perpendicular to the path

Figure 2-83 shows three path/profile configurations, only one of which constitutes a valid configuration for a face-sweep operation. (NOTE: The cubic volumes shown in Figure 2-83 are included for positional reference only.)



(a) Invalid (b) Invalid

(c) Valid

A

B

A

B

CD

Figure 2-83: Allowed face configurations for sweeping a face

The validities of the configurations shown in the figure are as follows.

• The configuration shown in Figure 2-83(a) is not valid, because edge AB is parallel to the path.

• The configuration shown in Figure 2-83(b) is not valid, because the normal to the face (ABC) is perpendicular to the path at its starting point (D).

• The combination shown in Figure 2-83(c) is valid, because none of its bounding edges is parallel to the path.

Specifying the Path

The sweep path can be defined by means of either an edge or a vector. If you specify an edge to define the path, the path can be straight or curved—depending on the shape of the edge. If you specify a vector to define the path, the path is straight by definition.



Example Face-Sweep Operations

Figure 2-84 and Figure 2-85 illustrate the results of the rigid face-sweep operation for two simple path/profile configurations. In each case, the profile face is planar and is bounded by three edges. The sweep paths shown in Figure 2-84 and Figure 2-85 are defined by a straight edge and a circular arc edge, respectively.

(a) Path and profile (b) Created volume

Path

Profile

Figure 2-84: Example rigid face sweep operation—straight path




Path

Profile

Figure 2-85: Example rigid face sweep operation—curved path

Performing a Perpendicular Sweep

Overview

Perpendicular sweep operations differ from rigid sweep operations in that, for perpendicular sweeps, the initial orientation between the profile and path is maintained along the entire length of the sweep path. Rigid sweeps, by contrast, maintain the orientation of the profile with respect to the global coordinate system along the sweep path.

As an example of the difference between rigid and perpendicular sweep operations, consider the profile and path shown in Figure 2-86(a). In this case, the profile consists of a planar square face aligned with the y-z coordinate plane, and the path is defined by a circular arc edge aligned with the x-y plane.



(a) Path and profile

(b) Rigid sweep

(c) Perpendicular sweep

PathProfile

Figure 2-86: Example Rigid and Perpendicular sweep operations—curved path

The differences between the created faces can be summarized as follows.

• If you perform a rigid sweep, GAMBIT maintains the orientation of the profile with respect to the global coordinate system, thereby creating the volume shown in Figure 2-86(b).

• If you perform a perpendicular sweep with a zero draft angle (see below), GAMBIT maintains the orientation between the path and profile and creates the volume shown in Figure 2-86(c).

Perpendicular Sweep Methods

GAMBIT provides two options for perpendicular face-sweep operations:

• Draft

• Twist

The Draft option specifies a fixed angle of deviation between the path and the face projection for the created volume. The Twist option allows you to revolve the profile through a specified angle along the length of the path.



u NOTE: In order to constitute a valid configuration for either a Draft or Twist operation, the profile and path must meet the following conditions:

• The profile must be planar

• The face normal cannot be perpendicular to the path

Draft Option

When you create a volume by means of the draft method, GAMBIT allows you to expand or contract the projected face by a specified angle along the path. Figure 2-87 shows a perpendicular draft sweep involving a profile and path identical to those shown in Figure 2-86(a). In this case the draft angle is specified as +10º, therefore the profile expands as it is swept along the profile curve.


Draft Angle = 10º

PathProfile

Figure 2-87: Perpendicular face sweep—draft option, 10º draft angle

The Effect of Draft Angle

As noted above, when you perform a perpendicular face sweep operation by means of the draft method, GAMBIT allows you to specify a draft angle for the created volume. The draft angle represents the extent to which the swept edges of the volume are expanded or contracted relative to those of the original profile.



Figure 2-88 shows the effect of draft angle on the shape of a volume created by sweeping a square profile along a straight path that is perpendicular to the face. In this case, the profile face is a square, planar face aligned with the y-z plane, the path is defined by a straight edge aligned with the x axis, and the draft angle is specified as 10º.

If you specify a positive draft angle, the profile expands along the length of the path (see Figure 2-88(c)). If you specify a negative draft angle, the profile contracts along the length of the path (see Figure 2-88(d)).

(a) Profile and path (b) Draft Angle = 0º

(c) Draft Angle = +10º (d) Draft Angle = -10º

Path

Profile

Figure 2-88: Perpendicular draft face sweep—effect of draft angle

The Effect of Draft Type

When you sweep a face by means of the perpendicular draft method and expand the profile by means of a positive draft angle, GAMBIT allows you to specify the following options for the expanded profile type:

• Extended

• Round

• Mixed



Figure 2-89 shows the effect of draft type on the shape of a volume created from a profile and path identical to those shown in Figure 2-88(a). The Extended option expands the profile with altering its basic shape (see Figure 2-89(a)). The Round option rounds the corners of the expanded profile as shown in Figure 2-89(b). The Mixed option combines elements of the Extended and Round options, as necessary, to fill gaps in the expanded profile.

(a) Extended draft option (b) Round draft option

Figure 2-89: Perpendicular face sweep, draft method—effect of draft type

Twist Method

When you perform a perpendicular sweep operation by means of the twist method, GAMBIT revolves the profile through a specified angle along the length of the path. The profile and path can be straight or curved.

As an example of the effects of the twist sweep procedure, consider the profile/path configurations shown in Figure 2-90. In each case, the profile consists of a square planar face aligned with the y-z plane. The paths shown in Figure 2-90(a) and (b) are defined by straight and circular arc edges, respectively.



u NOTE: When you employ a twist sweep procedure, GAMBIT twists the profile face about the specified path—rather than projecting the path start location onto the face surface geometry. Consequently, the results of the twist face-sweep operation depend, in part, on the orientation and distance between the profile and path.

(a) Profile and straight path (b) Profile and curved path

Figure 2-90: Twist-method face sweep—example profiles and paths

Figure 2-91 and Figure 2-92 show the results of a perpendicular twist face-sweep procedure applied to the profiles and paths shown in Figure 2-90(a) and (b), respectively. Figure 2-91 shows results for draft-angle values of +90º and +360º. Figure 2-92 shows results for draft-angle values of +90º and +180º.



(a) Twist Angle = +90º (b) Twist Angle = +360º

Figure 2-91: Twist-method face sweep—straight path results

(a) Twist Angle = +90º (b) Twist Angle = +180º

Figure 2-92: Twist-method face sweep—curved path results



Using the Sweep Real Faces Form

To open the Sweep Real Faces form (see below), click the Sweep Real Faces command button on the Geometry/Volume subpad.

The Sweep Real Faces form includes the following specifications.

Faces ¬ specifies one or more faces that constitute the sweep profile.

Path: —————————————————————————

l Edge specifies that the path is described by the length, orienta-tion, and sense of an existing edge.

Edge ¬ specifies the edge to be used as the sweep path.

R Reverse specifies that the direction of the path is reversed with respect to the sense of the specified edge.



l Vector specifies that the path is described by a vector.

When you select the Vector option, GAMBIT displays a command button titled Define Vector. When you click the Define Vector command button, GAMBIT opens the Vector Definition form, which allows you to specify parameters that define the path vector. For instructions on using the Vector Definition form, see “Using the Vector Definition Form“ in Section 2.1.4.

Type: —————————————————————————

l Rigid specifies a rigid sweep operation.

l Perpendicular specifies a perpendicular sweep operation.

Option: ——————————————————————

l Draft specifies the perpendicular draft method.

l Twist specifies the perpendicular twist method.

Angle specifies the draft or twist angle.

Type: —————————————————————

l Extended specifies that an expanded profile projection reflects the basic shape of the profile.

l Round specifies that an expanded profile projection is to contain rounded edges.

l Mixed employs elements of the Extended and Round options to fill gaps in the expanded profile.




Revolve Real Faces

The Revolve Real Faces command allows you to form a volume by revolving a face through a specified angle

To create a volume by means of the Revolve Real Faces option, you must specify the following parameters:

• One or more faces to be revolved

• The axis of rotation

• The angle through which the face is revolved about the axis

• Draft angle and type

The rotational axis does not have to be coincident with one of the edges of the face to be swept, but it must lie in the same plane as the profile face (see Figure 2-93).

Axis ofrevolution

Profile

Angle of revolution

θ > 0Created volume

Figure 2-93: Face revolve parameters



Specifying Faces to Be Revolved

To create a volume by means of the Revolve Real Faces form, you must spec-ify one or more faces to be revolved about the axis of rotation. Each specified face can include any combination of straight and curved edges as long as all the edges comprising the face lie in a single plane.

Specifying the Axis of Rotation

In order to constitute a valid axis of rotation for the face-revolve operation, the axis must lie in the plane of the face. To specify the axis of rotation, you must define the axis by means of the Vector Definition form. For a description of the Vector Definition form and its operation, see “Using the Vector Definition Form“ in Section 2.1.4. The conventions regarding the angle of rotation for the Revolve Real Faces operation are identical to those described in “Rotating an Entity“ in Section 2.1.4.

Specifying the Angle of Rotation

The angle of rotation is defined according to the right-hand rule relative to the direction of the axis vector. That is, when the rotational axis is oriented such that its vector points away from the observer, angles swept in the clockwise direction are defined as positive (see Figure 2-93, above).

Specifying Draft Angle and Type

When you create a volume by revolving a face, GAMBIT allows you to spec-ify a draft angle and type to be applied in conjunction with the revolution of the face. The draft angle represents the extent to which the profile is expanded or contracted as the face is revolved. The draft type determines whether or not the edges of an expanded profile are rounded in the process of creating the volume.

Figure 2-94 shows two volumes created by revolving a rectangular face and specifying a positive draft angle—that is, an expansion of the profile. In Figure 2-94(a), the draft type is extended, therefore the basic shape of the face does not change as it is revolved. In Figure 2-94(b), the draft type is round, therefore the corners of the revolved face are rounded with respect to the original profile.



Axis of revolution Axis of revolution

Profile Profile

(a) Extended (b) Round

Figure 2-94: Revolving faces—effect of draft angle and type



Using the Revolve Real Faces Form

To open the Revolve Real Faces form (see below), click the Revolve Real Faces command button on the Geometry/Volume subpad.

The Revolve Real Faces form includes the following specifications.

Faces ¬ specifies one or more faces to be revolved.

Angle specifies the angle through which the face is to be revolved.

Deg q Rad

specifies the units for the angle of revolution as either degrees (Deg) or radians (Rad).

Axis: contains two components:


• The coordinates of the start and end points for a vector defining the rotational axis



Draft: —————————————————————————

l Extended specifies expanding or contracting the profile face as it is revolved according to the specified draft angle.

l Round specifies that the corners of an expanded profile are rounded.

Angle specifies the draft angle.




Form Real Volume From Wireframe

The Form Real Volume From Wireframe command allows you to form a volume from a set of existing edges.

To create a volume by means of the Form Real Volume From Wireframe option, you must specify a set of edges that define the volume. The edge specifi-cations are subject to the following restrictions:

• The set of edges must describe an entire closed volume

• All specified edges must possess at least one endpoint vertex that is coincident with that of one other edge in the set

• All edge loops must be joined to the overall set of loops

GAMBIT does not require that edges specified for the wireframe are con-nected at their endpoints. During the creation process, GAMBIT deletes coin-cident vertices, thereby connecting the edges used to form the volume.

Figure 2-95 shows four different sets of edges, only one of which constitutes a valid wireframe for the creation of a volume by means of the Form Real Volume From Wireframe form. Each set represents a slight variation on a set of edges that constitutes the wireframe of a cube. The sets shown in Figure 2-95 are allowed or not allowed for the following reasons:

a) Allowed—All of the edges possess at least one endpoint vertex that is coincident with that of at least one other edge; there are no edges that are wholly internal to the cube

b) Not allowed—The circular edges of the cylindrical region cannot be joined to any part of the edges that comprise the cube

c) Not allowed—There are four edges in the set that cannot be joined in to the edges of the cube

d) Not allowed—The edges of the pyramidal region exist entirely within the volume represented by the edges of the cube



(a) Allowed (b) Not allowed

(d) Not allowed(c) Not allowed

Figure 2-95: Allowable wireframe configurations

If GAMBIT cannot resolve the specified set of edges into a valid volume, it completes as much as the creation process as is possible—including the crea-tion of faces—and displays a warning in the Transcript window.



Using the Form Real Volume From Wireframe Form

To open the Form Real Volume From Wireframe form (see below), click the Form Real Volume From Wireframe command button on the Geometry/ Volume subpad.

The Form Real Volume From Wireframe form includes the following specifica-tions.

Edges ¬ specifies the edges to be used in forming the volume.




2.5.2 Create Volume

The Create Volume command button allows you to perform the following operations.


Create Real Brick Creates a volume in the shape of a rectangular brick

Create Real Cylinder Creates a volume in the shape of a cylinder

Create Real Prism Creates a volume in the shape of a regular prism

Create Real Pyramid Creates a volume in the shape of a truncated pyramid

Create Real Frustum Creates a volume in the shape of a frustum

Create Real Sphere Creates a volume in the shape of a sphere

Create Real Torus Creates a volume in the shape of a torus



Create Real Brick

The Create Real Brick command allows you to create a volume in the shape of a rectangular brick.

To create a volume by means of the Create Real Brick command, you must specify the following parameters:

• The dimensions of the brick


• The position of the brick relative to the origin of the reference coordi-nate system

Specifying the Dimensions

When you create a rectangular brick volume by means of the Create Real Brick option, GAMBIT applies the width, depth, and height specifications to the x, y, and z directions, respectively. To define the locations of the brick edges relative the origin of the reference coordinate system, you must specify the position of the brick (see below).

Specifying the Position of the Brick

To orient the brick relative to the reference coordinate system, you must spec-ify the directions in which to apply the dimensions of the edges—that is, whether GAMBIT applies the width, depth, and height dimension parameters in the positive or negative direction with respect to each of the coordinate axes. The nine allowable direction options are as follows:

• +X +Y +Z

• +X +Y -Z

• +X -Y +Z

• +X -Y -Z

• -X +Y +Z

• -X +Y -Z

• -X -Y +Z

• -X -Y -Z

• Centered



Figure 2-96 shows the effect of four different direction options on the position of a cube created by means of the Create Real Brick form.

(a) +X +Y +Z (b) +X -Y +Z

(d) Centered(c) -X +Y +Z

Figure 2-96: Effect of direction option on brick position



Using the Create Real Brick Form

To open the Create Real Brick form (see below), click the Create Real Brick command button on the Geometry/Volume subpad.

The Create Real Brick form includes the following specifications.

Width (X) specifies the dimension of the brick in the x direction.

Depth (Y) specifies the dimension of the brick in the y direction.

Height (Z) specifies the dimension of the brick in the z direction.

Coordinate ¬ Sys.

specifies the reference coordinate system.

Direction —————————————————————————

+X+Y+Z q +X+Y -Z +X -Y +Z +X -Y -Z -X +Y +Z -X +Y -Z -X -Y +Z -X -Y -Z Centered

specifies the direction of each brick dimension relative to the reference coordinate system. The X, Y, and Z directions correspond to the brick Width, Depth, and Height parame-ters, respectively. The centered option specifies that the center of the brick coincides with the origin of the reference coordinate system.




Create Real Cylinder

The Create Real Cylinder command allows you to create a circular or elliptical cylinder possessing a constant cross-sectional area.

To create a volume by means of the Create Real Cylinder command, you must specify the following parameters:

• The height of the cylinder

• The radii that define the cylinder cross section


• The axis location

Specifying the Cylinder Height

The height of the cylinder represents length of the cylinder along its axis. By default, the cylinder axis coincides with the z axis of the reference coordinate system. To change the orientation of the cylinder, you must specify the axis location (see below).

Specifying the Cylinder Radii

To define the cross section of the cylinder, you must specify its major and minor axes. To do so, you must specify two radii—Radius 1 and Radius 2—each of which is aligned with a coordinate axis. Either radius can constitute the major axis of the cylinder cross section. If you do not specify Radius 2, GAMBIT creates a circular cylinder of radius Radius 1.

By default, Radius 1 is aligned with the x axis, and Radius 2 is aligned with the y axis. If you change the orientation of the cylinder by specifying the axis location (see below), the axes corresponding to Radius 1 and Radius 2 change as well. The following table summarizes the relationship between axis loca-tion, Radius 1, and Radius 2.

Axis Location Radius 1 Axis Radius 2 Axis

z x y

y z x

x y z



Specifying the Axis Location

To locate and orient the cylinder, you must specify its axis location relative to the reference coordinate system. The axis location specification includes a coordinate axis and a direction. There are nine possible options for the axis location, each of which represents a different combination of three directions (Positive, Centered, and Negative) and three coordinate axes (X, Y, and Z). The default axis location is Positive Z.

Figure 2-97 shows the effects of four different axis locations on the position of an elliptical cylinder created by means of the Create Real Cylinder form. In this example, the cylinder Height, Radius 1, and Radius 2 specifications are 7, 3, and 2, respectively.

(a) Positive Z (b) Centered Z

(d) Centered X(c) Negative Y

Figure 2-97: Effect of axis location on cylinder position and orientation



Using the Create Real Cylinder Form

To open the Create Real Cylinder form (see below), click the Create Real Cylin-der command button on the Geometry/Volume subpad.

The Create Real Cylinder form includes the following specifications.

Height specifies the length of the cylinder in the direction of its speci-fied axis.

Radius 1 specifies one of two radii defining the cross section of the cylinder.

Radius 2 specifies the other of two radii defining the cross section of the cylinder.

Coordinate ¬ Sys.




Axis Location —————————————————————————

Positive Z q Centered Z Negative Z Positive X Centered X Negative X Positive Y Centered Y Negative Y

specifies the cylinder axis and the direction in which the cylinder is created relative to the axis. There are three pos-sible options for each axis:

• Positive—applies the Height dimension in the posi-tive axis direction relative to the origin of the refer-ence coordinate system

• Centered—centers the cylinder at the origin of the reference coordinate system

• Negative—applies the Height dimension in the nega-tive axis direction relative to the origin of the refer-ence coordinate system




Create Real Prism

The Create Real Prism command allows you to create a regular prism possess-ing a constant cross-sectional area. Each side of the prism is parallel to the prism axis.

To create a volume by means of the Create Real Prism command, you must specify the following parameters:

• The height of the prism

• The number of sides of the prism

• Two radii that define an ellipse that circumscribes the prism cross section



Specifying the Prism Height

The height of the prism represents length of the prism along its axis—that is, perpendicular to its cross section. By default, the prism axis coincides with the z axis of the reference coordinate system. To change the orientation of the prism, you must specify the axis location (see below).

Specifying the Number of Prism Sides

To create a prism, you must specify the number of its sides (n � 3). GAMBIT constructs the prism such that each side is parallel to the prism axis.

The positions of the prism sides depend, in part, on whether you specify an odd number or even number of sides. If you specify an odd number of sides, GAMBIT constructs the prism such that one of its corner vertices lies within a coordinate plane of the reference coordinate system. If you specify an even number of vertices, GAMBIT constructs the prism such that one of its sides is parallel to a coordinate plane of the reference system.

Figure 2-98 shows the cross sections (in the x-y plane) of four prisms, each of which is circumscribed by a circular cylinder. In Figure 2-98(a), each prism possesses an odd number of sides. In Figure 2-98(b), each prism possesses an even number of sides. Note the following characteristics:

• The uppermost vertices of the triangle and pentagon in Figure 2-98(a) are coincident and lie in the y-z plane

• The uppermost sides of the square and hexagon in Figure 2-98(b) are parallel to the x-z plane.



n = 3

x

y

n = 4

(a) (b)

n = 5 n = 6

Figure 2-98: Effect of the number of prism sides

Specifying the Prism Radii

To define the dimensions of the prism, you must specify the major and minor axes of an ellipse by which its cross section is circumscribed. To do so, you must specify two radii—Radius 1 and Radius 2—each of which is aligned with a coordinate axis. Either radius can constitute the major axis of the ellipse. If you do not specify Radius 2, GAMBIT circumscribes the prism by a circular cylinder of radius Radius 1.

By default, Radius 1 is aligned with the x axis, and Radius 2 is aligned with the y axis. If you change the orientation of the cylinder by specifying the axis location (see below), the axes corresponding to Radius 1 and Radius 2 change, as well. The following table summarizes the relationship between axis loca-tion, Radius 1, and Radius 2 with respect to the corresponding coordinate axes.

Axis Location Radius 1 Axis Radius 2 Axis

z x y

y z x

x y z



The Effect of Radii Specifications

If you specify values for Radius 1 and Radius 2 that are identical to each other (or do not specify a value for Radius 2) GAMBIT creates a prism the cross section of which is circumscribed by a circle (see Figure 2-98, above). If you specify values for Radius 1 and Radius 2 that differ from each other, GAMBIT creates a prism the cross section of which is circumscribed by an ellipse.

The procedure by which GAMBIT creates a prism circumscribed by an ellipse can be thought of as a two-step process:

1. Construct a prism circumscribed by a circular cylinder the radius of which is equal to the minor axis of the ellipse

2. Reposition the corner vertices of the cross section along lines parallel to the major axis of the ellipse

Figure 2-99 shows the effect of specifying an elliptical boundary on the cross section of a five-sided prism oriented with an axis location in the Positive Z direction. In Figure 2-99(a), Radius 1 constitutes the major axis of the ellipse, therefore GAMBIT locates the corner vertices of the cross section along lines parallel to its corresponding axis—that is, the x axis. In Figure 2-99(b), Radius 2 constitutes the major axis; therefore, GAMBIT locates the corner vertices along lines parallel to the y axis.

x

y

(a) Radius 1 > Radius 2

Circularcross section

Elliptical cross section

(b) Radius 1 < Radius 2

Figure 2-99: Effect of radii on prism cross section



Specifying the Axis Location

To locate the prism in the model domain, you must specify its axis location relative to the reference coordinate system. The axis location specification includes a coordinate axis and a direction. For a description of the axis loca-tion specification, see “Create Real Cylinder,” above.

Using the Create Real Prism Form

To open the Create Real Prism form (see below), click the Create Real Prism command button on the Geometry/Volume subpad.

The Create Real Prism form includes the following specifications.

Height specifies the height of the prism.

Sides specifies the number of sides (n � 3) of the prism.

Radius 1 specifies one of two radii that describe the ellipse that circum-scribes the prism.

Radius 2 specifies the other of two radii that describe the ellipse that cir-cumscribes the prism.

Coordinate ¬ Sys.




Axis Location —————————————————————————


specifies the axis of the prism and the direction in which the prism is created relative to the axis. There are three possible options for each axis:


• Centered—centers the prism at the origin of the ref-erence coordinate system





Create Real Pyramid

The Create Real Pyramid command allows you to create a volume in the shape of a pyramid—that is, a prism possessing a non-constant cross-sectional area.

To create a volume by means of the Create Real Pyramid command, you must specify the following parameters:

• The height of the pyramid

• The number of sides of the pyramid

• Two radii that define an ellipse that circumscribes the cross section at the base of the pyramid

• One radius that defines the size of the top of the pyramid relative to its base



Specifying the General Pyramid Parameters

Four of the seven parameters required to specify a pyramid are identical to those required to specify a prism. The identical parameters are as follows:

• Height

• Number of sides

• Reference coordinate system

• Axis location

For a description of how to specify these parameters, see “Create Real Prism,” above.



Specifying the Pyramid Radii

When you create a pyramid by means of the Create Real Pyramid form, GAMBIT constructs a volume in the shape of a prism the base and top of which differ only in size. To define size and shape of the base and top, you must specify three radii—Radius 1, Radius 2, and Radius 3.

Radius 1 and Radius 2 constitute the axes of an ellipse that circumscribes the base of the pyramid. They are specified according to the same procedure used to specify the radii of a prism (see “Create Real Prism,” above). Radius 3 specifies the size of the top of the pyramid relative to Radius 1.

Figure 2-100 shows a three-sided prism with an elliptical base defined by Radius 1 (minor axis) and Radius 2 (major axis). The top of the pyramid is identical in shape to the pyramid base, but the sizes of its edges differ from those of the base by the ratio Radius 3:Radius 1.

x

zy

Radius 3

Radius 1

Radius 2

Figure 2-100: Pyramid radii specifications



Using the Create Real Pyramid Form

To open the Create Real Pyramid form (see below), click the Create Real Pyra-mid command button on the Geometry/Volume subpad.

The Create Real Pyramid form includes the following specifications.

Height specifies the height of the pyramid.

Sides specifies the number of sides (n � 3) of the pyramid.

Radius 1 specifies one of two radii that define the major and minor axes of the ellipse that circumscribes the pyramid base.

Radius 2 specifies the other radius of the ellipse that circumscribes the pyramid base.

Radius 3 specifies the radius that defines the size of the top of the pyra-mid relative to the size of its base. (NOTE: The defining ratio is Radius 3: Radius 1.)

Coordinate ¬ Sys.




Axis Location —————————————————————————


specifies the axis of the pyramid and the direction in which the pyramid is created relative to the axis. There are three possible options for each axis:


• Centered—centers the pyramid at the origin of the reference coordinate system





Create Real Frustum

The Create Real Frustum command allows you to create a volume in the shape of a frustum—that is, a cylinder of non-constant cross-sectional area.

To create a volume by means of the Create Real Frustum command, you must specify the following parameters:

• The height of the frustum

• Two radii that define an ellipse that constitutes the base of the frustum

• One radius that defines the size of the top of the frustum relative to its base



Specifying the General Frustum Parameters

Three of the six parameters required to specify a frustum are identical to those required to specify a cylinder. The identical parameters include the following:

• Height

• Reference coordinate system

• Axis location

For a description of how to specify these parameters, see “Create Real Cylinder,” above.

Specifying the Frustum Radii

When you create a frustum by means of the Create Real Frustum form, GAMBIT constructs a cylindrical volume the base and top of which differ only in size. To define the size and shape of the base and top, you must spec-ify three radii—Radius 1, Radius 2, and Radius 3.

Radius 1 and Radius 2 are the axes of the ellipse that constitutes the base of the frustum. Radius 3 specifies the size of the top of the frustum relative to Radius 1.



Figure 2-101 shows a frustum with an elliptical base defined by Radius 1 (minor axis) and Radius 2 (major axis). The top of the frustum is identical in shape and orientation to the base, but the lengths of its axes differ from those of the base by the ratio of Radius 3:Radius 1.

x

zy

Radius 3

Radius 1

Radius 2

Figure 2-101: Frustum radii specifications



Using the Create Real Frustum Form

To open the Create Real Frustum form (see below), click the Create Real Frus-tum command button on the Geometry/Volume subpad.

The Create Real Frustum form includes the following specifications.

Height specifies the height of the frustum.

Radius 1 specifies one of two radii that define of the ellipse that consti-tutes the frustum base.

Radius 2 specifies the other radius of the ellipse that constitutes the frustum base.

Radius 3 specifies the radius that defines the size of the frustum top rela-tive to the size of its base. (NOTE: The defining ratio is Radius 3:Radius 1.)

Coordinate ¬ Sys.




Axis Location —————————————————————————


specifies the axis of the frustum and the direction in which the frustum is created relative to the axis. There are three possible options for each axis:


• Centered—centers the frustum at the origin of the reference coordinate system





Create Real Sphere

The Create Real Sphere command allows you to create a volume in the shape of a sphere.

To create a sphere by means of the Create Real Sphere form, you must specify the radius of the sphere and the coordinate system the origin of which consti-tutes the center of the sphere.

Using the Create Real Sphere Form

To open the Create Real Sphere form (see below), click the Create Real Sphere command button on the Geometry/Volume subpad.

The Create Real Sphere form includes the following specifications.

Radius specifies the radius of the sphere.

Coordinate ¬ Sys.

specifies the coordinate system the origin of which constitutes the center of the sphere.




Create Real Torus

The Create Real Torus command allows you to create a volume in the shape of a torus.

To create a torus by means of the Create Real Torus command, you must spec-ify the following parameters:

• The circumferential radius

• The radius of the torus tube


• The coordinate axis that constitutes the axis of the torus

Specifying the Radii of the Torus

To define the dimensions of a torus, you must specify two radii (see Figure 2-102). The circumferential radius (Radius 1) defines the size of the circle that constitutes the center of the torus tube. The tube radius (Radius 2) defines the size of the tube itself.

Axis Radius 1 (Circumference)Radius 2 (Tube)

Figure 2-102: Torus radius specifications



Specifying the Axis of the Torus

To orient the torus in the model domain, you must specify the coordinate axis that constitutes the central axis of the torus. The axis options include X axis, Y axis, and Z axis.

Using the Create Real Torus Form

To open the Create Real Torus form (see below), click the Create Real Torus command button on the Geometry/Volume subpad.

The Create Real Torus form includes the following specifications.

Radius 1 specifies the circumferential radius of the torus with respect to its center axis.

Radius 2 specifies the radius that defines the size of the torus tube.

Coordinate ¬ Sys.

specifies the coordinate system that constitutes the center of the torus.

Center Axis —————————————————————————

Z axis q X axis Y axis

specifies the coordinate axis that constitutes the torus center axis.




2.5.3 Boolean Operations

The Boolean Operations command button allows you to perform the following operations.


Unite Real Volumes Unites two or more real volumes into one real volume

Subtract Real Volumes Subtracts the intersecting region(s) between two or more volumes

Intersect Real Volumes Creates a volume representing the intersection between two or more volumes

Overview

Each of the commands listed above allows you to perform a Boolean operation involving two or more intersecting volumes. Figure 2-103 illustrates the results of each of the Boolean volume operations on an intersecting cube and sphere.



(a) Specified volumes (b) Unite

(d) Intersect(c) Subtract (volume.2 from volume.1)

volume.2volume.1

Figure 2-103: Boolean volume operations

Retaining the Specified Volumes

Each volume Boolean operation form includes at least one Retain option. When you perform a Boolean operation involving a set of specified volumes, GAMBIT replaces the specified volumes with a single volume that constitutes the result of the operation. If you select the Retain option, GAMBIT retains the original volumes when it performs the Boolean operation.



Unite Real Volumes

The Unite Real Volumes command allows you to unite two or more intersect-ing volumes into a single volume.

Using the Unite Real Volumes Form

To open the Unite Real Volumes form (see below), click the Unite command button on the Geometry/Volume subpad.

The Unite Real Volumes form includes the following specifications.

Volumes ¬ specifies the set of volumes to be united.

R Retain specifies that the original volumes are retained.



Subtract Real Volumes

The Subtract Real Volumes command allows you to perform a Boolean sub-traction of one or more volumes from a single target volume.

Using the Subtract Real Volumes Form

To open the Subtract Real Volumes form (see below), click the Subtract com-mand button on the Geometry/Volume subpad.

The Subtract Real Volumes form includes the following specifications.

Volume ¬ specifies the target volume from which the intersecting region is subtracted.

R Retain specifies that the target volume is retained.

Subtract —————————————————————————

Volumes ¬ specifies one or more volumes that constitute the subtraction tools.

R Retain specifies that all subtraction-tool volumes are retained.



Intersect Real Volumes

The Intersect Real Volumes command allows you to perform a Boolean inter-section of two or more real volumes.

Using the Intersect Real Volumes Form

To open the Intersect Real Volumes form (see below), click the Intersect com-mand button on the Geometry/Volume subpad.

The Intersect Real Volumes form includes the following specifications.

Volumes ¬ specifies the set of volumes to be intersected.

R Retain specifies that the original volumes are retained.



2.5.4 Blend Volumes

The Blend Volumes command allows you to round or bevel (chamfer) the edges of one or more volumes.

To perform a blend operation, you must specify the following parameters:

• The volume(s) containing the edges and/or vertices that are to be blended

• One or more blend procedures to be performed

Each blend procedure specification consists of an edge or vertex and an asso-ciated blend type. When you click the Apply command button on the Blend Volumes form, GAMBIT executes all of the blend procedure specifications that are currently defined throughout the model.

Specifying Edge Blend Type

GAMBIT provides three types of edge blend procedures:

• Constant radius round

• Variable radius round

• Constant chamfer

Figure 2-104 illustrates the basic shape of each type of edge blend procedure as performed on a single edge of a cube.



(a) Unblended volume (b) Constant radius round

(d) Constant chamfer(c) Variable radius round

Edge to beblended

Figure 2-104: Edge blend types

The following sections describe the basic specifications and operations of the blend procedure types listed above.



Constant-Radius Round Edge Blend Procedure

To define a constant-radius round edge blend procedure, you must specify the following parameters:

• The edge to be blended

• The radius of the blend

When you perform the blend operation, GAMBIT replaces the specified edge with a curved face (see Figure 2-105). The shape of the face represents a sur-face formed by a ball of the specified radius rolling between the two faces that share the edge and touching them only at the two curves of tangency.

Edge to be blended

Rounded face

Blend radius

Figure 2-105: Constant-radius round edge blend specifications



Variable-Radius Round Edge Blend Procedure

To define a variable-radius round edge blend procedure, you must specify the following parameters:


• The start and end radii of the blend

When you perform the blend operation, GAMBIT replaces the specified edge with a rounded face the radius of which varies linearly along the length of the edge. The start and end radii specifications define the radius of the blend at the start and end endpoints of the edge, respectively (see Figure 2-106).

Edge sense

Start radiusEnd radius

Figure 2-106: Variable-radius round edge blend specifications



Constant-Chamfer Edge Blend Procedure

To define a constant-chamfer edge blend procedure, you must specify the fol-lowing parameters:


• The left and right ranges for the blend

When you perform the blend operation, GAMBIT replaces the specified edge with a face the size and position of which is determined by the left and right range values as shown in Figure 2-107.

Left range

Right range

Chamfer face

Figure 2-107: Constant-chamfer edge blend specifications



Specifying Multiple Edge Blend Procedures

When you perform a blend operation, GAMBIT applies all currently specified blend procedures to the model. If you specify blend procedures for more than one edge before performing the blend operation, GAMBIT applies the appro-priate specifications to each edge.

If you specify edge blend procedures for two or more edges that are connected to each other, GAMBIT creates curves and faces where appropriate to repre-sent the intersection of the blended edges. The types of edges and faces created at the intersection depend on both the individual edge blend specifications and the sequence in which the blend operations are performed.

The Effect of Edge Blend Specifications

As an example of the effect of blend specifications on the configuration of blended edges, consider the cubic volume shown in Figure 2-108.

(a) (b) (c)

(d) (e) (f)

1 2

3

Figure 2-108: Edge blend configurations

Figure 2-108(b), (c), (d), (e), and (f) illustrate the effect of edge blend proce-dure definitions on the blending of Edges 1 and 2 in Figure 2-108(a). The definitions corresponding to each figure are as follows.



Figure Edge Blend Procedure Definitions

(a) Original cube—no blended edges

(b) Edge 1: Constant-radius round blend Edge 2: Constant-radius round blend Radius 1 = Radius 2

(c) Edge 1: Constant-radius round blend Edge 2: Constant-radius round blend Radius 1 < Radius 2

(d) Edge 1: Constant-radius round blend Edge 2: Variable-radius round blend

(e) Edge 1: Constant-chamfer blend Edge 2: Constant-chamfer blend Left and right range values identical for both edges

(f) Edge 1: Constant-radius round blend Edge 2: Constant-chamfer blend



The Effect of Operation Sequence

When you apply blend procedures to three or more edges that intersect at a single vertex, the final shape of the blended edges depends, in part, on the sequence in which the blend operations are carried out. For example, Figure 2-109 illustrates the effect of blend operation sequence on the two-step blend-ing of Edges 1, 2, and 3 in Figure 2-108(a).

(a)

Step 1 Step 2

(b)

Step 1 Step 2

3

421

Figure 2-109: The effect of edge blend operation sequence



The following table summarizes the blend operation sequences illustrated in Figure 2-109.

Figure Edge Blend Operation Sequence

(a) Step 1: Blend Edges 1 and 2 Radius 1 = Radius 2

Step 2: Blend Edge 3 Radius 3 > Radius 1

(b) Step 1: Blend Edge 3 NOTE: When you blend Edge 3, GAMBIT creates Edge 4.

Step 2: Blend Edges 1, 4, and 2 Radius 1 = Radius 4 = Radius 2 < Radius 3

Note that the procedures illustrated in Figure 2-109(a) and (b) are similar in that Edge 3 is blended by itself, and Edges 1 and 2 are blended in tandem. The difference in the final configurations is due to the sequence in which the blend operations are carried out.

Specifying Vertex Blend Type

If you specify blend procedures for three or more edges that intersect at a common vertex, you can also specify a vertex blend procedure. When you perform a vertex blend operation, GAMBIT replaces the specified vertex with a face each edge of which is connected to its neighboring face.

To completely define a vertex blend procedure, you must specify the following parameters:

• The vertex to which the procedure applies

• Bulge

• Setback



Bulge Parameter

The bulge parameter determines the degree to which the face created at the vertex is bowed. Its allowable values range from 0 (slightly bowed) to 2 (highly bowed). (NOTE: The default value for the bulge parameter is 1.)

u NOTE: The bulge parameter affects only the shape of the surface of the face created at the blended vertex—not the position or orientation of its bounding edges. As a result, the bulge parameter does not affect the appearance of the wireframe view of the volume. To view the effect of the bulge parameter on the resulting face shape, you must display a shaded view of the volume. (See the GAMBIT User’s Guide, Chapter 3.)

Setback Parameter

The setback parameter determines the distance by which the associated edge-blend faces are offset from the initial vertex location (see Figure 2-110).

(a) Setback = 0 (b) Setback > 0

Figure 2-110: The effect of setback specifications



You can specify setback values either for the vertex, itself, or for each individ-ual edge that intersects at the vertex. The edge and vertex setback specifica-tions interact according to the following rules:

• If you specify a vertex setback value, GAMBIT overrides any setback specifications for the edges that intersect at the vertex.

• If you do not specify a vertex setback value, GAMBIT applies setback values as specified for each individual edge.

Using the Blend Volumes Form

To open the Blend Volumes form (see below), click the Blend command button on the Geometry/Volume subpad.

The Blend Volumes form includes the following specifications.

Volumes ¬ specifies the volume containing the edges and vertices to be blended.

Define Blend Types: ———————————————————————

Edge opens the Edge Blend Type form, which allows you to define edge blend procedures (see “Using the Edge Blend Type Form,” below).

Vertex opens the Vertex Blend Type form, which allows you to define vertex blend procedures (see “Using the Vertex Blend Type Form,” below).



Using the Edge Blend Type Form

To open the Edge Blend Type form (see below), click the Edge command button on the Blend Volumes form.

The Edge Blend Type form includes the following specifications.

Edges ¬ specifies the edge(s) to which the blend procedure definition is to apply.

l Define specifies that an edge blend procedure is to be defined the specified edge(s).

l Remove specifies that a currently defined edge blend procedure is to be removed from the specified edge(s).

Options: —————————————————————————

l Constant radius round

specifies a constant-radius round blend.

Radius specifies the radius of a constant-radius round blend.

l Variable radius round

specifies a variable-radius round blend.



Start Radius specifies the start endpoint radius of a variable-radius round blend.

End Radius specifies the end endpoint radius of a variable-radius round blend.

l Constant chamfer

specifies a constant-chamfer blend.

Left range specifies the left range value for the blend.

Right range specifies the right range value for the blend.

Start Setback specifies the setback value applicable at the start endpoint vertex of the specified edge.

End Setback specifies the setback value applicable at the end endpoint vertex of the specified edge.



Using the Vertex Blend Type Form

To open the Vertex Blend Type form (see below), click the Vertex command button on the Blend Volumes form.

The Vertex Blend Type form includes the following specifications.

Vertices ¬ specifies one or more vertices to which the current blend definition applies.

l Define specifies that a blend procedure is to be defined for the specified vertex (or vertices).

l Remove specifies that a currently defined edge blend procedure is to be removed from the specified vertex (or vertices).

Bulge specifies the bulge shape factor for the vertex blend procedure. (Allowable values: 0 � Bulge � 2)

Setback specifies the setback value for the vertex blend procedure.



2.5.5 Modify Volume Color/Label

The Modify Volume Color/Label command button allows you to perform two operations.


Modify Volume Color Changes the color of the geometry, mesh, and shading associated with one or more volumes as displayed in the graphics window

Modify Volume Label Changes a volume label




Modify Volume Color

The Modify Volume Color command allows you to change the displayed color of the geometry and/or mesh and/or shading associated with one or more volumes.

Using the Modify Volume Color Form

To open the Modify Volume Color form (see below), click the Modify Color command button on the Geometry/Volume subpad.

The Modify Volume Color form includes the following specifications.

Volume ¬ specifies one or more volumes for which the color is to be changed.

Color: —————————————————————————

R Geometry specifies modifying the color of the volume(s).

R Mesh specifies modifying the color of the mesh associated with the volume(s).

R Shade specifies modifying the color of the shading associated with the volume(s).

For specific instructions on setting the Geometry, Mesh, or Shade colors in Section 2.2.4.



Modify Volume Label

The Modify Volume Label command allows you to change the label associated with any volume.

Using the Modify Volume Label Form

To open the Modify Volume Label form (see below), click the Modify Label command button on the Geometry/Volume subpad.

The Modify Volume Label form includes the following specifications.

Volume ¬ specifies the volume to be modified.

Label specifies a new label for the volume. (See Section 2.1.1).



2.5.6 Move/Copy/Align Volumes

The Move/Copy/Align Volumes command button allows you to perform two operations.


Move/Copy Volumes Moves and copies volumes

Align Volumes Aligns volumes and connected geometry with existing topological entities




Move/Copy Volumes

The Move/Copy Volumes command allows you to reposition and/or reorient one or more volumes or to create copies of volumes. For a general description of the procedures and specifications required to move and/or copy entities, see “Moving an Entity“ and “Copying an Entity,” respectively, in Section 2.1.4.

Using the Move/Copy Volumes Form

To open the Move/Copy Volumes form (see below), click the Move/Copy com-mand button on the Geometry/Volume subpad.

For a complete description of the specifications available on the Move/Copy Volumes form, see “Using Move/Copy Forms“ in Section 2.1.4.



Align Volumes

The Align Volumes command allows you to reposition and/or reorient a volume so that it coincides with another volume or is aligned with a plane defined by three vertices. (For a general description of the procedure and specifications required to align an entity, see “Aligning an Entity,” in Section 2.1.4.)

Using the Align Volumes Form

To open the Align Volumes form (see below), click the Align command button on the Geometry/Volume subpad.

For a complete description of the specifications available on the Align Volumes form, see “Using Align Forms“ in Section 2.1.4.



2.5.7 Split/Merge Volumes

The Split/Merge Volumes command button allows you to perform the fol-lowing operations.


Split Volume Splits an existing volume into one or more real or virtual volumes

Merge Volumes Merges two or more existing volumes into a virtual volume




Split Volume

The Split Volume command allows you to split an existing volume into one or two real or virtual volumes.

To split a volume by means of the Split Volume command, you must specify the following parameters:

• Target volume

• Split type

The target volume specifies the volume to be split by the Split Volume operation. The split type determines the type of split tool to be used for the split (volume, face(s), or locations) and type of geometry to be produced from the operation (real or virtual).

Specifying the Target Volume

GAMBIT allows you to split either real or virtual volumes by means of the Split Volume operation but places the following restrictions on the type of faces that can be created from the split:

• If you split a real volume, GAMBIT can create real or non-real volumes.

• If you split a non-real volume, GAMBIT creates only non-real volumes.


GAMBIT provides the following types of volume-split options:

• Volume (Real)

• Face (Real)

• Faces (Virtual)

Each option differs from the others with respect to the type of split tool used and the type of geometry created from the split operation. The following subsections describe the options listed above.

Specifying a Volume (Real) Split Operation

The Volume (Real) split option allows you to split a real target volume using a real split-tool volume. (NOTE: You cannot use the Volume (Real) option to split a non-real volume.) When you split a volume using the Volume (Real) split option, GAMBIT creates a set of real volumes from the split operation.



Volume (Real) Boolean Operations

When you split a volume using the Volume (Real) option, GAMBIT creates one or more volumes each of which constitutes the result of a different Boolean operation. The operations are as follows:

• Intersect the split-tool volume and the target volume

• Subtract the intersection volume from the target volume

Figure 2-111 illustrates the volume split operation as applied to a cube and a sphere. The cube constitutes the target volume; the sphere constitutes the split tool and is centered at one corner of the cube (see Figure 2-111(a)).

(a) (b)

(d)(c)

Split-toolvolume

Volume tobe split

volume.2

volume.1

Figure 2-111: Volume-split operation

To split the volume, GAMBIT performs the following operations:

1. Intersect the cube and sphere to create volume.2 in Figure 2-111(b))

2. Subtract the intersected volume (volume.2) from the cube to create volume.1 in Figure 2-111(c))

The final split volume appears as shown in Figure 2-111(d).



Volume (Real) Suboptions

The Volume (Real) split option includes the following suboptions:

• Retain

• Connected

• Bidirectional

If you specify the Retain suboption, GAMBIT retains the split-tool volume upon completion of the split operation. If you do not specify the Retain option, GAMBIT deletes the split-tool volume.

If you specify the Connected option, GAMBIT connects the volumes that result from the split operation along their common face(s). If you do not specify the Connected option, the split operation creates disconnected volumes.

If you specify the Bidirectional option, GAMBIT splits and retains the split-tool volume as well as the target volume. For example, Figure 2-112 shows the volumes that result from the specification of the Bidirectional option for the split illustrated in Figure 2-111.

volume.2

volume.1

volume.3

Figure 2-112: Volume (Real) split operation—Bidirectional option



Specifying a Face (Real) Split Operation

The Face (Real) split option allows you to split a real target volume using a real split-tool face. (NOTE: You cannot use the Face (Real) option to split a non-real volume.) When you split a volume using the Face (Real) split option, GAMBIT creates a set of real volumes from the split operation.

Face (Real) Boolean Operations

When you split a volume using the Face (Real) option, GAMBIT creates either one or two volumes, depending on whether the face fully or partially intersects the volume. If the face fully intersects the volume, GAMBIT creates two separate volumes. If the face only partially intersects the volume, GAMBIT creates a single volume that contains a connected, dangling face.

Face (Real) Suboptions

The Face (Real) split option includes the following suboptions:

• Retain

• Connected

• Bidirectional

If you specify the Retain suboption, GAMBIT retains the split-tool face upon completion of the split operation. If you do not specify the Retain option, GAMBIT deletes the split-tool face.

If you specify the Connected option, GAMBIT connects the volumes that result from the split operation along their common face(s). If you do not specify the Connected option, the split operation creates disconnected volumes.

If you select the Bidirectional option, GAMBIT splits the split-tool face as well as the volume to be split. Figure 2-113 shows the entities that result from specifying the Bidirectional option when splitting a sphere with a fully-intersecting rectangular face.



volume.1

volume.2

face.1

Split-toolface

Volume tobe split

Figure 2-113: Volume split by fully-intersecting face—Bidirectional option

Specifying a Faces (Virtual) Split Operation

The Faces (Virtual) split option allows you to split a real or non-real target volume using one or more real or non-real faces. If you specify more than one face as the split tool, all specified split-tool faces must be connected to adjacent split-tool faces and must share boundary edges with the volume boundary. The Faces (Virtual) split operation produces only virtual geometry and includes a Retain suboption that allows you to retain the split-tool face(s).



Using the Split Volume Form

To open the Split Volume form (see below), click the Split command button on the Geometry/Volume subpad.

The specifications on the Split Volume form are as follows.

Volume ¬ specifies the volume to be split.

Split with —————————————————————————

Volume (Real) q Face (Real) Faces (Virtual)

specifies the split type.

The specifications available on the lower section of the Split Volume form depend on the specified Split with option as follows.



Volume (Real) Split Option

When you specify the Volume (Real) option, the lower section of the Split Volume form appears as shown above and includes the following specifications.

Volume ¬ specifies the volume that constitutes the split tool.

R Retain specifies retaining the split-tool volume at the conclusion of the split operation.

R Connected specifies connecting the faces(s) that constitute(s) the boundary between the volumes resulting from the split operation.

R Bidirectional specifies that both the target volume and split-tool volume are split by the split operation.

Face (Real) Split Option

When you specify the Face (Real) option, the lower section of the Split Volume form appears as shown below and includes the following specifications.

Face ¬ specifies the face that constitutes the split tool.


R Connected specifies connecting the faces(s) that constitute(s) the boundary between the volumes resulting from the split operation.

R Bidirectional specifies that both the target volume and split-tool face are split by the split operation.



Faces (Virtual) Split Option

When you specify the Faces (Virtual) option, the lower section of the Split Volume form appears as shown below and includes the following specifications.

Faces ¬ specifies the face(s) that constitute(s) the split tool.

R Retain specifies retaining the split-tool faces at the conclusion of the split operation.



Merge Volumes

The Merge Volumes command allows you to merge real or virtual volumes into a single real or virtual volume.

When you merge volumes by means of the Merge Volumes form, GAMBIT creates a single real or virtual volume from the set of specified real and/or vir-tual volumes. Each volume in the set of specified volumes must be connected to at least one other volume in the set by means of a shared, connected face. (NOTE: GAMBIT deletes the shared faces in the process of merging the volumes.)

During virtual merge operations, GAMBIT deletes the volume mesh from the volumes being merged. However, GAMBIT automatically preserves existing meshes on faces that are not deleted in the merge operation.

Using the Merge Volumes Form

To open the Merge Volumes form (see below), click the Merge command button on the Geometry/Volume subpad.

The Merge Volumes form includes the following specifications.

Volumes ¬ specifies two or more volumes to be merged.

l Real specifies that the merged volume is real.

l Virtual specifies that the merged volume is virtual.



2.5.8 Heal/Convert Volumes

The Heal/Convert Volumes command button allows you to perform the fol-lowing operations.


Heal Real Volume Heals real volume geometry

Convert Volumes Converts non-real volumes to real volumes




Heal Real Volume

The Heal Real Volume command attempts to heal geometry problems associ-ated with model volumes.

Overview

GAMBIT real geometry operations employ ACIS modeling techniques. ACIS modeling algorithms require a high degree of precision and accuracy in the geometric data that describe the model. Such precision and accuracy manifests in the form of tight distance tolerances and completeness of connectivity information.

In most cases, model geometry data generated from within GAMBIT automatically meet the stringent integrity standards required by the ACIS modeler. However, several GAMBIT operations—for example, Boolean operations—can sometimes produce geometry that fails to meet the ACIS standards. In addition, geometry imported to GAMBIT from outside sources may not meet such standards due to any of the following factors:

• Inherent numerical limitations in the system used to generate the geometry

• Limitations of data transfer through neutral file formats

• Differences in tolerance settings between the model-generating pro-gram and GAMBIT

The Heal Real Volume command attempts to detect and repair geometry prob-lems associated with model volumes. Such problems include curve and surface definitions that do not match the volume topology. The healing operation is a three-step process that involves simplifying geometry, stitching together loose faces (if necessary), and building new geometry to repair geometry and topology problems.

u NOTE: The GAMBIT healing operations—Heal Real Faces (see Section 2.4.8) and Heal Real Volume—are not guaranteed to correct all geometry and topol-ogy problems in the model. In general, both operations should be used with caution, because they are not robust and sometimes produce peculiar model geometry.



Specifying the Geometry simplification Option

As noted above, the healing operation involves three steps:

• Geometry simplification

• Stitching

• Geometry building

In the geometry simplification step, GAMBIT converts NURBS data to ana-lytic data, where possible, to within a specified tolerance. In the stitching step, GAMBIT attempts to connect edges and vertices within an iterated tolerance value. In the geometry building step, GAMBIT modifies surface and edge geometry to bring it within a specified tolerance (if possible).

GAMBIT allows you to control the geometry simplification step by means of the Geometry simplification option on the Heal Real Volume form. The Geometry simplification option allows you to specify whether or not GAMBIT employs geometry simplification when healing the volume.

If you select the Geometry simplification option, you can also specify a Tolerance value. The Tolerance value is used to determine whether or not NURBS sur-faces can be approximated by analytic surfaces. If the Geometry simplification Tolerance is too loose, approximate analytic fits to NURBS geometry may be obtained. In such cases, the gaps between surfaces may increase, and healing in subsequent steps may be more difficult or may fail.

Using the Heal Real Volume Form

To open the Heal Real Volume form (see below), click the Heal command button on the Geometry/Volume subpad.

The Heal Real Volume form includes the following specifications.



Volume ¬ specifies the volume for which GAMBIT attempts the heal operation.

All q Pick

• All specifies all volumes in the model.

• Pick specifies volumes selected by means of the Volumes list box. (NOTE: If you pick a volume in the graphics window or click in the Volumes list box, GAMBIT automatically selects the Pick option.)

R Geometry simplification

attempts to simplify geometry during the healing operation.

Tolerance specifies the tolerance value for simplification.



Convert Volumes

The Convert Volumes command converts one or more non-real (faceted and/or virtual) volumes to real volumes. The conversion process preserves both the topology and any existing mesh(es) associated with the converted volume(s). In addition, all non-real faces, edges, and vertices associated with the vol-ume(s) are converted to real faces, edges, and vertices, respectively.

u NOTE (1): A non-real volume cannot be converted to a real volume unless all lower topology associated with the non-real volume is also capable of con-version. This restriction requires that all faces of the non-real volume include mapped meshes (see “Convert Faces,” above). In addition, GAMBIT cannot convert volumes for which guest/host relationships exist.

u NOTE (2): Hidden entities that serve as hosts for virtual entities may become active (that is, visible) when their guest entities are converted to real geo-metry.

Using the Convert Volumes Form

To open the Convert Volumes form (see below), click the Convert Volumes command button on the Geometry/Volume subpad.

The Convert Volumes form includes the following specifications.

Volumes ¬ specifies which non-real volumes are to be converted to real volumes.

All q Pick





2.5.9 Summarize/Check/Query Volumes and Total Entities

The Summarize/Check/Query Volumes and Total Entities command button lets you to perform two operations.


Summarize Volumes Displays volume summary informa-tion in the Transcript window

Check Volumes Checks the topological and geometric validity of model volumes

Query Volumes Opens the volume query list





Summarize Volumes

The Summarize Volumes command displays volume summary information in the Transcript window.

Using the Summarize Volumes Form

To open the Summarize Volumes form (see below), click the Summarize com-mand button on the Geometry/Volume subpad.

The Summarize Volumes form includes the following specifications.

Volumes ¬ specifies one or more volumes for which information is to be summarized in the Transcript window.

All q Pick





Check Volumes

The Check Volumes command assesses the topological and/or geometric valid-ity of volumes in the model and summarizes the results in the Transcript window.

When you execute the Check Volumes command, GAMBIT checks the model to determine its validity with respect to either or both of the following types of characteristics:

• Topology

• Geometry


Topology Check


For a given volume, the Check Volumes topology check operation examines the model to ensure that it meets the following criteria:

• Lower-topology faces are visible and correctly reference the volume.

• Sense information (in the form of co-faces) exists for all faces.

• Virtual guest entities correctly reference the volume as a host.

u NOTE: Failure of the topology check for any volume in the model constitutes a serious problem for the model as a whole. GAMBIT does not currently include any tools that allow you to repair problems that cause failures of topology checks.

Geometry Check

Geometrical validity is an assessment of the model with respect to proximity and shape characteristics—such as the distances between connected edges and/or the mathematical continuity of model curves and surfaces. The Check Volumes geometry check criteria are as follows:



• All real volumes correctly reference the ACIS model.

• No real volumes exhibit problems related to continuity, degeneracies, or singularities.

• Any virtual-volume hosts are of the correct type—that is, volumes. (NOTE: The volume geometry check operation also checks the validity of host geometry.)

u NOTE: Volume healing operations (see Section 2.5.8) may apply to volumes that fail the geometry check.

Using the Check Volumes Form

To open the Check Volumes form (see below), click the Check command button on the Geometry/Volume subpad.

The Check Volumes form includes the following specifications.

Volumes ¬ specifies the volumes to be included in the checking operations.

All q Pick



R Check Topology specifies a topology check on the selected volumes.

R Check Geometry specifies a geometry check on the selected volumes.



Query Volumes

The Query Volumes command allows you to identify the location and/or the names of specific volumes.

Using the Query Volumes Form

To open the Query Volumes form (see below), click the Query command button on the Geometry/Volume subpad.

For a general description of using the Query Volumes form, see “Using the Query Vertices Form“ in Section 2.2.7, above.



Total Entities






2.5.10 Delete Volumes

The Delete Volumes command deletes one or more volumes from the model.

Retaining Volume Faces

By default, when you delete a volume, GAMBIT deletes the faces—including their edges and vertices—that constitute parts of the volume. To retain the faces when the volume is deleted, unselect the Lower Geometry option at the bottom of the Delete Volumes form. When you delete a volume and retain its faces, the resulting faces are connected to each other by means of their com-mon edges and vertices.

u NOTE: When you delete a volume, GAMBIT does not delete its faces, edges, and vertices that constitute components of other volumes.

Deleting Associated Vertices

When you delete a volume with associated vertices created by means of the Create Vertex On Volume command, GAMBIT deletes any virtual vertices that are associated with the volume. (The virtual vertex cannot exist without the host volume.)

Deleting Virtual Volumes

If you delete a virtual volume, GAMBIT deletes all lower topology and virtual hierarchy that is associated with the volume and is not associated with any other entities in the model.



Using the Delete Volumes Form

To open the Delete Volumes form (see below), click the Delete command button on the Geometry/Volume subpad.

The Delete Volumes form includes the following specifications.

Volumes ¬ specifies one or more volumes to be deleted.

All q Pick



R Lower Geometry

specifies that all faces, edges, and vertices that constitute parts of the volumes are deleted.

Group Commands CREATING THE GEOMETRY


2.6 Group Commands

The following commands are available on the Geometry/Group subpad.


Create Group Creates a group composed of existing topological entities

Modify Group Modifies the composition of a group

Modify Group Color Modify Group Label

Modifies group colors; modifies group labels

Move/Copy Groups Align Groups

Moves and/or copies groups; aligns groups with existing entities

Summarize Groups Check Groups Query Groups Total Entities

Displays group summary information; checks validity of topology and geometry; opens a group query list; displays entity totals

Delete Groups Deletes groups

CREATING THE GEOMETRY Group Commands


2.6.1 Create Group

The Create Group command allows you to create groups of topological entities.

Overview

To create a group, you must specify a list of existing topological entities that constitute members of the group. Available entities include vertices, edges, faces, volumes, and other groups. You can also explicitly include or exclude from the new group one or more lower-topology components associated with any or all members of the group.

Including and Excluding Lower Topology

When you add an entity to a group, GAMBIT implicitly includes in the group all lower topology associated with the entity. For example, if you add a face to a group, GAMBIT implicitly includes in the group the edges and vertices associated with the face.

For any group member other than a vertex, GAMBIT allows you to explicitly include or exclude lower-topology components of the entity. For example, it is possible to create a group that includes a specified face but explicitly excludes all but one of the vertices associated with the face.

GAMBIT provides the following four options for explicitly including or excluding lower topology associated with an entity that is a member of a group:

• Include all lower topology

• Include selected lower-topology components

• Exclude all lower topology

• Exclude selected lower-topology components

The first three options listed above are available directly by means of Edit Lower Topology forms, such as that shown in Figure 2-114.



Figure 2-114: Example Edit Lower Topology form

To execute the fourth option, you must perform the following steps.

1. Use the appropriate Edit Lower Topology form to include all lower-topology components of the specified type

2. Delete from the group list only those components to be excluded from the created group

As an example of the procedure outlined above, consider a case in which a single edge, labeled edge.4, is to be added to a group but one of its two end-point vertices, labeled vertex.7, is to be excluded from the group. The fol-lowing procedure outlines the steps necessary to include edge.4 and exclude vertex.7 from the group.

1. Open the Create Group form.

2. Add edge.4 to the list of entities comprising the group.

3. Open the Edit Edge Lower Topology form (see Figure 2-114).

4. Specify the Include all vertices option, and click Apply.

5. Close the Edit Edge Lower Topology form.

6. Delete vertex.7 from the entity list displayed on the Create Group form.



The Effect of Excluding Lower Topology

The primary purpose of excluding lower topology from members of a group is to customize the application of boundary zone types. If you specify a boundary condition for a group, GAMBIT applies the boundary condition to all entities that are members of the group but are not explicitly excluded from the group. For example, it is possible to apply a “wall” boundary condition to three sides of a four-sided face so that the fourth side can be treated as a “free surface.”

The exclusion of lower topology from members of a group does not affect group meshing operations. For example, if you mesh a group that includes a face one edge of which is explicitly excluded from the group, GAMBIT grades and meshes the edge when it meshes the face.

Using the Create Group Form

To open the Create Group form (see below), click the Create Group command button on the Geometry/Group subpad.

The Create Group form includes the following specifications.

Label | Type o lists the labels (Label) and types (Type) of all entities currently existing in the group to be created.

Remove removes the currently highlighted entity from the list of group members.



Edit opens the Edit Lower Topology form corresponding to the cur-rently highlighted entity. (See “Using Edit Lower Topology Forms,” below.)

Volumes q Faces Edges Vertices Groups

specifies the type of entity to be added to the created group.

Volumes ¬ Faces Edges Vertices Groups

specifies the individual entity to be added to the created group.

Label specifies a label for the new group. (See Section 2.1.1.)



Using Edit Lower Topology Forms

Edit Lower Topology forms allow you to explicitly include or exclude lower-topology components associated with entities that comprise members of the created group. There are four types of Edit Lower Topology forms:

• Edit Edge Lower Topology

• Edit Face Lower Topology

• Edit Volume Lower Topology

• Edit Group Lower Topology

The following sections describe the specifications available on each of the forms listed above.



Using the Edit Edge Lower Topology Form

To open the Edit Edge Lower Topology form (see below), highlight an edge label in the Create Group form entity list, and click the Edit command button.

The Edit Edge Lower Topology form includes the following specifications.

Filter: specifies the edge for which lower topology is to be included or excluded from the created group.

Vertices: —————————————————————————

l Exclude all vertices

specifies that all vertices associated with the specified edge are excluded from the created group.

l Include all vertices

specifies that all vertices associated with the specified edge are included in the created group.

l Include selected vertices

specifies that only selected vertices associated with the specified edge are included in the created group.

Vertices ¬ specifies the vertices associated with the specified edge that are explicitly included in the new group.



Using the Edit Face Lower Topology Form

To open the Edit Face Lower Topology form (see below), highlight a face label in the Create Group form entity list, and click the Edit command button.

The Edit Face Lower Topology form includes the following specifications.

Filter: specifies the face for which lower topology is to be included or excluded from the created group.

Vertices: —————————————————————————


specifies that all vertices associated with the specified face are excluded from the created group.


specifies that all vertices associated with the specified face are included in the created group.


specifies that only selected vertices associated with the specified face are included in the created group.

Vertices ¬ specifies the vertices that are explicitly included in the created group.



Edges: —————————————————————————

l Exclude all edges

specifies that all edges associated with the specified face are excluded from the created group.

l Include all edges specifies that all edges associated with the specified face are included in the created group.

l Include selected edges

specifies that only selected edges associated with the speci-fied face are included in the created group.

Edges ¬ specifies the edges that are to be explicitly included in the created group.

R Include attached faces

specifies that any faces that share connected geometry with the specified face are included in the created group.



Using the Edit Volume Lower Topology Form

To open the Edit Volume Lower Topology form (see below), highlight a volume label in the Create Group form entity list, and click the Edit command button.

The Edit Volume Lower Topology form includes the following specifications.

Filter: specifies the volume for which lower topology is included or excluded from the created group.

Vertices: —————————————————————————


specifies that all vertices associated with the specified vol-ume are excluded from the created group.


specifies that all vertices associated with the specified vol-ume are included in the created group.




specifies that only selected vertices associated with the specified volume are included in the created group.


Edges: —————————————————————————

l Exclude all edges

specifies that all edges associated with the specified volume are excluded from the created group.

l Include all edges specifies that all edges associated with the specified volume are included in the created group.


specifies that only selected edges associated with the speci-fied volume are included in the created group.


Faces: —————————————————————————

l Exclude all faces specifies that all faces associated with the specified volume are excluded from the created group.

l Include all faces specifies that all faces associated with the specified volume are included in the created group.

l Include selected faces

specifies that only selected faces associated with the speci-fied volume are included in the created group.

Faces ¬ specifies the faces that are to be explicitly included in the created group.



Using the Edit Group Lower Topology Form

To open the Edit Group Lower Topology form (see below), highlight a group label in the Create Group form entity list, and click the Edit command button.

The Edit Group Lower Topology form includes the following specifications.

Filter: specifies the group for which lower topology is included or excluded from the created group.



Vertices: —————————————————————————


specifies that all vertices associated with the specified group are excluded from the created group.


specifies that all vertices associated with the specified group are included in the created group.


specifies that only selected vertices associated with the specified group are included in the created group.


Edges: —————————————————————————

l Exclude all edges

specifies that all edges associated with the specified group are excluded from the created group.

l Include all edges specifies that all edges associated with the specified group are included in the created group.


specifies that only selected edges associated with the speci-fied group are included in the created group.


Faces: —————————————————————————

l Exclude all faces specifies that all faces associated with the specified group are excluded from the created group.

l Include all faces specifies that all faces associated with the specified group are included in the created group.


specifies that only selected faces associated with the speci-fied group are included in the created group.

Faces ¬ specifies the faces that are to be explicitly included in the created group.



Volumes: —————————————————————————

l Exclude all faces specifies that all volumes associated with the specified group are excluded from the created group.

l Include all faces specifies that all volumes associated with the specified group are included in the created group.


specifies that only selected volumes associated with the specified group are included in the created group.

Volumes ¬ specifies the volumes that are to be explicitly included in the created group.

R Include attached faces

specifies that any faces that share connected geometry with the specified group are included in the created group.



2.6.2 Modify Group

The Modify Group command allows you to modify the population of entities within an existing group.

Using the Modify Group Form

To open the Modify Group form (see below), click the Modify Group command button on the Geometry/Group subpad.

The Modify Group form includes the following specifications.

Group ¬ specifies the group to be modified.

Label | Type o lists the labels (Label) and types (Type) of all entities currently existing in the specified group.

Remove removes the currently highlighted entity from the list of group members.

Edit opens the Edit Lower Topology form corresponding to the currently highlighted entity. (See “Using Edit Lower Topology Forms“ in Section 2.6.1, above.)



Volumes q Faces Edges Vertices Groups

specifies the type of entity to be added to the specified group.

Volumes ¬ Faces Edges Vertices Groups

specifies the individual entity to be added to the specified group.



2.6.3 Modify Group Color/Label

The Modify Group Color/Label command button allows you to perform two operations.


Modify Group Color Changes the color of the geometry, mesh, and shading associated with one or more groups as displayed in the graphics window

Modify Group Label Changes a group label




Modify Group Color

The Modify Group Color command allows you to change the displayed color of the geometry and/or mesh and/or shading associated with one or more groups.

Using the Modify Group Color Form

To open the Modify Group Color form (see below), click the Modify Color command button on the Geometry/Group subpad.

The Modify Group Color form includes the following specifications.

Groups ¬ specifies one or more groups for which the color is to be modified.

Color: —————————————————————————

R Geometry specifies modifying the color of all geometry associated with the specified group(s).

R Mesh specifies modifying the color of the mesh associated with the specified group(s).

R Shade specifies modifying the color of the shading associated with the group(s).

For specific instructions on setting the Geometry or Mesh colors, see Section 2.2.4.



Modify Group Label

The Modify Group Label command allows you to change the label associated with any group.

Using the Modify Group Label Form

To open the Modify Group Label form (see below), click the Modify Label command button on the Geometry/Group subpad.

The Modify Group Label form includes the following specifications.

Group ¬ specifies the group to be modified.

Label specifies a new label for the group. (See Section 2.1.1).



2.6.4 Move/Copy/Align Groups

The Move/Copy/Align Groups command button allows you to perform the fol-lowing operations.


Move/Copy Groups Moves and/or copies groups

Align Groups Aligns groups with existing topologi-cal entities




Move/Copy Groups

The Move/Copy Groups command allows you to reposition and/or reorient one or more groups or to create copies of groups. For a general description of the procedures and specifications required to move and/or copy entities, see “Moving an Entity“ and “Copying an Entity,” respectively, in Section 2.1.4.

Using the Move/Copy Groups Form

To open the Move/Copy Groups form (see below), click the Move/Copy com-mand button on the Geometry/Group subpad.

For a complete description of the specifications available on the Move/Copy Groups form, see “Using Move/Copy Forms“ in Section 2.1.4.



Align Groups

The Align Groups command allows you to reposition and/or reorient a group so that it is aligned with a plane defined by three existing vertices. (For a gen-eral description of the procedure and specifications required to align an entity, see “Aligning an Entity,” in Section 2.1.4.) When you translate a group using the Align Groups form, GAMBIT translates all vertices, edges, faces, and vol-umes that constitute parts of the group.

Using the Align Groups Form

To open the Align Groups form (see below), click the Align command button on the Geometry/Groups subpad.

For a complete description of the specifications available on the Align Groups form, see “Using Align Forms“ in Section 2.1.4.



2.6.5 Summarize/Check/Query Groups and Total Entities

The Summarize/Check/Query Groups and Total Entities command button allows you to perform the following operations.


Summarize Groups Displays group summary information in the Transcript window

Check Groups Checks the topological and geometric validity of model groups

Query Groups Opens the group query list





Summarize Groups

The Summarize Groups command displays group summary information in the Transcript window.

Using the Summarize Groups Form

To open the Summarize Groups form (see below), click the Summarize com-mand button on the Geometry/Group subpad.

The Summarize Groups form includes the following specifications.

Groups ¬ specifies one or more groups for which information is to be summarized in the Transcript window.

All q Pick

• All specifies all groups in the model.

• Pick specifies groups selected by means of the Groups list box. (NOTE: If you pick a group in the graphics window or click in the Groups list box, GAMBIT automatically selects the Pick option.)



Check Groups

The Check Groups command assesses the topological and/or geometric valid-ity of entity groups and subgroups in the model and summarizes the results in the Transcript window.

When you execute the Check Groups command, GAMBIT checks the model to determine its validity with respect to either or both of the following types of characteristics:

• Topology

• Geometry


Topology Check


For a given group, the Check Groups topology operation examines all entities in the group according to the individual check criteria that are applicable to each entity type. For descriptions of such criteria for vertices, edges, faces, and volumes, see Sections 2.2.7, 2.3.7, 2.4.9, and 2.5.9, respectively.

Geometry Check

Geometrical validity is an assessment of the model with respect to proximity and shape characteristics—such as the distances between connected edges and/or the mathematical continuity of model curves and surfaces. For a given group, the Check Groups topology operation examines all entities in the group according to the check criteria that are applicable to each entity type. For descriptions of such criteria for vertices, edges, faces, and volumes, see Sections 2.2.7, 2.3.7, 2.4.9, and 2.5.9, respectively.



Using the Check Groups Form

To open the Check Groups form (see below), click the Check command button on the Geometry/Group subpad.

The Check Groups form includes the following specifications.

Groups ¬ specifies the groups to be included in the checking operations.

All q Pick



R Check Topology specifies a topology check on the selected groups.

R Check Geometry specifies a geometry check on the selected groups.



Query Groups

The Query Groups command allows you to identify the locations and/or the names of specific groups.

Using the Query Groups Form

To open the Query Groups form (see below), click the Query command button on the Geometry/Group subpad.

For a general description of using the Query Groups form, see “Using the Query Vertices Form“ in Section 2.2.7, above.



Total Entities






2.6.6 Delete Groups

The Delete Groups command deletes one or more groups from the model.

Deleting Group Member Entities

When you delete a group, GAMBIT disassociates its member entities and deletes the group label, thereby removing the group from the list of available groups. In doing so, GAMBIT retains or deletes the member entities of the group according to the following rules.

• If you delete a group and do not select the Lower topology option, GAMBIT does not delete its member entities from the model.

• If you select the Lower topology option when deleting a group, GAMBIT deletes all member entities that do not constitute parts of higher-topology entities.

As an example of the first rule, consider a group labeled group.3 that consists of two faces, labeled face.7 and face.18. If you delete group.3 and do not select the Lower topology option, GAMBIT disassociates group.3 and removes it from the list of available groups but does not delete either face.7 or face.18 from the model.

As an example of the second rule, consider a group labeled group.1 that con-sists of the following members: edge.3, edge.6, edge.9, face.2, and face.8. Furthermore, assume the following.

• edge.3 and edge.6 constitute parts of face.2

• face.2 does not constitute part of any volume

• edge.9 constitutes one side of a face that is not a member of group.1

• face.8 constitutes part of a volume that is not a member of group.1

If you delete group.1 and select the Lower topology option, GAMBIT disassoci-ates group.1 and deletes face.2, including edge.3 and edge.6, but does not delete edge.9 or face.8.



Deleting Virtual Groups

If you delete a virtual group, GAMBIT deletes all lower topology and virtual hierarchy that is associated with the group and is not associated with any other entities in the model.

Using the Delete Groups Form

To open the Delete Groups form (see below), click the Delete command button on the Geometry/Group subpad.

The Delete Groups form includes the following specifications.

Groups ¬ specifies one or more groups to be deleted.

All q Pick



R Lower Geometry

specifies that all lower-topology entities that constitute parts of the groups are deleted.

MESHING THE MODEL


3. MESHING THE MODEL When you click the Mesh command button on the Operation toolpad, GAMBIT opens the Mesh subpad. The Mesh subpad contains command but-tons that allow you to perform mesh operations involving boundary layers, edges, faces, volumes, and groups.

The symbols associated with each of the Mesh subpad command sets are as follows.

Symbol Command Set

Boundary Layer

Edge

Face

Volume

Group

The following sections of this chapter describe the commands associated with each of the command buttons listed above.

Boundary Layers MESHING THE MODEL


3.1 Boundary Layers

3.1.1 Overview

Boundary layers define the spacing of mesh node rows in regions immediately adjacent to edges and/or faces. They are used primarily to control mesh den-sity and, thereby, to control the amount of information available from the computational model in specific regions of interest.

As an example of a boundary layer application, consider a computational model that includes a cylinder representing a pipe through which flows a viscous fluid. Under normal circumstances, it is likely that the velocity gradients are large in the region immediately adjacent to the pipe wall and small near the center of the pipe. By attaching a boundary layer to the face that represents the pipe wall, you can increase the mesh density near the wall and decrease the density near the center of the cylinder, thereby obtaining sufficient information to characterize the gradients in both regions while minimizing the total number of mesh nodes in the model.

To define a boundary layer, you must specify the following information:

• Boundary-layer algorithm

• Height of the first row of mesh elements

• Growth factor—which specifies the height of each succeeding row of elements

• Total number of rows—which defines the depth of the boundary layer

• Edge or face to which the boundary layer is attached

• Face or volume that defines the direction of the boundary layer

You can also specify the creation of a transition boundary layer—that is, a boundary layer for which the mesh node pattern changes with each succeeding layer. If you specify a transition boundary layer, you must also specify the transition pattern and number of transition rows.

MESHING THE MODEL Boundary Layers


3.1.2 Boundary Layer Commands

The following commands are available on the Mesh/Boundary Layer subpad.


Create Boundary Layer Creates a boundary layer attached to an edge or face

Modify Boundary Layer Modifies the definition of an existing boundary layer

Modify Label Modifies boundary layer labels

Summarize Boundary Layers Displays existing boundary layers in the graphics window

Delete Boundary Layers Deletes boundary layers



Create Boundary Layer

The Create Boundary Layer command allows you to define the spacing of mesh nodes in the vicinity of an edge or face.

To create a boundary layer, you must specify the following parameters:

• Definition

• Transition characteristics

• Attachment

The definition parameters include: the algorithm used to determine first-row element heights, a set of size parameters, internal continuity and corner shape characteristics. The transition characteristics determine the arrangement of mesh nodes in the region immediately adjacent to the attachment entity. The attachment parameters include the entity to which the boundary layer is attached and the entity that specifies the direction of the boundary layer.

Specifying the Definition

To define the boundary layer, you must specify the following characteristics:

• Algorithm

• Size

• Internal continuity

• Corner shape

The algorithm specifies the method that GAMBIT employs to determine the first-row element height(s). Size characteristics include parameters such as the number of rows and first-row height(s) for the boundary layer. The internal continuity characteristic determines the behavior of the boundary-layer imprint in regions where it overlaps the imprint(s) of adjoining boundary layers. The corner shape characteristic determines the shape of the mesh in the region surrounding Corner or Reversal vertices that connect edges to which boundary layers are attached.



Specifying the Algorithm

As noted above, a boundary-layer definition consists of a set of size parameters that includes the height of the first row (that is, the row adjacent to the attachment entity), a growth factor, and the total number of rows in the boundary layer. The algorithm specification determines the method that GAMBIT uses to calculate the height(s) of the elements in the first row of the boundary layer. GAMBIT provides the following algorithm types.

• Uniform—specifies that heights of all first-row boundary-layer elements are equal to each other across the entire span (edge length or face surface area) of the attachment entity.

• Aspect ratio based—computes the first-row element heights as a fixed percentage of the edge mesh element lengths for the edge or face to which the boundary layer is attached.

As an example of the differences between the algorithms described above, consider the two 2-D boundary layers shown in Figure 3-1, each of which is attached to the lower edge of a square face. In this case, the attachment entity (edge) is graded in a non-linear fashion such that it includes five intervals and a grading ratio of 1.25. (For a description of edge grading and meshing operations, see Section 3.2.1, below.) In both cases shown in Figure 3-1, the boundary layer includes four rows and is created using a growth factor of 1.2.

(a) Uniform (b) Aspect ratio based

Figure 3-1: Comparison of Uniform and Aspect ratio based algorithms



For the Uniform boundary layer (Figure 3-1(a)), the first row of the boundary layer exhibits a uniform height across the span of the attachment edge. As a result, each succeeding row of the boundary layer also exhibits a uniform height.

For the Aspect ratio based boundary layer (Figure 3-1(b)), the heights of the elements in the first row of the boundary layer vary according to the corresponding element length on the attachment edge. Consequently, the first-row elements increase in height from left to right across the edge, because the edge mesh is graded to increase from left to right. In this case, the first-row element heights for the boundary layer elements represent 20% of the corres-ponding edge element lengths.

Figure 3-1 illustrates that the first-row heights—and, therefore, the choice of algorithm—affect(s) the shape of the entire boundary layer. In this case, both boundary layers employ a growth factor of 1.2, therefore each row of the boundary layer is 20% thicker than the preceding row. Figure 3-1 shows that the growth factor amplifies the effect of the first-row heights on boundary layer shape across the span of the boundary layer.

For boundary layers that are attached to uniformly graded edges, the shape of the boundary layer is independent of the algorithm specified for its construction. For example, Figure 3-2 shows Uniform and Aspect ratio based boundary layers for a configuration similar to that shown in Figure 3-1, above, but for which the attachment edge is uniformly graded. Because the edge element lengths are uniform across the edge, the heights of all first-row elements for the Aspect ratio based boundary layer are equal to each other, therefore the boundary layer is identical to the Uniform boundary layer in this case.



(a) Uniform (b) Aspect ratio based

Figure 3-2: Uniform vs. Aspect ratio based algorithms—uniformly graded edge

Specifying the Size Characteristics

To define the size of the boundary layer, you must specify three of four parameters that describe the sizes of the boundary-layer rows. The parameters to be specified differ slightly from each other according to the algorithm used to determine the first-row heights (see “Specifying the Algorithm,” above).

Parameters for the Uniform Algorithm

For boundary layers that employ the Uniform algorithm, the boundary-layer size specification involves three of the following parameters.

• First-row height

• Growth factor

• Number of rows

• Total depth

The first three parameters listed above are defined as follows (see Figure 3-3).



• The first-row height (a) specifies the distance between the edge or face to which the boundary layer is attached and the first full row of mesh nodes.

• The growth factor represents the ratio

b/a

where b is the distance between the first and second full rows and a is the height of the first row. The distance between any two rows in the boundary layer is equal to the distance between the preceding two rows times the growth factor.

• The number of rows (n) specifies the total number of full rows of mesh nodes in the boundary layer.

All three parameters affect the total depth (D) of the boundary layer.

1

2

3

n

ab

c

D

Figure 3-3: Boundary layer size characteristics—Uniform algorithm



Parameters for the Aspect-Ratio-Based Algorithm

For boundary layers that employ the Aspect ratio based algorithm, the boundary-layer size specification involves three of the following parameters.

• First percent

• Growth factor

• Number of rows

• Last percent

The first three parameters listed above are defined as follows (see Figure 3-4).

• The first percent (F) specifies the height of the first row, at any given edge node, relative to the average length of the edge elements on either side of the node. The effect of the first-percent value on boundary layer row height depends, in part, on whether a given node is interior or exterior to the attachment entity (see below).

• The growth factor represents the ratio

b ai i

where b is the distance between the first and second rows at a given edge node, and a is the height of the first row at the node. The distance between any two rows in the boundary layer at a given edge node is equal to the distance between the preceding two rows times the growth factor.

• The number of rows (n) specifies the total number of full rows of mesh nodes in the boundary layer.

All three parameters affect the last percent of the boundary layer, which represents the height of the uppermost row at a given node as a percent of the edge lengths associated with the node.



aF

l0 0100= ��

�� a

F l li

i i= ��

+��

��

+

100 211 6

F = First percent specification

l0 l1 l2 l3

a1a2

a3

a4

a0

b1

b2

b3

b0

b4

Figure 3-4: Boundary layer size characteristics—Aspect ratio based algorithm

For interior nodes on the attachment entity, the general specification of row height can be expressed mathematically as

aF l l

ii i= ��

��

+��

��

+

100 211 6

where ai is the height of the first row at node i, F is the First percent value specified on the Create Boundary Layer form, and li and li+1 are the lengths of the attachment-entity edge elements on either side of node i.

For exterior nodes on the attachment entity—for example, nodes located at edge endpoints—the row height can be expressed as

aF

l0 0100= ��

��

where a0 is the height of the first row at the exterior node, and l0 is the length of the attachment-entity edge element adjacent to the node.



Specifying Internal Continuity

When you attach a boundary layer to a face that constitutes part of a volume, GAMBIT imprints the boundary layer on all adjoining faces that are also part of the volume (see Figure 3-5(a)). If you attach boundary layers to two or more adjoining faces of a volume, the boundary-layer imprints necessarily overlap on any faces that are shared as common neighbors by the faces to which the boundary layers are attached (see Figure 3-5(b)).

(a)

A

Boundary layer imprintsImprint overlaps

(b)

B

A

Attachment face Attachment faces

Figure 3-5: Boundary-layer imprints

The Internal continuity option on the Create Boundary Layer form determines the manner in which GAMBIT imprints boundary layers on adjoining faces as well as the mesh pattern in regions of imprint overlap.

• If you select the Internal continuity option, GAMBIT does not imprint the boundary layers of adjoining faces onto each other. In addition, GAMBIT modifies the mesh patterns in the overlap regions such that the imprints are “dovetailed” together (see Figure 3-6(a)).

• If you do not select the Internal continuity option, GAMBIT imprints boundary layers on adjoining faces in the manner described above (Figure 3-6(b)).



(a) Internal continuity on

A

B B

A

(b) Internal continuity off

Figure 3-6: Effect of the Internal continuity option

In addition to affecting the mesh pattern in the imprint-overlap regions, the Internal continuity option directly affects which types of meshing schemes are appropriate for volumes to which boundary layers have been applied. For example, the volume shown in Figure 3-6(b) can be meshed using a Map meshing scheme—resulting in the mesh shown in Figure 3-7(a). By contrast, the volume shown in Figure 3-6(a) cannot be meshed using a Map scheme, because the vertex located at the lower right corner of the front face (and imprint overlap region) is necessarily treated as a Side vertex. To mesh the volume shown in Figure 3-6(a), it is most reasonable to apply a Pave meshing scheme to the front face, then apply a Cooper meshing scheme to the volume, using the front and back faces as source faces (see Figure 3-7(b)).



(a) Map volume mesh

(b) Pave face meshCooper volume mesh

Source faces

Figure 3-7: Effect of Internal continuity option on allowable meshing schemes

Specifying the Corner Shape

GAMBIT allows you to control the shape of the mesh in the region surround-ing a Corner or Reversal vertex that connects two edges to which boundary lay-ers are attached. To do so, you must select or unselect (default) the Wedge corner shape option on the Create Boundary Layer form. The Wedge corner shape option produces the following effects (see Figure 3-8):

• If you select the Wedge corner shape option, GAMBIT creates a wedge-shaped boundary-layer region surrounding the connecting vertex (Figure 3-8(a)).

• If you unselect the Wedge corner shape option, GAMBIT creates a block-shaped boundary-layer region surrounding the connecting vertex (Figure 3-8(b)).

If two edges meet at a Corner or Reversal vertex, and each edge possesses a separate boundary layer, then to create a wedge-shaped boundary layer at the corner, you must select the Wedge corner shape option when creating each separate boundary layer.



(a) Wedge corner shape on (b) Wedge corner shape off

Figure 3-8: Effect of Wedge corner shape option

Specifying the Transition Characteristics

The boundary-layer transition characteristics consist of two components:

• Transition pattern

• Number of transition rows

Specifying the Transition Pattern

The transition pattern determines the arrangement of mesh nodes in the region near the outermost row of the boundary layer. Boundary layer transition patterns are defined by the ratio

A:B

where B is the number of mesh intervals in a given row and A is the number of mesh intervals in the immediately preceding full row. GAMBIT allows you to specify any of four transition patterns—1:1, 4:2, 3:1, or 5:1.

Figure 3-9 shows four different two-row boundary layers representing each of the four transition patterns listed above.



(a) 1:1 (b) 4:2

(c) 3:1 (d) 5:1

Figure 3-9: Boundary layer transition patterns

u NOTE: Edges can host any of the four transition patterns, but faces can host only the 1:1 transition pattern.

Specifying the Number of Transition Rows

When you specify any transition pattern other than 1:1, you must also specify the number of transition rows—that is, the number of outermost rows to which the transition pattern is applied. GAMBIT applies the 1:1 pattern to all rows other than the transition rows. Figure 3-10 shows the effect of the number of transition rows on a boundary layer consisting of three rows with the transition pattern 4:2.



(a) One transition row (b) Two transition rows

Figure 3-10: Effect of number of transition rows

Specifying the Attachment Entity and Direction

To define the location of a boundary layer, you must specify the edge or face to which the boundary layer is attached. If the edge or face is shared by two or more faces or volumes, respectively, you must also specify the face or volume that defines the direction of the boundary layer. For example, each edge of a rectangular brick volume is shared by two rectangular faces. If you attach a boundary layer to one of the edges of the volume, you must specify which of the corresponding faces defines the direction of the boundary layer.

When you specify an edge or face to which to attach a boundary layer, GAMBIT highlights the edge or face in the graphics window and displays the following items:

• The boundary layer as currently specified

• An arrow that indicates the direction of the boundary layer

You can change the direction of the boundary layer either by means of the Attachment (Edge or Face) list box on the Create Boundary Layer form or by means of the mouse.



Changing Direction by Means of the List Box

When you specify an edge or face in the Attachment list box on the Create Boundary Layer form, the list box displays both the specified entity itself and the face or volume that defines the direction of the boundary layer. To change the direction of the boundary layer by means of the list box, you can perform either of the following operations.

1) Specify the edge or face again in the Attachment list box

2) Use the Edge List or Face List paired pick-list form to specify the entity and direction of the boundary layer (see “Using the Edge List or Face List Form,” below).

Changing Direction by Means of the Mouse

To change the direction of the boundary layer by means of the mouse, Shift-middle-click the entity to which the boundary layer is attached.

Specifying Multiple Boundary Layers

GAMBIT allows you to apply a given boundary layer definition to more than one edge or face at a time. To do so, you must include in the Attachment entity pick list all of the entities to which the currently defined boundary layer is to be attached.

You can add an edge or face to the Attachment entity pick list on one of the following ways:

• Input the entity name directly in the Attachment list box or select the entity from the entity pick-list form

• Pick the entity in the graphics window



Using the Create Boundary Layer Form

To open the Create Boundary Layer form (see below), click the Create Boundary Layer command button on the Mesh/Boundary Layer subpad.

The Create Boundary Layer form contains the following specifications.

R Show displays the boundary layer(s) in the graphics window as they are created and defined.



Definition: —————————————————————————

Algorithm: contains two radio buttons that specify the boundary layer algorithm. GAMBIT provides two algorithm options:

• Uniform

• Aspect ratio based

For a description of the algorithm options, see “Specifying the Algorithm,” above.

First row (a) (Uniform algorithm only) specifies the height of the row nearest to the edge or face to which the boundary layer is attached (see “Parameters for the Uniform Algorithm,” above).

First percent (Aspect ratio based algorithm only) specifies the height of the row nearest to the edge or face to which the boundary layer is attached as a percentage of the edge element length on the attachment entity (see “Parameters for the Aspect-Ratio-Based Algorithm,” above).

Growth –��– factor (b/a)

specifies the growth factor—that is, the ratio of the height of each row relative to that of the immediately preceding row.

Rows –��– specifies the total number of rows in the boundary layer.

Depth (D) (Uniform algorithm only) specifies the total depth of the boundary layer.

Last percent (Aspect ratio based algorithm only) specifies the height of the uppermost boundary layer row as a percentage of the edge element length on the attachment entity.

R Internal continuity

specifies that boundary-layer imprints are dovetailed in overlapping regions (see “Specifying Internal Continuity,” above).

R Wedge corner shape

specifies that the boundary-layer forms a wedge shape in the region surrounding a Corner or Reversal vertex (see “Specifying the Corner Shape,” above).



Transition Pattern:

contains four radio buttons that specify the transition pattern. The pattern options are 1:1, 4:2, 3:1, and 5:1. (See “Specifying the Transition ,” above.)

Transition –��–

Rows

specifies the number of transition rows for transition pat-terns 4:2, 3:1, and 5:1. (NOTE: You must use the slide bar, rather than the associated text box, to set the number of transition rows.)

Attachment: —————————————————————————

Edges q Faces

specifies whether the boundary layer is attached to an edge or a face.

Edges ¬ Faces

specifies the edge or face to which the boundary layer is attached. (NOTE: When you click the pick list button on the Attachment entity list box, GAMBIT opens a paired pick list form titled Edge List or Face List. For instructions in using the paired pick list form, see “Using the Edge List or Face List Form,” below.)

Label specifies a label for the boundary layer.



Using the Edge List or Face List Form

When you specify an edge or face to which a boundary layer is attached, GAMBIT adds the edge or face to a paired pick list. The paired pick list includes both the attachment entity itself (edge or face) and the entity that defines the direction of the boundary layer (face or volume). You can modify the edge or face paired pick list by means of either the Edge List or Face List pick-list form, respectively. Both forms operate according to the following general principles described for the Edge List form.

To open the Edge List form (see below), select Edge in the Attachment field on the Create Boundary Layer form and click the associated pick list button.

The Edge List paired pick-list form operates in a manner similar to that of con-ventional pick-list forms (see GAMBIT User’s Guide, Chapter 3). It differs from the conventional forms only in that the Picked scroll list includes two columns.

• The left column lists the edge to which the boundary layer is attached.

• The right column lists the face that defines the direction of the bound-ary layer.



When you add an edge to the Picked scroll list by means of the right-arrow command button, GAMBIT adds the edge to the Edge column and automati-cally includes one of its associated faces in the Face column. (The face defines the direction of the boundary layer.) If you add the same edge again to the Picked scroll list, GAMBIT creates a second entry for the edge in the Edge column and includes another of its associated faces in the Face column. When the Face column includes all faces associated with a given edge, GAMBIT removes that edge from the Available column.



Modify Boundary Layer

The Modify Boundary Layer command allows you to modify the specifications for any existing boundary layer.

Using the Modify Boundary Layer Form

To open the Modify Boundary Layer form (see below), click the Modify Boundary Layer command button on the Mesh/Boundary Layer subpad.

(For a description of the options and specifications available on the Modify Boundary Layer form, see “Create Boundary Layer,” above.)



Modify Boundary Layer Label

The Modify Boundary Layer Label command allows you to change the label associated with any boundary layer.

Using the Modify Boundary Layer Label Form

To open the Modify Boundary Layer Label form (see below), click the Modify Label command button on the Mesh/Boundary Layer subpad.

The Modify Boundary Layer Label form includes the following specifications.

B.L. ¬ specifies the boundary layer to be modified.

Label specifies a new label for the boundary layer.



Summarize Boundary Layers

The Summarize Boundary Layers command displays one or more existing boundary layers in the graphics window.

Using the Summarize Boundary Layers Form

To open the Summarize Boundary Layers form (see below), click the Summarize command button on the Mesh/Boundary Layer subpad.

The Summarize Boundary Layers form contains the following specification.

B.L.s ¬ specifies the boundary layer(s) for which summary information is to be displayed.



Delete Boundary Layers

The Delete Boundary Layers command allows you to delete one or more exist-ing boundary layers.

Using the Delete Boundary Layers Form

To open the Delete Boundary Layers form (see below), click the Delete com-mand button on the Mesh/Boundary Layers subpad.

The Delete Boundary Layers form includes the following specification.

B.L.s ¬ specifies the boundary layer(s) to be deleted.

MESHING THE MODEL Edge Meshing Commands


3.2 Edge Meshing Commands

The following commands are available on the Mesh/Edge subpad.


Mesh Edges Creates mesh nodes along edges

Set Edge Element Type Specifies edge element types used throughout the model

Link Edge Meshes Unlink Edge Meshes

Creates and deletes mesh hard links between edges

Split Meshed Edge Splits an edge at a mesh node

Summarize Edge Mesh Displays mesh grading information

Delete Edge Meshes Deletes existing mesh nodes from edges


Edge Meshing Commands MESHING THE MODEL


3.2.1 Mesh Edges

The Mesh Edges command allows you to grade or mesh any or all edges in the model. When you grade an edge, GAMBIT applies the mesh node spacing specifications but does not create mesh nodes on the edge. When you mesh an edge, GAMBIT creates mesh nodes according to the specifications.

To perform a grading or meshing operation, you must specify the following parameters:

• Edge(s) to which the grading specifications apply

• Grading scheme

• Mesh node spacing (number of intervals)

• Edge meshing options

Specifying Edges

When you specify one or more edges for a grading or meshing operation, you must specify the following options:

• Soft-link

• Reverse

When you soft-link two or more edges, GAMBIT links the edges for meshing purposes so that any grading or meshing specifications applied to one edge can be simultaneously applied to the other edges as well. When you reverse an edge, GAMBIT reverses the sense of the edge; therefore, any directional grading scheme associated with the edge is also reversed.

In addition to the soft-link and reverse options described above, GAMBIT allows you to specify whether or not to impose the grading parameters of the first edge specified in the Edges list on all other parameters in the list (see “Imposing First-Edge Grading and Spacing Parameters,” below).

Soft-linking Edges

When you specify more than one edge for a grading or meshing operation, GAMBIT allows you to create soft links between the specified edges. When you grade or mesh an edge that is soft-linked to other edges, you can simulta-neously apply the grading or meshing specifications to all of the edges that are soft-linked to the specified edge.



Forming, Maintaining, and Breaking Soft Links

When you specify two or more edges for a grading or meshing operation, you must specify the status of any soft links that involve the edges. The three soft-link status options are as follows:

• Form—forms soft links between the edges

• Maintain—maintains all existing soft links that involve the edges

• Break—breaks any existing soft links that involve the edges

When you Form soft links between two or more edges, GAMBIT creates a “chain” of links between the specified edges. If you form a soft link involving an edge that is part of an existing soft-link chain, GAMBIT breaks the existing soft link associated with the edge. That is, no single edge is allowed to consti-tute part of more than one soft-link chain.

When you Maintain soft links, GAMBIT does not form or break any existing soft links associated with the specified edge(s).

When you Break a soft link associated with an edge, GAMBIT removes the edge from the soft-link chain but does not break any other soft links in the chain. That is, any other edges that are part of the soft-link chain remain soft-linked to each other.

Grading or Meshing Soft-link Chains

When you grade or mesh an edge that constitutes part of an existing soft-link chain, GAMBIT allows you to specify whether the grading or meshing speci-fications apply to all edges that belong to the chain (the Pick with links option). The general rules pertaining to the Pick with links option are as follows.

• To grade or mesh all edges that belong to an existing chain, select the Pick with links option on the Mesh Edges form and specify one of the edges that belongs to the chain.

• To grade or mesh an edge that constitutes part of a soft-link chain without grading or meshing the other edges in the chain, unselect the Pick with links option before specifying the edge. To maintain all links between the specified edge and all edges to which it is soft-linked, select the Soft links:Maintain option before specifying the edge.



Reversing Edges

When you mesh an edge using a non-uniform grading scheme, GAMBIT grades or meshes the edge relative to its sense. For example, if you mesh an edge using a First Length scheme (see below) and specify a first interval length of 2, GAMBIT locates the first mesh node at a distance of 2 units from the edge start vertex.

When you specify edges for a grading or meshing operation, GAMBIT allows you to change their respective senses by means of the Reverse command button on the Mesh Edges form. If you reverse the sense of an edge the grading of which is non-uniform, the grading or meshing scheme is also reversed. For example, if you mesh an edge using a First Length grading scheme and specify a first interval length of 2, then click Reverse to reverse the sense of the edge, GAMBIT meshes the edge such that the last mesh node is located at a distance of 2 from the edge end vertex.

If you apply the Reverse option to an edge that is part of a soft-link chain and select the Pick with links option, GAMBIT reverses the sense and, therefore, the grading of all edges in the chain.

Imposing First-Edge Grading and Spacing Parameters

When you specify a set of edges for grading and/or meshing, you can also determine whether or not to impose the grading parameters of the first edge specified in the Edges list on all other edges in the list. To impose the first-edge grading and/or spacing parameters on the other specified edges, you must select the Use first edge settings option on the Mesh Edges form. By default, the Use first edge settings option is selected.

Grading Parameters

If you specify a set of edges at least one of which differs from the others with respect to its Grading parameters, the Use first edge settings option produces the following effects on the Grading section of the Mesh Edges form.

• If you select the Use first edge settings option, the Grading settings remain active and display the settings of the first edge specified in the Edges list.

• If you unselect the Use first edge settings option and select an edge the grading parameters of which differ from the currently displayed para-meters, the Grading settings become inactive and the displayed settings are those of the most recently selected edge.



Spacing Parameters

The behavior of the Spacing section of the Mesh Edges form is identical to that of the Grading section (see above) with respect to the Use first edge settings option.

u NOTE: The Grading and Spacing sections of the Mesh Edges form behave independently of each other with respect to the Use first edge settings option.

Specifying the Grading Scheme

GAMBIT provides the following types of edge mesh grading schemes.

• Successive Ratio

• First Length

• Last Length

• First Last Ratio

• Last First Ratio

• Exponent

• Bi-exponent

• Bell Shaped

The first six schemes listed above are non-symmetric schemes—that is, they can produce grading patterns that are not necessarily symmetric about the center of the edge. The last two schemes are symmetric schemes—that is, they are constrained to produce grading patterns that are symmetric about the center of the edge.

Non-Symmetric Grading Schemes

For each of the non-symmetric grading schemes, GAMBIT positions mesh nodes along the edge such that the ratio of any two succeeding interval lengths is constant. That is,

ll

Ri

i

+ =1

where li and li+1 are the lengths of intervals i and i+1, respectively, and R is a fixed value (see Figure 3-11). For any given number of intervals (n), the grading schemes differ from each other only with respect to the manner in which GAMBIT determines the value of the interval length ratio, R.



. . .

Start End

Interval lengths

ll

Ri

i

+ = =1 Constant

Mesh node location

l1 l3l2 lnln-1

Figure 3-11: Edge mesh grading parameters

u NOTE: When you mesh an edge, GAMBIT positions the mesh nodes based, in part, on the edge element type as currently specified on the Set Edge Element Type form (see “Set Edge Element Type,” below).

• If you specify 2-node edge elements, GAMBIT creates mesh nodes only at the endpoints of the edge mesh intervals.

• If you specify 3-node edge elements, GAMBIT creates an additional mesh node at the center of each mesh interval.

For example, if you specify the 3-node edge element type and grade an edge such that it includes five mesh intervals, GAMBIT creates 11 mesh nodes on the edge. Six of the mesh nodes define the endpoints of the mesh intervals; the other five are located at the centers of the intervals.

The mesh node locations presented throughout this section are based on the 2-node edge element type.



Grading Scheme Input Parameters

For all non-symmetric grading schemes other than the Exponent scheme, the interval length ratio, R, is a function of the following parameters:

• Total edge length, L

• Number of intervals, n

• Length of the first interval (l1) or last interval (ln) on the edge

For the Exponent scheme, R is a function of L, n, and a user-specified input parameter, x.

The following table lists the formulas that GAMBIT uses to determine the interval length ratios (R) for each of the non-symmetric grading schemes. The table also lists the pertinent input parameters and the corresponding titles of the input fields on the Mesh Edges form.

Scheme Formula Parameter Field Title

Successive Ratio None R Ratio

First Length R

Ll

i

i

n-

=

Ê =1

1 1

l1 Length

Last Length R

Ll

i n

i

n

n

-

=

Ê =1

ln Length

First Last Ratio R

lln

n

=��- -

1

1 1/1 6

lln

1 Ratio

Last First Ratio R

lln

n

=��

-

1

1 1/1 6

lln

1

Ratio

Exponent R eL

n x=

-4 94 912 x Ratio



As an example of the differences between input parameters for the non-sym-metric grading schemes, consider the straight, graded edge shown in Figure 3-12. The edge possesses a length of 15 units (L = 15) and is to be graded such that it contains four intervals (n = 4), each of which is twice as long as the previous interval (R = 2).

Edge length: L = 15Number of intervals: n = 4Ratio: R = 2

Start End

l1 = 1 l2 = 2 l3 = 4 l4 = 8

Figure 3-12: Edge grading example

The grading parameters required by each of the non-symmetric schemes to create the grading shown in Figure 3-12 are as follows.

Scheme Ratio Length

Successive Ratio 2

First Length 1

Last Length 8

First Last Ratio 0.125

Last First Ratio 8

Exponent 0.6848



Double-Sided Grading

When you grade or mesh an edge using a non-symmetric scheme, you must specify whether the grading scheme is single-sided or double-sided. Double-sided grading differs from single-sided grading in that the edge is divided into two separate segments for grading purposes, and each segment is graded according to its own grading parameter. (NOTE: GAMBIT does not allow you to specify different grading schemes for each segment.) If you specify more than one edge and select a double-sided grading scheme, GAMBIT applies the double-sided scheme to all edges in the set of specified edges.

u NOTE: Double-sided grading is not explicitly available for the Exponent grad-ing scheme. To apply an Exponent scheme to two segments of a single edge, use the Bi-exponent symmetric grading scheme (see below).

Center of Grading

When you specify double-sided grading, GAMBIT positions either a node or an interval at the center of grading for the edge. The form of the grading center (node or interval) depends on the total number of edge intervals (n) as follows (see Figure 3-13).

• If n is even, GAMBIT locates a mesh node at the center of grading.

• If n is odd, GAMBIT locates a mesh interval at the center of grading.



Start End

Center node (n even)

. . .l2 1,l1 1,. . . l2 2, l1 2,ln�,1 ln�,2

Segment 1 Segment 2

Start End

Center interval (n odd)

. . .l2 1,l1 1, . . . l2 2, l1 2,l ln n� �, ,1 2 ,

Segment 1Segment 2

Rl

li

i1

1 1

1

= + ,

,

Rl

li

i1

1 2

2

= + ,

,

Figure 3-13: Double-sided grading—location of grading center

The location of the center node (n even) or the location and size of the center interval (n odd) is determined according to the following rules.

• If n is even, GAMBIT grades the edge such that the lengths of the intervals on either side of the center node are equal.

• If n is odd, GAMBIT grades the edge such that the length of the center interval conforms to the meshing parameters specified for both seg-ments of the edge.

As an example of the effect of interval number on double-sided grading, con-sider the edge shown in Figure 3-14. The edge possesses a length of 8 units and is to be graded such that R1 =1.5 and R2 = 1.0.



Start End

L = 8

Rlli

i1

1 1

1

= =+ ,

,

1.5 Rlli

i2

1 2

2

= =+ ,

,

1.0

Figure 3-14: Double-sided grading scheme—example

Figure 3-15 and Figure 3-16 show the effect of specifying 7 and 8 intervals, respectively, on the grading of the edge shown in Figure 3-14.



Start End

R2 = 1.0

R1 = 1.5

Center interval

l1 1, l2 1, l l4 1 4 2, ,= l3 2, l2 2, l1 2,l3 1,

n = 7

Figure 3-15: Double-sided grading scheme, n = 7

Start End

R2 = 1.0

R1 = 1.5

Center node

l4 1, l4 2,

n = 8

l3 1,l2 1,l1 1, l3 2, l2 2, l1 2,

Figure 3-16: Double-sided grading scheme, n = 8



The following table lists the interval lengths for the double-sided grading schemes shown in Figure 3-15 and Figure 3-16.

Interval Figure 3-15 (n = 7) Figure 3-16 (n = 8)

1 0.44 0.37

2 0.66 0.56

3 0.99 0.83

4 1.48 1.25

5 1.48 1.25

6 1.48 1.25

7 1.48 1.25

8 1.25

Note that, if you specify seven intervals for the edge (n = 7), GAMBIT grades the edge such that the length of the center interval satisfies the grading ratios for both edge segments (see Figure 3-15). That is,

l l4 1 4 2, ,= = 1.48

ll4 1

3 1

,

,

= =1.48

0.991.5

and ll4 2

3 2

,

,

= =1.48

1.481.0 .

If you specify eight intervals for the edge (n = 8), GAMBIT grades the edge such that the lengths of the intervals on either side of the center node are equal (see Figure 3-16). That is,

l l4 1 4 2, ,= = 1.25

ll4 1

3 1

,

,

= =1.25

0.831.5

and ll4 2

3 2

,

,

= =1.25

1.251.0 .



Double-Sided Grading Input Parameters

When you grade or mesh an edge by means of a double-sided grading scheme, you must specify grading parameters for both segments of the edge. The fol-lowing table lists double-sided grading input parameters as they appear on the Mesh Edges form for each of the available grading schemes. (For descriptions of the parameters, see Figure 3-13.)

Scheme Parameter Field Title

Successive Ratio R1

R2

Ratio 1 Ratio 2

First Length l1 1,

l1 2,

Length 1 Length 2

Last Length ln� ,1

ln� ,2

Length 1 Length 2

First Last Ratio lln

1 1

1

,

,�

lln

1 2

2

,

,�

Ratio 1

Ratio 2

Last First Ratio lln� ,

,

1

1 1

lln� ,

,

2

1 2

Ratio 1

Ratio 2

As an example of the specification of double-sided grading input parameters, consider the examples shown in Figure 3-15 and Figure 3-16, above. The fol-lowing tables list the parameters that are required to create the grading schemes shown in the figures.



Double-sided grading input parameters, Figure 3-15 (n = 7):

Scheme Ratio 1 Ratio 2 Length 1 Length 2

Successive Ratio 1.5 1

First Length 0.44 1.48

Last Length 1.48 1.48

First Last Ratio 0.297 1

Last First Ratio 3.36 1

Double-sided grading input parameters, Figure 3-16 (n = 8)

Scheme Ratio 1 Ratio 2 Length 1 Length 2

Successive Ratio 1.5 1

First Length 0.37 1.25

Last Length 1.25 1.25

First Last Ratio 0.297 1

Last First Ratio 3.36 1

Symmetric Grading Schemes

GAMBIT provides two symmetric grading schemes for edge meshing:

• Bi-exponent

• Bell Shaped

Both schemes grade a given edge such that mesh node placement is symmetric about the center of the edge. The schemes differ from each other in the manner in which GAMBIT determines the mesh node spacing along the edge.

Bi-Exponent Scheme

The Bi-exponent scheme divides the edge into two segments of equal length and applies the Exponent grading scheme separately to each segment. The Exponent input parameter, x—specified by means of the Ratio field on the Mesh Edges form—produces the following grading characteristics for the Bi-exponent scheme.



x Grading Characteristic

< 0.5 Mesh nodes are densest near the center of grading and least dense near the endpoints of the edge.

= 0.5 Mesh nodes are evenly spaced along the entire edge.

> 0.5 Mesh nodes are densest near the endpoints of the edge and least dense near the center of grading.

Bell Shaped Scheme

The Bell Shaped scheme grades the edge such that the mesh node density obeys a normal distribution centered at the geometric center of the edge. The user-specified input parameter for the Bell Shaped scheme—specified by means of the Ratio field on the Mesh Edges form—produces grading characteristics identical to those shown above for the Bi-exponent scheme.

Specifying Node Spacing

The interval length ratio, R, is a function of both the edge length, L, and the number of intervals, n (see above). GAMBIT provides three different ways to specify the number of intervals on an edge.

• Interval count

• Interval size

• Shortest edge (%)

Interval Count

When you select the Interval count option, you must input the actual number of mesh intervals to be placed on the edge. GAMBIT grades or meshes the edge with enough nodes to result in the specified number of intervals. That is,

m n= +1

where m is the total number of mesh nodes on the edge, including the end-points. For example, if you specify an interval count of 6 (n = 6), GAMBIT grades or meshes the edge with 7 nodes (m = 7), thereby creating 6 intervals on the edge.



Interval Size

When you select the Interval size option, you must input an interval length. GAMBIT uses the interval length to determine the total number of intervals on the edge according to the following equation:

nLd

=

where n is the number of intervals on the edge, L is the edge length, and d is the interval size (user input). If n is a non-integer, GAMBIT rounds to the nearest whole number to determine the number of intervals on the edge.

Shortest Edge (%)

When you select the Shortest edge (%) option, you must input an interval size value expressed as a percentage of edge length. GAMBIT calculates the global interval size (d) for the current edge-meshing operation as follows:

dx

L= ��100 min

where x is the Shortest edge (%) input value, and Lmin is the length of the short-est edge currently existing in the entire model. (NOTE: When you select the Shortest edge (%) option, GAMBIT highlights the graphics window display of the shortest edge.)

GAMBIT uses the resulting value of d to calculate the total numbers of inter-vals for all edges specified for the current edge-meshing operation. For exam-ple, if the shortest edge in the model is 10 units in length, and you mesh an edge that is 30 units long and specify the Shortest edge (%) option with x = 20 (%), GAMBIT calculates the number of intervals, n, on the meshed edge as follows:

nd

= �� = �

��

�

�

��

�

�

��=30 30

20100

1015

1 6 .

Therefore, GAMBIT creates 15 intervals on the meshed edge.



Specifying Edge Meshing Options

GAMBIT provides the following edge meshing options:

• Mesh

• Remove old mesh

• Ignore size functions

If you select the Mesh option, GAMBIT creates mesh nodes when it applies the grading specifications listed on the Mesh Edges form. If you Apply the cur-rently specified parameters without selecting the Mesh option, GAMBIT applies the node distribution parameters to the edge(s) but does not create mesh nodes.

If you select the Remove old mesh option, GAMBIT deletes any currently existing mesh and/or grading information from the specified edge(s).

If you select the Ignore size functions option, GAMBIT ignores any existing size-function specifications that would otherwise affect the edge mesh.



Using the Mesh Edges Form

To open the Mesh Edges form (see below), click the Create Mesh command button on the Mesh/Edge subpad.

The Mesh Edges form contains the following options and specifications.

Edge and Soft-link Specifications

Edges ¬ specifies one or more edges to which the currently specified grading and/or meshing operations apply.

R Pick with links

specifies that all edges hard-linked or soft-linked to the picked edge(s) are graded and/or meshed according to the currently specified grading scheme.



Reverse reverses the sense and grading of all specified edges.

NOTE: If the Pick with links option is selected (see above), the Reverse command button reverses the sense of all edges selected by means of the Edges list box as well as all edges linked to those edges.

Soft link —————————————————————————

Form q Break Maintain

specifies whether soft links are formed, broken, or main-tained during the edge meshing process.

• Form—forms soft links between all specified edges

• Break—breaks existing soft links associated with the specified edges

• Maintain—maintains all current soft links

R Use first edge settings

imposes the grading and spacing parameters of the first edge specified in the Edges list on all other edges in the list.

Grading —————————————————————————

R Apply specifies that the currently displayed grading specifications are applied to all picked edges.

Default resets grading specifications to their default values.

Type ————————————————————————

Successive Ratio q First Length Last Length First Last Ratio Last First Ratio Exponent Bi-exponent Bell Shaped

specifies the grading scheme (see “Specifying the Grading Scheme,” above).



Invert converts currently specified grading-scheme lengths or ratios into their reciprocal values. For example, if you specify Successive Ratio grading with a First Ratio of 2.5, the Invert command button converts the First Ratio to 0.4. That is,

1

2.50.4= .

R Double sided specifies that all specified edges are graded according to a double-sided scheme. (NOTE: This option is not available for the Exponent, Bi-exponent, or Bell Shaped schemes.)

Grading Parameters

The middle section of the Mesh Edges form contains slide bars that allow you to specify grading parameters. GAMBIT displays only those slide bars that are applicable to the currently specified grading scheme. The following subsec-tions describe the parameters associated with the slide bars for each of the five grading types. For a detailed description of the parameters associated with each type of grading, see “Grading Scheme Input Parameters,” above.

Successive-Ratio Parameters

Ratio –��– (single-sided) specifies the ratio of successive interval lengths (R) along all specified edges.

Ratio 1 –��– (double-sided) specifies the ratio of successive interval lengths (R) along the segments of all specified edges nearest to their respective start vertices.

Ratio 2 –��– (double-sided) specifies the value of R along the seg-ments of all specified edges nearest to their respective end vertices.



First-Length Parameters

Length –��– (single-sided) specifies the length of the first interval on all specified edges (l1).

Length 1 –��– (double-sided) specifies the length of the first interval on the segments of the specified edges nearest to their respective start vertices (l1 1, ).

Length 2 –��– (double-sided) specifies the length of the first interval on the segments of the edges nearest to their respective end vertices (l1 2, ).

Last-Length Parameters

Length –��– (single-sided) specifies the length of the last interval on all specified edges (ln).

Length 1 –��– (double-sided) specifies the length of the last interval on the segments of the edges nearest to their respective start vertices (ln� ,1).

Length 2 –��– (double-sided) specifies the length of the last interval on the segments of the edges nearest to their respective end vertices (ln� ,2 ).



First-Last Ratio Parameters

Ratio –��– (single-sided) specifies the ratio of the first interval length to the last interval length on the specified edges (l ln1 ).

Ratio 1 –��– (double-sided) specifies the ratio of the first interval length to the last interval length on the segments of the specified edges nearest to their respective start vertices (l ln1 1 1, ,� ).

Ratio 2 –��– (double-sided) specifies the ratio of the first interval length to the last interval length on the segments of the specified edges nearest to their respective end vertices (l ln1 2 2, ,� ).

Last-First Ratio Parameters

Ratio –��– (single-sided) specifies the ratio of the last interval length to the first interval length on the specified edges (l ln 1 ).

Ratio 1 –��– (double-sided) specifies the ratio of the last interval length to the first interval length on the segments of the specified edges nearest to their respective start vertices (l ln� , ,1 1 1 ).

Ratio 2 –��– (double-sided) specifies the ratio of the last interval length to the first interval length on the segments of the specified edges nearest to their respective end vertices (l ln� , ,2 1 2 ).

Exponent Parameter

Ratio –��– specifies the input parameter, x, that determines the ratio (R) of successive interval lengths for the Exponent grading scheme (see above).



Bi-exponent Parameter

Ratio –��– specifies the input parameter, x, that determines the ratio (R) of successive interval lengths for the Bi-exponent grading scheme (see above).

Bell Shaped Parameter

Ratio –��– specifies the input parameter, x, that determines the shape of the mesh node distribution for the Bell Shaped grading scheme.

Mesh Node Spacing Parameters

Spacing —————————————————————————

R Apply specifies that the currently displayed spacing parameters are applied to all specified edges.

Default resets mesh node spacing specifications to their default values.

Interval size q Interval count Shortest edge (%)

specifies the method used to determine the total number of mesh nodes on any edge. The three available methods are as follows:

• Interval size—specifies the size of intervals (constant ratio grading only)

• Interval count—specifies the number of intervals along the edge

• Shortest edge (%)—specifies that the interval size represents a percentage of the length of the shortest edge in the list of specified edges

Value specifies a numerical value associated with the method used to determine the total number of intervals on any edge.



Grading and Meshing Options

Options —————————————————————————

R Mesh specifies that the edges are to be meshed. If you do not specify the Mesh option, GAMBIT grades but does not create mesh nodes on the edges.

R Remove old mesh

specifies that any existing mesh nodes and/or elements are removed from the edges.

R Ignore size functions

specifies that GAMBIT ignores any existing size-function specifications that would otherwise affect the edge mesh.



3.2.2 Set Edge Element Type

The Set Edge Element Type command allows you to specify the number of edge nodes upon which all face and volume meshes are based.

The edge element type determines the number of edge mesh nodes corre-sponding to face and volume elements in the model. There are two edge element type options:

• 2 node

• 3 node

When you specify the 2 node option, GAMBIT creates meshes such that every edge node constitutes one endpoint of an mesh edge element and, therefore, one corner of a mesh face or volume element. When you specify the 3 node option, GAMBIT creates an additional mesh node in the center of each edge mesh element. As a result, only two out of every three edge mesh nodes con-stitute corners of mesh face or volume elements.

Figure 3-17 shows the effect of edge element type on quadrilateral face mesh elements. In Figure 3-17(a), the edge element type is specified as 2 node, therefore, each edge mesh node constitutes one corner of a face element. In Figure 3-17(b), the edge element type is specified as 3 node, therefore, only two out of every three edge mesh nodes constitute corners of face elements.



(a) 2 node (b) 3 node

Face mesh elements

Edges

Figure 3-17: 2 node and 3 node edge element types

The Effect on Face and Volume Element Types

When you change the edge element type specification, GAMBIT automati-cally changes all corresponding face and volume element types. Likewise, when you change the face or volume element types, GAMBIT automatically changes the edge element type. The following table summarizes the general correspondence between GAMBIT edge, face, and volume element types.

Edge Face Volume

Nodes Shape Nodes Shape Nodes

2 Triangle Quadrilateral

3 4

Tetrahedral Hexahedral

Wedge

Pyramid

4 8

6

5

3 Triangle

Quadrilateral

6

9

Hexahedral

Tetrahedral

Wedge Pyramid

27

10

18 13



For a description of the face and volume element types listed above, see “Set Face Element Type” and “Set Volume Element Type,” below.

Using the Set Edge Element Type Form

To open the Set Edge Element Type form (see below), click the Set Edge Element Type command button on the Mesh/Edge subpad.

The Set Edge Element Type form contains the following options.

l 2 node specifies that the mesh is based on two-node edge mesh elements.

l 3 node specifies that the mesh is based on three-node edge mesh elements.



3.2.3 Link/Unlink Edge Meshes

The Link/Unlink Edge Meshes command button allows you to perform the fol-lowing operations.


Link Edge Meshes Creates hard links between edges

Unlink Edge Meshes Deletes hard links between edges




Link Edge Meshes

The Link Edge Meshes command allows you to create a hard link between two or more edges. When you create hard links between edges in a set, GAMBIT associates the edges with each other such that any meshing or splitting operation applied to one or more of the edges is similarly applied to all edges in the set. For example, if you grade or mesh an edge that is hard-linked to another edge, GAMBIT grades or meshes both edges according to the grading scheme and parameters applied to the specified edge. Likewise, if you split an edge that is hard-linked to another edge, GAMBIT splits both edges.

Linking Edge Endpoint Vertices

When you hard-link a set of edges, GAMBIT automatically creates hard links between the endpoint vertices of the edges. The links are created such that the start endpoint vertices of all edges in the set are hard-linked to each other, and the end endpoint vertices of all edges in the set are hard-linked to each other.

GAMBIT does not allow you to hard-link two edges if their endpoint vertices are already linked to each other by means of an existing hard link. For example, consider the set of connected edges shown in Figure 3-18.

edge.1 edge.4

Link 1

edge.2

edge.3

Link 2

vertex.2 vertex.3

vertex.4vertex.1

Figure 3-18: Edge hard-link restriction—example



If you create a hard link between edge.1 and edge.4 (Link 1), GAMBIT does not allow you to also create a hard link between edge.2 and edge.3 (Link 2), because vertex.1 and vertex.2 are already linked to vertex. 3 and vertex.4, respectively.

Reversing the Grading Orientation

When you select an edge for hard-linking, GAMBIT allows you to reverse the orientation of grading on the edge relative to its start and end endpoint vertices. To reverse the grading orientation of an edge, Shift-middle-click the edge in the graphics window when selecting it for hard-linking. (NOTE: If you reverse the grading orientation, GAMBIT does not change the sense of the edge.)

As an example of the effect of reversing the grading orientation, consider the two hard-linked edges shown in Figure 3-19, one of which is meshed using a successive-ratio grading scheme with a first ratio of 2.

edge.1

Mesh nodes

a) Without reverse orientation

�

�

edge.2

edge.1

b) With reverse orientation

edge.2

Start vertices

End vertices

Figure 3-19: Linked edge meshes—effect of reverse orientation

If you do not reverse the grading orientation of either edge, the grading scheme for edge.1 is exactly duplicated on edge.2 (see Figure 3-19(a)). If you do reverse the grading orientation, the grading scheme on edge.2 is exactly reversed relative to that of edge.1 (see Figure 3-19(b)).



Specifying the Periodic Option

The Link Edge Meshes command includes a Periodic option that allows you to specify that the edges are periodically linked. Periodically linked edges are constrained such that they must behave identically to each other with respect to any virtual edge-split and vertex-move operations.

As an example of the effect of periodic linking, consider the square, planar face shown in Figure 3-20, two edges (edge.1 and edge.3) of which are hard-linked to each other.

(a) (b)

edge.1 edge.3

v_vertex.5 v_vertex.6Split point

v_edge.5 v_edge.7

v_edge.8v_edge.6Linked edges

Figure 3-20: Virtual splitting of two hard linked edges

If you perform a virtual split of edge.1 at the split point shown in Figure 3-20(a), GAMBIT splits both edges to create the geometric entities shown in Figure 3-20(b). (NOTE: In this example, the hard link was created such that the grading orientations of edge.1 and edge.3 point in the same direction, therefore v_edge.5 and v_edge.7 are equal in length. If the grading orientations had opposed each other when the link was created, v_edge.8 would be equal in length to v_edge.5, and v_edge.7 would be equal in length to v_edge.6).



If you move v_vertex.5 in Figure 3-20 by means of the Slide Virtual Vertex command (see Section 2.2.2), the final state of v_vertex.6 depends on two factors:

• The state of the Move with links option on the Slide Virtual Vertex form

• Whether or not the link between edge.1 and edge.3 is Periodic

Specifically, the rules governing the vertex move can be summarized as follows (see Figure 3-21):

Periodic link Move with links option Move v_vertex.6 Figure 3-21

Yes On Yes (a)

Yes Off Yes (a)

No On Yes (a)

No Off No (b)

For example, if edge.1 and edge.3 are periodically linked, GAMBIT moves v_vertex.6 regardless of the state of the Move with links option. Likewise, if you specify the Move with links option, GAMBIT moves v_vertex.6 regardless of whether the link between edge.1 and edge.3 is periodic.



(b) v_vertex.6 unmoved

v_vertex.5

v_vertex.6

(a) v_vertex.6 moved


Figure 3-21: v_vertex.6 move states—Periodic and Move with links options

Using the Link Edge Meshes Form

To open the Link Edge Meshes form (see below), click the Link command button on the Mesh/Edge subpad.

The Link Edge Meshes form contains the following specifications.

Edges ¬ specifies the edges to be hard-linked.

R Periodic specifies that the edges are to be periodically linked.



Unlink Edge Meshes

The Unlink Edge Meshes command allows you to delete existing hard links associated with one or more edges. When you unlink an edge, GAMBIT deletes the link(s) between the specified edge and the edge to which it is hard-linked.

Using the Unlink Edge Meshes Form

To open the Unlink Edge Meshes form (see below), click the Unlink command button on the Mesh/Edge subpad.

The Unlink Edge Meshes form contains the following specifications.

Edge ¬ specifies the edge(s) for which the hard link is to be deleted.

R Lower topology specifies that all vertex hard links that are associated with the specified edge are deleted along with the corresponding edge hard links.



3.2.4 Split Meshed Edge

The Split Meshed Edge command allows you to split a real or virtual edge at a mesh node.

When you split an edge at a mesh node, GAMBIT splits the edge into two virtual edges that share a common virtual endpoint vertex. The common vertex is located at the position of the specified node.

When you specify the edge to be split, GAMBIT displays its existing mesh in the graphics window. To specify the exact mesh node at which the edge is to be split, either pick the node in the graphics window (using the mouse) or select the mesh node by means of the Mesh Node pick-list form.

Using the Split Meshed Edge Form

To open the Split Meshed Edge form (see below), click the Split Edge com-mand button on the Mesh/Edge subpad.

The Split Meshed Edge form contains the following specifications.

Edge ¬ specifies the edge to be split.

Split With —————————————————————————

Node specifies the node at which the edge is to be split.



3.2.5 Summarize Edge Mesh

The Summarize Edge Mesh command summarizes edge mesh information in the Transcript window and displays edge mesh nodes in the graphics window. GAMBIT also allows you to display numbers corresponding to the intervals and nodes associated with the specified edge.

Using the Summarize Edge Mesh Form

To open the Summarize Edge Mesh form (see below), click the Summarize command button on the Mesh/Edge subpad.

The Summarize Edge Mesh form contains the following options and specifica-tions.

Edge ¬ specifies the edge for which summary information is to be displayed.

Component —————————————————————————

l Elements specifies that the mesh summary display is based on mesh elements.

All q Pick

specifies whether GAMBIT displays all element and/ or node numbers or only those corresponding to selected elements.

Pick ¬ specifies the elements for which element and/or node numbers are to be displayed.

R Element labels specifies that element numbers are displayed.



R Node labels specifies that node numbers are displayed.

l Nodes specifies that the edge mesh summary display is based on mesh nodes.

All q Pick

specifies whether GAMBIT displays all node numbers or only those corresponding to selected nodes.

Pick ¬ specifies the nodes for which node numbers are displayed.

R Node labels specifies that node numbers are to be displayed.



3.2.6 Delete Edge Meshes

The Delete Edge Meshes command allows you to delete mesh nodes on one or more edges.

Using the Delete Edge Meshes Form

To open the Delete Edge Meshes form (see below), click the Delete command button on the Mesh/Edge subpad.

The Delete Edge Meshes form contains the following specifications.

Edges ¬ specifies the edge(s) from which the mesh is to be deleted.

All q Pick



R Reset to default values

specifies that the mesh node grading parameters associated with the specified edge(s) are to be reset to their default values.

Face Meshing Commands MESHING THE MODEL


3.3 Face Meshing Commands

The following commands are available on the Mesh/Face subpad.


Mesh Faces Creates mesh nodes on faces

Move Face Nodes Split Quad Meshes

Adjusts mesh node positions on a face; splits quadrilateral face mesh elements into triangular elements

Smooth Face Meshes Adjusts face mesh node positions to improve uniformity of node spacing

Set Face Vertex Type Specifies the characteristics of a face mesh in the vicinity of a corner

Set Face Element Type Specifies face element types used throughout the model

Link Face Meshes Unlink Face Meshes

Creates or removes mesh hard links between faces

Modify Meshed Geometry Split Meshed Face

Converts mesh edges to topological edges; splits faces along boundaries defined by mesh node locations

Summarize Face Mesh Check Face Meshes

Displays mesh information in the graphics window; summarizes face mesh quality information

Delete Face Meshes Deletes existing mesh nodes and/or elements from faces

MESHING THE MODEL Face Meshing Commands


3.3.1 Mesh Faces

The Mesh Faces command allows you to create the mesh for one or more faces in the model. When you mesh a face, GAMBIT creates mesh nodes on the face according to the currently specified meshing parameters.

To mesh a face, you must specify the following parameters:

• Face(s) to be meshed

• Meshing scheme

• Mesh node spacing

• Face meshing options

Specifying the Faces

GAMBIT allows you to specify any face for a face meshing operation; how-ever, the shape and topological characteristics of the face, as well as the vertex types associated with the face, determine the type(s) of mesh scheme(s) that can be applied to the face.

Specifying the Meshing Scheme

To specify the face meshing scheme, you must specify two parameters:

• Elements

• Type

The Elements parameter defines the shape(s) of the elements that are used to mesh the face. The Type parameter defines the pattern of mesh elements on the face.

The following sections describe the parameters listed above and their effects on the overall face mesh.



Specifying Scheme Elements

GAMBIT allows you to specify any of the following face meshing Elements options.

Option Description

Quad Specifies that the mesh includes only quadrilateral mesh elements

Tri Specifies that the mesh includes only triangular mesh elements

Quad/Tri Specifies that the mesh is composed primarily of quadrilat-eral mesh elements but includes triangular corner elements at user-specified locations (see “Set Face Vertex Type,” below)

Each of the Elements options listed above is associated with a specific set of Type options (see below).

Specifying Scheme Type

GAMBIT provides the following face meshing Type options.

Option Description

Map Creates a regular, structured grid of mesh elements

Submap Divides an unmappable face into mappable regions and creates structured grids of mesh elements in each region

Pave Creates an unstructured grid of mesh elements

Tri Primitive Divides a three-sided face into three quadrilateral regions and creates a mapped mesh in each region

Wedge Primitive Creates triangular elements at the tip of a wedge-shaped face and creates a radial mesh outward from the tip

As noted above, each of the Elements options is associated with a specific set of one or more of the Type options listed above. The following table shows the correspondence between each of the face meshing Elements and Type options. (NOTE: Shaded cells marked with an “X” represent allowable combi-nations of options.)



Elements

Type Quad Tri Quad/Tri

Map � �

Submap �

Pave � � �

Tri Primitive �

Wedge Primitive �

Each of the allowable combinations shown in the table above results in a spe-cific pattern of mesh nodes for any given face. In addition, each is associated with a set of restrictions that govern when it can or cannot be applied. The following sections describe the patterns and restrictions associated with each of the allowable combinations of Elements and Type options listed above.

u NOTE (1): In the following sections, face meshing scheme types that allow more than one Elements option are differentiated from each other by means of prefixes that represent the options—for example, Quad-Map and Quad/Tri-Map. Scheme types that allow only one Elements option are referred to without an associated prefix—for example, Submap.

u NOTE (2): When you specify a face on the Mesh Faces form, GAMBIT auto-matically evaluates the face with respect to its shape, topological characteris-tics, and vertex types and sets the Scheme option buttons to reflect a recom-mended face meshing scheme. If you specify more than one face for a meshing operation, the scheme represented by the Scheme option buttons reflects the recommended scheme for the most recently specified face. You can enforce a meshing scheme, and thereby override any recommended scheme, by means of the Scheme option buttons on the Mesh Faces form. When you enforce a meshing scheme, GAMBIT applies the specified scheme to all currently picked faces.



Quad-Map Meshing Scheme

When you apply the Quad-Map meshing scheme to a face, GAMBIT meshes the face using a regular grid of quadrilateral face mesh elements, such as those shown in Figure 3-22.

Figure 3-22: Quad-Map face meshing scheme—example mesh

The Quad-Map meshing scheme is applicable primarily to faces that are bounded by four or more edges, however not all such faces are suitable for mapping. To be “mappable,” a face must not violate restrictions related to the following parameters:

• Vertex types

• Edge mesh intervals

The vertex-type and edge mesh interval restrictions for the Quad-Map meshing scheme are as follows.



Vertex Types

To be mappable, a face must represent a logical rectangle. (For the exception to this criterion, see NOTE (1), below.) To represent a logical rectangle, a face must include four End type vertices, and all other vertices associated with the face must be designated as Side type vertices.

Figure 3-23 shows four planar faces, two of which are mappable and two of which are not mappable. The faces shown in Figure 3-23(a) and (c) are map-pable, because each includes four End type vertices and all other vertices asso-ciated with the face are Side type vertices. The face shown in Figure 3-23(b) is not mappable, because it includes only three End type vertices. The face shown in Figure 3-23(d) is not mappable, because one of its vertices is designated as a Reversal type vertex.

End End

End

End

(a) Mappable

End

End

Side

EndSide

(b) Not mappable

End

End

End

End

Side

SideSide

End

End

EndEnd

Side

Reversal

Side

(c) Mappable (d) Not mappable

Figure 3-23: Quad-Map face meshing scheme—face suitability

u NOTE (1): If a face is bounded by two edges each of which, by itself, consti-tutes a closed loop, GAMBIT can employ the Quad-Map meshing scheme even if the vertex type designations do not define a logical rectangle. For example, GAMBIT automatically applies the Quad-Map meshing scheme to a cylindrical face, even though the circles that constitute the face boundary edges possess only one vertex each and both vertices are, by default, designated as Side type vertices.



u NOTE (2): If you enforce a Quad-Map meshing scheme on a face, GAMBIT evaluates the face with respect to its vertex type designations. If the vertex types do not meet the criteria outlined above, GAMBIT attempts to change the vertex types so that the face is rendered mappable.

If the specified face includes more than four vertices, there are multiple con-figurations of vertex types that satisfy the vertex-type criteria. For example, if the face includes five vertices, there are five possible vertex-type configura-tions that allow the creation of a Quad-Map mesh, because any of the five vertices can be designated as the Side vertex. When GAMBIT automatically changes vertex types, it attempts to employ the configuration that minimizes distortion in the mesh.

Each vertex-type configuration results in a unique node pattern for the mapped mesh. To enforce a specific node pattern on a mapped mesh, manually specify the vertex types such that they meet the Quad-Map scheme vertex-type criteria outlined above. (See “Set Face Vertex Type,” below.)

Edge Mesh Intervals

If you grade or mesh the edges of a face prior to creating a mapped mesh, you must specify the edge mesh intervals such that the numbers of mesh intervals on opposing sides of the logical rectangle are equal. For meshing purposes, a single side of the logical rectangle consists of all edges that exist between any two End type vertices.

u NOTE: If you do not grade or mesh the edges of a face prior to creating the mapped mesh, GAMBIT automatically assigns edge mesh intervals such that they satisfy the criteria described above.

As an example of the edge mesh interval restriction, consider the face shown in Figure 3-24. The face includes four End type vertices and one Side type vertex.



End

Side

End End

Endedge.1

edge.5

edge.4

edge.3

edge.2

Figure 3-24: Mappable planar face consisting of five edges

The four sides of the logical rectangle that bounds the face can be defined as follows.

Side Edge

1 edge.2

2 edge.3

3 edge.4

4 edge.1 and edge.5

For the face to be mappable, the number of mesh intervals on edge.2 (Side 1) must be equal to that on edge.4 (Side 3). Likewise, the combined number of intervals on edge.1 and edge.5 (Side 4) must be equal to the number of inter-vals on edge.3 (Side 2).



u NOTE (1): If you grade or mesh one or more edges of a face and apply a Quad-Map meshing scheme to the face, GAMBIT automatically meshes the remaining edges such that the numbers of intervals on opposing sides of the face satisfy the criteria outlined above. For example, if you grade or mesh edge.3 in Figure 3-24 such that it contains 10 intervals, GAMBIT meshes edge.1 and edge.5 such that they include a combined total of 10 intervals.

u NOTE (2): GAMBIT does not include the edge mesh interval restriction when evaluating a face with respect to a recommended meshing scheme. As a result, GAMBIT may recommend a Quad-Map meshing scheme for a face that is mappable with respect to its vertex-type configuration but which cannot be mapped, because it violates the edge mesh interval restriction.

u NOTE (3): If you create a mesh link between two edges that constitute opposing sides of a logical rectangle, the edges automatically satisfy the edge mesh interval restriction described above.



Quad/Tri-Map Meshing Scheme

The Quad/Tri-Map meshing scheme is applicable only to geometry that consti-tutes a narrow, logical sliver consisting of two sides—such as that shown in Figure 3-25. Either side may consist of more than one edge.

Trielement

edge.2

Trielement

edge.1

Figure 3-25: Quad/Tri-Map face meshing scheme—example mesh

When you apply the Quad/Tri-Map meshing scheme, GAMBIT creates triangu-lar mesh elements at the two endpoints of the sides and creates quadrilateral elements across the rest of the face. The vertex-type and edge mesh interval restrictions for the Quad/Tri-Map meshing scheme are as follows.

Vertex Types

To employ the Quad/Tri-Map meshing scheme to a sliver-shaped face, you must specify the vertices as follows:

• Tips of the sliver—Trielement

• All other vertices—Side

Edge Mesh Intervals

If you grade or mesh the edges that comprise the sides of a sliver-shaped face before applying the Quad/Tri-Map meshing scheme, you must specify the edge grading such that the sides possess identical numbers of intervals.



Submap Meshing Scheme

When you apply the Submap meshing scheme to a face, GAMBIT divides the face into one or more mappable regions and creates a mapped mesh in each region. Like the Map meshing scheme, the Submap meshing scheme is subject to restrictions related to vertex types and edge mesh intervals. The vertex-type and edge mesh interval restrictions for the Submap meshing scheme are as follows.

Vertex Types

To constitute a submappable face, a face must possess only End, Side, Corner, and Reversal vertices. In addition, the total number of End vertices, NE , must satisfy the following equation:

N N NE C R= + +4 2

where NC and NR are the total numbers of Corner and Reversal type vertices, respectively, on the face. That is, for every Corner type vertex, the face must possess an additional End vertex, and for every Reversal vertex, the face must possess two additional End vertices.

The shape of the mesh generated by means of the Submap face meshing scheme depends on the type and arrangement of vertex types on the face. As an example of the effect of vertex types, consider the faces shown in Figure 3-26 and Figure 3-27, each of which consists of an identical planar L-shaped face, one corner of which is truncated at an angle.



A: End

C: Corner

G: Side

F: End E: End

D: End

B: End

H

Figure 3-26: Submap face meshing scheme—inside Corner vertex

A: End

C: Reversal

G: End

F: End E: End

D: End

B: End

H

Figure 3-27: Submap face meshing scheme—inside Reversal vertex



In Figure 3-26, the inside corner vertex (C) is designated as a Corner vertex, therefore, in order to be submappable, the face must possess five End type ver-tices (A, B, D, E, and F). The Submap meshing scheme divides the face into the following two mapped regions:

• A, B, C, H, F, G

• C, D, E, H

In Figure 3-27, the inside corner vertex (C) is designated as a Reversal vertex, therefore, in order to be submappable, the face must possess six End type vertices (A, B, D, E, F, and G). In this case, the Submap meshing scheme divides the face into the following two mapped regions:

• A, B, C, H, G

• C, D, E, F, H

u NOTE: If you enforce a Submap meshing scheme on a face, GAMBIT evalu-ates the face with respect to its vertex type designations. If the vertex types do not meet the criteria outlined above, GAMBIT attempts to change the vertex types so that the face is submappable.

For most submappable faces, there are multiple configurations of vertex types that satisfy the vertex-type criteria. Each vertex-type configuration results in a unique node pattern for the submapped mesh. When GAMBIT automatically changes vertex types, it attempts to employ the configuration that minimizes distortion in the mesh. To enforce a specific node pattern on a submapped mesh, manually specify the vertex types such that they meet the Submap scheme vertex-type criteria outlined above. (See “Set Face Vertex Type,” below.)

Edge Mesh Intervals

If you grade or mesh the edges of a face before applying the Submap scheme, the edge mesh grading schemes must be specified such that the total numbers of intervals on opposite sides of any given submapped region are equal. For example, in Figure 3-26, the number of intervals (I) on each side of the sub-mapped regions can be expressed as follows:

I I IAGF BC DE= + = + =9 11 20

and I I IFHE AB CD= + = + =11 9 20 .

Similarly, in Figure 3-27, the number of intervals (I) on each side of the sub-mapped regions are



I IBCH AG= = 12

and I IHCD EF= = 12 .

u NOTE (1): If you grade or mesh one or more edges of a face before applying a Submap meshing scheme to the face, GAMBIT automatically meshes the remaining edges such that the numbers of intervals on opposing sides of the face satisfy the criteria outlined above.

u NOTE (2): GAMBIT does not include the edge mesh interval restriction when evaluating a face with respect to a recommended meshing scheme. As a result, GAMBIT may recommend a Submap meshing scheme for a face that is sub-mappable with respect to its vertex-type configuration but which cannot be submapped, because it violates the edge mesh interval restriction outlined above.



Quad-Pave Meshing Scheme

When you apply the Quad-Pave meshing scheme, GAMBIT creates an unstructured face mesh consisting of quadrilateral mesh elements (see Figure 3-28).

Figure 3-28: Quad-Pave face meshing scheme—example mesh

You can apply the Quad-Pave meshing scheme to any face that consists of a closed loop of edges. The vertex-type and edge mesh interval restrictions for the Quad-Pave meshing scheme are as follows.

Vertex Types

There are no restrictions on vertex types associated with a Quad-Pave mesh.

Edge Mesh Intervals

If you grade or mesh all of the boundary edges of a face before applying the Quad-Pave meshing scheme, you must specify the grading such that the total number of mesh intervals on all edges is an even number. If you grade some, but not all, of the face boundary edges, GAMBIT automatically meshes the remaining edges such that the total number of edge mesh intervals is even.



Tri-Pave Meshing Scheme

When you apply the Tri-Pave meshing scheme, GAMBIT creates a face mesh consisting of irregular triangular mesh elements, such as that shown in Figure 3-29.

Figure 3-29: Tri-Pave face meshing scheme—example mesh

The vertex-type and edge mesh interval restrictions for the Tri-Pave meshing scheme are as follows.

Vertex Types

There are no restrictions on vertex types associated with the Tri-Pave meshing scheme.

Edge Mesh Intervals

There are no restrictions on the edge mesh intervals for the Tri-Pave meshing scheme.



Quad/Tri-Pave Meshing Scheme

When you apply the Quad/Tri-Pave meshing scheme to a face, GAMBIT creates a paved mesh that consists primarily of quadrilateral elements but employs triangular mesh elements in any corners the edges of which form a very small angle with respect to each other. You can also impose the creation of triangular mesh elements in corners of the face by setting the associated vertices as Trielement vertices. Figure 3-30 shows a Quad/Tri-Pave mesh in which vertices A, D, and E are set as Trielement vertices.

A: Trielement

B: Corner

E: Trielement D: Trielement

C: End

F: Side

Figure 3-30: Quad/Tri-Pave face meshing scheme—example mesh

The vertex-type and edge mesh interval restrictions for the Quad/Tri-Pave meshing scheme are as follows.



Vertex Types

There are no restrictions on vertex types associated with the Quad/Tri-Pave meshing scheme, however, you can enforce the creation of either triangular or quadrilateral corner elements by means of the Trielement or Notrielement vertex types, respectively, as follows:

• If you specify a vertex as a Notrielement vertex, GAMBIT creates a quadrilateral element at the vertex location regardless of the angle between its associated edges.

• If you specify a vertex as a Trielement vertex, GAMBIT creates a trian-gular element at the vertex location regardless of the angle between its associated edges.

Edge Mesh Intervals

If you grade or mesh all of the edges that comprise the boundary of a face before applying the Quad/Tri-Pave meshing scheme, you must specify the grad-ing such that

N I Ntotal T= -

is an even number, where Itotal is the total number of mesh intervals on all edges, and NT is the total number of triangle mesh elements. If you grade some, but not all, of the edges, GAMBIT automatically meshes the ungraded edges such that N is an even number.



Tri Primitive Meshing Scheme

The Tri Primitive meshing scheme allows you to create a submapped mesh on a three-sided face. (NOTE: Any side of the three-sided face may consist of more than one edge.) When you apply the Tri Primitive meshing scheme to a three-sided face, GAMBIT locates a point internal to the face that serves as a common endpoint for three mappable subregions.

Figure 3-31 shows a triangular, planar face meshed according to the Tri Primitive meshing scheme. Note that the face is divided into three mappable regions, each of which shares a common endpoint (D). The regions are defined by the quadrilaterals AFDE, FBGD, and EDGC.

A: End

D

C: End

B: End

F

G

E

Figure 3-31: Tri Primitive face meshing scheme—example mesh

The vertex-type and edge mesh interval restrictions for the Tri Primitive mesh-ing scheme are as follows.

Vertex Types

The Tri Primitive meshing scheme requires that the vertices at the corners of the three sides of the face are specified as End vertices (see Figure 3-31, above) and that all other vertices are specified as Side vertices.



Edge Mesh Intervals

If you grade or mesh the sides of the face before applying the Tri Primitive meshing scheme, you must specify the grading such that the total number of intervals on the three sides of the face is an even number. In addition, the grading must satisfy the following criterion:

I I Ii j k+ � + 2

where Ii and I j are the numbers of intervals on any two sides, and Ik is the

number of intervals on the remaining side.



Wedge Primitive Meshing Scheme

The Wedge Primitive meshing scheme allows you to create a radial mesh on a three-sided face. (NOTE: Any side of the three-sided face may consist of more than one edge.) When you apply the Wedge Primitive meshing scheme, GAMBIT creates a mapped mesh that includes a group of triangular mesh ele-ments emanating from common endpoint (see Figure 3-32).

B: End

A: Trielement

C: End

Figure 3-32: Wedge Primitive face meshing scheme—example mesh

The vertex-type and edge mesh interval restrictions for the Wedge Primitive meshing scheme are as follows.

Vertex Types

The Wedge Primitive meshing scheme requires that the vertices at the corners of the three sides of the face are specified as End vertices (see Figure 3-33) and that all other vertices are specified as Side vertices.



C: End

A: Trielement

E: End

B: Side

D: Side

Figure 3-33: Wedge Primitive face meshing scheme—vertex-types

Face meshes created by means of the Wedge Primitive mesh scheme consist of regular quadrilateral mesh elements and a group of triangular mesh elements that share a common endpoint. The group of triangular elements exists at the Trielement type vertex. To create the mesh, GAMBIT constructs a series of mesh grid lines that emanate from the Trielement type vertex to the opposite side of the logical triangle—that is, to the edges that exist between the two End type vertices (see Figure 3-33, above).

Edge Mesh Intervals

If you grade or mesh the face boundary edges before applying the Wedge Primitive meshing scheme, you must specify the grading such that the total numbers of intervals on opposite sides of the logical triangle are equal. For meshing purposes, the opposite sides of the logical triangle are defined as all edges that exist between the Trielement type vertex and each End type vertex. For example, in Figure 3-33, the combined numbers of edge mesh intervals on the edges AB and BC must equal the total number of intervals on edge AE.



Specifying Node Spacing

When you specify mesh node spacing on the Mesh Faces form, GAMBIT applies the specification to all edges associated with any specified faces that are not currently graded or meshed. GAMBIT provides three different ways to specify the number of intervals on the edges of a face.

• Interval count

• Interval size

• Shortest edge (%)

For a description of the three edge mesh interval spacing options listed above, see “Specifying Node Spacing” in Section 3.2.1.

Specifying Face Meshing Options

GAMBIT includes the following primary options on the Mesh Faces form:

• Mesh

• Remove old mesh


Mesh Option

If you select the Mesh option, GAMBIT meshes the picked face(s) according to the parameters as currently specified on the Mesh Faces form. If you Apply the meshing specifications without selecting the Mesh option, GAMBIT applies the currently specified mesh parameters to the face(s) but does not create the mesh.

Remove old mesh Option

If you select the Remove old mesh option, GAMBIT deletes any currently existing mesh from the specified face(s). If you delete a face mesh using the Remove old mesh option, GAMBIT enables the Remove lower mesh option—which allows you to specify whether or not to delete the mesh on the face boundary edges. If you select the Remove lower mesh option, GAMBIT deletes the edge mesh(es) when it deletes the face mesh(es). If you do not select the option, GAMBIT deletes the face mesh but retains any associated edge meshes.

Ignore size functions Option

If you select the Ignore size functions option, GAMBIT ignores any existing size function specifications that would otherwise affect the face mesh.



Using the Mesh Faces Form

To open the Mesh Faces form (see below), click the Mesh command button on the Mesh/Face subpad.

The Mesh Faces form contains the following specifications.

Faces ¬ specifies the faces to be meshed.

Scheme: —————————————————————————

R Apply specifies that the meshing scheme indicated on the option button is applied to all currently picked faces.

Default resets the meshing scheme option button to its default algo-rithm value (Undetermined).

Elements: ————————————————————————

Quad q Tri Quad/Tri

specifies the mesh element shape. (NOTE: Each Elements option is associated with its own set of allow-able Type options (see “Specifying Scheme Elements,” above).)



Type: ————————————————————————

Map q Submap Pave Tri Primitive Wedge Primitive

specifies the type of meshing scheme used to mesh the specified face(s).

Spacing: —————————————————————————

R Apply specifies that the current mesh node spacing parameters are applied to all currently picked faces.

Default resets the mesh node spacing parameters to their default values.

Value specifies the numerical component of the mesh node spac-ing parameters.


specifies the measurement unit component of the mesh node spacing parameters.

Options —————————————————————————

R Mesh specifies that a new mesh is created in the picked face(s).

R Remove old mesh

specifies the deletion of any current mesh that is associated with the picked face(s).


specifies that GAMBIT ignores any existing size-function specifications that would otherwise affect the face mesh.



3.3.2 Move Face Nodes/Split Quad Meshes

The Move Face Nodes/Split Quad Meshes command button allows you to perform the following operations.


Move Face Nodes Adjusts face-element corner nodes within the interior of a meshed face

Split Quad Meshes Splits quadrilateral face mesh elements into triangular elements




Move Face Nodes

The Move Face Nodes command allows you to reposition any or all face-element corner nodes that exist in the interior of a meshed face. You can move the mesh nodes either by means of the Move Face Nodes form or by means of the mouse.

To move a face node, you must specify the following parameters:

• The meshed face upon which the nodes exist

• The number of the node to be moved

• The coordinates of the new node location

The following paragraphs describe the specifications listed above as well as the procedure required to move face mesh nodes by means of the mouse.

Specifying the Face

When you specify a face for which mesh nodes are to be moved, GAMBIT highlights the face the graphics window and displays the corresponding mesh as a series of grid lines. Face nodes are located at the intersections of the grid lines.

Specifying the Node Number

To specify a node to be moved, you must input the corresponding node num-ber on the Move Face Nodes form. To open a complete list of available node numbers associated with the specified face:

1. Click the Nodes pick list button.

2. Click All on the Nodes pick list form.

When you click the All command button, GAMBIT fills the Nodes pick list with the numbers of all nodes associated with the specified face and displays the nodes on the mesh grid in the graphics window. (NOTE: The Nodes list includes only those nodes that constitute face-element corner nodes that are interior to the face.) When you select a node number from the Nodes pick list, GAMBIT highlights the node in the graphics window.

To move a series of nodes, select and specify the coordinates of each node in turn. When you have selected and moved all nodes, click Apply on the Move Face Nodes form.



Specifying Node Coordinates

To specify the new coordinates of a face mesh node, you must specify the ref-erence coordinate system and the coordinate parameters corresponding to the new node location. You can input the coordinate parameters with respect to either the Global or Local coordinate system. If you specify a node location that does not lie on the specified face, GAMBIT automatically adjusts the coordinate parameters so that the new node location lies on the face.

Using the Mouse to Move Face Nodes

To use the mouse to move face nodes:

1. Pick the face upon which the nodes are to be moved.

2. Shift-right-click in the graphics window to accept the selection.

3. Pick (Shift-left-click) the node to be moved and drag it to its new location.

To move a series of mesh nodes, pick and drag each node in turn. When you have finished moving all nodes, Shift-right-click the mouse in the graphics window to accept and apply the new node positions.



Using the Move Face Nodes Form

To open the Move Face Nodes form (see below), click the Move Face Nodes command button on the Mesh/Face subpad.

The Move Face Nodes form contains the following specifications.

Face ¬ specifies the meshed face upon which nodes are to be moved.

Nodes ¬ specifies the node to be moved.

R Smooth specifies that the face mesh is to be smoothed.

Coordinate ¬ Sys.


Type ————————————————————————


specifies the reference coordinate system type.

Global | Local allows you to define the location of the node with respect to either the Global or Local coordinate system.



Split Quad Meshes

The Split Quad Meshes command splits quadrilateral face-mesh elements into triangular elements. To accomplish the split operation, GAMBIT creates mesh edges between existing nodes of the quadrilateral mesh but does not alter the original positions of the mesh nodes in the process.

As an example of the Split Quad Meshes operation, consider the quad-meshed face shown in Figure 3-34(a). In this example, the face is bounded by an edge loop consisting of five edges and has been meshed by means of a Quad:Pave scheme.

(a) Before Split Quad operation (b) After Split Quad operation

Figure 3-34: Split Quad Meshes example

If you perform the Split Quad Meshes operation on the face shown in Figure 3-34(a), GAMBIT splits the quadrilateral mesh elements into triangular elements to create the mesh shown in Figure 3-34(b).

Excluding Boundary Layer Faces

The Split Quad Meshes form includes an Exclude boundary layer faces option that allows you to prohibit GAMBIT from splitting quad mesh elements in face boundary layers. As an example of the effect of the Exclude boundary layer faces option, consider the meshed face shown in Figure 3-35. The face is similar to that shown in Figure 3-34, above, but includes a boundary layer along the left side.



Boundary layer

Figure 3-35: Quad-meshed face with boundary layer

Figure 3-36 shows the effect of the Exclude boundary layer faces option on the Split Quad Meshes operation for the face shown in Figure 3-35.

(a) Exclude boundary layer faces off (b) Exclude boundary layer faces on

Figure 3-36: Effect of Exclude boundary layer faces option



The effects can be summarized as follows:

• If you do not select the Exclude boundary layer faces option when executing the Split Quad Meshes operation, GAMBIT splits all mesh quads on the face (see Figure 3-36(a)).

• If you do select the Exclude boundary layer faces option, GAMBIT splits only the quad mesh elements that do not constitute parts of the boundary layer (see Figure 3-36(b)).

Using the Split Quad Meshes Form

To open the Split Quad Meshes form (see below), click the Split command button on the Mesh/Face subpad.

The Split Quad Meshes form contains the following specifications.

Faces ¬ specifies the meshed face(s) for which the quad mesh is to be split into triangular elements.

R Exclude boundary layer faces

specifies that quad face elements in boundary-layer regions are to be excluded from the split operation.



3.3.3 Smooth Face Meshes

The Smooth Face Meshes command adjusts the node locations for one or more face meshes.

When you smooth a face mesh, GAMBIT automatically adjusts the mesh node locations to improve the uniformity of the spacing between nodes across the face. To smooth a face mesh, you must specify the following parameters:

• The face(s) for which the mesh is to be smoothed

• The smoothing scheme

• The Smooth edges option

Specifying the Smoothing Scheme

GAMBIT provides the following smoothing schemes:

• Length-weighted Laplacian (L-W Laplacian)

• Centroid Area (Centroid Area)

• Winslow (Winslow)

The following table summarizes the basic features of the algorithm employed by each scheme.

Algorithm Features

Length-weighted Laplacian • Uses the average edge length of the elements surrounding each node

• Tends to average element edge lengths

Centroid Area • Equalizes areas of adjacent elements

Winslow • Optimizes element shapes with respect to perpendicularity

• Applies only to quadratic elements



Specifying the Smooth edges Option

When you smooth a face mesh, by default, GAMBIT does not modify the positions of mesh nodes located on the boundary edges of the face. To allow GAMBIT to modify the positions of such edge mesh nodes, you must specify the Smooth edges option on the Smooth Face Meshes form.

Using the Smooth Face Meshes Form

To open the Smooth Face Meshes form (see below), click the Smooth Mesh command button on the Mesh/Face subpad.

The Smooth Face Meshes form contains the following specifications.

Faces ¬ specifies the face(s) for which the mesh is to be smoothed.

Scheme contains an option button that allows you to specify one of three smoothing algorithms (see above).

L-W Laplacian q Centroid Area Winslow

specifies the mesh smoothing algorithm.

R Smooth edges

specifies that the mesh nodes located on the edges of the face are to be included in the face smoothing operation.



3.3.4 Set Face Vertex Type

The Set Face Vertex Type command allows you to define the characteristics of a face mesh in the vicinity of a specified vertex. The vertex-type specifications also determine which face meshing scheme GAMBIT selects as the default scheme.

To set vertex types, you must specify the following parameters.

• The face upon which the vertex types are to be defined

• The vertex type

• The vertices to which the type specification is to be applied

Specifying the Face

GAMBIT vertex types are specific to the faces upon which they are set. Therefore, to specify the type designation of an individual vertex, you must also specify a face associated with that vertex.

An individual vertex may possess as many vertex type designations as the number of faces to which it is attached. For example, it is possible for a vertex to possess a Side type designation with respect to one face and an End type designation with respect to another.

Specifying Vertex Types

The structure of any given face mesh in the vicinities of an individual vertex is a function of the face meshing scheme and vertex type. There are six vertex types (see Figure 3-37):

• End

• Side

• Corner

• Reversal

• Trielement

• Notrielement



(a) End

End vertex

(c) Corner

Cornervertex

(d) Reversal

Reversalvertex

(e) Trielement

Trielementvertex

(f) Notrielement

Notrielementvertex

(b) Side

Side vertex

Figure 3-37: Face vertex types

Each vertex type differs from the others in the following ways:

• The number of face mesh lines that intersect the vertex

• The angle between the edges immediately adjacent to the vertex

• The face mesh scheme to which it applies

The following table summarizes the characteristics of the vertex types shown in Figure 3-37.



Vertex Type

Intersecting Grid Lines

Angle Between Edges

Applicable Mesh Scheme

End 0 0 120�< < �θ Quad-Map Quad/Tri-Map Quad-Submap Pave Tri-Primitive Wedge Primitive

Side 1 120 216�� < �θ Quad-Map Quad/Tri-Map Quad-Submap Pave Tri-Primitive Wedge Primitive

Corner 2 216 3085�� < �θ . Quad-Map Quad-Submap

Reversal 3 3085 360. �� < �θ Quad-Map Quad-Submap

Trielement 0 Acute (User specified)

Quad/Tri-Map Tri-Primitive Wedge Primitive

Notrielement 0 Acute (User specified)

Quad/Tri-Map Tri-Primitive Wedge Primitive

u NOTE: GAMBIT ignores vertex types when meshing a face according to the Pave mesh scheme.

The following sections describe the general effect of each vertex type on the shape of the face mesh in the vicinity of a specified vertex.



End Vertex Type

When you specify a vertex as the End vertex type and do not specify a Pave meshing scheme, GAMBIT creates the face mesh such that only two mesh element edges intersect at the vertex (see Figure 3-37(a)). As a result, the mapped and submapped face mesh patterns on both sides of the End vertex terminate at the edges adjacent to the vertex.

Side Vertex Type

When you specify a vertex as the Side vertex type and do not specify a Pave meshing scheme, GAMBIT creates the face mesh such that three mesh ele-ment edges intersect at the vertex (see Figure 3-37(b)). GAMBIT treats the two topological edges that are adjacent to the vertex as a single edge for the purposes of meshing.

Corner Vertex Type

When you specify a vertex as the Corner vertex type and do not specify a Pave meshing scheme, GAMBIT creates the face mesh such that four mesh element edges intersect at the vertex (see Figure 3-37(c)). The Corner vertex type cannot be applied to vertices the adjacent edges of which form angles less than 180�.

Reversal Vertex Type

When you specify a vertex as the Reversal vertex type, GAMBIT creates the face mesh such that five mesh element edges intersect at the vertex (see Figure 3-37(d)). When you apply a Submap meshing scheme to a face that includes a Reversal vertex, GAMBIT creates a line of mesh edges that extends from the Reversal vertex to a topological edge on an opposite side of the face. GAMBIT treats the resulting line and each adjacent edge as a single edge for the purposes of meshing.

Trielement and Notrielement Vertex Types

When you specify a vertex as the Trielement vertex type, GAMBIT creates a triangular element (see Figure 3-37(e)) at the vertex, regardless of the default element type that would otherwise be created using either the Quad/Tri-Map, Tri-Primitive, or Wedge Primitive face meshing schemes.

When you specify a Notrielement vertex type, GAMBIT creates a quadrilateral element at the vertex, regardless of the default element type that would other-wise be created.



The Effects of Vertex Types on Face Meshes

To understand the general effects of vertex types on the structures of face meshes, consider the planar face shown in Figure 3-38. The following three examples illustrate the effects of different vertex-type specifications applied to vertices C, F, and G on the shape of the resulting mesh.

A

C D

G

F E

B

Figure 3-38: Seven-sided planar face



In Figure 3-39, vertices C, F, and G are specified as Side vertices, therefore, GAMBIT treats sides BCD and EFGA as if each were a single edge. As a result, the entire face represents a mappable region, and GAMBIT creates a single checkerboard pattern for the mesh.

A: End

C: Side D: End

G: Side

F: Side E: End

B: End

Figure 3-39: Example face mesh—Side inside corner vertex



In Figure 3-40, vertices C, F, and G are specified as Corner, Side, and End type vertices, respectively. As a result, the face is submappable, and GAMBIT creates two separate checkerboard patterns for the mesh. The upper-left sub-mapped region is defined by the polygon ABCHFG. The lower-right sub-mapped region is defined by CDEH. For both regions, the node at point H serves as an End type vertex for the purposes of mesh creation.

A: End

C: Corner D: End

G: End

F: Side E: End

B: End

H

Figure 3-40: Example face mesh—Corner inside corner vertex



In Figure 3-41, vertices C, F, and G are specified as Reversal, End, and End vertices, respectively. As a result, the face is submappable, similar to that shown in Figure 3-40. The upper-left submapped region is defined by the polygon ABCHG. The lower-right submapped region is defined by CDEFH.

Unlike the mesh shown in Figure 3-40, the mesh in Figure 3-41 does not ter-minate at vertex C. Instead, GAMBIT treats the sides BCH and HCD as single edges when creating the mesh.

A: End

C: Reversal D: End

G: End

F: End E: End

B: End

H

Figure 3-41: Example face mesh—Reversal inside corner vertex



Using the Set Face Vertex Type Form

To open the Set Face Vertex Type form (see below), click the Set Face Vertex Type command button on the Mesh/Face subpad.

The Set Face Vertex Type form contains the following options and specifica-tions.

Face ¬ specifies the face upon which the vertex type is to be set.

Type contains a field of six radio buttons that specify the vertex type for all vertices selected by means of the Vertices list box in the lower part of the form. The available vertex types are End, Side, Corner, Reversal, Trielement, and Notrielement.

Vertices ¬ specifies one or more vertices to which the currently specified vertex type is applied.

R Boundary layer only

specifies that the vertex type applies only to any boundary layers adjacent to the specified vertices.



3.3.5 Set Face Element Type

The Set Face Element Type command allows you to specify the mesh node configuration associated with either of two available face element shapes.

To set the face element type, you must specify the node pattern associated with each of the face element shapes. There are two face element shapes avail-able in GAMBIT:

• Quadrilateral

• Triangle

Each face element shape is associated with three different node patterns, and each node pattern is characterized by the number of nodes in the pattern. Figure 3-42 and Figure 3-43 show the node patterns associated with the quad-rilateral and triangular face element types, respectively.

(a) 4 node (c) 9 node(b) 8 node

Figure 3-42: Quadrilateral face element types




Figure 3-43: Triangular face element types

When you set a face element type, GAMBIT applies the type to all face ele-ments of the specified shape. For example, if you specify 8-node quadrilateral face elements, GAMBIT locates mesh nodes according to the 8-node pattern for all quadrilateral face elements produced in the subsequent face meshing operation. (NOTE: For a description of the relationships between edge, face, and volume element types, see “Set Edge Element Type,” above.)

u NOTE: Finite-element solvers, such as the FIDAP solver, employ higher-order elements (for example, 8-node and 9-node quadrilateral elements). Finite-volume solvers, such as FLUENT/UNS, employ only linear elements (for example, 4-node quadrilateral elements).



Using the Set Face Element Type Form

To open the Set Face Element Type form (see below), click the Set Face Element Type command button on the Mesh/Face subpad.

The Set Face Element Type form contains the following specifications.

Quadrilateral allows you to specify the quadrilateral face element node pattern. The available node patterns include 4 node, 8 node, and 9 node.

Triangle allows you to specify the triangular face element node pattern. The available node patterns include 3 node and 6 node.



3.3.6 Link/Unlink Face Meshes

The Link/Unlink Face Meshes command button allows you to perform the fol-lowing operations.


Link Face Meshes Creates hard links between faces

Unlink Face Meshes Deletes hard links between faces


u NOTE (1): Face-mesh linking is required for periodic and cyclic boundary zones, because it insures that meshes match on linked face pairs.

u NOTE (2): When you mesh one of two faces that constitutes part of a linked pair of faces, GAMBIT stores only one copy of the mesh in the database in addition to the transformation matrix. As a result, the linking of face meshes reduces memory use.



Link Face Meshes

The Link Face Meshes command allows you to create a mesh hard link between two faces. When you create hard links between faces in a set, GAMBIT associates the faces with each other such that any meshing or splitting operation applied to one or more of the faces is similarly applied to all faces in the set. For example, if you mesh a face that is hard-linked to another face, GAMBIT meshes both faces according to the grading scheme and parameters applied to the specified face. Likewise, if you split a boundary edge of a face that is hard-linked to another face, GAMBIT splits the corres-ponding edge on the other face.

To create a mesh hard-link between two faces, you must specify the following parameters for each face:

• The face to be hard-linked

• A vertex that serves as a reference point for the face mesh

• The orientation of the mesh on the linked face relative to its edge loop sense

• Whether or not the faces are periodically linked

Specifying Faces

When you hard-link two faces, the faces to be hard-linked must possess identical numbers of edges. In addition, if a face possesses more than one edge loop, any face to which it is hard-linked must possess an identical number of edge loops, and the edge loops that correspond to each other must possess identical numbers of edges.

As an example of this restriction, consider the six faces shown in Figure 3-44. Of all possible combinations represented by the faces in the figure, only the following faces may be hard-linked to each other:

• face.1 and face.2

• face.4 and face.5



(a) (b) (c)

(d) (e) (f)

face.1 face.3face.2

face.4 face.6face.5

Figure 3-44: Face edge loop hard-link examples

The rules governing the permissibility of hard-links for the faces shown in Figure 3-44 are as follows.

• face.1 and face.2 can be hard-linked, because each possesses a single edge loop consisting of five edges. Neither can be hard-linked to face.3, face.4, face.5, or face.6, however, because each of those faces is defined by an outer edge loop consisting of four edges.

• face.3 cannot be hard-linked to face.4, face.5, or face.6, because it pos-sesses a single edge loop, whereas each of the other faces possesses at least two edge loops.

• face.4 and face.5 can be linked to each other, because each possesses outer and inner edge loops consisting of four and three edges, respec-tively.

• face.6 cannot be linked to either face.4 or face.5, because it possesses two inner edge loops—one consisting of three edges (triangle) and the other consisting of one edge (circle).



Specifying Reference Vertices

When you hard-link two faces, you must specify one reference vertex for each edge loop of each face. The reference vertex determines the relationship between the edges of each face with respect to meshing. As an example of the effect of reference vertex specification, consider the two hard-linked faces shown in Figure 3-45 and Figure 3-46. In both figures, face.1 possesses a boundary layer attached to its left edge.

face.1 face.2

Reference vertices

Figure 3-45: Face hard-link—identical reference vertex positions



face.1 face.2

Reference vertices

Figure 3-46: Face hard-link—differing reference vertex positions

In Figure 3-45, the reference vertices are located at identical positions on each face, therefore the mesh scheme applied to face.1 is exactly duplicated on face.2. In Figure 3-46, the reference vertex locations differ between faces, therefore the location of the boundary layer on face.2 is different from that on face.1.

Specifying Mesh Orientation

If you create a hard link between two faces the edge loop senses of which are reversed relative to each other, you must reverse the orientation of the linked mesh in order to create identical meshes on both faces. As an example of this principle, consider the two hard-linked faces shown in Figure 3-47. The bottom edge of face.1 is graded toward its left endpoint vertex, and the senses of the edge loops for the faces are reversed relative to each other.



face.1 face.2

Reference vertices Edge sense

Figure 3-47: Face hard-link—orientation relative to edge loop sense

If you specify reference vertices at identical positions on both faces, GAMBIT constructs a mesh on the linked face (for example, face.2) that is different in orientation from that constructed on the specified face (for example, face.1). To create identical meshes on both faces when you specify reference vertices as shown in Figure 3-47, you must specify the Reverse orientation option when you create the mesh hard link.

Specifying the Periodic Option

The Link Face Meshes command includes a Periodic option that allows you to specify that the faces are periodically linked. Periodically linked faces are constrained such that they must behave identically to each other with respect to any virtual edge-split and vertex-move operations. For a general description of the effect of periodic linking on the boundary edges of periodically linked faces, see “Link Edge Meshes,” in Section 3.2.3, above.



Using the Link Face Meshes Form

To open the Link Face Meshes form (see below), click the Link command button on the Mesh/Face subpad.

The Link Face Meshes form contains the following specifications.

Face ¬ specifies the first of two faces to be hard-linked.

Vertices ¬ specifies one or more reference vertices on the first of the hard-linked faces. (NOTE: You must specify one reference vertex for each edge loop associated with the face.)

Link With —————————————————————————

Face ¬ specifies the second of two faces to be hard-linked.

Vertices ¬ specifies one or more reference vertices on the second hard-linked face (see above).

R Reverse orientation

specifies that the edge meshing on the second of the two hard-linked faces is reversed relative to the first.

R Periodic specifies that the faces are to be periodically linked.



Unlink Face Meshes

The Unlink Face Meshes command allows you to delete existing hard links associated with two faces. To delete a hard link, you must specify both faces associated with the link.

Using the Unlink Face Meshes Form

To open the Unlink Face Meshes form (see below), click the Unlink command button on the Mesh/Face subpad.

The Unlink Face Meshes form contains the following specifications.

Faces ¬ specifies the face(s) for which the hard link is to be deleted.

R Lower topology specifies that any edge hard links that are associated with the face hard link are deleted along with the face hard link.



3.3.7 Modify Meshed Geometry / Split Meshed Face

The Modify Meshed Geometry / Split Meshed Face command button allows you to perform the following operations.


Modify Meshed Geometry Converts mesh edges to topological edges.

Split Meshed Face Splits a face along lines defined by an existing mesh.

The following sections describe each of these operations.



Modify Meshed Geometry

The Modify Meshed Geometry command allows you to convert mesh edges to topological edges and to modify geometry associated with imported mesh information.

To perform a Modify Meshed Geometry operation, you must first create a con-version list—that is, a list of mesh edges that are to be converted to topologi-cal edges. To create the list, you must specify the following parameters:

• The meshed face of interest

• The mesh edges that are to be included in the list

Specifying the Face

You can specify any meshed face for a mesh-edge conversion operation. The number of edges that can be automatically added to the conversion list depends, in part, on the shape of the face (see below).

Specifying the Mesh Edges

GAMBIT provides two different methods of adding edges to the conversion list.

• Automatic

• Manual

When you use the automatic method, GAMBIT automatically adds mesh edges to the conversion list based on a criterion involving the angle between any two adjacent mesh element faces. When you use the manual method, GAMBIT allows you to select specific mesh edges to be added to or removed from the list (see below).



Using the Automatic Method

To employ the automatic method of adding mesh edges to the list, you must specify a minimum Angle criterion. The Angle criterion represents the value of θ min in the equation

θ φmin max= -180

where φ max is the maximum angle (in degrees) between adjacent mesh ele-ment faces the common edge of which is converted to a topological edge (see Figure 3-48).

fq

Mesh element faces

Mesh edge to be converted

Mesh node

Figure 3-48: Automatic-method angle criterion

When you employ the automatic method, GAMBIT applies the Angle criterion to all mesh element faces associated with the specified topological face. If θ θ� min for any two mesh element faces, GAMBIT adds the mesh edge that is common to the faces to the conversion list. If θ θ< min , GAMBIT does not add the mesh edge to the conversion list.

Note that, for a planar face, θ = 0 across the entire face. As a result, if you specify θ min = 0 and employ the automatic method for a planar face, GAMBIT adds all of the mesh edges associated with the face to the conver-sion list. Similarly, if you specify θ min > 0 and employ the automatic method



for a planar face, GAMBIT does not add any mesh edges to the conversion list.

u NOTE: When you perform a Modify Meshed Geometry operation, GAMBIT highlights mesh edges in the graphics window according to the following default color code:

• Blue—Detected/picked mesh edges

• Orange—Undetected/unpicked mesh edges

Specifying the Manual Method

When you employ the manual addition method, GAMBIT allows you to per-form the following operations each of which corresponds to a separate option on the Modify Meshed Geometry form.

Option Description

Add Adds mesh edges to the conversion list

Remove Removes mesh edges from the conversion list

Remove spurs Removes continuous strings of dangling mesh edges from the conversion list

Adding Edges

To add an individual mesh edge to the conversion list, you must select the Add option and specify the mesh edge to be added. To specify the mesh edge, you can either input its corresponding number in the Mesh edge list box on the Modify Meshed Geometry form, or pick (Shift-left-click) the edge in the graph-ics window by means of the mouse.

u NOTE: When you click the pick list button located at the right side of the list box, GAMBIT displays the current conversion list.



Removing Edges

You can remove an edge from the conversion list in either of two ways.

• Select the Remove option and specify the edge to be removed (see “Adding Edges,” above).

• Use the standard procedure for deleting an item from a pick list (see the GAMBIT User’s Guide, Chapter 3).

Removing Spurs

“Spurs” are defined as strings of one or more edges in the conversion list that do not attach at both ends to other topological boundaries (see Figure 3-49).

Mesh node

Spur

Figure 3-49: Example spur

When you select the Remove spurs option and specify an edge that constitutes part of a spur, GAMBIT removes from the conversion list all edges associated with the spur.



Using the Modify Meshed Geometry Form

To open the Modify Meshed Geometry form (see below), click the Modify Meshed Geometry command button on the Mesh/Face subpad.

The Modify Meshed Geometry form contains the following options and specifi-cations.

Face ¬ specifies the face to which mesh edge conversion operations are to be applied.

Automatic: —————————————————————————

Angle –��– specifies the maximum angle between mesh element faces for which the associated mesh edges are added to the con-version list.

Manual: —————————————————————————

l Add specifies that the picked mesh edge is added to the conver-sion list.

l Remove specifies that the picked mesh edge is removed from the conversion list.

l Remove spurs specifies that the spur associated with the picked mesh edge is removed from the conversion list.



Mesh edges ¬ specifies the mesh edges to which the Add, Remove, and Remove spurs operations apply.

R Keep original edge

specifies the removal of any existing topological edge that is associated with a removed mesh edge.



Split Meshed Face

The Split Meshed Face command allows you to split a meshed face into two virtual faces.

When you split a face by means of the Split Meshed Face command, GAMBIT creates two virtual faces that share a common virtual edge. The shape of the virtual edge is determined by the nodes that define the split path. Once the virtual faces are created, GAMBIT retains them even if you delete the mesh that was used to define their shapes.

To split a meshed face by means of the Split Meshed Face command, you must specify the following parameters.

• The meshed face to be split

• The mesh nodes that define the split path

Specifying the Face

You can use the Split Meshed Face command to split any real or virtual face that is currently meshed.

Specifying the Split Path Mesh Nodes

To split a face using mesh nodes, you must specify two or more mesh nodes that define the path of the split. Two of the mesh nodes must be located on the edges of the face. The other mesh nodes that define the split path may exist anywhere else internal to the face, but none of them may lie on one of the edges of the face.

Figure 3-50 illustrates the effect of splitting a real face by means of the Split Meshed Face form. Figure 3-50(a) shows the mesh and four mesh nodes that define the split path. Figure 3-50(b) shows the two virtual faces that result from the split operation.



Split-path mesh nodes

(a) (b)

face.1

v_face.2

v_face.3

Figure 3-50: Face split by mesh nodes

Using the Split Meshed Face Form

To open the Split Meshed Face form (see below), click the Split Meshed Face command button on the Mesh/Face subpad.

The Split Meshed Face form contains the following specifications.

Face ¬ specifies the face to be split.

Split With —————————————————————————

Nodes ¬ specifies the mesh nodes that define the split path.



3.3.8 Summarize/Check Face Meshes

The Summarize/Check Face Meshes command button lets you perform the following operations.


Summarize Face Mesh Summarizes general face mesh infor-mation in the Transcript window

Check Face Meshes Displays face mesh quality informa-tion in the Transcript window




Summarize Face Mesh

The Summarize Face Mesh command summarizes general face mesh informa-tion in the Transcript window and displays face nodes in the graphics window. GAMBIT also allows you to display the numbers corresponding to the ele-ments and nodes associated with the specified face.

Using the Summarize Face Mesh Form

To open the Summarize Face Mesh form (see below), click the Summarize command button on the Mesh/Face subpad.

The Summarize Face Mesh form contains the following options and specifica-tions.

Face ¬ specifies the face for which information is to be summarized.

Component —————————————————————————

l Elements specifies that the mesh summary display is based on mesh elements.

All q Pick

specifies whether GAMBIT displays all element and/ or node numbers or only those corresponding to selected elements.

Pick ¬ specifies the elements for which element and/or node numbers are to be displayed.

R Element labels specifies that element numbers are displayed.



R Node labels specifies that node numbers are displayed.

l Nodes specifies that the face mesh summary display is based on mesh nodes.

All q Pick

specifies whether GAMBIT displays all node numbers or only those corresponding to selected nodes.

Pick ¬ specifies the nodes for which node numbers are displayed.

R Node labels specifies that node numbers are to be displayed.



Check Face Meshes

The Check Face Meshes command displays 2-D mesh quality data. When you execute the Check Face Meshes command, GAMBIT displays the following elements in the Transcript window:

• A table that summarizes 2-D mesh quality statistical information for all faces specified on the Check Face Meshes form

• A summary statement that includes the total number of inverted mesh elements and the number of specified faces that contain inverted elements

Tabular 2-D Mesh Quality Data

The Check Face Meshes tabular output represents the statistical distribution of element quality values for the current default 2-D quality metric. Table 3.1 shows an example of such output for a face mesh evaluated according to the EquiAngle Skew quality metric. Output such as that shown in Table 3.1 consti-tutes a numerical representation of the mesh quality histogram that is displayed on the Examine Mesh form when you choose the Display Type:Range option (see Section 3.4.2 of the GAMBIT User’s Guide).

Table 3.1: Example Check Face Meshes tabular output

From value To value Count in range % of total count (114) -------------------------------------------------------------

0 0.1 36 31.58 0.1 0.2 46 40.35 0.2 0.3 20 17.54 0.3 0.4 6 5.26 0.4 0.5 2 1.75 0.5 0.6 4 3.51 0.6 0.7 0 0.00 0.7 0.8 0 0.00 0.8 0.9 0 0.00 0.9 1 0 0.00

------------------------------------------------------------- 0 1 114 100.00

In addition to the tabular output shown in Table 3.1, the Check Face Meshes command displays the minimum and maximum values of element quality for the set of specified faces, thus:

Measured minimum value: 0.0286973 Measured maximum value: 0.587398



This minimum and maximum element quality information is not available by means of any other GAMBIT operation.

Specifying the Quality Metric

As noted above, the Check Face Meshes command evaluates 2-D mesh element quality according to the current default mesh quality metric. To change the metric used to evaluate element quality for the Check Face Meshes command, you must modify the default 2-D mesh quality metric by means of the Edit Defaults form. To do so:

1. Open the Edit Defaults form.

2. Click the MESH tab to open the MESH defaults subform.

3. Select the EXAMINE radio button to display the EXAMINE variables.

4. Modify the ELEMENT_2D_QUALITY variable.

(For a complete description of the procedures required to modify default vari-ables by means of the Edit Defaults form, see Section 4.2.4 of the GAMBIT User’s Guide.)

For example, to evaluate 2-D elements on the basis of the Aspect Ratio metric:

1. Use the procedure described above to set Aspect Ratio as the default quality metric (ELEMENT_2D_QUALITY=2 )

2. Execute the Check Face Meshes command.

u NOTE: Check Face Meshes command tabular output, such as that shown in Table 3.1, above, includes all 2-D elements that possess shapes for which the current default quality metric applies. For example, if you specify Aspect Ratio as the default quality metric, the tabular output includes all quadrilateral and triangular elements associated with the faces specified on the Check Face Meshes form. However, if you specify Diagonal Ratio as the default quality metric, the tabular output includes only quadrilateral elements, because the Diagonal Ratio metric does not apply to triangular elements.



Summary Statement

The Check Face Meshes summary statement indicates the number of specified faces that “fail” the mesh check—for example,

0 out of 2 meshed face(s) failed mesh check.

In the context of the Check Face Meshes command, any face that includes at least one inverted mesh element fails the mesh check.

Using the Check Face Meshes Form

To open the Check Face Meshes form (see below), click the Check command button on the Mesh/Face subpad.

The Check Face Meshes form contains the following specification.

Faces ¬ specifies the faces for which mesh element quality is to be evaluated.



3.3.9 Delete Face Meshes

The Delete Face Meshes command deletes the mesh from one or more meshed faces. When you delete a face mesh, GAMBIT allows you to retain or delete all edge mesh nodes associated with the face.

Using the Delete Face Meshes Form

To open the Delete Face Meshes form (see below), click the Delete command button on the Mesh/Face subpad.

The Delete Face Meshes form contains the following options and specifica-tions.

Faces ¬ specifies the face(s) for which the mesh is deleted.

All q Pick



R Remove unused lower mesh

specifies that all edge meshes associated with the specified face(s) are to be deleted along with the face mesh(es).

Volume Meshing Commands MESHING THE MODEL


3.4 Volume Meshing Commands

The following commands are available on the Mesh/Volume subpad.


Mesh Volumes Creates mesh nodes throughout a volume

Smooth Volume Meshes Adjusts volume mesh node positions to improve uniformity of node spacing

Set Volume Element Type Specifies volume element types used throughout the model

Link Volume Meshes Unlink Volume Meshes

Creates or removes mesh hard links between volumes

Modify Meshed Geometry Converts mesh edges to topological edges

Summarize Volume Mesh Check Volume Meshes

Displays mesh information in the graphics window; displays 3-D mesh quality information

Delete Volume Meshes Deletes existing mesh nodes from volumes


MESHING THE MODEL Volume Meshing Commands


3.4.1 Mesh Volumes

The Mesh Volumes command allows you to create a mesh for one or more vol-umes in the model. When you mesh a volume, GAMBIT creates mesh nodes throughout the volume according to the currently specified meshing parame-ters.

To mesh a volume, you must specify the following parameters:

• Volume(s) to be meshed

• Meshing scheme


• Meshing options

Specifying the Volume

GAMBIT allows you to specify any volume for a meshing operation; how-ever, the shape and topological characteristics of the volume, as well as the vertex types associated with its faces, determine the type(s) of mesh scheme(s) that can be applied to the volume.

Specifying the Meshing Scheme

To specify the meshing scheme, you must specify two parameters:

• Elements

• Type

The Elements parameter defines the shape(s) of the elements that are used to mesh the volume. The Type parameter defines the meshing algorithm and, therefore, the overall pattern of mesh elements in the volume.

The following sections describe the parameters listed above and their effects on the overall volume mesh.

Specifying Scheme Elements

GAMBIT allows you to specify any of the following volume meshing Elements options. (NOTE: For descriptions of the basic shapes of each of the mesh elements listed below, see Section 3.4.3.)



Option Description

Hex Specifies that the mesh includes only hexahedral mesh elements

Hex/Wedge Specifies that the mesh is composed primarily of hexahedral mesh elements but includes wedge elements where appropriate

Tet/Hybrid Specifies that the mesh is composed primarily of tetrahedral mesh elements but may include hexahedral, pyramidal, and wedge elements where appropriate

Each of the Elements options listed above is associated with a specific set of Type options (see below).

Specifying Scheme Type

GAMBIT provides the following volume meshing Type options.

Option Description

Map Creates a regular, structured grid of hexahedral mesh elements

Submap Divides an unmappable volume into mappable regions and creates a structured grid of hexahedral mesh elements in each region

Tet Primitive Divides a four-sided volume into four hexahedral regions and creates a mapped mesh in each region

Cooper Sweeps the mesh node patterns of specified “source” faces through the volume

TGrid Creates a mesh that consists primarily of tetrahedral mesh elements but which may also contain hexahe-dral, pyramidal, and wedge mesh elements

Stairstep Creates a regular hexahedral mesh and a correspond-ing faceted volume that approximates the shape of the original volume



As noted above, each of the Elements options is associated with a specific set of one or more of the Type options. The following table shows the correspon-dence between each of the volume meshing Elements and Type options.

(NOTE: Shaded cells marked with an “�” represent allowable combinations of options.)

Elements Option

Type Option Hex Hex/Wedge Tet/Hybrid

Map �

Submap �

Tet Primitive �

Cooper � �

TGrid �

Stairstep �

Each of the allowable combinations shown in the table above results in a unique pattern of mesh nodes for any given volume. In addition, each is asso-ciated with a set of restrictions that govern the types of volumes to which it can be applied. The following sections describe the patterns and restrictions associated with each of the allowable combinations of options listed above.

u NOTE (1): Of the Type options listed above, only the Cooper option is associ-ated with more than one Elements option. Therefore, in the following sections, the volume meshing scheme types are differentiated from each other only by their respective Type names—for example, Tet Primitive.

u NOTE (2): When you specify a volume on the Mesh Volumes form, GAMBIT automatically evaluates the volume with respect to its shape, topological char-acteristics, and vertex types and sets the Scheme option buttons to reflect a recommended volume meshing scheme. If you specify more than one volume for a meshing operation, the scheme represented by the Scheme option buttons reflects the recommended scheme for the most recently picked volume. If you enforce a meshing scheme, by means of the Scheme option buttons on the Mesh Volumes form, GAMBIT applies the specified scheme to all currently picked volumes.



u NOTE (3): Some of the meshing schemes listed above create mesh node pat-terns that cannot be employed by certain solvers that are included in the GAMBIT Solvers menu on the main menu bar. The following table shows the correspondence between the solvers available on the Solvers menu and the mesh scheme types listed above. (NOTE: The FLUENT 4 solver requires a structured grid, and the NEKTON solver requires hexahedral mesh elements.)

Type Option

Solver Map Submap Tet Primitive

Cooper TGrid Stairstep

FIDAP � � � � � �

FLUENT/UNS � � � � � �

FLUENT 5 � � � � � �

FLUENT 4 � � � �

NEKTON � � � � �

RAMPANT � � � � � �

POLYFLOW � � � � � �

Generic � � � � � �



Map Meshing Scheme

When you apply the Map meshing scheme to a volume, GAMBIT meshes the volume using an array of hexahedral mesh elements, such as those shown in Figure 3-51.

Figure 3-51: Map volume meshing scheme—array of hexahedral elements

Each mesh element includes at least eight nodes—located at the corners of the element. If you specify an alternative volume element node pattern, GAMBIT creates either 20 or 27 nodes per mesh element (see “Set Volume Element Type,” below).



General Applicability

The Map volume meshing scheme can only be applied to volumes that can be meshed such that the mesh represents a logical cube. To represent a logical cube, a volume mesh must satisfy the following general requirements.

1. There must exist exactly eight mesh nodes that are attached to only three mesh element faces. (These eight mesh nodes comprise the corners of the logical cube.)

2. Each of the eight corner mesh nodes must be connected to three other corner mesh nodes by means of a straight chain of mesh edges—that is, a chain of mesh edges all of which belong to a single logical row of mesh nodes.

According to the criteria described above, the most basic form of a mappable volume is a rectangular brick, such as that shown in Figure 3-51, above. For such a volume, the mesh nodes located at the corner vertices of the brick con-stitute the corners of the mesh cube.

Although the strict definition of volume mappability is best expressed in terms of the mesh itself, it is possible to state mappability requirements in terms of the general geometrical configuration of a given volume. Specifically, volume mappability criteria may be stated as follows:

To be mappable, a volume should contain six sides, each of which can be rendered mappable by the correct specification of vertex types.

(For an exception to the criteria described above, see “Mapping Volumes with Less Than Six Faces,” below.)

u NOTE: Any side of the volume may consist of more than one face.

As an example of the application of the general rule stated above, consider the volumes shown in Figure 3-52.



(a) (b)

(c) (d)

Figure 3-52: Map volume meshing scheme—example volumes

Of the volumes shown in the figure, only the brick shown in Figure 3-52(a) is mappable in its primitive form. However, it is possible to transform the other volumes into mappable volumes by means of vertex-type assignments and vir-tual geometry operations. The following sections describe the operations required to render each volume mappable.

Transforming Volumes Into Mappable Forms

As noted above, the volumes shown in Figure 3-52(b), (c), and (d) are not mappable in their primitive forms, but each can be transformed into a mappa-ble volume by means of either vertex-type specifications or virtual geometry operations. Specifically, the operations that are required to transform each volume are as follows.

Figure 3-52 Shape Operation

(b) Pentagonal prism Vertex-type specification

(c) Cylinder Virtual edge-split

(d) Clipped cube Virtual face collapse



Pentagonal Prism—Specifying Vertex Types

To transform the pentagonal prism shown in Figure 3-52(b) into a mappable volume, you must specify its vertex types such that the top and bottom faces are mappable. To do so, you must specify one vertex on each of the top and bottom faces as a Side vertex and all other vertices as End vertices (see Figure 3-53(a)).

(a) (b)

Side

Side

EndEnd

EndEnd

End

End

EndEnd

A

B

C

Figure 3-53: Mappable pentagonal prism volume

Figure 3-53(b) shows the Map volume mesh that results from the vertex speci-fications shown in Figure 3-53(a). Note that faces A and B in the figure com-prise one side of the logical mesh cube and that face C, by itself, constitutes the opposing side.

When you assign vertex types to transform a prism into a mappable volume, you must specify the vertex types such that the Side vertices on the top and bottom faces are connected to each other by means of a single vertical edge. For example, if you assign vertex types according to the specifications shown in Figure 3-54, GAMBIT cannot create a Map volume mesh in the prism, because the configuration cannot be made to represent a logical mesh cube.



Side

End

EndEnd

End

End

Side

End

EndEnd

Figure 3-54: Unmappable pentagonal prism volume



Cylinder—Splitting Edges and Faces

The cylinder shown in Figure 3-52(c) is not mappable in its primitive form, but it is possible to transform the cylinder into a mappable volume by means of virtual edge-split and face-split operations. (For descriptions of the virtual edge-split and face-split operations, see the appendix of this guide.)

If you split the edges that circumscribe the end caps and use the resulting vertices to split the cylindrical face into four separate faces, the end faces become mappable (see Figure 3-55(a)), and the cylinder becomes topo-logically equivalent to the brick shown in Figure 3-52(a). As a result, the cylinder can be meshed according to the Map meshing scheme (see Figure 3-55(b)).

(b)(a)

End

End

End

End

End

End

End

End

Figure 3-55: Mappable cylinder



Clipped Cube—Collapsing a Face

The clipped cube shown in Figure 3-52(d) is not mappable in its primitive form, but it can be rendered mappable by means of a virtual face collapse operation. (For a description of the virtual face collapse operation, see the appendix of this guide.) When you collapse the triangular face between its three neighboring faces, GAMBIT creates the virtual volume shown in Figure 3-56(a).

(b)(a)

Figure 3-56: Mappable brick without corner

The volume shown in Figure 3-56(a) is topologically equivalent to the brick shown in Figure 3-52(a). If all of its vertices are specified as End vertices, the volume represents a logical meshing cube and can, therefore, be meshed according to a Map volume meshing scheme (see Figure 3-56(b)).



Mapping Volumes with Less Than Six Faces

As a general rule, the Map volume meshing scheme is applicable only to vol-umes that include six or more faces. It is possible, however, to transform some volumes that contain fewer than six faces into mappable volumes. As an example of such a transformation, consider the sliver-shaped volume shown in Figure 3-57(a). The volume is bounded by four faces and is not mappable in its primitive form.

(a)

(b)

(c)

a

b

c

d

fe

gh

Figure 3-57: Mappable volume with four faces

You can transform the sliver-shaped volume shown in Figure 3-57 into a map-pable form by performing a virtual split operation on each of the curved edges and specifying the vertex types as follows (see Figure 3-57(b)):

• Vertices a, b, c, and d are End vertices with respect to all faces

• Vertices e, f, g, and h are Side vertices with respect to the curved faces and End vertices with respect to the sliver-shaped end caps

Figure 3-57(c) shows the final form of the Map volume mesh.



Submap Meshing Scheme

When you apply the Submap meshing scheme to a volume, GAMBIT subdi-vides the volume into logical mesh cubes each of which can be mapped according to a Map meshing scheme.


To be submappable, a volume must be configured such that it satisfies both of the following criteria:

• Each face must be either mappable or submappable

• Opposing submappable faces must be configured consistently with respect to their vertex types

The following sections illustrate each of these criteria.

Face Mappability and Submappability

In order for GAMBIT to apply a Submap meshing scheme to a volume, each face that bounds the volume must be either mappable or submappable. Figure 3-58 shows four volumes, three of which meet the criteria described above. The volumes shown in Figure 3-58(a), (b), and (c) are submappable, because the faces of each volume are, themselves, submappable. The volume shown in Figure 3-58(d) is not submappable, because the end face of the cylindrical protrusion on the top of the volume is neither mappable nor submappable.



(a) (b)

(c) (d)

Figure 3-58: Submap volume meshing scheme—submappability criterion

Opposing-Face Vertex Types

The face mappability/submappability criterion described above constitutes a necessary but insufficient condition for volume submappability. It is possible, for example, to construct a volume that cannot be meshed according to the Submap meshing scheme even though all of its faces are either mappable or submappable.

To apply the Submap meshing scheme to a volume, the face vertex types must be specified such that the face submap meshes on opposing faces of the volume are similar in shape and form. As an example of this requirement, consider the volume shown in Figure 3-59. The volume consists of an L-shaped brick the outside corner of which is truncated at an angle.



(a)

(c)

End

Corner

Side

End

Corner

Side

End

Reversal

End

End

Reversal

End

End

Corner

Side

End

Reversal

End

(b)

Figure 3-59: Submap volume meshing scheme— L-shaped volume

The L-shaped faces that comprise the top and bottom sides of the volume can be submapped in a number of ways, each of which is a function of the vertex types that are assigned to the faces. Figure 3-59 shows face submap meshes that result from three different configurations of vertex types.

The configurations shown in Figure 3-59(a) and (b) can be meshed according to the Submap volume meshing scheme, because the vertex types and meshes on the top and bottom faces of the volume are consistent with each other. By contrast, GAMBIT cannot apply the Submap volume meshing scheme to the volume shown in Figure 3-59(c), because the Submap meshes on the top and bottom faces differ in form.



Tet Primitive Meshing Scheme

The Tet Primitive volume meshing scheme applies only to volumes that consti-tute logical tetrahedra. To constitute a logical tetrahedron, a volume must include only four sides, each of which constitutes a logical triangle. (NOTE: Any side of the logical tetrahedron may consist of more than one face.) When you apply the Tet Primitive meshing scheme, GAMBIT creates Tri Primitive meshes on each of the faces of the tetrahedron, then subdivides the volume into four hexahedral quadrants and creates a Map-type volume mesh in each quadrant.

As an example of the Tet Primitive meshing scheme, consider the tetrahedral volume shown in Figure 3-60(a). If you apply the Tet Primitive meshing scheme to the volume, GAMBIT creates Tri Primitive meshes on each face (see Figure 3-60(b)), then subdivides the volume into four quadrants and meshes each quadrant with hexahedral mesh elements. Figure 3-60(c) shows a cutaway view of the final mesh.

(a)

(c)

(b)

Figure 3-60: Tet Primitive volume meshing scheme



Cooper Meshing Scheme

When you apply the Cooper meshing scheme to a volume, GAMBIT treats the volume as consisting of one or more logical cylinders each of which is com-posed of two end caps and a barrel (see Figure 3-61). Faces that comprise the caps of such cylinders are called “source” faces; faces that comprise the barrels of the cylinders are called “non-source” faces. (For restrictions related to the specification of faces for the Cooper meshing scheme, see “Face Characteristics,” below.)

Non-sourcefaces

Source face

Source face

(a) Original volume (b) Logical cylinder

Cap

Barrel

Cap

Figure 3-61: Cooper volume meshing scheme—logical cylinder

The Cooper meshing scheme involves the following operations.

Step Operation

1 Create Map and/or Submap meshes on each of the non-source faces.

2 Imprint the source faces onto each other.

3 Mesh the source faces.

4 Project the source-face mesh node patterns through the volume



As an example of the procedure outlined above, consider the volume shown in Figure 3-62. The volume represents the union of a cube, a cylinder, and a tri-angular prism.

Figure 3-62: Cooper volume meshing scheme—example volume

If you apply the Cooper meshing scheme to the volume shown in Figure 3-62, GAMBIT performs the following operations (see Figure 3-63).

Step Operation

1 Mesh the non-source faces (see Figure 3-63(a)).

2 Imprint the source faces onto each other (see Figure 3-63(b)). (NOTE: Regions A’ and B’ represent the imprinting of faces A and B, respectively.)

3 Mesh each of the source faces (see Figure 3-63(c)).

4 Project the source-face mesh node patterns through the volume (see Figure 3-63(d)).



B’

BA’

A

(a) (b)

(c) (d)

Figure 3-63: Cooper volume meshing scheme—example volume


In general, the Cooper meshing scheme applies to volumes that demonstrate either of the following characteristics.

• At least one face is neither mappable nor submappable.

• All faces are mappable or submappable, but the vertex types are speci-fied such that the volume cannot be divided into mappable subvolumes (see “Submap Meshing Scheme: Opposing-Face Vertex Types,” above).

Faces that meet either of the criteria outlined above, as well as those that are logically parallel to such faces, constitute source faces for the volume and the end caps of the corresponding logical cylinder.

u NOTE: The Submap volume meshing scheme, described above, constitutes a special version of the Cooper meshing scheme. If a volume is configured such that it can be meshed by either the Submap scheme or the Cooper scheme, it is usually desirable to mesh the volume by means of the Submap scheme.



Face Characteristics

The Cooper volume meshing scheme imposes the following restrictions on the volumes to which it applies.

1) All non-source faces must be mappable or submappable.

2) Source faces onto which a mesh will be imprinted must not be previ-ously meshed.

3) Source faces must not include dual enclosed loops (see NOTE, below).

4) Source faces that are linked to other faces must be linked such that they do not interfere with the Cooper meshing algorithm. (For a description of face mesh links, see “Link Face Meshes” in Section 3.3.6.)

Figure 3-64 shows four volumes that illustrate the application of the criteria outlined above.

(a) (b)

A

C

B

A

B

(c) (d)

Figure 3-64: Non-Cooper-able volumes

The volumes shown in Figure 3-64 violate the restrictions outlined above for the following reasons.



Volume Criterion Reason

Figure 3-64(a) (1) It is impossible to construct a logical cyl-inder the barrel of which is mappable.

Figure 3-64(b) (2) GAMBIT cannot imprint the mesh from faces B and C onto face A, because face A possesses an existing mesh.

Figure 3-64(c) (3) The top and bottom faces of the logical cylinder each include an internal edge loop (see NOTE, below).

Figure 3-64(d) (4) Face A is linked to face B, therefore GAMBIT cannot imprint the face A mesh onto face B, because the imprint would violate the operation of the mesh link.

u NOTE: To apply the Cooper meshing scheme to a volume such as that shown in Figure 3-64(c), you must first split the upper and lower rectangular source faces as shown in Figure 3-65.

Figure 3-65: Cooper-able volume with internal edge loops



Specifying Source Faces

When you apply the Cooper volume meshing scheme to a volume, you must specify the source faces that define the end caps of the logical cylinder. The source faces also define the longitudinal direction of the logical cylinder. For certain volumes, there exist more than one valid set of source faces. For such volumes, the final form of the mesh depends, in part, on the selection of source faces.

u NOTE: When you specify a Cooper meshing scheme for a volume, GAMBIT automatically determines which faces are likely source faces. To override the automatically selected set of source faces, specify an alternative set of faces on the Mesh Volumes form.

As an example of the effect of source-face selection on a mesh, consider the annular volume shown in Figure 3-66. The volume includes four faces—the end faces, labeled A and B, and the inner and outer cylindrical faces, labeled C, and D, respectively.

A

B

C

D

Figure 3-66: Annular volume



If you mesh the annular volume by means of a Cooper volume meshing scheme and specify faces A and B as the source faces, GAMBIT maps the inner and outer cylinders and paves the end faces, then sweeps the paved mesh through the annular volume along its axis. The resulting mesh appears as shown in Figure 3-67(a), below.

(a) (b)

Figure 3-67: Cooper mesh of an annular volume, end source faces

If you specify faces C and D as the source faces, GAMBIT maps the end faces and paves the inner and outer cylindrical faces, then sweeps the paved mesh node pattern in a radial direction through the volume. The resulting mesh appears as shown in Figure 3-67(b).

u NOTE (1): In the example given above, the inner and outer faces are regular in shape, therefore, the paved meshes on the cylindrical faces are identical in appearance to mapped mesh node patterns.

u NOTE (2): There are no restrictions on the types of face-meshing schemes that can be applied to faces that constitute source faces for the Cooper volume meshing scheme. For example, if you apply a Tri-Pave meshing scheme to a source face and employ a Cooper meshing scheme, GAMBIT creates wedge elements in the meshed volume.



TGrid Meshing Scheme

When you apply the TGrid meshing scheme to a volume, GAMBIT creates a mesh that consists primarily of tetrahedral mesh elements but which may also contain elements that possess other shapes. If you mesh one or more faces of the volume by means of a Quad or Quad/Tri scheme before applying the TGrid volume meshing scheme, GAMBIT creates hexahedral, pyramidal, and/or wedge elements where appropriate in proximity to the previously meshed faces.

The TGrid meshing algorithm may be summarized as follows.

Step Description

1 Mesh all unmeshed faces by means of a Tri-Pave scheme

2 If boundary layers are attached to any of the faces on the volume, generate hexahedral or prism elements in the regions adjacent to the boundary layers and to faces that contain quadrilateral or triangular face elements, respectively.)

3 If any quadrilateral face elements exist on the volume faces (or the tops of their attached boundary layers), generate pyramidal volume elements to create a transition from the associated hexa-hedral/quadrilateral elements to the tetrahedral elements that will occupy the remainder of the volume.

4 Mesh the remainder of the volume with tetrahedral elements.

As an example of effect of face meshes on the TGrid scheme, consider the rec-tangular brick volume shown in Figure 3-68. Figure 3-68(a) shows the general shape of the tetrahedral mesh elements that are created in the volume if none of the faces are meshed prior to the application of the TGrid scheme or if all pre-meshed faces are meshed by means of a Tri-Pave scheme. If you create a Quad-Map mesh on one of the faces of the brick prior to applying the TGrid meshing scheme (see Figure 3-68(b)), GAMBIT creates an array of pyramidal mesh elements in proximity of that face (see Figure 3-68(c)) and creates tetra-hedral elements throughout the rest of the volume.



(a) (b)

(c)

Figure 3-68: TGrid meshing scheme

u NOTE (1): The TGrid meshing scheme imposes no restrictions on the types of edge or face meshes that can be previously applied to the volume.

u NOTE (2): You can control the refinement for the tetrahedral mesh by means of the GAMBIT program defaults. The program defaults also allow you to control several aspects of prism boundary layer elements. For a description of the use of GAMBIT program defaults, see Section 4.2.4 of the GAMBIT User’s Guide.

u NOTE (3): In general, it is best to avoid creating quadrilateral face mesh ele-ments with aspect ratios greater than 5 on the boundaries of any volume to be meshed by means of the TGrid meshing scheme. Face mesh elements with high aspect ratios produce highly skewed transition pyramidal elements. As a result, the TGrid volume meshing may fail or produce low-quality elements.



u NOTE (4): If you employ a face boundary layer when meshing a volume by means of the TGrid meshing scheme, it is best to attach the boundary layer to the face itself rather than to its bounding edges. If you apply the boundary layers to the bounding edges rather than to the face, the TGrid scheme will create pyramidal elements on the side faces but not on the face itself. As a result, the volume will not contain boundary layers of transition elements in the region adjacent to the face.



Stairstep Meshing Scheme

The Stairstep meshing scheme creates and meshes a faceted volume the shape of which approximates the volume to be meshed. GAMBIT does not mesh the original volume itself, and the created faceted volume is not connected to any existing geometry—including geometry to which the original volume is connected.

As an example of the effect of the Stairstep meshing scheme, consider the volume (volume.1) shown in Figure 3-69. The volume is an elliptical cylinder 10 units long with major and minor axis radii of 5 and 3 units, respectively.

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�

volume.1

�

Figure 3-69: Stairstep meshing scheme—original elliptical, cylindrical volume

If you mesh the elliptical cylinder shown in Figure 3-69 by means of the Stairstep scheme using an overall interval size of 1, GAMBIT creates and meshes the faceted volume (f_volume.2) shown in Figure 3-70. Note that the shape of the faceted volume crudely approximates the shape of the original elliptical cylinder and that all mesh elements are cubic hexahedra of uniform size.



f_volume.2

�

�

Figure 3-70: Stairstep meshing scheme—creation of faceted volume

Using a Template Mesh Volume

In the general Stairstep meshing scheme described above, the created mesh consists entirely of cubic hexahedral mesh elements the sizes of which can vary according to user-specified default settings and any existing mesh information associated with edges and/or faces of the volume to be meshed. It is possible, however, to employ a template mesh volume that serves as an initial overlay grid to start the Stairstep meshing procedures. In some cases, the use of a template mesh volume can greatly improve the density and element quality of the Stairstep mesh.

To employ a template mesh volume, you must create and mesh a volume that completely encloses the volume to be meshed by the Stairstep scheme. You can mesh the template mesh volume using any applicable volume meshing scheme—such as Cooper or Map—but the template mesh must consist of 8-node hexahedral elements and must not contain any hanging nodes. GAMBIT uses the mesh of the template mesh volume as the initial subdivision for the Stairstep scheme.



Stairstep Mesh Refinement

Overview

If you apply the Stairstep meshing scheme to a volume that includes edges and/or faces for which mesh interval size information exists, GAMBIT refines the hexahedral mesh in the region of the edges and/or faces. If the existing interval length for an edge is less than the overall length specified for the Stairstep scheme, GAMBIT creates smaller cubic hexahedral mesh elements in the proximity of the edge and also creates a transition region located near to the edge. For example, if you specify an interval size of 0.5 for the elliptical front face of volume.1 in Figure 3-69 and mesh the volume using the Stairstep scheme with an overall interval length specification of 1, GAMBIT creates the meshed, faceted volume shown in Figure 3-71.

�

�

Hanging nodes��

Figure 3-71: Stairstep meshing scheme—faceted volume with transition region

Refinement Options

GAMBIT provides three different options for refining the mesh in the Stairstep scheme. One option allows the existence of hanging nodes such as those shown in Figure 3-71. The other two options disallow the existence of hanging nodes by propagating the refined mesh either across the volume in the directions of the coordinate axes to the limit of the volume boundaries or throughout the entire volume.

You can control the Stairstep mesh refinement algorithm by means of a GAMBIT default variable named STAIRSTEP_MESH_TYPE. To modify the STAIRSTEP_MESH_TYPE default variable:




2. Access the MESH default definition subform.

3. Choose the GOCARTS option.

4. Select and modify the STAIRSTEP_MESH_TYPE default variable.

(For complete instructions regarding the use of the Edit Defaults form, see Chapter 4 of the GAMBIT User’s Guide.)

The value of the STAIRSTEP_MESH_TYPE default variable affects Stairstep mesh refinement in the following manner.

Value Description

0 Allows hanging nodes in the region of mesh refinement

1 Disallows hanging nodes by propagating the refined mesh in the directions of the coordinate axes to the volume boundaries

2 Disallows hanging nodes by propagating the refined mesh throughout the volume

As an example of the effect of the STAIRSTEP_MESH_TYPE default variable on the Stairstep mesh, consider the volume shown in Figure 3-72. The volume consists of a cube with a spherical cutout in one corner. Each edge of the cube is 10 units long, and the sphere radius is 4 units.



Figure 3-72: Stairstep meshing scheme—cube with cutout corner

Figure 3-73 shows the effect of the STAIRSTEP_MESH_TYPE default variable value on the final Stairstep mesh configuration. In each case, the edge interval lengths for the straight and curved edges are 1.0 and 0.25, respectively.



(a) No refinement (b) STAIRSTEP_MESH_TYPE = 0

(d) STAIRSTEP_MESH_TYPE = 2(c) STAIRSTEP_MESH_TYPE = 1

Figure 3-73: Effect of STAIRSTEP_MESH_TYPE default variable


The Stairstep meshing scheme is applicable to all volumes.



Specifying Volume Meshing Options

GAMBIT includes the following primary options on the Mesh Volumes form:

• Mesh

• Remove old mesh


Mesh Option

If you select the Mesh option, GAMBIT meshes the picked volume(s) according to the parameters as currently specified on the Mesh Volumes form. If you Apply the meshing specifications without selecting the Mesh option, GAMBIT applies the currently specified mesh parameters to the volume(s) but does not create the mesh.

Remove old mesh Option

If you select the Remove old mesh option, GAMBIT deletes any currently existing mesh from the specified volume(s). If you delete a volume mesh using the Remove old mesh option, GAMBIT enables the Remove lower mesh option—which allows you to specify whether or not to delete the mesh on the faces and edges that define the volume. If you select the Remove lower mesh option, GAMBIT deletes the face and edge mesh(es) when it deletes the volume mesh(es). If you do not select the option, GAMBIT deletes the volume mesh(es) but retains any associated face and edge meshes.

Ignore size functions Option

If you select the Ignore size functions option, GAMBIT ignores any existing size function specifications that would otherwise affect the volume mesh.



Using the Mesh Volumes Form

To open the Mesh Volumes form (see below), click the Mesh command button on the Mesh/Face subpad.

The Mesh Volumes form contains the following options and specifications.

Volumes ¬ specifies the volume(s) to be meshed.

Scheme: —————————————————————————

R Apply specifies that the meshing scheme indicated on the option button is applied to all currently picked volumes.

Default resets the meshing scheme option button to its default algo-rithm value (Undetermined).

Elements: ————————————————————————

Hex q Hex/Wedge Tet/Hybrid

specifies the types of elements to be used in meshing the volume(s).



Type: ————————————————————————

Map q Submap Tet Primitive Cooper TGrid Stairstep

specifies the type of meshing scheme to apply to the volume(s).

NOTE (1): If you specify the Cooper meshing scheme, GAMBIT displays a Sources list box (see below) that allows you to specify source faces for the scheme.

NOTE (2): If you specify the Stairstep meshing scheme, GAMBIT displays a Template list box (see below) that allows you to specify a template mesh volume as the starting point for the Stairstep algorithm.

Spacing: —————————————————————————

R Apply specifies that the current mesh node spacing parameters are applied to all currently specified volume(s).

Default resets the mesh node spacing parameters to their default values.

Value specifies the numerical component of the mesh node spac-ing parameters.


specifies the measurement unit for the mesh node spacing parameters.



Options —————————————————————————

R Mesh specifies that a new mesh is created in the specified volume(s).

R Remove old mesh

specifies the deletion of any current mesh that is associated with the specified volume(s) and created by means of the Mesh Volumes form.

R Lower unused mesh

specifies that all lower-topology (face and edge) meshes associated with the specified volume(s) are deleted when the volume mesh is deleted unless they are associated with other meshed topology.


specifies that GAMBIT ignores any existing size-function specifications that would otherwise affect the volume mesh.



3.4.2 Smooth Volume Meshes

The Smooth Volume Meshes command allows you to smooth the spacing of mesh nodes throughout one or more volumes.

When you smooth a volume mesh, GAMBIT automatically adjusts mesh node locations in order to improve the uniformity of spacing between nodes throughout the mesh. To smooth a volume mesh, you must specify the follow-ing parameters:

• The volume for which the mesh is to be smoothed

• The smoothing scheme

Specifying the Smoothing Scheme

GAMBIT provides the following mesh smoothing schemes:

• Length-weighted Laplacian (L-W Laplacian)

• Equipotential (Equipotential)

The following table summarizes the basic features of the algorithms employed by each scheme.

Algorithm Features

Length-weighted Laplacian Uses the average edge length of the elements surrounding each node

Equipotential Adjusts node locations to equalize the vol-umes of the mesh elements surrounding each node



Using the Smooth Volume Meshes Form

To open the Smooth Volume Meshes form (see below), click the Smooth Mesh command button on the Mesh/Volume subpad.

The Smooth Volume Meshes form contains the following options and specifi-cations.

Volumes ¬ specifies the volume(s) for which the mesh is to be smoothed.

Scheme —————————————————————————

L-W Laplacian q Equipotential

specifies the mesh smoothing algorithm. (For a general description of each algorithm, see “Specifying the Smoothing Scheme,” above.)

R Smooth Edges specifies that mesh nodes located on the edges of the volume faces are included in the smoothing operation.

R Smooth Faces specifies that mesh nodes located on all faces associated with the volume are included in the smoothing operation.



3.4.3 Set Volume Element Type

The Volume Element Type command allows you to specify the number of mesh nodes and the node pattern associated with any of four available volume element shapes.

To set the volume element type, you must specify the numbers of nodes asso-ciated with each of the volume element shapes. There are four volume element shapes available in GAMBIT:

• Hexahedron

• Wedge

• Tetrahedron

• Pyramid

Every volume element shape is associated with as many as five different node patterns. Each node pattern is characterized by the number of nodes in the pattern. The node patterns associated with each volume element shape are as follows:

Shape Numbers of Nodes

Hexahedron 8, 20, 27

Wedge 6, 15, 18

Tetrahedron 4, 10

Pyramid 5, 13, 14

When you set a volume element type, GAMBIT applies the specified mesh node pattern to all volume elements of the specified shape. For example, if you specify 20-node wedge volume elements, GAMBIT locates mesh nodes according to the 20-node pattern for all wedge volume elements produced in the subsequent volume meshing operation.

Figure 3-74, Figure 3-75, Figure 3-76, and Figure 3-77 show the placement of nodes for each of the node patterns listed above.




(c) 27 node

= Node on element edge= Node on element face= Node in element center

Figure 3-74: Hexahedron volume element node patterns


(c) 18 node

= Node on element edge= Node on element face

Figure 3-75: Wedge volume element node patterns




= Node on element edge

Figure 3-76: Tetrahedron volume element node patterns


(c) 14 node

= Node on element edge= Node on element face

Figure 3-77: Pyramid volume element node patterns



Using the Set Volume Element Type Form

To open the Set Volume Element Type form (see below), click the Set Volume Element Type command button on the Mesh/Volume subpad.

The Set Volume Element Type form contains the following specifications.

Hexahedron specifies the hexahedron volume element type: 8 node, 20 node, or 27 node.

Wedge specifies the wedge volume element type: 6 node, 15 node, or 18 node.

Tetrahedron specifies the tetrahedron volume element type: 4 node or 10 node.

Pyramid specifies the pyramid volume element type: 5 node, 13 node, or 14 node.



3.4.4 Link/Unlink Volume Meshes

The Link/Unlink Volume Meshes command button allows you to perform the following operations.


Link Volume Meshes Creates hard links between volumes

Unlink Volume Meshes Deletes hard links between volumes




Link Volume Meshes

The Link Volume Meshes command allows you to create a hard link between two volumes. When you mesh a volume that is hard-linked to another volume, GAMBIT applies identical mesh parameters to both volumes. The volumes to be linked must satisfy the following criteria:

• They must be topologically identical to each other.

• The corresponding faces of each volume must be hard-linked to each other prior to execution of the Link Volume Meshes command.

As an example of the second criterion listed above, consider the two cylindri-cal volumes shown in Figure 3-78. The volumes are topologically identical and differ from each other geometrically only with respect to their cross-sectional dimensions.

volume.1 volume.2

face.2face.3

face.1

face.5

face.6face.4

Figure 3-78: Example volumes to be hard-linked

To create a hard link between the two volumes, you must first create hard links between face.1 and face.4, face.2 and face.5, and face.3 and face.6. (For instructions on the creation of hard links between faces, see “Link Face Meshes,” in Section 3.3.6, above.)



Using the Link Volume Meshes Form

To open the Link Volume Meshes form (see below), click the Link command button on the Mesh/Volume subpad.

The Link Volume Meshes form contains the following specifications.

Volume ¬ specifies the first of two volumes to be hard-linked.

Link With —————————————————————————

Volume ¬ specifies the second of the two volumes to be hard-linked.



Unlink Volume Meshes

The Unlink Volume Meshes command allows you to delete an existing link between two volumes. To delete the link, you must specify both volumes associated with the link.

Using the Unlink Volume Meshes Form

To open the Unlink Volume Meshes form (see below), click the Unlink com-mand button on the Mesh/Volume subpad.

The Unlink Volume Meshes form contains the following options and specifica-tions.

Volumes ¬ specifies the volumes between which the link is to be deleted.

R Lower topology

specifies that any face or edge hard links that are associated with the volume hard link are deleted along with the volume hard link.



3.4.5 Modify Meshed Geometry

The Modify Meshed Geometry command allows you to convert exterior mesh edges to topological edges. When you convert a mesh edge to a topological edge, GAMBIT creates a real straight edge the endpoints of which are located at the mesh-node endpoints of the mesh edge.

For a description of the procedures and specifications involved in creating a conversion list, see “Modify Meshed Geometry,” in Section 3.3.7, above.

Using the Modify Meshed Geometry Form

To open the Modify Meshed Geometry form (see below), click the Modify Meshed Geometry command button on the Mesh/Volume subpad.

For a general description of the procedures and specifications involved in using the Modify Meshed Geometry form, see “Using the Modify Meshed Geometry Form,” in Section 3.3.7, above.



3.4.6 Summarize/Check Volume Meshes

The Summarize/Check Volume Meshes command button lets you to perform the following operations.


Summarize Volume Mesh Summarizes general volume mesh information in the Transcript window

Check Volume Meshes Displays 3-D mesh quality informa-tion in the Transcript window




Summarize Volume Mesh

The Summarize Volume Mesh command displays a summary of volume mesh information in the Transcript window.

Using the Summarize Volume Mesh Form

To open the Summarize Volume Mesh form (see below), click the Summarize command button on the Mesh/Volume subpad.

For a general description of the use of the Summarize Volume Mesh form, see Section 3.3.8, above.



Check Volume Meshes

The Check Volume Meshes command displays 3-D mesh quality data. When you execute the Check Volume Meshes command, GAMBIT displays the fol-lowing elements in the Transcript window:

• A table that summarizes 3-D mesh quality statistical information for all volumes specified on the Check Volume Meshes form

• A summary statement that includes the number of inverted elements and the number of specified volumes that contain inverted mesh elements

Tabular 3-D Mesh Quality Data

The Check Volume Meshes tabular output represents the statistical distribution of element mesh quality values for the current default 3-D quality metric. Table 3.2 shows an example of such output for a volume mesh evaluated according to the EquiAngle Skew quality metric. Output such as that shown in Table 3.2 constitutes a numerical representation of the mesh quality histogram that is displayed on the Examine Mesh form when you choose the Display Type:Range option (see Section 3.4.2 of the GAMBIT User’s Guide).

Table 3.2: Example Check Volume Meshes tabular output

From value To value Count in range % of total count (1463) --------------------------------------------------------------

0 0.1 286 19.55 0.1 0.2 671 45.86 0.2 0.3 341 23.31 0.3 0.4 88 6.02 0.4 0.5 66 4.51 0.5 0.6 11 0.75 0.6 0.7 0 0.00 0.7 0.8 0 0.00 0.8 0.9 0 0.00 0.9 1 0 0.00

--------------------------------------------------------------

0 1 1463 100.00

In addition to the tabular output shown in Table 3.2, the Check Volume Meshes command displays the minimum and maximum values of element quality for the set of specified volumes, thus:

Measured minimum value: 0.0274079 Measured maximum value: 0.553874



This minimum and maximum element quality information is not available by means of any other GAMBIT operation.

Specifying the Quality Metric

As noted above, the Check Volume Meshes command evaluates mesh element quality according to the current default 3-D mesh quality metric. To change the metric used to evaluate element quality for the Check Volume Meshes com-mand, you must modify the default 3-D mesh quality metric by means of the Edit Defaults form. To do so:


2. Click the MESH tab to open the MESH defaults subform.

3. Select the EXAMINE radio button to display the EXAMINE variables.

4. Modify the ELEMENT_3D_QUALITY variable.

(For a complete description of the procedures required to modify default vari-ables by means of the Edit Defaults form, see Section 4.2.4 of the GAMBIT User’s Guide.)

For example, to evaluate 3-D elements on the basis of the Aspect Ratio metric:

1. Use the procedure described above to set Aspect Ratio as the default quality metric (ELEMENT_3D_QUALITY=2 )

2. Execute the Check Volume Meshes command.

u NOTE: Check Volume Meshes command tabular output, such as that shown in Table 3.2, includes all 3-D elements that possess shapes for which the current default quality metric applies. For example, if you specify EquiAngle Skew as the default 3-D quality metric, the tabular output includes all hexahedral, tetrahedral, prism, and wedge elements associated with the volumes specified on the Check Volume Meshes form. However, if you specify Aspect Ratio as the default 3-D quality metric, the tabular output includes only hexahedral and tet-rahedral elements, because the Diagonal Ratio metric does not apply to prism or wedge elements.



Summary Statement

The Check Volume Meshes summary statement indicates the number of speci-fied volumes that “fail” the mesh check—for example,

0 out of 2 meshed volume(s) failed mesh check.

In the context of the Check Volume Meshes command, any volume that includes at least one inverted mesh element fails the mesh check.

Using the Check Volume Meshes Form

To open the Check Volume Meshes form (see below), click the Check com-mand button on the Mesh/Volume subpad.

The Check Volume Meshes form contains the following specification.

Volumes ¬ specifies the volumes for which mesh element quality is to be evaluated.



3.4.7 Delete Volume Meshes

The Delete Volume Meshes command allows you to delete the mesh from one or more volumes. When you delete a volume mesh, GAMBIT allows you to retain or delete all face meshes and edge meshes associated with the volume.

Using the Delete Volume Meshes Form

To open the Delete Volume Meshes form (see below), click the Delete com-mand button on the Mesh/Volume subpad.

The Delete Volume Meshes form contains the following options and specifica-tions.

Volumes ¬ specifies the volume(s) for which the mesh is to be deleted.

All q Pick




specifies that all face meshes and edge meshes associated with the specified volume(s) are to be deleted along with the volume mesh(es).

Group Meshing Commands CREATING THE GEOMETRY


3.5 Group Meshing Commands

The following commands are available on the Mesh/Group subpad.


Mesh Groups Creates a mesh for all components of a group

Summarize Group Meshes Check Group Meshes

Summarizes general group mesh information; summarizes group mesh quality information

Delete Group Meshes Deletes the mesh from groups

The following sections describe the purpose and operation of each of the com-mands listed above.

CREATING THE GEOMETRY Group Meshing Commands


3.5.1 Mesh Groups

The Mesh Groups command activates meshing operations for one or more groups of topological entities.

Overview

When you mesh a group by means of the Mesh Groups command, GAMBIT performs meshing operations for all of the topological entities that comprise components of the group. If you apply meshing parameters to any or all com-ponents of the group prior to executing the Mesh Groups command, GAMBIT meshes those components according to their previously applied parameters. All other components of the group are meshed according to the default mesh-ing parameters. For example, if you mesh a group that includes three edges to one of which has been previously applied a double-sided, successive-ratio grading scheme, GAMBIT honors the applied scheme when it meshes the group but meshes the other two edges according to the current default grading scheme.

Group Meshing Parameters

To perform a group meshing operation, you must specify the following parameters:

• Group name(s)


The group name(s) parameter specifies the name of one or more existing groups the components of which are to be meshed. The mesh node spacing parameter specifies the number of edge mesh intervals that are to be created on all edges for which a grading scheme has not been previously applied.

For a description of the mesh node spacing specifications, see “Specifying Node Spacing,” in Section 3.2.1.



Using the Mesh Groups Form

To open the Mesh Groups form (see below), click the Mesh command button on the Mesh/Group subpad.

The Mesh Groups form includes the following specifications.

Groups ¬ specifies the group(s) to be meshed.

Spacing —————————————————————————

R Apply specifies that the current mesh node spacing parameter is applied to all components of the group.

Default resets the mesh node spacing parameter to its default values.

Value specifies the numerical component of the mesh node spac-ing parameter.


specifies the unit definition of the mesh node spacing parameter.

Options —————————————————————————

R Mesh specifies that a new mesh is created for the specified group(s).

R Remove old mesh

specifies the deletion of any current mesh that is associated with the specified group(s) and created by means of the Mesh Groups form.



R Remove lower mesh

specifies that all lower-topology (volume, face, and edge) meshes associated with the specified group(s) are deleted.



3.5.2 Summarize/Check Group Meshes

The Summarize/Check Group Meshes command button lets you to perform the following operations.


Summarize Group Meshes Summarizes general group mesh information in the Transcript window

Check Group Meshes Displays mesh quality information in the Transcript window




Summarize Group Meshes

The Summarize Group Meshes command displays in the Transcript window mesh summary information for all topological entities that comprise the com-ponents of a group.

Using the Summarize Group Meshes Form

To open the Summarize Group Meshes form (see below), click the Summarize command button on the Mesh/Group subpad.

The Summarize Group Meshes form contains the following options and speci-fications.

Groups ¬ specifies the group for which summary information is dis-played in the Transcript window.



Check Group Meshes

The Check Group Meshes command displays mesh quality data for entities associated with specified groups. When you execute the Check Group Meshes command, GAMBIT displays the following items in the Transcript window:

• Tables that summarize 2-D and 3-D mesh quality statistical informa-tion for all faces and volumes associated with the specified group(s)

• Summary statements that include the numbers of inverted 2-D or 3-D elements as well as the numbers of specified faces and volumes in the specified group(s) that contain inverted mesh elements

Tabular Mesh Quality Data

The Check Group Meshes tabular outputs represent the statistical distributions of element mesh quality values for the current default 2-D and 3-D quality metrics. For descriptions of the information contained in such outputs, as well as the procedures for specifying the quality metrics, see Sections 3.3.8 and 3.4.6 in this guide.

Summary Statement

The Check Group Meshes summary statements indicate the numbers of faces and/or volumes in the specified group(s) that “fail” the mesh check. In the context of the Check Group Meshes command, any face or volume that includes at least one inverted mesh element fails the mesh check.

Using the Check Group Meshes Form

To open the Check Group Meshes form (see below), click the Check command button on the Mesh/Group subpad.

The Check Group Meshes form contains the following specification.

Groups ¬ specifies the groups for which mesh element quality is to be evaluated.



3.5.3 Delete Group Meshes

The Delete Group Meshes command removes the mesh from all topological entities that comprise components of one or more groups.

When you delete the mesh for one or more groups, GAMBIT allows you to delete all meshes that are associated with the lower-topology of the group components. To delete the mesh associated with such components, select the Remove lower unused mesh option on the Delete Group Meshes form.

As an example of the effect of the Remove lower unused mesh option, con-sider a group (group.1) that contains only a single volume (volume.1) and a single, separate face (face.7).

• If you delete the mesh from group.1 and select the Remove lower unused mesh option, GAMBIT deletes all vertex, edge, face, and volume meshes associated with volume.1 and face.7.

• If you delete the mesh from group.1 and do not select the Remove lower unused mesh option, GAMBIT deletes the volume mesh from volume.1 but retains all vertex, edge, and face meshes associated with volume.1. Likewise, GAMBIT deletes the face mesh from face.7 entity but retains all vertex and edge meshes associated with face.7.



Using the Delete Group Meshes Form

To open the Delete Group Meshes form (see below), click the Delete command button on the Mesh/Group subpad.

The Delete Group Meshes form includes the following specifications.

Groups ¬ specifies the groups containing topological entities from which the mesh is to be removed.

All q Pick


• Pick specifies groups selected by means of the Groups list box. (NOTE: If you pick a group in the graphics window or click in the Group list box, GAMBIT automatically selects the Pick option.)


specifies the deletion of all meshes that are associated with the lower geometry of the components of the specified group(s).

SPECIFYING ZONE TYPES Overview


4. SPECIFYING ZONE TYPES

4.1 Overview

Zone-type specifications define the physical and operational characteristics of the model at its boundaries and within specific regions of its domain. There are two classes of zone-type specifications:

• Boundary types

• Continuum types

Boundary-type specifications, such as WALL or VENT, define the characteristics of the model at its external or internal boundaries. Continuum-type specifica-tions, such as FLUID or SOLID, define the characteristics of the model within specified regions of its domain.

The following sections briefly describe boundary-type and continuum-type specifications and illustrate their purposes in the definition of an example computational model involving simple geometry.

4.1.1 Boundary Type Specifications

Boundary-type specifications define the physical and operational characteris-tics of the model at those topological entities that represent model boundaries. For example, if you assign an INFLOW boundary type specification to a face entity that is part of three-dimensional model, the model is defined such that material flows into the model domain through the specified face. Likewise, if you specify a SYMMETRY boundary type to an edge entity that is part of a two-dimensional model, the model is defined such that flow, temperature, and pressure gradients are identically zero along the specified edge. As a result, physical conditions in the regions immediately adjacent to either side of the edge are identical to each other.

Overview SPECIFYING ZONE TYPES


u NOTE: To apply a “periodic” boundary condition for use with a FLUENT solver, you must first create a mesh hard link between the pair of edges (2-D) or faces (3-D) to which the boundary condition is to apply. (For a description of mesh hard links, see Section 3.2.3.) In addition, you must assign a PERIODIC boundary type to both edges (or faces) in the pair, and both edges (or faces) must constitute members of a single entity set (see Figure 4-1).

Figure 4-1: Periodic boundary condition specifications—FLUENT solver

For a complete description of the procedures required to specify boundary types, see Section 4.2.1, below.

SPECIFYING ZONE TYPES Overview


4.1.2 Continuum Type Specifications

Continuum-type specifications define the physical characteristics of the model within specified regions of its domain. For example, if you assign a FLUID con-tinuum-type specification to a volume entity, the model is defined such that equations of momentum, continuity, and species transport apply at mesh nodes or cells that exist within the volume. Conversely, if you assign a SOLID contin-uum-type specification to a volume entity, only the energy and species trans-port equations (without convection) apply at the mesh nodes or cells that exist within the volume.

4.1.3 The Effect of Zone Type Specifications

As an example of the effect of zone-type specifications on the specification of a computational model, consider the geometry shown in Figure 4-2—which consists of a single volume in the shape of a straight, elliptical cylinder. The geometry includes one volume, three faces, two edges, and two vertices.

volume.1

face.1

face.3

face.2

�

�

vertex.1

vertex.1

Figure 4-2: Boundary- and continuum-type specifications

The geometry shown in Figure 4-2 can be used to model many different types of transport problems, including fluid flow through a straight, elliptical pipe and heat conduction through a solid, elliptical rod. Table 4-1 and Table 4-2 show the zone-type specifications associated with the fluid flow and heat con-duction problems, respectively.

Overview SPECIFYING ZONE TYPES


Table 4-1: Fluid flow problem, zone-type specifications

Entity Zone Zone Type

face.1 Boundary WALL

face.2 Boundary INFLOW

face.3 Boundary OUTFLOW

volume.1 Continuum FLUID

Table 4-2: Heat conduction problem, zone-type specifications

Entity Zone Zone Type

face.1 Boundary WALL

volume.1 Continuum SOLID

u NOTE: Computational solvers differ from each other in the manner in which they utilize boundary-type and continuum-type specifications. For descriptions of the use of boundary- and continuum-type specifications that are available in a specific solver, consult the solver documentation.

SPECIFYING ZONE TYPES Zones Commands


4.2 Zones Commands

When you click the Zones command button on the Operation toolpad, GAMBIT opens the Zones subpad. The Zones subpad contains command buttons that allow you to add, modify, and delete boundary- and continuum-type specifications. The symbols associated with each of the Zones subpad commands are as follows.


Boundary Types Allows you to create, modify, and delete boundary-type specifications

Continuum Types Allows you to create, modify, and delete continuum-type specifications

The following sections of this chapter describe each of the Zones commands listed above.

Zones Commands SPECIFYING ZONE TYPES


4.2.1 Boundary Types

The Boundary Types command allows you to assign boundary-type specifica-tions to topological entities that represent model boundaries.

To create a boundary-type specification, you must specify the following parameters:

• Name

• Type

• Entity set

The Name parameter is an overall label that is assigned to the specification. The Type parameter is a solver-specific keyword that represents a physical or operational characteristic, such as WALL or INFLOW. The Entity set consists of one or more topological entities to which the Type specification applies.

Specifying the Name

When you assign a boundary-type specification, you can assign a name to the specification. The name constitutes an overall label for the boundary-type specification. It may consist of any combination of alphanumeric characters and/or symbols that are valid with respect to the solver into which the mesh is to be read.

u NOTE: The Polyflow solver imposes special restrictions on boundary and con-tinuum names. Specifically, boundary and continuum names for meshes created for the Polyflow solver must obey the following naming format:

name.number

where name is the boundary or continuum name, and number is a unique integer. For example, in a given model, boundary entities can be assigned names such as inflow.1, outflow.2, and wall.3.

Specifying the Type

Each computational solver is associated with a unique set of allowable bound-ary types. For detailed descriptions of the boundary types that are available for each of the solvers supported by GAMBIT, consult the appropriate solver documentation.



u NOTE: If you change solvers after assigning boundary-type specifications, GAMBIT retains only those specifications that are valid with respect to the new solver. For example, if you select the FIDAP solver and assign WALL and SLIP boundary-type specifications, then change to the FLUENT/UNS solver, GAMBIT retains only the WALL boundary-type specification—because the SLIP boundary type is not valid in the FLUENT/UNS solver. If you reselect the FIDAP solver, GAMBIT restores the previous FIDAP-valid boundary-type specifications as well as any new specifications that are valid with respect to the FIDAP solver.

Specifying Entity Sets

Each boundary-type specification must include an entity set. The entity set constitutes one or more topological entities to which the Type specification applies. To add an entity to an entity set, you must specify the following parameters:

• Type

• Label

The type parameter defines the general type of entity that is to be added to the entity set. The label parameter specifies the name of a specific entity that is to be added to the set.

Specifying the Entity Type

The option button in the Entity section of the Specify Boundary Types form allows you to specify the general type of the entity that is to be added to the entity set. The entity types available for boundary-type specifications include Edges, Faces, and Groups.

If you select the Groups option, GAMBIT displays an Edit command button immediately to the right of the Entity list box. When you click the Edit com-mand button, GAMBIT opens either the Create Group or Modify Group form. The Create Group and Modify Group forms allow you to create or modify, respectively, groups of entities that are to be included in the boundary-type specification entity set. (For a description of the use of the Create Group and Modify Group forms, see Chapter 2 of this guide.)



u NOTE: The Entity section of the Specify Boundary Types form contains an option button and a list box that allow you to specify the type and label, respectively, of one or more entities that are to be added to the entity set. The Entity section also contains a scroll list that displays the Label and Type of all entities that currently exist in the entity set.

Specifying the Entity Label

To add an entity to an entity set, you must specify its label. You can specify the label in one of three ways:

1. Input the label in the Entity section list box.

2. Select the label from the associated pick list.

3. Use the mouse to pick the entity in the graphics window.



Using the Specify Boundary Types Form

To open the Specify Boundary Types form (see below), click the Boundary Types command button on the Zones subpad.

The Specify Boundary Types form contains the following specifications.

Action: —————————————————————————

l Add creates a new boundary-type specification. To create a new boundary-type specification, input the appropriate Name, Type, and Entity parameters, and click Apply.



l Modify modifies an existing boundary-type specification. To select a boundary-type specification for modification, highlight (left-click) its name in the Name|Type scroll list (see below). To modify the boundary-type specification, change the Name, Type, and/or Entity parameters, and click Apply.

l Delete deletes an existing boundary-type specification. To select a boundary-type specification for deletion, highlight (left-click) its name in the Name|Type scroll list (see below). To delete the boundary-type specification, click Apply.

l Delete all deletes all existing boundary-type specifications.

Name | Type o lists the names (Name) and types (Type) of all existing bound-ary-type specifications.

R Show labels displays labels for all currently-defined boundary types while the Specify Boundary Types form is open.

Name: specifies the name associated with the current boundary-type specification.

Type: —————————————————————————

VENT q WALL …

specifies the boundary type.

NOTE: Each computational solver is associated with a unique set of available boundary types (see, “Specifying the Type,” above).

Entity: —————————————————————————

Groups q Faces Edges

specifies the general type of topological entity to which the boundary type is assigned.

NOTE (1): Boundary-type specifications may include enti-ties of more than one kind. For example, some solvers allow a single boundary-type specification to include edges, faces, and/or volumes.



NOTE (2): If you specify the Groups option, GAMBIT dis-plays a command button, titled Edit, immediately to the right of the Groups list box. The Edit command button allows you to create or modify a group that is part of the set of entities that comprise the boundary-type specification.

• To create a group for inclusion in the boundary-type specification, click Edit.

• To modify an existing group that is part of the boundary-type specification, highlight the group label in the Entity list (see below) and click Edit.

When you click Edit to create or modify a group, GAMBIT opens either the Create Group or Modify Group forms, re-spectively. For instructions concerning the use of the Create Group or Modify Group forms, see “Using the Create Group Form” or “Using the Modify Group Form,” respectively, in Chapter 2 of this guide.

Groups ¬ Faces Edges

specifies the entity (or entities) to which the boundary type is assigned.

Label | Type o lists the label (Label) and type (Type) of all topological entities currently associated with the current boundary-type specifica-tion.

Remove deletes the currently highlighted entity from the list of entities associated with the boundary-type specification.

Edit opens an Edit Lower Topology form, which allows you to spec-ify whether or not lower geometry and/or geometry connected to the currently highlighted entity is included in the boundary-type specification. For instructions in the use of the Edit Lower Topology forms, see “Using Edit Lower Topology Forms” in Chapter 2 of this guide.



4.2.2 Continuum Types

The Continuum Types command allows you to define the physical characteris-tics of the model in any region defined by a set of topological entities. The physical characteristics, in turn, determine which transport equations apply to the problem.

To create a continuum-type specification, you must specify the following parameters:

• Name

• Type

• Entity set

The Name parameter is an overall label that is assigned to the specification. The Type parameter is a solver-specific keyword that represents a physical or operational characteristic, such as WALL or INFLOW. The Entity set consist of one or more topological entities to which the Type specification applies.

Specifying the Name

The specifications for continuum-type Name parameters are identical to those of boundary-type Name parameters, above. (See Section 4.2.1, above.)

Specifying the Type

There are four continuum types, each of which is associated with a set of fun-damental transport equations. The four continuum types are as follows:

• FLUID

• POROUS

• SOLID

• Conjugate (FLUENT 4 only)

u NOTE: For a detailed description of the equations associated with the contin-uum types, consult the appropriate solver documentation.



Specifying Entity Sets

The specifications for continuum-type Entity sets are similar to those for boundary-types, above. (See Section 4.2.1, above.) They differ only in that you can assign continuum-type specifications only to Faces, Volumes, and Groups.

Using the Specify Continuum Types Form

To open the Specify Continuum Types form (see below), click the Continuum Types command button on the Zones subpad.

The Specify Continuum Types form contains the following specifications.



Action: —————————————————————————

l Add creates a new continuum-type specification. To create a new continuum-type specification, input the appropriate Name, Type, and Entity parameters, and click Apply.

l Modify modifies an existing continuum-type specification. To select a continuum-type specification for modification, highlight (left-click) its name in the Name|Type scroll list (see below). To modify the continuum-type specification, change the Name, Type, and/or Entity parameters, and click Apply.

l Delete deletes an existing continuum-type specification. To select a continuum-type specification for deletion, highlight (left-click) its name in the Name|Type scroll list (see below). To delete the continuum-type specification, click Apply.

l Delete all deletes all existing continuum-type specifications.

Name | Type o lists the names (Name) and types (Type) of all currently existing continuum-type specifications.

R Show labels displays labels for all currently-defined continuum types while the Specify Continuum Types form is open.

Name: specifies the name associated with the continuum-type speci-fication.

Type: —————————————————————————

FLUID q POROUS SOLID Conjugate

specifies the continuum-type.

NOTE: Each computational solver is associated with a spe-cific set of available continuum types (see, Section 4.2.1, above).



Entity: —————————————————————————

Groups q Volumes Faces

specifies the general type of topological entity to which the continuum type is assigned.

NOTE (1): The set of topological entities that are associated with a given continuum-type specification can include enti-ties of more than one type. For example, some solvers allow a given continuum-type specification to include one or more groups, volumes, and/or faces.

NOTE (2): If you specify the Group option, GAMBIT dis-plays a command button, titled Edit, immediately to the right of the Group list box. The Edit command button allows you to create or modify a group that is part of the set of entities that comprise the continuum-type specification.

• To create a group for inclusion in the continuum-type specification, click Edit.

• To modify an existing group that is part of the con-tinuum-type specification, highlight the group label in the Entity list (see below) and click Edit.

When you click Edit to create or modify a group, GAMBIT opens either the Create Group or Modify Group forms, re-spectively. For instructions concerning the use of the Create Group or Modify Group forms, see “Using the Create Group Form” or “Using the Modify Group Form,” respectively, in Chapter 2 of this guide.

Group ¬ Volume Face Edge

specifies the particular entity (or entities) to which the con-tinuum attribute is assigned.

Label | Type o lists the labels (Label) and types (Type) of all topological enti-ties currently associated with the current continuum-type speci-fication.

Remove deletes the currently highlighted entity from the list of entities associated with the continuum-type specification.



Edit opens an Edit Lower Topology form, which allows you to spec-ify whether or not lower geometry and/or geometry connected to the currently highlighted entity is included in the continuum-type specification. For instructions in the use of the Edit Lower Topology forms, see “Using Edit Lower Topology Forms” in Chapter 2 of this guide.

USING THE MODELING TOOLS


5. USING THE MODELING TOOLS

When you click the Tools command button on the Operation toolpad, GAMBIT opens the Tools subpad. The Tools subpad provides access to the following GAMBIT operations.

Symbol Command Set Description

Coordinate System Create, modify, and display coordi-nate systems, grids, and rulers

Size Function Create functions that control the size of mesh element edges in proximity of specified model entities

Turbo Create and mesh collections of volumes that together represent flow regions surrounding turbomachinery blades

(NOTE: The Turbo Functions commands represent a specialized command set that can be licensed from Fluent. They are not included in the standard set of GAMBIT functions.)

Coordinate Systems USING THE MODELING TOOLS


5.1 Coordinate Systems

5.1.1 Overview

Coordinate systems provide reference points and directions for GAMBIT operations such as the construction of volume primitives and geometry Move and Copy operations. GAMBIT performs all such operations with respect to a specified coordinate system. For example, if you create a rectangular brick volume according to the specifications shown in Figure 5-1, GAMBIT creates a unit cube one corner of which is located at the center of coordinate system c_sys.1.

Figure 5-1: Example Create Real Brick form specifications

There are two types of coordinate systems:

• Global (c_sys.1)

• Local

The global coordinate system, c_sys.1, is a permanent system that serves as the default coordinate system for all GAMBIT geometry operations. Local coordi-nate systems allow you to perform GAMBIT geometry operations at localized regions in the model domain. They are particularly useful for the creation of geometry in regions that are distant from the center of the model.

u NOTE: GAMBIT does not allow you to delete the global coordinate system.

USING THE MODELING TOOLS Coordinate Systems


5.1.2 Coordinate System Commands

The following commands are available on the Tools/Coordinate System subpad.


Create Coordinate System Creates local coordinate systems

Modify Coordinate System Changes the coordinate system label and default system type

Activate Coordinate System Activates a coordinate system

Display Grid Displays a point grid or line grid aligned with one of the coordinate planes

Display Ruler Displays a ruler along any or all of the coordinate axes

Summarize Coordinate Systems

Displays the global coordinates of all currently defined coordinate system origins and axis vectors

Delete Coordinate Systems Deletes coordinate systems




Create Coordinate System

The Create Coordinate System command allows you to create a local coordi-nate system for use in creating and manipulating model geometry.

To create a coordinate system, you must specify the following parameters.

• System type

• Location and orientation

Specifying the System Type

There are three types of coordinate systems: Cartesian, cylindrical, and spheri-cal. They differ from each other only with respect to the manner in which the coordinates for any given location are expressed. The coordinate specifications for eacH-type of system are as follows.

System Type Coordinate Specifications

Cartesian

Cylindrical

Spherical

When you perform modeling operations such as creating vertices or moving volumes, GAMBIT allows you to specify the relevant coordinates or offset parameters with respect to either the global coordinate system (c_sys.1) or the currently active local coordinate system. The default coordinate parameters for the local system are those defined for the system when it is created or modified (see “Modify Coordinate System,” below).

For example, if you create a local coordinate system labeled c_sys.2 and spec-ify the system type as spherical, then activate the system and open the Create Real Vertex form, the default coordinate parameters shown in the Local text boxes on the Create Real Vertex form are r (r), t ( ) and p ( ) rather than x (x), y (y), and z (z). To change the Local text box coordinate parameters on any form, specify the coordinate system type using the Type option button located on the form.



Specifying the Location and Orientation

You can specify the location and orientation of the new system by means of two options available on the Create Coordinate System form. The two options are as follows:

• Offset/Angle

• Vertices

The Offset/Angle option allows you to specify the following parameters for the new system:

• The coordinates of its origin

• The angle (in degrees) by which each of its coordinate axes are rotated relative to a reference system.

The Vertices option allows you to specify existing vertices that define the origin, x axis, and x-y plane for the new system. The specifications associated with each option are described below.



Using the Create Coordinate System Form

To open the Create Coordinate System form (see below), click the Create Coordinate System command button on the Tools/Coordinate System subpad.

The Create Coordinate System form contains the following options and specifi-cations.

Type —————————————————————————


specifies the type of coordinate parameters to be used in defining the coordinate system.

Location and orientation:

contains two radio buttons that allow you to specify the manner in which the location of the new coordinate system is defined. The two available options are Offset/Angle and Vertices. The following sections describe the specifications required for each option.



Specifying Coordinate System Offset and Angle

When you select the Offset/Angle option, the middle section of the Create Coordinate System form appears as shown above. The corresponding options and specifications are as follows.

Reference Sys ¬ specifies the existing coordinate system relative to which the new coordinate system is located.

Angle contains three sets of option buttons and text boxes that allow you to specify the rotation of the new coordinate system rela-tive to the reference system.

Each option button allows you to specify whether the corre-sponding text box value (in degrees) represents a rotation with respect to the x, y, or z axis. For example, if you specify X and 35 using the topmost option button and text field, respectively, GAMBIT rotates the new coordinate system about the x axis by an angle of 35� relative to the reference system. GAMBIT applies the rotation operations in sequence according to the specifications in the top, middle, and bottom fields. For exam-ple, if you specify the parameters

X = 35, Y = 27

in the top and middle fields, respectively, GAMBIT rotates the new system first by 35� about the x axis, then by 27� about the y axis. If, on the other hand, you specify the parameters

Y = 27, X = 35

in the top and middle fields, respectively, GAMBIT rotates the new system first by 27� about the y axis, then by 35� about the x axis. The final orientations of the systems that result from the two operations are not identical.

Offset contains three text boxes that allow you to specify the X, Y, and Z coordinates of the origin of the new system relative to the ref-erence system.



Specifying Vertices That Define the New System

To specify the location and orientation of the new system by means of verti-ces, you must specify three vertices (see Figure 5-2):

• Origin

• X axis

• XY plane

zy

x

x-y plane

Origin

XY plane

X axis

Figure 5-2: Defining a new coordinate system using vertices

The location of the origin of the system is defined by the Origin vertex. The direction of the x axis is defined by a vector that points from the Origin vertex toward the X axis vertex. The orientation of the x-y plane is defined such that it contains both the x-axis vector and a vector that points from the Origin vertex to the XY plane vertex.



When you select the Vertices option, the middle section of the Create Coordi-nate System form appears as shown below.

The options and specifications available for the Vertices option are as follows.

Origin ¬ specifies the vertex that defines the location of the origin of the new system.

X axis ¬ specifies the vertex that defines the direction of the x axis for the new system.

XY plane ¬ specifies the vertex that defines the orientation of the x-y plane for the new system.

Specifying the System Label

Label specifies a label for the new coordinate system.



Modify Coordinate System

The Modify Coordinate System command allows you to change the coordinate system label and the default system parameter type.

Using the Modify Coordinate System Form

To open the Modify Coordinate System form (see below), click the Modify command button on the Tools/Coordinate System subpad.

The Modify Coordinate System form contains the following options and speci-fications.

Coordinate ¬ Sys

specifies the coordinate system to be modified.

Type —————————————————————————


specifies the type of coordinate parameters to be used as the default type for the modified coordinate system.

Label specifies a label for the coordinate system.



Activate Coordinate System

The Activate Coordinate System command allows you to activate an existing coordinate system.

When you activate a coordinate system, GAMBIT uses the system as the default reference system for operations such as creating, moving, and copying topological entities.

Using the Activate Coordinate System Form

To open the Activate Coordinate System form (see below), click the Activate Coordinate System command button on the Tools/Coordinate System subpad.

The Activate Coordinate System form contains the following specification.

Coordinate ¬ System

specifies the coordinate system to be activated.



Display Grid

The Display Grid command allows you to activate and display a grid associated with any existing coordinate system.

Overview

When you activate and display a grid, GAMBIT displays a rectangular planar grid in the graphics window. The dimensions of the grid are defined relative to the coordinate system with which it is associated. The grid is always parallel to one of the Cartesian coordinate planes but may be offset from the origin of the coordinate system.

Using the Mouse to Create Vertices

When the grid is displayed in any graphics window quadrant, GAMBIT allows you to create vertices by means of the mouse—regardless of whether the Create Vertex form is open. To create a vertex by means of the mouse, Ctrl-right-click at the desired vertex location. GAMBIT creates the vertex at the selection point—which is defined as the point of intersection between the grid plane and a line normal to the screen that passes through the cursor location.

Specifying the Grid Parameters

To define and display a grid, you must specify the following parameters.

• Coordinate system

• Visibility

• Grid definition

• Snap option

• Grid type

The following sections describe each of the specifications listed above.



Specifying the Coordinate System

GAMBIT allows you to define and display a grid for any existing coordinate system. When you define and display a grid, GAMBIT activates the coordinate system associated with the grid.

Specifying Visibility

When you define and display a grid, GAMBIT allows you to specify the graphics window quadrants in which the grid is displayed. You can specify that the grid is displayed in any or all quadrants, but each specified quadrant displays only the currently active grid. For example, you cannot simultane-ously display an x-z grid in one quadrant and a y-z grid in a separate quadrant.

Defining the Grid

To define the grid, you must specify its orientation, location, dimensions, and characteristics by means of the Plane, Axis, Offset, Minimum, Maximum, and Increment specifications on the Display Grid form. The specifications are defined as follows.

Specification Definition

Plane Coordinate plane with which the grid plane is aligned

Axis Axis of the Plane for which grid values are currently being specified

Offset Location of the grid plane along an axis normal to the Plane and with respect to the origin of the coordinate system

Minimum Minimum coordinate value for the grid plane along the currently specified Axis

Maximum Maximum coordinate value for the grid plane along the currently specified Axis

Increment Distance between grid lines along the currently specified Axis



Specifying the Snap Option

When you create a grid, GAMBIT allows you to specify that any vertices cre-ated by means of the mouse are “snapped” to the grid. When a vertex is snapped to the grid, it is created at the grid point nearest to the selection point rather than at the selection point itself. To activate the snap option for any grid, select the Snap checkbox at the bottom of the Display Grid form.

Specifying the Grid Type

The grid type determines the manner in which the grid is displayed. There are two grid-type options: Points and Lines. When you select the Points option, GAMBIT displays the grid as a matrix of parallel rows of points. When you select the Lines option, GAMBIT displays the grid as a series of intersecting perpendicular lines.



Using the Display Grid Form

To open the Display Grid form (see below), click the Grid command button on the Tools/Coordinate System subpad.

The Display Grid form contains the following specifications.

Coordinate ¬ Sys

specifies and activates the coordinate system corresponding to the grid.

R Visibility specifies whether or not the grid is displayed in the currently active graphics window quadrants.

(quadrant command buttons) enable or disable any or all quad-rants with respect to grid visibility.



Plane contains three radio buttons that allow you to specify the Carte-sian coordinate plane that contains the grid. The Plane options are XY, YZ, and XZ.

Axis contains two radio buttons that allow you to specify the grid coordinate axis to which the current specifications apply. For example, if you select the XZ Plane option, the Axis options are X and Z. If you select the Z Axis option, the subsequent specifi-cations for Minimum, Maximum, Increment, and the displayed grid values apply only to the z axis.

X, Y, or Z Offset specifies the distance by which the grid plane is offset from the origin of the coordinate system along an axis normal to the specified Plane. For example, if you select the XZ Plane option, this field is labeled Y offset and allows you to specify the dis-tance by which the grid is offset from the origin in the y direc-tion.

Minimum specifies the lower limit of the grid range measured with respect to the specified coordinate system.

Maximum specifies the upper limit of the grid range measured with respect to the specified coordinate system.

Increment specifies the spacing increment between grid lines or parallel rows of grid points.

Update list generates a sequence of evenly-spaced grid-line location values based on the currently displayed Minimum, Maximum, and Increment parameters. The values appear in the Values scroll list located in the middle section of the form.

Values o displays a list of grid-line location values for the currently selected grid coordinate axis. (NOTE: The scroll list heading indicates the plane and axis corresponding to the currently dis-played values. For example, if you select the XZ Plane and Z Axis options, the heading is XZ_plane Z Values.)

The command buttons and text box located immediately to the right of and below the scroll list, respectively, allow you to modify the automatically generated grid-line location values as follows.



Delete deletes one current grid-line location value. To remove a value from the scroll list, select (left-click) the value, then click Delete.

Unselect unselects the currently selected value.

Delete All deletes all currently displayed values in the scroll list.

Value: allows you to modify a currently displayed value or to create a new value to be included in the list.

To modify a currently displayed value, select (left-click) it from the scroll list, then input the new value in the Value text box and press Enter. GAMBIT automatically updates the scroll list to reflect the modified value.

To create a new value, Unselect any currently selected value, then input the new value in the Value text box and press Enter. GAMBIT automatically updates the scroll list to reflect the new value.

Options: —————————————————————————

R Snap activates the snap feature for the grid. The snap feature affects vertex creation in the following manner.

• If you select the snap feature, each vertex created by means of the mouse is automatically located at the grid point that is nearest to the selection point.

• If you do not select the snap feature, each vertex created by means of the mouse is located at the selection point itself.

Grid: contains two option buttons that allow you to specify whether the grid is displayed as a matrix of points (Points) or as a series of intersecting perpendicular lines (Lines).



Display Ruler

The Display Ruler command allows you to display rulers along any or all of the axes in the currently active coordinate system.

To display a ruler along any of the coordinate axes, you must specify the fol-lowing parameters.

• Display status (On or Off)

• Range status (On or Off)

• Number of intervals and subintervals

If the range status is on, you must also specify the lower and upper limits of the ruler range.

Specifying the Display Status

The display status determines whether or not the ruler is displayed in the graphics window. To display or erase the ruler for any particular axis in the active coordinate system, select On or Off, respectively, in the Ruler field corre-sponding to the axis.

Specifying the Range Status

The range status determines whether the lower and upper limits of the ruler are user-specified or automatically set by GAMBIT for any particular axis. To specify the range status for any axis, select On or Off in the Range field corre-sponding to the axis. The range status specification operates in the following manner.

• If you specify the range status as On for any axis, GAMBIT allows you to specify the lower and upper limits for the ruler in the Min and Max text boxes corresponding to the axis.

• If you specify the range status as Off for any axis, GAMBIT automati-cally determines the lower and upper limits of the axis ruler.



When GAMBIT automatically determines the lower and upper limits for an axis ruler, it constructs a theoretical “bounding box” that encompasses all components of the model domain, including topological entities, coordinate systems, and rulers themselves. The bounding box represents a rectangular brick volume the edges of which are aligned with the axes of the global coor-dinate system, c_sys.1.

When GAMBIT displays a ruler with an automatically determined range, it sets the range so that the ruler is exactly contained by the sides of the bound-ing box. If you increase the length of a user-specified ruler beyond the current limits of the bounding box, GAMBIT increases the size of the bounding box to accommodate the new ruler dimensions. GAMBIT also adjusts all currently displayed, automatically determined rulers so that, again, they are exactly con-tained by the sides of the bounding box.

Specifying the Intervals and Subintervals

The number of intervals for any axis determines the locations along the ruler at which GAMBIT displays tic marks and corresponding numbers. The number of subintervals determines the spacing of tic marks between numbered marks. For example, if you specify a ruler range of −5 to +5 with 10 intervals and 2 subintervals, GAMBIT displays a ruler that contains numbered tic marks at −5, −4, −3, −2, −1, 0, 1, 2, 3, 4, and 5 and tic marks without numbers at −4.5, −3.5, −2.5, −1.5, −0.5, 0.5, 1.5, 2.5, 3.5, and 4.5.



Using the Display Ruler Form

To open the Display Ruler form (see below), click the Display Ruler command button on the Tools/Coordinate System subpad.

The Display Ruler form contains the following options and specifications.

Ruler: contains a field of three option buttons that turn the ruler dis-play On or Off for the X, Y, and Z axes of the active coordinate system.

Range: contains a field of three option buttons that specify whether the ruler range is user-specified (On) or automatically determined (Off) for the x (X), y (Y) and z (Z) axes of the active coordinate system.

Min: contains a field of three text boxes that specify the lower limit of the ruler for the x (X), y (Y) and z (Z) axes of the active coordinate system.

Max: contains a field of three text boxes that specify the upper limit of the ruler for the x (X), y (Y) and z (Z) axes of the active coordinate system.

Intervals: contains a field of three text boxes that specify the numbered tic marks for the x (X), y (Y) and z (Z) axes of the active coordi-nate system.

Subintervals specifies the number of intermediate intervals between num-bered tic marks for all displayed rulers.



Summarize Coordinate Systems

The Summarize Coordinate Systems command allows you to display (in the Transcript window) summary information for one or more coordinate systems.

When you summarize a coordinate system, GAMBIT displays four sets of global x, y, and z coordinates corresponding to the system. One set defines the origin of the system. The other three define the endpoints of unit vectors that point from the origin in the directions of the x, y, and z axes.

Using the Summarize Coordinate Systems Form

To open the Summarize Coordinate Systems form (see below), click the Sum-marize command button on the Tools/Coordinate System subpad.

The Summarize Coordinate Systems form contains the following specification.

Coordinate ¬ Systems

specifies the coordinate system(s) about which information is to be displayed in the Transcript window.



Delete Coordinate Systems

The Delete Coordinate Systems command allows you to delete one or more existing local coordinate systems. (NOTE: You cannot delete the global coor-dinate system, c_sys.1.)

Using the Delete Coordinate Systems Form

To open the Delete Coordinate Systems form (see below), click the Delete command button on the Tools/Coordinate System subpad.

The Delete Coordinate Systems form contains the following specification.

Coordinate ¬ Systems

specifies the coordinate system(s) to be deleted.

USING THE MODELING TOOLS Size Functions


5.2 Size Functions

5.2.1 Overview

Size functions allow you to control the size of mesh-element edges for geometric edge entities and for faces or volumes that are meshed using triangular or tetrahedral elements, respectively. Size functions are similar to boundary layers in that they control the mesh characteristics in the proximity of the entities to which they are attached. They differ from boundary layers with respect to the manner in which they are defined and the manner in which they control the mesh. Whereas boundary layers prescribe specific mesh patterns and the sizes of mesh elements within those patterns, size functions control the following properties:

• Maximum mesh-element edge lengths (fixed-type size function)

• Angles between normals for adjacent mesh elements (curvature-type size function)

• Number of mesh elements employed in the gaps between two geometric entities (proximity-type size function)

The following sections describe the GAMBIT commands used to create, modify, summarize, and delete size functions.

Size Functions USING THE MODELING TOOLS


5.2.2 Size Function Commands

The Tools/Size-Function subpad includes the following commands.

Symbol Command(s) Description

Create Size Function Creates and attaches a size function

Modify Size Function Modifies an existing size function

View Size Function Displays an existing size function in the graphics window

Summarize Size Functions Displays summary information for an existing size function

Delete Size Functions Deletes an existing size function

The following sections describe the commands listed above.



Create Size Function

The Create Size Function command creates a size function and attaches it to a specified entity.

Size functions allow you to control the size of the mesh in regions surrounding a specified entity. Specifically, they can be used to limit the mesh-interval size on any edge or the mesh-element edge size on any face or volume that is meshed using triangular or tetrahedral elements, respectively.

u NOTE: GAMBIT size functions are not designed for use with face or volume meshing schemes other than the triangular and tetrahedral schemes, respec-tively.

As an example of the effect of size functions on simple volume meshes, consider the meshed cube shown in Figure 5-3.

Source vertex

Figure 5-3: Example size function attached to a cube corner vertex



In this example, a size function has been attached to the volume and defined with respect to one of the eight corner vertices (the source vertex) on the cube. When the volume is meshed using tetrahedral elements, the size function restricts the size of the element edges in proximity to the source vertex. As a result, the tetrahedral elements in the region surrounding the source vertex are small in comparison to those used to mesh the volume as a whole, and the mesh-element edge length increases with distance from the source vertex.

u NOTE: To apply size-function specifications when meshing a model, GAMBIT employs a background grid constructed by subdividing the bounding box. Specifically, GAMBIT subdivides the bounding box into a set of subsec-tions and assigns size data to the corners of each subsection. To compute the size of any given mesh element that exists within a size-function region, GAMBIT interpolates between the values assigned to the subsection corners.

The number of background-grid subsections affects the speed and accuracy of the size-function application. If the number of subsections is very small, computational time is minimized, but the interpolated element sizes may constitute only crude approximations of the effects of the size-function para-meters. Conversely, if the number of subsections is very large, the interpolated element sizes may accurately reflect the size-function specifications, but computational time may be prohibitive.

To create the background grid, GAMBIT divides the bounding box into a specified number of sections, then divides each section into the same number of subsections, and so on. The total number of subsections, N, in the final background grid can be computed by the formula:

N = nq

where n is the number of subsections created by each division, and q is the number of division steps. For example, if n = 8 (that is, each division divides the previous sections into octants), and q = 5 (that is, the bounding box undergoes five divisions), the total number of subsections is N = 8

5 = 32,768.

You can control the values of n (indirectly) and q (directly) by means of two default variables, which can be modified by means of the Edit Defaults form. The relevant default variables are as follows:

• TOOLS.SFUNCTION.BGRID_MAX_LINE_NUM = k

• TOOLS.SFUNCTION.BGRID_MAX_TREE_DEPTH = q

where n = (k – 1)3.



Size-Function Specifications

To create a size function, you must define the following specifications:

• Type

• Entities

• Parameters

The type specification determines the algorithm used by the size function to control the mesh-element edge size. The entities specification determines which geometric entities are used as the source and attachment entities for the size function. The size function parameters define the exact characteristics of the size function. (NOTE: The entities and parameters required to specify a size function differ according to size-function type.)

Specifying the Size-Function Type

GAMBIT provides the following types of size functions:

• Fixed—specifies the maximum mesh element edge length as a function of distance from a given source entity

• Curvature—specifies the maximum angle between normals for adjacent mesh elements

• Proximity—specifies the number of mesh-element cells to be located in gaps between surfaces in a volume

The following sections describe the effects of each of these size-function types and outline the parameters required for their specification.



Fixed Size Functions

Fixed size functions limit the length of mesh-element edges within a region specified by the distance from an existing entity. To define a fixed size function, you must specify two types of entities:

• Source

• Attachment

The source entity defines the center of the region in which the size function applies. The attachment entity is the entity for which the mesh is to be affected by the size function. Each individual fixed size function is associated with only one source entity but may be associated with one or more attachment entities.

As an example of the difference between source and attachment entities for a fixed size function, consider the configuration shown in Figure 5-3, above. In this example, one corner vertex on the cube is specified as the source entity, and the cube itself is specified as the attachment entity.

Specifying the Source Entity

For fixed size functions, source entity locations and types determine the locations and shapes of the size functions. For example, a fixed size function defined with a vertex as the source entity is centered at the source vertex location and shaped as a sphere. Similarly, a fixed size function defined with a straight edge as the source entity is centered on the edge and is shaped like a cylindrical capsule with rounded ends. GAMBIT allows you to specify vertices, edges, faces, or volumes as source entities.

For the purposes of describing the effect of source-entity type on fixed size functions, source entities can be grouped into two general categories:

• Component source entities

• Non-component source entities

Component source entities constitute components of the entity to be meshed—such as lower-topology vertices, edges, and faces on a given attachment volume. Non-component source entities exist apart from the entity to be meshed—such as vertices, edges, faces, and/or volumes that are located near to the attachment entity but which are not part of its lower topology.



u NOTE: GAMBIT does not distinguish between component and non-component source entities when creating and attaching fixed size functions—that is, identical rules of construction, attachment, and effect apply to botH-types of source entities. The distinction between component and non-component source entities is employed here as a useful tool for describing the effects of fixed size functions on various meshing scenarios.

Component Source Entities

As noted above, component source entities constitute components of the entities to which their size functions are attached. For example, the vertex that serves as the source entity for the fixed size function shown in Figure 5-3, above, is a component source entity, because it constitutes the corner vertex of the cubic volume to which the size function is attached.

The following paragraphs describe the effects of fixed size functions that employ vertex, edge, and face component source entities on meshes of the cubic volume shown in Figure 5-3. In each case, the cubic volume itself serves as the attachment entity, and the size-function distance is specified as less than the length of an edge of the cube (see “Specifying the Parameters,” below).

u NOTE: Although it is possible to specify a single entity as both the source entity and attachment entity for a given fixed size function, doing so is of little practical use, because the size function does not affect its source entity. For example, if you select the volume shown in Figure 5-3 as both the source entity and attachment entity and mesh the volume with tetrahedral elements, GAMBIT meshes the interior of the volume with elements of an approximately uniform size.

Vertex Component Source Entities

Figure 5-4 shows the effect of a fixed size function defined using a corner vertex of the cube as the source entity. (NOTE: The surface mesh shown in Figure 5-4 is identical to that shown in Figure 5-3, above.) For illustrative purposes, Figure 5-4 includes a cutaway sphere representing the outer boundary of the size-function region. In this case, the fixed size function is centered at the source vertex and is shaped as a sphere. Because the source vertex is a corner vertex of the cube, only one octant of the size function affects the mesh within the cube.



Sizing-function boundary

Source vertex

Figure 5-4: Meshed cube—fixed size function with vertex source entity

Edge Component Source Entities

Figure 5-5 shows the effect of a fixed size function defined using one edge of the cube as the source entity. For illustrative purposes, Figure 5-5 includes a cutaway cylindrical capsule representing the outer boundary of the size-function region. The size function is centered along the source edge and is shaped as a cylindrical capsule with rounded ends. In this case, however, neither of the rounded ends intersects the meshable region of the attachment entity, therefore only one quadrant of the cylindrical portion of the capsule affects the volume mesh.




Source edge

Figure 5-5: Meshed cube—fixed size function with edge source entity

Face Component Source Entities

Figure 5-6 shows the effect of a fixed size function defined using one face of the cube as the source entity. For illustrative purposes, Figure 5-6 includes a cutaway volume that represents the outer boundary of the size-function region. The size function is centered on the face and is shaped as a square wafer with rounded ends.

Because the source entity is only one face of the cube, the rounded edges and corners of the wafer-shaped region do not affect the volume mesh at all. Consequently, the fixed size function acts similarly to a boundary layer in that the mesh-element size increases at a fixed rate in the direction normal to the source face.




Source face

Figure 5-6: Meshed cube—fixed size function with face source entity

Non-Component Source Entities

As noted above, GAMBIT does not require that source entities constitute components of their corresponding attachment entities. For example, it is possible to create a fixed size function that employs one bounding edge of a given volume as the source entity and a separate (nearby) volume as the attachment entity. It is also possible to create and employ an edge the explicit purpose of which is to serve as a source entity and to locate the edge either inside or outside its corresponding attachment entities.

As an example of a non-component source entity, consider the configuration shown in Figure 5-7. The configuration consists of a cubic volume and a separate vertex located outside the volume. If you employ the non-component vertex as the source entity for a size function attached to the volume, then mesh the volume using tetrahedral elements, GAMBIT creates a mesh such as that shown in the figure. (NOTE: For illustrative purposes, Figure 5-7 includes a cutaway sphere that represents the outer boundary of the size function.) In this case, only the outer portion of one octant of the size function affects the mesh on the attachment entity. Consequently, the effect of the size function on the mesh is less pronounced than that shown in Figure 5-4, above.




Source vertex

Figure 5-7: Fixed size function—non-component source entity

As a second example of the effect of a non-component source entity, consider the configuration shown in Figure 5-8. In this case, the non-component source vertex is located within a cubic volume to which the fixed size function is attached.



Internal source vertex

Figure 5-8: Internal, non-component source entity

If you define a fixed size function using the same distance and growth parameters employed for the examples shown above and mesh the volume using tetrahedral elements, GAMBIT creates a mesh such as that shown in Figure 5-9. (NOTE: Figure 5-9 shows an internal plane cut of 3-D tetrahedral elements, rather than the surface mesh shown in the figures above, and includes a cutaway representation of the outer boundary of the size function.)

In this case, the mesh elements are small in immediate proximity to the source vertex and increase in size to the size-function boundary. As noted above, the mesh-element sizes outside the boundary are determined by parameters input on the Mesh Volumes form.




Internal mesh,3-D plane cut

Figure 5-9: Meshed volume—internal, non-component source entity

Specifying the Attachment Entity

Fixed size functions can be attached to any edge, face, or volume entity, including any edge or face that constitutes a component of a higher-topology entity. All of the examples described above involve fixed size functions for which the attachment entity constitutes the entity to be meshed—that is, the cubic volume. It is possible, however, to attach a fixed size function to one or more edges or faces of the volume, rather than to the volume itself, and to thereby influence the volume mesh characteristics indirectly.

As an example of the effect of attaching a fixed size function to a component of a higher-topology entity, consider the mesh configuration shown in Figure 5-10. This example involves a fixed size function in which a corner vertex is specified as the source entity and an adjacent edge is specified as the attachment entity. The growth and distance parameters for the size function are identical to those used in the examples described above.



Attachment edge

Source vertex

Influenced faces

Figure 5-10: Meshed cubic volume—fixed size function attached to an edge

Because the size function is attached to one edge of the cube, rather than to the entire cubic volume, it directly influences the mesh-element edge length only on the edge to which it is attached. Consequently, the meshes on the faces that share the attachment edge as a boundary are strongly influenced by the size function, but the mesh on the face with which those faces share a common vertex (the source vertex) is largely unaffected.

As a second example of the effect of attaching a fixed size function to a component of a higher-topology entity, consider the mesh configuration shown in Figure 5-11, in which a corner vertex again serves as the source entity but the fixed size function is attached to an adjacent face. In this case, the size function directly influences the mesh-element sizes on the attachment face and strongly influences the meshes on the two faces that share a corner vertex (the source vertex) with the attachment face.



Attachment face

Source vertex

Influenced faces

Figure 5-11: Meshed cubic volume—fixed size function attached to a face

Specifying the Parameters

To define and create a fixed size function, you must specify the following parameters:

• Start size

• Growth rate

• Distance

• Size limit

The start size is the mesh-element edge length in the region immediately adjacent to the source entity. The growth rate represents the increase in mesh-element edge length with each succeeding layer of elements. For example, a growth rate of 1.2 results in a 20% increase in mesh-element edge length with each succeeding layer of elements. The distance specification determines the overall dimension of the size function—that is, the size of its outer boundary. The size-limit specification represents the maximum allowable mesh-element edge length for the attachment entity either inside or outside the outer boundary of the size function.



Curvature Size Functions

Curvature size functions limit the allowable angle between outward-pointing normals for any two adjacent mesh elements located immediately adjacent to the surface of a source entity. They are particularly useful for geometric configurations that include highly curved surfaces and volume regions which tetrahedral elements of a reasonable size may not fit.

As an example of the effect of a curvature size function, consider the configuration shown in Figure 5-12. The configuration consists of a thin elliptical cylinder meshed with tetrahedral elements of a uniform size. Because the cylinder narrows in its two blade-edge regions, GAMBIT is unable to fully mesh the geometry using mesh elements of the specified size. Consequently, the resulting mesh represents only a crude approximation of the cylinder shape.

Figure 5-12: Meshed elliptical cylinder—without curvature size function

To better approximate the shape of the elliptical cylinder shown in Figure 5-12, it is possible to reduce the specified, uniform mesh-element size such that GAMBIT is able to create elements in the narrow, blade-edge regions. Reducing the mesh-element size, however, can significantly increase the total



number of mesh elements required to mesh the geometry and result in unnecessary mesh refinement in the thick, center region of the cylinder.

As an alternative to reducing the overall mesh-element size, it is possible to refine the mesh by creating and attaching a curvature size function to the cylinder. Figure 5-13 shows the effect of such a size function for which the curved face of the cylinder is specified as the source entity, and the cylinder itself is specified as the attachment entity.

Figure 5-13: Meshed elliptical cylinder—including curvature size function

The curvature size function illustrated in Figure 5-13 limits the allowable angle between outward-pointing normals for the faces of any two adjacent mesh elements located immediately adjacent to the highly curved surface. To satisfy the restriction of the size function, GAMBIT necessarily reduces the sizes of elements used in the narrow, blade-edge regions of the cylinder (see Figure 5-14). In the broad, center region of the cylinder, however, the curvature size-function requirement is satisfied by larger elements. As a result, the mesh demonstrates a natural grading in mesh-element size from the narrow regions to the broad region, and the final mesh approximates the cylinder geometry.



Figure 5-14: Elliptical cylinder, curvature size function—mesh plane cut

Specifying the Source and Attachment Entities

To define a curvature size function, you must specify two types of entities:

• Source

• Attachment

The source entity specifies the face adjacent to which the size function applies. The attachment entity is the edge, face, or volume for which the mesh is to be affected by the size function. For example, in the meshed elliptical cylinder shown in Figure 5-13, the curved face of the cylinder is the source entity, and the cylindrical volume itself is the attachment entity.




To define and create a curvature size function, you must specify the following parameters:

• Angle

• Growth rate

• Distance

• Size limit

The angle is the maximum allowable angle between outward-pointing normals for any two adjacent mesh elements located immediately adjacent to the surface of a source entity. The growth rate represents the increase in mesh-element edge length with each succeeding layer of elements from the attachment edge or face. For example, a growth rate of 1.2 results in a 20% increase in mesh-element edge length with each succeeding layer of elements. The distance specification determines the maximum distance from the source entity at which the size function applies. The size-limit specification represents the maximum allowable mesh-element edge length for the attachment entity either inside or outside the size function boundary.

Proximity Size Functions

Proximity size functions specify the number of mesh-element layers that are created in gaps between faces on a volume. Consequently, they provide a convenient means of refining the mesh in regions that include narrow gaps while allowing the use of larger elements within the bulk volume.

As an example of the effect of a proximity size function, consider the configuration shown in Figure 5-15. The configuration consists of a cubic volume with a narrow, cut-out channel.



Source volume

Attachment face

Cut-out channel

Figure 5-15: Proximity size function—cube with cut-out channel

If you mesh the volume shown in Figure 5-15 (using tetrahedral mesh elements) without attaching a proximity size function to the narrow, gap face at the bottom of the channel, GAMBIT creates a mesh such as that shown in Figure 5-16(a). In this case, the element size is specified such that elements at the bottom of the channel are exactly as wide as the gap face, itself. As a result, numerical computations based on the mesh cannot provide information for locations within the gap face. It is possible to refine the mesh in the gap region by reducing the global mesh element size, but doing so can result in a substantial increase in the total number of mesh elements.

If you attach a proximity size function to the gap face shown in Figure 5-15 and mesh the volume, GAMBIT creates a mesh such as that shown in Figure 5-16(b). In this case, the proximity size function is specified such that GAMBIT creates three mesh elements in the gap. The resulting mesh is refined in the region of the gap face but employs larger elements in the bulk volume. Consequently, numerical computations based on the mesh do provide information for locations within the gap face but are not hindered by the increase in element number that would result from an overall decrease in global mesh element size.



(a) Without size function (b) With size function

Figure 5-16: Proximity size function example—effect of size function

Specifying the Source and Attachment Entities

To define a curvature size function, you must specify two types of entities:

• Source

• Attachment

The source entity specifies the face or volume employed as a reference to define the gaps in which the size function applies. The attachment entity is the volume for which the mesh is to be affected by the size function (see NOTE, below). For example, in the example shown in Figure 5-16, the smaller cube is the source entity, and the larger cube is the attachment volume.

u NOTE: In general, a single entity serves as both the source and attachment entity for a given proximity size function.




To define and create a proximity size function, you must specify the following parameters:

• Cells per gap

• Growth rate

• Distance

• Size limit

The cells-per-gap specification determines the number of layers of mesh elements to be located in the gaps between the source and attachment entities. The growth rate represents the increase in mesh-element edge length with each succeeding layer of elements. The distance specification determines the maximum gap width to which the size function applies. The size-limit spec-ification represents the maximum allowable mesh-element edge length for the attachment entity either inside or outside the size function boundary.



Using the Create Size Function Form

To open the Create Size Function form (see below), click the Create Size Function command button on the Tools/Size-Function subpad.

The Create Size Function form includes the following specifications.

Type: —————————————————————————

Fixed q Curvature Proximity

specifies the type of size function to be created.

Entities: —————————————————————————

Source: ———————————————————————�

Volumes q Faces Edges Vertices

specifies the type of entity that serves as the source of the size function. (NOTE: The size function type determines which entity types are included in the Source option list.)



Volumes ¬ Faces Edges Vertices

specifies the entity that serves as the basis for the size function.

Attachment: ———————————————————————

Volume q Face Edge

specifies the type of entity to which the size function is attached. (NOTE: The size function type determines which entity types are included in the Attachment option list.)

Volume ¬ Face Edge

specifies the entity to which the size function is attached.

Aside from the Type and Entities specifications described above, the only specification on the Create Size Function form that is common to all size-function types is the Label specification located at the bottom of the form, which is as follows:

Label specifies a label for the size function.

The Parameters section of the Create Size Function form varies according to the Type of size function to be created. The following subsections describe the Parameters options and specifications for each of the three Type options listed above. (NOTE: For a description of size-types and their associated parameters, see “Specifying the Size-Function Type,” above.)



Fixed Size-Function Parameters

When you select the Type:Fixed option on the Create Size Function specification form, the Parameters section of the form appears as shown above. The options included in the Type:Fixed Parameters section are as follows.

Start size specifies the desired edge length for all mesh elements immediately adjacent to the Attachment entity.

Growth rate specifies the growth rate for the size function. (NOTE: The growth rate must be greater than unity (1).)

Distance specifies a maximum distance from the Source entity to the outer boundary that defines the region within which the size function applies.

Size limit specifies a maximum size for a mesh-element edge inside and outside of the size-function outer boundary.



Curvature Size-Function Parameters

When you select the Type:Curvature option on the Create Size Function specification form, the Parameters section of the form appears as shown below.

The options included in the Type:Curvature Parameters section are as follows.

Angle specifies the maximum allowable angle between outward-pointing normals for the faces of any two adjacent mesh elements located immediately adjacent to the source entity surface.


Distance specifies a maximum distance from the Source entity to the outer boundary that defines the region within which the size function applies.

Size limit specifies a maximum size for a mesh-element edge inside and outside of the size-function outer boundary.



Proximity Size-Function Parameters

When you select the Type:Proximity option on the Create Size Function specification form, the Parameters section of the form appears as shown below.

The options included in the Type:Proximity Parameters section are as follows.

Cells/gap specifies the number of layers of mesh elements to be located in the gap region designated by the source entity.


Distance specifies a maximum gap width to which the size function applies.

Size limit specifies a maximum size for a mesh element edge inside the radius of the size function.



Modify Size Function

The Modify Size Function command allows you to change the characteristics of an existing size function.

Using the Modify Size Function Form

To open the Modify Size Function form (see below), click the Modify Size Function command button on the Tools/Size-Function subpad.

The Modify Size Function form is similar to the Create Size Function form with the following exceptions:

• It includes an S.Function pick list that allows you to select the existing size function to be modified.

• It does not include a Type option button or Source entity specification fields.

u NOTE: You cannot modify either the Type or Source specifications when modifying a size function by means of the Modify Size Function specification form. To change the Type or Source specifications for a size function, you must delete the existing size function and create a new size functions according to the new specifications.

For a description of the other options and specifications available on the Modify Size Function form, see “Using the Create Size Function Form,” above.



View Size Function

The View Size Function command allows you to display the shape and location of a size function. The display appears in the GAMBIT graphics windows as an isosurface the shape of which reflects the region(s) of influence for the size functions. GAMBIT allows you to customize the display (Color filled) and/or Crosshatch and to specify the value represented by the isosurface.

u NOTE (1): To display a size function by means of the View Size Function form, you must first specify the size function (S. Function) and initialize the display parameters by means of the Initialize pushbutton.

u NOTE (2): The shapes and locations of size-function displays vary according to size-function type. For example, a Fixed size-function appears as a regularly shaped surface centered at the size-function source entity. By contrast, Curvature size-functions appear as centered at the regions most affected by the size-function and may manifest as multiple surfaces for a single size function.

Using the View Size Function Form

To open the View Size Function form (see below), click the View Size Function command button on the Tools/Size-Function subpad.

The View Size Function form includes the following specifications.

S. Function ¬ specifies the size function to be displayed.

Initialize computes the parameters necessary to display the size function.



Isosurface display mode:

specifies the characteristics of the display.

R Color filled colors and shades the surface of the displayed size-function region.

Crosshatch: includes check boxes that specify whether the size-function display includes cross-hatch marks in the x, y, and z directions.

Iso value: specifies the value represented by the size of the displayed size-function surface.



Summarize Size Functions

The Summarize Size Functions command displays size-function summary information in the Transcript window.

Using the Summarize Size Functions Form

To open the Summarize Size Functions form (see below), click the Summarize command button on the Tools/Size Function subpad.

The Summarize Size Functions form contains the following specification.

S.F.s ¬ specifies the size function(s) for which summary information is to be displayed.



Delete Size Functions

The Delete Size Functions command deletes one or more existing size functions.

Using the Delete Size Functions Form

To open the Delete Size Functions form (see below), click the Delete command button on the Tools/Size Function subpad.

The Delete Size Functions form includes the following specification.

S.F.s ¬ specifies the size function(s) to be deleted.

USING THE MODELING TOOLS Turbo Operations


5.3 Turbo Operations

5.3.1 Overview

GAMBIT turbo operations allow you to model flow scenarios that involve turbomachinery components such as fans or turbochargers. The purpose of such operations is to create and mesh a turbo volume—that is, a model composed of one or more real volumes that together represent the flow envir-onment in the region surrounding an individual turbomachinery blade. The turbo volume always includes boundaries that represent the hub, casing, inlet, outlet, and blade and may also include boundaries that represent a splitter—a turbomachinery component attached to the hub the purpose of which is to direct flow between the blades.

This section describes the functions and procedures required to perform basic turbo modeling. It also describes the operations that GAMBIT employs to create and mesh the turbo volume. Specifically, it includes:

• A description of turbo component types

• A summary of the functions available on the Turbo toolpad

• An outline of the general procedure required for creating, meshing, and viewing a turbo volume. The procedure takes the form of a simple example that illustrates the use of GAMBIT turbo functions. (NOTE: Subsequent sections describe each of the turbo functions in detail.)

Turbo Operations USING THE MODELING TOOLS


Turbo Component Types

For GAMBIT modeling purposes, turbomachinery configurations are con-sidered to consist of four component types (see Figure 5-17):

• Hub

• Casing

• Blades

• Splitters (Not shown)

Blades

Hub

Casing

Figure 5-17: GAMBIT turbo components

The hub and casing define the inner and outer radial boundaries of the turbo flow environment. Blades are attached to the hub and are used to move or direct fluid through the environment. Splitters (not shown in Figure 5-17) are optional components that are attached to the hub and located between the blades. They are typically used to direct flow through the environment in proximity of the blades.



Turbo Functions

The purpose of the GAMBIT turbo operations is to create and mesh a model that represents a section of the flow environment surrounding an individual blade. Specifically, the GAMBIT turbo functions allow you to perform the following operations.

• Specify the shapes and locations of the hub and casing

• Define the shapes of blades and (optionally) splitters

• Create a turbo volume—that is, a model that represents the flow region surrounding an individual blade

• Assign zone types to faces of the turbo volume

• Decompose the turbo volume according to a predefined template in order to facilitate meshing

• Perform standard GAMBIT meshing operations on the turbo volume

• Display the turbo volume in a standard turbo cascade view

The following example illustrates the application of these operations to the creation and meshing of a simple turbo model. For detailed descriptions of the functions associated with the operations, see Section 5.3.2, below.



Turbo Modeling Procedure

In GAMBIT, the most basic procedure of modeling of a turbomachinery configuration such as that shown in Figure 5-17 involves the following steps.

Step Operation Description

1 Define and create the turbo profile

Specify edges that describe the shapes and locations of the hub, casing, blades, and (optionally) splitters and specify the axis of revolution. Employ the specifications to create a wireframe shell that is used to define the shape of the turbo volume.

2 Create the turbo volume Create a set of one or more real volumes that encompasses the region surrounding an individual turbo blade.

3 Assign turbo zone types Specify faces or sets of faces that comprise standard turbo zone types—for example, hub or casing.

4 Decompose the turbo volume Apply a standard face decomposition tem-plate to the hub, casing, and any inter-mediate faces of the turbo volume and modify the decomposition, if necessary, to facilitate meshing.

5 Mesh the turbo volume Create a mesh throughout the turbo model.

6 View the turbo volume Display the turbo volume in a standard turbo view.

As a general example of the procedure described above, consider the turbo configuration shown in Figure 5-17, above. The configuration consists of a hub and casing the curved surfaces of which are aligned with the axis of rotation, eight turbo blades, and no splitters. Each turbo blade is curved, like an airplane wing and tapered toward the tip, and all are slightly skewed with respect to the axis of rotation. The base of each blade is flush with the curved surface of the hub, and a small clearance exists between the casing and blade tips.



The following sections employ the configuration described above to describe and illustrate the steps required to create and mesh a turbo volume. They also describe steps that are not immediately related to the modeling of this example but which illustrate general GAMBIT turbo modeling options.

Step 1—Defining and Creating the Turbo Profile

The first step in the GAMBIT turbo modeling process involves defining and creating a turbo profile. A turbo profile is a wireframe that GAMBIT uses to define the shape of a turbo volume. To define the turbo profile, you must specify edges that describe the turbo components and an axis of revolution that determines the general shape of the configuration. When you create a turbo profile, GAMBIT uses the edge and axis specifications to create the wireframe.

u NOTE: In GAMBIT, turbo profile creation and turbo volume creation are separate operations, and each employs its own specification form. The opera-tions are separated in GAMBIT so that you can manipulate the created profile, if necessary, and thereby control the shape and meshing characteristics of the turbo volume.

Defining the Turbo Profile

To define a turbo profile, you must specify the following information:

• The edges that describe the profile, including:

– One real edge or a set of real, connected edges that describe(s) the shape and location of the hub

– One real edge or a set of real, connected edges that describe(s) the shape and location of the casing

– Two or more sets of connected, real edges that describe the cross-sectional shapes of the turbo blades

– Two or more sets of connected, real edges that describe the shapes of the splitters (optional)

• The axis of revolution for the turbo configuration

For the turbo configuration shown in Figure 5-17, the profile can be defined by the collection of real edges shown in Figure 5-18. The collection consists of 14 edges. Two of the edges describe the shapes and locations of the hub and casing. The other 12 edges comprise two sets of six edges each, and each set defines a planar cross section of the blade. The centermost vertices on the inlet



and outlet tips of the blade cross-section edge sets are shown as the leading and trailing vertices, respectively, in Figure 5-18.

Blade cross-sectionedge sets

Hub edge

Casing edge

x

z

y

Leading vertices

Trailingvertices

Flow direction

Figure 5-18: Edges used to define a turbo profile

In this example, the edges that define the hub and casing are aligned with the turbomachinery axis of revolution, which, in this case, is the x axis of the global coordinate system. As a result, they will produce hub and casing faces the curved surfaces of which are aligned with the axis of revolution.

Each of the blade cross sections shown in Figure 5-18 consists of six connected edges. Two of the edges in each set define the large curved surfaces on the pressure and suction sides of the blade; the other four edges in each set define small curved surfaces at the inlet and outlet blade tips. The blade cross sections in this example represent planar cuts through an individual blade at two distinct radial distances from the rotational axis.

u NOTE (1): In general, GAMBIT does not require the blade-cut cross sections to be planar.



u NOTE (2): Each set of edges that describes a blade cross section must consist of either two, four, or six edges. GAMBIT does not allow you to specify odd numbers of edges to describe a blade cross section, nor does GAMBIT allow you to specify more than six edges in a set.

Specifying Edges That Describe the Profile

In GAMBIT, the edges that describe a turbo profile are specified by means of their inlet vertices—that is, the vertices on the side that is nearest to the expected inlet to the flow region. For example, Figure 5-19 shows the vertex specifications required to define the turbo profile for this example in terms of the input fields on the Create Turbo Profile form. The Create Turbo Profile specifications for this example are as follows:

• Hub Inlet vertex—vertex on the inlet end of the hub edge

• Casing Inlet vertex—vertex on the inlet end of the casing edge

• Blade Tips vertices—the leading vertices on each of the two blade cross sections

Hub Inlet vertex

Casing Inlet vertex

Blade Tips vertices

x

z

y

Figure 5-19: Turbo profile vertex specifications, no splitter



Figure 5-20 shows a set of vertex specifications similar to those shown in Figure 5-19 but including vertices to define a splitter (Splitters vertices) as well as a turbo blade.

Hub Inlet vertex

Casing Inlet vertex

Blade Tips vertices

x

z

y

Splitters vertices

Rotationaldirection

Figure 5-20: Turbo profile vertex specifications, including splitter

u NOTE: To facilitate creation of the turbo volume (see below), GAMBIT smoothes each profile edge by replacing its geometry definition with a simple NURBS representation. To perform the smoothing operation, GAMBIT gener-ates sampling points at equal intervals in model space on the original geometry. You can control the smoothing operation by means of two default variables:

• GEOMETRY.EDGE.NUM_SAMPLING_POINTS—specifies the number of sampling points

• TURBO.GENERAL.SMOOTH_BLADE_PROFILES—specifies whether or not the edges are smoothed during turbo volume construction

For instructions regarding the specification of GAMBIT default variables, see Section 4.2.4 in the GAMBIT User’s Guide.



Specifying the Axis of Revolution

In addition to the vertex specifications described above, the turbo definition requires specification of an axis of revolution. The axis specification is made by means of the Vector Definition form, which is accessed by means of the Axis:Define pushbutton on the Create Turbo Profile form. (For a complete description of the Vector Definition form and its specifications, see Section 2.1.4 of this guide.)

In this example, the x axis of the global coordinate system serves as the axis of revolution for the turbo profile, therefore the correct Vector Definition form specifications are:

• Method: Coord. Sys. Axis

• Coordinate Sys.: c_sys.1

• Positive X axis

u NOTE (1): The importance of the axis direction specification on turbo volume construction depends on whether or not the turbo configuration includes a splitter. The dependence can be stated as follows.

• For configurations that do not include a splitter, the axis direction does not affect the turbo volume construction in any way. (NOTE: The axis direction does affect the graphical orientation for the turbo views (see “Step 6—Viewing the Turbo Volume,” below).)

• For configurations that do include a splitter, the axis direction must be specified such that the splitter follows the turbo blade on a rotational path defined by the right-hand rule. For example, in Figure 5-20 (above), the Positive X axis specification defines the rotational direction shown in the figure—in which the splitter follows the turbo blade. An axis specification of Negative X would define a rotational direction opposite that shown in the figure, and the splitter would precede the blade, therefore Negative X constitutes an invalid axis specification for this example.

u NOTE (2): In this example, the hub edge is located at a distance of 10 units from the x axis of the global coordinate system (not shown). The distance between the axis of revolution and the hub and casing edges, in conjunction with the pitch specification, determines the angular width of the hub and casing faces, respectively. GAMBIT does not allow you to specify an axis of revolution that is coincident with either the hub or casing edges.



Creating a Turbo Profile

When you apply the specifications described above and execute the Create Turbo Profile command, GAMBIT creates the turbo profile shown in Figure 5-21. The turbo profile is a wireframe configuration that GAMBIT uses to define the turbo volume. In addition to the blade cross-section edge sets, which are identical to those specified in the turbo profile definition, it consists of the following components:

• Inlet and outlet rail edges

• Medial edges

Medial edges

Inlet rail edges

Outlet rail edges

x

z

y

Figure 5-21: Turbo profile

GAMBIT uses the inlet and outlet rail edges to define the inlet (front) and outlet (back) faces, respectively, of the turbo volume. Similarly, GAMBIT uses the medial edges to define the periodic (side) faces of the turbo volume. The bottom and top faces of the turbo volume are defined by the hub and casing edges, respectively, and by the uppermost and lowermost blade cross sections (see below).



Inlet and Outlet Rail Edges

The inlet and outlet rail edges are real, circular edges that are formed by revolving vertices about the axis of revolution. The innermost and outermost rail edges are formed by revolving the endpoint vertices of the hub and casing edges, respectively (see Figure 5-21). If the turbo profile specification includes more than two sets of blade cross-section edges, GAMBIT creates intermediate rail edges, as well. The intermediate rail edges are formed by the following process.

1) Project the leading and trailing vertices for each intermediate blade cross section onto imaginary discs defined by the innermost and outermost inlet and outlet rail edges, respectively.

2) Create a vertex at each projection point.

3) Revolve the projected vertices about the axis of revolution to create the intermediate rail edge.

As a result of this process, each blade cross section is associated with its own corresponding set of inlet and outlet rail edges. For example, if the defining sets of edges for this example include a third set of blade cross-section edges located halfway between the other two, the resulting turbo profile appears as shown in Figure 5-22.

Medial edges

Inlet rail edges

Outlet rail edges

x

z

y

Figure 5-22: Turbo profile for three blade cross-section edge sets



Medial Edges

Medial edges are virtual edges the center portions of which pass through the approximate middles of the blade cross sections (see Figure 5-21). They are used in the turbo volume creation process to define the shapes of the periodic faces that serve as the side boundaries for the turbo volume. The endpoint vertices of each medial edge lie on (and are hosted by) the inlet and outlet rail edges corresponding to the edge.

Because medial edges are virtual edges, you can change their shapes by sliding their endpoint vertices along their respective host rail edges. By sliding the endpoint vertex of a medial edge and thereby changing its shape, you can alter the shapes of the periodic faces for the turbo volume.

u NOTE: When you slide the endpoint vertex of a medial edge, GAMBIT changes the shape of the edge subject to the constraint that the medial edge must pass through both the leading and trailing tips of the blade cross section that corresponds to the edge.



Step 2—Creating the Turbo Volume

A turbo volume is a set of one or more real volumes that, together, enclose the flow region immediately surrounding the turbomachinery blade. Figure 5-23 shows a simple turbo volume based on the turbo profile shown in Figure 5-21. The turbo volume shown in Figure 5-23 consists of a single real volume that encompasses a blade-shaped void. (For examples of turbo volumes that consist of more than one real volume, see “Specifying the Tip Clearance” and “Specifying the Number of Spanwise Sections,” below.)

x

z

y

Figure 5-23: Example turbo volume

Figure 5-24 shows a turbo profile similar to that shown in Figure 5-23 but including a splitter the characteristics of which are defined by the Splitters specifications shown in Figure 5-20.



x

z

y

Figure 5-24: Example turbo volume, including splitter

Turbo Volume Types

There are two general types of turbo volumes:

• Passage-to-passage

• Blade-to-blade

The turbo volume shown in Figure 5-23 is a passage-to-passage volume.

In a passage-to-passage turbo volume, the turbo volume represents a section of the flow region that completely encompasses the turbo blade, and the blade is represented by a blade-shaped void in the center of the volume. The shapes of the periodic (side) faces of the turbo volume represent projections of the turbo profile medial edges. If the turbo profile includes a splitter, the splitter also manifests as a void in the turbo volume, and the void is completely encompassed by the boundaries of the model.

A blade-to-blade turbo volume represents only that portion of the flow domain that exists entirely between turbo blades. Consequently, the shapes of its periodic (side) faces are determined by the shapes of the pressure and suction sides of the blade, itself, rather than by the medial edges, and the volume does



not include a void that represents the blade unless the profile includes a splitter.

u NOTE: The current version of GAMBIT creates only passage-to-passage turbo volumes. Future GAMBIT versions may allow the creation of blade-to-blade turbo volumes, as well.

Turbo Volume Specifications

The shape, size, and characteristics of any turbo volume are determined by its turbo profile and by the following specifications:

• Pitch

• Tip clearance

• Number of spanwise sections

The pitch determines the angular (lateral) width of the turbo volume. The tip clearance specifies the distance between the casing and the tip of the blade. The number of spanwise sections specification determines the number of individual volumes that comprise the entire turbo volume.

Specifying the Pitch

The pitch determines the angular width of the turbo volume. GAMBIT allows you to specify the pitch angle either directly (in degrees) or in terms of the total number of blades attached to the turbomachinery hub.

As an example of the effect of the pitch specification on the width of the turbo volume, consider the turbo volumes shown in Figure 5-25, each of which is based on the turbo profile shown in Figure 5-21. Figure 5-25(a) shows the turbo volume created with a pitch angle of 45° (8 blades). Figure 5-25(b) shows the turbo volume created with a pitch angle of 36° (10 blades).



(a) 45°, 8 blades

(b) 36°, 10 blades

Figure 5-25: Effect of pitch on turbo volume size

The 8-pitch turbo volume is wider than the 10-pitch turbo volume, but in both cases, the void representing the turbo blade is located in the center of the volume.



Specifying the Tip Clearance

The tip-clearance specification allows you to account for clearance between the turbo blade tips and the casing. You can specify the tip clearance either in terms of a uniform distance from the casing or by means of an edge the swept shape of which truncates the tip of the turbo blade.

GAMBIT turbo volumes that include a tip clearance are composed of three or more real volumes that represent two distinct regions of the model. Two of the volumes define the region of the turbo volume between the blade tip and the casing. The other volume (or volumes) define(s) the region immediately sur-rounding the blade.

Turbo Volume Regions

When you specify a tip clearance, the resulting turbo volume consists of two distinct regions (see Figure 5-26):

• Clearance region

• Blade region

Clearance region

Blade region

Figure 5-26: Turbo volume with tip clearance



The clearance and blade regions represent, respectively, the parts of the model domain that exist above and around the turbo blade. The clearance region consists of two real volumes and extends in thickness between the tip of the blade and the casing. The blade region consists of one or more real volumes that surround the void that represents the turbo blade and extends in thickness from the hub surface to the bottom of the clearance region.

Figure 5-27 illustrates the three volumes that make up the clearance and blade regions for the turbo volume shown in Figure 5-26—that is, the plug volume, outer plug volume, and outer blade volume.

(a) Turbo volume (b) Plug volume

(c) Outer plug volume (d) Outer blade volume

Figure 5-27: Clearance and blade regions

Clearance Region

The clearance region consists of two connected volumes: the plug volume and the outer plug volume. The plug volume (Figure 5-27(b)) constitutes the region immediately above the blade tip. Its shape represents an extension of the blade tip through the clearance region, and its thickness extends from the blade tip to the casing surface. The outer plug volume (Figure 5-27(c)) constitutes the portion of the clearance region outside the perimeter of the plug volume.



Blade Region

The blade region (Figure 5-27(d)) consists of one or more volumes that together constitute the part of the model immediately surrounding the void that represents the turbo blade. For the example shown above, the blade region consists of a single outer blade volume. It is possible, however, to split the blade region horizontally into a set of separate, connected volumes in order to facilitate meshing operations, in which case the blade region consists of more than one volume. The number of volumes included in the blade region is determined by the number of spanwise sections specified when creating the turbo volume (see “Specifying the Number of Spanwise Sections,” below).

Tip-clearance Options

GAMBIT provides two options for specifying the tip-clearance:

• Distance

• Tip-edge inlet

The distance specification is an absolute distance measurement that constitutes a uniform thickness applied to the clearance region. The tip-edge inlet option specifies the leading vertex of an edge that defines the shape of the underside of the clearance region.

Specifying the Distance Option

When you specify a tip-clearance distance, the resulting clearance region is of uniform thickness across the entire turbo volume (see Figure 5-26, above). As a result, the contours of the face that constitutes the underside of the clearance region are projections of those of the casing surface.

Specifying the Tip-edge Inlet Option

As an alternative to specifying a uniform thickness for the tip clearance, GAMBIT allows you to specify an edge the swept surface of which constitutes the underside of the clearance region. To specify such an edge, you must specify its endpoint vertex on the inlet side of the turbo profile.

As an example of the effect of the tip-edge inlet specification, consider the set of edges shown in Figure 5-28. This set of edges is identical to that used to define the turbo profile described above (see Figure 5-18) but includes an extra edge the purpose of which is to define the underside of the clearance region. In this example, the tip edge slopes downward toward the inlet side of the turbo profile.



Tip edgeTip edge inlet vertex

x

z

y

Flow direction

Figure 5-28: Edges used to define a turbo profile, including tip edge

Figure 5-29 illustrates the difference between the distance and tip-edge inlet options on the configuration of the turbo volume for this example. If you specify the tip clearance by means of the distance option, GAMBIT creates a turbo volume such as that shown in Figure 5-29(a) (which is identical to that shown in Figure 5-26, above). In this turbo volume, the plug and outer plug regions are of uniform thickness across the turbo volume, and the blade-tip shape follows the contours of the casing surface. If you specify the tip clearance by means of the tip-edge inlet option and specify the tip edge shown in Figure 5-28, GAMBIT creates the turbo volume shown in Figure 5-29(b). In this case, the clearance region narrows from the inlet to the outlet side of the turbo volume, and the blade tip is not aligned with the casing surface.



(b) Tip-edge inlet option

(a) Distance option

Figure 5-29: Effect of distance and tip-edge inlet options on clearance volume

Specifying the Number of Spanwise Sections

When you create a turbo volume, GAMBIT allows you to automatically split the turbo volume into horizontal (spanwise) sections, which can aid in meshing the turbo volume as a whole, especially for complex blade configurations. To specify the number of spanwise sections for the turbo volume, you must input a value for the Spanwise sections specification on the Create Turbo Volume form (see “Create Turbo Volume” in Section 5.3.2, below).

Each spanwise section consists of a separate real volume, and each volume is connected to those above and/or below it. Figure 5-30 shows a turbo volume for this example divided into two spanwise sections.



Spanwise sections

Figure 5-30: Example turbo volume divided into spanwise sections

GAMBIT creates the spanwise sections such that the turbo volume as a whole is divided into sections of equal radial width. As a result, the outermost spanwise section can differ in thickness from the others due to volume taken up by a clearance region. For example, in Figure 5-30, the spanwise section nearest the casing is slightly thinner than the section adjacent to the hub because of the volume occupied by the clearance region.

u NOTE (1): Because the spanwise sections are equally spaced between the hub and casing, rather than between the hub and underside of the clearance region, it is possible to create a turbo volume in which one or more spanwise sections intersects the underside of the clearance region itself. Although such turbo volumes represent collections of valid real volumes, they can render unusable the GAMBIT turbo operations that are designed to facilitate meshing—such as the Decompose Turbo Volume command—and thereby render the turbo volume difficult to mesh. Consequently, it is sometimes necessary to limit the number of spanwise sections in order to prevent the creation of such intersected volumes.



u NOTE (2): The number of spanwise sections is independent of the number of blade cross sections specified in the turbo profile. For example, the turbo volume shown in Figure 5-30, above, can be created using either the profile shown in Figure 5-21 or that shown in Figure 5-22.

Step 3—Assigning Turbo Zone Types

In addition to the operations described above, GAMBIT provides special tools that aid in meshing and viewing the turbo volume. Although you can mesh and view the turbo volume by conventional means, the special tools facilitate such operations by splitting the volume according to the predefined template decomposition and by displaying views of the turbo volume that cannot be created by any of the conventional GAMBIT graphics operations. To employ the special tools, you must assign turbo zone types to certain faces the turbo volume. The zone-type assignments define boundaries of the turbo volume according to six predefined categories:

• Hub and casing

• Inlet and outlet

• Pressure and suction

Figure 5-31 shows an example assignment of turbo zone types for the turbo volume shown in Figure 5-23, above.



(a) Hub and casing faces (b) Inlet and outlet faces

(c) Pressure faces (d) Suction faces

Hub face

Casing faceInlet face

Outlet face

Figure 5-31: Example turbo volume zone-type assignments

Specifying the Hub and Casing Faces

The hub and casing turbo zone types are assigned to the faces on the hub and casing, respectively, of the turbo volume (see Figure 5-31(a)). For any turbo volumes that involves a tip clearance, the casing zone-type assignment must include the uppermost face of the plug volume in addition to any faces on the uppermost surface of the outer plug volume (see Figure 5-27, above).

Specifying the Inlet and Outlet Faces

The inlet and outlet turbo zone types are assigned to the faces on the influx and outflow sides, respectively, of the turbo volume. The number of faces included in the inlet and outlet turbo zone-type assignments depends on the construction of the turbo volume. If the turbo volume does not include either spanwise sections or a tip-clearance volume, the inlet and outlet zone-type assignments each consist of a single face (see Figure 5-31(b)). If the turbo volume does include spanwise sections and/or a tip-clearance volume, the inlet and outlet turbo zone-type assignments each consist of multiple faces.



Specifying the Pressure and Suction Faces

The pressure and suction zone types are assigned to the faces that surround the void that represents the turbo blade (see Figure 5-31(c) and (d)). They designate the sides of the blade that are subject to high and low pressure, respectively, in actual operation of the turbomachinery blade.

The number of faces included in each zone-type assignment depends on two factors:

• The number of edges specified in each blade cross-section edge set

• Whether or not the turbo volume includes spanwise sections

For example, each blade cross-section employed in this example includes six edges (see Figure 5-18). As a result, the void in the turbo volume that represents the blade is bounded by six faces—three on each side of the blade. Therefore, for the turbo volume shown in Figure 5-31, the pressure and suction turbo zone-type assignments can each contain as many as three faces. If the turbo volume includes spanwise sections (such as those shown in Figure 5-30), the pressure and suction zone-type assignments can contain up to six faces each.

u NOTE (1): As noted above, GAMBIT allows you to specify up to three faces each for the pressure and suction zone-type assignments for the turbo volume shown in Figure 5-31. However, GAMBIT requires only one face each for the zone-type assignments. If you specify more than one face for a pressure or suction turbo zone-type assignment, the specified faces are merged into a single face during subsequent turbo decomposition operations (see “

Step 4—Decomposing the Turbo Volume,” below). For example, if you specify three faces each for the pressure and suction turbo zone-type assignments, the volume resulting from the turbo decomposition includes only two boundary faces for the void that represents the turbo blade.

u NOTE (2): The pressure and suction turbo zone-type assignments must include only side faces that constitute boundaries on the void that represents the turbo blade. GAMBIT does not allow you to include side faces of the plug volume when assigning turbo pressure and suction zone-types.

If the turbo profile includes a splitter, the pressure and suction faces on the splitter must be included in the pressure and suction zone-type specifications, respectively (see Figure 5-32).



(a) Pressure faces

(b) Suction faces

Figure 5-32: Pressure and suction zone-type assignments, including splitter

Executing the Define Turbo Zones Command

When you execute the Define Turbo Zones command, GAMBIT automatically creates boundary zones associated with the six zone types listed above. In addition, GAMBIT creates a periodic zone that includes the side faces of the turbo volume. GAMBIT automatically associates solver-specific boundary zone designations, such as WALL or OUTLET, with the turbo zones. By default, GAMBIT uses FLUENT 5 boundary zones types. If you specify the FIDAP, FLUENT/UNS, or RAMPANT solver, however, GAMBIT assigns boundary zones associated with the specified solver.

u NOTE: When you assign turbo zone types to a turbo volume, GAMBIT automatically creates mesh links between the faces that comprise the periodic group.



Step 4—Decomposing the Turbo Volume

GAMBIT turbo decomposition operations allow you to modify the turbo volume in order to facilitate meshing. When you decompose a turbo volume, GAMBIT splits edges and faces according to a predefined “H-type” template. In addition, GAMBIT sets face vertex types to accommodate face map meshing schemes, applies default meshing parameters to edges of the turbo volume, and creates mesh links between source faces, where appropriate, in order to ensure that mesh characteristics are consistent throughout the model.

u NOTE: You must assign turbo zone types before decomposing a turbo volume. GAMBIT will not decompose a turbo volume for which turbo zone types have not been assigned.

As an example of the effect of decomposition on a turbo volume, consider the turbo volume shown in Figure 5-23, above. If you assign turbo zone types as shown in Figure 5-31 and decompose the turbo volume, GAMBIT modifies the turbo volume as shown in Figure 5-33.

To create the decomposition shown in Figure 5-33, GAMBIT merges the pressure- and suction-face sets to create individual pressure and suction faces, respectively, and splits the hub and casing faces into four connected faces each. In addition, GAMBIT sets the hub and casing face vertex types to accommodate map meshes and links the horizontal faces and edges to facilitate consistent meshing throughout the turbo volume.



a

a’

Figure 5-33: Example turbo volume decomposition

u NOTE (1): For turbo volumes that include splitters, the decomposition is configured differently from that shown in Figure 5-33. For a description of the decomposition for turbo volumes that include splitters, see “Decomposition Template,” below.

u NOTE (2): As noted above, GAMBIT creates mesh links between the source faces when decomposing a turbo volume. In addition, GAMBIT assigns default edge meshing parameters to the edges involved in the decomposition. You can change the default meshing parameters by means of default variables available on the Edit Defaults form. For a list of the available parameters, their default settings, and a description of their correspondence to edges resulting from a turbo decomposition, see “Default Grading Parameters" in Step 5, below.

u NOTE (3): As a first step in decomposing a turbo volume, GAMBIT splits the edges that define the blade and splitter cross sections, as well as the edges that define the boundaries of the periodic (side) faces. To determine the locations at which to split such edges, GAMBIT employs adjustable default parameters. You can specify the parameters, and thereby control the split locations, by means of the Edit Defaults form (see “Default Splitting Parameters,” below).



Automatic Geometry Linking

In addition to the mesh links described above, GAMBIT links the virtual vertices on all source faces so that if you adjust the position of a vertex on one face, GAMBIT automatically adjusts the position of the corresponding vertices on the other faces. For example, if you move vertex a in Figure 5-33 to the center of its host edge, GAMBIT moves vertex a’ to the center of its host edge, as well.

Tip Clearance and Spanwise Sections

If you decompose a turbo volume that includes a tip clearance and/or spanwise sections, GAMBIT splits the underside of the tip clearance region, as well as all horizontal faces associated with the spanwise sections, in the pattern used to split the hub and casing. For example, if you decompose the turbo volume shown in Figure 5-30, GAMBIT creates the turbo volume shown in Figure 5-34.

Figure 5-34: Decomposed turbo volume including tip and sections



Decomposition Template

As noted above, GAMBIT employs an H-type decomposition template when decomposing a turbo volume. Figure 5-35 shows the H-type template for a turbo volume that does not include a splitter (such as that shown in Figure 5-23, above).

Blade void

Figure 5-35: Decomposition template

To perform the decomposition, GAMBIT splits each of the horizontal faces into four connected faces by means of four virtual edges. As noted above, the splitting edges are virtual edges, therefore you can slide their endpoint vertices along their host edges and thereby modify the meshing characteristics the turbo volume.

For turbo volumes that include splitters, the decomposition results in the splitting of faces as shown in Figure 5-36.



Blade void

Splitter void

Figure 5-36: Decomposition template—turbo volume including splitter

In this case, each of the horizontal faces is split into six faces by seven virtual edges.

Default Splitting Parameters

GAMBIT employs a set of default parameters to determine the split points for the edges that define the blade and splitter cross sections, as well as the edges that define the boundaries of the periodic (side) faces. You can adjust the default parameters, and thereby specify the split-point locations, by means of the Edit Defaults form as follows:

1) Select Edit from the GAMBIT main menu bar.

2) Select Defaults… from the Edit menu to open the Edit Defaults form.

3) Select the TURBO tab on the Edit Defaults form.

4) Select and modify the appropriate default variable.

The following subsections describe the split-point parameters that GAMBIT uses when decomposing a turbo volume. (NOTE: The default specifications differ according to whether or not the turbo volume includes a splitter.)



Turbo Blade Only

Figure 5-37 shows a horizontal surface for a decomposed turbo volume that includes a turbo blade but does not include a splitter. The surface consists of four faces that surround a void region representing the blade. The faces are bounded by 18 edges, 12 of which—a through l—are directly associated with the periodic and blade surfaces of the turbo volume.

e

g

h

f

a

i

b

d

cj

k

l

Figure 5-37: Edge designations for split-point defaults—turbo blade only

Prior to decomposition, the surface shown in Figure 5-37 consisted of a single face with a blade-shaped void. The face was bounded by six edges, four of which were directly associated with the periodic and blade surfaces of the turbo volume. The four edges and their definitions with respect to those shown in Figure 5-37 can be defined as follows:

• A (= aic)—suction-side periodic surface of the turbo volume

• B (= ejg)—suction side of the blade

• C (= fkh)—pressure side of the blade

• D (= bld)—pressure-side periodic surface of the turbo volume

GAMBIT determines the decomposition split points for edges such as those shown in Figure 5-37 by means of a set of default variables that specify the



lengths of the post-split edges relative to those of the edges being split. For example, GAMBIT determines the length of edge c in Figure 5-37 by means of a default variable named, SPLIT_PARAMETER2, the value of which con-stitutes the fraction of edge A represented by the length of edge c. By default, GAMBIT assigns a value of 0.1 to SPLIT_PARAMETER2, therefore it splits edge A such that the length of edge c represents ten percent of the original length of the edge A.

Table 5.1 shows the relevant split-parameter default variables and formulas that determine the lengths of the edges shown in Figure 5-37.

Table 5.1: Default split parameters—turbo blade only

Edge(s) Default Variable Value Formula

a, b SPLIT_PARAMETER1 0.1

c, d SPLIT_PARAMETER2 0.1

e, f SPLIT_PARAMETER3 0.1

g, h SPLIT_PARAMETER4 0.1

i A − (a + c)

j B − (e + g)

k C − (f + h)

l D − (b + d)

u NOTE: Each default variable shown in Table 5.1 specifies the lengths of two edge splits in the decomposition operation. For example, the SPLIT_ PARAMETER1 variable specifies both the length of edge a relative to that of edge A and the length of edge b relative to that of edge D.

Turbo Blade and Splitter

Figure 5-38 shows a horizontal surface for a decomposed turbo volume that includes a turbo blade and a splitter. The surface consists of six faces that surround void regions representing the blade and splitter. The faces are bounded by 29 edges, 21 of which—a through u—are directly associated with the periodic, blade, and splitter surfaces of the turbo volume.



f

h

l

i

a

k

c

b m

e

j

d

n

g

op

q

r

s

t

u

Figure 5-38: Edge designations for split-point defaults—blade and splitter

Prior to decomposition, the surface shown in Figure 5-38 consisted of a single face with a blade- and splitter-shaped voids. The face was bounded by eight edges, six of which were directly associated with the periodic, blade, and splitter surfaces of the turbo volume. The six edges and their definitions with respect to those shown in Figure 5-38 can be defined as follows:

• A (= aopc)—suction-side periodic surface of the turbo volume

• B (= eqg)—suction side of the blade

• C (= firh)—pressure side of the blade

• D (= jsl)—suction side of the splitter

• E (= ktm)—pressure side of the splitter

• F (= bnud)—pressure-side periodic surface of the turbo volume

The SPLIT_PARAMETER default variables described above for the turbo-only edge splits also control edge splits for turbo volumes the include a splitter. Table 5.2 shows the relevant split-parameter default variables and formulas that determine the lengths of the edges shown in Figure 5-38.



Table 5.2: Default split parameters—blade and splitter

Edge(s) Default Variable Value Formula

a, b SPLIT_PARAMETER1 0.1

c, d SPLIT_PARAMETER2 0.1

e, f SPLIT_PARAMETER3 0.1

g, h SPLIT_PARAMETER4 0.1

i SPLIT_PARAMETER5 0.4

j, k SPLIT_PARAMETER6 0.1

l, m SPLIT_PARAMETER7 0.1

n SPLIT_PARAMETER8 0.4

o A − (a + p + c)

p A − (a + o + c)

q B − (e + g)

r C − (f + i + h)

s D − (j + l)

t E − (k + m)

u F − (b + n + d)

u NOTE: GAMBIT calculates the combined length of edges o and p by the formula: (o + p) = A − (a + c). GAMBIT locates the split point between edges o and p such that it coincides with the split point between edges n and u on edge F.



Performing the Decomposition

The GAMBIT turbo volume decomposition operation is invoked by means of the Decompose Turbo Volume specification form. To open the Decompose Turbo Volume form, click the Decompose Turbo Volume command button on the Turbo toolpad. (NOTE: As noted above, you must assign turbo zone types before decomposing a turbo volume. GAMBIT will not decompose a turbo volume for which turbo zone types have not been assigned.)

The Decompose Turbo Volume specification form contains a display field that shows the H-type decomposition template to be applied to the turbo volume. When you click Apply on the form, GAMBIT automatically decomposes the turbo volume according to the template.

Step 5—Meshing the Turbo Volume

A GAMBIT turbo volume is composed of one or more real volumes each of which can be meshed according to standard GAMBIT meshing techniques. For example, you can mesh the turbo volume shown in Figure 5-23 without modification by means of the Tet/Hybrid or Stairstep volume meshing techniques. Alternatively, you can apply a Pave mesh to the casing face and employ the Cooper volume meshing technique to mesh the volume.

Although it is possible to mesh turbo component volumes without modifica-tion, the decomposition techniques described above facilitate meshing by creating mappable source faces the shapes and dimensions of which can be adjusted as necessary to improve element quality. In addition to creating mappable source faces, decomposition facilitates meshing by creating interior edges that can be specially graded or refined in areas of interest.

Effect of Decomposition on Turbo Volume Meshes

Decomposed turbo volumes such as that shown in Figure 5-33, facilitate meshing by increasing user control over the meshing characteristics of the source faces—in this case, the hub and casing faces. Figure 5-39 illustrates the effect of such control by contrasting meshes created for a non-decomposed and decomposed turbo volume. In both cases, the meshes shown in Figure 5-39 represent the results of the Cooper volume meshing scheme wherein the casing and hub faces serve as source faces for the scheme.

The casing face for the non-decomposed turbo volume (Figure 5-39(a)) can be meshed only by means of the Pave meshing scheme because it does not meet the topological criteria required for either the Map, Submap, or Tri Primitive schemes. By contrast, each of the faces that comprise the casing surface for the



decomposed turbo volume (Figure 5-39(b)) does meet the criteria required for the Map meshing scheme, therefore each face can be individually mapped.

(b) Mesh of decomposedturbo volume

(a) Mesh of non-decomposedturbo volume

Figure 5-39: Effect of decomposition on volume mesh

In this example, the decomposed-volume mesh contains hexahedral elements that are more regular than those of the mesh for the non-decomposed volume. In addition, the decomposed volume provides flexibility with regard to adjust-ing and customizing the mesh.

Modifying Meshes on Virtual Source Faces

The internal edges that are used to split the hub and casing faces on the decomposed volume are virtual edges, therefore you can adjust their positions by sliding their endpoint vertices along their respective host edges. By sliding the vertices, you can adjust the shape of the existing mesh or modify the orientations of the edges prior to meshing. As an example of the effect of adjusting the split-edge orientations for a decomposed turbo volume, consider the meshed turbo volume shown in Figure 5-40.



Figure 5-40: Effect of adjusted decomposition on volume mesh

In this case, the split-edge endpoint vertices hosted by the boundary edges on the blade-shaped void have been moved toward the tips of the blade, thereby eliminating sharp corners in the face geometries. As a result of these changes, the mesh shown in Figure 5-40 demonstrates generally superior element quality in the regions surrounding the blade tips than does the mesh shown in Figure 5-39(b). (NOTE: In Figure 5-40, the edges used to split the source faces are graded toward the blade, and the interval assignments on the blade tip are adjusted to reduce the number of small, highly-skewed elements.)

Automatic Face Mesh Links on the Turbo Volume

Figure 5-41 shows the types of face-mesh links that exist on a decomposed turbo volume. When you create a turbo volume, GAMBIT automatically creates mesh links between periodic faces of the volume (see faces A-A’ in Figure 5-41(a)). When you decompose a turbo volume, GAMBIT also links casing-surface faces to the corresponding faces on the hub surface and on any other source surfaces, such as those that represent the underside of the clearance region or the intermediate faces between spanwise links (see faces A-A’ , B-B’ , C-C’ , and D-D’ in Figure 5-41(b)).



(b) Linked source faces

(a) Linked periodic faces

A

A’

A’

D’

C’

B’

AD

CB

Figure 5-41: Face mesh links on a decomposed turbo volume

As an example of the effect of mesh linking on a turbo volume, consider the face meshes shown in Figure 5-42. In this case, the meshing of the casing face closest to the inlet side of the turbo volume results in the automatic meshing of the corresponding face on the hub surface. The edge grading parameters (with respect to interval ratio and number of intervals) are identical for each meshed face.



Linked faces

Figure 5-42: Linked-face meshing on decomposed turbo volume

Default Grading Parameters

When you decompose a turbo volume, GAMBIT automatically applies default interval-count and grading parameters to the edges that result from the decomposition operation. You can adjust the default parameters by means of the Edit Defaults form as follows:

1) Select Edit from the GAMBIT main menu bar.

2) Select Defaults… from the Edit menu to open the Edit Defaults form.

3) Select the TURBO tab on the Edit Defaults form.

4) Select and modify the appropriate default variable.

The following subsections describe the general GAMBIT default meshing parameters for edges resulting from a turbo decomposition operation. (NOTE: The default specifications differ according to whether or not the turbo volume includes a splitter.)



Turbo Blade Only

Figure 5-43 shows a source surface for decomposed turbo volume that includes a turbo blade but does not include a splitter. The source surface consists of four faces and includes 16 edges: a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, and p.

a

c

d

bg

h

j

i

f

k

l

m

n

o

p

e

Figure 5-43: Edge designations for decomposition defaults—turbo blade only

Default Interval Counts

GAMBIT directly assigns default mesh interval counts for nine of the edges shown in Figure 5-43. For example, the GAMBIT default variable PTP_SINGLE_INT1 determines the default interval count for edge a. The default interval counts for the other edges can be represented by formulas involving the edges for which GAMBIT assigns the interval counts. For example, the default count for edge n is identical to that for edge k. Table 5.3 shows the relevant default variables and formulas that determine the default interval counts for the edges shown in Figure 5-43.



Table 5.3: Default interval settings—turbo blade only

Edge Default Variable Count Formula

a PTP_SINGLE_INT1 6

b PTP_SINGLE_INT2 50

c PTP_SINGLE_INT3 6

d PTP_SINGLE_INT4 6

e b

f PTP_SINGLE_INT5 6

g PTP_SINGLE_INT6 20

h g

i PTP_SINGLE_INT7 20

j i

k PTP_SINGLE_INT8 20

l b

m PTP_SINGLE_INT9 20

n k

o l

p m

Default Grading Ratios

In addition to assigning default interval counts, GAMBIT assigns default grading parameters to some of the edges shown in Figure 5-43. For example, the GAMBIT default variable, PTP_SINGLE_GRAD1, determines the default grading schemes employed on edges a, c, d, and f. Table 5.4 lists the edges for which default grading schemes can be specified, along with the GAMBIT default variables associated with the settings. In addition, Table 5.4 shows the default grading types and grading ratios employed for each set of edges. (NOTE: All edges shown in Figure 5-43 and not listed in Table 5.4 are



assigned a uniform default grading of unity (1). The default grading value for such edges cannot be altered by means of any GAMBIT default variable.)

Table 5.4: Default grading parameters—turbo blade only

Edge Default Variable Ratio Grading

a PTP_SINGLE_GRAD1 1.2 Single-sided, away from f

b PTP_SINGLE_GRAD2 1.01 Double-sided

c PTP_SINGLE_GRAD1 1.2 Single-sided, away from d

d PTP_SINGLE_GRAD1 1.2 Single-sided, away from c

e PTP_SINGLE_GRAD2 1.01 Double-sided

f PTP_SINGLE_GRAD1 1.2 Single-sided, away from a

g PTP_SINGLE_GRAD3 1.1 Single-sided, away from a

h PTP_SINGLE_GRAD3 1.1 Single-sided, away from c

i PTP_SINGLE_GRAD3 1.1 Single-sided, away from f

j PTP_SINGLE_GRAD3 1.1 Single-sided, away from d

k PTP_SINGLE_GRAD4 1.0 Single-sided, away from g

l PTP_SINGLE_GRAD2 1.01 Double-sided

m PTP_SINGLE_GRAD4 1.0 Single-sided, away from h

n PTP_SINGLE_GRAD4 1.0 Single-sided, away from i

o PTP_SINGLE_GRAD2 1.01 Double-sided

p PTP_SINGLE_GRAD4 1.0 Single-sided, away from j

Vertex Types

Vertex types (and boundary-layer vertex types) are defined as appropriate on the edges that define the turbo blade. All other vertex types are set to End.



Turbo Blade and Splitter

Figure 5-44 shows a source surface for decomposed turbo volume that includes both a turbo blade and a splitter. The source surface consists of six faces and includes 28 edges: a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v1, v2, w, x, y, z, and aa.

g

d

j

bn

oq

p

f

u

m

v1

w

x

s

t

e

k

v2

a

h i

l

aa

zy

c

r

Figure 5-44: Edge designations for default grading—turbo blade and splitter

Default Interval Assignments

GAMBIT assigns default interval counts for 16 of the edges shown in Figure 5-44. The default interval counts for the other edges can be represented as formulas involving the edges for which GAMBIT assigns the interval counts. For example, the default setting for edge p cannot be directly set by means of a GAMBIT default variable. Rather, it is calculated by: p=h+m+q+s. Table 5.5 shows the default variables and formulas that determine the default interval counts for the edges shown in Figure 5-44.



Table 5.5: Default interval counts—turbo blade and splitter


a PTP_DOUBLE_INT1 6

b PTP_DOUBLE_INT2 50

c PTP_DOUBLE_INT3 6

d PTP_DOUBLE_INT4 6

e PTP_DOUBLE_INT5 25

f PTP_DOUBLE_INT6 25

g PTP_DOUBLE_INT7 6

h PTP_DOUBLE_INT8 6

i e

j PTP_DOUBLE_INT9 6

k PTP_DOUBLE_INT10 6

l e

m PTP_DOUBLE_INT11 6

n PTP_DOUBLE_INT12 20

o n

p h+m+q+s

q PTP_DOUBLE_INT13 20

r q

s PTP_DOUBLE_INT14 20

t s

u PTP_DOUBLE_INT15 20

v1 f



Table 5.5: (Continued)


v2 e

w PTP_DOUBLE_INT16 20

x u

y f

z e

aa w

Default Grading Ratios

In addition to assigning default interval counts, GAMBIT assigns default grading parameters to some of the edges shown in Figure 5-44. Table 5.6 shows the default grading parameters employed for each edge in the figure. (NOTE: All edges shown in Figure 5-44 and not listed in Table 5.6 are assigned a uniform default grading of unity (1). The default grading value for such edges cannot be altered by means of any GAMBIT default variable.)

Table 5.6: Default edge grading settings—turbo blade and splitter

Edge Default Variable Setting Grading

a PTP_DOUBLE_GRAD1 1.2 Single-sided, away from g

b PTP_DOUBLE_GRAD2 1.01 Double-sided

c PTP_DOUBLE_GRAD1 1.2 Single-sided, away from d

d PTP_DOUBLE_GRAD1 1.2 Single-sided, away from c

e PTP_DOUBLE_GRAD3 1.05 Single-sided, away from d

f PTP_DOUBLE_GRAD3 1.05 Single-sided, away from g

g PTP_DOUBLE_GRAD1 1.2 Single-sided, away from a

h PTP_DOUBLE_GRAD1 1.2 Single-sided, away from m



Table 5.6: (Continued)

Edge Default Variable Setting Grading

i PTP_DOUBLE_GRAD3 1.05 Double-sided

j PTP_DOUBLE_GRAD1 1.2 Single-sided, away from k

k PTP_DOUBLE_GRAD1 1.2 Single-sided, away from j

l PTP_DOUBLE_GRAD3 1.05 Double-sided

m PTP_DOUBLE_GRAD1 1.2 Single-sided, away from h

n PTP_DOUBLE_GRAD4 1.1 Single-sided, away from a

o PTP_DOUBLE_GRAD4 1.1 Single-sided, away from c

p PTP_DOUBLE_GRAD4 1.1 Single-sided, away from g

q PTP_DOUBLE_GRAD4 1.1 Double-sided

r PTP_DOUBLE_GRAD4 1.1 Double-sided

s PTP_DOUBLE_GRAD4 1.1 Single-sided, away from m

t PTP_DOUBLE_GRAD4 1.1 Single-sided, away from k

u PTP_DOUBLE_GRAD5 1.0 Single-sided, away from n

v1 PTP_DOUBLE_GRAD3 1.05 Single-sided, away from n

v2 PTP_DOUBLE_GRAD3 1.05 Single-sided, away from o

w PTP_DOUBLE_GRAD5 1.0 Single-sided, away from o

x PTP_DOUBLE_GRAD5 1.0 Single-sided, away from p

y PTP_DOUBLE_GRAD3 1.05 Single-sided, away from p

z PTP_DOUBLE_GRAD3 1.05 Single-sided, away from t

aa PTP_DOUBLE_GRAD5 1.0 Single-sided, away from t



Vertex Types

Vertex types (and boundary-layer vertex types) are defined as appropriate on the edges that define the turbo blade. All other vertex types are set to End.



Step 6—Viewing the Turbo Volume

In addition to the standard graphics-window viewing options for display of a turbo volume, GAMBIT allows you to view any turbo volume in a special cascade-view format. In a cascade-view display format, a turbo-volume radial surface—that is, the hub surface, casing surface, or any upper or lower surface associated with a spanwise section—is displayed as if projected onto a flat, two-dimensional plane. Figure 5-45 shows cascade views of the hub and shroud for the simple turbo volume (no splitter) in the example outlined above.

(a) Hub

(b) Casing

Figure 5-45: Cascade views of hub and casing for example turbo volume



Displaying a Cascade View

When you invoke a cascade view, by means of the Cascade option on the View Turbo Volume specification form, GAMBIT displays the cascade view in all of the graphics-window quadrants specified as active on the View Turbo Volume specification form. When you turn Off the cascade view, GAMBIT returns the affected graphics windows to the model perspectives that they displayed prior to the turning on of the cascade view.

For a description of the options available on the View Turbo Volume specifica-tion form, see “View Turbo Volume,” in Section 5.3.2, below.

u NOTE: GAMBIT does not allow you to resize, reorient, zoom, or otherwise alter the cascade view of a turbo volume.

Effect of Profile Axis Direction

As noted in “Step 1—Defining and Creating the Turbo Profile,” above, the turbo profile axis direction affects the graphical orientation for turbo views. The effect of the axis direction on the turbo view orientation depends, in part, on whether the turbo configuration flow direction is axial, radial, or mixed.

As an example of the effect of turbo profile axis on the turbo view, consider the turbo configurations shown in Figure 5-46. Figure 5-46(a) shows the simple, 8-blade turbo volume employed to illustrate the turbo modeling procedure outlined above, in which flow enters and exits the blade array in the −z direction (straight flow direction). Figure 5-46(b) shows the configuration for a low-speed centrifugal compressor in which flow enters the blade array in the −z direction and exits in the radial direction (mixed flow direction).



+z+z

(a) Straight flow direction (b) Mixed flow direction

Flow

Inflow

Outflow

Figure 5-46: Effect of profile axis direction—example configurations

Figure 5-47 and Figure 5-48 show the effect of turbo profile axis direction on the turbo view of the hub for the blade configurations shown in Figure 5-46(a) and Figure 5-46(b), respectively.



(a) Positive Z profile axis (b) Negative Z profile axis

Figure 5-47: Turbo view of hub—straight flow configuration

(a) Positive Z profile axis (b) Negative Z profile axis

Figure 5-48: Turbo view of hub—mixed flow configuration



5.3.2 Turbo Commands

The Tools/Turbo subpad includes the following commands.


Create Turbo Profile Creates a wireframe structure that can be used to create a turbo volume

Slide Virtual Vertex Changes the position of a virtual vertex along a host edge or face

Create Turbo Volume Creates a set of one or more volumes that models the flow environment sur-rounding a turbo blade

Define Turbo Zones Assigns boundary faces of the turbo volume to predefined turbo zone types

Decompose Turbo Volume Splits and modifies edges and faces of a turbo volume in order to facilitate meshing

Split Edge Merge Edges (Virtual) Split Face

Splits or merges existing edges or splits existing faces

Create Boundary Layer Modify Boundary Layer

Creates or modifies boundary layers associated with the turbo volume

Mesh Edges Mesh Faces Mesh Volumes

Generates meshes for edges, faces, or volumes

Link Edge Meshes Unlink Edge Meshes Link Face Meshes Unlink Face Meshes

Links and unlinks edge and face meshes




View Turbo Volume Displays a turbo volume in either of two standard views

Four of the commands listed above are specific to GAMBIT turbo function-ality. They are:

• Create Turbo Profile

• Create Turbo Volume

• Decompose Turbo Volume

• View Turbo Volume

All other commands on the Turbo subpad are also accessible by means of either the Geometry or Mesh subpads. They are included on the Turbo subpad in order to facilitate turbo operations. The following sections describe the each of the four Turbo commands and reference the appropriate sections of this guide that describe the other functions listed above.



Create Turbo Profile

The Create Turbo Profile command allows you to define a set of specifications that describe the shape of a turbomachinery blade and the general configura-tion of its flow environment.

Specifying the Turbo Profile

A turbo profile is a set of specifications that describes the shape of a turbo-machinery blade and the general configuration of its flow environment. To define and create a profile in GAMBIT, you must specify the following infor-mation:

• Hub contour

• Casing contour

• Blade cross-sections

• Splitter (optional) cross-sections

The hub and casing contours define the axial shapes of the turbomachinery hub and casing, respectively. In GAMBIT, each is specified by means of single edge.

To define the overall shape of the blade, you must specify at least two blade cross sections. Each cross-section definition consists of two, four, or six of edges each of which represents a planar cut of the blade at a given distance from the axis. Splitter cross sections (optional) define the shape of any splitters included in the turbo configuration and are defined in the same way that blades are defined—by specifying sets of two, four, or six edges that describe the splitter cross section.

In GAMBIT, the edges for each of the turbo specifications listed above are specified in terms of their endpoint vertices on the inlet side of the turbo configuration. Specifically, the required vertex specifications (as defined on the Create Turbo Profile form) are as follows:

• Hub—Hub Inlet vertex

• Casing—Casing Inlet vertex

• Blade—Blade Tips vertices

• Splitter (optional)—Splitters vertices



As an example of turbo profile specification, consider the set of edges shown in Figure 5-49. The set consists of 26 edges. Two of the edges represent the shapes of the hub and casing. Twelve of the other 24 edges comprise two sets of six edges each, and each set defines the blade cross section at a distinct level. The remaining edges also comprise two sets of six edges each, and each set defines the cross section of a splitter.

Hub Inlet vertex

Casing Inlet vertex

Blade Tips vertices

x

z

y

Splitters vertices

Figure 5-49: Edges used to define a turbo profile

When you define a turbo profile and execute the Create Turbo Profile command, GAMBIT creates a wireframe configuration that serves as the basis for a turbo volume. For example, if you define a turbo profile by means of the edges shown in Figure 5-49 and execute the Create Turbo Profile command, GAMBIT creates the profile shown in Figure 5-50.



Medial edges

Inlet rail edges

Outlet rail edges

x

z

y

Figure 5-50: Example turbo profile

The turbo profile consists of the following elements:

• Original hub, casing, and blade-profile edges

• Inlet and outlet rail edges

• Medial edges

For a description of these elements and their use in defining the shape of the turbo volume, see “Step 1—Defining and Creating the Turbo Profile,” in Section 5.3.1, above.



Using the Create Turbo Profile Form

To open the Create Turbo Profile form (see below), click the Create Turbo Profile command button on the Tools/Turbo subpad.

The Create Turbo Profile form includes the following specifications.

Hub Inlet ¬ specifies the endpoint vertex at the inlet end of the edge or set of connected edges that describe(s) the hub profile.

Casing Inlet ¬ specifies the endpoint vertex at the inlet end of the edge or set of connected edges that describe(s) the casing profile.

Axis ——————————————————————————

Define opens the Vector Definition form, which allows you to specify a vector that defines the axis of revolution for the turbo profile (see “Using the Vector Definition Form” in Section 2.1.4 of this guide).

Blade Tips ¬ specifies the vertices located at the leading (inlet) ends of the edge sets that describe the blade shape. (NOTE: Each vertex specified in the Blade Tips list box must represent a separate set of edges that describe the blade cross section.)

R Splitters ¬ (Optional) specifies the vertices located at the leading (inlet) ends of the edge sets that describe the splitter shape. (NOTE: Each vertex specified in the Splitters list box must represent a separate set of edges that describe the splitter cross section.)



Slide Virtual Vertex

For GAMBIT turbo modeling, the Slide Virtual Vertex command allows you to slide the endpoint vertices of the turbo-profile medial edges along their host rail edges, thereby adjusting the positions of the edges. By adjusting the positions of the linking edges, you can affect the shapes of the periodic faces that GAMBIT creates when it creates the turbo volume.

You can also use the Slide Virtual Vertex command to adjust the positions of linked vertices created during face-split operations associated with turbo decomposition. By adjusting the positions of such vertices, you can alter the shapes of the turbo-volume source faces to facilitate meshing or alter the shape of the mesh for previously-meshed source faces.

Sliding Spanwise-Linked Vertices

The Turbo version of the Slide Virtual Vertex form includes a Move With Links option that allows you to slide entire sets of linked vertices by means of a single operation. If you select the Move With Links option and slide a vertex, GAMBIT automatically slides all of the other linked vertices along their respective host edges. If you unselect the Move With Links option and slide a vertex, GAMBIT does not slide the other linked vertices.

u NOTE: If you slide a vertex the host edge of which is periodically linked to another edge, GAMBIT moves the corresponding vertex on the linked edge regardless of whether or not you select the Move with links option. (For a description of edge linking operations, see Section 3.2.3 of this guide.)

As an example of the effect of the Move With Links option, consider the turbo profile shown in Figure 5-51. If you select the Move With Links option and slide a vertex on one of the inlet rail edges in the clockwise direction, GAMBIT automatically slides the other vertices on the inlet rail edges in the clockwise direction, as well.



Linked inlet vertices

Inlet rail edges

x

z

y

Figure 5-51: Linked inlet vertices in a turbo profile



Using the Slide Virtual Vertex Form

To open the Slide Virtual Vertex form (see below), click the Slide Virtual Vertex command button on the Geometry/Vertex subpad.

For a description of the Slide Virtual Vertex form and its use, see Section 2.2.2 in this guide.



Create Turbo Volume

The Create Turbo Volume command allows you to generate a turbo volume based on the currently-defined turbo profile. A turbo volume is a set of one or more real volumes that enclose the flow region surrounding a turbo blade. (NOTE: There are two general types of turbo volumes: passage-to-passage and blade-to-blade. The current version of GAMBIT creates only passage-to-passage turbo volumes such as that shown in Figure 5-23, above. For a description of the differences between the passage-to-passage and blade-to-blade volumes, see “Turbo Volume Types,” in Section 5.3.1.)

Specifying the Turbo Volume

To create a turbo volume, you must create a turbo profile and specify the following information on the Create Turbo Volume form:

• Pitch

• Tip Clearance

• Spanwise Sections

The Pitch determines the swept angle represented by the turbo volume. The Tip Clearance specifies the distance between the casing and the tip of the blade. The Spanwise Sections specification determines the number of horizontal sections (excluding the tip-clearance region) into which the turbo volume is divided.

For descriptions of the specifications listed above and their effects on the turbo volume creation, see “Turbo Volume Specifications,” in Section 5.3.1,” above.



Using the Create Turbo Volume Form

To open the Create Turbo Volume form (see below), click the Create Turbo Volume command button on the Tools/Turbo subpad.

The Create Turbo Volume form contains the following specification.

Pitch specifies the swept angle represented by the turbo volume.

Blade count q Angle

specifies the units represented by the numerical value in the Pitch text input field. For the Blade count option, the Pitch must be specified as an integer value. For the Angle option, the angle must be expressed in units of degrees. (NOTE: Angle = 360/Blade count.)

R Tip Clearance: specifes that the turbo volume includes a tip-clearance between the top of the blade and the casing. The tip clearance distance can be specified as either an absolute distance or by means of an edge that defines the tip clearance. (For a description of the two types of specifications and their effects on the tip-clearance region of a turbo volume, see “Specifying the Tip Clearance,” in “Step 2—Creating the Turbo Volume,” above.)

l Distance specifies an absolute distance that represents the tip clearance.

l Tip edge inlet ¬ specifies the leading (inlet) vertex on an edge that defines the shape and location of the tip-clearance volume.



Spanwise Sections: specifies the number of horizontal sections (excluding the tip-clearance region) into which the turbo volume is divided during creation.



Define Turbo Zones

The Define Turbo Zones command allows you to assign turbo zone types to faces of the completed turbo volume. Zone-type specifications are required for turbo volume decomposition and viewing operations and can also be used to assign solver-specific zone types to internal and external boundaries on the turbo volume.

Specifying Turbo Zones

Turbo zone-type assignments define boundaries of the turbo volume according to six predefined categories:

• Hub

• Casing

• Inlet

• Outlet

• Pressure

• Suction

Figure 5-52 shows zone-type specifications for the simple turbo volume with no tip-clearance region shown in Figure 5-23, above.



(a) Hub and Casing faces (b) Inlet and Outlet faces

(c) Pressure faces (d) Suction faces

Hub

CasingInlet

Outlet

Figure 5-52: Turbo zone-type specifications

The number of faces included in any individual zone-type specification depends on the configuration of the turbo volume. For description of the rules that govern turbo zone-type specifications, see “Step 3—Assigning Turbo Zone Types,” in Section 5.3.1, above.



Using the Define Turbo Zones Form

To open the Define Turbo Zones form (see below), click the Grid command button on the Tools/Turbo subpad.

The Define Turbo Zones form contains the following specifications.

Hub ¬ specifies the face that comprises the turbo-volume hub.

Casing ¬ specifies the face(s) that comprise(s) the turbo-volume casing.

Inlet ¬ specifies the face(s) that comprise(s) the turbo-volume inlet.

Outlet ¬ specifies the face(s) that comprise(s) the turbo-volume outlet.

Pressure ¬ specifies the face(s) that comprise(s) the pressure side of the turbo blade.

Suction ¬ specifies the face(s) that comprise(s) the suction side of the turbo blade.



Decompose Turbo Volume

The Decompose Turbo Volume command automatically decomposes a turbo volume according to a predefined “H-type” template. The decomposition operation splits turbo-volume faces and sets face vertex types to facilitate meshing (see “Step 4—Decomposing the Turbo Volume,” above).

Using the Decompose Turbo Volume Form

To open the Decompose Turbo Volume form (see below), click the Decompose Turbo Volume command button on the Tools/Turbo subpad.

The Decompose Turbo Volume form includes an option button that contains only the H option and a diagram that illustrates the H-type decomposition template. To decompose the current turbo volume, click Apply.



Split/Merge Geometry Operations

The Split/Merge Geometry command button allows you to perform the following operations.


Split Edge Splits an existing edge into two real or vir-tual edges (see “Split Edge” in Section 2.3.5)

Merge Edges (Virtual) Merges two or more existing edges into a virtual edge (see “Merge Edges (Virtual)” in Section 2.3.5)

Split Face Splits an existing face into two real or virtual faces (see “Split Face” in Section 2.4.7)

For descriptions of the commands listed above, see the corresponding referenced sections in this guide.



Create/Modify Boundary Layers

The Create/Modify Boundary Layers command button allows you to perform the following operations.


Create Boundary Layer Creates a boundary layer attached to an edge or face

Modify Boundary Layer Modifies the definition of an existing boundary layer

For descriptions of the commands listed above, see Section 3.1.2 in this guide.



Mesh Edges/Faces/Volumes

The Mesh Edges/Faces/Volumes command button allows you to perform the following operations.


Mesh Edges Creates mesh nodes on edges (see Section 3.2.1)

Mesh Faces Creates mesh elements on faces (see Section 3.3.1)

Mesh Volumes Creates mesh elements on volumes (see Section 3.4.1)




Link/Unlink Edge/Face Meshes

The Link/Unlink Edge/Face Meshes command button allows you to perform the following operations.


Link Edge Meshes Creates hard links between edges (see “Link Edge Meshes” in Section 3.2.3)

Unlink Edge Meshes Deletes hard links between edges (see “Unlink Edge Meshes” in Section 3.2.3)

Link Face Meshes Creates hard links between faces (see “Link Face Meshes” in Section 3.3.6)

Unlink Face Meshes Deletes hard links between faces (see “Unlink Face Meshes” in Section 3.3.6)




View Turbo Volume

The View Turbo Volume command allows you to display cascade surfaces of a turbo volume. Cascade surfaces are radial sections of the turbo volume defined by the hub, casing, and spanwise-section faces. When you view a cascade surface of the turbo volume, GAMBIT displays the cascade view in any graphics quadrants specified as active on the View Turbo Volume form. When you turn Off the cascade view, GAMBIT returns all quadrants in which the view was displayed to their display state prior to display of the cascade view.

Specifying the Turbo View

To view a cascade surface of the turbo volume by means of the View Turbo Volume form, you must specify the following options and/or information:

• Display status

• Active window(s)

The display-status specification determines whether or not GAMBIT displays a turbo view in one or more of the graphics quadrants. The active-window specification determines the quadrants in which the view is to be displayed.

GAMBIT provides two display-status options:

• Cascade surface

• Off

If you select the Cascade surface option and click Apply on the View Turbo Volume form, GAMBIT displays a cascade surface in all of the graphics quadrants that are specified as active on the Windows button bar (see below). If you select the Off option, GAMBIT returns any quadrants in which a cascade surface is currently displayed to the model view they displayed before the View Turbo Volume command was activated.



Using the View Turbo Volume Form

To open the View Turbo Volume form (see below), click the View Turbo Volume command button on the Tools/Turbo subpad.

The View Turbo Volume form contains the following specifications.

l Cascade surface: turns on the turbo view display.

l Hub specifies display of the hub surface.

l Casing specifies display of the casing surface.

l Spanwise specifies display of one of the intermediate, spanwise-sectioning surfaces.

l Off turns off the turbo view display.

Windows

(quadrant command buttons) enable or disable any or all quadrants with respect to display of the turbo view.

POSTPROCESSING RESULTS Overview


6. POSTPROCESSING RESULTS

u NOTE: This chapter describes postprocessing capabilities that are available only in the Fluent FlowLab software package—which is derived from the GAMBIT program. Consequently, this chapter pertains only to the direct use of FlowLab and/or to the use of GAMBIT to create FlowLab templates.

6.1 Overview

GAMBIT postprocessing commands allow you to display results generated by numerical simulations. Some of the GAMBIT postprocessing commands dis-play numerical values sampled at a single point or x-y plots of values sampled along a vector that intersects the model domain; others display postprocessing surfaces or volumes upon which or within which results are displayed in the graphics window. Figure 6-1 shows an example of a cylindrical postprocess-ing object the surface of which displays colored bands that represent pressure levels along the section of a pipe filled with a flowing fluid.

Cylindrical postprocessing object

Pipe

Figure 6-1: Example cylindrical postprocessing object

The generation and display of results such as those shown in Figure 6-1 require two basic operations:

• Import of the results files that define the results

• Use of the GAMBIT postprocessing commands to display the results

Overview POSTPROCESSING RESULTS


6.1.1 Importing Results Files

To display postprocessing results for any given simulation, you must import two files into GAMBIT:

• A results database

• A neutral file

The results-database file contains the results data for the simulation. The neutral file contains coordinate and connectivity information for the model. For instructions concerning the importation of results-database and neutral files for postprocessing purposes, see Section 4.1 of the GAMBIT User’s Guide.

6.1.2 Using the Postprocessing Commands

When you click the Post command button on the Operation toolpad, GAMBIT opens the Postprocessing toolpad (see Figure 6-2).

Figure 6-2: Postprocessing toolpad

The Postprocessing toolpad includes two sections:

• Postprocessing Objects panel

• Postprocessing Operation subpad



The Postprocessing Objects panel lists all currently defined postprocessing objects and allows you to modify, copy, or delete any object and to activate or deactivate any object in any of the GAMBIT graphics-window quadrants. The Postprocessing Operation subpad contains command buttons that allow you to display or plot numerical results or to create new postprocessing objects.

The following sections describe the operation of both components of the Postprocessing toolpad.

Postprocessing Objects Panel

The Postprocessing Objects panel contains three fields (see below):

• Object list window

• Operation button array

• Active quadrant command bar

Object list window

Operationbuttonarray

Active quadrant command bar

The object list window lists all existing postprocessing objects. The operation button array contains five buttons (arranged vertically) that allow you to modify, copy, delete, activate, or deactivate any of the objects listed in the object list window. The Active quadrant command bar contains a set of five buttons (arranged horizontally) that define the graphics-window quadrants to which the Activate and Deactivate commands apply.



Object List Window

The object list window contains a list of all existing postprocessing objects. To select a postprocessing object for modification, copying, deletion, activa-tion, or deactivation, left-click the object name in the object list window. (NOTE: GAMBIT highlights the name of the currently selected object.)

Operation Button Array

The operation button array is located on the right side of the object list window and includes five command buttons:

• Modify

• Copy

• Delete

• Activate

• Deactivate

To perform any of the operations on an existing postprocessing object, left-click the object name to select it from the object list and click the operation command button.




Modify Postprocessing Object

When you select a postprocessing object from the object list and click the Modify command button, GAMBIT opens a Modify Object form. The displayed Modify Object form corresponds to the type of postprocessing object selected. For example, if you select a plane object named plane_object.1 from the object list and click the Modify command button, GAMBIT opens a Modify Plane Object form such as that shown below.

Modify Object forms allow you to alter the display specifications for the objects to which they correspond. For example, if you open the Modify Plane Object form shown above and change any specification on the form, GAMBIT alters the definition of the plane object named plane_object.1, which, in turn, alters the object display in the graphics window.

Modify Object forms are identical in layout and operation to their correspond-ing Create Object forms (see Section 6.2, below), but they cannot be used to create new postprocessing objects. For example, if you change the Label specification on the Modify Plane Object form shown above, GAMBIT renames the existing plane object rather than creating a new plane object with the new label name.



Copy Postprocessing Object

When you select a postprocessing object from the object list and click the Copy command button, GAMBIT opens a Copy Object form. The displayed Copy Object form corresponds to the type of postprocessing object selected. For example, if you select a plane object named plane_object.1 from the object list and click the Copy command button, GAMBIT opens a Copy Plane Object form such as that shown below.

Copy Object forms allow you to create new objects the initial specifications of which are identical to those of the object to be copied. For example, if you open the Copy Plane Object form shown above and click Apply, GAMBIT creates a new plane object named plane_object.1_copy the specifications of which are identical to those of plane_object.1. If you change the form specifi-cations before clicking Apply, the new object differs from its parent object only with respect to the altered specifications.

Copy Object forms are identical in layout and operation to their corresponding Create Object forms. For a complete list of the available Create Object forms and their specifications, see Section 6.2, below.

Delete Postprocessing Object

When you select a postprocessing object from the object list and click the Delete command button, GAMBIT deletes the selected postprocessing object and removes its label from the object list window.



Activate Postprocessing Object

When you select a postprocessing object from the object list and click the Activate command button, GAMBIT activates the object for display in the graphics-window quadrants that are currently specified as enabled on the Active quadrant command bar. To activate an object for display only in selected quadrants:

1) Select the object from the object list window.

2) Use the buttons on the Active quadrant command bar to specify the quadrant(s) in which the object is to be displayed.

3) Click the Activate command button.

u NOTE: GAMBIT allows you to display any number of postprocessing objects simultaneously in any given graphics-window quadrant.

Deactivate Postprocessing Object

When you select a postprocessing object from the object list and click the Deactivate command button, GAMBIT deactivates display of the object in the graphics-window quadrants that are currently specified as enabled on the Active quadrant command bar. To deactivate a displayed object only in selected quadrants:

1) Select the object from the object list window.

2) Use the buttons on the Active quadrant command bar to specify the quadrant(s) in which the displayed object is to be deactivated.

3) Click the Deactivate command button.

Active Quadrant Command Bar

The Active quadrant command bar contains five buttons that allow you to specify graphics-window quadrants for the Activate and Deactivate operations on the operation button array. Each button toggles its corresponding quadrant between the enabled and disabled states. The enable states are displayed on the quadrant buttons according to the following convention:

• Enabled quadrants are displayed in red.

• Disabled quadrants are displayed in gray.

To change the enable state of a quadrant, click the corresponding quadrant command button. To enable all quadrants, click All.



Postprocessing Operation Subpad

The Postprocessing Operation subpad is displayed immediately below the Postprocessing Objects panel and provides access to the following GAMBIT postprocessing operations.

• Sample Point

• Sample Line

• Create Geometric Object

• Create Isosurface Object

• Create Simulation Object

The Sample Point and Sample Line commands display numerical values of simulation results sampled at a single point or along an intersecting vector, respectively. The Create Geometric Object commands create postprocessing objects in the shapes of planes, cubes, cylinders, or spheres. The Create Isosurface Object command creates a postprocessing object the shape of which is defined by a surface of constant value for one of the simulation results variables. The Create Simulation Object command creates a postprocessing object the shape of which is defined by an existing topological object—for example, a face or volume.

The following section describes the postprocessing commands associated with each of the command buttons located on the Postprocessing Operation subpad.

POSTPROCESSING RESULTS Postprocessing Commands


6.2 Postprocessing Commands

The Postprocessing Operation subpad contains command buttons that allow you to display or plot numerical results or to create new postprocessing objects. The symbols associated with each of the Postprocessing Operation subpad commands are as follows.


Sample Point Displays the numerical value of a solution result sampled at a specified point in the model

Sample Line Displays an x-y plot showing the variation in magnitude of a specified results variable along a vector that intersects the model

Create Geometric Object Displays contours or vectors repre-senting the magnitude of solution variables on a specified plane, cube, cylinder, or sphere object

Create Isosurface Object Displays an isosurface corresponding to a constant value of a specified solution variable

Create Simulation Object Displays contours or vectors repre-senting the magnitude of solution variables on a geometric entity

The following sections describe the Postprocessing commands listed above.

Postprocessing Commands POSTPROCESSING RESULTS


6.2.1 Sample Point

The Sample Point command displays the value of a specified degree of freedom (that is, a results variable) at a given location in the model domain. The location of the sample point is specified by means of its coordinates, and the degree of freedom is specified by means of an option button that includes all available degrees of freedom for the current results database. GAMBIT displays the sampled value in the Value field on the Sample Point form.

Using the Sample Point Form

To open the Sample Point form (see below), click the Sample Point command button on the Postprocessing Operation subpad.

The Sample Point form includes the following specifications.

Location: specifies the coordinates of the sample point.

Coordinate ¬ Sys.

specifies the coordinate system with respect to which the sample point is specified. (See Section 2.1.3 of this guide.)

Type ———————————————————————


specifies the type of coordinate parameters to be used in specifying the sample point.



Global | Local specifies the location of the sample point with respect to either the Global or Local system.

DOF: —————————————————————————

x-coordinates q y-coordinates z-coordinates …

specifies the degree of freedom (DOF) to be sampled. (NOTE: The available degrees of freedom vary according to solution results but include by default, as a minimum, the x, y, and z coordinates of the point location.)

Value: displays the value of the specified degree of freedom at the sample-point location.



6.2.2 Sample Line

The Sample Line command creates and displays an x-y plot for which the x axis represents the distance along a vector that intersects the model, and the y axis represents value of a specified degree of freedom from the set of simula-tion results.

As an example of an x-y plot created by means of the Sample Line command, consider the model shown in Figure 6-1, above. The model represents a section of straight pipe with a circular cross section through which fluid flows. If you open the Sample Line specification form, define a sample vector along the centerline of the pipe, and select the pressure degree of freedom (DOF), GAMBIT displays the x-y plot shown in Figure 6-3.

Figure 6-3: Sample Line plot—pressure along the centerline of the pipe



The x-y plot shown in Figure 6-3, above, illustrates an almost-linear decrease in pressure from the inlet to the outlet of the pipe.

Similarly, if you select the velocity-magnitude degree of freedom (DOF) and define the sample vector such that it bisects the outlet face and is perpendicu-lar to the centerline of the pipe, GAMBIT displays the x-y plot shown in Figure 6-4. This plot constitutes a velocity profile for fluid flow at the pipe outlet and demonstrates the parabolic profile that is characteristic of laminar fluid flow.

Figure 6-4: Sample Line plot—velocity profile

(NOTE: The number of points plotted in any Sample Line plot is a function of the number of mesh elements employed by the model.)



Using the Sample Line Form

To open the Sample Line form (see below), click the Sample Line command button on the Postprocessing Operation subpad.

The Sample Line form contains the following specifications.

Definition: displays the endpoint coordinates of a vector that defines the line along which the specified degree of freedom is to be sampled.

Vector opens the Vector Definition form, which allows you to spec-ify a vector that defines the sampling line for the x-y plot (see “Using the Vector Definition Form” in Section 2.1.4 of this guide).

DOF: —————————————————————————

x-coordinates q y-coordinates z-coordinates …

specifies the degree of freedom (DOF) to be displayed on the x-y plot. (NOTE: The available degrees of freedom vary according to solution results but include by default, at a minimum, the x, y, and z coordinates along the plot line.)



6.2.3 Create Geometric Object

The Create Geometric Object command buttons allows you to create surfaces or volumes upon which or within which contours and/or vectors representing the magnitude of specified solution variables can be displayed. The following operations are accessible by means of the Create Geometric Object command button.


Create Plane Object Creates a plane postprocessing object

Create Cube Object Creates a cube postprocessing object

Create Cylinder Object Creates a cylinder postprocessing object

Create Sphere Object Creates a sphere postprocessing object




Create Plane Object

The Create Plane Object command creates a postprocessing object in the shape of a cutting plane.

When you create and display a plane postprocessing object, GAMBIT dis-plays solution results on a planar surface that intersects the geometric entity to which the object is attached. For example, if you define a plane object to display velocity contours on an x-z plane that intersects the center of the pipe shown in Figure 6-1, above, GAMBIT creates a display such as that shown in Figure 6-5.

yz

x

Figure 6-5: Example plane object—velocity contours, centered, x-z plane cut

In this case, the velocity contours appear as smooth bands the colors of which represent velocity magnitudes. GAMBIT allows you to define the contours such that they are displayed in any of several alternative forms.



Plane-Object Specifications

To characterize a plane postprocessing object, you must specify the following information:

• Orientation vector and Level—specifies the location and orientation of the cutting plane

• Attachment—specifies the geometric entity for which the postprocess-ing results are to be displayed

• Halfspace—specifies the region of the Attachment entity, relative to the position of the cutting plane, for which results are to be displayed

• Attributes—determines the degrees of freedom (for example, velocity or pressure) to be displayed and the format (contours or vectors) of the graphics display

The following sections describe the specifications listed above.

Specifying the Orientation Vector and Level

To define the orientation and location of the cutting plane, you must specify an Orientation vector the origin of which lies in the plane and the direction of which is normal to the plane (see Figure 6-6).

Cutting plane

Orientation vector

Figure 6-6: Cutting plane—Orientation vector



For example, the plane postprocessing object shown in Figure 6-5, above, employs the positive (or negative) y axis of the global coordinate system as the Orientation vector, therefore the cutting plane is aligned with the x-z coor-dinate plane. (NOTE: The global coordinate system, which is not shown in the figure, is located along the centerline of the pipe.)

To specify the Orientation vector, you must input its parameters on the Vector Definition form, which is accessed by means of the Orientation vector:Define pushbutton on the Create Plane Object specification form (see below). For a general description of the Vector Definition form and its use, see “Using the Vector Definition Form,” in Section 2.1.4 in this guide.

After the cutting plane is defined, you can adjust its position by means of the Level slider bar on the Create Plane Object form. The Level slider bar adjusts the position of the cutting plane within the boundaries of the attachment entity but does not affect the orientation of the plane.


The Attachment specification determines the geometric entity for which post-processing results are to be displayed. GAMBIT allows you to specify either a face, volume, or group as an attachment entity. The attachment entity deter-mines the appearance of the plane object as follows:

• If you specify a face as the attachment entity, the resulting plane object consists of any curves that represent the intersection of the cutting plane and the face.

• If you specify a volume as the attachment entity, the resulting plane object constitutes a two-dimensional, planar surface such as that shown in Figure 6-5, above.

• If you specify a group as the attachment entity, the resulting plane object constitutes the intersection of the plane with any volumes and/or faces in the group.

Specifying the Halfspace Region

The Halfspace specification determines the region of the attachment entity, relative to the cutting plane, for which results are to be displayed. GAMBIT provides the following Halfspace options.



Option Description

+ Displays results in the region of the attachment entity located above the cutting plane

0 Displays results in the region of the attachment entity exactly intersected by the cutting plane

- Displays results in the region of the attachment entity located below the cutting plane

As an example of the effect of the Halfspace specification, consider the plane object shown in Figure 6-7.

yz

x

Figure 6-7: Plane object—velocity contours, Halfspace (-) option

The plane object shown in Figure 6-7 is similar to that shown in Figure 6-6 but is defined using the Halfspace (-) option. As a result, GAMBIT displays results for the region of the pipe located below the cutting plane.

GAMBIT allows you to combine Halfspace options when creating or modify-ing plane postprocessing objects. For example, if you specify both the (-) and (0) Halfspace options for the plane postprocessing object shown above, GAMBIT displays results for the lower half of the pipe and for the surface that represents the intersection of the cutting plane and the internal volume of the pipe (see Figure 6-8).



yz

x

Figure 6-8: Plane object—velocity contours, Halfspace (-) and (0)

Specifying the Plane-Object Attributes

The Attributes specification determines the style of graphics display and degree of freedom for which information is to be displayed on the postproc-essing object. GAMBIT provides two types of postprocessing attributes for plane objects:

• Contour

• Vector

Contour attributes display results in the form of lines, bands, clouds, or wires that represent various magnitude levels for a specified degree of freedom. Vector attributes display results in the form of vector fields. GAMBIT allows you to display either or both attribute types on any plane postprocessing object.

To specify characteristics for contour and vector attributes, you must define the attributes by means of the Specify Contour Attributes and Specify Vector Attributes forms, respectively. The Specify Contour Attributes and Specify Vector Attributes forms are accessible by means of the Edit pushbuttons located immediately to the right of the Contour and Vector check boxes on the Create Plane Object form.



u NOTE: Many of the contour and vector display options described here employ colors to represent numerical magnitude. The GAMBIT postprocessing color convention is defined such that the colors blue and red represent the minimum and maximum magnitudes, respectively, for any given degree of freedom. For example, if you specify a pressure contour plot for a results database in which the pressure values vary from a 0.5 to 2.0, GAMBIT constructs the contour plot color spectrum such that blue and red represent pressure values of 0.5 and 2.0, respectively.

The Contour and Vector headings on the Create Plane Object form (and all other forms used to create geometric objects) indicate the degrees of freedom represented by the current postprocessing display and its associated color spectrum. The specific information included in the headings is as follows.

• Contour headings indicate the degree of freedom used to plot the contour. For example, a heading that reads “Contour: pressure” on the Create Plane Object form indicates that colors on the plane-cut contour plot represent pressure magnitude.

• Vector headings indicate both the degree of freedom represented by the displayed vectors and the color used in the vector display. For example, a heading that reads “Vector: velocity vectors” and “Color: magnitude” on the Create Plane Object form indicates that the displayed vectors represent velocity vectors, and their colorations represent vector magnitude.

The Contour and Vector specification regions on the Create Plane Object form (and all other forms used to create geometric objects) include color bars that constitute legends for the respective Contour and Vector displays.

Specifying Contour Attributes

When you click the Edit pushbutton associated with the Contour check box on the Create Plane Object form, GAMBIT opens the Specify Contour Attributes form (see “Using the Specify Contour Attributes Form,” below). The Specify Contour Attributes form allows you to define the degree of freedom for which contour information is to be displayed on the plane postprocessing object, as well as the graphical appearance of the contour.

To define a contour attribute, you must specify the following information:

• DOF (degree of freedom)

• Contour Type

• Color Map



The DOF specification represents the degree of freedom for which information is to be displayed. The Contour Type specification determines the manner in which the information is displayed. The Color Map options control the color-display characteristics of the contour.

Specifying the Degree of Freedom (DOF)

For any plane-object contour, GAMBIT allows you to specify the degree of freedom to be displayed by means of the DOF option button on the Specify Contour Attributes form. The allowable degrees of freedom for any contour depend on the type(s) of data available in the imported results database but include, at a minimum, x, y (and z, for 3-D simulations) coordinates.

Specifying the Contour Type

GAMBIT allows you to specify the following types of contours:

• Lines

• Bands

• Smooth

• Wire-isosurfaces

• Isosurfaces

• Cloud

Each contour type differs from the others with respect to its appearance on postprocessing surfaces and volumes. The following subsections describe the effect of each contour-type specification on the display of results for the straight pipe example shown above.



Lines Contours

When you specify a Lines contour for a plane object, GAMBIT displays a set of color-coded curves across the region defined by the intersection of the cut-ting plane and the attachment entity. Each curve represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-9 shows a plane object defined with respect to the pressure degree of freedom and employing the Lines contour type. For this contour, GAMBIT displays a series of curves (which appear as straight line segments) at specific intervals along the length of the pipe. Each curve represents the intersection of the cutting plane with a given pressure isobar in the flow stream. By default, GAMBIT divides the pipe longitudinally into 10 intervals. It is possible, however, to control the line-spacing (or band width) by means of options available in the Color Map section of the Specify Contour Attributes form (see “Specifying the Color Map,” below).

If you select the Lines option and specify the Halfspace (-) and/or (+) options on the Create Plane Object form, GAMBIT displays curves in the region(s) of the attachment entity below and/or above the cutting plane. For example, Figure 6-10 shows a plane object the contour specifications of which are identical to those shown in Figure 6-9, but for which the Halfspace (-) and (0) options are specified on the Create Plane Object form.

yz

x

Figure 6-9: Plane object—pressure, Lines contour, Halfspace (0)



yz

x

Figure 6-10: Plane object—pressure, Lines contour, Halfspace (-) and (0)

GAMBIT allows you to modify the number of lines displayed, as well as the minimum and maximum values represented by the Lines contour, by means of the Color Map options on the Specify Display Attributes form (see “Specifying the Color Map,” below).



Bands Contours

When you specify a Bands contour for a plane object, GAMBIT displays a set of colored bands across the region defined by the intersection of the cutting plane and the attachment entity. Each band represents the level of magnitude of the contour degree of freedom evaluated at one end of the band.

Figure 6-11 shows a plane object defined with respect to the pressure degree of freedom and employing the Bands contour type. Each band in this contour represents an isobaric value at one end of the band. By default, GAMBIT divides the pipe into 10 intervals. It is possible, however, to control the number and width of the bands by means of the Color Map options on the Specify Contour Attributes form (see “Specifying the Color Map,” below).

If you select the Bands option and specify the Halfspace (-) and/or (+) options on the Create Plane Object form, GAMBIT displays the series of discrete, colored bands on the in the region(s) below and/or above the cutting plane. For example, Figure 6-12 shows a plane object the contour specifications of which are identical to those shown in Figure 6-11, above, but for which the Halfspace (-) and (0) options are specified on the Create Plane Object form.

yz

x

Figure 6-11: Plane object—pressure, Bands contour, Halfspace (0)



yz

x

Figure 6-12: Plane object—pressure, Bands contour, Halfspace (-) and (0)

GAMBIT allows you to modify the number of bands displayed, as well as the minimum and maximum values represented by the Bands contour, by means of the Color Map options on the Specify Display Attributes form (see “Specifying the Color Map,” below).



Smooth Contours

When you specify a Smooth contour for a plane object, GAMBIT displays a smoothly graded color spectrum across the region defined by the intersection of the cutting plane and the attachment entity. The colors of the displayed spectrum represent an approximation of the continuous change in magnitude for the degree of freedom associated with the contour.

Figure 6-13 shows a plane object defined with respect to the pressure degree of freedom and employing the Smooth contour type. For this contour, GAMBIT displays a smoothly graded spectral band along the length of the pipe.

If you select the Smooth option and specify the Halfspace (-) and/or (+) options on the Create Plane Object form, GAMBIT displays the smoothly graded color spectrum in the region(s) below and/or above the cutting plane. For example, Figure 6-14 shows a plane object the contour specifications of which are identical to those shown in Figure 6-13, above, but for which the Halfspace (-) and (0) options are specified on the Create Plane Object form.

yz

x

Figure 6-13: Plane object—pressure, Smooth contour, Halfspace (0)



yz

x

Figure 6-14: Plane object—pressure, Smooth contour, Halfspace (-) and (0)

GAMBIT allows you to modify minimum and maximum values represented by the Smooth contour colors by means of the Color Map options on the Specify Display Attributes form (see “Specifying the Color Map,” below).



Wire-isosurfaces Contours

When you specify a Wire-isosurfaces contour for a plane object, GAMBIT displays a set of color-coded, wire-frame surfaces within the 3-D region(s) of the attachment entity located below and/or above the cutting plane. Each surface represents a constant level of magnitude for the degree of freedom associated with the contour, and each is crosshatched with a regular, quadri-lateral matrix of lines that represents the shape of the surface.

Figure 6-15 shows a plane object defined with respect to the pressure degree of freedom, employing the Wire-surface contour type, and for which the Halfspace (-) option is specified on the Create Plane Object form. For this contour, GAMBIT displays a series of crosshatched surfaces at specific inter-vals along the length of the pipe. Each surface represents a unique pressure isobar in the flow stream.

yz

x

Figure 6-15: Plane object—pressure, Wire-isosurfaces, Halfspace (-)

GAMBIT allows you to modify the number of wire isosurfaces displayed, as well as the minimum and maximum values represented by the Wire-isosurface contour, by means of the Color Map options on the Specify Display Attributes form (see “Specifying the Color Map,” below).



u NOTE: Wire-isosurface contours are applicable only to 3-D regions of volume attachment entities—that is, to the region(s) of an attachment volume located below and/or above the cutting plane. If you specify a Wire-isosurface contour for the cutting plane only, by selecting only the Halfspace (0) option on the Create Plane Object form, the plane-object display is identical to that for a Lines contour applied to the cutting plane (see Figure 6-9, above).



Isosurfaces Contours

When you specify an Isosurfaces contour for a plane object, GAMBIT displays a set of color-coded surfaces within the 3-D region(s) of the attachment entity located below and/or above the cutting plane. Each surface represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-16 shows a plane object defined with respect to the pressure degree of freedom, employing the Isosurfaces contour type, and for which the Halfspace (-) option is specified on the Create Plane Object form. Each dis-played surface represents a unique pressure isobar in the flow stream.

yz

x

Figure 6-16: Plane object—pressure, Isosurfaces, Halfspace (-)

GAMBIT allows you to modify the number of isosurfaces displayed, as well as the minimum and maximum values represented by the Isosurfaces contour, by means of the Color Map options on the Specify Display Attributes form (see “Specifying the Color Map,” below).



u NOTE: Isosurfaces contours are applicable only to 3-D regions of volume attachment entities—that is, to the region(s) of an attachment volume located below and/or above the cutting plane. If you specify an Isosurfaces contour for the cutting plane only, by selecting only the Halfspace (0) option on the Create Plane Object form, the plane-object display is identical to that for a Bands contour applied to the cutting plane (see Figure 6-11, above).



Cloud Contours

When you specify a Cloud contour for a plane object, GAMBIT displays a cloud of points within the 3-D region(s) of the attachment entity located below and/or above the cutting plane. Each point is color-coded in a manner similar to that used by the Bands option to display color bands on the cutting plane surface. That is, the 3-D region is divided into discrete intervals, and all of the points displayed in a given interval are assigned the same color.

Figure 6-17 shows a plane object defined with respect to the pressure degree of freedom, employing the Cloud contour type, and for which the Halfspace (-) option is specified on the Create Plane Object form. The set of color intervals shown in the figure constitutes a banded representation of pressure change along the length of the pipe.

yz

x

Figure 6-17: Plane object—pressure, Cloud, Halfspace (-)

The displayed cloud density is constant across the attachment entity and does not correspond to the magnitude any degree of freedom. GAMBIT allows you to adjust the density, along with other cloud characteristics, by means of the Density specification of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).



u NOTE: Cloud contours are applicable only to 3-D regions of volume attach-ment entities—that is, to the region(s) of an attachment volume located below and/or above the cutting plane. If you specify a Cloud contour for the cutting plane only, by selecting only the Halfspace (0) option on the Create Plane Object form, the plane-object display is identical to that for a Smooth contour applied to the cutting plane (see Figure 6-13, above).

Specifying Color Map and Density

The lower portion of the Specify Contour Attributes form includes the follow-ing sections:

• Color Map

• Density

The Color Map section includes three input fields that specify the numbers of intervals displayed on the postprocessing contour and the range of values rep-resented by the contour. The Density section consists of an input field that allows you to control the displayed point density for Cloud contours.

Specifying the Color Map

The Color Map section on the Specify Contour Attributes form includes the fol-lowing input fields:

• Intervals

• Minimum (and Restore pushbutton)

• Maximum (and Restore pushbutton)

The Intervals input field specifies the total number of intervals (bands) included in the postprocessing contour. The Minimum and Maximum input fields specify, respectively, the minimum and maximum values of the degree of freedom represented by the contour. The Restore pushbuttons restore the global minimum and maximum values for the specified degree of freedom to the Minimum and Maximum input fields, respectively.

By default, GAMBIT defines each postprocessing contour according to the following rules:

• The entire global range of values for the specified degree of freedom is represented on the contour.

• The global range of values for the specified degree of freedom is divided into 10 evenly spaced intervals.



• The color of each interval represents the lowest value of the specified degree of freedom in the interval.

• The display-color spectrum is defined such that the colors blue and red represent global minimum and maximum values, respectively, for the specified degree of freedom.

As an example of the effect of these defaults, consider the Bands contour shown in Figure 6-12, above. In the flow simulation illustrated this figure (and all other figures shown above), the pressure degree of freedom varies globally from a minimum value of 0.0 to a maximum value of 318.6. Consequently, each color band shown in Figure 6-12 represents a pressure increment of 31.86 (= 318.6/10). Furthermore, the color of each band represents the lowest value of pressure in the band—for example, the blue band on the left side of the figure represents pressure values from 0.0 to 31.86. Figure 6-18 shows a Bands contour identical to that shown in Figure 6-12 but for which the pres-sure intervals are annotated to show the pressure values associated with each band.

yz

x

0.0

95.6

31.9

318.6

254.9

191.2

127.4

63.7 286.7

223.0

159.3

Figure 6-18: Plane object—pressure, annotated Bands contour



u NOTE: As noted above, the color red represents the maximum global value for the specified degree of freedom. As a result, none of the contours shown in the figures above include a red color interval. GAMBIT determines the color for each band based on the minimum value in each interval. For example, in Figure 6-18, the color of the rightmost interval (286.7–318.6) is dark orange and represents the lowest pressure value in the interval—that is, 286.7.

The Intervals specification in the Color Map section on the Specify Contour Attributes form allows you to specify the total number of intervals included in the contour. (NOTE: Allowable Interval values range from 1 to 254.) For example, if you create a Bands contour such as that shown in Figure 6-12, above, and specify an Intervals value of 4 (while maintaining the default Minimum and Maximum values), GAMBIT displays a contour such as that shown in Figure 6-19.

yz

x

0.0

79.7

318.6

159.3

238.9

Figure 6-19: Plane object—pressure, Bands, Intervals = 4

In this case, the entire range of pressure values for the flow simulation is dis-played as four intervals, each of which represents a pressure increment of approximately 79.65 (= 318.6/4). The color of the rightmost interval repre-sents a pressure value of 238.9—that is, the minimum value of pressure in that interval.



The Minimum and Maximum input fields in the Color Map section on the Specify Contour Attributes form allow you to define the lower and upper limits of the range of values for which intervals are displayed. For example, if you create a Bands contour such as that shown in Figure 6-12, above, and specify Minimum and Maximum values of 100 and 200, respectively, (while maintain-ing the default Intervals value) GAMBIT displays a pressure contour such as that shown in Figure 6-20.

yz

x200.0

100.0p < 100.0

p > 200.0

Figure 6-20: Plane object—pressure, Bands, Minimum = 100, Maximum = 200

In this figure, the region in which pressure values are between 100 and 200 is subdivided into 10 intervals, and the intervals are assigned colors identical to those shown in Figure 6-12, above. The regions in which pressure is less than 100 (Minimum) or greater than 200 (Maximum) are displayed in light gray and red, respectively.

The effects of the Interval, Minimum, and Maximum specifications are most easily detected on contours that involve sharp divisions between intervals, such as Lines, Bands, Wire-isosurfaces, and Isosurfaces contours, but Smooth and Cloud contours are affected by the specifications, as well. For example, Figure 6-21 shows a Cloud contour plotted using Interval, Minimum, and Maximum specifications identical to those used in Figure 6-20.



yz

x200.0

100.0p < 100.0

p > 200.0

Figure 6-21: Plane object—pressure, Cloud, Minimum = 100, Maximum = 200

Specifying Cloud Density

In addition to controlling the number of displayed intervals and the values rep-resented by the extremes of the display-color spectrum, GAMBIT allows you to control the density (number) of points displayed by means of the Density input field on the Specify Display Attributes form. The Density value consti-tutes a factor by which GAMBIT multiplies the default density. For example, the Cloud contour shown in Figure 6-17, above, represents a Density value of 4, which represents a density four times greater than the GAMBIT default cloud density. Figure 6-22 shows a similar Cloud contour with a specified density of 2.



yz

x

Figure 6-22: Plane object—pressure, Cloud, Halfspace (-), Density = 2

Specifying Vector Attributes

When you click the Edit pushbutton associated with the Vector check box on the Create Plane Object form, GAMBIT opens the Specify Vector Attributes form (see “Using the Specify Vector Attributes Form,” below). The Specify Vector Attributes form allows you to define the degree of freedom for which vectors are to be displayed on the plane postprocessing object, as well as the graphical appearance of the vectors.

Figure 6-23 shows a velocity vector plot for the example described above, in which fluid flows through a section of straight pipe. In this figure, the velocity magnitudes are represented by the vector colors and by the lengths of the vectors. The velocity directions are represented by the directions of the dis-played vectors.

In this example, most of the velocity vectors point in the general direction of fluid flow—that is, the positive x direction—especially near the downstream end of the pipe. Consequently, all of the velocity vectors appears to be aligned with the cutting plane. A magnified view of the postprocessing object reveals, however, that many of velocity vectors point away from the cutting plane, especially in the regions near the upstream end of the pipe. The vector plot shown in Figure 6-23 represents the Halfspace (0) option on the Create Plane Object form, therefore, only those vectors the origins of which are inter-sected by the cutting plane are displayed.



yz

x

Figure 6-23: Plane object—example velocity vector plot

To define a vector display, you must specify the following information:


• Color

• Vector Magnitude

• Arrowheads

• Components

The following subsections describe the specifications listed above.


For any given vector plot, you must specify the degree of freedom to be dis-played by means of the DOF option button on the Specify Vector Attributes form. The allowable degrees of freedom for any vector plot depend on the type(s) of data available in the results database and do not include scalar prop-erties such as pressure or temperature.



Specifying the Color

The Color specification determines the method by which GAMBIT assigns vector colors. The Specify Vector Attributes form includes three Color options:

• Magnitude

• DOF

• Fixed

If you specify the Magnitude option, the resulting vector colors correspond to the magnitude of the degree of freedom (DOF) being plotted. For example, in Figure 6-23, above, the vectors displayed near the centerline of the pipe are dark orange (corresponding to a high magnitude), and the vectors near the pipe walls are green or blue (corresponding to a low magnitude). In this case, the vector colors illustrate the fact that the velocity is higher near the center of the pipe than it is near the walls.

If you specify the DOF option, the resulting vector colors correspond to the magnitude of a specified degree of freedom. For example, you can plot veloc-ity vectors the colors of which correspond to local pressure or temperature in the fluid domain.

If you specify the Fixed option, GAMBIT uses one uniform color for all vectors. (NOTE: The Fixed color is selected by means of the Set Color form (see “Using the Set Color Form” in Section 2.2.4 of this guide).)

Specifying the Vector Magnitude

The Vector Magnitude specification consists of the following components:

• Minimum and Maximum (and Restore pushbuttons)

• Scale

The Minimum and Maximum text fields allow you to specify the range of values represented by the displayed vectors. For example, if you specify Minimum and Maximum values of 0 and 1.25, respectively, for a velocity vector plot such as that shown in Figure 6-23, above, GAMBIT displays only those vectors that possess magnitudes between 0 and 1.25. (NOTE: The Restore pushbuttons restore the global minimum and maximum values for the specified degree of freedom to the Minimum and Maximum input fields, respectively.)

When you display a vector field on a GAMBIT postprocessing object, the lengths of the displayed vectors (and sizes of any associated arrowheads) represent the local magnitudes of the specified degree of freedom. For example, in Figure 6-23, above, the displayed vector lengths and arrowhead



sizes represent the local velocity magnitudes across the region of the pipe intersected by the cutting plane. By default, GAMBIT scales all displayed vectors such that the length of the longest vector (which represents the highest magnitude for its associated degree of freedom) is 10 percent of the length of the longest diagonal of the model bounding box.

GAMBIT allows you to control the vector sizes (relative to the default sizes) by means of the Scale option on the Specify Vector Attributes form. For example, if you specify a Scale factor of two (2), GAMBIT doubles the lengths of all displayed vectors relative to their default lengths. Similarly, if you specify a Scale factor of 0.5, GAMBIT halves the lengths of all displayed vectors relative to their default lengths.

Specifying the Arrowheads Option

The Arrowheads option allows you to specify whether or not the displayed vectors include arrowheads at their tips to indicate their direction.

• If you select the Arrowheads option, GAMBIT displays arrowheads at the tips of all displayed vectors.

• If you do not select the Arrowheads option, GAMBIT displays the vectors without arrowheads.

Specifying the Components Options

The Components options allow you to show the x, y, and/or z component vectors for all displayed vectors. For example, if you specify the x, y, and z Components options for the vector plot shown in Figure 6-23, above, GAMBIT displays four vectors at each point of origin—the original velocity vector and its x, y, and/or z component vectors.



Using the Create Plane Object Form

To open the Create Plane Object form (see below), click the Create Plane Object command button on the Postprocessing subpad.

The Create Plane Object form includes the following specifications.

Label specifies a label for the new plane object.

Orientation vector:

displays the endpoint coordinates of a vector that defines ori-entation of the plane object. The orientation is defined such that the vector direction is normal to the plane, and the Start endpoint of the vector is located within the plane.

Define opens the Vector Definition form, which allows you to spec-ify a vector that defines the plane orientation (see “Using the Vector Definition Form” in Section 2.1.4 of this guide).



Level –��– adjusts the position of the cutting plane within the boundaries of the attachment entity but does not affect the orientation of the plane.

Attachment: —————————————————————————

Group q Volume Face

specifies the attachment entity type.

Group ¬ Volume Face

specifies the attachment entity.

Halfspace: specifies the region of the model to be displayed. For plane objects, the available Halfspace options are as follows:

(+)—displays results for regions of the attachment entity that exist above the cutting plane

(0)—displays results for the region of the attachment entity that is exactly intersected by the cutting plane

(-)—displays results for regions of the attachment entity that exist below the cutting plane

(NOTE: Halfspace options are not mutually exclusive.)



Attributes: specifies the type(s) of postprocessing attributes associated with the plane object. For plane objects, GAMBIT provides two types of postprocessing attributes:

• Contour • Vector

The Contour attribute displays data in the form of discrete or continuous contours. The Vector attribute displays vector fields.

Each Attributes option is associated with an Edit pushbutton, which accesses the specification form appropriate to the option. For example, if you click the Edit pushbutton associated with (and located to the right of) the Contour check box, GAMBIT opens the Specify Contour Attributes form. For descriptions of the Specify Contour Attributes and Specify Vector Attributes forms, see, respectively, “Using the Specify Contour Attributes Form” and “Using the Specify Vector Attributes Form,” below.

The Contour and Vector headings on the Create Plane Object form display the degrees of freedom represented by the current postprocessing display and its associated color spectrum. The specific information included in the headings is as follows.

• Contour headings indicate the degree of freedom used to plot the contour. For example, a heading that reads “Contour: pressure” on the Create Plane Object form indicates that colors on the plane-cut contour plot represent pressure magnitude.


The Contour and Vector specification regions on the Create Plane Object form include color bars that constitute legends for the respective Contour and Vector displays.



Using the Specify Contour Attributes Form

To open the Specify Contour Attributes form (see below), click the Contour:Edit pushbutton on any Create Postprocessing Object form—for example, the Create Plane Object form. (NOTE: The Specify Contour Attributes form shown below does note include the Density option, which is available only for the Contour Type:Cloud option.)

The Specify Contour Attributes form includes the following specifications.

DOF: —————————————————————————

x-coordinates q y-coordinates z-coordinates ...

specifies the degree of freedom for which a contour is to be displayed. (NOTE: The available degrees of freedom vary according to the results database but include, at a mini-mum, x-coordinates, y-coordinates, and z-coordinates.)



Contour Type specifies the type of contour to be displayed. Available contour types include:

• Lines

• Bands

• Smooth


• Isosurfaces

• Cloud

For descriptions of these contour types, see the appropriate subsection in “Specifying the Contour Type,” above.

Color Map: contains input fields that define the characteristics of the color mapping that GAMBIT employs on the contour display.

Intervals specifies the total number of distinct bands to be included in the contour display.

Minimum specifies the value represented by the lowest (blue) end of the contour color spectrum.

Restore restores the Minimum input field value to the global minimum for the specified degree of freedom.

Maximum specifies the value represented by the highest (red) end of the contour color spectrum.

Restore restores the Maximum input field value to the global maximum for the specified degree of freedom.

Density (Cloud option only) specifies the density of points displayed to create the cloud (see “Specifying Cloud Density,” above).



Using the Specify Vector Attributes Form

To open the Specify Vector Attributes form (see below), click the Vector:Edit pushbutton on any Create Postprocessing Object form—for example, the Create Plane Object form.

The Specify Vector Attributes form includes the following specifications.

DOF —————————————————————————

velocity vectors q …

specifies the degree of freedom for which a contour is to be displayed. (NOTE: The available degrees of freedom vary according to the current results database.)

Color specifies the manner in which GAMBIT determines the colors of the displayed vectors. Available options include:

• Magnitude—Vector colors indicate the local magnitude of the degree of freedom represented by the vectors.

• DOF—Vector colors indicate the local magnitude of a specified degree of freedom.

• Fixed—All vectors are displayed using a single, specified color.



Color (cont.) (NOTE: To specify the Fixed color used to display the vectors, click the colored bar located to the right of the Fixed option. When you click the colored bar, GAMBIT opens the Set Color form, which allows you to specify a color. For a description of the Set Color form, see “Using the Set Color Form” in Section 2.2.4 of this guide.)

Minimum specifies the minimum value for which vectors are displayed.

Restore restores the Minimum input field value to the global minimum for the specified degree of freedom.

Maximum specifies the maximum value for which vectors are displayed.

Restore restores the Maximum input field value to the global maximum for the specified degree of freedom.

Scale specifies the lengths of the displayed vectors relative to their default lengths (see “Specifying the Vector Magnitude,” above).

R Arrowheads specifies whether GAMBIT includes arrowheads at the tips of all displayed vectors.

Components includes three check boxes that allow you to specify the display of the x, y, and/or z component vectors for each displayed vector.



Create Cube Object

The Create Cube Object command creates a postprocessing object in the shape of a cube.

When you create and display a cube postprocessing object, GAMBIT displays solution results on a cubic volume. For example, if you define a small cube object to display banded velocity contours for the model shown in Figure 6-1, above, GAMBIT creates a display such as that shown in Figure 6-24.

yz

x

Figure 6-24: Example cube object—Bands velocity contours

In this case, the velocity contours appear as bands the colors of which repre-sent velocity magnitudes. The color gradation displayed on this object illustrates that velocity is greater in the center of the pipe than it is near the walls.



Cube-Object Specifications

To characterize a cube postprocessing object, you must specify the following information:

• Orientation vector and Dimension—specifies the location, orientation, and size of the cube


• Halfspace—specifies the region of the Attachment entity, relative to the space bounded by the cube, for which results are to be displayed


Specifying the Orientation Vector and Dimension

The Orientation vector and Dimension specifications define the location, orientation, and size of the cube. Figure 6-25 shows the effect of such speci-fications on the display of three cube objects, each of which differs from the others only with respect to its Orientation vector and Dimension specifications.

yz

x

Orientation vector:(5.0,0,0) to (5.0,1,0)

Dimension = 0.318


Dimension = 0.393


Dimension = 0.168

x = 0

x = 10

Figure 6-25: Cube objects—Orientation vector and Dimension specifications



The origin and direction of the Orientation vector define the location and orientation of the cube, respectively. Specifically, the vector origin defines the location of the center of the cube, and GAMBIT orients the cube such that the Orientation vector points toward the center of one of the faces on the cube.

To specify the Orientation vector, you must input its parameters on the Vector Definition form, which is accessed by means of the Orientation vector:Define pushbutton on the Create Cube Object specification form (see below). For a general description of the Vector Definition form and its use, see “Using the Vector Definition Form,” in Section 2.1.4 in this guide.

In Figure 6-25, the Orientation vector specifications for the three cube objects differ from each other only with respect to the x coordinates of their respec-tive vector Start points. The y and z coordinates of the vector Start points are zero (0) in all three cases, and the vector End points are specified such that the faces of each cube are aligned with the x, y, and z global coordinate planes.

The Dimension specification represents one half of the length of a cube edge. For example, if you input a Dimension value of 0.25, GAMBIT constructs a cube each edge of which has a length of 0.50. Cube size affects the appear-ance of the cube object by virtue of its effect on the size of the flow region encompassed by the cube. If the cube object is defined such that it extends outside the boundary of the entity to which it is attached, GAMBIT clips the object at the entity boundary. For example, the edges of the largest cube object shown in Figure 6-25 extend outside the boundary of the pipe, therefore the cube object is clipped by the boundary. (NOTE: In this case, the Halfspace (0) specification is applied to all three cubes, therefore the inner regions of the cubes are empty, and the clipped regions of the largest cube appear transpar-ent. For a description of the effect of the Halfspace option on cube postproc-essing objects, see “Specifying the Halfspace Region,” below.)


The Attachment specification determines the geometric entity for which post-processing results are to be displayed. GAMBIT allows you to specify either a face, volume, or group as an attachment entity. The attachment entity deter-mines the appearance of the cube object as follows:

• If you specify a face as the attachment entity, GAMBIT displays post-processing results for only those regions of the face intersected by the cube.

• If you specify a volume as the attachment entity, the resulting cube object constitutes a three-dimensional, cubic volume such as that shown in Figure 6-24, above.



• If you specify a group as the attachment entity, the resulting cube object constitutes the intersection of the cube with any volumes and/or faces in the group.

For example, the cube object shown in Figure 6-26 is defined with the cylin-drical pipe face as the Attachment entity, and the Dimension is specified such that the cube object extends beyond the boundaries of the pipe. As a result, GAMBIT displays only those regions of the cylindrical Attachment face that are intersected by the cube.

u NOTE: In Figure 6-26, the cube object is defined with the Halfspace (0) and (-) options. If the object had been specified without the Halfspace (-) option, only the outlines of the intersecting regions would appear on the postprocess-ing graphics display.

yz

x Cube object boundary

Attachment face

Intersecting regions

Figure 6-26: Cube object—Face Attachment entity, Halfspace (0) and (-)


The Halfspace specification determines the region of the attachment entity, relative to the cubic volume, for which results are to be displayed. GAMBIT provides the following Halfspace options for cube objects.



Option Description

+ Displays results in the region of the attachment entity located outside the cube

0 Displays results in the region of the attachment entity inter-sected by the surface of the cube

- Displays results in the region of the attachment entity located inside the cube

As an example of the effect of the Halfspace specification, consider the cube objects shown in Figure 6-27, which differ only with respect to their Halfspace specification. Both objects are defined to display wire-isosurface, velocity-magnitude contours.

(a) Halfspace (0) and (-)

(b) Halfspace (0)

yz

x

Figure 6-27: Cube object—comparison of Halfspace options

The cube object shown in Figure 6-27(a) is specified using the Halfspace (0) and (-) options, therefore the object shows wire-isosurface contours within the cube as well as on its surface. The cube object shown in Figure 6-27(b) is specified using only the Halfspace (0) option, therefore the wire-isosurface contours appear only on its surface.



Specifying the Cube-Object Attributes

The Attributes specifications for cube objects are similar to those for plane objects (see “Specifying Contour Attributes” in “Create Plane Object,” above). Differences between the specifications for the two object types are largely due to the differences in dimensionality—that is, planes and cubes are 2-D and 3-D objects, respectively.

For cube objects, GAMBIT provides two types of postprocessing attributes:

• Contour

• Vector

Contour attributes display results in the form of lines, bands, clouds, or wires that represent various magnitude levels for a specified degree of freedom. Vector attributes display results in the form of vector fields. GAMBIT allows you to display either or both types of attributes on any cube object.

u NOTE: Many of the contour and vector display options described here employ colors to represent numerical magnitude. For a general description of the specifications and uses of postprocessing colors, see “Specifying the Plane-Object Attributes,” above.


To define a contour attribute for a cube object, you must specify the following information:


• Contour Type

• Color Map



For any cube-object contour, GAMBIT allows you to specify the degree of freedom to be displayed by means of the DOF option button on the Specify Contour Attributes form. The allowable degrees of freedom for any contour depend on the type(s) of data available in the imported results database but include, at a minimum, x, y (and z, for 3-D simulations) coordinates.





• Lines

• Bands

• Smooth


• Isosurfaces

• Cloud

The contour types listed above are identical to those described for plane objects (see “Specifying the Contour Type” in “Create Plane Object,” above). For cube objects, however, the Lines, Bands, and Smooth contour types apply only to objects defined using the Halfspace (0) option (see below).



Lines Contours

When you specify a Lines contour for a cube object, GAMBIT displays a set of color-coded curves on the surface of the cube. Each curve represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-28 shows a cube object defined with respect to the velocity magni-tude degree of freedom and employing the Lines contour type. For this contour, GAMBIT displays a series of closed curves on the surface of the cube. Each curve represents the intersection of the cube surface with a given velocity-magnitude isosurface in the pipe. By default, GAMBIT displays curves representing the boundaries between 10 different levels of velocity magnitude. It is possible, however, to control the number of levels displayed (that is, the band width) by means of options available in the Color Map section of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-28: Cube object—velocity magnitude, Lines contour, Halfspace (0)

u NOTE: Lines contours can only be applied to the postprocessing surfaces, therefore, for cube objects, they appear in the graphics display only when the Halfspace (0) option is selected. Conversely, the Halfspace (+) and (-) options do not affect Lines contour displays.



Bands Contours

When you specify a Bands contour for a cube object, GAMBIT displays a series of colored bands across the surface of the cube. Each band represents the level of magnitude of the contour degree of freedom evaluated on one side of the band.

Figure 6-29 shows a cube object defined with respect to the velocity magni-tude degree of freedom and employing the Bands contour type. Each displayed band represents the intersection of the cube surface with a region of velocity magnitudes in the pipe. By default, GAMBIT displays bands representing the boundaries between 10 different levels of velocity magnitude. It is possible, however, to control the number of levels displayed (that is, the band width) by means of options available in the Color Map section of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-29: Cube object—velocity magnitude, Bands contour, Halfspace (0)

u NOTE: Bands contours can only be applied to the postprocessing surfaces, therefore, for cube objects, they appear in the graphics display only when the Halfspace (0) option is selected. Conversely, the Halfspace (+) and (-) options do not affect Bands contour displays.



Smooth Contours

When you specify a Smooth contour for a cube object, GAMBIT displays a smoothly graded color spectrum across the surface of the cube. The colors of the displayed spectrum represent an approximation of the continuous change in magnitude for the degree of freedom associated with the contour.

Figure 6-30 shows a cube object defined with respect to the velocity magni-tude degree of freedom and employing the Smooth contour type. For this contour, GAMBIT displays a smoothly graded spectral band across the surface of the cube. The Color Map section of the Specify Contour Attributes form allows you to modify and refine the Smooth display characteristics (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-30: Cube object—velocity magnitude, Smooth contour, Halfspace (0)

u NOTE: Smooth contours can only be applied to the postprocessing surfaces, therefore, for cube objects, they appear in the graphics display only when the Halfspace (0) option is selected. Conversely, the Halfspace (+) and (-) options do not affect Smooth contour displays.




When you specify a Wire-isosurfaces contour for a cube object, GAMBIT displays a set of color-coded wires in a region defined in reference to the cube—that is, inside and/or outside the cube. Each wire represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-31 shows a cube object defined with respect to the velocity magni-tude degree of freedom and employing the Wire-isosurfaces contour type. For this contour, GAMBIT displays a series of wires, each of which is color-coded to represent a different magnitude level. The Color Map section of the Specify Contour Attributes form allows you to modify and refine the Wire-isosurfaces display characteristics (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-31: Cube object—Wire-isosurfaces contour, Halfspace (-)

u NOTE: If you specify the Halfspace (0) option, Wire-isosurfaces contours appear as Lines contours on the surface of the cube (see Figure 6-28, above).




When you specify an Isosurfaces contour for a cube object, GAMBIT displays a set of color-coded surfaces in a region defined in reference to the cube—that is, inside and/or outside the cube. Each surface represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-32 shows a cube object defined with respect to the velocity magni-tude degree of freedom and employing the Isosurfaces contour type. For this contour, GAMBIT displays a series of surfaces, each of which is color-coded to represent a different magnitude level. The Color Map section of the Specify Contour Attributes form allows you to modify and refine the Isosurfaces display characteristics (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-32: Cube object—Isosurfaces contour, Halfspace (-)

u NOTE: If you specify the Halfspace (0) option, Isosurfaces contours appear as Bands contours on the surface of the cube (see Figure 6-29, above).



Cloud Contours

When you specify a Cloud contour for a cube object, GAMBIT displays a cloud of discrete points in a region defined in reference to the cube—that is, inside and/or outside the cube. Each point is color-coded in a manner similar to that used by the Bands option.

Figure 6-32 shows a cube object defined with respect to the velocity magni-tude degree of freedom and employing the Cloud contour type. The displayed cloud density is constant and does not correspond to the magnitude any degree of freedom. GAMBIT allows you to adjust the density, along with other cloud characteristics, by means of the Density specification of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-33: Cube object—Cloud contour, Halfspace (-)

u NOTE: If you specify the Halfspace (0) option, Cloud contours appear as Smooth contours on the surface of the cube (see Figure 6-30, above).




The functions of the Color Map and Density sections of the Specify Contour Attributes form for 3-D postprocessing objects, such as cube objects, are similar to those for the plane object (see “Specifying Color Map and Density” in “Specifying the Plane-Object Attributes,” above). For example, Figure 6-34 shows the effect of increasing the number of Intervals on the appearance of a Lines contour of velocity magnitude for a cube object.

(a) Intervals = 10

(b) Intervals = 20

yz

x

Figure 6-34: Cube object—effect of Intervals value on Lines contour

For a description of the effect of the Density specification, see “Specifying Cloud Density” in “Specifying the Plane-Object Attributes,” above.


Vector-attribute specification for cube objects is similar to that for plane objects (see “Specifying Vector Attributes” in “Specifying the Plane-Object Attributes,” above). If you specify the Halfspace (0) option for a vector plot on a cube object, GAMBIT plots vectors the origins of which exist on the surface of the cube. If you specify the Halfspace (+) or (-) options, GAMBIT plots vectors outside or inside the cube, respectively.



Using the Create Cube Object Form

To open the Create Cube Object form (see below), click the Create Cube Object command button on the Postprocessing subpad.

The Create Cube Object form contains the following specifications.

Label specifies a label for the new cube object.

Orientation vector:

displays the endpoint coordinates of a vector that defines the orientation of the cube object. The Start endpoint defines the center of the cube, and the End endpoint defines the vector direction such that the vector points toward the center of a face on the cube.

Define opens the Vector Definition form, which allows you to spec-ify a vector that defines the cube orientation (see “Using the Vector Definition Form” in Section 2.1.4 of this guide).



Dimension –��– specifies the size of the cube. (NOTE: The Dimension value represents one half of the length of an edge of the cube.)

Attachment: —————————————————————————

Group q Volume Face




Halfspace: specifies the region of the model to be displayed. For cube objects, the available Halfspace options are as follows:

(+)—displays results for regions of the attachment entity that exist inside the cube

(0)—displays results for the region of the attachment entity that is exactly intersected by the cube surface

(-)—displays results for regions of the attachment entity that exist outside the cube


Attributes: specifies the type(s) of postprocessing attributes associated with the object. For cube objects, GAMBIT provides two types of postprocessing attributes:





Attributes: (cont.)

Each Attributes option is associated with an Edit pushbutton, which accesses the specification form appropriate to the option. For example, if you click the Edit pushbutton associated with (and located to the right of) the Contour check box, GAMBIT opens the Specify Contour Attributes form.

For descriptions of the contour and vector types as applied to cube postprocessing objects, see “Specifying the Cube-Object Attributes,” above. For descriptions of the Specify Contour Attributes and Specify Vector Attributes forms, see, respec-tively, “Using the Specify Contour Attributes Form” and “Using the Specify Vector Attributes Form” in “Create Plane Object,” above.

The Contour and Vector headings on the Create Cube Object form display the degrees of freedom represented by the current postprocessing display and its associated color spectrum. The specific information included in the headings is as follows.

• Contour headings indicate the degree of freedom used to plot the contour. For example, a heading that reads “Contour: pressure” on the Create Cube Object form indicates that colors on the cube-object contour plot represent pressure magnitude.

• Vector headings indicate both the degree of freedom represented by the displayed vectors and the color used in the vector display. For example, a heading that reads “Vector: velocity vectors” and “Color: magnitude” on the Create Cube Object form indicates that the displayed vectors represent velocity vectors, and their colorations represent vector magnitude.

The Contour and Vector specification regions on the Create Cube Object form include color bars that constitute legends for the respective Contour and Vector displays.



Create Cylinder Object

The Create Cylinder Object command creates a postprocessing object in the shape of a cylinder.

When you create and display a cylinder postprocessing object, GAMBIT displays solution results on a cylindrical volume. For example, if you define a cylinder object to display banded pressure contours for the model shown above, GAMBIT creates a display such as that shown in Figure 6-42.

yz

x

Figure 6-35: Example cylinder object—Bands pressure contours

In this case, the pressure contours appear as bands the colors of which repre-sent pressure magnitudes. The color gradation displayed on this object illus-trates that pressure is higher near the pipe inlet (right side) than it is at the outlet (left side).



Cylinder-Object Specifications

To characterize a cylinder postprocessing object, you must specify the follow-ing information:

• Axis—specifies the location and direction of the cylinder axis

• Radius—specifies the size of the cylinder


• Halfspace—specifies the region of the Attachment entity, relative to the space bounded by the cylinder, for which results are to be displayed


The following sections describe the specifications listed above.

Specifying the Axis

The Axis specification defines the location and direction of the cylinder axis. For example, the cylinder postprocessing object shown in Figure 6-35, above, employs the positive (or negative) x axis of the global coordinate system as the Axis vector, therefore the cylinder is aligned with the axis of the pipe. (NOTE: The global coordinate system, which is not shown in the figure, is located along the centerline of the pipe.)

To specify the Axis vector, you must input its parameters on the Vector Definition form, which is accessed by means of the Axis:Define pushbutton on the Create Cylinder Object specification form (see below). For a description of the Vector Definition form and its use, see “Using the Vector Definition Form,” in Section 2.1.4 in this manual.

Specifying the Radius

The Radius specification defines the radial size of the cylinder. For example, for the cylinder object shown in Figure 6-35, above, the Radius is defined such that the cylinder object exists entirely within the domain of the pipe boundaries. After the Radius is defined, you can adjust its position by means of the slider bar on the Create Cylinder Object form.




The Attachment specification determines the geometric entity for which post-processing results are to be displayed. GAMBIT allows you to specify any face, volume, or group as an attachment entity for a cylinder postprocessing object. The attachment entity determines the appearance of the cylinder object as follows:

• If you specify a face as the attachment entity, GAMBIT displays post-processing results for only those regions of the face intersected by the cylinder.

• If you specify a volume as the attachment entity, the resulting cylinder object constitutes a three-dimensional, cylindrical volume such as that shown in Figure 6-35, above.

• If you specify a group as the attachment entity, the resulting cylinder object constitutes the intersection of the cylinder with any volumes and/or faces in the group.


The Halfspace specification determines the region of the attachment entity, relative to the cylindrical volume, for which results are to be displayed. GAMBIT provides the following Halfspace options for cylinder objects.

Option Description

+ Displays results in the region of the attachment entity located outside the cylinder

0 Displays results in the region of the attachment entity inter-sected by the surface of the cylinder

- Displays results in the region of the attachment entity located inside the cylinder

The effect of the Halfspace specification for cylinder objects is identical to that for cube objects (see Figure 6-27 in “Cube-Object Specifications,” above).



Specifying the Cylinder-Object Attributes

The Attributes specifications for cylinder objects are identical to those for cube objects (see “Specifying the Cube-Object Attributes,” above). For example, for cylinder objects, GAMBIT provides two types of postprocessing attributes:

• Contour

• Vector

Contour attributes display results in the form of lines, bands, clouds, or wires that represent various magnitude levels for a specified degree of freedom. Vector attributes display results in the form of vector fields. GAMBIT allows you to display either or both types of attributes on any cylinder object.



To define a contour attribute for a cylinder object, you must specify the fol-lowing information:


• Contour Type

• Color Map





For any cylinder-object contour, GAMBIT allows you to specify the degree of freedom to be displayed by means of the DOF option button on the Specify Contour Attributes form. The allowable degrees of freedom for any contour depend on the type(s) of data available in the imported results database but include, at a minimum, x, y (and z, for 3-D simulations) coordinates.



• Lines

• Bands

• Smooth


• Isosurfaces

• Cloud

The following sections describe the contour types listed above.



Lines Contours

When you specify a Lines contour for a cylinder object, GAMBIT displays a set of color-coded curves on the surface of the cylinder. Each curve represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-36 shows a cylinder object defined with respect to the pressure degree of freedom and employing the Lines contour type. For this contour, GAMBIT displays a series of closed curves on the surface of the cylinder. Each curve represents the intersection of the cylindrical surface with a given pressure isosurface in the pipe. By default, GAMBIT displays curves repre-senting the boundaries between 10 different levels of pressure. It is possible, however, to control the number of levels displayed (that is, the band width) by means of options available in the Color Map section of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-36: Cylinder object—Lines contour, Halfspace (0)

u NOTE: Lines contours can only be applied to the postprocessing surfaces, therefore, for cylinder objects, they appear in the graphics display only when the Halfspace (0) option is selected. Conversely, the Halfspace (+) and (-) options do not affect Lines contour displays.



Bands Contours

When you specify a Bands contour for a cylinder object, GAMBIT displays a series of colored bands across the surface of the cylinder. Each band repre-sents the level of magnitude of the contour degree of freedom evaluated on one side of the band.

Figure 6-37 shows a cylinder object defined with respect to the pressure degree of freedom and employing the Bands contour type. Each displayed band represents the intersection of the cylindrical surface with a region of pressure in the pipe. By default, GAMBIT displays bands representing the boundaries between 10 different levels of pressure. It is possible, however, to control the number of levels displayed (that is, the band width) by means of options available in the Color Map section of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-37: Cylinder object—Bands contour, Halfspace (0)

u NOTE: Bands contours can only be applied to the postprocessing surfaces, therefore, for cylinder objects, they appear in the graphics display only when the Halfspace (0) option is selected. Conversely, the Halfspace (+) and (-) options do not affect Bands contour displays.



Smooth Contours

When you specify a Smooth contour for a cylinder object, GAMBIT displays a smoothly graded color spectrum across the surface of the cylinder. The colors of the displayed spectrum represent an approximation of the continuous change in magnitude for the degree of freedom associated with the contour.

Figure 6-38 shows a cylinder object defined with respect to the pressure degree of freedom and employing the Smooth contour type. For this contour, GAMBIT displays a smoothly graded spectral band across the surface of the cylinder. The Color Map section of the Specify Contour Attributes form allows you to modify and refine the Smooth display characteristics (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-38: Cylinder object—Smooth contour, Halfspace (0)

u NOTE: Smooth contours can only be applied to the postprocessing surfaces, therefore, for cylinder objects, they appear in the graphics display only when the Halfspace (0) option is selected. Conversely, the Halfspace (+) and (-) options do not affect Smooth contour displays.




When you specify a Wire-isosurfaces contour for a cylinder object, GAMBIT displays a set of color-coded wires in a region defined in reference to the cylinder—that is, inside and/or outside the cylinder. Each wire represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-39 shows a cylinder object defined with respect to the pressure degree of freedom and employing the Wire-isosurfaces contour type. For this contour, GAMBIT displays a series of wires, each of which is color-coded to represent a different pressure level. The Color Map section of the Specify Contour Attributes form allows you to modify and refine the Wire-isosurfaces display characteristics (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-39: Cylinder object—Wire-isosurfaces contour, Halfspace (-)

u NOTE: If you specify the Halfspace (0) option, Wire-isosurfaces contours appear as Lines contours on the surface of the cylinder (see Figure 6-36, above).




When you specify an Isosurfaces contour for a cylinder object, GAMBIT displays a set of color-coded surfaces in a region defined in reference to the cylinder—that is, inside and/or outside the cylinder. Each surface represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-40 shows a cylinder object defined with respect to the pressure degree of freedom and employing the Isosurfaces contour type. For this contour, GAMBIT displays a series of surfaces, each of which is color-coded to represent a different pressure level. The Color Map section of the Specify Contour Attributes form allows you to modify and refine the Isosurfaces display characteristics (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-40: Cylinder object—Isosurfaces contour, Halfspace (-)

u NOTE: If you specify the Halfspace (0) option, Isosurfaces contours appear as Bands contours on the surface of the cylinder (see Figure 6-37, above).



Cloud Contours

When you specify a Cloud contour for a cylinder object, GAMBIT displays a cloud of discrete points in a region defined in reference to the cylinder—that is, inside and/or outside the cylinder. Each point is color-coded in a manner similar to that used by the Bands option.

Figure 6-41 shows a cylinder object defined with respect to the pressure degree of freedom and employing the Cloud contour type. The displayed cloud density is constant and does not correspond to the magnitude any degree of freedom. GAMBIT allows you to adjust the density, along with other cloud characteristics, by means of the Density specification of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-41: Cylinder object—Cloud contour, Halfspace (-)

u NOTE: If you specify the Halfspace (0) option, Cloud contours appear as Smooth contours on the surface of the cylinder (see Figure 6-38, above).




The functions of the Color Map and Density sections of the Specify Contour Attributes form for cylinder postprocessing objects are identical to those for cube objects (see “Specifying Color Map and Density” in “Specifying the Cube-Object Attributes,” above).


Vector-attribute specification for cylinder objects is identical to that for plane objects (see “Specifying Vector Attributes” in “Specifying the Cube-Object Attributes,” above).



Using the Create Cylinder Object Form

To open the Create Cylinder Object form (see below), click the Create Cylinder Object command button on the Postprocessing subpad.

The Create Cylinder Object form includes the following specifications.

Label specifies a label for the new cylinder object.

Axis: displays the endpoint coordinates of a vector that defines the cylinder axis.

Define opens the Vector Definition form, which allows you to spec-ify a vector that defines the cylinder axis (see “Using the Vector Definition Form” in Section 2.1.4 of this guide).

Radius –��– specifies the radial size of the cylinder.



Attachment: —————————————————————————

Group q Volume Face




Halfspace: specifies the region of the model to be displayed. For cylinder objects, the available Halfspace options are as follows:

(+)—displays results for regions of the attachment entity that exist outside the cylinder

(0)—displays results for the region of the attachment entity that is exactly intersected by the surface of the cylinder

(-)—displays results for regions of the attachment entity that exist inside the cylinder


Attributes: specifies the type(s) of postprocessing attributes associated with the object. For cylinder objects, GAMBIT provides two types of postprocessing attributes:






Attributes: (Cont.)

For descriptions of the contour and vector types as applied to cylinder postprocessing objects, see “Specifying the Cylinder-Object Attributes,” above. For descriptions of the Specify Contour Attributes and Specify Vector Attributes forms, see, respectively, “Using the Specify Contour Attributes Form” and “Using the Specify Vector Attributes Form” in “Create Plane Object,” above.

The Contour and Vector headings on the Create Cylinder Object form display the degrees of freedom represented by the current postprocessing display and its associated color spectrum. The specific information included in the headings is as follows.

• Contour headings indicate the degree of freedom used to plot the contour. For example, a heading that reads “Contour: pressure” on the Create Cylinder Object form indicates that colors on the cylinder-object contour plot represent pressure magnitude.


The Contour and Vector specification regions on the Create Cylinder Object form include color bars that constitute legends for the respective Contour and Vector displays.



Create Sphere Object

The Create Sphere Object command creates a postprocessing object in the shape of a sphere.

When you create and display a sphere postprocessing object, GAMBIT displays solution results on a spherical volume. For example, if you define a small sphere object to display banded velocity contours for the model shown in Figure 6-1, above, GAMBIT creates a display such as that shown in Figure 6-42.

yz

x

Figure 6-42: Example sphere object—Bands velocity contours

In this case, the velocity contours appear as bands the colors of which represent velocity magnitudes. The color gradation displayed on this object illustrates that velocity is greater in the center of the pipe than it is near the walls.



Sphere-Object Specifications

To characterize a sphere postprocessing object, you must specify the follow-ing information:

• Radial vector and Radius—specifies the location and size of the sphere


• Halfspace—specifies the region of the Attachment entity, relative to the space bounded by the sphere, for which results are to be displayed


Specifying the Radial Vector and Radius

The Radial vector and Radius specifications define the location and size of the sphere, respectively. (NOTE: GAMBIT uses the Start point of the Radial vector to define the location of the center of the sphere and ignores the vector End point specification.) The effects of these specifications on the postproc-essing object display are similar to those for cube objects (see Figure 6-25 in “Cube-Object Specifications,” above). For example, if you define a sphere object such that it extends outside the boundary of the entity to which it is attached, GAMBIT clips the object at the entity boundary (see Figure 6-43).

yz

x

Figure 6-43: Clipped sphere object—Smooth velocity contours




The Attachment specification determines the geometric entity for which post-processing results are to be displayed. GAMBIT allows you to specify any face, volume, or group as an attachment entity for a sphere postprocessing object. The attachment entity determines the appearance of the sphere object as follows:

• If you specify a face as the attachment entity, GAMBIT displays post-processing results for only those regions of the face intersected by the sphere.

• If you specify a volume as the attachment entity, the resulting sphere object constitutes a three-dimensional, spherical volume such as that shown in Figure 6-42, above.

• If you specify a group as the attachment entity, the resulting cylinder object constitutes the intersection of the cylinder with any volumes and/or faces in the group.


The Halfspace specification determines the region of the attachment entity, relative to the spherical volume, for which results are to be displayed. GAMBIT provides the following Halfspace options for sphere objects.

Option Description

+ Displays results in the region of the attachment entity located outside the sphere

0 Displays results in the region of the attachment entity inter-sected by the surface of the sphere

- Displays results in the region of the attachment entity located inside the sphere

The effect of the Halfspace specification for sphere objects is identical to that for cube objects (see Figure 6-27 in “Cube-Object Specifications,” above).



Specifying the Sphere-Object Attributes

The Attributes specifications for sphere objects are identical to those for cube objects (see “Specifying the Cube-Object Attributes,” above). For example, for sphere objects, GAMBIT provides two types of postprocessing attributes:

• Contour

• Vector

Contour attributes display results in the form of lines, bands, clouds, or wires that represent various magnitude levels for a specified degree of freedom. Vector attributes display results in the form of vector fields. GAMBIT allows you to display either or both types of attributes on any sphere object.



To define a contour attribute for a sphere object, you must specify the fol-lowing information:


• Contour Type

• Color Map



For any sphere-object contour, GAMBIT allows you to specify the degree of freedom to be displayed by means of the DOF option button on the Specify Contour Attributes form. The allowable degrees of freedom for any contour depend on the type(s) of data available in the imported results database but include, at a minimum, x, y (and z, for 3-D simulations) coordinates.





• Lines

• Bands

• Smooth


• Isosurfaces

• Cloud

The following sections describe the contour types listed above.



Lines Contours

When you specify a Lines contour for a sphere object, GAMBIT displays a set of color-coded curves on the surface of the sphere. Each curve represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-44 shows a sphere object defined with respect to the velocity magni-tude degree of freedom and employing the Lines contour type. For this contour, GAMBIT displays a series of closed curves on the surface of the sphere. Each curve represents the intersection of the spherical surface with a given velocity-magnitude isosurface in the pipe. By default, GAMBIT displays curves representing the boundaries between 10 different levels of velocity magnitude. It is possible, however, to control the number of levels displayed (that is, the band width) by means of options available in the Color Map section of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-44: Sphere object—Lines contour, Halfspace (0)

u NOTE: Lines contours can only be applied to the postprocessing surfaces, therefore, for sphere objects, they appear in the graphics display only when the Halfspace (0) option is selected. Conversely, the Halfspace (+) and (-) options do not affect Lines contour displays.



Bands Contours

When you specify a Bands contour for a sphere object, GAMBIT displays a series of colored bands across the surface of the sphere. Each band represents the level of magnitude of the contour degree of freedom evaluated on one side of the band.

Figure 6-45 shows a sphere object defined with respect to the velocity magni-tude degree of freedom and employing the Bands contour type. Each displayed band represents the intersection of the spherical surface with a region of velocity magnitudes in the pipe. By default, GAMBIT displays bands repre-senting the boundaries between 10 different levels of velocity magnitude. It is possible, however, to control the number of levels displayed (that is, the band width) by means of options available in the Color Map section of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-45: Sphere object—Bands contour, Halfspace (0)

u NOTE: Bands contours can only be applied to the postprocessing surfaces, therefore, for sphere objects, they appear in the graphics display only when the Halfspace (0) option is selected. Conversely, the Halfspace (+) and (-) options do not affect Bands contour displays.



Smooth Contours

When you specify a Smooth contour for a sphere object, GAMBIT displays a smoothly graded color spectrum across the surface of the sphere. The colors of the displayed spectrum represent an approximation of the continuous change in magnitude for the degree of freedom associated with the contour.

Figure 6-46 shows a sphere object defined with respect to the velocity magni-tude degree of freedom and employing the Smooth contour type. For this contour, GAMBIT displays a smoothly graded spectral band across the surface of the sphere. The Color Map section of the Specify Contour Attributes form allows you to modify and refine the Smooth display characteristics (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-46: Sphere object—Smooth contour, Halfspace (0)

u NOTE: Smooth contours can only be applied to the postprocessing surfaces, therefore, for sphere objects, they appear in the graphics display only when the Halfspace (0) option is selected. Conversely, the Halfspace (+) and (-) options do not affect Smooth contour displays.




When you specify a Wire-isosurfaces contour for a sphere object, GAMBIT displays a set of color-coded wires in a region defined in reference to the sphere—that is, inside and/or outside the sphere. Each wire represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-47 shows a sphere object defined with respect to the velocity magni-tude degree of freedom and employing the Wire-isosurfaces contour type. For this contour, GAMBIT displays a series of wires, each of which is color-coded to represent a different magnitude level. The Color Map section of the Specify Contour Attributes form allows you to modify and refine the Wire-isosurfaces display characteristics (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-47: Sphere object—Wire-isosurfaces contour, Halfspace (-)

u NOTE: If you specify the Halfspace (0) option, Wire-isosurfaces contours appear as Lines contours on the surface of the sphere (see Figure 6-44, above).




When you specify an Isosurfaces contour for a sphere object, GAMBIT displays a set of color-coded surfaces in a region defined in reference to the sphere—that is, inside and/or outside the sphere. Each surface represents a constant level of magnitude for the degree of freedom associated with the contour.

Figure 6-48 shows a sphere object defined with respect to the velocity magni-tude degree of freedom and employing the Isosurfaces contour type. For this contour, GAMBIT displays a series of surfaces, each of which is color-coded to represent a different magnitude level. The Color Map section of the Specify Contour Attributes form allows you to modify and refine the Isosurfaces display characteristics (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-48: Sphere object—Isosurfaces contour, Halfspace (-)

u NOTE: If you specify the Halfspace (0) option, Isosurfaces contours appear as Bands contours on the surface of the sphere (see Figure 6-45, above).



Cloud Contours

When you specify a Cloud contour for a sphere object, GAMBIT displays a cloud of discrete points in a region defined in reference to the sphere—that is, inside and/or outside the sphere. Each point is color-coded in a manner similar to that used by the Bands option.

Figure 6-49 shows a sphere object defined with respect to the velocity magni-tude degree of freedom and employing the Cloud contour type. The displayed cloud density is constant and does not correspond to the magnitude any degree of freedom. GAMBIT allows you to adjust the density, along with other cloud characteristics, by means of the Density specification of the Specify Contour Attributes form (see “Specifying Color Map and Density,” below).

yz

x

Figure 6-49: Sphere object—Cloud contour, Halfspace (-)

u NOTE: If you specify the Halfspace (0) option, Cloud contours appear as Smooth contours on the surface of the sphere (see Figure 6-46, above).




The functions of the Color Map and Density sections of the Specify Contour Attributes form for sphere postprocessing objects are identical to those for cube objects (see “Specifying Color Map and Density” in “Specifying the Cube-Object Attributes,” above).


Vector-attribute specification for sphere objects is identical to that for plane objects (see “Specifying Vector Attributes” in “Specifying the Cube-Object Attributes,” above).



Using the Create Sphere Object Form

To open the Create Sphere Object form (see below), click the Create Sphere Object command button on the Postprocessing subpad.

The Create Sphere Object form contains the following specifications.

Label specifies a label for the new sphere object.

Radial vector: displays the endpoint coordinates of a vector the Start endpoint of which defines the center of the sphere.

Define opens the Vector Definition form, which allows you to spec-ify a vector that defines the center of the sphere (see “Using the Vector Definition Form” in Section 2.1.4 of this guide).

Radius –��– specifies the size of the sphere.



Attachment: —————————————————————————

Group q Volume Face




Halfspace: specifies the region of the model to be displayed. For cube objects, the available Halfspace options are as follows:

(+)—displays results for regions of the attachment entity that exist inside the sphere

(0)—displays results for the region of the attachment entity that is exactly intersected by the surface of the sphere

(-)—displays results for regions of the attachment entity that exist outside the sphere


Attributes: specifies the type(s) of postprocessing attributes associated with the object. For sphere objects, GAMBIT provides two types of postprocessing attributes:






Attributes: (cont.)

For descriptions of the contour and vector types as applied to sphere postprocessing objects, see “Specifying the Sphere-Object Attributes,” above. For descriptions of the Specify Contour Attributes and Specify Vector Attributes forms, see, respectively, “Using the Specify Contour Attributes Form” and “Using the Specify Vector Attributes Form” in “Create Plane Object,” above.

The Contour and Vector headings on the Create Sphere Object form display the degrees of freedom represented by the current postprocessing display and its associated color spectrum. The specific information included in the headings is as follows.

• Contour headings indicate the degree of freedom used to plot the contour. For example, a heading that reads “Contour: pressure” on the Create Sphere Object form indicates that colors on the sphere-object contour plot represent pressure magnitude.

• Vector headings indicate both the degree of freedom represented by the displayed vectors and the color used in the vector display. For example, a heading that reads “Vector: velocity vectors” and “Color: magnitude” on the Create Sphere Object form indicates that the displayed vectors represent velocity vectors, and their colorations represent vector magnitude.

The Contour and Vector specification regions on the Create Plane Object form include color bars that constitute legends for the respective Contour and Vector displays.



6.2.4 Create Isosurface Object

The Create Isosurface Object command creates a postprocessing object the shape of which is defined by the isosurface of a specified degree of freedom. For example, if you create an isosurface object specified by a velocity mag-nitude of 0.85 for the model shown in Figure 6-1, above, and specify the display of a Bands pressure contour, GAMBIT displays the postprocessing object shown in Figure 6-50.

yz

x

Figure 6-50: Example isosurface object—Bands pressure contours

In this case, the shape of the postprocessing object is defined by the isosurface upon which velocity magnitude equals 0.85. As a result, the object is approximately cylindrical but is flared toward the pipe inlet (right side), reflecting the fact that velocity is greater near the walls of the pipe inlet than it is near the walls throughout the remainder of the pipe.



Isosurface-Object Specifications

To characterize an isosurface postprocessing object, you must specify the following information:

• DOF and Value—specifies the degree of freedom and value that defines the shape of the isosurface


• Halfspace—specifies the region of the Attachment entity, relative to the space bounded by the cylinder, for which results are to be displayed


Specifying the DOF and Value

The DOF and Value specifications determine the shape and position of the iso-surface object. As an example of the effect of such specifications, consider the isosurface objects shown in Figure 6-51, each of which is defined with respect to the velocity magnitude degree of freedom (DOF).

(a) Velocity = 0.85

(b) Velocity = 1.35

yz

x

Figure 6-51: Isosurface object—effect of Value on contour shape



The isosurface objects shown in Figure 6-51(a) and (b) are defined by velocity magnitudes of 0.85 and 1.35, respectively. The object defined by a velocity magnitude of 0.85 is larger than that defined by a magnitude of 1.35, because the velocity is lower near the pipe walls than it is near the center of the pipe, therefore the 0.85 pressure isobar is located near to the pipe wall. In addition, the object defined by a velocity magnitude of 1.35 is closed near the inlet (right) side of the pipe, because the fluid enters the pipe with a uniform veloc-ity less than 1.35.


The Attachment specifications for isosurface objects are identical to those for geometric postprocessing objects (see Section 6.2.3, above).


The Halfspace specifications for isosurface objects are similar to those for geometric postprocessing objects (see Section 6.2.3, above). In general, the Halfspace options produce the following effects on the isosurface display.

Option Description

+ Displays results in the region(s) of the attachment entity for which the degree of freedom that defines the isosurface is greater than the value that defines the isosurface shape

0 Displays results in the region(s) of the attachment entity defined exactly by the value of the degree of freedom that defines the isosurface shape

- Displays results in the region(s) of the attachment entity for which the degree of freedom that defines the isosurface is less than the value that defines the isosurface shape

As an example of the effect of the Halfspace option on isosurface objects, consider the isosurface object shown in Figure 6-52. This object is similar to that shown in Figure 6-50 but is defined with Halfspace (0) and (-) options. As a result, the object includes two components:

• The isosurface itself

• A set of annular disks located in the region between the isosurface and the pipe wall, where the velocity magnitude is less than 0.85, each of which represents a different pressure isobar



If you specify the Halfspace (+) option for this object, GAMBIT displays a set of disks inside the isosurface, where the velocity magnitude is greater than 0.85.

yz

x

Figure 6-52: Isosurface object—velocity, Value = 0.85 Halfspace (0) and (-)

As a second example of the effect of the Halfspace options on isosurface objects, consider the isosurface object shown in Figure 6-53, which is defined by a pressure value of 200. In this case, the isosurface object does not enclose a volumetric space. Consequently, with respect to its Halfspace and Attributes specifications, it behaves like a plane postprocessing object (see “Create Plane Object,” above). Figure 6-53(a) shows the isosurface object created using only the Halfspace (0) option. Figure 6-53(b) shows the isosurface object created using the Halfspace (0) and (+) options.



(a) Halfspace (0)

(b) Halfspace (0), (+)

yz

x

Figure 6-53: Isosurface object—pressure, Value = 200

For a complete description of the effects of the Halfspace and Attributes speci-fications on volumetric and surface postprocessing objects, such as those shown in Figure 6-52 and Figure 6-53, above, see Section 6.2.3, above.

Specifying the Isosurface-Object Attributes

For isosurface objects, GAMBIT provides two types of postprocessing attributes:

• Contour

• Vector

Contour attributes display results in the form of lines, bands, clouds, or wires that represent various magnitude levels for a specified degree of freedom. Vector attributes display results in the form of vector fields. GAMBIT allows you to display either or both types of attributes on any cylinder object. The Attributes contour and vector attribute specifications for isosurface objects are identical to those for geometric objects, such as planes and cubes (see “Specifying the Plane-Object Attributes” and “Specifying the Cube-Object Attributes,” above).



Using the Create Isosurface Object Form

To open the Create Isosurface Object form (see below), click the Create Isosurface Object command button on the Postprocessing subpad.

The Create Isosurface Object form contains the following specifications.

Label specifies a label for the new sphere object.

DOF —————————————————————————

pressure q …

specifies the degree of freedom a given value of which defines the shape of the isosurface object. (NOTE: The available degrees of freedom vary according to the current results database.)

Value –��– specifies the value that defines the shape of the isosurface.



Attachment: —————————————————————————

Group q Volume Face




Halfspace: specifies the region of the model to be displayed. For isosur-face objects, the available Halfspace options are as follows:

(+)—displays results for regions of the attachment entity the DOF values of which are greater than the isosur-face value

(0)—displays results for the region of the attachment entity the DOF values of which are equal to the isosurface value

(-)—displays results for regions of the attachment entity the DOF values of which are less than the isosurface value


Attributes: specifies the type(s) of postprocessing attributes associated with the object. For isosurface objects, GAMBIT provides two types of postprocessing attributes:






Attributes: (Cont.)

For descriptions of the contour and vector types as applied to isosurface postprocessing objects, see “Specifying the Plane-Object Attributes” and “Specifying the Cube-Object Attributes,” above. For descriptions of the Specify Contour Attributes and Specify Vector Attributes forms, see, respec-tively, “Using the Specify Contour Attributes Form” and “Using the Specify Vector Attributes Form” in “Create Plane Object,” above.

The Contour and Vector headings on the Create Plane Object form display the degrees of freedom represented by the current postprocessing display and its associated color spectrum. The specific information included in the headings is as follows.

• Contour headings indicate the degree of freedom used to plot the contour. For example, a heading that reads “Contour: pressure” on the Create Isosurface Object form indicates that colors on the isosurface-object contour plot represent pressure magnitude.

• Vector headings indicate both the degree of freedom represented by the displayed vectors and the color used in the vector display. For example, a heading that reads “Vector: velocity vectors” and “Color: magnitude” on the Create Isosurface Object form indicates that the displayed vectors represent velocity vectors, and their colorations represent vector magnitude.

The Contour and Vector specification regions on the Create Isosurface Object form include color bars that constitute legends for the respective Contour and Vector displays.



6.2.5 Create Simulation Object

The Create Simulation Object command creates a postprocessing object the shape of which is defined by the entire entity to which it is attached. For example, if you create a simulation object in which the pipe shown in Figure 6-1, above, comprises the attachment entity and specify the display of a Bands pressure contour, GAMBIT displays the postprocessing object shown in Figure 6-54.

yz

x

Figure 6-54: Example simulation object—Bands pressure contours

In this case, the pressure contours appear as cylindrical bands on the surface of the volume.

Simulation-Object Specifications

To characterize a simulation postprocessing object, you must specify the fol-lowing information:

• Definition—specifies the geometric entity for which the postprocessing results are to be displayed

• Attributes—determines the degrees of freedom (for example, velocity or pressure) to be displayed and the format (contours, vectors, or parti-cles) of the graphics display



u NOTE: Simulation objects do not include Halfspace options, because the attachment (Definition) entity constitutes the entire space for which results are to be displayed. For example, for the simulation object shown in Figure 6-54, above, the pipe itself constitutes the attachment entity.

Specifying the Definition

The Definition specification for simulation objects that employ contour or vector displays is identical to the Attachment specification for geometric or isosurface objects (see “Specifying the Attachment Entity” in Section 6.2.4, above). That is, the Definition entity defines the entity for which results are to be displayed. For simulation objects, GAMBIT allows you to specify any vertex, edge, face, volume, or group for which results are available as the Definition entity.

For particle displays, the Definition entity specifies the starting (injection) surface(s) for a set of massless particles the paths of which are traced into the flow stream (see “Specifying Particle Attributes,” below).

Specifying the Simulation-Object Attributes

For simulation objects, GAMBIT provides the following types of postprocess-ing attributes:

• Contour

• Vector

• Particle

Contour attributes display results in the form of lines, bands, clouds, or wires that represent various magnitude levels for a specified degree of freedom. Vector attributes display results in the form of vector fields. Particle attributes display the paths of theoretical, massless particles for models involving fluid flow. GAMBIT allows you to display any or all types of attributes on any simulation object.

Specifying Contour and Vector Attributes

The contour and vector Attributes specifications for simulation objects are identical to those for geometric and isosurface objects. For descriptions of the Attributes specifications for geometric and isosurface objects, see Sections 6.2.3 and 6.2.4, above.



Specifying Particle Attributes

When you click the Edit pushbutton associated with the Particle check box on the Create Simulation Object form, GAMBIT opens the Specify Particle Attributes form (see “Using the Specify Particle Attributes Form,” below). The Specify Particle Attributes form allows you to define the degree of free-dom for which particle paths are to be displayed on the simulation postproc-essing object, as well as the graphical appearance of the particles.

Figure 6-55 shows a particle plot for the model shown in Figure 6-1, in which fluid flows through a section of straight pipe. In this figure, the particle path colors represent velocity magnitudes throughout the pipe.

yz

x

Figure 6-55: Example simulation object—example particle plot

To define a particle plot, you must specify the following information and/or options:


• Particle Color

• Type

• Thickness

• End Time

The following subsections describe the specifications listed above.




For any given particle plot, you must specify the degree of freedom to be displayed by means of the DOF option button on the Specify Particle Attributes form. The allowable degrees of freedom for any particle plot depend on the type(s) of data available in the results database and do not include scalar prop-erties such as pressure or temperature.

Specifying the Particle Color

The Particle Color specification determines the method by which GAMBIT assigns colors to the particles and particle paths. The Specify Particle Attributes form includes three Particle color options:

• Magnitude

• DOF

• Fixed

If you specify the Magnitude option, the resulting particle path colors corre-spond to the magnitude of the degree of freedom (DOF) being plotted. For example, in Figure 6-23, above, the paths displayed near the centerline of the pipe are dark orange (corresponding to high magnitude), and the paths near the pipe walls are green or blue (corresponding to low magnitude). In this case, the particle path colors illustrate the fact that the velocity is higher near the center of the pipe than it is near the walls.

If you specify the DOF option, the resulting particle path colors correspond to the magnitude of a specified degree of freedom. For example, you can plot particle paths based on a velocity degree of freedom and specify that the colors of the paths correspond to local pressure or temperature in the fluid domain.

If you specify the Fixed option, GAMBIT uses one uniform color for all vectors. (NOTE: The Fixed color is selected by means of the Set Color form (see “Using the Set Color Form” in Section 2.2.4 of this guide).)

Specifying the Type

The Type specification determines whether GAMBIT plots particle paths on a particle plot. The Specify Particle Attributes form includes two Type options:

• Point

• Line



If you specify the Point option, the resulting particle path colors consist of a series of points. If you specify the Line option, GAMBIT creates lines that trace the point locations on their path through the model domain.

Specifying the Thickness

The Thickness specification defines the thickness of lines used in the particle plot.

Specifying the End Time

The End Time specification defines amount of time represented by the post-processing particle display. For example, Figure 6-56 shows a particle display similar to that shown in Figure 6-55 but with an End Time specification of 5—which represents less time than is necessary for particles released at the pipe inlet to reach the outlet.

yz

x

Figure 6-56: Example simulation object—particle plot, End Time = 5



Using the Create Simulation Object Form

To open the Create Simulation Object form (see below), click the Create Simulation Object command button on the Postprocessing subpad.

The Create Simulation Object form contains the following specifications.

Label specifies a label for the new simulation object.

Definition: —————————————————————————

Group q Volume Face Edge Vertex

specifies the definition entity type.

Group ¬ Volume Face Edge Vertex

specifies the definition entity.



Attributes: specifies the type(s) of postprocessing attributes associated with the object. For sphere objects, GAMBIT provides two types of postprocessing attributes:

• Contour • Vector • Particle

The Contour attribute displays data in the form of discrete or continuous contours. The Vector attribute displays vector fields. The Particle attribute displays particle paths through the model for scenarios involving fluid flow.


For descriptions of the contour and vector types as applied to surface- and volume-type simulation postprocessing objects, see “Specifying the Plane-Object Attributes” and “Specifying the Sphere-Object Attributes,” above. For descriptions of the Specify Contour Attributes and Specify Vector Attributes forms, see, respectively, “Using the Specify Contour Attributes Form” and “Using the Specify Vector Attributes Form” in “Create Plane Object,” above. For a description of the Specify Particle Attributes form, see “Using the Specify Particle Attributes Form,” below.

The Contour, Vector, and Particle headings on the Create Simulation Object form display the degrees of freedom repre-sented by the current postprocessing display and its associated color spectrum. The specific information included in the headings is as follows.

• Contour headings indicate the degree of freedom used to plot the contour. For example, a heading that reads “Contour: pressure” on the Create Simulation Object form indicates that colors on the simulation-object contour plot represent pressure magnitude.

• Vector headings indicate both the degree of freedom represented by the displayed vectors and the color used in the vector display. For example, a heading that reads “Vector: velocity vectors” and “Color: magnitude” on the Create Simulation Object form indicates that the displayed vectors represent velocity vectors, and their colorations represent vector magnitude.



Attributes: (cont.)

• Particle headings indicate both the degree of freedom represented by the displayed particles and the color used in the particle display. For example, a heading that reads “Particle:velocity vectors” and “Color:magnitude” on the Create Simulation Object form indicates that the displayed particles follow velocity streamlines, and their colorations represent vector magnitude.

The Contour and Vector specification regions on the Create Simulation Object form include color bars that constitute legends for the respective Contour and Vector displays.



Using the Specify Particle Attributes Form

To open the Specify Particle Attributes form (see below), click the Particle:Edit pushbutton on the Create Simulation Object form.

The specifications on the Specify Particle Attributes form are as follows.

DOF —————————————————————————

velocity vectors q …

specifies the degree of freedom for which a particle path is to be displayed. (NOTE: The available degrees of freedom vary according to the current results database.)

Particle Color specifies the manner in which GAMBIT determines the colors of the displayed particle paths. Available options include:

• Magnitude—Particle and path colors indicate the local magnitude of the degree of freedom represented by the particle.

• DOF—Particle and path colors indicate the local magnitude of a specified degree of freedom.

• Fixed—All particles and paths are displayed using a single, specified color.

(NOTE: To specify the Fixed color used to display the particles and/or paths, click the colored bar located to the right of the Fixed option. When you click the colored bar, GAMBIT opens the Set Color form, which allows you to specify a color. For a description of the Set Color form, see “Using the Set Color Form” in Section 2.2.4 of this guide.)



Type specifies the type of particle display. Available options include:

• Point—Plots particles only

• Line—Plots particles and paths

Thickness specifies the thickness of lines used in the plot.

End Time specifies the length of time represented by the particle plot.

© Fluent Inc., Nov-01 Index-1

INDEX

A

Activate Coordinate System, 5-11 activating postprocessing objects, 6-7 Active quadrant command bar, 6-7 adjusting meshes, A-64 Align forms, 2-41 aligning

edges, 2-140 entities, 2-33 faces, 2-232 groups, 2-387 vertices, 2-75 volumes, 2-342

arcs circular, 2-90 conic, 2-103 elliptical, 2-100, 2-178 fillet, 2-106

axis of revolution, turbo, 5-63

B

background, virtual, A-4 Bands contours

2-D objects, 6-25 3-D objects, 6-58

blade-to-blade turbo volume, 5-69 blend types, 2-323 Blend Volumes, 2-323 Boolean operations, A-63

face, 2-215 volume, 2-318

boundary layers, 3-2 algorithms, 3-5 creating, 3-4 definition, 3-4 deleting, 3-26 internal continuity, 3-11

modifying, 3-23 parameters, 3-2 summarizing, 3-25 transition patterns, 3-14 transition rows, 3-15

boundary types, 4-1 entity sets, 4-7 labels, 4-8 specifying, 4-6

brick, 2-295

C

cascade view, 5-103 chamfering edges, 2-327 Check Edges, 2-156 Check Face Meshes, 3-132 Check Faces, 2-261 Check Group Meshes, 3-196 Check Groups, 2-390 Check Vertices, 2-79 Check Volume Meshes, 3-186 Check Volumes, 2-360 checking

edges, 2-156 face meshes, 3-132 faces, 2-261 group meshes, 3-196 groups, 2-390 vertices, 2-79 volume meshes, 3-186 volumes, 2-360

circles (full), 2-97 circular arcs, 2-90 circular faces, 2-175 cleaning up geometry, A-46

Index MODELING GUIDE

Index-2 © Fluent Inc., Nov-01

Cloud contours 2-D objects, 6-33 3-D objects, 6-62

Collapse Face (Virtual), 2-246 collapse operations, A-37 Color Map specifications, 6-34 command buttons, 1-4 conic arcs, 2-103 Connect Edges, 2-124 Connect Faces, 2-221 connect operations, A-31 Connect Vertices, 2-61 connecting

edges, 2-124, A-33 faces, 2-221 vertices, 2-61, A-31

connection types, 2-61, 2-124, 2-221 construct operations, A-36 continuum types, 4-3

entity sets, 4-13 specifying, 4-12

control elements, 1-2 conversion list, 3-121 Convert Edges, 2-153 Convert Faces, 2-258 Convert Vertices, 2-76 Convert Volumes, 2-357 converting

edges, 2-153 faces, 2-258 vertices, 2-76 volumes, 2-357

Cooper meshing scheme, 3-153 coordinate systems, 2-5

activating, 5-11 creating, 5-4 deleting, 5-22 global, 2-5, 5-2 local, 5-5 location and orientation, 5-5

modifying, 5-10 overview, 5-2 parameters, 2-6 reference, 2-15 summarizing, 5-21 type, 5-4

copying edges, 2-139 entities, 2-30 faces, 2-231 groups, 2-386 meshes, 2-32 postprocessing objects, 6-6 vertices, 2-74 volumes, 2-341

Corner vertex types, 3-103 Create Boundary Layer, 3-4 Create Coordinate System, 5-4 Create Cube Object, 6-50 Create Cylinder Object, 6-67 Create Face From Wireframe, 2-167 Create Group, 2-367, 4-7 Create Isosurface Object, 6-97 Create Plane Object, 6-16 Create Real Brick, 2-295 Create Real Circular Arc, 2-90 Create Real Circular Face, 2-211 Create Real Circular Face From Vertices,

2-175 Create Real Conic Arc, 2-103 Create Real Cylinder, 2-298 Create Real Edge From Vertices, 2-115 Create Real Elliptical Arc, 2-100 Create Real Elliptical Face, 2-213 Create Real Elliptical Face From Vertices,

2-178 Create Real Face From Vertex Rows, 2-186 Create Real Fillet Arc, 2-106 Create Real Frustum, 2-311 Create Real Full Circle, 2-97

MODELING GUIDE Index


Create Real Net Surface Face, 2-183 Create Real Parallelogram Face, 2-171 Create Real Polygon Face, 2-173 Create Real Prism, 2-302 Create Real Pyramid, 2-307 Create Real Rectangular Face, 2-209 Create Real Skin Surface Face, 2-181 Create Real Sphere, 2-315 Create Real Torus, 2-316 Create Real Vertex, 2-45 Create Simulation Object, 6-105 Create Size Function, 5-25 Create Sphere Object, 6-82 Create Straight Edge, 2-87 Create Turbo Profile, 5-109 Create Turbo Volume, 5-116 Create Vertex On Edge, 2-46 Create Vertex On Face, 2-49 Create Vertices At Edge Intersections, 2-54 Create Virtual Vertex On Volume, 2-52 creating

boundary layers, 3-4 coordinate systems, 5-4 edges, 2-86

circular arc, 2-90 conic arc, 2-103 elliptical arc, 2-100 fillet arc, 2-106 full circle, 2-97 NURBS, 2-115 projecting, 2-120 revolve vertices, 2-118 straight, 2-87

faces, 2-208 circular, 2-175, 2-211 elliptical, 2-178, 2-213 net-surface, 2-183 parallelogram, 2-171 polygonal, 2-173 rectangular, 2-209

revolve edges, 2-190 skin-surface, 2-181 sweep edges, 2-193 vertex rows, 2-186 wireframe, 2-167

geometry, 2-1 grids, 5-12 groups, 2-367, 4-11, 4-15 postprocessing objects, 6-15 size functions, 5-25 turbo profiles, 5-109 vertices, 2-44, 2-46, 2-49, 2-52, 2-54

by mouse, 5-12 volumes, 2-294

brick, 2-295 cylinder, 2-298 frustum, 2-311 prism, 2-302 pyramid, 2-307 sphere, 2-315 torus, 2-316

cube postprocessing object, 6-50 curvature size functions, 5-38 cylinder, 2-298 cylinder postprocessing object, 6-67

D

dangling edges, removing, 2-250 deactivating postprocessing objects, 6-7 Decompose Turbo Volume, 5-122 decomposing geometry, A-63 Define Turbo Zones, 5-119 Delete Boundary Layer, 3-26 Delete Coordinate Systems, 5-22 Delete Edge Meshes, 3-65 Delete Edges, 2-161 Delete Face Meshes, 3-135 Delete Faces, 2-266 Delete Group Meshes, 3-197 Delete Groups, 2-394



Delete Size Functions, 5-54 Delete Vertices, 2-84 Delete Volume Meshes, 3-189 Delete Volumes, 2-364 deleting

boundary layers, 3-26 coordinate systems, 5-22 edge meshes, 3-65 edges, 2-161 face meshes, 3-135 faces, 2-266 group meshes, 3-197 groups, 2-394 postprocessing objects, 6-6 size functions, 5-54 vertices, 2-84 volume meshes, 3-189 volumes, 2-364

Density specification, 6-38 Disconnect About Real Edge, 2-131 Disconnect About Real Face, 2-225 Disconnect About Real Vertex, 2-67 disconnecting

edges, 2-131 faces, 2-225 vertices, 2-67

Display Grid, 5-12 Display Ruler, 5-18 displaying rulers, 5-18 double-sided grading, 3-35 draft method, 2-279

E

Edge Blend Type form, 2-334 edge source entities, 5-30 edges

aligning, 2-140 checking, 2-156 circular arc, 2-90 conic arc, 2-103

connecting, 2-124 converting, 2-153 copying, 2-139 creating, 2-86 deleting, 2-161 deleting mesh, 3-65 disconnecting, 2-131 element types, 3-52 elliptical arc, 2-100 fillet arc, 2-106 full circle, 2-97 hard-linking, 3-56 linking meshes, 3-56 merging, 2-150 meshing, 3-28, 3-31 modifying

color, 2-136 label, 2-137

moving, 2-139 NURBS, 2-115 projecting, 2-120 querying, 2-159 revolving vertices, 2-118 soft-linking, 3-28, 3-30 splitting, 2-142, 3-62 straight, 2-87 summarizing, 2-155 summarizing meshes, 3-63 unlinking meshes, 3-61

Edit Edge Lower Topology form, 2-372 Edit Face Lower Topology form, 2-373 Edit Group Lower Topology form, 2-377 Edit Volume Lower Topology form, 2-375 element types

edges, 3-52 face, 3-109 volumes, 3-175

elliptical arcs, 2-100, 2-178 End vertex types, 3-103



entities aligning, 2-7, 2-33 copying, 2-7, 2-30 labels, 2-2 moving, 2-7, 2-8 orphan, A-36 parasite, A-36 picking, 2-4 reflecting, 2-12, 2-21 rotating, 2-10, 2-20 scaling, 2-13, 2-22, 2-31, 2-40 specifying, 2-4 totaling, 2-83 translating, 2-9, 2-19 virtual, 2-57

entity sets, 4-7, 4-13

F

face source entities, 5-31 faces

aligning, 2-232 checking, 2-261 circular, 2-175, 2-211 collapsing, 2-246 connecting, 2-221 converting, 2-258 copying, 2-231 creating, 2-208 deleting, 2-266 deleting meshes, 3-135 disconnecting, 2-225 elliptical, 2-178, 2-213 forming, 2-165 healing, 2-253 intersecting, 2-219 linking meshes, 3-113 merging, 2-242 mesh checking, 3-132 mesh element type, 3-109 meshing, 3-67

modifying color, 2-228 label, 2-229

moving, 2-231 moving mesh nodes, 3-92 net-surface, 2-183 parallelogram, 2-171 polygonal, 2-173 querying, 2-264 rectangular, 2-209 revolving edges, 2-190 simplifying, 2-250 skin-surface, 2-181 smoothing meshes, 3-98 splitting, 2-234, 3-127 splitting quad meshes, 3-95 subtracting, 2-218 summarizing, 2-260 summarizing mesh, 3-130 sweeping edges, 2-193 uniting, 2-217 vertex rows, 2-186 vertex types, 3-100 wireframe, 2-167

files neutral, 6-2 results-database, 6-2

fillet arcs, 2-106 radius, 2-110 trimming edges, 2-111

Filter specification, 2-81 fixed size functions, 5-28 font conventions, 1-6 foreground, virtual, A-4 Form Real Volume From Wireframe, 2-291 format conventions, 1-2 forming

faces, 2-165 volumes, 2-270

revolve faces, 2-286



stitch faces, 2-271 sweep faces, 2-273 wireframe, 2-291

forms Activate Coordinate System, 5-11 Align, 2-41 Blend Volumes, 2-333 Check Edges, 2-158 Check Face Meshes, 3-134 Check Faces, 2-263 Check Group Meshes, 3-196 Check Groups, 2-391 Check Vertices, 2-80 Check Volume Meshes, 3-188 Check Volumes, 2-361 Collapse Face (Virtual), 2-249 Connect Edges, 2-129 Connect Faces, 2-223 Connect Vertices, 2-65 Convert Edges, 2-153 Convert Faces, 2-258 Convert Vertices, 2-76 Convert Volumes, 2-357 Copy Postprocessing Object, 6-6 Create Boundary Layer, 3-18 Create Coordinate System, 5-6 Create Cube Object, 6-64 Create Cylinder Object, 6-79 Create Face From Wireframe, 2-169 Create Group, 2-369, 4-7 Create Isosurface Object, 6-102 Create Plane Object, 6-43 Create Real Brick, 2-297 Create Real Circular Arc, 2-94 Create Real Circular Face, 2-211 Create Real Circular Face From Vertices,

2-176 Create Real Conic Arc, 2-105 Create Real Cylinder, 2-300 Create Real Edge From Vertices, 2-117

Create Real Elliptical Arc, 2-101 Create Real Elliptical Face, 2-214 Create Real Elliptical Face From Vertices,

2-179 Create Real Face From Vertex Rows,

2-189 Create Real Fillet Arc, 2-114 Create Real Frustum, 2-313 Create Real Full Circle, 2-98 Create Real Net Surface Face, 2-185 Create Real Parallelogram Face, 2-172 Create Real Polygon Face, 2-174 Create Real Prism, 2-305 Create Real Pyramid, 2-309 Create Real Rectangular Face, 2-209 Create Real Skin Surface Face, 2-182 Create Real Sphere, 2-315 Create Real Torus, 2-317 Create Real Vertex, 2-45 Create Simulation Object, 6-110 Create Size Function, 5-45 Create Sphere Object, 6-94 Create Straight Edge, 2-89 Create Turbo Profile, 5-112 Create Turbo Volume, 5-117 Create Vertex On Edge, 2-47 Create Vertex On Face, 2-50 Create Vertices At Edge Intersections,

2-56 Create Virtual Vertex On Volume, 2-52 Decompose Turbo Volume, 5-122 Define Turbo Zones, 5-121 Delete Boundary Layer, 3-26 Delete Coordinate Systems, 5-22 Delete Edge Meshes, 3-65 Delete Edges, 2-162 Delete Face Meshes, 3-135 Delete Faces, 2-267 Delete Group Meshes, 3-198 Delete Groups, 2-395



Delete Size Functions, 5-54 Delete Vertices, 2-84 Delete Volume Meshes, 3-189 Delete Volumes, 2-365 Disconnect About Real Edge, 2-134 Disconnect About Real Face, 2-226 Disconnect About Real Vertex, 2-68 Display Grid, 5-15 Display Ruler, 5-20 Edge Blend Type, 2-334 Edge List, 3-21 Edit Edge Lower Topology, 2-372 Edit Face Lower Topology, 2-373 Edit Group Lower Topology, 2-377 Edit Volume Lower Topology, 2-375 Form Real Volume From Wireframe,

2-293 Heal Real Faces, 2-256 Heal Real Volume, 2-355 Intersect Real Faces, 2-219 Intersect Real Volumes, 2-322 Link Edge Meshes, 3-60 Link Face Meshes, 3-118 Link Volume Meshes, 3-181 Merge Edges (Virtual), 2-152 Merge Faces (Virtual), 2-245 Merge Volumes, 2-352 Mesh Edges, 3-45 Mesh Faces, 3-89 Mesh Groups, 3-192 Mesh Volumes, 3-170 Modify Boundary Layer, 3-23 Modify Boundary Layer Label, 3-24 Modify Coordinate System, 5-10 Modify Edge Color, 2-136 Modify Edge Label, 2-137 Modify Face Color, 2-228 Modify Face Label, 2-229 Modify Group, 2-380, 4-7 Modify Group Color, 2-383

Modify Group Label, 2-384 Modify Meshed Geometry, 3-125, 3-183 Modify Postprocessing Object, 6-5 Modify Size Function, 5-50 Modify Vertex Color, 2-70 Modify Vertex Label, 2-72 Modify Volume Color, 2-338 Modify Volume Label, 2-339 Move Face Nodes, 3-94 Move/Copy, 2-17 Project Edge On Face, 2-122 Query Edges, 2-159 Query Faces, 2-264 Query Groups, 2-392 Query Vertices, 2-82 Query Volumes, 2-362 Revolve Edges, 2-192 Revolve Real Faces, 2-289 Revolve Vertices, 2-119 Sample Line, 6-14 Sample Point, 6-10 Set Color, 2-71 Set Edge Element Type, 3-54 Set Face Element Type, 3-111 Set Face Vertex Type, 3-108 Set Volume Element Type, 3-178 Simplify Faces, 2-251 Slide Virtual Vertex, 2-58, 5-115 Smooth Face Mesh, 3-99 Smooth Volume Mesh, 3-174 Specify Boundary Types, 4-9 Specify Continuum Types, 4-13 Specify Contour Attributes, 6-46 Specify Particle Attributes, 6-113 Specify Vector Attributes, 6-48 Split Edge, 2-146 Split Face, 2-239 Split Meshed Edge, 3-62 Split Meshed Face, 3-128 Split Quad Meshes, 3-97



Split Volume, 2-349 Stitch Faces, 2-272 Subtract Real Faces, 2-218 Subtract Real Volumes, 2-321 Summarize Boundary Layers, 3-25 Summarize Coordinate Systems, 5-21 Summarize Edge Mesh, 3-63 Summarize Edges, 2-155 Summarize Face Mesh, 3-130 Summarize Faces, 2-260 Summarize Group Meshes, 3-195 Summarize Groups, 2-389 Summarize Size Functions, 5-53 Summarize Vertices, 2-78 Summarize Volume Meshes, 3-185 Summarize Volumes, 2-359 Sweep Edges, 2-206 Sweep Real Faces, 2-284 Total Entities, 2-83 Unite Real Faces, 2-217 Unite Real Volumes, 2-320 Unlink Edge Meshes, 3-61 Unlink Face Meshes, 3-119 Unlink Volume Meshes, 3-182 Vector Definition, 2-23 Vertex Blend Type, 2-336 View Size Function, 5-51 View Turbo Volume, 5-128

frustum, 2-311

G

geometry completeness, A-48 consistency, A-46 creating, 2-1 decomposing, A-63 general operations, 2-2 projecting, 2-14 simplifying, A-53

virtual, A-1 applications, A-45 fundamentals, A-4 operations, A-20

Geometry commands, 2-1 Edge, 2-85 Face, 2-163 Group, 2-366 Vertex, 2-43 Volume, 2-268

grading center of, 3-35 double-sided, 3-35 schemes, 3-33

graphic format conventions, 1-2 grids

defining, 5-13 displaying, 5-12 overview, 5-12 parameters, 5-12 snap option, 5-14 type, 5-14 visibility, 5-13

groups aligning, 2-387 checking, 2-390 checking mesh, 3-196 copying, 2-386 creating, 2-367, 4-11, 4-15 deleting, 2-394 deleting meshes, 3-197 meshing, 3-191 modifying, 2-380, 4-11, 4-15


moving, 2-386 querying, 2-392 summarizing, 2-389 summarizing meshes, 3-195

guest entities, A-9



H

hard links, 3-56, 3-113 Heal Real Faces, 2-253 Heal Real Volume, 2-354 healing


host entities, A-9

I

internal continuity, 3-11 interpolant entities, A-12 interpolating, 2-116 Intersect Real Faces, 2-219 Intersect Real Volumes, 2-322 intersecting


interval length ratio, 3-33 isosurface postprocessing objects, 6-97 Isosurfaces contours


L

labels, 2-2 layout format, 1-4 Lines contours


Link Edge Meshes, 3-56 Link Face Meshes, 3-113 Link Volume Meshes, 3-180 linking

meshes edges, 3-56 faces, 3-113 volumes, 3-180

periodic edges, 3-58 faces, 3-117

linking endpoint vertices, 3-56

M

Map meshing scheme, 3-141 medial edges, 5-66 Merge Edges (Virtual), 2-150 Merge Faces (Virtual), 2-242 merge operations, A-21 merge types, 2-151, 2-242 Merge Volumes, 2-352 merging

edges, 2-150, A-23 faces, 2-242, A-21, A-58 volumes, 2-352

Mesh Edges, 3-28 Mesh Faces, 3-67 Mesh Groups, 3-191 Mesh operations

Boundary Layer commands, 3-3 Edge commands, 3-27 Face commands, 3-66 Group commands, 3-190 Volume commands, 3-136

mesh orientation, 3-116 Mesh subpad, 3-1 meshed geometry, 3-121 meshing, 3-1

cube with cutout corner, A-60 edges, 3-28 faces, 3-67 groups, 3-191 virtual edges, A-8 volumes, 3-137

meshing schemes edges, 3-31



faces Quad/Tri-Map, 3-75 Quad/Tri-Pave, 3-82 Quad-Map, 3-70 Quad-Pave, 3-80 Submap, 3-76 Tri Primitive, 3-84 Tri-Pave, 3-81 Wedge Primitive, 3-86

volumes Cooper, 3-153 Map, 3-141 Stairstep, 3-163 Submap, 3-149 Tet Primitive, 3-152 TGrid, 3-160

Modify Boundary Layer, 3-23 Modify Boundary Layer Label, 3-24 Modify Coordinate System, 5-10 Modify Edge Color, 2-136 Modify Edge Label, 2-137 Modify Face Color, 2-228 Modify Face Label, 2-229 Modify Group, 2-380, 4-7 Modify Group Color, 2-383 Modify Group Label, 2-384 Modify Meshed Geometry, 3-121, 3-183 Modify Size Function, 5-50 Modify Vertex Color, 2-70 Modify Vertex Label, 2-72 Modify Volume Color, 2-338 Modify Volume Label, 2-339 modifying

boundary layers, 3-23 label, 3-24

coordinate systems, 5-10 edges


faces color, 2-228 label, 2-229

groups, 2-380, 4-11, 4-15 color, 2-383 label, 2-384

meshed geometry, 3-121, 3-183 postprocessing objects, 6-5 size functions, 5-50 vertices


volumes color, 2-338 label, 2-339

Move Face Nodes, 3-92 Move/Copy forms, 2-17 moving

edges, 2-139 entities, 2-8

lower topology, 2-16 face mesh nodes, 3-92 faces, 2-231 groups, 2-386 vertices, 2-74 volumes, 2-341

N

net-surface face, 2-183 neutral files, 6-2 node spacing, 3-42 Notrielement vertex types, 3-103 NURBS curves, 2-115

O

object list window, 6-4 operation button array, 6-4 orphan entities, A-18, A-36

edges, A-18 faces, A-19



P

parallelogram face, 2-171 parasite entities, A-13, A-36

edges, A-14 vertices, A-13

passage-to-passage turbo volume, 5-68 periodic boundary conditions, 4-2 periodic linking

edges, 3-58 faces, 3-117

perpendicular sweep, 2-198, 2-277 picking entities, 2-4 pitch, 5-69 plane postprocessing object, 6-16 plug volume, 5-72 polygonal faces, 2-173 position parameter

u, 2-46, 2-49 v, 2-49

postprocessing Active quadrant command bar, 6-7 Attachment entities


Attributes specifications, 6-20 commands, 6-9 contour attributes, 6-21

types, 6-22 Halfspace options


importing results files, 6-2 object list window, 6-4 objects

activating, 6-7 copying, 6-6 cube, 6-50, 6-51 cylinder, 6-67, 6-68 deactivating, 6-7 deleting, 6-6

isosurface, 6-97, 6-98 modifying, 6-5 plane, 6-16, 6-17 simulation, 6-105 sphere, 6-82, 6-83

operation button array, 6-4 Operation toolpad, 6-2 operations, 6-1 vector attributes, 6-39

Postprocessing commands Create Cube Object, 6-50 Create Cylinder Object, 6-67 Create Isosurface Object, 6-97 Create Plane Object, 6-16 Create Simulation Object, 6-105 Create Sphere Object, 6-82 Sample Line, 6-12 Sample Point, 6-10

Postprocessing Objects panel, 6-3 Postprocessing Operation subpad, 6-8 Postprocessing toolpad, 6-2 preserving first-edge shape, 2-127 preserving split-edge shape, 2-127 prism, 2-302 Project Edge On Face, 2-120 projecting edges, 2-120 proximity size functions, 5-41 pyramid, 2-307

Q

Quad/Tri-Map meshing scheme, 3-75 Quad/Tri-Pave meshing scheme, 3-82 Quad-Map meshing scheme, 3-70 Quad-Pave meshing scheme, 3-80 Query Edges, 2-159 Query Faces, 2-264 Query Groups, 2-392 Query Vertices, 2-81 Query Volumes, 2-362



querying edges, 2-159 faces, 2-264 groups, 2-392 vertices, 2-81 volumes, 2-362

R

rail edges, 5-65 reflecting an entity, 2-12, 2-21 removing

bumps, A-57 spurs, 3-124

removing dangling edges, 2-250 results-database files, 6-2 retaining

edges, 2-266 faces, 2-216, 2-319, 2-364 group members, 2-394

Reversal vertex types, 3-103 reverse grading, 3-30, 3-57 revolution angle and axis, 2-119 Revolve Edges, 2-190 Revolve Real Faces, 2-286 Revolve Vertices, 2-118 revolving

edges, 2-190 faces, 2-286 vertices, 2-118

rigid sweep, 2-194, 2-274 rotating an entity, 2-10, 2-20 rotation angle and axis, 2-191, 2-287 rulers

displaying, 5-18 intervals, 5-19 range, 5-18

S

Sample Line, 6-12 Sample Point, 6-10

scaling an entity, 2-13, 2-22, 2-31 Set Color form, 2-71 Set Edge Element Type, 3-52 Set Face Element Type, 3-109 Set Face Vertex Types, 3-100 Set Volume Element Type, 3-175 setting face vertex types, 3-100 setting volume element types, 3-175 shape parameter, 2-104 Side vertex types, 3-103 Simplify Faces, 2-250 simplifying faces, 2-250 simplifying geometry, A-53 simulation postprocessing objects, 6-105 size functions

attachment entities, 5-35, 5-40, 5-43 creating, 5-25 curvature, 5-38 deleting, 5-54 fixed, 5-28 modifying, 5-50 overview, 5-23 parameters

curvature, 5-41 fixed, 5-37 proximity, 5-44

proximity, 5-41 source entities, 5-28, 5-40, 5-43

edge, 5-30 face, 5-31 vertex, 5-29

specifications, 5-27 type, 5-27

curvature, 5-38 fixed, 5-28 proximity, 5-41

summarizing, 5-53 viewing, 5-51

skin-surface face, 2-181 Slide Virtual Vertex, 2-57, 5-113, A-17



sliding vertices, 2-57 sliding virtual vertices, 5-113 Smooth contours


Smooth Face Mesh, 3-98 Smooth Volume Mesh, 3-173 smoothing

face meshes, 3-98 volume meshes, 3-173

snap option, 5-14 soft-links, 3-28, 3-30 solvers, 4-6

effect on boundary types, 4-7 source entities, 5-28

edge, 5-30 external, 5-32 face, 5-31 internal, 5-33 vertex, 5-29

spacing, 3-42 spanwise sections, 5-75 Specify Boundary Types, 4-9 Specify Continuum Types, 4-13 sphere, 2-315 sphere postprocessing object, 6-82 Split Edge, 2-142 Split Face, 2-234 Split Meshed Edge, 3-62 Split Meshed Face, 3-127 split operations, A-27 split path mesh nodes, 3-127 split point, 2-143, A-28 Split Quad Meshes, 3-95 split tool, 2-143, A-27, A-30 Split Volume, 2-344 splitting

edges, 2-142, 3-62, A-27 faces, 2-234, 3-127, A-29 quad meshes, 3-95

volumes, 2-344 spurs, 3-124 Stairstep meshing scheme, 3-163 Stitch Faces, 2-271 Submap meshing scheme, 3-76, 3-149 subset entities, A-11 Subtract Real Faces, 2-218 Subtract Real Volumes, 2-321 subtracting


Summarize Boundary Layers, 3-25 Summarize Coordinate Systems, 5-21 Summarize Edge Mesh, 3-63 Summarize Edges, 2-155 Summarize Face Mesh, 3-130 Summarize Faces, 2-260 Summarize Group Meshes, 3-195 Summarize Groups, 2-389 Summarize Size Functions, 5-53 Summarize Vertices, 2-78 Summarize Volume Mesh, 3-185 Summarize Volumes, 2-359 summarizing

boundary layers, 3-25 coordinate systems, 5-21 edge meshes, 3-63 edges, 2-155 face meshes, 3-130 faces, 2-260 group meshes, 3-195 groups, 2-389 size functions, 5-53 vertices, 2-78 volume meshes, 3-185 volumes, 2-359

superset entities, A-10 Sweep Edges, 2-193 Sweep Real Faces, 2-273 sweep types, 2-194, 2-274



sweeping edges, 2-193 faces, 2-273

T

T-connect operations, 2-126, A-39 template mesh volume, 3-164 Tet Primitive meshing scheme, 3-152 TGrid meshing scheme, 3-160 tip clearance, 5-71

options, 5-73 T-Junctions option, 2-126 tolerance criteria, 2-151, 2-243 toolpad command buttons, 1-4 Tools commands, 5-1

Coordinate System, 5-3 Activate Coordinate System, 5-11 Create Coordinate System, 5-4 Delete Coordinate Systems, 5-22 Display Grid, 5-12 Display Ruler, 5-18 Modify Coordinate System, 5-10 Summarize Coordinate Systems, 5-21

Size Function, 5-24 Create Size Function, 5-25 Delete Size Functions, 5-54 Modify Size Function, 5-50 Summarize Size Functions, 5-53 View Size Function, 5-51

Turbo, 5-107 Create Turbo Profile, 5-109 Create Turbo Volume, 5-116 Create/Modify Boundary Layers, 5-124 Decompose Turbo Volume, 5-122 Define Turbo Zones, 5-119 Link/Unlink Edge/Face Meshes, 5-126 Mesh Edges/Faces/Volumes, 5-125 Slide Virtual Vertex, 5-113 Split/Merge Geometry, 5-123 View Turbo Volume, 5-127

topological validity, 2-390 edges, 2-156 faces, 2-261 groups, 2-390 vertices, 2-79 volumes, 2-360

torus, 2-316 Total Entities, 2-83 transition patterns, 3-14 transition rows, 3-15 translating an entity, 2-9, 2-19 Tri Primitive meshing scheme, 3-84 Trielement vertex types, 3-103 Tri-Pave meshing scheme, 3-81 turbo

blade cross sections, 5-60 cascade view, 5-103 component types, 5-56 decomposition, 5-81

automatic linking, 5-83 functions, 5-57 meshing, 5-90

default grading parameters, 5-94 face mesh links, 5-92

modeling procedure, 5-58 operations, 5-55 profile

axis of revolution, 5-63 creating, 5-64 defining, 5-59 medial edges, 5-66 rail edges, 5-65 specifications, 5-61

tip-clearance options, 5-73 viewing, 5-103 volume

blade-to-blade, 5-69 creating, 5-67 passage-to-passage, 5-68 plug volume, 5-72



regions, 5-71 spanwise sections, 5-75 specifications, 5-69

pitch, 5-69 tip clearance, 5-71, 5-73

types, 5-68 zone types, 5-77

casing, 5-78 hub, 5-78 inlet, 5-78 outlet, 5-78 pressure, 5-79 suction, 5-79

turbo functions create profile, 5-109 create volume, 5-116 decomposition, 5-122 slide virtual vertex, 5-113 viewing, 5-127 zone-type definition, 5-119

twist method, 2-203, 2-281

U

Unite Real Faces, 2-217 Unite Real Volumes, 2-320 uniting


Unlink Mesh Edges, 3-61

V

validity criteria, A-46 Vector Definition form, 2-23 Vertex Blend Type form, 2-336 vertex source entities, 5-29 vertex types, 3-71, 3-100 vertices

aligning, 2-75 checking, 2-79 connecting, 2-61

converting, 2-76 copying, 2-74 creating, 2-44, 2-46, 2-49, 2-52

by mouse, 5-12 creating at intersections, 2-54 deleting, 2-84 disconnecting, 2-67 link reference, 3-115 linking, 3-56 modifying


moving, 2-74 querying, 2-81 sliding, 2-57 summarizing, 2-78

View Size Function, 5-51 View Turbo Volume, 5-127 viewing size functions, 5-51 virtual

entities categories, A-9 classes, A-10 guest, A-9 host, A-9 interpolant, A-12 orphan, A-18 parasite, A-13 subset, A-11 superset, A-10

geometry applications, A-45 fundamentals, A-4 operations, A-20

high-level, A-37 low-level, A-20

operations adjusting meshes, A-64 collapse, A-37 connect, A-12, A-31



construct, A-36 geometry clean-up, A-46 merge, A-21, A-23

restrictions, A-25 simplifying geometry, A-53 split, A-11, A-27, A-29

restrictions, A-30 T-connect, A-39

virtual geometry, A-1 virtual operations, A-2

merge, A-5 volumes

aligning, 2-342 blending, 2-323 brick, 2-295 checking, 2-360 checking mesh, 3-186 converting, 2-357 copying, 2-341 creating, 2-294 cylinder, 2-298 deleting, 2-364 deleting meshes, 3-189 forming, 2-270

revolve faces, 2-286 stitch faces, 2-271 sweep faces, 2-273 wireframe, 2-291

frustum, 2-311 healing, 2-354 intersecting, 2-322 linking meshes, 3-180 merging, 2-352 mesh element types, 3-175

modifying color, 2-338 label, 2-339

moving, 2-341 prism, 2-302 pyramid, 2-307 querying, 2-362 smoothing meshes, 3-173 sphere, 2-315 splitting, 2-344 subtracting, 2-321 summarizing, 2-359 summarizing meshes, 3-185 torus, 2-316 uniting, 2-320

W

Wedge Primitive meshing scheme, 3-86 wireframe, 2-167, 2-291 Wire-isosurfaces contours


X

x-y plots, 6-12

Z

zone types, 4-1 Zones commands

Specify Boundary Types, 4-6 Specify Continuum Types, 4-12

gambit user guide

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