geometry modeling

C O N T E N T SMSC.Patran Reference Manual Part 2: Geometry Modeling MSC.Patran Reference Manual, Part 2: Geometry ModelingCHAPTER

1Introduction to Geometry Modeling

Overview of Capabilities, 2

Concepts and Definitions, 4 Parameterization, 5 Topology, 10

- Topological Congruency and Meshing, 12 Connectivity, 15 Effects of Parameterization, Connectivity and Topology in MSC.Patran, 17 Global Model Tolerance & Geometry, 18

Types of Geometry in MSC.Patran, 19 Trimmed Surfaces, 20 Solids, 24 Parametric Cubic Geometry, 25

- Limitations on Parametric Cubic Geometry, 25 Matrix of Geometry Types Created, 27

Building An Optimal Geometry Model, 30 Building a Congruent Model, 31 Building Optimal Surfaces, 33 Decomposing Trimmed Surfaces, 37 Building B-rep Solids, 40 Building Degenerate Surfaces and Solids, 41

2Accessing, Importing & Exporting Geometry

Overview, 46

Direct Geometry Access of CAD Geometry, 47 Accessing Geometry Using MSC.Patran Unigraphics, 47 Accessing Geometry Using MSC.Patran ProENGINEER, 55

PATRAN 2 Neutral File Support For Parametric Cubic Geometry, 57

3Coordinate Frames

Coordinate Frame Definitions, 60

Overview of Create Methods For Coordinate Frames, 63

Translating or Scaling Geometry Using Curvilinear Coordinate Frames, 66

4Create Actions Overview of Geometry Create Action, 70

Creating Points, Curves, Surfaces and Solids, 74 Create Points at XYZ Coordinates or Point Locations (XYZ Method), 74 Create Point ArcCenter, 79 Extracting Points, 81

- Extracting Points from Curves and Edges, 81- Extracting Single Points from Surfaces or Faces, 84- Extracting Multiple Points from Surfaces or Faces, 86- Extracting Multiple Points from Surfaces or Faces, 88- Parametric Bounds for Extracting Points from a Surface, 90

Interpolating Points, 91- Between Two Points, 91- Interpolating Points on a Curve, 94

Intersecting Two Entities to Create Points, 97 Creating Points by Offsetting a Specified Distance, 107 Piercing Curves Through Surfaces to Create Points, 109 Projecting Points Onto Surfaces or Faces, 112 Creating Curves Between Points, 117

- Creating Curves Through 2 Points, 117- Creating Curves Through 3 Points, 119- Creating Curves Through 4 Points, 123

Creating Arced Curves (Arc3Point Method), 128 Creating Chained Curves, 131 Creating Conic Curves, 133 Extracting Curves From Surfaces, 137

- Extracting Curves from Surfaces Using the Parametric Option, 137- Extracting Curves From Surfaces Using the Edge Option, 142

Creating Fillet Curves, 144 Fitting Curves Through a Set of Points, 148 Creating Curves at Intersections, 150

- Creating Curves at the Intersection of Two Surfaces, 150- Creating Curves at the Intersection of a Plane and a Surface, 154- Intersect Parameters Subordinate Form, 157- Creating Curves at the Intersection of Two Planes, 158

Manifold Curves Onto a Surface, 160- Manifold Curves onto a Surface with the 2 Point Option, 160- Manifold Curves onto a Surface With the N-Points Option, 164- Manifold Parameters Subordinate Form, 167

Creating Curves Normally Between a Point and a Curve (Normal Method), 168

Creating Offset Curves, 171- Creating Constant Offset Curve, 171- Creating Variable Offset Curve, 173- Parameterization Control for Variable Offset Curve, 174

Projecting Curves Onto Surfaces, 176- Project Parameters Subordinate Form, 182

Creating Piecewise Linear Curves, 183 Creating Spline Curves, 185

- Creating Spline Curves with the Loft Spline Option, 185- Creating Spline Curves with the B-Spline Option, 189

Creating Curves Tangent Between Two Curves (TanCurve Method), 193

Creating Curves Tangent Between Curves and Points (TanPoint Method), 195

Creating Curves, Surfaces and Solids Through a Vector Length (XYZ Method), 199

Creating Involute Curves, 203- Creating Involute Curves with the Angles Option, 203- Creating Involute Curves with the Radii Option, 206

Revolving Curves, Surfaces and Solids, 208 Creating Orthogonal Curves (2D Normal Method), 214

- Creating Orthogonal Curves with the Input Length Option, 214- Creating Orthogonal Curves with the Calculate Length Option, 218

Creating 2D Circle Curves, 222 Creating 2D ArcAngle Curves, 226 Creating Arced Curves in a Plane (2D Arc2Point Method), 229

- Creating Arced Curves with the Center Option, 229- Creating Arced Curves with the Radius Option, 233- Arc2Point Parameters Subordinate Form, 236

Creating Arced Curves in a Plane (2D Arc3Point Method), 237 Creating Surfaces from Curves, 240

- Creating Surfaces Between 2 Curves, 240- Creating Surfaces Through 3 Curves (Curve Method), 243- Creating Surfaces Through 4 Curves (Curve Method), 246- Creating Surfaces from N Curves (Curve Method), 248

Creating Composite Surfaces, 250 Decomposing Trimmed Surfaces, 255 Creating Surfaces from Edges (Edge Method), 257 Extracting Surfaces, 260

- Extracting Surfaces with the Parametric Option, 260- Extracting Surfaces with the Face Option, 264

Creating Fillet Surfaces, 266 Matching Adjacent Surfaces, 270 Creating Constant Offset Surface, 272 Creating Ruled Surfaces, 274 Creating Trimmed Surfaces, 278

- Creating Trimmed Surfaces with the Surface Option, 280- Creating Trimmed Surfaces with the Planar Option, 281- Auto Chain Subordinate Form, 282- Creating Trimmed Surfaces with the Composite Option, 284

Creating Surfaces From Vertices (Vertex Method), 287 Extruding Surfaces and Solids, 289 Gliding Surfaces, 294

- Gliding Surfaces with the 1 Director Curve Option, 294- Gliding Surfaces with the 2 Director Curve Option, 296

Creating Surfaces and Solids Using the Normal Method, 298 Creating Surfaces from a Surface Mesh (Mesh Method), 305

- Created Tessellated Surface from Geometry Form, 306 Creating Midsurfaces, 307

- Creating Midsurfaces with the Automatic Option, 307- Creating Midsurfaces with the Manual Option, 309

Creating Solid Primitives, 311- Creating a Solid Block, 311- Creating Solid Cylinder, 314- Creating Solid Sphere, 317- Creating Solid Cone, 320

- Creating Solid Torus, 323- Solid Boolean operation during primitive creation, 326

Creating Solids from Surfaces (Surface Method), 327- Creating Solids from Two Surfaces, 327- Creating Solids from Three Surfaces (Surface Method), 330- Creating Solids from Four Surfaces (Surface Method), 333- Creating Solids with the N Surface Option, 336

Creating a Boundary Representation (B-rep) Solid, 338 Creating a Decomposed Solid, 340 Creating Solids from Faces, 343 Creating Solids from Vertices (Vertex Method), 346 Gliding Solids, 348

Creating Coordinate Frames, 350 Creating Coordinate Frames Using the 3Point Method, 350 Creating Coordinate Frames Using the Axis Method, 353 Creating Coordinate Frames Using the Euler Method, 355 Creating Coordinate Frames Using the Normal Method, 358 Creating Coordinate Frames Using the 2 Vector Method, 361 Creating Coordinate Frames Using the View Vector Method, 362

Creating Planes, 363 Creating Planes with the Point-Vector Method, 363 Creating Planes with the Vector Normal Method, 365 Creating Planes with the Curve Normal Method, 367

- Creating Planes with the Curve Normal Method - Point Option, 367- Creating Planes with the Curve Normal Method-Parametric

Option, 369 Creating Planes with the Plane Normal Method, 371 Creating Planes with the Interpolate Method, 372

- Creating Planes with the Interpolate Method - Uniform Option, 372- Creating Planes with the Interpolate Method - Nonuniform Option, 374

Creating Planes with the Least Squares Method, 375- Creating Planes with the Least Squares Method - Point Option, 375- Creating Planes with the Least Squares Method - Curve Option, 377- Creating Planes with the Least Squares Method - Surface Option, 379

Creating Planes with the Offset Method, 381 Creating Planes with the Surface Tangent Method, 383

- Creating Planes with the Surface Tangent Method - Point Option, 383- Creating Planes with the Surface Tangent Method - Parametric

Option, 385 Creating Planes with the 3 Points Method, 387

Creating Vectors, 389 Creating Vectors with the Magnitude Method, 389 Creating Vectors with the Interpolate Method, 391

- Between Two Points, 391 Creating Vectors with the Intersect Method, 393 Creating Vectors with the Normal Method, 395

- Creating Vectors with the Normal Method - Plane Option, 395- Creating Vectors with the Normal Method - Surface Option, 397- Creating Vectors with the Normal Method - Element Face Option, 399

Creating Vectors with the Product Method, 402 Creating Vectors with the 2 Point Method, 404

5Delete Actions Overview of the Geometry Delete Action, 408

Deleting Any Geometric Entity, 409

Deleting Points, Curves, Surfaces, Solids, Planes or Vectors, 410

Deleting Coordinate Frames, 411

6Edit Actions Overview of the Edit Action Methods, 414

Editing Points, 416 Equivalencing Points, 416

Editing Curves, 418 Breaking Curves, 418

- Breaking a Curve at a Point, 418- Breaking a Curve at a Parametric Location, 422- Breaking a Curve at a Plane Location, 425

Blending a Curve, 426 Disassembling a Chained Curve, 429 Extending Curves, 431

- Extending a Curve With the 1 Curve Option, 431- Extending a Curve Using the Through Points Type, 436- Extending a Curve Using the Full Circle Type, 438- Extending a Curve With the 2 Curve Option, 440

Merging Existing Curves, 443 Refitting Existing Curves, 447 Reversing a Curve, 448 Trimming Curves, 451

- Trimming a Curve With the Point Option, 451- Trimming a Curve Using the Parametric Option, 454

Editing Surfaces, 457 Surface Break Options, 457

- Breaking a Surface With the Curve Option, 457- Breaking a Surface With the Surface Option, 461- Breaking a Surface With the Plane Option, 463- Breaking a Surface With the Point Option, 465- Breaking a Surface Using the 2 Point Option, 469- Breaking a Surface With the Parametric Option, 471

Blending Surfaces, 475 Disassembling Trimmed Surfaces, 478 Matching Surface Edges, 481

- Matching Surface Edges with the 2 Surface Option, 481- Matching Surface Edges with the Surface-Point Option, 484

Extending Surfaces, 486- Extending Surfaces with the 2 Surface Option, 486- Extending Surfaces to a Curve, 488- Extending Surfaces to a Plane, 490- Extending Surfaces to a Point, 492- Extending Surfaces to a Surface, 494- Extending Surfaces with the Percentage Option, 496

- Extending Surfaces with the Fixed Length Option, 498 Refitting Surfaces, 500 Reversing Surfaces, 501 Sewing Surfaces, 503 Trimming Surfaces to an Edge, 505 Adding a Fillet to a Surface, 507 Removing Edges from Surfaces, 508

- Removing Edges from Surfaces with Edge Option, 508- Removing Edges from Surfaces with Edge Length Option, 509

Adding a Hole to Surfaces, 510- Adding a Hole to Surfaces with the Center Point Option, 510- Adding a Hole to Surfaces with the Project Vector Option, 512- Adding a Hole to Surfaces with the Inner Loop Option, 514

Removing a Hole from Trimmed Surfaces, 516 Adding a Vertex to Surfaces, 518 Removing a Vertex from Trimmed Surfaces, 520

Editing Solids, 522 Breaking Solids, 522

- Breaking Solids with the Point Option, 522- Breaking Solids with the Parametric Option, 526- Breaking Solids with the Curve Option, 531- Breaking Solids with the Plane Option, 533- Breaking Solids with the Surface Option, 535

Blending Solids, 538 Disassembling B-rep Solids, 541 Refitting Solids, 543

- Refitting Solids with the To TriCubicNet Option, 543- Refitting Solids with the To TriParametric Option, 544- Refitting Solids with the To Parasolid Option, 545

Reversing Solids, 546 Solid Boolean Operation Add, 548 Solid Boolean Operation Subtract, 550 Solid Boolean Operation Intersect, 552 Creating Solid Edge Blends, 554

- Creating Constant Radius Edge Blends from Solid Edges, 554- Creating Chamfer Edge Blend from Solid Edges, 556

Imprinting Solid on Solid, 558 Solid Shell Operation, 560

Editing Features, 562 Suppressing a Feature, 562 Unsuppressing a Feature, 563 Editing Feature Parameters, 564 Feature Parameter Definition, 565

7Show Actions Overview of the Geometry Show Action Methods, 568

The Show Action Information Form, 569

Showing Points, 570 Showing Point Locations, 570 Showing Point Distance, 571

- Showing Point Distance with the Point Option, 571- Showing Point Distance with the Curve Option, 573- Showing Point Distance with the Surface Option, 575- Showing Point Distance with the Plane Option, 577- Showing Point Distance with the Vector Option, 579

Showing the Nodes on a Point, 581

Showing Curves, 582 Showing Curve Attributes, 582 Showing Curve Arc, 583 Showing Curve Angle, 584 Showing Curve Length Range, 586 Showing the Nodes on a Curve, 587

Showing Surfaces, 588 Showing Surface Attributes, 588 Showing Surface Area Range, 589 Showing the Nodes on a Surface, 590 Showing Surface Normals, 591

Showing Solids, 593 Showing Solid Attributes, 593

Showing Coordinate Frames, 594 Showing Coordinate Frame Attributes, 594

Showing Planes, 595 Showing Plane Attributes, 595 Showing Plane Angle, 596 Showing Plane Distance, 598

Showing Vectors, 599 Showing Vector Attributes, 599

8Transform Actions Overview of the Transform Methods, 602

Transforming Points, Curves, Surfaces, Solids, Planes and Vectors, 605 Translating Points, Curves, Surfaces, Solids, Planes and Vectors, 605 Rotating Points, Curves, Surfaces, Solids, Planes and Vectors, 619 Scaling Points, Curves, Surfaces, Solids and Vectors, 629 Mirroring Points, Curves, Surfaces, Solids, Planes and Vectors, 640 Moving Points, Curves, Surfaces, Solids, Planes and Vectors by Coordinate

Frame Reference (MCoord Method), 648 Pivoting Points, Curves, Surfaces, Solids, Planes and Vectors, 656 Positioning Points, Curves, Surfaces, Solids, Planes and Vectors, 665 Vector Summing (VSum) Points, Curves, Surfaces and Solids, 674 Moving and Scaling (MScale) Points, Curves, Surfaces and Solids, 683

Transforming Coordinate Frames, 690 Translating Coordinate Frames, 690 Rotating Coordinate Frames, 693

9Verify Actions Verify Action, 698

Verifying Surface Boundaries, 698 Verifying Surfaces for B-reps, 700

- Update Graphics Subordinate Form, 701 Verify - Surface (Duplicates), 702

10Associate Actions Overview of the Associate Action, 704

Associating Point Object, 705 Associating Curve Object, 707

11Disassociate Actions

Overview of the Disassociate Action Methods, 710 Disassociating Points, 711 Disassociating Curves, 712 Disassociating Surfaces, 713

12The Renumber Action... Renumbering Geometry

Introduction, 716

Renumber Forms, 717 Renumber Geometry, 718

INDEX MSC.Patran Reference Manual, 719Part 2: Geometry Modeling

MSC.Patran Reference Manual, Part 2: Geometry Modeling

CHAPTER

1 Introduction to Geometry Modeling

Overview of Capabilities

Concepts and Definitions

Types of Geometry in MSC.Patran

Building An Optimal Geometry Model

PART 2Geometry Modeling1.1 Overview of CapabilitiesA powerful and important feature of MSC.Patran is its geometry capabilities. Geometry can be:

Created. Directly accessed from an external CAD part file. Imported from an IGES file or a PATRAN 2 Neutral file.

Complete Accuracy of Original Geometry. MSC.Patran maintains complete accuracy of the original geometry, regardless of where it came from. The exact mathematical representation of the geometry (e.g., Arc, Rational B-Spline, B-rep, Parametric Cubic, etc.) is consistently maintained throughout the modeling process, without any approximations or conversions.

This means different versions of the geometry model are avoided. Only one copy of the geometry design needs to be maintained by the engineer, whether the geometry is in a separate CAD part file or IGES file or the geometry is part of the MSC.Patran database.

Below are highlights of the geometry capabilities:

Direct Application of Loads/BCs and Element Properties to Geometry. All loads, boundary conditions (BC) and element property assignments can be applied directly to the geometry. When the geometry is meshed with a set of nodes and elements, MSC.Patran will automatically assign the loads/BC or element property to the appropriate nodes or elements.

Although you can apply the loads/BCs or element properties directly to the finite element mesh, the advantage of applying them to the geometry is if you remesh the geometry, they remain associated with the model. Once a new mesh is created, the loads/BC and element properties are automatically reassigned.

For more information, see Introduction to Functional Assignment Tasks (Ch. 1) in the MSC.Patran Reference Manual, Part 5: Functional Assignments.

Direct Geometry Access. Direct Geometry Access (DGA) is the capability to directly access (or read) geometry information from an external CAD user file, without the use of an intermediate translator. Currently, DGA supports the following CAD systems:

EDS/Unigraphics Pro/ENGINEER by Parametric Technology CATIA by Dassault Systemes EUCLID 3 by Matra Datavision CADDS 5 by Computervision

With DGA, the CAD geometry and its topology that are contained in the CAD user file can be accessed. Once the geometry is accessed, you can build upon or modify the accessed geometry in MSC.Patran, mesh the geometry, and assign the loads/BC and the element properties directly to the geometry.

For more detailed information on DGA, see Direct Geometry Access of CAD Geometry (p. 47).

Import and Export of Geometry. There are three file formats available to import or export geometry:

IGES

3CHAPTER 1Introduction to Geometry Modeling PATRAN 2 Neutral File Express Neutral File

In using any of the file formats, MSC.Patran maintains the original mathematical form of the geometry. (That is, the geometry is not approximated into the parametric cubic form.) This means the accuracy of the geometry in all three files is maintained.

For more information on the import and export capabilities for IGES, PATRAN 2 Neutral File, and the Express Neutral File, see Accessing, Importing & Exporting Geometry (Ch. 2).

MSC.Patran Native Geometry. You can also create geometry in MSC.Patran (native geometry). A large number of methods are available to create, translate, and edit geometry, as well as methods to verify, delete and show information.

MSC.Patrans native geometry consists of:

Points Parametric curves Bi-parametric surfaces Tri-parametric solids Boundary represented (B-rep) solids

All native geometry is fully parameterized both on the outer boundaries and within the interior (except for B-rep solids which are parameterized only on the outer surfaces).

Fully parameterized geometry means that you can apply varying loads or element properties directly to the geometric entity. MSC.Patran evaluates the variation at all exterior and interior locations on the geometric entity.

PART 2Geometry Modeling1.2 Concepts and DefinitionsThere are many functions in MSC.Patran that rely on the mathematical representation of the geometry. These functions are:

Applying a pressure load to a curve, surface or solid. Creating a field function in parametric space. Meshing a curve, surface or solid. Referencing a vertex, edge or face of a curve, surface or solid.

For every curve, surface or solid in a user database, information is stored on its Parameterization, Topology and Connectivity which is used in various MSC.Patran functions.

The concepts of parameterization, connectivity and topology are easy to understand and they are important to know when building a geometry and an analysis model.

The following sections will describe each of these concepts and how you can build an optimal geometry model for analysis.

5CHAPTER 1Introduction to Geometry ModelingParameterizationAll MSC.Patran geometry are labeled one of the following:

Point (0-Dimensions) Curve (1-Dimension) Surface (2-Dimensions) Solid (3-Dimensions)

Depending on the order of the entity - whether it is a one-dimensional curve, a two-dimensional surface, or a three-dimensional solid - there is one, two or three parameters labeled , ,

that are associated with the entity. This concept is called parameterization.

Parameterization means the X,Y,Z coordinates of a curve, surface or solid are represented as functions of variables or parameters. Depending on the dimension of the entity, the X,Y,Z locations are functions of the parameters , , and .

An analogy to the parameterization of geometry is describing an , location as a function of time, t. If and , as changes, and will define a path. Parameterization of geometry does the same thing - as the parameters , , and change, it defines various points on the curve, surface and solid.

The following describes how a point, curve, surface and solid are parameterized in MSC.Patran.

Point. A Point in MSC.Patran is a point coordinate location in three-dimensional global XYZ space.

Since a point has zero-dimensions, it has no associated parameters, therefore, it is not parameterized.

Figure 1-1 Point in MSC.Patran

Curve. A Curve in MSC.Patran is a one-dimensional point set in three-dimensional global XYZ space. A curve can also be described as a particle moving along a defined path in space.

Another way of defining a curve is, a curve is a mapping function, , from one-dimensional parametric space into three-dimensional global XYZ space, as shown in Figure 1-3.

1 23

1 2 3X Y

t X X t( )= Y Y t( )= t X Y1 2 3

P(X,Y,Z)z

x y

1( )

PART 2Geometry ModelingA curve has one parametric variable, , which is used to describe the location of any given point, , along a curve, as shown in Figure 1-2.

Figure 1-2 Curve in MSC.Patran

The parameter, , has a range of , where at , is at endpoint and at , is at endpoint .

A straight curve can be defined as:

Eq. 1-1

Figure 1-3 Mapping Function Phi for a Curve

Eq. 1-1 of our straight curve can be represented as:

Eq. 1-2

The derivative of in Eq. 1-2, would give us Eq. 1-3 which is the tangent of the straight curve.

Eq. 1-3

Because the curve is straight, is a constant value. The tangent, , also defines a vector for the curve, which is the positive direction of .

1P

V1

V2

1

P

z

x y

1 0 1 1 1 0= P V11 1= P V2

P 1.0 1( )V1 1V2+=

0 11

(1)

1z

x y

V1

V2

0 1 1

1 1.0 1( )V1 1V2+=

1( )

1 V2 V1=

1 11

7CHAPTER 1Introduction to Geometry ModelingFor any given curve, the tangent and positive direction of at any point along the curve can be found. (The vector, , usually will not have a length of one.)

Surface. A surface in MSC.Patran is a two-dimensional point set in three-dimensional global XYZ space.

A surface has two parameters, and , where at any given point, , on the surface, can be located by and , as shown in Figure 1-4.

Figure 1-4 Surface in MSC.Patran

A surface generally has three or four edges. Trimmed surfaces can have more than four edges. For more information, see Trimmed Surfaces (p. 20).

Similar to a curve, and for a surface have ranges of and . Thus, at , , is at and at , , is at .

A surface is represented by a mapping function, , which maps the parametric space into the global XYZ space, as shown in Figure 1-5.

Figure 1-5 Mapping Function Phi for a Surface

The first order derivatives of results in two partial derivatives, and :

1 1

1 2 P P1 2

V2

V3

V4

V1

2

1

P

z

x y

1 2 0 1 1 0 2 1 1 0= 2 0= P V1 1 1= 2 1= P V3

1 , 2( )

(1,2)

z

x y

12

2

1(0,0) (1,0)

(1,1) (0,1)

V1

V2

V3

V40 1 10 2 1

1 , 2( ) 1 2

PART 2Geometry ModelingEq. 1-4

where is the tangent vector in the direction and is the tangent vector in the direction.

At any point for a given surface, and which define the tangents and the positive and directions can be determined.

Usually and are not orthonormal, which means they do not have a length of one and they are not perpendicular to each other.

Solid. A solid in MSC.Patran is a three-dimensional point set in three-dimensional global XYZ space.

A solid has three parameters, , , and , where at any given point, , within the solid, can be located by , , and , as shown in Figure 1-6.

Figure 1-6 Solid in MSC.Patran

A solid generally has five or six sides or faces. (A B-rep solid can have more than six faces.)

The parameters , and have ranges of , , and . At (0,0,0) is at and at (1,1,1), is at .

Note: The above definition applies to tri-parametric solids only. MSC.Patran can also create or import a B-rep solid, which is parameterized on the outer surface only, and not within the interior. See B-rep Solid (p. 24) for more information.

1 T 1 and 2 T2==

T1 1 T2 2

T1 T2 12

T1 T2

1 2 3 P P1 2 3

V7

V3

V6

V5

V1

V4

V23

2

1

P

z

x y

1 2 3 0 1 1 0 2 1 0 3 1 PV1 P V7

9CHAPTER 1Introduction to Geometry ModelingA solid can be represented by a mapping function, , which maps the parametric space into the global XYZ space, as shown in Figure 1-7.

Figure 1-7 Mapping Function Phi for a Solid

If we take the first order derivatives of , we get three partial derivatives, , and , shown in Eq. 1-5:

Eq. 1-5

Where is the tangent vector in the direction, is the tangent vector in the direction, and is the tangent vector in the direction.

At any point within a given solid, , and , which define the tangents and positive , and directions can be determined.

1 , 2 3,( )

(1,2,3)

z

x y

21

3

(0,0,0) (1,0,0)

(1,1,0)

(1,1,1) (0,0,1)

(0,1,1)

(1,0,1)

1

32

V1

V5

V6

V7

V3

V4

0 1 10 2 10 3 1

1 , 2 3,( ) 1 2 3

1 T 1, 2 T 2, 3 T3===

T1 1 T2 2T3 3

T1 T2 T3 12 3

PART 2Geometry ModelingTopologyTopology identifies the kinds of items used to define adjacency relationships between geometric entities.

Every curve, surface and solid in MSC.Patran has a defined set of topologic entities. You can reference these entities when you build the geometry or analysis model. Examples of this include:

Creating a surface between edges of two surfaces. Meshing an edge or a face of a solid. Referencing a vertex of a curve, surface or solid to apply a loads/BC.

Topology is invariant through a one-to-one bicontinuous mapping transformation. This means you can have two curves, surfaces or solids that have different parameterizations, but topologically, they can be identical.

To illustrate this concept, Figure 1-8 shows three groups of surfaces A-D. Geometrically, they are different, but topologically they are the same.

Figure 1-8 Topologically Equivalent Surfaces

Topologic Entities: Vertex, Edge, Face, Body. The types of topologic entities found in MSC.Patran are the following:

Vertex Defines the topologic endpoint of a curve, or a corner of a surface or a solid. A vertex is separate from a geometric point, although a point can exist on a vertex.

Edge Defines the topologic curve on a surface or a solid. An edge is separate from a geometric curve, although a curve can exist on an edge.

D

C

B

AA

B

CD

* Surface A is not connected to Surface D

A* B

D* C

1CHAPTER 1Introduction to Geometry ModelingVertex, Edge and Face ID Assignments in MSC.Patran. The connectivity for a curve, surface and solid determines the order in which the internal vertex, edge and face IDs will be assigned. The location of a geometric entitys parametric axes defines the point where assignment of the IDs for the entitys vertices, edges and faces will begin.

Figure 1-9 and Figure 1-10 show a four sided surface and a six sided solid with the internal vertex, edge and face IDs displayed. If the connectivity changes, then the IDs of the vertices, edges and faces will also change.

For example, in Figure 1-9, the edge, ED3, of Surface 11 would be displayed as:

Surface 11.3

The vertex, V4, in Figure 1-9 would be displayed as:

Surface 11.3.1

V4 has a vertex ID of 1 that belongs to edge 3 on surface 11.

The face, F1, of Solid 100 in Figure 1-10 would be displayed as:

Solid 100.1

The edge, ED10, in Figure 1-10 would be displayed as:

Solid 100.1.3

Face Defines the topologic surface of a solid. A face is separate from a geometric surface, although a surface can exist on a face.

Body A group of surfaces that forms a closed volume. A body is usually referenced as a B-rep solid or a Volume solid, where only its exterior surfaces are parameterized. See Solids (p. 24) for more information.

Important: Generally, when modeling in MSC.Patran, you do not need to know the topologic entities internal IDs. When you cursor select a topologic entity, such as an edge of a surface, the ID will be displayed in the appropriate listbox on the form.

Figure 1-9 Vertex & Edge Numbering for a Surface

Figure 1-10 Face Numbering for a Solid

ED2

ED3

ED4

ED1

V3

V4V1

V2

1

2F1

F3

F6

F5

F2

F4

12

3

11100

V8

V4

ED12

ED7

ED6

ED1

ED10ED2

ED3ED5

ED4

ED8

ED9

ED11

V2

V1

V3

V5

V6

V7

PART 2Geometry ModelingED10 has an edge ID of 3 that belongs to face 1 on solid 100.

The vertex, V6, in Figure 1-10 would be displayed as:

Solid 100.1.2.2

V6 has a vertex ID of 2 that belongs to edge 2 on face 1 on solid 100.

Topological Congruency and Meshing

When meshing adjacent surfaces or solids, MSC.Patran requires the geometry be topologically congruent so that coincident nodes will be created along the common boundaries.

Figure 1-11 shows an example where surfaces 1 through 3 are topologically incongruent and surfaces 2 through 5 are topologically congruent. The outer vertices are shared for surfaces 1 through 3, but the inside edges are not. Surfaces 2 through 5 all have common edges, as well as common vertices.

There are several ways to correct surfaces 1 through 3 to make them congruent. See Building a Congruent Model (p. 31) for more information.

Figure 1-11 Topologically Incongruent and Congruent Surfaces

For a group of surfaces or solids to be congruent, the adjacent surfaces or solids must share common edges, as well as common vertices.

(MSC.Software Corporations MSC.Patran software product required adjacent surfaces or solids to share only the common vertices to be considered topologically congruent for meshing.)

1

2

3

2

3

4

5

Topologically Incongruent Topologically Congruent

1CHAPTER 1Introduction to Geometry ModelingGaps Between Adjacent Surfaces. Another type of topological incongruence is shown in Figure 1-12. It shows a gap between two pairs of surfaces that is greater than the Global Model Tolerance. This means when you mesh the surface pairs, coincident nodes will not be created along both sides of the gap.

Figure 1-12 Topologically Incongruent Surfaces with a Gap

MSC recommends two methods for closing surface gaps:

Use the Create/Surface/Match form. See Matching Adjacent Surfaces (p. 270). Use the Edit/Surface/Edge Match form. See Matching Surface Edges (p. 481).

For more information on meshing, see Introduction to Functional Assignment Tasks (Ch. 1) in the MSC.Patran Reference Manual, Part 5: Functional Assignments.

Non-manifold Topology. Non-manifold topology can be simply defined as a geometry that is non-manufacturable. However, in analysis, non-manifold topology is sometimes either necessary or desirable. Figure 1-13 shows a surface model with a non-manifold edge.

Figure 1-13 Non-manifold Topology at an Edge

Vertices are Shared, Edges are Not

Incongruent Surfaces

Gap > Global ModelTolerance

PART 2Geometry ModelingThis case may be perfectly fine. A non-manifold edge has more than two surfaces or solid faces connected to it. Therefore, two solids which share a common face also give non-manifold geometry (both the common face and its edges are non-manifold).

In general, non-manifold topology is acceptable in MSC.Patran. The exception is in the creation of a B-rep solid where a non-manifold edge is not allowed. The Verifying Surface Boundaries (p. 698) option detects non-manifold edges as well as free edges.

1CHAPTER 1Introduction to Geometry ModelingConnectivityIn Figure 1-2, Figure 1-4, and Figure 1-6 in Parameterization (p. 5), the axes for the parameters, , , and , have a unique orientation and location on the curve, surface and solid.

Depending on the orientation and location of the , , and axes, this defines a unique connectivity for the curve, surface or solid.

For example, although the following two curves are identical, the connectivity is different for each curve (note that the vertex IDs are reversed):

Figure 1-14 Connectivity Possibilities for a Curve

For a four sided surface, there are a total of eight possible connectivity definitions. Two possible connectivities are shown in Figure 1-15. (Again, notice that the vertex and edge IDs are different for each surface.)

Figure 1-15 Two Possible Connectivities for a Surface

1 2 3

1 2 3

V1

V2

1

V1

V2

1

V2

V3

V4

V1

2 1

ED1

ED2

ED3ED4

ED2

ED3

ED1ED4

V2

V3

V4

V1

2

1

PART 2Geometry ModelingFor a tri-parametric solid with six faces, there are a total of 24 possible connectivity definitions in MSC.Patran - three orientations at each of the eight vertices. Two possible connectivities are shown in Figure 1-16.

Figure 1-16 Two Possible Connectivities for a Solid

Plotting the Parametric Axes. MSC.Patran can plot the location and orientation of the parametric axes for the geometric entities by turning on the Parametric Direction toggle on the Geometric Properties form, under the Display/Display Properties/Geometric menu. See Geometry Preferences (p. 296) in the MSC.Patran Reference Manual, Part 2: Basic Functions for more information.

Modifying the Connectivity. For most geometric entities, you can modify the connectivity by altering the orientation and/or location of the parametric axes by using the Geometry applications Edit actions Reverse method. See Overview of the Edit Action Methods (p. 414).

For solids, you can also control the location of the parametric origin under the Preferences/Geometry menu and choose either the MSC.Patran Convention button or the PATRAN 2.5 Convention button for the Solid Origin Location.

V7

V3

V6

V5

V1

V4

V232

1

V8

V3

V6

V5

V1

V4

V2

3

2

1V8

1CHAPTER 1Introduction to Geometry ModelingEffects of Parameterization, Connectivity and Topology in MSC.PatranThe geometrys parameterization and connectivity affect the geometry and finite element analysis model in the following ways:

Defines Order of Internal Topologic IDs. The parameterization and connectivity for a curve, surface or solid define the order of the internal IDs of their topologic entities. MSC.Patran stores these IDs internally and displays them when you cursor select a vertex, edge or face. See Vertex, Edge and Face ID Assignments in MSC.Patran (p. 11) for more information.

Defines Positive Surface Normals. Using right hand rule by crossing a surfaces direction with its direction, it defines the surfaces positive normal direction ( direction). This affects many areas of geometry and finite element creation, including creating B-rep solids. See Building An Optimal Geometry Model (p. 30) for more information.

Defines Positive Pressure Load Directions. The parameterization and connectivity of a curve, surface or solid define the positive direction for a pressure load, and it defines the surfaces top and bottom locations for an element variable pressure load. See Create Structural LBCs Sets (p. 19) in the MSC.Patran Reference Manual, Part 5: Functional Assignments for more information.

Helps Define Parametric Field Functions. If you reference a field function that was defined in parametric space, when creating a varying loads/BC or a varying element or material property, the loads/BC values or the property values will depend on the geometrys parameterization and the orientation of the parametric axes. See Fields Forms (p. 144) in the MSC.Patran Reference Manual, Part 5: Functional Assignments for more information.

Defines Node and Element ID Order For IsoMesh. The MSC.Patran mapped mesher, IsoMesh, will use the geometric entitys parameterization and connectivity to define the order of the node and element IDs and the element connectivity. (The parameterization and connectivity will not be used if the mesh will have a transition or change in the number of elements within the surface or solid.) See IsoMesh (p. 15) in the MSC.Patran Reference Manual, Part 3: Finite Element Modeling for more information.

12 3

PART 2Geometry ModelingGlobal Model Tolerance & GeometryMSC.Patran uses the Global Model Tolerance when it imports or accesses geometry, when it creates geometry, or when it modifies existing geometry.

The Global Model Tolerance is found under the Preferences/Global menu. The default value is 0.005.

When creating geometry, if two points are within a distance of the Global Model Tolerance, then MSC.Patran will only create the first point and not the second.

This rule also applies to curves, surfaces and solids. If the points that describe two curves, surfaces or solids are within a distance of the Global Model Tolerance, then only the first curve, surface or solid will be created, and not the second.

For more information on the Global Model Tolerance, see (p. 57) in the MSC.Patran Reference Manual, Part 1: Basic Functions.

Important: For models with dimensions which vary significantly from 10 units, MSC recommends you set the Global Model Tolerance to .05% of the maximum model dimension.

1CHAPTER 1Introduction to Geometry Modeling1.3 Types of Geometry in MSC.PatranGenerally, there are four types of geometry objects in MSC.Patran:1

Point (default color is cyan) Parametric Curve (default color is yellow) Bi-Parametric Surface (default color is green) Tri-Parametric Solid (default color is dark blue)

MSC.Patran also can access, import, and create Trimmed Surfaces, B-rep Solids and Volume Solids. See Trimmed Surfaces (p. 20) and Solids (p. 24) for more information.

You also can create parametric cubic curves, surfaces and solids, which are recognized by the PATRAN 2 neutral file. See Parametric Cubic Geometry (p. 25) for more information.

For more information on the types of geometry that can be created, see Matrix of Geometry Types Created (p. 27).

1The default colors are used if the Display Method is set to Entity Type, instead of Group, on the Graphics Preferences form under the Preferences/Graphics menu.

PART 2Geometry ModelingTrimmed SurfacesTrimmed surfaces are a special class of bi-parametric surfaces. Trimmed surfaces can be accessed from an external CAD user file; they can be imported from an IGES or Express Neutral file; and they can be created in MSC.Patran.

Unlike other types of bi-parametric surfaces, trimmed surfaces can have more than four edges, and they can have one or more interior holes or cutouts.

Also, trimmed surfaces have an associated parent surface that is not displayed. A trimmed surface is defined by identifying the closed active and inactive regions of the parent surface. This parent surface defines the parameterization and curvature of the trimmed surface.

You can create three types of trimmed surfaces in MSC.Patran:1

General Trimmed Surface (default color is magenta) Simply Trimmed Surface (default color is green) Composite Trimmed Surface (default is magenta) Ordinary Composite Trimmed Surface (default color is green)

(Green is the default color for both a simply trimmed surface and a general, bi-parametric surface.)

General Trimmed Surface. A general trimmed surface can have any number of outer edges and any number of inner edges which describe holes or cutouts. These outer and inner edges are defined by a closed loop of chained curves. (Chained curves can be created with the Create/Curve/Chain form. See Creating Chained Curves (p. 131).) An example is shown in Figure 1-17.

All general trimmed surfaces, whether they are accessed, imported or created, have a default color of magenta.2


Important: Simply trimmed surfaces and ordinary composite trimmed surfaces can be meshed with IsoMesh or Paver. General trimmed surfaces and composite trimmed surfaces can only be meshed with Paver. See Meshing Surfaces with IsoMesh or Paver (p. 15) in the MSC.Patran Reference Manual, Part 3: Finite Element Modeling for more information. Also note that some geometric operations are not currently possible with a general trimmed surface, e.g., a general trimmed surface can not be used to create a triparametric solid.


2CHAPTER 1Introduction to Geometry ModelingFigure 1-17 General Trimmed Surface

Simply Trimmed Surface. A simply trimmed surface can only have four outer edges. It cannot have any inner edges, or holes or cutouts. A simply trimmed surface reparametrizes the bounded region of the parent and is called an overparametrization. An example is shown in Figure 1-18. (A simply trimmed surface can have three sides, with one of the four edges degenerating to a zero length edge.)

Like a general trimmed surface, a simply trimmed surfaces outer edges are defined by a closed loop of chained curves. See Creating Chained Curves (p. 131).

All simply trimmed surfaces, whether they are accessed, imported or created, have a default color of green. 1


Outer Surface Edges

Inner Edges orHoles

PART 2Geometry ModelingFigure 1-18 Simply Trimmed Surface

Sometimes a three of four sided region which define a trimmed surface will be created as a general trimmed surface instead. This occurs when the overparametrization distorts the bounded region of the parent to such an extent that it would be difficult to mesh and use for analysis.

Composite Trimmed Surface. The composite trimmed surface is a kind of supervisor surface that allows a collection of surfaces to be considered as one surface defined within a specific boundary. This surface can also have holes in it. Evaluations on the composite trimmed surface is similar to evaluations on the MSC.Patran trim surface (General Trimmed Surface). The big difference is that it is three to five times slower than ordinary surfaces.

The composite trimmed surface should be considered a tool. Once the surface is built, it is a single entity, yet processes on multiple surfaces, relieving the applications of the task of determining where and when to move from one surface to another.

APPLICATION: The composite trimmed surface supervisor is a bounded PLANAR trim surface. It acquires its name from the type of service it performs. Let us, for a moment, consider the composite trimmed surface to be a cloud in the sky. The sun, being the light source behind the cloud, creating a shadow on planet earth only in the area blocked by the cloud. The same is true with the composite trimmed surface, except a view vector is given to determine the light direction. Under Surfaces replace planet earth. The valid region on the Under Surfaces is defined by where the outline of the composite trimmed surface appears.

Underlying Invisible Parent Surface

Four Outer Edges

2CHAPTER 1Introduction to Geometry ModelingSTEPS_BUILDING: There are three basic steps in building a composite trimmed surface.

RULES:

1. The composite trimmed surface domain must not encompass any dead space. If any portion has a vacancy (no Under Surface under it), unpredictable results will occur.

2. Processing along the view vector must yield a single intersection solution at any position on the underlying surfaces within the composite trimmed surfaces domain.

Ordinary Composite Trimmed Surface. The only difference between an Ordinary Composite Trimmed Surface and the Composite Trimmed Surface is that this type will have only four edges comprising the outer loop and no inner loops.

Step 1 Creating the outer perimeter curve. In most cases this is a MSC.Patran curve chain entity.

Step 2 Selecting an acceptable view direction for the view vector and planar Composite trimmed surface entity. The view vector is the most important aspect of building a composite trimmed surface. The resulting view vector must yield only one intersection solution at any position on the Under Surfaces. The user must select the proper view for the location of the composite trimmed surface with some forethought and eliminate the possibility of any of the underlying surfaces wrapping around in back of one another. In some cases this may not be possible! The user must then create more than one composite trimmed surface.

Additionally, since the composite trimmed surface supervisor is PLANAR, it cannot encompass more than a 180 degree field of view. An example of this would be a cylindrically shaped group of surfaces. It would probably take three properly placed composite trimmed surface to represent it; one for every 120 degrees of rotation.

Step 3 Determines which currently displayed surfaces will be become part of the composite trimmed surface domain (Under Surfaces). The user may individually select the correct underlying surfaces or, if wanting to select all visible surfaces, the user must place into ERASE all surfaces which might cause multiple intersections and then select the remaining visible surfaces.

PART 2Geometry ModelingSolidsThere are three types of solids that can be accessed or imported, or created in MSC.Patran:1

Tri-Parametric Solid (default color is dark blue) B-rep Solid (default color is white) Volume Solid (default color is pink or light red)

on (p. 2) lists the types of solids created with each Geometry Application method.

Tri-Parametric Solid. All solids in MSC.Patran, except for B-rep solids and volume solids, are tri-parametric solids. Tri-parametric solids are parameterized on the surface, as well as inside the solid. Tri-parametric solids can only have four to six faces with no interior voids or holes.

Tri-parametric solids can be meshed with IsoMesh or TetMesh.

B-rep Solid. A B-rep solid is formed from a group of topologically congruent surfaces that define a completely closed volume. Only its outer surfaces or faces are parameterized and not the interior. An example is shown in Figure 1-19.

The group of surfaces that define the B-rep solid are its shell. A B-rep shell defines the exterior of the solid, as well as any interior voids or holes. Shells can be composed of bi-parametric surfaces and/or trimmed surfaces.

B-rep solids can be created with the Create/Solid/B-rep form. See Creating a Boundary Representation (B-rep) Solid (p. 338) on using the form.

Figure 1-19 B-rep Solid in MSC.Patran

B-rep solids are meshed with TetMesh. See Meshing Solids (p. 17) in the MSC.Patran Reference Manual, Part 3: Finite Element Modeling for more information.


Important: IsoMesh will create hexagonal elements if the solid has five or six faces, but some wedge elements will be created for the five faced solid. IsoMesh will create a tetrahedron mesh for a four faced solid. See Meshing Solids (p. 17) in the MSC.Patran Reference Manual, Part 3: Finite Element Modeling.

2CHAPTER 1Introduction to Geometry ModelingParametric Cubic GeometryParametric cubic geometry is a special class of parameterized geometry. Parametric cubic geometry is supported in MSC.Patran by the PATRAN 2 neutral file and the IGES file for import and export.

You have the option to create parametric cubic curves, bi-parametric cubic surfaces and tri-parametric cubic solids, by pressing the PATRAN 2 Convention button found on most Geometry application forms.

Parametric cubic geometry can also be created in MSC.Patran, which are referred to as grids, lines, patches and hyperpatches.

Parametric cubic geometry is defined by a parametric cubic equation. For example, a parametric cubic curve is represented by the following cubic equation:

Eq. 1-6

where represents the general coordinate of the global coordinates X,Y, and Z; , , , and are arbitrary constants; and is a parameter in the range of .

For more information on parametric cubic geometry, see MSC.Patran Reference Manual.

Limitations on Parametric Cubic Geometry

There are some limitations on parametric cubic geometry.

Limits on Types of Curvature. There are limits to the types of curvature or shapes that are allowed for a parametric cubic curve, surface or solid (see Figure 1-20).

Eq. 1-7 and Eq. 1-8 below represent the first and second derivatives of Eq. 1-6:

Eq. 1-7

Eq. 1-8

Eq. 1-7 shows that a parametric cubic curve can only have two points with zero slope and Eq. 1-8 shows that it can only have one point of inflection, as shown in Figure 1-20.

Figure 1-20 Limitations of the Parametric Cubic Curvature

Important: Unless you intend to export the geometry using the PATRAN 2 neutral file, in most situations, you do not need to press the PATRAN 2 Convention button to create parametric cubic geometry.

Z 1( ) S113

= S212

S31 S4+ + +

Z 1( ) S1 S2 S3S4 1 0 1 1

Z 1( ) 3S112

= 2S21 S3+ +

Z 1( ) 6S11= 2S2+

YES YES YES YES

YES NO NO NO

PART 2Geometry ModelingLimits on Accuracy of Subtended Arcs. When you subtend an arc using a parametric cubic curve, surface or solid, the difference between the true arc radius and the arc radius calculated by the parametric cubic equation will increase. That is, as the angle of a subtended arc for a parametric cubic entity increases, the accuracy of the entity from the true representation of the arc decreases.

Figure 1-21 shows that as the subtended angle of a parametric cubic entity increases, the percent error also increases substantially beyond 75 degrees.

When creating arcs with parametric cubic geometry, MSC recommends using Figure 1-21 to determine the maximum arc length and its percent error that is acceptable to you.

For example, if you create an arc length of 90 degrees, it will have an error of 0.0275% from the true arc length.

For most geometry models, MSC recommends arc lengths represented by parametric cubic geometry should be 90 degrees or less. For a more accurate model, the parametric cubic arc lengths should be 30 degrees or less.

Figure 1-21 Maximum Percent Error for Parametric Cubic Arc

3.0

2.5

2.0

1.5

1.0

0.5

00 15 30 45 60 75 90

Total Subtended Angle in Degrees

Per

cent

Err

or in

the

Rad

ius

(x 1

0-2 )

Percent Error = 100*(Computed Radius - Actual Arc Radius) / Actual Radius

2CHAPTER 1Introduction to Geometry ModelingMatrix of Geometry Types CreatedAll Geometry Application forms use the following Object menu terms:

Point Curve Surface Solid Plane Vector Coordinate Frame

MSC.Patran will create a specific geometric type of the parametric curve, bi-parametric surface and tri-parametric solid based on the method used for the Create action or Edit action.

Table 1-1, and list the types of geometry created for each Create or Edit action method. The tables also list if each method can create parametric cubic curves, surfaces or solids by pressing the PATRAN 2 Convention button on the application form. (Parametric cubic geometry is recognized by the PATRAN 2 neutral file for export.)

For more information on each Create or Edit action method, see Overview of Geometry Create Action (p. 70) and/or Overview of the Edit Action Methods (p. 414).

Table 1-1 Types of Curves Created in MSC.Patran

Create or Edit Method Type of CurvePATRAN 2

Convention? (Parametric Cubic)

XYZ Parametric Cubic Not Applicable

Arc3Point Arc Yes

2D Arc2Point Arc Yes

2D Arc3Point Arc Yes

2D Circle Circle Yes

Conic Parametric Cubic N/A

Extract Curve On Surface Yes

Fillet Parametric Cubic N/A

Fit Parametric Cubic N/A

Intersect PieceWise Cubic Polynomial Yes

Involute Parametric Cubic N/A

Normal Parametric Cubic N/A

2D Normal Parametric Cubic N/A

2D ArcAngles Arc Yes

Point Parametric Cubic N/A

PART 2Geometry ModelingProject Curve On Surface Yes

PWL Parametric Cubic N/A

Revolve Arc Yes

Spline, Loft Spline option PieceWise Cubic Polynomial Yes

Spline, B-Spline option PieceWise Rational Polynomial Yes

Spline, B-Spline option NURB* Yes

TanCurve Parametric Cubic N/A

TanPoint Parametric Cubic N/A

Chain Composite Curve No

Manifold Curve On Surface Yes

* NURB splines are created if the NURBS Accelerator toggle is pressed OFF (default is ON) on the Geometry Preferences form, found under the Preferences/Geometry menu. This is true whether you create the spline in MSC.Patran or if you import the spline from an IGES file. See Geometry Preferences (p. 296) in the MSC.Patran Reference Manual, Part 2: Basic Functions for more information. If the NURBS Accelerator is ON, PieceWise Rational Polynomial splines will be created instead.

Table 1-2 Types of Surfaces Created in MSC.Patran

Create or Edit Method Type of Surface PATRAN 2


XYZ Parametric Bi-Cubic Not Applicable

Curve Curve Interpolating Surface Yes

Decompose Trimmed Surface Yes

Edge Generalized Coons Surface Yes

Extract Surface On Solid Yes

Extrude Extruded Surface Yes

Fillet Parametric Bi-Cubic N/A

Glide Parametric Bi-Cubic N/A

Match Parametric Bi-Cubic N/A

Normal Sweep Normal Surface N/A

Revolve Surface of Revolution Yes

Table 1-1 Types of Curves Created in MSC.Patran (continued)

Create or Edit Method Type of CurvePATRAN 2


2CHAPTER 1Introduction to Geometry ModelingRuled Ruled Surface No

Vertex Curve Interpolating Surface Yes

Trimmed (Surface Option) Trimmed Surface No

Trimmed (Planar Option) Trimmed Surface No

Trimmed (Composite Option)

Composite Trimmed Surface No

Table 1-3 Types of Solids Created in MSC.Patran

Create or Edit Method Type of Solid PATRAN 2


XYZ Parametric Tri-Cubic Not Applicable

Extrude Extruded Solid Yes

Face Solid 5Face, Solid 6Face Yes

Glide Glide Solid Yes

Normal Sweep Normal Solid Yes

Revolve Solid of Revolution Yes

Surface Surface Interpolating Solid Yes

Vertex Parametric Tri-Cubic N/A

B-rep Ordinary Body No

Decompose Tri-Parametric Yes

Table 1-2 Types of Surfaces Created in MSC.Patran (continued)

Create or Edit Method Type of Surface PATRAN 2


PART 2Geometry Modeling1.4 Building An Optimal Geometry ModelA well defined geometry model simplifies the building of the optimal finite element analysis model. A poorly defined geometry model complicates, or in some situations, makes it impossible to build or complete the analysis model.

In computer aided engineering (CAE) analysis, most geometry models do not consist of neatly trimmed, planar surfaces or solids. In some situations, you may need to modify the geometry to build a congruent model, create a set of degenerate surfaces or solids, or decompose a trimmed surface or B-rep solid.

The following sections will explain how to:

Build a congruent model. Verify and align surface normals. Build trimmed surfaces. Decompose trimmed surfaces into three- or four-sided surfaces. Build a B-rep solid. Build degenerate surfaces or solids.

3CHAPTER 1Introduction to Geometry ModelingBuilding a Congruent ModelMSC.Patran requires adjacent surfaces or solids be topologically congruent so that the nodes will be coincident at the common boundaries. See Topological Congruency and Meshing (p. 12) for more information.

For example, Figure 1-22 shows surfaces 1, 2 and 3 which are incongruent. When meshing with Isomesh or Paver, MSC.Patran cannot guarantee the nodes will coincide at the edges shared by surfaces 1, 2 and 3.

Figure 1-22 Incongruent Set of Surfaces

To make the surfaces in Figure 1-22 congruent, you can:

Use the Edit/Surface/Edge Match form with the Surface-Point option. See Matching Surface Edges (p. 481) on using the form.

Or, break surface 1 with the Edit/Surface/Break form. See Surface Break Options (p. 457) on using the form.

The following describes the method of using the Edit/Surface/Break form.

To make surfaces 1 through 3 congruent, we will break surface 1 into surfaces 4 and 5, as shown in Figure 1-23:

1

2

3

2

3

4

5

PART 2Geometry ModelingFigure 1-23 Congruent Set of Surfaces

The entries for the Edit/Surface/Break form are shown below:

Since Auto Execute is ON, we do not need to press the Apply button to execute the form.

Figure 1-24 Cursor Locations for Surface Break

Geometry

Action: Edit

Object: Surface

Method: Break

Option: Point

Delete Original Surfaces Pressing this button will delete surface 1, after the break.

Surface List: Surface 1 Cursor select or enter the ID for surface 1.

Break Point List Point 10 Cursor select or enter the ID for point 10, as shown in Figure 1-24.

1

2

3

10

Cursor select Surface 1 for the Surface List on the form.

Cursor select Point 10 for the Point List on the form.

3CHAPTER 1Introduction to Geometry ModelingBuilding Optimal SurfacesBuilding optimal surfaces will save time and it will result in a better idealized finite element analysis model of the design or mechanical part.

Optimal surfaces consist of a good overall shape with no sharp corners, and whose normal is aligned in the same direction with the other surfaces in the model.

Avoid ing Sharp Corners. In general, MSC.Software Corporation (MSC) recommends that you avoid sharp inside corners when creating surfaces. That is, you should generally try to keep the inside corners of the surfaces to 45 degrees or more.

The reason is that when you mesh surfaces with quadrilateral elements, the shapes of the elements are determined by the overall shape of the surface, see Figure 1-25. The more skewed the quadrilateral elements are, the less reasonable your analysis results might be.

For further recommendations, please consult the vendor documentation for your finite element analysis code.

Figure 1-25 Surfaces With and Without Sharp Corners

Note: You can use the surface display lines to predict what the surface element shapes will look like before meshing. You can increase or decrease the number of display lines under the menus Display/Display Properties/Geometric. See Geometric Attributes (p. 257) in the MSC.Patran Reference Manual, Part 2: Basic Functions.

Surfaces With Sharp Corners

1

2

3

4

1

2

3

4

Optimal Surface Shapes

PART 2Geometry ModelingVerifying and Aligning Surface Normals Using Edit/Surface/Reverse. MSC.Patran can determine the positive normal direction for each surface by using right hand rule and crossing the parametric and axes of a surface. Depending on the surfaces connectivity, each surface could have different normal directions, as shown in Figure 1-26.

Figure 1-26 Opposing Normals for Two Surfaces

The normal direction of a surface affects finite element applications, such defining the positive pressure load direction, the top and bottom surface locations for a variable pressure load, and the element connectivity.

Use the Edit/Surface/Reverse form to display the surface normal vectors, and to reverse or align the normals for a group of surfaces. See Reversing Surfaces (p. 501) on using the form.

Important: In general, you should try to maintain the same normal direction for all surfaces in a model.

1 2

2

1

1

2

3CHAPTER 1Introduction to Geometry ModelingExample of Verifying and Aligning Surface Normals. For example, Figure 1-27 shows a group of eight surfaces that we want to display the normal vectors, and if necessary, reverse or align the normals. To display the surface normals without reversing, do the following:

Figure 1-27 Group of Surfaces to Verify Normals

You should see red arrows drawn on each surface which represent the surface normal vectors, as shown in Figure 1-28.

Figure 1-28 Surface Normal Vectors

Geometry

Action: Edit

Object: Surface

Method: Reverse

Surface List Surface 1:8 Make sure you turn Auto Execute OFF before cursor selecting surfaces 1-8.

And do not press Apply. Apply will reverse the normals.

Draw Normal Vectors

1 2 3 4

5 6 7 8

1 2 3 4

5 6 7 8

PART 2Geometry ModelingAlign the normals by reversing the normals for surfaces 1 through 4:

Figure 1-29 shows the updated normal directions which are now aligned.

Figure 1-29 Aligned Surface Normal Vectors

Surface List Surface 1:4

-Apply-

Draw Normal Vectors This will plot the updated normal vector directions.

1 2 3 4

5 6 7 8

3CHAPTER 1Introduction to Geometry ModelingDecomposing Trimmed SurfacesTrimmed surfaces are preferred for modeling a complex part with many sides. However, there may be areas in your model where you may want to decompose, or break, a trimmed surface into a series of three or four sided surfaces.

One reason is that you want to mesh the surface area with IsoMesh instead of Paver. (IsoMesh can only mesh surfaces that have three or four edges.) Another reason is that you want to create tri-parametric solids from the decomposed three or four sided surfaces and mesh with IsoMesh.

To decompose a trimmed surface, use the Geometry applications Create/Surface/Decompose form. See Decomposing Trimmed Surfaces (p. 255) on using the form.

When entered in the Create/Surface/Decompose form, the select menu that appears at the bottom of the screen will show the following icons:

Example. Figure 1-30 shows trimmed surface 4 with seven edges. We will decompose surface 4 into four four-sided surfaces.

Figure 1-30 Trimmed Surface to be Decomposed

Point/Vertex/Edge Point/Interior Point. This will select a point for decomposing in the order listed. If not point or vertex is found, the point closest to edge will be used or a point will be projected onto the surface.

Use cursor select or directly input an existing point on the surface. If point is not on the surface, it will be projected onto the surface.

Use to cursor select a point location on an edge of a trimmed surface.

Use to cursor select a point location inside a trimmed surface.

Use to cursor select a vertex of a trimmed surface.

2120

22

23

2425

26

3

PART 2Geometry ModelingOur first decomposed surface will be surface 3, as shown in Figure 1-31. The figure shows surface 3 cursor defined by three vertex locations and one point location along an edge. The point locations can be selected in a clockwise or counterclockwise direction.

Figure 1-31 Point Locations for Decomposed Surface 4

Figure 1-32 shows the remaining decomposed surfaces 5, 6 and 7 and the select menu icons used to cursor define the surfaces. Again, the point locations can be selected in a clockwise or counterclockwise direction.

4

Use

to cursor select these three vertices.

Use

to cursor select this point location along the edge.

4

5

7

6

Use

to cursor select these three vertices for Surface 5.

Use

to cursor select this point along the edge for Surface 5.

Use

to cursor select these four vertices for Surface 7.

Use

to cursor select these three vertices for Surface 6.

Use

to cursor select this point along the edge for Surface 6.

3CHAPTER 1Introduction to Geometry ModelingFigure 1-32 Point Locations for Decomposed Surfaces 5, 6 and 7

Use Surface Display Lines as a Guide. Generally, the surface display lines are a good guide to where the trimmed surface can be decomposed. MSC recommends increasing the display lines to four or more. The display lines are controlled under the menus Display/Display Properties/Geometric. See Geometry Preferences (p. 296) in the MSC.Patran Reference Manual, Part 2: Basic Functions for more information.

PART 2Geometry ModelingBuilding B-rep SolidsBoundary represented (B-rep) solids are created by using the Geometry applications Create/Solid/B-rep form. See Creating a Boundary Representation (B-rep) Solid (p. 338) for more information on the form.

There are three rules to follow when you create a B-rep solid in MSC.Patran:

1. The group of surfaces that will define the B-rep solid must fully enclose a volume.

2. The surfaces must be topologically congruent. That is, the adjacent surfaces must share a common edge.

3. The normal surface directions for the exterior shell must all point outward, as shown in Figure 1-33. That is, the normals must point away from the material of the body. This will be done automatically during creation as long as rules 1 and 26 are satisfied.

B-rep solids created in MSC.Patran can only be meshed with TetMesh.

Figure 1-33 Surface Normals for B-rep Solid

Important: At this time, MSC.Patran can only create a B-rep solid with an exterior shell, and no interior shells.

Y Z

X

89

107

1

2

34

5

6

1

4CHAPTER 1Introduction to Geometry ModelingBuilding Degenerate Surfaces and SolidsA bi-parametric surface can degenerate from four edges to three edges. A tri-parametric solid can degenerate from six faces to four or five faces (a tetrahedron or a wedge, respectively).

The following describes the best procedures for creating a degenerate triangular surface and a degenerate tetrahedron and a wedge shaped solid.

Building a Degenerate Surface (Triangle). There are two ways you can create a degenerate, three-sided surface:

Use the Create/Surface/Edge form with the 3 Edge option. See Creating Surfaces from Edges (Edge Method) (p. 257) on using the form.

Or, use the Create/Surface/Curve form with the 2 Curve option. See Creating Surfaces Between 2 Curves (p. 240) on using the form.

Figure 1-34 illustrates the method of using the Create/Surface/Curve form with the 2 Curve option. Notice that the apex of the surface is defined by a zero length curve by using the Curve select menu icon shown in Figure 1-34.

Figure 1-34 Creating a Degenerate Surface Using Create/Surface/Curve

Building a Degenerate Solid

Four Sided Solid (Tetrahedron). A four sided (tetrahedron) solid can be created by using the Create/Solid/Surface form with the 2 Surface option, where the starting surface is defined by a point for the apex of the tetrahedron, and the ending surface is an opposing surface or face, as shown in Figure 1-35.

Five Sided Solid (Pentahedron). A five sided (pentahedron) solid can be created by using:

Important: IsoMesh will create hexahedron elements only, if the solid has six faces. Some wedge elements will be created for a solid with five faces. IsoMesh will create tetrahedron elements only, for a solid with four faces. TetMesh will create tetrahedron elements only, for all shaped solids.

Cursor select this point twice

using this icon:

in the Curve select menu for theStarting or Ending Curve List.

Cursor select thisedge or curve for theStarting or Ending Curve List.

PART 2Geometry Modeling The Create/ Solid/Face form with the 5 Face option. See Creating Solids from Faces (p. 343) on using the form.

The Create/Solid/Surface form with the 2 Surface option. See Creating Solids from Surfaces (Surface Method) (p. 327) on using the form.

Figure 1-36 and Figure 1-37 illustrate using the Create/Solid/Surface form to create the pentahedron and a wedge.

Figure 1-35 Creating a Tetrahedron Using Create/Solid/Surface

Figure 1-36 Creating a Pentahedron Using Create/Solid/Surface

highlight

in the select menu, and cursor

and

select this point twice for thefirst edge of the surface.

Highlight again,

then, cursor select this samepoint twice again.

Cursor select this surface or face for theEnding Surface List.

For the Starting Surface List,

highlight

in the select menu, and cursor

and

select this point twice for thefirst edge of the surface.

Highlight again,

then, cursor select this samepoint twice again.



4CHAPTER 1Introduction to Geometry ModelingFigure 1-37 Creating a Wedge Using Create/Solid/Surface

highlight

in the select menu, and cursorselect this curve twice.



PART 2Geometry Modeling

MSC.Patran Reference Manual, Part 2: Geometry Modeling

CHAPTER

2 Accessing, Importing & Exporting Geometry Overview

Direct Geometry Access of CAD Geometry

PATRAN 2 Neutral File Support For Parametric Cubic Geometry

PART 2Geometry Modeling2.1 OverviewMSC.Patran can access geometry from an external CAD system user file. Geometry can also be imported (or read) from a PATRAN 2 Neutral file or from an IGES file. MSC.Patran can export (or write) some or all geometry to an external PATRAN 2 Neutral file or IGES file.

Geometry can be accessed or imported into the user database either by using the File/Import menus or by using the File/CAD Model Access menus on the MSC.Patran main form. Geometry can be exported from the database using the File/Export menus.

For more information on executing the File/Import and File/Export forms, see Importing Models (p. 26) and Export (p. 110) in the MSC.Patran Reference Manual, Part 2: Basic Functions.

For more information on accessing CAD models, see Direct Geometry Access of CAD Geometry (p. 47).

For more information on import and export support of geometry for the PATRAN 2 Neutral file, see PATRAN 2 Neutral File Support For Parametric Cubic Geometry (p. 57).

For more information on which IGES entities are supported by MSC.Patran for importing and exporting, see Supported IGES Entity Types - Import (p. 51) and Supported IGES Entity Types -Export (p. 116) in the MSC.Patran Reference Manual, Part 2: Basic Functions.

4CHAPTER 2Accessing, Importing & Exporting Geometry2.2 Direct Geometry Access of CAD GeometryMSC.Patran can directly access geometry from an external CAD file for the following CAD systems that are listed in Table 2-1.

This unique Direct Geometry Access (DGA) feature allows you to access the CAD geometry and its topology that are contained in the CAD file. Once the geometry is accessed, you can build upon or modify the accessed geometry in MSC.Patran, mesh the geometry, and assign the loads and boundary conditions as well as the element properties directly to the geometry.

You can execute a specific MSC.Patran CAD Access module by using the File/Importing Models menus on the main form. See Importing Models (p. 26) in the MSC.Patran Reference Manual, Part 2: Basic Functions for more information.

For more information on using MSC.Patran ProENGINEER, see Importing Pro/ENGINEER Files (p. 118) in the MSC.Patran Reference Manual, Part 1: Basic Functions.

For more information on using MSC.Patran Unigraphics, see Importing Unigraphics Files (p. 128) in the MSC.Patran Reference Manual, Part 1: Basic Functions.

Accessing Geometry Using MSC.Patran UnigraphicsIf MSC.Patran Unigraphics is licensed at your site, you can access the geometric entities from an external EDS/Unigraphics part file.

Features of MSC.Patran Unigraphics

Unigraphics part file can be accessed in MSC.Patran using one of two methods. The first method is express file based import. The second method is direct parasolid transmit file based import. In both cases, Unigraphics geometry is imported and stored in a MSC.Patran database.

MSC.Patran uses the original geometry definitions of the accessed entities, without any approximations. Parasolid evaluators are directly used for entities imported via the direct parasolid method.

Table 2-1 Supported CAD Systems and Their MSC.Patran CAD Access Modules

Supported CAD System MSC.Patran CAD Access Module *

* Each MSC.Patran CAD Access module must be licensed before you can access the appro-priate external CAD file. You can find out which MSC.Patran products are currently li-censed by pressing the MSC.Software Corporation (MSC) icon on the main form, and then pressing the License button on the form that appears.

EDS/Unigraphics MSC.Patran Unigraphics

Pro/ENGINEER by Parametric Technology MSC.Patran ProENGINEER

CATIA by Dassault Systemes MSC.Patran CATIA

EUCLID 3 by Matra Datavision MSC.Patran EUCLID 3

CADDS 5 by Computervision MSC.Patran CADDS 5

PART 2Geometry Modeling CAD Access filters are provided that can be selected based on the defined EDS/Unigraphics entity types, levels, and layers.

You can automatically create MSC.Patran groups when accessing the geometry based on the defined entity types, levels, or layers.

For more information on using MSC.Patran Unigraphics, see Importing Unigraphics Files (p. 128) in the MSC.Patran Reference Manual, Part 1: Basic Functions.

Tips For Accessing EDS/Unigraphics Geometry for Express File Based Import

1. When you execute EDS/Unigraphics, make sure the solid to be accessed is topologically congruent with no gaps (see Figure 2-1). For more information, see Topological Congruency and Meshing (p. 12).

Verify that the edges of the solids adjacent faces share the same end points or vertices, and that there are no gaps between the faces.

2. You can improve MSC.Patran Unigraphics performance by reducing the number of entities to be processed by using the Entity Type filter on the MSC.Patran Import form and unselect or un-highlight all entities of a particular type that you do not want, before you access the part file. For example, you can unselect the entity type, Bounded-Plane, to eliminate all bounded plane entities. For the direct parasolid import option, the entity type filter can be used for wire body/sheet body/solid body only.

3. Put those entities in EDS/Unigraphics that you want to access into specific layers. Then select to only those layers in the MSC.Patran Import form before importing the part.

4. Make sure the MSC.Patran Global Model Tolerance is reset to an appropriate value if you will be accessing long thin surfaces and solids with small dimensions (default is 0.005). For example, set the tolerance value so that it is smaller than the smallest edge length (greater than 10.0E-6) in the model. This will improve model usability on some models.

Figure 2-1 Topologically Congruent Surfaces for MSC.Patran Unigraphics

NOT Topologically Valid(lacking congruent edge)

Gap Zero GapFace 1 Face 1

Face 2

Topologically Valid(with congruent edge)

Face 2

4CHAPTER 2Accessing, Importing & Exporting GeometryTips For Accessing Parasolid Geometry. This section provides helpful hints and recommendations regarding the usage of MSC.Patran as it pertains to Parasolid integration.

Solid Geometry Guidelines

Disassembling Solids

The Edit/Solid/Disassemble function in the Geometry Application can be used to create simply trimmed surfaces (green 4-sided) with one command. This can be a big timesaver if the B-rep Solid is being disassembled to eventually create tri-parametric solids (blue) for Hex meshing. This command will convert all 4-sided B-rep Solid faces into simply trimmed surfaces (green) which then can be used to construct tri-parametric solids.

Solids Break If difficulties are encountered in breaking a solid:

1. First disassemble the original solid (Edit/Solid/Disassemble).

2. Try to reconstruct a new solid using Create/Solid/B-rep. If this is unsuccessful due to gaps between surfaces, use the Edit/Surface/Sew and try again. If a solid is created, continue with the break operation.

3. If steps (a) and (b) were unsuccessful:

Break the trimmed surfaces from the disassembled solid (step (a)). If this operation is slow, refit the surfaces (Edit/Surface/Refit) before the break operation.

Create the additional surfaces in the interior required to enclose the individual solid volumes.

Create the new individual solids using Create/Solid/B-rep. If the B-rep can not be created due to surface gaps, use Edit/Surface/Sew and try again.

Global Model Tolerance

After successful access of Unigraphics geometry via the Parasolid Direct method, the Global Model Tolerance will be set relative to the models geometric characteristics. This tolerance is the recommended tolerance for MSC.Patran applications to use for best results.

Solids - Group Transform

Group transform for solids is not supported. For information about transforming solids in pre-release format, see (p. 50).

PART 2Geometry ModelingMeshing Guidelines

Hybrid TetMesher - Global Edge Lengths

The Hybrid tetmesher only accepts global edge lengths for mesh criteria if attempting to directly mesh a solid. If you encounter difficulties, decrease the global edge length.

Hybrid TetMesher - Mesh Control

The Hybrid tetmesher does not write nodes that lie on solid edges into the mesh seed table. This limits the ability of the Hybrid tetmesher to recognize existing meshes. For example, if your requirements are: (1) to match adjacent meshes (i.e., multiple solids); (2) that the mesh be able to recognize a hard curve/point; or (3) to define mesh seed prior to solid meshing, follow these steps:

Define any desired hard points/curves and mesh seeds. Surface mesh the geometry using the paver, creating triangular

elements which completely enclose the desired geometric volume.

Invoke the Hybrid tetmesher, using the previously created triangular elements as input.

Paver If the paver exhibits difficulties meshing some geometry or making congruent meshes:

Delete any existing mesh on the problematic geometry. Perform an Edit/Surface/Refit. Do an Edit/Surface/Edge Match if congruency is an issue. Mesh again.

5CHAPTER 2Accessing, Importing & Exporting GeometryPRE-RELEASE CAPABILITY: Solid Geometry Guidelines

Solids - Group

Transform

Group transform for solids is not supported. If a transformed solid is required, consider the following alternatives: (1) Perform the transformation in the native CAD system and then again access the desired geometry in MSC.Patran; (2) Enable an environment variable before executing MSC.Patran. At the system prompt, type:

setenv P3_UG_ENTITY_FILTER 1

which allows the transformation of Parasolid solid geometry and perform the transformation. If a solid is successfully constructed, continue as planned. If not, either:

Mesh the original solid and transform the resulting finite element mesh, with the limitation being that element properties and loads/boundary conditions will have to be assigned directly to the finite elements; or

Try to reconstruct a B-rep solid from the constituent surfaces that result from the transformation, by first using Geometry tools such as Edit/Surface/Sew, Edit/Surface/Edge Match, etc., to reconnect the surfaces and then use Create/Solid/B-rep.

Initially access the original geometry (Unigraphics only) using the Express Translation method. If a solid is successfully imported, a transformation of the geometry is supported.

Surface/Curve Geometry Guidelines

Surface Congruency

Unigraphics does not automatically enforce surface congruency. Typically, CAE applications require congruent meshes; therefore, geometric surfaces must usually be congruent. Accessing geometry through Parasolid simply retrieves the Unigraphics geometry exactly as it is defined; an explicit action must be taken to sew geometric surfaces, otherwise they will not be congruent.

It is recommended that models with surfaces be sewn up in Unigraphics prior to access by MSC.Patran. MSC.Patran offers the ability to also invoke the Unigraphics surface sew tool; in fact, this is the default operation when accessing Sheet Bodies.

Unigraphics Sew With Verify During Geometry Access

Unigraphics Sew and Verify Boundary toggles are, by default, ON during import. The Verification entails placement of markers at all incongruent surface edges, thus allowing a user to quickly identify whether the Unigraphics Sew was completely (or partially) successful. The markers may be removed using the Broom icon.

PART 2Geometry ModelingProblem Unigraphics Entities From Import

MSC.Patran detects three different types of anomalies during Unigraphics part file import:

a) Suspect939 Entities: Sometimes Unigraphics needs to take special actions to convert surfaces from earlier version parts. These surfaces are attributed with Suspect939. Although for the most part these surfaces are usable, Unigraphics recommends that these surfaces be replaced. As such, MSC.Patran will not attempt to include these surfaces in the Unigraphics sewing, and we recommend that these surfaces be refitted once imported into MSC.Patran. You will find these surfaces in a group named, _UG_SUSPECT.

b) Invalid Entities: Before importing the Unigraphics model, MSC.Patran will check each surface and curve entities to ensure consistency and validity. Occasionally, some entities do not pass the checks. These invalid entities will be excluded from both UG sewing and MSC.Patran import. If you see such a message in the invoke window, you should go back to UG to ensure the model is valid. Please reference the next section, Unigraphics Model Checks (p. 52) for steps to do this check. One recommended way is to refit/reconstruct the surface in Unigraphics and then reimport it into MSC.Patran.

If UG sewing is turned on for the MSC.Patran import, there is a chance that invalid entities are created by the UG sew. These entities will be brought into MSC.Patran and put into a group named, _UG_INVALID. As there is no guarantee that entities in this group will work with any applications, we strongly recommend you first commit/save the MSC.Patran database and then reconstruct these bodies if possible.

c) Gap Surfaces: Sometimes surfaces, that are degenerate or are/close to being zero area, appear in the model. These surfaces are called gap surfaces. If there are any such gap surfaces, they will be in a group named, _GAP_SURFACE. Please inspect the imported model and determine if these gap surfaces should be removed from the model.

Unigraphics Model Checks

Unigraphics provides geometry evaluation tools which are extremely useful in judging the quality of a model. Here are some geometry/topology checks Unigraphics can perform and provide results with any UG part: (1) In Unigraphics V13.0, Info is available at the top menu bar, under Info/Analysis/Examine Geometry. If you use this on surfaces and any are ill-defined, they will be flagged as suspect. (2) In Unigraphics V13.0, Info is available at the top menu bar. To run all checks:

Use Info->Analysis->Examine Geometry... Choose Set All Checks, then OK. Choose Select All to check the entire model currently selectable.

NOTE: Default Distance tolerance is 0.001 units and Default Angle tolerance is 0.5 units.

Surface/Curve Geometry Guidelines

5CHAPTER 2Accessing, Importing & Exporting GeometryMSC.Patran Surface Sew

In addition to accessing the Unigraphics surface sew tool, MSC.Patran offers an additional capability to sew surfaces beyond what Unigraphics supports (e.g., resolution of T-edges). If the Unigraphics surface sew does not resolve all incongruences, try using the MSC.Patran surface sew as well. This capability can be accessed through Edit/Surface/Sew in the Geometry application. If both the Unigraphics and MSC.Patran surface sew tools cannot remove all of the gaps and incongruencies, then two options are available. The first option is to refit all of the surfaces (Edit/Surface/Refit). Sometimes, after this operation, these surfaces can be sewn together (Edit/Surface/Sew).

The other option for sewing the model using MSC.Patran surface sewing is to increase the global tolerance in MSC.Patran and sew the model again. Changing the global tolerance in MSC.Patran is generally not recommended, but in this case may be necessary. The necessity of increasing the global tolerance is determined by checking the incongruent edges of the model (Verify/Surface/Boundary) to see if they share vertices, or by the gap closure operation when gaps cannot be closed between surface since the edge curves are too far apart. The tolerance value should be set to a value just larger than the distance between the vertices to be equivalenced (vertices which should be shared at the ends of incongruent curves), or just larger than the allowable gap closure tolerance which is issued by the sewing (or edge match) operation.

(Note that there are cases where sewing will report that gaps exist which are not really gaps. This is because the operation of checking for gaps does not necessarily know about the engineering intent of the model. We suggest that the user check the gaps reported to make sure that they are gaps. Furthermore, we suggest that the global tolerance be increased conservatively, e.g., double the tolerance instead of increasing it by an order of magnitude.)

Refitting Geometry

The technique of refitting geometry has been identified as a potentially viable method of removing problematic geometry that prevents subsequent meshing, application of LBCs, editing, transformi

geometry modeling

Engineering