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C O N T E N T SMSC.Patran Reference Manual

Part 2: Geometry Modeling

ClOptionsC.Patran Reference Manualntents iii Options

1Introduction toGeometryModeling

s Overview of Capabilities, 2

s Concepts and Definitions, 4

Parameterization, 5

Topology, 10

- Topological Congruency and Meshing, 12 Connectivity, 15

Effects of Parameterization, Connectivity and Topology in MSC.Patran,

Global Model Tolerance & Geometry, 18

s 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

s Building An Op timal Geometry Model, 30

Building a Congruent Model, 31

Building Optimal Surfaces, 33

Decomposing Trimmed Surfaces, 37

Building B-rep Solids, 40

Building Degenerate Sur faces and Solids, 41

2Accessing,Importing &ExportingGeometry

s Overview, 46

s Direct Geometry Access of CAD Geometry, 47

Accessing Geometry Using MSC.Patran Un igraphics, 47

Accessing Geometry Using MSC.Patran ProENGINEER, 55

s PATRAN 2 Neu tral File Sup port For Parametric Cubic Geometry, 57

3CoordinateFrames

s Coordinate Frame Definitions, 60

s Overview of Create Methods For Coordinate Frames, 63

s Translating or Scaling Geometry Using Cu rvilinear Coordinate Frames, 66

4Create Actions s Overview of Geometry Create Action, 70

MSC.Patran Reference ManPart 2: Geometry Modeling

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ClOptionsC.Patran Reference Manualntents iv Options

s Creating Points, Curves, Surfaces and Solids, 74

Create Points at XYZ Coord inates 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 Mu ltiple Points from Surfaces or Faces, 86- Extracting Mu ltiple Points from Surfaces or Faces, 88- Parametric Boun ds for Extracting Points from a Sur face, 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 Throu gh Surfaces to Create Points, 109

Projecting Points Onto Sur faces 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 Param etric 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 Cu rves at the Intersection of a Plane and a Surface, 154- Intersect Parameters Subord inate Form, 157- Creating Curves at the Intersection of Two Planes, 158

Manifold Curves Onto a Surface, 160

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

Creating Curves Normally Between a Point and a Curve (Norm al

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 Subord inate Form, 182 Creating Piecewise Linear Curves, 183


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ClOptionsC.Patran Reference Manualntents v Options

Creating Spline Curves, 185

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

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

Creating Cu rves Tangent Between Curves and Points

(TanPoint Method), 195

Creating Cu rves, Sur faces and Solids Throu gh 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 Cu rves, Surfaces and Solids, 208

Creating Orthogonal Curves (2D N ormal Method), 214- Creating Orthogonal Curves with the Input Length Option, 214- Creating Orthogonal Curves with the Calculate Length Op tion, 218

Creating 2D Circle Curves, 222

Creating 2D ArcAngle Curves, 226

Creating Arced Curves in a Plane (2D Arc2Point Method), 229

- Creating Arced Cu rves with the Center Option, 229- Creating Arced Cu rves with the Radius Option, 233- Arc2Point Parameters Subord inate 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 Throu gh 3 Curves (Curve Method), 243- Creating Surfaces Throu gh 4 Curves (Curve Method), 246- Creating Surfaces from N Cu rves (Curve Method), 248

Creating Composite Surfaces, 250

Decomposing Trimm ed 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 Sur face Option, 280- Creating Trimmed Surfaces with the Planar Op tion, 281- Auto Chain Subordinate Form, 282- Creating Trimmed Surfaces with the Composite Option, 284

Creating Surfaces From Vertices (Vertex Method), 287

Extrud ing Surfaces and Solids, 289

Gliding Surfaces, 294

- Gliding Surfaces with the 1 Director Curve Option, 294


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ClOptionsC.Patran Reference Manualntents vi Options

- Gliding Surfaces with the 2 Director Curve Option, 296

Creating Surfaces and Solids Using the Norm al 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 d uring p rimitive 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 Sur face Option, 336

Creating a Bound ary 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

s 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 N ormal Method, 358

Creating Coordinate Frames Using the 2 Vector Method, 361

Creating Coordinate Frames Using the View Vector Method, 362

s 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 N ormal 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, 3

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


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ClOptionsC.Patran Reference Manualntents vii Options

- 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 Sur face Tangent Method - Point Option, 38- Creating Planes with the Surface Tangent Method - Parametric

Option, 385

Creating Planes with the 3 Points Method, 387

s Creating Vectors, 389

Creating Vectors with the Magnitud e Method, 389

Creating Vectors w ith 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 Norm al Method - Plane Option, 395- Creating Vectors with the Normal Method - Sur face Option, 397- Creating Vectors with the Normal Method - Element Face Option, 39

Creating Vectors with the Product Method, 402

Creating Vectors with the 2 Point Method , 404

5Delete Actions s Overview of the Geometry Delete Action, 408

s Deleting Any Geometric Entity, 409

s Deleting Points, Curves, Sur faces, Solids, Planes or Vectors, 410

s Deleting Coordinate Frames, 411

6Edit Actions s Overview of the Edit Action Methods, 414

s Editing Points, 416

Equivalencing Points, 416s Editing Curves, 418

Breaking Curves, 418

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

Blend ing a Curve, 426

Disassembling a Chained Curve, 429

Extending Curves, 431

- Extending a Curve With the 1 Curve Option, 431- Extending a Cu rve Using the Through Points Type, 436- Extending a Curve Using the Full Circle Type, 438
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ClOptionsC.Patran Reference Manualntents viii Options

- 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

s Editing Surfaces, 457

Surface Break Options, 457

- Breaking a Sur face With the Curve Option, 457- Breaking a Sur face With the Surface Option, 461

- Breaking a Surface With the Plane Option, 463- Breaking a Sur face With the Point Option, 465- Breaking a Surface Using the 2 Point Op tion, 469- Breaking a Sur face With the Parametric Option, 471

Blend ing Surfaces, 475

Disassembling Trimmed Surfaces, 478

Matching Surface Edges, 481

- Matching Surface Edges with the 2 Surface Option, 481- Matching Surface Edges w ith the Surface-Point Op tion, 484

Extending Surfaces, 486

- Extending Sur faces with the 2 Sur face Option, 486

- Extend ing Surfaces to a Curve, 488- Extending Sur faces to a Plane, 490- Extending Sur faces to a Point, 492- Extending Surfaces to a Surface, 494- Extending Sur faces with the Percentage Opt ion, 496- Extending Sur faces 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 Op tion, 509

Add ing a Hole to Surfaces, 510

- Add ing a H ole to Surfaces with the Center Point Option, 510- Add ing a Hole to Surfaces with the Project Vector Option, 512- Add ing a Hole to Surfaces with the Inner Loop Op tion, 514

Removing a Hole from Trimmed Sur faces, 516

Add ing a Vertex to Sur faces, 518

Removing a Vertex from Trimmed Sur faces, 520

s Editing Solids, 522

Breaking Solids, 522
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ClOptionsC.Patran Reference Manualntents ix Options

- Breaking Solids w ith the Point Option, 522

- Breaking Solids w ith the Parametric Option, 526- Breaking Solids with the Curve Op tion, 531- Breaking Solids w ith the Plane Option, 533- Breaking Solids w ith 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 w ith the To Parasolid Option, 545

Reversing Solids, 546

Solid Boolean Operation Ad d, 548 Solid Boolean Operation Subtract, 550

Solid Boolean Op eration Intersect, 552

Creating Solid Edge Blends, 554

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

Imp rinting Solid on Solid, 558

Solid Shell Operation, 560

s Editing Features, 562

Sup pressing a Feature, 562

Unsupp ressing a Feature, 563 Editing Feature Parameters, 564

Feature Parameter Definition, 565

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

The Show Action Information Form, 569

s Showing Points, 570

Showing Point Locations, 570

Showing Point Distance, 571- Showing Point Distance with the Point Option, 571- Showing Point Distance with the Cu rve 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 Nod es on a Point, 581

s Showing Curves, 582

Showing Curve Attributes, 582

Showing Curve Arc, 583

Showing Curve Angle, 584 Showing Curve Length Range, 586
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Showing the Nodes on a Curve, 587

s Showing Surfaces, 588

Showing Surface Attributes, 588

Showing Sur face Area Range, 589

Showing the Nodes on a Surface, 590

Showing Surface Normals, 591

s Showing Solids, 593

Showing Solid Attributes, 593

s Showing Coordinate Frames, 594

Showing Coordinate Frame Attributes, 594

s Showing Planes, 595

Showing Plane Attributes, 595

Showing Plane Angle, 596

Showing Plane Distance, 598

s Showing Vectors, 599

Showing Vector Attributes, 599

8Transform Actions

s

Overview of the Transform Methods, 602s Transforming Points, Curves, Surfaces, Solids, Planes and Vectors, 605

Translating Points, Curves, Surfaces, Solids, Planes and Vectors, 605

Rotating Points, Curves, Sur faces, Solids, Planes and Vectors, 619

Scaling Points, Curves, Sur faces, Solids and Vectors, 629

Mirroring Points, Curv es, Sur faces, Solids, Planes and Vectors, 640

Moving Points, Curves, Sur faces, Solids, Planes and Vectors by Coordina

Frame Reference (MCoord Method ), 648

Pivoting Points, Curves, Surfaces, Solids, Planes and Vectors, 656

Positioning Points, Cur ves, Sur faces, Solids, Planes and Vectors, 665

Vector Summ ing (VSum ) Points, Curves, Surfaces and Solids, 674

Moving an d Scaling (MScale) Points, Curves, Surfaces and Solids, 683

s Transforming Coordinate Frames, 690

Translating Coordinate Frames, 690

Rotating Coordinate Frames, 693

9Verify Actions s Verify Action, 698

Verifying Sur face Boundaries, 698

Verifying Surfaces for B-reps, 700- Upd ate Graphics Subordinate Form, 701
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ClOptionsC.Patran Reference Manualntents xi Options

Verify- Surface (Dup licates), 702

10Associate Actions s Overview of the Associate Action, 704

Associating Point Object, 705

Associating Curve Object, 707

11DisassociateActions

s Overview of the Disassociate Action Methods, 710

Disassociating Points, 711

Disassociating Curves, 712

Disassociating Surfaces, 713

12The RenumberAction...Renumbering Geometry

s Introduction, 716

s Renumber Forms, 717

Renumber Geometry, 718

INDEX s MSC.Patran Reference Manu al, 719Part 2: Geometry Modeling
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ClOptionsRT 2: Geometry Modelingroduction to Geometry Modeling 1 Options

MSC.Patran Reference Manual, Part 2: Geometry Modeling

CHAPTER

1Introduction to Geometry Modeling

s Overview of Capabilities

s Concepts and Definitions

s Types of Geometry in MSC.Patran

s Building An Optimal Geometry Mod el

Return


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ClOptionsRT 2: Geometry Modelingroduction to Geometry Modeling 1.1 2 Options

1.1 Overview of Capabilities

A p owerful and importan t feature of MSC.Patran is its geometry capabilities. Geometry can b

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 thoriginal geometry, regardless of where it came from. The exact mathematical representation o

the geometry (e.g., Arc, Rational B-Spline, B-rep, Parametric Cubic, etc.) is consistently

maintained throughout the mod eling process, without any approximations orconversions.

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 separa

CAD p art file or IGES file or the geometr y is par t 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 p roperty assignments can be ap plied d irectly to the

geometry. When the geometry is meshed w ith a set of nodes and elements, MSC.Patran w ill

autom atically assign the loads/ BC or element property to the app ropriate nodes or elements.

Although you can apply the loads/ BCs or element p roperties directly to the finite element m es

the advantage of applying them to the geometry is if you rem esh the geometry, they remain

associated with the mod el. Once a new m esh is created, the loads/ BC and element p roperties

are au tomatically reassigned.

For more information, seeIntroduction to Functional Assignment Tasks (Ch. 1) in theMSC.Patran Reference Manual, Part 5: Functional Assignments.

Direct Geometry Access. Direct Geometry Access (DGA) is the capability to d irectly access(or read ) geometry information from an externalCAD user file, without the u se of an

intermediate translator. Currently, DGA sup ports the following CAD systems:

EDS/ Unigraphics

Pro/ ENGINEER by Parametric Technology

CATIA by Dassault Systemes

EUCLID 3 by Matra Datav ision

CADDS 5 by ComputervisionWith DGA, the CAD geometry and its topology that are contained in th e CAD user file can be

accessed. Once the geometry is accessed, you can build up on or mod ify the accessed geometr

in MSC.Patran, mesh the geometry, and assign the loads/ BC and the element prop erties direct

to the geometry.

For m ore detailed information on DGA, seeDirect Geometry Access of CAD Geometry(p. 47).

Import and Export of Geometry. There are three file formats available to imp ort or expor tgeometry:

IGES
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PATRAN 2 Neu tral File

Express Neu tral File

In using any of the file formats, MSC.Patran m aintains the original mathematical form of the

geometr y. (That is, the geometry is not app roximated into the param etric cubic form.) This

mean s the accuracy of the geom etry in all three files is main tained .

For m ore information on the imp ort and export capabilities for IGES, PATRAN 2 Neutral File

and the Express Neu tral File, seeAccessing, Importing & Exporting Geometry (Ch. 2).

MSC.Patran Native Geometry. You can also create geometry in MSC.Patran (nativegeometry). A large nu mber of methods are available to create, translate, and edit geometry, a

well as method s to verify, delete and show information.

MSC.Patrans native geometry consists of:

Points

Parametric curves

Bi-param etric sur faces

Tri-parametric solids

Bound ary represented (B-rep) solids

All native geometry is fully param eterized both on the ou ter bound aries and w ithin the interi

(except for B-rep solids which are parameterized on ly on the outer surfaces).

Fully parameterized geometry m eans that you can app ly varying loads or element p roperties

directly to the geometr ic entity. MSC.Patran evalu ates the variation a t all exterior and in terio

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1.2 Concepts and Definitions

There are m any fun ctions in MSC.Patran th at rely on the mathematical representation of the

geometry. These functions are:

App lying a p ressure 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 d atabase, informat ion is stored on itsParameterization, Topologyan d Connectivitywhich is u sed in various MSC.Patran fun ction

The concepts of param eterization, connectivity and topology are easy to und erstand and they

are important to know wh en building a geometry and an analysis mod el.

The following sections will describe each of these concepts and how you can build an op tima

geometry m odel for analysis.


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Parameterization

All MSC.Patran geom etry are labeled on e of the following:

Point (0-Dimensions)

Curve (1-Dimension)

Sur face (2-Dimensions)

Solid (3-Dimensions)

Depend ing on the order of the entity - whether it is a one-dimensional curve, a two-dimension

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.

Param eterization means the X,Y,Z coord inates of a curve, surface or solid are represented as

functions of variables or param eters. Depend ing 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 o

time, t. If and , as changes, an d will define a path . Parameterizatio

of geometry does the same thing - as the param eters , , and change, it defines varioupoints on the curve, sur face and solid.

The following describes how a p oint, curve, surface and solid are parameterized in MSC.Patra

Point. A Point in MSC.Patran is a point coord inate location in three-dimensiona l global XYZspace.

Since a point has zero-dim ensions, it has no associated p aram eters, 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 XY

space. A curve can a lso be d escribed as a p article moving along a defined path in space.

Another way of defining a curve is, a curve is a map ping function, , from one-dimension

param etric space into three-dimensional global XYZ space, as show n inFigure 1-3.

1 23

1 2 3

X Y

t X X t ( )= Y Y t( )= t X Y

1 2 3

P(X,Y,Z)

z

x y

1( )


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A curve has one param etric variable, , wh ich 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

Figure 1-3 Mapping Function Phi for a Curve

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

Eq. 1

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

Eq. 1

Because the curve is straight , is a constant value. The tangent, , also defines

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 1 V2+=

0 11

(1)

1z

x y

V1

V2

0 1 1

1 1.0 1( ) V1 1 V2+=

1( )

1 V2 V1=

1

1

1


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For any given curve, the tangent and positive d irection of at any point along the curve can b

found . (The vector, , usu ally will not have a length of one.)

Surface. A surface in MSC.Patran is a tw o-dimensional point set in three-dimensional globaXYZ space.

A surface has two param eters, and , where at any given point, , on the surface, can b

located by and , as shown inFigure 1-4.

Figure 1-4 Surface in MSC.Patran

A sur face generally has th ree or four edges. Trimmed surfaces can have m ore than four edge

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 map ping function, , which map s the param etric space in

the global XYZ space, as show n in Figure 1-5.

Figure 1-5 Mapping Function Phi for a Surface

The first order derivatives of results in two par tial 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

1

22

1

(0,0) (1,0)

(1,1)(0,1)

V1

V2

V3

V40 1 1

0 2 1

1 , 2( ) 1


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Eq. 1

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 an

directions can be determined .

Usually and are not orthonorm al, wh ich means they do not have a length of one andthey are not perp endicular to each other.

Solid. A solid in MSC.Patran is a three-dimensiona l point set in three-dimensional global XYspace.

A solid has three param eters, , , 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 ap plies to tri-param etric solids only. MSC.Patran can a lso create

or impor t a B-rep solid, wh ich is param eterized on the outer su rface only, and not

within the interior. See B-rep Solid (p. 24) for m ore information.

1 T1 an d 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 V1 P V7


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A solid can be represented by a map ping function, , wh ich map s the parametric

space into th e global XYZ space, as show n in Figure 1-7.

Figure 1-7 Mapping Function Phi for a Solid

If we take the first ord er derivatives of , we get three pa rtial der ivatives,

and , shown in Eq. 1-5:

Eq. 1

Where is the tangent vector in the direction, is the tangent vector in the directio

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

2

1

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 1

0 2 1

0 3 1

1 , 2 3,( ) 1 2 3

1T

1 , 2T

2 , 3T

3===

T1 1 T2 2T3 3

T1 T2 T3 2 3


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Topology

Topology identifies the kind s of items u sed to d efine ad jacency relationships between geometr

entities.

Every curve, surface and solid in MSC.Patran has a d efined set of topologic entities. You can

reference these entities wh en you build th e geometry or analysis mod el. Examp les of this

include:

Creating a su rface between edges of two sur faces.

Meshing an ed ge or a face of a solid.

Referencing a vertex of a curve, surface or solid to ap ply a loads/ BC.

Topology is invariant th rough a one-to-one bicontinuous m app ing transformation. This mean

you can h ave two curves, surfaces or solids th at have d ifferent p arameterizations, but

topologically, they can be id entical.

To illustrate th is concept , Figure 1-8 show s three grou ps of surfaces A-D. Geometrically, theyare different, but top ologically they are the same.

Figure 1-8 Topologically Equivalent Surfaces

Topologic Entities: Vertex, Edge, Face, Body. The types of topologic entities foun d inMSC.Patran are the following :

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

Edge Defines the topologic curve on a sur face or a solid. An edge is separate from ageometric 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


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Vertex, 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 an d face IDs will be

assigned . The location of a geometric entitys parametric axes defines the p oint where

assignment of the IDs for the entitys vertices, edges and faces will begin.

Figure 1-9 an d Figure 1-10 show a four sided surface and a six sided solid w ith the internalvertex, edge and face IDs disp layed. If the connectivity changes, then the IDs of the vertices,

edges and faces will also chan ge.

For example, in Figure 1-9, the edge, ED3, of Sur face 11 would be d isplayed as:Surface 11.3

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

Surface 11.3.1

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

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

Solid 100.1

The ed ge, ED10, in Figure 1-10 wou ld be d isplayed as:

Solid 100.1.3

Face Defines the top ologic surface of a solid . A face is separate from a geom etric surface,althou gh a su rface can exist on a face.

Body A grou p of surfaces that forms a closed volume. A bod y is usually referenced as a Brep solid or a Volum e solid , where only its exterior surfaces are param eterized. SeeSolids (p. 24) for m ore information.

Important: Generally, when modeling in MSC.Patran, you d o not need to know the topolog

entities internal IDs. When you cursor select a topologic entity, such as an edge

a surface, the ID will be displayed in the app ropriate listbox on the form.

Figure 1-9 Vertex & Edge Numberingfor 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

11

100

V8

V4

ED12

ED7

ED6

ED1

ED10 ED2

ED3ED5

ED4

ED8

ED9

ED11

V2

V1

V3

V5

V6

V7


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ED10 has an edge ID of 3 that belongs to face 1 on solid 100.

The vertex, V6, in Figure 1-10 wou ld 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 MeshingWhen m eshing ad jacent surfaces or solids, MSC.Patran requires the geometry be topologicall

congru ent so that coincident nod es will be created along the common bound aries.

Figure 1-11 shows an examp le where su rfaces 1 through 3 are topologically incongruent andsurfaces 2 through 5 are topologicallycongruent. 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 a

common vertices.

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

Figure 1-11 Topologically Incongruent and Congruent Surfaces

For a g roup of surfaces or solids to be congruent, the ad jacent su rfaces or solids mu st share

comm on ed ges, as well as comm on vertices.

(MSC.Software Corpora tions MSC.Patran software produ ct required adjacent surfaces or solid

to share on ly the comm on vertices to be considered topologically congruent for m eshing.)

1

2

3

2

3

4

5

Topologically Incongruent Topologically Congruent


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Gaps Between Adjacent Surfaces. Another type of topological incongru ence is shown inFigure 1-12. It shows a gap between tw o pa irs of surfaces that is greater than theGlobal ModTolerance. This mean s wh en you m esh the surface pa irs, coincident nod es will not be created

along both sides of the gap.

Figure 1-12 Topologically Incongruent Surfaces with a Gap

MSC recomm ends two method s for closing sur face 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 m ore information on m eshing, seeIntroduction to Functional Assignment Tasks (Ch.in theMSC.Patran Reference Manual, Part 5: Functional Assignments.

Non-manifold Topology. Non-manifold top ology can be simply defined as a geometry that non-manufacturable. However, in analysis, non-manifold top ology is sometimes either

necessary or desirable. Figure 1-13 shows a su rface mod el with a non-manifold ed ge.

Figure 1-13 Non-manifold Topology at an Edge

Vertices are Shared, Edges are Not

Incongruent Surfaces

Gap > Global ModelTolerance
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This case may be perfectly fine. A non-manifold edge has more than two surfaces or solid face

connected to it. Therefore, two solids wh ich share a common face also give non-manifold

geometry (both the common face and its edges are n on-manifold).

In general, non-manifold top ology is acceptable in MSC.Patran . The exception is in the creatio

of a B-rep solid wh ere a non-manifold edge is not allowed. The Verifying Surface Boundarie(p. 698) option d etects non-man ifold ed ges as well as free edges.
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Connectivity

In Figure 1-2, Figure 1-4, and Figure 1-6 in Parameterization (p. 5), the axes for th eparam eters, , , and , have a un ique orientation and location on the curve, surface and

solid.

Depend ing on the orientation and location of the , , and axes, this defines a un ique

connectivity for the curve, sur face or solid.

For example, although the following tw o curves are iden tical, the connectivity is d ifferent for

each curve (note that the ver tex IDs are reversed ):

Figure 1-14 Connectivity Possibilities for a Curve

For a four sided sur face, there are a tota l of eight possible connectivity definitions. Two p ossib

connectivities are shown in Figure 1-15. (Again, notice that the vertex and ed ge IDs are differefor each su rface.)

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

ED2ED3

ED1ED4

V2

V3

V4

V1

2

1


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For a tri-parametr ic solid w ith six faces, there are a tota l of 24 possible conn ectivity d efinition

in MSC.Patran - three orientations at each of the eight ver tices. Two possible connectivities ar

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 theparam etric axes for the geometric entities by tu rning on the Param etric Direction toggle on th

Geometric Properties form, und er the Display/ Display Properties/ Geometric menu . See

Geometry Preferences (p. 296) in theMSC.Patran Reference Manual, Part 2: Basic Functions fomore information.

Modifying the Connectivity. For most geometric entities, you can modify the connectivity baltering the orientation and/ or location of the parametric axes by using the Geometry

applications Edit actions Reverse m ethod . See Overview of the Edit Action Methods (p. 41

For solids, you can also control the location of the parametric origin u nder the

Preferences/ Geometry menu and choose either the MSC.Patran Convention button or th e

PATRAN 2.5 Convention bu tton for the Solid Origin Location.

V7

V3

V6

V5

V1

V4

V23

2

1

V8

V3

V6

V5

V1

V4

V2

3

2

1V8
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Effects of Parameterization, Connectivity and Topology inMSC.Patran

The geometrys parameterization and connectivity affect the geometry and finite element

analysis mod el in th e following w ays:

Defines Order of Internal Topologic IDs. The param eterization and connectivity for a curvsur face or solid d efine the order of the intern al IDs of their top ologic entities. MSC.Patran store

these IDs internally and displays them when you cursor select a vertex, edge or face. See VerteEdge and Face ID Assignments in MSC.Patran (p. 11) for more information.

Defines Positive Surface Normals. Using right hand ru le by crossing a sur faces d irectiowith its direction, it defines the surfaces positive norm al direction ( direction). This affec

man y areas of geometry and finite element creation, includ ing creating B-rep solids. SeeBuilding An Optimal Geometry Model (p. 30) for m ore information.

Defines Positive Pressure Load Directions. The p arameterization and connectivity of acurve, surface or solid d efine the p ositive direction for a pressure load, and it defines the

sur faces top and bottom locations for an element variable pressure load. SeeCreate Structur

LBCs Sets (p. 19) in th eMSC.Patran Reference Manual, Part 5: Functional Assignments for moreinformation.

Helps Define Parametric Field Functions. If you reference a field function that was definedin param etric space, when creating a varying loads/ BC or a varying element or m aterial

prop erty, the loads/ BC values or the property values will depend on the geometrys

param eterization an d the orientation of the p arametric axes. SeeFields Forms (p. 140) in theMSC.Patran Reference Manual, Part 5: Functional Assignments for m ore information.

Defines Node and Element ID Order For IsoMesh. The MSC.Patran m app ed mesher,IsoMesh, will use the geom etric entitys parameter ization and connectivity to define the ord er

the nod e and element IDs and the element connectivity. (The parameterization and connectiviwill not be used if the mesh will have a transition or change in the nu mber of elements w ithin

the su rface or solid.) SeeIsoMesh (p. 15) in the MSC.Patran Reference Manual, Part 3: FiniteElement Modeling for m ore information.

12 3
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Global Model Tolerance & Geometry

MSC.Patran uses the Global Model Tolerance when it imp orts or accesses geometry, when it

creates geometry, or wh en it m odifies existing geometry.

The Global Model Tolerance is found un der th e Preferences/ Global menu . The d efault value

0.005.

When creating geometr y, if two points are within a d istance of the Global Model Tolerance, theMSC.Patran will only create the first point and not the second .

This ru le also app lies to curves, surfaces and solids. If the points that d escribe two curves,

sur faces or solids are within a d istance of the Global Model Tolerance, then only the first curv

surface or solid will be created, and not the second .

For more information on the Global Model Tolerance, see (p. 57) in theMSC.Patran Reference

Manual, Part 1: Basic Functions.

Important: For models with d imensions which vary significantly from 10 units, MSC

recommend s you set the Global Model Tolerance to .05% of the maximum m od

dimension.
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1.3 Types of Geometry in MSC.Patran

Generally, 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 isgreen)

Tri-Parametric Solid (default color is dark blue)

MSC.Patran also can access, imp ort, and create Trimm ed Sur faces, B-rep Solids and Volume

Solids. See Trimmed Surfaces (p. 20) and Solids (p. 24) for m ore information.

You also can create param etric cubic curves, surfaces and solids, which are recognized by the

PATRAN 2 neutral file. See Parametric Cubic Geometry (p. 25) for m ore information.

For m ore information on the typ es of geometry th at can be created, see Matrix of GeometryTypes Created (p. 27).

1

The default colors are used if the Display Meth od is set to Entity Type, instead of Group, onthe Graph ics Preferences form und er the Preferences/ Graph ics menu .


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Trimmed Surfaces

Trimmed su rfaces are a special class of bi-param etric surfaces. Trimmed sur faces can be

accessed from an external CAD user file; they can be imp orted from an IGES or Express Neu tr

file; and they can be created in MSC.Patran.

Unlike other types of bi-param etric surfaces, trimm ed surfaces can h ave more th an four ed ge

and they can have one or more interior holes or cutouts.

Also, trimmed su rfaces have an associated p arent surface that is not d isplayed. A trimmed

surface is defined by iden tifying the closed active and inactive regions of the parent surface. Th

parent su rface defines the param eterization and curvature of the trimmed surface.

You can create three typ es of trimm ed su rfaces 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 TrimmedSurface (default color is green)

(Green is the d efault color for both a simp ly trimmed surface and a general, bi-parametric

surface.)

General Trimmed Surface. A general trimm ed surface can have any nu mber of outer edgesand any nu mber of inner edges which d escribe holes or cutou ts. These outer and inner edges ar

defined by a closed loop of chained curves. (Chained curves can be created w ith the

Create/ Curve/ Chain form. See Creating Chained Curves (p. 131).) An examp le is shown inFigure 1-17.

All general trimmed su rfaces, whether they are accessed, imp orted or created, have a d efault

color of magenta.2

1The default colors are used if the Display Meth od is set to Entity Type, instead of Group, on

the Graph ics Preferences form und er the Preferences/ Graph ics menu .

Important: Simply trimm ed su rfaces and ordinary composite trimmed surfaces can be

meshed with IsoMesh or Paver. General trimm ed surfaces and composite

trimmed surfaces can on ly be meshed with Paver. See Meshing Surfaces withIsoMesh or Paver (p. 15) in theMSC.Patran Reference Manual, Part 3: FiniteElement Modeling for m ore information. Also note that some geometric operation

are not currently possible with a general trimm ed su rface, e.g., a general trimm e

surface can not be used to create a triparametric solid.

2

The default colors are u sed if the Display Method is set to Entity Type, instead of Group , onthe Graph ics Preferences form und er the Preferences/ Graph ics menu .
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Figure 1-17 General Trimmed Surface

Simply Trimmed Surface. A simply trimm ed sur face can only have four outer ed ges. It cannohave any inner ed ges, or holes or cutou ts. A simply trimm ed sur face reparam etrizes the

bounded region of the paren t and is called an overp arametrization. An example is shown in

Figure 1-18. (A simply trimmed surface can h ave three sides, with one of the four ed gesdegenerating to a zero length ed ge.)

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

All simp ly trimmed surfaces, whether they are accessed, imported or created, have a d efault

color ofgreen. 1

1

The default colors are u sed if the Display Method is set to Entity Type, instead of Group , onthe Graph ics Preferences form und er the Preferences/ Graph ics menu .

Outer Surface Edges

Inner Edges orHoles


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Figure 1-18 Simply Trimmed Surface

Sometimes a three of four sided region w hich d efine a trimm ed su rface will be created as a

general trimm ed su rface instead. This occurs wh en the overparam etrization distorts the

bounded region of the paren t to such an extent that it would be difficult to mesh and u se for

analysis.

Composite Trimmed Surface. The comp osite trimmed surface is a kind of supervisor surfacthat a llows 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 surfac

is similar to evalu ations on th e MSC.Patran tr im surface (General Trimm ed Surface). The big

difference is that it is three to five times slower th an ordinary su rfaces.

The comp osite trimmed surface should be considered a tool. Once the surface is built, it is a

single entity, yet processes on mu ltiple surfaces, relieving the ap plications of the task of

determining where and w hen to move from one surface to another.

APPLICATION:The comp osite trimmed su rface supervisor is a boun ded PLANAR trim surfacIt acqu ires its nam e from the type of service it performs. Let us, for a mom ent, consider the

comp osite trimmed surface to be a cloud in the sky. The sun, being the light source behind th

cloud , creating a shadow on planet earth only in the area blocked by th e cloud . The same is tru

with the composite trimmed surface, except a view vector is given to d etermine the light

direction. Under Surfaces replace planet earth. The valid region on the Under Surfaces is

defined by where the outline of the composite trimm ed surface appears.

Underlying Invisible Parent Surface

Four Outer Edges


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STEPS_BUILDING: There are three basic steps in building a comp osite trimmed su rface.

RULES:

1. The composite trimmed surface domain mu st not encomp ass any d ead space. If anyportion h as a vacancy (no Un der Sur face un der it), unp redictable results will occu

2. Processing along the view vector must yield a single intersection solution at any

position on the un derlying surfaces within the comp osite trimmed surfaces dom ain

Ordinary Composite Trimmed Surface. The only difference between an Ord inary Comp osiTrimm ed Surface and the Comp osite Trimm ed Surface is that this type w ill have only four edge

comp rising the outer loop and no inner loops.

Step 1 Creating the outer p erimeter curve. In most cases this is a MSC.Patran curvechain entity.

Step 2 Selecting an acceptable view d irection for the view vector and p lanarComposite trimmed surface entity. The view vector is the most importan t

aspect of building a composite trimm ed surface. The resu lting view vectormu st yield only one intersection solution at an y position on the Under

Sur faces. The user mu st select the p roper view for the location of the

comp osite trimmed surface with some forethought and eliminate the

possibility of any of the und erlying surfaces wrap ping arou nd in back of one

another. In some cases this may not be possible! The user m ust then create

more than one comp osite trimmed surface.

Additionally, since the comp osite trimmed su rface sup ervisor is PLANAR, it

cannot encomp ass more than a 180 degree field of view. An examp le 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 wh ich currently displayed su rfaces will be become part of thecomp osite trimmed su rface dom ain (Under Surfaces). The u ser may

individu ally select the correct un derlying surfaces or, if want ing to select all

visible surfaces, the user must p lace into ERASE all sur faces which might

cause multiple intersections and then select the remaining visible surfaces.


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Solids

There are three typ es of solids that can be accessed or imp orted, 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 w ith each Geometry Application method .

Tri-Parametric Solid. All solids in MSC.Patran , except for B-rep solids and volum e solids, artri-parametric solids. Tri-parametric solids are parameterized on the surface, as well as inside

the solid. Tri-pa rametric solids can only have four to six faces with n o interior void s or holes.

Tri-parametric solids can be m eshed w ithIsoMesh or TetMesh.

B-rep Solid. A B-rep solid is formed from a grou p of topologically congruent sur faces thatdefine a comp letely closed volume. Only its outer surfaces or faces are parameterized and no

the interior. An example is shown in Figure 1-19.

The group of surfaces that define the B-rep solid ar e its shell. A B-rep shell defines the exterio

of the solid, as well as any in terior voids or holes. Shells can be comp osed of bi-param etric

surfaces and/ or trimm ed surfaces.

B-rep solids can be created with the Create/ Solid/ B-rep form. See Creating a BoundaryRepresentation (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. SeeMeshing Solids (p. 17) in theMSC.Patran ReferenManual, Part 3: Finite Element Modeling for m ore information.

1

The default colors are used if the Display Meth od is set to Entity Type, instead of Group, onthe Graph ics Preferences form und er the Preferences/ Graph ics menu .

Important: IsoMesh will create hexagonal elements if the solid h as five or six faces, but som

wedge elements will be created for the five faced solid. IsoMesh will create a

tetrahedron m esh for a four faced solid. SeeMeshing Solids (p. 17) in the

MSC.Patran Reference Manual, Part 3: Finite Element Modeling.
http://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdfhttp://../fem_modeling/mesh_forms.pdf


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Parametric Cubic Geometry

Param etric cubic geometry is a special class of param eterized geom etry. Param etric cubic

geometry is supported in MSC.Patran by the PATRAN 2neutralfile and the IGES file for impo

and export.

You have the op tion to create param etric cubic curves, bi-param etric cubic surfaces and tri-

param etric cubic solids, by pressing the PATRAN 2 Convention button foun d on most

Geometry ap plication forms.

Param etric cubic geometr y 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 param etr

cubic curve is represented by the following cubic equation:

Eq. 1

where represents the general coordinate of the global coordinates X,Y, and Z; , ,

and are arbitrary constants; and is a param eter 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 param etric cubic geometry.

Limits on Types of Curvature. There are limits to the types of curvatu re or shapes that areallowed for a parametric cubic curve, sur face or solid (seeFigure 1-20).

Eq. 1-7 an d Eq. 1-8below represent the first and second d erivatives ofEq. 1-6:

Eq. 1

Eq. 1

Eq. 1-7 shows th at a param etric cubic curve can only have two points with zero slope and Eq.

8 shows that it can only have one p oint of inflection, as shown in Figure 1-20.

Figure 1-20 Limitations of the Parametric Cubic Curvature

Important: Unless you intend to export th e geometry using the PATRAN 2 neutral file, in

most situations, you d o not need to press the PATRAN 2 Convention button to

create parametr ic cubic geometry.

Z 1( ) S113

= S212

S31 S4+ + +

Z 1( ) S1 S2 SS4 1 0 1 1

Z 1( ) 3S112

= 2S21 S3+ +

Z 1( ) 6S11= 2S2+

YES YES YES YES

YESNO NO

NO


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Limits on Accuracy of Subtended Arcs. When you subtend an arc using a parametric cubcurve, surface or solid, the difference between th e true arc radius an d the arc rad ius calculate

by the param etric cubic equation will increase. That is, as the angle of a subtend ed arc for a

parametric cubic entity increases, the accuracy of the entity from the tru e representation of th

arc decreases.

Figure 1-21shows that as the subtend ed angle of a parametric cubic entity increases, the perceerror also increases substantially beyond 75 degrees.

When creating arcs with p arametric cubic geometry, MSC recommend s usingFigure 1-21 todetermine the maximum arc length an d 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 th

true arc length.

For m ost geometry models, MSC recommend s arc lengths represented by par ametric cubic

geometry shou ld be 90 degrees or less. For a more accurate mod el, the p arametric 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

PercentErrorintheRadius(x10-2)

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


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Matrix of Geometry Types Created

All Geometry App lication forms use the following Object m enu terms:

Point

Curve

Surface

Solid

Plane

Vector

Coordinate Frame

MSC.Patran will create a specific geometric type of the param etric curve, bi-param etric surfac

and tri-parametric solid based on th e method used for the Create action or Edit action.

Table 1-1, an dlist the types of geometry created for each Create or Edit action method. Thetables also list if each m ethod can create parametr ic cubic curves, surfaces or solids by p ressin

the PATRAN 2 Convention bu tton on th e app lication form. (Parametric cubic geometry isrecognized by the PATRAN 2 neutral file for export.)

For m ore information on each Create or Edit action method , seeOverview of Geometry CreatAction (p. 70) and / orOverview 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/ AFit 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
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Project Curve On Surface Yes

PWL Parametric Cubic N/ A

Revolve Arc Yes

Spline, Loft Sp line op tion PieceWise Cubic Polynomial Yes

Spline, B-Sp line op tion PieceWise Rational Polynomia l 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

*N URB splines are created if the NURBS Accelerator toggle is pressed OFF (default isON) on the Geometry Preferences form, found u nd er the Preferences/ Geometry menu .

This is true w hether you create the spline in MSC.Patran or if you import the sp line from

an IGES file. SeeGeometry Preferences (p. 296) in theMSC.Patran Reference Manual,Part 2: Basic Functions for more information. If the N URBS 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 SurfacePATRAN 2


XYZ Parametric Bi-Cubic Not Applicable

Curve Curve Interpolating Surface Yes

Decompose Trimmed Surface Yes

Edge Generalized Coons Surface YesExtract 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

http://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdf


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Ruled Ruled Surface No

Vertex Curve Interpolating Surface Yes

Trimmed (Surface Option) Trimmed Surface No

Trimmed (Planar Option) Trimmed Surface No

Trimmed (Composite

Option)

Com posite Trim med Surface N o

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 SurfacePATRAN 2



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1.4 Building An Optimal Geometry Model

A w ell defined geometry m odel simplifies the building of the op timal finite element analysis

mod el. A p oorly defined geometry m odel complicates, or in some situations, makes it

impossible to bu ild or complete the analysis model.

In compu ter aided engineering (CAE) analysis, most geometry mod els do not consist of neatl

trimmed , planar su rfaces or solids. In some situations, you m ay need to mod ify the geometry t

build a congru ent model, create a set of degenerate surfaces or solids, or d ecomp ose a trimme

surface or B-rep solid.

The following sections will explain how to:

Build a congruent model.

Verify and align surface normals.

Build trimmed surfaces.

Decomp ose trimmed surfaces into three- or four-sided surfaces.

Build a B-rep solid .

Build d egenerate surfaces or solids.


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Building a Congruent Model

MSC.Patran requires adjacent su rfaces or solids be topologically congruen t so that the nod es w

be coinciden t at th e common boundar ies. See Topological Congruency and Meshing (p. 12for m ore information.

For examp le, Figure 1-22shows surfaces 1, 2 and 3 which are incongruent. When m eshing wiIsomesh or Paver, MSC.Patran cannot guarantee the nod es will coincide at the edges shared b

sur faces 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 w ith the Surface-Point option. See Matchin

Surface Edges (p. 481) on using the form.

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

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

To m ake sur faces 1 throu gh 3 congruent, we will break sur face 1 into surfaces 4 and 5, as show

in Figure 1-23:

1

2

3

2

3

4

5
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Figure 1-23 Congruent Set of Surfaces

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

Since Auto Execute is ON, we d o not need to press the Ap ply bu tton to execute the form.

Figure 1-24 Cursor Locations for Surface Break

x Geometry

Action: Edit

Object: SurfaceMethod: Break

Option: Point

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

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

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

1

2

3

10

Cursor selectSurface 1 for the

Surface List onthe form.

Cursor select Point10 for the Point Liston the form.


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Building Optimal Surfaces

Building optimal sur faces will save time and it will result in a better idealized finite element

analysis mod el of the d esign or mechanical part.

Optimal surfaces consist of a good overall shape with n o sharp corners, and whose normal is

aligned in the same d irection with the other sur faces in the mod el.

Avoid ing Sharp Corners. In general, MSC.Softwar e Corpora tion (MSC) recommend s thatyou avoid sharp inside corners w hen creating su rfaces. That is, you should generally try to kee

the inside corners of the su rfaces to 45 degrees or more.

The reason is that when you mesh su rfaces with qu adrilateral elements, the shapes of the

elements are determ ined by th e overall shape of the surface, see Figure 1-25. The m ore skewethe qu adrilateral elements are, the less reasonable your analysis results might be.

For further recommenda tions, please consult the vend or d ocum entation for your finite elemen

analysis code.

Figure 1-25 Surfaces With and Without Sharp Corners

Note: You can use the su rface d isplay lines to p redict what the su rface element shapes w ill

look like before meshing. You can increase or d ecrease the number of display lines

und er the menu s Display/ Display Properties/ Geometric. SeeGeometric 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
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Verifying and Aligning Surface Normals Using Edit/Surface/Reverse. MSC.Patran candetermine the positive norm al direction for each surface by using right hand ru le and crossin

the param etric and axes of a surface. Depen ding on the sur faces connectivity, each

surface could h ave d ifferent n ormal d irections, as shown in Figure 1-26.

Figure 1-26 Opposing Normals for Two Surfaces

The norm al direction of a surface affects finite elemen t applications, such defining the positiv

pressure load direction, the top and bottom sur face locations for a va riable pressure load, and

the element connectivity.

Use the Edit/ Surface/ Reverse form to d isplay the surface normal vectors, and to reverse or alig

the normals for a grou p of surfaces. SeeReversing Surfaces (p. 501) on using the form.

Important: In general, you should try to m aintain the sam e normal direction for all surface

in a model.

1 2

2

1

1

2
http://-/?-http://-/?-http://-/?-


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Example of Verifying and Aligning Surface Normals. For example, Figure 1-27 shows agroup of eight su rfaces that w e want to d isplay the normal vectors, and if necessary, reverse o

align th e norm als. To display the surface normals without reversing, do the following:

Figure 1-27 Group of Surfaces to Verify Normals

You shou ld see red arrow s draw n on each surface wh ich repr esent the surface normal vector

as shown in Figure 1-28.

Figure 1-28 Surface Normal Vectors

x Geometry

Action: Edit

Object: Surface

Method: Reverse

Surface List Surface 1:8 Make sure you turn Auto Execute OFbefore 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


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Align the norm als by reversing th e norm als for sur faces 1 through 4:

Figure 1-29 shows the up dated n ormal 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 vectdirections.

1 2 3 4

5 67 8


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Decomposing Trimmed Surfaces

Trimm ed surfaces are preferred for modeling a complex part w ith man y sides. However, ther

may be areas in your mod el wh ere you may w ant to decompose, or break, a trimmed surface

into a series of three or four sided surfaces.

One reason is that you want to m esh the su rface area w ith IsoMesh instead of Paver. (IsoMes

can only mesh surfaces that have th ree or four edges.) Another reason is that you want to crea

tri-parametric solids from the decomposed three or four sided surfaces and mesh w ith IsoMes

To decompose a trimmed surface, use the Geometry app lications Create/ Sur face/ Decomp os

form. SeeDecomposing Trimmed Surfaces (p. 255) on using the form.

When entered in the Create/ Sur face/ Decomp ose form, the select menu that appears at the

bottom of the screen will show the following icons:

Example. Figure 1-30shows trimmed surface 4 with seven edges. We will decompose surfac4 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 i

the ord er listed . If not point or vertex is found , the point closest to edge will be use

or a p oint will be p rojected on to the su rface.

Use cursor select or d irectly input an existing point on the surface. If point is not onthe su rface, it will be projected onto th e 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 su rface.

21

20

22

23

2425

26

3


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Our first d ecomposed su rface will be surface 3, as shown in Figure 1-31. The figure show ssurface 3 cursor defined by three vertex locations and one p oint location along an edge. The

point locations can be selected in a clockwise or coun terclockwise direction.

Figure 1-31 Point Locations for Decomposed Surface 4

Figure 1-32 shows the remaining d ecomp osed sur faces 5, 6 and 7 and the select menu iconsused to cursor d efine the surfaces. Again , the point locations can be selected in a clockwise or

counterclockwise direction.

4

Use

to cursor selectthese three

vertices.

Use

to cursor selectthis pointlocation along

the edge.

4

5

7

6

Use

to cursor select thesethree vertices for

Surface 5.

Use

to cursor select thispoint along the edge

for Surface 5.

Use

to cursor select thesefour vertices forSurface 7.

Use

to cursor select thesethree vertices for

Surface 6.Use

to cursor select thispoint along the edgefor Surface 6.


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Figure 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 guidto wh ere the trimmed surface can be decomposed. MSC recomm ends increasing the display

lines to four or m ore. The display lines are controlled u nd er the menu s Display/ Display

Properties/ Geometric. SeeGeometry Preferences (p. 296) in theMSC.Patran Reference M anuaPart 2: Basic Functions for m ore information.
http://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdfhttp://../basic_functions/preferences_forms.pdf


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Building B-rep Solids

Boun dary rep resented (B-rep) solids are created by u sing the Geometry ap plications

Create/ Solid/ B-rep form. SeeCreating a Boundary Representation (B-rep) Solid (p. 338) fomore information on the form.

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

1. The group of sur faces that will define the B-rep solid mu st fully enclose a volum e.2. The surfaces must be topologically congru ent. That is, the adjacent surfaces must sha

a common edge.

3. The normal surface directions for the exterior shell mu st all point outw ard, as show

in Figure 1-33. That is, the normals mu st point away from the m aterial of the body.This will be d one au tomatically du ring creation as long as ru les 1 and 26 are satisfie

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

Figure 1-33 Surface Normals for B-rep Solid

Important: At th is time, MSC.Patran can only create a B-rep solid w ith an exterior shell, and

no interior shells.

Y Z

X

89

107

1

2

34

5

6

1


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Building Degenerate Surfaces and Solids

A bi-parametric surface can d egenerate from four edges to th ree edges. A tri-parametric solid

can degenerate from six faces to four or five faces (a tetrah edron or a w edge, respectively).

The following describes the best procedu res for creating a d egenerate triangular su rface and

degenerate tetrahedron and a w edge shaped solid.

Building a Degenerate Surface (Triangle). There are tw o ways you can create a degeneratethree-sided surface:

Use the Create/ Sur face/ Edge form w ith the 3 Edge option. SeeCreating Surfacesfrom 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 Curveoption. Notice that the apex of the surface is defined by a zero length curve by u sing the Curv

select menu icon show n 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 (tetrahed ron) solid can be created by u sing thCreate/ Solid/ Sur face form with th e 2 Surface option, where the starting surface is defined by

point for the ap ex of the tetrahed ron, and the end ing sur face is an op posing sur face or face, a

shown in Figure 1-35.

Five Sided Solid (Pentahedron). A five sided (pentah edron) solid can be created by u sing:

Important: IsoMesh will create hexahed ron elements on ly, if the solid has six faces. Somewedge elements will be created for a solid with five faces. IsoMesh will create

tetrahedron elements only, for a solid w ith four faces. TetMesh w ill 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 the

Starting or Ending

Curve List.


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The Create/ Solid/ Faceform w ith the 5 Face option. See Creating Solids from Face(p. 343) on using the form.

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

Figure 1-36an d Figure 1-37 illustrate using the Create/ Solid/ Sur face form to create thepentahedron 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 cur

geometry modeling1

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