C O N T E N T SMSC.Patran Reference Manual Part 2: Geometry
ModelingCHAPTERMSC.Patran Reference Manual, Part 2: Geometry
Modeling
1Introduction to Geometry Modelings s
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
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2Accessing, Importing & Exporting Geometrys s
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
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3Coordinate Framess s s
Coordinate Frame Definitions, 60 Overview of Create Methods For
Coordinate Frames, 63 Translating or Scaling Geometry Using
Curvilinear Coordinate Frames, 66
4Create Actionss s
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
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- 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
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5Delete Actionss s s s
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 Actionss s
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
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- 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
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7Show Actionss
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
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- 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
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8Transform Actionss s
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
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9Verify Actionss
Verify Action, 698 Verifying Surface Boundaries, 698 Verifying
Surfaces for B-reps, 700 - Update Graphics Subordinate Form, 701
Verify - Surface (Duplicates), 702
10Associate Actionss
Overview of the Associate Action, 704 Associating Point Object,
705 Associating Curve Object, 707
11Disassociate Actionss
Overview of the Disassociate Action Methods, 710 Disassociating
Points, 711 Disassociating Curves, 712 Disassociating Surfaces,
713
12The Renumber Action... Renumbering Geo metry INDEXs s
Introduction, 716 Renumber Forms, 717 Renumber Geometry, 718
MSC.Patran Reference Manual, 719 Part 2: Geometry Modeling
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MSC.Patran Reference Manual, Part 2: Geometry Modeling
CHAPTER
1
Introduction to Geometry Modeling
s Overview of Capabilities s Concepts and Definitions s Types of
Geometry in MSC.Patran s Building An Optimal Geometry Model
PART 2Geometry Modeling
1.1
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
ComputervisionWith 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
CHAPTER 1Introduction to Geometry Modeling
PATRAN 2 Neutral File Express Neutral FileIn 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) solidsAll 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 Modeling
1.2
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.
CHAPTER 1Introduction to Geometry Modeling
ParameterizationAll 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 1 , 2 , 3 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 1 ,
2 , and 3 . An analogy to the parameterization of geometry is
describing an X , Y location as a function of time, t t. If X = X (
t ) and Y = Y ( t ) , as t changes, X and Y will define a path.
Parameterization of geometry does the same thing - as the
parameters 1 , 2 , and 3 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.
z
P(X,Y,Z) y
x
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, ( 1 ) , from one-dimensional parametric space
into three-dimensional global XYZ space, as shown in Figure
1-3.
PART 2Geometry Modeling
A curve has one parametric variable, 1 , which is used to
describe the location of any given point, P , along a curve, as
shown in Figure 1-2.
P 1z V1
V2
x
y Figure 1-2 Curve in MSC.Patran
The parameter, 1 , has a range of 0 1 1 , where at 1 = 0 , P is
at endpoint V1 and at 1 = 1 , P is at endpoint V2 . A straight
curve can be defined as: P = ( 1.0 1 )V1 + 1 V2 Eq. 1-1
(1)V2 z 0 1 1 x y V1
0
1
1
1
Figure 1-3 Mapping Function Phi for a Curve Eq. 1-1 of our
straight curve can be represented as: 1 = ( 1.0 1 )V1 + 1 V2 Eq.
1-2
The derivative of ( 1 ) in Eq. 1-2, would give us Eq. 1-3 which
is the tangent of the straight curve. 1 = V2 V1 Eq. 1-3
Because the curve is straight, 1 is a constant value. The
tangent, 1 , also defines a vector for the curve, which is the
positive direction of 1 .
CHAPTER 1Introduction to Geometry Modeling
For any given curve, the tangent and positive direction of 1 at
any point along the curve can be found. (The vector, 1 , 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, 1 and 2 , where at any given point, P
, on the surface, P can be located by 1 and 2 , as shown in Figure
1-4.
V2
2V1
P 1V3
z
x
yV4
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,
1 and 2 for a surface have ranges of 0 1 1 and 0 2 1 . Thus, at 1 =
0 , 2 = 0 , P is at V1 and at 1 = 1 , 2 = 1 , P is at V3 . A
surface is represented by a mapping function, ( 1 , 2 ) , which
maps the parametric space into the global XYZ space, as shown in
Figure 1-5.
(1,2)(0,1) (1,1) V2
2(0,0)
2 1(1,0) V1
z
1V4
V3
0 2 1
0 1 1
x
y
Figure 1-5 Mapping Function Phi for a Surface The first order
derivatives of ( 1 , 2 ) results in two partial derivatives, 1 and
2 :
PART 2Geometry Modeling
1 = T 1 and 2 = T 2
Eq. 1-4
where T 1 is the tangent vector in the 1 direction and T 2 is
the tangent vector in the 2 direction. At any point for a given
surface, T 1 and T 2 which define the tangents and the positive 1
and 2 directions can be determined. Usually T 1 and T 2 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, can be located by 1 , 2 , and
1 , 2 , and 3 , where at any given point, P , within the solid, P 3
, as shown in Figure 1-6.
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.
V6
V5
3 2zV1
V2
P
V7
1x yV4
V3
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 1 , 2 and 3 have ranges of 0 1 1 , 0 2 1 , and 0 3 1 .
At (0,0,0) P is at V1 and at (1,1,1), P is at V7 .
CHAPTER 1Introduction to Geometry Modeling
A solid can be represented by a mapping function, ( 1 , 2 , 3 )
, which maps the parametric space into the global XYZ space, as
shown in Figure 1-7.
(1,2,3)(0,1,1) (0,0,1) (1,1,1) V5 V6
3
2 1
(1,0,1)
3(1,1,0)
V7
2V1
(0,0,0)
(1,0,0)
1V4
V3
0 1 1 0 2 1 0 3 1 x
z
y
Figure 1-7 Mapping Function Phi for a Solid If we take the first
order derivatives of ( 1 , 2 , 3 ) , we get three partial
derivatives, 1 , 2 and 3 , shown in Eq. 1-5: 1 = T 1 , 2 = T 2 , 3
= T 3 Eq. 1-5
Where T 1 is the tangent vector in the 1 direction, T 2 is the
tangent vector in the 2 direction, and T 3 is the tangent vector in
the 3 direction. At any point within a given solid, T 1 , T 2 and T
3 , which define the tangents and positive 1 , 2 and 3 directions
can be determined.
PART 2Geometry Modeling
TopologyTopology 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.
A B C D D* A*
A B C D
C B
* Surface A is not connected to Surface D
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 Edge 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. 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.
CHAPTER 1Introduction to Geometry Modeling
Face Body
Defines the topologic surface of a solid. A face is separate
from a geometric surface, although a surface can exist on a face. A
group of surfaces that forms a closed volume. A body is usually
referenced as a Brep solid or a Volume solid, where only its
exterior surfaces are parameterized. See Solids (p. 24) for more
information.
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 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. 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 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.V7 V2 ED2 V3 ED11 F6 V6
ED1 F4 ED5 V3 F2 ED8
ED7 V8
ED6
100V5
ED12
11
ED3 ED10 ED2 F1 F5 V2
ED3 F3 V4
2V1 ED4 V4
ED9
3
ED4
1Figure 1-9 Vertex & Edge Numbering for a Surface
ED1
2
V1
1
Figure 1-10 Face Numbering for a Solid
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
PART 2Geometry Modeling
ED10 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 MeshingWhen 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.
2 1 3
4
2
5
3
Topologically Incongruent
Topologically Congruent
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.)
CHAPTER 1Introduction to Geometry Modeling
Gaps 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.
Incongruent Surfaces
Gap > Global Model Tolerance
Vertices are Shared, Edges are Not
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
PART 2Geometry Modeling
This 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.
CHAPTER 1Introduction to Geometry Modeling
ConnectivityIn Figure 1-2, Figure 1-4, and Figure 1-6 in
Parameterization (p. 5), the axes for the parameters, 1 , 2 , and 3
, have a unique orientation and location on the curve, surface and
solid. Depending on the orientation and location of the 1 , 2 , and
3 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):
V2
V1
1V1 V2
1
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.)V2 ED1 V3 ED2 ED2 V2 ED3
2V1
1ED4 ED3 V4
V3 ED1
2
1ED4 V1
V4
Figure 1-15 Two Possible Connectivities for a Surface
PART 2Geometry Modeling
For 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.V6 V6
V5
V5 V2 V7 V2 V8 V3 V4 V1
3 2V1
V8
1 2
3V3
1
V4
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.
CHAPTER 1Introduction to Geometry Modeling
Effects 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 1 direction
with its 2 direction, it defines the surfaces positive normal
direction ( 3 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.
PART 2Geometry Modeling
Global 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. 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. For more information on the Global Model Tolerance, see
(p. 57) in the MSC.Patran Reference Manual, Part 1: Basic
Functions.
CHAPTER 1Introduction to Geometry Modeling
1.3
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 Modeling
Trimmed 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.) 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.
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
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. 2The 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.
CHAPTER 1Introduction to Geometry Modeling
Inner Edges or Holes
Outer Surface Edges
Figure 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
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 Modeling
Four Outer Edges
Underlying Invisible Parent Surface
Figure 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.
CHAPTER 1Introduction to Geometry Modeling
STEPS_BUILDING: There are three basic steps in building a
composite trimmed surface. Step 1 Step 2 Creating the outer
perimeter curve. In most cases this is a MSC.Patran curve chain
entity. 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.
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.
PART 2Geometry Modeling
SolidsThere 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.
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. 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.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.
CHAPTER 1Introduction to Geometry Modeling
Parametric 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
triparametric cubic solids, by pressing the PATRAN 2 Convention
button found on most Geometry application forms. 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. 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: Z ( 1 ) = S1 1 + S2 1 + S3 1 + S43 2
Eq. 1-6
where Z ( 1 ) represents the general coordinate of the global
coordinates X,Y, and Z; S 1 , S 2 , S 3 , and S 4 are arbitrary
constants; and 1 is a parameter in the range of 0 1 1 . For more
information on parametric cubic geometry, see MSC.Patran Reference
Manual.
Limitations on Parametric Cubic GeometryThere 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: Z ( 1 ) = 3S 1 1 + 2S 2 1 + S 3
Z ( 1 ) = 6S 1 1 + 2S 22
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. 18 shows that it can only have one
point of inflection, as shown in Figure 1-20.
YES
YES
YES
YES
YES
NO
NO
NO
Figure 1-20 Limitations of the Parametric Cubic Curvature
PART 2Geometry Modeling
Limits 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.
Percent Error = 100*(Computed Radius - Actual Arc Radius) / Actual
Radius 3.0 Percent Error in the Radius (x 10-2) 2.5 2.0 1.5 1.0 0.5
0 0 15 30 45 60 75 90 Total Subtended Angle in Degrees Figure 1-21
Maximum Percent Error for Parametric Cubic Arc
CHAPTER 1Introduction to Geometry Modeling
Matrix of Geometry Types CreatedAll Geometry Application forms
use the following Object menu terms:
Point Curve Surface Solid Plane Vector Coordinate
FrameMSC.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 PATRAN 2 Convention? (Parametric Cubic) Not
Applicable Yes Yes Yes Yes N/A Yes N/A N/A Yes N/A N/A N/A Yes
N/A
Create or Edit Method XYZ Arc3Point 2D Arc2Point 2D Arc3Point 2D
Circle Conic Extract Fillet Fit Intersect Involute Normal 2D Normal
2D ArcAngles Point
Type of Curve Parametric Cubic Arc Arc Arc Circle Parametric
Cubic Curve On Surface Parametric Cubic Parametric Cubic PieceWise
Cubic Polynomial Parametric Cubic Parametric Cubic Parametric Cubic
Arc Parametric Cubic
PART 2Geometry Modeling
Table 1-1 Types of Curves Created in MSC.Patran (continued)
PATRAN 2 Convention? (Parametric Cubic) Yes N/A Yes Yes Yes Yes N/A
N/A No Yes
Create or Edit Method Project PWL Revolve Spline, Loft Spline
option Spline, B-Spline option Spline, B-Spline option TanCurve
TanPoint Chain Manifold
Type of Curve Curve On Surface Parametric Cubic Arc PieceWise
Cubic Polynomial PieceWise Rational Polynomial NURB* Parametric
Cubic Parametric Cubic Composite Curve Curve On Surface
* 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 PATRAN 2 Convention? (Parametric Cubic) Not Applicable
Yes Yes Yes Yes Yes N/A N/A N/A N/A Yes
Create or Edit Method XYZ Curve Decompose Edge Extract Extrude
Fillet Glide Match Normal Revolve
Type of Surface Parametric Bi-Cubic Curve Interpolating Surface
Trimmed Surface Generalized Coons Surface Surface On Solid Extruded
Surface Parametric Bi-Cubic Parametric Bi-Cubic Parametric Bi-Cubic
Sweep Normal Surface Surface of Revolution
CHAPTER 1Introduction to Geometry Modeling
Table 1-2 Types of Surfaces Created in MSC.Patran (continued)
PATRAN 2 Convention? (Parametric Cubic) No Yes No No No
Create or Edit Method Ruled Vertex Trimmed (Surface Option)
Trimmed (Planar Option) Trimmed (Composite Option)
Type of Surface Ruled Surface Curve Interpolating Surface
Trimmed Surface Trimmed Surface Composite Trimmed Surface
Table 1-3 Types of Solids Created in MSC.Patran PATRAN 2
Convention? (Parametric Cubic) Not Applicable Yes Yes Yes Yes Yes
Yes N/A No Yes
Create or Edit Method XYZ Extrude Face Glide Normal Revolve
Surface Vertex B-rep Decompose
Type of Solid Parametric Tri-Cubic Extruded Solid Solid 5Face,
Solid 6Face Glide Solid Sweep Normal Solid Solid of Revolution
Surface Interpolating Solid Parametric Tri-Cubic Ordinary Body
Tri-Parametric
PART 2Geometry Modeling
1.4
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.
CHAPTER 1Introduction to Geometry Modeling
Building 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.
2 1
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 MatchingSurface 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:
4
2
5 3
PART 2Geometry Modeling
Figure 1-23 Congruent Set of Surfaces The entries for the
Edit/Surface/Break form are shown below:
x GeometryAction: Object: Method: Option: Delete Original
Surfaces Surface List: Break Point List Surface 1 Point 10 Edit
Surface Break PointPressing this button will delete surface 1,
after the break. Cursor select or enter the ID for surface 1.
Cursor select or enter the ID for point 10, as shown in Figure
1-24.
Since Auto Execute is ON, we do not need to press the Apply
button to execute the form.
Cursor select Surface 1 for the Surface List on the form.
2 110Cursor select Point 10 for the Point List on the form.
3
Figure 1-24 Cursor Locations for Surface Break
CHAPTER 1Introduction to Geometry Modeling
Building 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.
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.
For further recommendations, please consult the vendor
documentation for your finite element analysis code.
1 2 4 3Surfaces With Sharp Corners
1
4 3
2
Optimal Surface Shapes
Figure 1-25 Surfaces With and Without Sharp Corners
PART 2Geometry Modeling
Verifying 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 1 and 2 axes of a surface. Depending on the surfaces
connectivity, each surface could have different normal directions,
as shown in Figure 1-26.
1 2
2 1
Figure 1-26 Opposing Normals for Two Surfaces Important: In
general, you should try to maintain the same normal direction for
all surfaces in a model. 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.
CHAPTER 1Introduction to Geometry Modeling
Example 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:
x GeometryAction: Object: Method: Surface List Draw Normal
Vectors Edit Surface Reverse Surface 1:8Make sure you turn Auto
Execute OFF before cursor selecting surfaces 1-8. And do not press
Apply. Apply will reverse the normals.
1
2
3
4
5
6
7
8
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.
1
2
3
4
5
6
7
8
Figure 1-28 Surface Normal Vectors
PART 2Geometry Modeling
Align the normals by reversing the normals for surfaces 1
through 4: Surface List -ApplyDraw Normal VectorsThis will plot the
updated normal vector directions.
Surface 1:4
Figure 1-29 shows the updated normal directions which are now
aligned.
1
2
3
4
5
6
7
8
Figure 1-29 Aligned Surface Normal Vectors
CHAPTER 1Introduction to Geometry Modeling
Decomposing 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:
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. Example. Figure 1-30 shows trimmed
surface 4 with seven edges. We will decompose surface 4 into four
four-sided surfaces.
20 21 26 3
24
25 22
23Figure 1-30 Trimmed Surface to be Decomposed
PART 2Geometry Modeling
Our 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.
4Use Use to cursor select these three vertices. to cursor select
this point location along the edge.
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.
4Use Use to cursor select these three vertices for Surface 5. to
cursor select this point along the edge for Surface 5.
5
7 6Use to cursor select these four vertices for Surface 7. Use
to cursor select this point along the edge for Surface 6.
Use to cursor select these three vertices for Surface 6.
CHAPTER 1Introduction to Geometry Modeling
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 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 Modeling
Building 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. Important: At this time,
MSC.Patran can only create a B-rep solid with an exterior shell,
and no interior shells.
8
9
4 3
7 1 6
10
2 Y X Z 1
5
Figure 1-33 Surface Normals for B-rep Solid
CHAPTER 1Introduction to Geometry Modeling
Building 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. 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.
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 Surfacesfrom Edges (Edge Method) (p. 257) on using the
form.
Or, use the Create/Surface/Curve form with the 2 Curve option.
See CreatingSurfaces 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.
Cursor select this point twice using this icon: Cursor select
this edge or curve for the Starting or Ending Curve List. in the
Curve select menu for the Starting or Ending Curve List.
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:
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 fromSurfaces (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.
For the Starting Surface List, highlight and
in the select menu, and cursor select this point twice for the
first edge of the surface. Highlight again,
then, cursor select this same point twice again. Cursor select
this surface or face for the Ending Surface List. Figure 1-35
Creating a Tetrahedron Using Create/Solid/Surface
For the Starting Surface List, highlight and
in the select menu, and cursor select this point twice for the
first edge of the surface. Highlight again,
then, cursor select this same point twice again. Cursor select
this surface or face for the Ending Surface List. Figure 1-36
Creating a Pentahedron Using Create/Solid/Surface
CHAPTER 1Introduction to Geometry Modeling
For the Starting Surface List, highlight in the select menu, and
cursor select this curve twice.
Cursor select this surface or face for the Ending Surface List.
Figure 1-37 Creating a Wedge Using Create/Solid/Surface
PART 2Geometry Modeling
MSC.Patran Reference Manual, Part 2: Geometry Modeling
CHAPTER
2
Accessing, Importing & Exporting Geometry
s Overview s Direct Geometry Access of CAD Geometry s PATRAN 2
Neutral File Support For Parametric Cubic Geometry
PART 2Geometry Modeling
2.1
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.
CHAPTER 2Accessing, Importing & Exporting Geometry
2.2
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. Table 2-1 Supported CAD Systems and Their
MSC.Patran CAD Access Modules Supported CAD System EDS/Unigraphics
Pro/ENGINEER by Parametric Technology CATIA by Dassault Systemes
EUCLID 3 by Matra Datavision CADDS 5 by Computervision MSC.Patran
CAD Access Module * MSC.Patran Unigraphics MSC.Patran ProENGINEER
MSC.Patran CATIA MSC.Patran EUCLID 3 MSC.Patran CADDS 5
* Each MSC.Patran CAD Access module must be licensed before you
can access the appropriate external CAD file. You can find out
which MSC.Patran products are currently licensed by pressing the
MSC.Software Corporation (MSC) icon on the main form, and then
pressing the License button on the form that appears.
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. Thefirst 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 anyapproximations. Parasolid evaluators
are directly used for entities imported via the direct parasolid
method.
PART 2Geometry Modeling
CAD Access filters are provided that can be selected based on
the definedEDS/Unigraphics entity types, levels, and layers.
You can automatically create MSC.Patran groups when accessing
the geometry basedon 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, BoundedPlane, 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.
Face 1
Gap
Face 1
Zero Gap
Face 2
Face 2
NOT Topologically Valid (lacking congruent edge)
Topologically Valid (with congruent edge)
Figure 2-1 Topologically Congruent Surfaces for MSC.Patran
Unigraphics
CHAPTER 2Accessing, Importing & Exporting Geometry
Tips 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.
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:
Solids Break
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
enclosethe individual solid volumes.
Create the new individual solids using Create/Solid/B-rep. If
theB-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.
Group transform for solids is not supported. For information about
transforming solids in pre-release format, see (p. 50).
Solids Group Transform
PART 2Geometry Modeling
Meshing Guidelines Hybrid TetMesher Global Edge Lengths Hybrid
TetMesher Mesh Control 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. 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 triangularelements
which completely enclose the desired geometric volume.
Invoke the Hybrid tetmesher, using the previously created
triangularelements 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.
CHAPTER 2Accessing, Importing & Exporting Geometry
PRE-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
elementmesh, 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
thatresult 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
theExpress 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 Modeling
Surface/Curve Geometry Guidelines Problem 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.
CHAPTER 2Accessing, Importing & Exporting Geometry
Surface/Curve Geometry Guidelines MSC.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,
transforming, etc. Edit/Curve/Refit and Edit/Surface/Refit are
available under the Geometry application. These functions will more
regularly parameterize poorly parameterized geometry (for surfaces,
this typically involves those with compound curvature), which can
currently lead to difficulties in successfully building CAE models.
Congruency and boundary definitions are retained.
PART 2Geometry Modeling
Surface/Curve Geometry Guidelines Edit/Surface/Refit As
previously mentioned, the Edit/Surface/Refit function in the
Geometry application can be used to successfully handle problematic
Sheet Body geometry. The situations where this applies include:
Accessing geometry with the Unigraphics Sew option disabledwith
subsequent attempts to make the surfaces congruent by using
MSC.Patrans surface sew, edge match, etc.
Difficulties rendering, meshing, edge matching,
disassembling,transforming, etc.
Surfaces that result from disassembling solid geometry (i.e.,
forregioning). Curves Coincident With Surface and Solid Edges Wire
Bodies coincident with Sheet Body and Solid Body edges are not
equivalenced. This is a different behavior from what occurs if the
Express Translation method is used. If coincident curves are not
detected by the user, they may, for example, apply a Loads/Boundary
Condition to what they believe is a surface or solid edge, when in
fact they are applying it to a curve. To avoid this situation:
Move all Wire Bodies to a separate group and post only
whenrequired.
If Wire Bodies are accessed, use the new Geometry
functionEdit/Point/Equivalence to connect the curve and
surface/solid vertices.
Disable access of Wire Bodies and only access when needed.
CHAPTER 2Accessing, Importing & Exporting Geometry
Accessing Geometry Using MSC.Patran ProENGINEERIf MSC.Patran
ProENGINEER is licensed at your site, you can access the geometric
entities from an external Pro/ENGINEER part file. You can execute
MSC.Patran ProENGINEER either from MSC.Patran or from Pro/ENGINEER
by doing one of the following: Executing MSC.Patran ProENGINEER
From MSC.Patran. Execute MSC.Patran ProENGINEER from MSC.Patran by
using the File/Import... menu and make sure the Pro/ENGINEER button
is pressed on the Import form. See Importing Pro/ENGINEER Files (p.
118) in the MSC.Patran Reference Manual, Part 1: Basic Functions
for more information. Executing MSC.Patran ProENGINEER From
Pro/ENGINEER Important: Make sure MSC.Patran ProENGINEER has been
properly installed by following the instructions in Selecting
Products (Ch. 3) in the MSC.Patran Installation and Operations
Guide. Execute MSC.Patran ProENGINEER from Pro/ENGINEER by doing
the following: 1. Execute Pro/ENGINEER by entering: p3_proe will
ask for the command name to run Pro/ENGINEER. Press if you want to
accept the default command pro.p3_proe Enter the command name for
running Pro/ENGINEER. [pro]?:
2. Open the Pro/ENGINEER assembly file or part file. Then,
select the Pro/ENGINEER menus in the following order:File Export
Model Patran Geom
The MSC.Patran menu will list