27239634 msc patran 301 course notes

MSC.Patran 301 Course Notes Introduction to MSC.Patran

Copyright 2000 MSC.Software Lec 7-87 Meshing Strategies

MeshingStrategies



Overview� Analysis requirements must be understood to build an

appropriate mesh, i.e. linear, nonlinear

� Geometry type and attributes must be considered beforemeshing, i.e. simple, trimmed surface

� MSC.Patran FEM application tools

❑ Meshers❑ Meshing control❑ Sweep / transform tools❑ Editing



Geometry in MeshingTrimmed Surfaces

Trimmed surfaces

Surfaces definition lead to poor mesh

Pave mesh of trimmed surfacesNote: elements are not uniformaround hole



Geometry in Meshing (continued)Composite Surface

� Create a Composite Surface to eliminate restrictions

❑ No problems with vertices or meshed edges

Composite Surface

Trimmed Surface Mesh

Composite Surface Mesh



Geometry in Meshing (continued)Surface Decompose

� Decompose trimmedsurfaces to allow for bettermeshing control

� Select vertices at edge orinternal positions or existingpoints.

New Mesh after Decompose

Trimmed Surface Mesh

New Decomposed Surfaces



Geometry in Meshing (continued)Tessellated Surface

Original Geometry Tri Mesh

Tessellated SurfaceShell Mesh fromTessellated Surface



Geometry in Meshing (continued)Tessellated Surface

� Tessellated Surfaces use the node positionsto build a surface.

� Mesh quality is not of concern except wheresevere curvature must be captured.

� FEM - Modify/Mesh/Sew tool sews gaps of atri meshed region for the purpose ofbuilding a tessellated surface.



Geometry in Meshing (continued)Geometry Characteristics

� Geometry characteristics which effect creation of finiteelements include Parameterization, Connectivity, Topology.

� Parametrics of geometry define a local system in which anypoint within that geometric entity can be located.

� Connectivity defines geometry orientations such as surfacenormals and edge order.

� Topology describes the adjacency relationships betweengeometric entities.



Geometry in Meshing (continued)Parameterization

� Imported geometry may exhibit irregular Parameterization.� Original geometry

❑ Irregular display lines❑ Irregular element pattern❑ Mesh smoothing will fix this.

� Refit surface

❑ Geometry/Edit/Surface/Refit❑ Better but still irregular❑ Mesh smoothing will fix this

� Refit curves, re-created surface

❑ Geometry/Edit/Curve/Refit❑ No irregularities exhibited

Display Lines



Geometry in Iso Meshing (continued)Connectivity

� Connectivity effects element and node ID order as well aselement normal/CID orientation

� Iso-Meshed surfaces followsurface parametrics whichare based on connectivity

� Node and element numberpatterns are based onconnectivity

� Element local coordinateframes are based on

❑ Element connectivity❑ Surface connectivity❑ Surface parametrics

C1C1



Geometry in Meshing (concluded)Topology

� Topology defines adjacencyrelationships. Shared edges of a surfaceare termed topologically congruent ifthey occupy the same model space anduse the same vertices.

� Topological congruency determineswhether coincident nodes are created oncommon boundaries.

� Verify/Surface/Boundaries checks forfree and manifold edges. If free edgesexist internal to the model then theseentities are topologically incongruent.

Incongruent Topology

Geometry - Verify/Surface/Boundary

Congruent Topology



Geometry in Meshing (concluded) FEM Applications

FEM Tools

� MSC.PATRAN has many features for creating Finite ElementModels

Meshing tools

Meshing controltools

Element creation/ editing tools

Iso mesher

Paver mesher

Tet mesher Automatic Solid Mesher to generate Tetrahedron Elements

Mesh seed Define element densities and bias

Hard points and Define additional control points and edges to the mesher

Mesh control Global edge length, auto hard points

Transforming create copies of existing elements or nodes, i.e.translating, rotating, mirroring. Sweeping creates elements bygenerating the next higher order element from base elements. e.g. 1Delement generates 2D element.

Surface Mesher for trimmed or simple surfaces Meshes complexsurfaces with an arbitrary number of boundary edges and internal holes.

Tradional Mapped Mesher for parametric geometry. Creates 1, 2 or 3dimensional elements

Editing Move, offset, edit, project or change attributes.

Reverse,

hard curves

Sweeping andTransforming



FEM ApplicationsMesh Type

� Solid tet meshing

❑ Automatic tet-mesh B-repsolids

❑ Curvature control

Finite Elements

CreateAction:

Hex9Hex20

-Apply-

MeshObject:

SolidType:

Output IDs

Element ID List

Global Edge Length

Node ID List

Element Topology

Input List

Hex8

TetMesh Parameters...

21325

21311

0.1

Node Coordinate Frames...

Mesher

IsoMesh TetMesh

Elm 1:124

��



Assembly Meshing for Parasolid Solid Assembly

❑ Provides a matching face mesh across multiple solid facesfor parasolid solid assemblies

Non-congruent Solidsassembly imported asparasolid

Non conguent solidsassembly created in Patran

Element faces at common faceafter meshing with assemblymeshing turned on

Element faces at commonface after meshing. (Assemblymeshing turned off)

Non-CongruentMeshes

CongruentMeshes



Assembly Meshing for Parasolid Solid Assembly(concluded)

❑ Once user has downloaded and installed this new meshcomponent, the environment variable must be setASSEMBLY_MESH_ON YES

❑ Some info on usage

❑ Works for Tetmeshes only❑ Solid-to-Solid Intersection

❑ If solids are intersecting and the intersecting volume issmall (<1% total volume) then meshing will continueusing assembly meshing after outputting a warningmessage

❑ non-mating solids

❑ If solids are separated by more than the parasolidtolerance, the no shared geometry will be found. Thesolids will be meshed as separate solids

❑ If all criteria are met, a conguent mesh is generated across thesolids at the touching faces. No equivalencing is required



Summary� MSC/PATRAN provides many tools to generate a finite

element model.

� In creation of a FEM, more than one method must usually beemployed.

� An understanding of the geometry tools and characteristicsof the geometry will make meshing easier.

� Mesh control tools are tools to helps provide for the desiredmesh prior to meshing.

� Editing tools allow the user to modify a mesh for the desiredresult after meshing.

27239634 msc patran 301 course notes

Documents

parasolid

assembly meshing

element faces

assembly meshing

common face

tessellated

meshing strategies

geometry characteristics