WORKSHOP 3 TESSELLATED SURFACE - FSB Online€¦ · IsoMesh-er. a. Finite Elements: Create / Mesh / Surface. b. Select Tria for Elem Shape, IsoMesh for Mesher, and Tria3 for Topology

WS3-1PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation

WORKSHOP 3

TESSELLATED SURFACE



Problem Description A continuous 2D quadrilateral element mesh needs to be created

for a set of surfaces. The problem is that the surfaces in the set arenot congruent because of the presence of gaps, non-coincidentadjacent vertices, and overlapping surface edges. Also, even if thesurfaces were all congruent some of the edges internal to the outerperimeter are too close to each other for the creation of a largeelement mesh.

The approach to be used for this workshop is to

Mesh the entire set of surfaces

Connect elements and fill gaps with elements

Create a single surface from the connected 2D element mesh

IsoMesh the created single surface


Suggested Exercise Steps1. Create a new database.2. Import the surface geometry.3. Determine where the surface free edges are.4. Create tri3 meshes using the IsoMesher.5. Sew the elements together.6. Observe where the free edges of the elements are.7. Create a group for the surface to be created from the tri3 elements.8. Create a surface from the 2D tri3 mesh.9. Display only the group with the new surface.10. Mesh the new surface using IsoMesh.11. Smooth the new surface mesh.12. Quit MSC.Patran.


Step 1. Create a New Database

Create a new database.a. File / New.b. Enter tessellated for File

Name.c. Click OK.d. Under New Model

Preferences, select Basedon Model Tolerance.

e. Select MSC.Nastran forAnalysis Code.

f. Select Structural forAnalysis Type.

g. Click on OK.

f

e

d

cb

a

g

Note that the tolerance specified is 0.005


Step 2. Import the Surface Geometry

Import the model geometry.a. File / Import.b. Change the Object and

Source to Model and Neutral,respectively.

c. Select non_cong_surfs.out.d. Click on Apply.e. Click Yes for the import

summary.

dc

ba


Step 3. Determine Where the Surface Free Edges Are

Determine where the surface freeedges are.

a. Geometry: Verify / Surface /Boundary.

b. Under Surface List selectthe entire model.

c. Click on Apply.d. Click on OK to the Update

Graphics dialogue box.

c

b

a

Note that there are numerous locations wherethere are surfaces free edges(indicated bymagenta circles).


Create tri3 mesh using theIsoMesh-er.

a. Finite Elements: Create /Mesh / Surface.

b. Select Tria for ElemShape, IsoMesh forMesher, and Tria3 forTopology.

c. Select all the surfaces inthe display for SurfaceList.

d. Deselect AutomaticCalculation.

e. Enter 2.0 for Global EdgeLength.

f. Click on Apply.

Step 4. Create Tri3 meshes using IsoMesh

ed

c

b

a Note that IsoMesh can be used because all ofthe surfaces are parametric.


Sew the elements together.a. Finite Elements: Modify /

Mesh / Sew.b. Enter 2.0 for Target Element

Edge Length.c. Select all the tri elements

under Tria Element List.d. Click on Apply.

Step 5. Sew the Elements Together

d

c

b

a

What does the Sew command do?The Sewing command will equivalence finiteelement nodes and create tri elements to fillany gaps. The quality of the tri elements maynot be very good, but that is acceptablebecause a surface is to be created from themand the original tri elements will be deleted afterthe surface has been created.


Now, check for element free edges.a. Finite Elements: Verify /

Element / Boundaries.b. Select Free Edges for

Display Type.c. Click on Apply.

Step 6. Look at the Element Free Edges

Hole in Tri3Mesh

c

b

a

Is it ok the have a hole in the mesh ?Yes. When the surface is created the inner loopcan be excluded. However, it is important torealize that the presence of inner loops, even ifthey are excluded in creating a surface, mayresult in inaccurate geometry at the location ofthe inner loops.


Step 7. Create a Group

Create a group for the surface to becreated from the tri3 elements. Makethe group “current”so when thesurface is created it will be placed in it.

a. Group: Create / Select Entity.b. Enter tess_surf for New Group

Name.c. Check the Make Current

checkbox.d. Click on Apply.

c

b

a


Create a surface from the 2D tri3mesh.

a. Geometry: Create / Surface /Mesh.

b. Select the tri3 elements forElement List.

c. Select the four corner nodesfor Outer Corner Nodes. Noadditional nodes are to beselected, under AdditionalVertex Nodes, so that aparametric surface will becreated.

d. Select None for Inner LoopOptions.

e. Click on Apply.

Step 8. Create a Surface From the 2D tri3 Mesh

e

d

c

b

a

c


Display only the group with the newsurface, tess_surf.

a. Group / Post…b. Select tess_surf for Select

Groups to Post.c. Click on Apply.d. Turn on the display lines.

Step 9. Display Only the Group With the New Surface

d

b

a

This is a parametric surface. The display linesare obviously not smooth. The elementscreated by IsoMesh-ing this surface will haveproblems.


Check various views of the modeleither by rotating it or using theview icons

Step 9. Display Only the Group With the New Surface


Mesh the new surface using IsoMesh (UseLarger Element Size).

a. Finite Elements: Create / Mesh /Surface.

b. Select Quad for Elem Size, IsoMeshfor Mesher, and Quad4 for Topology.

c. Select Surface 602 (the new surface)for Surface List.

d. Deselect Automatic Calculation andenter 6.0 for Global Edge Length.

e. Click on Apply.

Step 10. Mesh the New Surface using IsoMesh

d

c

b

a


Step 11. Smooth the New Surface Mesh

Smooth the new 2D surface mesh usingan application in Finite Elements.

a. Finite Elements: Modify / Mesh /Surface.

b. Select the newly created tessellatedsurface, Surface 602, for SurfaceList.

c. Click on Apply.

c

b

a


Erase the Geometry so that themesh can be seen better.

a. Display / Plot/Erase.b. Under Geometry click on

Erase.c. Click OK.

Step 11. Smooth the New Surface Mesh (Cont.)

c

b

a


Step 11. Smooth the New Surface Mesh (Cont.)

Before Smoothing After Smoothing

The quality of the quad elements can bechecked for the two meshes using FiniteElements: Verify / Quad / All.


Quite MSC.PATRAN.a. File / Close.

This ends this exercise.

Step 12. Quit MSC.Patran

a


Documents

WORKSHOP 3 TESSELLATED SURFACE - FSB Online€¦ · IsoMesh-er. a. Finite Elements: Create / Mesh / Surface. b. Select Tria for Elem Shape, IsoMesh for Mesher, and Tria3 for Topology