workshop 3 tessellated surface - fsb online€¦ · isomesh-er. a. finite elements: create / mesh /...
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WS3-1PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
WORKSHOP 3
TESSELLATED SURFACE
WS3-2PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
WS3-3PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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
WS3-4PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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.
WS3-5PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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
WS3-6PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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
WS3-7PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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).
WS3-8PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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.
WS3-9PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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.
WS3-10PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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.
WS3-11PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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
WS3-12PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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
WS3-13PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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.
WS3-14PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
Check various views of the modeleither by rotating it or using theview icons
Step 9. Display Only the Group With the New Surface
WS3-15PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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
WS3-16PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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
WS3-17PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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
WS3-18PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
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.
WS3-19PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation
Quite MSC.PATRAN.a. File / Close.
This ends this exercise.
Step 12. Quit MSC.Patran
a
WS3-20PAT302, Workshop 3, December 2004Copyright2004 MSC.Software Corporation