文本案例msc.patran courses课程

1、- or -WORKSHOP 10HEX & TET SOLID ELEMENT MESHProblem DescriptionThis workshop involves creating a tetrahedral and hexahedral element mesh for a geometric solid. The tetrahedral mesh can be created quickly and easily using the standard TetMesh mesher.The hexahedral mesh involves much more work. This

2、workshop demonstrates some of the possible techniques that can be used.The task involves dividing the geometry into two parts. Groups are used to organize the parts. A hex mesh for the first part is created using a combination of IsoMesh and Paver meshes, then sweeping them to create the hex solid e

3、lements.The hex elements for the second part are created by using the IsoMesh mesher. First, parametric (blue) solids must be created. The techniques used are simple. There is one difficulty associated with creating two solids; they are very skewed, and this affects the meshing.The hex element meshe

4、s are combined, and their continuity is investigated.Suggested Exercise StepsCreate a databaseImport a parasolid file with single solidCreate a tet mesh using TetMesh; check element qualityClose the database, and create a new oneImport the same parasolid fileDisassemble the solid and remove unwanted

5、 surface vertices to generate simple surfaces. As finding all the vertices can e a tedious task, delete the surfaces and solid, and import a different model file with surfaces already prepared.Create a plane to break the surfaces into two groups, then break the surfaces with the plane.After breaking

6、 the surfaces, place each set into a different group.Suggested Exercise Steps (Cont.)Begin with the base model, and create a parametric surface to fill the hole.Create mesh seeds for the first two surfacesCreate Quad4 elements at the base, to be sweptCreate Hex8 Elements by Sweeping Quad4s at the ba

7、seCreate Seeds, IsoMesh, then Sweep to Hex8sCreate Mesh Seeds in preparation for Paver MeshCreate Paver Mesh using SeedsComplete Sweeping Quads to create HexesDelete Quad Elements and connect Hex ElementsPost Group “Top” with Surfaces for creating parametric SolidsCreate Parametric Solids from param

8、etric SurfacesCreate Curves to be used for creating SurfacesSuggested Exercise Steps (Cont.)Create Parametric Surfaces from CurvesCreate Parametric Solids from SurfacesDisplay both parts of the ModelCreate Mesh Seeds to force Congruent Hex MeshesCreate Hex Meshes for the “Top” Part of ModelConnect H

9、exes in “Top” Part of ModelDetermine Quality of Hex MeshStep 1. Create a DatabaseCreate a new database:File / NewEnter tet as the File name.Click OK.Select Based on Model for Tolerance.Select Nastran for Analysis Code and select Structural for Analysis Type. Click OK. bfedcabcdStep 2. Import Parasol

10、id FileImport the parasolid.xmt file:File / ImportChange the Source to Parasolid.xmt.Select part.xmt.Click Apply and click OK when the import summary appears.aStep 3. Create a TetMesh MeshTetMesh the solid: Elements: Create / Mesh / SolidSet Elem Shape to Tet and set Mesher to TetMesh.Under Input Li

11、st, select Solid 1.Under Global Edge Length, enter 5.Click Apply.Change to Iso 3 view and Smooth shaded.abcdeffStep 3. Create a TetMesh Mesh (Cont.)Check the quality of the elements:Elements: Verify / Tet / AllClick Apply.abThis method was straightforward and quick. It can be observed that about 650

12、0 Tet10 Elements and 10,000 Nodes were created.Step 4. Close the DB and create a new DBCreate a database and specify the New Model Preferences:File / CloseFile / NewEnter hex8 as the File name.Click OK.Select Based on Model for Tolerance.Select MD Nastran for Analysis Code and Structural for Analysi

13、s Type. Click OK.cdgfebaStep 5. Import the Parasolid File againImport the parasolid file part.xmt:File / ImportSelect part.xmt.Click Apply and click OK when the import summary appears. abcdStep 6. Disassemble the Parasolid SolidPrepare the solid so that a hex mesh can be created. Start by disassembl

14、ing the parasolid:Geometry: Edit / Solid / DisassembleFor Solid List, select Solid 1.Click Apply. Select Yes when asked to delete the original solids.Click on the Label Control icon and turn the surface labels on.abceeStep 6. Disassemble the Parasolid Solid (Cont.)Note that the surfaces are trimmed

15、Where possible, create parametric surfaces (green) from the trimmed surfaces. Tools available for this include:Geometry: Create / Surface / CurveGeometry: Edit / Surface / Remove VertexGeometry: Edit / Surface / RefitGeometry: Edit / Surface / DisassembleMake sure that the parametric (green) surface

16、s accurately represent the faces (trimmed surfaces) of the part without gaps or cracks.abStep 6. Disassemble the Parasolid Solid (Cont.)It may be difficult to remove all the vertices because of the difficulty in identifying them. Therefore, delete the model and import an IGES file with all surfaces

17、already edited. Delete the model.File: ImportChange the Source to IGES.Switch off Import to ParasolidSelect the file surfaces.igs, then click Apply.In order to simplify the exercise the newly imported surfaces are already edited.edbcStep 7. Create a Plane to Break the SurfacesBreak the surfaces to c

18、reate two regions for creating hex8 elements. A plane is used to break the surfaces.Select Iso 1 ViewGeometry: Create / Plane / 3 PointsFor Point 1 List, select Point 17.For Point 2 List, select Point 18.For Point 3 List, select Point 5.*abcd*a17185Step 7. Create a Plane to Break the Surfaces (Cont.

19、)Break the surfaces with the newly created plane:Geometry: Edit / Surface / BreakOption: PlaneSurface List: select all surfacesBreak Plane List: select Plane 1Select Yes for All when asked to delete original surfaces.abcdNote that selecting all surfaces ensures that any surface intersected by Plane

20、1 gets broken, while nonintersecting surfaces remain unchanged.Step 8. Place each set of Surfaces into different GroupsCreate two groups for different regions of the model. Start with the “base” region of the model:Group: CreateEnter base for New Group Name.Check Unpost All Other Groups.Go to Prefer

21、ences/Picking and change the Rectangle/Polygon Picking to Enclose entire entity. Change to the Right Side view.For Entity Selection, select the surfaces indicated in the figure.Click Apply.abcegdfShown here is the base region of the model. The entities in the two regions of the model are to be place

22、d in different groups to facilitate meshing.Step 8. Place each set of Surfaces into different Groups (Cont.)Step 8. Place each set of Surfaces into different Groups (Cont.)Post the group, default_group, and create a group for the remaining region of the model:Post the group default_group.Group / Cre

23、ateFor the New Group Name enter top.Check Unpost All Other Groups.Go to Preferences: Picking and change the Rectangle/Polygon Picking to Enclose any portion of entity. Switch to the Right Side view, and under Entity Selection select the surfaces indicated in the figure.Click Apply.cdffafebgStep 8. P

24、lace each set of Surfaces into different Groups (Cont.)Step 9. Create a Parametric Surface to Fill HoleEnclose the base region with surfaces by creating a parametric surface where the plane is:Post the group base.Click on the Iso 1 view icon.Geometry: Create / Surface / CurveSet the Option to 2 Curv

25、e.Under Starting Curve List, select Surface 22.3.Under Ending Curve List, select Surface 13.2.Click Apply (if necessary).acdefgbStep 10. Create Mesh Seeds for first two SurfacesCreate a mesh seed for the base so that a quad mesh can be applied (the quad mesh will later be swept to create a hex8 mesh

26、).Elements: Create / Mesh Seed / UniformEnter 9 for the Number.For Curve List, select Surface 13.1.Repeat the procedure, setting the Number to 3 and select Surface 26.1 for the Curve List.Repeat the same procedure, setting the Number to 4 and select Surface 26.4 and Surface 8.4 for the Curve List.ab

27、cStep 11. Create Quad4 Elements to be SweptMesh surface 13 using the Paver:Elements: Create / Mesh / SurfaceSet Elem Shape to Quad, set Mesher to Paver and set Topology to Quad4.For Surface List, select Surface 13.Enter 3.0 for Global Edge Length.Click Apply.abcdeStep 11. Create Quad4 Elements to be

28、 Swept (Cont.)Mesh another surface using IsoMesh:Elements: Create / Mesh / SurfaceSet Elem Shape to Quad, set Mesher to IsoMesh and set Topology to Quad4.For Surface List, select Surface 26.Enter 3.0 for the Global Edge Length.Click Apply.abcdeStep 11. Create Quad4 Elements to be Swept (Cont.)Shown

29、here are the surface meshes for part of the base. The meshes will be swept to create a hex mesh for the base part of the model.Step 12. Create Hex8 Elements by Sweeping Quad4sSweep the surface meshes to the first section:Elements: Sweep / Element / ExtrudeClick on Mesh Control, enter 3 for Number.Cl

30、ick OK.Click under Direction Vector and select the Base and Tip Points icon. Then select tip and base points as shown in the figure.For selecting the Base Entity List entities, use the Meshed Entity icon, then the Meshed Surface icon.Select Surfaces 13 and 26 for the Base Entity List.Click Apply.abc

31、dgfbddeStep 12. Create Hex8 Elements by Sweeping Quad4s (Cont.)Step 12. Create Hex8 Elements by Sweeping Quad4s (Cont.)Sweep the free faces of the hex elements to the next section:Elements : Sweep / Element / ExtrudeClick on Mesh Control, enter 1 for Number, and then click OK.Click under Direction V

32、ector and select the Base and Tip points icon. Then, select the base and tip points as shown in the figure.Go to Preferences: Picking and select Enclose entire entity.Change to Left Side view and click on the Elements face icon.Under Base Entity List, select the element faces as shown in the figure.

33、Click Apply.fcabbfbccgdefeStep 12. Create Hex8 Elements by Sweeping Quad4s (Cont.)The elements have been swept twice to create the illustrated model. Note that the nodes line up as they should.Step 13. Create Seeds, IsoMesh, then Sweep to Hex8sIsoMesh the surface in a corner (Surface 18) to create e

34、lements that will be swept. First, because of the curvature (90 degree bend), it is necessary to create mesh seeds.Switch to the Iso 1 view and zoom into Surface 18.Elements: Create / Mesh Seed / UniformEnter 4 for the Number.For Curve List, select Surface 7.2 (or Surface 18.1).abcddStep 13. Create

35、Seeds, IsoMesh, then Sweep to Hex8s (Cont.)Mesh surface 18 using IsoMesh, then sweep the elements created:Elements: Create / Mesh / SurfaceSet Elem Shape to Quad, Mesher to IsoMesh and Topology to Quad4.For Surface List, select Surface 18.Uncheck Automatic Calculation, and enter 3.0 for the Global E

36、dge Length.Click Apply.abcdceStep 13. Create Seeds, IsoMesh, then Sweep to Hex8s (Cont.)Sweep the elements created:Elements: Sweep / Element / ExtrudeClick on Mesh Control, enter 1 for Number, and then click OK.Click under Direction Vector, and select Base and Tip Points icon. Then select the base a

37、nd tip points as shown in the figure.For selecting the Base Entity List entities, use the Meshed Entity filter, and then the Meshed Surface icon.Select Surface 18 for the Base Entity List.Click Apply.ecabecfcddStep 14. Create Mesh Seeds in preparation for Paver MeshPaver mesh Surface 12, so that the

38、 mesh can be swept to create hex elements for the rest of the base. The mesh to be created must match the one already created by sweeping. In order to do this, mesh seeds are to be created using existing nodes.Elements: Create / Mesh Seed / TabularFor the Coordinate Type, select Node and Point.Under

39、 the Nodes or Points List, select the 13 nodes as shown in the figure.Select Surface 12.2 under Curve List.abcddcStep 14. Create Mesh Seeds in preparation for Paver Mesh (Cont.)The model so far, with mesh seeds displayed.Step 15. Create Paver Mesh using SeedsMesh surface 12:Elements: Create / Mesh /

40、 SurfaceFor Elem Shape, select Quad, set Mesher as Paver and set Topology as Quad4.Select Surface 12 for Surface List.Enter 3.0 for Global Edge LengthClick Apply.abcdceStep 15. Create Paver Mesh using Seeds (Cont.)Step 16. Complete Sweeping Quads to create HexesComplete sweeping element faces and 2D

41、 quad elements to the side of the model:Elements: Sweep / Element / ExtrudeClick on Mesh Control and enter 8 for Number, and click OK.Click under Direction Vector and select the Base and Tip Points icon. Then select the base and tip points as shown in the figure.Under Base Entity List, click on the

42、Elements Face icon.Switch the view to Left View, and select the elements as indicated.Click Apply.abcdfceStep 16. Complete Sweeping Quads to create Hexes (Cont.)Step 16. Complete Sweeping Quads to create Hexes (Cont.)Complete sweeping 2D quad elements to the side of the model:Elements: Sweep / Eleme

43、nt / ExtrudeClick on Mesh Control and enter 8 for Number, then click OK.Click under Direction Vector and select the Base and Tip Points icon. Then select the base and tip points as shown in the figure.Under Base Entity List, click on the 2D element filter.Switch the view to Top View, and select the

44、elements as indicated.Click Apply.abcdfceStep 16. Complete Sweeping Quads to create Hexes (Cont.)Step 17. Delete Quad Elements and connect Hex ElementsDelete 2D elements, then equivalence:Elements: Delete / ElementElements: Equivalence / All / Tolerance CubeDelete 2D ElementsEquivalenceStep 17. Dele

45、te Quad Elements and connect Hex Elements (Cont.)Completed hex mesh for the base part of the model. Now, verify that all the hex elements are connected.Elements: Verify / Element / Boundaries.Select Free Edges for Display Type.Click Apply.Click Reset Graphics.abcdIn hex meshes, free edges typically

46、coincide with physical edges. However, one physical edge of this part does not appear as a free edge. Why?Step 18. Post Group “Top” With Surfaces for Blue SolidsCreate parametric solids for the remainder of the model, and IsoMesh them with hex elements. Post the group top:Group: PostUnder Select Gro

47、ups to Post, select top.Click Apply, then Cancel.Click on the Iso 1 view icon.abcdStep 19. Create Parametric Solids from SurfacesCreate the first parametric solid using two surfaces:Geometry: Create / Solid / SurfaceSet the Option to 2 Surface.Select Surface 23 for the Starting Surface List.Select S

48、urface 3 for the Ending Surface List.abcdStep 19. Create Parametric Solids From Surfaces (Cont.)Create the second solid:Select Surface 17 for the Starting Surface List.Select Surface 2 for the Ending Surface List.Solids 1 and 2 have been created.abStep 20. Create Curves to be used for creating Surfa

49、cesTo create the remaining solids, it will be necessary to create some curves, surfaces from the curves, then solids from the surfaces:Geometry: Edit / Curve / BreakRotate the view to get the following view of the model.Set the Option to Parametric.Enter 0.7 for the Break Point.Select Surface 4.2 an

50、d 4.4 for the Curve List.Increase the point size.acdefeeacdStep 20. Create Curves to be used for creating Surfaces (Cont.)Break curves again to obtain all needed curves:Set the Break Point to 0.5.Under Curve List, select Curve 1 and 3.Select “Yes” or “Yes for All” to delete the original curves.abSte

51、p 21. Create Parametric Surfaces From CurvesCreate surfaces using the curves just created and previously existing surface or solid edges:Geometry: Create / Surface / CurveOption: 2 CurveSelect curves or edges for Starting Curve List and Ending Curve List.Starting Curve ListEnding Curve ListSurface 1

52、.4Curve 2Surface 1.2Curve 4Solid 2.2.3Curve 6Solid 2.2.1Curve 8Surface 5.4Curve 5Surface 5.2Curve 7abStep 22. Create Parametric Solids from SurfacesCreate the parametric solids:Geometry: Create / Solid / SurfaceSet Option to 2 Surface.Select the surfaces, as specified in the table, for Starting Surf

53、ace List and Ending Surface List.Starting Surface ListEnding Surface ListSurface 27Surface 28Surface 29Surface 30Surface 31Surface 32abccStep 22. Create Parametric Solids from Surfaces (Cont.)Step 23. Post Both Parts of the ModelPost the groups for the base and top portions of the model.Step 24. Cre

54、ate Mesh Seeds for Congruent Hex MeshesElements: Create / Mesh Seed / TabularCheck Node and Point.Select the nodes shown in the figure. It may be easier to select the nodes by erasing the five solids that were just created.Select the two edges for Surface 26 indicated by the thick lines.Click Apply

55、if necessary.abccWe will now IsoMesh the five new parametric solids. It is desired to have the hex mesh in Solid 1 and the base part of the model congruent to each other. To ensure this, mesh seeds are to be created on the two unseeded edges of Surface 26.deStep 25. Create Hex Meshes for “Top” Part

56、of ModelIsoMesh the five new solids:Elements: Create / Mesh / SolidSelect Hex for Elem Shape and IsoMesh for Mesher.Under Solid List, select Solid 1:5.Uncheck Automatic Calculation and enter 3.0 for Global Edge Length.Click Apply.abcdeStep 25. Create Hex Meshes for “Top” Part of Model (Cont.)Solid 1

57、.1.3Solid 1.2.3IsoMesh issues an error message. Meshing Solid 1 with the constraint from the mesh seeds on the edges of Surface 26, coupled with the solids poor shape helped cause the failure.Another factor affecting this is the interaction with the other solids when trying to mesh all five in one o

58、peration. Meshing the solids in sequence rather than all at once may help.Step 25. Create Hex Meshes for “Top” Part of Model (Cont.)IsoMesh only Solid 1:Elements: Create / Mesh / SolidSelect Hex for Elem Shape.Select IsoMesh for Mesher.Under Solid List, select Solid 1.Specify 3.0 for Global Edge Len

59、gth.Click ApplyUnder Solid List, select Solid 2.Specify 3.0 for Global Edge Length.Click Apply.Under Solid List, select Solid 3:5.Specify 3.0 for Global Edge Length.Click Apply.Meshing in sequence gets around the problem in this case.Step 26. Connect Hexes in “Top” Part of ModelConnect the hex elements:Switch to wireframe view Elements: Equivalence / All / Tolerance CubeClick ApplyIt can be seen from the equivalence markers that in some areas full equivalencing has not occ