WORKSHOP 4 MESH ON MESH 2D

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Christian Washington
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1 WORKSHOP 4 MESH ON MESH 2D WS4-1

2 WS4-2

3 Problem Description This exercise introduces another method of creating a 2D mesh for a set of non-congruent surfaces. So far non-congruent surfaces have been dealt with using several methods. They are composite surface, trimmed composite surface, and tessellated surface. This method involves the use of the Mesh/On Mesh tool. This involves creating a high quality continuous 2D mesh from poor quality 2D continuous mesh. The poor quality mesh can be created by meshing a set of non-congruent surfaces, then sew-ing; this is what is to be done for this workshop. WS4-3

4 Suggested Exercise Steps 1. Create a new database. 2. Import a MSC.Patran neutral file. 3. Create a Tri3 Element mesh for each surface. 4. Connect the triangular elements by sew-ing. This includes equivalencing and element creation. 5. Repeat Step 4 using a different target element edge length. 6. Using the Mesh/On Mesh tool create a mesh for the model that can be used for analysis. 7. Because the initial mesh is too coarse repeat Step 6 using a smaller element size. 8. In order to create a mesh that follows the model geometry more closely mesh select surface edges with Bar2 Elements for use with the Mesh/On Mesh application. 9. Create the final mesh, that will follow the model geometry, using the Mesh/ On Mesh application. WS4-4

Enter mesh_on_mesh for the file name and click OK. c. Select the Based on Model toggle under Tolerance.

5 Step 1. Create a New Database Create a new database called mesh_on_mesh.db and set the new model preferences. a. Click on the File New icon. b. Enter mesh_on_mesh for the file name and click OK. c. Select the Based on Model toggle under Tolerance. d. Make sure that the Analysis Code and Analysis Type are set to MSC.Nastran and Structural, respectively. e. Click OK. b e d c WS4-5

Change Source: to Neutral and select the file,

6 Step 2. Import MSC.Patran neutral file Import the MSC.Patran neutral file called non_cong_surfs.out. a. File/Import b. Change Source: to Neutral and select the file, non_cong_surfs.out. c. Click Apply. d. Click Yes for both messages that appear. e. Click the Front view icon. WS4-6

7 Step 2. Import MSC.Patran neutral file (Cont.) Shown below is the model geometry WS4-7

Shape, Mesher, and Topology to Tria, IsoMesh, and Tria3, respectively. c.

8 Step 3. Create 2D Tri Element Meshes A single 2D congruent mesh that is coincident the surfaces is needed. First, IsoMesh all the surfaces using tri3 elements. a. Elements: Create / Mesh / Surface. b. Set Elem. Shape, Mesher, and Topology to Tria, IsoMesh, and Tria3, respectively. c. Under Surface List select the entire model by dragging a box around it. d. Remove check from Automatic Calculation, and enter 5.0 for Global Edge Length. e. Click Apply. a d b c WS4-8

9 Step 4. Sew the Elements Equivalence and create tri elements by sewing the mesh. a. Elements: Modify / Mesh / Sew. b. Enter 5.0 for the Target Element Edge Length. c. Under Tria Element List select the entire model by dragging a box around it, and click Apply. c a b WS4-9

10 Step 4. Sew the Elements (Cont.) Check the free edges of the model to see if the sewing technique worked. a. Elements: Verify / Element / Boundaries. b. Set the Display Type to Free Edges. c. Click Apply. d. Click the Reset Graphics button. b a c d WS4-10

11 Step 5. Re-sew the Elements Undo and repeat the sew command, using a different Target Element Edge Length. a. Click on the Undo icon. b. Elements: Modify / Mesh Sew. c. Enter 20.0 for the Target Element Edge Length. d. Under Tria Element List select the entire model. e. Click Apply. d b c e WS4-11

12 Step 5. Re-sew the Elements (Cont.) Check the free edges of the model to see if the sewing technique worked. a. Elements: Verify / Element / Boundaries. b. Set the Display Type to Free Edges. c. Click Apply. d. Click on the Reset Graphics button. There are no element free edges internal to the mesh. This tri mesh is not acceptable for performing a finite element analysis. However, it is acceptable for using the MSC.Patran Mesh/On Mesh capability to create a mesh that can be used to perform an analysis. WS4-12 b c a d

for an analysis. a. Elements: Create/Mesh/ On Mesh. b. Select the ch

13 Step 6. Create a Mesh Using the Mesh/On Mesh Tool a Use the Mesh/On Mesh tool to create a mesh that can be used for an analysis. a. Elements: Create/Mesh/ On Mesh. b. Select the checkbox for Delete Elements. c. Under 2D Elem List select the entire model. d. Enter 5.0 for Global Edge Length. e. Click Apply. f. Click on the Plot/Erase icon. g. Click on Erase under Geometry. h. Click on the Smooth Shaded icon. c b d g e WS4-13

14 Step 6. Create a Mesh Using the Mesh/On Mesh Tool (Cont.) This mesh is too coarse. Therefore, it will be necessary to undo the previous step, and run the Mesh/On Mesh application again, this time with a smaller element size. WS4-14

15 Step 7. Create Another Mesh With the Mesh/On Mesh Tool Undo the previous Mesh/On Mesh creation, and create a new one with a smaller element size. a. Click on the Undo icon. b. Elements: Create/Mesh/ On Mesh c. Make sure the Delete Elements toggle is on. d. Under 2D Elem List select the entire model. d. Enter 2.5 under Global Edge Length. f. Click Apply. WS4-15

Step 7. Create Another Mesh With the Mesh/On Mesh Tool (Cont.) Although this mesh is much finer it still does not follow the original model geometry closely enough.

16 Step 7. Create Another Mesh With the Mesh/On Mesh Tool (Cont.) Although this mesh is much finer it still does not follow the original model geometry closely enough. It will be necessary to do another Mesh/On Mesh operation, with a slightly smaller element size and with control using 1D elements on some of the surface edges. The control on the edges is achieved by using 1D Bar2 elements shown in the following step. Copyright 2004 MSC.Software Corporation WS4-16

elements. a. Click on the Undo icon. b. Click on the Plot/Erase icon. c. Click on Erase under FEM. d. Click on Plot under Geometry. e.

17 Step 8. Mesh Surface Edges With Bar2 Elements Undo the mesh created by the Mesh/ On Mesh application, and re-mesh using select edges with Bar2 elements. a. Click on the Undo icon. b. Click on the Plot/Erase icon. c. Click on Erase under FEM. d. Click on Plot under Geometry. e. Click on OK. f. Elements: Create/Mesh/ Curve. g. Change the Topology to Bar2. h. Under Curve List select the indicated curves (shown on next page) i. Remove the check for Automatic Calculation and enter 2.0 for Global Edge Length. j. Click Apply. Copyright 2004 MSC.Software Corporation WS4-17

18 Step 8. Mesh Surface Edges With Bar2 Elements (Cont.) Illustrated here are the surface edges that are to be meshed with Bar2 elements. There are 26 edges. To the left the arrows point to 8 of the edges. Below 18 of the edges are shown as thick lines. Copyright 2004 MSC.Software Corporation WS4-18

Step 9. Create the Final Mesh Use the Mesh/On Mesh application to create a final mesh that should follow the geometry. a. Elements: Create/Mesh/On Mesh.

Under 2D Elem List select the entire model. g. Enter 2.0 for Global Edge Length. h. Click on Apply. i. Click on the Plot/Erase icon.

20 Step 9. Create the Final Mesh Use the Mesh/On Mesh application to create a final mesh that should follow the geometry. a. Elements: Create/Mesh/On Mesh. b. Make sure the Delete Elements toggle is on. c. Click Feature Selection d. Under Soft Bars select all the 1D bar elements. e. OK f. Under 2D Elem List select the entire model. g. Enter 2.0 for Global Edge Length. h. Click on Apply. i. Click on the Plot/Erase icon. j. Click on Erase under Geometry. k. Click on the Smooth Shaded icon. Copyright 2004 MSC.Software Corporation WS4-20

21 Step 9. Create the Final Mesh (Cont.) Illustrated here is the final mesh created by the Mesh/On Mesh application. Observe how the mesh follows the model geometry far better than for the previous meshes. Copyright 2004 MSC.Software Corporation WS4-21

WORKSHOP 10 HEX VS TET SOLID ELEMENT MESH

WORKSHOP 10 HEX VS TET SOLID ELEMENT MESH VS WS10-1 WS10-2 Problem Description This workshop is for creating a tetrahedral and hexahedral element mesh for a geometric solid. The tetrahedral mesh can be