HyperWorks Tip/Trick 389

Applications: HyperMesh

Application version: 5.1 and greater

Computer hardware: All supported

Computer operating systems: All supported Windows and UNIX

Categories: Subcategories Meshing:

Create elements, Check and edit mesh quality

Topic: A checklist for reviewing a tria mesh before tetra meshing it and tips for tetra meshing.

Topic details: You can use the following checklist to review the tria elements prior to creating a tetra mesh with them. Doing so can help you avoid troubleshooting why HyperMesh (HM) cannot tetra mesh the volume(s). If you are unsure how to perform each check, see the annotated checklist at the end of this tip/trick.

Pre tetra meshing checklist:

Check for and delete duplicate elements.

Make sure all tria elements are of the same order, 1st or 2nd.

Check for quad elements and split them into tria elements.

Check for and correct tria elements with very small angles.

Check for and correct tria elements with small edge lengths.

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Check for and remove free element edges within the volume of tria elements. The volume has to be closed; it cannot contain "holes".

Check for and remove "T" or discontinuous connections (edges connected to two or more elements) in the group of tria elements.

Scenarios causing free element edges and / or T-connections: 1. Internal partitions in the volume of tria elements. If these are required, split the model into separate

volumes and tetra mesh separately.

2. Duplicate meshes on a surface. If these meshes are different from each other, then they cannot be detected by using the duplicate elements check. However, the T-connections check may outline the boundary since the definition of a T-connection is any element edge connected to two or more elements.

Tips for tetra meshing using HM: 1. When selecting the tria elements in the tetramesh panel, make sure to select only those elements

that make up the closed volume. To view the volume's interior, use the hidden line panel on the Post page while in performance graphics mode. (Press F1 to go to this panel.) Use the fill plot and cutting functionality. The cut plane can be dragged in the graphics area.

2. When the tetra mesher fails to mesh a part, the elements it was working on when it failed are automatically saved to the HM user mark. Go to the mask panel to display the elements on the mark and turn off the display for all other elements. In the mask panel, click elems and then click retrieve. Click elems one more time and then click reverse. Finally, click mask. Only the elements saved to the user mark are now displayed in the graphics area. Usually, the elements causing the mesher to fail are attached to the elements on the user mark. Use the find panel on the Tool page or the Find Attached macro on the QA macro menu page to identify the elements that are attached to the displayed ones. Examine these elements and use the above checklist to determine why the mesher failed.

3. If the tetra mesher still fails to generate a tetra mesh, check for element penetration using the penetration panel on the Tool page.

Annotated pre tetra meshing checklist:

Following is information on how to perform the checks in the checklist above. Refer to HM on-line help for more information about how to use the panels or functionality mentioned below.

Check for and delete duplicate elements . Go to the check elems / 2-d sub-panel on the Tool page to find duplicate elements. (You can press the keyboard key F10 to go to this panel.) Save any failed elements by clicking save failed. Then go to the delete panel on the Tool page to retrieve and delete them.

Make sure all tria elements are of the same order, 1st or 2nd. Go to the mask panel on the Tool page. (You can press the keyboard key F5 to go to this panel.) Mask all of the 1st (or 2nd) order tria elements. Use by config to select them. If there are any tria elements still displayed in the graphics area, they may be 2nd (1st) order elements. Use the order change panel on the 2D page to switch the order for these elements.

Check for quad elements and split them into tria elements.

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Go to the mask panel. Mask all of the tria elements using by config to select them. If there are any quad elements displayed split them into tria elements. Go to the split panel on the 2D page. Use the plate elements sub-panel to divide the quad elements into tria elements.

Check for and correct tria elements with very small angles. In the check elems / 2-d sub-panel, use the min angle functionality to identify tria elements with very small angles. The recommended minimum angle is 10. Save any failed elements and retrieve them in other panels to modify them.

Check for and correct tria elements with small edge lengths. In the check elems panel, in the 2-d sub-panel, use the length functionality to identify elements with edge lengths much smaller than the average element length in the model. Save any failed elements and retrieve them in other panels to modify them.

Check for and remove free element edges within the volume of tria elements. The volume has to be closed; it cannot contain "holes". When no free edges exist, the volume is closed. Use the edges panel on the Tool page to check for and remove free element edges.

Check for and remove "T" or discontinuous connections (edges connected to two or more elements) in the group of tria elements.

Use the edges panel on the Tool page to do this. Click the toggle after find: to switch from free edges to T-connections.

Author: Altair HyperWorks Technical Support Group (ps,wst)

Date this entry was last reviewed: May, 2003

Keywords: HyperMesh, tetra mesh, tria, tetramesh. tetras, check

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HyperWorks Tip/Trick 389Applications:Application version:Computer hardware:Computer operating systems:Categories: SubcategoriesTopic:Topic details:Pre tetra meshing checklist:Scenarios causing free element edges and / or T-connections:Tips for tetra meshing using HM:Annotated pre tetra meshing checklist:

Author:Date this entry was last reviewed:Keywords: