The mesh generated by Netgen is surface or volume?

About the development of the FEM module/workbench.

Moderator: bernd

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freecadlzh
Posts: 102
Joined: Fri Mar 06, 2020 12:52 pm

The mesh generated by Netgen is surface or volume?

Post by freecadlzh » Thu Aug 20, 2020 1:52 am

In Part I created a Sphere and a Cylinder. Then cut them by Part\Boolean operation. Then got a Custom geometry,looks like below:
2020-08-20_093157.png
2020-08-20_093157.png (131.63 KiB) Viewed 317 times
Then in FEM workbench,I clicked the "Fem mesh from shape by Netgen" button, and then got the Fem mesh. The mesh looks like above.

My questions is:
I need to dissect the cavity of the above custom model.Therefore, I think the most basic subdivision unit should be tetrahedron.
However, from the results of the dissection, I feel that only the surface of the model is dissected. The basic unit of the subdivision is triangle, and the cavity of the model is not dissected, and no tetrahedron is used.

I don't know if my guess is correct?

If is correct. How to divide the cavity of the model by tetrahedron (or other body elements)?
keithsloan52
Posts: 1450
Joined: Mon Feb 27, 2012 5:31 pm

Re: The mesh generated by Netgen is surface or volume?

Post by keithsloan52 » Sat Aug 22, 2020 11:43 am

My GDML workbench https://github.com/KeithSloan has an option to create 3D Tetrahedron Mesh using Gmsh.

It creates a GDML object, but you can then use another option to create a FreeCAD mesh from a GDML Mesh.

These are the two related icons.
TetraIcons.png
TetraIcons.png (20.25 KiB) Viewed 236 times
Just select a FreeCAD object and use the right hand icon to create a GDML Tetrahedron, then select it and use the icon on the left to create a FreeCAD mesh from the GDML Mesh

See example below
3D Tetrahedron.png
3D Tetrahedron.png (66.62 KiB) Viewed 236 times
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bernd
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Location: Zürich, Switzerland

Re: The mesh generated by Netgen is surface or volume?

Post by bernd » Mon Aug 24, 2020 4:36 am

netgen FEM mesher does second order volume tetrahedrons. In standard view it is disabled to show them for performence reasons. right click on fem mesh object and shows info shows mesh information. Furthermore the inner mesh elements can be shown change the view psrameter show inner to true.
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