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Combining Extrusion 3D, Netgen 3D, and Viscous Layers.

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Combining Extrusion 3D, Netgen 3D, and Viscous Layers.

Posted by Carl Birger Jenssen at April 23. 2019

Hello,

I am trying to generate a mesh for a pipe network with a combination of Extrusion 3D and Netgen 3D, together with Viscous Layers. I have managed to do this for simple cases, but for more complex cases I just cannot make it work.

The aim is to use unstructured meshing in complex regions combined with extrusion and high aspect ratio cells in long pipes.

For simple test cases, depending on the order of the sub-meshes in the meshing process it sometimes works, and sometimes not. The problem is that the boundary layer mesh is not continuous between the between the Extrusion 3D and Netgen 3D regions. Other times the mesh generation fails with the error message: "Invalid input mesh. Intersecting triangles". I struggle to understand the logic, and to find a procedure that will always work even for a simple test case. For the real life pipe network I don't manage at all.

Is there a way to do this in a foolproof manner, and is this indeed supposed to be possible? Anyone who has experience with something similar?

Every suggestion will be appreciated

Carl B.

Re: Combining Extrusion 3D, Netgen 3D, and Viscous Layers.

Posted by Saint Michael at April 23. 2019

Hi

Can you share simple test cases that do not work?

St.Michael

Re: Combining Extrusion 3D, Netgen 3D, and Viscous Layers.

Posted by Carl Birger Jenssen at April 23. 2019

Yes I can.

 

Here I have enclosed a Python dump of the study.

 

If you clip the mesh in the zx-plane you will see the problem.

 

Carl B.
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Re: Combining Extrusion 3D, Netgen 3D, and Viscous Layers.

Posted by Saint Michael at April 23. 2019

Hi Carl,

This is strange that setting sub-mesh priority does not work.

To have meshing working here, it is necessary that unstructured sub-mesh to be computed before Extrusion 3D. It works OK if I compute sub-meshes T1 and T2 separately in GUI (via "Compute Sub-mesh" in contextual menu) and then compute the hole mesh.

To avoid computing every sub-mesh manually, you can prevent computing Extrusion before unstructured sub-meshes by assigning Extrusion 3D algo after computing unstructured sub-meshes. I.e. first you create unstructured sub-meshes and compute the mesh, then assign Extrusion 3D algo and compute the mesh again.

Note that you can face failure of Extrusion 3D if base faces of a cylindrical part are differently meshed. In this case a reported error looks like "Mesh on faces #38 and #25 seems different".

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St.Michael

Re: Combining Extrusion 3D, Netgen 3D, and Viscous Layers.

Posted by Carl Birger Jenssen at April 24. 2019

Hi St. Michael,

Thank you very much for the prompt and informative answer.

I follow your procedure, and it almost works now for the real-life pipe network, but unfortunately there is still a problem related to the boundary layer mesh that I am working on. Hopefully I can sort this out and post a summary for future reference.

Carl B.

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