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[mesh manipulation] How to convert tetrahedral to polyhedral mesh in OpenFOAM

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Old   July 12, 2020, 22:09
Default How to convert tetrahedral to polyhedral mesh in OpenFOAM
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Nguyen Duy Trong
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Hi everyone,

Hope you are fine and doing well.

I am trying to convert tetrahedral mesh to polyhedral mesh using polyDualMesh utility in OpenFOAM at:
https://openfoamwiki.net/index.php/P...esh_generation

I can work until step 4, but for the steps 5 and 6, there are some options in commands and I do not know how to use it correctly.
Could someone please help me to clear the command in steps 5 and 6.
My mesh now is as below.
Thank you in advance.
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File Type: jpg meshconvert.jpg (183.5 KB, 13 views)
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Old   July 13, 2020, 07:17
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What are you trying to achieve? Convert a 3D tet-mesh into a 3D polyhedral mesh, or converting a 2D triangular mesh into a 2D polyhedral mesh.

Note, that the page you linked to was last modified in 2011. Things might be a little bit different now. The page you linked to, seems to be specifically about 2D meshes.

For a 3D mesh, I use the following steps:
  • import a tet mesh, e.g. ideasUNVToFoam
  • run polyDualMesh to create a polyhedral mesh
  • run combinePatchFaces to clean up the mesh

See the attached images for each step.
Attached Images
File Type: jpg cylinder.jpg (53.0 KB, 13 views)
File Type: jpg polyhedralMesh.jpg (47.2 KB, 12 views)
File Type: jpg combineFaces.jpg (46.0 KB, 14 views)
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Old   July 13, 2020, 09:10
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Quote:
Originally Posted by GerhardHolzinger View Post
What are you trying to achieve? Convert a 3D tet-mesh into a 3D polyhedral mesh, or converting a 2D triangular mesh into a 2D polyhedral mesh.



Note, that the page you linked to was last modified in 2011. Things might be a little bit different now. The page you linked to, seems to be specifically about 2D meshes.



For a 3D mesh, I use the following steps:


  • import a tet mesh, e.g. ideasUNVToFoam
  • run polyDualMesh to create a polyhedral mesh
  • run combinePatchFaces to clean up the mesh



See the attached images for each step.


Hi,

Thanks for your comment
I am trying to convert 2D tetra to 2D polyhedral.
I understand that there are some modifications in that link then I do not know how to work correctly with that.
Could you please share with me some hints with setSet and subsetMesh. I really donít understand it well.
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Old   July 14, 2020, 03:12
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Gerhard Holzinger
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For a 2D mesh, I would recommend the following approach:
  • Convert the 2D triangular mesh into a polyhedral mesh *
  • Extrude one cell layer from the front or back patch, discard the initial mesh


* Note: OpenFOAM only deals with 3D meshes, even in 2D cases. In a 2D case, the mesh is one cell in thickness. Thus, a triangular 2D mesh is in reality a prismatic mesh, with cells having a triangular base.

See the attached images for some snapshots of the process.
Attached Images
File Type: jpg elbowPolyDualMesh.jpg (63.3 KB, 14 views)
File Type: jpg elbowPolyExtruded.jpg (69.6 KB, 14 views)
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Old   July 14, 2020, 04:11
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Quote:
Originally Posted by GerhardHolzinger View Post
For a 2D mesh, I would recommend the following approach:
  • Convert the 2D triangular mesh into a polyhedral mesh *
  • Extrude one cell layer from the front or back patch, discard the initial mesh


* Note: OpenFOAM only deals with 3D meshes, even in 2D cases. In a 2D case, the mesh is one cell in thickness. Thus, a triangular 2D mesh is in reality a prismatic mesh, with cells having a triangular base.

See the attached images for some snapshots of the process.
Thanks for your guidance,

Yes, I have already converted 2D triangular mesh into polyhedral mesh with step 2+3 as in tutorial and my mesh now has 2 layers as your 1st figure (please see the attachement).
However, I do not know how to extrude one cell layer from the front or back as you said and how to discard the initial mesh
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File Type: jpg meshconvert_02.jpg (141.1 KB, 10 views)
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Old   July 16, 2020, 06:35
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Quote:
Originally Posted by GerhardHolzinger View Post
For a 2D mesh, I would recommend the following approach:
  • Convert the 2D triangular mesh into a polyhedral mesh *
  • Extrude one cell layer from the front or back patch, discard the initial mesh


* Note: OpenFOAM only deals with 3D meshes, even in 2D cases. In a 2D case, the mesh is one cell in thickness. Thus, a triangular 2D mesh is in reality a prismatic mesh, with cells having a triangular base.

See the attached images for some snapshots of the process.
Hi,

I can make both front and back are polyhedral cell mesh but I do not know why my internalMesh is strange like this.

Could you please help me to explain it.
Attached Images
File Type: jpg back.jpg (88.1 KB, 11 views)
File Type: jpg front.jpg (87.9 KB, 8 views)
File Type: jpg internalMesh.jpg (118.7 KB, 9 views)
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Old   July 16, 2020, 16:01
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Quote:
Originally Posted by ndtrong View Post
Thanks for your guidance,

Yes, I have already converted 2D triangular mesh into polyhedral mesh with step 2+3 as in tutorial and my mesh now has 2 layers as your 1st figure (please see the attachement).
However, I do not know how to extrude one cell layer from the front or back as you said and how to discard the initial mesh



See the commented extrudeMeshDict of OpenFOAM, e.g. here https://github.com/OpenFOAM/OpenFOAM...xtrudeMeshDict


This should be rather self-explanatory.
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Old   July 16, 2020, 21:20
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Quote:
Originally Posted by GerhardHolzinger View Post
See the commented extrudeMeshDict of OpenFOAM, e.g. here https://github.com/OpenFOAM/OpenFOAM...xtrudeMeshDict


This should be rather self-explanatory.
Thank you so much for your suggestion with your link
The problem has been solved.
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