Mesh shows a diagonal when none exists

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markinca
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Mesh shows a diagonal when none exists

Post by markinca »

When showing a CFD mesh within FreeCAD (CfdOF), there appears to be a diagonal across the mesh cell when in fact, one does not actually exist. Paraview shows no diagonal.

Why does FreeCAD show this and is there a way to disable this?

First pic is FreeCAD, second is Paraview.
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NewJoker
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Re: Mesh shows a diagonal when none exists

Post by NewJoker »

You won’t get more information regarding CfdOF here, posts about FEM/CFD are moved to their subforums anyway. So let’s keep the discussion there: viewtopic.php?p=684158#p684158
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markinca
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Re: Mesh shows a diagonal when none exists

Post by markinca »

Is CfdOF or FreeCAD rendering the view? I had assumed it was FreeCAD.
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NewJoker
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Re: Mesh shows a diagonal when none exists

Post by NewJoker »

Pretty much the only person that can help with that is the dev of CfdOF workbench. Other developers, active on this forum, most likely won’t be able to help with that.
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saso
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Re: Mesh shows a diagonal when none exists

Post by saso »

If I am not mistaken the issue is how FC opens/imports the mesh, it actually does not directly opens the original mesh as it was created in this case by snappyHexMesh and as its is also used by the solver, but on opening/importing the mesh in FC it actually gets changed by the import that I guess is done by SMESH, so this is not just a visual thing... Hopefully someone can correct me if I am wrong :|
jeno
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Re: Mesh shows a diagonal when none exists

Post by jeno »

markinca wrote: Thu May 25, 2023 7:36 pm When showing a CFD mesh within FreeCAD (CfdOF), there appears to be a diagonal across the mesh cell when in fact, one does not actually exist.
For me it looks like they exist. If you take a closer look you will see that Paraview surpress the visual representation of edges (yellow marks).
paraview.png
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Seems not consistent for me. It shows sometimes tris (orange circle as example) and a lot of quads. But I assume the mesh topology is all tri.
So it is a question who - FC or Paraview - is wrong.

cheers
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NewJoker
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Re: Mesh shows a diagonal when none exists

Post by NewJoker »

Those triangles are likely faces of wedge elements. There shouldn’t be tetrahedrons in this mesh. FreeCAD displays the surface mesh with triangles only even though the FEM workbench can display quads as well.
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markinca
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Re: Mesh shows a diagonal when none exists

Post by markinca »

Both snappyHexMesh and cfMesh are supposed to be generating Hex-Dominant meshes so Paraview should be the correct one as that is a cfMesh version. The snappyHexMesh is similar and has the same diagonals in FreeCAD that should not be there.
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oliveroxtoby
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Re: Mesh shows a diagonal when none exists

Post by oliveroxtoby »

The paraview display is the correct one. CfdOF imports only the surface of the mesh as a visual aid and unfortunately the utility used to extract the surface mesh also triangulates it.

The message displayed in the status window when the surface mesh is loaded: "Triangulated representation of the surface mesh is shown - Please view in Paraview for accurate display. " was intended to clear up such confusion.
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markinca
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Re: Mesh shows a diagonal when none exists

Post by markinca »

Thanks for clearing this up.

I take it there is no way to disable the triangulation during the mesh import?
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