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Meshing faces - A beginner's question

Posted Mar 24, 2018, 2:05 p.m. EDT Mesh Version 5.3a 4 Replies

Nabs
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Hi everyone, apologies if this may seem trivial but I've been struggling to create a separate mesh for separate faces in my model.

The geometry is a simple I-beam of length 4m but thicknesses of 6.7mm and 11.8mm along the web and flanges respectively, created from extruding the cross section. Clearly a much finer mesh is required for the faces with comparatively smaller thicknesses than the span, however whatever I try, when selecting the domain for the mesh it just selects the entire geometry. Tried to use domain partitioning via faces and mesh control faces but this did not do the trick. This probably has a really simple answer which I'll be banging my head over but would really appreciate some help here.

Thanks!

4 Replies Last Post Apr 3, 2018, 7:13 a.m. EDT
Erik Bornhöft COMSOL Employee

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Posted: 6 years ago Mar 28, 2018, 6:04 a.m. EDT

Hi Nabs,

have a look at the meshing tutorials found in "File->Application Libraries->Comsol Multiphysics->Meshing Tutorials"

In your meshing sequence you can add "size" subnodes to your element type node (e.g. "Free Tetrahedral") and select "Geometric Entity: Boundary" and then define different mesh size settings for selected boundaries . That way it will mesh the domain with Tetrahedrals but will consider your mesh size settings on the selected boundaries in your "size" nodes.

For regular geometries as yours you could also consider the option "swept" as mesh type. This will create hexahedrons or prisms. The faces on both sides will have the same number of elements though.

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Best regards,
Erik

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Erik Bornhöft
COMSOL Germany
Hi Nabs, have a look at the meshing tutorials found in "File->Application Libraries->Comsol Multiphysics->Meshing Tutorials" In your meshing sequence you can add "size" subnodes to your element type node (e.g. "Free Tetrahedral") and select "Geometric Entity: Boundary" and then define different mesh size settings for selected boundaries . That way it will mesh the domain with Tetrahedrals but will consider your mesh size settings on the selected boundaries in your "size" nodes. For regular geometries as yours you could also consider the option "swept" as mesh type. This will create hexahedrons or prisms. The faces on both sides will have the same number of elements though.
Nabs
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Posted: 6 years ago Mar 28, 2018, 10:16 a.m. EDT

Hi Erik,

Thanks for the response, helped me realise that I could add a Size node to Free Tetrahedral then select individual faces to mesh. I have assigned a much finer mesh to the thin faces around the I-beam compared to a 'Normal' mesh on the remaining faces, however a warning appears stating "Domain has a region that is much thinner than the specified minimum element size." even though the minimum element size for the fine mesh is smaller than the thicknesses. Any idea what could be wrong? I'll attach the file if you feel like having a look, would be grateful!

Thanks

Hi Erik, Thanks for the response, helped me realise that I could add a Size node to Free Tetrahedral then select individual faces to mesh. I have assigned a much finer mesh to the thin faces around the I-beam compared to a 'Normal' mesh on the remaining faces, however a warning appears stating "Domain has a region that is much thinner than the specified minimum element size." even though the minimum element size for the fine mesh is smaller than the thicknesses. Any idea what could be wrong? I'll attach the file if you feel like having a look, would be grateful! Thanks

Attachments:

Erik Bornhöft COMSOL Employee

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Posted: 6 years ago Apr 3, 2018, 5:58 a.m. EDT

Maybe you set only the minimum size for surfaces but not in the size node for the domain itself? Don't worry though: the domain will still be meshed, it is only a warning message saying the actually used minimum size for the tetrahedrals had to fall below the set minimum size in the domain size node to make it work.

-------------------
Best regards,
Erik

*********************
Erik Bornhöft
COMSOL Germany
Maybe you set only the minimum size for surfaces but not in the size node for the domain itself? Don't worry though: the domain will still be meshed, it is only a warning message saying the actually used minimum size for the tetrahedrals had to fall below the set minimum size in the domain size node to make it work.
Nabs
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Posted: 6 years ago Apr 3, 2018, 7:13 a.m. EDT

If I input custom minimum element size to the original Size node under Mesh 1 then it creates the same mesh around the entire geometry. It should be fine I think, the free tetrahedral mesh with two different sizes looks ok.

If I input custom minimum element size to the original Size node under Mesh 1 then it creates the same mesh around the entire geometry. It should be fine I think, the free tetrahedral mesh with two different sizes looks ok.

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