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Missing tets along line when meshing with ICEM CFD

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Old   March 17, 2006, 14:46
Default Missing tets along line when meshing with ICEM CFD
  #1
Georges P. Côté
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Hi, I've been having intermittent trouble while meshing a solid model with ICEM.

I am meshing a cyclic portion of a turbine with 3D tets. The solid model is defined by a "solid point" inside the surfaces.

I generate a mesh, using the function 'Mesh Volume by geometry'. When meshing is done, often there are missing elements along some edges. And it happens whether or not the line mesh size/global mesh size is fine or coarse.

Suppose a cube with a side measuring 100. The mesh can be as fine as 5 (so ~20 nodes per cube edge), but in the middle of one edge there can be a missing element.

I just don't understand. This problem is intermittent, and meshing twice from the same parameters will or wont generate missing chunks.

Is there anyone who has had this problem before? Maybe I am doing something wrong, but this has never really happened with others meshing programs, such as Ansys or IDEAS.

Thanks for helping, Georges
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Old   March 18, 2006, 02:38
Default Re: Missing tets along line when meshing with ICEM
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TB
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Have you defined a curve to describe that problematic edge?

It will also be useful to tell which version of ICEM you're using.
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Old   March 18, 2006, 05:30
Default Re: Missing tets along line when meshing with ICEM
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Chebeba
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In my experience the way to get around that is to start with a surface mesh (Mesh > Surface Meshing > Patch Based), and then run the volume mesher "From Surface Mesh".

This way you also have way more control over the end result.

(Use Mesh > Set Surface Mesh Size to assign sizes to all or individual surfaces)

/C
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Old   March 18, 2006, 14:15
Default Re: Missing tets along line when meshing with ICEM
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Jeff
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The first step in creating a mesh is ALWAYS to go Repair Geometry and use Create Topology. This creates explicite curves on all your edges.

If you don't do this, ICEM will not force element edges/nodes along the sharp geometric edges. It will instead try to wrap elements around the corner. Sometimes they'll line up, sometimes they won't.

Under Create Topology, you can also set a minimum angle on which to create the edges. If you bump this up a bit from the default (30 I think?) you won't get too many extra edges in the place you don't want them.

Jeff
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Old   March 20, 2006, 11:31
Default Re: Missing tets along line when meshing with ICEM
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Georges P. Côté
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Yes, all curves are described.

I am using AI*Environment 10.
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Old   March 20, 2006, 11:59
Default Re: Missing tets along line when meshing with ICEM
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Georges P. Côté
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Thanks Jeff. I used to repair the model's topology when creating the solid prior to meshing. I thought this insured me (and it did) that the model didn't have a hole.

Then, being confident that the imported model was always properly imported (from Catia V5, through Ansys Workbench 10), I stopped using Repair Topology and used a solid point placed inside the model, instead of creating a true solid. A collegue told me that it was best to have a minimum of manipulations between the geometric model and it's mesh. But I'll try to use Repair Topology. I'll keep you updated.

Just to be sure... every edge of my model is properly defined as a line, when I display lines only. Does build topology only create new lines (with surface matching and such), or does it define new internal parameters?

Thanks a lot! Georges

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Old   March 23, 2006, 01:34
Default Re: Missing tets along line when meshing with ICEM
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kake
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Maybe you need a patch if you are using 10.0
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