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# Meshing a domain with singular points

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### Meshing a domain with singular points

Posted by ABBALLE Thomas at September 08. 2009

Good morning board!

I have a problem meshing my domain, and I would like to ask for help.

My domain is made by  cutting a sphere from a cube. In most of cases, it'is quite simple, but here the sphere is tangent to the cube, (cf attachment) so there is a singular point (the tangent point) and I can't find a way to mesh my domain.

When I compute my mesh using BLSURF and GHS3D, SALOME gives me the error message "One boundary point lies within a surface face".

To solve this I would like to force my mesh to use the singular point as a node, but I can't find how to do this. Does anyone have a solution?

Thanks

Thomas ABBALLE

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### Re: Meshing a domain with singular points

Posted by DAVID Gilles at September 08. 2009

Hello Thomas,

In your case, one solution is to make a partition of your geometry with a "cross" (see joined picture) on the top face.
This will force the surfacic mesh to pass through the tangent point. Then GHS3D will be happy because there will be no node on a surface face.
The drawback is that it forces the mesh to pass through the newly created edges as well.

With this solution the mesh has 2450 triangles and 22056 tetra (no hypothesis for GHS3D and geometric mesh for BlSurf).

The next version of Salome (5.1.3) shouldl allow you to tell BlSurf to pass through a point. In this case the partition operation won't be needed anymore, but it will be necessary to merge coincident nodes (one from the sphere, one from the 'pass through point' hypothesis).

With this solution I obtained a mesh with 1690 triangles and 15891 tetras (no hypothesis for GHS3D and geometric mesh for BlSurf).

You can retrieve the 2 meshes as MED files at this adress: http://dl.free.fr/pOyaqh41p

Regards,
Gilles

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### Re: Meshing a domain with singular points

Posted by ABBALLE Thomas at September 09. 2009

Hello Gilles,

I have got a question: will Salome 5.1.3 able to pass through a set of points? The example I proposed here is juste a test case, and my real cases might have more than one singular points.

In the meantime, I will use the "cross" idea to suit my problems.

Cheers,

Thomas

### Re: Meshing a domain with singular points

Posted by DAVID Gilles at September 09. 2009

About 5.1.3, yes it will be possible to tell BlSurf to pass through a set of points. It will be the case for Ghs3d as well

Regards,

Gilles