[Gmsh] Illegal tets message

Christophe Geuzaine cgeuzaine at ulg.ac.be
Fri Jul 19 07:32:03 CEST 2013

On 18 Jul 2013, at 10:25, Steve Daley <stevedaley at sky.com> wrote:

> I am running GMSH to produce the tet mesh around a closed ended circular cylinder at 135 degrees angle of incidence to use in a CFD simulation.  I use a STL file to define the cylinder triangular surface. The outer boundary of the volume is a six faced box.
> GMSH produces a tet mesh around the scylinder inside the box but outputs a message  "NN illegal tets are still in the mesh" where NN is a number depending on the number of triangles in the STL file.  How does GMSH decide a tet is an "illegal tet" ?

If it's quality is low (0 <= gamma <= 0.1). You can check the detailed quality in Tools->Statistics. Applying both optimizers can help in that case (ours, and Netgen's: -optimize, -optimize_netgen)

> For other cases, GMSH also outputs the message "NN points could not be inserted". NN is again a number.  Is there any way to find out why there are problems with these points and where they are ?

That's just an informational message (for us); it has no impact on the quality/validity of the final mesh.

> For these, I can send you my STL and GEO files if that will help.
> Finally, because I'm trying CFD mesh generation cases, I'm trying to limit the volume of the mesh to say one half of the body as the problem has a plane of symmetry.  I'm trying to use the Compound Line to define the geometry edge profile where the profile may be made up of 100 points.  Is there any restriction on the number of points that can make up a compound line ?   Even though its only a cylinder, I need that number of points to get the tets near to the surface to be quite small to resolve the flow solution.
> Any help would be gratefully received.
> Many thanks
> Steve Daley
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Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 

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