[Gmsh] [PROBLEM] Elements normals
Christophe Geuzaine
cgeuzaine at ulg.ac.be
Thu Mar 12 20:52:08 CET 2009
Xavier Mencaglia wrote:
> Dear,
>
> I'm currently using the version 2.2.4 of GMSH to mesh a stp file which
> was created by Catia V5 R18.
> When I check the normals of the surfaces of the step file, they are well
> oriented.
> And then I mesh the step file (2D mesh - triangle elements only) and I
> check the normals of the elements. I can see some normals that were
> inverted during the meshing operations. So some normals remain stable,
> pointing in the same direction as the normals in the step file and some
> normals are inverted.
> It's a little bit problematic for me because I'm working with composites
> so I need to know and control the normals of the FE. The stacking
> sequence is strongly dependent on normals orientation especially if
> composites are not symmetric.
>
> So I have 2 questions about that:
>
> 1/ Is this problem well known and is it linked to the way the mesh is
> performed ?
> 2/ If this situation is normal, could you explain me why some normals
> are inverted ? What is the rule that pilots this mechanism ?
Hi Xavier - The situation is (sort of) "normal". We make sure to orient
the normals correctly for Gmsh models, but could not figure out a nice
way to do it with OpenCascade models, due to the fact that the
orientation of the bounding edges of a surface in OCC do not seem to
match the orientation of the surface.
The routine that performs the reorientation is
void orientMeshGFace::operator()(GFace *gf)
at the end of Mesh/meshGFace.cpp.
Let us know if you have any ideas on how to fix this: it is indeed a
annoying problem...
Christophe
>
> Thanks in advance for your answer,
>
> Kind regards,
>
--
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine