[Gmsh] Multilevel mesh partition element interface quality

[Christophe Geuzaine]

Hi Andre - Could you try again with a recent build and tell us if things improved?

Thanks,

Christophe

On 31 Oct 2012, at 06:18, Andre Nicolle <andre at cfdandip.co.uk> wrote:

> Dear gmsh user group
> 
> I have been struggling with meshing a stl file of a human mesh. The stl surface is in good shape with a closed surface which when loaded into gmsh and meshed using the procedure outlined in https://geuz.org/trac/gmsh/wiki/STLRemeshing forms a three-dimensional mesh. Unfortunately the tetrahedron element quality is very poor. On further investigation we found that this was caused by poor quality elements on the 2D surface after the surface was remeshed. We tried using  Mesh.Algorithm: 1 = MeshAdapt, 2=Automatic, 5=Delaunay, 6=Frontal and found that in general Frontal gave us the best elements which were all very good quality except on the interface between the multilevel mesh partitions.  Information on the partition stage of 2-D meshing is given below.
> 
> Attached is a picture showing the line-up of poor quality elements around the waist of the human. Nearly all the other 2-D triangular elements have a mesh quality indicator gamma > 0.5, however elements on theinterface have gamma approximately 0.03 which we believe is where the 3-D mesh problem is starting from.
> 
> Could somebody give us some advice on how best to solve this problem as I imagine it is a mistake on our implementation. If further information is required please let me know what would be helpful to diagnose the problem.
> 
> Any help would be gratefully received
> 
> Andre
> 
> gmsh version 2.6.1
> 
> Info    : Meshing surface 200 (Compound surface, MeshAdapt)
> Warning : Wrong topology: Genus=0, Nb boundaries=0, AR=1
> Info    : -----------------------------------------------------------
> Info    : --- Split surface 200 in 2 parts with Multilevel Mesh partitioner
> Info    : Building graph...
> Info    : Partitioning graph...
> Info    : Launching Chaco graph partitioner
> Info    : Done partitioning graph
> Info    : *** Mesh partition: level (1-0) is ZERO-GENUS (AR=5, NB=1)
> Info    : *** Mesh partition: level (1-1) is ZERO-GENUS (AR=4, NB=1)
> Info    : Multiscale Partition SUCCESSFULLY PERFORMED : 2 parts (3.26 s)
> Info    : *** Starting parametrize compounds:
> Info    : Parametrize Compound Line (2) = 1 discrete edge
> Info    : Parametrize Compound Surface (203) = 201 discrete face
> Info    : Parametrizing surface 203 with 'convex map'
> 
> 
> Warning : Mesh generation error summary
> Warning :     1 warning
> Warning :     0 errors
> Warning : Check the full log for details
> 
> 
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine