[Gmsh] meshing partitions

Hansjoerg Seybold hansjoerg at fisica.ufc.br
Mon May 11 16:32:48 CEST 2020

Thanks a lot for the reply. Using the visibility filter worked. I
created a simple test case (attached)
which creates the two mesh pieces. So now I have two meshes
multizone_1.msh and multizone_2.msh
which I can load in a geo file
Merge "multizone_1.msh";
Merge "multizone_2.msh";
Coherence Mesh;
Save "multizone_merged.msh";
Save "multizone_merged.bdf";
I understood that the coherence mesh removes the duplicate nodes on
the common edge and the above
script displays the mesh in the gui correctly.
However the export is distorted as the node ordering is not updated.
I would get the development snapshot to try to use the mesh tag
suggestion, but how would I do the reordering
starting from the script above?

regarding openmp:

We (the IT cluster staff at ETH Zurich and myself) tried to get the
openmp version of gmsh running on the cluster (CentOS 6), but without
I managed to compile and run it on my ubuntu PC, but with very little
speedup for the selected meshing algorithm.
I tested openmp with two physical groups active and -nt 2, on a finer
LC as in the attached geo for speed measurements and Mesh.Algorithm =
9; gmsh-4.4.1,
a significant speedup could only be observed for del2d, but quality
tests showed that the 'pack' algorithm gave the best meshing result
BTW, is it possible to apply different meshing algorithms to different
physical groups?

Regarding the 5 days meshing: I am using quad meshing (algo 9) with a
not too sophisticated sizing function but with a very large domain,
del2d is orders
of magnitudes faster.

Thanks a lot for the help.


On Sun, May 10, 2020 at 9:05 AM Christophe Geuzaine <cgeuzaine at uliege.be> wrote:
> > On 9 May 2020, at 18:09, Hansjoerg Seybold <hansjoerg at fisica.ufc.br> wrote:
> >
> > Hello,
> > I am trying to mesh a model consisting of several physical groups each
> > group at a time and then merge the meshes for the different physical
> > groups afterwards. The reason why I am trying to perform this "domain
> > decomposition" is that the meshing of the full model takes over 5 days
> > and exceeds the runtime limit of the queuing system.
> >
> > However I could not find a simple way to apply the  "Mesh 2" to a
> > specific physical group. Gmsh always tries to mesh the whole model.
> >
> You could either delete the parts you don't want to mesh; or hide the parts you don't want to mesh (cf. the `Show` and `Hide` commands in .geo script, or `setVisibility()` in the api) and use the `Mesh.MeshOnlyVisible` option.
> > My question would be if anybody has a hint how to perform this meshing
> > in parts and how to combine the resulting meshes into a single final
> > model.
> >
> That's trickier as each mesh will be independent. The development snapshot allows you to set the starting node/element tag (Mesh.FirstNodeTag, Mesh.FirstElementTag), which will help. Removing duplicate nodes when you merge things together can be done with Coherence Mesh (in .geo files) or removeDuplicateNodes() in the api.
> PS: 5 days to perform a 2D mesh ? Anything special in the geometry/size field? If you don't do this already at least recompile Gmsh with OpenMP enabled, and mesh in parallel?
> Christophe
> > Thank you very much.
> >
> > Best,
> > hansjoerg
> >
> > _______________________________________________
> > gmsh mailing list
> > gmsh at onelab.info
> > http://onelab.info/mailman/listinfo/gmsh
>> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
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