[Gmsh] Remeshing with GMesh in 2D

[Dr. Stephan Schmidt]

Am 30.04.2016 um 09:55 schrieb Christophe Geuzaine <cgeuzaine at ulg.ac.be>:
> 
>> 
>> On 29 Apr 2016, at 17:57, Dr. Stephan Schmidt <stephan.schmidt at mathematik.uni-wuerzburg.de <mailto:stephan.schmidt at mathematik.uni-wuerzburg.de>> wrote:
>> 
>> Dear Prof. Geuzaine,
>> 
>> many thanks for the feedback! I have tried to use exactly the same procedure, but gmsh simply crashes without an error message when I try to e.g. refine the remeshed mesh.
>> 
>> Attached is a very minimal working example: „channel_orig.msh“ is the original mesh created by gmsh itself. It appears to be valid in all regards, my flow solver works flawlessly on this. „Remesh_channel.geo“ is the file I actually open for remeshing and I manage to remesh the geometry successfully.
>> 
>> But whenever I try to refine the rather coarse remeshed cannel using the gui, gmsh crashes without throwing any error messages and I am stuck on how to make a finer mesh. I am using the following build and version of gmsh:
>> 
> 
> Can you try with a recent nightly build? It works fine on my machine.

I tried again today with the latest nightly build:
Info    : -------------------------------------------------------
Info    : Gmsh version   : 2.12.1-svn
Info    : Build OS       : MacOSX
Info    : Build options  : Ann Bamg Bfgs Blas(Custom) Blossom Chaco DIntegration Dlopen Fltk Gmm Jpeg(Fltk) Kbipack Lapack(Custom) MathEx Med Mesh Metis Mmg3d Mpeg NativeFileChooser Netgen ONELAB ONELABMetamodel OpenCascade OpenGL OptHom PETSc Parser Plugins Png(Fltk) Post SLEPc Salome Solver Taucs TetGen/BR Tetgen1.5 Voro3D Zlib
Info    : Build date     : 20160502
Info    : Build host     : Christophes-Mac.local
Info    : Packager       : geuzaine
Info    : Executable     : /Applications/Gmsh.app/Contents/MacOS/gmsh

and still, gmsh crashes without an error message (segfault?) if I try to do „refine by splitting“ on the remeshed geometry I get from running „Remesh_Hole.geo“. Maybe it is OSX Gui specific?



I also have crashes without error messages (even in the nightly build) if the .msh files contains disjoint geometries of the same physical marker, that is a planar graph with 4 end points = two graphs with two end points each but of the same physical attribute number:
If the upper and lower wall of the channel are both exported to the .msh file using elm-type 1 with attribute „5“ to denote no-slip walls, for example
$Elements
...
9373 1 2 5 5 185 186
...
$EndElements

then gmsh crashes without error (segfault?) while doing the CreateTopology step. See attached files, test_5.msh contains this situation (upper and lower wall = two lines with attributes 5 5), where as test_234.msh is the same file without those 2-Point line elements. The crash does not happen if the upper and lower channel walls have separate attributes, e.g.
51 51
for upper
52 52
for lower.

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