[Gmsh] Remeshing with GMesh in 2D

[Christophe Geuzaine]

> On 29 Apr 2016, at 17:57, Dr. Stephan Schmidt <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.


> Info    : -------------------------------------------------------
> Info    : Gmsh version   : 2.11.0
> 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 Tetgen(1.5) Voro3D Zlib
> Info    : Build date     : 20151107
> Info    : Build host     : Christophes-Mac.local
> Info    : Packager       : geuzaine
> Info    : Executable     : /Applications/Gmsh.app/Contents/MacOS/gmsh
> Info    : Home directory : /Users/schmidt/
> Info    : Launch date    : Fri Apr 29 17:47:49 2016
> Info    : Command line   : /Applications/Gmsh.app/Contents/MacOS/gmsh
> Info    : -------------------------------------------------------
> 
> I would be very thankful if you could kindly provide feedback with respect to this:
> 
> - How can I generate a finer mesh? Ideally, I would love to carry over the Delauney-weights associated with the original points into the remeshing information.

You can use any of the standard methods to define element sizes: global factor, fields (e.g. defined on a mesh), etc.

> - Does the remeshed mesh also contain the same physical boundaries as the original mesh or do I have to re-identify the different boundaries afterwards manually? I know from the .stl 3D example how to do this when each physical boundary is contained within its own 

Currently the "compounds" create new geometrical entities - you thus need to define the Physical entities using the new tags.

However, we are working on a new implementation of the remeshing tools for Gmsh 3.0, which will change the workflow: the "Compound" command will become a meshing constraint command, and will not create new entities.

Christophe

> .stl file, but I would much appreciate hints on how to match a compound quantity with a physical surface and consequently a boundary marker in the case here, where everything stems from a single .msh file.
> 
> Regards and many thanks,
> Stephan Schmidt
> 
> <channel_orig.msh>
> <Remesh_channel.geo>
> 
>> Am 28.04.2016 um 21:53 schrieb Christophe Geuzaine <cgeuzaine at ulg.ac.be>:
>> 
>>> 
>>> On 27 Apr 2016, at 01:49, Dr. Stephan Schmidt <stephan.schmidt at mathematik.uni-wuerzburg.de> wrote:
>>> 
>>> Dear all,
>>> 
>>> I am trying to use gmsh to remesh a 2D geometry.
>>> 
>>> So far, following the 3D examples (that is having a 2D stl surface as input to generate a 3D mesh) work fabulously just following the examples on compound surfaces, such as the one found here:
>>> http://people.sc.fsu.edu/~jburkardt/examples/gmsh/t13.geo
>>> 
>>> But for my problem, I would need to remesh a 2D geometry (that is having a non-overlapping planar graph in a .msh file as input) seeking a 2D triangle mesh as output with reparameterized boundary graphs.
>>> 
>>> Is there any way of doing this as elegantly as the above link does for surfaces?
>>> 
>> 
>> Sure, you can use the exact same procedure...
>> 
>> 
>>> Regards and many thanks,
>>> Stephan Schmidt
>>> _______________________________________________
>>> 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
>> 
>> Tetrahedron V, July 4-5 2016: http://tetrahedron.montefiore.ulg.ac.be
>> Free software: http://gmsh.info | http://getdp.info | http://onelab.info
> 
> _______________________________________________
> 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

Tetrahedron V, July 4-5 2016: http://tetrahedron.montefiore.ulg.ac.be
Free software: http://gmsh.info | http://getdp.info | http://onelab.info