[Gmsh] detect negative jacobians

[Christophe Geuzaine]

> On 30 Mar 2016, at 07:30, Bernd Hahnebach <gmsh at b75.ch> wrote:
> 
> Thanks Christophe!
> 
> I got the problem of the high order meshes by reading a big part of the paper. :-) :-)  Is there any user documentation or an example how to use the HighOrderTools around?
> 
> Just to get it the right way done. How does it work in the gui?
> 

1) Load the geometry
2) Mesh (e.g. press "3" to do a 3D mesh)
3) Open "High order tools"
   - Choose the polynomial order and press "Generate" (this will create high order elements)
   - Press "Regularize" (this will optimize the high order elements)


> - Load the geometry (in my case a BRep)
> - make the adjustments on Tools --> Options --> Geometry and Mesh --> one of them is 2nd order mesh
> - In GMSH Tree press Mesh 1D, 2D, 3D
> - on 3D I get negative Jacobians if the mesh order in options is set to two
> - do not use any optimization, do not use the order buttons (mesh is 2nd order already)
> - open HighOrderTools
> - Generate 2nd order vertices
> - Regularize with given values
> 
> - Or do I have to start with a 1st order mesh and use Generate 2nd order vertices on a 1st order mesh?
> - Should any of the optimizations be done before the HighOrderTools?
> 
> kind regards bernd
> 
> 
> Zitat von Christophe Geuzaine <cgeuzaine at ulg.ac.be>:
> 
>> 
>>> On 24 Mar 2016, at 19:06, Christophe Geuzaine <cgeuzaine at ulg.ac.be> wrote:
>>> 
>>>> 
>>>> On 24 Mar 2016, at 12:27, Bernd Hahnebach <gmsh at b75.ch> wrote:
>>>> 
>>>> 
>>>> What is the recommended way to avoid such negative jacobians? Attached the geometry of the mesh above.
>>>> 
>> 
>> And to avoid such negative jacobians, you can use the "High order tools" (in the Mesh menu). This is still experimental, but works quite well. The algorithms are described (in part) in
>> 
>> T. Toulorge, C. Geuzaine, J.-F. Remacle, J. Lambrechts. Robust untangling of curvilinear meshes. Journal of Computational Physics 254, pp. 8-26, 2013. http://gmsh.info/doc/preprints/gmsh_untangling_preprint.pdf
>> 
>> Christophe
>> 
>> 
>> --
>> 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
>> 
>> 
>> 
> 
> 
> 
> 
> 
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-- 
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