[Gmsh] detect negative jacobians

[Christophe Geuzaine]

> On 24 Mar 2016, at 12:27, Bernd Hahnebach <gmsh at b75.ch> wrote:
> 
> Hi GMSH users and developers,
> 
> Is it possible to check a mesh in gmsh in the regard of negative jacobians? If yes, is it possible to show such elements in gmsh gui? 

Yes (see attached picture):

- Load your mesh
- Open Tools->Plugins->AnalyzeCurvedMesh
- Select "0" in the first option (to compute the Jacobian determinant J and plot min(J))

To accurately visualize the curved grid (and post-processing dataset):

- Select "Adapt visualization grid" in the view options ("General" tab)
- Increase the "High-order element subdvisions" in the mesh options ("Aspect" tab)

This can all be scripted of course.

The calculation method is described in the following paper:

Johnen, A., Remacle, J. F., & Geuzaine, C. (2013). Geometrical validity of curvilinear finite elements. Journal of Computational Physics, 233, 359-372. http://gmsh.info/doc/preprints/gmsh_curved_preprint.pdf

Christophe




> Attached a mesh wich has negative jacobians to test with.
> 
> mesh: Shape_mesh_negative_jacobian.unv.zip (remove .zip)
> http://forum.freecadweb.org/download/file.php?id=21583&sid=a7b68cea7fa02126487316248b875c2d
> 
> 
> What is the recommended way to avoid such negative jacobians? Attached the geometry of the mesh above.
> 
> geometry: Shape.brep
> http://forum.freecadweb.org/download/file.php?id=21588
> 
> 
> kind regards bernd
> 
> 
> 
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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

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