[Gmsh] gmsh-2.5.1: 2D unstructured mixed triangle-quadrangle problem (recombine+angle)

[Christophe Geuzaine]

On 01 Nov 2011, at 15:02, Pierre Saramito wrote:

> Hi everybody,
> 
> I'm trying to generate an unstructured mixed triangle-quadrangle
> 2D meshes with gmsh. It works well until gmsh-2.5.0 but I have
> a problem with the new gmsh-2.5.1 : the mesh contains only quadrangles.
> 
> I first generate a triangular use the "Recombine" operator with the
> optional angle argument :
> // from the gmsh documentation (parag. 6.3.3):
> Recombine Surface { expression-list } | "*" < = expression >;
>    Recombines the triangular meshes of the surfaces listed in 
>    expression-list into mixed triangular/quadrangular meshes.
>    The optional expression on the right hand side specifies the
>    maximum difference (in degrees) allowed between the largest
>    angle of a quadrangle and a right angle (a value of 0 would only
>    accept quadrangles with right angles; a value of 90 would allow
>    degenerate quadrangles; default value is 45). 
> 
> In attachment: the test file. I have tried to change the
> "angle" value (0, 45, 90, etc), without any success with gmsh-2.5.1.
> 
> Thank you for any helps and/or comments,
> 
> Pierre
> 
> Note: this unstructured mixed mesh is used for testing a finite element
> library (rheolef), so I do not want a structured mixed mesh.
> 

Hi Pierre,

Indeed: with Gmsh 2.5.1 we introduce a new algorithm that by default generates fully quadrangular meshes ("blossom"). You can revert to the old algorithm with

Mesh.RecombinationAlgorithm = 0;

All the best,

Christophe


> -- 
> Pierre.Saramito at imag.fr
> Directeur de Recherche CNRS
> Laboratoire Jean Kuntzmann, Grenoble, France
> http://www-ljk.imag.fr/membres/Pierre.Saramito
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine