[Gmsh] Hybrid mesh and combine triangles in quadrilaterals
Christophe Geuzaine
cgeuzaine at ulg.ac.be
Wed Oct 22 21:07:54 CEST 2008
Durufle Marc wrote:
> Hi,
> I have two questions :
>
> 1- How do you create hybrid meshes in 2-D (quad-dominant with a few
> triangles) ?
> Until now, I am using the Recombine option, but often I get non-convex
> quadrilaterals.
> In the picture attached to this message, you can see that two elements
> (in black) are non-convex
> quads and that's a problem ... So, often I change the characterisc
> length in the hope that I will have only
> fine quadrilaterals. Is it possible to require that all quadrilaterals
> are convex ?
>
Yes. In your file you use
Recombine Surface {1,s0[0]} = 100;
which means that you allow quads with angles between 90-100 and 90+100
degrees (which does not make sense).
Use
Recombine Surface {1,s0[0]} = 45;
instead, which will allow angles between 90-45=45 and 90+45=135 degrees.
(45 is the default if you don't specify anything, i.e., with just
"Recombine Surface {1,s0[0]}".)
We are working on an automatic full quad algorithm, but it's not ready
yet. In the meantime for simple geometries you could also use
Transfinite meshes to generate a full quad mesh (see attached file).
> 2- In 3-D, when I try "Recombine Volume", it doesn't work. So, how is it
> possible with gmsh
> to create 3-D hexahedral-dominant meshes (with some tets, pyramids and
> wedges) ?
Non. Your only choices for generating hex/prism/pyramid meshes are
extruded (see "Extrude Surface") or transfinite (see "Transfinite
Volume") grids.
>
> Thank you for your help.
>
> PS : I am using gmsh 2.24
>
>
>
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--
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine
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