[Gmsh] Hybrid mesh and combine triangles in quadrilaterals
Christophe Geuzaine
cgeuzaine at ulg.ac.be
Fri Oct 24 19:22:56 CEST 2008
Fabian wrote:
> Hi,
>
> I just saw the geometry and wonder, if there is a chance to extrude the
sure: cf. attached file.
> surfaces and create a transfinite volume?
> It's probably not working due to more than six surfaces building the
> volumen!? Would be nice, if this would work, though...
>
> Fabian
>
> Christophe Geuzaine wrote:
>> 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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>>>
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>>
>>
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>
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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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