[Gmsh] Hybrid mesh and combine triangles in quadrilaterals

[Christophe Geuzaine]

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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> 
> 
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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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