[Gmsh] Hybrid mesh and combine triangles in quadrilaterals

[Christophe Geuzaine]

Fabian wrote:
> Hi Christophe,
> 
> Christophe Geuzaine wrote:
>> Fabian wrote:
>>  
>>> Hi,
>>>
>>> I just saw the geometry and wonder, if there is a chance to extrude 
>>> the     
>>
>> sure: cf. attached file.
>>   
> Oh, thanks! Am I able to declare any progression or bump to the extrude 
> volume as well? Would be great.
> 

You can specify the number of elements and the relative height of each
extruded layer. For example:

Extrude {0, 0, 1} {
   Surface{9, 1};
   Layers{{1,1,1,1,1,1}, {0.05,0.15,0.5,0.85,0.95,1}};
   Recombine;
}

You could thus generate a progression with something like this:

n = 6;
r = 2;
a = (r - 1) / (r^n - 1);
one[0] = 1;
layer[0] = a;
For i In {1:n-1}
   one[i] = 1;
   layer[i] = layer[i-1] + a * r^i;
EndFor
Extrude {0, 0, 1} { Surface{9, 1}; Layers{one[], layer[]}; Recombine; }





> Fabian
> 
> 
>>  
>>> 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
>>>>>
>>>>>
>>>>>
>>>>> ------------------------------------------------------------------------ 
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> gmsh mailing list
>>>>> gmsh at geuz.org
>>>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>>>             
>>>>   
>>>> ------------------------------------------------------------------------ 
>>>>
>>>>
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>>>
>>>     
>>
>>
>>   
> 
> 
> 


-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine