[Gmsh] get mesh volume

[Christophe Geuzaine]

Hi Juan - Indeed, Gmsh does not guarantee that the Delaunay criterion is satisfied.

Christophe


> On 3 May 2018, at 22:00, Juan Sanchez <juan.e.sanchez at gmail.com> wrote:
> 
> Hello,
> 
> Does anyone know how to get gmsh to output a mesh, where all
> tetrahedra meet the Delaunay condition of having their circumcenter
> inside their volume?  For my example, it seems like this condition is
> not being met, even though I have tried these options:
> Mesh.OptimizeNetgen=1;
> Mesh.OptimizeThreshold=1;
> 
> Regards,
> 
> Juan
> 
> 
> On Tue, May 1, 2018 at 7:51 AM, Juan E. Sanchez
> <juan.e.sanchez at gmail.com> wrote:
>> Hello,
>> 
>> Thanks for the check, and the useful script.
>> 
>> Upon further analysis, the circumcenter of many of the tetrahedron are
>> outside their respective volumes.  This is where the additional volume is
>> coming from in my calculations.
>> 
>> This is affecting the results of the control volume method I am using, since
>> the total volume of the structure is not conserved.
>> 
>> Is there anything I can do to force the circumcenters to be inside of the
>> tetrahedron?
>> 
>> Regards,
>> 
>> Juan
>> 
>> 
>> 
>> On 5/1/18 2:01 AM, Christophe Geuzaine wrote:
>>> 
>>> 
>>> You can run this script, e.g. compute_volume.geo :
>>> 
>>> Merge "3dblock.msh";
>>> Plugin(NewView).Run;
>>> Plugin(ModifyComponents).Expression0 = "1";
>>> Plugin(ModifyComponents).Run;
>>> Plugin(Integrate).Dimension = 3;
>>> Plugin(Integrate).Run;
>>> 
>>> You'll get
>>> 
>>> Info    : Running '/Applications/Gmsh.app/Contents/MacOS/gmsh vol.geo -'
>>> [Gmsh 3.0.7, 1 node, max. 1 thread]
>>> Info    : Started on Tue May  1 09:00:57 2018
>>> Info    : Reading 'vol.geo'...
>>> Info    : Reading '3dblock.msh'...
>>> Info    : 6790 vertices
>>> Info    : 32825 elements
>>> Info    : Done reading '3dblock.msh'
>>> Info    : Running Plugin(NewView)...
>>> Info    : Done running Plugin(NewView)
>>> Info    : Running Plugin(ModifyComponents)...
>>> Info    : Done running Plugin(ModifyComponents)
>>> Info    : Running Plugin(Integrate)...
>>> Info    : Step 0: integral = 1.000000000000803e-15
>>> Info    : Done running Plugin(Integrate)
>>> Info    : Done reading 'vol.geo'
>>> Info    : Stopped on Tue May  1 09:00:57 2018
>>> 
>>> 
>>> 
>>>> On 30 Apr 2018, at 22:58, Juan E. Sanchez <juan.e.sanchez at gmail.com
>>>> <mailto:juan.e.sanchez at gmail.com>> wrote:
>>>> 
>>>> Hello,
>>>> 
>>>> Is there a way to get the mesh volume calculated by gmsh?
>>>> 
>>>> My simulator is calculating a volume of 1.09e-15 for the attached
>>>> structure, but it should be 1e-15.
>>>> 
>>>> Before I added these flags
>>>> Mesh.OptimizeNetgen=1;
>>>> Mesh.OptimizeThreshold=1;
>>>> 
>>>> I was getting 1.17e-15.
>>>> 
>>>> I am summing the volume for each tetrahedron sub volume from the edge
>>>> center, to the element center, to the centers of each triangle face of the
>>>> edge.
>>>> 
>>>> If my calculation is correct, are there flags I can use to improve the
>>>> situation?
>>>> 
>>>> I am running version 3.06.
>>>> 
>>>> gmsh -3 3dblock.geo
>>>> 
>>>> 
>>>> Regards,
>>>> 
>>>> Juan
>>>> <3dblock.geo>_______________________________________________
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>>> 
>>> 
>> 
> 
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