[Gmsh] Removing a volume from an ambient volume

[Travis Thompson]

Dave,

I certainly will.  I checked the options for the 3d algorithm; they
have been set to Tetgen + Delauney, so this has been the one that was
crashing all along.  I tried changing it to Netgen for grins - Gmsh
did not crash but the message console complained with about 200 lines
of:
"Info    : WARNING:  Intersecting elements<Number> and <Number>"

The files that are attached:

plainGeom.geo : The naked geometry

GeomWithVolumeElement.geo:  The geometry where the ambient box has
been selected as the 'volume' and the interior object has been
selected as the 'hole'


Note: it is a bit difficult to see that the interior object is closed
as the top surface of the interior object is coplanar with the
bounding box.. but if you click around you can see that the top plane
'closing off' the interior object is indeed there :)

I appreciate your help!

-Travis Thompson
Graduate Student
Dept. of Mathematics, Texas A&M University


On Wed, Oct 29, 2008 at 8:37 AM, David Colignon
<David.Colignon at ulg.ac.be> wrote:
> Hi Travis,
>
> solution a) should have worked. Can you send us your .geo file to check ?
> And can you try with with the Tetgen 3D meshing algorithm instead of netgen
> ?
>
> Cheers,
>
> Dave
>
> --
> David Colignon, Ph.D.
> Collaborateur Logistique du F.R.S.-FNRS
> CÉCI - Consortium des Équipements de Calcul Intensif
> ACE - Applied & Computational Electromagnetics
> Sart-Tilman B28
> Université de Liège
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>
>
>
> Travis Thompson wrote:
>>
>> Hello.  I have been working with Gmsh for a finite elements project at
>> Texas A&M university in college station, tx.
>>
>> I am new to Gmsh and have been stuck on a particular problem for a
>> while now; I was hoping maybe someone could shed some light on it.
>> The setup is fairly simple.  I have a 3 dimensional rectangle which
>> completely contains another 3 dimensional object.
>>
>> The object inside the box is completely closed; i will refer to this
>> object as Object A.  If I attach a volume element to object A and mesh
>> the box + object A everything works wonderfully.  I get a nice 2d mesh
>> on the bounding box and a nice 3d mesh inside object A.
>>
>> The problem is that I need a 3d mesh inside the bounding box and i
>> want *no mesh* in the interior of object A (that is, I want to mesh
>> the complement of Object A with respect to the bounding box).
>>
>> What I have tried:
>> a) I have tried attaching a volume element to the ambient bounding box
>> and selecting Object A as 'a hole'
>> b) I have tried attaching a volume element to the bounding box and a
>> volume element to Object A with the intention of Deleting the volume
>> element attached to object A *after* computing the mesh.
>>
>> However both (a) and (b) lead to gmsh crashing (same error on both
>> windows and Linux versions)
>> The error is:
>>
>> ----------------------------
>> Assertion Failed!
>>
>> Program: c:\program files\gmsh-2.2.4-Windows\gmsh.exe
>> File: tetgen.cxx
>> Line: 22506
>>
>> Expression: matchflag == true
>> ---------------------------
>>
>> I would imagine that what I am trying to do is quite basic; ie:
>> meshing the complement of an object inside an ambient object.  I have
>> been through the documentation but due to my lack of familiarity with
>> Gmsh I have failed to figure out a method.
>>
>> If anyone can shed any light on this I would greatly appreciate it!
>>
>> Thank you in advance!
>>
>> -Travis Thompson
>> Graduate Student
>> Dept of Mathematics, Texas A&M University
>>
>> _______________________________________________
>> gmsh mailing list
>> gmsh at geuz.org
>> http://www.geuz.org/mailman/listinfo/gmsh
>
>
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