[Gmsh] Removing a volume from an ambient volume

[Christophe Geuzaine]

Travis Thompson wrote:
> 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'

Surfaces 3 and 11 overlap in your model. So there should in fact be no 
hole in your volume, but 2 separate volumes: see attached file.

> 
> 
> 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
>> 4000 Liège - BELGIQUE
>> Tél: +32 (0)4 366 37 32
>> Fax: +32 (0)4 366 29 10
>> WWW:    http://hpc.montefiore.ulg.ac.be/
>> Agenda: http://www.google.com/calendar/embed?src=david.colignon%40gmail.com
>>
>>
>>
>> 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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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine
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