[Gmsh] meshing multiple objects
Christophe Geuzaine
cgeuzaine at ulg.ac.be
Mon Jan 5 13:54:39 CET 2009
Felix Wolfheimer wrote:
> Dear Wing,
>
> thanks for pointing out again the problem. I think that the problem of a
> computational domain filled with regions/shapes of different material
> properties is quite common in the field of computational electrodynamics
> (this is exactly the field I'm working on). I know, that the commercial
> computational electromagnetic codes based on a frequency domain approach
> with tetrahedral grids can handle such problems and generate a mesh which is
> conformal to all material boundaries in the model. I've tried to find
> information on how to generate such a mesh with open source
> programs/libraries and tried some of the open source meshing tools as well
> but the result always was that they are very good at meshing a single object
> (even of very complex geometrical shape) but are unable to handle material
> boundaries. I wonder if there is anything I've missed...
>
I'm not sure I understand. Gmsh has always supported meshes which are
conformal to all material boundaries in the model. The geometry must
simply contain one volume per material... Look e.g. at the first 3D
tutorial "tutorial/t2.geo": the model contains 2 volumes, to which you
can assign separate material properties.
> I also wish you a happy and successful year 2009.
>
> Best regards
>
> Felix
>
> -----Ursprüngliche Nachricht-----
> Von: wing [mailto:yongjin.liu at gmail.com]
> Gesendet: Montag, 29. Dezember 2008 16:27
> An: Christophe Geuzaine
> Cc: Felix Wolfheimer; gmsh at geuz.org
> Betreff: Re: [Gmsh] meshing multiple objects
>
> Christophe Geuzaine wrote:
>> Felix Wolfheimer wrote:
>>
>>> Dear Christophe,
>>>
>>> thank you for the quick reply. The two (or more) solids model objects
> with
>>> different material properties. Thus, I want to create a mesh that is
>>> conformal to the material interface, such that a tetrahedron of the
>>> generated mesh is located entirely in solid 1 or in solid 2 and,
>>> additionally, the tetrahedrons at the interface region (the face where
> the
>>> two solids touch) should share a common face. That is, the material
>>> interface should be handled somehow as a single face shared by both
> solids.
>>> However, in the file generated by the solid modeler the two solids are
> two
>>> independent objects and, thus, the mesh is created independently for each
> of
>>> the objects. It would be nice to know, if there is any easy way to modify
>>> the step or iges file, such that a mesh with the properties described
> above
>>> is created. Is there any option in gmsh which would allow the creation of
>>> such a mesh directly from the step or iges file?
>>>
>>> Please find the file test.stp, which contains a very simple model of two
>>> bricks where the one brick has been trimmed by the other.
>>>
>>>
>> The boundary of the first cube has not been correctly subdivided, which
>> results in partially overlapping surfaces... which causes the 3D mesh to
>> fail.
>>
>>
>>
>>
>>> Thanks and best regards
>>>
>>> Felix
>>>
>>> -----Ursprüngliche Nachricht-----
>>> Von: Christophe Geuzaine [mailto:cgeuzaine at ulg.ac.be]
>>> Gesendet: Mittwoch, 12. November 2008 20:00
>>> An: Felix Wolfheimer
>>> Cc: gmsh at geuz.org
>>> Betreff: Re: [Gmsh] meshing multiple objects
>>>
>>> Felix Wolfheimer wrote:
>>>
>>>> Hi Gmsh Experts,
>>>>
>>>>
>>>>
>>>> I would like to create a tetrahedral mesh from iges or step models. The
>>>> models contain parts which touch each other (result of Boolean
>>>> operations). However, when I read the model with gmsh the interface
>>>> region where the solids touch is meshed twice (once for the first object
>
>>>> and once for the second). Additionally, the tetrahedrons at the
>>>> interface overlap arbitrarily. Is there any way to read a CAD model and
>>>> mesh it with gmsh such that the surface of the interface region of the
>>>> two solids is meshed only once?
>>>>
>>>>
>>> You have to make sure that the solid modeler creates the correct
>>> geometry for the intersecting objects (intersection curves, etc.)
>>>
>>> Can you send the step file?
>>>
>>>
>>>
>>>
>>>>
>>>>
>>>> Best regards
>>>>
>>>>
>>>>
>>>> Felix
>>>>
>>>>
>>>>
>>>> PS: The screenshot enclosed to this mail may show you the result I get
>>>> when I try to mesh two cylinders, where the first cylinder was trimmed
>>>> by the second one.
>>>>
>>>>
>>>>
>>>>
>>>> ------------------------------------------------------------------------
>>>>
>>>> _______________________________________________
>>>> gmsh mailing list
>>>> gmsh at geuz.org
>>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>>
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> gmsh mailing list
>>> gmsh at geuz.org
>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>
>>
>>
> Hi all,
> the problem of overlapping surfaces is just one point of Felix's
> question. The other point is that he want multiple solids (volumes?) so
> that he can apply material properties to different bodies.
> I have the same question on this part. Say, I have a PCB (Printed
> Circuit Board) with several components mounted on it. I want to conduct
> a heat transfer simulation for this unit (PCB+components). I found that
> because of the Christophe Geuzaine wrote:
>> Felix Wolfheimer wrote:
>>
>>> Dear Christophe,
>>>
>>> thank you for the quick reply. The two (or more) solids model objects
> with
>>> different material properties. Thus, I want to create a mesh that is
>>> conformal to the material interface, such that a tetrahedron of the
>>> generated mesh is located entirely in solid 1 or in solid 2 and,
>>> additionally, the tetrahedrons at the interface region (the face where
> the
>>> two solids touch) should share a common face. That is, the material
>>> interface should be handled somehow as a single face shared by both
> solids.
>>> However, in the file generated by the solid modeler the two solids are
> two
>>> independent objects and, thus, the mesh is created independently for each
> of
>>> the objects. It would be nice to know, if there is any easy way to modify
>>> the step or iges file, such that a mesh with the properties described
> above
>>> is created. Is there any option in gmsh which would allow the creation of
>>> such a mesh directly from the step or iges file?
>>>
>>> Please find the file test.stp, which contains a very simple model of two
>>> bricks where the one brick has been trimmed by the other.
>>>
>>>
>> The boundary of the first cube has not been correctly subdivided, which
>> results in partially overlapping surfaces... which causes the 3D mesh to
>> fail.
>>
>>
>>
>>
>>> Thanks and best regards
>>>
>>> Felix
>>>
>>> -----Ursprüngliche Nachricht-----
>>> Von: Christophe Geuzaine [mailto:cgeuzaine at ulg.ac.be]
>>> Gesendet: Mittwoch, 12. November 2008 20:00
>>> An: Felix Wolfheimer
>>> Cc: gmsh at geuz.org
>>> Betreff: Re: [Gmsh] meshing multiple objects
>>>
>>> Felix Wolfheimer wrote:
>>>
>>>> Hi Gmsh Experts,
>>>>
>>>>
>>>>
>>>> I would like to create a tetrahedral mesh from iges or step models. The
>>>> models contain parts which touch each other (result of Boolean
>>>> operations). However, when I read the model with gmsh the interface
>>>> region where the solids touch is meshed twice (once for the first object
>
>>>> and once for the second). Additionally, the tetrahedrons at the
>>>> interface overlap arbitrarily. Is there any way to read a CAD model and
>>>> mesh it with gmsh such that the surface of the interface region of the
>>>> two solids is meshed only once?
>>>>
>>>>
>>> You have to make sure that the solid modeler creates the correct
>>> geometry for the intersecting objects (intersection curves, etc.)
>>>
>>> Can you send the step file?
>>>
>>>
>>>
>>>
>>>>
>>>>
>>>> Best regards
>>>>
>>>>
>>>>
>>>> Felix
>>>>
>>>>
>>>>
>>>> PS: The screenshot enclosed to this mail may show you the result I get
>>>> when I try to mesh two cylinders, where the first cylinder was trimmed
>>>> by the second one.
>>>>
>>>>
>>>>
>>>>
>>>> ------------------------------------------------------------------------
>>>>
>>>> _______________________________________________
>>>> gmsh mailing list
>>>> gmsh at geuz.org
>>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>>
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> gmsh mailing list
>>> gmsh at geuz.org
>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>
>>
>>
> Hi all,
> the problem of overlapping surfaces is just one point of Felix's
> question. The other point is that he want multiple solids (volumes?) so
> that he can apply material properties to different bodies.
> I have the same question on this part. Say, I have a PCB (Printed
> Circuit Board) with several components mounted on it. I want to conduct
> a heat transfer simulation for this unit (PCB+components). I found that
> because of the overlapping surfaces I cannot mesh the PCB and the
> components as separate solids. And when I model the PCB and components
> as a single solid (just by boolean operation), the meshing is OK but I
> cannot apply material properties (heat conductivity, surface emissivity,
> etc.) to different components now because they are now a single solid.
> Maybe this is a silly question, but, actually I was stuck here for a while.
>
> Thanks in advance and happy new year.
> wing
>
>
> _______________________________________________
> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh
>
>
--
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine