[Gmsh] surface mesh, connect the faces of a compound

Bernd Hahnebach calculix at b75.ch
Wed Sep 23 15:18:52 CEST 2015 

Hi Germán,


thanks for the hints and the backgoundinformations. I'll give them a try.


Installing the GMSH Macro takes just a few seconds and works very well  
and the macro could be changed without changing FreeCAD code.

Regarding integrading GMSH in FreeCAD the way it is done with  
CalculiX. Yeah it would be for sure possible. Integrating the macro in  
FreeCAD takes time to develop. It's like most feature requests on open  
source software. It has to be done by someone.

For CalculiX the integration had to be done, because there was and is  
still plenty of code needed for an calculix input file writer and  
calculix output file reader. Where GMSH just accepts standard file  
formats like step and unv.

Hope that helps. Your are welcome to disscuss anything in the regard  
of FreeCAD on the forum http://forum.freecadweb.org/

Bernd


Zitat von Theler German Guillermo <gtheler at cites-gss.com>:

> Hi Bernd
>
> I have already been trying to mesh a solid composed of more than one
> FreeCAD parts with partial success.
> As you can see in this previous thread
>
> http://www.geuz.org/pipermail/gmsh/2015/009588.html
>
> I was having the same problem you got in the first place: common faces
> exported by FreeCAD are taken as different faces and FEM or FVM
> computations are not possible.
>
> I tried
>
> Geometry.OCCConnectFaces = 1;
>
> and it works on planar faces but fails with a segmentation fault on
> other general faces. Christophe told me that the current algorithm only
> works with plane faces, maybe someone more familiar with OCE may
> implement a better algorithm.
>
>
> BTW, it always seemed a pitty to me that FreeCAD cannot embed Gmsh as an
> API due to GPL vs LGPL :-(
> Nevertheless, FreeCAD forks and execs calculix (which is a allowed as
> stated in https://www.gnu.org/licenses/gpl-faq.html#GPLAndPlugins ).
> Why does Gmsh cannot be treated in the same way so an external macro is
> avoided?
>
>
>
> --
> Germán Theler :: CTO Ingeniería & TICs
>
> CITES ? Centro de Innovación Tecnológica Empresarial y Social S.A.
> Dirección General Sancor Seguros
> Grupo Sancor Seguros
> tel +54 3493 ?428 500 ? Int.: 3374
> gtheler at cites-gss.com
> www.cites-gss.com - www.gruposancorseguros.com
>
>
>
> On Wed, 2015-09-23 at 12:15 +0200, Bernd Hahnebach wrote:
>> Hi Dave,
>>
>> thanks for the tipp regarding the gui and using the options over
>> there. I had not worked with the gui before. I did some teste with
>> some modells and the different options. I need to work more to get
>> used to the gui of GMSH. Up to date it worked out well for some models.
>>
>> I have a further question in this regard. What would be needed for
>> beam or solid meshes ?
>>
>>
>> beam meshes (or edge meshes) --> connect the edges where they share
>> the same vertice --> ?
>>
>> shell mehes --> connect the faces where they share the same edge -->
>> -string "Geometry.OCCSewFaces=1;"
>>
>> solid meshes (or volume meshes) --> connect the solids where they
>> share the same face --> ?
>>
>>
>> I could provide steps if needed.
>>
>>
>> Kind regards Bernd
>>
>>
>>
>>
>> Zitat von David Colignon <david.colignon at ulg.ac.be>:
>>
>> >
>> > On 22/09/15 08:03, Bernd Hahnebach wrote:
>> >
>> >> Hi David,
>> >>
>> >> thanks for the fast reply. It is what I would like to have connect
>> >> the faces if they share an edge. Yes the provided option
>> >> seams to do the trick.
>> >>
>> >> -string "Geometry.OCCSewFaces=1;"
>> >>
>> >> It worked on the simple provided part compound_of_faces.step and on
>> >> one with 10 faces beam-10faces.step. With bothe the FEA
>> >> worked out very well :-) On a more sophisticated part
>> >> mechanical-part.step it seam to work out too but I get non positive
>> >> jacobian during FEA, but that seams to be another part of the story.
>> >
>> >
>> > Hi,
>> >
>> > for more complicated parts, you should also open your step file
>> > directly with Gmsh, and try the other options "Remove degenerated
>> > edges and faces", "Remove small edges", ... in Tools -> Options ->
>> > Geometry -> General and also look at the Info messages.
>> >
>> > Regards,
>> >
>> > Dave
>> >
>> >>
>> >> Downloadlink is still:
>> >>  
>> https://cloud.woelkli.com/public.php?service=files&t=1cfd13febed7694726b902cdb36476d4
>> >>
>> >> I need to test on more examples. I will report back.
>> >>
>> >> kind regards bernd
>> >>
>> >>
>> >>
>> >>
>> >> Zitat von David Colignon <david.colignon at ulg.ac.be>:
>> >>
>> >>>
>> >>> Hi Bernd,
>> >>>
>> >>> can you try with adding    the
>> >>>
>> >>> -string "Geometry.OCCSewFaces=1;"
>> >>>
>> >>> option ?
>> >>>
>> >>> This should work with relatively simple geometries, i.e. faces
>> >>> sharing a common line.
>> >>>
>> >>> Regards,
>> >>>
>> >>> Dave
>> >>>
>> >>> --
>> >>> David Colignon, Ph.D.
>> >>> 1er logisticien de recherche
>> >>> Université de Liège
>> >>> ACE - Applied & Computational Electromagnetics
>> >>> Sart-Tilman B28
>> >>> 10, Grande Traverse
>> >>> 4000 Liège - BELGIQUE
>> >>> Tél: +32 (0)4 366 37 32
>> >>> http://www.ulg.ac.be/nic4
>> >>>
>> >>> On 21/09/15 19:25, Bernd Hahnebach wrote:
>> >>>> Hi there,
>> >>>>
>> >>>> This is my first post to the mailing list so I may introduce
>> >>>> myself first. The "identifier" given to
>> >>>> me by my parents is Bernd and this corresponds to what most
>> >>>> people call myself. The bred to feed
>> >>>> myself an my familiy I earn in an engineering office near Zuerich
>> >>>> in Switzerland. I'm structural
>> >>>> engineer in the building industry. In my spare time I develop on
>> >>>> the FEM Workbench and on the Arch
>> >>>> Workbench of the parametric open source cad plattform FreeCAD.
>> >>>> This is why I'm gone write to this list.
>> >>>>
>> >>>>
>> >>>> FreeCAD uses for internal parametric surface and solid meshing
>> >>>> netgen. AFAIK due to licence
>> >>>> incompatibility between FreeCAD and GMSH it has never been an
>> >>>> option to use GMSH instead. But there
>> >>>> exists a FreeCAD macro which uses the GMSH installed on ones
>> >>>> computer for meshing. Most users mainly
>> >>>> use this GMSH macro for meshing their models including myself.
>> >>>> The macro exports a *.step meshes
>> >>>> with GMSH and imports the *.unv mesh back into FreeCAD. Babbled
>> >>>> enought,the important part of the
>> >>>> post ...
>> >>>>
>> >>>>
>> >>>> I run into trouble with meshing compunds of faces. The faces
>> >>>> where not connected to each other and
>> >>>> thus a Finite Element Analysis will fail to work without manual
>> >>>> connection off all the faces of the
>> >>>> compund. As a example a very simple compund of just two faces is taken.
>> >>>>
>> >>>> mesh command:
>> >>>> gmsh compound_of_faces.step -3 -format unv -o
>> >>>> compound_of_faces.unv -algo netgen -clmax 100,00
>> >>>> -order 2 -optimize
>> >>>>
>> >>>> gmsh --version
>> >>>> 2.8.5
>> >>>> on Debian Jesie
>> >>>>
>> >>>> I was wondering if it is possible to tell GMSH to mesh a
>> >>>> connected Surface Mesh of a compund of faces?
>> >>>>
>> >>>> The files could be downloaded here:
>> >>>>  
>> https://cloud.woelkli.com/public.php?service=files&t=1cfd13febed7694726b902cdb36476d4
>> >>>>
>> >>>>
>> >>>> Kind Regards and thanks to all people who have ever contributed
>> >>>> to GMSH development.
>> >>>>
>> >>>> Bernd
>> >>>>
>> >>>>
>> >>>>
>> >>>> _______________________________________________
>> >>>> gmsh mailing list
>> >>>> gmsh at geuz.org
>> >>>> http://www.geuz.org/mailman/listinfo/gmsh
>> >>>
>> >>
>> >>
>> >>
>> >
>> >
>> >
>>
>>
>>
>>
>> _______________________________________________
>> gmsh mailing list
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>> http://www.geuz.org/mailman/listinfo/gmsh
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