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

Wed Sep 23 13:37:24 CEST 2015

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
> >>>
> >>
> >>
> >>
> >
> >
> >
>
>
>
>
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> gmsh at geuz.org
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