Quad Mesh

About the development of the FEM module/workbench.

Moderator: bernd

User avatar
bernd
Veteran
Posts: 12849
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland
Contact:

Re: Quad Mesh

Post by bernd »

it works well even on bigger models and it is a few times faster than the comercial software we use for structural engineering analysis ... I am quit excited.

screen2.png
screen2.png (640.12 KiB) Viewed 2073 times
paullee
Veteran
Posts: 5097
Joined: Wed May 04, 2016 3:58 pm

Re: Quad Mesh

Post by paullee »

Look interesting ! 8-)

Would e.g. the dresses in Microelly's post on Jan 30, 2017 generate co-planar quad mesh. ?

Or quad mesh can be non -coplanar in the first place ?

Thanks
fandaL
Posts: 440
Joined: Thu Jul 24, 2014 8:29 am

Re: Quad Mesh

Post by fandaL »

bernd wrote: Thu Jul 29, 2021 6:13 am tried this again ...

- set "Recombine All" to True
- set "Recombination Allgorithm" to Blossum full-quad"

Works gread for first order meshes. Quad4 faces are meshed by Gmsh. But it fails for second order meshes. The quadratic edges will be meshed but the faces are linear. The file is attached. Use print mesh info. The quad8 mesh test has 25 nodes.

Anyone an idea how to get the quad8 faces?
GMSH makes second order quad elements. The issue is that they are lost on the way to FC.

If you find *.geo file with commands for GMSH and open it in GMSH you will see they are there. But if you save as unv and import to FC there are only quad4 elements. The strange thing is that if you import this unv file back to GMSH (which has created it), it will load only quad4 elements (I mean first order quad elements).
If you import this unv to Salome, it behaves like FC - quad4 imported.
If you import this unv to Mecway, it reads quad8 elements. Theoretically we can modify our unv reader to import such unv, but if these unv are "wrong" I would rather ask GMSH devs to look at it, since I have not found unv documentation.

If you want to get quad8 elements to FC today, you can do work around:
Open geo file (made by FC) in GMSH and export as med file. Import to Salome and export to unv. Finally import this new unv to FC.
or
Open geo file in GMSH and export as inp. Edit inp file by changing *ELEMENT, type=CPS4 to *ELEMENT, type=S8. Import this inp to FC.
aerospaceweeb
Posts: 118
Joined: Fri Apr 09, 2021 3:26 am

Re: Quad Mesh

Post by aerospaceweeb »

Hello,

I'm having some trouble finding the "recombine" tool. Is there a macro that is already written that can perform the equivalencing of nodes in FreeCAD FEM? I was writing a simple but inefficient function that did it for all nodes in the FreeCAD object, but I realized I should probably look around to see if someone else had done it already.
User avatar
bernd
Veteran
Posts: 12849
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland
Contact:

Re: Quad Mesh

Post by bernd »

@fanaL: great find. I will continue on this too.

@aerospaceweeb:
screen.png
screen.png (153.53 KiB) Viewed 1956 times
User avatar
bernd
Veteran
Posts: 12849
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland
Contact:

Re: Quad Mesh

Post by bernd »

moved the mesh glue posts in a separate topic ... https://forum.freecadweb.org/viewtopic.php?f=18&t=60680
chlai
Posts: 8
Joined: Tue Jan 11, 2022 9:29 pm

Re: Quad Mesh

Post by chlai »

Hello,

Recently I am trying to generate quad8 mesh in FreeCAD (ideally via Gui). Is there any way to do it?

Or this is the only way for now?
fandaL wrote: Thu Jul 29, 2021 4:12 pm If you want to get quad8 elements to FC today, you can do work around:
Open geo file (made by FC) in GMSH and export as med file. Import to Salome and export to unv. Finally import this new unv to FC.
or
Open geo file in GMSH and export as inp. Edit inp file by changing *ELEMENT, type=CPS4 to *ELEMENT, type=S8. Import this inp to FC.
Regards
fandaL
Posts: 440
Joined: Thu Jul 24, 2014 8:29 am

Re: Quad Mesh

Post by fandaL »

chlai wrote: Thu Feb 03, 2022 7:06 pm Recently I am trying to generate quad8 mesh in FreeCAD (ideally via Gui). Is there any way to do it?
Try the parameters as suggested by Bernd above (red elipses), but use "Second Order Linear = True"

Otherwise, GMSH makes second order quads with 9 nodes (one is in the middle of the element) and FreeCAD does not read the unv file correctly. I guess it is due to smesh library used also in Salome, which imports same elements (quadratic edges and linear quads instead of quadratic quads).
Post Reply