FEM object types

About the development of the FEM module/workbench.

Moderator: bernd

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HarryvL
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Re: FEM object types

Postby HarryvL » Fri Apr 06, 2018 11:07 am

Thanks I will try when I have access to my computer.

Yes the higher eigen-modes (that go with high frequencies) can look funny, but the first one should be a simple symmetric sway pattern perpendicular to the plane of the structure.
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HarryvL
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Re: FEM object types

Postby HarryvL » Fri Apr 06, 2018 6:25 pm

The rectangular beam section indeed works. However, the result is very sensitive to mesh refinement (U_max = 16.1 mm, 202 mm, 281 mm for the three meshes below) and plain wrong for the coarsest mesh :shock: That should certainly not be the case for the simple beam element. I first want to find out what causes this before I move forward with the more complicated mixed-mesh example. I will report back on that in a separate post.

EDIT: Hmmmmmm - I suspect it is has to do with the loads !! How are uniform loads distributed over the element nodes? This needs to be done in a manner consistent with the element shape function, not just equally spread out. That would explain why in the coarsest mesh the mid-node moves up !!

PB_Static_Disp_Mesh1.png
PB_Static_Disp_Mesh1.png (215.65 KiB) Viewed 391 times
PB_Static_Disp_Mesh2.png
PB_Static_Disp_Mesh2.png (216.02 KiB) Viewed 391 times
PB_Static_Displ_Mesh3.png
PB_Static_Displ_Mesh3.png (218.12 KiB) Viewed 391 times
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bernd
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Re: FEM object types

Postby bernd » Fri Apr 06, 2018 7:16 pm

load are consistent with shape functions! At least rhey should, see input file.

But beams in ccx les than 2.13 have some problems, see https://forum.freecadweb.org/viewtopic.php?f=18&t=16044
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HarryvL
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Re: FEM object types

Postby HarryvL » Sat Apr 07, 2018 12:48 am

Some further views on the CCX three-noded beam element behaviour: https://forum.freecadweb.org/viewtopic. ... 38#p226038
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HarryvL
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Re: FEM object types

Postby HarryvL » Mon Apr 09, 2018 8:12 pm

Happy to report a pleasing result mixing Plates and Beams. Pedestrian bridge loaded with 1 kN/m2 on central span only.


PB_2_Def_1.png
PB_2_Def_1.png (261.47 KiB) Viewed 334 times

PB_2_Def_Detail_1.png
PB_2_Def_Detail_1.png (298.02 KiB) Viewed 334 times

PB_2_Def_Detail_2.png
PB_2_Def_Detail_2.png (313.78 KiB) Viewed 334 times


However this raises quite a few questions that I will post separately to prevent polluting this post on mixed meshes.
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HarryvL
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Re: FEM object types

Postby HarryvL » Mon Apr 09, 2018 9:02 pm

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HarryvL
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Re: FEM object types

Postby HarryvL » Mon May 28, 2018 4:08 am

bernd wrote:
Sun Apr 01, 2018 6:50 am
because your ubuntu has an older version of occt. What you could do is compile occt yourself. It is on 7.2 allready. There are various topics araound to occt. If you are able to compile FreeCAD it is simple to compile occt too.

If you use ppa newer version of occt was use to compile.

Ahh probably ready packages are available too, there have been disscusdions around. You may ask in instatallation part of the forum.

Ahh you may use ppa to create geometry and just do the FEM part with my branch.

A few possibilities ...
Bernd, I never quite managed to resolve this and it is quite frustrating to have to move between FC-Daily and local version all the time. I managed to download and compile a new OCCT 7.2 but dont know how to link this to FC. Is there a path in a FC make file that needs to be set?
Jee-Bee
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Re: FEM object types

Postby Jee-Bee » Mon May 28, 2018 5:18 am

@bernd had a nice script before... but don't know it that is still valid.
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bernd
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Re: FEM object types

Postby bernd » Mon May 28, 2018 7:03 am

https://gist.github.com/berndhahnebach and https://forum.freecadweb.org/viewtopic.php?f=4&t=18967

I have updated it on my local machine to occt 7.2 on Debian Stretch. But did not have the time to update the ubuntu ones. But in the regard of cmake and occt I did not had to change anything. Means you should find what you are looking for harry.

bernd
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HarryvL
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Re: FEM object types

Postby HarryvL » Mon May 28, 2018 4:41 pm

Wooooow. That worked really well. Thanks Bernd.
Everything works now. My new concrete stuff + Boolean Fragments + Netgen (which I never had on Ubuntu).

I see from the script that when it runs it starts from scratch (deletes the whole directory). Can I now do a simple pull request and compile/make to incorporate changes from my repository? Will it know to find OCCT and NETGEN?