Calculix does not implement *Section Print properly?

About the development of the FEM module/workbench.

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mxynewcastle
Posts: 4
Joined: Thu Aug 15, 2019 9:22 am

Calculix does not implement *Section Print properly?

Postby mxynewcastle » Thu Aug 15, 2019 10:21 am

Dear FreeCAD users,

It is a great pleasure to post my first question in the forum. :D

I have been stuck with my FEM within FreeCAD 0.17 for a while.

Here is a simple bar test, which has two fixed supports and a line-load. What I am trying to do is to export reaction forces and moments at the two supports.

Using *Node Print, reaction forces have been printed in a .dat file successfully, as expected. However, the reaction moments bit is not working by using *Surface and *Section Print. From my point of view, it does not make sense at all.

Can anyone please have a look in my attached simple test case? Great great thanks!!!

Xiangyin
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PrzemoF
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Re: Calculix does not implement *Section Print properly?

Postby PrzemoF » Thu Aug 15, 2019 10:51 am

Welcome to the forum!

Please read this:
https://forum.freecadweb.org/viewtopic.php?f=18&t=12212
and that:
https://forum.freecadweb.org/viewtopic.php?f=3&t=2264

TL;DR: Upgrade to 0.18, test again, provide version details is problem persist.
mxynewcastle
Posts: 4
Joined: Thu Aug 15, 2019 9:22 am

Re: Calculix does not implement *Section Print properly?

Postby mxynewcastle » Thu Aug 15, 2019 11:01 am

PrzemoF wrote:
Thu Aug 15, 2019 10:51 am
Welcome to the forum!

Please read this:
https://forum.freecadweb.org/viewtopic.php?f=18&t=12212
and that:
https://forum.freecadweb.org/viewtopic.php?f=3&t=2264

TL;DR: Upgrade to 0.18, test again, provide version details is problem persist.
Thank you very much PrzemoF ! I am updating the version and doing it again. Will let users know very soon in hours. Thanks again.
mxynewcastle
Posts: 4
Joined: Thu Aug 15, 2019 9:22 am

Re: Calculix does not implement *Section Print properly?

Postby mxynewcastle » Thu Aug 15, 2019 12:09 pm

Hi dear all,

Just an update here after lunch.

I updated my FreeCAD from 0.17 to 0.18.3. However, *Section Print still does not work for node-type surfaces.

Really appreciate if any help could be provided...
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Kunda1
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Re: Calculix does not implement *Section Print properly?

Postby Kunda1 » Thu Aug 15, 2019 3:23 pm

Can you test on 0.19_pre as well... actually to stay on top of FEM changes consider using 0.19_pre
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mxynewcastle
Posts: 4
Joined: Thu Aug 15, 2019 9:22 am

Re: Calculix does not implement *Section Print properly?

Postby mxynewcastle » Fri Aug 16, 2019 9:47 am

Hi thanks everyone, really appreciate your suggestions

I think I have solved this issue by defining those surfaces as element-surfaces first, but still with FreeCAD 0.17. I do believe it is a problem of CalculiX. Nothing to do with FreeCAD.

Cheers
UR_
Posts: 1153
Joined: Tue Jan 03, 2017 8:42 pm

Re: Calculix does not implement *Section Print properly?

Postby UR_ » Sun Aug 18, 2019 11:35 am

Attached you will find a small example file, how to evaluate section forces and moments.

Because FreeCAD FEM doesn't support them (in opposite to reaction forces) some manual edits are neccessary to modify .inp file before launching ccx.

example:
arc shaped cantilever beam, with fixed side on the left and area load on the right side.
Furthermore there is a arbitrary section, where forces and moments are of interest.

Screenshot 002.png
Screenshot 002.png (35.59 KiB) Viewed 581 times

After FreeCAD has generated .inp file, these changes had to be applied manually.
Please note, a contact constraint is abused to obtain section data

Code: Select all

***********************************************************
** added manually to INP file
** outputs --> dat file
*SECTION PRINT,SURFACE=DEP1,NAME=SP1
SOF,SOM



*** delete this section manually
************************************************************
** Contact Constraints
** written by write_constraints_contact function
** FemConstraintContact
*CONTACT PAIR, INTERACTION=INT1,TYPE=SURFACE TO SURFACE
DEP1,IND1
*SURFACE INTERACTION, NAME=INT1
*SURFACE BEHAVIOR,PRESSURE-OVERCLOSURE=LINEAR
1000000.0 

Then ccx delivers this dat file:


total force (fx,fy,fz) for set FEMCONSTRAINTFIXED and time 0.1000000E+01
-1.414564E-07 -5.972259E+04 -3.507967E-08

statistics for surface set DEP1 and time 0.1000000E+01
total surface force (fx,fy,fz) and moment about the origin(mx,my,mz)
2.546585E-10 -1.846843E-10 -6.622258E-12 1.188596E-10 -2.596607E-10 -1.653098E-08

center of gravity and mean normal
3.468083E+01 4.029853E+01 -4.533302E-16 3.053682E-16 6.453659E-17 -1.723737E-16

moment about the center of gravity(mx,my,mz)
3.857269E-10 -4.893261E-10 1.363913E-10

area, normal force (+ = tension) and shear force (size)
4.514068E+03 6.698723E-26 3.146476E-10





done with:
OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.17681 (Git)
Build type: Release
Branch: master
Hash: e94af7ff5e873f263cac51d7d47df68eca183250
Python version: 3.7.3
Qt version: 5.9.7
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: German/Germany (de_DE)



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bernd
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Location: Zürich, Switzerland

Re: Calculix does not implement *Section Print properly?

Postby bernd » Mon Aug 26, 2019 12:34 pm

issue #3126 has some more links in the regard of section forces