FEM analysis : ccx_dat_file empty

About the development of the FEM module/workbench.

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Toutatis
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FEM analysis : ccx_dat_file empty

Post by Toutatis »

Hi everybody,

this is my first message on the forum, and I find it extremly cool to have such possibility to ask for help.

My problem is, I would like to access and read the ccx_dat_file generated after a CalculiX modelization, but in my case, the file is empty after the run.

I have no error during the run, it says the .frd file and .dat file are generated, but the thing is there is no "blue tick" on the file, and in the repertory, the dat file has a weight of 0 Ko....

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I want to read the .dat file to get access to the reaction forces on my static analysis.

Latest version 0.19.4 installed, several researchs on the forum and on google but no solution found until now. So thank you very much if you could help me with that! ;)

Alex
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NewJoker
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Re: FEM analysis : ccx_dat_file empty

Post by NewJoker »

From what I know, currently, reaction forces are written to the .dat file only for FEM ConstraintFixed.

This topic should belong to the FEM subforum.
Toutatis
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Re: FEM analysis : ccx_dat_file empty

Post by Toutatis »

As simple as that. I thought we could have reactions forces also with ConstraintDisplacement, which is mechanically not the same than a Fixed Constraint. I tried with fixed constraint and it works.

Anyway, thank you for the reply! :)

Alex
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NewJoker
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Re: FEM analysis : ccx_dat_file empty

Post by NewJoker »

Toutatis wrote: Fri May 27, 2022 8:29 am I thought we could have reactions forces also with ConstraintDisplacement, which is mechanically not the same than a Fixed Constraint.
Normally, it should be possible but it's just not yet implemented. Hopefully, someone will add it in the future.
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vkt
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Re: FEM analysis : ccx_dat_file empty

Post by vkt »

Many thanks for the information on this post. I am an experienced Abaqus user but new to FreeCAD. I am trying to get nodal heat flux output to .dat file via NODE PRINT. I have been able to get reactions to .dat using the method discussed above, but get no output to .dat when requesting TEMP and HFL via NODE PRINT for my thermomechanical analysis. Any advise much appreciated as otherwise FreeCAD is very useful for me. Thanks
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NewJoker
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Re: FEM analysis : ccx_dat_file empty

Post by NewJoker »

vkt wrote: Mon Dec 19, 2022 5:27 pm but get no output to .dat when requesting TEMP and HFL via NODE PRINT
HFL is an integration point variable and thus it has to be requested using *EL PRINT. TEMP is not available in CalculiX.
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vkt
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Re: FEM analysis : ccx_dat_file empty

Post by vkt »

Many thanks for that. I have tried a few cases and find that NT gives temperatures at nodes via *NODE PRINT, but there is no output for RFL11 which should give the nodal heat fluxes that I am seeking. I can get integration point heat fluxes via HFL in *EL PRINT. These could be printed for a layer of elements adjacent to the surface of interest, but I think that it would be difficult and inaccurate to process these results into the total heat flux through the surface. I also tried to get the total heat flux by defining a surface via *SURFACE and using *SECTION PRINT specifying the output for SOAREA (surface area) and SOH (surface heat flux), but got no output.
I would be happy to support further development if necessary to get the total surface heat flux output working.

Thanks again.

Running FreeCAD 0.20.1 on Windows 10.
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vkt
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Re: FEM analysis : ccx_dat_file empty

Post by vkt »

OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.1.29410 (Git)
Build type: Release
Branch: releases/FreeCAD-0-20
Hash: f5d13554ecc7a456fb6e970568ae5c74ba727563
Python 3.8.10, Qt 5.15.2, Coin 4.0.1, Vtk 8.2.0, OCC 7.6.3
Locale: English/United Kingdom (en_GB)
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NewJoker
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Re: FEM analysis : ccx_dat_file empty

Post by NewJoker »

vkt wrote: Wed Dec 21, 2022 5:40 pm there is no output for RFL11 which should give the nodal heat fluxes that I am seeking.
RFL stores only external concentrated heat sources (basically reaction fluxes).

vkt wrote: Wed Dec 21, 2022 5:40 pm I also tried to get the total heat flux by defining a surface via *SURFACE and using *SECTION PRINT specifying the output for SOAREA (surface area) and SOH (surface heat flux), but got no output.
You are trying to use Abaqus output variable in CalculiX again. CalculiX's syntax is only partially compatible with Abaqus. Check the documentation (especially sections about keywords and output variables): http://www.dhondt.de/ccx_2.20.pdf
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vkt
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Re: FEM analysis : ccx_dat_file empty

Post by vkt »

Many thanks for that. From the CalculiX manual, I tried using *SECTION PRINT with output set to FLUX for heat fluxes for my thermo-mechanical problem (and an equivalent static anlysis case) in association with *SURFACE, TYPE=NODE, but got no output to the .dat file in either case. I found a similar issue discussed in the topic below and wondered if this was why I am not getting *Section Print output and if there is a workaround? I could possibly use element face based surfaces but that I think that would be more difficult to impliment.

Thanks again.

https://forum.freecadweb.org/viewtopic. ... 09#p327009
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
.
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