Reaction force request
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and Helpful information for the FEM forum
Re: Reaction force request
this is a simple fem I made on a cube in FreeCAD. and the .dat file (I changed the file extension from .dat to .txt to upload here!) Surprisingly I checked it on Linux and got the same thing... (where am I doing wrong?!)
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Re: Reaction force request
The output in *.dat file is a sum of reaction forces (with components Fx, Fy, Fz). E.g. if you have a beam fixed at both ends and you use one Fixed Constraint object for both ends, total reaction force (as printed) will correspond to external load. If you will use one Fixed Constraint object for one end and second Constraint for the other, *.dat file will contain information for one and for the other.
Otherwise Calculix can print reaction forces per each node, if you change *.inp file from
to
where ConstraintFixed is name corresponding to appropriate constraint object.
Side note: CalculiX calculates reaction forces without forces applied directly to constrained nodes, so that your reaction force is slightly lower than applied load 3000 N.
Otherwise Calculix can print reaction forces per each node, if you change *.inp file from
Code: Select all
*NODE PRINT, NSET=ConstraintFixed, TOTALS=ONLY
RF
Code: Select all
*NODE PRINT, NSET=ConstraintFixed, TOTALS=YES
RF
Side note: CalculiX calculates reaction forces without forces applied directly to constrained nodes, so that your reaction force is slightly lower than applied load 3000 N.
Re: Reaction force request
wow thanks a lot. I was really confused! now I get it!
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Re: Reaction force request
Do we need to change something in the FreeCAD FEM inp file in this regard?
Re: Reaction force request
No, if I understood the hex41434’s question correctly, it was only about understanding what is in ccx_dat_file object. We can rather write some note about reaction forces to documentation. I have just mentioned it at https://wiki.freecadweb.org/FEM_Calculi ... _interface
Reaction forces can be found in ccx_dat_file which contains reaction force components (fx, fy, fz) for each Fixed Constraint.
Re: Reaction force request
@fandal and bernd
this is a great feature for fixed constraints!
Is it possible to let it work , if one side is x,y,z fixed, rotation free, and the other side y,z fixed and rotation free?
I was not able to do for non fixed constaints..
OS: Windows 10 (10.0)
Word size of FreeCAD: 64-bit
Version: 0.20.25334 (Git)
Build type: Release
Branch: master
Hash: 433c52c290681992346b6cda6482bf6a73d74e25
Python version: 3.8.10
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.2
Locale: German/Germany (de_DE)
this is a great feature for fixed constraints!
Is it possible to let it work , if one side is x,y,z fixed, rotation free, and the other side y,z fixed and rotation free?
I was not able to do for non fixed constaints..
OS: Windows 10 (10.0)
Word size of FreeCAD: 64-bit
Version: 0.20.25334 (Git)
Build type: Release
Branch: master
Hash: 433c52c290681992346b6cda6482bf6a73d74e25
Python version: 3.8.10
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.2
Locale: German/Germany (de_DE)
Re: Reaction force request
I have looked at it. This commit
https://github.com/fandaL/FreeCAD/commi ... 88df9caf6e
makes the same for Constraint displacement. I added if condition
Code: Select all
if not femobj["Object"].xFree or not femobj["Object"].yFree or not femobj["Object"].zFree:
@bernd
It should work on FEM examples, but I got to little trouble with definition of free and fixed DOFs in FEM example:
Constraints -> Displacement -> RC Wall 2D
In the property editor, there are zFix and zFree checked simultaneously. Does it have some meaning? In the Constraint displacement GUI, when I click zFix, it unchecks zFree and opposite, but property editor enables to switch on both simultaneously. Should the behaviour be that one is checked and second unchecked as allowed by GUI? I would use only zFix and zDisplacement, omitting zFree parameter.
Re: Reaction force request
good catch git commit a0d860679ef6
this should never happen. IMHO the data model of constraint displacement could be better, but I never spent the time to change anything in this regard.
cheers bernd
this should never happen. IMHO the data model of constraint displacement could be better, but I never spent the time to change anything in this regard.
cheers bernd
Re: Reaction force request
Will you go for a PR? Some unit tests would need to be adapted to get this into master.fandaL wrote: ↑Mon Aug 09, 2021 7:57 pmI have looked at it. This commit
https://github.com/fandaL/FreeCAD/commi ... 88df9caf6e
makes the same for Constraint displacement. I added if condition
...
cheers bernd