Reaction force request

About the development of the FEM module/workbench.

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Reaction force request

Postby poimsm » Mon Feb 13, 2017 11:32 pm

Any one knows how to calculate reaction forces on FEM FreeCAD 0.17? Thanks!
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Re: Reaction force request

Postby makkemal » Tue Feb 14, 2017 5:46 am

FreeCAD does not read reaction forces into results yet
You need to add RF to the *Node file card and the ... de159.html

Then on the freecad side read the results in in the file and pass them to VTK
This is not a difficult one for you to add yourself
Thanks for the contribution
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Re: Reaction force request

Postby fandaL » Tue Feb 14, 2017 9:28 am

Hi Poimsm, welcome to the forum.

You can request reaction forces in .frd file by

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or in .dat file - where it is practical to limit them on some nodeset

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*NODE PRINT,NSET=FemConstraintFixed
this prints reaction forces in x, y, z for all nodes. For me it is practical to ask for total reaction forces

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You can easily add this into your .inp file after similar lines when you generates it in FreeCAD, when you insert nodeset(s) which names you can find under *BOUNDARY card in the generated .inp file - something like "FemConstraintFixed".

if TOTALS=YES then you get it in nodes and also totals

However, there are some difficulties with reaction forces. I doubt it is possible to get reaction moments. From ... #nodeprint
The external forces are the sum of the reaction forces, concentrated loads (*CLOAD) and distributed loads (*DLOAD) in the node at stake. Only in the absence of concentrated loads in the node and distributed loads in any element to which the node belongs, the external forces reduce to the reaction forces. Forces induced by multiplpoint constraints are not calculated. Since single point constraints defined in transformed coordinates are converted into multiple point constraints in the global rectangular system, the force in a node in which a SPC is defined in local coordinates are not correctly delivered upon using the RF key in combination with the *NODE PRINT keyword card.
So if you apply loads through rigid body elements, then reaction forces are wrong. If you apply load on fixed node, then this load (e.g. portion of pressure on element face) is not counted to reactions.
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Re: Reaction force request

Postby ulrich1a » Tue Feb 14, 2017 10:20 am

The newer manuals of ccx like version 2.11 have an extra section regarding reaction forces. Have a look here: ... de177.html