Unit enforced displacement and rotation validity check

[Alberto94]

Dear Sir/Madam,

The unit enforcement displacement and rotation valitidy check is a check described in the following link, in the FEMCI book:

https://femci.gsfc.nasa.gov/validitychecks/vc1.html

Basically, it consists on setting free all nodes of the model except one, which is given a unit displacement in one direction. The whole model should then move as a solid body one unit in that same direction.

I have been attempting to this check on a very simple model, but I have been unsuccessful. This is making me doubt other simulations that I have done in the past. Would you be so kind to have a quick look? I have tried changing many parameters but nothing seems to work. I am attaching both the bdf input file and the f06 output file. Note the wrong displacements of the grid points on the f06 file.

Thank you very much in advance for your reply.

Kind regards,
Alberto.

 

[dmapguru]

The unit enforced displacement analysis is based on the pretext that your model is not singular. Your model appears to contain only ROD elements which have axial and torsional behaviour only (no bending); this makes them incapable or transmitting in plane bending loads.

Run the model in SOL 103 (if it will run without massless mechanisms) and if you get any rigid body modes, it will never solve in statics. Add boundary conditions to remove the rigid body modes in a statically determinate configuration, and then try the enforced displacement analysis.

DG

 

[Alberto94]

Thank you very much for your detailed reply sir.