Releasing a forced displacement

[kellnerp]

In NE Nastran the SPCD command will enforce a displacement on a node. In a non-linear run placing the SPCD command in a SUBCASE and then removing it in the next SUBCASE results in the enforced displacement being ramped down leaving me where I started. My goal is to remove the enforced displacement simply be removed and the structure then find it's free state. There is contact in this model.

Does anyone have an idea as to how to remove the SPCD displacement without having it ramp back to zero?

 

[nazariosr]

Maybe the NOLIN forcing functions could do the trick instead of SPCD????

 

[kellnerp]

I'm doing non-linear static so NOLIN is out of the picture. Somebody suggested using a gap to allow load in one direction and relieve the load when the SPCD moves back to zero. That seems to be doing the trick. Thanks for the suggestion.

 

[fkmeyers]

Loads will ramp back to zero. SPCD is treated like a LOAD. Use the SPC entry which is selected from the case control using SPC. If you specify a different SPC from one subcase to the next, it will immediately change to that new SPC. Is that what you want to do? If so you have to add this by hand in the editor because FEMAP does not support it.

 

[kellnerp]

Thanks. SPC did the trick.

 

[ThomasH]

I think you can do this within FEMAP using the text dialogs in Executive Control etc.

Basically, anything you can do in the text editor can be done in FEMAP buy sometimes it's a bit more complicated. On the other hand, if you use Analysis Set's you only have to do it once. There are Pros and Cons to both methods.

Regards

Thomas

 

[kellnerp]

I just edited my .nas file with UltraEdit and put in the additional boundary conditions. If I had started out on this path I would have just created several different constraint sets. I am not sure what you are refering to in Executive Control. I haven't used that yet.

 

[zerodof]

Can any body advise on the best practice for calculating point mobility using Nastran.