Obtain results with NASTRAN

The way Nastran works is that it first assembles the global stiffness matrix and then it removes the constraint degrees of freedom (SPC's) from it. Therefore, there is no way that you could solve a problem with different constraint sets (SPC's) in a single analysis. If you set up different constraint sets in the case control, Nastran will essentially save the uncondensed stiffness matrix and remove the SPC degrees-of-freedom and re-solve the stiffness matrix with each case. The program will appear to run only once, but it will actually give you different results for each SPC-set. If you need to combine your results, you might want to do this by combining the output using your post-processor. I would only do this if the actual boundary conditions did not change and you want to combine load cases (superposition).

Dear friend,

To run one or more Bc's, in Nastran, use spcadd card for n number of the Bc's and specify loadsteps for each subcases. i.e., for each and every Bc's specify subcases.

I think if you try to do the above mentioned point, u will get the result.

kumaravel.

kumaravel,

I believe that the SPCADD will only combine the SPC sets in Nastran. In jwirtz's example, it would be equivalent to running Load Case 1 with Constraint Sets 1 and 2 simultaneously. If that is what is desired, then the SPCADD would be the proper way to combine the constraints. If you want to run an analysis using Load Case 1 with independent Constraint Sets 1 and 2, I believe you will need to run two separate subcases and combine the results later (if the combination is meaningful).

pj