NASTRAN SOL 106 Output

[patolon]

Hello!

I've got a quick question about SOL 106 that I am using for non linear buckling.

I've got 10 load cases (10,20,30,40,50,60,70,80,90,100 bar pressure cases), and I would like to predict buckling for that.

The output gives me ALPHA values, usually not far from eigenvalues. From this ALPHA I can calculate Pcr, from the incremental load case.

But I don't know how to interpret these results! What does that mean exactly? For each load case I have a Pcr, so how do I known I have buckling?
It's a bit confusing, compared to linear buckling where I have a set of buckling load factors for the given load. But here, as the load is incremental, it looks like buckling will occur at each load step.

Hope someone can clarify that!!

cheers

 

[JBlack68]

Are you not confusing sol 105 (buckling) with sol 106 (non linear)?

[ul]
[li][/li]
[li]sol105 will give you the buckling load (buckling factor * applied load)[/li]
[li]you don't really have load cases in sol106, so your reference to such things is confusing[/li]
[li]if you mean that you are ramping the load from 10 to 100 then fair enough otherwise it doesn't mean anything[/li]
[li]if you do run a sol106 (from load =10 to 100) and monitor a displacement (out of plane),the total load reaction, anything you think is suitable really, then the curve load vs. output may show a "kink" which may correspond to the buckling of the structure. Whether is the overall buckling or a local buckling I cannot say![/li]
[/ul]

 

[patolon]

Thanks for your reply.

Well, if I want to know if buckling will occur at 100bar, I have 10 load cases, up to 100 bar.

But from the f06 file; there is an ALPHA value for each of the load cases, so it seems like buckling is predicted for each case!!

Also, looking at the displacement of the grid point; nastran gives me the eigenvector displacements which are 10E-18 so zero...

How can I get the actual displacement so that I can plot F vs displacement and visualize buckling?

Thanks!