Riks analysis

[Senad83]

Hi,

I'm doing some buckling analysis of a simply supported plate. I've ran linear buckling analysis to find the eigenvalues and used the lowes eigenvalue in a Riks analysis to seed an imperfection. But I expirience some wierd things. If I seed my imperfection to 1, the analysis complete and I can easely find the results. But if I seed the imperfection to 5, the analysis will not complete. The same happends if I run Riks analysis whitout seeding any imperfection. Do anybody know what could cause this?

Regards

Senad

 

[Andrea Mino]

The post buckling analysis is very sensitive analysis.
Do you try to take a step before analysis of buckling with a load of 90% of the first eigenvalue analysis of buckling not preloaded ?
Remember to active the nlgeom parameter to on.
After this, you can use this new values for imperfection.
The result is more precise and less parameter sensitive.

I hope I have been clear.

Bye

Minoand

 

[Senad83]

What I notice is that this is avoid by using a larger load in both the buckling and Riks analysis. So instead of using 1 N, I can use 1000 N and avoid the problem. I find this odd. I've used nlgeom, but the step before analysis of buckling I did not understand. Do you mean that I should run a general static step with a "dead load" before the Riks analysis?

Regards

Senad

 

[Andrea Mino]

Yes.
The buckling analysis is a linear pertubation analysis, so if you evalute a preload structure the results could be different.
Bye
minoand