Exact Displacements in an Eigenvalue Problem!

[Sajjad2164]

Hello
I've performed a linear (eigenvalue) and non-linear buckling problem, and everything went perfect except for a question I couldn't find its answer to. The question was that when you applied a fraction of eigenvalues to your nonlinear buckling analysis, do you know exactly the magnitude of the displacements you applied as the geometry imperfections? To answer the following question, I performed a simple problem (rectangular plate modeled by shell elements) and found its first five eigenvalues. The displacements are somehow scaled. I'm assuming if I multiply the scale factor to the magnitude of the displacements I'd get the exact values of those displacements, and I'd be able to answer the question I was asked! Do you agree with that statement? If anyone can guide me on this issue I'll appreciate it!

 

[FEA way]

Unfortunately, you can’t get real displacements from linear buckling analysis by just multiplying them by a factor. Displacements in this type of analysis are normalized so that the maximum is 1. To get actualt magnitudes of deformation you have to perform nonlinear buckling analysis (with or without imperfections in form of scaled mode shapes from preceding linear buckling study).