Negative eigenvalues 2

[Senad83]

Hey,

I'm doing buckling analysis with 5 eigenvalues. One of the is negative, but my analysis still completes with out errors or warnings. Does anybody know how I can avoid the negative eigenvalues?

Senad

 

[johnhors]

Arbor,

Assuming you have modelled the whole pressure vessel then the vast majority of your structure will be in tension, hence the many negative eigenvalues found by Abaqus. There may be a considerable number of these encountered before Abaqus spits out the positive eigenvalue you seek. I am not aware of any means of suppressing negative eigenvalues. Have you considered running a static large deflection non-linear analysis using NLGEOM instead? This may be more appropriate than a buckling analysis for this type of problem.

 

[arbor]

johnhors,

You are right about my model and the eigenvalues. I have several approaches to check different failure modes of a pressure vessel based on ASME code. The approaches include linear elastic and non-linear plastic analysis. The code also requires to check buckling when there is compressive stress. There is no very good analytical solution for head knuckle buckling load. So I am trying to see if ABAQUS can help for this case. Thanks

Arbor