Hi guys,
I have a very simple cylindrical pipe inside which a negative (vacuum) pressure is acting, and hence it "buckles" under that pressure. I performed a modal analysis and obtained different modes and the corresponding displacements (around 5mm) for each modes.
I am inputting this results file as the *IMPERFECTION file for the Abaqus Riks analysis step for the same model. I am scaling the modes by different values.
The analysis is converging, but I hardly see any deformation (it is in the order of 0.5).
I feel I am missing something. I don't know what though. Could someone please shed some light?
Hi Claudio,
Thank you for such a good explanation. I am now more clear about how geometric imperfections and modes work.
I found out where I was going wrong.
I was performing a frequency analysis (without any loading, since it doesn't require any) and reading the nodal displacement values. Abaqus has a 'Buckling' frequency analysis also, where you can add the normalized load conditions (in my case, a distributed pressure of 1 bar) on the internal surface of the cylinder. I requested the nodal displacements for about 10 modes, scaled them down by a few factors and used them as an input for the Abaqus Riks analysis (which actually performs the Buckling analysis with actual loading conditions). I was able to obtain good results and a smooth transition, post-buckling.
Also, the Master thesis report of Tim Chen that you provided the link for is really good. I haven't gone through in details, but seems to be very informative to me. Thanks once again!
An excellent review paper on buckling with 303 references is Ikeda, K., and K. Murota, 2008, "Asymptotic and Probabilistic Approach to Buckling of Structures and Materials," ASME Applied Mechanics Reviews, Vol. 61.
http://appliedmechanicsreviews.asmedigitalcollection.asme.org/article.aspx?articleid=1399016
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