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please help for postbuckling analysis in ANSYS

Submitted by Talha Ekmekyapar on

I am trying to perform postbuckling analysis of plates in ANSYS. But something confuses my mind. After linear buckling analysis I use scaled firtst buckling mode shape to generate initial imperfections. Then I initiate nonlinear geometric analysis by NLGEOM command. Collapse load or final converged iteration changes according to NSUBST option. I am trying to give higher Substep to obtain more sensitive and reliable results like 10000. But NSUBST with 100 sometimes reaches higher loads than using 10000. Which one is a correct approach?

Could anyone help me?

Thanks alot....................

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Jayadeep U. B.

Hi,

I am not an expert, but I will just add two points, which appears relevant to me.

1. A more accurate analysis should predict lower buckling loads, and hence I don't see anything confusing in your observations.  However, the exact load, which you are going to consider as the buckling load, may need some serious considerations, as the non-linear analysis is going to give you a continuous curve.

2. If you need to perform post-buckling analysis, I believe that you will have to perform a displacement controlled analysis.  I don't think, even arc-length controls are going to give you convergence beyond the buckling load in a load controlled analysis.  Isn't it possible to get the buckling load from reaction solutions in case of displacement control?

Hope the above points are useful. Regards,

Jayadeep U.B.

Fri, 05/22/2009 - 16:40 Permalink
Talha Ekmekyapar

First thanks for your interest

I investigated displacement controlled analysis for postbuckling after your suggests. Some research papers and ANSYS help menu mention about that. But they are not clear and I could not conceive how to adopt my APDL code. So could you give a basic APDL code for displacement controlled postbuckling analysis.

Best regards.

Talha Ekmekyapar

Mon, 05/25/2009 - 07:55 Permalink
Jayadeep U. B.

Dear Talha,

I am not working extensively in ANSYS nowadays, and I do not have any APDL codes.  To be frank, I have never done a postbuckling analysis, and hence I am not even competent to write one... The above comment was just based on my conceptual understanding of the problem.

Regards,

Jayadeep 

Tue, 05/26/2009 - 04:27 Permalink
jagadish.Gunda

I did post-buckling for beams and plates. But for  cylindrical shells there is a problem.  The first buckled mode after the nonlinear solution completed is different from

the linear buckling mode. In nonlinear modes there is no crests and trough ( m and n loops). How to tackle this problem. Can anybody  resolve this using ansys APDL.??

 Jagadish

 

Fri, 12/18/2009 - 06:15 Permalink