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Negative Buckling Factors

Hello,

I've running a topology optimization with a buckling constrain (which is possible, since I'm working on a shell-element). The results are not satisfying, because of two practical problems:

1) I need to specify very large frequency ranges for buckling modes, since the optimization the design space will use a higher thickness then the optimization results. This is making it difficult to find buckling modes.

2) The solver returns a negative response value for the buckling factors. How is this even mathematically/physically possible?

See attachment:

<?xml version="1.0" encoding="UTF-8"?>

I would really appreciate help on this topic - thank you!

Galerkin

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Altair Forum User

2) The solver returns a negative response value for the buckling factors. How is this even mathematically/physically possible?

In general, with negative factor your current structure with current loading got never buckling phenomenon.

The negative sign means that you have to change the direction of your load so that buckling could be possible.

Altair Forum User

Thank you, that explains a lot. What I still don't get is the physical background. If we agree that lambda=Fref/Fact, and we have only magnitudes and not vectors in this equation, how can we possibly obtain a negative figure?

Altair Forum User

What can I do in practice to solve the '-lambda' problem?

Altair Forum User

Any ideas?

Altair Forum User

Hi Galerkin,

Negative buckling means the tendency to buckling when the loading is reversed. The load factor (lamda or buckling eigenvalue) changes the sign accordingly. Eg: The A thin pressure vessel subjected to internal pressure might be stable for buckling.. however fails when the loading is from the opposite external side.

Altair Forum User

Hi Prakash,

the problem is the following: if I use a large thickness, buckling modes are not found in the optimization. If I use a small thickness, buckling is dominant and no feasible solution will be the output.

What can I do to omit this problem? I didn't get any useful results.

http://i.imgur.com/Ufniy0H.png

Thank you

Galerkin

Altair Forum User

Any solution for this?

Altair Forum User

Any solution for this?

If you can not get solution here, you have to contact your Altair local support for this.