No buckling modes found in an optimization process

Joao_21860

Hello everyone,

 

I am running a composite size optimization (OptiStruct version 2017.2) and considering displacements and buckling factors as the constraints of my problem. However, for some iterations and loadsteps, I am receiving the message 'no buckling modes found'.  I already tried increasing the number of requested buckling modes in the EIGRL cards as I saw someone suggesting in another forum, however this problem keeps happening.

 

Does anyone know how to solve this issue or what is the root of the problem?

Joao_21860

Anyone?

 

I have 3 buckling loadsteps and the buckling factors (BF) can be obtained without problems in a simple analysis.

 

I noticed that during optimization the BF cannot be found for the loadstep with the largest BF value (analysis results). Also, the BF are finally calculated when the values get closer to the constraint I am using (3).

 

Is it possible that the optimization only returns BF values for a certain range?

Adriano_Koga

@Joao

 

OptiStruct uses a mechanism called Screening that filters out the design constraints in optimization depending on how far they are from the boundaries (targets).

In your case, probably the bucklinf factors are more tha 50% above your target, and that's why OS doesn't take them into account in the very beginning.

As the optimization progresses, the constraints are closer from the target values, thus OS starts 'looking at them' back again. 

Q.Nguyen-Dai

@Joao show us your model?

Joao_21860

@Adriano A. Koga

 

It seems that's the case. The values start showing back when they are no higher than 4.5. Thank you!

Joao_21860

@Q.Nguyen-Dai

 

I unfortunately cannot upload my model right now, but it seems we found the cause. Thank you!