stress constraint in design variable vs. as constraint topology optimization

ElineH

Hi,

 

I know this question is already asked multiple times but I still haven't fully understood it.

 

What is the exact difference when I define my stress constraint in the design variable of topology optimization or when I add it as a response and then a constraint of the optimization.

 

When I add it in the design variable, without any other constraint it doesn't do anything (see attachment). 

Opposite to when I define it as a response and constraint. Then it does give results, although not very good ones.

When I apply them both on one design, it gives a different result then when I only apply one of them 2.

 

I do topology optimization of a hook with a minimum compliance and no other constraints or requirements.

 

thank you!

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Simon Križnik

Hi,

 

Stress constraint is not recommended in the design concept stage: topology, topography and free-size optimization.



The stress constraint definition in a topology optimization is a global constraint and does not target local stress concentrations.  These areas can be addressed subsequently through size, shape, and free shape optimization or a combination thereof.  Artificial stress concentrations are filtered out during topology optimization with stress constraints.  These include regions around rigid connections, concentrations due to hard geometric features such as corners, etc.

 

Stress constraints for a partial domain of the structure are not allowed because they often create an ill-posed optimization problem since the elimination of the partial domain would remove all stress constraints.  Consequently, global stress constraint applies to the entire model when active, including both design and non-design regions. Stress constraints may not work well in a model where there is a large differential in response values between design and non-design spaces. In these cases, it is recommended to modify the problem formulation to say, compliance based for example. It is not recommended to use the global stress constraint along with a mass/volume constraint. The constrained mass/volume may not allow the stress constraint to be satisfied.

 

DRESP1-card stress constraint is used in subsequent design fine-tuning stage such as size, shape and free shape optimization.