Topology Optimization with Changing Wall Thickness and Max Stress Considered

Altair Forum User

Hello, 

 

I am in need of help setting up an Optistruct run. I want to optimize wall thickness with a upper limit on stress. I have used a 2D automesh and I have a DTPL that veries wall thickness of the main body a base of 1.0mm to 10mm (defined by material property). I have the objective of the Optimization to Minimize VolFrac, and the responses set to VolFrac and StaticStress. Lastly I have set the upper bound of StaticStress to be the Failure stress with a OptimizationConstraint. 

 

Whenever I run the Optimization the wall thickness does not very with every iteration (stays at 1.0mm). Attached is my .hm model. Is there a tutorial that shows you how to do this? 

 

Thanks!

 

 

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Simon Križnik

Hi,

 

topology optimization uses element density as a design variable, not thickness. The objective of topology optimization is to determine where to locate ribs in the designable region. Non-zero base thickness is defined to avoid holes and set constant minimum thickness. The maximum thickness, which is defined by the T field on the PSHELL card, should be the allowable depth of the rib.

 

For details on base thickness refer to tutorial: 

OS-T: 2020 Increasing Natural Frequencies of an Automotive Splash Shield with Ribs

 

Stress constraint can be defined in the topology panel itself i.e. within the DTPL card.  However (form Optistruct Help):

 

 

 

 

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.

 

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.

 

 

Some observations/recommendations:

• the static stress constraint in the range 5-282 MPa on z1 causes optimization to produce infeasible results. Use stress constraint on DTPL instead and address detailed stress constraints in subsequent size, shape, and free shape optimization (or a combination thereof).
• there are forces in the 'Constraints' load collector
• using only 1st order triangular elements is not recommended. Use 2nd order trias or 1st order quads instead
• use analysis>optimization>opti control>CHECKER=1 to reduce checkerboard effect

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