composite free size optimization

Hallo everybody.

 

I want to run a free size optimization with Optistruct. My model is an Formula Student Monocoque. Everything is ok until I set the optimization. I have got 9 loadcases. One of them is pure torsion. Now, that´s what I have done so far.

 

- I set the design variable 'free size'

- I set a response static displacement and took two nodes (dof 3) with an dconstraint, lower an upper bound and all loadsteps

- I set a response mass with an objective min

 

I set the cards:

- PARAM, in_rel=-2

- GLOBAL_OUTPUT_REQUEST:  CSTRAIN and CSTRESS

- OUTPUT: FSTOSZ

 

I set opticontrol:

- DESMAX= 80

- OBJTOL= 0.005

- DELTOP= 0.5

 

The Check is ok, but when I start an optimization there is an fatal error after about 20 minutes.

INFEASIBLE DESIGN

 

Then I tried to make an new response.

The displacement response only with the loadstep with the pure torsion and another response with composite failure and the other eight loadsteps. But the free size card don´t support that response. The check and optimization .out files are attached.

 

 

FInaly my question. Is there any way, how I can fix it. Or another way I can run an optimization?

 

Thanks for your help

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