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DRESP2 stress not equal with DRESP1 stress

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I would like to calculate a special safety value from stress responses, and using it in topology optimization.

The test of this calculation is started with a simple problem.
DRESP1 case 1:
- constaint: DRESP1 (von mises stress response, one selected element)
- objective: DRESP1 volume 
DRESP2 case 1:

- only response: DRESP1 (von mises stress response, one selected element)

- constaint: DRESP2, (equation response) is calculated the following equation a(x)=x and using the DRESP1 von mises response
- objective: DRESP1 volume 

In this case the changes on design variables are the same, and the results are the same. :)

Than i changed the response element quantity to 2 and the DRESP1 and DRESP2 case results are different

I have tried to change constraint screening, nothing has changed
I have tried to look on sensitivity values, but no stress values included in *.asens files or *_topol.h3d files

I have tried to compare it with displacement response/constraint and they are good, so the DRESP1 and DRESP2 with 2 response nodes has the same results.

Is this problem connected to Stress-NORM aggregation ?
How can i turn ON Stress-NORM aggregation in DRESP2 case?
How can i examine the stress response sensitivities?
Did i miss someting in the setup?

I have attached the 2 different *.hm and *.fem files







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On ‎1‎/‎17‎/‎2019 at 2:25 PM, Rahul R said:

Please refer some information from online help for stress response.

Stress Response.pdf

Thank you, Rahul!
The document was helpful.

I have tried out to set DOPTPRM, PNORM , 1 it means that the stress-norm calulates the average of the stress values divided by the response constraint value.

The constraint value is 50, and the von mises result of the 2 choosen elements in the iteration 0 was 68.86 and 38.26 (from the results) so the stress norm value should be (68.86/50+38.26/50)/2=1.0712 , but in the output file this value is 1.377.

Can you explain me the difference?

I have attached, the *.hm file, so you can check it.

Thank you again!



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