Topography Optimization with OptiStruct - Error

[mizzjoey]

Dear all.

Hi. I've been trying to run some topography optimization on a structural part. I'm applying a simple static (downward) force on a node and I set the volume as the objective to min, and have not been able run the analysis due to the error below:

ERROR # 148 FROM SUBROUTINE chkapx
Invalid Design Problem.
All the sensitivities of the objective function are zero.

***** FATAL OPTIMIZATION ERROR *****


This error occurred in subroutine appdrv

***** FATAL ERROR ENCOUNTERED *****

Can any of you help explain to me.. what is this error? How can I fix my model?

Thanks a lot

jo

 

[GregLocock]

That's a new one on me.

The usual way I debug an optimesh deck is by a laborious reading of the deck, usually I've got a data container error.

Oh, and I always do the tutorial before running a real job.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BenAltair]

Jo,
Did you apply a design constraint? Otherwise the optimized solution is to remove all material and let the node deform into infinity. The simplest design constraints to define are displacements or compliance under the Responses panel. Then you can set the limits of the response under the DConstraints panel. As Greg mentioned (thanks Greg!), it's easiest to go through a tutorial then apply the same setup for your model.

Regards,
Ben

 

[BenAltair]

Jo,
I did some more research and this error is often caused when the base thickness is the same as the shell thickness in the PSHELL card. Both may be equal to 1.0. Optistruct defines the design space as the difference between these thickness values. When the difference is 0.0 there is no design space and you will receive the "Invalid Design Problem" error.

Let us know if you can't resolve this error.

Regards,
Ben