Optistruct - Compliance formulation in model withThermal + Mechanical loads

AlfonsoSerrano10

Hello,

I am exploring different optimization setups for a model with a unique load case which consists of:

- SPCs → coming from enforced displacements (that is nonzero SPCs)

- Mechanical Loads → bearing loads

- Thermal Loads → different temperatures in whole model

My first thought was that a minimize Compliance objective would output bad results, as compliance has opposite behaviour in stiffness for applied forces (first formula) and applied displacements (second formula).

However, the densities countour looks like this:

That is a good optimization result with a Discretness index of 0.49 and a 0.15 design volfrac constraint achieved. I have also reviewed the .asens files and the sensitivies for the compliance response are both negative and positive across the elements.

I wonder how is the software counting for both compliance formulations in the sensitivities calculation.

Thanks.

Kind regards,

Alfonso

Kranzeder

That is tricky.

For force driven loading you have to minimize compliance to get a stiff design.

For displacement driven loading you have to maximize compliance to get stiff design.

In case you combine both things in one loadstep the optimization will look for those sensitivities which have the most impact and go for these .

If you have imbalance for sensitivities between the different loadings (which I think this is the case in general) one of the loadings will more or less lose the battle and is ignored.

Finally, the above mentioned does not prevent the solution to be discrete.

The only chance you have in such a combination, is to have single loadsteps with single compliance responses for each loading type. As long as you do linear static this is valid, because finally it is superpositioned anyway.

Then use a DRESP2 function response to combine and weight them.

e.g. Ctotal = W1*C1 + W2*(1/C2) + W3*C3….  (I hope you get the point)

In case you need responses where all the single loadcases are combined, feel free to add you initial combined loadcase and use responses from this loadstep.

Now use Ctotal as your objective and minimize.