Costfunction
 

Hello dear all,

I've been working on a problem to min. some cost functions with an adjoint method using adjoint NS-equations and gradient.

In all tests I became a constant decreasing cost function. Till the last test, where the cost function look like this:


http://storage.workupload.com/image/g6YsgK3c


Is there an appropriate argument, why is this so? Is that generally correct? :confused:

Sincerely, Olivia

You do not provide any information. What kind of answer are you even expecting?

Well you are right. A cost function was drag/lift ratio and the object was an NACA 4415-airfoil. During the optimization the airfoil converged to a thin plate. Drag coefficient was constantly decreasing; lift coef. too, but not as rapid as drag. So, drag/lift ratio was also decreasing but only till step 50, then it was increasing. I've wondered why. I thougt it can be either because of solver was incorrect or because it is physically not really possible to minimize ratio further. I'm not sure.

Is this enough information? Can you help me?