Costfunction

entropie · July 9, 2014, 04:16

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:

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

Sincerely, Olivia

Bernhard · July 10, 2014, 09:35

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

entropie · July 11, 2014, 04:35

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?

July 9, 2014, 04:16	Costfunction	#1
entropie New Member Olivia Nalen Join Date: Apr 2014 Location: Vancouver Posts: 19 Rep Power: 12	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: Is there an appropriate argument, why is this so? Is that generally correct? Sincerely, Olivia

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July 10, 2014, 09:35		#2
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 21	You do not provide any information. What kind of answer are you even expecting?

July 11, 2014, 04:35		#3
entropie New Member Olivia Nalen Join Date: Apr 2014 Location: Vancouver Posts: 19 Rep Power: 12	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?