Excel like goal-seek type functionality in OpenFOAM

benk · April 30, 2010, 16:02

This is a long shot, but is there an excel like goal-seek functionality in OpenFoam?

In one of my custom made solvers I have a non-linear algebraic equation and I need to iterate for a value inside the equation, like:

Val = [exp(b*a) + exp(-c*a)]

I know everything except a, which I want to find.

benk · April 30, 2010, 16:40

I guess I'm looking for a built in Newton's method in OpenFoam. It's fairly easy to implement actually (as long as the analytical derivative is known).

chegdan · April 30, 2010, 16:46

Openfoam has a root finding method that I have never used but noticed while looking around in the source. Take a look at:

/OpenFOAM/OpenFOAM-1.5-dev/src/ODE/findRoot/BisectionRoot
and
/OpenFOAM/OpenFOAM-1.5-dev/src/ODE/findRoot/RiddersRoot

of course this is in your particular version, mine being the 1.5-dev type. You could also do some sort of newton-raphson type root finding or many others that are in the Numerical recipes books with:

lhs-rhs=0 and find the root of your function of a.

Hope this helps.

Dan

benk · April 30, 2010, 16:50

Interesting, I'll take a look at that. Thanks.

April 30, 2010, 16:02	Excel like goal-seek type functionality in OpenFOAM	#1
benk Senior Member Ben K Join Date: Feb 2010 Location: Ottawa, Canada Posts: 140 Rep Power: 20	This is a long shot, but is there an excel like goal-seek functionality in OpenFoam? In one of my custom made solvers I have a non-linear algebraic equation and I need to iterate for a value inside the equation, like: Val = [exp(ba) + exp(-ca)] I know everything except a, which I want to find.

April 30, 2010, 16:46	Root finding	#3
chegdan Senior Member Daniel P. Combest Join Date: Mar 2009 Location: St. Louis, USA Posts: 621 Rep Power: 0	Openfoam has a root finding method that I have never used but noticed while looking around in the source. Take a look at: /OpenFOAM/OpenFOAM-1.5-dev/src/ODE/findRoot/BisectionRoot and /OpenFOAM/OpenFOAM-1.5-dev/src/ODE/findRoot/RiddersRoot of course this is in your particular version, mine being the 1.5-dev type. You could also do some sort of newton-raphson type root finding or many others that are in the Numerical recipes books with: lhs-rhs=0 and find the root of your function of a. Hope this helps. Dan

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April 30, 2010, 16:40		#2
benk Senior Member Ben K Join Date: Feb 2010 Location: Ottawa, Canada Posts: 140 Rep Power: 20	I guess I'm looking for a built in Newton's method in OpenFoam. It's fairly easy to implement actually (as long as the analytical derivative is known).

April 30, 2010, 16:50		#4
benk Senior Member Ben K Join Date: Feb 2010 Location: Ottawa, Canada Posts: 140 Rep Power: 20	Interesting, I'll take a look at that. Thanks.