[Friendly]

Hi,

I would like to transform my force vectors to scalars directly in OpemFOAM while solving. I am using the following lines in my controldict to get the force vectors:

forces_fixedWall
    {
        type forces;
        libs ("libforces.so");
        writeControl timeStep;
        writetInterval 1;
        patches (fixedWall); 
pname p;
Uname U;
        rhorhoInf;
        rhoInf 1; 
        CofR (0 0 0);
    }

What I want is the force normal to the surface as scalar without calculating it manually by using the dot product with the normal vector.

Does anyone know how to do it?


Greetings

Friendly

[louisgag]

Hi,

Assuming that your fixedWall patch does not rotate, one option would be to change the localSystem_ value in the forces.C code, but that would require some code reading and testing...

Another simpler option, is to "hack" the drag coefficient by making it return the force values instead of the drag coefficient and feed it the direction(s) you are interested in as:

liftDir         (0 0 1);
dragDir         (1 0 0);

You can find drag coefficient examples in the following tutorials:

./compressible/sonicFoam/RAS/nacaAirfoil/system/controlDict:66: dragDir (0.970839 0.239733 0);
--
./incompressible/pisoFoam/LES/motorBike/motorBike/system/controlDict:105: dragDir (1 0 0);
--
./incompressible/pisoFoam/LES/motorBike/motorBike/system/forceCoeffs:21: dragDir (1 0 0);
--
./incompressible/simpleFoam/motorBike/system/forceCoeffs:24: dragDir (1 0 0);

All you would need to do apart from setting the wanted drag direction is to ensure

(Aref * magUInf^2 * rhoInf) / 2 = 1

and, obviously, test to ensure the formulas are those...

Hope this helps,