[sz617896964]

Dear all

I am new to OpenFoam.I tried to find out how to get the force coefficients by putting the code in the controlDict. As shown below,

application icoFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 100;

deltaT 0.001;

writeControl timeStep;

writeInterval 5;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable true;


functions
{

forceCoeffs1
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
writeControl timeStep;
enabled true;
writeInterval 10;
patches (
body
); //change to your patch name
rho rhoInf;
rhoInf 1000; // rhoInf - reference density
CofR (0 0 0); // CofR - Centre of rotation
liftDir (0 1 0); // dragDir - Direction of drag coefficient
dragDir (1 0 0);// liftDir - Direction of lift coefficient
pitchAxis (0 0 0); // pitchAxis - Pitching moment axis
magUInf 1.0; // magUinf - free stream velocity magnitude
lRef 1; // lRef - reference length, which is the chord length for an airfoil and the diameter for a cylinder
Aref 12.0; // Aref - reference area, which is the chord*span for an airfoil, and diameter*length for your cylinder
}
}

It always show "Floating point exception (core dumped). However, if I change the pitchAxis (0 0 0) to pitchAxis (0 0 1), it will work. I do not know why. In fact, I do not need to know the pitching moment in my case. Would you please do me a favour to explain it?

Kind regards,
Ze

[alexeym]

Hi,

During creation of the forceCoeffs function object axes vectors are normalised, to make their lengths equal to one. Normalisation is made by division axis vector by its norm. If you set axis vector to (0 0 0), its magnitude becomes 0, and you get FPE.

If you do not need pitching moment, simply ignore it.