Question about the force functions in the airfoil example
 

Hey Foamers,

I am working on the airfoil example that is provided with the openfoam. I am trying to calculate the drag and lift coefficients by implementing a special file for that. Even thought I have got results for both the drag and the lift, some commands don't make sense. I am wondering if someone could explain these lines.

Regards,

forceCoeffs
{
type forceCoeffs;
functionObjectLibs ( "libforces.so" ); <----------------------------------------------- Can somebody explain this command?
outputControl timeStep;
outputInterval 1;

patches ( "" );
pName p;
UName U;
rhoName rhoInf;
log true;

liftDir (0 1 0); <----------------------------------------------- Can somebody explain this command?
dragDir (1 0 0); <----------------------------------------------- Can somebody explain this command?
CofR (0 0 0);
pitchAxis (0 0 0); <----------------------------------------------- Can somebody explain this command?

magUInf 75.00; // Free stream velocity magnitude
rhoInf 1.225;
lRef 1; <----------------------------------------------- Can somebody explain this command?
Aref 1; <----------------------------------------------- Can somebody explain this command?