[flowris]

Quick question: I use forces to calculates forces and moments on a moving object. The forces are well calculated, but the moment is not, and I think this is because the center of rotation (CofR) is fixed in system/controlDict:

functions
{
forces
{
type forces;
functionObjectLibs ( "libforces.so" );
outputControl timeStep;
outputInterval 1;
patches (foil);
pName p;
UName U;
rhoName rhoInf;
log true;
rhoInf 1000;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 1);
magUInf 0.4;
lRef 0.1;
Aref 0.002;
}

I know at any time where this point is (can be seen from the dynamicMeshDict), but can forces change its CofR?

[lovecraft22]

I don't have much of experience on this but if you know where your CofR is in time, then you can easily evaluate the moment around any other point P:

Mp1 = Mp2 + p2p1 x F

Where:

Mp1 = moment around point p1
Mp2 = moment around point p2
p2p1 = vector going from p2 to p1
F = the force which generates the moment
x = cross product

[flowris]

Brilliant!

[louisgag]

Originally Posted by lovecraft22

p2p1 = vector going from p2 to p1

am I wrong or this vector should p1p2, instead of p2p1 ?