CFD Online Discussion Forums - Moment coefficient on moving mesh

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Moment coefficient on moving mesh

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:

Code:

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?

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

Quote:

Originally Posted by lovecraft22 (Post 367330)

p2p1 = vector going from p2 to p1

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