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-   -   Moment coefficient on moving mesh (http://www.cfd-online.com/Forums/openfoam-post-processing/103503-moment-coefficient-moving-mesh.html)

 flowris June 19, 2012 12:08

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?

 lovecraft22 June 19, 2012 17:15

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 June 20, 2012 01:33

Brilliant!

 louisgag October 28, 2015 12:31

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 ?

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