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# Coast Down Testing Methods

## Coast Down Testing Methods

(OP)
I was looking into using a coast down test method to calculate the mechanical friction in the driveline of a wind turbine.  I know the coast down test is used probably most frequently for testing cars, which is why I posted here.

In the coast down test, is there a known method of finding the value of the frictional force if I know the velocity profile of the rotating turbine coasting down?

What i'm thinking is that if I have a plot of rotational kinetic energy (KE = 1/2Iw^2) vs. time, the slope will be negative and will represent the power loss (energy/time).  Since Power = Fv (or Power = Frw), knowing the slope of the energy vs. time graph (Power) and the velocity, F (force of friction) can be calculated.  This is assuming that F is relatively constant with speed.  Am I on the right track?

### RE: Coast Down Testing Methods

Yes, except that your friction is likely to vary with speed, depending on your bearing type.

measuring the efficincy of power transmission devices is tricky - differential amnufacturers use a method based on measuring the heat radiated by each bearing, for example.

Cheers

Greg Locock

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