Question about Sum of the out-of-plane moments

Dear all,

Recently, I am trying to sum up the blade 1,2,3 out-of-plane moments using FAST. The results suggest me that the sum of the blade out-of-plane moments tends to a constant, and has a prefered constant angle (in a stationaty coordinate system). Is this result reasonable? If yes, is the fact caused by the teeter? Or I had some bug in my proceedure, which is the following:


Where M1, M2, M3 are Blade 1, 2, 3 out of plane moments(RootMyc1,RootMyc2,RootMyc3)
A is the Azimuth angle(Azimuth)

I appreciate any discussion and consideration. Thank you.


Zhichao Yu

Dear Zhichao,

Your equations look correct for a 3-bladed rotor when the azimuth angle “A” is defined as zero degres for blade 1 pointing up. I don’t really understand your point about teeter because a 3-bladed turbine would not have a teeter degree of freedom. A constant rotor-total out-of-plane moment and direction would suggest that the rotor thrust and center-of-thrust remain stationary. I would expect this to be the case when simulating with a steady wind speed, but not if the wind is time-varying.

Best regards,

Thank you so much, Dr. Jonkman. Now I will continue the work about the out-of-plane moments.