3P frequency fixed frame

Dear Jason,
If I’m not wrong a 1P load in the rotating frame causes only a 0P and 3P load in the fixed frame. I’d like to see this effect on fast,I mean that I need to have only a 3P load on the fixed frame…but if i consider no turbulence,no yaw error,no shear but only Tower Shadow I see 3P but also other components! How can I run a simulation that gives me only 3P frequency loads in the fixed frame?
Thank you!

Dear Alessandro,

I agree that a true 1P load in the rotating frame would only cause 0P and 3P loads in the fixed frame.

However, tower shadow induces more than 1P loads in the rotating frame. A true 1P signal would be sinusoidal with a frequency of 1P. But because the tower shadow only directly impacts a small portion of the blade during a revolution, the tower shadow will induce higher-order harmonic loads in the rotating frame. Thus, I would expect the tower shadow to induce 0P, 3P, 6P and higher harmonic loads in the fixed frame.

Best regards,

Dear Jason,
Thank you for your answer!..The problem is that I have measured accelerations that shows really high 3P component in the fixed frame…so I’am trying to tune the Fast Model to see this effect.Do you have idea about how build a model that underlines the effect of 3P loads in the fixed even if with smaller components like 6P and 9P…?

Dear Alessandro,

Well, what you proposed originally…the inclusion of tower shadow will cause a strong 3P response in the fixed frame (as well as higher harmonics).

Best regards,

Dear Jason,
Thank you for the answer!
Can you suggest me some references to read or explain why tower shadow causes also others components than 1P in the rotating frame?

Dear Alessandro,

I tried to explain that in my post above. A true 1P signal would be sinusoidal with a frequency of 1P. While a tower-shadow-induced load in the rotating frame will have a strong 1P effect, it will not be a pure sinusoid, but will include higher-order harmonics.

Best regards,