Phase shift in blade root flap wise bending moment

4

Dear @Suresh.Nakkala,

To design a pitch controller for a 3-bladed rotor, I would normally expect that you’d:

  1. Extract a periodic linearized model from OpenFAST (e.g., as you said, in 36 increments of 10 degrees)
  2. Apply MBC3 to each of these linear models
  3. Azimuth average the MBC3-transformed linear models, resulting in a linear time-invariant (LTI) model
  4. Eliminate the generator azimuth state from the LTI model
  5. Design your controller

When you simulate with the LTI model, I would expect that you’d post-process results in the rotating frame of reference (e.g., blade root flapwise bending moment) as follows:

  1. Compute the MBC-transformed outputs from the LTI model
  2. Integrate the generator speed to get the azimuth angle (which was eliminated as a state from the LTI model)
  3. Apply the inverse MBC3 to transform the outputs back into the rotating frame of reference

Are these the steps you have followed?

This process has been discussed previously on this forum, e.g., see: questions about reference control input and FAST linearization V7 - #7 by Yanhua.Liu.

Best regards,