I am posting a message concerning the linearization method in order to develop a LQ controller. I am working on the paper “Optimal Control of a Ballast-Stabilized Floating Wind Turbine”, S. Christiansen, T. Knudsen and T. Bak.
But I do not understand to following step:
I understand that to know mt, kt and dt we need to run a FAST simulation. But how can I choose a constant wind and a blade pitch angle increasing from for example 14° to 16°?
And what means “The results were analysed using Lennart Ljung’s system
identification toolbox  to identify the tower parameters.”?
Any advice are very welcome. Thank you in advance.
Assuming you are using FAST v8, you can use the “Steady” wind model (WindType = 1) in the InflowWind module for simple simulations with constant wind. Also, the override pitch maneuvers in the ServoDyn module (input parameters TPitManS, PitManRat, and BlPitchF) can be set up to easily force a step in pitch angle from 14 to 16 degrees (i.e., set PitManRat to be very high).
I’m not familiar with that paper, but I believe that statement is simply referring to the System Identification Toolbox available within MATLAB.
That said, the linearization functionality of FAST can be used to directly obtain the linear system matrices of the wind turbine model, without the need for “black-box” style system-identification techniques.