FAST Linearization

Dear Jason

Firstly, Allow me to compliment you and your team on the great work that you are doing on wind turbines. I would like to put before you a problem which I have been facing while linearizing the NREL 5MW offshore wind turbine for obtaining the pitch sensitivity. I have referred to the original post where you have explained the process (Gain Scheduling) and also the FAST manual but I am still encountering difficulties. I am posting them as below.

  1. I am able to obtain the correct blade pitch angles for each steady wind speed using the FAST Linearization tool (CalcStudy = True)(e.g wind speed 18 m/s). The magnitudes of the rotor power, generator power, rotor torque as shown in the measurements column also appear correctly. So far so good.

  2. In the next step, When I turn off all the other dofs except for the Yaw control DOF and perform linearization using the blade pitch angles obtained from above step (CalcStudy = False), I get a zero coefficient corresponding to the rotor power term in the D matrix with respect to collective blade pitch. The rotor power also appears as a near zero term in the measurement column. Thus I obtain the pitch sensitivity as zero.

I have been using FAST_v7.02.00d-bjj for all my simulations. Is there a problem with the version with respect to linearization or is there a mistake on my part. The relevant fst, linearization file and .lin output file are attached here with my post. Please help me out.

I will be very grateful for your response.

Tuhin Roy
NREL.txt (17.4 KB)
NREL_LIN.txt (28.8 KB)
NRELOffshrBsline5MW_Linear.txt (2.1 KB)

Dear Jason,

I got the answer & it is working fine.