# FAST linearization V7

Dear Jason,

Thank you so much for your quick email response and answer. Actually, I have applied inverse MBC to the linear model. The figure is after inverse MBC transformation. Does this mean the linear model is not so exact and have some accuracy problem?

Thank you again and all the best to you.

Yanhua

Dear Yanhua,

Have you applied the inverse MBC3 transform to the outputs i.e. have you taken the collective, cosine, and sine flapwise bending moments and converted them to individual blade bending moments? I would expect this to yield oscillations in the individual blade bending moment if the cosine and/or sine terms are nonzero; are they?

Best regards,

Dear Jason,

Sorry for the delay. Yep, I have applied the inverse MBC to the individual blade bending moments and also the cosine and/or sine terms are nonzero. The blade bending moments did not show any periodicity in 1P after inverse MBC. I tried another linearization by adding tower DOFs. But the results are similar and still fail to show the periodicity in 1P. So do you think what the possible problems are? Thanks a lot. I really feel desperate about this.

Happy Easter! Enjoy the holiday. And all the best to you.

Yanhua

Dear Yanhua,

I would guess that the problem is related to how you are applying the inverse MBC. I guess you wrote a script that that takes the collective, cosine, and sign terms and converts them individual blade coordinates i.e. q_b = q_0 + q_cCOS(azimuth_b) + q_sSIN(azimuth_b)–is that correct? Then, if q_c and/or q_s are nonzero, then q_b should naturally be periodic with the blade azimuth angle.

Best regards,

Dear Jason,

Nope, I think that the inverse MBC is right. I found something is wrong with my linearization results. I linearized the NREL 5MW wind model at 18m/s with two DOFs like Generator DOF and 1st blade flapwise bending DOF (using Test18.fst). The inputs used are three individual pitch angles and the horizontal wind speed is set as the disturbance input.

Can you ask a question about the set of VSContrl in “SERVODYN.dat”? Should we set this as 0 or 1? If I set as 1 (I tried), are the related parameters in “Simple variable-speed torque control” right?

I found the original 9 inputs including “Blade 1/2/3 pitch command” and “Extended input: collective blade-pitch command”. Because i want to design individual pitch control, I chose “Blade 1/2/3 pitch command” as the inputs. However, I have a confusion about the difference between “Blade 1/2/3 pitch command” and “Extended input: collective blade-pitch command”. If I chose the before as the inputs, do I need the latter one as the inputs? Thanks a lot.

By the way, I attached my linearization files. Can you help me to check and make sure everything is right?

Thanks a lot. All the best.

Yanhua

Dear Yanhua,

Yes, if you set VSContrl = 1 then the related parameters in the “simple variable-speed torque control” section are used. If you set VSContrl = 0, then you should select either GenModel = 1 or GenModel = 2 during a linearization analysis.

The “collective blade-pitch command” was added as an input to show the influence of consistent blade-pitch commands across all blades. You can always set the inputs you don’t need to zero.

Your input files look fine to me.

Best regards,