Linearization of the "NRELOffshrBsline5MW_Monopile_RF" model

Dear Mehdi,

I’m sorry, but I don’t really understand your question.

Best regards,

Lets explain more.

As you know the monopile wind turbine working in specific condition shows specific attitude. How is it possible to get individual and total damping terms of aerodynamic, structrual and hydrodynamics through FAST, like what did you do for barge pitch damping ratio in fig 7-5 of your PhD dissertation ?? What about stiffness ? In this way I think I can find my coefficients a_i, a_ii, b_i, b_ii?? Or I couldnt?

Dear Mehdi,

The aerodynamic, structural, and hydrodynamic mass, stiffness, and damping are all included in the linearization output of FAST v7, when those corresponding features are enabled. (To be clear: you must disable the radiation damping from potential flow when linearizing with FAST v7, and so the radiation damping is not included in the FAST v7 linearization output, but the radiation added mass from potential flow, and the added mass and viscous damping from strip theory, are included.)

As I said in my prior post, you can derive the coefficients you seek, but you must beware that the FAST model is more complicated than your model and you must specify your own L, I_yy, etc.

Best regards,

In order to get those coefficients, I have to calculate the derivative of power and torque coefficient of rotor with respect to blade pitch angle, rotor rotational speed, wind speed.
Whats your opinion to calculate these derivatives?

Dear Mehdi,

These derivatives can all be calculated through the linearization functionality of FAST v7.

Best regards,

I amazed what is the reason of existence such differences between the thrust derivative with respect to wind speed achieved through Open-Loop and Ideal Closed Loop?
I know how you computed them, but unfortunately couldnt understand the behind theory of their such differences in results.
If it is possible help me to understand those differences.

Dear Mehdi,

The aerodynamic thrust is strongly related to the blade-pitch angle. In Open-Loop, the blade-pitch angle is not varied with the perturbations in wind speed. In Ideal Closed Loop, the blade-pitch angle is always correlated with the wind speed.

Best regards,

In order to get those coefficients, I have to calculate the derivative of rotor thrust and torque with respect to blade pitch angle, rotor rotational speed, wind speed. You said that these derivatives can all be calculated through the linearization functionality of FAST v7. Could you please tell me how is it possible using linearization functionality of FAST v7? I have read the FAST users guide but couldnt find how to calculate these derivatives.

Best regards,

Dear Mehdi,

Add the rotor thrust (RotThrust) and rotor torque (RotTorq) outputs to the model. Include the collective blade-pitch angle as a control input (CntrlInpt = 4) and the hub-height wind speed as a disturbance input (Disturbnc = 1) in the linearized model. The derivatives you want will show up in the linearized state matrices C, D, and D_d.

Best regards,

Have you computed all of them (derivative of rotor thrust and torque with respect to blade pitch angle, rotor rotational speed, wind speed)?
I see some of them in your PhD dissertation but not all of them. please let me know where i can find them.

Dear Mehdi,

No, I haven’t.

Best regards,

Hello everybody,

I am trying to linearize the 5MW Baseline Wind Turbine with OC3 Monopile using FAST v7.02. After downloading the model from “http://wind.nrel.gov/public/jjonkman/NRELOffshrBsline5MW/”, I did the following modifications:

  1. NRELOffshrBsline5MW_Monopile_RF.fst:

AnalMode = 2, PCMode = 0, VSContrl = 0, GenDOF = False, RotSpeed = (4, 6, 8rpm)

  1. NRELOffshrBsline5MW_AeroDyn.ipt:

StallMod = STEADY, WindFile = (simulate new wind .wnd file using TurbSim for steady wind)

  1. 90m_12mps_steady.inp (derived from Test #19 in FAST v8.16):

TurbModel = NONE

  1. NRELOffshrBsline5MW_Platform_Monopile_RF.dat

WaveMod = 0,

I am trying to derive the Gambell Diagram, but the solution does not appear to converge for rotor speed 4, 6 and 8rpm. In the other cases I have convergence (RotSpeed = 0, 2, 10, 12, 14rpm). I tried to increase the duration, but I see that the displacement and velocity 2-Norms don’t reduce with time.

What options do I have? What should I do?

Thank you very much!

Best regards

Georgios

Dear Georgios,

I’m not sure why the FAST steady-state solution is not converging for your case. Can you share how DispTol and VelTol are changing with rotation?

It sounds like you want to generate a Campbell diagram, but a Campbell diagram is usually derived without aerodynamics (CompAero = False). To get the proper drivetrain, blade edgewise, and tower side-to-side modes, it is also important to enable the generator DOF (GenDOF = True).

Best regards,

Dear Jason,

Thank you very much for your help. Indeed, I was able to derive steady states for all the cases of rpm, by neglecting the aerodynamics.

Best regards

Georgios