Controllers compiled with FAST v7 Seismic Module

1

Dear Sir,

it would help if you can confirm which controllers are active/compiled with FAST v7 Seismic module. Till now I have only used the .exe with bladed dll for my investigations.

I see that no yaw control is active. Is that how it should be?

Thanking You
Subham

2

Dear @Kashyap.Subham,

FAST v7 has similar controls capability as newer versions of OpenFAST including simple built-in options, user-defined routines, an interface to MATLAB/Simulink, and the Bladed-style DLL controller (DISCON). The Seismic version of FAST v7 should support all of this options, depending on the compile options you’ve set. If you are using the precompiled binary executable of the Seismic version of FAST v7 provided by NREL, this will support a Bladed-style DLL controller, but not the user-defined routines or MATLAB/Simulink interface.

NREL has not provided a baseline yaw controller except for what is provided in ROSCO: GitHub - NREL/ROSCO: A Reference Open Source Controller for Wind Turbines. You can also use the override yaw maneuvers controlled directly through the input file of FAST v7.

Bets regards,

3

Dear Sir,

  1. If I understand correctly, should a DLL compiled with the ROCSO run similarly to the DLL with which the FAST v7 Seismic has been compiled?
    In the FAST v7 Seismic Archive, I see a DFORRT.DLL and a DISCON.DLL.What is the difference between the two? In addition, I also see a DISCON.f90 which has the parameters with the Bladed style DLL.

  2. Can you give me an overview of how these files are utilized/instead used? I am sorry for asking such broad questions. Is there any advantage to using a Bladed style DLL?

  3. I also came across your paper on a floating wind turbine investigating the influence of control on the damping of pitch motion. You had incorporated different sensor measurements in the controller, such as tower motion. Can you share any files from that project that can serve me as study material, especially the control files?

  4. Also, how can I generate damping ratios at different wind speeds using FAST v7 for a specific mode of the system? Something similar was done in your paper (as mentioned in 3).

Well, I believe it’s a lot of questions. Each day with FAST has been enriching. I am just learning by trial and error. I would appreciate your help.

Thanks
Subham

4

Dear @Kashyap.Subham,

Here are my responses:

  1. Yes, as long as the ROSCO controller you are using does not rely on inputs to the controller (through the avrSWAP array) that have only recently been added to OpenFAST (e.g., the extended Bladed interface inputs documented here are not available in FAST v7: 4.2.11.2. Extended Bladed Interface — OpenFAST v3.4.1 documentation), the same ROSCO controller should also be able to be used in FAST v7. The DFORRT.dll was provided because some computers that did not have a compiler installed needed it to run FAST v7; you should not need this if you compiling yourself.

  2. I’m not sure I really understand your question. The Bladed-style controller interface is a wind industry standard used by many engineering software for interfacing wind turbine controllers.

  3. I believe you are referring to the following paper: https://www.nrel.gov/docs/fy08osti/42589.pdf; is that correct? It has been many years since I looked at this, but I believe all of the control logic implemented for that paper is available in the DISCON_ITIBarge.f90 source file available here: r-test/DISCON_ITIBarge.F90 at main · OpenFAST/r-test · GitHub. (Selecting between the different control options would require a change and recompiling of this source file.) That said, the ROSCO controller has far more advanced controls capability, so, I recommend using that over this controller if you are interested in advanced controls options.

  4. I would follow the guidance provided in that paper. Recent improvements to the linearization functionality of OpenFAST have improved the capability to calculate damping ratios (functionality not available in FAST v7).

Best regards,

5

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Dear Sir,
I have highlighted the two ways mentioned for measuring thrust sensitivity using FAST. Method 1, I believe, is calculated by running a typical simulation with a uniform wind field while I keep the control systems (gen torq and blade-pitch switched on). Am I correct?

Method 2, I completely fail to understand. So, I set up a linearization study. Wherein I keep the blade pitch at the desired pitch angle and run the simulation? And the thrust sensitivity calculation using the central difference scheme. How is that implemented?

Is It possible to assess tower/aerodynamic damping ratios using the above methods for a bottom-fixed offshore wind turbine with seismic loads?

Thanks
Subham

6

Dear @Kashyap.Subham,

In Method 1, I agree that you run time-domain solutions with uniform wind input. Run separate simulations at each wind speed and record the steady-state response (of thrust) after all transients die out. Plot the curve of thrust versus wind speed and find the derivative of this curve.

In Method 2, the derivative is calculated directly by the linearization functionality of FAST v7. If you select rotor thrust as an output and include wind speed perturbations as input, then the derivative of the thrust with respect to wind speed is included in the linearized output-transmission (D) matrix. Again, OpenFAST computes this far better than FAST v7.

Tower/aerodynamic damping is a property of the full-system modes of the system, independent of the source of excitation.

Best regards,