How to simulate turbine shutdown correctly

Hello everyone.

I want to simulate turbine shutdown at a given time by pitching the blades. When I set the value of ‘WakeMod’ to ‘1’, FAST aborted after the simulated time of turbine shutdown and warned ‘There is no valid value of phi for these operating conditions’. So I have to set the value of ‘WakeMod’ to ‘0’. But is it suitable for the calculation of aerodynamic load when turbine is working? Or there is another real correct way to simulate turbine shutdown at a given time by pitching the blades?

And I am curious about how to apply a high-speed shaft brake to achieve shutdown. Does it mean that ‘TimGenOf’ be not used(set to a large value) and only the function in ‘HIGH-SPEED SHAFT BRAKE’ section be used to achieve shutdown?

Best regards.

Dear Haoyu,

You should set WakeMod = 1 (or 2 for DBEMT) when simulating a shutdown case because the WakeMod = 0 option is not valid when the turbine is operating. The error regarding “no valid value of phi” was fixed in versions of AeroDyn v15 newer than from FAST v8.16. I suggest that you upgrade from FAST v8.16 to OpenFAST: github.com/OpenFAST/openfast.

Normally, a high-speed shaft brake is not used to shut down a wind turbine (instead, the pitch-control system would do this). Regardless, the generator would be disengaged before the shutdown, which you can model by setting TimGenOf to the time just before the shutdown event.

Best regards,

Dear Jason,

I successfully use the OpenFAST to simulate a turbine shutdown case. It is a wonderful tool. I appreciate for your help.

And I have another question. In some cases, I want to simulate a large platform displacement. However,the output of OpenFAST is many NaNs, which means OpenFAST failed to calculate. And it warned ‘Small angle assumption violated in SUBROUTINE SmllRotTrans() due to a large platform displacement (ElastoDyn SetCoordSy).’ and ‘HydroDyn_CalcOutput: Angles in GetSmllRotAngs() are larger than 0.4 radians.’ I also tried in FAST v8.16 and it aborted, giving a similiar error warning.

So could I modify the OpenFast’s source code, in order to simulate a large platform displacement? If so, which part of code should I modify?

Best regards.

Dear Haoyu.Wu,

Getting warnings regarding a “small angle assumption violated” or “NaNs” in the output are suggestive of a physical or numerical instability in your simulation. Changing the source code is likely not the solution. Changing the input settings will likely solve the problem. I would search this forum for “instability” to see how others have solved similar problems.

Best regards,

Dear Jason,

Thank you for your advice! I would search this forum for further solution.

Best regards.

Hi, Jason,
I would like to ask that the parameter “WakeMod” is in which kind of input file?
best regards.

Dear @Deyi.Fu,

WakeMod is an input parameter of AeroDyn v15 and is documented here: 4.2.1.2. Input Files — OpenFAST v3.1.0 documentation. AeroDyn v15 modeling guidance is provided here: 4.2.1.4. Modeling Considerations — OpenFAST v3.1.0 documentation.

Best regards,

Dear Jason,
Thank you!
best regards.