How to simulate turbine shutdown correctly

Discuss the theory and modeling of rotor aerodynamics.

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Haoyu.Wu
Posts: 4
Joined: Thu May 16, 2019 4:27 am
Organization: Shanghai Jiao Tong University
Location: China

How to simulate turbine shutdown correctly

Postby Haoyu.Wu » Fri Dec 13, 2019 5:06 am

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.

Jason.Jonkman
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Location: Boulder, CO
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Re: How to simulate turbine shutdown correctly

Postby Jason.Jonkman » Fri Dec 13, 2019 7:09 am

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: https://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,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Haoyu.Wu
Posts: 4
Joined: Thu May 16, 2019 4:27 am
Organization: Shanghai Jiao Tong University
Location: China

Re: How to simulate turbine shutdown correctly

Postby Haoyu.Wu » Sat Dec 14, 2019 6:40 am

Jason.Jonkman wrote: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: https://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.

Jason.Jonkman
Posts: 5728
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: How to simulate turbine shutdown correctly

Postby Jason.Jonkman » Sat Dec 14, 2019 8:10 am

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,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Haoyu.Wu
Posts: 4
Joined: Thu May 16, 2019 4:27 am
Organization: Shanghai Jiao Tong University
Location: China

Re: How to simulate turbine shutdown correctly

Postby Haoyu.Wu » Sat Dec 14, 2019 11:03 pm

Jason.Jonkman wrote: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.


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