Abnormal pitch angle fluctuations

Wind & Water Computer-Aided Engineering Software Tools
1

Dear everyone,

I am simulating the fatigue loads of an onshore wind turbine by using 5MW Baseline.

The settings are modified based on Test #18. The DBEMT and Beddoes-Leishman unsteady model are adopted in AD15 and the NacYaw in ED is changed from -30 to 30 to consider yawed situation. Settings in Servodyn are kept as default. The PCMode in ServoDyn is chosen as 5.

Above 500 cases are run and the only difference is the inflow condition. For each yaw angle, the WndSpd, IECturbc and PLExp are changed in turn.

However, as shown in the figure below, it was found that in some high-speed cases (mainly 21-25m/s), the average GenPwr in ten minutes were very low. After checking the out file, the pitch angle shows abnormal fluctuations between 30° -90° 180°, which results in very low and even negative power output (shown in the second figure).

A total number of 66 out of 540 cases shows abnormal.

Could anyone help solve this problem?

Thanks in advance
Ruiyang He

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2

Dear Ruiyang He,

A couple questions / clarifications:

  • Are you initializing the rotor speed and blade-pitch angles in ElastoDyn based on their expected (mean values) for each mean hub-height wind speed? If not, the controller can sometimes get confused and not recover.
  • Have you disabled the nacelle-yaw DOF in ElastoDyn (YawDOF = False). Alternatively, have you set the neutral yaw angle in ServoDyn (YawNeut) to match the initial yaw angle in ElastoDyn (otherwise, the nacelle-yaw angle would snap quickly back to zero-degrees due to the yaw spring in ServoDyn, which could cause other problems)?

Best regards,

3

Dear Dr.Jason,

  1. I only set NacYaw in ED but didn’t initialize the rotor speed and pitch angle and let them as zero, so I only recorded the last 600s of the total 700s simulation, is that ok?
    I noticed your suggestion in other posts that these parameters should be initialized according to Figure 9-1 in Definition of a 5-MW Reference Wind Turbine for Offshore System Development. However, I have to give up it since thousands of cases need to be run under different inflow conditions.

2.Yes, I have disabled YawDOF (also learned from other posts in forum). The YCMode in Servodyn is set as 0, and so is YawNeut. Is that right?

The corresponding settings are attached. Are they reasonable?

Thanks,
Ruiyang He

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4

Dear Ruiyang He,

Regarding (1), this is likely the problem. The baseline controller for the NREL 5-MW wind turbine does not have control logic for wind turbine start-up implemented; so, initializing the rotor speed and blade-pitch angles to zero could cause problems with the control behavior. As recommended, you should initialize the rotor speed and blade-pitch angle to their respective mean values at each mean wind speed (based on Figure 9-1 from the NREL 5-MW specifications report for that turbine). Instead of doing this manually, I suggest you write a script to modify the input files accordingly.

Regarding (2), given that you’ve disabled YawDOF, there is no need to set YawNeut in ServoDyn equal to NacYaw in ElastoDyn.

Best regards,

5

Dear Dr.Jason,

I am pleased to let you know that the problems are solved based on your suggestions.

I really appreciate that. Thank you once again!

yours,
Ruiyang He