As the total number of installations increase in quantity and rated capacity, offshore wind turbines are increasingly subjected to harsher environments and decreased accessibility. Therefore, structural durability and reliability are important parameters to be considered on the design of offshore wind turbines. One of the most promising ways to address the durability and reliability related issues is the early detection of mass and aerodynamic rotor imbalances. Current practices in rotor fault diagnostics do not take into account the stochastic fluctuations of the offshore wind turbine operation conditions, which can impact the detection of false positive rotor imbalance alarms. Therefore, more probabilistic methods are necessary to improve the accuracy of rotor imbalance diagnostics. The research question that this work addresses is: can the current imbalance detection techniques for an offshore wind turbine be improved through a systematic uncertainty quantification of the turbine operation conditions? In order to address this question, a uncertainty quantification framework was proposed to model uncertainties of wind speed, pitch angle, and blade mass density using assumed probability density functions based on data/information available for these parameters. These parameters are subsequently fed into FAST, an aero-elastic wind turbine model developed by the National Renewable Energy Laboratory, to obtain the dynamic and power output parameters for several conditions of the imbalance in the rotor. The results indicate that a 10% variation in the mean wind speed causes significant differences in power output for a given pitch angle error in aerodynamic imbalance, and for a given blade mass density increase at a given blade section for mass imbalance due to the cubic relation of wind speed to the power output. In some cases, as much as a 1,500 kW difference in power output is experienced because of the cubic relation of wind speed to the offshore wind turbine power output. In addition, by analyzing the stochastic rotor imbalance conditions over time, the results indicate that the power fluctuations due to rotor imbalances are significant over the simulated time. These results conclude that an uncertainty quantification framework can be a useful tool in detecting rotor imbalances for current and future wind energy projects.


Uncertainty Quantification of Mass and Aerodynamic Rotor Imbalance for Offshore Wind Turbines

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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