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Structural Monitoring and Maintenance
  Volume 4, Number 2, June 2017 , pages 115-131

Monitoring of wind turbine blades for flutter instability
Bei Chen, Xu G. Hua, Zi L. Zhang, Biswajit Basu and Soren R.K. Nielsen

    Classical flutter of wind turbine blades indicates a type of aeroelastic instability with fully attached boundary layer where a torsional blade mode couples to a flapwise bending mode, resulting in a mutual rapid growth of the amplitudes. In this paper the monitoring problem of onset of flutter is investigated from a detection point of view. The criterion is stated in terms of the exceeding of a defined envelope process of a specific maximum torsional vibration threshold. At a certain instant of time, a limited part of the previously measured torsional vibration signal at the tip of blade is decomposed through the Empirical Mode Decomposition (EMD) method, and the 1st Intrinsic Mode Function (IMF) is assumed to represent the response in the flutter mode. Next, an envelope time series of the indicated modal response is obtained in terms of a Hilbert transform. Finally, a flutter onset criterion is proposed, based on the indicated envelope process. The proposed online flutter monitoring method provided a practical and direct way to detect onset of flutter during operation. The algorithm has been illustrated by a 907-DOFs aeroelastic model for wind turbines, where the tower and the drive train is modelled by 7 DOFs, and each blade by means of 50 3-D Bernoulli-Euler beam elements.
Key Words
    wind turbine; flutter monitoring; envelope process; Hilbert-Huang transform
Bei Chen and Xu G. Hua: Key Laboratory for Wind and Bridge Engineering, Department of Civil Engineering, Hunan University, Changsha 410082, China
Zi L. Zhang: Department of Engineering, Aarhus University, Aarhus 8000, Denmark
Biswajit Basu: School of Engineering, Trinity College Dublin 2, Ireland
Soren R.K. Nielsen: Department of Civil Engineering, Aalborg University, Aalborg 9000, Denmark

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