Nonlinear Behaviour Diagnosis for Horizontal-Axis Wind Turbine Blades Subjected to Inconstant Wind Excitations

Abstract

Wind energy has attracted great attention from scientists and engineers in the field, and wind turbines apply an increasingly important role in the efforts of changing our energy structure in a direction with more environment-friendly, green, and renewable energy to be applied in our society. Nonlinear responses of the wind turbine blades have significant effects on the operation, maintenance, and service life of the wind turbines. This chapter intends to characterize the nonlinear behaviour of the Horizontal-Axis Wind Turbine (HAWT) blades subjected to inconstant wind excitations. The combined excitations of aerodynamic forces, elastic forces, and inertia forces including Coriolis forces acting on the blades are considered in the investigation of the present chapter. Geometric nonlinearity of a blade and the nonlinear rotation of the blade subjected to inconstant wind loads are reflected in the analytical model established in the investigation. Various types of responses of the blades are analysed in the investigation, including periodic, nonperiodic, quasiperiodic, and chaotic vibrations, corresponding to the parameters of the system and the inconstant wind excitations considered. Quantitative examinations on the influences of different external excitations due to the wind loads on the nonlinear responses of the blade are conducted. The nonlinear responses of the blade are characterized with the newly developed periodicity-ratio (P-R) method, and the results are compared with that of the Lyapunov exponent method. The present chapter shows the characteristics and efficiency and accuracy of the P-R method in comparing with the other approaches of nonlinear vibration characterizations. The results of the research described in this chapter have significances in designing and manufacturing the horizontal-axis wind turbines and the turbine blades and provide guidance for quantitatively characterizing the nonlinear behaviour of wind turbine blades.