On the effects of structural modifications in the large wind turbine dynamics

In this paper a numerical procedure for the investigation of the dynamic behavior of large wind turbines is developed. The aeroelastic modeling is capable to take into account the dynamic environment in which the wind turbines operate by considering the effects of the atmospheric boundary layer and the weight load of the rotating blades. The aerodynamic loads are simulated by the 2D quasi-steady aerodynamic formulation, derived from Greengberg's theory, whereas the structural dynamics of the flexible wind-turbine blade, undergoing significant elastic displacements, has been described by a nonlinear flap-lag-torsion slender-beam differential model. The loading condition and the kinematic effects are described for different configurations of the rotor using a tapered and twisted blade representative of commercial installations. Then, blade structural modifications, represented by structural weakening, are introduced to investigate the effects of local delamination (damages) of the composite compound on the dynamic response of the system giving then useful information concerning the fatigue life of the system. Sensitivity analyses have been performed varying the spanwise location and the magnitude of the reduction of stiffness. Moreover, the effects of a blade mounting error in the pitch angle have been investigated highlighting the critical loading arising from an aerodynamically unbalanced rotor. Copyright © 2011 by L. Balis Crema, G. Coppotelli, C. Grappasonni