Vibration of Wind Turbines Under Seismic Excitations

Abstract eng:
Edgewise vibrations can be of significant concern in wind turbines, as this mode is lightly damped and can lead to violent vibrations. In fact, under certain conditions the first edgewise mode may exhibit a very low or even negative damping (Staino et al. 2012). The effects of seismic excitations on wind turbine vibration were investigated in the literature, however, the blade-tower interactions and effects of wind turbulence were not considered. Edgewise vibration of a three-bladed Horizontal-Axis Wind Turbine (HAWT) under the action of operational loads and seismic ground motions is presented in this paper. The turbine model describes the dynamics of edgewise vibrations considering the aerodynamic properties of the blade, variable mass and stiffness per unit length and taking into account the effect of centrifugal stiffening, gravity and the interaction between the blades and the tower. Aerodynamic loads corresponding to a combination of steady wind including the wind shear and the effect of turbulence are computed by applying the modified Blade Element Momentum (BEM) theory. An edgewise reduced order model is adopted where each blade is modeled as a Bernoulli–Euler cantilever beam vibrating in its fundamental mode. The seismic load is contributed by ground motions due to earthquakes simulated as stochastic processes. In the case study presented for a 5-MW National Renewable Energy Laboratory (NREL) wind turbine, the influence of seismic excitation on the vibration in rotor plane of the nacelle is significant as shown in Figure 1.

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