Transient analysis of wind turbine tower during earthquake

Wind energy is one of the fastest growing renewable energy sources that can effectively reduce greenhouse gas emissions. Wind turbines are designed for a ۲۰ year lifetime at least therefore considering earthquake condition in their designing load cases for seismically active regions is necessary. In this paper a set of transient finite element simulations using Abaqus dynamic implicit formulation are conducted to investigate the effect of different pre-assumptions on obtained seismic loads. In first case, nacelle and rotor are modeled as an isotropic mass point. In case II, nacelle and rotor moments of inertia are also considered. In case III, rotor blades are modeled using generalized beam elements therefore, in this case both moments of inertia and stiffness of blades are added to the model. Typical wind turbine design guide lines suggest analytical and spectrum analysis based on case I pre-assumptions. This paper, studies the transient behavior of more realistic models to verify the accuracy of standard proposed earthquake calculations. Ground acceleration time series are generated based on standard earthquake spectrums. The results reveal that considering nacelle and rotor inertia over-estimates the seismic wave loads. Case I and case III are in acceptable agreement where considering only top mass provides a reliable design load, but for obtaining optimum tower design, modeling the blades can be helpful.

Keywords:

transient behavior , forced vibration , wind turbine tower design , seismic analysis