Dynamic Analysis of Offshore Monopile Wind Turbine Including the Effects of Wind-Wave Loading and Soil Properties

An engineering approach to dynamic analysis of an offshore monopile wind turbine is presented in this paper. The wind-wave coupling for shallow water conditions is considered. Different wind, wave and current loads on the wind turbine within the cut-in and cut-off conditions are taken into account. The hydrodynamic loading is computed based on the corresponding sea-states. The interaction between the foundation and the soil is simulated by nonlinear springs, which stiffness properties are obtained from the axial load transfer (t-z) curve, the tip load-displacement (Q-z) curve and the lateral load-deflection (p-y) curve. Three types of soil conditions are considered in the simulations, i.e., 100% sand layer, 50% sand layer (top) and 50% clay layer (bottom), as well as 100% clay layer. For a given current speed, the variations of the static and the dynamic responses of the wind turbine due to the effects of different wind-wave load combinations and soil conditions have been investigated and discussed.