Dynamic impedance of monopiles for offshore wind turbines considering scour-hole dimensions

Abstract

This study presents an effective solution to evaluate the dynamic impedances of scoured monopiles for offshore wind turbines in a wide excitation frequency range, which can properly account for both the effects of the scour-hole dimensions as well as of the soil stress histories, and the evaluation of these complex-valued impedance functions can be later used to take into account the soil-structure interaction in efficiently performing dynamic/seismic analyses of the scour-affected offshore wind turbines through substructuring techniques. Based on the common soil-pile configurations encountered in offshore practice, a series of parametric analyses are performed by using the presented solution to examine the dynamic impedance of scoured monopiles through varying scour-hole dimensions. The results show that the effects of scour-hole dimensions do not sensibly modify the overall trends of the impedance, but they do reduce the oscillation amplitudes and resonant frequencies or quantities of the impedance when compared with those before scour in the frequency range of practical interest; the scour depth has a significant impact on the monopile's impedance at most frequencies, while the effects of the width and slope angle of the scour hole should not be negligible in certain frequency ranges.