Lateral responses of monopile-supported offshore wind turbines in sands under combined effects of scour and earthquakes

Abstract

Offshore wind turbines (OWTs) supported by monopiles can be vulnerable to scour and liquefaction triggered by waves and earthquakes. However, the combined effects of scour and earthquakes on the monopile-supported OWTs in sands are not fully appreciated. This study proposes a practical method to evaluate the post-scour seismic responses of piles in sands and applies it to analyze the monopile-supported OWTs. This method introduces a new concept that relates scour-hole geometric conditions to soil liquefaction potential. Using the proposed method, a parametric study was conducted to evaluate the effects of scour-hole dimensions, sand relative densities, and input ground motions on the lateral responses of OWTs. The results showed that scour shifted the fundamental frequency of the OWT system into the rotor frequency range, causing resonance. An increase in scour depth increased the dynamic responses of the monopile and tower, which was less significant in liquefied than in non-liquefied condition. • A practical method is proposed to simulate dynamic soil-pile interactions in sands under scoured conditions. • Computer scripts are developed to analyze post-scour seismic responses of monopile-supported offshore wind turbines (OWTs). • A parametric study was conducted in time domain to investigate lateral responses of a selected monopile-supported OWT. • Contributions of inertial and kinematic interactions to dynamic responses of OWT were assessed by cross-correlation analyses. • The scour effect on the dynamic responses of OWT was more remarkable in the non-liquefied case than in the liquefied case.