Centrifuge model tests on scoured offshore wind turbines with large-diameter semi-rigid monopiles

Abstract

Monopile-supported offshore wind turbines (OWTs) in seismically active regions are exposed to the combined risks of potential earthquakes and scour. Existing studies mainly focus on the seismic response of small-diameter piles, with limited research on large-diameter monopiles (diameter greater than 3m), particularly under scour conditions. To address this gap, this study conducted a series of centrifuge shake-table tests on large-diameter monopiles at scoured sites. Primary attention is paid to the frequency characteristics of the OWT system, structural accelerations, displacements, and bending moments in the monopile. A comparison is also made between the seismic responses of large-diameter and small-diameter piles. The results demonstrate that scour has a more pronounced effect on the higher-order modal frequencies of the OWT system. Under seismic excitation, the acceleration at the pile head is significantly greater than that of the superstructure. Scour may amplify the high-order modal responses of the OWT system, which warrants sufficient attention in seismic design. Furthermore, the tests reveal that the bending strain of small-diameter piles is predominantly induced by inertial effect. In contrast, for large-diameter piles, the bending strain is primarily governed by the kinematic effect of the soil. These findings provide valuable insights for future numerical simulations and theoretical studies.