Centrifuge and Numerical Investigations on Responses of Monopile-Supported Offshore Wind Turbines with Riprap Scour Protection Under Earthquakes

Riprap scour protection is commonly employed to protect against local scour around large-diameter monopile foundations for offshore wind turbines (OWTs), and considering its influence on the static and dynamic behavior of monopiles may also provide the opportunity for further optimization of monopile design. However, only limited studies have gradually begun to investigate the contribution of scour protection to monopile bearing capacity, while its effects on the seismic responses of monopile-supported OWTs deployed in seismic zones have attracted even less attention. In this study, a series of centrifuge shaking table tests were conducted on large-diameter monopile foundations under both initial and scour protection conditions. Then, to further investigate the effects of scour protection parameters on the seismic response of offshore wind turbines, a three-dimensional finite element model was developed and validated based on experimental results. The results demonstrate that the presence of scour protection not only slightly increases the first natural frequency but also alters seismic responses of the OWT. Lower peak responses at the lumped mass are observed under Chi-Chi excitation, while lower peak bending moments of the pile occur under Kobe excitation. Additionally, seismic responses are more sensitive to variations in the scour protection length than its elastic modulus. Therefore, compared to material selection, greater emphasis should be placed on optimizing the scour protection length by comprehensively considering environmental loads, site conditions, and turbine dynamic characteristics. This study quantifies the effects of scour protection on the seismic responses of monopile-supported offshore wind turbines, which can provide new insights into seismic design optimization of offshore wind turbines with riprap scour protection.