Seismic response of monopile-supported offshore wind turbines under combined wind, wave and hydrodynamic loads at scoured sites

Abstract

Many monopile-supported offshore wind turbines (OWTs) have been installed in seismic regions. To determine the seismic response of monopile-supported OWTs accurately, it is crucial to simulate dynamic soil-pile interactions properly. Meanwhile, the additional soil nonlinearity caused by wind–wave loadings and pile scour induced by wave–current actions make seismic analysis more challenging. However, current guidelines for the seismic design of OWTs often fail to adequately consider the above problems. This study creatively presents an integrated analysis of the dynamic responses of scoured monopile-supported OWTs under combined seismic, wind and wave excitations. A novel dynamic p–y relationship being capable of reasonably reflecting soil degradation is adopted to model the soil–pile interactions. The effects of combined stochastic wind–wave and hydrodynamic loads, and different scour conditions are comprehensively incorporated in the OWT model to conduct the systematic seismic analyses. The results indicate that scour can induce excessive displacement and bending moments in an OWT structure under combined loads, threatening its safe operation. With increasing scour depth, the load combination effect becomes less pronounced, and the responses are mainly induced by wind–wave loads. These results can shed light on the seismic response of monopile-supported OWTs located in complex paralic environments.