Seismic assessment of offshore wind turbines via time-domain uncoupled analyses

For seismic assessment of offshore wind turbines in seismically-active areas, International Standards and Guidelines allow combining two separate analyses under wind-waves and earthquake, respectively. The separate earthquake response is generally computed including anadditional aerodynamic damping in the structural model. Some work has already been done to estimate appropriate levels of aerodynamic damping for uncoupled analyses on land-based wind turbines but, to date, no similar data is available on offshore wind turbines. This paper proposes a time-domain implementation of uncoupled analyses for seismic assessment of offshore wind turbines, and investigates pertinent levels of aerodynamic damping. The case study is a 5-MW wind turbine, resting on a tripod in intermediate waters.