Abstract
The temporal evolution of storms is relevant for permanent rotations of monopile-supported offshore wind turbines, as the load cycles encountered during these 35- or 42-hour events can be critical. Existing design standards do not provide guidance on selecting the peak period during the storm evolution, nor do they consider the operational state of the turbine. Previous work defined a storm profile based on hindcast data for the North Sea. The present work examines storm sequences at five relevant locations and finds that the previously defined profile generally agrees well with the observations at all locations. The storm profile disregards wind-wave misalignment, wind and wave directions, and the separation of wind sea and swell sea. Based on aero-hydro-servo-elastic simulations of two different turbines, the effect of separating wind sea and swell sea is found to be small. The effect of the operational condition of the turbine is found to be important, with an operational turbine giving larger mean loads and a parked turbine giving larger load variations. The effect of the emergency shutdown event during the load sequence depends on the turbine and wind speed during the shutdown.
