Wave Climate Hindcast for the Design of Offshore Wind Energy Structures in the German Bight

Design of offshore wind turbines against ultimate limit state requires estimation of the most severe wave loading expected during the life of the wind turbine. Measured wind and wave data spanning sufficient duration to statistically predict these maximum loads are generally not available for most areas considered for wind farm development. One method used to develop the necessary design criteria is numerical simulation of environmental conditions at an offshore development site. Here, the effectiveness of the simulation methodology is assessed by critical comparison between design values based on simulated environmental conditions and equivalent design values based on measured buoy data. Specifically, the wind-wave activity in the German Bight is simulated for a twelve-year period using WaveWatch-III and SWAN. The simulation results are used to predict the significant wave height, the fifty-year mean-maximum wave height, and the fifty-year mean-maximum wave loading on a turbine support structure. Extreme values of significant wave heights are generally observed to be overpredicted compared with the hindcast methodology. In the load and response calculation the influence of the associated wave period is found to have a greater effect than this relatively small overprediciton of wave heights.