Joint Description Methods of Wind and Waves for the Design of Offshore Wind Turbines

Wind and wave loads are equally important for the design of offshore wind energy structures. For the design against an ultimate limit state or fatigue, the engineer has to estimate the combination of loads that are likely to occur simultaneously during the design life of the wind turbine. This is quite a complex task, involving different wind/wave models, load-calculation methods and statistical analysis of simultaneous extreme wind and wave conditions. Moreover, reliable and realistic methods for the assessment of the service life of an offshore wind energy converter under combined wind and wave loads are necessary. However, the current design guidelines (Det Norske Veritas or German Lloyd) provide hardly any information on how to model the wind and wave correlation. In this article, several approaches for obtaining the required wind-wave correlation for the design have been investigated. Manual wave forecasting methods, spectral sea state descriptions and numerical wave model data have been compared to simultaneously measured wind and wave data from the FINO research platform in the German Bight of the North Sea. The used approaches are general and can be easily applied to different data sets from different regions.