On the Characterization of Hurricane Wind and Wave Generated Loads for the Proposed Wind Farms Sites Off the Northeast Coast of the US

The assessment of extreme environmental loads, including those that are generated by hurricanes, remains a key challenge in the development of wind farms off the US Northeast coast. In this study, we evaluated the sources of uncertainty in the extreme wind and wave loads (e.g. 50-year return period as suggested by IEC standards) for the proposed sites offshore Rhode Island and Massachusetts. At first, we demonstrated the range of uncertainty of wave and wind loads with various return periods using a generalized Pareto distribution based on various datasets at a number of stations around the sites. Further, an advanced coupled ocean-atmospheric model (COAWST: Coupled Ocean Atmosphere Wave Sediment Transport) was developed to assess the environmental loads for a particular hurricane. After validation of the model using historical hurricanes (e.g. Hurricane Sandy in 2012), several synthetic tropical storms that represented wind with various probabilities were simulated. The spatial and temporal variability of the wind and wave loads within the proposed sites were investigated. Results showed that the spatial variation of wind and wave loads during a hurricane are significant (up to 40% for wave loads). Additionally, the correlation of wind and wave loads depended on the tracks of hurricane and the bathymetry. Therefore, using simplified statistical methods that ignore the characteristics of hurricanes can lead to inappropriate estimation of extreme wind and wave loads. Also, we demonstrated that there is a large uncertainty range for waves or wind with a specific return period which should be considered in the design.