Generic Hurricane Extreme Seas State: An Engineering Approach

摘要

Extreme sea states, which the IEC 61400-3 (2008) standardrequires for the ultimate limit state (ULS) analysis of offshorewind turbines are derived to establish the design basis for theconceptual layout of deep water floating offshore wind turbinefoundations in hurricane affected areas. Especially in the initialphase of floating foundation concept development, site specificmetocean data are usually not available. As the areas of interestare furthermore not covered by any design standard, in terms ofdesign sea states, generic and in engineering terms applicableenvironmental background data is required for a type specificconceptual design. ULS conditions for different return periodsare developed, which can subsequently be applied in siteindependentanalysis and conceptual design. Recordingsprovided by National Oceanic and AtmosphericAdministration (NOAA), of hurricanes along the US east coastand the Gulf of Mexico (1851 - 2009) and Japanese east coast(1951 -2009) form the basis for Weibull extreme value analysesto determine return period respective maximum wind speeds.Unidirectional generic sea state spectra are obtained byapplication of the empirical models for hurricane generates seasby Young (1998, 2003, and 2006), requiring maximum windspeeds, forward velocity and radius to maximum wind speed.An averaged radius to maximum sustained wind speeds,according to Hsu et al. (1998) and averaged forward speed ofcyclonic storms are applied in the initial state. In a second stepthe influence of the forward velocity is investigated and relatedto the assumption of an extended fetch.