Design standards for wind turbines such as the guidelines from the International ElectrotechnicalCommission (IEC) require, for at least one design load case, statistical extrapolation of loadsfrom limited simulation analyses. Extrapolation refers to prediction of a rare load fractile.Several statistical extrapolation techniques are possible; one includes the use of the peak-overthresholdmethod in which load maxima between successive upcrossings of a selected thresholdare defined as the extremes for random variables. With such "extremes" models, it is common tofit parametric distributions to the loads data and to then attempt to predict load levels associatedwith rare occurrence rates (in ten minutes), generally on the order of one in 1 million or evenrarer. Structural reliability principles can be employed to improve the efficiency in suchcomputations. In this study, ultimate limit states will be evaluated for a 5MW offshore windturbine by first studying short-term load statistics (conditional on wind speed and wave height);then, upon integration of these short-term distributions with site-specific environmental climatedescriptions, long-term turbine loads will be derived.
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