Effect of wind and wave directionality on the structural performance of non-operational offshore wind turbines supported by jackets during hurricanes

Risk of hurricane damage is an important factor in the development of the offshore wind energy industry in the United States. Hurricane loads on an offshore wind turbine (OWT), namely wind and wave loads, not only exert large structural demands, but also have temporally changing characteristics, especially with respect to their directions. Waves are less susceptible to rapid changes, whereas wind can change its properties over shorter time scales. Misalignment of local winds and ocean waves occurs regularly during a hurricane. The strength capacity of non-axisymmetric structures such as jackets is sensitive to loading direction and misalignment relative to structural orientation. As an example, this work examines the effect of these issues on the extreme loads and structural response of a non-operational OWT during hurricane conditions. The considered OWT is a 5MW turbine, supported by a jacket structure and located off the Massachusetts coast. A set of 1000 synthetic hurricane events, selected from a catalog simulating 100,000years of hurricane activity, is used to represent hurricane conditions, and the corresponding wind speeds, wave heights and directions are estimated using empirical, parametric models for each hurricane. The impact of wind and wave directions and structural orientation are quantified through a series of nonlinear static analyses under various assumptions for combining the directions of wind and wave and structural orientation for the considered example structure. Copyright (c) 2016 John Wiley & Sons, Ltd.