• Energy Research

AbstractRisk 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 5 MW turbine, supported by a jacket structure and located off the Massachusetts coast. A set of 1000 synthetic hurricane events, selected from a catalog simulating 100,000 years 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 © 2016 John Wiley & Sons, Ltd.

Abstract This paper introduces a framework for the assessment of damage of offshore wind turbines (OWTs) supported by jackets under extreme environmental loadings. Performance levels/damage states, ranging from operational/undamaged to near collapse/severely damaged, are defined based on static pushover analyses. An example performance assessment is presented for an OWT supported by a jacket based on environmental conditions for a site off Massachusetts along U.S. Atlantic coast. The environmental conditions are characterized based on two methods for estimating wind and wave conditions, one on extrapolation of NOAA buoy measurements and one on a stochastic hurricane catalog, and two models for extreme wave height, one on the crest height and one on the zero-up-crossing height. Using probabilistic models for demands and capacities, two curves of fragility, one estimating the initiation of yielding and the other estimating the onset of collapse, are developed to distinguish between the three damage states. The curves are applied to four combinations of two environmental hazard models and two extreme wave height models, and significant differences are found in the probability of damage among the four combinations of models. The findings have potential implications for the evaluation of the overall risk profile and associated performance for offshore wind farms.