The United States Department of Energy has implemented the Wind Partnerships for Advanced Component Technologies (WindPact) program to explore the most advanced wind-generating technologies for improving reliability and decreasing energy costs. The first step in the WindPact program is a scaling study to bound the optimum sizes for wind turbines, to define size limits for certain technologies, and to scale new technologies. The technical activities are divided into the following four projects:
Assessing the risk posed by severe storms to offshore wind turbines (OWTs) is a challenging task. Stochastic environmental conditions represent the main source of variable loading; consequently, a high level of uncertainty is associated with assessing structural demand on OWT structures. Failure of any of the primary structural components implies both complete loss of the OWT and loss of earnings associated with production stoppage. In this paper, we propose the use of a probabilistic risk modelling framework to assess the structural risk posed by extreme weather conditions to OWTs. To achieve this, fragility functions are developed for OWTs on monopile foundations exposed to extreme metocean conditions using dynamic aeroelastic simulations. Structural fragility represents a key component of any probabilistic risk model and expresses the likelihood of different levels of damage experienced by an OWT over a range of wind and wave hazard intensities. We compare the effect of various modelling and analysis choices on the obtained fragility functions and investigate potential interdependencies between failure modes of OWT structural components. Results from this study highlight how different assumptions affect the estimated structural performance and the resulting structural fragility of a case-study OWT. We apply the proposed framework to two case-study sites, one in the USA East Coast and one in the North Sea, discussing possible outcomes of the proposed framework.
During their operational life, offshore wind turbines (OWTs) may be exposed to severe storms, resulting in extreme wind and wave loading acting on the OWT structure (and substructure). This paper proposes quantifying financial losses associated with an OWT exposed to extreme wind and waves using a probabilistic risk modelling framework, as a first step towards evaluating offshore wind farm (OWF) resilience. The proposed modelling framework includes a number of novel elements: 1) the development of site-specific fragility relationships (i.e., likelihood of different levels of damage experienced by an OWT over a range of hazard intensities), properly accounting for uncertainties in both structural capacity and demands; 2) the implementation of a closed-form technique, based on a combinatorial system reliability approach, to assess failure consequences (e.g., financial loss) for both structural and nonstructural components; 3) a coherent treatment of epistemic uncertainties across the framework (e.g., sampling variability in fragility estimation), providing loss results accounting for uncertainty of estimation. These aspects can allow for more informative comparisons of various design solutions in terms of structural fragility and risk and/or an improved evaluation of probabilistic losses for decision making. An illustrative application to two case-study sites is presented as a simplified walk-through of the calculation steps in the proposed framework, discussing possible outcomes. For instance, the results from the illustrative application indicate the structural components play an important role in the overall risk profile of an OWT, but this depends on the site-specific wind and wave conditions. The calculation of losses provides a foundation from which a more detailed assessment of OWT and OWF resilience could be developed.
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