Fatigue reliability assessment of offshore wind turbines with stochastic availability

In this paper, the impact on lifetime estimation of an offshore wind turbine by introducing a stochastic model for the availability is investigated. Offshore bottom-fixed wind turbines typically have an average downtime of 4–10% due to e.g. grid- or mechanical failures including a potentially long response time for recovery. During the non-operational conditions, the fatigue damage in the foundation is accumulating significantly faster. Designing the wind farm based on a conservative downtime fraction will lead to design conservatism with respect to the foundation, which will be quantified in this paper using a structural reliability analysis.