Reliability analysis of floating offshore wind turbine considering multiple failure modes under extreme typhoon-wave condition

Abstract

Reliability assessment of floating offshore wind turbines (FOWTs) under extreme load conditions is significant for the structural safety design of FOWTs deployed in typhoon-prone areas. The FOWT system may undergo multiple dependent failure modes due to its high dimensional and multi-body coupled dynamic characteristics, warranting adequate attention in reliability assessment. This study proposes a structural reliability method for FOWTs considering multiple failure modes under extreme typhoon-wave conditions. Initially, the joint probability distribution of extreme wind-wave conditions under typhoon impact is established by integrating typhoon hazard analysis and a copula-based conditional modeling method. Subsequently, the 50-year return period environmental contour is determined by means of the inverse first-order reliability method. Following this, the probability density evolution method in combination with a constructed equivalent extreme-value response process is used for the reliability analysis of FOWTs under multiple failure modes. The reliability of an FOWT under extreme wind-wave conditions is evaluated numerically through the proposed method, demonstrating its effectiveness compared to the Monte Carlo simulation method. Furthermore, the multiple failure modes of FOWTs are proven to be correlated, emphasizing its necessity in the reliability-based design of FOWTs.