Vulnerability analysis of offshore wind turbines considering the correlation of wind and waves

Abstract

Vulnerability analysis, by considering load and structural uncertainties, provides an approach to reducing costs through optimized structural performance utilization. Addressing limitations in existing research regarding wind-wave correlation and performance level, this manuscript employs measured wind-wave data to estimate coherence functions using a 4th-order bandpass filter and 12th-order vector autoregressive. By analyzing wind-wave coherence under different sea states, a coherence function model is established and validated. OpenFAST is then utilized to generate wind-wave load time histories incorporating wind-wave correlations. An OWT numerical model is established in ANSYS to investigate dynamic responses, involving platform pitching, nacelle acceleration, and stress of tower and blade. A unified damage evaluation indicator and a three-stage performance level division standard for OWTs are proposed accordingly. The study subsequently conducts vulnerability analysis considering both wind-wave correlations and three-stage performance level. The study demonstrate that the proposed division standard effectively distinguishes between slight, moderate, and severe damage of OWT, with significant probability variations under identical load. This provides a reference for the design to fully utilize performance of OWTs. Notably, probabilities of achieving each performance level increase when wind-wave correlations are considered compared to uncorrelated cases, underscoring the necessity of incorporating wind-wave correlation in performance-based OWT design.