The impact of low-level jets in the atmospheric boundary layer on the operation of large-scale floating offshore wind turbines

Abstract

Low-level jets (LLJs) commonly occur in the marine offshore atmospheric boundary layer. They are characterized by irregular wind shear, which can significantly affect the performance and safety of floating wind turbines. This paper presents a comprehensive analysis framework to evaluate the effect of LLJs on the dynamic loads and structural response of large-scale floating offshore wind turbines (OWTs) during operation. In the proposed framework, LLJ-induced irregular vertical profiles of wind speed, direction, and turbulence are modeled using polynomial functions and smoothed spectra calibrated with measurement data. The floating OWT is simulated using an Aero-Hydro-Servo-Structural (AHSS) coupled model, based on the beam theory. The wind speed time histories simulated with the LLJ characteristics are utilized to excite the OWT model, enabling detailed load and response analysis. Using two benchmark turbines [a 15 MW OWT (15OWT) and a 22 MW OWT (22OWT)], this study investigates how key LLJ parameters such as jet height, jet intensity, and wind veer angles influence structural response. Results reveal that LLJs can cause a significant increase in dynamic response, even under the same hub-height wind speeds, raising the risk of blade-tower collision. Moreover, the effect of LLJs becomes more pronounced with increasing turbine size. The response analysis results are utilized to develop a rapid evaluation method for LLJ-induced effects, providing a basis for designing mitigation strategies to reduce operational risks in floating OWTs.