Ice-Induced Frequency Lock-in Vibration Analysis of Bottom Fixed Wind Turbine Structure

Abstract Ice induced vibration is a serious problem for offshore structures in the ice-covered sea area. Especially when ice moves at low speeds against structures, the coupling of the ice crushing failure process and structural vibration will induce lock-in between ice loads and structural vibration. The strong vibration of the structure has been found in the lock-in process and the loading scenario has been named as frequency lock-in (FLI) vibration, which is a dangerous loading condition that needs to be considered in the design. However, no practical analysis method for FLI vibration is available in existing industry standards due to the lack of understanding of the underlying mechanism. To solve this problem, an FLI analysis method is proposed in this paper based on the ductile damage-collapse mechanism for offshore wind turbine structures. The sample study of a 5MW fixed monopile wind turbine shows that the probability of FLI occurrence on an offshore wind turbine is less than that on an oil platform and lighthouses because the wind turbine has a high rise and low-frequency characteristics. The analysis also shows that the magnitude of the FLI vibration is larger than the random vibration caused by continuous brittle ice crushing.