Innovative Method for Large Corrective Maintenance of Floating Offshore Wind Turbines

Abstract Floating offshore wind turbines (FOWT) offer unique operational and maintenance (O&M) challenges and opportunities compared to their fixed-bottom counterparts. Situated further from shore, FOWT benefit from stronger, more consistent winds, but this increased distance leads to longer travel times and harsher conditions, reducing accessibility. Traditional jack-up vessels become impractical in deeper waters. Additionally, the inherent motions of FOWT introduce complexity to maintenance strategies. As wind turbine dimensions continue to grow, major component replacements (MCR) require heavier lifts at greater heights. The conventional MCR approach for semi-submersible FOWT is the tow-to-port strategy, which can be complex, time-consuming, and costly. Consequently, there is a growing need to explore alternative onsite options. This article introduces a novel floating-to-floating method for FOWT MCR, developed and numerically tested using a leading software for the dynamic analysis of offshore marine systems. The component to be replaced, also referred to as "package" below, is typically first removed from the wind turbine nacelle, and a replacement part is then re-installed. The method comprises: A motion-compensated offshore crane capable of lifting components and adjusting winch length based on the package relative distance from its target on the nacelle.Horizontal control lines (tag lines) connected to the package base, passing through deflectors at the nacelle top, and linked to winches or capstans. To ensure a safe package transfer between the offshore crane and the nacelle, relative motion should not exceed a few centimeters when the package lands onto the nacelle. Numerical analysis results confirm that this method enables accurate transfers with low tension in the tag lines. This innovative approach promises to enhance the efficiency and safety of maintenance operations for floating offshore wind turbines, addressing the unique challenges posed by their remote locations and size.