Research on the Wet-Tow Transportation of Floating Offshore Wind Turbines

Abstract

　Wet-tow transportation of floating offshore wind turbines (FOWTs) is affected by weather and sea conditions and may become a bottleneck in the supply chain. However, there has been no accumulated knowledge on the towing of FOWTs, and the impact on the supply chain has not been clarified. In this study, dynamic analyses are conducted for three different semi-submersible floating designs, and the towing performance of each design is examined. Furthermore, the influence of the towing performance on the overall construction flow is examined using data of actual sea conditions. The results show that when the lower-hull is exposed on the water surface due to de-ballasting, the pitch and roll natural periods are shortened, which causes large motions depending on the wave period and wave direction. It causes an increase in the waiting time before the departure of towing in winter and an increase in uncertainty. When towed with the lower-hull submerged, the motion is small and FOWTs can be towed throughout the year. Depending on the design of the floating body, more towing force is required to maintain sufficient towing speed when the lower-full is submerged, and a trade-off occurs between the steadiness of construction and the cost of transportation.