Dynamic analysis of a 15 MW semi-taut mooring floating offshore wind turbine at intermediate water depth: Investigating mooring line failure under operating and parked conditions

Abstract

The potential sites for floating offshore wind turbines (FOWTs) in Taiwan are primarily located in water depths ranging from 50 m to 100 m, where the mooring system design is the major challenge that needs to be overcome. In this study, a planned test site at a water depth of 70 m is selected as the case study. The aim is to evaluate the engineering feasibility and investigate possible conflicts in navigational safety due to mooring failure. To address this, fully coupled Aero-Servo-Hydro-Mooring simulations for a 15 MW FOWT under operating and parked conditions have been performed. Two common types of semi-taut mooring configurations, including chain-polyester-chain and chain-nylon-chain, are investigated, and the numerical results are compared against those of full chain-catenary mooring. The study includes several scenarios: setting environmental conditions with limited observation data, validating simulation tools, examining catenary and semi-taut mooring configurations, ensuring compliance with offshore standards, analyzing the effects of mooring line failure, and conducting a sensitivity analysis of rope length in semi-taut moorings. The findings show that the mooring failure scenario can result in a significant drift distance and a substantial drop in power generation. This can pose issues for both ocean space utilization and the stability of the power conversion system. Overall, the process of this study can be useful in the site selection of evaluating a potential site for the FOWT at different water depths.