Experimental Investigation on Station-Keeping Performance of Novel Passive Constant Tension Mooring Systems for Floating Wind Turbines

Abstract The station-keeping of floating offshore wind turbines (FOWTs) for large-scale deployment presents significant engineering challenges, including high costs, environmental impacts and supply chain constraints. This study introduces a new small-footprint gravity-based passive constant tension (GPCT) mooring solution, grounded in the "Length-Varying Tension-Fixed" (LVTF) mooring theory, to address these challenges. The proposed GPCT solution employs a gravity-based passive tensioning mechanism (GPTM) to maintain constant mooring line tension while allowing for variable line lengths, offering an environmentally friendly, scalable, and cost-effective alternative to conventional mooring systems with fixed line lengths and dynamic tension. A key focus of this work is the experimental validation of the GPCT mooring concept through scaled tank model tests conducted at Shanghai Jiao Tong University. Two mooring system configurations were investigated: the single shared anchor (SSA) configuration and the multi-spread anchor (MSA) configuration. The SSA configuration, with 2-line and 3-line setups, was tested using a barge model, which characterized the mooring system restoring force versus horizontal offset under varying pretension conditions. The MSA configuration, with a 4-line setup, was evaluated for a novel 4-column self-installing Spar-type FOWT platform supporting a 16MW wind turbine designed for deployment in the South China Sea. A distinctive vortex-induced motion (VIM) yaw response was observed under the current-dominated conditions for the 4-column Spar FOWT with the MSA GPCT mooring system. The experimental results validated the LVTF constant tension mooring theory and confirmed the technical feasibility of the small-footprint GPCT mooring concept for large-scale FOWTs. The findings demonstrated the GPCT mooring system's capability to ensure effective station-keeping across diverse configurations, establishing a solid foundation for scalable, cost-effective, and sustainable new mooring solutions for the floating offshore wind energy industry.