Experimental Comparison of Constant Tension Mooring and Catenary Mooring System for a Semi-Submersible Floating Wind Turbine

Abstract The mooring system is a crucial component of the semi-submersible floating wind turbine, but designing mooring systems in regions with water depths less than 100 meters remains challenging. An innovative design, constant tension mooring, offers the advantages of a reduced footprint and lower cost, is well-suited for semi-submersible floating wind turbine. In this paper, a specially designed constant tension mooring system featuring suspended counterweights for a 16MW semi-submersible floating wind turbine is tested and compared with the traditional catenary design. Comparative model tests of the constant tension and catenary designs are conducted, taking into account the turbulent wind, wave and current loads under actual operational conditions. The survivability of the constant tension mooring design is tested under a 50-year extreme sea state, the safety factor of the mooring loads is 1.92, which meets the requirements of the standards. Although the horizontal drift is larger compared to the catenary design, it still meets the design requirements, and the constant tension design exhibits a reduced motion response near the natural period compared to the catenary system. The design also achieves a 70% reduction in total mooring line length and an 80% reduction in mooring radius compared to the catenary mooring, thereby offering potential cost savings.