Dynamic Response of Mooring Systems for Deep-Water Semi-Submersibles under Wave Fluid-Structure Interaction

Abstract

The exploration of offshore hydrocarbon resources has increasingly moved towards deep and ultra-deep waters, necessitating robust floating production systems. Among these, semi-submersibles are widely utilized due to their favorable motion characteristics; however, their station-keeping relies heavily on complex mooring systems that are susceptible to fatigue and failure under extreme environmental loads. This paper presents a comprehensive investigation into the dynamic response of mooring systems for deep-water semi-submersibles, specifically focusing on the non-linear fluid-structure interaction (FSI) between the hull, the mooring lines, and the incident wave field. We employ a fully coupled time-domain analysis method that integrates diffraction-radiation theory for large-volume structures with a finite element model based on the lumped mass formulation for mooring dynamics. The study examines the impact of wave frequency, significant wave height, and current velocities on the tension variations and displacement vectors of the mooring lines. Results indicate that neglecting the fluid-structure interaction effects leads to a significant underestimation of peak tension loads, particularly in the splash zone and at the fairlead connections. Furthermore, the coupling effect induces low-frequency drift motions that amplify fatigue damage accumulation. This research provides critical insights for optimizing mooring designs and enhancing the safety margins of deep-water floating platforms.