Research on the tension characteristics of a buoy-mooring line system with seabed contact

Abstract

Traditional modeling approaches for mooring lines exhibit limitations in capturing nonlinear behaviors under large displacement and deformation conditions. In this study, a buoy-enhanced mooring line model incorporating seabed contact is developed based on the Absolute Nodal Coordinate Formulation (ANCF). The influence of the buoy on tension characteristics is analyzed to provide insights for the optimization of mooring system design. First, the mass matrix, stiffness matrix, and generalized elastic force vector of the mooring line element are derived based on ANCF. The model incorporates external forces such as Morison’s hydrodynamic load, seabed contact forces, and the buoyancy provided by the added buoy. The dynamic equations of the mooring line are then formulated using the Lagrange multiplier method. Second, the accuracy and efficiency of the proposed model are validated through dynamic simulation case studies involving a flexible coiled beam model, an underwater buoy-mooring line model, a mooring system subjected to irregular wave excitation, and a system under harmonic motion excitation. Finally, the effects of buoy configuration and installation position on both static and dynamic tensions in the mooring line are analyzed. The influence of the buoy on the impact amplification factor and system stability under various harmonic excitations and ocean current conditions is also discussed. Results indicate that appropriate buoy configuration can significantly reduce the tension in the mooring line, mitigate the alternating slackening and tightening phenomena, and thereby enhance overall system stability.