Dynamic response and fatigue damage of catenary mooring cables based on ANCF

Abstract

Based on the absolute nodal coordinate formulation (ANCF), this paper develops a numerical model for computing the dynamics and fatigue damage of catenary mooring cables. The catenary mooring cable is modeled using ANCF elements, with hydrodynamic loads incorporated through the Morison equation and seabed reaction forces simulated by spring-based seabed resistance. After validating the ANCF mooring cable model through a comparison with Orcaflex, the effects of incident flow direction and various excitations on the dynamic characteristics and fatigue damage of the mooring cable are discussed. Subsequently, the validation results of the ANCF mooring cable model are compared with those from MoorDyn, further highlighting the model’s effectiveness and practicality in engineering applications. Subsequently, by varying the mooring line length, the dynamic characteristics under different length conditions are analyzed, and fatigue damage is evaluated. The study reveals the impact of incident flow direction and mooring line length on the dynamic characteristics and fatigue damage. It is found that shortening the mooring line significantly enhances the constraints on the SPAR platform and affects the fatigue damage of the mooring line. Effective mitigation of fatigue damage can be achieved by avoiding the most unfavorable incident flow direction or adjusting the length of the mooring line.