Influence of Tangential Hydrodynamic Force and Inclination Angle Calculation on the Dynamic Responses Analysis of Mooring Line Based on Lumped Mass Method

Research on mooring line response offers a scientific foundation and technical backing for ocean engineering management. The lumped mass method is commonly used to calculate the dynamic responses of mooring line, pioneered by Walton and Polachek, although it ignores the tangential hydrodynamic force. Nakajima addressed this limitation, but the inclination angle calculation for each element is approximated by the average of the adjacent two nodes. To accurately assess the influences of these factors, this work introduces the tangential hydrodynamic force component into the equation of motion for mooring line dynamic analysis based on the lumped mass method. Meanwhile, we improve the discretization process of lumped mass nodes, analyzing half of the connected spring at both ends of each lumped mass node respectively. The detailed formulation and motion equation for static and dynamic mooring line analysis are presented. The time-domain solution procedure based on the finite difference method is adopted. Finally, different external excitations are applied to calculate the dynamic responses of mooring line. The results show that the top tension increases by about 2%-5% considering the contribution of tangential hydrodynamic force, and the inclination angle calculation significantly influences the dynamic configuration of the mooring line when it is intense change.