Dynamic model of cable tension and configuration for vessel at anchor

Abstract

A numerical model considering the seabed friction is developed to investigate the dynamic behavior of anchor cable in this paper. In the model, the anchor cable was divided into hanging and lying parts. The governing equations of hanging and lying anchor cables were established respectively based on finite difference method and coupled according to the boundary conditions. The coupled equations of anchor cable were solved by Newton iteration and the static anchor cable parameters used for the initial values were confirmed by double bisection method. To illustrate the reasonability and validity of the model, several simulations of vessel sway in wind with different time and space step sizes and different seabed friction coefficients were presented. The simulation results show that anchor cable snap load is 3–5 times of average tension, the variation of anchor cable bearing is 2 times of ship heading, and the sway amplitude of the ship’s center of gravity is about one times of ship length. Compared with the experimental data, the model and algorithm in this paper can successfully provide the realistic prediction of the dynamic tension and configuration of anchor cable, and can be used as a reference for anchoring operation. Farther, this paper found out that the normal seabed friction coefficient has considerable impact on the cable tension.