Finite element modeling of a single-point multi-segment mooring in water waves

In this study, a finite element model is developed to simulate the problem of a single-point multi-segment mooring subjected to water waves. The governing equation for cable structure is derived from the principle of virtual work. A finite element method is then used to obtain the discrete equations for numerical computation. Due to high nonlinearity of the discrete equations of motion for cables, further manipulations, including incremental and iterative schemes, are used in the solution procedures, where the implicit Newmark's method is chosen for time integration. To describe the wave forces, the Morison equation is used to calculate the drag forces on cables, and the fluid motion generated by water wave is based on potential wave theory, in which the linear wave is applied. The initial equilibrium configuration of the cable structure, which is required before dynamic analysis, is calculated by the viscous relaxation technique in static analysis. Good agreement between numerical results is shown in calculation of a single-buoy relaxation. Comparisons of the present results of the four-segment mooring with an iterative model also confirm applicability of the present numerical model. Meanwhile, effects caused by nonlinear waves are also demonstrated.