Comparative analysis on dynamic characteristics of deepwater hybrid mooring line

For study dynamic characteristics of the deepwater hybrid mooring line, considering the two hybrid mooring lines is completely identical while other conditions are kept unchanged, and the top end tension-static offset characteristic curve of the two mooring lines is consistent as much as possible, the polyester rope is as the substitute for the wire, then the method of numerical simulation is adopted to carry on the comparative analysis on dynamic characteristic. And the natural frequency, complex stiffness and mooring-induced damping are compared. After the establishment of two-dimensional nonlinear finite element dynamic model of the hybrid mooring line, the calculation on stiffness of the hybrid mooring line is accomplished through the iterative method based on the empirical formula proposed by Del Vecchio in 1992. When the wave drift motion and wave frequency oscillations of the floating platform are specified, the consequent variations of stiffness are compared respectively. The mooring line and seabed interaction are based on the hypothesis of rigid seabed. The fluid drag force and inertia force on the mooring line are calculated according to the Morrison formula. The dynamic analysis is executed through time-domain nonlinear finite element method accounting for the oscillations of the moored floating platform. The energy absorbed from the oscillation of the floating platform in the mooring line is worked out, and then the mooring-induced damping is achieved. Finally, the wave drift motion and wave frequency oscillations of the floating platform are specified, the consequent variations of the mooring-induced damping are compared.