Damping calculation of a deepwater catenary mooring line

A deepwater catenary mooring line damping mainly includes hydrodynamic drag damping, internal damping and friction damping caused by seabed interaction. Hydrodynamic drag and friction damping are significantly affected by a floating platform while internal damping is dependent on material properties. The energy dissipated by a mooring line due to floating platform oscillation was used to calculate mooring-induced damping. The interaction between mooring line and seabed was based on the hypothesis of rigid seabed. The fluid drag force and inertia force on the mooring line were calculated according to Morrison formula. Under various current velocity distribution conditions, the non-linear dynamic analysis of the mooring line was performed in time-domain with the finite element method. Moreover, the dynamic responses of the mooring line were computed under the wave drift oscillation and the wave frequency oscillation of the floating platform. The maximum tension and the hydrodynamic dampings of the mooring line were compared under the different working conditions. Considering the contact friction between the mooring line and seabed, the maximum tensions of the mooring line were compared under different friction coefficients and the friction damping was calculated.