Effects of mooring line dynamics on position keeping of a floating production system

Abstract

In order to investigate the effects of mooring lines damping on slow drift motion of floating vessel, a parametric study on the coupled dynamics of floating structure and its mooring system was carried out. Hydrodynamic forces on floating structure of ship type were estimated by 3-D panel method. Mooring catenaries were discretized according lumped-mass model. Two time integration schemes were combined in solving coupled dynamics: Runge-Kutta method of 4th order was used for integration of motion equation of floating structure and Newmark method was implemented for solving mooring lines dynamics. The object of parametric study was TPS (Turret Moored Production System) with a tanker of 124,400 ton, which was one of standard models for comparative study in FPS 2000 workshop (1989, Norway). Mooring system was designed for two different mooring stiffnesses using catenary equation. Contact problem of mooring lines with seafloor was modeled by mass-spring-damper system. Three kinds of non-linear simulations were conducted: free decay simulation, quasi-static analysis of mooring lines and non-linear analysis of mooring lines dynamics. The results confirmed the remarkable effects of mooring lines damping on the resonance amplitude of slow drift motion of moored vessel depending on mooring stiffness.