In this paper, a study is made on the dynamic behavior of a FPSO-Shuttle tanker system in current, wind and waves. A three dimensional singularity distribution method is used to describe the fluid motion based on potential theory. For the estimation of wind and current forces, OCIMF data are used. The static and dynamic stability of the FPSO-Shuttle tanker system is analyzed based on using the linearized equations of motion in surge, sway and yaw modes. Nonlinear responses of the system are simulated numerically. Based on it, the stability is examined from the viewpoint of the design parameters like the turret position, the mooring stiffness, the hawser length and its tension, it is found that the FPSO-Shuttle tanker system shows a quite different stability from those of the FPSO and the shuttle tanker. The main feature is that the FPSO-Shuttle tanker system does not have a fixed point but a limit cycle, although it is a dissipative and linearly stable system.
Recently turret-moored FPSOs(Floating Pro-duction Storage & Offioading) are increasingly deployed for oil exploitation in deep water marginal fields. In such a case, crude oil is normally transported by a fleet of shuttle tankers, which are connected to the FPSO through the hawser during the loading process. Thus the relative motion between the FPSO and the shuttle tanker is critical for safe operation. Fig. 1 shows a typical FPSO-Shuttle tanker system. Generally the FPSO is permanently moored by turret-mooring lines, while the shuttle tanker is positioned by dynamic positioning system(DPS). The DPS is a device to maintain the desired position and heading of the vessel with the help of thrusters in the presence of disturbances caused by wind, current and waves.
