The paper deals with floating systems (VLCC's converted to FPSO's) moored in deep water in the presence of currents. The offioading operation is carried out in a tandem arrangement from the FPSO to a shuttle ship of lesser capacity. According to the classical theory of dynamic systems, a study of the behavior of floating units is developed by determining the equilibrium position and then performing a local stability analysis about this position. This analysis is complemented by time domain simulations. This procedure is extended to the case of systems in spread mooring configuration. The other systems can be seen as particular cases.
These last years the conversion of VLCC's (Very Large Crude Carrie0 into FPSO (Floating, Production, Storage and Offioading) units has been used by Petrobras in Brazil offshore to exploit oil in deep water, a consequence of the necessity of large storage unit with the capability to transfer the oil to shuttle ships. A group of VLCC hulls was converted to FPSO, with the installation of process plants, turrets and so on. The use of these units grew up the last years. Mostly common ships have been moored in single point (SPM), at the sea-floor through an installed turret (TMS), in spread mooring configuration (SMS) and also with the use of dynamic positioning system (DPS). This has motivated the development of many different works about their dynamics. The stability analysis of this kind of system is based on the theory of dynamic systems expressing the hydrodynamic forces acting on the bodies as function of their velocity components. First the equilibrium positions of the system are determined and around these positions the stability of the system is studied. This is not a very difficult job when the number of variables is small.
