Dynamic Behaviour of a Turret FPSO in Single and Tandem Configurations in Realistic Sea Environments

A comprehensive analysis of the dynamics of ship-type Floating, Production, Storage and Offloading systems anchored through a turret system (Turret-FPSO) is presented. Firstly, the behavior of the FPSO unit alone is examined under the combined action of wind, current and waves. Wave forces are represented by second-order effects such as slow drift forces, as well as wave-current interaction corrections to mean drift forces, namely wave drift damping. The influence of the vessel’s draft and of the longitudinal position of the turret is also assessed. The study of the dynamics of the system is performed by calculating static equilibrium solutions and evaluating their stability properties. Relevant ranges of environmental parameters such as wind and current speeds, wave spectra, and respective angles of incidence are investigated. Numerical results are obtained and shown in bifurcation diagrams depicting the evolution of steady-state responses as a function of environmental parameters. The system displays a variety of different regimes of solutions in which both their number and their stability may change as one or more parameters are varied. The stability analysis of the Turret-FPSO system is extended to include the tandem configuration with a shuttle vessel. The main features of this more intricate scenario are summarized in 3D bifurcation diagrams.