Dynamic Behavior of a DICAS FPSO and Shuttle Vessel under the Action of Wind, Current and Waves

摘要

Floating, Production, Storage and Offloading (FPSO) systems consist of a large tanker moored to the seabed operating as an offshore production facility. During the offloading operation, another tanker (the shuttle vessel) is attached to the FPSO through a flexible hawser to allow the safe connection of a hose for cargo transfer. In previous works we have applied a nonlinear dynamical systems approach to investigate the behavior of these systems under the action of wind and current. Both Differentiated Compliant Anchoring System DICAS and turret FPSO mooring arrangements were considered. For the present study we have taken a DICAS system, and performed a numerical investigation of the influence of the action of sea waves in addition to wind and current. Suitable spectra were employed, and second-order effects such as slow drift forces, as well as wave-current interaction corrections to mean drift forces, namely wave drift damping, were calculated. The predicted dynamics for the system were calculated for relevant ranges of environmental parameters such as wind and current speeds, wave spectra, and respective angles of incidence. The influence of the draft of the vessels was also inspected. Results were summarized in bifurcation diagrams displaying the evolution of steady-state responses as a function of parameters characterizing the environmental state. The stability of steady-state responses was investigated using time-domain simulations. The results were also employed to illustrate the production of diagrams in which inadequate (or unacceptable) dynamic solutions are identified.