Coupled Dynamic Analysis Of Inner Turret Moored FPSO

The inner turret moored FPSO is a floating multi-body system, existing not only coupling between inner turret and mooring cables, but also coupling between inner turret and FPSO hull. The surge, sway and yaw motion can easily reach to substantial amplitude due to second-order forces. Heave, roll and pitch motion may resonant with first-order wave forces. The turret is generally positioned close to the bow in order to obtain better weathervane effect.The target of this paper was to investigate motion and force response of a inner turret moored FPSO in random sea state. The impact of influencing parameters on motion and force response was also considered.The wind and current load on the FPSO hull were calculated based on OCIMF specifications; the first-order and second order wave forces were calculated adopting three-dimensional potential flow theory. Basing on the theory of computational dynamics of multi-body systems, the coupling dynamic model and algorithm of turret and FPSO hull was established. The coupling algorithm between inner turret and mooring cables was considered adopting lumped mass model. Both of the two algorithms were programed by Matlab, and then verified through case studies. Ultimately the coupled dynamic analysis of inner turret moored FPSO was carried out, and the impact of influencing parameters was also studied.The study shows that:the energy of FPSO surge motion is concentrated in the low-frequency region; the energy of hull heave and pitch motion is concentrated in the wave frequency region; the wave frequency components and low frequency component are both significant in cable tensioa Peak period and peak factor has significant impact on the FPSO low frequency and wave frequency motions; When the natural period of hull pitch close to the peak period, the pitch motion increases, and if the turret close to the bow, the vertical motion of the mooring cable would get more violent, causing the increase of cable tension. During the transition from full to ballast condition, natural period of FPSO, mooring stiffness, and environmental load changes, resulting in significant decrease of surge motion and cable tension; in the non-collinear load condition, changes of environment loads reduce surge motion and increase heave pitch motion...