Coupled dynamics between a turret-moored FPSO and a semi-submersible accommodation platform

Abstract

In multi-body offshore systems, a telescopic gangway is often adopted for personnel transfer, the feasibility and safety of which are crucial. The coupled dynamics and gangway responses of a turret-moored floating production storage and offloading (FPSO) unit and a semi-submersible accommodation platform (AP) were investigated numerically in this study. Both side-by-side arrangement and the configuration that AP is tandem at the stern of FPSO were considered. The hydrodynamics considering multi-body wave interaction were calculated in frequency domain based on potential theory. The non-linearity of second-order wave drifts, moorings, and turret was fulfilled in time domain. We focused mainly on the effects of multi-body interactions on hydrodynamics and gangway responses. The hydrodynamic interactions have a negligible effect on the global motions of FPSO, whereas it more strongly affects AP. The interference is more intense in side-by-side scenario than in tandem configuration. The gangway responses are governed by relative translational motions between two vessels and are also related to its initial arrangement. Since weathervaning of FPSO can cause a large yaw offset, non-collinear sea states are considered, in addition to cases with different significant wave heights. Extreme gangway responses are predicted according to Weibull distribution, by which the environment criteria are determined.