Numerical and experimental studies on dynamic gangway response between monohull flotel and FPSO in non-parallel side-by-side configuration

As an important equipment, gangway and its safety are crucial during offshore operation, and its dynamic response raises concerns especially when gangway is deployed between two free-floating structures. In this paper, the response of a passive telescopic gangway between monohull flotel and FPSO in nonparallel side-by-side configuration is investigated numerically and experimentally. The numerical model is established within the frequency domain, where the hydrodynamics are solved by 3D potential flow theory. The nonlinear factor, roll damping, is treated by using stochastic linearization. The connection between gangway and vessel is assumed to be an ideal joint, subsequently, gangway responses are derived by properly taking into account various motions of flotel and FPSO. Gangway responses such as its extension and rotation are presented in simulation as well as measurement. To interpret physics, firstly vessel global motions in single-body and multi-body cases are compared; then, relative motions between gangway points at flotel and FPSO ends are illustrated. Notably, the impact of multi-body hydrodynamic interaction is analyzed. The interaction triggers two types of couplings i.e. coupling between two vessels as well as coupling within one vessel such as coupled sway and pitch which does not exist in the single-body case. Therefore, the contribution of respective degree of freedom (DOF) of flotel and FPSO to gangway response are detailedly discussed. The simulation has generally good agreement with the model test. Most extra peaks or troughs observed in results those reflect hydrodynamic and mechanical couplings are well captured.