Effect of inner free surfaces and multi-body hydrodynamic interactions on motions of LNG carrier and floating terminal
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The hydrodynamic interactions between an FT (Floating Terminal) and LNGC (Liquefied Natural Gas Carrier) in a side-by-side offloading arrangement as well as the dynamic coupling between the floating-body and inner-liquid motions are investigated by a potential-viscous hybrid method in time domain. For the time-domain simulation of the vessel motion, the hydrodynamic coefficients and wave forces are obtained by a potential-theory-based 3D diffraction/radiation panel program in the frequency domain. The ensuing simulations of vessel motions in time domain are carried out by using the convolution-integral method. The liquid motions in inner tanks are simulated in time domain by an FDM Navier-Stokes solver with a SURF scheme. The computed sloshing forces and moments are fed into the time integration of ship motion, and the updated ship motion is in turn inputted as the excitation force for liquid tanks; this is repeated for the ensuing time steps. For comparison, we independently developed a sloshing-motion coupled analysis program based on linear potential theory in the frequency domain. The developed computer programs are applied to the side-by-side offloading operation between the FT and LNGC. The frequency-domain results qualitatively reproduce the coupling effects, but the peaks are in general overpredicted compared to the experimental and time-domain results. The liquid-sloshing and vessel-motion interaction effects can further be intensified in the case of multiple floating bodies. by The International Society of Offshore and Polar Engineers.
