The current demand in liquefied natural gas (LNG) encouraged the design of various concepts for floating LNG (FLNG) liquefaction or regasification facilities. With increasing transport distance, e.g. from remote marine locations to the onshore gas supply net, gas pipelines become uneconomic compared to shuttle carriers for LNG (LNGC). Due to its high energy density, offshore transfer from processing terminals to carriers and from carriers back to receiving terminals has to be analyzed in detail. During the transfer period, free fluid surfaces occurring in the cargo tanks of the LNGC are leading to a significant decrease of the initial intact stability and altered motion behavior. This paper focusses on the influence of resonant tank sloshing on the LNGC’s roll and surge motions. Analyses of transverse and longitudinal sloshing yield a surprising phenomenon: the frequency shift Δω between the theoretical natural frequency of the tank alone and the respective motion peak for a vessel with four tanks mounted to the hull. Force measurements between tank and hull reveal a peak at the tank’s natural frequency that causes strong liquid motions with related forces and moments on the hull but no increased vessel motions. Additional investigations comprise the offloading situation with a multi-body arrangement of LNGC and a FLNG (the MPLS20 system) in tandem and briefly also in side-by-side configuration. The slow drift motions on the turret-moored FLNG are exemplarily investigated in head seas.

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