Liquefied natural gas (LNG) carriers have played and will continue to play a key role in ocean gas transportation with the increasing demand for energy. Safe operation of LNG carriers requires the knowledge of global and local fluid pressures imposed by the sloshing liquid. As LNG carriers are required to operate in different environmental conditions, safety is a primary consideration in such operations. LNG carriers are often subjected to significant sloshing loads during their operational life. The motion of the LNG carriers as they move across oceans cause the liquid in the containers to slosh. Liquid sloshing may cause large internal stress and deformation in the walls of containers, particularly when the external forcing frequency of the ship is close to that of the natural sloshing frequencies. This effect is a critical consideration in ship design. The objective of this work is to find an effective numerical model solving the coupled internal sloshing and external seakeeping interaction for small/medium LNG carriers. To assess the influence of the liquid motion in tanks on the overall body behavior, a three-dimensional method for dynamic coupling between liquid motion in ship tanks (sloshing) and rigid body motions of ships (seakeeping) in the frequency domain, is considered. The method is formulated under the classical assumptions of linear potential theory and boundary integral equation methods, which are used to solve both interior sloshing and exterior seakeeping. Two tank LNG carriers have been analyzed and the typical coupling effects (two peaks) of the sway and roll transverse motions in the beam have been presented. This method produces quick and reliable results of ship motions.


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