The impact pressure due to sloshing motion in the liquid cargo hold is one of the most important load factors when designing new liquid cargo hold and containment system for membrane-type LNG carriers. The magnitude, effective area and duration of the impact load are all important when considering structural response of the containment system. The strength of the containment system is also dependent on the spatial and temporal pattern of the impact load. This paper describes a numerical and experimental scheme to evaluate full-scale sloshing load and impact strength of the containment system. The scheme consists of seakeeping/sloshing analysis to identify the critical wave condition for the sloshing model test, sloshing model test to measure the sloshing impact load on rigid tank wall, evaluation of full-scale impact load by the ‘composite’ scale law and a hydro-viscoelastic-fracture analysis of containment system with consideration of fluid-structure interaction during the vibratory motion of the containment system. The newly introduced composite scale law revealed that the existing ad-hoc scale law is still applicable to the existing operational condition at high filling level but not applicable to the partial filling conditions. Fluid-structure interaction between LNG and containment system is considered during the dynamic structural analysis of containment system with the LNG modeled as an acoustic medium. The containment system in LNG tank, which is a composite structure of metal membrane, polyurethane foam, plywood laminate insulator and steel hull, is modeled as a two dimensional composite structure. All of the structural elements are treated as linear elastic material except polymer and plywood insulators that show viscoelastic behavior at high loading rate, which is the case in the sloshing impact load. The attenuation due to the fluid-structure interaction, material damping and the effect of locality and duration of the impact load on the structure response is investigated by the proposed numerical scheme.

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