Long-term approach for assessment of sloshing loads in LNG carrier, part II: Grouping method

Abstract

Assessing the sloshing loads has been a significant issue in designing the cargo containment system (CCS) of a liquefied natural gas carrier (LNGC). The sloshing problem contains numerous physical and technical uncertainties. The long-term approach has been suggested to reduce the possible uncertainties, but it has not been a feasible option owing to the incalculable number of experimental cases. Daewoo Shipbuilding and Marine Engineering Co., Ltd., Hyundai Heavy Industry Co., Ltd., Samsung Heavy Industry Co., Ltd., Korean Register, and Seoul National University conducted extensive sloshing model tests for the 174 K S-LNGC. To consider the long-term approach, Part I describes the differences between short- and long-term approaches based on the guidelines of different classification societies. To address the significant number of experimental conditions required for the long-term approach, a grouping method is investigated (Part II). Although this grouping method is typically used in practical design, it has not been validated, and its applicability is yet to be determined. In Part II, the sea states are classified using 16 different grouping methods. The long-term exceedance probabilities and pressures are obtained individually and then compared with the results obtained from fully considering all sea states. After performing the general sloshing model test of the shipbuilding industry, the sloshing impact pressure of a liquefied natural gas cargo model is measured via 6DoF irregular simulations, where the upper section of the cargo hold structure is considered. Long-term pressures are locally and globally investigated and compared among 16 different sea states and all the sea states. Based on the results, the best grouping method is suggested for the long-term approach.