This paper presents the results of the sloshing experiments having fluids in a model tank with various density ratios. The experimental modeling is performed with mixed gas of sulfur hexafluoride (SF6) and nitrogen (N2), because the modeling consisting water and air is not considered representative enough to estimate sloshing pressure in an actual LNG cargo tank. Two-dimensional model and 1/50-scale three-dimensional model tank have been manufactured, and three different filling levels are considered with the irregular motions. Each condition has five different density ratios using different composition of gas. The decrease of sloshing pressure is predicted when the density ratio increases.
Sloshing in LNG carriers can lead to large impacts on the containment system. It is important to assess these impact pressures and forces for adequate design of containers. Because of stochastic character of sloshing, experimental analysis is mainly recommended by ship classification societies (ABS, 2006; DNV, 2006). An experimental system for sloshing has been settled down in Seoul National University (SNU) to predict pressure impacts (AMEC, 2010). Dimensionless numbers for this application have been studied, but none of them have drawn a complete conclusion. Global behavior of the fluids is governed by the Froude number, so the ullage pressures should be Froude scaled (Bass et al., 1980). The local behavior, however, needs another scaling law. To find out appropriate scaling law for local phenomenon of sloshing, analytic, numerical (Braeunig et al., 2009), and experimental studies have been conducted. Acoustic scaling including the density ratio has been theoretically identified, which is to be relevant as well as Froude scaling to the sloshing problem (Dias et al., 2007). During the impact, transfer of momentum between liquid and gas is occurred, so the den density ratio has an influence on the impact pressure.
