Sloshing and swirling in a spherical LNG tank

Abstract

Recently, the awareness regarding environmental issues is increasing all over the world. Natural gas is an attractive energy option because of its environmental performance. Regarding its transportation, Moss type tank, a spherical tank, is one of the most used cargo containment systems. In this research, the behavior of the partially filled spherical tank of LNG carriers is examined. The motions of the liquid inside the tank are divided into four types in this study, i.e., planar wave, sloshing, steady-state swirling and non-steady-state swirling. Sloshing and swirling are easy to occur as the excitation amplitude becomes larger. The force and the pressure on the tank wall are also studied by both model experiments and numerical simulations. The non-dimensional force becomes smaller as the excitation amplitude becomes larger because of its nonlinearity. Regarding the pressure, each motion type has its own characteristic time history. For example, the pressure history has two peaks when the excitation frequency is high. The effect of the position of the rotation center is also examined. Considering the sloshing effect on the spherical tank, the results show that the rotation center located close to the center of the tank is advantageous.