Experimental and Numerical Investigation of Sloshing in Marine LNG Fuel Tanks

In the last 15 years, there has been an increasing number of LNG-fuelled ships carrying C-type tanks, classified as pressure vessels. Experience have shown that vessel motion combined with low bunkering temperature can result in rapid pressure drop. The form of the tank heads has a spherical shape, and its influence on the sloshing requires further investigation. In this study, we look at the sloshing characteristics in a small cylindrical tank with 2:1 semi-elliptic heads undergoing a harmonic pitch motion with different filling levels and frequencies, but with constant amplitude. Results from numerical simulations are compared with laboratory experiments performed at NTNU in Ålesund. Numerical simulations are performed with the open-source CFD tool OpenFOAM. Both two- and three-dimensional simulations are compared to the experiments, but it is found that three-dimensional effects cannot be excluded in these tanks. Presented results are non-dimensional wave elevation in the tank as well as general description of the sloshing characteristics. The results show interesting wave patterns due to the spherical shape of the tank heads, and the agreement between the measured non-dimensional free-surface elevation and simulations is good. At higher filling, a violent jet is formed because the tank heads lead the water back with high speed.