Qualitative Sloshing Computations for the Assessment of Membrane LNG Cargo Containment System Design

Long duration numerical sloshing simulations and model tests have been carried out to assess membrane LNG cargo containment system design. In the sloshing model tests, resonance periods of the tank were taken into consideration for the selection of critical sea states in viewpoint of sloshing loads. For the sloshing scenario of the most probable highest extreme impact pressure used in sloshing model tests, impact pressures were calculated and statistically post-processed for critical locations in a cargo hold of LNG carrier using full scale 5-hour numerical simulations. In the numerical simulations, violent sloshing behaviors could be reproduced using a general-purpose commercial CFD code which uses PLIC VOF method to capture the free surface evolutions. For validation of the numerical calculations, 2-dimensional sloshing simulation was first performed for a rectangular tank and a good agreement with experimental data was shown. For use in the assessment of the tank design, 3-dimensional numerical sloshing simulations were performed using four degrees of freedom irregular ship motions and the statistically processed impact pressures were compared with those of the sloshing model tests. The comparison showed that the 3-dimensional long duration numerical sloshing simulation can be a qualitative computational tool for use in the assessment of the membrane LNG cargo containment system design.