This article presents a numerical study of the coupled ship motions and tank sloshing of a liquefied natural gas carrier. To solve this coupled problem, we have developed a time-domain numerical method. The method combines a ship motion solver based on strip theory and a computational fluid dynamics sloshing solver. The method has been applied to a liquefied natural gas carrier model to investigate the coupling effect in regular waves. Simulations for four different loading conditions were carried out, and the results of ship motion response amplitude operators and free surface movement amplitudes were presented in frequency domain. The coupling effect on ship motions and sloshing has been discussed. Based on the assumption of linearity of ship motions and wave, the authors used the ship motion response amplitude operators (with coupling effect) obtained in regular wave conditions to generate ship motion time histories in irregular waves. Sloshing in tanks was then simulated by using the ship motion time histories in irregular wave conditions. The calculated impact pressure time histories were analyzed by using the exceedance probability function.

The present paper proposes a numerical method for calculating the coupled ship motions and sloshing in time-domain. In the present method, strip theory is used to solve the ship motion problem and a finite difference method is used for the sloshing problem; both problems are calculated in time domain. To verify the computational results, first the calculated force due to sloshing was compared to experimental data and good agreement was found. Next, the authors compared the numerical and experimental results for ship motions, and the accuracy of numerical computation was confirmed. Finally, the wave height at certain position in the tank was compared. Even near the natural frequency of the tank, the numerical results based on the present method showed good agreement with the experimental ones. Moreover, a special case when tank is fully filled with liquid was discussed, and both experimental and computational results showed that the influence of liquid cargo is different from the solid one although the tank is completely filled.