Analysis of liquid tank sway and fatigue of LNG carriers

This study investigates sloshing dynamics in LNG carrier cargo tanks and the resulting fatigue damage. By employing a sea state combination methodology, complex short-term sea conditions are effectively consolidated into equivalent sea states, enabling the statistical quantification of long-term wave-induced loads acting on the vessel. The hydrodynamic software AQWA is utilized to conduct dynamic analyses of the ship, from which the dynamic response characteristics—namely roll, pitch, yaw, sway, surge, and heave—are extracted. These responses serve as the excitation inputs for tank sloshing simulations, which are performed under three different filling levels: 50%, 70%, and 90%. The sloshing dynamics under each condition are thoroughly analyzed. Subsequently, fatigue damage assessment of the tank structure is carried out by integrating the rain-f counting method with S-N curve data. Results indicate that the cumulative fatigue damages for the three filling levels are 6.654e−4, 3e−4, and 2.2215e−4, respectively, all of which are significantly below the critical fatigue damage threshold. This confirms that the structural integrity of the cargo tank meets the required safety standards during operation.