Sloshing is the liquid movement in the container excited by the motion. The sloshing flow becomes more violent and results in intensive liquid impact when the excitation period gets closer to the resonance period of internal liquid. This sloshing impact is the most critical load component in the structural design of LNG Cargo Containment Systems (CCSs) of LNG carriers or FLNGs.
In this study, the structural assessment was performed against sloshing loads for a two-row Mark III membrane type CCS of FLNG. She was designed to be installed in Northwestern Australia gas field where the wind sea and swell components are simultaneously measured. Two distinct sea states are considered for structural analysis. One is the sea states on the contour line corresponding to 100-year return period in wave scatter diagram. These sea states are usually used for the prediction of extreme motions of floater and termed extreme sea states. Another is the sea states that have high probability of occurrence. The latter is considered to investigate the effect of the long term exposure on sloshing loads. Evaluation of the structural safety of CCS and hull structure was conducted in sequence of CFD-based scenario screening, sloshing model tests and statistical fittings of Utilization Ratios (URs).
In conclusion, it was found that all of probable sea states had to be fully considered at screening for the sloshing assessment. Even though the sea states with high probability of occurrence have smaller significant wave heights than extreme sea states, those sea states might cause the largest sloshing load.