In this paper, the methodology to predict sloshing severity is elaborated step by step. Since sloshing phenomenon is critical factor for designing LNG CCS (Liquefied natural gas cargo containment system), there have been plenty of approaches to estimate sloshing loads. Among the various methods, sloshing model test is considered the most reliable but expensive way. Therefore, prescreening sea-states which can cause severe sloshing load is important to carry out sloshing model test efficiently. The prescreening method based on Rankine Panel Method is fast in computation, and with the empirical modification, it shows good accuracy.
Ever since importance of sloshing load inside LNG Cargo was raised by ship building industries, the studies on sloshing assessment have been improved through the time. Malenica et al. (2017) summarized various approaches to evaluate sloshing loads on LNG CCS, and it contains sloshing model tests and numerical computations. However, it has been well known that numerical computations consume lots of time and not accurate enough yet to estimate sloshing impact especially on the tank roof. Therefore, most of the ship classification societies suggest sloshing model test for estimating sloshing loads (ABS, 2006; BV, 2011; DNV, 2014; LR, 2009).
There are several recommendations on the sloshing model test as followings: model test for one case should last for at least five hours of real time scale; model test should cover various sea-states with different heading angles; enormous amount of pressure sensors should be installed on the model tank so that high sloshing impact could be investigated on the focused area. For more details on the sloshing model tests, it is described in Kim et al. (2012). However, fulfilling those requirements on the experiment is expensive and time consuming process.
To carry out sloshing model test efficiently, appropriate prescreening method should be applied. If the prescreening method can skim out several sea-states which are insufficient to generate sloshing loads, then test condition could be concentrated more on the severe sea-states. According to Kim et al. (2014), the more duration of sloshing model test is increased, the better reliabilities of statistical value could be obtained. Therefore, more repeat test can be carried out on the critical sea-state within the limited time and budget based on the prescreening result. In fact, Kwon et al. (2017) already applied such kind of a prescreening method on the floating LNG Carrier.
