The development of a periodic boundary layer and time discretization in a sloshing flow is examined using a CFD model. The boundary layer is found to vary significantly throughout the simulation and depth of penetration is an indication for required grid resolution. Time step size is varied systematically to determine a suitable time discretization. Time step independence is determined by comparison of the sloshing pressure history and fluid center of gravity displacement. Fluid momentum, center of gravity displacement and impact pressure of a resonant sloshing flow are used to confirm a suitable combination of spatial and temporal resolution for sloshing impact.
When a tank is partially filled with a fluid and subjected to an external excitation force, sloshing occurs (Olsen, 1976). Ships with large ballast tanks and liquid bulk cargo carriers, such as very large crude carriers (VLCCs), are at risk of exposure to sloshing loads during their operational life (Rizzuto and Tedeschi, 1997). The inclusion of structural members within the tanks dampens the sloshing liquid sufficiently in all but the most severe cases. However, this approach is not used for Liquefied Natural Gas (LNG) carriers and the accurate calculation of the sloshing loads is an essential element of the LNG tank design process (Bass et al., 1980; Knaggs, 2006). The increase in global demand for LNG has resulted in a new generation of LNG tankers with a capacity in excess of 200,000 m3, compared to 140,000 m3 today. A prerequisite for the safe operation of these LNG tankers is an accurate calculation of the sloshing loads experienced by the containment system (Han et al., 2005; Card and Lee, 2005). The work of Abramson (1966) summarizes the methods available in modern sloshing analysis, and Ibrahim (2005) gives an up-to-date survey of analytical and computational sloshing modeling techniques.
