Experimental and numerical investigation of 2D sloshing: scenarios near the critical filling depth

Sloshing is an important issue for LNG tanks and in general when partially filled tanks are on-board of a vessel. This resonance phenomenon may be connected with complex motions of the filled liquid that can couple with the ship motions and can represent a danger for the tank strucure and for the stability of the ship. In this context, it is very important to identify the possible scenarios associated with the sloshing. Present analysis is a part of the research activities reported in Colagrossi et al. (2004) and Lugni et al. (2005) and uses both 2D sloshing experiments performed in a rectangular tank L = H = 1 m long and b = 0.1 m wide (see left sketch in figure 1), and the 2D SPH solver (Colagrossi and Landrini 2003 and Colagrossi 2005). In particular it is the logical continuation of the experimental investigation presented in Colagrossi et al. (2004). There, sloshing phenomena in the case of filling depth h/L = 0.35, i.e. slightly higher than the critical value h/L = 0.337 (Faltinsen et al. 2000), were investigated. By varying the excitation period T of the sinusoidal horizontal motion of the tank, and by increasing its amplitude of oscillation, some peculiar phenomena were observed for T near the linear sloshing natural period T1, i.e. an asymmetric behavior of the wave elevation along the tank, as well as alternation of the breaking phenomenon at the two tank sides. Such phenomena are connected with important water-wall interactions and with the vortex generation consequent to the post breaking phenomena. Because of their complex features, they can not be predicted by potential-flow models. Further, to our knowledge no documentation of them is available in the literature. With the aim to identify the main physical mechanisms involved and responsible for the observed phenomena, a dedicated experimental and numerical investigation has been performed by choosing the excitation period near T1 and reducing it progressively. For each examined T , the excitation amplitude A was varied and the features of the resulting sloshing events have been analyzed. Within the studied region of the T/T1-A/L plane four main scenarios have been identified. They are presented in the table of figure 1 and can be listed as events: (I) without free-surface breaking, (II) with alternate breaking, (III) long-time randomic asymmetric behavior, (IV) with local splashing jets. The fundamental