Wave-Impact in a sloshing tank: hydroelastic challenges

Abstract

Wave-impact in sloshing flows is an important issue for the safety of the Liquefied Natural Gas (LNG) carriers. Although LNG tanks have filling restrictions, they must be able to operate at any filling depth. The full understanding of the physical phenomena and the accurate evaluation of the local loads in sloshing-induced slamming events occurring in completely, partially or barely filling conditions, is a challenge of the research field. Violent free-surface motions in a sloshing tank generally occur when the energy spectrum of the ship motion is focused in the frequency region close to the lowest sloshing mode of the tank. Slamming events may occur originating impulsive and large local loads that undermine the integrity of the structure. Depending on the local flow features before the impact, several and complex scenarios can characterize the physical evolutions of a wave impact in a sloshing flow. For example, when the impact angle between water and body is small, air entrapment may occur making important the compressibility of the air and its interaction with the free surface. In contrast, for an incipient breaking wave approaching a vertical wall, flip-through event may happen causing localized and large loads without any air-entrapment or flat-impact may occur. In all these cases, when the typical temporal duration of the local load is comparable with the lowest natural period of the structure, hydroelasticity matters affecting the integrity of the structure. Present research investigation pursues the experimental study about the kinematic and dynamic features of a wave impacting a rigid vertical wall of a 2D sloshing tank in shallow water conditions. Previous papers, have emphasized how the maximum pressure around the impact area is an unreliable indicator of the maximum load (with value of the standard deviation up to 50%), because of the stochastic behaviour of the impact phenomena. Here, the strain distribution along a deformable aluminum plate inserted in a rigid vertical wall of a sloshing tank has been measured to characterize the features of the local loads