Water Shipping on a Vessel in Head Waves

We present an investigation based on experimental and numerical studies for the bow-deck wetness in head-sea conditions of a stationary ship, with a blunt bow. Three-dimensional water-on-deck experiments have been carried out by focusing wave packets against the model of a ESSO Osaka tanker. The experiments give a fundamental description of the dynamics of water shipping and provide some useful data for the development of three-dimensional numerical methods. In particular, the observations confirm the formation of a cavity entrapping air during the initial stages of the water shipping. Near the fore portion of the deck, the local ship geometry affects shape and complexity of the cavity evolution, always characterized by free-surface breaking and dispersion of bubbles in the main water field. To deal with this flow conditions, we present a Domain Decomposition (DD) strategy to solve numerically the problem. A boundary element method (BEM) for the outer field, where smooth though steep waves are present, and a Volume-of-Fluid (VOF) method for the Navier-Stokes equations in the breaking region have been coupled by the DD. The present approach represents a compromise between efficiency, robustness and capability of capturing the fragmentation of the air-water interface, which occurs at several stages during the flow evolution. The method is applied by assuming the flow to be two dimensional in the longitudinal ship plane, but no limitations exist to extend it to three dimensions. The DD approach appeared rather promising, although comparisons with reference solutions demonstrate that numerical inaccuracies develop in the VOF solver so far adopted. Altra Lingua sommario Italian