Impact flows and loads on ship-deck structures

Abstract

The shipping of water on the deck of a vessel in head-sea conditions and zero-forward speed is investigated by experimental and numerical means. Through the experimental observations the main stages of the fluid-dynamic phenomenon are identified. For the considered conditions, water shipping initiates with water front overturning onto the deck, entrapping air, and then flowing along the initially dry deck up to impacting against vertical superstructures. Numerically, the water-on-deck phenomena are studied by considering a simplified two-dimensional flow problem. The theoretical model relies on the assumption of inviscid fluid in irrotational motion. Through comparison against experimental data, it is shown that the potential-flow model suffices to give a robust and efficient estimate of green-water loads until large breaking phenomena, usually following impact events, are observed. A boundary element method with piecewise-linear shape functions for geometry and boundary data is used for the numerical solution. The fluid–structure interaction is studied by coupling the nonlinear potential flow model with a linear Euler beam to represent a portion of the deck house under the action of the shipped water. The loading conditions related to violent fluid impacts and air-cushion effects are discussed. Upon considering realistic parameters, the occurrence of critical conditions for structural safety is discussed. The role of hydroelasticity is addressed in the case of fluid impacting against a vertical wall.