Numerical and Experimental Investigation of Violent Seakeeping Phenomena

A 3D weakly non linear potential flow algorithm in the time domain is developed to predict the wave-induced loads on a ship in rough sea conditions. Froude-Krylov and hydrostatic second-order terms are taken into account for the global hydrodynamics. Water-on-deck occurrence and flow on the deck are studied by coupling the weakly non linear model for the external flow field with a shallow-water model for the water shipped onto the deck. Local and global induced green-water loads on the vessel are predicted using an empirical formula for the deck pressure (Buchner 1995). This includes both the hydrostatic contribution accounting for the body accelerations and a dynamic pressure term connected with the time derivatives of the water level along the deck and of the ship motions. All the elements of the resulting combined solver have been verified and validated. An ad hoc experimental campaign on a patrol ship model interacting with a large amplitude wave system is on-going, concerning both regular and irregular waves. The tests are aimed to measure global motions of the vessel, occurrence of water on deck, amount of shipped water, green-water induced local loads on the deck and horizontal force caused on a deck superstructure. The water-shipping events are also recorded with a digital video camera. Preliminary results and comparisons with the developed model are reported.