An Experimental Investigation on Bow Water Shipping

Abstract

The water on deck caused on a restrained ship model without forward speed in head waves is studied experimentally by using a transient test technique. A single water-shipping event is induced by the wave packet, and the severity of the interaction is controlled by the wave-packet steepness. Three different bow geometries are considered. Two of them are analytical hull forms, and the last is the ESSO-Osaka tanker. The models are equipped with a transparent-material deck to study the flow-field evolution by image analysis. A vertical wall is placed at a certain distance from the forward perpendicular to mimic the presence of deck structures. Velocity of the shipped water along the deck, pressure field on the deck, and horizontal impact force on the wall are measured. The main fluid-dynamic aspects of the green-water phenomenon are highlighted. For the tested cases, water shipping starts always with the free surface exceeding the freeboard, plunging onto the deck, and forming complex cavities entrapping air inside. The geometry of the air cavity depends on the hull form and the wave steepness. Then the water propagates along the deck. In general, the water front is strongly three dimensional because of the water entering along the deck contour. The interaction of the shipped water with the vertical structure consists of impact, run up-run down cycle, and backward plunging of the water onto the deck, still wetted. The evolution of the pressure field follows that of the water front. Pressure peaks are associated with the impact against the vertical wall, and by the backward plunging of the water on the deck, at the end of the run up-run down cycle of the water. It is shown that both these stages can be of importance from the structural point of view. I am sad to report that Maurizio Landrini was killed in a motorcycle accident on June 26, 2003. Maurizio was an outstanding marine hydrodynamist who had been selected as the 2003 Georg Weinblum Lecturer. He was born on March 2, 1963, and earned his Ph.D. degree in Theoretical and Applied Mechanics at the University of Rome. Except for short periods as a visiting researcher at the Ocean Engineering Laboratory, University of California, Santa Barbara, and the Department of Marine Technology, Norwegian University of Science and Technology, he worked his entire career at INSEAN, the Italian Ship Model Basin. He has authored or coauthored over 80 papers. He was a personal friend and innovative researcher with whom I have spent many hours discussing hydrodynamics. He will be greatly missed in the marine hydrodynamics community. Robert F. Beck