The air cushioning action during the horizontal impact of a flat plate on a water surface is investigated both theoretically and experimentally. In the presented theory, flow of the air layer between the flat plate and the water surface is analyzed by means of the characteristic curve method for the one-dimensional compressible fluid, while the water surface is determined with the aid of the boundary element method by disregarding the gravitational effect and the compressibility. In the calculation of air flow, the initial values and the boundary condition at the plate edge are investigated by introducing acceptable assumptions. The calculated time histories of impulsive pressure are in good agreement with experimental results.
In the first report, it is clarified that a small cargo ship of length 48m in ballast condition is subjected to large hogging moment due to bottom slamming. In this report, the strength of the ship at S. S. 7 against hogging moment is estimated with the help of experiments for a structural component. The collapsing strength of S. S. 7 is significantly reduced by the existence of bottom corrugations which may be caused by slamming previously. Bottom corrugations reduce the effective stiffness of the bottom plates and also the section modulus I/y for bottom. Compared with the value of hogging moment caused by slamming, the strength of the ship may be insufficient for preventing the structural failure of the ship, although it is much larger than the required strength against the bending moment expected by the linear conventional theory.
A container ship suffered serious structural damage in her fore body due to slamming in heavy seas in the North Pacific Ocean in January, 1977. She was in the fully laden condition and voyaged to Kobe from Oakland, California, U. S. A. A long brittle crack propagated in the fore and aft direction in shell plating of the flare part on the starbord side. The inner structures, such as longitudinals, web frames and side stringers, on the side shell of the same side were collapsed, and deck and shell plating on the port side was buckled. Furthermore, No. 2 Hatch was distorted in a parallelepiped. In the present paper, the damages are investigated from the view point of ship hydroelasticity with the aid of fracture mechanics. The results obtained suggest the importance of ship handling as well as structural design for preventing serious damages in large container ships.
In this paper, the buckling strength of bottom plating in ship structures is discussed theoretically and experimentally. Bottom plate is subjected to edge thrusts and lateral pressure at the same time. Since it deflects from the beginning, the critical point of buckling can not be determined with the aid of the usual buckling theory. When the lateral pressure is small, buckling occurs at a certain value of the edge thrust. In case of large lateral pressure, on the other hand, considerable deflections appear due to lateral pressure alone and grows gradually with the increase of edge thrusts ; then any critical state does not appear. The buckling tests were conducted with rectangular plates of the aspect ratio 3 to 1 on an apparatus with a tank. The results of the experiments are in good accordance with the present elastic theory based on the principle of minimum potential energy and the optimization technique.
