Dispersion of spilled oil by a cavitating jet at sea

This article presents the possibility of using a high-speed water jet for the dispersion of spilled oil at sea. Laboratory experiments showed that a high-speed water jet is very effective in dispersing heavy oil. Two methods were examined and compared using freshwater. The first method was to disperse an oil layer on the water surface using a cavitating jet ejected upward at an angle of 45°. A target plate was placed at the interface of the water and oil layer to enhance the collapse of cavitating bubbles. The second method was to eject a high-speed water jet vertically downward from the air. A guide plate with a guide hole was placed under the oil layer with no target plate as such. The second method showed an improved dispersion ability and thus its effectiveness was examined using an oil layer on seawater. The dispersion of oil was better in seawater than in freshwater, probably because seawater contains natural surfactants.     

Fatigue strength improvement for ship structures by Ultrasonic Peening

Ultrasonic Peening has attracted recent attention as a fatigue strength improvement method. The main features of Ultrasonic Peening are generation of compressive residual stress and smoothing of weld toe radius. However, for ship structures, various loads act on the hull structure over a ship??s life, including the construction period, and the compressive stress field of structural members generated by Ultrasonic Peening may change. In order to verify the technique's benefits to ship structures, the influence of load history on the improvement effects on fatigue strength by Ultrasonic Peening needs to be clarified. In this paper, the improvement effects on fatigue strength by Ultrasonic Peening for welding joints were confirmed by experiments with several joint type specimens. In addition, fatigue tests modeling launching, when the stress conditions of a ship's structure changes significantly, were carried out in order to clarify the influence of load history in a ship??s life. Consequently, some cases that have the possibility of decreasing or increasing the improvement effects on fatigue strength by Ultrasonic Peening were clarified, and some efficient methods of Ultrasonic Peening for ship structures were suggested.