AN EXPERIMENTAL 2D+T INVESTIGATION OF BREAKING BOW WAVES
Duncan, James H.
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This experimental research is part of a larger project whose broad goal is to improve our understanding of the dynamics of breaking bow waves including the entrainment of air bubbles into the flow and the generation of turbulence and vorticity. The bow waves studied in this project are generated with a technique known as 2D+T. In this technique, a two-dimensional wave maker moves horizontally and deforms in a manner that approximates the time varying intersection of one side of the hull of the three-dimensional ship and a fixed vertical plane oriented normal to the ships path. Under many conditions, the wave generated by the wave maker breaks by the formation of a plunging jet and creates a turbulent two-phase flow. The specific objectives for this thesis were to construct the wave tank; assemble, test and improve the 2D+T wave maker; develop a technique for measuring the wave profiles; develop a holographic PIV technique for measurement of bubble size distributions and motions; and to measure and analyze the surface profile histories of the wave system as a function of the equivalent forward speed of the ship model. Measurements were performed for ship model profiles simulating a realistic ship. The histories of the surface profiles of the breakers were measured with a photographic technique that employs a laser light sheet, fluorescent dye and a high-speed digital movie camera. The images record the wave profile at the center plane of the tank where the light sheet intersects the water surface. The results of the measurements include observations of the main features of the wave patterns, plots of the entire wave pattern around the equivalent ship model, and the time histories of various geometric parameters including the contact point of the water surface on the hull, the wave crest, the plunging jet and the splash created by the jet impact. A scaling study was made to examine the exects of the ship speed on these geometric parameters.