Physics of Breaking Bow Waves: A Parametric Investigation using a 2D+T Wave Maker
Duncan, James H
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A mechanical 2-dimensional wave maker with a flexible surface was used to create waves similar to those formed at the bow of a moving ship. Utilizing the 2D+T approximation, the wave maker was programmed so that its deformable wave board creates a time sequence of shapes that simulate the line of intersection between one side of the hull of a slender ship model moving at constant speed and an imaginary vertical plane oriented normal to the ship model track. Instead of trying to simulate a particular ship hull, however, the wave maker simulates a parametric set of flat plate motions that contain components of typical bow shapes. The resulting surface waves were measured using a cinematic laser-induced fluorescence technique and the resulting wave profiles were analyzed. A tremendous variation of wave shapes was observed. A variety of wave characteristics including the peak contact point height, peak wave height, wave crest speed and plunging jet thickness distribution were measured and related to the corresponding wave maker motion parameters. Despite the complexity of the wave maker motions, it was observed that wave maker velocity and acceleration along the water line were the wave maker parameters with the strongest influence on many of the measured wave characteristics. Additional analysis reveals that the initial acceleration of the wave maker affects some wave characteristics, especially those related to plunging jet behavior, but does not significantly affect the overall size and shape of the wave. It was also observed that the behavior of wave formation and breaking ranged between two distinct modes. The first mode consists of an overdriven wave that contains a pronounced vertical jet along the face of the wave maker. The overdriven wave breaks close to the wave maker, before a wave crest has fully formed. The second mode is a more slowly developing wave that breaks further away from the wave maker. The developing waves do not contain the pronounced vertical jet observed in overdriven waves. The two modes appear to be related to the initial wave maker acceleration and amount of water displaced by the wave maker.