AEM Seminar: On the Impact of a Deep-Water Plunging Breaker on a Wall with Finite Vertical Extent
James Duncan, Professor, Department of Mechanical Engineering, University of Maryland
2:30 PM on 2017-02-10
The impact of a plunging breaker on a 2D wall with finite vertical extent is explored experimentally in a wave tank equipped with a programmable wave maker. The experiments are conducted with the wall positioned at one streamwise location relative to the wave maker and at nine heights relative to the undisturbed water level. A single, repeatable wave maker motion that produces a plunging breaker (nominal wavelength of 1.18 m) via a dispersively focused wave packet is used for all experiments. The water surface profile at the streamwise vertical center plane of the wall is measured with a cinematic laser-induced fluorescence technique and the impact pressures on the wall are measured with piezoelectric dynamic pressure transducers. It is found that the impact behavior varies dramatically with the vertical position of the bottom edge of the wall and can be divided into three categories. In the first category, the bottom of the wall is well below the mean water level and remains submerged throughout the impact. Here, the water surface arc with upward curvature found between the wave crest and the wall shrinks to a point without wave breaking during the impact. At the end of this convergence, a high-speed vertical jet forms along the wall. This “flip-through” behavior includes a local maximum wall pressure of very short duration. In the second category, the bottom edge of the wall is close to the undisturbed water surface and transitions from submerged to airborne several times during the impact. This process creates ripples that propagate along the water surface and modify the behavior of the impact significantly. Air entrainment is very likely to occur under these conditions and corresponding high-frequency oscillations are found in the wall pressure signals. In the third category, the bottom edge of the wall is well above the mean water level but below the level of the wave crest. Here, the breaker is undisturbed before the main crest hits the lower corner of the wall. The highest wall pressures are found in these cases.
This work is supported by the Office of Naval Research.