Experiment

The plunging wave-breaking process for impulsive flow over a bump in a shallow water flume is described, which is relevant to ship hydrodynamics since it includes the effects of wave-body interactions and the wave breaking direction is opposite to the mean flow. Phase averaged measurements (relative to the time at which the maximum wave height is reached just before the first plunge) are conducted, including the overall flume flow and 2D PIV center-plane velocities and turbulence inside the plunging breaking wave and bottom pressures under the breaking wave. A total number of 226 individual plunging wave-breaking tests were conducted, which all followed a similar time line Dt_T=22.9 s consisting of startup (Dt_S =12.5 s =54.6%Dt_T), steep wave formation (Dt_SWF =0.9 s =3.9%Dt_T), plunging wave breaking (Dt_PWB=1.4 s =6.1%Dt_T), and chaotic wave breaking swept downstream (Dt_CWB=8.1 s =35.4%Dt_T) time phases. The plunging wave breaking process consists of four repeated plunging events each with three [jet impact (plunge), oblique splash and vertical jet] sub-events, which were identified first using complementary CFD. Video images with red dye display the plunging wave breaking events and sub-events. The first and second plunges take the longest 38.1%Dt_PWB and 23.9%Dt_PWB, respectively, whereas the last two plunges take 19%Dt_PWB and 19.1%Dt_PWB, respectively. Oblique splashes and vertical jets account for 23.8%Dt_PWB and 66.7%Dt_PWB, respectively. The wave profile at maximum height, first plunge, bump and wave breaking vortex and entrapped air bubble trajectories, entrapped air bubble diameters, kinetic, potential, and total energy, and bottom pressures are analyzed. Similarities and differences are discussed with the previous deep water or sloping beaches experimental and computational studies.