Groups of Breaking Waves: Experiments

摘要

Experiments were conducted with periodic wave groups incident on a plane beachwith a slope of 1:35.05. The wave groups were composed of a series of cnoidal waves with varying wave heights. Emphasis was on obtaining a number of measurements inside the surf zone. The analysis of the data shows that the location of the start of breaking of the individual waves in a group is affected by the groupiness of the waves. The H/h ratio at breaking was seen to have a wider variation for the individual waves in the group than for monochromatic waves. In all cases, some groupiness was conserved inside the surf zone, but in some cases it was reversed in the sense that the higher waves in the group before breaking became the smallest after and vice versa. It was also found that even inside the surf zone, all nonlinear interactions result in energy at frequencies that are multiples of the group frequency, although, as expected, the energy is more evenly distributed between the different frequencies. The long wave motion is forced at the group frequency and can be resolved into two components, an incident forced wave and a free standing wave. The standing wave is generated because the free outgoing long wave is reflected at the wavemaker, where there was no absorption of waves. The amplitude of the incident forced wave varies along the tank, whereas the standing wave is shown largely to agree with a linear representation of a free standing wave system.