A COMPARISON OF 2-DIMENSIONAL AND 3-DIMENSIONAL WAVE BREAKING

The influence of directionality on wave-packet evolution and in partic ular on the onset of breaking was explored through laboratory experime nt. Lateral tapering was applied to the input signal to produce a rang e of crest lengths, with greater directionality created by diffraction for the shorter crests. The wave shape, local and global wave steepne ss, and surface displacement spectra were used to characterize the wav e fields. The observations suggest that directionality can accelerate or suppress the onset of breaking, and additionally can influence both the Ideal wave steepness at breaking as well as the breaking severity . Directionality, however, did not alter the observed up-frequency ene rgy transfer associated with wave focusing. when no breaking occurred this energy shift was completely reversed. With breaking the shifted e nergy was lost, that is, passed from the wave to the turbulent energy field. The short-crested wave packet lost 16% of its energy as a resul t of breaking, while a comparable two-dimensional breaker lost 22%.