Spectra Evolution of Single Wave Packets in Finite Water Depth

A series of physical experiments were conducted to investigate the spectra evolution of single wave packets. Chirped-typed wave groups were selected in this study. Nine wave packets varying initial amplitudes and wave components were generated in the wave flume. Hence both non-breaking and breaking wave groups can be performed. It is found that the evolution process is far more than the linear superposition, and that it experiences significant nonlinear process. The modulational instability is found in the evolution of wave groups. For non-breaking groups, it is found that the most non-breaking energy dissipation occurs in the vicinity of the spectral peak (f/f_p = 0.9–1.1). The non-breaking dissipation energy for spectral peak depends on depend on BFI (Benjamin-Feir Index). For breaking cases, the energy level of the above-peak frequency region (f/f_p = 1.1–2.0) first increase slightly, and decrease during breaking occurring, but the overall change is limited. However, the below-peak frequency region (f/f_p = 0.5–0.9) gains with the expense energy of the peak and above-peak frequency regions and the growth depends on the initial spectra width.