Investigation of the generation of infra-gravity waves

Three different types of wave profiles including mono-chromatic, bi-chromatic and tri-chromatic waves, were generated on bottom slopes of 1/10, 1/20 and 1/40 in a super wave flume at the Tainan Hydraulics Laboratory (THL) to investigate the generation of infra-gravity waves. The wave steepness and bottom slopes were shown to determine the generation mechanism of infra-gravity waves, which are usually the principal dynamics in the swash zone. These results show that the varied infra-gravity waves would be locally forced by nonlinear wave groups, especially at the outer breakpoint. In order to understand the physical nature of infra-gravity waves, the characteristics of the energy transport of each chosen wave is examined by means of wavelet and auto-bispectral analysis. Finally, a detailed analysis of the hydrodynamics of the shoaling process is also discussed in this paper.