VARIATIONS OF STATISTICS FOR RANDOM WAVES PROPAGATING OVER A BAR

A series of physical experiments were conducted on the variations of statistics (skewness, kurtosis, groupiness) in random waves propagating over a submerged symmetrical bar. Random waves were generated using JONSWAP spectra while varying initial spectral width, wave height and peak frequency. It was found that the initial spectral width has a negligible effect on the variations of these statistical parameters. An abrupt change in wave groupiness is caused by wave breaking. Variations in the skewness and kurtosis mainly depend on the local water depth and wave height and period. Furthermore, the relationship between the skewness and kurtosis in the shoaling region is well predicted by the formula of Mori and Kobayashi (1998), but on the crest of the bar, the formula should be adjusted. Additionally, extreme waves that satisfy the definition of freak waves can be formed in the shoaling region close to the top of the bar. The probability occurrence of the freak waves has a negligible relationship with the initial spectral width, but the appearance of the extreme waves encounters with the increase of groupiness.