Experimental study of freak waves due to three-dimensional island terrain in random wave

An experimental study is carried out for waves passing an isolated reef terrain in a wave tank. A three-dimensional model of a representative and isolated reef terrain in the West Pacific is built. Random wave trains with various periods and wave heights are generated by a wave maker using the improved JONSWAP spectrum. It is observed that there are different kinds of generation processes and waveforms of freak waves. The freak wave factor H-m/H-s (where H-m is the maximum wave height of wave series, and H-s is significant wave height) is analyzed in detail, in terms of the skewness, kurtosis and water depth, as well as the relationship between freak wave height H-fr and skewness. The freak wave factor H-m/H-s is found to be in positive correlation with the kurtosis, while larger H-fr tends to be related with bigger skewness. The rapid variation of water depth, such as slope and seamount, contributes to the occurrence probability of freak waves.