Probability of Ocean Freak Wave Occurrence
Leng-Hsuan Tseng Dong-Jiing Doong
Department of Marine Environmental Informatics, National Taiwan Ocean University, Keelung, Taiwan
Abstract
Freak or rogue waves are the abnormal waves with a height exceeding twice or more the significant wave height; they appear on the sea surface only for a short time. Freak waves have high impacts on ships in the ocean as well as offshore and coastal structures. They are also a hazard to the people at the coast.
The scientific goal of this study is to understand the occurrence probability of the freak waves in the ocean. This study mines the freak waves from in-situ measurement at Taiwanese waters. Extreme statistics theory was applied. The definition of dangerous freak wave used in this study is the wave whose wave height is twice bigger than the significant wave height and the significant wave height should larger than 1m. According to this criterion, 262 freak waves were found from Longdong buoy and 51 were found from Taitung deep sea buoy.
The probabilities of occurrence of freak waves both are . However, the probability of occurrence of dangerous freak wave (significant wave height larger than 1m) in deep sea is much higher than in shallow water. Results also show that the occurrences of freak waves have high correlation with kurtosis and grouping factor. Kurtosis of more than 75% freak wave cases are higher than 3.5.
