In the last paper (ISOPE'99) the author found the fairly strong correlation between Abnormality Index, that is, Hmax/Hs (AI) and the kurtosis of the sea surface deflection distribution by the analysis of actual sea waves data acquired both in the North Sea of offshore Norway as well as the North Pacific Ocean 500 nautical miles southeast of the Japanese Islands. The analysis is now carried out for Yura site data taken by Ship Research Institute during 1987 and 1990 in which we have the same tendency as for AI. Some of the short term statistical analysis are presented such as surface deflection, wave height distribution and joint distribution of wave height and period. Long term nature of the distribution of AI is examined and a statistical test is performed for the fitting to the theoretical curve. The regressions between wave height statistics H8, Hrms etc are calculated and compared with theoretical or empirical relations proposed so far. Finally, some examples of observed Freak waves are presented.
Several years ago, Ship Research Institute conducted an At-Sea Experiment project for ocean floating structure at the offshore of Yura site in the Sea of Japan (see Ohkawa et.al.(1994)). In the course of this project, they installed three ultra-sonic wave gauges on the seabed in the vicinity of the floating structure. The great amount of wind and waves data were acquired during the period from January 1987 to May 1990. The location of Yura site is shown in Fig. 1 and the specification of the data used in this study is tabulated in Table 1. An example of the long term wave climate is shown in Fig. 2.
