Wave Analysis Using Rainflow Information

In this paper, the convenience of extending the use of the rainflow analysis to the ocean engineering field is discussed. Since this concept comes from the fatigue damage field, its appropriateness to better estimate wave cycles is analyzed. The rainflow range (magnitude and location) and period are analyzed and compared to those resulting from the traditional method of zero-down-crossing wave counting. It will be shown that the concepts can be extended to the ocean engineering field, and that developing a wave-by-wave analysis containing all the information about what happens in each cycle is possible. One of the main conclusions reached is that the rainflow counting method identifies a wider range of wave periods than those detected by the zero-down-crossing counting method without the need of a previous filtering. The rainflow counting method is able to detect waves that oscillate over and under a reference level, which are not detectable with the zero-down-crossing counting method. Another conclusion is that while the zero-down-crossing counting method refers to a given level to identify waves, the rainflow counting method makes possible to know from where and where to the cycles take place. Some of the applications of this research are oriented to determine natural frequency oscillations in docks, wave groups, overtopping increase, long period movements in armor breakwaters, and the damage associated with these phenomena.