Characterizing Dangerous Waves for Ocean Wave Energy Converter Survivability

Ocean Wave Energy Converters (OWECs) operating on the water surface are subject to storms and other extreme events. In particular, high and steep waves, especially breaking waves, are likely the most dangerous to OWECs. A method for quantifying the breaking severity of waves is presented and applied to wave data from Coastal Data Information Program station 139. The data are wave height and length statistics found by conducting a zero-crossing analysis of time-series wave elevation records. Data from two of the most severe storms in the data set were analyzed. In order to estimate the breaking severity, two different steepness-based breaking criteria were utilized, one being the steepness where waves begin to show a tendency to break, the other the steepness above which waves are expected to break. Breaking severity is assigned as a fuzzy membership function between the two conditions. The distribution of breaking severity is found to be exponential. It is shown that the highest waves are not necessarily the most dangerous. Even so, waves expected to be breaking are observed being up to 17 meters tall at station 139.