Survivability is a term that is widely used in the ocean wave energy industry, but the term has never been defined in that context. The word itself seems to have an intrinsic meaning that people understand; this fact often leads to the term’s misuse and its confusion with “reliability”. In order to design systems that are capable of long term survival in the ocean environment, it must be clear what “survivability” means and how it affects the design process and ultimately the device being deployed. Ocean energy is relatively predictable over the span of months, days, and even hours, which makes it very promising as a form of renewable energy. However, the variation of the energy content of ocean waves in a given location is likely high due to the effect of storms and the seasons. Wave energy converters must be built to be reliable while operating and survivable during severe conditions. Therefore, probabilistic design practices must be used to insure reliability and survivability in conditions that are constantly changing. Reliability is used to numerically express the failures of a device that occur while the system is operational, and it is usually expressed in terms of the mean time between failure (MTBF). However, in the context of ocean wave energy converters, the devices are likely to be continuously deployed in conditions that push them beyond their operating limits. During these times it is likely that wave energy converters will be placed in some sort of “survival mode” where the device sheds excess power, reducing system loading. Survivability is focused specifically on failures that occur during these times, when the device is experiencing conditions that surpass its operational limits. Developing a highly survivable wave energy converter is an outstanding goal, but without a standard definition of the term survivability, progress towards that goal cannot be measured. The purpose of this paper is to provide an initial definition for survivability, and to introduce a simple metric that provides an objective comparison of the survivability of varying wave energy converter technologies.
This paper illustrates the status of wave energy development in Pacific rim countries by characterizing the available resource and introducing the region's current and potential future leaders in wave energy converter development. It also describes the existing licensing and permitting process as well as potential environmental concerns. Capabilities of Pacific Ocean testing facilities are described in addition to the region's vision of the future of wave energy.
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.
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