Wave Energy Dissipation and the Distribution of Breaking Crests

University Of Washington, Seattle WA

Investigators

Abstract

The objectives of this study are to simultaneously measure the speed-distribution of breaking crest lengths and energy dissipation due to wave breaking in a large lake. The data will be used to test Phillips [1985] formulation for the turnover rate and energy dissipation and determine the extent to which passive and active infrared techniques can provide a remote measurement of energy dissipation due to wave breaking. Emphasis will be on adequately characterizing small-scale and microscale wave breaking using the unique capabilities of infrared imaging to quantify the occurrence of microbreaking and the surface area disrupted by wave breaking at all scales. Field experiments will be conducted to simultaneously measure the distribution of breaking wave crest lengths, the surface turnover rate, and the energy dissipation rate. The experiment will be conducted on Lake Washington to provide a relatively simple wave field and to gather the required amount of data. Intellectual Merit The scale distribution of breaking waves is important for quantifying dissipation relevant to wave models, for improving our understanding of mixed layer processes, and for the safety of ships and marine structures. Phillips' formulation relating energy dissipation due to breaking to the distribution of breaking crest lengths as a function of crest speed, provides a framework with which to quantify wave breaking and potentially infer breaking dynamics from kinematic and geometric measurements alone. Although there have been a number of recent measurements of the distribution of breaking crest lengths, none have been made in conjunction with dissipation measurements. Furthermore, the previous techniques used to measure the distribution of breaking crest lengths are not able to cover small-scale and microscale breaking waves. The proposed activity will address the need for simultaneous measurements of the distribution of breaking crest lengths and the energy dissipation rate from scales of whitecaps to microbreakers. Broader Impacts The project will promote teaching, training, and learning through participation of a graduate student in all aspects of the work and the participation of two undergraduates in the summer experiments. The undergraduates will participate via the Washington Space Grant Summer Undergraduate Research Program (SURP), through which the principal investigator has mentored students in the past. Efforts will be made to recruit students from an underrepresented group, which the program emphasizes. The infrastructure for research will be enhanced by building a reusable underwater tower for near-surface measurements and developing new infrared measurement capabilities. The benefits to society consists of a contribution to our understanding of the natural environment that will lead to better parameterizations of wave breaking relevant to wave modeling, mixed-layer processes, and the safety of ships and marine structures.