Modeling Steep Surface Waves Evolving Under Wind Forcing And Energy Dissipation Due To Wave Breaking

Ocean waves play an important role in many areas of science and engineering, notably climatology, meteorology, ocean environment, marine transport, and coastal engineering. They are generated by drawing energy from wind, evolve through nonlinear wave interactions, and are eventually dissipated by wave breaking. When fully developed, ocean waves have wavelengths that span scales from centimeters (capillary waves) to kilometers (tsunami). Computationally resolving models for ocean waves over such a wide range of spatial scales is an enormous challenge, and it is impractical to solve the full hydrodynamic equations over a large surface area of the ocean. These facts have produced an increasing interest in developing a novel and efficient computational tool that can simultaneously treat wind forcing, breaking wave dissipation, and nonlinear wave interactions. This research project aims to contribute to the development of such a tool. Once it is developed, the computational model would be useful for researchers working on physical oceanographic processes and climate change, because the traNational Science Foundation er of energy and momentum across the air-sea boundary is fundamental to their work. A graduate student is involved in the project.

To predict accurately the evolution of nonlinear surface waves, the investigator and his colleagues develop a reliable and efficient phase-resolving wave model combined with theoretical models of wave breaking and wind-wave interaction. Through numerical simulations using a pseudo-spectral method and controlled laboratory experiments, the predictive capability of the integrated wave model is examined for steep surface waves evolving under wind forcing. To achieve this goal, a robust breaking criterion is first determined though numerical simulations of the wave model and then is confirmed with laboratory experiments. Then, through viscous boundary layer analyses at the deformed surface of steep waves, the viscous energy dissipation rate and the air pressure distribution over the free surface, as well as a criterion of airflow sEnvironmental Protection Agencyration, is identified in terms of local flow and wave characteristics. By coupling the results of the boundary layer analyses with measurements of wave breaking and wind-wave interaction experiments, the energy dissipation and wind forcing terms are determined and integrated into the wave prediction model. Finally, the resulting wave model is validated by comparing its numerical solutions with laboratory experiments.