Wave-current interaction induced by standing long waves in the surf zone Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/7p88cm02q

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  • This dissertation has focused on the charateristics of bubbles generated by breaking waves and the feedback of wave-current interaction on the forcing mechanism of low frequency wave especially basin seiching wave. For the first study, Optical image capture observations of breaking waves in a laboratory surf zone are presented. The observations demonstrate episodic production of surface foam events as regular waves traverse the surf zone. The experimental conditions consist of regular waves in a freshwater flume and wave breaking is depth-induced over fixed, barred bathymetry. The optical image data are used to track the decay time of individual events. In addition, the frequency and spacing of discrete foam events are analyzed both in the time and wavenumber domains and the observations are compared to existing theory. The second study examined the effects of wave-current interaction on the response and the generation of the basin standing waves in terms of water elevation and currents. We carried out coupled models between the incident waves and wave-induced currents. The incident waves and currents are coupled through the wave forcing effect (radiation stress gradient) and wave-current interaction terms. The wave fields are described by solving the wave action balance and wave number equations in terms of wavenumber, frequency, and energy with inclusion of energy dissipation due to breaking. We utilize the model over various beach slopes and primary wave conditions in order to discuss the responses and relationship between the responses, and primary wave field and beach slope. The results show that the basin standing wave interacts with the incident wave to produce negative feedback in terms of water elevation and current on the mild non-dimensional bed slope (β), otherwise it causes the positive feedback on the steep slope regime when wave-current interaction is considered. The cross-correlation function between the short wave and incoming basin seiching component of elevation is analyzed. The results confirm the distinctive phase relation of the short wave and incoming basin seiching between mild and steep slope regimes. Consequently, this phase shift links to an energy transfer mechanism between the short wave and the basin seiching responses. This effect also relates to the different basin standing wave mechanisms, whereas the negative response on the mild slope regime is conductive to long wave generation by bound wave releasing and the positive response on the steep slope regime leads to time-varying breakpoint forcing. These mechanisms agree well with the surf beat similarity parameter.
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