Graduate Thesis Or Dissertation

 

Laboratory observations and numerical modeling of inner surf and swash zone hydrodynamics on a steep slope Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5m60qv78q

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  • Laboratory data of free surface elevations and fluid velocities were obtained using a laser-Doppler velocimeter for the case of a periodic wave plunging over an impermeable, steep (1:10) slope with a fixed bottom roughness. The measurements were conducted over 15 cross-shore locations from the outer surf zone to the swash zone with approximately 10 vertical points at each location, including the bottom boundary layer and some points above the trough level. Various hydrodynamic quantities, including the ensemble averaged turbulent kinetic energy (❬k❭) and turbulence intensities (❬u'²❭) and (❬w'²❭), were estimated to better understand inner surf and swash zone hydrodynamics induced by strongly plunging waves. In the surf zone, the ensemble averaged horizontal fluid velocity (❬u❭) near the bottom led in phase compared to ❬u❭ in the upper layer, and ❬u❭ at the bore front exceeded the theoretical wave celerity. At the impinge point, a strong return flow occurred that was greater in magnitude than the onshore directed velocity. In the surf zone, ❬k❭was largest just below trough level with a forward shift in phase of the peak intensity. The turbulent energy was mostly dissipated after the passage of the crest at this location. ❬u❭ near the bottom was leading in phase with a sharp vertical gradient in ❬u❭ indicating that boundary layer processes may have been important. In the swash zone, the vertical gradient of ❬u❭ was relatively small compared to the vertical gradient of ❬u❭in the surf zone and may be due to the effect that the strong downrush had on turbulent mixing. The time-averaged estimate of turbulent kinetic energy (❬k❭) was vertically uniform over the inner surf and swash zone. Numerical simulations of the inner surf and swash hydrodynamics were carried out using 1D (RBREAK2 and FUNWAVE1D), 2D (COBRAS) models. All of the models accurately predicted several hydrodynamic quantities, however, they predicted that the waves broke slightly seaward of the experimental impinge point. COB RAS overpredicted the ❬k❭ by 2-3 times in the inner surf zone but the prediction improved in the swash zone. In this study COBRAS was the most suited model to predict the hydrodynamics at the impinge point.
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