Degree Type

Thesis

Date of Award

2015

Degree Name

Master of Science

Department

Civil, Construction, and Environmental Engineering

First Advisor

Chris Rehmann

Abstract

Fluxes in stratified water bodies such as lakes and oceans are often controlled by turbulence and mixing at sloping boundaries. One mechanism of boundary mixing is the reflection of internal waves from slopes; when the angle  that the internal wave ray makes with the horizontal is equal to the slope angle --that is, when the ratio  = sin/sin = 1, critical reflection occurs. Critical reflection is thought to increase vertical mixing in lakes and contribute to the shaping of continental shelves in the ocean. Experiments were conducted to measure in detail the turbulence generated by near-critical and supercritical internal waves impinging on a slope. Velocity fields were measured with particle image velocimetry (PIV) and used to derive two-dimensional fields of dissipation. Harmonics were observed in the velocity fields in some cases with  1, and the angle of the harmonics agreed with theoretical predictions of others. The highest dissipation was patchily distributed near the slope, and it formed a layer whose thickness was within 20-25% of the values predicted by previous researchers. For supercritical waves (>1), high values of dissipation were not confined solely in a layer near the slope. The high dissipation also appeared in regions with reflecting waves, harmonics, and--in some cases--the incident waves. Regions of high turbulent kinetic energy coincided with regions of high dissipation for all cases. Values of /νN2 were small near the slope. Maximum values were O(1), while values based on cycle-averaged dissipation were less than 0.2. In these cases, the patchy nature of the dissipation suggests that little mixing will occur.

Copyright Owner

Zhimin Li

Language

en

File Format

application/pdf

File Size

47 pages

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