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Document Type

Thesis - University Access Only

Award Date

2015

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

First Advisor

Francis Ting

Abstract

Previous studies have shown that a large amount of sediment transport in the surf zone is induced by breaking waves. Various parameters have been used to parameterize sediment concentration and transport rate. However, very little is known about individual sediment particle movement under breaking waves. The objective of these experiments is to obtain individual sediment particle data along with fluid velocity information using two phase flow techniques. Thus, making it possible to quantitatively describe sediment transport under plunging breaking waves. These experiments were performed with the use of laboratory flume and a piston type wave maker. The waves used had a wave height and period of 0.115 meters and 4.0 seconds, respectively. A three dimensional (3D) imaging camera manufactured by TSI was used to capture fluid tracer particles (13 microns in diameter, silver coated, hollow glass spheres) and sediment particles (0.125 to 0.15 mm diameter yellow glass beads) simultaneously. A separation technique was developed to separate the sediment particles from the tracer particles based on the particle spot size and intensity. Uncertainties in the sediment particle velocities were established by evaluating the position and velocity of the particles in still water images. Sediment velocities were then compared to fluid xv velocities so that conclusions could be drawn on the vertical and horizontal velocities of the sediment. Five different wave cycles were examined in detail. Time series for sediment suspension, vertical velocity, longitudinal velocity, turbulent kinetic energy, shear stress, and vorticity are plotted. Histograms for individual frames are plotted to show how the distribution of different parameters change when more or less sediment particles are detected. Cross correlations are also calculated in order to determine which parameters have the largest impact on sediment suspension. Vertical velocity, turbulent kinetic energy, shear stress, and vorticity of the fluid around sediment particles all seem to have an impact on the number of sediment particles in suspension when vortices impinge on the bottom. These experiments also show that sediment is also capable of being moved by non-local processes, and that sediment particles are capable of being trapped and carried to different locations by vortices. A splash pattern caused by downward flow from the plunging waves lifts many sediment particles into suspension, and then is transported onshore or offshore depending on the direction of the turbulent and wave induced velocity. Positive longitudinal flux is observed in some, but not all, of the wave cycles discussed.

Library of Congress Subject Headings

Waves -- Analysis
Water waves -- Analysis
Sediment transport
Particles

Description

Includes bibliographical references (pages 177-180)

Format

application/pdf

Number of Pages

212

Publisher

South Dakota State University

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Rights Statement

In Copyright