Experimental Study of Particle Motion on a Smooth Bed under Shoaling Waves Using Particle Image Velocimetry
Publication: Journal of Engineering Mechanics
Volume 136, Issue 7
Abstract
The motion of spherical particles (diameter 1.58 mm, specific gravity 2.5) on 2 and 3% plane slope was studied in a laboratory wave flume for shoaling wave conditions. The range of wave-height-to-water-depth ratio was , the range of Keulegan-Carpenter number was , and the maximum particle Reynolds number was 240. The instantaneous sediment particle position and the associated fluid velocity field were measured simultaneously in the bottom boundary layer using a particle image velocimetry (PIV) system. The measurement plane was parallel to the bed and located at a height of 1/2 particle diameter above the bed. Morphological image processing techniques were used to separate the fluid (tracers) and solid (glass spheres) phases from the same PIV images based on their signature sizes. The separated image files were processed to determine the displacement, velocity, and acceleration of the individual sediment particles and the corresponding fluid velocity and total acceleration. These measurements were used to calculate the individual terms (inertia, gravity, pressure gradient, added mass, drag, lift, and friction) in the equation of motion for the sediment particle. It was found that the drag force was the largest force in the equation of motion. The equation of motion could not be balanced when bottom friction was modeled as dry or rolling friction. The equation was balanced approximately by introducing a viscous friction term of the form , where viscosity; particle velocity; and length scale. Much of the drag force was canceled out by this frictional force, resulting in increased importance of the pressure gradient force. The study also evaluated several commonly used formulas for calculating the drag coefficient. It was found that the formula developed for steady motion in an infinite fluid described the measured data better than other formulas. It was also found that using the free-stream local fluid acceleration instead of the total fluid acceleration in the vicinity of the particle had negligible effects on the calculated total resultant force.
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Acknowledgments
This study was supported by the National Science Foundation (NSF) through Grant No. UNSPECIFIEDOCE-0525676. The support of NSF is gratefully acknowledged.
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Information & Authors
Information
Published In
Journal of Engineering Mechanics
Volume 136 • Issue 7 • July 2010
Pages: 865 - 876
Copyright
© 2010 ASCE.
History
Received: Dec 24, 2008
Accepted: Dec 18, 2009
Published online: Dec 22, 2009
Published in print: Jul 2010
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