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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Sediment management and morphodynamics : Image-based measurement of bed-load transport in closed channel flow
Image-based measurement of bed-load transport in closed channel flow
Author : MIAO WEI(1), CHEN HUAI(1),CHEN QIGANG(2),LI DANXUN(1)
ABSTRACT
We introduce a novel instrument for measuring bed-load transport in closed channel flows. The instrument is based on
modern innovations in high-frequency acquisition and processing of digital images, and its novelty allows for quantifying
instantaneous sediment transport rate in an efficient and non-intrusive way. With this instrument, experiments were
conducted in a closed rectangular channel under various water pressures. For each experiment, uniform sediment
particles were paved on the flat bed, and their motions were recorded with a high-speed camera. Velocities of active
particles (particle entrained to motion) were calculated by identifying and tracking particles in motion. The effects of
various parameters were analyzed, including sampling frequency, sampling area, flow intensity, and water pressure.
Preliminary analysis of the experimental results yields interesting new findings. Bed load transport displays a streak-like
pattern on the bed, i.e, sediment particles tend to be entrained into motion in patches rather than individually. This nonuniformity
indicates that large-scale coherent structures near channel bed may play an important role in “picking up”
sediment particles. The sampling frequency affects the percentage of particles in motion as well as their velocities; the
sediment transport rate, however, seems to be irrelevant to sampling frequency. The streamwise and spanwise particle
velocities exhibit Gaussian and exponential probability density functions, respectively. The absolute pressure exerts
negligible influence on the entrainment of non-cohesive particle, and the threshold of Shields number for bed load
initiation is about 0.03. The experiments show that variation in instrumental parameters may substantially alter the final
results.
File Size : 1,193,306 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Sediment management and morphodynamics
Date Published : 19/08/2015
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