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| Titel |
Frequency pattern of turbulent flow and sediment entrainment over ripples using image processing |
| VerfasserIn |
A. Keshavarzi, J. Ball, H. Nabavi |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 16, no. 1 ; Nr. 16, no. 1 (2012-01-13), S.147-156 |
| Datensatznummer |
250013118
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| Publikation (Nr.) |
 copernicus.org/hess-16-147-2012.pdf |
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| Zusammenfassung |
| River channel change and bed scourings are source of major environmental
problem for fish and aquatic habitat. The bed form such as ripples and dunes
is the result of an interaction between turbulent flow structure and
sediment particles at the bed. The structure of turbulent flow over ripples
is important to understand initiation of sediment entrainment and its
transport. The focus of this study is the measurement and analysis of the
dominant bursting events and the flow structure over ripples in the bed of a
channel. Two types of ripples with sinusoidal and triangular forms were
tested in this study. The velocities of flow over the ripples were measured
in three dimensions using an Acoustic Doppler Velocimeter with a sampling
rate of 50 Hz. These velocities were measured at different points within the
flow depth from the bed and at different longitudinal positions along the
flume. A CCD camera was used to capture 1500 sequential images from the bed
and to monitor sediment movement at different positions along the bed.
Application of image processing technique enabled us to compute the number
of entrained and deposited particles over the ripples. From a quadrant
decomposition of instantaneous velocity fluctuations close to the bed, it
was found that bursting events downstream of the second ripple, in Quadrants
1 and 3, were dominant whereas upstream of the ripple, Quadrants 2 and 4
were dominant. More importantly consideration of these results indicates
that the normalized occurrence probabilities of sweep events along the
channel are in phase with the bed forms whereas those of ejection events are
out of phase with the bed form. Therefore entrainment would be expected to
occur upstream and deposition occurs downstream of the ripple. These
expectations were confirmed by measurement of entrained and deposited
sediment particles from the bed. These above information can be used in
practical application for rivers where restoration is required. |
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