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Formation of a sandy near-bed transport layer from a fine-grained bed under oscillatory flow

Liang, Hanzhuang and Lamb, Michael P. and Parsons, Jeffrey D. (2007) Formation of a sandy near-bed transport layer from a fine-grained bed under oscillatory flow. Journal of Geophysical Research C, 112 (C2). pp. 1-14. ISSN 0148-0227. doi:10.1029/2006JC003635.

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Bed surface coarsening was found to be an important effect for the formation of ripples and the dynamics of the boundary layer above a predominantly silt-sized sediment bed (median particle size equal to 26 μm; ~20% fine sand, 70% silt, 10% clay) under oscillatory flow (with orbital velocities of 0.32-0.52 m/s) in a laboratory wave duct. Following bed liquefaction, substantial winnowing of the bed surface occurred due to entrainment of finer material into suspension. Bed surface coarsening was quantified with micro-scale visualization using a CCD (charged-coupled device) camera. Under most wave orbital velocities investigated, the coarse surface particles were mobilized as a near- bed transport layer approximately 4 grain-diameters thick. The transport of these coarse sediments ultimately produced suborbital or anorbital ripples on the bed, except for the highest orbital velocities considered where the bed was planar. Micro-scale visualizations were used to construct a maximum (particle) velocity profile extending through the near-bed transport layers using particle-streak velocimetry (PSV). These profiles had a distinctive kink in log linear space at the height of the transport layer, suggesting that the near-bed sediment transport reduced skin friction and contributed to the boundary roughness through extraction of momentum.

Item Type:Article
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Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2007 by the American Geophysical Union. Received 13 April 2006; revised 13 September 2006; accepted 4 October 2006; published 6 February 2007. Financial support for the work performed was provided by grants from ONR (N00014-03-10138), NSF (EAR-0309887), and the American Chemical Society Petroleum Research Fund. The authors wish to thank T. Maxworthy and A. M. Fincham for lending us the optical system.
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-03-10138
American Chemical Society Petroleum Research FundUNSPECIFIED
Subject Keywords:size 26 mum; boundary roughness; skin friction; near bed sediment transport; PSV; particle streak velocimetry; maximum particle velocity profile; anorbital bed ripples; suborbital bed ripples; near bed transport layer; wave orbital velocity; CCD camera; fine material entrainment; bed surface winnowing; bed liquefaction; laboratory wave duct; clay; fine sand; silt sized sediment bed; boundary layer dynamics; ripple formation; bed surface coarsening; oscillatory flow; fine grained bed; sandy transport layer formation
Issue or Number:C2
Record Number:CaltechAUTHORS:LIAjgrc07
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13631
Deposited By: Tony Diaz
Deposited On:27 May 2009 21:36
Last Modified:08 Nov 2021 22:39

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