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Water 2015, 7(1), 81-98; doi:10.3390/w7010081

Volumetric Concentration Maximum of Cohesive Sediment in Waters: A Numerical Study

1
Department of Civil Engineering, Chungnam National University, Daejeon 305-764, Korea
2
School of Civil and Environmental Engineering, Kookmin University, Seoul 136-702, Korea
3
Department of Civil and Environmental Engineering, Hanbat National University, Daejeon 305-719, Korea
*
Author to whom correspondence should be addressed.
Academic Editor: Miklas Scholz
Received: 31 October 2014 / Accepted: 8 December 2014 / Published: 24 December 2014
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Abstract

Cohesive sediment has different characteristics compared to non-cohesive sediment. The density and size of a cohesive sediment aggregate (a so-called, floc) continuously changes through the flocculation process. The variation of floc size and density can cause a change of volumetric concentration under the condition of constant mass concentration. This study investigates how the volumetric concentration is affected by different conditions such as flow velocity, water depth, and sediment suspension. A previously verified, one-dimensional vertical numerical model is utilized here. The flocculation process is also considered by floc in the growth type flocculation model. Idealized conditions are assumed in this study for the numerical experiments. The simulation results show that the volumetric concentration profile of cohesive sediment is different from the Rouse profile. The volumetric concentration decreases near the bed showing the elevated maximum in the cases of both current and oscillatory flow. The density and size of floc show the minimum and the maximum values near the elevation of volumetric concentration maximum, respectively. This study also shows that the flow velocity and the critical shear stress have significant effects on the elevated maximum of volumetric concentration. As mechanisms of the elevated maximum, the strong turbulence intensity and increased mass concentration are considered because they cause the enhanced flocculation process. This study uses numerical experiments. To the best of our knowledge, no laboratory or field experiments on the elevated maximum have been carried out until now. It is of great necessity to conduct well-controlled laboratory experiments in the near future. View Full-Text
Keywords: cohesive sediment; flocculation process; turbulence; volumetric concentration; elevated maximum cohesive sediment; flocculation process; turbulence; volumetric concentration; elevated maximum
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Byun, J.; Son, M.; Yang, J.-S.; Jung, T.-H. Volumetric Concentration Maximum of Cohesive Sediment in Waters: A Numerical Study. Water 2015, 7, 81-98.

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