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Two-Phase Modeling of Sediment Clouds in a Current

Author(s): Adrian C. H. Lai; Bing Zhao; Adrian W. K. Law; E. Eric Adams; J. W. Er

Linked Author(s): Wing Keung, Adrian Law, Eric Adams

Keywords: Two-phase flows; Buoyancy driven flows; Sediment clouds; Dredging; Land reclamation

Abstract: The release of sedimentsinto an ambient currentappears in many engineering applications, such as land reclamation and dredging waste disposal. In many cases, the release time is short and a sediment cloud which resembles an instantaneous negatively buoyant source is formed. Different from a single-phase buoyant release, it hastwo phasescomposed of the sediment particles, and the entrained ambient fluid into the sediment cloud. During its descent, a dense spherical thermal is first formed, followed by the formation of a bowl shape sediment swarm when the thermal circulation can no longer hold the sediment particles. Its characteristics, such as trajectory, width and velocity, also change with time during the descent. It is important to be able to predict the transient characteristics of a sediment cloud efficiently to optimize the engineering operations or to perform environmental impact assessment. In this paper, we extend Lai et al. (2013) ’s two-phase model for a sediment cloud in quiescent ambient conditionsto account for the effect of an ambient current. The entrained fluid characteristics are solved by an integral model of a spherical thermal in each time step. The flow field induced by the sediment cloud is approximated by a Hill's spherical vortex centered at the centroid and with the volume of the entrained fluid. The ambient current is then superimposed on to the flow field assuming the vortex is being passively advected. The motion of each computational particle is then computed accordingly. The model prediction is compared with experimental data in the literature. We shall show that the predicted bottom mass deposition distribution and other characteristics are all in reasonable agreement with past observation.


Year: 2013

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