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Title:The influence of steps topography on the behavior of density currents – a numerical study
Author(s):Zhao, Zihe
Advisor(s):Best, James Leonard; Parker, Gary; Jewett, Brian Ford
Department / Program:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):turbidity currents
cyclic steps
numerical model
Abstract:Recent advances in high-resolution multibeam bathymetric imaging have revealed step-like structures interpreted as cyclic steps, or sediment waves, along the bottom of deep-sea canyons and channel levees. These bed features are formed by turbidity currents, and in turn, influence the flow characteristics of the density currents and their sediment transport behavior, thus affecting sedimentation in the oceans. To explore the interaction between density currents and stepped topographies, a series of depth-resolved numerical experiments with a lock-exchange setup were conducted using k-epsilon, two-dimensional and three-dimensional Large Eddy Simulation (LES) models. The results of the present study clearly indicate that compared with a constant slope bed, vertical steps, or “stair-case” shaped bed topographies significantly decrease the overall dense fluid transport efficiency, cause a much more rapid loss of dense fluid at the density current head, and preferentially trap dense fluid at the leeside of steps, thereby decelerating the current front at the late stage of flow evolution. Density underflow over a series of steps with smooth downward-concave geometries behaves largely similarly to the flow over a constant slope bed. To a much lesser degree, an increase in step size causes an effect similar to imposing a vertical step bed. While simulations with the three-dimensional LES numerical model most accurately represent the flow behavior, the k-e model represents vortex generation poorly and the two-dimensional LES model represents only weak eddy dissipation.
Issue Date:2018-07-12
Rights Information:Copyright 2018 Zihe Zhao
Date Available in IDEALS:2018-09-27
Date Deposited:2018-08

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