Journal ArticleDOI
The formation of ripples and dunes on an erodible bed
TLDR
In this paper, a two-dimensional stability analysis of flow of low Froude number over an erodible bed is presented, and the results are strongly dependent on the two parameters z0, the roughness length of the bed, and β, the effect of the local bed slope on the bed load transport.Abstract:
A two-dimensional stability analysis is presented of flow of low Froude number over an erodible bed. Particular regard is given to the modelling of the turbulent flow close to the bed. In contrast to previous theories that use a constant eddy-viscosity approach the present theory predicts the occurrence of two separate modes of instability, with wavelengths related to the roughness of the bed and the depth of the flow. It is postulated that these two modes correspond to the formation of ripples and dunes respectively. The results are strongly dependent on the two parameters z0, the roughness length of the bed, and β, the effect of the local bed slope on the bed-load transport. Using physically plausible estimates for these parameters the results of the analysis are in good agreement with observations for both ripples and dunes.read more
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Granular Media: Between Fluid and Solid
TL;DR: In this article, the granular solid: statics and elasticity of granular liquid and granular gases are discussed at the grain level, and the interaction between granular media, statics, elasticity and plasticity at the liquid level.
Journal ArticleDOI
The fluid dynamics of river dunes: A review and some future research directions
TL;DR: In this article, the authors summarized the principal features of mean and turbulent flow over alluvial sand dunes and highlighted some possible focus areas for future research: (1) the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field, (2) three-dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress, (3) flow field modification resulting from bed form superimposition and amalgamation, (4) the scale and topology of dunes-related turbulence and its interactions
Journal Article
The fluid dynamics of river dunes : A review and some future research directions : Marine sandware and river dune dynamics
TL;DR: In this paper, the authors summarized the principal features of mean and turbulent flow over alluvial sand dunes and highlighted some possible focus areas for future research: (1) the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field, (2) three-dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress, (3) flow field modification resulting from bed form superimposition and amalgamation, (4) the scale and topology of Dune-related turbulence and its interactions
Journal ArticleDOI
Mean flow and turbulence structure over fixed, two-dimensional dunes: implications for sediment transport and bedform stability
Sean J. Bennett,James L. Best +1 more
TL;DR: In this paper, the authors measured the downstream and vertical components of velocity at more than 1800 points over one dune wavelength and constructed a set of contour maps for all mean flow and turbulence parameters, which are assessed using higher moment measures and quadrant analysis.
Journal ArticleDOI
Finite-amplitude alternate bars
TL;DR: In this paper, a predictive theory is proposed to determine the development of finite-amplitude alternate bars in straight channels with erodible bottoms, where an equilibrium amplitude of bedforms is reached as t → ∞ within a wide range of values of the parameter (β − βc)/βc, where t is the time, β is the width ratio of the channel and βc is its critical value below which bars would not form.
References
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Journal ArticleDOI
Experiments on a Gravity-Free Dispersion of Large Solid Spheres in a Newtonian Fluid under Shear
TL;DR: In this article, a large number of spherical grains of diameter D = 0.13 cm were sheared in Newtonian fluids of varying viscosity (water and a glycerine-water-alcohol mixture) in the annular space between two concentric drums.
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On the generation of surface waves by shear flows
TL;DR: In this paper, an approximate solution to the boundary value problem is developed for a logarithmic profile and the corresponding spectral distribution of the energy transfer coefficient calculated as a function of wave speed.
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Saltation of uniform grains in air
TL;DR: In this paper, the interaction between a turbulent wind and the motion of uniform saltating grains of sand or soil, so massive as to fail to enter into suspension, is examined on the basis of two complementary hypotheses.
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The flow of cohesionless grains in fluids
TL;DR: In this article, it was shown that if the bed is composed entirely of potentially mobile grains a stress-equilibrium relation at the bed surface can be defined whereby the magnitude of a certain "bed load" of grains in transit over unit bed area is given in terms of the applied tangential stress.
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Spatially averaged flow over a wavy surface
J. Dungan Smith,Scott McLean +1 more
TL;DR: In this paper, velocity profiles obtained by averaging these flow data along lines of constant distance above the riverbed are examined, and it is shown that they can be constructed from well-known uniform flow results used in conjunction with a hypothesis about the structure of internal boundary layers.