Mobile layer in oscillatory sheet flow
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In this article, the authors reported measurements of mobile layer thickness and the velocity and concentration distributions within the mobile layer in oscillatory sheet flow Tests were carried out with sand, PVC, and acrylic granules in an oscillatory water tunnel Velocities were measured with a laser Doppler anemometer, and concentrations with conductivity probes.Abstract:
Measurements are reported of mobile layer thickness and the velocity and concentration distributions within the mobile layer in oscillatory sheet flow Tests were carried out with sand, PVC, and acrylic granules in an oscillatory water tunnel Velocities were measured with a laser Doppler anemometer, and concentrations were measured with conductivity probes The measurements of mobile layer thickness appear to confirm the importance of the parameter S = (ρU o ω/(ρ s -ρ)g) At low values of this parameter the measurements tend toward the unique curve which would be expected if pressure gradient and inertia effects were negligible On the other hand, the velocity profile measurements show some influence of pressure gradient and inertia even for values of S as low as 012 At higher values of S a type of plug flow is observed in which the sediment comes to rest as the flow reverses and then begins to move again as a solid blockread more
Citations
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Concentrations in oscillatory sheet flow for well sorted and graded sands
Tom O'Donoghue,Scott Wright +1 more
TL;DR: In this article, a new empirical equation is presented which characterises the time-dependent concentration profile in the sheet flow layer, and the dependence of both parameters on flow and bed conditions is analysed.
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Flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well-sorted and graded sands
Tom O'Donoghue,Scott Wright +1 more
TL;DR: In this paper, velocities were measured using an ultrasonic velocity profiler (UVP) capable of measuring deep within the sheet flow layer and the results showed that the near-bed velocity leads the main flow velocity by approximately 21° and a small offshore-directed current is generated near the bed.
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Phase lags in oscillatory sheet flow: experiments and bed load modelling
TL;DR: In this article, a semi-unsteady model was developed that includes the effects of phase lags on the net transport rate in oscillatory sheet flow, which showed that phase lag becomes important for fine sand, high velocities and short wave periods.
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Effects of wave shape on sheet flow sediment transport
TL;DR: In this article, a two-phase model is implemented to study the effects of wave shape on the transport of coarse-grained sediment in the sheet flow regime, based on balance equations for the average mass, momentum, and fluctuation energy for both the fluid and sediment phases.
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Settling velocity of sediments at high concentrations
TL;DR: In this article, a simple method of determining n is presented using standard equations for the clear water settling velocity and the seepage flow within fixed sediment beds, and the resulting values for n are compared with values derived from new and existing laboratory data for beach and filter sands.
References
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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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TL;DR: In this paper, the reduction to a vacuum correction is considered, which is the only correction that is necessary for a simple pendulum to swing in a vacuum environment, due to the buoyancy of the fluid.
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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.
Journal ArticleDOI
Observations of rapidly flowing granular-fluid materials
Daniel M. Hanes,Douglas L. Inman +1 more
TL;DR: In this paper, the authors studied the shearing of a mixture of cohesionless glass spheres and air or water in an annular, parallel-plate shear cell designed after Savage (1978) and found that the shear and normal stresses were quadratically dependent upon the mean shear rate.
Journal ArticleDOI
Sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow
Abstract: An experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action. Wave-induced oscillatory flow conditions near the seabed were simulated at full scale (1:1) in a new large oscillating water tunnel. Two sets of experiments (series A and B) were carried out. During series A, bed forms and wave-cycle averaged suspended sediment concentrations were measured under sinusoidal waves. Series B focused on measurement of the wave-cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows (upper shoreface conditions) and was aimed at the verification of quasi-steady formulas for the description of cross-shore sediment transport.
Bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness. Only the measured ripple dimensions under asymmetric waves (series B) showed good agreement with Nielsen's (1979) relations. For most of the series B experiments the bed was plane (sheet flow), the net sediment transport was directed “onshore” and the measured transport rates showed a strong correlation with the velocity moment . An empirical quasi-steady transport model is proposed which is based on the new tunnel data and other existing data sets. The limitations of the quasi-steady model approach became clear in the rippled-bed regime and through the presence of a consistent influence of the wave period in plane-bed conditions. In rippled-bed conditions the suspended concentration profiles followed a negative exponential distribution. For most of the experiments the measured concentration decay length showed a linear relation with the ripple height. In plane-bed/sheet flow conditions the measured suspended concentration profiles followed a negative power function. The power or concentration decay parameter was constant (α ≃ 2.1) for a wide range of velocity conditions. It is suggested that the mobile bed (sheet flow layer) has a strong damping effect on the mixing of suspended sediments (turbulence damping).
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