Analysis of Bed‐Load Motion at High Shear Stress

Wilson, Kenneth

doi:10.1061/(asce)0733-9429(1987)113:1(97)

Cited by 166 publications

(171 citation statements)

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“…Here 15s/D5o is the relative sheet flow layer thickness, "2 is a constant which is equal to 10.0 [Wilson, 1987] Swart's [1974] formula for the wave friction factor with a roughness height equal to the grain diameter (k s = Ds0 ) shows that an increasing grain diameter leads to slightly increasing friction factors and thus to slightly increasing values of dc or/5s. The mobility of the bed and the high sediment concentrations in the sheet flow layer affect the transport processes in several ways.…”

Section: Introductionmentioning

confidence: 99%

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Mobile‐bed effects in oscillatory sheet flow

Dohmen-Janssen¹,

Hassan²,

Ribberink³

2001

J. Geophys. Res.

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Abstract. Field observations often show a considerable variation in mean grain size along the coastal profile. Under high waves in shallow water, bed ripples are washed out, and sheet flow becomes the dominant transport mode: large amounts of sand are transported in a thin layer close to the bed, i.e., the sheet flow layer. This paper focuses on grain size influences on transport processes in oscillatory sheet flow. Experiments were carried out in the Large Oscillating Water Tunnel (LOWT) of Delft Hydraulics, in which near-bed orbital velocities in combination with a net current can be simulated at full scale. Three uniform sands with different mean grain size were used. It was found that in contradiction to expressions found in literature, both the erosion depth and the sheet flow layer thickness are larger for fine sand (Ds0 = 0.13 mm) than for coarser sand (Ds0 -> 0.21 mm). Measured time-averaged velocity and concentration profiles indicate that the presence of a sheet flow layer leads to an increased flow resistance and to damping of turbulence and that these effects are stronger for a thicker sheet flow layer (i.e., for fine sand). These mobile-bed effects are analyzed further by comparing the measurements with the results of a one-dimensional vertical advection-diffusion boundary layer model. Simulating the mobile-bed effects in the model by introducing an increased roughness height and a reduced turbulent eddy viscosity showed that the roughness height is of the order of the sheet flow layer thickness and that turbulence damping increases for a decreasing grain size. 27,103

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Section: Introductionmentioning

confidence: 99%

“…Examples are the steady flow model of Wilson [1987], the two-layer model of Kaczmarek [1990] [1998], and the two-phase flow models of Asano [1990] and Dong and Zhang [1999].…”

Section: Introductionmentioning

confidence: 99%

Mobile‐bed effects in oscillatory sheet flow

Dohmen-Janssen¹,

Hassan²,

Ribberink³

2001

J. Geophys. Res.

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“…The bed load is the part of the total load which is travelling immediately above the bed by rolling, sliding, or saltating and is supported by hydrodynamic forces [10]. The suspended load, on the other hand, is the part of the load which is primarily supported by the fluid turbulence [11].…”

Section: Mode Of Sediment Transportmentioning

confidence: 99%

Hydrodynamic investigation of fluvial sediment transport with Soil Protrusion Apparatus (SPA)

Jayaratne

Salim

2014

Open Engineering

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Abstract:In order to understand sediment transport process based on knowledge of their soil properties and hydrodynamic behaviour a series of 2D laboratory controlled small-scale experiments were conducted using the Ahlborn sediment mobile bed tank (4.0×0.6×0.2 m). Experiments were conducted in smooth and rough bed conditions with purposely-built Soil Protrusion Apparatus (SPA) to measure the basic parameters on which erosion depends. Sediment deposition patterns in equilibrium stage associated with different bed roughness and particle size distributions were fundamentally investigated. Extended physical modelling of crescent zones also included analysing their grain size distribution. Dimensional analysis and multiple linear regression methods were employed to derive a simple empirical relationship for erosion rate (ER) in terms of the shear stress (τs), average grain diameter (d 50 ) and soil protrusion (z) for smooth and rough sediment bed conditions. These analyses also suggest ways to refine empirical models, examining transport rates to explore the limits of erosion and deposition influences in shallow flow conditions.

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“…Bed load transport rates have been measured experimentally using bed load traps, leading to empirical formulae (e.g., Meyer-Peter and Müller, 1948;Wilson, 1966;Ribberink, 1998). The most common formulations relate the non-dimensional transport rate Φ B to the Shields parameter as:…”

Section: Current Approachesmentioning

confidence: 99%

Parameterization of near-bed processes under collinear wave and current flows from a two-phase sheet flow model

Amoudry

Liu

2010

Continental Shelf Research

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Sediment transport models require appropriate representation of near-bed processes. We aim here to explore the parameterizations of bed shear stress, bed load transport rate and near-bed sediment erosion rate under the sheet flow regime. To that end, we employ a one-dimensional two-phase sheet flow model which is able to resolve the intrawave boundary layer and sediment dynamics at a length scale on the order of the sediment grain. We have conducted 79 numerical simulations to cover a range of collinear wave and current conditions and sediment diameters in the range 210 µm to 460 µm. The numerical results confirm that the intrawave bed shear stress leads the free stream velocity, and we assess an explicit expression relating the phase lead to the maximum velocity, wave period and bed roughness. The numerical sheet flow model is also used to provide estimates for the bed load transport rate and to inspect the near-bed sediment erosion. A common bed load transport rate formulation and two typical reference concentration approaches are assessed. A dependence of the bed load transport rate on the sediment grain diameter is observed and parameterized. Finally, the intrawave near-bed vertical sediment flux is further investigated and related to the time derivative of the bed shear stress.

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Analysis of Bed‐Load Motion at High Shear Stress

Cited by 166 publications

References 3 publications

Mobile‐bed effects in oscillatory sheet flow

Mobile‐bed effects in oscillatory sheet flow

Hydrodynamic investigation of fluvial sediment transport with Soil Protrusion Apparatus (SPA)

Parameterization of near-bed processes under collinear wave and current flows from a two-phase sheet flow model

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