Sand Transport Over Rippled Beds in Oscillatory Flow

Werf, Jebbe J. van der; Ribberink, Jan S.

doi:10.1142/9789812709554_0206

Cited by 11 publications

(21 citation statements)

References 65 publications

(245 reference statements)

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“…As for the sheet-flow regime, this 'offshore' transport is caused by phase-lag effects, but now taking place in a much thicker suspension layer. For a recent overview of present knowledge about this sand transport regime, reference is made to van der Werf [15].…”

Section: Sand Motion Around Oscillatory Vortex Ripples 31 Generalmentioning

confidence: 99%

“…A more extended series of other tunnel experiments [12,15,49] and wave flume experiments by Thorne et al [52], consisting of 48 different conditions, provide a more general insight into the average thickness of the suspension transport layer and the shape of the mean sediment concentration profile above the bed. For a wide range of mobility number in the ripple regime ( rms = 12-100) and for medium sand (D 50 = 0.21-0.44 mm), it is found that the time-and bedaveraged sediment concentration profile can generally be described as an exponentially decaying function of the distance above the ripple crest z = z 0 , i.e.…”

Section: Suspended Sand Concentrationsmentioning

confidence: 99%

“…Given the measured ripple migration speed (c = +18 mm/min), the mean total transport (obtained from sand trap measurements and bed profiling, see [15,49]) and assuming a constant ripple shape, the time-averaged near-bed transport along the ripple can be calculated using the mass conservation principle. In this calculation the measured storage of suspended sediment in the water column is included.…”

Section: Suspended Sand Fluxesmentioning

confidence: 99%

“…Van der Werf [15] has shown that severe empirical adjustments of the eddy viscosity and sediment entrainment functions are needed for a 1DV RANS model to give reasonable estimates of net transport rates in the ripple regime.…”

Section: Downloaded By [University Of Chicago Library] At 14:09 19 Nomentioning

confidence: 99%

“…The present paper explains this variable behaviour in transport using insights from experiments conducted in the LOWT and AOFT in the period 1994 to date [11][12][13][14][15]. The paper provides an overview of key results from the experiments and presents new results based on new analysis of the combined data sets.…”

Section: Introductionmentioning

confidence: 99%

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Sand motion induced by oscillatory flows: Sheet flow and vortex ripples

Ribberink¹,

Werf²,

Donoghue

et al. 2008

Journal of Turbulence

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A large series of field-scale experiments on turbulent sand-laden flows, conducted in preceding years in the LOWT and AOFT large oscillating water tunnels are reviewed and reanalysed. Using the combined experimental data sets, new insights are obtained on the detailed sand transport processes occurring in sheet-flow and ripple regime conditions. For sheet flow (i) new equations are presented relating maximum erosion depth and sheet-flow layer thickness to the maximum Shields parameter; (ii) detailed analysis of sediment flux data shows the dominance of the current-related flux in the sheet-flow layer and the different characters of the current-related flux for fine and medium sands; (iii) a RANS-diffusion type model is shown to reproduce important trends in net transport rate related to grain size, velocity and wave period and to predict the magnitude of net transport rate to within a factor 2 of measured values. For the ripple regime it is shown that (i) asymmetric waves generate negative ('offshore') streaming and the current-related suspended sediment flux associated with this streaming appears to be of the same order of magnitude as the wave-related suspended sediment flux; (ii) time-averaged near-bed transport and time-averaged suspended transport appear to be of about equal magnitude but of opposite sign, and are concentrated on the 'onshore' flank of the ripple for asymmetric wave conditions; (iii) near-bed transport along the onshore flank is generated by sand transported over the ripple crest during the 'onshore' half-cycle. Net sand transport under asymmetric waves can be 'onshore' directed or 'offshore' directed, depending on the degree of unsteadiness in the sand flux behaviour during the wave cycle. Dimensionless phase-lag parameters are presented, for sheet flow and ripples, which can discriminate between predominantly quasi-steady behaviour (resulting in 'onshore' transport) and predominantly unsteady behaviour (resulting in 'offshore transport').

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Section: Sand Motion Around Oscillatory Vortex Ripples 31 Generalmentioning

confidence: 99%

Section: Suspended Sand Concentrationsmentioning

confidence: 99%

Section: Suspended Sand Fluxesmentioning

confidence: 99%

Section: Downloaded By [University Of Chicago Library] At 14:09 19 Nomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sand motion induced by oscillatory flows: Sheet flow and vortex ripples

Ribberink¹,

Werf²,

Donoghue

et al. 2008

Journal of Turbulence

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Sand motion induced by oscillatory flows: sheet flow and vortex ripples

Ribberink¹,

Werf²,

O’Donoghue³

2007

ERCOFTAC Series

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Detailed measurements of velocities and suspended sand concentrations over full‐scale ripples in regular oscillatory flow

Werf¹,

Doucette²,

et al. 2007

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[1] The knowledge and modeling of wave-induced sand transport over rippled beds still has significant shortcomings, which is partly related to a lack of measurements of the detailed processes from controlled laboratory experiments. We have carried out new measurements of the detailed time-dependent velocity and suspended sand concentration field around vortex ripples for regular oscillatory flow conditions. The fact that the ripples were mobile and the flow conditions were full-scale makes these measurements unique. We made velocity measurements for 14 different flows and concentration measurements for three of these flows. The velocity and concentration field above ripples are dominated by the generation and ejection of vortices on the ripple flanks around the time of flow reversal. Vortex formation results in near-ripple flow reversals ahead of free-stream reversals and velocity maxima near the ripple crest that are much higher than the free-stream maxima. Asymmetry in the free stream produces steady circulation cells with dominant offshore mean flow up the ripple lee slope, balanced by weaker onshore streaming up the ripple stoss slope as well as higher up in the flow. The timeand bed-averaged horizontal velocity profile comprises an offshore streaming near the bed and an onshore drift higher up in the flow. The vortices are responsible for three main concentration peaks: one just after on-offshore flow reversal associated with the passage of a sand-laden vortex followed by two smaller peaks due to advected suspension clouds generated by vortex action at the neighboring onshore ripples. The sand flux field measured for one typical asymmetric flow condition is dominated by an offshore flux associated with the suspended sand cloud generated by vortex shedding from the ripple's lee slope around the time of on-offshore flow reversal. The net (time-averaged) currentrelated and wave-related horizontal sand fluxes are generally offshore directed and mostly contained within 1.5 ripple heights above the ripple crest. The wave-related suspended transport component is larger, but the contribution of the current-related suspended sand transport cannot be neglected. In addition to the measured offshore net transport of suspended sand, there is an onshore-directed transport very close to the ripple surface. The total net transport is in the offshore direction for this specific asymmetric flow condition.Citation: van der Werf, J. J., J. S. Doucette, T. O'Donoghue, and J. S. Ribberink (2007), Detailed measurements of velocities and suspended sand concentrations over full-scale ripples in regular oscillatory flow,

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Sand Transport Over Rippled Beds in Oscillatory Flow

Cited by 11 publications

References 65 publications

Sand motion induced by oscillatory flows: Sheet flow and vortex ripples

Sand motion induced by oscillatory flows: Sheet flow and vortex ripples

Sand motion induced by oscillatory flows: sheet flow and vortex ripples

Detailed measurements of velocities and suspended sand concentrations over full‐scale ripples in regular oscillatory flow

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