Boundary layer flow and net sediment transport beneath asymmetrical waves

Holmedal, Lars Erik; Myrhaug, Dag

doi:10.1016/j.csr.2005.11.004

Cited by 42 publications

(41 citation statements)

References 19 publications

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“…This is consistent with Holmedal & Myrhaug (2006) who, using a k-ε model, showed there was no significant effect of a/k s on the near-bed residual for velocity-skewed flow. They indicated that although the time-averaged stress will increase with increasing roughness, leading to a larger negative mean flow (in the case of an infinite tunnel), the finite length of the tunnel will lead to a stronger return flow with increasing roughness, which consequently does not lead to significant changes in the residual velocity profile.…”

Section: A Van Der a T O'donoghue A G Davies And J S Ribbesupporting

confidence: 80%

“…The mechanism giving rise to the residual velocity is the asymmetry in turbulence intensity between the two flow half-cycles, which leads to the generation of a time-averaged, height-dependent stress within the boundary layer (Trowbridge & Madsen 1984;Davies & Li 1997;Holmedal & Myrhaug 2006). Figure 11 presents the residual velocity profiles for all of the present 12 experiments.…”

Section: Time-averaged Flowmentioning

confidence: 99%

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Experimental study of the turbulent boundary layer in acceleration-skewed oscillatory flow

O’Donoghue

Davies

et al. 2011

J. Fluid Mech.

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Experiments have been conducted in a large oscillatory flow tunnel to investigate the effects of acceleration skewness on oscillatory boundary layer flow over fixed beds. As well as enabling experimental investigation of the effects of acceleration skewness, the new experiments add substantially to the relatively few existing detailed experimental datasets for oscillatory boundary layer flow conditions that correspond to full-scale sea wave conditions. Two types of bed roughness and a range of highReynolds-number, Re ∼ O(10 6 ), oscillatory flow conditions, varying from sinusoidal to highly acceleration-skewed, are considered. Results show the structure of the intrawave velocity profile, the time-averaged residual flow and boundary layer thickness for varying degrees of acceleration skewness, β. Turbulence intensity measurements from particle image velocimetry (PIV) and laser Doppler anemometry (LDA) show very good agreement. Turbulence intensity and Reynolds stress increase as the flow accelerates after flow reversal, are maximum at around maximum free-stream velocity and decay as the flow decelerates. The intra-wave turbulence depends strongly on β but period-averaged turbulent quantities are largely independent of β. There is generally good agreement between bed shear stress estimates obtained using the loglaw and using the momentum integral equation, and flow acceleration skewness leads to high bed shear stress asymmetry between flow half-cycles. Turbulent Reynolds stress is much less than the shear stress obtained from the momentum integral; analysis of the stress contributors shows that significant phase-averaged vertical velocities exist near the bed throughout the flow cycle, which lead to an additional shear stress, −ρũw; near the bed this stress is at least as large as the turbulent Reynolds stress.

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Section: A Van Der a T O'donoghue A G Davies And J S Ribbesupporting

confidence: 80%

Section: Time-averaged Flowmentioning

confidence: 99%

Experimental study of the turbulent boundary layer in acceleration-skewed oscillatory flow

O’Donoghue

Davies

et al. 2011

J. Fluid Mech.

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“…(16). A similar technique was used by Holmedal and Myrhaug (2006). Here we instead forced the average horizontal velocity to match u ∞ , similar to how the physical water tunnel is forced.…”

Section: Boundary Conditions and Forcingmentioning

confidence: 99%

Large eddy simulation of sediment transport over rippled beds

Harris

Grilli

2014

Nonlin. Processes Geophys.

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Abstract. Wave-induced boundary layer (BL) flows over sandy rippled bottoms are studied using a numerical model that applies a one-way coupling of a "far-field" inviscid flow model to a "near-field" large eddy simulation (LES) NavierStokes (NS) model. The incident inviscid velocity and pressure fields force the LES, in which near-field, wave-induced, turbulent bottom BL flows are simulated. A sediment suspension and transport model is embedded within the coupled flow model. The numerical implementation of the various models has been reported elsewhere, where we showed that the LES was able to accurately simulate both mean flow and turbulent statistics for oscillatory BL flows over a flat, rough bed. Here we show that the model accurately predicts the mean velocity fields and suspended sediment concentration for oscillatory flows over full-scale vortex ripples. Tests show that surface roughness has a significant effect on the results. Beyond increasing our insight into wave-induced oscillatory bottom BL physics, sophisticated coupled models of sediment transport such as that presented have the potential to make quantitative predictions of sediment transport and erosion/accretion around partly buried objects in the bottom, which is important for a vast array of bottom deployed instrumentation and other practical ocean engineering problems.

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“…Intermediate transport models are also empirical transport formulas, but phase-lag effects are included in a parameterized way (Ahmed and Sato, 2003;Camenen and Larson, 2005;Dibajnia and Watanabe, 1992;Dohmen-Janssen et al, 2002). Full unsteady sediment transport models are based on a full time-dependent simulation of both velocities and concentrations during the wave cycle at different elevations above the bed (Fredsøe, 1984;Guizien et al, 2003;Hassan and Ribberink, 2010;Holmedal and Myrhaug, 2006;Holmedal and Myrhaug, 2009;Kranenburg et al, 2013;Ribberink and Al-Salem, 1995;Ruessink et al, 2009;Uittenbogaard et al, 2001). The process-based unsteady models are advanced approaches.…”

Section: Numerical Simulation For Sediment Transport Under Combined Wmentioning

confidence: 99%

“…These models can be divided into three different classes (Hassan and Ribberink, 2010;: empirical quasi-steady transport models, intermediate transport models, and fully unsteady sediment transport models (process based). Fully unsteady sediment transport models are based on a time-dependent simulation of both velocities and concentrations during the wave cycle at different elevations above the bed (Fredsøe, 1984;Guizien et al, 2003;Hassan and Ribberink, 2010;Holmedal and Myrhaug, 2006;Kranenburg et al, 2013;Ribberink and Al-Salem, 1995;Ruessink et al, 2009;Uittenbogaard et al, 2001). The process-based unsteady models are based on more advanced approaches, and this study focuses on this kind of model.…”

Section: Introductionmentioning

confidence: 99%

Modelling and Analysis of Fine Sediment Transport in Wave-Current Bottom Boundary Layer

Zuo¹

2018

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Although all care is taken to ensure integrity and the quality of this publication and the information herein, no responsibility is assumed by the publishers, the author nor IHE Delft for any damage to the property or persons as a result of operation or use of this publication and/or the information contained herein. A pdf version of this work will be made available as Open Access via http://repository.tudelft.nl/ihe. This version is licensed under the Creative Commons To my family AbstractThe evolution and utilization of estuarine and coastal regions are greatly restricted by sediment problems. Inspired by the Caofeidian sea area in Bohai Bay, China, this study aims to better understand silty sediment transport under combined action of waves and currents, especially in the wave-current bottom boundary layer (BBL), and to improve our modelling approaches in predicting estuarine and coastal sediment transport.Field observations were carried out in northwestern Caofeidian sea area of Bohai Bay and field data were collected on several other silt-dominated coasts. Analysis shows that silt-dominated sediments are sensitive to flow dynamics: the suspended sediment concentrations (SSCs) increase rapidly under strong flow dynamics (i.e., waves or strong tidal currents which can stir up sediments), and high concentrations cause heavy sudden back siltation in navigation channels. In the following, details of silty sediment transport are studied, focusing on the BBL and high concentration layer (HCL).From laboratory experiments and theoretical analysis, an expression for sediment incipient motion is proposed for silt-sand sediment under combined wave and current conditions. The Shields number was revised by adding the cohesive force and additional static pressure, leading to an extended Shields curve.To study the HCL, a process based 1DV model was developed for flow-sediment dynamics near the bed in combined wave-current conditions. Based on the physical processes, special approaches for sediment movement were introduced, including approaches for different bed forms (rippled bed and 'flat-bed'), hindered settling, stratification effects, mobile bed effects, reference concentration and critical shear stress. The HCL was simulated and sensitivity analysis was carried out by the 1DV model on factors that impact the sediment concentration in the HCL. The results show that the HCL is affected by both flow dynamics and bed forms; the thickness of the HCL is about twice the height of the wave boundary layer; bed forms determine the shape of the concentration profile near the bottom, and flow dynamics determine the magnitude. For finer sediment, stratification effects and mobile bed effects impact the sediment concentration greatly.Finally, based on the 1DV model, the formulations of the mean sediment concentration profile of silty sediments were studied. By solving the time-averaged diffusion equation for SSC and considering the effects of bed forms, stratification and hindered settling, expressions for time-averaged SSC profile...

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Boundary layer flow and net sediment transport beneath asymmetrical waves

Cited by 42 publications

References 19 publications

Experimental study of the turbulent boundary layer in acceleration-skewed oscillatory flow

Experimental study of the turbulent boundary layer in acceleration-skewed oscillatory flow

Large eddy simulation of sediment transport over rippled beds

Modelling and Analysis of Fine Sediment Transport in Wave-Current Bottom Boundary Layer

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