Simulation of Sand in Plunging Breakers

Pedersen, Carsten; Deigaard, Rolf; Fredsøe, Jørgen; Hansen, Ernst Albin

doi:10.1061/(asce)0733-950x(1995)121:2(77)

Cited by 16 publications

(5 citation statements)

References 16 publications

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“…[9] In this paper, we conduct critical evaluation of the predictive capability of the proposed dilute sediment suspension models in terms of both the wave-averaged as well as the instantaneous sediment concentration. We demonstrate that these new models improve upon the earlier cross-shore sediment transport models of Pedersen et al [1995] and Duy and Shibayama [1997] in terms of providing a complete two-equation turbulence closure, a more robust free surface tracking scheme for breaking waves based on the volume of fluid (VOF) method, and a better description of fluid-sediment interactions in the two-phase approach. However, in terms of predicting instantaneous suspended sediment concentration, large discrepancies remain.…”

Section: Introductionmentioning

confidence: 91%

“…Because of the limitation on computational resources at the present time, in the sediment transport models that are used to simulate the entire surf zone, the concentrated sediment transport region near the bed can not be resolved. Hence near‐bed sediment boundary conditions such as the sediment pickup function or the reference concentration need to be prescribed [e.g., Deigaard et al , 1986; Pedersen et al , 1995; Li and Davies , 1996; Savioli and Justesen , 1996; Duy and Shibayama , 1997]. At present, comprehensive tests for the available near‐bed sediment boundary conditions for phase‐ and depth‐resolving models under waves are still scarce.…”

Section: Introductionmentioning

confidence: 99%

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Toward modeling turbulent suspension of sand in the nearshore

Hsu

Liu

2004

J. Geophys. Res.

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[1] We present two depth-and phase-resolving models, based on single-and two-phase approaches for suspended sediment transport under water waves. Both models are the extension of a wave hydrodynamic model Cornell Breaking Wave and Structure (COBRAS). In the two-phase approach, dilute two-phase mass and momentum equations are calculated along with a fluid turbulence closure based on balance equations for the fluid turbulence kinetic energy k f and its dissipation rate f . In the single-phase approach the fluid flow is described by the Reynolds-Averaged Navier-Stokes equations, while the sediment concentration is calculated by an advection-diffusion equation for the conservation of sediment mass. The fluid turbulence is calculated by k f -f equations that incorporate the essential influence of sediment, which can also be consistently deduced from the two-phase theory. By adopting a commonly used sediment flux boundary condition near the bed the proposed models are tested against laboratory measurements of suspended sediment under nonbreaking skewed water waves and shoaling broken waves. Although the models predict wave-averaged sediment concentrations reasonably well, the corresponding time histories of instantaneous sediment concentration are less accurate. We demonstrate that this is due to the uncertainties in the near-bed sediment boundary conditions. In addition, we show that under breaking waves the near-bed sediment pickup cannot be solely parameterized by the bottom friction, suggesting that other effects may also influence the near-bed sediment boundary conditions. INDEX TERMS: 4546

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Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Toward modeling turbulent suspension of sand in the nearshore

Hsu

Liu

2004

J. Geophys. Res.

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“…[2] A detailed understanding of the flow and sedimentary processes within the surf and swash zones is of major engineering, as well as societal, importance. The intense production of turbulence and vorticity associated with breaking waves [e.g., Pedersen et al, 1995] make these regions of special significance within coastal sediment transport and morphology. In particular, surf and swash zone processes govern the exchange of sands between the emerged and submerged portions of the beach, and are therefore responsible for determining shoreline configurations, including, e.g., beach accretion or recession.…”

Section: Introductionmentioning

confidence: 99%

Laboratory observations of flow and sediment transport induced by plunging regular waves

Sumer

Güner

Hansen

et al. 2013

J. Geophys. Res. Oceans

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[1] Two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered: (1) a rigid-bed experiment, allowing direct (hot film) measurements of bed shear stresses and (2) a sediment-bed experiment, allowing for the measurement of pore-water pressures as well as observation of sediment suspension and bed morphological changes. Both experiments utilize the same initial bed profile and wave forcing. The experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions, whereas their corresponding turbulent fluctuations are amplified even more strongly, by a factor of 5-6. The plunging processes lead to a series of vortices, whose formation may be explained as the result of shear layer instability. Measurements show that these vortices can significantly enhance peaks in the offshoredirected bed shear stresses. Moreover, near-bed pore pressure measurements indicate that these vortices cause large upward-directed pressure gradients, which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event. These findings are related to the induced morphological changes over both short and long time scales. The present results are also compared and contrasted with previous experiments utilizing a similar methodology, but involving plunging solitary waves.

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“…Possible mechanisms suggested for the intermittent variations include bed forms (ripples and megaripples), large waves in a wave group, vortices and turbulence generated by breaking waves and bores, wave-induced boundary ventilation, and coherent motions including shear instability in the turbulent boundary layer. Numerical timedependent models developed to predict sediment suspension include vertical diffusion models for spilling waves [Deigaard et al, 1986] and for nonbreaking waves [Li and Davies, 1996], a discrete vortex model for plunging waves [Pedersen et al, 1995], and a convection-diffusion model [Duy and Shibayama, 1997]. The comparisons of these models for breaking waves were limited to the mean concentration under monochromatic waves probably because of the large uncertainty of the timedependent bottom boundary condition for the concentration and because of extensive computation time to simulate irregular waves.…”

Section: Introductionmentioning

confidence: 99%

Sand suspension, storage, advection, and settling in surf and swash zones

Kobayashi¹,

Johnson²

2001

J. Geophys. Res.

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Abstract. A time-dependent cross-shore sediment transport model in the surf and swash zones on beaches is developed to predict both beach accretion and erosion under the assumptions of alongshore uniformity and normally incident waves. The model is based on the depth-integrated sediment continuity equation, which includes sediment suspension by turbulence generated by wave breaking and bottom friction, sediment storage in the entire water column, sediment advection by waves and wave-induced return current, and sediment settling on the movable bottom. The hydrodynamic input required for this sediment transport model is predicted using the finite-amplitude shallow-water equations including bottom friction. The developed model is compared with three large-scale laboratory tests with accretional, neutral (little), and erosional beach profile changes under regular waves. The model predicts sediment suspension under the steep front of breaking waves and due to bottom friction in the swash zone. The computed depth-averaged sediment concentration does not respond to local sediment suspension instantaneously because of the sediment storage and advection. The mean sediment concentration becomes large in comparison to the oscillatory concentration with the decrease of the normalized sediment fall velocity. The net cross-shore sediment transport rate is shown to be the small difference between the onshore transport rate due to the positively correlated oscillatory components of the suspended sediment volume per unit area and the horizontal sediment velocity and the offshore transport rate due to the product of the mean suspended sediment volume and the mean horizontal sediment velocity. Relatedly, the net accretion or erosion rate of the movable bottom is determined by the small difference between the mean sediment settling rate and the mean suspension rate caused by wave breaking and bottom friction. The present computation is limited to the initial beach profile change, but the numerical model is capable of predicting the accretional, erosional, and neutral profile changes.

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Simulation of Sand in Plunging Breakers

Cited by 16 publications

References 16 publications

Toward modeling turbulent suspension of sand in the nearshore

Toward modeling turbulent suspension of sand in the nearshore

Laboratory observations of flow and sediment transport induced by plunging regular waves

Sand suspension, storage, advection, and settling in surf and swash zones

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