Transport processes of uniform and mixed sands in oscillatory sheet flow

Hassan, Wael; Ribberink, Jan S.

doi:10.1016/j.coastaleng.2005.06.002

Cited by 80 publications

(121 citation statements)

References 29 publications

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“…The most noticeable feature, which persists for the entire cycle and is also clearly visible in figure 11, is a well-established layer of finer particles below the initial bed level. This layer develops very quickly (it is visible after just one flow cycle) and is armoured by a layer of coarser particles above, consistent with the laboratory findings of Hassan & Ribberink (2005). During onshore acceleration, when the bed is rapidly mobilized, the high-concentration sheet-flow layer is very coarse up to the point of maximum velocity.…”

Section: In Suspensionsupporting

confidence: 74%

“…a switch from offshore transport towards onshore transport or vice versa (Egiazaroff 1965). Under oscillatory flows, particle exchange between the bedload and the suspended load is fairly dynamic through competing settling and entrainment effects (Hassan & Ribberink 2005). Therefore, in order to understand the grain size effects, the transport processes within both the suspension layer and the high-concentration bed region need to be examined hand in hand.…”

Section: Introductionmentioning

confidence: 99%

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Particle based modelling and simulation of natural sand dynamics in the wave bottom boundary layer

Finn

Apte

2016

J. Fluid Mech.

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Sand transport and morphological change occur in the wave bottom boundary layer due to sand particle interactions with an oscillatory flow and granular interactions between particles. Although these interactions depend strongly on the characteristics of the particle population, i.e. size and shape, little is known about how natural sand particles behave under oscillatory conditions and how variations in particle size influence transport behaviour. To enable this to be studied numerically, an Euler-Lagrange point-particle model is developed which can capture the individual and collective dynamics of subaqueous natural sand grains. Special treatments for particle collision, friction and hydrodynamic interactions are included to take into account the wide size and shape variations in natural sands. The model is used to simulate sand particle dynamics in two asymmetric oscillatory flow conditions corresponding to the vortex ripple experiments of Van der Werf et al. (J. Geophys. Res., vol. 112, 2007, F02012) and the sheet-flow experiments of O'Donoghue & Wright (Coast. Engng, vol. 50, 2004, pp. 117-138). A comparison of the phase resolved velocity and concentration fields shows overall excellent agreement between simulation and experiments. The particle based datasets are used to investigate the spatio-temporal dynamics of the particle-size distribution and the influence of three-dimensional vortical features on particle entrainment and suspension processes. For the first time, it is demonstrated that even for the relatively well-sorted medium-size sands considered here, the characteristics of the local grain size population exhibit significant space-time variation. Both conditions demonstrate a distinct coarse-over-fine armouring at the bed surface during low-velocity phases, which restricts the vertical mobility of finer fractions in the bed, and also results in strong pickup events involving disproportionately coarse fractions. The near-bed layer composition is seen to be very dynamic in the sheet-flow condition, while it remains coarse through most of the cycle in the vortex ripple condition. Particles in suspension spend more time sampling the upward directed parts of these flows, especially the smaller fractions, which delays particle settling and enhances the vertical size sorting of grains in suspension. For the submillimetre grain sizes considered, most † Email address for correspondence: J.Finn@liv.ac.uk

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Section: In Suspensionsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Particle based modelling and simulation of natural sand dynamics in the wave bottom boundary layer

Finn

Apte

2016

J. Fluid Mech.

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“…Important earlier contributions were also made by the research group at University of Cambridge (Ahilan and Sleath, 1987;Dick and Sleath, 1992;Zala-Flores and Sleath, 1998). A little later, very detailed data were published by the researchers from Delft Hydraulics or those having the opportunity to use the large oscillatory water tunnel (LOWT) at WL|Delft Hydraulics (Ribberink and Al-Salem, 1995;McLean et al, 2001;Dohmen-Janssen et al, 2001;DohmenJanssen and Hanes, 2002;Hassan and Ribberink, 2005). The relatively recent contributions are a series of work completed at University of Aberdeen (O'Donoghue and Wright, 2004a, b;Van der et al, 2010), where a large-scale oscillatory flow tunnel (AOFT) equipped with advanced measuring instruments was built in 1999.…”

Section: Introductionmentioning

confidence: 99%

A two-phase approach to wave-induced sediment transport under sheet flow conditions

Chen

Niu

et al. 2011

Coastal Engineering

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A numerical model for the general description of the sediment transport under oscillatory sheet flow conditions is developed based on a two-fluid representation of the two-phase turbulent flows. The governing equations of the model are the Reynolds averaged continuity equations and equations of motion for both the fluid and the sediment phases. The two phases are coupled by the interphase forces including the resistance force, the inertia force, and the lift force. Turbulence closure of the fluid phase is based on a slightly modified k-ε model while an algebraic particle-turbulence model is applied to the sediment phase. The numerical method is based on the modified SIMPLE scheme and an improved time stepping technique. The model is validated by the published data for the symmetrical oscillatory sheet flows generated in an oscillatory flow tunnel at the University of Tokyo and for both the symmetrical and the asymmetrical oscillatory sheet flows generated in an oscillatory flow tunnel at University of Aberdeen. The numerical results on the temporal and spacial variation of the sediment concentration, the horizontal velocities of the two phases, the horizontal and vertical fluxes of the sediment phase, as well as the thickness of the sheet flow layer all show satisfactory agreement with the laboratory data. The model is also shown to predict the net sediment transport rate with a reasonably good accuracy.

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“…Most methods are based on laboratory studies and linear wave theory (e.g. Bagnold, 1946;Manohar, 1955;Rance and Warren, 1969;Komar and Miller, 1973;Madsen and Grant, 1976;Migniot, 1977;Hammond and Collins, 1979;Rigler and Collins, 1983;White, 1989;Asano, 1990;Soulsby and Whitehouse, 1997;Dong and Zhang, 1999;Le Roux, 2001;Nielsen and Callaghan, 2003;Hassan and Ribberink, 2005;Wang, 2007) and are therefore not directly applicable to non-linear wave conditions in the field. The required horizontal semi-excursion (A δ ) or the orbital velocity at the top of the boundary layer (U δ ) can be measured in the laboratory, but has been impractical under field conditions because the thickness of the boundary layer was uncertain.…”

Section: Equations For Sediment Entrainmentmentioning

confidence: 99%

WAVECALC: an Excel-VBA spreadsheet to model the characteristics of fully developed waves and their influence on bottom sediments in different water depths

et al. 2010

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The generation and growth of waves in deep water is controlled by winds blowing over the sea surface. In fully developed sea states, where winds and waves are in equilibrium, wave parameters may be calculated directly from the wind velocity. We provide an Excel spreadsheet to compute the wave period, length, height and celerity, as well as horizontal and vertical particle velocities for any water depth, bottom slope and distance below the reference water level. The wave profile and propagation can also be visualized for any water depth, modeling the sea surface change from sinusoidal to trochoidal and finally cnoidal profiles into shallow water. Bedload entrainment is estimated under the wave crest and trough, respectively, using the horizontal water particle velocity at the top of the boundary layer.The calculations are programmed in an Excel file called WAVECALC, which is available online to authorized users. Although many of the recently published formulas are based on theoretical arguments, the values agree well with several existing theories and limited field and laboratory observations. WAVECALC is a user-friendly program intended for sedimentologists, coastal 2 engineers and oceanographers, as well as marine ecologists and biologists. It provides a rapid means to calculate many wave characteristics required in coastal and shallow marine studies and can also serve as an educational tool.

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Transport processes of uniform and mixed sands in oscillatory sheet flow

Cited by 80 publications

References 29 publications

Particle based modelling and simulation of natural sand dynamics in the wave bottom boundary layer

Particle based modelling and simulation of natural sand dynamics in the wave bottom boundary layer

A two-phase approach to wave-induced sediment transport under sheet flow conditions

WAVECALC: an Excel-VBA spreadsheet to model the characteristics of fully developed waves and their influence on bottom sediments in different water depths

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