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Jan S. Ribberink - One of the best experts on this subject based on the ideXlab platform.
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wave boundary layer hydrodynamics and Sheet Flow properties under large scale plunging type breaking waves
Journal of Geophysical Research, 2019Co-Authors: Guillaume Fromant, Tom Odonoghue, David Hurther, J Van Der Zanden, Ivan Caceres, Jan S. RibberinkAbstract:Wave boundary layer (WBL) dynamics are measured with an Acoustic Concentration and Velocity Profiler (ACVP) across the Sheet Flow-dominated wave-breaking region of regular large-scale waves breaking as a plunger over a developing breaker bar. Acoustic Sheet Flow measurements are first evaluated quantitatively in comparison to Conductivity Concentration Meter (CCM+) data used as a reference. The near-bed orbital velocity field exhibits expected behaviors in terms of wave shape, intrawave WBL thickness, and velocity phase leads. The observed fully turbulent Flow regime all across the studied wave-breaking region supports the model-predicted transformation of free-stream velocity asymmetry into near-bed velocity skewness inside the WBL. Intrawave concentration dynamics reveal the existence of a lower pickup layer and an upper Sheet Flow layer similar to skewed oscillatory Sheet Flows, and with similar characteristics in terms of erosion depth and Sheet Flow layer thickness. Compared to the shoaling region, differences in terms of Sheet Flow and hydrodynamic properties of the Flow are observed at the plunge point, attributed to the locally enhanced wave breaker turbulence. The ACVP-measured total Sheet Flow transport rate is decomposed into its current-, wave-, and turbulence-driven components. In the shoaling region, the sand transport is found to be fully dominated by the onshore skewed wave-driven component with negligible phase lag effects. In the outer surf zone, the total net flux exhibits a three-layer vertical structure typical of skewed oscillatory Sheet Flows. However, in the present experiments this structure originates from offshore-directed undertow-driven flux, rather than from phase lag effects.
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Wave Boundary Layer Hydrodynamics and Sheet Flow Properties under Large‐Scale Plunging‐Type Breaking Waves
Journal of Geophysical Research. Oceans, 2019Co-Authors: Guillaume Fromant, Dominic A. Van Der A, Tom O'donoghue, David Hurther, J Van Der Zanden, Ivan Caceres, Jan S. RibberinkAbstract:Wave boundary layer (WBL) dynamics are measured with an Acoustic Concentration and Velocity Profiler (ACVP) across the Sheet Flow-dominated wave-breaking region of regular large-scale waves breaking as a plunger over a developing breaker bar. Acoustic Sheet Flow measurements are first evaluated quantitatively in comparison to Conductivity Concentration Meter (CCM+) data used as a reference. The near-bed orbital velocity field exhibits expected behaviors in terms of wave shape, intrawave WBL thickness, and velocity phase leads. The observed fully turbulent Flow regime all across the studied wave-breaking region supports the model-predicted transformation of free-stream velocity asymmetry into near-bed velocity skewness inside the WBL. Intrawave concentration dynamics reveal the existence of a lower pickup layer and an upper Sheet Flow layer similar to skewed oscillatory Sheet Flows, and with similar characteristics in terms of erosion depth and Sheet Flow layer thickness. Compared to the shoaling region, differences in terms of Sheet Flow and hydrodynamic properties of the Flow are observed at the plunge point, attributed to the locally enhanced wave breaker turbulence. The ACVP-measured total Sheet Flow transport rate is decomposed into its current-, wave-, and turbulence-driven components. In the shoaling region, the sand transport is found to be fully dominated by the onshore skewed wave-driven component with negligible phase lag effects. In the outer surf zone, the total net flux exhibits a three-layer vertical structure typical of skewed oscillatory Sheet Flows. However, in the present experiments this structure originates from offshore-directed undertow-driven flux, rather than from phase lag effects.
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Bed level motions and Sheet Flow processes in the swash zone: observations with a new conductivity-based concentration measuring technique (CCM+)
Coastal Engineering, 2015Co-Authors: J Van Der Zanden, Ivan Caceres, José M. Alsina, René Buijsrogge, Jan S. RibberinkAbstract:Detailed measurements of bed level motions and Sheet Flow processes in the lower swash are presented. The measurements are obtained during a large-scale wave flume experiment focusing on swash zone sediment transport induced by bichromatic waves. A new instrument (CCM+) provides detailed phase-averaged measurements of Sheet Flow concentrations, particle velocities, and bed level evolution during a complete swash cycle. The bed at the lower swash location shows a clear pattern of rapid erosion during the early uprush and progressive accretion during the middle backwash phase. Sheet Flow occurs during the early uprush and mid and late backwash phases. Sheet Flow sediment fluxes during these instances are highest in the pick-up layer. Sediment entrainment from the pick-up layer occurs not only during instances of high horizontal shear velocities but also in occurrence of wave–backwash interactions. As opposed to oscillatory Sheet Flow, the pivot point elevation of the Sheet Flow layer is time-varying during a swash event. Moreover, the upper Sheet Flow layer concentrations do not mirror the concentrations in the pick-up layer. Both differences suggest that in the lower swash zone the dynamics of the upper Sheet Flow layer are not only controlled by vertical sediment exchange (such as in oscillatory Sheet Flows) but are strongly affected by horizontal advection processes induced by the non-uniformity of the Flow.
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Bed-level motions and Sheet-Flow processes in the swash zone
2015Co-Authors: J Van Der Zanden, Ivan Caceres, José M. Alsina, Jan S. RibberinkAbstract:The swash-zone is a highly dynamic area with large sediment fluxes within a shallow, transient water layer. Connecting the surf zone to the beach, the swash is a relevant area for coastal morphology. Obtaining high-quality measurements in the swash has been proven challenging. Therefore, the complex physical processes driving sediment transport in the swash are poorly understood. We present results of recent large-scale wave-flume experiments, focusing on Sheet-Flow sediment transport in the swash zone.
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Two-phase modeling of Sheet-Flow beneath waves and its dependence on grain size and streaming
Advances in Water Resources, 2014Co-Authors: Wouter Kranenburg, Tian-jian Hsu, Jan S. RibberinkAbstract:We study erosion depth and sediment fluxes for wave-induced Sheet-Flow, and their dependency on grain size and streaming. Hereto, we adopt a continuous two-phase model, applied before to simulate Sheet-Flow of medium and coarse sized sand. To make the model applicable to a wider range of sizes including fine sand, it appears necessary to adapt the turbulence closure of the model. With an adapted formulation for grain–carrier Flow turbulence interaction, good reproductions of measured erosion depth of fine, medium and coarse sized sand beds are obtained. Also concentration and velocity profiles at various phases of the wave are reproduced well by the model. Comparison of sediment flux profiles from simulations for horizontally uniform oscillatory Flow as in Flow tunnels and for horizontally non-uniform Flow as under free surface waves, shows that especially for fine sand onshore fluxes inside the Sheet-Flow layer increase under influence of progressive wave effects. This includes both the current-related and the wave-related contribution to the period-averaged Sheet-Flow sediment flux. The simulation results are consistent with trends for fine and medium sized sediment flux profiles observed from tunnel and flume experiments. This study shows that the present two-phase model is a valuable instrument for further study and parameterization of Sheet-Flow layer processes.
Daniel M Hanes - One of the best experts on this subject based on the ideXlab platform.
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Parameterization of a Two-Phase Sheet Flow Model and Application to Nearshore Morphology
2016Co-Authors: Steve Elgar, Tian-jian Hsu, Daniel M HanesAbstract:The overall objective is to develop and test with laboratory and field observations a model that predicts sediment transport and morphological change in the nearshore for a range of wave conditions and sediment characteristics. The specific objectives of this project were to 1. parameterize the wave-induced bottom stress and sediment transport rate using a two-phase Sheet Flow model, 2. couple the sediment transport model with a time-domain Boussinesq hydrodynamic model to predict beach profile evolution, and 3. improve the two-phase Sheet Flow model by comparing its predictions with laboratory and field observations of sediment transport. Work Completed 20051110 027 A small-scale two-phase model [Hsu et al. 2004] that concurrently calculates bedload and suspended load transport processes was used to parameterize sediment transport. An earlier study [Hsu and Hanes 2004] considered simple wave shapes and suggested that most transport may be in-phase with bottom stress and hence the transport rate can be parameterized by a power law. In the beginning of this project, realistic wave forcing time series measured during the Duck94 [Gallagher et al. 1998] and SwashX [Raubenheimer 2002] field experiments were utilized to drive the two-phase model and a diluted suspended load model [Hsu and Liu 2004]. The validity of the power law approach was confirmed for typical sand grain sizes (d>-0.2mm) and wave periods (T>5sec). The limitation of the power law approach due to the effect of breaking wave turbulence also was studied using field data. The power law must be accompanied with a prediction of bottom stress to obtain the transport rate. Similar to that predicted by a discrete element model [Drake and Calantoni 2001], model results tested here with realistic wave forcing also suggest that under strong pitched-forward sea-swell waves, th
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Parameterization of a Two-Phase Sheet Flow Model and Application to Nearshore Morphology
2005Co-Authors: Tian-jian Hsu, Steve Elgar, James T. Kirby, Daniel M HanesAbstract:Abstract : The overall objective is to develop and test with laboratory and field observations a model that predicts sediment transport and morphological change in the nearshore for a range of wave conditions and sediment characteristics. The specific objectives of this project were to: 1. parameterize the wave-induced bottom stress and sediment transport rate using a two-phase Sheet Flow model, 2. couple the sediment transport model with a time-domain Boussinesq hydrodynamic model to predict beach profile evolution, and 3. improve the two-phase Sheet Flow model by comparing its predictions with laboratory and field observations of sediment transport.
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Sheet Flow and suspended sediment due to wave groups in a large wave flume
Continental Shelf Research, 2005Co-Authors: Marjolein C Dohmenjanssen, Daniel M HanesAbstract:A series of sand bed experiments was carried out in the Large Wave Flume in Hannover, Germany as a component of the SISTEX99 experiment. The experiments focussed on the dynamic sediment response due to wave group forcing over a flat sand bed in order to improve understanding of cross-shore sediment transport mechanisms and determine sediment concentrations, fluxes and net transport rates under these conditions. Sediment concentrations were measured within the Sheet Flow layer (thickness in the order of 10 grain diameters) and in the suspension region (thickness in the order of centimetres). Within the Sheet Flow layer, the concentrations are highly coherent with the instantaneous near-bed velocities due to each wave within the wave group. However, in the suspension layer concentrations respond much more slowly to changes in near-bed velocity. At several centimetres above the bed, the suspended sediment concentrations vary on the time scale of the wave group, with a time delay relative to the peak wave within the wave group. The thickness of the Sheet Flow changes with time. It is strongly coherent with the wave forcing, and is not influenced by the history or sequence of the waves within the group. The velocity of the sediment was also measured within the Sheet Flow layer some of the time (during the larger wave crests of the group), and the velocity of the fluid was measured at several cm above the Sheet Flow layer. The grain velocity and concentration estimates can be combined to estimate the sediment flux. The estimates were found to be consistent with previous measurements under monochromatic waves. Under these conditions, without any significant mean current, the sediment flux within the Sheet Flow layer was found to greatly exceed the sediment flux in the suspension layer. As a result, net transport rates under wave groups are similar to those under monochromatic waves.
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effects of wave shape on Sheet Flow sediment transport
Journal of Geophysical Research, 2004Co-Authors: Daniel M Hanes, Tian-jian HsuAbstract:[1] A two-phase model is implemented to study the effects of wave shape on the transport of coarse-grained sediment in the Sheet Flow regime. The model is based on balance equations for the average mass, momentum, and fluctuation energy for both the fluid and sediment phases. Model simulations indicate that the responses of the Sheet Flow, such as the velocity profiles, the instantaneous bed shear stress, the sediment flux, and the total amount of the mobilized sediment, cannot be fully parameterized by quasi-steady free-stream velocity and may be correlated with the magnitude of local horizontal pressure gradient (or free-stream acceleration). A net sediment flux in the direction of wave advance is obtained for both skewed and saw-tooth wave shapes typical of shoaled and breaking waves. The model further suggests that at critical values of the horizontal pressure gradient, there is a failure event within the bed that mobilizes more sediment into the mobile Sheet and enhances the sediment flux. Preliminary attempts to parameterize the total bed shear stress and the total sediment flux appear promising.
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Sheet Flow dynamics under monochromatic nonbreaking waves
Journal of Geophysical Research, 2002Co-Authors: C. Marjolein Dohmen-janssen, Daniel M HanesAbstract:For the first time, detailed measurements of sediment concentrations and grain velocities inside the Sheet Flow layer under prototype surface gravity waves have been carried out in combination with measurements of suspension processes above the Sheet Flow layer. Experiments were performed in a large-scale wave flume using natural sand. Sand transport under high waves in shallow water is mainly contained within the so-called “Sheet Flow layer,” a thin layer (10–60 grain diameters) in which the volume concentration of sand decreases by an order of magnitude from a value near 0.6 at the stationary bed. The thickness of the layer varies over a wave cycle and the maximum thickness increases with increasing peak Shields stress. The concentrations within the Sheet Flow layer vary approximately synchronously with the orbital velocity measured by an Acoustic Doppler Velocimeter (ADV) located 0.1 m above the bed, with typical phase lags of 0–π/5. In contrast, the suspended sediment concentrations a few centimeters and higher above the bed exhibit larger phase lags. Grain velocities were successfully measured in the middle and upper portions of the Sheet Flow layer around the time of their maximums. These velocities increased weakly with elevation from approximately 50% to 70% of the velocity outside the wave boundary layer. The observations are compared to previous experimental work and are found to be mainly consistent with observations in steady unidirectional Flows and in oscillating water tunnels (OWTs), although differences in the suspended sediment concentration and the total sediment transport rate are apparent. Observations are also compared to two very different models: a 1DV suspension model for oscillatory Flow with enhanced boundary roughness and a two-phase collisional grain Flow model for steady unidirectional Flow. While the suspension model describes the velocity profile fairly well and the collisional model describes the concentration profile well, neither model accurately predicts both the velocity and the concentration and therefore the sediment flux over the full vertical extent of the Sheet Flow.
Julien Chauchat - One of the best experts on this subject based on the ideXlab platform.
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A two-phase model for Sheet Flow regime based on dense granular Flow rheology
Journal of Geophysical Research, 2013Co-Authors: Thibaud Revil-baudard, Julien ChauchatAbstract:A two-phase model having a μ(I) rheology for the intergranular stresses and a mixing length approach for the turbulent stresses is proposed to describe the Sheet Flow regime of sediment transport. In the model two layers are considered, a dilute suspension layer and a dense sediment bed layer. The concentration profile is obtained from the dilatancy law Φ(I) in the sediment bed layer and from a Rouse profile in the suspension layer. The comparison of velocity profile, concentration profile and macroscopic parameters (sediment flux, thickness and roughness) with experimental data shows a good agreement. These comparisons demonstrate that the dense granular rheology is relevant to describe intense bed-load transport in turbulent regime (Sheet Flow). The transition from the dense static bed to the dilute suspension is well described by the present model. Also, the different regimes of the dense granular rheology seems to be able to capture the transition between collision dominant and turbulent fluctuations dominant Sheet Flows, depending on the particles characteristic.
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A two‐phase model for Sheet Flow regime based on dense granular Flow rheology
Journal of Geophysical Research: Oceans, 2013Co-Authors: Thibaud Revil-baudard, Julien ChauchatAbstract:[1] A two-phase model having a μ(I) rheology for the intergranular stresses and a mixing length approach for the turbulent stresses is proposed to describe the Sheet Flow regime of sediment transport. In the model, two layers are considered: a dilute suspension layer and a dense sediment bed layer. The concentration profile is obtained from the dilatancy law ϕ(I) in the sediment bed layer and from a Rouse profile in the suspension layer. The comparison of velocity profile, concentration profile, and macroscopic parameters (sediment transport rate, thickness, and roughness) with experimental data shows a good agreement. These comparisons demonstrate that the dense granular rheology is relevant to describe intense bed-load transport in turbulent regime (Sheet Flow). The transition from the dense static bed to the dilute suspension is well described by the present model. Also, the different regimes of the dense granular rheology seems to be able to capture the transition between collision-dominant and turbulent-fluctuations-dominant Sheet Flows, depending on the particle's characteristics.
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a two phase model for Sheet Flow regime based on dense granular Flow rheology
Journal of Geophysical Research, 2013Co-Authors: Thibaud Revilbaudard, Julien ChauchatAbstract:[1] A two-phase model having a μ(I) rheology for the intergranular stresses and a mixing length approach for the turbulent stresses is proposed to describe the Sheet Flow regime of sediment transport. In the model, two layers are considered: a dilute suspension layer and a dense sediment bed layer. The concentration profile is obtained from the dilatancy law ϕ(I) in the sediment bed layer and from a Rouse profile in the suspension layer. The comparison of velocity profile, concentration profile, and macroscopic parameters (sediment transport rate, thickness, and roughness) with experimental data shows a good agreement. These comparisons demonstrate that the dense granular rheology is relevant to describe intense bed-load transport in turbulent regime (Sheet Flow). The transition from the dense static bed to the dilute suspension is well described by the present model. Also, the different regimes of the dense granular rheology seems to be able to capture the transition between collision-dominant and turbulent-fluctuations-dominant Sheet Flows, depending on the particle's characteristics.
Monika Nitsche - One of the best experts on this subject based on the ideXlab platform.
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The onset of chaos in vortex Sheet Flow
Journal of Fluid Mechanics, 2002Co-Authors: Robert Krasny, Monika NitscheAbstract:Regularized point-vortex simulations are presented for vortex Sheet motion in planar and axisymmetric Flow. The Sheet forms a vortex pair in the planar case and a vortex ring in the axisymmetric case. Initially the Sheet rolls up into a smooth spiral, but irregular small-scale features develop later in time: gaps and folds appear in the spiral core and a thin wake is shed behind the vortex ring. These features are due to the onset of chaos in the vortex Sheet Flow. Numerical evidence and qualitative theoretical arguments are presented to support this conclusion. Past the initial transient the Flow enters a quasi-steady state in which the vortex core undergoes a small-amplitude oscillation about a steady mean. The oscillation is a time-dependent variation in the elliptic deformation of the core vorticity contours; it is nearly time-periodic, but over long times it exhibits period-doubling and transitions between rotation and nutation. A spectral analysis is performed to determine the fundamental oscillation frequency and this is used to construct a Poincaré section of the vortex Sheet Flow. The resulting section displays the generic features of a chaotic Hamiltonian system, resonance bands and a heteroclinic tangle, and these features are well-correlated with the irregular features in the shape of the vortex Sheet. The Poincaré section also has KAM curves bounding regions of integrable dynamics in which the Sheet rolls up smoothly. The chaos seen here is induced by a self-sustained oscillation in the vortex core rather than external forcing. Several well-known vortex models are cited to justify and interpret the results.
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the onset of chaos in vortex Sheet Flow
Journal of Fluid Mechanics, 2002Co-Authors: Robert Krasny, Monika NitscheAbstract:Regularized point-vortex simulations are presented for vortex Sheet motion in planar and axisymmetric Flow. The Sheet forms a vortex pair in the planar case and a vortex ring in the axisymmetric case. Initially the Sheet rolls up into a smooth spiral, but irregular small-scale features develop later in time: gaps and folds appear in the spiral core and a thin wake is shed behind the vortex ring. These features are due to the onset of chaos in the vortex Sheet Flow. Numerical evidence and qualitative theoretical arguments are presented to support this conclusion. Past the initial transient the Flow enters a quasi-steady state in which the vortex core undergoes a small-amplitude oscillation about a steady mean. The oscillation is a time-dependent variation in the elliptic deformation of the core vorticity contours; it is nearly time-periodic, but over long times it exhibits period-doubling and transitions between rotation and nutation. A spectral analysis is performed to determine the fundamental oscillation frequency and this is used to construct a Poincar´ e section of the vortex Sheet Flow. The resulting section displays the generic features of a chaotic Hamiltonian system, resonance bands and a heteroclinic tangle, and these features are well-correlated with the irregular features in the shape of the vortex Sheet. The Poincar´ e section also has KAM curves bounding regions of integrable dynamics in which the Sheet rolls up smoothly. The chaos seen here is induced by a self-sustained oscillation in the vortex core rather than external forcing. Several well-known vortex models are cited to justify and interpret the results. Vortex Sheets are commonly used in fluid dynamics to represent thin shear layers in slightly viscous Flow (Batchelor 1967; Sa!man 1992). Here we present simulations of vortex Sheet motion in planar and axisymmetric Flow using a regularized point-vortex method. The initial condition corresponds to potential Flow past either a flat plate or a circular disk, and the Sheet rolls up to form a vortex pair in the planar case and a vortex ring in the axisymmetric case. The vortex pair is a model for the trailing wake behind an aircraft (Spalart 1998) and the vortex ring describes the starting Flow discharged from a circular tube (Shari! & Leonard 1992; Lim & Nickels 1995). The present work is concerned with the long-time dynamics of the pair/ring. Vortex Sheet simulations encounter a number of di"culties due to Kelvin‐Helmoltz instability and singularity formation (Birkho! 1961; Moore 1979; Krasny 1986). To overcome these di"culties, we represent the Sheet as a set of regularized point vortices. This approach was originally developed for vortex Sheet motion in planar Flow (Chorin & Bernard 1973; Anderson 1985; Krasny 1987) and was later extended to the case of axisymmetric Flow (Dahm, Frieler & Tryggvason 1992; Caflisch, Li & Shelley 1993).
J Van Der Zanden - One of the best experts on this subject based on the ideXlab platform.
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wave boundary layer hydrodynamics and Sheet Flow properties under large scale plunging type breaking waves
Journal of Geophysical Research, 2019Co-Authors: Guillaume Fromant, Tom Odonoghue, David Hurther, J Van Der Zanden, Ivan Caceres, Jan S. RibberinkAbstract:Wave boundary layer (WBL) dynamics are measured with an Acoustic Concentration and Velocity Profiler (ACVP) across the Sheet Flow-dominated wave-breaking region of regular large-scale waves breaking as a plunger over a developing breaker bar. Acoustic Sheet Flow measurements are first evaluated quantitatively in comparison to Conductivity Concentration Meter (CCM+) data used as a reference. The near-bed orbital velocity field exhibits expected behaviors in terms of wave shape, intrawave WBL thickness, and velocity phase leads. The observed fully turbulent Flow regime all across the studied wave-breaking region supports the model-predicted transformation of free-stream velocity asymmetry into near-bed velocity skewness inside the WBL. Intrawave concentration dynamics reveal the existence of a lower pickup layer and an upper Sheet Flow layer similar to skewed oscillatory Sheet Flows, and with similar characteristics in terms of erosion depth and Sheet Flow layer thickness. Compared to the shoaling region, differences in terms of Sheet Flow and hydrodynamic properties of the Flow are observed at the plunge point, attributed to the locally enhanced wave breaker turbulence. The ACVP-measured total Sheet Flow transport rate is decomposed into its current-, wave-, and turbulence-driven components. In the shoaling region, the sand transport is found to be fully dominated by the onshore skewed wave-driven component with negligible phase lag effects. In the outer surf zone, the total net flux exhibits a three-layer vertical structure typical of skewed oscillatory Sheet Flows. However, in the present experiments this structure originates from offshore-directed undertow-driven flux, rather than from phase lag effects.
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Wave Boundary Layer Hydrodynamics and Sheet Flow Properties under Large‐Scale Plunging‐Type Breaking Waves
Journal of Geophysical Research. Oceans, 2019Co-Authors: Guillaume Fromant, Dominic A. Van Der A, Tom O'donoghue, David Hurther, J Van Der Zanden, Ivan Caceres, Jan S. RibberinkAbstract:Wave boundary layer (WBL) dynamics are measured with an Acoustic Concentration and Velocity Profiler (ACVP) across the Sheet Flow-dominated wave-breaking region of regular large-scale waves breaking as a plunger over a developing breaker bar. Acoustic Sheet Flow measurements are first evaluated quantitatively in comparison to Conductivity Concentration Meter (CCM+) data used as a reference. The near-bed orbital velocity field exhibits expected behaviors in terms of wave shape, intrawave WBL thickness, and velocity phase leads. The observed fully turbulent Flow regime all across the studied wave-breaking region supports the model-predicted transformation of free-stream velocity asymmetry into near-bed velocity skewness inside the WBL. Intrawave concentration dynamics reveal the existence of a lower pickup layer and an upper Sheet Flow layer similar to skewed oscillatory Sheet Flows, and with similar characteristics in terms of erosion depth and Sheet Flow layer thickness. Compared to the shoaling region, differences in terms of Sheet Flow and hydrodynamic properties of the Flow are observed at the plunge point, attributed to the locally enhanced wave breaker turbulence. The ACVP-measured total Sheet Flow transport rate is decomposed into its current-, wave-, and turbulence-driven components. In the shoaling region, the sand transport is found to be fully dominated by the onshore skewed wave-driven component with negligible phase lag effects. In the outer surf zone, the total net flux exhibits a three-layer vertical structure typical of skewed oscillatory Sheet Flows. However, in the present experiments this structure originates from offshore-directed undertow-driven flux, rather than from phase lag effects.
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Bed level motions and Sheet Flow processes in the swash zone: observations with a new conductivity-based concentration measuring technique (CCM+)
Coastal Engineering, 2015Co-Authors: J Van Der Zanden, Ivan Caceres, José M. Alsina, René Buijsrogge, Jan S. RibberinkAbstract:Detailed measurements of bed level motions and Sheet Flow processes in the lower swash are presented. The measurements are obtained during a large-scale wave flume experiment focusing on swash zone sediment transport induced by bichromatic waves. A new instrument (CCM+) provides detailed phase-averaged measurements of Sheet Flow concentrations, particle velocities, and bed level evolution during a complete swash cycle. The bed at the lower swash location shows a clear pattern of rapid erosion during the early uprush and progressive accretion during the middle backwash phase. Sheet Flow occurs during the early uprush and mid and late backwash phases. Sheet Flow sediment fluxes during these instances are highest in the pick-up layer. Sediment entrainment from the pick-up layer occurs not only during instances of high horizontal shear velocities but also in occurrence of wave–backwash interactions. As opposed to oscillatory Sheet Flow, the pivot point elevation of the Sheet Flow layer is time-varying during a swash event. Moreover, the upper Sheet Flow layer concentrations do not mirror the concentrations in the pick-up layer. Both differences suggest that in the lower swash zone the dynamics of the upper Sheet Flow layer are not only controlled by vertical sediment exchange (such as in oscillatory Sheet Flows) but are strongly affected by horizontal advection processes induced by the non-uniformity of the Flow.
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Bed-level motions and Sheet-Flow processes in the swash zone
2015Co-Authors: J Van Der Zanden, Ivan Caceres, José M. Alsina, Jan S. RibberinkAbstract:The swash-zone is a highly dynamic area with large sediment fluxes within a shallow, transient water layer. Connecting the surf zone to the beach, the swash is a relevant area for coastal morphology. Obtaining high-quality measurements in the swash has been proven challenging. Therefore, the complex physical processes driving sediment transport in the swash are poorly understood. We present results of recent large-scale wave-flume experiments, focusing on Sheet-Flow sediment transport in the swash zone.
