Lagrangian measurements of incipient motion in oscillatory flows

Frank, D. P.; Foster, D. L.; Sou, In Mei; Calantoni, Joseph; Chou, Pai H.

doi:10.1002/2014jc010183

Cited by 35 publications

(24 citation statements)

References 19 publications

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“…The phase lead of the near‐bed horizontal velocities relative to the free‐stream horizontal velocities within a turbulent boundary layer is expected to attenuate rather quickly with distance away from the bed. A conservative estimate of 10° was assumed for the SSG packed bed trials, based on the phase lead expected in a turbulent boundary layer typically ranging from 5° to 20° [ Davies , ; Foster et al ., ; Hay et al ., ], as well as previously calculated phase lead values with one exposed SSG [ Frank et al ., ].…”

Section: Resultsmentioning

confidence: 99%

“…A critical threshold of 0.11 was assumed for

| ϒ |

for the SSG trials based on the experiments with one exposed SSG presented in Frank et al . []. Although the combined parameter values varied between 0.1 and 0.2, they never approached 0 and are all greater than the critical threshold.…”

Section: Resultsmentioning

confidence: 99%

“…The average value for trials with one exposed SSG was also included, described in Frank et al . []. The critical thresholds for acetate beads and gravel were lower than for the SSGs, indicating sensitivity to grain diameter.…”

Section: Discussionmentioning

confidence: 97%

“…The combined effects of the shear stress and pressure gradient acting on the bed were quantified with a combined parameter [ Sleath , ; Foster et al ., ] as follows

ϒ = θ_{R 98} \frac{d_{50}}{h} + S

where

θ_{R 98}

is the Shields parameter calculated with the formulation of Ribberink [], h is the mobile bed thickness, and S is the Sleath parameter.

| ϒ | > K C_{b}

for sediment motion to occur [ Foster et al ., ; Frank et al ., ]. K is the static coefficient of friction, and C b is the volumetric sediment concentration at the bed [ Sleath , ; Foster et al ., ].…”

Section: Methodsmentioning

confidence: 99%

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Incipient motion of surf zone sediments

et al. 2015

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Incipient motion experiments were conducted with natural gravel, acetate beads, and coarsegravel-sized electronic grains called Smart Sediment Grains in a Small-Oscillatory Flow Tunnel. Measurements of fluid velocity were made using Particle Image Velocimetry. The strength of the fluid shear stresses and the pressure gradients were examined for a range of oscillatory flow conditions at the onset of motion of the sediment particles to determine which mechanism had induced particle motion. The three sediment types utilized in these experiments facilitated an assessment of the effects of sediment grain size diameter, shape, and density on incipient motion. Results suggested that the onset of sediment motion was dominated by the pressure gradients for flows with small orbital excursion amplitudes, by the shear stresses for flows with large orbital excursion amplitudes and by the combined effects for intermediate flows. The denser, angular gravel required greater free-stream accelerations to trigger sediment motion than the spherical, less dense acetate beads, and Smart Sediment Grains. A combined parameter for incipient motion that accounts for the simultaneous effects of both shear stresses and pressure gradients while depending on the static coefficient of friction and the packing concentration of the mobile bed layer was evaluated for accuracy using a range of sediment types. The results suggested that the combined parameter may be a better indicator of sediment mobilization under oscillatory flows than the typically assumed shear stress criterion.

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Section: Resultsmentioning

confidence: 99%

“…A critical threshold of 0.11 was assumed for

| ϒ |

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 97%

“…The combined effects of the shear stress and pressure gradient acting on the bed were quantified with a combined parameter [ Sleath , ; Foster et al ., ] as follows

ϒ = θ_{R 98} \frac{d_{50}}{h} + S

where

θ_{R 98}

is the Shields parameter calculated with the formulation of Ribberink [], h is the mobile bed thickness, and S is the Sleath parameter.

| ϒ | > K C_{b}

Section: Methodsmentioning

confidence: 99%

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Incipient motion of surf zone sediments

et al. 2015

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“…While these types of formulations have been found to be generally accurate in the surf zone (Deigaard et al, 1991;Soulsby et al, 1993), recent research suggests that incipient motion under some conditions may be driven by pressure gradients or a combination of pressure gradients and shear stress forcing (Sleath, 1999;Foster et al, 2006;Terrile et al, 2006;Nichols and Foster, 2009;Frank et al, 2014Frank et al, , 2015. In particular, pressure gradient forcing can become important under large accelerations, such as occur under moderately energetic waves with shorter periods (T < 5 s; Frank et al, 2015).…”

Section: Implications and General Uncertainty In Sediment Mobility Fomentioning

confidence: 99%

Nearshore dynamics of artificial sand and oil agglomerates

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Long

et al. 2015

Marine Pollution Bulletin

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Large‐eddy simulation of wave‐breaking induced turbulent coherent structures and suspended sediment transport on a barred beach

et al. 2017

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To understand the interaction between wave‐breaking induced turbulent coherent structures and suspended sediment transport, we report a Large‐Eddy Simulation (LES) study of wave‐breaking processes over a near‐prototype scale barred beach. The numerical model is implemented using the open‐source CFD toolbox, OpenFOAM®, in which the incompressible three‐dimensional filtered Navier‐Stokes equations for the water and air phases are solved with a finite volume scheme. A volume of fluid (VOF) method is used to capture the evolution of the water‐air interface. The numerical model is validated with measured free surface elevation, turbulence‐averaged flow velocity, turbulent intensity, and for the first time, the intermittency of breaking wave turbulence. Simulation results confirm that as the obliquely descending eddies (ODEs) approach the bottom, significant bottom shear stress is generated. Remarkably, the collapse of ODEs onto the bed can also cause drastic spatial and temporal changes of dynamic pressure on the bottom. By allowing sediment to be suspended from the bar crest, intermittently high sediment suspension events and their correlation with high turbulence and/or high bottom shear stress events are investigated. The simulated intermittency of sediment suspension is similar to previous field and large wave flume observations. Coherent suspension events account for only 10% of the record but account for about 50% of the sediment load. Model results suggest that about 60%∼70% of coherent bottom stress events are associated with surface‐generated turbulence. Nearly all the coherent sand suspension events are associated with coherent turbulence events due to wave‐breaking turbulence approaching the bed.

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Lagrangian measurements of incipient motion in oscillatory flows

Cited by 35 publications

References 19 publications

Incipient motion of surf zone sediments

Incipient motion of surf zone sediments

Nearshore dynamics of artificial sand and oil agglomerates

Large‐eddy simulation of wave‐breaking induced turbulent coherent structures and suspended sediment transport on a barred beach

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