Observations of the vertical structure of turbulent oscillatory boundary layers above fixed roughness beds using a prototype wideband coherent Doppler profiler: 1. The oscillatory component of the flow

Hay, Alex E.; Zedel, Len; Cheel, Richard; Dillon, Jeremy

doi:10.1029/2011jc007113

Cited by 19 publications

(35 citation statements)

References 42 publications

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“…The larger contribution of

\overset{true¯}{v'^{2}}

could be due to the ripples not being quite two‐dimensional. In addition, there is more noise in the horizontal velocity measurements than the vertical velocity measurements due to the transducer geometry implemented in the MFDop [ Hay et al ., ]. It is also worth noting that similar anisotropy, i.e.,

\overset{true¯}{u'^{2}} > \overset{true¯}{v'^{2}} > \overset{true¯}{w'^{2}}

, has been observed in rough turbulent boundary layers in unidirectional flow [ Raupach et al ., ].…”

Section: Resultsmentioning

confidence: 99%

“…Following Hay et al . [], only the data from cycles having a cycle‐mean correlation, at 7.3 to 9.3 cm above mean bed level, exceeding 85% were included in the phase averaging. Low correlations are due to patchiness in the lime seeding of the RippleKart tank.…”

Section: Analysis Methodsmentioning

confidence: 99%

“…The velocity of the bed relative to the stationary MFDop was determined at r b . It has been shown that

u (r_{b}, t)

is an accurate estimate of the Kart motion by independently measuring the velocity of the Kart using an in‐air acoustic travel time motion sensor and a flat reflector plate mounted to the Kart [ Hay et al ., ; Hare , ]. The best fit sinusoid to the MFDop time series (spanning all cycles) was obtained using

u (r_{b}, t) = a \sin ω_{K} t + b \cos ω_{K} t

where

ω_{K} = 2 π / T_{K}

is the angular frequency of the Kart oscillation.…”

Section: Analysis Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Observations of the space-time structure of flow, turbulence, and stress over orbital-scale ripples

Hare

Hay

Zedel

et al. 2014

J. Geophys. Res. Oceans

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The spatial and temporal structure of flow, turbulence, and stress over equilibrium orbital-scale sand ripples are investigated at turbulence-resolving scales with a wide-band coherent Doppler profiler (MFDop) and an oscillating tray apparatus. The oscillation period and horizontal excursion were 10 s and 0.5 m. A single trial was also executed at 0.6 m excursion. Ripple wavelength and amplitude were 25 and 2.2 cm. Ensemble-averaged velocity profiles were acquired with 3 mm vertical resolution at 42 Hz. The spatial pattern of flow as a function of oscillation phase was determined by combining the phase-averaged velocity measurements from trials with the MFDop at different positions relative to a particular ripple crest. The MFDop measurements are used to investigate the coevolution of the lee vortex, turbulent kinetic energy, Reynolds stress, and turbulence production as a function of phase. Shear stress is determined from the vertically integrated vorticity equation and the double-averaged momentum equations. Friction factors obtained from the two methods are comparable and range from 0.1 to 0.2.

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“…The larger contribution of

\overset{true¯}{v'^{2}}

\overset{true¯}{u'^{2}} > \overset{true¯}{v'^{2}} > \overset{true¯}{w'^{2}}

, has been observed in rough turbulent boundary layers in unidirectional flow [ Raupach et al ., ].…”

Section: Resultsmentioning

confidence: 99%

Section: Analysis Methodsmentioning

confidence: 99%

“…The velocity of the bed relative to the stationary MFDop was determined at r b . It has been shown that

u (r_{b}, t)

u (r_{b}, t) = a \sin ω_{K} t + b \cos ω_{K} t

where

ω_{K} = 2 π / T_{K}

is the angular frequency of the Kart oscillation.…”

Section: Analysis Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Observations of the space-time structure of flow, turbulence, and stress over orbital-scale ripples

Hare

Hay

Zedel

et al. 2014

J. Geophys. Res. Oceans

Self Cite

View full text Add to dashboard Cite

show abstract

“…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%

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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“…The angle at which sediment started moving α tray , and average particle velocities u were determined via video observations, and via a prototype wide-band coherent Doppler profiler (MFDop) (Hay et al, 2008(Hay et al, , 2012a. In this study, the main interest was to determine how easily the gravel and sand can be mobilized in comparison to each other, and other gravel types.…”

Section: Physical Simulation Of Sediment Remobilizationmentioning

confidence: 99%

The impact of particle shape on the angle of internal friction and the implications for sediment dynamics at a steep, mixed sand–gravel beach

et al. 2014

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Abstract. The impact of particle shape on the angle of internal friction, and the resulting impact on beach sediment dynamics, is still poorly understood. In areas characterized by sediments of specific shape, particularly non-rounded particles, this can lead to large departures from the expected sediment dynamics. The steep slope (1 : 10) of the mixed sand-gravel beach at Advocate Harbour is stable in large-scale morphology over decades, despite a high tidal range of 10 m or more, and intense shore-break action during storms. The Advocate sand (d < 2 mm) was found to have an elliptic, plate-like shape (Corey Shape Index, CSI ≈ 0.2-0.6). High angles of internal friction of this material were determined using direct shear, ranging from φ ≈ 41 to 49 • , while the round to angular gravel was characterized as φ = 33 • . The addition of 25 % of the elliptic plate-like sand-sized material to the gravel led to an immediate increase in friction angle to φ = 38 • . Furthermore, re-organization of the particles occurred during shearing, characterized by a short phase of settling and compaction, followed by a pronounced strong dilatory behavior and an accompanying strong increase of resistance to shear and, thus, shear stress. Long-term shearing (24 h) using a ring shear apparatus led to destruction of the particles without re-compaction. Finally, submerged particle mobilization was simulated using a tilted tray submerged in a waterfilled tank. Despite a smooth tray surface, particle motion was not initiated until reaching tray tilt angles of 31 • and more, being ≥ 7 • steeper than for motion initiation of the gravel mixtures. In conclusion, geotechnical laboratory experiments quantified the important impact of the elliptic, plate-like shape of Advocate Beach sand on the angles of internal friction of both pure sand and sand-gravel mixtures. The resulting effect on initiation of particle motion was confirmed in tilting tray experiments. This makes it a vivid example of how particle shape can contribute to the stabilization of the beach face.

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Observations of the vertical structure of turbulent oscillatory boundary layers above fixed roughness beds using a prototype wideband coherent Doppler profiler: 1. The oscillatory component of the flow

Cited by 19 publications

References 42 publications

Observations of the space-time structure of flow, turbulence, and stress over orbital-scale ripples

Observations of the space-time structure of flow, turbulence, and stress over orbital-scale ripples

Incipient motion of surf zone sediments

The impact of particle shape on the angle of internal friction and the implications for sediment dynamics at a steep, mixed sand–gravel beach

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