Vertical Variations of Fluid Velocities and Shear Stress in Surf Zones

Cox, Daniel T.; Kobayashi, Nobuhisa; Okayasu, Akio

doi:10.1061/9780784400890.009

Cited by 25 publications

(38 citation statements)

References 8 publications

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“…Also shown in Figure 8 are measurements of turbulent kinetic energy by Ting and Kirby [1994] and Cox et al [1994], which are very similar to measurements at stations 2 and 3 presented here. Figures 9, 10, and 11 show the resulting length scales at stations 1, 2, and 3, respectively.…”

Section: Resultssupporting

confidence: 66%

Dissipation of isotropic turbulence and length‐scale measurements through the wave roller in laboratory spilling waves

Govender

Mocke²,

Alport

2004

J. Geophys. Res.

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[1] The measurement of turbulence dissipation rates and length scales associated with three-dimensional isotropic structures under spilling waves breaking in a laboratory surf zone is presented. Dissipation rates were estimated from the spectral characteristics of the turbulence velocities in the inertial subrange, and length scales were estimated using measurements of the turbulent kinetic energy and dissipation rate. The spatial velocity flow fields for the above analysis were measured using digital correlation image velocimetry. A unique set of measurements that spans the entire water column, including the aerated portion near the crest of the wave, is presented. Dissipation rates were found to reach a maximum above the effective trough level, with over 80% of the depth integrated dissipation occurring in this upper zone. The total depth integrated turbulence dissipation rate is found to be up to an order of magnitude smaller than the local rate of wave energy dissipation due to breaking, the primary turbulence production source. The length scale is found to increase in magnitude below the surface, consistent with the idea that turbulence production occurs above the trough level in the vicinity of the wave roller and is transported downward toward the bed.INDEX TERMS: 4546 Oceanography: Physical: Nearshore processes; 4568 Oceanography: Physical: Turbulence, diffusion, and mixing processes; 4558 Oceanography: Physical: Sediment transport; KEYWORDS: digital correlation image velocimetry, dissipation rates, length scales, turbulent kinetic energy, wave breaking, surf zone Citation: Govender, K., G. P. Mocke, and M. J. Alport (2004), Dissipation of isotropic turbulence and length-scale measurements through the wave roller in laboratory spilling waves,

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Section: Resultssupporting

confidence: 66%

Dissipation of isotropic turbulence and length‐scale measurements through the wave roller in laboratory spilling waves

Govender

Mocke²,

Alport

2004

J. Geophys. Res.

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“…where P is the production rate of k, (b'w') is the destruction rate of k due to the negative buoyancy fluctuation b' due to suspended sediment, and e is the dissipation rate of k. The temporal change, advection, and diffusion of k may be neglected relative to P and e in (4) on the basis of the order-ofmagnitude analysis of turbulence measured below the breaking wave trough by Cox et al [1994] for the case of no sediment. These neglected terms in (4) are more difficult to parameterize than those retained in (4).…”

Section: Sediment Continuity Equationmentioning

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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“…According to Cox et al (1994), the length scale increases from the outer to the inner surf zone (in the lab), being in the range 0.04-0.18h. Higher values can be reached in the field, up to 0.43h in the swash zone (Flick and George, 1990); further field experiments revealed a length scale of 0.58h in the inner surf zone (Rodriguez et al, 1999).…”

Section: Turbulence Scalesmentioning

confidence: 99%

“…Laser Doppler Velocimetry is widely used, with several limitations in the aerated region due to bubble presence (Nadaoka and Kondoh, 1982;Cox et al, 1994;Losada et al, 2000).…”

Section: Measurements Techniques In the Surf And Swash Areamentioning

confidence: 99%

Turbulence in the swash and surf zones: a review

Longo

Petti

Losada

2002

Coastal Engineering

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This paper reviews mainly conceptual models and experimental work, in the field and in the laboratory, dedicated during the last decades to studying turbulence of breaking waves and bores moving in very shallow water and in the swash zone. The phenomena associated with vorticity and turbulence structures measured are summarised, including the measurement techniques and the laboratory generation of breaking waves or of flow fields sharing several characteristics with breaking waves. The effect of air entrapment during breaking is discussed. The limits of the present knowledge, especially in modelling a two-or three-phase system, with air and sediment entrapped at high turbulence level, and perspectives of future research are discussed. D

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Vertical Variations of Fluid Velocities and Shear Stress in Surf Zones

Cited by 25 publications

References 8 publications

Dissipation of isotropic turbulence and length‐scale measurements through the wave roller in laboratory spilling waves

Dissipation of isotropic turbulence and length‐scale measurements through the wave roller in laboratory spilling waves

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

Turbulence in the swash and surf zones: a review

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