Velocity measurements close to rippled beds in oscillatory flow

Abstract

The results are reported of velocity measurements in oscillatory flow over rippled beds. Velocities were measured with a laser-doppler anemometer in both an oscillating tray rig and an oscillatory flow water channel. Both self-formed and artificial ripples were examined. In addition, some measurements were made with an apparently plane bed with intense sediment motion.The experimental results were compared with the predictions of Kalkanis (1964), Kajiura (1968), Bakker (1973, 1974) and Sleath (1974). The closest agreement between theory and experiment was obtained with the method of Sleath.Measurements of the Eulerian drift velocities showed drift towards the adjacent ripple crest in the immediate vicinity of the bed and away from the crest further out.

Numerical simulation of oscillatory flows over a rippled bed by immersed boundary method

“…[ 10 ]), are positioned at the center of the seabed. The ripple which is considered as a good approximation of an actual sea ripple shape [ 3 ] is used in this work.…”

“…It is noted that the processes described above can apply to many combinations of different Reynolds number and KC number, such as ( Re , Kc ) = (20, 1), (20,2), (20,3), (20,4) Figs. 8 and 9 show, respectively, the vorticity field and streamlines at some typical moments within a half cycle.…”

“…It is noted that there are many independent length scales in the oscillatory flow over a rippled bed, and the length scale involved in the definition of flow parameters is different among researchers. In the Reynolds number, for example, the length UT / 2 π was used in [ 8 , 9 ]; Stokes layer thickness, defined as δ = √ νT /π, was used by Blondeaux and Vittori [ 10 ]; ripple wavelength λ was used by Du Toit and Sleath [ 3 ].…”

Sediment dynamics over sand ridges on a tideless mid-outer continental shelf

“…Nonetheless, besides the importance of advection processes, the bed shear stress under waves or waves and currents, playing a fundamental role in the resuspension process, is a function of the previous velocity and acceleration time history (Byatt-Smith, 1970;Liu and Orfila, 2004;Simarro et al, 2008). Second, the enormous importance of ripple bed vortex entrainment in resuspension and suspended sediment transport has widely been recognized for regular and also irregular waves (Bijker et al, 1976;Nakato et al, 1977;Nielsen, 1981;Toit and Sleath, 1981;Fredsoe et al, 1999;Thorne et al, 2003;Nichols and Foster, 2007;van der Werf et al, 2007;Davies and Thorne, 2008;Thorne et al, 2009;Murray et al, 2011). All the above-mentioned studies focus on pure wave conditions (without currents).…”

Implementation of physical boundary conditions into computational domain in modelling of oscillatory bottom boundary layers

“…Jonsson [14] reviewed experimental and analytical studies and proposed an analytical method for the solution of the equation describing rough turbulent boundary layers. Most of the models mentioned in the literature that were developed for flat bed have been discussed by Du Toit and Sleath [15]. Starting from late 1990, with the advances of more powerful computers two-equations models and higher-order turbulence models have been introduced into complex flows.…”