Suspended sediment concentration and the ripple–dune transition

Schindler, Rob; Robert, André

doi:10.1002/hyp.1505

Cited by 21 publications

(28 citation statements)

References 26 publications

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“…The results indicate that the shape of the dunes have a major influence on the flow features, where as the effect of dune roughness is limited to the near wall region extending to a distance of about 80% of the dune height about the crest. Bennett and Best, (1996), Best (2005 a, b), Lopez et al, (2000), Robert and Uhlman (2001) and Schindler and Robert (2004) have shown that suspended sediment concentration increases with increase in scale and magnitude of turbulent structures. Schindler and Robert (2005) www.intechopen.com have concluded that the transition from 2-D to 3-D bed forms, result in increased sediment transport, increased turbulence and increased bed form migration rate.…”

Section: Effect Of Flow Depthmentioning

confidence: 98%

Bed Forms and Flow Mechanisms Associated with Dunes

Balachandar¹,

Reddy²

2011

Sediment Transport - Flow and Morphological Processes

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Section: Effect Of Flow Depthmentioning

confidence: 98%

Bed Forms and Flow Mechanisms Associated with Dunes

Balachandar¹,

Reddy²

2011

Sediment Transport - Flow and Morphological Processes

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“…The main objective of this section is to provide novel insights into the hydrodynamic processes that drive the complex morphological features we discussed in the previous section. Specifically, we seek to probe questions that have been at the centre of extensive debate in the literature, including, among other things: the linkage between coherent structures in the turbulent boundary layer and the initial bed instability (Colombini 2004;Venditti & Church 2005;Venditti et al 2006;Chou & Fringer 2010;Omidyeganeh & Piomelli 2013a,b), the role of flow separation off sand wave crestlines as a means for sand wave migration (Kostaschuk 2000;Schindler & Robert 2004;Best 2005;Colombini & Stocchino 2012) and the origin of low-frequency coherent structures rising to the water surface, also known as surface 'boils' (Jackson 1976;Yalin 1992;Venditti & Bennett 2000;Best 2005).…”

Section: Coupled Bed-flow Interactionsmentioning

confidence: 99%

Numerical simulation of sand waves in a turbulent open channel flow

2014

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We develop a coupled hydro-morphodynamic numerical model for carrying out large-eddy simulation of stratified, turbulent flow over a mobile sand bed. The method is based on the curvilinear immersed boundary approach of Khosronejad et al. (Adv. Water Resour., vol. 34, 2011, pp. 829-843). We apply this method to simulate sand wave initiation, growth and evolution in a mobile bed laboratory open channel, which was studied experimentally by Venditti & Church (J. Geophys. Res., vol. 110, 2005, F01009). We show that all the major characteristics of the computed sand waves, from the early cross-hatch and chevron patterns to fully grown three-dimensional bedforms, are in good agreement with the experimental data both qualitatively and quantitatively. Our simulations capture the measured temporal evolution of sand wave amplitude, wavelength and celerity with good accuracy and also yield three-dimensional topologies that are strikingly similar to what was observed in the laboratory. We show that near-bed sweeps are responsible for initiating the instability of the initially flat sand bed. Stratification effects, which arise due to increased concentration of suspended sediment in the flow, also become important at later stages of the bed evolution and need to be taken into account for accurate simulations. As bedforms grow in amplitude and wavelength, they give rise to energetic coherent structures in the form of horseshoe vortices, which transport low-momentum near-bed fluid and suspended sediment away from the bed, giving rise to characteristic 'boil' events at the water surface. Flow separation off the bedform crestlines is shown to trap sediment in the lee side of the crestlines, which, coupled with sediment erosion from the accelerating flow over the stoss side, provides the mechanism for continuous bedform migration and crestline rearrangement. The statistical and spectral properties of the computed sand waves are calculated and shown to be similar to what has been observed in nature and previous numerical simulations. Furthermore, and in agreement with recent experimental findings (Singh et al., Water Resour. Res., vol. 46, 2010, pp. 1-10), the spectra of the resolved velocity fluctuations above the bed exhibit a distinct spectral gap whose width increases with distance from the bed. The spectral gap delineates the spectrum of turbulence from the low-frequency range associated with very slowly evolving, albeit energetic, coherent structures induced by the migrating sand waves. Overall the numerical simulations reproduce the laboratory observations with good accuracy and elucidate the physical phenomena governing the interaction between the turbulent flow and the developing mobile bed.

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“…As the ADV cannot distinguish between a phase difference of 1818 and À1798, the velocity recorded in the ADV file will change sign, producing a dramatic spike in the velocity data (Wahl, 2000). Aliasing may be generated when the effective distance to the boundary changes during sampling (Schlinder and Robert, 2004) or when there is interference from previous pulses reflected from boundaries with irregular profiles (Dey and Barbhuiya, 2005). In our experiments, aliasing occurred when fish were very close to the sampling volume.…”

Section: U N C O R R E C T E D P R O O Fmentioning

confidence: 84%

“…Spikes, which will be eliminated, are those points outside of elliptical projection on the ellipsoid onto the three principal phase-space planes (uÀDu, DuÀD 2 u, uÀD 2 u). (3) Despiking filter has been used in different fields, such as in the study of turbulence in flumes (Biron et al, 2004;Schlinder and Robert, 2004;Dey and Barbhuiya, 2005;Scott et al, 2005) and in the measurement of turbulence in estuaries (Chanson et al, 2005). …”

Section: Data Post-processingmentioning

confidence: 99%

Study of fish swimming activity using acoustical Doppler velocimetry (ADV) techniques

Masaló

Reig

Oca

2008

Aquacultural Engineering

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The suitability of using acoustic Doppler velocimetry (ADV) to study fish swimming activity is evaluated in this study. ADV makes it possible to detect and quantify the relationship between fish density and the turbulence generated by fish swimming activity and to show differences in fish swimming patterns during the scotophase (dark period) and photophase (light period), which has been previously described by other authors. Turbulence was evaluated using the root mean square of velocity (RMS) as an indicator of fish swimming activity, and an ADV probe with an internal sampling rate of 100 Hz, which took 25 velocity data per second.Experiments at the laboratory scale using zebra fish showed a positive correlation between turbulence (RMS), caused by fish swimming activity, and density. The relationship between density and RMS was strongly linear (r 2 = 0.964). In an ongrowing farm, daily turbulence patterns caused by fish swimming activity were evaluated with sea bass at two densities: 35.5 kg m À3 (average weight of 48 g), and 11.8 kg m À3 (average weight of 11.7 g). Greater activity was detected during the photophase, indicating that light has a substantial affects sea bass swimming activity. Average RMS at a density of 35.5 kg m À3 was 3.632 and 2.428 cm s À1during photophase and scotophase, respectively, while working at a density of 11.8 kg m À3, average RMS was 1.728 and 1.419 cm s À1 during the photophase and scotophase, respectively. ADV is a rapid and reliable method to evaluate fish swimming activity at laboratory scales as well as at commercial facilities. However, ADV configuration parameters must be properly chosen in order to obtain the highest possible number of good velocity data. Data post-processing was done by filtering velocity data using correlation (COR > 70), signal-to-noise ratio (SNR > 5) and despiking filters. COR provides a measure of quality of each velocity data, ranging from 0 to 100, and SNR indicates the intensity of the reflected acoustic signal expressed in dB. Finally, despiking filter eliminates spikes generated by fish located near the probe or between the probe and point of measurement. Post-processing showed that COR filter eliminated the higher number of velocity data. #

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Suspended sediment concentration and the ripple–dune transition

Cited by 21 publications

References 26 publications

Bed Forms and Flow Mechanisms Associated with Dunes

Bed Forms and Flow Mechanisms Associated with Dunes

Numerical simulation of sand waves in a turbulent open channel flow

Study of fish swimming activity using acoustical Doppler velocimetry (ADV) techniques

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