Closed-Conduit Bed-Form Initiation and Development

Coleman, Stephen E.; Fedele, J. J.; García, Marcelo H.

doi:10.1061/(asce)0733-9429(2003)129:12(956)

Cited by 61 publications

(86 citation statements)

References 14 publications

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“…More details can be found in Coleman et al (2003). They found that the initial instabilities have a well defined wavelength, which scales with the grains diameters but not with the fluid flow.…”

Section: Comparison To Experimental Datamentioning

confidence: 99%

“…The analysis presented here is two-dimensional, which is justified by taking into consideration the Squire's Theorem for parallel flows (Drazin and Reid, 2004): the most unstable modes in parallel flows are two-dimensional.…”

Section: Linear Stability Modelmentioning

confidence: 99%

“…A granular bed is not a continuum media, limiting the definition of small perturbations (undulations) on the bed surface and the employment of a continuum spectrum of normal modes (which are the basis of linear hydrodynamic stability analysis, Drazin and Reid (2004)). This limitation can be handled by supposing that the granular bed undulations need only to be smaller than some fluid flow scales (as the flow depth or the logarithmic layer of a turbulent boundary-layer, for example), as done by many authors (Kennedy, 1963;Engelund, 1970;Richards, 1980;Elbelrhiti et al, 2005 andAndreotti, 2006).…”

Section: Linear Stability Modelmentioning

confidence: 99%

“…Their linear stability analysis was not able to explain the experimental results. Coleman et al (2003) experimentally studied the granular bed instabilities in a closed-conduit turbulent liquid flow (without freesurface effects). Their experimental test section was a 6 m long horizontal closed-conduit of rectangular cross-section (300 mm wide by 100 mm high), and they employed water as the fluid media and glass beads as the granular media.…”

Section: Comparison To Experimental Datamentioning

confidence: 99%

See 3 more Smart Citations

Initial instabilities of a granular bed sheared by a turbulent liquid flow: length-scale determination

Franklin¹

2010

J. Braz. Soc. Mech. Sci. & Eng.

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Section: Comparison To Experimental Datamentioning

confidence: 99%

Section: Linear Stability Modelmentioning

confidence: 99%

Section: Linear Stability Modelmentioning

confidence: 99%

Section: Comparison To Experimental Datamentioning

confidence: 99%

See 2 more Smart Citations

Initial instabilities of a granular bed sheared by a turbulent liquid flow: length-scale determination

Franklin¹

2010

J. Braz. Soc. Mech. Sci. & Eng.

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“…If the sand discharge is quantified by bulk volume (including both sand and intergrain voids) per unit time, the dimensions of sand flux are the square of length over time (L 2 /T), because the volume per width is measured in units of L 2 . It is known that when a bedform develops from a flat bed, the migration velocity decreases, but the size of the bedform increases asymptotically (Baas 1994;Coleman et al 2003;Perillo et al 2014). However, the actual time dependence of the sand flux has rarely been measured; this is probably due to the difficulty of doing so.…”

Section: Temporal Changes In Sand Flux Compared With Flume Experimentsmentioning

confidence: 99%

Simple stochastic cellular automaton model for starved beds and implications about formation of sand topographic features in terms of sand flux

Endo

2016

Prog. in Earth and Planet. Sci.

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A simple stochastic cellular automaton model is proposed for simulating bedload transport, especially for cases with a low transport rate and where available sediments are very sparse on substrates in a subaqueous system. Numerical simulations show that the bed type changes from sheet flow through sand patches to ripples as the amount of sand increases; this is consistent with observations in flume experiments and in the field. Without changes in external conditions, the sand flux calculated for a given amount of sand decreases over time as bedforms develop from a flat bed. This appears to be inconsistent with the general understanding that sand flux remains unchanged under the constant-fluid condition, but it is consistent with the previous experimental data. For areas of low sand abundance, the sand flux versus sand amount (flux-density relation) in the simulation shows a single peak with an abrupt decrease, followed by a long tail; this is very similar to the flux-density relation seen in automobile traffic flow. This pattern (the relation between segments of the curve and the corresponding bed states) suggests that sand sheets, sand patches, and sand ripples correspond respectively to the free-flow phase, congested phase, and jam phase of traffic flows. This implies that sand topographic features on starved beds are determined by the degree of interference between sand particles. Although the present study deals with simple cases only, this can provide a simplified but effective modeling of the more complicated sediment transport processes controlled by interference due to contact between grains, such as the pulsatory migration of grain-size bimodal mixtures with repetition of clustering and scattering.

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Bed form genesis from bed defects under unidirectional, oscillatory, and combined flows

Perillo

Prokocki

Best

et al. 2014

J. Geophys. Res. Earth Surf.

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New experimental data on bed form initiation under unidirectional, oscillatory, and combined flows are presented to gain quantitative insight into bed form genesis from artificially generated defects on a flat sediment-laden bed. Planform changes revealed in time-lapse photography allowed study of the evolution of the downstream and upstream edges of defects from their initial geometric center. Based on this temporal data set and flow velocity profiles, it was observed that combined flow bed forms share the same bed form initiation processes as unidirectional and oscillatory flows, which are reflected directly in the generation of similar geometric patterns regardless of the hydrodynamic conditions. The development of these bed defects is strongly coupled to the direction and magnitude of the shear stress applied to the bed throughout the wave cycle. Under current-dominated combined flow conditions, no defect propagation occurred in the upstream direction, despite the presence of flow reversal. In addition, spectral analysis of the evolution of the downstream and upstream edges of the defects demonstrated that (i) periodicity in the defect growth pattern scales with the wave period for pure oscillatory flows; (ii) wave-dominated combined flows possess a period-driven peak with respect to defect growth in experiments with relatively short wave periods, but this peak is absent in experiments possessing relatively long wave periods (T >15 s); and (iii) current-dominated combined flows and pure unidirectional flows do not display a period-driven peak in defect growth. These results suggest that the occurrence of long-period combined flow bed forms may be underrepresented in the sedimentary record.

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Closed-Conduit Bed-Form Initiation and Development

Cited by 61 publications

References 14 publications

Initial instabilities of a granular bed sheared by a turbulent liquid flow: length-scale determination

Initial instabilities of a granular bed sheared by a turbulent liquid flow: length-scale determination

Simple stochastic cellular automaton model for starved beds and implications about formation of sand topographic features in terms of sand flux

Bed form genesis from bed defects under unidirectional, oscillatory, and combined flows

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