Numerical Study of Near-Bed Turbulence Structures Influence on the Initiation of Saltating Grains Movement

Bialik, Robert J.

doi:10.2478/johh-2013-0026

Cited by 17 publications

(9 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The first regime, corresponding to continuous particle motion between collisions with the bed, is superdiffusive with γ x ,γ y > 0.50, and the initiation of movement when particles are subject to acceleration takes place for tu*/d ≤ 3. This is in agreement with the threshold found by Bialik et al () through the application of a turbulent structures generator that discriminated between the near‐field and ballistic subranges (Bialik, ), and close to the threshold observed by Campagnol et al (), tu*/d = 1.5–2.5. Within this region the longitudinal diffusive scaling coefficient indicates a superballistic regime, 1.0 < γ x < 2.0, with exponents dependent on transport conditions and bed material.…”

Section: Discussion: Temporal and Spatial Scales Of Diffusive Regimessupporting

confidence: 92%

Diffusive Regimes of the Motion of Bed Load Particles in Open Channel Flows at Low Transport Stages

Cecchetto

Tregnaghi

Bottacin‐Busolin

et al. 2018

Water Resources Research

View full text Add to dashboard Cite

The stochasticity of fluid and sediment parameters has been identified as a source of diffusion, particularly anomalous diffusion at different temporal and spatial scales of bed load particle trajectories. Data from two sets of flume experiments are presented, one data set has gravel particle trajectories tracked over a limited area and was used in identifying the influence of different shear stress conditions on diffusive processes. A new experiment was performed using spherical particles moving as bed load in an annular flume in order to address concerns about censorship effects caused by the size of the detection window. An annular flume allowed collection of practically uncensored particle trajectories over longer time period than has been previously possible in the laboratory. Three diffusive regimes were observed at distinct stages of particle motion: (i) ballistic regime at the local range; (ii) Fickian diffusion at the intermediate range; (iii) subdiffusion at the global range. Characteristic time scales separate the regimes and correlate with the mean traveling and resting times of particles. Fickian diffusion in the intermediate range is first recognized as a result of the balance between intermittent weak transport and near‐bed turbulence, as first predicted by Nikora et al. (2002, https://doi.org/10.1029/2001WR000513). In the global range, extreme values were observed in the distribution of particle resting times, suggesting that two types of distributions (related to surface motion and vertical mixing) were responsible for the subdiffusion at longer time scales. Diffusion was found to be anisotropic at all stages of particle motion.

show abstract

Section: Discussion: Temporal and Spatial Scales Of Diffusive Regimessupporting

confidence: 92%

Diffusive Regimes of the Motion of Bed Load Particles in Open Channel Flows at Low Transport Stages

Cecchetto

Tregnaghi

Bottacin‐Busolin

et al. 2018

Water Resources Research

View full text Add to dashboard Cite

show abstract

“…Their impact in a particular phase of the particles' movement determines the shape of the particles' trajectory. Particularly striking is the dominant role of the sweeps events in the initial motion of the grains, which was confirmed by experimental (Cameron 2006) and numerical (Bialik 2013) studies. The negative values of the vertical velocity decrease the lift force and should thus reduce the entrainment, but the results of simulations and experiments indicate a completely different role of sweeps events.…”

Section: Initiation Of Saltating Grains Movementsupporting

confidence: 54%

“…Moreover, the results suggested that ejections have the smallest part in this process. More details on the quadrant analysis technique and the results can be found in Bialik (2013).…”

Section: Initiation Of Saltating Grains Movementmentioning

confidence: 99%

“…It seems, however, that in the case of the saltation in rivers, more important in sediment transport and the incipient motion of grains are near-bed turbulence structures, and in particular those associated with the fluctuation in streamwise velocity (e.g., Drake et al 1988;Nelson et al 1995). Bialik (2013) used the previously proposed 3D Lagrangian model of saltation (Bialik et al 2012) to analyse the influence of the near-bed turbulence structures on the motion of the saltating particles. One of the most important ingredients in this model was the generator for the flow velocity field originally proposed by Nikora et al (2001), which is based on the Monte Carlo simulation of time series of velocity fluctuation.…”

Section: Initiation Of Saltating Grains Movementmentioning

confidence: 99%

See 1 more Smart Citation

Lagrangian Modelling of Saltating Sediment Transport: A Review

Bialik

2015

GeoPlanet: Earth and Planetary Sciences

Self Cite

View full text Add to dashboard Cite

One hundred years of research on the saltation in rivers, both experimental and numerical, has allowed for a fairly good improvement of our knowledge of the physics of the saltation process. Lagrangian modelling has played a huge role in this field and has made it possible to apply the knowledge obtained in the analysis of processes associated with the movement of sediment particles. The present paper briefly reviews the current state-of-the-art of the Lagrangian modelling of saltating grains in open channels and highlights recent findings in three areas in which employment of the Lagrangian models of saltation improve our understanding of sediment transport in rivers, namely: initial motion of saltating grains, diffusion of particles and calculation of the bedload transport rate. The particular challenges in all of these research areas are discussed and future ways forward are presented.

show abstract

“…(1) is supplemented with a trajectory equation, bed-collision sub-model based on the impulse momentum equations, and a Monte-Carlo generator of flow velocity field, initially proposed in [16] and later also used to simulate saltating grains movement in a 2D model [2]. The model equations can easily be solved numerically using the fourth-order Runge-Kutta method and employing the following initial conditions [3,4]:…”

Section: Introductionmentioning

confidence: 99%

Diffusion of bedload particles in open-channel flows: distribution of travel times and second-order statistics of particle trajectories

et al. 2015

Self Cite

View full text Add to dashboard Cite

The motion of bedload particles is diffusive and occurs within at least three scale ranges: local, intermediate and global, each of which with a distinctly different diffusion regime. However, these regimes, extensions of the scale ranges and boundaries between them remain to be better defined and quantified. These issues are explored using a Lagrangian model of saltating grains over the uniform fixed bed. The model combines deterministic particle motion dynamics with stochastic characteristics such as probability distributions of step lengths and resting times. Specifically, it is proposed that a memoryless exponential distribution is an appropriate model for the distribution of rest periods while the probability that a particle stops after a current jump follows a binomial distribution, which is a distribution with lack of memory as well. These distributions are incorporated in the deterministic Lagrangian model of saltating grains and extensive numerical simulations are conducted for the identification of the diffusive behavior of particles at different time scales. Based on the simulations and physical considerations, the local, intermediate, and global scale ranges are quantified and the transitions from one range to another are studied for a spectrum of motion parameters. The obtained results demonstrate that two different time scales should be considered for parameterization of diffusive behavior within intermediate and global scale ranges and for defining the localintermediate and intermediate-global boundaries. The simulations highlight the importance of the distributions of the step lengths and resting times for the identification of the boundaries (or transition intervals) between the scale ranges.

show abstract

Numerical Study of Near-Bed Turbulence Structures Influence on the Initiation of Saltating Grains Movement

Cited by 17 publications

References 34 publications

Diffusive Regimes of the Motion of Bed Load Particles in Open Channel Flows at Low Transport Stages

Diffusive Regimes of the Motion of Bed Load Particles in Open Channel Flows at Low Transport Stages

Lagrangian Modelling of Saltating Sediment Transport: A Review

Diffusion of bedload particles in open-channel flows: distribution of travel times and second-order statistics of particle trajectories

Contact Info

Product

Resources

About