Collisional Langevin approach to bed load sediment velocity distributions

2021 ◽  
Author(s):  
Kevin Pierce ◽  
Marwan Hassan
Keyword(s):  
Velocity Distribution ◽  
Full Range ◽  
Transport Rate ◽  
Bed Load ◽  
Langevin Model ◽  
Gamma Distributions ◽  
Turbulent Drag ◽  
Langevin Approach ◽  
Particle Bed ◽  
Load Sediment

<p>Bed load experiments reveal a range of possibilities for the downstream velocity distributions of moving particles, including normal, exponential, and gamma distributions. Although bed load velocities are key for understanding fluctuations in transport rates, existing models have not accounted for the full range of observations. Here, we present a generalized Langevin model of particle transport that includes turbulent drag and episodic particle-bed collisions. By means of analytical calculations, we demonstrate that momentum dissipation by particle-bed collisions controls the form of the bed load velocity distribution. As collisions vary between elastic and inelastic, the velocity distribution interpolates between normal and exponential. These results add context to conflicting experiments on bed load velocities and suggest that granular interactions regulate sediment dynamics and transport rate fluctuations.</p>

Bed Load Transport under Complex Flow

2011 ◽  
Vol 255-260 ◽  
pp. 3589-3593
Author(s):  
Chun Rong Liu ◽  
Dao Lin Xu
Keyword(s):  
Sediment Transport ◽  
Time History ◽  
Shear Velocity ◽  
Transport Rate ◽  
Bed Load ◽  
Complex Flow ◽  
Sediment Transport Rate ◽  
Load Transport ◽  
History Of ◽  
Load Sediment

In this paper, the backward-facing step flow and the sediment transport downstream step were studied experimentally. The critical incipient bed shear velocity is obtained by the results of bed shear velocity and sediment incipient probability. It was found that the critical incipient bed shear velocity depends on the flow structures under the complex flow. By using the new critical incipient bed shear obtained in this paper and calculating the Shields parameter based on instantaneous bed shear velocity, the bed load sediment transport rate downstream step was given. The time history of the bed profile downstream step was calculated by bed load sediment transport rate and compared that obtained by the digital images. Good agreement was observed.

scholarly journals Relative Transportability for Non-uniform Bed Load Sediment Transport

2018 ◽  
Vol 153 ◽  
pp. 042006
Author(s):  
Li Zhijing ◽  
Li Dazhi ◽  
Liu Xiaobin ◽  
Jin Zhongwu ◽  
Chen Dasong
Keyword(s):  
Sediment Transport ◽  
Bed Load ◽  
Load Sediment

scholarly journals A computer model for meandering rivers with multiple bed load sediment sizes: 1. Theory

2001 ◽  
Vol 37 (8) ◽  
pp. 2227-2241 ◽  
Author(s):  
Tao Sun ◽  
Paul Meakin ◽  
Torstein Jøssang
Keyword(s):  
Computer Model ◽  
Bed Load ◽  
Meandering Rivers ◽  
Load Sediment

Numerical modelling of bed load sediment traps in sewer systems by density currents

1999 ◽  
Vol 39 (9) ◽  
pp. 153-160 ◽  
Author(s):  
F. Schmitt ◽  
V. Milisic ◽  
J.-L. Bertrand-Krajewski ◽  
D. Laplace ◽  
G. Chebbo
Keyword(s):  
Sediment Trap ◽  
Sediment Traps ◽  
Bed Load ◽  
Density Currents ◽  
Solid Concentration ◽  
Two Phase ◽  
Trap Design ◽  
Continuous Layer ◽  
Sewer Systems ◽  
Load Sediment

A model with density currents has been developed and tested to simulate bed load sediment traps. In this model, the bed load layer over the pipe invert is considered as a continuous layer characterised by a density and a viscosity which depends on the solid concentration. A set of equations has been established that describes the trapping of the bed load material as the dynamics of two non-miscible fluids over and in the bed load sediment trap. The Fluent package has been used and adapted to solve the equations of the model. The VOF method (Volume Of Fluid) has been chosen to solve the two phase approach according to a Euler-Euler scheme. Several series of simulations have been carried out in order to assess the influence of the slot position and trap design on efficiency. The results obtained agree with previous empirical findings, and allow confirmation (in a more reliable manner than before) that the best sediment trap design involves a centrally-placed slot with the two plates covering the trap reservoir placed at the same height as one another.

On the prediction of bed-load sand transport rate in air

Sedimentology ◽  
1994 ◽  
Vol 41 (6) ◽  
pp. 1241-1251 ◽  
Author(s):  
I. K. McEWAN ◽  
B. B. WILLETTS
Keyword(s):  
Transport Rate ◽  
Sand Transport ◽  
Bed Load ◽  
Sand Transport Rate

Interspike interval distributions of spiking neurons driven by fluctuating inputs

2011 ◽  
Vol 106 (1) ◽  
pp. 361-373 ◽  
Author(s):  
Srdjan Ostojic
Keyword(s):  
Coefficient Of Variation ◽  
Cortical Neurons ◽  
Interspike Interval ◽  
Full Range ◽  
Spiking Neurons ◽  
Neuron Models ◽  
Integrate And Fire ◽  
Gamma Distributions ◽  
Spiking Neuron Models ◽  
Analytical Tools

Interspike interval (ISI) distributions of cortical neurons exhibit a range of different shapes. Wide ISI distributions are believed to stem from a balance of excitatory and inhibitory inputs that leads to a strongly fluctuating total drive. An important question is whether the full range of experimentally observed ISI distributions can be reproduced by modulating this balance. To address this issue, we investigate the shape of the ISI distributions of spiking neuron models receiving fluctuating inputs. Using analytical tools to describe the ISI distribution of a leaky integrate-and-fire (LIF) neuron, we identify three key features: 1) the ISI distribution displays an exponential decay at long ISIs independently of the strength of the fluctuating input; 2) as the amplitude of the input fluctuations is increased, the ISI distribution evolves progressively between three types, a narrow distribution (suprathreshold input), an exponential with an effective refractory period (subthreshold but suprareset input), and a bursting exponential (subreset input); 3) the shape of the ISI distribution is approximately independent of the mean ISI and determined only by the coefficient of variation. Numerical simulations show that these features are not specific to the LIF model but are also present in the ISI distributions of the exponential integrate-and-fire model and a Hodgkin-Huxley-like model. Moreover, we observe that for a fixed mean and coefficient of variation of ISIs, the full ISI distributions of the three models are nearly identical. We conclude that the ISI distributions of spiking neurons in the presence of fluctuating inputs are well described by gamma distributions.

scholarly journals Evaluation of an acoustic Doppler technique for bed-load transport measurements in sand-bed Rivers

2018 ◽  
Vol 40 ◽  
pp. 02053 ◽  
Author(s):  
S. Conevski ◽  
A. Winterscheid ◽  
N. Ruther ◽  
M. Guerrero ◽  
C. Rennie
Keyword(s):  
Transport Model ◽  
Transport Rate ◽  
Qualitative Assessment ◽  
Bed Load ◽  
Apparent Velocity ◽  
Digital Cameras ◽  
Statistical Correlations ◽  
Hydraulic Conditions ◽  
Load Transport ◽  
Bed Load Transport

The bottom tracking (BT) feature of the acoustic Doppler current profilers (ADCP) have emerged as a promising technique in evaluating the bed load. Strong statistical correlations are reported between the ADCP BT velocity and the transport rate obtained by physical sampling or dune tracking; however, these relations are strictly site-specific and a local calibration is necessary. The direct physical sampling is very labor intensive and it is prone to high instrument uncertainty. The aim of this work is to develop a methodology for evaluating the bed load transport using commercial ADCPs without calibration with physical samples. Relatively long stationary measurements were performed in a sand-bed and sand gravel rivers, using three different ADCPs working at 3MHz, 1.2MHz and 0.6MHz. Simultaneously, bed load samples were collected with physical samplers, and the riverbed was closely observed with digital cameras mounted on the samplers. It is demonstrated that the kinematic transport model can yield a relatively good estimate of the transport rate by directly using filtered apparent velocity, the knowledge of the hydraulic conditions and instrument-related calibration coefficients. Additionally, the ADCP data can help in qualitative assessment of the physical sampling. Future investigation of the backscattering echo and further confirmation of the BT apparent velocity should be performed in laboratory-controlled conditions.

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