Laboratory Study on Sediment Diffusion and Deposition into Blind Channels

Any waterway with one end closed and the other open is generally called a blind channel. The main flow tends to expand, separate, and cause circulation at the mouth of blind channels. The main flow continuously transfers momentum and sediment into the circulation region through the turbulent mixing region (TMR) between them, thus leading to a large amount of sediment deposition in the blind channels. This paper experimentally investigated the properties of the water flow and sediment diffusion in TMR, demonstrating that both water flow and sediment motion in TMR approximately coincide with a similar structure as in the free mixing layer induced by a jet. The similarity functions of flow velocity and sediment concentration are then assumed, based on observation, and the resulting calculation of these functions is substantially facilitated. For the kind of low velocity flow system of blind channels with a finite width, a simple formula for the sediment deposition rate in blind channels is established by analyzing the gradient of crosswise velocity and sediment concentration in TMR.

Experimental Study on Flow and Sediment Movement in Cavity Circulations

This paper reports a flume experiment of flow and sediment movement in a cavity. The flow velocity, sediment concentration and the mechanism of hydraulic sorting in the circulation flow are discussed. The quantity and patterns of sediment deposition in the circulation area are studied as well.

Behaviour of a puff of resuspended sediment: a conceptual model

The particulate matter concentration above the seabed is usually assumed to decrease with height, following an exponential or Rouse profile. Many particulate matter concentration profiles with a peak were found on the North Mediterranean bottom water at a few tens of metres above the bottom. A particle size signal at the same altitude was found in this area and on the New York Eight shelf. It is assumed that this unexpected shape is due to a cloud of resuspended cohesive sediments originating from an impulse resuspension process. A simplified three-dimensional numerical model is proposed to describe the behaviour of resuspended particulate matter that originates from a sediment impulse vertically injected in the bottom water. This model reproduces the concentration profile shape observed, and it gives indications concerning the length and time characteristics of such a cloud, depending on the water velocity and bottom boundary layer properties.

Influences of the Fish-Mouth Project and the Groins on the Flow and Sediment Ratio of the Yangtze River Waterway

A depth-integrated two-dimensional numerical model of current, salinity and sediment transport was proposed and calibrated by the observation data in the Yangtze River Estuary. It was then applied to investigate the flow and sediment ratio of the navigati

Sediment incipience in turbulence generated in a square tank by a vertically oscillating grid

The failure of hydraulic structures in many estuaries and coastal regions around the world has been attributed to sediment transport and local scour. The sediment incipience in homogenous turbulence generated by oscillating grid is studied in this paper. The turbulent flow is measured by particle tracer velocimetry (PTV) technique. The integral length scale and time scale of turbulence are obtained. The turbulent flow near the wall is measured by local optical magnification. The sediment incipience is described by static theory. The relationship of probability of sediment incipience and the turbulent kinetic energy were obtained experimentally and theoretically. The distribution of the turbulent kinetic energy near the wall is found to obey the power law and the turbulent energy is further identified as the dynamic mechanism of sediment incipience.

A non-equilibrium sediment transport model for rill erosion

Sediment transport in rill flows exhibits the characteristics of non-equilibrium transport, and the sediment transport rate of rill flow gradually recovers along the flow direction by erosion. By employing the concept of partial equilibrium sediment transport from open channel hydraulics, a dynamic model of rill erosion on hillslopes was developed. In the model, a parameter, called the restoration coefficient of sediment transport capacity, was used to express the recovery process of sediment transport rate, which was analysed by dimensional analysis and determined from laboratory experimental data. The values of soil loss simulated by the model were in agreement with observed values. The model results showed that the length and gradient of the hillslope and rainfall intensity had different influences on rill erosion. Copyright (c) 2006 John Wiley & Sons, Ltd.

Vertical sediment distribution

So far, various calculation models for the vertical distribution of suspended sediment concentration have been produced by several investigators from different theories. The limitations of all these models imply that it is possible to find a more reasonable model, for which each previous model can be included as special case. The formulation of a reasonable general model is the purpose of this paper.

A New Model for Sediment Transport

The problem of predicting sediment transportation by water waves is treated analytically with the rate of wave energy dissipation or wave damping. With resorting to the theory of shallow water waves and the basis of Yamamoto’s Coulomb-damped poroelastic model, the Boussinesq-type equation has been derived over a variation depth bed. For convenience Cnoidal wave is just discussed, The Cnoidal wave with complex wave length and wave velocity, which are as a function of wave frequency, water depth, permeability, Poisson’s ratio and complex elastic moduli of bed soil, is applied to analyse the rate of sediment transportation. Considering the sediment transportation depended on the shear stress near-bed or the horizontal velocity, the conclusion of Yamamoto’s experiment in clay bed has been extended to general situation. It could be figured out that the model should provide a method to avoid the undistinguishable factors during sediment transport processes and relate mass transport with the sediment peculiarities.

Atomistic Simulation On Size-Dependent Yield Strength And Defects Evolution Of Metal Nanowires

A simple derivation based on continuum mechanics is given, which shows the surface stress is critical for yield strength at ultra-small scales. Molecular dynamics (MD) simulations with modified embedded atom method (MEAM) are employed to investigate the mechanical behaviors of single-crystalline metal nanowires under tensile loading. The calculated yield strengths increasing with the decrease of the cross-sectional area of the nanowires are in accordance with the theoretical prediction. Reorientation induced by stacking faults is observed at the nanowire edge. In addition. the mechanism of yielding is discussed in details based on the snapshots of defects evolution. The nanowires in different crystallographic orientations behave differently in stretching deformation. This study on the plastic properties of metal nanowires will be helpful to further understanding of the mechanical properties of nanomaterials. (C) 2009 Elsevier B.V. All rights reserved.

Shape effects on the yield stress and deformation of silicon nanowires: A molecular dynamics simulation

The tension and compression of single-crystalline silicon nanowires (SiNWs) with different cross-sectional shapes are studied systematically using molecular dynamics simulation. The shape effects on the yield stresses are characterized. For the same surface to volume ratio, the circular cross-sectional SiNWs are stronger than the square cross-sectional ones under tensile loading, but reverse happens in compressive loading. With the atoms colored by least-squares atomic local shear strain, the deformation processes reveal that the failure modes of incipient yielding are dependent on the loading directions. The SiNWs under tensile loading slip in {111} surfaces, while the compressive loading leads the SiNWs to slip in the {110} surfaces. The present results are expected to contribute to the design of the silicon devices in nanosystems.

Studies of ion energy and yield from argon clusters heated by intense femtosecond laser pulses

Using time-of-flight spectrometry, the interaction of intense femtosecond laser pulses with argon clusters has been studied by measuring the energy and yield of emitted ions. With two different supersonic nozzles, the dependence of average ion energy (E) over bar on cluster size (n) over bar in a large range of (n) over bar approximate to 3 x 10(3) similar to 3 x 10(6) has been measured. The experimental results indicate that when the cluster size (n) over bar <= 3 x 10(5), the average ion energy (E) over bar proportional to (n) over bar (0.5), Coulomb explosion is the dominant expansion mechanism. Beyond this size, the average ion energy gets saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic expansion behavior. We also find that with the increasing gas backing pressure, there is a maximum ion yield, the ion yield decreases as the gas backing pressure is further increased.

Effect of laser spot size on fusion neutron yield in laser-deuterium cluster interactions

The effect of the laser spot size on the neutron yield of table-top nuclear fusion from explosions of a femtosecond intense laser pulse heated deuterium clusters is investigated by using a simplified model, in which the cluster size distribution and the energy attenuation of the laser as it propagates through the cluster jet are taken into account. It has been found that there exists a proper laser spot size for the maximum fusion neutron yield for a given laser pulse and a specific deuterium gas cluster jet. The proper spot size, which is dependent on the laser parameters and the cluster jet parameters, has been calculated and compared with the available experimental data. A reasonable agreement between the calculated results and the published experimental results is found.

Two overrun phenomena and their effects on fusion yield in the Coulomb explosion of heteronuclear clusters

Two overrun effects in the Coulomb explosion dynamics of heteronuclear clusters have been investigated theoretically by the use of a simplified electrostatic model. When the charge-to-mass ratio of light ions is higher than that of heavy ions, the light ions can overtake the heavy ions inside the cluster and acquire a higher kinetic energy. Further, if the charge density of the heavy ions is twice as high as that of the light ions, i.e. a proposed competitive parameter xi = rho BqB/rho AqA > 2, the inner light ions can overtake those light ions on the surface of the cluster and form a shock shell during the explosion, which might drive the intracluster collision and fusion of the light ions. Different regimes of nuclear fusion are discussed and the corresponding neutron yields are estimated. Our analysis indicates that the probability of intracluster fusion is quite low even if deuterated heteronuclear clusters such as (DI)(n) with large size and high competitive parameter are employed. However, heteronuclear clusters are still a better candidate compared with homonuclear clusters for enhancing the total intercluster fusion yield because both a higher energy region and a higher proportion of deuterons distributing in the energy region can be created in the deuterated heteronuclear clusters.