Movement Of Sand Particles Research Articles

Numerical Solution of Fence Performance for Reduction of Sand Deposition on Railway Tracks

Movement of sand particles in nature creates many problems for humans. One of these problems is deposition of particles on rails that decreases the speed of the train or in some cases hampers the reversal of the train rails. In this paper, the motion of sand particles over railway track embankment, and how these particles settle on railway tracks are investigated. Moreover, the performance of different fences of different heights and distances has been compared. It can be stated that particles velocity is highest on the embankment slope and up to the fence and lowest around the fence. Most of the particles deposition is on the slopes or near the embankment. Fences with different heights, distances (from the railway's longitudinal axis), and porosities are compared. Using the appropriate fence depends on the geographic and environmental factors, but in general the use of a fence with a height of 1 meter positioned at distance of 3 meters from the railway's longitudinal axis, and with 20% porosity is recommended.

Turbulence burst over four micro-topographies in the wind tunnel

Investigating the mechanisms of wind-sand movement is essential to deeply understand sand storm and desertification process, and further to control the wind-sand hazards. It is considered that turbulence burst may have great influence on the motion of sand particles. But current theoretical and experimental studies mostly concentrate on the turbulence burst over flat surface or in the water. Sand dunes and sand ripples are basic forms of desert landscape, and the slope gradient will inevitably affect the frequency of turbulence burst. In this paper, instantaneous velocities over 4 different sand surfaces, including smooth flat bed, flat sand bed, sand bed with ripples and slope bed, are measured using one-dimensional hot wire detector. The results show that for the slope sand surface, wind field in leeward slope region is a buffering zone, which doesn't obey logarithmic function. On the flat sand surface, the distribution of turbulence intensity and Reynolds normal stress are gradually decreasing along the height of boundary layer. On the slope sand surface, the stronger turbulence behavior happens near the top of slope. Based on Mu-level method analysis, it is found that the turbulence bursts on both flat sand surface and sand ripples mainly occur near the surface, and gradually decrease with the height. Compared to flat sand surface, the burst frequency is 30%~50% higher on the sand ripples surface, which indicates that micro-topography have an influence on the turbulence burst. This work may be helpful in understanding the initiation and transportation of sand storm, as well as the desertification process.

318 転動する車輪下における砂粒軌跡の再現性について(機素潤滑設計III)

318 転動する車輪下における砂粒軌跡の再現性について(機素潤滑設計III)

Sand particle dislodgement in windblown sand

The incipient motion of sand particle from sand bed plays a very important role in the prediction of windblown sand. In this paper, we proposed a new method for predicting the incipient motion of sand particle based on wind speed fluctuation as follows, when the wind speed is larger than the critical wind speed, if the total impulse on sand particle is larger than the critical impulse, incipient motion of sand particle would take place, otherwise if not. Furthermore, from the analysis of entrainment in the rolling and lifting modes, we come to the following conclusion. When the average wind speed is smaller than the critical wind speed, if the average wind speed is used to judge the incipient motion of sand particle, one will underestimate the number of sand particles jumping from the bed, if the instantaneous wind speed is used to judge incipient motion of sand particle, one will overestimate the number of sand particles jumping from the bed; When the average wind speed is larger than the critical wind speed, either the average or the instantaneous wind speeds is used to judge the incipient motion of sand particles, one will overestimate the number of sand particles jumping from the bed.

Spray drag effect of fluidized sand for a supersonic vehicle

This paper deals with fluidized sand simulation in order to estimate the impact of sand particle motion on the BLOODHOUND SuperSonic Car (SSC) drag forces, such phenomenon is known as a spray drag effect. A gas-particle model is used to simulate the sand particles that rise from the ground because of the strong shockwave-desert surface interaction. A finite volume scheme is used to discretise the continuous model with a special treatment of the solid phase equations. An indefinitely differentiable and anisotropic limiter to reinforce the method stability and reduce any excessive smearing is applied. To estimate the area where sand particles are detached from the ground, a criterion based on pressure change is proposed. The model is first validated on ac urved 90 � bend test case with comparison to experimental results and then applied to the supersonic car.

Image-Segmentation Technique to Analyze Deformation Profiles in Different Direct Shear Tests

Abstract Results from interface shear tests on sand–geosynthetic interfaces are examined in light of surface roughness of the interacting geosynthetic material. Three different types of interface shear tests carried out in the frame of direct shear-test setup are compared to understand the effect of parameters like box fixity and symmetry on the interface shear characteristics. Formation of shear bands close to the interface is visualized in the tests and the bands are analyzed using image-segmentation techniques in MATLAB. A woven geotextile with moderate roughness and a geomembrane with minimal roughness are used in the tests. The effect of surface roughness of the geosynthetic material on the formation of shear bands, movement of sand particles, and interface shear parameters are studied and compared through visual observations, image analyses, and image-segmentation techniques.

Analysis of sand particles’ lift-off and incident velocities in wind-blown sand flux

In the research of windblown sand movement, the lift-off and incident velocities of saltating sand particles play a significant role in bridging the spatial and temporal scales from single sand particle’s motion to windblown sand flux. In this paper, we achieved wind tunnel measurements of the movement of sand particles near sand bed through improving the wind tunnel experimental scheme of particle image velocimetry (PIV) and data processing method. And then the influence of observation height on the probability distributions of lift-off and incident velocities of sand particles was analyzed. The results demonstrate that the observation height has no obvious influence on the distribution pattern of the lift-off and incident velocities of sand particles, i.e., the probability distribution of horizontal and vertical velocities of lift-off and incident sand particles follow a Gaussian distribution and a negative exponential distribution, respectively. However, it influences the center of the Gaussian distribution, the decay constant and the amplitude of the negative exponential distribution.

Experimental and theoretical study of the trajectories of saltating sand particles over desert areas

Transport of sand particles over desert areas in the lower saltation layer is studied experimentally and theoretically. The trajectories of saltating sand particles are reconstructed by means of high-speed video recording. An instantaneous concentration profile of saltating sand in a layer from 0 to 40 mm is presented. A numerical model of sand particle movement in the surface air layer is developed. The influence of the model parameters on the saltating sand trajectories is analyzed. A method for solution of the inverse problem of saltating sand dynamics is proposed. The reconstruction of dynamic parameters of the problem from saltating sand trajectories is presented. It is found that some turbulent parameters can be estimated from the trajectory measurement data.

A new statistical model for threshold friction velocity of sand particle motion

A theoretical formulation of threshold friction velocity of sand particles is established by considering the equilibrium of moment forces acting on an irregular particle following Bagnold's scheme. Owing to the statistical nature of the microstructure of soil surface, of the particle shape and of positions in the bed, the threshold friction velocity is random. Based on the probability theory of multi-dimension random variable, the probability of the threshold friction velocity, its mean value and standard deviation are calculated. The mean value and standard deviation are fitted as functions of sand particle's diameter. A formula of ‘wet’ threshold friction velocity is also given.

Measurement and simulation of sand saltation movement under fluctuating wind in a natural field environment

Extensive research on the near surface movement of sand particles has focused on wind tunnel experiments, theoretical analysis, and numerical simulation of sand saltation under ideal and controllable conditions. Most field observations are results on the average rate of sand transport over some hours or the whole day. However, researchers found recently that the effect of turbulent characteristics of near surface wind in real atmospheric boundary layers on the sand transport rate was obvious. The turbulent characteristics would cause a significant discrepancy between field observation and simulation of sand transport rate. In this work, a field experiment in a real-time system was designed to synchronously measure physical quantities, such as fluctuating wind velocity in the near surface region, sand transport intensity, temperature, and humidity, with the frequency of 1 Hz, at two points on a homogeneous flat sand surface located in the Minqin area, which is between the edges of the Badain Jaran Desert and the Tengger Desert. The relationship between the saltation events and some physical properties, such as the fluctuating wind velocity, temperature, and humidity, was studied. On the basis of the field observation results, a numerical model was developed to simulate sand movement under the fluctuating wind. The overall features of the experimental measurements were reproduced by simulation.

The effects of atmospheric stability intensity on the movement of windblown sand

Using a model that couples wind flow with the motion of sand particles under different atmospheric stability intensities, this paper studied the effects of atmospheric stability on the trajectory and velocity of sand particles in the saltation layer, and the duration before a steady state was achieved. The vertical velocity, horizontal distance, and the maximum height of saltating sand particles increased with increasingly negative stability intensity under unstable conditions. The wind–sand flow reached equilibrium more quickly with increasingly negative stability intensity under unstable conditions, but reached equilibrium more slowly with increasing stability intensity under stable conditions.

Effect of velocity hiatuses in oscillatory flow on migration and geometry of ripples: wave-flume experiments

A series of wave-flume experiments was conducted to closely look at characteristics of geometry and migration of wave-generated ripples, with particular reference to the effect of velocity ‘hiatuses’ during which the near-bed flow velocity becomes much smaller than the threshold of sediment movement. Three types of wave patterns were generated: two types for simulating waves with intervening velocity hiatuses; and regular waves for comparison purposes. In the former two types, two different wavelengths of water waves were generated alternately in the course of a wave test: the wave with a longer wavelength was set large enough to mobilize the bottom sediment, whereas the wave with a shorter wavelength was set too small to mobilize the sediment. The former two types were designed to be different in sequence of convexity and concavity of wave patterns. The sequence with the convex–concave longer wave and successive convex–concave shorter wave was described as a ‘zero-up-crossing’ wave pattern, and the inverse sequence was described as a ‘zero-down-crossing’ wave pattern. The ripples developed under oscillatory flow with intervening hiatuses manifested the following characteristics in geometry and migration. (i) The morphological characteristics of ripples, namely wavelength, height and the ripple steepness, are unaffected by the intervening hiatuses of velocity. (ii) The directions of ripple migration under the zero-up-crossing and zero-down-crossing wave patterns corresponded well with the directions of the flow immediately before onset of the hiatuses. (iii) The observation of sand particle movement on the ripple surface indicated that, under the zero-up-crossing waves, the velocity hiatus prevents the entrained sediment cloud from being thrown onshore, and thus the sediment grains thrown onshore are fewer than those thrown offshore. As a result of the sediment movement over one wave-cycle, the net sediment transport is directed offshore under the zero-up-crossing wave pattern. (iv) The velocity of ripple migration was highly correlated with acceleration skewness. Under most of the zero-up-crossing (zero-down-crossing) wave patterns, flow acceleration skewed negative (positive) and ripples migrated offshore (onshore).

Application of Rouse Concentration Profile to Aeolian Sand Transport

This study demonstrated applicability of Rouse concentration profile in suspension for fluvial sand transport to aeolian sand transport in order to investigate universal system for the sand transports in water and air and to obtain knowledge of vertical profile of aeolian sand transport flux. Comparison of the Rouse concentration profile and wind-tunnel experimental results indicated that the Rouse concentration profiles underestimated the experimental results when the mode of sand particle motion was classified into saltation by Rouse number; however, the Rouse profiles agreed with the experimental results when the mode was suspension during strong wind conditions. It is revealed that the aeolian sand is transported in suspension during strong wind events and the Rouse profile can be applied to the aeolian sand transport.

Saltation and suspension of wind-blown particle movement

Several factors that affect the trajectories of sand particles in a wind-blown sand flux are analyzed by considering the stochastic movement of sand particles transported within turbulent flow in the atmospheric boundary layer. The results show that there are remarkably different trajectories for particles with the same diameter, the same vertical liftoff velocity from sand bed and the same friction velocity of wind because of the presence of turbulence flow. The vertical fluctuating velocity of sand particles can be regarded as a reflection of the transport mode, which is related to not only the diameters and liftoff velocity of sand particles but also the shear stress velocity of wind. The critical liftoff velocity and the fraction of each transport mode are calculated for the given particle diameter and friction velocity of wind. A comparison of the predicted fraction and the statistical fraction with and without the wind-sand couple effect is made.

The dependency of sand transport rate by wind on the atmospheric stability: A numerical simulation

A theoretical model of the process for wind–sand flow is developed through consideration of the coupling between wind flow and the motion of sand particles under different atmospheric stability conditions. Using this model, we studied the effects of atmospheric stability on the sand transport rate, the number of sand particles per unit area and time, and the duration before a steady state is achieved in detail. The results show that atmospheric stability has a strong effect on the movement of the wind–sand flow, and produces results with different characteristics from those previously reported in the literature which apply only to conditions of neutral stability. Under unstable conditions, the wind–sand flow reached equilibrium more quickly, with a higher total sand flux and sand flux at all heights than under neutral or stable conditions.

Experimental Study of Fine Sand Particle Settling in Turbulent Open Channel Flows over Rough Porous Beds

Results are presented from laboratory studies investigating the behavior of fine sand particles within turbulent open channel flow conditions flowing over rough, porous beds. A particle tracking technique was employed to record and analyze sand particle motion within the flow, while mean and fluctuating flow velocities were measured by an acoustic Doppler velocimeter probe. Measured particle settling rates show a strong influence from flow turbulence, being generally enhanced in the near-bed and intermediate flow regions and retarded in the outer flow region, compared to their fall velocity in still water conditions. Experiments also reveal the relative degree of settling enhancement to increase with decreasing particle size. Correlation between particle and small-scale fluid motions is demonstrated through a quadrant analysis technique, with higher-order events for the two phases found to be dominated by ejections and sweeps associated with the bursting process. Particle interactions with large-scale turbulent flow structures, revealed through flow visualization with a moving frame of reference, are found to result in particle accumulation in peripheral trajectories on the downflow side of local eddy structures. Analytical and theoretical considerations suggest that both these turbulence scales provide preferential transportation mechanisms that will account for the enhanced sand particle settling rates observed.

Visualization of saltating sand particle movement near a flat ground surface

Movement of natural sand particles (d=200-300 μm) in a simulated atmospheric boundary layer was visualized using a digital high-speed camera. The consecutive particle images recorded at 2000 fps (frame per second) enabled us to observe the particle transport in detail, especially near the flat sand surface. Various modes of sand saltation were identified. The transverse motion of particles, often ignored in previous studies, was also visualized. In addition, instantaneous velocity fields of saltating particles were obtained using a particle tracking velocimetry (PTV), and statistical analysis of saltating particle trajectories was performed. The qualitative and quantitative results of the present study will be useful for understanding the basic physics of transport of saltating sand particles.

RETRACTION: Numerical simulation of a wind-sand flow under different conditions of atmospheric stability

A theoretical model for wind-sand flow is developed by considering the coupling between wind flow and sand particle motion, the latter subject to the Magnus effect, under different atmospheric stability conditions. Using this model, the characteristics of the wind-sand flow are discussed in detail. The results show that the atmospheric stability and the Magnus effect both have a strong influence on wind profiles and on the trajectories of sand particles. This approach produces results with characteristics that differ from those previously reported; the latter only applying to atmospheric conditions of neutral stability. The saltating sand reaches a greater height under non-neutral stability than under neutral stability, while the maximum horizontal distance is greater under unstable conditions and is smaller under stable conditions than under conditions of neutral stability.

Next-Generation Expandable-Completion Systems

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 97281, "Next-Generation Expandable-Completion Systems," by Gareth Innes, SPE, Quentin Morgan, SPE, Ally Macarthur, SPE, and Annabel Green, SPE, Weatherford, prepared for the 2005 SPE/IADC Middle East Drilling Technology Conference and Exhibition, Dubai, UAE, 12–14 September. In many cases, openhole completions could provide maximum well productivity. However, use of the method has been impeded by the inability to achieve effective zonal isolation. An expandable completion that combines slotted- and solid-expandable technology and uses conventional unexpanded premium connections can deliver freely configurable completion architecture. Introduction Expandable sand screens provide direct contact of the screen with the formation as a means of reducing completion skin and improving sand-retention characteristics. The base technology is being integrated with new and conventional downhole technologies to enable multizone completions. A common conventional approach used to complete and commingle multizone unconsolidated reservoirs has been to, first, set and cement casing in the wellbore to isolate zones. The zones of interest then would be perforated before installation of a screen and placing gravel to control solids migration. This cased-hole sand-control technique has worked reasonably well but has a history of high completion skins. Also, the resulting smaller inside diameter makes the subsequent design and installation of selective-production upper-completion strings difficult, limiting the overall achievable functionality. In many cases, emulating an openhole high-deviation or horizontal completion strategy can increase well productivity. To enable these productivity gains and facilitate selective production handling, zonal-isolation technologies were combined with compliantly expanded screens to create a sandface completion with cased-hole functionality. Zonal-isolation technologies that satisfy functionality and expandable performance criteria include swelling elastomers and solid expandables. Expandable-Completion Development An expandable screen comprises three sandwiched layers: the base pipe, filter media, and outer protective shroud. The base pipe is slotted, as is the outer shroud. These slots open during expansion to accommodate the change in diameter, while overlapped layers of filter media slide across each other to maintain sand-retention integrity. The use of slots allows expansion ratios up to 80% greater than the original diameter. The entire length of the original design was expanded, including the connectors. The original expandable screen was designed for use in single-zone openhole applications. Large exposed filter area and variable borehole contact (known as compliant expansion) provide gravel-pack functionality. The design premise was that a compliantly expanded filter that could eliminate as much of the annular gap as practicable would promote rapid formation stabilization and minimize the movement of sand particles around the screen during the transient sand-production period. The large, directly exposed filter surface was designed to minimize pressure drops in the screen and sandpack composite caused by mud particles and formation fines.

1610 水平気流中の自然砂粒子の運動と風紋形成について

1610 水平気流中の自然砂粒子の運動と風紋形成について