Image-Aided Analysis of Ballast Particle Movement Along a High-Speed Railway

As a core infrastructure of high-speed railways,ballast layers constituted by graded crushed stones feature noteworthy particle movement compared with normal railways,which may cause excessive settlement and have detrimental effects on train operation.However,the movement behavior remains ambiguous due to a lack of effective measurement approaches and analytical methods.In this study,an image-aided technique was developed in a full-scale model test using digital cameras and a colorbased identification approach.A total of 1274 surface ballast particles were manually dyed by discernible colors to serve as tracers in the test.The movements of the surface ballast particles were tracked using the varied pixels displaying tracers in the photos that were intermittently taken during the test in the perpendicular direction.The movement behavior of ballast particles under different combinations of train speeds and axle loads was quantitatively evaluated.The obtained results indicated that the surface ballast particle movements were slight,mainly concentrated near sleepers under low-speed train loads and greatly amplified and extended to the whole surface when the train speed reached 360 km.h-1.Additionally,the development of ballast particle displacement statistically resembled its rotation.Track vibration contributed to the movements of ballast particles,which specifically were driven by vertical acceleration near the track center and horizontal acceleration at the track edge.Furthermore,the development trends of ballast particle movements and track settlement under long-term train loading were similar,and both stabilized at nearly the same time.The track performance,including the vibration characteristics,accumulated settlement,and sleeper support stiffness,was determined to be closely related to the direction and distribution of ballast particle flow,which partly deteriorated under high-speed train loads.

Physical Simulation of Nonmetallic Particle Movement in Al Melt under Electromagnetic Field

Physical simulation is used to study the movement of nonmetallic particles in Al melt in electro- magnetic field. It is found that the terminal velocity of particles in different Reynolds number range has different functions. By confirming drag force coefficient of nonmetallic particles with Reynolds number in the range of 0.2-10 and 10-25 respectively, two functions of terminal ve- locity for spherical nonmetallic particles have been got accordingly, which provide a theoretical basis for separating nonmetallic inclusions from Al melt in electromagnetic field.

Experimental study and numerical simulation of gas/particle flow in tunneling of mine

Respiration particles can be collected into a dust catcher by an inside inhalingand outside pressing particle collector. The work environment of the grab operator in tunneling mining was improved when a dust catcher is placed before the working face of thegrab operator. The particle movement was affected by the gas flow. The flow field insideand outside the dust collector was simulated. The effect of the operating parameter wasanalyzed. The numerical results show a good approach to predict the gas flow and particledistribution in the inside and outside of the particle collector.

Inconsistent effect of dynamic load waveform on macro-and micro-scale responses of ballast bed characterized in individual cycle:a numerical study

Cyclic load is widely adopted in laboratory to simulate the effect of train load on ballast bed.The effectiveness of such load equivalence is usually testified by having similar results of key concerns of ballast bed,such as deformation or stiffness,while the consistency of particle scale characteristics under two loading patterns is rarely examined,which is insufficient to well-understand and use the load simplification.In this study,a previous laboratory model test of ballast bed under cyclic load is rebuilt using 3D discrete element method(DEM),which is validated by dynamic responses monitored by high-resolution sensors.Then,train load having the same magnitude and amplitude as the cyclic load is applied in the numerical model to obtain the statistical characteristics of inter-particle contact force and particle movements in ballast bed.The results show that particle scale responses under two loading patterns could have quite deviation,even when macro-scale responses of ballast bed under two loading patterns are very close.This inconsistency indicates that the application scale of the DEM model should not exceed the validation scale.Moreover,it is important to examine multiscale responses to validate the effectiveness of load simplification.

Experimental study on influence of blade angle and particle size on particle mechanics on a batch-operated single floor of a multiple hearth furnace

In industry,multiple hearth furnaces are used for the thermal treatment of particulate material.The current contribution concentrates on the experimental analysis of particle mechanics for a batch-operated single floor of a multiple hearth furnace.The particles are agitated on the circular floor by a single,rotating rabble arm equipped with three flat rabble blades of 10 mm thickness.The blade angle,defined as the angle,which the blade is inclined against the tangential direction,is varied from 0°to 90°.A single layer of spherical polyoxymethylene(POM)particles with three different diameters(5,10 and 20 mm)is placed on the floor.To analyze the results,two parameters have been extracted from image analysis when the bed of particles is agitated,first,the area not covered by particles and second,the frequency distribution of the mean distance among the particles.The particle free surface area increases with the inclination of the blades.The evolution of the particle free surface area differs for the different particle diameters.In general,the maximum particle free area for all blade angles is the largest for the 5 mm particles followed by the 20 mm particles.For the 10 mm particles,the particle free surface area starts for a blade angle of 0°at larger values than for the 20 mm particles but the values fall below the values for the 20 mm particles for larger blade angles.The reason for this behavior is discussed in detail.The mean distance among the particles is a parameter characterizing the length scales dominating the effects on the floor.The frequency distribution of the mean distance among particles provides infor-mation about the morphology of the particle bulk,for example,whether the free surface area is inter-spersed with particles.

On interaction between freely moving bodies and fluid in a channel flow

The interaction between free fast-moving bodies(or particles)and the fluid surrounding them is studied,motivated by applications in different branches of industry,biomedicine,the environment and science such as flying droplets,ice growth,dust,impacts,food grains,sport,complexity and storms.New inviscid-based modelling and results on the behaviour of two interacting bodies inside a channel flow are described.This is followed by discussion of the more-bodies extension with a view to treating arrays of bodies in a rational manner.Significant dependences on initial conditions and on the comparative body masses and moments of inertia are found for the occurrence of body-body impacts as opposed to wall-body impacts and for the associated impact times.

Meso-level simulation of gas hydrate dissociation in low-permeability sediments

This paper presents a meso-level simulation of gas hydrate dissociation in low-permeability marine sediments. Interstitial pores are defined to describe fluid flow and particle movement. The proposed model couples multiphase fluid flow with particle movement to simulate the thermodynamics of gas hydrate dissociation triggered by sharp temperature rises. Hydrates respond quickly to temperature rise in low-permeability sediments. Dissociation causes pore pressure to rise rapidly to equilibrium then steadily increase above equilibrium pressure. Lower permeability sediment builds up greater excess pore pressure as the dissipation of pore pressure is constrained.

Estimating the change of porosity in the saturated zone during air sparging

Air sparging is a remedial method for groundwater. The remedial region is similar to the air flow region in the saturated zone. If soil particles are transported during air sparging, the porosity distributions in the saturated zone change, which may alter the flow path of the air. To understand better the particle movement, this study performed a sandbox test to estimate the soil porosity change during air sparging. A clear fracture was formed and the phenomenon of particle movement was observed when the air injection was started. The moved sand filled the porous around the fracture and the reparked sand filled the fracture, reducing the porosity around the fracture. The results obtained from the photographs of the sandbox, the current measurements and the direct sand sample measurements were close to each other and are credible. Therefore, air injection during air sparging causes sand particle movement of sand, altering the characteristic of the sand matrix and the air distribution.

Study of the influence of discharge loop parameters on anode side on generation characteristics of metal plasma jet in a pulsed vacuum discharge

In a pulsed vacuum discharge,the ejection performance of a metal plasma jet can be effectively improved by preventing charged particles from moving to the anode.In this paper,the effects of resistance and capacitance on the anode side on the discharge characteristics and the generation characteristics of plasma jet are investigated.Results show that the existence of a resistor on the anode side can increase the anode potential,thereby preventing charged particles from entering the anode and promoting the ejection of charged particles along the axis of the insulating sleeve nozzle.The application of a capacitor on the anode side can not only absorb electrons at the initial stage of discharge,increasing the peak value of the cathode hump potential,but also prevent charged particles from moving to the anode,thereby improving the ejection performance of the plasma jet.In addition,the use of a larger resistance and a smaller capacitance can improve the blocking effect on charged particles and further improve the ejection performance of the plasma jet.Results of this study will provide a reference for the improvement of the ejection performance of plasma jets and their applications.

Effect of Chute Rotation on Particles Movement for Bell-less Top Blast Furnace

For the bell-less top blast furnace, when particles move along the chute, the particlesr motion direction and the frictional force acting on them will change due to the chute rotation, which consequently influences the velocity at the tip of chute, changes the burden flow width and impact point, and finally affects the stock profile and gas f[ow distribution. So the influence of chute rotation needs to be considered when calculating the burden trajectory with a mathematical model. The mathematical model was established to analyze the influence of Coriolis force on particle velocity at chute tip as well as height and width of burden flow in chute, and to summarize the effect of Coriolis force on burden distribution, thereby making the calculation result more accurate.