scholarly journals Effects of dynamic fragmentation on the impact force exerted on rigid barrier: centrifuge modelling

2019 ◽  
Vol 56 (9) ◽  
pp. 1215-1224 ◽  
Author(s):  
C.W.W. Ng ◽  
C.E. Choi ◽  
D.K.H. Cheung ◽  
Y. Cui
Keyword(s):  
Volume Fraction ◽  
Impact Force ◽  
Inertial Particles ◽  
Size Segregation ◽  
Centrifuge Modelling ◽  
Rigid Barrier ◽  
Flow Energy ◽  
Dynamic Fragmentation ◽  
Large Particles ◽  
The Impact

Bi-dispersity is a prerequisite for grain-size segregation, which transports the largest particles to the flow front. These large and inertial particles can fragment upon impacting a barrier. The amount of fragmentation during impact strongly influences the force exerted on a rigid barrier. Centrifuge modelling was adopted to replicate the stresses for studying the effects of bi-dispersity in a granular assembly and dynamic fragmentation on the impact force exerted on a model rigid barrier. To study the effects of bi-dispersity, the ratio between the diameters of small and large particles (δs/δl), characterizing the particle-size distribution (PSD), was varied as 0.08, 0.26, and 0.56. The volume fraction of the large particles was kept constant. A δs/δl tending towards unity characterizes inertial flow that exerts sharp impulses, and a diminishing δs/δl characterizes the progressive attenuation of these sharp impulses by the small particles. Flows dominated by grain-contact stresses (δs/δl < 0.26), as characterized by the Savage number, are effective at attenuating dispersive stresses of the large particles, which are responsible for reducing dynamic fragmentation. By contrast, flows dominated by grain-inertial stresses (δs/δl > 0.26) exhibit up to 66% more impulses and 4.3 times more fragmentation. Dynamic fragmentation of bi-disperse flows impacting a rigid barrier can dissipate about 30% of the total flow energy.

scholarly journals Asymmetric flux models for particle-size segregation in granular avalanches

2014 ◽  
Vol 757 ◽  
pp. 297-329 ◽  
Author(s):  
P. Gajjar ◽  
J. M. N. T. Gray
Keyword(s):  
Particle Size ◽  
Small Particle ◽  
Volume Fraction ◽  
Free Surface Flows ◽  
Two Dimensions ◽  
Combined Processes ◽  
Maximum Point ◽  
Size Segregation ◽  
Flux Function ◽  
Large Particles

AbstractParticle-size segregation commonly occurs in both wet and dry granular free-surface flows through the combined processes of kinetic sieving and squeeze expulsion. As the granular material is sheared downslope, the particle matrix dilates slightly and small grains tend to percolate down through the gaps, because they are more likely than the large grains to fit into the available space. Larger particles are then levered upwards in order to maintain an almost uniform solids volume fraction through the depth. Recent experimental observations suggest that a single small particle can percolate downwards through a matrix of large particles faster than a large particle can be levered upwards through a matrix of fines. In this paper, this effect is modelled by using a flux function that is asymmetric about its maximum point, differing from the symmetric quadratic form used in recent models of particle-size segregation. For illustration, a cubic flux function is examined in this paper, which can be either a convex or a non-convex function of the small-particle concentration. The method of characteristics is used to derive exact steady-state solutions for non-diffuse segregation in two dimensions, with an inflow concentration that is (i) homogeneous and (ii) normally graded, with small particles above the large. As well as generating shocks and expansion fans, the new asymmetric flux function generates semi-shocks, which have characteristics intersecting with the shock just from one side. In the absence of diffusive remixing, these can significantly enhance the distance over which complete segregation occurs.

scholarly journals Numerical Investigation of Multiple-Impact Behavior of Granular Flow on a Rigid Barrier

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3228
Author(s):  
Bei Zhang ◽  
Yu Huang ◽  
Ping Lu ◽  
Chunxiang Li
Keyword(s):  
Impact Force ◽  
Dead Zone ◽  
Particle Interaction ◽  
Impact Behavior ◽  
Particle Collision ◽  
Rigid Barrier ◽  
Impact Mechanism ◽  
The Dead ◽  
Multiple Impact ◽  
The Impact

The debris–barrier interaction issue has gained considerable attention among the engineering community, but most researches have only focused on the single-surge impact condition, with the multiple-surge impact mechanism still lacking clarity. However, multiple-surge impact is more typical in the field. Thus, we conduct some numerical simulations based on the discrete element method (DEM) and present a series of results that provide preliminary insights into the multiple-surge impact mechanism. The DEM model is firstly calibrated using physical experimental results and then used to investigate the flow kinematics, impact dynamics and energy evolution of the successive impact process. The results indicate that compared with single-surge conditions, the barrier is safer under multiple-surge impact as the deposition spreading distance is extended by 6–20% and the impact force is reduced by 6–30%. The dead zone formed by the previous surge behaves as a cushioning layer and a medium for momentum transfer. Three mechanisms of energy dissipation during surge–dead-zone interactions were identified: friction and penetration at the interaction face between the surge and dead zone, inelastic deformation of the dead zone, and inter-particle interaction within the surge. Each component was analyzed, which shows that inter-particle collision friction accounts for over 60% of the total energy loss during surge–dead-zone interaction. In addition, the performance of granular jump theory in predicting the multiple-surge impact force is assessed, and some possible modifications are proposed. Finally, some engineering implications from the presented numerical results are discussed.

Interaction between dry granular flow and rigid barrier with basal clearance: analytical and physical modelling

2020 ◽  
Vol 57 (2) ◽  
pp. 236-245 ◽  
Author(s):  
Clarence Edward Choi ◽  
Charles Wang Wai Ng ◽  
Haiming Liu ◽  
Yu Wang
Keyword(s):  
Granular Flow ◽  
Impact Force ◽  
Particle Diameter ◽  
Physical Modelling ◽  
Impact Model ◽  
Jump Height ◽  
Rigid Barrier ◽  
Physical Experiments ◽  
Dry Granular Flow ◽  
The Impact

Some types of barriers are designed with a clearance between the bottom of the barrier and the channel bed. This feature allows small discharges to pass, thereby reducing the maintenance required over the service life of the barrier. Aside from the practical function of a clearance, it influences the impact force, jump height, and discharge. In this paper, a series of physical experiments was conducted using a 6 m long flume to model the interaction between dry granular flow and rigid barrier with a basal clearance. The ratio between the clearance and particle diameter Hc/D was varied from 0 to 10. The channel inclination was varied from 15° to 35° to achieve different Froude numbers before impact. A new impact model for predicting impact force exerted on the barrier with a basal clearance is presented and evaluated. Results reveal that Hc ≥ 3D is capable of reducing the impact force and overflow. Findings from this study highlight the importance of considering the effects of basal clearance on the design of multiple-barrier systems.

An experimental study of the motion of concentrated suspensions in two-dimensional channel flow. Part 2. Bidisperse systems

1998 ◽  
Vol 363 ◽  
pp. 57-77 ◽  
Author(s):  
M. K. LYON ◽  
L. G. LEAL
Keyword(s):  
Large Particle ◽  
Particle Concentration ◽  
Volume Fraction ◽  
Balance Model ◽  
Concentration Profiles ◽  
Size Segregation ◽  
Small Particles ◽  
Concentrated Suspensions ◽  
Particle Volume ◽  
Large Particles

In this paper we report experimental velocity and concentration profiles for suspensions possessing a bidisperse distribution of particle size undergoing pressure-driven flow through a parallel-wall channel. In addition to the overall concentration distributions determined by implementing the modified laser Doppler velocimetry method described in Part 1 (Lyon & Leal 1998), concentration profiles for the particles of each size were measured by sampling the position of marked tracer particles across 60% of the channel gap. Non-uniform overall particle concentration distributions and blunted velocity profiles were found at bulk particle volume fractions of 0.30 and 0.40, which were equal to the monodisperse data of Part 1, within experimental uncertainty. The large-particle concentration profiles were non-uniform down to a large-particle bulk volume fraction of 0.075, while non-uniform distributions of the small particles were only found when the volume fraction of small particles in the bulk was greater than or equal to 0.20. Experiments in which at least half the suspended particulate volume was occupied by large particles revealed enrichment of the large particles in the centreline region of the channel. This size segregation was found to increase as the total number of suspended particles decreased. Finally, the data from experiments in which a uniform small-particle concentration profile was measured were compared with suspension balance model (McTigue & Jenkins 1992; Nott & Brady 1994) predictions for parameter values that corresponded only to the large particles. While close agreement with the large-particle concentration profiles was found, this comparison also reflected the fact that the small particles bring the suspension viscosity to a regime that is more sensitive to the particle concentration, rather than simply providing an increment in background viscosity to the suspending liquid.

scholarly journals THEORY OF LIQUID DISPERSION BY THE NOZZLES

2019 ◽  
Vol 14 (2) ◽  
pp. 95-99 ◽  
Author(s):  
Борис Иванов ◽  
Boris Ivanov ◽  
Булат Зиганшин ◽  
Bulat Ziganshin ◽  
Рустем Шарафеев ◽  
...  
Keyword(s):  
Impact Force ◽  
Aerodynamic Resistance ◽  
Erosive Wear ◽  
Spray Angle ◽  
Test Results ◽  
Pressure Drops ◽  
Mode Of Operation ◽  
Large Particles ◽  
The Impact ◽  
Atomization Pressure

The main characteristics are considered and calculations of the main indicators of nozzle devices are given. Laboratory tests of nozzles of various configurations were carried out to determine the working width of the spot at different distances to the irrigated surface and the angle of the spray pattern, and dependencies were established to determine their effective mode of operation. As a result of testing nozzles with different spray patterns when determining the impact force of the jet, it was found that as the spray angle increases, the value of the impact force of the jet F decreases. This is due to the fact, that with an increase in the initial jet velocity, the torch length reaches a maximum, not only does the kinetic energy increase, but the sizes (diameters) of the sprayed medium drops, which leads to a decrease in droplet mass and an increase in the aerodynamic resistance of the torch jet particles. A bench for determining the impact force of a jet of various nozzles was developed and test results were obtained. During operation, due to the erosive wear of the jet holes of the nozzles, its diameter increases, as a result, the working atomization pressure drops, and the number and size of large particles increase. Therefore, periodically it is necessary to check the diameter of the nozzle holes and not to use nozzles, that have a hole diameter greater than the initial one by 10 or more percent. In the study of nozzles, the dependences of nozzles’ characteristics on the initial parameters of the outflow of the liquid jet to the dispersity and shape of the torch were established. The values of irrigation spot width are established depending on the angle of the torch and the distance from the nozzle to the irrigated surface. The magnitude of the impact force of the jet, which occurs at the point of contact of the fluid jet with the irrigated surface, is determined.

Dense Particulate Flow in a Cold Gas Dynamic Spray System

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
B. Samareh ◽  
A. Dolatabadi
Keyword(s):  
Volume Fraction ◽  
Stagnation Pressure ◽  
Bow Shock ◽  
Particulate Flow ◽  
Normal Velocity ◽  
Particle Interactions ◽  
Expansion Waves ◽  
Large Particles ◽  
Compression And Expansion ◽  
The Impact

The effect of particle-gas and particle-particle interactions in a cold spray process is studied when the particle loading is high. To examine the effect of the presence of a dense particulate flow on the supersonic gas, an Eulerian-Eulerian approach is used. It is found that when the volume fraction of the injected particles is increased, the turbulence of the gas phase will be augmented by the motion of particles and consequently, the shape, the strength, and the location of the compression and expansion waves will be altered. Shock-particle interactions are demonstrated for various volume fractions. Another important parameter, which will affect the spraying deposition efficiency, is the substrate stand-off distance. It is found that the stagnation pressure alternates for different stand-off distances because of the formation of compression and expansion waves outside the nozzle exit. The particle normal velocity on impact is a strong function of the stagnation pressure on the substrate as particles must pierce through the bow shock formed on that region. The effect of the particle size and number density are also studied for different loading conditions. It is found that small and large particles behave differently as they pass through shock diamonds and the bow shock, i.e., in the case of very small particles, as the loading increases, the impact velocity increases, while, for the large particles, the trend is reversed.

Some thought on the Estimating of the Impact Force by an Experiment

2019 ◽  
Vol 7 (2) ◽  
pp. 205-213
Author(s):  
Yong-Doo Kim ◽  
Seung-Jae Lim ◽  
Hyun-Ung Bae ◽  
Kyoung-Ju Kim ◽  
Chin-Ok Lee ◽  
...  
Keyword(s):  
Impact Force ◽  
The Impact

scholarly journals Nanofluid flow containing carbon nanotubes with quartic autocatalytic chemical reaction and Thompson and Troian slip at the boundary

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Muhammad Ramzan ◽  
Jae Dong Chung ◽  
Seifedine Kadry ◽  
Yu-Ming Chu ◽  
Muhammad Akhtar
Keyword(s):  
Mathematical Model ◽  
Carbon Nanotubes ◽  
Drag Force ◽  
Chemical Reaction ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Surface Drag ◽  
Nanofluid Flow ◽  
Velocity Parameter ◽  
The Impact

Abstract A mathematical model is envisioned to discourse the impact of Thompson and Troian slip boundary in the carbon nanotubes suspended nanofluid flow near a stagnation point along an expanding/contracting surface. The water is considered as a base fluid and both types of carbon nanotubes i.e., single-wall (SWCNTs) and multi-wall (MWCNTs) are considered. The flow is taken in a Dacry-Forchheimer porous media amalgamated with quartic autocatalysis chemical reaction. Additional impacts added to the novelty of the mathematical model are the heat generation/absorption and buoyancy effect. The dimensionless variables led the envisaged mathematical model to a physical problem. The numerical solution is then found by engaging MATLAB built-in bvp4c function for non-dimensional velocity, temperature, and homogeneous-heterogeneous reactions. The validation of the proposed mathematical model is ascertained by comparing it with a published article in limiting case. An excellent consensus is accomplished in this regard. The behavior of numerous dimensionless flow variables including solid volume fraction, inertia coefficient, velocity ratio parameter, porosity parameter, slip velocity parameter, magnetic parameter, Schmidt number, and strength of homogeneous/heterogeneous reaction parameters are portrayed via graphical illustrations. Computational iterations for surface drag force are tabulated to analyze the impacts at the stretched surface. It is witnessed that the slip velocity parameter enhances the fluid stream velocity and diminishes the surface drag force. Furthermore, the concentration of the nanofluid flow is augmented for higher estimates of quartic autocatalysis chemical.

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