The transient dynamics of dilation waves in granular phase transitions during silo discharge

Fullard, Luke; Davies, Clive E; Lube, Gert; Neather, A.C.; Bréard, E.; Shepherd, Brittany J.

doi:10.1007/s10035-016-0685-2

Cited by 15 publications

(9 citation statements)

References 34 publications

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“…These authors observed the formation and propagation of density waves in the central flowing zone during the discharge. Later similar phenomena were also reported by Le Pennec et al 15 and Fullard et al 16 . All these researchers ascribed the appearances of fluctuations to the buildup and collapse of dynamic arches in the flowing zone.…”

Section: Introductionsupporting

confidence: 76%

Fluctuation of particles during funnel flow discharge from flat‐bottomed silos

et al. 2021

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Although resonant motion of particles during mass flow discharge from silos has been extensively investigated by earlier researchers, the appearance of such phenomenon during funnel flow discharge has not been emphasized. In this work, the flow behavior of particles during funnel flow discharge from flat‐bottomed silos has been investigated by conducting three‐dimensional Discrete Element Method (DEM) simulations. It is found that particles in the upper part of flowing zone move collectively, manifested by the oscillatory fluctuations of the velocity and the non‐Gaussian characteristics of the fluctuations of individual velocity around the average. Correlation analysis and discrete Fourier transform have been performed to characterize the emission and propagation of velocity fluctuation. It is found that the observed resonant motion of particles is induced by the regular fluctuation of contact force between particles, and there exists an intermediate region in the converging part of the flowing zone. The bottom boundary of this region corresponds to the emission source from which the velocity wave propagates upward and downward. Its upper boundary coincides with that of the converging part of the flowing zone and is featured by the most violent fluctuation of contact force. The simulation results thus suggest that the discharge of granular assembly seems to be determined by the rheological behavior of particles in this intermediate region.

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Section: Introductionsupporting

confidence: 76%

Fluctuation of particles during funnel flow discharge from flat‐bottomed silos

et al. 2021

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“…To reduce PIV noise error, once a steady flow was established 5 s of images were analysed and then averaged to achieve a smooth velocity field. Silos have been shown to have an initial transient in the development of the steady velocity field (but not in the flow rate) [18], so the 5 s of images was selected after approximately 40 s of flow to ensure that the steady regime had been reached. This averaged 2D velocity field could then be used to calculate its divergence and the shear rate of the flow as detailed in §4.…”

Section: Methodsmentioning

confidence: 99%

“…While there has been much progress in classifying granular behaviour experimentally [5][6][7][8][9][10][11] and using mathematical modelling [12][13][14][15], there remains a need for further work to fully understand the physics of granular phenomena. For silo flows, in particular, there is a large body of experimental and numerical work ( [16][17][18][19][20][21][22][23][24][25], for example). Most silo studies focus on the case where there is a single silo opening (where the particles discharge under gravity) located at the centre of the silo.…”

Section: Introductionmentioning

confidence: 99%

The dynamics of granular flow from a silo with two symmetric openings

et al. 2019

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The dynamics of granular flow in a rectangular silo with two symmetrically placed exit openings is investigated using particle image velocimetry (PIV), flow rate measurements and discrete element modelling (DEM). The flow of mustard seeds in a Perspex silo is recorded using a high-speed camera and the resulting image frames are analysed using PIV to obtain velocity, velocity divergence and shear rate plots. A change in flow structure is observed as the distance L between the two openings is varied. The mass flow rate is shown to be at a maximum at zero opening separation, decreasing as L is increased; it then reaches a minimum before rising to an equilibrium rate close to two times that of an isolated (non-interacting) opening. The flow rate experiment is repeated using amaranth and screened sand and similar behaviour is observed. Although this result is in contrast with some recent DEM and physical experiments in silo systems, this effect has been reported in an analogous system: the evacuation of pedestrians from a room through two doors. Our experimental results are replicated using DEM and we show that inter-particle friction controls the flow rate behaviour and explains the discrepancies in the literature results.

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“…its packing fraction decreases. This effect was first noticed by Reynolds [39] and has been reported in the literature of sheared granular media [40][41][42][43][44][45] and flow in hoppers [46][47][48][49][50][51] or silos [52]. Shear-induced dilation occurs because when a granular medium is subjected to a local shear it must expand by creating more void spaces to allow the grains to pass by each other and overcome the grains interlocking.…”

Section: Mechanics Of Powder Spreadingmentioning

confidence: 79%

A DEM study of powder spreading in additive layer manufacturing

Fouda

Bayly

2019

Granular Matter

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In this paper, discrete element method simulations were used to study the spreading of an idealised, blade based, powder coating system representative of the spreading of spherical, mono-sized, non-cohesive titanium alloy (Ti6AlV4) particles in additive layer manufacturing applications. A vertical spreader blade was used to accelerate a powder heap across a horizontal surface, with a thin gap between the blade and the surface, resulting in the deposition of a thin powder layer. The results showed that it is inevitable to deposit a powder layer with a lower packing fraction than the initial powder heap due to three mechanisms: shear-induced dilation during the initiation of powder motion by the spreader; dilation and rearrangement due to powder motion through the gap; and the inertia of the particles in the deposited powder layer. It was shown that the process conditions control the contribution of these three mechanisms, and that the velocity profile in the shear layer in front of the gap is critical to the final deposited layer packing fraction. The higher the mean normalised velocity in the shear layer the lower the deposited layer packing fraction. The gap thickness and the spreader blade velocity affect the properties of the deposited layer; with the former increasing its packing fraction and the latter decreasing it. The analysis presented in this study could be adapted to powders of different materials, morphologies and surface properties. Keywords Additive manufacturing (AM) • Powder spreading • Discrete element method (DEM) • Dilation • Metal powders • Powder bed fusion List of symbols d Particle diameter t Time v velocity x, y, z Cartesian coordinates δ Gap thickness Δ Change in packing fraction Packing fraction Subscripts 1, 2, 3 First, second and third packing fraction reduction mechanisms, respectively back Interrogation region at the back of the spreader front Interrogation region in front of the spreader p Particle w Spreader ∞ Final

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The transient dynamics of dilation waves in granular phase transitions during silo discharge

Cited by 15 publications

References 34 publications

Fluctuation of particles during funnel flow discharge from flat‐bottomed silos

Fluctuation of particles during funnel flow discharge from flat‐bottomed silos

The dynamics of granular flow from a silo with two symmetric openings

A DEM study of powder spreading in additive layer manufacturing

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