Clogging and avalanches in quasi-two-dimensional emulsion hopper flow

Fraction of clogging configurations sampled by granular hopper flow

We measure the fraction $F$ of flowing grain configurations that precede a clog, based on the average mass discharged between clogging events for various aperture geometries. By tilting the hopper, we demonstrate that $F$ is a function of the hole area projected in the direction of the exiting grain velocity. By varying the length of slits, we demonstrate that grains clog in the same manner as if they were flowing out of a set of smaller independent circular openings. The collapsed data for $F$ can be fit to a decay that is exponential in hole width raised to the power of the system dimensiona…

Granular discharge and clogging for tilted hoppers

We measure the flux of spherical glass beads through a hole as a systematic function of both tilt angle and hole diameter, for two different size beads. The discharge increases with hole diameter in accord with the Beverloo relation for both horizontal and vertical holes, but in the latter case with a larger small-hole cutoff. For large holes the flux decreases linearly in cosine of the tilt angle, vanishing smoothly somewhat below the angle of repose. For small holes it vanishes abruptly at a smaller angle. The conditions for zero flux are discussed in the context of a {\it clogging phase dia…

Intermittency and Velocity Fluctuations in Hopper Flows Prone to Clogging

We experimentally study the dynamics of granular media in a discharging hopper. In such flows, there often appears to be a critical outlet size $D_c$ such that the flow never clogs for $D > D_c$. We report on the time-averaged velocity distributions, as well as temporal intermittency in the ensemble-averaged velocity of grains in a viewing window, for both $D < D_c$ and $D > D_c$, near and far from the outlet. We characterize the velocity distributions by the standard deviation and the skewness of the distribution of vertical velocities. We propose a measure for intermittency based on the two-…

Effect of interstitial fluid on the fraction of flow microstates that precede clogging in granular hoppers

We report on the nature of flow events for the gravity-driven discharge of glass beads through a hole that is small enough that the hopper is susceptible to clogging. In particular, we measure the average and standard deviation of the distribution of discharged masses as a function of both hole and grain sizes. We do so in air, which is usual, but also with the system entirely submerged under water. This damps the grain dynamics and could be expected to dramatically affect the distribution of the flow events, which are described in prior work as avalanche-like. Though the flow is slower and th…

基石是关键：利用可解释机器学习探究二维颗粒漏斗中的堵塞过程

Cornerstones are the Key Stones: Using Interpretable Machine Learning to Probe the Clogging Process in 2D Granular Hoppers

本文通过超过5万次实验和可解释机器学习（线性SVM）分析，发现潜在拱基石位置是二维颗粒漏斗堵塞的关键因素，并通过改变固定基石颗粒位置验证其可显著影响排出质量。

A Trap Model for Clogging and Unclogging in Granular Hopper Flows

Granular flows through narrow outlets may be interrupted by the formation of arches or vaults that clog the exit. These clogs may be destroyed by vibrations. A feature which remains elusive is the broad distribution $p(τ)$ of clog lifetimes $τ$ measured under constant vibrations. Here, we propose a simple model for arch-breaking, in which the vibrations are formally equivalent to thermal fluctuations in a Langevin equation; the rupture of an arch corresponds to the escape from an energy trap. We infer the distribution of trap depths from experiments and, using this distribution, we show that t…

Topological rearrangements and stress fluctuations in quasi-two-dimensional hopper flow of emulsions

We experimentally study the shear flow of oil-in-water emulsion droplets in a thin sample chamber with a hopper shape. In this thin chamber, the droplets are quasi-2D in shape. The sample is at an area fraction above jamming and forced to flow with a constant flux rate. Stresses applied to a droplet from its neighbors deform the droplet outline, and this deformation is quantified to provide an ad hoc measure of the stress. As the sample flows through the hopper we see large fluctuations of the stress, similar in character to what has been seen in other flows of complex fluids. Periods of time …

颗粒漏斗流中的随机动力学：一种构型模式控制堵塞的稳定性

Stochastic dynamics of granular hopper flows: a configurational mode controls the stability of clogs

本文提出一个耦合流速与隐藏构型模式的现象学模型，统一解释漏斗流中临时堵塞、永久堵塞及非高斯流速统计，并成功复现大规模实验数据，揭示堵塞稳定性由静态拱结构特征控制。

Ergodicity breaking dynamics of arch collapse

Gravity driven flows such as in hoppers and silos are susceptible to clogging due to the formation of arches at the exit whose failure is the key to re-initiation of flow. In vibrated hoppers, clog durations exhibit a broad distribution, which poses a challenge for devising efficient unclogging protocols. Using numerical simulations, we demonstrate that the dynamics of arch shapes preceding failure can be modeled as a continuous time random walk (CTRW) with a broad distribution of waiting times, which breaks ergodicity. Treating arch failure as a first passage process of this random walk, we a…

在料斗中混合软质与刚性颗粒：软颗粒诱发流动间歇性与雪崩现象

Mixing soft and rigid particles in a hopper: soft particles induce flow intermittency and avalanches

本文通过准二维料斗实验研究软硬颗粒混合物的重力驱动流动，发现软颗粒虽降低出口速度却提高总排放速率，并诱发间歇性与雪崩现象，同时揭示临时拱的失效由形成最大键角的颗粒决定。

稠密悬浮液的漏斗流：一个二维微流控模型系统

Hopper flows of dense suspensions: a 2D microfluidic model system

本研究提出一种二维微流控装置，通过原位光刻制造颗粒并利用 Quake 阀压实，实验研究了稠密悬浮液在漏斗通道中的流动，发现其恒定排出速率与类似 Beverloo 标度规律，并验证了堵塞统计规律。

不同重力下的颗粒堵塞：统一标度

Granular clogging across gravities: a unified scaling

通过引入颗粒邦德数作为控制参数，建立了统一标度，预测低重力下颗粒堵塞行为，并利用微重力实验验证了其有效性。