CoarseGrain_21stDec.m from The dynamics of granular flow from a silo with two symmetric openings

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 <i>L</i> between the two openings is varied. The mass flow rate is shown to be at a maximum at zero opening separation, decreasing as <i>L</i> 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.

本研究采用粒子图像测速法（Particle Image Velocimetry, PIV）、流量测量与离散元建模（Discrete Element Modelling, DEM），针对带有两个对称布置出料口的矩形料仓内的颗粒流动动力学特性展开研究。研究中以高速摄影机记录了有机玻璃料仓内芥菜籽的流动过程，并通过粒子图像测速法对所得图像帧进行分析，以获取速度场、速度散度与剪切率分布图。随着两个出料口间距L的改变，观测到流动结构发生变化。研究表明，质量流量在出料口间距为零时达到最大值，随间距L增大而逐渐降低，随后降至最小值，之后回升至接近单个独立（无相互作用）出料口流量两倍的平衡值。本研究后续又分别采用苋菜籽与筛分砂重复了流量实验，均观测到了相似的流动特性。尽管该结果与近期料仓系统中部分离散元建模与物理实验的结论相悖，但类似现象已在同类系统中被报道：即人员通过两扇门从房间疏散的过程。本研究通过离散元建模复现了实验结果，并证实颗粒间摩擦力是调控流量行为的核心因素，同时解释了现有文献中实验结果存在分歧的原因。