ROLE OF MODEL PARTICLE SHAPE IN DISCRETE ELEMENT MODELS OF BED STRUCTURE IN CONTAINERS

Abstract

ABSTRACT A container comprising 5,000 particles was simulated to investigate the role of particle shape on the bed structure of particulate materials. The effect of particle shape on the packing structure of granular beds was investigated in terms of bed height, the distribution of solid fraction, coordination number and the force acting at the bottom of the container. The solid fraction of the beds, which ranged from 0.7–0.9 for spherical particles and 0.6–0.8 for elongated particles, shows a compacted structure for beds of spherical particles. The average bed's solid fraction was 0.825 and 0.750 for beds of spherical and elongated particles, respectively. The overall reduction in the average solid fraction was about 8% as aspect ratio of particles changed from 1 to 4. The solid fraction frequency distribution of the beds implied a wider variety of void shape and size for elongated particles. There was also a significant difference between the coordination number of spherical particles and nonspherical particles. The coordination number was 4.7 and 3.6 for spherical and elongated particles, respectively. However, the change in the magnitude of coordination number was greater (15.1%) in between beds of spherical and nonspherical particles (particles of aspect ratio 2), than in between beds with aspect ratio 2 and 4 (11.3%). The numerical results indicated that for a reliable prediction of real material behavior via discrete element models, the employed model should be capable of manipulating individual elements with shape as close as possible to the shape of real particles. PRACTICAL APPLICATIONSAs most of the agricultural materials comprise a system of individual nonspherical particles, a suitable discrete element (DE) model should be employed to gain realistic results. The DE models with spherical particles are very simple, which are less costly, while these models cannot predict the accurate behavior of systems comprising nonspherical particles. Hence, for such materials, using nonspherical models such as multisphere models is a must. Examples of such produce that need models with nonspherical or elongated elements are kernels and some fruits, whereas some other agricultural particles that are nearly spherical can be successfully simulated with DE models of spherical elements. The DE model employing the multisphere method (MSM) can be used for either case (spherical or nonspherical) to study the agricultural particulate materials processing operations on a particle scale (microscale), such as collision forces between individual grain and fruits that cannot easily be gained from experiments.