J.G. Loughran

On upscaling of discrete element models: similarity principles

Purpose – The main purpose of this paper is to derive a set of similarity principles for discrete element modelling so that a numerical model can exactly reproduce the physical phenomenon concerned. Design/methodology/approach – The objective is achieved by introducing the concepts of particle “strain” and “stress” so that some equivalence between the physical system and the numerical model can be established. Findings – Three similarity principles, namely geometric, mechanical and dynamic, under which the numerical model can exactly reproduce the mechanical behaviour of a physical model are proposed. In particular, the concept of the scale invariant interaction law is further introduced. The scalability of a number of most commonly used interaction laws in the discrete element modelling is examined. Research limitations/implications – This is a preliminary research for a very important and challenging topic. More research, particularly in the understanding of the convergent properties of discrete element models, is needed. Originality/value – The paper provides some important theoretical guidances to computational modelling of particle systems using discrete element techniques.

Application of porous media mechanics to the numerical simulation of the rolling of sugar cane

A finite element solution to the rolling of two‐phase materials is presented and applied to the rolling of prepared sugar cane. The generalized Biot theory is extended and modified to suit the present problem and the velocity of the solid skeleton and the pore pressure are taken as the primary unknowns. The finite element approach is applied to the governing equations for spatial discretization, followed by time domain discretization by standard difference methods. A constitutive relation evaluated from a finite element simulation of experiments performed on a constrained compression test cell is employed. The computational model of the rolling of prepared cane with two rolls is presented. The material parameters of prepared cane are described and their variation during the rolling process are derived and discussed. Numerical results are presented to illustrate the performance and capability of the model and solution procedures.

MULTI-VARIATE ANALYSIS OF FRICTIONAL INTERACTION BETWEEN GROOVED ROLLERS AND PREPARED SUGARCANE

The Australian sugar industry utilizes rolling almost exclusively for extraction of sucrose from prepared sugarcane. The feeding and extraction performance of rolling mills is strongly dependent on the friction coefficient between counter-rotating rolls and the fibro-porous sugarcane blanket. Rolls are circumferentially grooved and roughened with weld droplets to assist juice drainage and maximize friction between rolls and blanket. Previous investigators have performed experimental measurements of the friction coefficient between metal surfaces and prepared cane or bagasse. This article develops a multi-variate empirical regression equation based on the experimental measurements of previous investigators to describe the dependence of the interfacial friction coefficient on normal pressure, groove angle, and relative rubbing speed. The friction coefficient was found to decrease exponentially with increasing normal pressure, decrease linearly with increasing rubbing speed, and increase with decreasing groove angle in accordance with simple wedge theory.

Image tensor analysis: a numerical tool for data acquisition and constitutive analysis of historic continua

Image measurement based on the Fast Fourier Transform convolution theorem has been combined with a finite difference algorithm to produce image tensor analysis (ITA), a numerical tool for experimental determination of deformation for historic continua. ITA allows the deformation within an image-compatible material body to be quantified using digital video footage taken from experimental events. Hence the deformation output from computational modelling of the same event can be directly compared to the measured deformation field given by the image-based numerical solution. The current research application of ITA aims to provide experimental deformation data and characterisation of the constitutive behaviour of the fibro-porous media prepared sugar cane. This paper outlines the numerical procedure of ITA and details the possible post processing applications with respect to both data acquisition and constitutive modelling.

Application of Image Measurement and Continuum Mechanics to the Direct Measurement of Two-Dimensional Finite Strain in a Complex Fibro-Porous Material

This paper outlines a computational procedure that has been implemented for the direct measurement of finite material strains from digital images taken of a material surface during plane-strain process experiments. The selection of both hardware and software components of the image processing system is presented, and the numerical procedures developed for measuring the 2D material deformations are described. The algorithms are presented with respect to two-roll milling of sugar cane bagasse, a complex fibro-porous material that undergoes large strains during processing to extract the sucrose-rich liquid. Elaborations are made in regard to numerical developments for other forms of experimentation, algorithm calibrations and measurement improvements. Finite 2D strain results are shown for both confined uniaxial compression and two-roll milling experiments.

DEM - a Virtual Laboratory for Studying Complex Particulate Flow Problems

Abstract This paper presents research into the development of a computational system for modelling of complex particulate flow problems using the discrete element method (DEM). Important features of the system are: 1) particle generation with user-specified particle angularity and distribution in two and three dimensions; 2) a range of adhesion laws to enable clumping of particles and subsequent fracture/floculation based on a user-defined tensile force; 3) specification of interparticle and particle/wall friction and cohesion; 4) general prescription of drag kinematics; 6) solution efficiency; 7) post processing involving user defined cutting planes and animation. With increasing computational power DEM is becoming a tool which can be used to explore complex modelling processes in three dimensions on a desktop computer. Results are given for two and three dimensional modelling of industrial flows: dragline bucket filling; flow from bottom dump rail wagons and silo flow.

Development of a Computational System for Modelling of Ground Engaging Processes with Application to Mining

ABSTRACT The Discrete Element Method (DEM) represents a powerful tool when coupled with conventional finite element techniques for modelling of industrial granular processes. The paper reports on the development of a computational system which accounts for particle angularity, and inter-particle adhesion. Results are presented for a case study involving 3 dimensional modelling of dragline bucket filling.