Measurement of particle interaction properties for the incorporation into Discrete Element Methods

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2005

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University of Cape Town

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Abstract
The principle aim of this research project is to measure parameters which are pertinent for numerical simulations in discontinuous media. One such numerical tool, the Discrete Element Method (DEM), is a promising technique for predicting the dynamics of charge motion with in a mill. Particle interactions in DEM are calculated by contact force and force displacement laws at each particle contact. These contact events are characterized by parameters that are often fitted or estimated due to the lack of accurate experimental measurements. The aim of this project is to experimentally measure the necessary interaction properties required for the DEM analysis and to test the DEM models against the measured experimental results. An in-flight binary collisions drop tester is constructed to measure the material interaction properties of two spheres. The collision event is captured photographically and pre- and post- relative velocities are measured. The binary collisions of the particles are carefully controlled by relay timing circuits and they are captured on digitized images using a SLR digital camera. The particles are illuminated using digital strobes controlled by a signal generator. The heights of the colliding particles are adjusted to vary the drop velocities prior to collision. The measured relative velocities arc applied in rigid body theory of binary impact to extract the required material interaction properties. The parameters measured from the binary collision include coefficients of tangential and normal restitution and friction. The analysis presented here draws on the work of Maw et al and Foerster et al, which is an extension of the Hertz theory of impact to the oblique impact of the elastic bodies with circular contacts. Initial numerical simulations using the viscous damping model is performed in Particle Flow Code (PFC) and a comparison between experimental and numerical results presented.
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Includes bibliographical references (leaves 213-215).

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