Year

2004

Degree Name

Doctor of Philosophy

Department

University of Wollongong, School of Mechanical, Materials & Mechatronic Engineering

Abstract

The mining industry is an immense field with granular flows (e.g. coal) occurring in numerous areas. Accordingly there are a significant number of problems that arise, with a great number requiring solutions that are difficult to achieve by conventional industrial means. The modelling of granular flow using the numerical technique known as Distinct Element Method (DEM) has great potential in industry, particularly for solving transfer point problems. The advantage of DEM for transfer applications is that an entire system can be simulated using the single numerical technique, as opposed to the existing situation where a myriad of design techniques are required (e.g. analytical solution for one component and graphical solution for another). DEM involves solving the equations of motion for the trajectory/rotation/orientation of each particle and modelling each collision between particles and between particles and boundary objects. The research presented a comprehensive overview of all of the available analytical processes available to design chute system components, such as material trajectory calculations, impact plate models, and gravity flow chute aspects. To the author’s knowledge, this was the first such review in the literature. A detailed comparison between the most common analytical design methods was conducted, recommendations for which method to use were established, and areas of weakness and further study were identified. It was found that: most areas apart from the prediction of the initial material discharge and trajectory were lacking in design method; often the few available design methods for chute components, such as impact plates and gravity flow chutes, were lengthy and often difficult to implement. A computer code was developed during the course of the research to simulate bulk material using the Distinct Element Method (DEM). A background into DEM and its application to modelling material flow at transfer points was presented. One major drawback found in the recent transfer studies was the lack of quantification of the velocity distributions obtained using the DEM against existing analytical design theories. Contour coloured particulate simulations have also been recently produced by a number of companies (e.g. Overland Conveyor Company Inc.) however the flow A b s t r a c t ii regimes observed from the relevant simulation screen captures were not adequately scrutinised. All the DEM mathematical formulation and numerical methods utilised for the current work were comprehensively described and relevant computational aspects were also detailed, such as the coding of a pre-processor and post-processor allowing animations of the DEM particles. A series of tests was conducted to gauge the validity of the computer code, and this produced satisfactory results. The DEM code was also applied to simulate two separate transfers originally designed by The Gulf Group using their EasyFlowTM technology, and currently in operation in industry in Lithgow, Australia. By observing animation screen captures the current research confirmed the advantage of maintaining particle speed through the system when using curved chute elements. Quantitative DEM velocity data were compared to the velocities predicted by the most favourable analytical methods. It was found that DEM generally produced velocity regimes close to those of the analytical techniques. However it also provided the additional benefit of providing data on stream characteristics such as impact forces and velocities in the vicinity of the hood and spoon elements, which are difficult to examine in detail using analytical methods. An analysis of the micro dynamics of individual particles also identified that there are differing scales of contact during the flow through a chute. Although the analytical methods do not allow closer scrutiny of the flowing stream at the micro scale, they have the advantage of providing much faster solutions and are good for chute designs for free flowing material transfers.

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