A dissertation submitted in fulfilment of the requirements for the degree of Master of Science in Engineering to the Faculty of Engineering and the Built Environment, School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, Johannesburg , 2018 / The Discrete Element Method (DEM) models and simulates the flow of gran
ular material through confining geometry. The method has the potential to
significantly reduce the costs associated with the design and operation of bulk
materials handling equipment. The challenge, however, is the difficulty of
determining the required input parameters. Previous calibration approaches
involved direct measurements and random parameter search. The aim of this
research was to develop a sequential DEM calibration framework, identify ap
propriate calibration experiments and validate the framework on real flows in
a laboratory-scale silo and chute.
A systematic and sequential DEM calibration framework was developed. The
framework consists of categorising the DEM input parameters into three cat
egories of determining the directly measured input parameters, obtaining the
literature acquired input parameters, and linking physical experiments with
DEM simulations to obtain the calibrated parameter values. The direct mea
surement parameters comprised the coefficients of restitution and the particle
to wall surface coefficient of rolling friction. Literature obtained parameters
were the Young’s Modulus and Poisson’s ratio. The calibrated parameters
comprised the particle to wall surface coefficient of sliding friction calibrated
from the wall fiction angle, the particle to particle friction coefficients (sliding
and rolling) calibrated from two independent angles of repose, particle den
sity calibrated from bulk density, and adhesion and cohesion energy densities.
The framework was then tested using iron ore with a particle size distribution
between +2mm and - 4.75 mm in LIGGGHTS DEM software.
i
Validation of the obtained input parameter values in the silo and chute showed
very good qualitative comparisons between the measured and simulated flows.
Quantitative predictions of flow rate were found to be particularly sensitive
to variations in the particle to particle coefficient of sliding friction. It was
concluded that due to their inherent limitations, angle of repose tests were not
totally reliable to calibrate the particle to particle coefficient of sliding friction.
Sensitivity tests conducted showed that in the quasi-static flow regime, only
the frictional parameters were dominant, while both the frictional and colli
sional parameters were dominant in the dynamic flow regime. These results are
expected to lay a solid foundation for further research in systematic DEM cali
bration and greatly increase the effectiveness of DEM models in bulk materials
handling applications. / XL2019
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/26654 |
| Date | January 2018 |
| Creators | Guya, Solomon Ramas |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (lxxvi, 302 leaves), application/pdf, application/pdf |
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