Calibration of discrete element modelling parameters for bulk materials handling applications
Guya, Solomon Ramas
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.
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
Guya, Solomon Ramas (2018) Calibration of discrete element modelling parameters for bulk materials handling applications, University of the Witwatersrand, Johannesburg, <http://hdl.handle.net/10539/26654>