The calibration of material properties for use in discrete element models

Horn, Etienne (2012-03)

Thesis (MScEng)--Stellenbosch University, 2012.

Thesis

ENGLISH ABSTRACT: One of the main challenges in using the Discrete Element Method (DEM) is to specify the correct input parameter values. In general, the models are sensitive to the input parameter values and accurate results can only be achieved if the correct values are specified. For the linear contact model, micro parameters such as the particle density, stiffness, coefficient of friction, as well as the particle size and shape distributions are required. Thus, there is a need for a procedure to accurately calibrate these parameters before any attempt can be made to accurately model a complete bulk materials handling system. Since the DEM is often used to model applications in the mining and quarrying industries, a calibration procedure was developed for materials that consist of relatively large (up to 40 mm in size) particles. A coarse crushed aggregate was used as the test material. Using a specially designed large scale shear box, the confined Young’s Modulus and internal friction angle of the material were measured by means of the confined compression test and the direct shear test respectively. The bulk (macro) density and porosity were also measured. The particle size distribution was measured while visual inspection was used to identify the different particle shapes. DEM models of the experimental set-up were developed and the input parameter values were varied iteratively until a close correlation between the experimental and numerical results was achieved. The resulting set of input parameter values were then verified through a series of anchor pull-out and angle of repose experiments and simulations. A good correlation between the experimental and numerical results was observed. In a study, independent of the calibration process, a half fraction factorial design was implemented to quantify the effect of the input parameter values on the bulk properties and to construct multiple linear regression models that relate the parameters to the bulk properties. The results were found to be in accordance with expected bulk behaviour, and can be used to develop advanced DEM calibration strategies. Based on the project outcomes, it was concluded that the developed calibration procedure performed satisfactorily and that the calibrated input parameters allow for the accurate modelling of the coarse aggregate.

AFRIKAANSE OPSOMMING: Een van die groot uitdagings in die gebruik van die Diskreet Element Metode (DEM) is om die korrekte invoer parameterwaardes te spesifiseer. Die modelle is in die algemeen sensitief vir die invoer parameterwaardes, en akkurate resultate kan slegs verkry word indien die korrekte waardes gespesifiseer word. Mikroparameters soos partikeldigtheid, styfheid, wrywingskoëffisiënt, die partikelgrootte verspreiding asook die partikelvorm verspreiding, word benodig vir die lineêre kontakmodel. ’n Prosedure word dus benodig om hierdie parameters akkuraat te kalibreer alvorens ’n volledige korrelagte materiaalhanteringstelsel akkuraat gemodelleer kan word. Aangesien die DEM gereeld in die modellering van myn- en gruisgroefbedryf toepassings gebruik word, is ’n kalibrasieprosedure ontwikkel vir materiaal wat bestaan uit relatief groot (tot 40 mm in grootte) partikels. Grofgebreekte klippe is as toetsmateriaal gebruik. Deur gebruik te maak van ’n spesiaal ontwerpte grootskaal-skuifboks is die ingeperkte Young se Modulus en die interne wrywingshoek van die materiaal gemeet deur middel van die ingeperkte kompressietoets en die direkte skuiftoets onderskeidelik. Die makro-digtheid en poreusheid is ook gemeet. Die partikelgrootte verspreiding is gemeet terwyl visuele inspeksie gebruik is om die verskillende partikelvorms te identifiseer. DEM modelle van die eksperimentele opstelling is ontwikkel en die invoer parameterwaardes is herhaaldelik gewysig totdat ’n goeie korrelasie verkry is tussen die eksperimentele en numeriese resultate. Die gevolglike stel invoer parameterwaardes is daarna geverifieer deur ’n reeks ankeruittrek- en natuurlike helling eksperimente en simulasies. In ’n studie, onafhanklik van die kalibrasieproses, is die half-fraksie faktoriaalontwerp geïmplementeer om die invoer parameterwaardes se effek op die makro eienskappe te kwantifiseer en om meervoudige lineêre regressiemodelle te ontwikkel wat die parameters met die makro eienskappe verbind. Die resultate was in ooreenstemming met die verwagte makro gedrag en kan gebruik word om gevorderde DEM kalibrasie-strategieë te ontwikkel. Daar is tot die gevolg gekom dat, gebaseer op die projekresultate, die ontwikkelde kalibrasieprosedure bevredigend presteer en dat die gekalibreerde invoer parameters die akkurate modellering van die grofgebreekte klippe toelaat.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/20088
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