Thesis (MScEng)--Stellenbosch University, 2012. / 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20088 |
| Date | 03 1900 |
| Creators | Horn, Etienne |
| Contributors | Coetzee, C. J., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 122 p. : ill. |
| Rights | Stellenbosch University |
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