The main objective of the research was to understand hemp processing at different stages through numerical simulations. Processing of hemp materials involves breaking the hemp into different sizes of particles and separating those particles into fractions of different sizes. Numerical models were developed using the discrete element method (DEM) to simulate hemp processing using a hammermill and separations of different hemp particles using a 3D vibratory screen-type separator. The models were implemented using a commercial DE code, the Particle Flow Code in Three Dimension (PFC3D). In the models, virtual hemp, hemp fibre and core were defined using clusters of PFC3D basic spherical particles which are connected by the PFC3D parallel bonds. The microproperties (e.g. particle stiffness and friction coefficient, and bond stiffness and strength) of these particles were calibrated. For calibrations, virtual tests were performed using PFC3D for hemp stem, fibre, and core. Those virtual tests included direct shear tests of fibre and core particles, tensile tests of fibre, and compression tests of hemp stems. The microproperties of these particles were calibrated through comparing results from the virtual tests with results from laboratory tests or literature data. Those calibrated particle microproperties were used in the PFC3D models developed for simulating the hammermill for hemp processing and the 3D vibratory separator for particle separation. These two machines were constructed using various PFC3D walls and lines, and had the main features and operational conditions as the real machines. The hammermill model was able to predict the power requirement of hammermill and particle dynamic behaviours (kinetic and strain energies) within the hammermill. The separator model was capable of predicting the separation efficiency of the 3D vibratory separator for separations of different hemp particle mixtures. The behaviour of the models reflected the real behaviour observed experimentally. The model results were reasonably good as compared with literature data and the test results. The models developed have the potential to simulate many other dynamic attributes of hemp particles with the machines. This study has laid a solid foundation for future studies of biomaterial-machine interactions using the DEM.

The objectives of the study were to evaluate the soil disturbances and manure dispersion created by the AerWay aerator in a silt loam soil; and to generate a calibrated and validated soil-tool model using Discrete Element Methods (DEM) that simulate the draft and vertical forces of the aerator. The experimental results showed that a trend indicated that the faster tractor speeds would disturb more soil. After one hour with the manure application rate of 42 000 L/ha, manure was spread to a depth of 250 mm, 200 mm in the forward direction and 100 mm in the lateral direction. The model draft forces had a relative error of 13.4-31.2% when compared to the literature data between 100-150 mm depth while the predicted vertical force was found to linearly increase until 150 mm depth at around 700 N per rolling tine and plateaus until the full insertion of 200 mm.

The objectives of the study were to evaluate the soil disturbances and manure dispersion created by the AerWay aerator in a silt loam soil; and to generate a calibrated and validated soil-tool model using Discrete Element Methods (DEM) that simulate the draft and vertical forces of the aerator. The experimental results showed that a trend indicated that the faster tractor speeds would disturb more soil. After one hour with the manure application rate of 42 000 L/ha, manure was spread to a depth of 250 mm, 200 mm in the forward direction and 100 mm in the lateral direction. The model draft forces had a relative error of 13.4-31.2% when compared to the literature data between 100-150 mm depth while the predicted vertical force was found to linearly increase until 150 mm depth at around 700 N per rolling tine and plateaus until the full insertion of 200 mm.

The main objective of the research was to understand hemp processing at different stages through numerical simulations. Processing of hemp materials involves breaking the hemp into different sizes of particles and separating those particles into fractions of different sizes. Numerical models were developed using the discrete element method (DEM) to simulate hemp processing using a hammermill and separations of different hemp particles using a 3D vibratory screen-type separator. The models were implemented using a commercial DE code, the Particle Flow Code in Three Dimension (PFC3D). In the models, virtual hemp, hemp fibre and core were defined using clusters of PFC3D basic spherical particles which are connected by the PFC3D parallel bonds. The microproperties (e.g. particle stiffness and friction coefficient, and bond stiffness and strength) of these particles were calibrated. For calibrations, virtual tests were performed using PFC3D for hemp stem, fibre, and core. Those virtual tests included direct shear tests of fibre and core particles, tensile tests of fibre, and compression tests of hemp stems. The microproperties of these particles were calibrated through comparing results from the virtual tests with results from laboratory tests or literature data. Those calibrated particle microproperties were used in the PFC3D models developed for simulating the hammermill for hemp processing and the 3D vibratory separator for particle separation. These two machines were constructed using various PFC3D walls and lines, and had the main features and operational conditions as the real machines. The hammermill model was able to predict the power requirement of hammermill and particle dynamic behaviours (kinetic and strain energies) within the hammermill. The separator model was capable of predicting the separation efficiency of the 3D vibratory separator for separations of different hemp particle mixtures. The behaviour of the models reflected the real behaviour observed experimentally. The model results were reasonably good as compared with literature data and the test results. The models developed have the potential to simulate many other dynamic attributes of hemp particles with the machines. This study has laid a solid foundation for future studies of biomaterial-machine interactions using the DEM.

No description available.

Shear banding is a commonly observed yet complex form of instability in granular media by which the deformation is localized in a narrow zone along a certain path. The aim of this study is to investigate the micromechanics of shear banding using the discrete element method (DEM). For this purpose, a model was developed and calibrated to simulate the macroscale behavior of sand under plane strain conditions. Upon validation against laboratory experiments, two types of confining boundaries, displacement- and force-controlled, were examined to study the kinematics of shear bands. A constant volume test was then used to investigate the evolution of antisymmetric stresses before, during, and after shear band formation. The results indicate that the antisymmetric stresses significantly increase within the shear band throughout the loading history, but may not describe the precursory shear band conditions. The DEM model is shown to properly capture the micromechanics of shear bands.

Cementation is known to significantly influence the mechanical and hydrologic properties of granular porous media by increasing the stiffness of the elastic response to stress and reducing permeability. The relationship between the changes in cementation and changes in permeability are well documented in literature. However, limited quantitative data exists on the relationship between changes in the amount of cementation and changes in the mechanical response of granular media. The goal of this research is to quantify the effects of cementation on the mechanical properties of granular porous media at the meso-scale and investigate the influence of the competing roles of mechanical and hydrologic properties on fluid flow and deformation at the macro-scale. To accomplish this goal, we developed a multiple scale approach that utilizes the parameterization control of meso-scale Discrete Element Method (DEM) models and the ability to couple fluid flow and solid deformation physics with macro-scale poro-elasticity models. At the meso-scale, a series of DEM models are designed to simulate biaxial tests of variably cemented sandstone in order to investigate the effects of cementation on the elastic and inelastic response of the porous media. The amount of cementation in the DEM model is quantified using a bond to grain ratio (BGR). The BGR is the number of bonds (the bonds represent the cement) divided by the number of grains in each model. The BGRs of the DEM models correlate to BGRs of natural samples and allow constraint of the percent cementation in the DEM models. A decrease in BGR from 2.25 to 1.00 results in a two fold decrease in shear modulus. The resulting shear moduli from the DEM models are used as input properties into two dimensional, axial symmetric poroelastic models of an isotropic confined aquifer. The poroelastic models address the implications of changes in mechanical properties and hydrologic properties on large scale fluid removal and deformation as well as address the importance of the competing roles of hydrologic and mechanical properties.

No description available.

Pavement is usually composed of aggregate, asphalt binder, and air voids; rigid pavement is built with hydraulic cement concrete; reinforced pavement contains steel. With these wide ranges of materials, different mechanical behaviors need to be defined in the pavement simulation. But so far, there is no research providing a comprehensive introduction and comparison between various contact models. This paper will give a detail exploration on the contact models that can be potentially used in DEM pavement simulation; in the analysis, it includes both a theoretical part, simulation results and computational time cost, which can reveal the fundamental mechanical behaviors for the models, and that can be a reference for researchers to choose a proper contact model. A new contact model—the power law viscoelastic contact model is implemented into software PFC 3D and is numerically verified. Unlike existing linear viscoelastic contact models, the approach presented in this thesis provides a detailed exploration of the contact model for thin film power-law creeping materials based on C.Y Chueng's work. This model is aimed at simulating the thin film asphalt layer between two aggregates, which is a common structure in asphalt mixtures. Experiments with specimens containing a thin film asphalt between two aggregates are employed to validate the new contact model. / Master of Science

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The increased necessity to obtain power from other sources than conventional fossil fuels has led to the growing interest in solar power. The problem with the proposed technology is that it can only provide power during the day and therefore requires some sort of storage system, if power is to be supplied throughout the day and night. A number of storage systems exist, but the one of particular interest for this research, is packed rock beds. Rock beds have the advantage that if designed right, they have the potential to be one of the most cost effective means of storing thermal energy for solar power plants. Discrete Element Models (DEM) of rock beds were therefore developed through both experimental and numerical procedures, by conducting a series of sensitivity, calibration and verification studies. The developed models were then used to study various aspects associated with rock beds, which were either too impractical, impossible or too expensive to conduct through actual experimental work. This research focused specifically on the potential of constructing self-supporting tunnels within the rock beds in order to improve the air flow uniformity through the bed, while minimizing the pressure drop. It was observed that if the appropriate steps were followed, stable self-supporting tunnels could be formed. Valuable information such as the rock orientations resulting from different packing directions could also be derived from the models and finally, a method to convert the DEM models into the appropriate format such that it could be imported into a CFD preprocessor for future CFD studies, was developed. / AFRIKAANSE OPSOMMING: Die verhoogde noodsaaklikheid om energie te verkry uit ander bronne as konvensionele fossielbrandstowwe, het gelei tot die groeiende belangstelling in sonkrag energie. Die probleem met die voorgestelde tegnologie is dat dit net energie gedurende die dag kan voorsien en dus word daar ’n stoorstelsel benodig indien energie deur beide die dag en nag voorsien moet word. Tans bestaan daar wel ’n aantal van hierdie stoorstelsels, maar die een wat van besondere belang is in hierdie navorsing, is verpakte klip beddens. Klip beddens het die voordeel dat, indien dit reg ontwerp is, dit oor die potensiaal beskik om een van die mees koste-doeltreffende middels te wees vir die stoor van termiese energie vir sonkragstasies. Diskreet Element Modelle (DEM) van die klip beddens is ontwikkel deur gebruik te maak van beide experimentele en numeriese metodes waartydens ’n reeks sensitiwiteits-, kalibrasie- en verifiëring studies uitgevoer is. Die ontwikkelde modelle is gebruik om verskeie aspekte van klip beddens te ondersoek, wat of te onprakties, onmoontlik of te duur is vanuit ’n eksperimentele oogpunt. Hierdie navorsing het spesifiek gefokus op die potensiaal om self-ondersteunende tonnels binne in die klip beddens te vorm, ten einde die egaligheid van die lugvloei deur die bed te verbeter, terwyl die drukval geminimeer word. Daar is waargeneem dat stabiele self-ondersteunende tonnels wel gevorm kon word indien die toepaslike stappe gevolg is. Waardevolle inligting soos die klip oriëntasies wat as gevolg van die verskillende verpakkings rigtings onstaan kon ook vanuit die model verkry word. Ten slotte is ’n metode ontwikkel om die DEM modelle na die toepaslike formaat te omskep sodat dit ten einde gebruik kan word in numeriese vloeidinamika studies.