<p>Most of the food, pharmaceutical, and chemical industries rely heavily on the supply of free-flowing powders that finds their application in raw materials, additives, and manufactured products. Improper storage conditions combined with environmental factors affect the free-flowing ability of powders. An undesirable transformation of these free-flowing powders into a coherent mass that resists flow is called caking.  </p> <p>Given the difficulty in quantifying the interparticle forces, both experimentally and numerically, most studies have considered only the humidity effect in powder caking. In this study, the interparticle forces in caked powders were quantified using the simplified Johnson-Kendall-Roberts (JKR) model to account for the material and environmental factors that influence powder caking. The cohesion energy density, which is the ratio of cohesive energy to volume of the particle, was used as the indicator of caking in powders. Simulated force chain network was used to track the relay of interparticle forces under compression. The model was validated experimentally by using caked isomalt powder. The results of the simulations demonstrated that an initial interparticle force of less than 0.01 N did not result in a caked mass. The cohesion energy density was found to be more sensitive to moisture content than consolidation pressure. A 33% increase in moisture at the same consolidation pressure increased the cohesion energy density by 42.45% while a 50% increase in consolidation pressure at the same moisture content increased the cohesion energy density only by 12.23%. </p> <p>In similar, to understand the progression of caking at the bulk level, the development of tensile strength in isomalt with changes in temperature, relative humidity, and consolidation pressures was modeled and validated using the finite element method. In this model, Darcy's equation and species transport equation was used to model the continuity and momentum transfer in porous media. The heat transfer equation was used to solve the energy and the solid bridging model was used to the tensile strength. This study revealed that storing isomalt above 25 ˚C and 85±0.1% RH could initiate caking or increase in tensile strength. An increase in RH from 85% to 86% increased the tensile strength magnitude by 42.7%. Additionally, the study recommends lowering the consolidation pressures during storage to less than 3 kPa.</p> <p>To mitigate caking, a powder flow aid device that could transmit vibration energy to powders through direct contact was developed. The device could be controlled remotely using an android application. The portable flow aid device was then tested under static and dynamic conditions and thereby the evolution of stresses during the operation of the device was mathematically analyzed. The decrease in static angle of repose of isomalt using the developed flow aid device for moisture contents of 3.84, 4.84, and 5.92 % was 45, 42.5, and 33 %. The dynamic analysis revealed that the developed device improved the flow rate of isomalt at 3.82% moisture by about 17.64%. On the other hand, a flow obstruction was observed in isomalt at moisture contents of 4.79% and 5.88%. The device was found to aid the flow of isomalt at 4.79% moisture. These observations were mathematically explained using the stress evolution model which predicted a flow obstruction for isomalt at 4.79 and 5.88% moisture contents.</p> <p> </p> <p><br></p>

Sublevel caving is an underground mass mining method that utilizes the gravity-induced material flow for ore extraction. The granular flowbehavior is one of the main phenomena describing this mining method’s efficiency; therefore, a good understanding of the flow behavior is essential.The knowledge of the material flow behavior evolved in the late 1950:s when the mining method became more commonly used. However, due tothe complexity of the granular material flow, all parameters are not well studied, and a lack of knowledge still exists. With the increasing mining depths, higher stresses will occur inside the rock mass. How these increased stresses influence flow behavioris one of the parameters that are not well studied. Unfortunately, manipulating these is challenging in physical material models and mighteven be impossible in field experiments. However, achieving such control is possible using a discrete element method software. The model developedfor this thesis simulates pre-stressed rock mass up to 50 MPa and monitors the flow behavior in the software PFC3D. The result showed that the increased stress had the potential of causing a stable configuration of material inside the opening ring, known as a hangup.The hang-up later was destabilized when the blast continued to the next ring. For the chosen blasting geometry, the shape of the draw zone of thematerial that reached the extraction point did not seem to be affected by the stresses. / Skivrasbrytning är en gruvbrytningsmetod som nytjar flödet av material som skapas av graviationen och dess effektivitet är starkt kopplad tillbetendet hos materialflödet. Sedan gruvbrytningsmetoden blev allt vanligare i slutet av 1950-talet har ett flertal experiments konstrueratsför att utvärdera de parametrar som har antagits ha en inverkan på flödet, vilket resulterat i en effektivare gruvbrytningsmetod. På grund avkomplexiteten hos materialflödet är inte alla parametrar lika väl studerade, och brist på kunskap existerar fortfarande. Med de fortsatt ökande djupen i gruvorna, förväntas allt högre spänningar inuti berget, och hur dessa påverkar materialflödet är inte välstuderat. Dessa spänningar är svåra att kontrollera i både materialmodeller och vid fältförsök. Med distinkt elementmetodprogramvara kan däremotspänningarna i berget kontrolleras och flödesbeteendet studeras. I den modell som byggts för detta arbete utvärderas spänningar upp till 50 MPai programvaran PFC3D. Resultatet från simuleringarna utförda i PFC3D visade att de ökade spänningarna kan orsaka upphängning av materialet i öppningskransen.Flödet återupprättades när brytningen fortgick till nästa krans. Utöver detta studerades flödesbeteendet av det material som nådde uttagspunkten,där visade resultatet att omgivningstrycket inte har en inverkan på flödet för den valda sprängningsgeometrin.

In this study, experiments and simulations were conducted to investigate ice and snow. The ice sintering force as a function of temperature, pressing force (contact load), contact duration, and particle size during the primary stage of sintering was formulated using experimental methods along with an approximate, semi-analytic, close-form solution. It was shown that the ice sintering force increases nearly linear with increasing external pressing force but best approximated as a power law for dependency on both contact duration and particle size. Moreover, the exponent of the power law for size dependence is around the value predicted by general sintering theory. The temperature dependence of the sintering force is highly nonlinear and follows the Arrhenius equation. It was observed that at temperatures closer to the melting point, a liquid bridge is observed upon these paration of the contacted ice particles. The ratio of ultimate tensile strength of ice to the axial stress concentration factor in tension is found as an important factor in determining the sintering force, and a value of nearly 1.1 MPa was estimated to best catch the sintering force of ice in different conditions. From the temperature dependency, the activation energy is calculated to be around 41.4 kJ/mol, which is close to the previously reported value. Also, the results for the sintering force suggest that smaller particles are “stickier” than larger particles. Moreover, cavitation and surface cracking is observed during the formation of the ice particles and these can be one of the sources for the variations observed in the measured ice sintering force values. The presence of a capillary bridge in contact between an ice particle and a "smooth" (or rough) Aluminum surface at relative humidity around 50% and temperatures below the melting point was experimentally demonstrated. Experiments were conducted under controlled temperature conditions and the mechanical instability of the bridge upon separation of the ice particle from the Aluminum surface with a constant speed was considered. It was observed that a liquid bridge with a more pronounced volume at temperatures near the melting point is formed. It was showen that the separation distance is proportional to the cube root of the volume of the bridge. The volume of the liquidbridge is used to estimate the thickness of the liquid layer on the ice particle and the estimated value was shown to be within the range reported in the literature. The thickness of the liquid layer decreases from nearly 56 nm at -1.7◦C to 0.2 nm at -12.7◦C. The dependence can be approximated with a power law, proportional to (TM − T)−β, where β &lt; 2.6. We further observe that for a rough surface, the capillary bridge formation in the considered experimental conditions vanishes. The Discrete Element Method (DEM) was employed to simulate the filling behavior of dry snow. Snow as a heterogeneous, hot material which is constituted from spherical ice particles which can form bonds. The bonding behavior of ice particles is important in determining the macroscopic behavior of snow. The bond diameter of ice-ice contacts as a function of time, compressive load, and strain rate is used and a DEM for dry snow was developed and programmed in MATLAB. A beam element with implemented damage model was used in the simulation. The simulated parameters were macroscopic angle of repose, packing density, and surface conditions as a function of temperature and fillingrate. The DEM results were able to verify the existing published experimental data. The simulation results showed that angle of repose of snow decreased with decreasing the temperature, the surface became irregular due to particles rotation and re-arrangement for lower falling speeds of particles, and density increased with depth of deposition.

The present work applies the hybrid Voronoi cell finite element method (VCFEM) within geomechanics. Coupled seepage and deformation analysis using the VCFEM incorporating body forces allows accurate analysis of earth dams. The development of a novel approach for simulating granular material behaviour using the combined finite-discrete element method (VCFEM-DEM) provides new insights into strain localization in granular materials. Chapter 1 provides background including summary literature reviews for all concepts in the title including seepage analysis, micromechanical and continuum mechanics theory, Voronoi diagrams, finite elements (FEM), discrete elements (DEM) and combined FEM-DEM. Chapter 1 concludes by detailing the contributions of the present work. Chapter 2 presents the VCFEM for seepage analysis. The numerical examples include an investigation of mesh sensitivity and a comparison of conforming shape functions. Polygonal elements with more than four nodes show a decrease in mesh sensitivity in free surface problems, compared with four-node quadrilateral elements. The choice of conforming shape function within the VCFEM analysis did not affect the results. Chapter 3 formulates and applies the VCFEM-DEM, showing that strain localization effects in granular materials are important at all scales. The VCFEM-DEM captures shear banding in biaxial compression tests, demonstrating that global shear strains and inhomogeneities in the shear stress field present after consolidation are early precursors to the failure mode. At the field scale, strain localization can lead to significant non-uniformity in subsurface stress distribution owing to self-weight. Chapter 4 presents the coupled VCFEM for seepage and deformation. A practical example of the design of an earth dam demonstrates the application of general body forces within a hybrid formulation, notably lacking in the literature. Chapter 5 concludes by summarizing the key observations of the present work, and providing direction for future research. The Appendix provides additional details related to numerical integration within the VCFEM. / Thesis / Doctor of Philosophy (PhD) / The focus of the present work is the simulation of geomechanical behaviour at multiple scales. This ranges from simulating the interaction of grains of sand in a laboratory compression test to the seepage of water through and deformation of a large dam constructed of granular material. The simulations use a numerical tool called the Voronoi cell finite element method (VCFEM), which the present work extends to allow accurate analysis of the flow of fluid through a porous medium, deformation of a granular material under load and coupled analysis of these phenomena. The development and testing of this numerical tool for use in geomechanical analysis is itself a contribution. The present work also contains new insights into how localized stresses and strains in a granular material that are present well before the peak strength can have an important influence on the mode of failure.

Cone crushers are used in both the construction and mining industries for the production of aggregates and extraction of ores. Aggregates are used when building for example houses, roads and railways, hence the cone crushers are a vital part of modern society. To ensure the performance of the cone crusher, it is important to properly adjust the feeding conditions. Using computational methods to virtually analyze the performance of the crushers is a more time and cost efficient solution compared to physical testing. This thesis was divided into two parts, where the main objective of the first part was to use the discrete element method (DEM) to analyze the segregation in cone crushers. Three different methods were developed, which later were utilized to compare the segregation for four different feeding conditions. Two of the analysis methods only considered the segregation in the feed hopper, whilst the third method aimed to give an understanding ofthe segregation inside the crushing chamber. The two first methods could successfully be used to compare how segregated the feed material was for the four feeding conditions, however, the third method proved to be both hard to validate and highly dependent on proper material flow inside the crushing chamber. The main objective during the second part of the thesis was to investigate the possibility of running the DEM simulations coupled to a multibody simulation (MBS) software. The simulation routine was then used to compare the foundation loads for the same four feeding conditions as in the first part. The subframe was later modeled as a flexible body to analyze and compare the stresses the subframe was subject to during operation for the same four feeding conditions. Setting up and running the coupled simulation was successful. Different simulation settings were tested, anda general guideline on how those settings should be defined was set up. The actual impact the coupling had on the foundation loads and stresses in the subframe was however almost non-existent. This could probably be directly related to the fact that the crushing forces in EDEM are known to be many times smaller than what they have been measured to in experiments. This also meant that changing the feeding conditions to alter the segregation did not have a noticeable effect on the results.

A computer program based on the discrete-element method has been developed to compute friction factors and Nusselt Numbers for fully-developed turbulent flows with randomly-rough surfaces. Formulations of the discrete-element model for fully-developed turbulent flows inside circular pipes and between infinite parallel plates with the necessary adaptations for randomly-rough surfaces are provided. Utilizing the output of a three-dimensional profilometer, proper description of the randomly-rough surface is necessary for use within the discrete-element model. Proper description of the randomly-rough surface is achieved by the McClain (2002) method of characterization. Predictions from the discrete-element model computer program are compared with the classical, laminar and turbulent, smooth-wall results. In addition to the smooth-wall evaluations, predictions are compared with experimental results for turbulent internal flows with deterministic surface roughness. Predictions from the model demonstrated excellent agreement in all cases. Friction factor and Nusselt Number predictions for fully-developed flows over randomly-rough surfaces are also presented. With the friction factor and Nusselt Number data, velocity profiles for flows over randomly-rough, deterministically-rough and smooth surfaces are provided for comparison.

Granular soils exhibit a generally beneficial change in engineering properties with time after deposition or densification, during a process commonly known as aging. Soil properties reported to change during aging include the small strain modulus and stiffness, penetration resistance, liquefaction resistance, and pile setup. Different hypotheses have been proposed to explain the occurrence of aging in granular soils, including cementation induced by dissolution of silica and precipitation at the particle contacts, cementation due to microbiological activity, internal stress redistribution caused by particle crushing, and buckling of the load chains due to particle slippage. New evidence points out that internal and time-dependent changes in the soil structure caused by particle slippage and rearrangement as the source of the time-dependent variations in soil properties. This investigation is focused on the study of aging at the particle scale to determine its main driving mechanism and define the factors which affect it. Results from an extensive laboratory testing program and computer simulations based on the discrete element method provide insight into the causes of aging and its effects on the macroscopic properties of sands based on the analysis of the interaction between sand grains. / Ph. D.

Optimizing proppant pack conductivity and proppant-transport and -deposition patterns in a hydraulic fracture is of critical importance to sustain effective and economical production of petroleum hydrocarbons. In this research, a numerical modeling approach, combining the discrete element method (DEM) with the lattice Boltzmann (LB) simulation, was developed to provide fundamental insights into the factors regulating the interactions between reservoir depletion, proppant-particle compaction and movement, single-/multiphase flows and non-Darcy flows in a hydraulic fracture, and fracture conductivity evolution from a partial-monolayer proppant concentration to a multilayer proppant concentration. The potential effects of mixed proppants of different sizes and types on the fracture conductivity were also investigated. The simulation results demonstrate that a proppant pack with a smaller diameter coefficient of variation (COV), defined as the ratio of standard deviation of diameter to mean diameter, provides better support to the fracture; the relative permeability of oil was more sensitive to changes in geometry and stress; when effective stress increased continuously, oil relative permeability increased nonmonotonically; the combination of high diameter COV and high effective stress leads to a larger pressure drop and consequently a stronger non-Darcy flow effect. The study of proppant mixtures shows that mixing of similar proppant sizes (mesh-size-20/40) has less influence on the overall fracture conductivity than mixing a very fine mesh size (mesh-size-100); selection of proppant type is more important than proppant size selection when a proppant mixture is used. Increasing larger-size proppant composition in the proppant mixture helps maintain fracture conductivity when the mixture contains lower-strength proppants. These findings have important implications to the optimization of proppant placement, completion design, and well production. In the hydraulic-mechanical rock-proppant system, a fundamental understanding of multiphase flow in the formation rock is critical in achieving sustainable long-term productivity within a reservoir. Specifically, the interactions between the critical dimensionless numbers associated with multiphase flow, including contact angle, viscosity ratio, and capillary number (Ca), were investigated using X-ray micro computed tomography (micro-CT) scanning and LB modeling. The primary novel finding of this study is that the viscosity ratio affects the rate of change of the relative permeability curves for both phases when the contact angle changes continuously. Simulation results also indicate that the change in non-wetting fluid relative permeability was larger when the flow direction was switched from vertical to horizontal, which indicated that there was stronger anisotropy in larger pore networks that were primarily occupied by the non-wetting fluid. This study advances the fundamental understanding of the multiphysics processes associated with multiphase flow in geologic materials and provides insight into upscaling methodologies that account for the influence of pore-scale processes in core- and larger-scale modeling frameworks. During reservoir depletion processes, reservoir formation damage is an issue that will affect the reservoir productivity and various phases in fluid recovery. Invasion of formation fine particles into the proppant pack can affect the proppant pack permeability, leading to potential conductivity loss. The combined DEM-LB numerical framework was used to evaluate the role of proppant particle size heterogeneity (variation in proppant particle diameter) and effective stress on the migration of detached fine particles in a proppant supported fracture. Simulation results demonstrate that a critical fine particle size exists: when a particle diameter is larger or smaller than this size, the deposition rate increases; the transport of smaller fines is dominated by Brownian motion, whereas the migration of larger fines is dominated by interception and gravitational settling; this study also indicates that proppant packs with a more heterogeneous particle-diameter distribution provide better fines control. The findings of this study shed lights on the relationship between changing pore geometries, fluid flow, and fine particle migration through a propped hydraulic fracture during the reservoir depletion process. / Doctor of Philosophy / Hydraulic fracturing stimulation design is required for unconventional hydrocarbon energy (e.g., shale oil and gas) extraction due to the low permeability and complex petrophysical properties of unconventional reservoirs. During hydrocarbon production, fractures close after pumping due to the reduced fluid pressure and increased effective stress in rock formations. In the oil and gas industry, proppant particles, which are granular materials, typically sand, treated sand, or man-made ceramic materials, are pumped along with fracturing fluids to prevent hydraulic fractures from closing during hydrocarbon extraction. In order to relate the geomechanical (effective stress), geometric (pore structure and connectivity), and transport (absolute permeability, relative permeability, and conductivity) properties of a proppant assembly sandwiched in a rock fracture, a geomechanics-fluid mechanics framework using both experiment and simulation methods, was developed to study the interaction and coupling between them. The outcome of this research will advance the fundamental understanding of the coupled, multiphysics processes with respect to hydraulic fracturing and benefit the optimization of proppant placement, completion design, and well production.

Asphalt mix design includes the determination of a gradation, asphalt content, other volumetric properties, the evaluation of mechanical properties and moisture damage potentials. In this study, a computational method is developed to aid mix design. Discrete element method (DEM) was used to simulate the formation of skeleton and voids structures of asphalt concrete of different gradations of aggregates. The optimum gradation could be determined by manipulating the particle locations and orientations and placing smaller particles in the voids among larger particles. This method aims at an optimum gradation, which has been achieved through experimental methods. However, this method takes the mechanical properties or performance of the mixture into consideration, such as inter-aggregate contacts and local stability. A simple visco-elastic model was applied to model the contacts between asphalt binder and aggregates. The surface texture of an aggregate particle can be taken into consideration in the inter-particle contact model. The void content before compactions was used to judge the relative merits of a gradation. Once a gradation is selected, the Voids in Mineral Aggregate (VMA) can be determined. For a certain air void content, the mastics volume or the binder volume or the asphalt content can be determined via a digital compression test. The surface area of all the aggregates and the film thickness can be then calculated. The asphalt content can also be determined using an alternative approach that is based on modeling the inter-particle contact with an asphalt binder layer. In this study, considering the necessity of preservation of the compaction temperature, the effect of various temperatures on Hot Mix Asphalt (HMA) samples properties has been evaluated. As well, to evaluate the effect of this parameter on different grading, two different grading have been used and samples were compacted at various temperatures. Air voids also influence pore water pressure and shrinkage of asphalt binder and mixture significantly. The shrinkage is measured on a digital model that represents beams in a steel mold and is defined as the linear autogenous deformation at horizontal direction. / Ph. D.

According to the Mine Health and Safety Administration (MSHA), between 2006 and 2016, the underground stone mining industry had the highest fatality rate in 4 out of 10 years, compared to any other type of mining in the United States. Additionally, the National Institute for Occupational Safety and Health (NIOSH) stated that structurally controlled instability is a predominant failure mechanism in underground limestone mines. This type of instability occurs when the different discontinuity sets intercept with each other forming rock blocks that displace inwards the tunnel as the excavation takes place, posing a great hazard for miners and overall mine planning. In recent years, Terrestrial laser scanning (TLS) has been used for mapping and characterizing fractures present in a rock mass. TLS is a technology that allows to generate a three-dimensional multimillion point cloud of a scanned area. In addition to this, the advances in computing power throughout the past years, have allowed numerical modeling codes to represent more realistically the behavior of a fractured rock masses. This work presents and implements a methodology that integrates laser scanning technology along with Discrete Element Modeling as tools for characterizing, preventing, and managing structurally controlled instability that may affect large-opening underground mines. The stability of an underground limestone mine that extracts a dipping ore body with a room and pillar (and eventual stoping) mining method is analyzed with this approach. While this methodology is proposed based on a specific case study that does not meet the requirements to be designed with current NIOSH published guidelines, this process proposes a general methodology that can be applied in any mine experiencing similar failure mechanisms, considering site-specific conditions. The aim of this study is to ensure the safety of mine workers and to reduce accidents that arise from ground control issues. The results obtained from this methodology allowed us to generate Probability Density Functions to estimate the probability of rock fall in the excavations. These models were also validated by comparing the numerical model results with those obtained from the laser scans. / M.S. / According to the Mine Health and Safety Administration (MSHA), between 2006 and 2016, the underground stone mining industry had the highest fatality rate in 4 out of 10 years, compared to any other type of mining in the United States. Additionally, the National Institute for Occupational Safety and Health (NIOSH) stated that structurally controlled instability is one of the main causes of rock falls in underground limestone mines. This type of instability occurs when the fractures present in the rock mass intercept each other forming rock blocks that displace into the tunnel as the excavation takes place and poses a great hazard for miners. In recent years, Terrestrial laser scanning (TLS) has been used for mapping and characterizing fractures present in a rock mass. TLS is a technology that allows to generate a three-dimensional multimillion point cloud of a scanned area. In addition to this, the advances in computing power throughout the past years, have allowed simulation softwares such as the Discrete Element Model (DEM) to represent more realistically the behavior of a fractured rock mass under excavation. The aim of this work was to develop and evaluate a methodology that could complement already exisiting design guidelines that may not apply to all kind of underground mines. The presented methodology evaluates rock failure due to presence of discontinuites, through the integration of TLS with DEM and considers site specific conditions. An area of a case study mine was assessed with this methodology, where several laser scans were performed. Information extracted from this laser scans was used to simulate the response of the rock mass under excavation by running Discrete Element Numerical Models. Results from these models allowed us to estimate the probability of rock failure in the analized areas. These, rock block failure probability estimations provide engineers a tool for characterizing, preventing, and managing structurally controlled instability, and ultimately improving workers safety.