This study aims to deduce an appropriate shape and density for an electronic free-cell that could be placed into a silo so that position and other desired physical parameters could be recorded. To determine how density and shape affects the trajectory and displacement of free cells, the trajectory and displacement of cylindrical, cuboid and triangular prism free-cells of equivalent volume was investigated in a discharging quasi 3D silo slice. The free-cells were placed at twelve different starting positions spread evenly over one half of the 3D slice. Tests were conducted using a monosized batch of spherical particles with a diameter of approximately 5 mm. Tests were also conducted in a binary mixture consisting of particles of different sizes (5 mm/4 mm) and the same density (1.28 g/cm3) and a binary mixture consisting of particles of different size (6 mm/5 mm) and different densities (1.16 g/cm3/1.28 g/cm3).The rotation of the free cells was also briefly discussed.Computer simulations were conducted using the Discrete Element Method (DEM). The simulation employed the spring-slider-dashpot contact model to represent the normal and tangential force components and the modified Euler integration scheme was applied to calculate the particle velocities and positions at each time step. One trial of each of the metal and plastic, cylindrical, cuboid and triangular prism free cells was compared with the average of three experimental trials. The trajectory and displacement of a representative particle positioned at the same starting position as the free cell was also obtained from DEM simulation and compared with the path and displacement of each of the free cells to determine which free cell followed the particle most closely and hence to determine a suitable free cell that would move with the rest of the grains. Spherical particles are idealised particles. Therefore tests were also conducted with a small number of polyhedral particles, to deduce their flow rate and the critical orifice width at which blockages were likely to form. Simulations were also conducted to test the feasibility of the DEM in modelling the behaviour of these polyhedral particles.Results indicate that for a free cell to move along the same trajectory and have the same displacement and velocity as an equivalent particle in the batch it should have a similar density to the majority of the other particles. A cylindrical free cell of similar density to the particles was found to follow the path of the representative particle more closely than the cuboid or triangular prism. Polyhedral particles were found to have a greater flow rate than spherical particles of equivalent volume.

<div>Thermal barrier coatings (TBCs) made of low thermal conductivity ceramic topcoats have been extensively used in hot sections of gas turbine engines, in aircraft propulsion and power generation applications. TBC damage may occur during gas turbine operations, due to either time- and cycle-dependent degradation phenomena, external foreign object damage, and/or erosion. The damaged TBCs, therefore, need to be removed and repaired during engine maintenance cycles. Although several coating removal practices have been established which are based on the trial-and-error approach, a fundamental understanding of coating fracture mechanisms during the removal process is still limited, which hinders further development of the process.</div><div>The objective of the thesis is to develop a particle-based coating removal modeling framework, using both the smoothed particle hydrodynamics (SPH) and discrete element modeling (DEM) methods. The thesis systematically investigates the processing-property relationships in the TBC removal processes using a modeling approach, thus providing a scientific tool for process design and optimization.</div><div>To achieve the above-mentioned objective, the following research tasks are identified. First a comprehensive literature review of major coating removal techniques is presented in Chapter 2. Chapter 3 discusses an improved SPH model to simulate the high-velocity particle impact behaviors on TBCs. In Chapter 4, the abrasive water jet (AWJ) removal process is modeled using the SPH method. In Chapter 5, an SPH model of the cutting process with regular electron beam physical vapor deposition (EB-PVD) columnar grains is presented. In Chapter 6, a 3D DEM cutting model with regular EB-PVD column grains is discussed. In Chapter 7, a 2D DEM cutting model based on the realistic coating microstructure is developed. Finally, in Chapter 8, based on the particle-based coating removal modeling framework results and analytical solutions, a new fracture mechanism map is proposed, which correlates the processing parameters and coating fracture modes.</div><div>The particle-based modeling results show that: (1) for the SPH impact model, the impact hole penetration depth is mainly controlled by the vertical velocity component. (2) The SPH AWJ simulation results demonstrate that the ceramic removal rate increases with incident angle, which is consistent with the fracture mechanics-based analytic solution. (3) The SPH model with regular EB-PVD columnar grains shows that it is capable to examine the stress evolutions in the coating with columnar grain structures, which is not available if a uniform bulk coating model was used. Additional analysis reveals that the fracture of the columnar grains during the cutting process is achieved through deflection and fracture of the grains, followed by pushing against neighboring grains. (4) The 3D DEM model with regular coating columnar grains shows that, during the coating removal process, a ductile-to-brittle transition is identified which depends on the cutting depth. The transition occurs at the critical cutting depth, which is based on the Griffith fracture criterion. At small cutting depths, the ductile failure mode dominates the cutting process, leading to fine cut particles. As the cutting depth exceeds the critical cutting depth, a brittle failure mode is observed with the formation of chunk-like chips. (5) The 2D DEM model with the realistic coating microstructure shows that there are densification and fracture during the foreign object compaction process, which qualitatively agrees with the experimental observations. (6) The newly proposed coating fracture mechanism map provides guidance to predict three fracture modes, i.e., ductile brittle, and mixed ductile-brittle, as a function of processing parameters, including the cutting depth and cutting speed. The map can be used to determine the processing conditions based on required TBC removal operations: rough cut (brittle mode), semi-finish (mixed ductile-brittle mode), and finish (ductile mode).</div><div><br></div>

<p>Discrete element method (DEM) modeling is a common way to model particulate systems and processes. Since the number of particles in most pharmaceutical processes is incredibly large, modeling these substantial magnitudes of particles individually using DEM is not computationally reasonable. To simplify the DEM modeling, agglomerates or groups of particles are modeled instead. This change creates a disconnect between the real particle parameter values and the simulated particle parameter values. Thus, efficient and accurate calibration is needed for effective modeling. </p> <p>The methodology proposed in this thesis utilized a single commonly used bulk flowability measurement device, an annular shear cell, to calibrate for these DEM parameters with the help of dimensional analysis, design of experiments, and statistical tools. Three bulk responses were studied from the ring shear cell: the incipient yield internal friction angle, the critical state internal friction angle, and the bulk cohesion. The most important DEM parameters were isolated and subjected to a dimensional analysis to increase the generality of the results. A modified full-factorial study was then set up using the identified dimensionless parameters. The final calibration results were then validated using an independent flow through an orifice test using a Flodex^TM. </p> <p>This thesis demonstrates this proposed calibration methodology using three different powder samples, lactose, (hydroxypropyl) methyl cellulose (HPMC), and ABT-089. Using the DEM simulation results and the experimental measurements, predictive models were created for all three powder samples. For HPMC, the calibration errors were large while using spherical particles, so a non-spherical particle shape was introduced using the glued-sphere model in DEM. The calibration process was repeated with simulated non-spherical particles with an aspect ratio of two to create a new model for HPMC. </p> <p>The overall calibration procedure and the three models, when validated with the Flodex simulations and measurements, successfully predicted the Flodex results within one Flowability index range for all three powder samples. This demonstrates that this methodology can be used to successfully calibrate various DEM simulation parameters.</p>

Integral bridges are designed without expansion joints or bearings to eliminate the maintenance and repair costs associated with them. Thus, the expansion and contraction due to daily and seasonal temperature variations of the deck of the bridge are restricted by the abutments, causing the abutments to move cyclically towards and away from the granular material used as backfill. This movement results in a stress accumulation in the backfill retained by the abutments. The Discrete Element Method (DEM) was used was used to perform a numerical sensitivity analysis, investigating the effect of granular particle shape on the response of backfill material retained by integral bridge abutments.   Two DEM software suites were used to perform the simulations, namely STAR-CCM+, a commercial code, and Blaze-DEM, a research code under development at the University of Pretoria. Blaze-DEM makes use of Graphics Processing Unit (GPU) computing as opposed to traditional Central Processing Unit (CPU) computing. Blaze-DEM delivered computational times over 150 times faster than the equivalent simulation in STAR-CCM+. The results from the numerical sensitivity analysis showed that the particles with lower sphericities (higher angularities) experienced larger accumulations of stresses on the abutment as opposed to the more spherical particles. This was suggested to be a result of particle interlocking and reorientation. / Dissertation (MEng)--University of Pretoria, 2018. / Civil Engineering / MEng / Unrestricted

The goal of the project was to characterize the granular flows impact on the gas flow in a packed-bed-reactor. The study was created at Swerim as a master's thesis for Luleå University of Technology. The packed-bed-reactor geometry used in this study is a scaled down blast furnace model. The granular flow was modelled using the discrete element method (DEM) in LS-DYNA. Four models were created with different sizes and size distribution of the particles. To study the granular flows impact on gas flow, porosity is extracted from the DEM models and analyzed, since porosity has a direct impact on the gas flow. The supervisors form Swerim, Joakim Eck and Martin Flemström created computational fluid dynamics (CFD) models in Ansys Fluent using the porosity from the DEM models. The DEM results are presented as granular flow profiles. This flow profile is created by injecting particles with alternating colors to see this profile. A total of 6 images are taken over the whole process. The porosity results are presented as a porosity field plots of the extracted porosity data using MATLAB. The CFD results are presented as plots of gas velocity and absolute pressure. The results show the different characteristics of the flow in the different DEM models, and how it relates to the different porosity fields that were found. Furthermore, the CFD models show how the flow of the gas is dependent on the porosity.

According to Swedish guidelines for high speed railways on embankment, the total settlement is limited to 20 mm over a track length of 10 m during the construction service life. The main objective of this thesis was to investigate the deformation in the subgrade (unbound layer) in a slab track, since there are very few studies related to high speed railways on high earth structure, discussing particularly the unbound layer. This thesis examined the unbound layer consisting of granular material by using the discrete element method (DEM) software PFC. There was a focus on the material compaction and deformations due to traffic loading. DEM has the benefit to be able to model deformation with due consideration of processes at microscale level. Two different particle shapes were tested: balls and clumps. The results showed that the settlements were small, possibly associated to the well compacted material and the simplifications in the model, such as the shape of the particles, absence of particle breakage and the applied traffic load. The clump simulations resulted in less settlements and permanent strains compared to the ball simulations. The higher the embankment the more settlements but less strains were produced for all the three simulations. One interesting parameter to study for the balls simulation was the friction between the particles. Increased friction contributed to less settlement. The maximum height of the embankment was limited to around 3,2 m due to time restraints. Simulations for higher embankments are needed to be performed in order to better understand the effect of the embankment height on settlements.

In soil, where trees and crops grow, heavy vehicles shear and compact the soil, leading to reduced plant growth and diminished nutrient recycling. Computer simulations offer the possibility to improve the understanding of these undesired phenomena. In this thesis, soils were modelled as large collections of contacting spherical particles using the Discrete Element Method (DEM) and the physics engine AGX Dynamics, and these entities were analyzed. In the first part of the thesis, soils, which were considered to be continua, were subjected to various controlled deformations and fields for quantities such as stress and strain were visualized using coarse graining (CG). These fields were then compared against analytical solutions. The main goal of the thesis was to evaluate the usefulness, accuracy, and precision of this plotting technique when applied to DEM-soils. The general behaviour of most fields agreed well with analytical or expected behaviour. Moreover, the fields presented valuable information about phenomena in the soils. Relative errors varied from 1.2 to 27 %. The errors were believed to arise chiefly from non-uniform displacement (due to the inherent granularity in the technique), and unintended uneven particle distribution. The most prominent drawback with the technique was found to be the unreliability of the plots near the boundaries. This is significant, since the behaviour of a soil at the surface where it is in contact with e.g. a vehicle tyre is of interest. In the second part of the thesis, a vehicle traversed a soil and fields were visualized using the same technique. Following a limited analysis, it was found that the stress in the soil can be crudely approximated as the stress in a linear elastic solid.

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This work aims to develop and implement a linear elastic grain-level micromechanical model based on the discrete element method using bonded contacts and an improved fracture criteria to capture both intergranular and transgranular microcrack initiation and evolution in polycrystalline ceramics materials. Gaining a better understanding of the underlying mechanics and micromechanics of the fracture process of brittle polycrystalline materials will aid in high performance material design. Continuum mechanics approaches cannot accurately simulate the crack propagation during fracture due to the discontinuous nature of the problem. In this work we distinguish between predominately intergranular failure (along the grain boundaries) versus predominately transgranular failure (across the grains) based on grain orientation and microstructural parameters to describe the contact interfaces and present the first approach at fracturing discrete elements. Specifically, the influence of grain boundary strength and stiffness on the fracture behavior of an idealized ceramic material is studied under three different loading conditions: uniaxial compression, brazilian, and four-point bending. Digital representations of the sample microstructures for the test cases are composed of hexagonal, prismatic, honeycomb-packed grains represented by rigid, discrete elements. The principle of virtual work is used to develop a microscale fracture criteria for brittle polycrystalline materials for tensile, shear, torsional and rolling modes of intergranular motion. The interactions between discrete elements within each grain are governed by traction displacement relationships.

Micromechanics of solidluid interactions can play a key role controlling macro-scale engineering behavior of granular media. The main objective of this study is to numerically investigate the micromechanics involved in solidluid mixtures to develop a better understanding of the macroscopic behavior of granular media for different applications. This is accomplished by developing a numerical model coupling the Discrete Element Method (DEM) and the Lattice Boltzmann Method (LBM) and employing it to study three distinct yet interrelated applications throughout the course of this research. In the first application, the DEM model is used to provide a clear relationship between energy dissipated by micro-scale mechanisms versus the traditional engineering definition based on macro-scale (continuum) parameters to develop a better understanding for the frictional behavior of granular media. Macroscopic frictional behavior of granular materials is of great importance for studying several complex problems such as fault slip and landslides. In the second application, the DEM-LBM model is employed for studying the undrained condition of dense granular media. While the majority of previous modeling approaches did not realistically represent non-uniform strain conditions that exist in geomechanical problems, including the LBM in the proposed model offers a realistic approach to simulate the undrained condition since the fluid can locally conserve the system volume. For the third application, the DEM-LBM model is used to study discontinuous shear thickening in a dense solidluid suspension. Shear thickening in a fluid occurs when the viscosity of the fluid increases with increasing applied strain rate. The DEM-LBM results for discontinuous shear thickening were compared to experimental data and proved to be an accurate approach at reproducing this phenomenon. The validated DEM-LBM model is then used to develop a physics-based constitutive model for discontinuous shear thickening-shear thinning in granular medialuid suspension. A closedorm model is then calibrated using the DEM-LBM model and validated against existing experimental test results reported in the literature. Findings of this research demonstrate how micromechanical modeling can be employed to address challenging problems in granular media involving solidluid interaction.