Dissertations / Theses: 'Discrete Element Method'

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Ardic, Omer. "Analysis Of Bearing Capacity Using Discrete Element Method." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607866/index.pdf.

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With the developments in computer technology, the numerical methods are used widely in geotechnical engineering. Finite element and finite difference are the most common methods used to simulate the behavior of soil and rock. Although the reliability of these methods are proven in several fields of application over the years, they are not equally satisfactory in every case and require sophisticated constitutive relations to model the discontinuous behavior of geomaterials since they assume the material is continuum or the location of discontinuum is predictable. The Discrete Element Method (DEM) has an intensive advantage to simulate discontinuity. This method is relatively new and still under development, yet it is estimated that it will replace of the continuum methods largely in geomechanics in the near feature. In this thesis, the theory and background of discrete element method are introduced, and its applicability in bearing capacity calculation of shallow foundations is investigated. The results obtained from discrete element simulation of bearing capacity are compared with finite element analysis and analytical methods. It is concluded that the DEM is a promising numerical analysis method but still have some shortcomings in geomechanical applications.

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Chu, Pengbo. "Discrete element method modelling of pulp lifter performance." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106300.

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Pulp lifter assembly is one of the important components at the discharge ends of grate-discharge grinding mills. It discharges grinded materials out through the discharge trunnion like a centrifugal pump running in the reverse direction to that required by a pump. Though it is widely known conventional pulp lifter design associates with drawbacks that cause inefficient discharge operation, little has been done to understand the causes of this particular happening. With the aim to better understand the effects of different pulp lifter designs on the discharge performance and also establish strategies for future design and operation of such equipment, this work is initiated.Three types of industry scaled pulp lifter designs, including two conventional designs and a new design, were comparably studied using Discrete Element Method (DEM) modeling technique. The discharge performances of these designs were evaluated against three criteria which include discharge rate, power consumption, and flow-back/carry-over. The results have shown that pulp lifter assembly with spiral designed radial arms possesses better discharge performance than that with straight radial arms. The discharge performances of three types of designs are also found to be sensitive to some specific design and operating parameters, such as number of vanes, mill rotational speed, the size of particle, and the coefficients of friction. Based on the results, five guidelines on future design and operation of pulp lifter assembly were established. L'assemblage du releveur de pates est l'une des composantes importantes à la sortie de grille termine-décharge des broyeurs. Il décharge des matériaux broyés à travers le tourillon de la décharge comme une pompe centrifuge fonctionnant en sens inverse à celui requis par une pompe. Bien qu'il soit largement connu conventionnels associés de pâte de conception lifter avec des inconvénients qui causent opération de décharge inefficaces, peu de travaux ont été fait pour comprendre les causes de cet événement particulier. Dans le but de mieux comprendre les effets des différentes conceptions du releveur pates sur la performance de décharge et également établir des stratégies pour la conception et l'exploitation futures d'un tel équipement, ce travail est lancé.Trois types de conceptions de releveur de pates d'industrie à l'échelle ont été étudiés, y compris deux conceptions classiques et un nouveau design, à l'aide de technique de modélisation méthode des éléments discrets (MED). Les performances de décharge de ces dessins ont été évalués en fonction de trois critères, qui comprennent le taux de décharge, la consommation d'énergie, et flow-back/carry-over. Les résultats ont montré que l'assemblage de pâte-lève comprenant des bras radiaux conçus en spirale possède une meilleure performance que celle de décharge avec des bras radiaux droits. Les performances de décharge de trois types de conceptions sont également trouvés à être sensibles à certains paramètres spécifiques de conception et d'exploitation, telles que le nombre d'aubes, la vitesse de rotation moulin, la taille des particules, et les coefficients de frottement. Basé sur les résultats, cinq lignes directrices sur la conception et le fonctionnement futurs de l'assemblage pâte-lève ont été établis.

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Brown, Nicholas John. "Discrete element modelling of cementitious materials." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8011.

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This thesis presents a new bonded particle model that accurately predicts the wideranging behaviour of cementitious materials. There is an increasing use of the Discrete Element Method (DEM) to study the behaviour of cementitious materials such as concrete and rock; the chief advantage of the DEM over continuum-based techniques is that it does not predetermine where cracking and fragmentation initiate and propagate, since the system is naturally discontinuous. The DEM’s ability to produce realistic representations of cementitious materials depends largely on the implementation of an inter-particle bonded-contact model. A new bonded-contact model is proposed, based on the Timoshenko beam theory which considers axial, shear and bending behaviour of inter-particle bonds. The developed model was implemented in the commercial EDEM code, in which a thorough verification procedure was conducted. A full parametric study then considered the uni-axial loading of a concrete cylinder; the influence of the input parameters on the bulk response was used to produce a calibrated model that has been shown to be capable of producing realistic predictions of a wide range of behaviour seen in cementitious materials. The model provides useful insights into the microscopic phenomena that result in the bulk loading responses observed for cementitious materials such as concrete. The new model was used to simulate the loading of a number of deformable structural elements including beams, frames, plates and rings; the numerical results produced by the model provided a close match to theoretical solutions.

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BOBADILLA, JORGE RAUL JARAMILLO. "MODELING OF THE SUBLEVEL CAVING METHOD USING THE DISCRETE ELEMENT METHOD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2013. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=35620@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO PROGRAMA DE EXCELENCIA ACADEMICA O método de exploração Sublevel Caving é um dos métodos de extração massiva mais usados na indústria mundial de exploração subterrânea, sendo considerado pela indústria de mineração, num futuro próximo dentre os substitutos naturais das atuais minas a céu aberto. Uma operação Sublevel Caving requer que o maciço rochoso circundante ao minério rompa continuamente e se movimente para dentro do espaço criado pela extração do minério. Análises existentes na literatura consideram apenas configurações parciais do processo Sublevel Caving sem considerar o processo evolutivo da extração, e o dano induzido ao maciço rochoso decorrente deste processo. Esta dissertação desenvolve uma modelagem numérica utilizando o método dos elementos discretos para simular o mecanismo de ruptura e a subsidência causada pelo método de exploração Sublevel Caving, analisando o referido efeito e suas consequências na evolução do mecanismo de ruptura e subsidência no Sublevel Caving. O software comercial Particle Flow Code (PFC2D) foi selecionado para esta modelagem devido à capacidade de simular, em um evento de excesso de tensão, o fraturamento do maciço rochoso e sua desintegração, desta forma, originam-se o fluxo do material e os deslocamentos em grande escala, os quais são considerados fenômenos físicos dominantes que regem a formação da subsidência e fraturamento num processo Sublevel Caving. Os resultados obtidos nesse estudo mostraram-se satisfatórios, reproduzindo adequadamente a superfície de subsidência induzida por Sublevel Caving, conseguindo-se uma simulação física realista da sua evolução desde o início do fraturamento até à subsidência final. The Sublevel Caving Method is one of the most massive extraction methods used in underground mining industry worldwide and is considered by the mining industry as one of the natural replacements of the current open cut mines in the near future. A Sublevel Caving operation requires that the rockmass surrounding the orebody continually fails and moves into the void created by ore extraction. This dissertation develops a modeling using the discrete element method to simulate the failure mechanism and subsidence caused by Sublevel Caving method. Analyses reported in the literature consider only partial configurations of process Sublevel Caving, without taking into consideration the excavation evolution process, and damage induced to the rock mass resulting from this process. This dissertation analyzes this effect and its consequences on the evolution of failure mechanism and subsidence in Sublevel Caving. Particle Flow Code (PFC2D) was selected for modeling because of its ability to simulate, if the event of excess stress, fracturing and disintegration of the rock mass and large-scale deformation and material flow, to be simulated, which are believed to be the dominant physical phenomena governing the formation of subsidence and fracturing of Sublevel Caving. The results obtained in this study were satisfactory, reproducing properly the surface subsidence induced by Sublevel Caving, allowing physically realistic simulation of its evolution since the beginning of the fracturing to final subsidence.

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Rougier, Esteban. "Discrete element method for simulation of gas micro-flows." Thesis, Queen Mary, University of London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522320.

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Kremmer, Martin. "A discrete element method for industrial granular flow applications." Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408906.

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Ness, Christopher John. "Suspension rheology and extrusion : a discrete element method study." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20392.

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A suspension is a fully saturated mixture of discrete solid particles and interstitial liquid. Examples of suspensions include pastes, slurries, cement, food-spreads, drilling fluids and some geophysical flows. The present work focusses on granular (as opposed to colloidal) suspensions, which we define as those for which the thermal motion of the solid particles is negligible. Despite such ubiquity in industry and nature, our understanding of the mechanical properties of suspensions lags behind that of their constituent solid and liquids. In this thesis, the discrete element method is used to simulate suspension flow in shear, capillary and constriction geometries, mapping and characterising the fundamental flow, or rheological, regimes. As a starting point (Chapter 2), we consider an established regime map for dry granular materials, appropriate for flows of sand, grains and dry debris. Taking guidance from shear flow simulations that consider the lubricating effect of an interstitial liquid, we recast the regime map for a general suspension, elucidating flows comparable to the dry material or to a viscous liquid, dependent on the shear rate, liquid viscosity and particle stiffness. We give an account of the microstructural traits associated with each regime. Motivated by recent groundbreaking theoretical, computational and experimental work, we incorporate the emerging picture of frictional shear thickening into our regime map (Chapter 3). Our shear flow simulations capture the shear thickening behaviour and demonstrate that it may, in principle, occur in any of the identified flow regimes. Our simulations of time-dependent shear flows (Chapter 4), specifically flow reversal, provide a detailed micro-mechanical explanation of a longstanding and previously unexplained experimental finding, guiding future experimentalists in decomposing the particle and liquid contributions to the viscosity of any suspension. Indeed, the findings have already been exploited in the devising of an experimental protocol that has successfully proven the dominance of particle contacts in driving shear thickening. We next consider suspension flow in a microchannel (Chapter 5), finding that the identified shear flow regimes are locally applicable to flows in complex geometries under inhomogeneous stress conditions only when the local mean shear rate exceeds temporal velocity fluctuations. A more comprehensive description is therefore required to fully characterise the flow behaviour in this geometry. Finally (Chapter 6), we simulate pressure driven suspension flow through a constriction geometry, observing highly inhomogeneous stress distributions and velocity profiles. The roles of particle and fluid properties are considered in the context of an industrial paste extrusion process.

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Tang, Lingwei. "Application of the discrete element method for concrete fracturing." Thesis, Swansea University, 2013. https://cronfa.swan.ac.uk/Record/cronfa42301.

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This project focuses on discrete element modelling of fracturing of concrete material at meso-scale, and particularly on calibration of the particle assembly parameters to reproduce phenomenological properties of concrete, and on applying the discrete element method to analyze the failure mechanisms in a three-point bending test and debonding between the FRP sheet and the concrete. The particle flow code PFC2D and PFC3D are employed to carry out the parametric study but only PFC2D is used in the case studies. The calibration of properties of the numerical samples is conducted to determine the effects of the particle level input parameters on the elastic constants, the uniaxial compressive strengths and failure mode of particle assembly. The input parameters are divided into two groups, model constitutive parameters (e.g., particle and bond stiffness, bond shear and normal strengths and friction coefficient) and geometric and physical parameters (e.g., particle and specimen size, particle distribution and loading velocity.). The analysis is constructed using dimensional analysis and numerical uniaxial tests. A random aggregate generation algorithm is incorporated in the DEM code to reproduce the aggregate structure in real concrete material. The aggregate generation algorithm utilizes polygon and polyhedron as the basic shapes of aggregate and is capable of producing multi-graded concrete specimens with aggregate content up to 80% and 60% for two-dimensional and three-dimensional samples respectively. The mode I fracture behavior of three-phased concrete is then simulated by performing a virtual three-point bending test. The mortar matrix phase is simulated with the linear elastic-pure-brittle and softening bond model to ensure a fair comparison. The dynamic debonding process between the FRP sheet and the concrete is simulated with a particle assembly by a regular hexagonal packing arrangement where the heterogeneity of concrete is taken into account by incorporating the Weibull distribution. Based on the analysis of the modelling results, it is conclude that the fracture behavior of concrete can be satisfactorily captured by meso-scale DEM model and comprehensive parameter study allows more confidently implementation of particle flow code.

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Bergström, Per. "Modelling Mechanics of Fibre Network using Discrete Element Method." Licentiate thesis, Mittuniversitetet, Avdelningen för kemiteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-34640.

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Low-density fibre networks are a fundamental structural framework of everyday hygiene products, such as baby diapers, incontinence and feminine care products, bathroom tissue and kitchen towels. These networks are a random assembly of fibres, loosely bonded and oriented in the plane direction. Designing such a complex network structure for better performance, better use of materials and lower cost is a constant challenge for product designers, requiring in-depth knowledge and understanding of the structure and properties on the particle (fibre) level. This thesis concerns the development of a computational design platform that will generate low-density fibre networks and test their properties, seamlessly, with the aim to deepening the fundamental understanding of the micromechanics of this class of fibre networks. To achieve this goal, we have used a particle-based method, the Discrete Element Method (DEM), to model the fibres and fibre networks. A fibre is modelled as a series of linked beads, so that one can consider both its axial properties (stretching and bending) and transverse properties (shearing,twisting and transverse compression). For manufacturing simulations, we developed the models for depositing fibres to form a fibre network, consolidating the fibre network, compressing to make a 3D-structured network, and creating creping. For testing the end-use performance, we have developed two models and investigated the micromechanics of the fibre network in uniaxial compression in the thickness direction (ZD) and in uniaxial tension in the in-plane direction. In the ZD-uniaxial compression of entangled (unbonded) fibrenetworks, the compression stress exhibits a power-law relationship with density, with a threshold density. During compression, the fibre deformation mode changed from fibre bending to the transverse compression of fibre. Accordingly, the transverse properties of the fibreshad a large impact on the constitutive relation. By considering a realistic value for the transverse fibre property, we were able to predict the valuesof the exponent widely observed in the experimental literature. We havefound that the deviation of the experimental values from those predictions by the earlier theoretical studies is due to the neglect of the transverse fibre property. For tensile properties of bonded networks, we have investigated scaling of network strength with density and fibre–fibre bond strength. The network strength showed beautiful scaling behaviour with both density and bond strength, with exponents 1.88 and 1.08 respectively. The elastic modulus of the network, on the other hand, showed a changing exponent(from 2.16 to 1.69) with density in accordance with previous results in the literature. We have also reconfirmed that, with increasing density, the deformation mode changes from bending to stretching. The predicted results for both elastic modulus and strength agreed very well with experimental data of fibre networks of varying densities reported in the literature. We have developed a computational platform, based on DEM, for accurately modelling a fibre network from its manufacturing process to product properties. This is a tool that allows a versatile design of materials and products used for hygiene products, providing a promising venue for exploring the parameter space of new material and process design. Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 2 och 3 (manuskript).At the time of the defence the following papers were unpublished: paper 2 and 3 (manuscript).

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Maknickas, Algirdas. "Modelling of elasticity properties of solids by the discrete element method." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20090713_142127-91304.

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Development of numerical methods and computation environments opened the possibility of new, more sophisticated mechanical objects modelling. In this context it is natural desire of the researchers to describe macroscopic mechanical characteristics of the materials by their microstructure, which can be adapted for simulation of the existing and future materials. For this purpose researchers are using intensively experimental and numerical methods for the development of which the highest priority is given. Numerical experiments are used because they are cheaper and allow the interpretation of already known results of experiments and provide information to new investigations. One of the methods used for modelling of macroscopic properties modelling is based on microscopic properties of material is discrete element method (DEM). The DEM traditionally was applied for the granular materials. The basic idea of DEM is that any physical structure could be described as a system of moving particles. This idea could be also applied to the description of solid deformable body. Particles forming solid body and existing interaction between them are of different nature than the granular materials because their models are often the result of physical and mathematical abstraction. The modelling of solid deformable body with the discrete elements is just at the initial stage and the unified approach to discrete elements models doesn’t exist. There are several versions of models, based on... [to full text] Tobulėjant skaitiniams metodams ir kompiuterinei technikai atsivėrė galimybė naujų, sudėtingesnių mechaninių objektų modeliavimui. Turėdami naujus sudėtingesnių objektų modelius tyrėjai gali pritaikyti aprašytas ir sumodeliuotas šių objektų savybes su mikro struktūros ypatumais esamų ar busimų savybių nustatymui bei naujų medžiagų kūrimui. Tam intensyviai naudojami kaip eksperimentiniai taip ir skaitiniai metodai, kurių tobulinimui šiuo metu yra skiriamas labai didelis dėmesys. Skaitinis eksperimentas, kaip medžiagos tyrimo būdas pasitelkiamas dar ir todėl kad yra pigesnis ir leidžia interpretuoti jau žinomus eksperimentų rezultatus, o taip suteikia žinių naujiems tyrimams. Vienas iš metodų, kuris modeliuoja makroskopines medžiagų savybes remdamasis medžiagos mikro savybėmis yra diskrečiųjų elementų metodas (DEM). DEM metodas remiasi idėja, kad bet kokia fizikinė struktūra gali būti aprašyta kaip judančių dalelių sistema. Ši idėja pradėta taikyti ir vientisam deformuojamam kūnui aprašyti. Skirtingai nuo biriųjų medžiagų, vientiso kūno dalelės ir tarp jų egzistuojančios sąveikos yra kitokios prigimties, o jų modeliai yra fizikinės ir matematinės abstrakcijos rezultatas. Vientiso deformuojamo kūno modeliavimas diskrečiais elementais yra tik pradinėje stadijoje, o vientiso požiūrio į diskrečių elementų modelius dar nėra. Yra kelios hipotetinės versijos, grindžiamos skirtingais požiūriais. Taikant DEM kūnui, pirmas žingsnis būtu tampriųjų savybių modeliavimas. Tai yra... [toliau žr. visą tekstą]

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Sadek, Mohammad. "Modeling biofibre (hemp) processing using the discrete element method (DEM)." Food & Process Engineering Institute Division of ASABE, 2011. http://hdl.handle.net/1993/18484.

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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.

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Gong, Guobin. "DEM [Discrete Element Method] simulations of drained and undrained behaviour." Thesis, University of Birmingham, 2008. http://etheses.bham.ac.uk//id/eprint/143/.

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This thesis reports the results of DEM (Discrete Element Method) simulations of the behaviour of granular material for axisymmetric compression and plane strain deformation under both drained and undrained conditions. The aim is to study the behaviour of saturated granular material using DEM and the objectives of this thesis are: • to explore the drained behaviour of granular material using DEM • to explore the undrained behaviour of loose samples of granular material with and without preshearing history, using DEM • to compare axisymmetric compression and plane strain behaviour of a granular material under both drained and undrained conditions, using DEM A servo-control mode with constant mean stress is used to model drained simulations, and a strain-control model with constant volume is used to model undrained simulations. A periodic cell is used for all the simulations. For the drained simulations, the results of both dense and loose systems are presented, and all the systems reach a unique critical state at large strains. For the undrained simulations, mainly the results of loose systems are presented. The influence of preshearing history is also examined for a loose system under undrained axisymmetric compression conditions. The concept of liquefaction is shown to strongly correlate with mechanical coordination number, and liquefaction is shown to be related to structural mechanism. An attempt has been made to compare the axisymmetric compression and plane strain deformation for the drained and undrained conditions respectively. Shear strength criteria are examined and the Lade criterion is shown to be the most appropriate failure criterion.

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Pagnoni, Tommaso. "Seismic vulnerability of historical structures with the discrete element method." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/84818.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002. Includes bibliographical references (p. 333-345). It is widely recognized that historical structures represent a cultural heritage which should be preserved and transmitted to future generations. In several countries, and particularly, in the Mediterranean area, where a large number of important monuments are exposed to seismic hazard, there is a growing interest for the problem of strengthening such structures in order to reduce their seismic vulnerability, while preserving their original architectural integrity. However the seismic vulnerability assessment of historical block structures is still a challenging task. In this work, after having explored the potentials and limitations of the Discrete Element Method for this type of problem, a new joint model for the quasistatic analysis of block structures is proposed. It accounts for (a) the non coplanarity of the contact surfaces, and (b) friction softening. The new model allowed a more accurate prediction of the inplane failure load and corresponding failure mechanism of opus quadratum walls (walls made of regular squared blocks without mortar). In particular it predicts the development of progressive internal displacements, and the formation of localized sliding band as observed in the experimental models. Such results confirm that even apparently negligible joint imperfections should not be ignored since they may cause significant modifications in the response of a block structure subjected to gravity and lateral loading. by Tommaso Pagnoni. Ph.D.

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Johnson, Scott M. (Scott Matthew) 1978. "Resolution of grain scale interactions using the Discrete Element Method." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/34375.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006. Includes bibliographical references (p. 201-221). Granular materials are an integral part of many engineering systems. Currently, a popular tool for numerically investigating granular systems is the Discrete Element Method (DEM). Nearly all implementations of the DEM, however, use spheres to represent particles despite mounting evidence showing that shape at multiple scales (sphericity, angularity, and friction) plays a role in granular material behavior. This thesis contributes a new non-spherical representation to model particles as ellipsoidal bodies. This is validated and benchmarked against current representations and is shown to have attractive computational efficiency and numerical stability. A numerical study of the formation of heaps using spheres and ellipsoids both validates the ellipsoid representation and illustrates shape-induced behavioral differences. Resolution of shape is extended by a new algorithm for a hierarchical, multi-scale representation of convex particle surface characteristics. Two applications are offered: (1) a micro-asperity model is used to demonstrate pair-wise interlocking, and (2) a surface-based cohesive contact law is validated using a series of virtual numerical pull-off tests, which agree well with experimental findings. An explicit quadrature algorithm based on quaternion rotation is developed and shown to more accurately determine rotational orientation with less computational effort than other common algorithms for integrating finite rotations. (cont.) Finally, a contact resolution algorithm between discrete elements and a polyhedral boundary is developed and shown to scale in O(M + N) versus common algorithms with scaling of O(NM), where N is the number of discrete elements and M the number of faces on the polyhedral boundary. These developments are illustrated with numerical studies to simulate the blending kinetics of cohesive, micron-scale pharmaceutical powders in V-shaped and cylindrical bench-scale blenders. by Scott Matthew Johnson. Ph.D.

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Peng, Bo. "Discrete Element Method (DEM) Contact Models Applied to Pavement Simulation." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/50399.

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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

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Yu, Y. "Micromechanical investigation of hydrate-bearing sediments with discrete element method." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1460501/.

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Natural methane hydrate soil sediments attract worldwide interest, as there is huge commercial potential in the immense global deposits of methane hydrate that lies under deep seabeds and permafrost regions. Methane hydrate develops and exists in the pores of soil sediments under the conditions of high pressure and low temperature. The methane hydrate-bearing sediment can be exploited to extract methane gas, as methane gas is the predominant element of natural gas. However, the sediment’s geomechanical behaviour is poorly understood, but it has impacts on geotechnical issues, such as the instability of the seabed sediment layers and wellbore collapse, and it may also cause various negative environmental effects, particularly in regards to the exploration and exploitation process. Hence, further scientific research is needed. Due to the limitations of in-situ and laboratory studies, in this PhD research, a numerical method Discrete Element Method (DEM) was employed to provide a unique particle-scale insight into the granular geomechanical behaviours of hydrate-bearing sediment. A comprehensive DEM research was performed in order to simulate two commonly used geomechanical investigation methods employed in hydrate-related studies: the triaxial compression test and seismic wave propagation. Accordingly, the six major contributions of this DEM research are: (1) two typical types of microscopic hydrate distribution patterns within soil pores were investigated via a consistent basic soil model: the pore-filling hydrate pattern and the cementation hydrate pattern; (2) The large-strain deformation and the critical state behaviours were explored; (3) a wave propagation study was performed using the DEM hydrate-bearing sediment samples; (4) the bonding strength effect in the cementation model was systematically discussed; (5) the effect of elongated soil particles on the geomechanical behaviours of sediments was studied; and most importantly (6) a comprehensive particle-scale microscopic analysis was conducted to assist the interpretation of the macro responses in the in-situ, laboratory and numerical studies.

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Tuley, Robert James. "Modelling dry powder inhaler operation with the discrete element method." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/7561.

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Dry powder inhalers (DPI) are a common asthma treatment. Despite the number of commercial devices available, little is known about their internal operation: the process of fluidising a powder dose into an inhalation airflow. This PhD aims to investigate this process, and demonstrate that it can be modelled computationally. . Experimental work is described to record high speed video of the dose fluidisation from simplified DPls. Typical DPI powders such as lactose are tested, along with cohesionless glass spheres and aluminium flakes. Two distinct dose fluidisation mechanisms are identified, labelled 'fracture' and 'erosion'. Lactose exhibits a fracture mechanism -- large agglomerates are produced as the powder bed cracks along lines of weakness. Glass or aluminium particles exhibit an erosion mechanism: powder is entrained into the flow as individual particles from the bed surface. The recorded video is quantitatively analysed to determine fluidisation timescales and pressures. Shear cell test results show that predicting the mechanism of fluidisation is not possible using averaged bulk powder properties. This suggests any DPI model must include the fundamental particle interactions. The discrete element method (OEM) is introduced as a computational technique capable of predicting DPI behaviour from individual particle properties. The numerical accuracy of the method is assessed, showing that time integration is limited to a maximum of 2nd order accuracy due to discontinuities in particle contact forces. A sensitivity analysis shows inter-particle cohesion is the dominant factor affecting OEM predictions. OEM is used to create a simple model of the dose fluidisation that occurs within a DPI. The results are compared with real powder behaviour. OEM is shown to capture the realistic fluidisation of both lactose and glass powder doses. It is concluded that OEM is a promising technique to predict DPI behaviour, although further work is required to quantify inter--particle cohesive parameters

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BENEDETTO, MATIAS FERNANDO. "Applications of the Virtual Element Method to Discrete Fracture Networks." Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2638416.

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We put forward in this work several novel applications of the Virtual Element Method in the context of Discrete Fracture Networks. A family of methods is presented here for solving Darcy flow, time dependent-problems and the complete transport equation in both diffusion-dominated and convection-dominated problems. We present as well an implementation of mixed Virtual Elements in the context of Discrete Fracture Networks.

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Nishiyama, Kenta. "Analysis of Soil-Tire Interaction Using a Two-Dimensional Finite Element-Discrete Element Method." Kyoto University, 2019. http://hdl.handle.net/2433/245298.

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Dallinger, Niels, and Jörg Hübler. "Simulation of Bottle Conveyors – Opportunities of the Discrete Element Method (DEM)." Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-231768.

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The Discrete Element Method (DEM) provides an approach to recognition of the problems within bottle conveyors at an early stage of the engineering process. Key points in bottle conveyor systems, such as buffers, ejectors, diverters and transfers can be numerically analyzed. It is possible to calculate forces on lateral guides and forces between bottles within accumulation situations. The DEM provides an alternative opportunity for the virtual process optimization and numeric case studies of conveying systems at beverage and food industries Die diskrete Elementmethode (DEM) ermöglicht in einem frühen Stadium des Engineering-Prozesses die Erkennung von Problemen in Flaschenförderern. Wichtige Systemelemente wie Puffer, Ausschleuser, Weichen und Übergabestellen können numerisch analysiert werden. Es ist somit u. a. möglich, Kräfte auf Seitenführungen und Kräfte zwischen den Flaschen innerhalb von Stausituationen zu berechnen. Die DEM bietet eine alternative Möglichkeit für die virtuelle Prozessoptimierung und die Durchführung numerischer Fallstudien von Fördersystemen u. a. in der Getränke- und Lebensmittelindustrie

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Al-Harbi, Hamad F. "Crystal plasticity finite element simulations using discrete Fourier transforms." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51788.

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Crystallographic texture and its evolution are known to be major sources of anisotropy in polycrystalline metals. Highly simplified phenomenological models cannot usually provide reliable predictions of the materials anisotropy under complex deformation paths, and lack the fidelity needed to optimize the microstructure and mechanical properties during the production process. On the other hand, physics-based models such as crystal plasticity theories have demonstrated remarkable success in predicting the anisotropic mechanical response in polycrystalline metals and the evolution of underlying texture in finite plastic deformation. However, the integration of crystal plasticity models with finite element (FE) simulations tools (called CPFEM) is extremely computationally expensive, and has not been adopted broadly by the advanced materials development community. The current dissertation has mainly focused on addressing the challenges associated with integrating the recently developed spectral database approach with a commercial FE tool to permit computationally efficient simulations of heterogeneous deformations using crystal plasticity theories. More specifically, the spectral database approach to crystal plasticity solutions was successfully integrated with the implicit version of the FE package ABAQUS through a user materials subroutine, UMAT, to conduct more efficient CPFEM simulations on both fcc and bcc polycrystalline materials. It is observed that implementing the crystal plasticity spectral database in a FE code produced excellent predictions similar to the classical CPFEM, but at a significantly faster computational speed. Furthermore, an important application of the CPFEM for the extraction of crystal level plasticity parameters in multiphase materials has been demonstrated in this dissertation. More specifically, CPFEM along with a recently developed data analysis approach for spherical nanoindentation and Orientation Imaging Microscopy (OIM) have been used to extract the critical resolved shear stress of the ferrite phase in dual phase steels. This new methodology offers a novel efficient tool for the extraction of crystal level hardening parameters in any single or multiphase materials.

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22

Monasse, Laurent. "Analysis of a discrete element method and coupling with a compressible fluid flow method." Phd thesis, Université Paris-Est, 2011. http://pastel.archives-ouvertes.fr/pastel-00672342.

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This work aims at the numerical simulation of compressible fluid/deformable structure interactions. In particular, we have developed a partitioned coupling algorithm between a Finite Volume method for the compressible fluid and a Discrete Element method capable of taking into account fractures in the solid. A survey of existing fictitious domain methods and partitioned algorithms has led to choose an Embedded Boundary method and an explicit coupling scheme. We first showed that the Discrete Element method used for the solid yielded the correct macroscopic behaviour and that the symplectic time-integration scheme ensured the preservation of energy. We then developed an explicit coupling algorithm between a compressible inviscid fluid and an undeformable solid. Mass, momentum and energy conservation and consistency properties were proved for the coupling scheme. The algorithm was then extended to the coupling with a deformable solid, in the form of a semi-implicit scheme. Finally, we applied this method to unsteady inviscid flows around moving structures: comparisons with existing numerical and experimental results demonstrate the excellent accuracy of our method

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Liu, Si Kai. "Discrete element simulation of particle crushing in one-dimensional compression." Thesis, University of Macau, 2017. http://umaclib3.umac.mo/record=b3691079.

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Pettersson, Thomas. "Analysis and implementation of the Smooth Discrete Element Method in AgX." Thesis, Linköpings universitet, Beräkningsmatematik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-121563.

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We encounter granular materials on a daily basis. We walk up a gravel path or we eat our breakfast cereals. When handling granular materials on an industrial scale it is important to do so efficiently, to avoid unnecessary energy losses, wear and tear. To help designing efficient tools for handling these materials engineers uses numerical simulations. This project investigates the difference between the two main approaches to simulation of granular materials, the Smooth- and Non-smooth Discrete Element Methods by implementing the Smooth method into AgX dynamics were the Non-smooth method already is implemented, and then setup and execute a range of experiments to investigate their differences. The investigation shows both advantages and weaknesses for both methods. The result of simulations with smooth discrete element method are more consistent than with the nonsmooth discrete element method with respect to choice of time step and other parameters that can be chosen for the simulation. Smooth discrete element method have problems when it comes to extreme situations. The relative simulation time for system as large as treated by this project (more than1000) can not be shown to depend on the size of the system.

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Yan, Beichuan. "Three-dimensional discrete element modeling of granular materials and its coupling with finite element method." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3315830.

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26

Irazábal, González Joaquín. "Numerical analysis of railway ballast behaviour using the Discrete Element Method." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/461536.

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The development of high-speed train lines has increased significantly during the last twenty-five years, leading to more demanding loads in railway infrastructures. Most of these infrastructures were constructed using railway ballast, which is a layer of granular material placed under the sleepers whose roles are: resisting to vertical and horizontal loads and facing climate action. Moreover, the Discrete Element Method was found to be an effective numerical method for the calculation of engineering problems involving granular materials. For these reasons, the main objective of the thesis is the development of a numerical modelling tool based on the Discrete Element Method which allows the users to understand better railway ballast mechanical behaviour. The first task was the review of the specifications that ballast material must meet. Then, the features of the available Discrete Elements code, called "DEMPack", were analysed. After those revisions, it was found that the code needed some improvement in order to reproduce correctly and efficiently the behaviour of railway ballast. The main deficiencies identified in the numerical code were related to the contact between discrete element particles and planar boundaries and to the geometrical representation of such a irregular material as ballast. Contact interactions between rigid boundaries and Discrete Elements are treated using a new methodology called the Double Hierarchy method. This new algorithm is based on characterising contacts between rigid parts (meshed with a Finite Element-like discretisation) and spherical Discrete Elements. The procedure is described in the course of the thesis. Moreover, the method validation and the assessment of its limitations are also displayed. The representation of irregular particles using the Discrete Element Method is a very challenging issue, leading to different geometrical approaches. In this work, a deep revision of those approaches was performed. Finally, the most appropriate methods were chosen: spheres with rolling friction and clusters of spheres. The main advantage of the use of spheres is their low computational cost, while clusters of spheres stand out for their geometrical versatility. Some improvements were developed for describing the movement of each kind of particles, specifically, the imposition of the rolling friction and the integration of the rotation of clusters of spheres. In the course of this work the way to fill volumes with particles (spheres or clusters) was also analysed. The aim is to control properly the initial granulometry and compactness of the samples used in the calculations. After checking the correctness of the numerical code with simplified benchmarks, some laboratory tests with railway ballast were computed. The aim was to calibrate the ballast material properties and validate the code for the representation of railway ballast behaviour. Once the material properties were calibrated, some examples of a real train passing through a railway ballast track were reproduced numerically. This calculations allowed to prove the possibilities of the implemented tool. El desarrollo de las líneas de alta velocidad ha aumentado significativamente durante los últimos veinticinco años, dando lugar a cargas más exigentes sobre las infraestructuras ferroviarias. La mayor parte de estas infraestructuras se construyeron con balasto, que es una capa de material granular colocada bajo las traviesas cuyas funciones principales son: resistir las cargas verticales y horizontales repartiéndolas sobre la plataforma y soportar las acciones climáticas. Además, se encontró que el Método de Elementos Discretos es muy eficaz para el cálculo de problemas de ingeniería que implican materiales granulares. Por estas razones se decidió que el objetivo principal de la tesis fuera el desarrollo de una herramienta de modelación numérica basada en el Método de Elementos Discretos que permita a los usuarios comprender mejor el comportamiento mecánico del balasto ferroviario. La primera tarea fue la revisión de las especificaciones que el balasto debe cumplir. A continuación, se analizaron las características del código de Elementos Discretos disponible, denominado "DEMPack". Después de esas revisiones, se encontró que el código necesitaba alguna mejora para poder reproducir correcta y eficientemente el comportamiento del balasto ferroviario. Las principales deficiencias identificadas en el código numérico estaban relacionadas con el contacto entre partículas y contornos planos y con la representación geométrica de un material tan irregular como es el balasto. Los contactos entre contornos rígidos y elementos discretos se tratan usando una nueva metodología llamada el "Double Hierarchy method". Este nuevo algoritmo se basa en la caracterización de contactos entre elementos rígidos (discretizados de forma similar a los elementos finitos) y elementos discretos esféricos. La descripción detallada del procedimiento se presenta a lo largo de la tesis. Además, también se muestra la validación del método y sus limitaciones. La representación de partículas irregulares utilizando el Método de Elementos Discretos se puede abordar desde diferentes enfoques geométricos. En este trabajo, se realizó una revisión de estos enfoques. Finalmente, se escogieron los métodos más adecuados: esferas con resistencia a la rodadura y clusters de esferas. La principal ventaja del uso de las esferas es su bajo coste computacional, mientras que los clusters de esferas destacan por su versatilidad geométrica. Se han desarrollado algunas mejoras para describir el movimiento de cada uno de los tipos de partículas, concretamente, la imposición de la resistencia a la rodadura y la integración de la rotación de clusters de esferas. En el curso de este trabajo también se analizó la forma de llenar volúmenes con partículas (esferas o clusters). El objetivo es controlar adecuadamente la granulometría inicial y la compacidad de la muestra. Después de comprobar el comportamiento del código numérico con tests simplificados, se emularon numéricamente algunos ensayos de laboratorio con balasto ferroviario. El objetivo era calibrar las propiedades del balasto y validar el código para representar con exactitud su comportamiento. Una vez calibradas las propiedades del material, se reprodujeron numéricamente algunos ejemplos de un tren pasando sobre una vía con balasto. Estos cálculos permiten demostrar las posibilidades de la herramienta numérica implementada.

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Das, Nivedita. "Modeling three-dimensional shape of sand grains using Discrete Element Method." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002072.

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Heesen, Eva [Verfasser]. "Zur Modellierung der Pfahlinstallation mit der Discrete Element Method / Eva Heesen." Aachen : Shaker, 2010. http://d-nb.info/1122546580/34.

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Majidi, Behzad. "Discrete Element Method Applied To The Vibration Process Of Coke Particles." Thesis, Université Laval, 2012. http://www.theses.ulaval.ca/2012/29386/29386.pdf.

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Les propriétés physiques, mécaniques et chimiques des matières premières ont un effet majeur sur la qualité des anodes en carbone pour le procédé de production d’aluminium. Ce travail tente d’étudier la faisabilité de l’application de simulation de la Méthode des Élément Discrets (DEM) à la technologie de production d’anodes. L’effet de la forme des particules et de la distribution de leurs tailles sur la densité apparente vibrée (VBD) d’échantillons de coke sec est étudié. Les particules de coke sont numérisées en utilisant des techniques d’imagerie à deux et trois dimensions. Ces images donnent les formes et les aspects réels des particules qui sont utilisées pour les modèles DEM pour les tests VBD pour le codage de flux de particules (PFC). Le coefficient de friction interne des particules de coke est estimé par la méthode de mesure d’angle au repos. Les résultats ont montrés comme attendu, que la VBD des échantillons de coke est affectée par la forme et la distribution de taille des particules. Les simulations à deux dimensions ont confirmé qu’en général, les échantillons formés de particules de tailles poly-dispersées ont une VBD plus haute que ceux dont la taille des particules est mono-dispersée. De plus, la VBD des échantillons augmente lorsque la fraction de grosses particules augmente. Cependant, la présence de 10 % massique de particules fines est nécessaire pour remplir les pores entre les grosses particules. De même pour la simulation 3D, le modèle suit la tendance des données expérimentales montrant que dans une éprouvette de 2,9 cm de diamètre, l’augmentation de la quantité de particules de - 4+6 mesh (de 3,36 à 4,76 mm) engendre une augmentation de la VBD. En conclusion, un modèle DEM approprié est capable de prédire le réarrangement des particules et l’évolution de la densité pendant le processus de vibration. Physical, mechanical and chemical properties of raw materials have considerable effects on quality of carbon anodes for aluminium smelting process. The present work attempts to investigate the feasibility of application of Discrete Element Method (DEM) simulations in anode production technology. Effects of coke particles shape and size distribution on vibrated bulk density (VBD) of dry coke samples are studied. Coke particles are digitized using two-dimensional and three-dimensional imaging techniques and real-shape particles are used in DEM models of VBD test in Particle Flow Code (PFC). Internal friction coefficient of coke particles were estimated by means of angle of repose tests. Results showed that, as expected, VBD of coke samples is affected by shape and size distribution of the particles. Two-dimensional simulations confirmed that in general, mixed-sized samples have higher VBD than mono-sized cokes and as the fraction of coarse particles increases vibrated bulk density increases. However, existence of 10 wt.% of fine particles to fill the pores between coarse particles is essential. For 3D simulations also, the model follows the trend of experimental data showing that in the container of 2.9 mm diameter, as the content of -4+6 mesh (3.36-4.76 mm) particles increase, VBD increases. It can be concluded that a well-tailored DEM model is capable of predicting the particle rearrangement and density evolution during the vibration process.

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URIBE, JUAN DAVID VELILLA. "OIL WELLS STABILITY IN FRACTURED MEDIA USING THE DISCRETE ELEMENT METHOD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2013. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=22127@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR A estabilidade de poços de petróleo é convencionalmente analisada empregando soluções analíticas que não são adequadas para modelagem de meios fraturados, devido a suposições de meio continuo. Esta dissertação tem como objetivo principal desenvolver uma metodologia computacional para geração de janela operacional utilizando uma solução numérica, adequada para meios fraturados. No trabalho foi escolhido o software UDEC (Universal Distinct Element Code), que é baseado no método dos elementos discretos (MED). Este método considera o maciço rochoso como a união de blocos de rocha intactos, unidos pelas fraturas e cujo comportamento físico para cada elemento pode ser analisado individualmente. A modelagem computacional no UDEC foi realizada mediante uma analise hidromecânica acoplada. Esta modelagem permitiu avaliar a influencia de alguns mecanismos que governam a estabilidade de poços, como: as tensões in situ, a poropressão e a orientação, espaçamento e persistência das famílias de fraturas. Os resultados numéricos mostram o efeito das fraturas na orientação e magnitude das tensões, além da magnitude da poropressão resultando em cálculos dos limites de colapso inferior e fratura superior da rocha mais realistas. The stability of oil wells is conventionally analyzed using analytical solutions that are often not suitable for modeling fractured media due to assumptions of continuous medium. This work has as main objective to develop a computational method for generating mud window using a numerical solution, suitable for fractured media. The software chosen for this work was the UDEC (Universal Distinct Element Code), which is based on discrete element method (DEM). This method considers the rock mass as the union of blocks of intact rock jointed by fractures, and whose physical behavior for each element can be analyzed individually. Computational modeling in UDEC was carried out in a coupled hydromechanical analysis. This modeling allowed to evaluate the influences of some of the mechanisms that govern the stability of wells, as in situ stresses, pore pressure and orientation, spacing and persistence of families of fractures. Numerical results show the effect of fracture orientation and magnitude of the stresses, besides the magnitude of the pore pressure resulting in more realistic calculations of lower collapse and upper fracture of the rock mass.

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Carrion, Schafer Benjamin. "Acceleration of the discrete element method on a reconfigurable co-processor." Thesis, University of Birmingham, 2003. http://etheses.bham.ac.uk//id/eprint/94/.

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Granular materials are important for many different disciplines, e.g. geomechanics, civil engineering and chemical engineering. Many approaches have been used to model their behaviour, but one of the best and most important is the Discrete Element Method (DEM). The DEM was first developed during the 70’s, but its widespread use has been hampered by its extremely computationally demanding nature. The DEM can be run on a parallel computer by farming out different sub-domains onto different processors. However, particles transiting from one sub-domain to another create communication and synchronisation overheads which limit the speed-up achieved by parallel processing. Also, if some cells become much more heavily populated than others, then there will be inefficiencies due to load imbalance between the processors. As a result of these effects, the speed-up achieved by running the DEM on parallel processor computers is far less than linear. This thesis describes work on the acceleration of the DEM using reconfigurable computing. A custom hardware architecture for the DEM has been designed and implemented on a Field Programmable Gate Array (FPGA) mounted on a reconfigurable computing card. The design exploits the low level parallelism of the DEM by using long, wide computational pipelines that compute many arithmetic operations concurrently. It also exploits the high level parallelism by overlapping the main computational tasks using domain decomposition techniques. Speed-ups of a factor of at least 30 per FPGA have been achieved for simulations involving 25,000 to 200,000 particles. A multi-FPGA system has been implemented that allows the full overlap of computation with communication, so that an almost linear speed-up can be achieved as the number of FPGAs is increased. The effect of the short wordlength arithmetic used in the FPGA has been investigated, and the accuracy of the simulations has been found to be acceptable.

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Patwa, Abhay. "Discrete element method model of the first break wheat milling process." Thesis, Kansas State University, 2014. http://hdl.handle.net/2097/18668.

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Master of Science Department of Grain Science and Industry Kingsly Ambrose It is a well-known phenomenon that the break-release, particle size and size distribution of wheat milling are functions of machine operational parameters and grain properties. Due to the non-uniformity in characteristics and properties of wheat kernel, the kernel physical and mechanical properties may affect the size reduction process. The discrete element method (DEM) is a numerical modeling technique that can be used to study and understand the effect of physical and mechanical properties of a material on processing. The overall objective of this study is to develop a DEM model of the 1st break wheat milling process. In this study, different physical and mechanical properties of wheat mill streams were determined for using as the input parameters in DEM model development. The particle size and size distribution (PSD), true, bulk and tapped density, young’s modulus, coefficient of static and rolling friction, and coefficient of restitution were measured for wheat kernel, 1st break and flour from hard red winter (HRW), hard red spring (HRS), and soft red winter (SRW) wheat. Overall moisture content was found to have a greater significant effect on the physical properties i.e. density and PSD of the mill streams than material properties i.e. Young’s modulus, coefficients of friction and coefficient of restitution. The DEM model of 1st break wheat milling was developed using both single and multi-sphere approaches. The single sphere approach simulated the size reduction of a spherical cluster of bonded particles with mono-sized particles. The model was simulated for hard red winter (HRW) wheat milling at 16% moisture levels and validated using lab scale milling trials giving a PSD of 437.73 m with a percent deviation of prediction of 235.37. The deviation of prediction was reduced to 192.29 with a mean PSD of 371.52 m by conducting sensitivity analysis by modifying the shear modulus and coefficient of restitution values. In the multi-sphere approach, a bonded cluster resembling a wheat kernel in shape and size was used to simulate the milling process. The model predicted a 1st break PSD of 412.65 µm which had a deviation of 185.89 from lab scale and 156.78 from plant scale milling. The model could however satisfactorily predict the variation in PSD from 1st break milling with moisture content with reasonable accuracy. Future capabilities using the model include performing additional sensitivity analysis to understand the effect of other mechanical properties of wheat on the 1st break PSD. It can also be used to improve the 1st break release during wheat milling.

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Yap, Fook Liong. "The application of the discrete element method to integral bridge backfill." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/333184/.

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Expansion joints and bearings of conventional bridges are easily damaged and this commonly incurs high maintenance costs. The concept of the integral bridge was to reduce the maintenance costs by removing those joints. However, the thermally induced expansion-contraction of the bridge superstructure is transferred through the integral bridge’s abutments due to lack of expansion joints. Seasonal thermal cyclic displacement of the integral abutment cyclically loads the bridge backfill material. It has been observed that the lateral earth pressure behind an integral abutment increases as a result of the cyclic loading. Previous studies attribute this increase in lateral pressure to the densification of the backfill material. Granular flow was suggested to have occurred displacing the particles to form a denser and therefore stiffer matrix. An alternative suggestion was that the particles reoriented to form a stiffer matrix that wasn’t necessarily denser. The objective of this research is to explore the behaviour of integral abutment backfill at a micromechanical level by utilising the discrete element method (DEM) and possibly verify these suggested causes of earth pressure build-up behind an integral abutment. DEM models of four granular materials consisting of different particle shapes were tested with 100 cycles of strain. The results indicate that densification occurred for all samples, but the build-up of horizontal pressure did not occur for the more rounded samples. It was further suggested that the particle shape in combination with the change in coordination number closely replicate the behaviour of the sample’s horizontal stress. Particle reorientation and displacements were observed to be small for samples of non-circular particles. Particle activity is concentrated in the smallest particles within the material. It is concluded that the build-up of horizontal stress is caused by the increase in particle contacts due to particle reorientation and not densification.

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Sallam, Amr M. "Studies on modeling angular soil particles using the discrete element method." [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000574.

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Silva, Marcel Rossetti da. "Sintering simulation of nickel and alumina composite using discrete element method." reponame:Repositório Institucional da UFSC, 2016. https://repositorio.ufsc.br/xmlui/handle/123456789/176061.

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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Química, Florianópolis, 2016. Made available in DSpace on 2017-05-31T14:14:50Z (GMT). No. of bitstreams: 1 345556.pdf: 2835210 bytes, checksum: 6d016e8d8d73ae27ff11f49ea1b35634 (MD5) Previous issue date: 2016 Sendo o resultado da combinação de dois ou mais materiais, os materiais compósitos possuem características únicas e são usados em sistemas de engenharia que necessitam alto desempenho e propriedades altamente específicas, como, por exemplo em aeronaves e equipamentos esportivos. Materiais compósitos podem ser produzidos pela "tecnologia do pó", na qual basicamente o pó metálico e/ou cerâmico é compactado e, por fim, sinterizado. A sinterização é um processo de densificação, onde ocorre a consolidação do material e é a etapa responsável por conferir força e resistência à peça. Assim, nota-se que o controle dessa etapa é determinante para se atingir as propriedades desejadas à peça final. Em paralelo, simulações numéricas do processo de sinterização são uma alternativa em relação a custosos e longos experimentos físicos. Uma metodologia de simulação numérica muito promissora é chamada de Método dos Elementos Discretos (DEM ? Discrete Element Method). Diferentemente dos métodos contínuos de simulação, o DEM considera cada partícula do sistema como um elemento distinto e é ideal para a simulação de meios granulares, como é o caso da sinterização. Assim, esse projeto tem por objetivo simular e analisar o processo de sinterização em estado sólido de materiais compósitos utilizando o Método dos Elementos Discretos. O software utilizado foi o MUSEN, desenvolvido na Universidade Tecnológica de Hamburgo (TUHH - Alemanha). Os materiais do compósito utilizado nas simulação são níquel (metal) e alumina (cerâmico). Especificamente, esse trabalho visa investigar a influência de diferentes proporções de metal/cerâmico em amostras monomodais (apenas um tamanho de partícula) durante a sinterização. Além disso, a influência de partículas maiores de metal em amostras bimodais também foi analisada. Entre as análises conduzidas, foi avaliado o crescimento do raio de contato das partículas entre os diferentes tipos de contatos: metal-metal, cerâmico-cerâmico e metal-cerâmico. O número de coordenação das partículas com esses 3 tipos de contato também foi investigado. Finalmente, a influência de diferentes parâmetros no comportamento de densificação foi analisada e correlacionada com o crescimento de raio de contato e número de coordenação entre as partículas. A partir dos resultados, foi possível confirmar que a modelagem modificada foi capaz de simular a sinterização de compósitos, mesmo para estruturas interpenetrantes. Os resultados das amostras monomodais foram divididos em três diferentes comportamentos de sinterização: controladas pelo metal, controladas pelo cerâmico e estruturas interpenetrantes. As amostras controladas pelo metal apresentaram as maiores taxas de densificação e atingiram as maiores densidades relativas ao final da simulação. As partículas de metal (neste caso níquel) possuem um potencial maior para sinterizar mais rápido que a alumina devido ao seus parâmetros cinéticos e energia superficial. Também foi observado que a adição de uma segunda fase com uma menor atividade de sinterização (alumina) reduz a densificação global em comparação com o puro metal e leva mais tempo para atingir a mesma densidade relativa. As estruturas interpenetrantes apresentaram as menores densificações globais dentre todas amostras devido à densificação independente da fase metálica e cerâmica. Esse comportamento conduziu à formação de muitas fissuras e rachaduras ao longo da amostra e a estrutura inicial foi perdida, formando na verdade uma estrutura porosa. Os resultados das amostras bimodais mostraram um crescimento mais lento do raio de contato para partículas maiores de níquel, como é esperado. Entretanto, a densificação global foi maior para amostras com maiores partículas de níquel. Esse comportamento não era esperado, porém pode ser explicado pela configuração das partículas em estruturas interpenetrantes. Nessas estruturas, não existe uma fase ?matriz?, a fase metálica e cerâmica formam redes contínuas de partículas, chamados de caminhos de percolação. Quando partículas menores estão presentes nessas estruturas, elas apresentam maior força de sinterização, rapidamente se atraem, formam longos aglomerados de partículas e a densificação global praticamente não ocorre. Por outro lado, partículas maiores induzem menores forças de sinterização. Assim, as forças viscosas entre contatos alumina-níquel são suficientes para manter esses contatos unidos e, consequentemente, a densificação global pode ser observada. Abstract : Composite is a class of material made by the combination of two or more materials, which produces a third one with unique characteristics. For this reason, composites have a wide range of engineering applications, such as spacecrafts and sports? equipment. Composite materials can be suitably produced by Powder Metallurgy. In this manufacturing process, the blend of different powders is shaped and later sintered at high temperatures for consolidation of the part. Thereby, sintering is considered a densification process, which is responsible for providing strength and stiffness to the material or composite. Moreover, its control is essential to reach the desired properties of the final part. In addition, numerical simulations of the sintering process represent an alternative procedure in relation to the lengthy and costly physical experiments. A well-known simulation technique is the Discrete Element Method (DEM). In contrast to continuum methods, DEM considers every particle of the system as a single element and it is recommended to simulate granular media, such as sintering. Thus, the general purpose of this project is to simulate and analyze the solid-state sintering process of composite materials when both materials are sintering using DEM. The software used is the MUSEN system, developed at TUHH ? Germany. The materials chosen for the composite are nickel (metal) and alumina (ceramic). Specifically, the present work aims to investigate the influence of varying contents of metal/ceramic in monosized samples during sintering. These contents range from metal volume fraction of 0.9 to 0.1, and include pure metal and ceramic bodies. Furthermore, the effect of larger metallic particles in the sample is also investigated for a constant metal volume fraction of 0.6. Among the analyses carried out, the contact size growth was evaluated considering the interfaces metal-metal, ceramic-ceramic and metal-ceramic. The coordination number of the particles within these three contacts is also analyzed. Finally, the influence of the varied parameters on the densification behavior is investigated and correlated with the contact size growth and coordination number evolution. The results have shown that the special modeling was capable to simulate sintering of composites even in case of interpenetrating structures. The simulation results of the monosized packing can be divided in three different sintering behaviors: metal-controlled, ceramic-controlled and interpenetrating structures. The metal-controlled samples have shown the highest densification rates and relative density evolution, as one might expect. The nickel particles have higher potential to sinter faster than alumina due to their kinetic parameters and surface energy. Hence, metal particles induce high forces to shrink the system and indirectly transfer forces to the sintering of ceramic phase. Interpenetrating structures have shown the lowest overall densification due to independent densification of metal and ceramic phase. It has led to large cracks through the samples and the initial structure has been lost. The results of bimodal packings have shown a slower growing of the contact radius for larger nickel particles, as expected. However, the global densification has been higher for samples with larger nickel particles. This unexpected behavior can be explained due to the particle configuration and distribution of forces in the interpenetrating structures. Smaller particles induce higher forces, quickly agglomerate themselves and are not capable to drive a global densification. On the other hand, larger particles induce weaker sintering forces. Thereby, the resistance force between nickel-alumina contacts is high enough to keep these contacts attached and, consequently, a global densification can be observed.

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Zhang, Hao. "Numerical investigation of particle-fluid interaction system based on discrete element method." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/284833.

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This thesis focuses on the numerical investigation of the particle-fluid systems based on the Discrete Element Method (DEM). The whole thesis consists of three parts, in each part we have coupled the DEM with different schemes/solvers on the fluid phase. In the first part, we have coupled DEM with Direct Numerical Simulation (DNS) to study the particle-laden turbulent flow. The effect of collisions on the particle behavior in fully developed turbulent flow in a straight square duct was numerically investigated. Three sizes of particles were considered with diameters equal to 50 µm, 100 µm and 500 µm. Firstly, the particle transportation by turbulent flow was studied in the absence of the gravitational effect. Then, the particle deposition was studied under the effect of the wall-normal gravity force in which the influence of collisions on the particle resuspension rate and the final stage of particle distribution on the duct floor were discussed, respectively. In the second part, we have coupled DEM with Lattice Boltzmann Method (LBM) to study the particle sedimentation in Newtonian laminar flow. A novel combined LBM-IBM-DEM scheme was presented with its application to model the sedimentation of two dimensional circular particles in incompressible Newtonian flows. Case studies of single sphere settling in a cavity, and two particles settling in a channel were carried out, the velocity characteristics of the particle during settling and near the bottom were examined. At last, a numerical example of sedimentation involving 504 particles was finally presented to demonstrate the capability of the combined scheme. Furthermore, a Particulate Immersed Boundary Method (PIBM) for simulating the fluid-particle multiphase flow was presented and assessed in both two and three-dimensional applications. Compared with the conventional IBM, dozens of times speedup in two-dimensional simulation and hundreds of times in three-dimensional simulation can be expected under the same particle and mesh number. Numerical simulations of particle sedimentation in the Newtonian flows were conducted based on a combined LBM - PIBM - DEM showing that the PIBM could capture the feature of the particulate flows in fluid and was indeed a promising scheme for the solution of the fluid-particle interaction problems. In the last part, we have coupled DEM with averaged Navier-Stokes equations (NS) to study the particle transportation and wear process on the pipe wall. A case of pneumatic conveying was utilized to demonstrate the capability of the coupling model. The concrete pumping process was then simulated, where the hydraulic pressure and velocity distribution of the fluid phase were obtained. The frequency of the particles impacting on the bended pipe was monitored, a new time average collision intensity model based on impact force was proposed to investigate the wear process of the elbow. The location of maximum erosive wear damage in elbow was predicted. Furthermore, the influences of slurry velocity, bend orientation and angle of elbow on the puncture point location were discussed. Esta tesis se centra en la investigación numérica de sistemas partícula-líquido basado en la técnica Discrete Element Method (DEM). La tesis consta de tres partes, en cada una de las cuales se ha acoplado el método DEM con diferentes esquemas/solucionadores en la fase fluida. En la primera parte, hemos acoplado los métodos DEM con Direct Numerical Simulation (DNS) para estudiar casos de "particle-laden turbulent flow". Se investigó numéricamente el efecto de las colisiones en el comportamiento de las partículas en el flujo turbulento completamente desarrollado en un conducto cuadrado recto. Tres tamaños de partículas se consideraron con diámetros de 50, 100 y 500 micrometros. En primer lugar, el transporte de partículas por el flujo turbulento se estudió en la ausencia del efecto gravitacional. Entonces, la deposición de partículas se estudió bajo el efecto de la fuerza de gravedad normal a la pared, en el que se discutieron la influencia de la tasa de colisiones en re-suspensión de las partículas y la fase final de la distribución de partículas en el suelo del conducto, respectivamente. En la segunda parte, se ha acoplado los métodos DEM con Lattice Boltzmann Method (LBM) para estudiar la sedimentación de partículas en flujo laminar newtoniano. Un nuevo metodo combinado LBM-IBM-DEM se presentó y ha sido aplicado para modelar la sedimentación de dos partículas circulares bi-dimensionales en flujos Newtonianos incompresibles. Se estudiaron casos de sedimentación en una cavidad de una sola esfera, y sedimentación de dos partículas en un canal, las características de la velocidad de la partícula durante la sedimentación y cerca de la base fueron también examinados. En el último caso, un ejemplo numérico de sedimentación de 504 partículas fue finalmente presentado para demostrar la capacidad del método combinado. Además, se ha presentado un método "Particulate Immersed Boundary Method" (PIBM) para la simulación de flujos multifásicos partícula-fluido y ha sido evaluado en dos y tres dimensiones. En comparación con el método IBM convencional, se puede esperar con el mismo número de partículas y de malla un SpeedUp docenas de veces superior en la simulación bidimensional y cientos de veces en la simulación en tres dimensiones. Se llevaron a cabo simulaciones numéricas de la sedimentación de partículas en los flujos newtonianos basados en una combinación LBM - PIBM - DEM, mostrando que el PIBM podría capturar las características de los flujos de partículas en el líquido y fue en efecto un esquema prometedor para la solución de problemas de interacción fluido-partícula. En la última parte, se ha acoplado el método DEM con las ecuaciones promediadas de Navier-Stokes (NS) para estudiar el transporte de partículas y el proceso de desgaste en la pared de una tubería. Se utilizó un caso de transporte neumático para demostrar la capacidad del modelo acoplado. Entonces se simuló el proceso de bombeo de hormigón, de donde se obtuvo la presión hidráulica y la distribución de la velocidad de la fase fluida. Se monitoreó la frecuencia de impacto de las partículas en la tubería doblada, se propuso un nuevo modelo de intensidad de colisión promediado en tiempo para investigar el proceso de desgaste del codo basado en la fuerza de impacto. Se predijo la ubicación del daño máximo desgaste por erosión en el codo. Además, se examinaron las influencias de la velocidad de pulpa, la orientación y el ángulo de curvatura del codo en la ubicación del punto de punción.

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Labra, C. A. (Carlos Andrés). "Advances in the development of the discrete element method for excavation processes." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/124837.

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Modelling of granular materials, soils and rocks has been a challenging topic of investigation for decades. Classical continuum mechanics has been used to idealize soils and rocks, and numerical solution techniques such as finite element method (FEM) has been used to model these materials. Considering the idealization of the material, continuum mechanics allows the analysis of phenomena with discontinuous nature such as fracture in rock or soil via damage models. However, in more complex processes like rock milling or crushing, this kind of models are usually not suitable. Discrete models are more appropriate for problems with multiple discontinuities and particulate materials. The discrete element method (DEM) has been gaining popularity in analysis of granular materials, soils and rocks. Many aspects of this method still require more profound investigation. This thesis presents new developments of the discrete element method improving effi ciency and accuracy of modelling of rock-like materials, especially in excavation processes. All the numerical algorithms has been implemented in an in-house software, which was then used to run numerical examples. The basic formulation of DEM with linear elastic-perfectly brittle contact model is presented. The main di erence with other models found in the literature is the consideration of global sti ness and strength parameters that are constants in the whole model. The result of a simulations is strongly related with the con guration of the particle assembly used. Particle assemblies should be su ciently compact and ensure the isotropy to reproduce the physical properties of the modelled material. This thesis presents a novel technique for the generation of highly dense particle assemblies in arbitrary geometries, satisfying all the requirements for accurate discrete element simulations. One of the key issues in the use of the DEM is the estimation of the contact model parameters. A methodology is proposed for the estimation of the contact model parameters yielding required macroscopic properties of the material. The relationships between the contact model parameters and the mechanical properties of brittle materials, as well as the influence of the particles assembly con guration on the macroscopic properties, are analysed. A major di culty in the application of the DEM to real engineering problems is the high computational cost in simulation involving a large number of particles. The most common way to solve this is the use of parallel computing techniques, where multiple processors are used. As an alternative, a coupling scheme between DEM and the finite element method (FEM) is proposed in the thesis. Within the hybrid DEM/FEM model, DEM is only used in the region of the domain where it provides an advantage over a continuum-based approach, as the FEM. The coupling is dynamically adapted, starting with the whole domain discretized with FEM. During the simulation, in the regions where a high stress level are found, a change of modelling method from continuum FEM to the discrete DEM is employed. Finally, all the developments are applied to the simulation of a real excavation process. An analysis of the rock cutting process with TBM disc cutters is performed, where DEM and the DEM/FEM coupling technique presents an important advantage over other simulation techniques. La modelación de materiales granulares, terrenos y rocas ha sido un desafío para la investigación por décadas. La mecánica del continuo clásica ha sido utilizada para idealizar terrenos y rocas, y técnicas numéricas de solución, como el método de los elementos finitos (FEM), han sido usadas para modelar estos materiales. Considerando la idealización del material, la mecánica del continuo permite el análisis de fenómenos de naturaleza discontinua como la fractura en rocas y terreno mediante modelos de daño. Sin embargo, en procesos mas complejos como la molienda o trituración de roca, este tipo de modelos no suelen ser adecuados. Los modelos discretos son mas apropiados para problemas con múltiples discontinuidades y material particulado. El método de los elementos discretos (DEM) ha ido ganando popularidad en el análisis de materiales granulares, terrenos y rocas. Sin embargo, muchos aspectos de este método todavía requieren una investigación mas profunda. Esta tesis presenta nuevos desarrollos del método de los elementos discretos para mejorar su eficiencia y precisión en el modelado de materiales como roca, especialmente para procesos de excavación. Todos los algoritmos numéricos se han implementado en el programa propio, que ha sido utilizado para probar distintos ejemplos. La formulación básica del DEM, con un modelo lineal de contacto elástico perfectamente frágil ha sido utilizado en el presente trabajo. La principal diferencia con otros modelos de la literatura es la consideración de que los parámetros de rigidez y fuerzas máximas son valores globales y constantes en todo el modelo. El resultado de la simulación está fuertemente relacionado con la configuración del ensamblaje de partículas utilizado. El ensamblaje de partículas debe ser suficientemente compacto y asegurar la isotropía de las propiedades físicas del material modelado. La tesis presenta una nueva técnica para la generación de ensamblajes de partículas de alta densidad para geometrías arbitrarias, satisfaciendo todos los requisitos para una simulación con elementos discretos correcta. Uno de los temas clave en el uso del DEM es la estimación de los parámetros del modelo de contacto. Se propone una metodología para la estimación de los parámetros del modelo de contacto siguiendo las propiedades macroscópicas requeridas en el material Las relaciones entre los parámetros del modelo y las propiedades mecánicas de materiales frágiles, así como su la influencia de la configuración del ensamblaje de partículas son analizadas. Una gran dificultad en la aplicación del DEM en problemas reales de ingeniería es el alto costo computacional de simulaciones que consideran un gran número de partículas. La solución mas común para resolver esto es el uso de técnicas de computación paralela, donde se utiliza un gran número de procesadores. Como vía alternativa, un esquema acoplado entre el DEM y el FEM expuesto en la tesis. Con el modelo híbrido DEM/FEM, el DEM es usado solo en las partes del dominio donde presenta ventajas sobre el enfoque continuo del FEM. El acoplamiento puede ser adaptado dinámicamente, comenzando con todo el dominio discretizado con FEM, y durante la simulación, en las regiones donde se encuentran altos niveles de tensión, se emplea un cambio del método de simulación de continuo (FEM) a discreto (DEM). Finalmente, todos los desarrollos son aplicados a la simulación de un proceso excavación real. Se realiza un estudio del proceso de corte de roca con discos costadores, utilizados en tuneladoras, donde el DEM y la técnica de acoplamiento presentan una importante ventaja sobre otras técnicas de simulación.

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Šmilauer, Václav. "Cohesive Particle Model using the Discrete Element Method on the Yade Platform." Phd thesis, Université de Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00502402.

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Cette thèse décrit un modèle de béton utilisant la méthode des éléments discrets (DEM) et le code de calcul Yade. La DEM discrétise un volume avec des particules (sphériques) dont les mouvements sont déterminés par des lois de comportement locales et les équations de Newton. La continuité du matériau est représentée par des contacts cohésifs entre les particules; les discontinuités apparaissent naturellement lors de l'endommagement de ces contacts. Le béton est considéré comme un matériau homogène; les particules ne sont qu'une méthode particulière de discrétisation et ne représentent pas la géométrie des granulats, du ciment ou des vides; la loi du comportement locale comprend l'endommagement, la plasticité et la viscosité; la calibration du modèle est décrite en détail. Ce modèle a été implementé dans la plateforme Yade, profondément enrichie pendant ce travail; cette thèse décrit pour la première fois de manière complète le code de calcul Yade. Si Yade est prévu principalement pour la DEM, la modularité et la possibilité d'utiliser grandes parties du code dans le développement de nouvelles approches (re-utilisabilité) y sont tout de même des éléments importants. La partie calcul est programmée en c++ pour la performance et le calcul parallèle (mémoire partagée). Des scripts en langage python, l'un des plus répandus des langage de script, sont utilisés pour décrire les simulations de manière rapide et concise, contrôler l'exécution et post-traiter les résultats; Python permet l'accès aux données internes en cours de simulation. La pérennité des développements est encouragée par la plateforme, en particulier par l'exigence de documentation.

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FERREIRA, CRISTIANE ARANTES. "STUDY OF MECHANICAL BEHAVIOR OF FIBER REINFORCED SOIL THROUGH DISCRETE ELEMENT METHOD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2010. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33093@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR PROGRAMA DE EXCELENCIA ACADEMICA Um grande número de novos materiais geotécnicos foi desenvolvido baseado na adição de materiais fibrosos, sendo incorporados como elementos de reforço. A técnica de solo reforçado pode ser representada pela produção e aplicação, não somente de fibra natural, mas também de fibras sintéticas e poliméricas. Estudos anteriores de solos reforçados com fibras de polipropileno têm mostrado melhora significativa das propriedades mecânicas dos solos, tais como o aumento da resistência de pico e resistência pós-pico, ductilidade e tenacidade. Estes resultados mostram um grande potencial deste tipo de fibra, quando utilizado como reforço de solos, por exemplo, em base de fundações superficiais, aterros sobre solos moles e liners de cobertura de aterros sanitários. A partir de ajustes matemáticos para determinar a interação entre solos granulares e observações do comportamento global em macro-escala tornou possível analisar o comportamento de solos granulares reforçados com fibras de uma forma micro-mecânica. A modelagem numérica do comportamento mecânico de solos reforçados com fibras de polipropileno, através de uma análise micro-mecânica, utiliza como ferramenta o Método dos Elementos Discretos (MED), que permite a representação do solo em 2D, a partir de um conjunto de partículas de elementos discretos circulares. O MED descarta a visão clássica do solo como uma forma contínua, proporcionando a possibilidade de modelá-lo como partículas constituintes. Sua formulação baseia-se no equilíbrio de forças e de deslocamentos gerados pelos contatos, os quais são descritos através das leis da física clássica, permitindo o mapeamento dos movimentos de cada partícula. A vantagem da micro-mecânica é a possibilidade de explicitar microestruturas, tais como fibras de polipropileno, responsáveis pela mudança no comportamento do solo. Com base no estudo deste fenômeno, causado pela inserção de fibras de polipropileno em materiais granulares, formulações matemáticas foram propostas com a finalidade de descrever o comportamento de solos reforçados através da implementação do código de elementos discretos (DEMlib). Após a calibração e validação do programa, a influência decorrente da inserção do reforço de fibra ao solo foi analisada, sendo realizadas simulações de ensaios biaxiais em amostras discretas de areia, com e sem o reforço fibroso. O comportamento micro-mecânico de misturas reforçadas permitiu avaliar os efeitos das mudanças no teor de fibras presente na matriz de solo, bem como diferentes rigidezes das fibras. Conclui-se que o estudo realizado pelo Método dos Elementos Discretos identificou a real interação entre as partículas do solo e do reforço em forma de fibra, indicando que as fibras, quando inseridas no solo, podem sofrer deformações plásticas de tração e alongamento até atingir a ruptura, proporcionando a melhora nos parâmetros mecânicos do solo. A large number of new geotechnical materials was developed based on the addition of fibrous materials being incorporated as reinforcement. The technique of reinforced soil can be represented by the production and application, not only natural fiber, but also synthetic fibers and polymer. Previous studies of soil reinforced with polypropylene fibers have shown significant improvement of mechanical properties of soils, such as increasing the resistance peak and postpeak strength, ductility and toughness. These results show a great potential for this type of fiber, when used as soil reinforcement, for example, based on shallow foundations, embankments over soft soils and liners for landfill cover. From mathematical adjustments to determine the interaction between granular soils and the observation of global macro-scale become possible to analyze the behavior of granular soils reinforced with fibers in a micro-mechanics. The numerical modeling of mechanical behavior of soil reinforced with polypropylene fibers, through a micro-mechanical analysis, the tool uses as the Discrete Element Method (DEM), which allows the representation of the soil in 2D, from a set of particles circular discrete elements. The MED rule out the classical view of soil as a continuous form, providing the ability to model it as a constituent particle. Its formulation is based on the balance of forces and displacements generated by the contacts, which are explained through the laws of classical physics, allowing the mapping of movements of each particle. The advantage of micro- mechanics is the possibility of explicit microstructures, such as polypropylene fibers, responsible for the change in the behavior of the soil. Based on the study of this phenomenon, caused by the insertion of polypropylene fibers in granular materials, mathematical formulations have been proposed in order to describe the behavior of reinforced soils through the implementation of the Code of discrete elements (DEMlib). After calibration and validation program, the influence due to the insertion of fiber reinforcement to the soil was analyzed, and simulations of biaxial tests on discrete samples of sand, with and without the fibrous reinforcement. The micro-mechanical behavior of blends reinforced allowed evaluating the effects of changes in fiber content present in the soil matrix and different rigidities of the fibers. We conclude that the study by the Discrete Element Method identified the actual interaction between the soil particles and the reinforcement in the form of fiber, indicating that the fibers, when inserted into the soil, may undergo plastic deformation and tensile elongation until the rupture, providing an improvement in mechanical parameters of soil.

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SILVA, ALAN BORGES DA. "SIMULATION OF THE MECHANICAL BEHAVIOR OF RAIL BALLAST BY DISCRETE ELEMENT METHOD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36346@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR PROGRAMA DE EXCELENCIA ACADEMICA Considerando o investimento do governo federal na expansão da malha ferroviária com o programa de aceleração do crescimento (PAC2) e com o programa de investimento em logística (PIL), vem sendo desenvolvidas no país inúmeras pesquisas envolvendo ferrovias, inclusive na área de materiais, como o lastro ferroviário, objeto de estudo deste projeto. Paralelamente, pesquisas com foco em modelagem computacional vem sendo desenvolvidas a fim de otimizar a avaliação do comportamento dos materiais. O projeto tem como objetivo desenvolver modelos computacionais para avaliar a capacidade do método dos elementos discretos em reproduzir o comportamento mecânico de lastro ferroviário submetido a carregamentos cíclicos, com base em um ensaio triaxial cíclico. O ensaio analisou o comportamento mecânico de duas distribuições granulométricas de lastro ferroviário, sendo a primeira sugerida por Indraratna et al. (2004), referente a alterações para melhorias da normativa australiana, enquanto a segunda, utiliza a normativa brasileira. O modelo computacional foi desenvolvido no software WooDEM (2012). Foram realizadas análises mecânicas do comportamento do lastro ferroviário considerando as coordenadas das partículas em relação ao tempo e a profundidade, a fim de determinar o deslocamento gerado pelo carregamento cíclico. Considering the federal government s investment in the expansion of the railway network with the growth acceleration program (PAC2) and with the investment in logistics program (PIL), numerous surveys involving railways have been developed in the country, including in the area of materials, such as the rail ballast, object of study of this project. In parallel, research focused on computational modeling has been developed in order to optimize the evaluation of the behavior of materials. This dissertation aims to develop computational models to evaluate the ability of the discrete element method to reproduce the mechanical behavior of cyclically loaded rail ballast, based on a cyclic triaxial test. The study analyzed the mechanical behavior of two rail ballast granulometric distributions, the first being suggested by Indraratna et al. (2004), regarding changes to improve Australian regulations, while the second, uses the Brazilian legislation. The computational model was developed in WooDEM software (2012). Mechanical analysis of the rail ballast behavior was performed considering the coordinates of the particles in relation to time and depth in order to determine the displacement generated by the cyclic loading.

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Chantharayukhonthorn, Maytee. "A hybrid discrete element and continuum method for multiscale granular media modeling." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122146.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019 Cataloged from PDF version of thesis. Includes bibliographical references (pages 95-98). Capturing the propagation of microscale physics to macroscale phenomena is intractable for many large systems. Scale propagation is a major issue in granular media, wherein two extremes are often taken. In one, granular materials are modeled as a continuum, which greatly reduces the number of degrees of freedom that describe the system and can thus be simulated relatively quickly. However continuum models are not always precise and have difficulty capturing certain effects such as particle size dependence. In discrete element methods (DEM), every grain and the interactions between them are simulated. DEM is accurate but solve time scales poorly with large grain numbers. Here, we present a hybrid simulation scheme, which seeks a best-of-both-worlds solution by bridging these two approaches. A mass of granular media is partitioned into three domains: a continuum domain represented using the material point method (MPM), discrete grains using DEM, and a transition zone of both MPM and DEM that are coupled via kinematic constraints. An "oracle" determines which areas of the domain are MPM and which are DEM, and converts between the two. In the canonical example of silo flow, flow with a sufficiently small orifice jams, resolving length scale dependent effects. Collapse of granular columns modeled with the hybrid method compare quantitatively well with pure discrete simulation and experiments in literature. A significant speedup is seen with the hybrid method over a similar domain of pure discrete grains. by Maytee Chantharayukhonthorn. S.M. S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering

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Chaumeil, Florian. "Using DEM-CFD method at colloidal scale." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8066.

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The aim of this work is to look into the applicability of Discrete Element Modelling (DEM) coupled to Computational Fluid Dynamics (CFD) to simulate micro-scale colloidal particles immersed in fluid. Numerical methods were implemented through the commercial framework of EDEM2.3. As opposed to dissolved matter, which behaves as a continuum within the fluid medium, particulate matter is made of discrete entities that interact amongst themselves, and with the fluid and any physical boundaries. Particulate matter is ubiquitous in many purification processes that would beneficiate from having an easy way to model particle dynamics immersed in water. In an effort to understand better the dynamics of particle deposition under surface forces and hydraulic forces, a micro-scale numerical model was built adopting both a mechanistic and a statistical approach to represent the forces involved in colloidal suspension. The primary aim of the model was to simulate particle aggregation, deposition and cluster re-suspension in real world micro-systems. Case studies include colloidal flocculation in a constricted tube, and colloidal fouling around membrane filtration feed spacers. This work used a DEM-CFD coupling method that combined the DEM particle flow simulation with hydrodynamics forces from a velocity field computed through CFD. It also implemented boundary-particle and particle-particle interactions by enabling the modelling of surface and interfacial forces. Two kinds of coupling method were considered: two-way and one-way coupling. Two-way coupling is suitable for high particle concentration flow where particle loading affects the hydrodynamics. One-way coupling is suitable for dispersed particle configuration where the flow field is assumed to be undisturbed by the particles. The advantages and drawbacks of both techniques for micron-size particles were investigated. EDEM 2.3 was customised with plug-ins to implement Van der Waals forces and Brownian forces and its post-processing features offered the ability to investigate easily the microparticles behaviour under the influence of fluid forces. In this context, DEM-CFD modelling using EDEM 2.3 represents an improvement on previously published works as it enables higher visibility and reproducibility along with increasing the number of potential users of such modelling. Emphasis was given in presenting original findings and validation results that illustrate DEMCFD applicability, with respect to modelling of hydraulically mediated colloidal surface interaction; while highlighting factors that limit the ability of the technique. For instance, the effect of particle disturbance on the surrounding medium currently proves difficult to model.

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Nel, Rick Guillaume. "Discrete element modelling of packed rock beds for thermal storage applications." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80147.

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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.

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Thakur, Subhash Chandra. "Mesoscopic discrete element modelling of cohesive powders for bulk handling applications." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9777.

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Many powders and particulate solids are stored and handled in large quantities across various industries. These solids often encounter handling and storage difficulties that are caused by the material cohesion. The cohesive strength of a bulk material is a function of its past consolidation stress. For example, high material cohesive strength as a result from high storage stresses in a silo can cause ratholing problems during discharge. Therefore, it is essential to consider the stress-history dependence when evaluating such handling behaviour. In recent years the Discrete Element Method (DEM) has been used extensively to study the complex behaviour of granular materials. Whilst extensive DEM studies have been performed on cohesionless solids, much less work exists on modelling of cohesive solids. The commonly used DEM models to model adhesion such as the JKR, DMT and linear cohesion models have been shown to have difficulty in predicting the stress-history dependent behaviour for cohesive solids. DEM modelling of cohesive solid at individual particle level is very challenging. To apply the model at single particle level accurately would require one to determine the model parameters at particle level and consider the enormous complexity of interfacial interaction. Additionally it is computationally prohibitive to model each and every individual particle and cohesion arising from several different phenomena. In this study an adhesive elasto-plastic contact model for the mesoscopic discrete element method (DEM) with three dimensional non-spherical particles is proposed with the aim of achieving quantitative predictions of cohesive powder flowability. Simulations have been performed for uniaxial consolidation followed by unconfined compression to failure using this model. Additionally, the scaling laws necessary to produce scale independent predictions for cohesionless and cohesive solids was also investigated. The influence of DEM input parameters and model implementation have been explored to study the effect of particle (meso-scale) properties on the bulk behaviour in uniaxial test simulation. The DEM model calibration was achieved using the Edinburgh Powder Tester (EPT) – an extended uniaxial tester to measure flowability of bulk solids. The EPT produced highly repeatable flowability measurements and was shown to be a good candidate for DEM model calibration. The implemented contact model has been shown to be capable of predicting the experimental flow function (unconfined compressive strength versus the prior consolidation stress) for a limestone powder which has been selected as a reference solid in the Europe wide PARDEM research network. Contact plasticity in the model is shown to affect the flowability significantly and is thus essential for producing satisfactory computations of the behaviour of a cohesive granular material. The model predicted a linear relationship between a normalized unconfined compressive strength and the product of coordination number and solid fraction. Significantly, it has been found that contribution of adhesive force to the limiting friction has a significant effect on bulk unconfined strength. Failure to include the adhesive contribution in the calculation of the frictional resistance may lead to under-prediction of unconfined strength and incorrect failure mode. The results provide new insights and propose a micromechanical based measure for characterising the strength and flowability of cohesive granular materials. Scaling of DEM input parameters in a 3D simulation of the loading regimes in a uniaxial test indicated that whilst both normal and tangential contact stiffness (loading, unloading, and load dependent) scales linearly with radius of the particle, the adhesive forces scales with the square of the radius of the particles. This is a first step towards a mesoscopic representation of a cohesive powder that is phenomenological based to produce the key bulk characteristics of a granular solid and the results indicate that it has potential to gain considerable computational advantage for large scale DEM simulations. The contact model parameters explored include particle contact normal loading stiffness, tangential stiffness, and contact friction coefficient. The DEM model implementation parameters included numerical time step, strain rate, and boundary condition. Many useful observations have been made with significant implications for the relative importance of the DEM input parameters. Finally the calibration procedure was applied to a spray dried detergent powder and the simulation results are compared to whole spectrum of loading regime in a uniaxial experiment. The experimental and simulation results were found to be in reasonable agreement for the flow function and compression behaviour.

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Kosteski, Luis Eduardo. "Aplicação do Método dos Elementos Discretos formado por barras no estudo do colapso de estruturas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/56589.

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No presente trabalho é apresentada uma versão do Método dos Elementos Discretos formado por barras (DEM) no estudo do colapso de estruturas. O Método dos Elementos Discretos foi introduzido, especialmente, para a simulação numérica de problemas de dano e fratura. Esse método tem habilidade natural para introduzir descontinuidades de uma maneira muito direta e intuitiva. Além disso, métodos discretos oferecem uma estrutura conveniente para dar conta da desordem da microestrutura do material por meio de modelos estatísticos. A versão do DEM utilizada neste trabalho consiste na discretização do contínuo em barras que formam uma treliça espacial regular, onde massas equivalentes são concentradas nos nós, e as rigidezes das barras são equivalentes ao contínuo que tentam representar. Leis uniaxiais de dano permitem modelar fratura e dano anisotrópico com relativa facilidade. Esta versão foi amplamente testada em diversos campos da Engenharia, entre eles, problemas dinâmicos, de impacto, geração e propagação de sismos, estudo de efeito de escala em rochas e concreto, análise da microestrutura de materiais. Este trabalho apresenta dois grandes temas, nos quais foram realizadas implementações no DEM que aumentam sua aplicabilidade. Também são implementadas modificações nas leis constitutivas antes utilizadas, e apresentadas, também, novas leis para dar flexibilidade na calibração dos modelos. São comparados os resultados utilizando as diversas leis na análise do efeito de escala de placas submetidas à tração. Também são analisados os resultados obtidos sob a óptica da teoria de escala multifractal. Neste campo, encontram-se respostas muito interessantes que explicam os mecanismos de fratura, assim como dão uma noção de que alterações deveriam ser realizadas no DEM para conseguir que o método fique completamente objetivo em relação à escala. Nesse processo, estudam-se diferentes formas de obter as dimensões fractais de placas de rocha submetidas à tração e é analisada a influência de alguns dos parâmetros do DEM, além da relação constitutiva utilizada. Finalmente, o DEM é introduzido dentro do sistema comercial Abaqus, com objetivo de resolver problemas com grande quantidade de graus de liberdade ou com as condições de contorno ou de carregamento muito complexos. Apresentam-se exemplos de validação e exemplos de aplicação que mostram as vantagens das inovações realizadas. This paper presents a version of the Truss-like Discrete Element Method in the study of the collapse of structures. The discrete element method was introduced especially for numerical simulation of fracture and damage problems. This method has the natural ability to introduce discontinuities in a very direct and intuitive way. Moreover, discrete methods offer a convenient framework to account for the disorder of the material microstructure by means of statistical models. The truss-like Discrete Element Method (DEM) used in this work represents the continuum by means of a periodic spatial arrangement of bars with the masses lumped at their ends. The rigidity of the bars is equivalent to the continuum to trying to represent. Uniaxial damage Laws allow model fracture and anisotropic damage with relative ease. This version was widely tested in various engineering fields including: dynamics problems, impact, generation and propagation of earthquakes, study of scale effect in rock and concrete analysis of the microstructure of materials. This work presents two major issues in witch were performed DEM implementations that increase its applicability. To obtain a better description of the model modifications in the constitutive laws are implemented and new ones are presented. The scale effect results of plates of rock subjected to traction obtained to different laws are compared. These obtained results are examined under the Multifractal scaling law theory. In this field, very interesting answers that explain the mechanisms of fracture are found. They gives some notions of which changes should be made in DEM to obtain a fully scale objective method. In the process, different ways to obtain the fractal dimension of rock plates subjected to traction are studied. The influence of some DEM parameter and constitutive laws are also analyzed. Finally, the DEM has been implemented within the commercial system ABAQUS to solve problems with a large number of degrees of freedom or very complex contour or loading conditions. Presents examples of validation and application that show the benefits of innovations through.

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Golchert, Dennis J. "Application of X-ray microtomography to discrete element method simulations of agglomerate breakage /." St. Lucia, Qld, 2003. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17509.pdf.

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Briend, Robin. "Modelling wheel-soil interactions using the discrete element method for tread shape optimization." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97205.

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The structure of a wheel intended for lunar applications requires an innovative design because of the Moon's specific environment. As in-situ prototype testing is obviously unfeasible, testing can only be conducted on lunar simulant soils, or through simulations. This study presents wheel-soil interaction simulations using the discrete element method (DEM) software EDEM and their use for tread shape optimization. The DEM parameters of EDEM's contact-model are first reviewed before presenting a systematic methodology of their calibration. The first step consists in measuring key properties of the real soil with basic experiments and simulating these experiments for different values of the virtual soil's design variables. The soil's response surfaces of the targeted properties are then computed, and an optimization algorithm is developed to determine the optimum sets of design variables that minimize the discrepancy of the properties between the real soil and the virtual one.Then, two different approaches of three-dimensional wheel-soil simulations are described. The first approach involves a displacement-controlled wheel, its tractive performance being measured for various grouser configurations. In the second approach, the wheel is torque-controlled and performances, such as power consumption or speed, are investigated and validated experimentally.This work proposes a soil simulation and shape optimization tool for the design of a rigid wheel tread that targets a need of the Canadian aerospace industry. La structure d'une roue destinée à une application lunaire doit être le fruit d'une conception innovante afin de s'adapter à l'environnement très particulier de la surface de la Lune. Comme les prototypes ne peuvent être testés sur site, des tests sont possibles uniquement sur Terre, sur des simulants de sol lunaire ou en simulations. Dans cette étude, des simulations d'interactions roue-sol utilisant la méthode des éléments distincts (MED) et le logiciel EDEM sont présentées, ainsi que leur utilité dans le cadre de l'optimisation de la géométrie de la bande de roulement.Tout d'abord, les paramètres MED intervenants dans le modèle de contact de EDEM sont passés en revue et une méthodologie systématique pour leur calibration est proposée. La première étape de cette méthodologie consiste à mesurer des propriétés importantes du sol à modéliser à l'aide d'expériences simples, puis de simuler ces expériences en variant les valeurs des paramètres MED. Les surfaces de réponse pour les propriétés ciblées sont ensuite calculées, et un algorithme d'optimisation détermine les valeurs optimales des paramètres afin de minimiser les différences entre les propriétés du sol réel et celles du sol virtuel.Ensuite, deux approches de simulations roue-sol tridimensionnelles sont décrites. La première approche implique une roue asservie en déplacements. Les performances en traction de la roue sont mesurées pour différentes configurations de la bande de roulement. Dans la deuxième approche, la roue est contrôlée par un couple moteur, et d'autres performances telles que la puissance consommée ou la vitesse peuvent ainsi être mesurées et validées expérimentalemnt.Enfin, les possibilités des simulations proposées en terme d'optimisation de la structure de la bande de roulement de roues rigides sont exposées.

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Kruggel-Emden, Harald [Verfasser]. "Analysis and Improvement of the Time-Driven Discrete Element Method / Harald Kruggel-Emden." Aachen : Shaker, 2008. http://d-nb.info/1164341219/34.

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Henriksson, Felix, and Joanna Minta. "Bucket-soil interaction for wheel loaders : An application of the Discrete Element Method." Thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-53357.

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Wheel loaders are fundamental construction equipment to assist handling of bulk material e.g. gravel and stones. During digging operations, it withstands forces that are both large and very complicated to predict. Moreover, it is very expensive to develop prototypes of wheel loader for verification. Consequently, the Discrete Element Method (DEM) was introduced for gravel modeling a couple of years ago to enable prediction of these forces. The gravel model is connected with a Multibody System (MBS) model of the wheel loader, in this thesis a Volvo L180G. The co-simulation of these two systems is a very computer intensive operation and hence, it is important to investigate which parameters that have the largest influence on the simulation results. The aim of this thesis is to investigate the simulation sensitivity with respect to co-simulation communication interval, collision detection interval and gravel normal stiffness.The simulation results are verified by comparison with measurement data from previous tests performed by Volvo CE. The simulations are compared to investigate the relevant parameters. The conclusion of this thesis is that DEM is a method that in a very good way can predict the draft forces during digging operations.

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Oladele, Temitope Philip. "A study of impact breakage of single rock specimen using discrete element method." Doctoral thesis, Faculty of Engineering and the Built Environment, 2020. http://hdl.handle.net/11427/32903.

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Comminution is a critical stage of mineral processing which aims to reduce the size of ore particles through breakage, consequently increasing the likelihood of the liberation of valuable minerals. However, comminution is highly energy-intensive and an understanding of the key breakage mechanisms has been identified as an important factor in improving the efficiency of the process. Several factors, such as pre-existing cracks, mineralogical composition, ore shape and size are known to affect ore breakage behaviour during breakage. To investigate breakage mechanisms, it is important to be able to determine how individual factor influences the breakage behaviour of rock specimens. However, isolating and investigating individual factors under experimental conditions is challenging and typically impractical. Numerical techniques such as the Bonded Particle Model-Discrete Element Method (BPMDEM) have been developed as a means of investigating in isolation, the effects of different factors on ore breakage behaviour under closely controlled breakage conditions using synthetic rock specimens. This study investigates how individual factors influence rock specimen breakage using BPM-DEM numerical methods. Numerical simulations were conducted using ESyS-particle 2.3.5, an open-source discrete element method (DEM) software package which uses Python-based libraries to generate geometries and simulations and a C++ engine for mathematical computations. Empirical calibration relationships were developed to relate microstructural model parameters to the macroscopic mechanical properties that are typically obtained from standard geotechnical breakage experiments. The robustness of the model was evaluated by considering the sensitivity of fracture measures to the variation of model resolution, size-dependency and macroscopic mechanical properties (Young's modulus and uniaxial compressive strength) of the numerical specimens. A comparative study of single rock specimen breakage using the current BPM-DEM and laboratory SILC experiments carried out by Barbosa et al. (2019) was conducted. The measured fracture force and fracture patterns at different sizes for both cylindrical and spherical synthetic rock specimens were examined. Furthermore, the model was used to study, in isolation, the influence of pre-existing cracks in rock specimens and differing mineralogical compositions upon measurable breakage properties. Numerical rock specimens with pre-existing cracks were constructed using a microcrack approach, while a unique approach with the insertion of "seed points" was developed and demonstrated to construct numerical rock specimens with varying mineralogical compositions. Results from the numerical simulations showed that a high model resolution with a sufficiently large number of DEM-spheres exhibited results with the least deviation and error with respect to fracture measures, and, was therefore considered numerically stable. The dependency of fracture measurements on specimen size showed an expected increase in the measured fracture force as the specimen size increases. The variation of the macroscopic Young's modulus and uniaxial compressive strength against the fracture measures emphasised that the locus of these mechanical properties against the fracture measure can be used to specify a calibration relationship. Results of the comparative study showed that for both cylindrical and spherical rock specimens, the DEM consistently predicted the fragment patterns as well as the increase in the measured fracture force as the specimen size increased. The investigation on the effect of pre-existing cracks revealed that an increasing number of pre-existing cracks in rock specimens necessitated lower fracture force and consequently produced a low amount of new fracture surface area. For the binary phase mineralogical composition in the study, it was found that the fracture force decreased with an increase in the concentration of the softer component due to the increased percentage of weakness in the specimen. It was concluded that, with an appropriate calibration exercise and a realistic specification of material properties from the evaluation study, the DEM as a tool was sufficient to act as a "virtual laboratory" to isolate and study the individual effects of factors that influence ore breakage. The understanding of these results highlighted two important points. Firstly, this study was able to unravel some of the possible causes of the inefficiency in comminution practices, whereby significant amounts of energy can be expended to achieve minimal gains in respect of enhancing liberation due to pre-weakening and mineralogical composition. Secondly, it emphasised some of the causes of the variation observed during ore characterisation on a laboratory breakage device, attributable to pre-weakening and mineralogical composition.

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Dissertations / Theses on the topic 'Discrete Element Method'

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