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1

Lee, Kai Teck. "Continuous granulation of pharmaceutical powder using a twin screw granulator." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4002/.

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Twin screw extruder (TSE) has been studied extensively as a granulator because it allows continuous processing. Initial work was carried out by comparing the TSE with conventional granulator shows that the mechanism of TSE granulation is different from conventional granulation with the absence of the consolidation stage. PEPT was also utilised and it reveals that the flow stream of the material is not only due to the conveying capacity but also the granulator fill, in particularly for the 90o mixing zone which is believed to be a dispersion type of mechanism driven by the granulator fill gradient. Residence time distribution was measured and simulated by fitting the experimental data using a continuous stirred tank reactors model. The model describes the experimental curves reasonably well when a plug flow fraction was considered. Generally the mean residence time (MRT) of the system is proportional to the mixing zone angle and is inversely proportional to the screw speeds and flowrate. A study using the variance reduction ratio demonstrates that the TSE granulator used in the present study is able to remove the feed instability given that the ratio of the frequency of the input stream fluctuation to the MRT is high.
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2

Djuric, Dejan. "Continuous granulation with a twin-screw Extruder." Göttingen Cuvillier, 2008. http://d-nb.info/989861163/04.

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3

DeGiuli, Eric. "Continuum limits of granular systems." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/44393.

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Despite a century of study, the macroscopic behaviour of quasistatic granular materials remains poorly understood. In particular, we lack a fundamental system of continuum equations, comparable to the Navier-Stokes equations for a Newtonian fluid. In this thesis, we derive continuum models for two-dimensional granular materials directly from the grain scale, using tools of discrete calculus, which we develop. To make this objective precise, we pose the canonical isostatic problem: a marginally stable granular material in the plane has 4 components of the stress tensor σ, but only 3 continuum equations in Newton’s laws ∇ ‧σ = 0 and σ = σT. At isostaticity, there is a missing stress-geometry equation, arising from Newton’s laws at the grain scale, which is not present in their conventional continuum form. We first show that a discrete potential ψ can be defined such that the stress tensor is written as σ = ∇ × ∇ × ψ, where the derivatives are given an exact meaning at the grain scale, and converge to their continuum counterpart in an appropriate limit. The introduction of ψ allows us to understand how force and torque balance couple neighbouring grains, and thus to understand where the stress-geometry equation is hidden. Using this formulation, we derive the missing stress-geometry equation ∆(F^ : ∇∇ψ) = 0, introducing a fabric tensor F^ which characterizes the geometry. We show that the equation imposes granularity in a literal sense, and that on a homo- geneous fabric, the equation reduces to a particular form of anisotropic elasticity. We then discuss the deformation of rigid granular materials, and derive the mean-field phase diagram for quasistatic flow. We find that isostatic states are fluid states, existing between solid and gaseous phases. The appearance of iso- staticity is linked to the saturation of steric exclusion and Coulomb inequalities. Finally, we present a model for the fluctuations of contact forces using tools of statistical mechanics. We find that force chains, the filamentary networks of con- tact forces ubiquitously observed in experiments, arise from an entropic instability which favours localization of contact forces.
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4

Mahmoud, M. A. "Continuously penetrating bodies in granular materials." Thesis, University of Southampton, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356027.

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5

Lute, Sushma. "Continuous twin screw wet granulation : a step towards mechanistic understanding." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/21442/.

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6

Barker, Thomas. "Well-posed continuum modelling of granular flows." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/wellposed-continuum-modelling-of-granular-flows(bcb5fb47-31cb-4168-a49d-0be2e1599786).html.

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Inertial granular flows lie in a region of parameter space between quasi-static and collisional regimes. In each of these phases the mechanisms of energy dissipation are often taken to be the defining features. Frictional contacts between grains and the transmission of energy through co-operative force chains dominate slowly sheared flows. In the opposite extreme infrequent high-energy collisions are responsible for dissipation in so-called gaseous granular flows. Borrowing from each of these extremes, it is postulated that during liquid-like flow, grain energy is transferred through frequent frictional interactions as the particles rearrange. This thesis focuses on the μ(I)-rheology which generalises the simple Coulomb picture, where greater normal forces lead to greater tangential friction, by including dependence on the inertial number I, which reflects the frequency of grain rearrangements. The equations resulting from this rheology, assuming that the material is incompressible, are first examined with a maximal-order linear stability analysis. It is found that the equations are linearly well-posed when the inertial number is not too high or too low. For inertial numbers in which the equations are instead ill-posed numerical solutions are found to be grid-dependent with perturbations growing unboundedly as their wavelength is decreased. Interestingly, experimental results also diverge away from the original μ(I) curve in the ill-posed regions. A generalised well-posedness analysis is used alongside the experimental findings to suggest a new functional form for the curve. This is shown to regularise numerical computations for a selection of inclined plane flows. As the incompressibility assumption is known to break down more drastically in the high-I and low-I limits, compressible μ(I) equations are also considered. When the closure of these equations takes the form suggested by critical state soil mechanics, it is found that the resultant system is well-posed regardless of the details of the deformation. Well-posed equations can also be formed by depth-averaging the μ(I)-rheology. For three-dimensional chute flows experimental measurements are captured well by the depth-averaged model when the flows are shallow. Furthermore, numerical computations are much less expensive than those with the full μ(I) system.
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7

Dunatunga, Sachith Anurudde. "A framework for continuum simulation of granular flow." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108935.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 119-124).<br>Granular materials have eluded continuum modeling attempts for centuries. A significant chunk of the complexity lies in the trans-phase behavior of granular media; while the material has a yield stress and can therefore act as a solid body, grains may also flow quickly much like a liquid. At low pressures and high velocities, the grains may even become disconnected from each other, resulting in a gas-like state where the only stresses are essentially due to occasional collisions between grains. Moreover, all three states are commonly found simultaneously in many industrial and natural processes, and individual grains may switch between these phases readily. A further complication is that typically the grain size is large compared to the geometries in which we are interested; these size effects can lead to mispredictions when purely local models (without an intrinsic length scale) are used. Due to these complexities, a highly favored technique is the discrete element method, which tracks each grain individually and updates the forces and displacements when grains contact each other. While extremely accurate, discrete methods require incredible amounts of computational power, severely restricting the sizes of problems that can be simulated. Continuum techniques can potentially scale better, as individual grain-grain interactions are no longer tracked, but require a constitutive model. Recent continuum models, such as in Jop, Forterre, and Pouliquen (2006) and Kamrin and Koval (2012) show promise in capturing many observed phenomena, yet current numerical techniques limit the applicability of these models due to computational or numerical issues. In this thesis, we explore a continuum framework for simulation of granular materials in the context of the material point method, which allows us to test these material models further than many existing continuum techniques and pave the way for efficient simulation of large-scale processes involving granular media.<br>by Sachith Anurudde Dunatunga.<br>Ph. D.
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8

Wilms, Annika [Verfasser], Peter [Gutachter] Kleinebudde, and Jörg [Gutachter] Breitkreutz. "Advancing towards a controlled continuous dry granulation line / Annika Wilms ; Gutachter: Peter Kleinebudde, Jörg Breitkreutz." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2021. http://d-nb.info/1225931991/34.

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9

Kent, Timothy Robert. "Mechanistic Understanding of the NOB Suppression by Free Ammonia Inhibition in Continuous Flow Aerobic Granulation Bioreactors." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/87706.

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A partial nitritation-anammox continuous flow reactor (CFR) was operated for eight months demonstrating that a mixture of large anammox-supported aerobic granules (ASAGs) and small conventional aerobic granules (CAGs) can be maintained stably for extended periods of time. The influent NH4+ was kept at 50 - 60 mg N L-1 to verify that the upper range of total ammonia nitrogen (TAN) for domestic wastewater can supply an inhibitory level of free ammonia (FA) for nitrite oxidizing bacteria (NOB) suppression in CFRs at pH around 7.8. The ammonia oxidizing bacteria (AOB):NOB activity ratio was determined for a series of granule sizes to understand the impact of mass diffusion limitation on the FA inhibition of NOB. When dissolved oxygen (DO) limitation is the only mechanism for NOB suppression, the AOB:NOB ratio was usually found in previous studies to increase with the granule size. However, the trend is reversed when FA has an inhibitory effect on NOB, as was observed in this study. The decrease in AOB:NOB ratio indicates that the resistance to the diffusion of FA along the granule radius limited its ability to inhibit NOB. This means smaller granules, e.g. diameter < 150 microns, are preferred for nitrite accumulation when high FA is present, e.g. in the partial nitritation-anammox process. The trend was further verified by observing the increase in the apparent inhibition coefficient, KI,FAapp, as granule size increased. This study for the first time quantified the effect of diffusion limitation on the KI,FAapp of NOB in granules and biofilms. A mathematical model was then utilized to interpret the observed suppression of NOB. The model predicted that NOB suppression was only complete at the granule surface. The NOB that did survive in larger granules was forced to dwell within the granule interior, where the FA concentration was lower than that in the bulk solution. This means FA inhibition can be taken advantage of as an effective means for NOB suppression in small granules and thin biofilms. Further, FA and DO were found to be both required for the stratification of AOB and NOB in partial nitritation-anammox CFRs. The structural stratification commonly observed in granules is then concluded to be a consequence but not a cause of the NOB suppression.<br>MS<br>A partial nitritation-anammox continuous flow reactor (CFR) was operated for eight months demonstrating that granular sludge can be maintained stably for extended periods of time. In this approach, NH3 is only partially converted to NO2 - (partial nitritation), and the conversion to NO3 - is prevented by the suppression of nitrite oxidizing bacteria (NOB). NH3 and NO2 - are then utilized by anammox bacteria to create N2 gas. The influent NH4 + fed to the reactor was kept at 50 to 60 mg N L-1 to verify that the upper range of total ammonia nitrogen (TAN) for domestic wastewater can supply a sufficiently high level of free ammonia (FA) to inhibit NOB growth in CFRs at a pH around 7.8. It is expected that the penetration of a substrate into granule sludge will experience diffusional resistance as it moves from water to denser solid material and is consumed by bacteria. The ammonia oxidizing bacteria (AOB):NOB activity ratio was determined for a series of granule sizes to understand the impact of mass diffusion limitation on the FA inhibition of NOB. When dissolved oxygen (DO) limitation is the only mechanism for NOB suppression, the AOB:NOB ratio was usually found in previous studies to increase with the granule size. However, the trend is reversed when FA has an inhibitory effect on NOB, as was observed in this study. The decrease in AOB:NOB ratio indicates that the resistance to the diffusion of FA, which increases with increasing granule size, along the granule radius limited its ability to inhibit NOB. This means smaller granules, e.g. diameter < 150 µm, are preferred for NO2 - accumulation when high FA is present. The trend was further verified by observing the increase in the apparent inhibition coefficient, KI,FAapp, as granule size increased. This coefficient quantifies the effectiveness of an inhibitor, with larger values indicating weaker inhibition. This study for the first time quantified the effect of diffusion limitation on the KI,FAapp of NOB in granules and biofilms. A mathematical model was then utilized to interpret the observed suppression of NOB. The model predicted that NOB suppression was only complete at the granule surface. The NOB that did survive in larger granules was forced to dwell within the granule interior, where the FA concentration was lower than that in the bulk solution. This means FA inhibition can be taken advantage of as an effective means for NOB suppression in small granules and thin biofilms. Further, FA and DO were found to be both required for the stratification of a layer of AOB at the surface over a layer of NOB in partial nitritation-anammox CFRs. The structural stratification commonly observed in granules is then concluded to be a consequence but not a cause of the NOB suppression.
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10

Meruane, Naranjo Carolina. "Continuum Equations for Studying the Dynamics of Dense Heterogeneous Granular Flows." Tesis, Universidad de Chile, 2010. http://www.repositorio.uchile.cl/handle/2250/102493.

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La mayoría de los flujos granulares densos en la naturaleza, tales como avalanchas de detritos, flujos piroclásticos, deslizamientos de tierra y avalanchas subacuáticas, están constituidos por una amplia gama de diferentes componentes sólidas inmersas en un fluido ambiente. Con el objeto de obtener una buena representación de la dinámica de estos flujos, se debe considerar los mecanismos de interacción entre los diferentes componentes de la mezcla. En este trabajo de tesis, se desarrolló un marco teórico basado en la teoría de mezcla para representar la dinámica de un flujo denso de material granular heterogéneo compuesto por varias especies sólidas con diferentes propiedades, sumergidas en un fluido Newtoniano. El sistema de ecuaciones obtenido fue resuelto numéricamente y validado mediante la comparación de los resultados numéricos con mediciones experimentales de flujos gravitacionales de material granular, generados por el colapso de una columna bidimensional de granos usando aire o agua como fluido ambiente. Esta teoría fue luego utilizada para investigar los efectos del fluido ambiente sobre la dinámica de flujos gravitacionales de material granular homogéneo, y los efectos de la segregación de partículas en la dinámica de flujos granulares compuestos por mezclas binarias de pequeñas y grandes partículas esféricas de igual densidad másica. Los resultados obtenidos sugieren que las ecuaciones propuestas capturan las características esenciales que describen la dinámica de flujos granulares densos heterogéneos. En particular, se demuestra que el fluido ambiente modifica la dinámica del flujo granular a través de cambios en la presión hidrodinámica del fluido e interacciones de arrastre entre el fluido y los sólidos. Por un lado, la presión hidrodinámica del fluido puede soportar el peso reducido de los sólidos, induciendo así una transición desde un flujo granular denso compactado a un flujo granular denso en suspensión. Por otro lado, las fuerzas de arrastre contrarrestan el movimiento de los sólidos, especialmente cerca de la pared. Además, se demuestra que la segregación del material granular aumenta la velocidad del frente debido a la expansión volumétrica del flujo. Este aumento en la velocidad del flujo es amortiguado por el fluido ambiente, comportamiento que es más pronunciado en agua que en aire. Por lo tanto, la velocidad del frente resulta del equilibrio entre la expansión volumétrica causada por la segregación y la fuerza de arrastre impuesta por el fluido ambiente. Los resultados de esta tesis permiten concluir que un modelo realista para flujos granulares heterogéneos debe considerar al menos tres componentes: granos grandes y pequeños, y el fluido ambiente. De esta forma, el marco teórico propuesto en esta tesis podría ser útil para estudiar la dinámica a gran escala de este tipo de flujos en la naturaleza, como lo son los flujos geofísicos. Los resultados principales de esta tesis fueron publicados en dos artículos científicos, el primero en el Journal of Fluid Mechanics (2010, 648: 381 - 404), y el segundo sometido a revisión en la misma revista.
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11

Rojas, Parra Eduardo Andrés. "Medios granulares densos: modelamiento continuo estacionario y aproximación a reología transiente." Tesis, Universidad de Chile, 2015. http://repositorio.uchile.cl/handle/2250/136487.

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Doctor en Ciencias de la Ingeniería, Mención Fluidodinámica<br>El estudio de la reología de medios granulares densos tuvo un fuerte impulso a raíz de la aparición del modelo reológico propuesto en GDR MiDi, 2004, el cual estableció una relación local entre el esfuerzo de corte normalizado por la presión y el número de inercia. Esta relación se cumple satisfactoriamente para distintos escurrimientos, cuando se presentan bajos gradientes de la velocidad de deformación. Por otro lado, este modelo resulta insatisfactorio para problemas con altos gradientes de la velocidad de deformación. Para estos últimos casos se han propuestos diversos modelos denominados no locales. El objetivo de la presente tesis es evaluar el desempeño de modelos reológicos, tanto locales como no locales, para sistemas distintos a los que dieron su origen, utilizando la modelación continua y discreta del medio granular, de la forma en que se explica a continuación: Problemas resueltos mediante modelación continua: El modelo local ya mencionado fue evaluado para dos sistemas estacionarios, estos son: (1) escurrimiento en celda Couette modificada y (2) flujo gravitacional en celda tipo block caving. La metodología en estos casos consistió en resolver numéricamente un modelo continuo, compuesto fundamentalmente por la ecuación de conservación de momentum del medio granular y la reología local incorporada a esta ecuación. Finalmente, se compararon los resultados de los modelos con datos obtenidos a partir de simulaciones discretas y experimentos. Problema resuelto mediante modelo discreto: En este caso el problema a resolver fue un sistema en estado transiente, compuesto por un medio granular bajo cizalle simple. De forma instantánea el medio granular es sometido a un cambio en el sentido de cizalle, generándose un periodo de relajación del sistema hasta volver al estado original. Para la simulación de este caso se utilizó un modelo de dinámica molecular, en el cual fueron creadas distintas configuraciones variando la altura del sistema y la densidad global del medio granular. Referente a los resultados obtenidos para el modelo de la celda Couette modificada, se logró predecir el campo de velocidades de rotación en los casos clasificados dentro del régimen demominado abierto, por el contrario, se encontraron importantes discrepancias en los regímenes de transición y cerrado. En cuanto al modelo para el problema de block caving, este arrojó una zona de extracción aislada de tamaño similar a la encontrada experimentalmente, además este modelo logró predecir el ángulo de falla a la salida del sistema. Con respecto al problema abordado con enfoque discreto, el principal resultado encontrado es que el medio granular relaja en dos fases asociadas a dos tipos de reologías. En una primera fase, el esfuerzo de corte normalizado en el centro del sistema se mueve siguiendo una nueva relación no local. En esta relación aparece el laplaciano del esfuerzo de corte normalizado, como una nueva variable. En una segunda fase, el esfuerzo de corte normalizado satisface la relación local dependiente del número de inercia antes señalada.
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12

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<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 95-98).<br>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.<br>by Maytee Chantharayukhonthorn.<br>S.M.<br>S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering
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Neugebauer, Christoph Verfasser], Achim [Gutachter] [Kienle, and Stefan [Gutachter] Palis. "Modeling, dynamics and control of continuous fluidized bed layering granulation processes / Christoph Neugebauer ; Gutachter: Achim Kienle, Stefan Palis." Magdeburg : Universitätsbibliothek Otto-von-Guericke-Universität, 2020. http://d-nb.info/1220035297/34.

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Neugebauer, Christoph [Verfasser], Achim [Gutachter] Kienle, and Stefan [Gutachter] Palis. "Modeling, dynamics and control of continuous fluidized bed layering granulation processes / Christoph Neugebauer ; Gutachter: Achim Kienle, Stefan Palis." Magdeburg : Universitätsbibliothek Otto-von-Guericke-Universität, 2020. http://d-nb.info/1220035297/34.

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15

Cawthorn, Christopher John. "Several applications of a model for dense granular flows." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/245044.

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This dissertation describes efforts to evaluate a recently proposed continuum model for the dense flow of dry granular materials (Jop, Forterre & Pouliquen, 2006, Nature, 441, 167-192). The model, based upon a generalisation of Coulomb sliding friction, is known to perform well when modelling certain simple free surface flows. We extend the application of this model to a wide range of flow configurations, beginning with six simple flows studied in detailed experiments (GDR MiDi, 2004, Eur. Phys. J. E, 14, 341-366). Two-dimensional shearing flows and problems of linear stability are also addressed. These examples are used to underpin a thorough discussion of the strengths and weaknesses of the model. In order to calculate the behaviour of granular material in more complicated configurations, it is necessary to undertake a numerical solution. We discuss several computational techniques appropriate to the model, with careful attention paid to the evolution of any shear-free regions that may arise. In addition, we develop a numerical scheme, based upon a marker-and-cell method, that is capable of modelling two-dimensional granular flow with a moving free surface. A detailed discussion of our unsuccessful attempt to construct a scheme based upon Lagrangian finite elements is presented in an appendix. We apply the marker-and-cell code to the key problem of granular slumping (Balmforth & Kerswell, 2005, J. Fluid Mech., 538, 399-428), which has hitherto resisted explanation by modelling approaches based on various reduced (shallow water) models. With our numerical scheme, we are able to lift the assumptions required for other models, and make predictions in good qualitative agreement with the experimental data. An additional chapter describes the largely unrelated problem of contact between two objects separated by a viscous fluid. Although classical lubrication theory suggests that two locally smooth objects converging under gravity will make contact only after infinite time, we discuss several physical effects that may promote contact in finite time. Detailed calculations are presented to illustrate how the presence of a sharp asperity can modify the approach to contact.
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Jemaat, Zulkifly Bin. "Treatment of complex industrial wastewaters containing ammonium and phenolic compounds using granular sludge in continuous airlift reactors." Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/117276.

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Esta tesis doctoral versa sobre la eliminación simultánea de compuestos fenólicos con reactores de biomasa granular trabajando en continuo. El estudio está dividido en dos partes principales; el primer tema trata sobre la modelización de la nitritación, mientras que el otro está dedicado al trabajo experimental sobre la nitritación y eliminación simultánea de compuestos fenólicos. En el estudio de modelización, se desarrolló un modelo matemático de biopelícula para describir la nitritación en reactores de biomasa granular aerobia operando en continuo. El modelo incorpora una estrategia de control del ratio [DO]/[TAN], para mantener un valor deseado de la relación entre las concentraciones de oxígeno disuelto (DO) en el efluente del reactor y nitrógeno amoniacal total [TAN]. El modelo se validó con un gran número de datos experimentales previamente publicados en la bibliografía, así como con datos obtenidos de reactores granulares tratando agua de rechazo a escala laboratorio y piloto. El modelo se utilizó para estudiar el efecto de: a) las consignas de DO y TAN, b) la temperatura de operación, c) las características de la biopelícula (tamaño de partícula, densidad) y d) la concentración de amonio en el afluente, sobre la consecución de la nitritación completa. Los resultados indicaron que la nitritación completa se mantuvo estable y se potenció usando la estrategia de control de la proporción [DO]/[TAN] en la operación del reactor de biomasa granular aerobia. Además, el modelo predijo que gránulos aerobios mayores a 1.5 mm y concentraciones altas de amonio en el afluente potenciaba la obtención de nitritación completa estable, mientras que la densidad de biopelículas tenía poca influencia en este estudio. Además se demostró que era posible la nitritación total a bajas temperaturas con reactores de biomasa granular. Para el trabajo experimental, se utilizó un reactor tipo airlift. Para la puesta en marcha del reactor, se utilizó como inóculo biomasa de un reactor de biomasa granular aerobia que realizaba eliminación de nutrientes. Como alimento del reactor se utilizó un agua residual sintética con un alto contenido de amonio (950 ± 25 mg N L-1). El reactor se operó hasta la obtención de nitritación parcial. Una vez obtenida la nitritación parcial, el reactor se bioaumentó con un lodo activo que contenía biomasa degradadora de p-nitrofenol (PNP) para mejorar el crecimiento de microorganismos degradadores de fenol sobre los gránulos nitrificantes. Acto seguido, mientras el reactor trataba una carga elevada de amonio, se añadieron progresivamente al afluente o-cresol (hasta 100 mg L-1) o PNP (hasta 15 mg L-1), siendo éstos alimentados al reactor con el objetivo de estudiar la nitritación parcial simultánea a la eliminación de o-cresol o de PNP. En el estudio de la nitritación parcial simultánea a la eliminación de o-cresol, se mantuvo el proceso de nitritación parcial estable durante más de 100 días de operación. Además, se obtuvo una biodegradación completa de o-cresol durante todo el periodo experimental. También se realizaron choques de carga de o-cresol, durante los cuales el proceso de nitritación parcial se mantuvo estable y sin verse afectado por esos eventos. Las cargas volumétricas obtenidas de nitrógeno (NLRV) y de o-cresol (CLRV) fueron de 1.1 g N L-1 d-1 y 0.11 g o-cresol L-1 d-1, respectivamente. El análisis de hibridación in situ de fluorescencia (FISH) indicó que en los gránulos había presencia del género Acinetobacter, de bacterias amonio-oxidantes betaproteobacteriales y de Nitrobacter sp. Posteriormente, se continuó con la operación del reactor, y se llevó a cabo un experimento relacionado con el funcionamiento del reactor bajo tres escenarios de alternancia secuencial de contaminantes (SAP). En cada uno de los escenarios SAP se añadieron 15 mg L-1 de compuestos fenólicos secundarios (i.e. PNP, fenol y 2-clorofenol (2CP)) al afluente por un periodo de tiempo corto (entre 20 y 25 años). Los resultados ilustraron que se mantuvo la nitritación parcial y la biodegradación de o-cresol sin mostrar ningún signo de inhibición por la presencia de PNP o de fenol. Sin embargo, en presencia de 2CP en el afluente, se registró durante tres días un 90% de la nitritación parcial y un 25% de la degradación de o-cresol. Estos resultados sugieren que las bacterias amonio oxidantes (AOB) son mas sensibles a la inhibición por 2CP que las heterótrofas (degradadoras de o-cresol). En el estudio de la nitritación simultánea a la eliminación de PNP, se mantuvo la nitritación durante la mayor parte del periodo operacional, obteniéndose un efluente adecuado para la desnitrificación heterotrófica. Sin embargo, durante los primeros 175 días, la biodegradación de PNP fue inestable, observándose diversos episodios de acumulación de PNP. Esta acumulación se determinó que era debida a las condiciones limitantes de DO. El incremento de la concentración de DO en el reactor de 2 a 4 mg O2 L-1 permitió obtener eliminación completa y estable de PNP hasta el fin del periodo experimental. Las NLRV y la carga de PNP obtenidas fueron de 1.0 g N L-1 d-1 y 16 mg PNP L-1 d-1, respectivamente. Además, se evaluó el funcionamiento del reactor realizando dos estudios de hambruna, i) hambruna de PNP y ii) hambruna total (parada del reactor). Los resultados mostraron que 2 días después al fin del periodo de hambruna se obtuvo una recuperación total de la degradación de PNP, mientas que la recuperación total de la nitritación simultánea a la eliminación de PNP se consiguió solo 11 después de volver a poner en marcha el reactor. En conclusión, el uso de reactores de biomasa granular aerobia para realizar nitritación simultánea a la eliminación de compuestos fenólicos es factible. Ésta podría ser considerada la mejor técnica disponible para el tratamiento aguas residuales industriales complejas con contenido de amonio en alta carga y compuestos fenólicos. Se ha probado que la biomasa granular aerobia es resistente a sobrecargas puntuales, a presencia alterna de compuestos recalcitrantes y a periodos de hambruna; estas condiciones, debido a los cambios de planificación de la producción, pueden encontrarse frecuentemente en plantas de tratamiento de aguas residuales industriales. En un futuro próximo, proponemos que la nitritación simultánea a la eliminación de compuestos fenólicos podría combinarse tanto con la desnitrificación heterotrófica o con el proceso anammox para una eliminación sostenible del nitrógeno.<br>The simultaneous nitritation and phenolic compounds removal using aerobic granular reactors in continuous mode were studied in this Ph.D. thesis. The study is divided into two main subjects; the first one is devoted to the modeling of nitritation while the other part is dedicated to the experimental work of simultaneous nitritation and phenolic compounds removal using granular reactors. In the modeling study, a mathematical biofilm model was developed to describe nitritation in aerobic granular reactors operating in continuous mode. The model incorporated a [DO]/[TAN] ratio control strategy to maintain the proportion between the concentrations of dissolved oxygen (DO) and total ammonia nitrogen (TAN) in the reactor effluent to a desired value. The model was validated with a large set of experimental results previously reported in the literature, as well as, data gathered from laboratory scale and pilot plant granular reactors treating reject water. The model was used to study the effect of: a) DO and TAN setpoints, b) operating temperature, c) biofilm characteristics (granules size, density) and d) ammonium concentrations in the influent on the achievement of full nitritation. The results indicated that full nitritation was stably maintained and enhanced by applying the [DO]/[TAN] ratio control strategy in the operation of aerobic granular sludge reactor. Moreover, the model predicted that aerobic granules size larger than 1.5 mm and high ammonium concentrations in the influent enhanced the achievement of stable full nitritation, while poor influence of the biofilm density was found with the simulation study. Furthermore, at low temperature, full nitritation with granular reactors was demonstrated to be possible. In the experimental work, an airlift reactor was employed. In the reactor start-up, granular sludge from a reactor performing biological nutrient removal was used as inoculum. A synthetic wastewater containing high-strength ammonium concentrations (950 ± 25 mg N L- 1) was fed into the airlift reactor. The reactor was operated until partial nitritation was obtained. Once partial nitritation was achieved, the airlift reactor was bioaugmented with pnitrophenol (PNP)-degrading activated sludge to enhance the growth of phenolic-degraders over the nitrifying granules. Immediately, o-cresol (up to 100 mg L-1) or PNP (up to 15 mg L- 1) were progressively added to the high-strength ammonium influent and fed into the reactor with the objective of studying the simultaneous partial nitritation and o-cresol removal and the simultaneous nitritation and (PNP) removal. First, in the study of simultaneous partial nitritation and o-cresol removal, a stably partial nitritation process was maintained for more than 100 days of operation. Moreover, full biodegradation of o-cresol was achieved during the whole experimental period. Also, o-cresol shock load events were applied and the partial nitritation process was kept stable and unaffected during these events. The achievable nitrogen loading rate (NLRv) and o-cresol loading rate (CLRv) were ca. 1.1 g N L-1d-1 and 0.11 g o-cresol L-1d-1, respectively. Analysis of fluorescent in-situ hybridization (FISH) indicated that Acinetobacter genus, betaproteobacterial ammonia-oxidizing bacteria and Nitrobacter sp. were present into the granules. Later, the operation of the reactor was continued, and an experiment devoted to the performance of the reactor under three sequentially alternating pollutant (SAP) scenarios was executed. In each one of the SAP scenarios, 15 mg L-1 of the secondary phenolic compounds (i.e. p-nitrophenol (PNP), phenol and 2-chlorophenol (2CP)) were added in the regular influent for a short period of time (between 20 to 25 days). The results illustrated that partial nitritation and o-cresol biodegradation were maintained without exhibiting any sign of inhibition by the presence of PNP or phenol. However, when 2CP was present in the influent, 90 % of the partial nitritation and 25 % of the o-cresol degradation was inhibited within three days. This finding suggests that the ammonia oxidizing bacteria (AOB) is more sensitive to 2CP inhibition than heterotrophs (o-cresol-degraders). Second, in the study of simultaneous nitritation and PNP removal, nitritation was maintained during most of the operation period producing an effluent suitable for heterotrophic denitrification. However, in the first 175 days, PNP biodegradation was unstable and several accumulation episodes occurred. The oxygen limiting condition was found to be the main explanation of these events. The increase of dissolved oxygen concentration (DO) in the reactor from 2 to 4 mg O2 L-1 permitted to achieve complete and stable PNP removal till the end of the experimental period. The achieved NLRv and PNP loading rate (PNP-LRv) were ca. 1.0 g N L-1d-1 and 16 mg PNP L-1d-1, respectively. Besides, the performance of the reactor was further assessed by performing two starvation studies, i) PNP starvation and ii) total starvation period (reactor shutdown). Results show that full recovery of PNP degradation was achieved within 2 days after the PNP starvation period ended, while full recovery of simultaneous nitritation and PNP removal was accomplished in just 11 days after the restart of the reactor. In conclusion, the use of continuous aerobic granular reactors for the simultaneous nitritation and phenolic compounds removal is feasible. This could be regarded as a best available technique for the treatment of complex industrial wastewaters containing high-strength ammonium concentrations and phenolic compounds. Aerobic granules are proven to be resistant and resilient to the shock loads, to the alternating presence of recalcitrant compounds and to starvation periods; conditions frequently found in industrial wastewater treatment plants due to changes on the industrial production schedules. In the near future, we propose the simultaneous nitritation and phenolic compounds removal should be combined with either heterotrophic denitrification or Anammox for sustainable nitrogen removal.
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17

Rja, Fi Allah Saïd. "Modélisation du comportement mécanique d'un matériau agrégataire." Tours, 2006. http://www.theses.fr/2006TOUR4030.

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L’étude porte sur le comportement thermomécanique d'un matériau agrégataire quasicompact. Ce matériau est constitué d’une agglomération de grains dont la taille peut atteindre le millimètre. Les réponses expérimentales mettent en évidence le caractère viscoplastique, endommageable et sensible à la pression hydrostatique du comportement. Les modèles existants, pour de tels matériaux, ont été généralement développés pour des régimes de sollicitation dynamique et sont mal appropriés à décrire le comportement en quasi-statique. Par conséquent un modèle ainsi que le protocole expérimental spécifique associé sont présentés. Le modèle est construit à partir des réponses issues des essais de traction, de compression uni-axiale et de compression tri-axiale sous confinement hydrostatique. Le modèle est isotrope et n'inclut qu'un nombre limité de paramètres. La limite de plasticité est décrite au moyen d'un critère parabolique à écrouissage isotrope. La règle d’écoulement est non-associée; un endommagement isotrope complète le modèle. La validation du modèle est réalisée au moyen d’essais sur structures par comparaisons expérience/simulation<br>The study relates to the thermomechanical behaviour of a quasi-compact aggregate. This material consists in agglomeration of grains whose size can reach the millimetre. The model is isotropic and includes only a limited number of parameters. The experimental response showsthe following characteristics: viscoplastic, damageable and sensitive to the hydrostatic pressure. For such materials, existing models were generally developed within the framework of the dynamic behaviour. They are not appropriate to a static study. Consequently a specific model and an experimental protocol are presented. The model is derived from the tensile tests, the compressive tests and the triaxial compression tests under hydrostatic containment. The plastic limit is described by the means of a parabolic criterion with isotropic hardening. The flow rule isnon-associated; an isotropic damage achieves the model. The validation of the model is illustrated by tests on structures
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18

Holman, James William. "Assessing the use of twin screw wet granulation in a multi stage manufacturing process for the continuous production of pharmaceutical products." Thesis, University of Surrey, 2013. http://epubs.surrey.ac.uk/807047/.

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Traditionally pharmaceutical manufacture is conducted on a batch basis but significant resources are being invested into the use of intensified continuous processes. This dissertation evaluates the use of a combined twin screw and segmented fluid bed drying process to produce granules on a continuous basis. The experimental program was conducted using structured Design of Experiments in three stages. • Wet granulation only: Investigated the initial relationships between liquid/solid ratio and power required for wet granulation, as well as granule structure using SEM Imaging. • Wet granulation and fluid bed drying: Concluded that the biggest control over, the measured mean granule size (d50) produced from the combined system was still the ratio of water to dry powder in the wet granulation. • Wet granulation through to compression: The effects of changes in the granulation process were not statically relevant on the final tablet for the process set up. The study also used PEPT data to assess motion within the TSG. The studies showed: • The time spent in the kneading zone directly after the liquid addition in relation to the overall time spent in the granulation process appears independent of the process j . set up at 32% ± 2%. • As the barrel speed of the granulator increases the relative time spent in the final ' breakage zone' of the TSG increases, therefore increasing breakage. Using the findings from the literature, the results of the experimental program were used to define the mechanisms occurring within the TSG. The experimental findings were input into a model to predict the outcome of collisions between particles. The model predicts agglomeration of the smaller particles to the larger ones and by calculating changes in the viscosity of the binder the subsequent secondary agglomeration of these granules can also be shown using this model The model is limited due to assumptions in deriving it. The model excludes capillary forces that if given sufficient time to form could have the same order of magnitude strength as other forces.
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19

Schmidt, Adrian [Verfasser], Peter [Gutachter] Kleinebudde, and Jörg [Gutachter] Breitkreutz. "Enabling end-to-end continuous manufacturing by API suspension feed and instantaneous drying in twin-screw wet granulation / Adrian Schmidt ; Gutachter: Peter Kleinebudde, Jörg Breitkreutz." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2018. http://d-nb.info/1159766959/34.

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20

Zemerli, Clément [Verfasser], and Arnulf [Akademischer Betreuer] Latz. "Continuum Mechanical Modeling of Dry Granular Systems: From Dilute Flow to Solid-Like Behavior / Clément Zemerli. Betreuer: Arnulf Latz." Kaiserslautern : Technische Universität Kaiserslautern, 2013. http://d-nb.info/1047096889/34.

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21

Meier, Robin [Verfasser], Peter [Akademischer Betreuer] Kleinebudde, and Jörg [Gutachter] Breitkreutz. "Process characterization and development of simplified, high drug loaded formulations for the continuous manufacturing of tablets, based on twin-screw granulation / Robin Meier ; Gutachter: Jörg Breitkreutz ; Betreuer: Peter Kleinebudde." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2016. http://d-nb.info/111868771X/34.

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22

Caserta, Alice Jordam. "Desenvolvimento de relações não-lineares para mecanismos de contato por meio de estudo analítico e numérico." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18149/tde-17112015-134233/.

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Fenômenos multifásicos são frequentemente observados na natureza, tais como nas gotas de chuva ou neve no ar, nos vulcões e tempestades de areia, e em diversas outras situações. Na solução desses problemas que envolvem escoamentos gás-sólidos e granulares são frequentemente utilizadas duas abordagens: a contínua (formulação Euleriana-Euleriana) e a discreta (formulação Euleriana-Lagrangiana). Na abordagem discreta pode-se utilizar dois modelos para descrever o contato entre as partículas: o modelo de esfera rígida e o modelo de esfera suave. Neste trabalho é realizado um estudo detalhado dos modelos de contato, com foco na modelagem de esfera suave, que é baseada em um sistema dinâmico mola-massa-amortecedor. Por meio desse estudo, com a finalidade de aprimorar o modelo de contato não-linear, são propostas duas relações para o mecanismo de contato de partículas. Essas relações são fundamentadas em um modelo dinâmico, com não-linearidades nas partes conservativas e dissipativas, não apresentando descontinuidades entre as acelerações do início e do fim do contato. A metodologia de desenvolvimento da presente pesquisa está dividida em três partes: pesquisa bibliográfica dos modelos de contato; estudo analítico e numérico desses modelos e testes de problemas com a realização de experimentos numéricos, utilizando o código computacional MFIX (Multiphase Flow with Interphase eXchange). As novas aproximações propostas neste trabalho são analisadas e aplicadas em três diferentes problemas: de dinâmica, escoamento gás-sólido e escoamento granular. Os resultados obtidos utilizando as relações são comparados com dados disponíveis na literatura, mostrando-se adequados para os casos investigados neste trabalho.<br>Multiphase flow are frequently observed in nature, such as rain drops in air or snowfalls, volcanoes and sandstorms, and several other situations. For solving these problems which involve gas-solid and granular flows are often used two models: the continuous model (Eulerian-Eulerian formulation) and the discrete model (Eulerian-Lagrangian formulation). There are two main contact models used in DEM, the hard-sphere model and the soft-sphere model. In this work is carried out a detailed study of contact models, focusing on soft-sphere model, based on a dynamic system modeled as nonlinear mass-spring-damper. In order to improve the nonlinear contact model, in this study it is proposed two new approximate relations for determining the damping coefficient and duration of contact for a specific nonlinear soft-sphere contact model where the contact force is continuous at the start and end of the contact. The methodology of the development of this work is divided into three parts: literature research of the contact models; analytical and numerical study of these models and test problems with numerical experiments, using the open source code MFIX (Multiphase Flow with Interphase eXchange). The proposed relations are analyzed and applied in three different problems: dynamic problem, gas-solid flow and granular flow. All results are compared with literature data showing good agreement for these cases studied in the present work.
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23

Mohd, Damanhuri Nor Alisa. "The numerical approximation to solutions for the double-slip and double-spin model for the deformation and flow of granular materials." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/the-numerical-approximation-to-solutions-for-the-doubleslip-and-doublespin-model-for-the-deformation-and-flow-of-granular-materials(9986ac45-e48c-4061-a299-a80b2e665c3e).html.

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The aim of this thesis is to develop a numerical method to find approximations to solutions of the double-slip and double-spin model for the deformation and flow of granular materials. The model incorporates the physical and kinematic concepts of yield, shearing motion on slip lines, dilatation and average grain rotation. The equations governing the model comprise a set of five first order partial differential equations for the five dependent variables comprising two stress variables, two velocity components and the density. For steady state flows, the model is hyperbolic and the characteristic directions and relations along the characteristics are presented. The numerical approximation for the rate of working of the stresses are also presented. The model is then applied to a number of granular flow problems using the numerical method.
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24

De, Abreu Corrêa Lúcio. "Large scale numerical wave propagation in a randomly-fluctuating continuum model of ballasted railway tracks." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC018/document.

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Une forte concurrence avec d'autres moyens de transport a poussé l’industrie ferroviaire à se réinventer et rechercher des performances toujours plus élevées. De nos jours, l’obtention de vitesses chaque fois plus élevées exige le développement de modèles numériques précis pour concevoir et prédire le comportement des voies ferrées sous les contraintes mécaniques imposées par le passage du convoi. Dans cette thèse, nous avons concentré l'étude sur la couche de ballast. Ce composant présente un comportement mécanique complexe, lié à la nature granulaire de ses composants, il peut être solide, liquide ou gazeux.Ce comportement dépend de l'état de contrainte et de l'historique de déformation du milieu.Deux classes de modèles numériques sont couramment utilisées pour prédire le comportement de ces systèmes : (1) les approches discrètes et (2) les approches continues. Pour ces premières, chaque grain du ballast est représenté par un corps rigide et interagit avec ses voisins parle biais de forces de contact non linéaires en utilisant, par exemple, la méthode de dynamique non régulière des contacts. En raison des limites de calcul, ce type de méthode ne peut résoudre que quelques mètres de longueur de ballast. Le couplage avec le sol sous la couche de ballast et avec les traverses reste également un problème non résolu dans la littérature. Pour les approches continues, le ballast est remplacé par un milieu continu homogénéisé, de façon à permettre l’utilisation de la méthode par éléments finis classique (EF). Cependant, ces modèles sont normalement utilisés avec des paramètres mécaniques homogènes, de sorte qu'ils ne représentent pas complètement l'hétérogénéité des déformations et des contraintes dans la couche de ballast.Nous étudions dans cette thèse une approche alternative, utilisant un modèle de continuum hétérogène stochastique, qui peut être résolu avec une méthode par éléments finis tout en conservant dans une large mesure l'hétérogénéité des champs de contrainte et de déformation.L'objectif de ce modèle continu est de représenter statistiquement l'hétérogénéité du champ de contraintes dans un modèle de milieu continu ainsi que dans un modèle granulaire discret. Pour ce faire, les propriétés mécaniques sont représentées à l'aide de champs aléatoires. La présente thèse est divisée en trois parties: (1) la construction du modèle et l'identification des paramètres du matériau continuum (densité marginale de premier ordre, moyenne, variance, modèle de corrélation) ;(2) la propagation des ondes dans une voie ferrée ballastée et (3) l’exploration préliminaire de deux ensembles de données expérimentales. La première partie définit le modèle du continuum à fluctuations aléatoires et identifie les paramètres de notre modèle de continuum sur de petits échantillons cylindriques de ballast discret. Des modèles continus équivalents aux échantillons discrets sont générés et résolus en utilisant la méthode EF, et le champ stochastique utilisé pour fournir les propriétés mécaniques. Un processus d'optimisation est utilisé pour trouver une variance normalisée pour le matériau hétérogène stochastique. La deuxième partie de ce travail se concentre sur la résolution des équations dynamiques sur un modèle à grande échelle d'une voie ferrée ballastée utilisant la méthode des éléments spectraux. L'influence de l'hétérogénéité est mise en évidence et étudiée. En conséquence,des courbes de dispersion sont obtenues. Enfin, la troisième partie présente deux jeux de données distincts de mesures expérimentales sur le matériau de ballast : (1) une boîte de ballast ; (2) un passage de train dans un segment de voie ferrée ballastée.Les courbes de mobilité ont été extraites de l'expérience sur les ballasts. Un problème inverse a été résolu afin d'estimer la vitesse de l'onde homogénéisée et la vitesse de l'onde locale dans le milieu. Les passages de trains enregistrés pour l'analyse de la vibration à moyenne fréquences<br>The stronger competition with other means of transportation has increased the demand for performance in the railway industry. One way to achieve higher performance is using accurate numerical models to design/predict railways tracks behaviour. Two classes of numerical models are commonly used to predict the behaviour of these systems: (i) discrete approaches and (ii) continuum approaches. In the former, each grain of the ballast is represented by a rigid body and interacts with its neighbours through nonlinear contact forces using, for example, the nonsmooth contact dynamics method. Due to computational limits, this kind of method can only solve a few meters-length of ballast. The coupling with the soil under the ballast layer and with the sleepers also remains an open problem. In continuum approaches, the ballast is replaced by a homogenized continuum and the classical Finite Element (FE) Method (or similar) is used. However, they are normally used with homogeneous mechanical parameters, so that they do not represent fully the heterogeneity of the strains and stresses within the ballast layer. We investigate in this thesis an alternative approach using a stochastic heterogeneous continuum model, that can be solved with a FElike method while retaining to a large degree the heterogeneity of the stress and strain fields. The objective of this continuous model is to represent statistically the heterogeneity of the stress field in a continuum model as well as in a discrete granular model. To do this, the mechanical properties are represented using random fields. The present thesis is divided into three parts: (1) the construction of the model and the identification of the parameters of the continuum material (first-order marginal density, mean, variance, correlation model, and correlation length); (2) wave propagation in a ballasted railway track. (3) preliminary exploration of two experimental datasets. The first part sets the randomly-fluctuating continuum model and identifies the parameters of our continuum model on small cylindrical samples of discrete ballast. Continuum models equivalent to the discrete samples are generated and solved using the FE method, and the stochastic field used as mechanical properties. An optimization process is used to find a normalized variance for the stochastic heterogeneous material. The second part of this work concentrates on the solution of the dynamical equations on a large-scale model of a ballasted railway track using the Spectral Element Method. The influence of the heterogeneity is highlighted and studied. As a result, dispersion curves are obtained. Finally, the third part presents two distinct datasets of experimental measurements on ballast material: (1) a ballast box; (2) a train passage in a segment of ballasted railway track. Mobility curves were extracted from the ballast box experiment. An inverse problem was solved in order to estimate the homogenized wave velocity and local wave velocity in the medium. The trains pass-by recorded for the analysis of the vibration at medium frequencies
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Kanso, Haydar. "Influence des phases magnétiques désordonnées sur les propriétés d'anisotropie d'échange des nanoplots F/AF : Etude par simulations Monte Carlo et comparaison à l'expérience." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR071/document.

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Notre objectif est d’améliorer la compréhension du phénomène d’anisotropie d’échange dans les nanoplots en comparaison aux films continus et d’étudier les effets du désordre magnétique à l’interface dans la couche AF sur les propriétés d’anisotropie d’échange. Dans un premier temps, nous avons utilisé un modèle granulaire qui prend en compte les phases magnétiques désordonnées à l’interface F/AF et nous modélisé ces phases par la présence de grains moins stables à l’interface dans la couche AF. De plus, dans le cas des nanoplots, nous avons pris en compte des grains moins stables localisés sur les bords de la couche AF pour reproduire les effets dus à la méthode de fabrication. Nous avons trouvé qu’il existe deux mécanismes de retournement de la couche F en dépendant de la valeur du couplage ferromagnétique. Si le couplage ferromagnétique faible, le retournement de la couche F s’amorce sur plusieurs centres de nucléation et s’effectue sans propagation. Alors que si le couplage ferromagnétique fort, le retournement de la couche F s’amorce en un seul centre de nucléation situé à un coin du nanoplot puis se propage à partir de ce coin. Ensuite notre modèle a permis d’expliquer les principales caractéristiques des comportements observés expérimentalement dans les bicouches Co/IrMn et NiFe/IrMn (pour différentes tailles latérales), à différentes températures de mesure et pour différentes épaisseurs de la couche AF. Plus précisément, les valeurs du champ d’échange simulé dans les films continus, à température ambiante, sont plus grandes que dans les nanoplots pour les faibles épaisseurs de la couche IrMn alors que c’est le contraire lorsque cette épaisseur augmente. Dans un deuxième temps, Nous avons utilisé un modèle atomique qui prend en compte la frustration magnétique dans la couche AF et la présence de défauts structuraux tels que les joints de grains et l’interdiffusion. Nous avons trouvé que l’effet combiné de la frustration, des joints de grains et de la surface induit des configurations magnétiques non colinéaires complexes (présence de domaines magnétiques) dans la couche AF à l’interface. Nos résultats montrent que la non-colinéarité des moments AF à l’interface diminue le couplage effectif à l’interface F/AF et diminue la constante d’anisotropie effective de la couche AF. Nos résultats montrent également que la présence de joints de grains lorsqu’il y a de la frustration renforce la stabilité de la couche AF à 0K alors qu’elle la diminue à température non nulle. Enfin, nous avons trouvé que l’interdiffusion diminue fortement le champ d’échange et rend la couche AF plus stable, ce qui correspond à une diminution du couplage effectif à l’interface. Il est important de noter que les valeurs du champ d’échange simulé sont dans ce cas réalistes, ce qui met en évidence que l’interdiffusion est probablement un des facteurs essentiels pour lesquels les champs d’échange mesurés expérimentalement sont nettement plus faibles que ceux prévus par les modèles simples<br>Our goal is to improve the comprehension of the exchange bias (EB) in nanodots in comparison with the continuous films and to study the effects of the interfacial magnetic disorder on the EB properties. Firstly, we use a granular model which considers disordered interfacial phases by considering less stable magnetic grains at the interface in the antiferromagnetic (AF) layer. We further model the effect of the nanofabrication process by considering less stable magnetic grains at the edges, due to grain cutting. Our results evidence two different mechanisms of the ferromagnetic (F) layer reversal depending on the magnitude of the coupling between F grains. In the weak coupling regime relative to the anisotropy, the exchange field is independent of the coupling. By contrast, in the strong coupling regime, the exchange field depends on the coupling. Our model also well explain some experimental features observed in NiFe/IrMn and Co/IrMn nanodots (for various lateral sizes) and continuous films, at various measurement temperatures and various AF thicknesses. More precisely, the simulated values of the exchange field in the continuous films, at room temperature, are larger than in the nanodots for small values of the AF thicknesses. However, it is the opposite when this thickness increases. Secondly, we use an atomic model which considers the magnetic frustration inside the AF layer and the presence of structural defects such as grain boundaries and interdiffusion. We found that the combination effect of grain boundaries, frustration and surface can result in complex magnetic configurations in the AF layer at the interface (magnetic domains). Our results show that the non-collinearity of the AF moments at the interface decreases the effective coupling at the interface and decreases the effective anisotropy constant of the AF layer. Our findings indicate that combination effect of grain boundaries and frustration make the AF layer more stable at 0 Kelvin and less stable at non-zero temperature. Our results show that the interdiffusion decrease the simulated values of the exchange field and make the AF more stable which corresponds to a decrease of the effective coupling at the interface. It is important to note that the simulated values of the exchange field are realistic values, which highlights that the interdiffusion is probably one of the essential factors which can give simulated values close to the experimental values
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26

Chiriatti, Léon. "Etude de l'adhérence armature-béton, influence des granulats de béton recyclé et apport des mesures acoustiques." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAD040/document.

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L'introduction de granulats de béton recyclé (i.e. granulats produits à partir des gravats issus de la démolition d'ouvrages en béton obsolètes) dans les formulations de béton impacte de manière significative le comportement structurel des éléments en béton armé. Ce travail est consacré à l'étude de l'influence des granulats de béton recyclé sur l'adhérence armature-béton. Dans un premier temps, un modèle analytique de l'adhérence armature-béton est développé. L'originalité du modèle proposé réside dans le nombre limité de paramètres physiques sur lesquels il est fondé. Ces paramètres physiques sont ensuite déterminés expérimentalement via la réalisation d'une campagne d'essais d'arrachement. Trois types de bétons, dont deux bétons de granulats de béton recyclé, sont étudiés. Le suivi de l'arrachement de l'armature est complété par des mesures acoustiques permettant d'obtenir des informations provenant du coeur de l'échantillon, où l'armature se trouve<br>The use of recycled concrete aggregate (i.e. aggregate produced from concrete demolition rubble) has a significant impact on the mechanical behavior of reinforced concrete members. This work focuses on the influence of recycled concrete aggregate on rebar-concrete bond. First, an analytical madel of the rebar-concrete bond is developed. The original feature of this modellies in the limited number of non-free physically-based parameters on which it is based. These parameters are then experimentally determined through a pull out test campaign. Three types of concrete, including two recycled aggregate concretes, are studied. Pull-out test monitoring is completed by acoustic measurements in order to obtain data from inside the concrete bulk, where the reinforcing bar is located
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27

Hussain, Hallshow. "Etude de la composition, du comportement mécanique et de l'endommagement d'un béton recyclé." Caen, 2002. http://www.theses.fr/2002CAEN2006.

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Gérer le devenir des déchets du bâtiment est un défi récent auquel sont confrontés les ingénieurs car seuls les déchets ultimes seront mis en décharge. Valoriser les bétons de démolition sans traitement préalable, et sans risques majeurs de pollution, pour en faire de nouveaux, est pour partie l'objectif de cette thèse. Les éléments essentiels liés aux caractéristiques des bétons et bétons recyclés sont récapitulés. Au-delà de la réutilisation -élaboration, composition, fabrication- l'étude du comportement de bétons recyclés sous sollicitation mécanique et de sa modélisation apparaît nécessaire en tant qu'élément de structure bâtie. En deuxième partie de la bibliographie, le comportement mécanique des bétons est étudiés. Différents modèles d'endommagement mécanique des bétons sont analysés ainsi que la fonction d'endommagement, le critère des contraintes, et le mode de dégradation des bétons. Le choix de la méthodologie expérimentale et des moyens mis en oeuvre font l'objet de la seconde partie. Puis la partie suivante s'intéresse aux dépouillements et à l'interprétation de nombreux essais. L'analyse a permis d'étudier le comportement de mortiers, l'affaissement et les performances d'un béton recyclé,. . . Une analyse plus fine est proposée sur les formules de Féret, de Bolomey, de Powers et britannique [etc]
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28

Loret, Benjamin. "Problèmes numériques et théoriques de la géomécanique." Paris 6, 1986. http://www.theses.fr/1986PA066239.

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Traitement numérique des milieux infinis de la géomécanique: méthodes d'équations intégrales régulières et singulières pour les structures géotechniques en conditions dynamiques; méthode de couplage itérative éléments finis/équations intégrales (applications au demi-espace et demi-plan); vibration d'un pieu fiché dans le demi espace stratifié. Comportement frottant des milieux granulaires: algorithmes locaux d'intégration numérique pour matériaux élastoplastiques type Drucker-Prager; partie élastique déformation des sols; influence de la contrainte moyenne. Problèmes liés à l'anisotropie en grandes transformations (rotations plastiques). Etude de deux types de bifurcation sur les sables; conséquences macroscopiques de la structure granulaire des sables; non-linéarité incrémentale et localisation des déformations.
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29

Peng, Cheng. "Apports de l’analyse microtomographique dans la modélisation des effets du séchage des matériaux à matrice cimentaire." Thesis, Lille 1, 2009. http://www.theses.fr/2009LIL10148/document.

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La dessiccation sur les matériaux cimentaires affecte les propriétés mécaniques et hydriques des matériaux : la résistance, le module d’Young, la fragilité, le teneur en eau, etc. L’objectif était ici de proposer un modèle qui a la capacité de décrire les principaux aspects des matériaux cimentaire sous compression et dessiccation.Puis une étude quadridimensionnelle du couplage entre dessiccation et fissuration est menée par microtomographie par rayons X. L’effet du retrait empêché par déformations différentielles entre les granulats et la matrice cimentaire est mis en évidence dans l’apparition de la fissuration, et dépend de leurs dimensions. En basant les phénomènes, nous avons proposé un modèle de l’endommagement hydrique en fonction de diamètre des granulats et le teneur en eau. Ensuite nous avons proposé un modèle de l’endommagement mécanique couplé à l’endommagement hydrique dans le cadre de la mécanique des milieux partiellement saturés.La comparaison des simulations numériques et les données expérimentales montre que le modèle reproduit les principaux aspects du comportement d’un mortier en fonction de la dessiccation<br>The desiccation on cement materials affects the mechanical properties and hydrous of the materials: the resistance, the module of Young, the fragility, and the moisture content, etc. The objective of the report is proposing a module which describes the main aspects of cement materials under the compression and desiccation.The four-dimensional study of the coupling between desiccation and fissuring is led by micro tomography by X-rays. The restrained shrinkage due to differential strains in aggregates and cementitious matrix is highlighted as the cause of apparition of microcracks, which relies on inclusion diameter. Base on the pheromones, it proposed a model of hydrous damage which relies on the aggregates’ diameter and the water content. Then it proposed a model of the mechanical damage coupled with the hydrous damage within the mechanics of the partially saturated milieu.At last, the comparison between the numeric simulations and the experimental data shows that the model reproduces the main aspects of the behavior of a mortar according to the desiccation
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30

Mesmacque, Alexandre. "Étude de l'endommagement des polymères en transport pneumatique." Lille 1, 2005. https://pepite-depot.univ-lille.fr/RESTREINT/Th_Num/2005/50376-2005-326.pdf.

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Cette étude a pour objectif d'identifier les paramètres responsables de l'endommagement des polymères en transport pneumatique et de comparer les mécanismes d'endommagement mis en jeu pour différents polymères. Le choix des dispositifs expérimentaux s'est porté sur les deux tests suivants: un test à échelle industrielle, id est une boucle de transport pneumatique, un test à échelle de laboratoire. Les essais sur la boucle de transport pneumatique ont été réalisés suivant deux procédures différentes. . . Les résultats illustrent l'influence des caractéristiques mécaniques des polymères sur les taux d'endommagement obtenus et l'influence des paramètres de transport pneumatique sur la génération de débris. Les essais sur la machine test d'endommagement ont été réalisés sur deux polymères: le polypropylène et le polystyrène. L'étude de l'effet des paramètres opératoires a montré l'influence du phénomène de fatigue sur l'endommagement des granulés mais également l'importance de la rugosité de la paroi impactée. Une analyse qualitative des débris obtenus pour ces deux tests nous permis d'identifier et de séparer les influences des vitesses normales et tangentielles d'impact sur les comportements mis en jeu lors de l'endommagement des granulés plastiques, ainsi que le rôle des caractéristiques mécaniques et morphologiques.
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31

Le, Viet Dung. "Modélisation et identification du comportement plastique visco-élastique endommageable d'un matériau agrégataire." Tours, 2007. http://www.theses.fr/2007TOUR4044.

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Cette étude porte sur le comportement thermomécanique d'un matériau agrégataire quasi-compact. Elle a pour objectif le développement d'un modèle de comportement répondant aux exigences requises pour une exploitation industrielle. Les réponses expérimentales mettnt en évidence un comportement comparable à celui des bétons, à savoir le caractère asymétrique (différence entre traction et compression) ainsi qu'une sensibilité à l'endommagement et à la pression hydrostatique. Une différence importante avec le comportement du béton concerne le comportement réversible qui est ici viscoélastique. Les modèles existants pour les matériaux du même type que celui étudié ne sont pas appropriés pour décrire complètement le comportement constaté. Par conséquent, un protocole expérimental spécifique a été développé à cette occasion. Il est présenté ainsi que le modèle qui en découle. Ce dernier est construit à partir des réponses issues des essais de traction, de compression uni-axiale et de compression tri-axiale sous confinement hydrostatique. Le modèle est isotrope et n'inclut qu'un nombre limité de paramètres. La limite de plasticité est décrite au moyen d'un critère parabolique à écrouissage isotrope. La règle d'écoulement est non-associée et un endommagement scalaire complète le modèle. Le modèle a été implanté dans le code de calcul Abaqus/standard sous la forme d'une procédure en Fortram. Une extension en température vient compléter la modélisation du comportement du matériau. La validation du modèle est effectuée sur la base de comparaisons avec plusieurs essais homogènes et sur structures<br>This research is achieved in the general frame work of the study of the thermomechanical behaviour of a quasi-compact aggregate. It has for objective the development of a new behaviour model satisfying to the particular requirements for an industrial exploitation. The model is isotropic and includes only a limited number of parameters. The experimental response shows a behaviour material comparable to concrete, to know the following characteristics : viscoelastic, damageable and sensitive to the hydrostatic pressure. For such materials, existing models were generally developped within the framework of the dynamic and static behaviour. They are not appropriate to simulate completely the material behaviour researched. Consequently, a specific model and an experimental protocol are presented. The model is derived from the tensile tests, the compressive tests and the triaxial compresssion tests under hydrostatic containment. The plastic limit is described by the means of a parabolic criterion with isotropic hardening. The flow rule is non-associated ; an isotropic damage achieves the model. Then, the developed model is implanted in the code of calculation standard abaqus by means of a numeric integration dealed with the shape of a procedure in Fortram. An extension in temperature comes to complete the modelling of the material behaviour. The dependance in temperature of the model parameters is taken into account in the Fortram subroutine. The validation of the model is done on the basis of several homogeneous tests as well as tests on structures by comparisons data/simulation
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32

Canel, Vincent. "Suivi acoustique de l'endommagement de matériaux granulaires cimentés : expériences et simulations." Thesis, Université Grenoble Alpes, 2021. http://www.theses.fr/2021GRALU001.

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L’endommagement et la cohésion des roches qui en résulte contrôlent le glissement et la nucléation des séismes. Ce phénomène n’étant pas bien compris, nous nous intéressons à l’interaction entre la friction au niveau de la faille et l’endommagement en volume environnant. Le principal objectif de cette thèse est d’analyser conjointement les données obtenues à l’échelle macroscopique lors d’expériences analogiques contrôlées en laboratoire et les résultats de modèles numériques donnant accès à des échelles inférieures.Les travaux réalisés lors de cette thèse s’articulent autour de trois expériences mécaniques menées sur deux types d’échantillon granulaire cimenté. Ces échantillons, initialement cohésifs, sont formés de billes de verres collées par un matériau ductile ou cassant. Les com- pressions oedométrique et uniaxiale sont complémentaires au test de cisaillement direct en boîte de Casagrande qui permet l’étude d’une interface frictionnelle dans un milieu endommagé. Les réponses des échantillons à ces différentes sollicitations mécaniques impliquent endommagement, glissement et friction et sont non seulement suivies mécaniquement mais aussi acoustiquement grâce à deux types de sondes ultrasonores. La première sonde, active, permet de surveiller les propriétés élastiques apparentes du milieu en étudiant la propagation d’ondes acoustiques et en particulier leur vitesse. L’évolution de cette dernière est en effet fortement corrélée à l’état du milieu. Sous chargement oedométrique, l’endommagement affecte la vitesse alors qu’en déchargement-rechargement une loi de milieu effectif purement granulaire et sec est retrouvée. La vitesse acoustique mesurée dans les échantillons cassants est aussi corrélée à des stick-slips qui ponctuent les contraintes macroscopiques. La seconde sonde, passive, consiste à enregistrer les émissions acoustiques produites dans le milieu et à analyser leurs lois statistiques proches de celles des séismes. Ainsi la valeur instantanée de b dans la loi de Gutenberg-Richter, le taux d’évènements à l’approche de la rupture, ou la correlation des évènements et la distribution des délais inter-évènements caractérisent différentes étapes du chargement du système.Pour mieux comprendre les aspects micro et mésoscopiques qui restent peu explorés expérimentalement, nous avons réalisé des simulations numériques quasi-statiques et dynamiques. Deux types de modélisations, par éléments finis et hybride (mêlant éléments finis pour les ponts de ciment et éléments discrets pour les billes), permettent de recourir à des lois élasto-plastiques avec endommagement pour les ponts plutôt qu’à des lois ad hoc générale- ment utilisées pour les décrire avec des éléments discrets seuls. Les géométries, mécanismes et protocoles expérimentaux ont guidé de près ces simulations qui mettent en évidence des phénomènes aux échelles des contacts inter-grains et des grains. Nous observons que la déformation plastique interne des ponts se localise en bandes de cisaillement et qu’elle est très hétérogène à l’échelle de l’échantillon. En réaction aux ruptures des ponts, des redistributions de contrainte et des réarrangements des contacts de Hertz guident l’évolution des chaînes de forces. Une chute de la vitesse des ondes acoustiques avec l’endommagement est observée à l’échelle macroscopique. Les évènements de rupture de ponts et de création ou de perte de contacts directs entre billes sont considérés équivalents à des sources d’émissions acoustiques, ce qui permet de les traiter similairement et de corréler leur comportement à l’évolution de l’échantillon<br>The damage and the resulting cohesion of the rocks control the slip and the earthquakes nucleation. This phenomenon is not well understood, that is why we are interested in the interplay between friction in the fault and damage of the surrounding volume. The main objective of this thesis is the coupled analysis of data obtained at the macroscopic scale in controlled laboratory experiments and of results of numerical models that allow to investigate smaller scales.The work produced during this thesis is based around three mechanical experiments performed on two kinds of cemented granular material samples. These samples, initially cohesive, are made of glass beads bonded with a ductile or brittle cement. The oedometric and uniaxial compressions are complementary to the direct shear test within a Casagrande box that allows to study a frictional interface in a surrounding damaged medium. The samples responses to these mechanical stresses involve damage, slip and friction and are not only monitored mechanically but also acoustically thanks to two kinds of ultrasounds probes. The first probe, said active, allows to monitor the apparent elastic properties of the sample by studying the acoustic waves propagation and especially their velocity. Its evolution is strongly correlated to the sample state. Under oedometric loading, the damage affects the velocity whereas under unloading-reloading an effective medium law for a dry and purely granular medium is recovered. The acoustic velocity measured in the brittle samples is also correlated to intermittent stick-slip events interspersing the macroscopic loading. The second probe, said passive, consists in recording the acoustic emissions emitted in the medium and in analyzing their statistical laws similar to the earthquakes ones. For instance, the instantaneous b- value in the Gutenberg-Richter law, the events rate as the rupture approaches, or the events clustering and inter-event distribution charactarize different stages of the system loading.To better understand the micro and mesoscopic aspects that remain not much explored experimentally, we developed quasistatic and dynamic numerical simulations. Two kinds of modeling, with finite elements and hybrid (coupling finite elements for the bonds and discrete elements for the beads), allow to employ elasto-plastic laws with damage for the bonds rather than ad hoc laws usually used to describe the bonds with discrete elements only. The experimental geometries, mechanisms and protocols have closely guided these simulations that highlight phenomena at the scales of the beads and their contacts. We observe that the intern bonds deformation is often localized in shear bands but that the macroscopic deformation is very heterogeneous at the sample scale. In reaction to the bonds ruptures, stress redistributions and contacts rearrangements guide the force chains evolution. An acoustic velocity drop with the damage is observed at the macroscopic scale. The events of bonds rupture and of creation or loss of direct contacts between the beads are considered as equivalents of acoustic emissions sources, what allows to treat them similarly and correlate their behavior to the sample evolution
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33

Zou, Zhenhai. "Etude de l'éjection de grains hors d'un cylindre pressurisé." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0412.

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Nous considérons un scénario hypothétique d’accident initié par une insertion de réactivité nucléaire entrainant la rupture de la gaine d’un crayon combustible. La violence du contact avec le fluide caloporteur dépendrait fortement du débit de fragment combustible, initialement confiné avec un gaz pressurisé, sortant du crayon. Ce travail de thèse a consisté à étudier cette dynamique en la modélisant par la vidange d’un milieu granulaire hors d’un silo pressurisé. Nous nous sommes d’abord concentrés sur le rôle de la géométrie interne du silo grâce à un fond incliné. Pour un faible angle d’inclinaison, l’orientation de l’écoulement granulaire (donc le débit) est contrôlée par la friction pariétale, tandis qu’une grande inclinaison détermine cette orientation. Nous nous sommes ensuite intéressés au rôle du gaz pressurisé d’abord en imposant une surpression d’air constante puis en considérant un cas transitoire dans lequel une surpression initiale provoque la rupture de l’orifice. Dans les deux configurations, le débit granulaire est mis à l’échelle par une loi de Beverloo modifiée où le gradient de pression du gaz près de l’orifice agit comme une force motrice supplémentaire qui peut être décrite par la loi de Forchheimer. Nous proposons un modèle quasi-stationnaire pour le débit granulaire ainsi qu’une simulation continue basée sur un modèle multiphasique qui reproduisent bien les résultats expérimentaux. A forts débits, nous observons une instabilité du jet, initiée par des oscillations de pression à l’orifice. Enfin nous avons montré que le milieu environnant agit sur la condition de pression à la sortie du silo<br>We consider a hypothetical scenario of reactivity initiated accident in a nuclear power plant. The violence of the so-called fuel-coolant interaction phenomena depends strongly on the flow rate of particles out of the gas pressurized rod. The aim of this thesis was to study how this discharge rate is driven by the internal geometry and the pressurized gas. We focused firstly on the discharge of a rectangular silo with an inclined bottom. For a small inclination angle, the granular flow orientation is controlled by the wall friction, whereas a large inclination angle fully determines this orientation. Secondly, we focused on two configurations with pressurized gas : a case with constant gas overpressure at the top of the silo and a more transient case for which an initial larger overpressure initiates the rupture of an orifice. The granular flow rate increases significantly with the gas flow, especially for the finer particles and the large overpressures. In both cases, the flow rate scales with a modified Beverloo law where the gas pressure gradient near the outlet acts as an additional driving force. The pressure gradient is well described by a Forchheimer resistance law through the granular medium. We therefore propose a quasi-steady model for the transient description of the granular flow rate. The two configurations were successfully reproduced by numerical simulations based on a continuum multiphase model. For the larger flow rates, instabilities of the granular jet were found to be initiated by pressure oscillations in the outlet region. The presence of water surrounding the silo only acts through an additional hydrostatic pressure effect
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34

Cavailles, Fanny. "Génération par enrobage à sec de particules composites à propriétés d'usages contrôlées." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2016. http://www.theses.fr/2016EMAC0018/document.

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L’enrobage à sec par action mécanique permet de formuler des particules composites dont les fonctionnalités et les propriétés physiques, comme l’écoulement, sont améliorées et cela sans l’ajout de solvant ou de liant. Actuellement la plupart des procédés d’enrobage à sec sont conduits en mode discontinu. L’objectif de ce travail est donc de développer et d’étudier une opération d’enrobage à sec par un procédé continu innovant, une extrudeuse bi-vis corotative sans filière, constituant une rupture technologique dans son domaine. Dans le cadre de ce travail, des sphères de cellulose microcristalline, appelées particules hôtes sont enrobées avec soit des talcs de différentes granulométries soit du stéarate de magnésium, nommées particules invitées. Dans un premier temps, le comportement des particules hôtes est étudié dans le procédé. Les particules sorties du procédé sont analysées par microscopie électronique à balayage, par granulométrie laser et par voluménométrie. Pour la configuration de vis présentant que des éléments de transport, la vitesse de rotation des vis (25 à 200 rpm) et le débit d’alimentation (0,5 à 2 kg/h) choisis influencent le taux de remplissage dans le fourreau, et pour un taux supérieur à environ 14 % : la quantité de particules endommagées est négligeable. Un taux de remplissage faible favorise les frictions particules-particules ou particules-métal au niveau de l’entrefer. L’ajout de zones de mélanges dans la configuration des vis accentue ce phénomène de brisure par l’augmentation des contraintes de cisaillement. Par ailleurs, des masses retenues de la poudre dans le fourreau évoluent linéairement en fonction de la masse de poudre transportée en un tour de vis pour différentes configurations de vis. Ces relations laissent penser à l’existence d’un volume mort. Les mesures de distribution de temps de séjour mettent en évidence par l’application d’un modèle d’association de réacteurs idéaux, la présence d’écoulement piston et d’un volume mort. Dans un second temps, la faisabilité d’une opération d’enrobage à sec par le procédé étudié est analysée. Une couche d’enrobage continu de talc modifiant le comportement hydrophile des particules hôtes, est obtenue pour une vitesse de rotation de vis de 50 rpm et une configuration de vis cisaillante. Le type de particules invitées influence la morphologie de la couche d’enrobage : de type film avec le stéarate de magnésium et de type discret avec le talc micronisé. Néanmoins les propriétés de taille, d’écoulement, de compressibilité des particules composites sont semblables à celle des particules hôtes, seule la propriété de mouillabilité est modifiée. La présence de stéarate de magnésium diminue le temps de séjour des particules dans le procédé grâce à son caractère lubrifiant<br>Dry particle coating with mechanical action allows the production of composite particles whose functionalities and physical properties, such as flowability, are improved thanks to the absence of solvent or binder. Currently, most of dry particle coating processes are carried out in a discontinous mode. The objective of this work is thus to develop and study a dry particle coating operation with a continuous innovative process, twin screw co-rotating extruder without die, constituting a technological rupture in this application field. For this, spherical particles of microcristalline cellulose, as host particles, are coated with either talc particles of two sizes or magnesium stearate particles (MgSt), as guest particles. Firstly, the host particles behaviour is studied in the process. The exiting particles are analyzed by scanning electronic microscopy, laser granulometry and tapping test. Regarding the transport configuration, the chosen screw speed (between 25 an 200 rpm) and the feed rate (between 0.5 and 2 kg/h) have an important influence on the filling level in the barrel. For a filling level superior to approximatly 14 %, the quantity of broken particles is not significant. A low filling level facilitates the particle-particle or particle-metal friction in the barrel gap. When more mixing zones are added to the screw configuration, the shear stresses increase and, therefore, the breakage particle phenomenon becomes more prominent. Futhermore, the retained powder mass increases linearly when the transported mass in one screw turn increases for all the screw configurations. These evolutions suggest the existence of a dead volume. The residence time distribution mesurements highlight, thanks to the application of flowing model, the presence of plug-flow and a dead volume. Secondly, the feasibility of using the process for dry particle coating is analyzed. A continuous coating layer of talc modifiying the hydrophilic behaviour of the host particles is obtained for a low screw rotation speed (50 rpm) and a screw configuration with one mixing zone. The type of guest particles influence the morphology of the coating layer: film layer with the MgSt particles and discontinous layer with the micronized talc. However, size, flow and compressibility of the coated particles are similar to the ones of the initial host particles, only the wettability properties are modified. The presence of MgSt decreases the particle mean residence time in the process thanks to its lubricant action
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35

Rahmanian, Nejat, and M. Ghadiri. "Strength and structure of granules produced in continuous granulators." 2013. http://hdl.handle.net/10454/6146.

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The effect of the operating conditions of three continuous high shear granulators on the internal structure and strength of granules has been investigated and the possibility of seeded granulation has been explored. In a recently concluded programme of research on the scale-up of a high shear granulator, Cyclomix (manufactured by Hosokawa Micron B.V., The Netherlands), a novel method of granulation called seeded granulation was introduced, where each granule contained, at its core, a large particle from the upper tail end of the feed particle size distribution. Seeded granulation is particularly useful for process control of continuous granulators as there is the potential to control granulation by the flow rate of the seed particles. Hence, the performance of three different types of continuous granulators in terms of granule strength and structure has been evaluated here; these are Extrudomix, Modulomix (manufactured by Hosokawa Micron, UK and The Netherlands, respectively) and the Nica M6 Turbine continuous granulator (manufactured by GEA, UK). Calcium carbonate (Durcal 65) powder was granulated using an aqueous solution of polyethylene glycol (PEG) as binder in the same ratio as used previously in our batch granulation, to allow comparison between the continuous and batch processes. The crushing strength was characterised by quasi-static side crushing between two platens using a mechanical testing machine. The internal structure and morphology were evaluated by scanning electron microscopy and the extent of seeding quantified. Granules produced in all the three continuous granulators were significantly weaker than those of the batch granulator tested previously. Among the continuous granulators only the Modulomix granulator produced some seeded granules. It is considered that longer residence time is necessary to produce seeded granules.
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36

Behjani, M. A., Nejat Rahmanian, Ghani N. F. b. A, and A. Hassanpour. "An investigation on process of seeded granulation in a continuous drum granulator using DEM." 2017. http://hdl.handle.net/10454/11613.

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Yes<br>Numerical simulation of wet granulation in a continuous granulator is carried out using Discrete Element Method (DEM) to discover the possibility of formation of seeded granules in a continuous process with the aim of reducing number of experimental trials and means of process control. Simple and scooped drum granulators are utilized to attain homogenous seeded granules in which the effects of drum rotational speed, particles surface energy, and particles size ratio are investigated. To reduce the simulation time a scale-up scheme is designed in which a dimensionless number (Cohesion number) is defined based on the work of cohesion and gravitational potential energy of the particles. Also a mathematical/numerical method along with a MATLAB code is developed by which the percentage of surface coverage of each granule is predicted precisely. The results show that use of continuous granulator is promising provided that a high level of shear is considered in the granulator design, e.g. it is observed that using baffles inside the drum granulators is essential for producing seeded granules. It is observed, moreover, that the optimum surface energy for scooped granulator with rotational speed of 50 rpm is 3 J/m2 which is close to the number predicted by Cohesion number. It is also shown that increasing the seed/fine size ratio enhances the seeded granulation both quantitatively (60% increase in seeds surface coverage) and qualitatively (more homogeneous granules).
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37

Bougie, Jonathan Lee. "Continuum simulations of fluidized granular materials." Thesis, 2004. http://hdl.handle.net/2152/1180.

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38

Bougie, Jonathan Lee Swift Jack B. "Continuum simulations of fluidized granular materials." 2004. http://wwwlib.umi.com/cr/utexas/fullcit?p3142697.

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39

Okeyo, Clint, D. F. Chowdhury, K. Cheung, and Nejat Rahmanian. "3D printed elastic mould granulation." 2018. http://hdl.handle.net/10454/16700.

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Yes<br>In the pharmaceutical industry, enhanced process understanding resulting in superior control of product attributes, has the potential to save up to 20% of process engineering and product development costs during drug development. With the aim of achieving enhanced process understating, a novel approach for granulation of fine powders is presented. First, a mould with the desired particle shape and size is created using 3D printing followed by casting using elastomeric material. The formulation is prepared through wet massing and tested as a thin film on flat elastomeric membranes. The thin film itself can be a product but it also gives a good indication of coating performance before coating the patterned elastic membrane with the formulation i.e., 3D printed elastic mould granulation. Results show that following granulation and drying, granules of controlled size and shape (e.g. cubic and 500 μm), strength, friability and flowability can be formed. The method presented may allow for more robust process development in particle engineering.<br>Research Development Fund Publication Prize Award winner, December 2018.
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40

Djuric, Dejan [Verfasser]. "Continuous granulation with a twin-screw extruder / vorgelegt von Dejan Djuric." 2008. http://d-nb.info/1000295206/34.

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41

Chang, Yu-Cheng, and 張育誠. "Fracture Toughness & Tensile Strength under Continuous Heat-induced Damage of Granular Material with Acoustic-optic Examination." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/80670893882702606566.

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碩士<br>國立臺灣科技大學<br>營建工程系<br>101<br>The material mechanic research of traditional temperature which put the specimen into high temperature furnace and heat it to the preset temperature can only obtain single temperature effect of the macroscopic fracture mechanism. This research obtain the continuity material damage distribution through continued heat treatment, and to do the BZ test and SCB test, also build to couple two nondestructive techniques: AE(acoustic emission) and ESPI (electronic speckle pattern interferometry), to find out the complete loading history and the damage relationship between macroscopic and microscopic of the material. The research also do the B.Z. test and SCB test by using different grain size and different ranges of temperature as variables. If the components in the material are subjected to heat treatment, the components will reveal different chemical and physical changes. For example, the cements around 200℃, the C-S-H becomes C-S+H2O. The temperature elevated up around 500℃,the Ca(OH)2 becomes CaO+H2O and the volume of cement material decreases 0.5%. For siliceous aggregate, the quartz is main component , it is changed from ? to ? phase around 500℃and the volume of quartz increases 0.4%. The increase of temperature caused KIC and tensile strength to decrease, the material fracture made the critical temperature to be around 450 to 500 ℃. According to microscopic test result, the grain size and temperature affect AE event very much. AE event decrease while temperature increase. The research got the similar result by using ESPI and SCB test to calculate KIC. Therefore, the research also confirm the feasibility of this method.
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Κανελλόπουλος, Γεώργιος. "Φαινόμενα μεταφοράς και συσσωμάτωσης σε δυναμικά συστήματα κοκκώδους ύλης". Thesis, 2013. http://hdl.handle.net/10889/7242.

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Τα κοκκώδη υλικά είναι αναπόσπαστο κομμάτι του κόσμου μέσα στον οποίο ζει ο άνθρωπος, και συνεπώς, για την καλύτερη κατανόηση του κόσμου αυτού, επιβάλλεται η μελέτη τους. Αυτός είναι και ο σκοπός της παρούσας διδακτορικής διατριβής. Επικεντρωνόμαστε σε διάδρομο μεταφοράς ο οποίος αποτελεί αντιπροσωπευτικό μοντέλο για πληθώρα εφαρμογών τόσο στην βιομηχανία όσο και στο φυσικό περιβάλλον. Αποτελεί επίσης χαρακτηριστικό παράδειγμα της οικογένειας ανοικτών πολυσωματιδιακών συστημάτων, η οποία βρίσκεται στην καρδιά της σύγχρονης επιστήμης της Πολυπλοκότητας. Αρχικά εισάγουμε το μοντέλο ροής στο οποίο το κοκκώδες υλικό αντιμετωπίζεται ως ένα ειδικό ρευστό (συνεχές μέσο) με εσωτερική απώλεια ενέργειας. Μελετάμε τη δυναμική ισορροπία που επικρατεί στο σύστημα υπό σταθερές συνθήκες, καθώς και την κατάρρευση της ομαλής ροής μέσω του σχηματισμού συσσωματώματος. Ειδική μνεία γίνεται στα πρόδρομα φαινόμενα της συσσωμάτωσης, τα οποία ερμηνεύουμε μέσω μίας αντίστροφης διακλάδωσης διπλασιασμού περιόδου. Διερευνώντας την εξάρτηση μεταξύ της μορφής της ροϊκής συνάρτησης και του τρόπου με τον οποίο το σύστημα μεταβαίνει σε καθεστώς συσσωμάτωσης αποκαλύπτουμε τόσο ποιοτικές όσο και ποσοτικές διαφορές σε σχέση με τον παραπάνω τύπο διακλάδωσης. Μια σημαντική παραλλαγή του συστήματος μεταφοράς προκύπτει εφαρμόζοντας ανατροφοδότηση του πρώτου δοχείου με το συνολικό υλικό που εκρέει από το τελευταίο. Η μαθηματική επεξεργασία αποδεικνύει ότι σε αυτήν την περίπτωση η δημιουργία συσσωματώματος συντελείται μέσω μιας διακλάδωσης Hopf αντί για διακλάδωσης διπλασιασμού περιόδου. Επιστρέφοντας στο αρχικό μας σύστημα, μελετάμε και το συνεχές όριο, θεωρώντας το διάδρομο μεταφοράς να έχει «άπειρο» μήκος. Η δυναμική ισορροπία, που ισοδυναμεί με το ισοζύγιο της μάζας ανάμεσα σε διαδοχικά δοχεία του διακριτού συστήματος, τώρα παίρνει τη μορφή μιας μη γραμμικής μερικής διαφορικής εξίσωσης δεύτερης τάξης με μη σταθερούς συντελεστές. Η προσεκτική μελέτη της εξίσωσης και των συντελεστών της, σε συνδυασμό πάντα με τις συνοριακές συνθήκες στην είσοδο και έξοδο του διαδρόμου, μας επιτρέπει όχι μόνο να αναπαραγάγουμε τα προηγούμενα αποτελέσματα υπό το πρίσμα του συνεχούς ορίου αλλά και να τα ερμηνεύσουμε βάσει φυσικών διεργασιών όπως είναι η μεταφορά (drift) και η διάχυση (diffusion). Ειδικότερα, η συσσωμάτωση συμβαίνει σε καθεστώς αρνητικής διάχυσης (antidiffusion). Κλείνουμε την διατριβή προτείνοντας γενικεύσεις των συστημάτων που ερευνήσαμε. Επεκτείνουμε το διάδρομο μεταφοράς σε πλέγματα δύο διαστάσεων και μελετάμε άλλα μοντέλα που σχετίζονται με ροές διακριτών σωματιδίων όπως είναι η κυκλοφορία οχημάτων στους αυτοκινητοδρόμους.<br>Granular materials are ubiquitous in nature and in our daily lives, and understanding their behavior is therefore of crucial importance. The present thesis wants to contribute to this. We focus on a conveyor belt, which is not only a representative model for numerous applications both in industry and the natural environment, but also a prime example of an open multi-particle system prone to spontaneous pattern formation. This places our study right in the center of the modern science of complexity. Initially we introduce the flux model, in which the granular material is treated as a special fluid (a continuous medium) with internal energy losses. We examine the dynamic equilibrium that exists in the system under steady state conditions and also the breakdown of this equilibrium when the inflow rate exceeds a certain critical threshold value, resulting in the formation of a cluster and the obstruction of the conveyor belt. We focus especially on the pre-clustering phenomena and find that these can be described mathematically by a reverse period doubling bifurcation. Investigating the relation between the precise form of the flux function and the way in which the transition to the clustered state takes place, we reveal that the above scenario via a reverse period doubling bifurcation is not universal. Also other bifurcation types are possible. An important variation of our transport system is obtained by applying a feedback mechanism: All the particles that flow out from the last compartment are inserted into the first, making the system closed with respect to matter (mass conservation). The mathematical analysis proves that in this case the cluster formation occurs via a Hopf bifurcation instead of a period doubling. Returning to our original system, we study its continuum limit by considering a conveyor belt of ‘infinite’ length. The dynamics of the system is now described by a second-order nonlinear partial differential equation with non-constant coefficients. A careful analysis of this PDE and its coefficients, in combination with the special boundary conditions at the entrance and exit of the system, allows us not only to reproduce the results of the discrete system in the setting of differential equations but also to interpret these results in terms of physical processes such as drift and diffusion. In particular, the clustering occurs when the diffusion coefficient becomes negative, which gives antidiffusion. We close this thesis by discussing several generalizations of the system investigated. Among other things we expand the one-dimensional conveyor belt to a two-dimensional lattice. We further propose to use a similar flux model for the study of other, non-granular instances of discrete particle flows, such as vehicles on a highway.
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