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Dissertations / Theses on the topic 'Particle packing'

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Published: 4 June 2021
Last updated: 13 February 2022

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1

Chan, Ka-wai, and 陳嘉威. "Particle packing modeling incorporating the wedging effect." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50900055.

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The packing of solid particles is an important research topic in particle mechanics and powder technology. However, it is difficult to predict and measure the packing density of particles. Although theoretical models for prediction and test methods for measurement have been developed, the predicted values and measured results do not always agree with each other. Through in-depth review of the theoretical predictions by the existing 2-parameter model and the respective measured results, it is postulated in this thesis that the discrepancies between the predicted values and measured results are mainly due to the wedging effect – a new interaction effect that has not been considered in previous packing models. The wedging effect occurs when some isolated fine particles are entrapped at the gaps between the coarse particles or when the gaps between the coarse particles are not wide enough for the formation of complete layers of fine particles. Such wedging effect would reduce the packing density and therefore should be considered in particle packing modeling. To provide additional measured results covering a wider range of size ratio than those published by others, a comprehensive experimental study of measuring the packing densities of binary mixes of mono-sized and rounded particles has been conducted. The wedging effect was further explained and more importantly quantified in the light of these experimental results. And, by incorporating the wedging effect, a 3-parameter packing model has been developed. The 3-parameter model was calibrated by fitting the theoretical predictions with the measured results of the comprehensive study conducted herein. After calibration, the theoretical predictions agree very well with the measured results, with the prediction error generally within 1.43%. Further, some of the particle packing models were evaluated by comparing with published test results. The particle packing models so evaluated include the 2-parameter model (with the loosening and wall effects incorporated), the compressible model (with the loosening, wall and compaction effects incorporated) and the 3-parameter model (with the loosening, wall and wedging effects incorporated). It was found that the accuracy of the models varies with both the size ratio and volumetric fractions of the binary mix. In general, when the size ratio is larger than 0.65, all the packing models are sufficiently accurate. However, when the size ratio is smaller than 0.65, the 2-parameter model and the compressible model would either over- or under-estimate the packing density with the prediction errors generally larger at around the volumetric fractions giving maximum packing density. On the other hand, within the whole range of size ratio from 0.02 to 0.74 covered by the test results used for evaluation of the packing models, the packing density prediction by the 3-parameter model are accurate to within an absolute error of 0.020. Overall, the better performance of the 3-parameter model may be attributed to the incorporation of the wedging effect. With the wedging effect incorporated, the 3-parameter model is the most accurate and generally applicable to the whole range of size ratio from 0 to 1.
published_or_final_version
Civil Engineering
Master
Master of Philosophy
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2

Zheng, Xiao-Qin Materials Science &amp Engineering Faculty of Science UNSW. "Packing of particles during softening and melting process." Awarded by:University of New South Wales. School of Materials Science & Engineering, 2007. http://handle.unsw.edu.au/1959.4/31517.

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Softening deformation of iron ore in the form of sinter, pellet, and lump ore in the cohesive zone of an ironmaking blast furnace is an important phenomenon that has a significant effect on gas permeability and consequently blast furnace production efficiency. The macroscopic softening deformation behavior of the bed and the microscopic deformation behavior of the individual particles in the packed bed are investigated in this study using wax balls to simulate the fused layer behavior of the cohesive zone. The effects of softening temperature, load pressure, and bed composition (mono - single melting particles, including pure or blend particles vs binary ??? two different melting point particles) on softening deformation are examined. The principal findings of this study are: 1. At low softening temperatures, an increase in load pressure increases the deformation rate almost linearly. 2. At higher softening temperatures, an increase in load pressure dramatically increases the deformation rate, and after a certain time there is no more significant change in deformation rate. 3. The bed deformation rate of a mono bed is much greater than that of a binary one. 4. In a binary system, the softening deformation rate increases almost proportionally with the increase in the amount of lower melting point wax balls. 5. In a mono system with blend particles, the content of the lower melting point material has a more significant effect on overall bed deformation than the higher melting point one. 6. The macro softening deformation of the bed behaves the theory of creep deformation. 7. A mathematical model for predicting bed porosity change due to softening deformation based on creep deformation theory has been developed. 8. Increase in load pressure also reduces the peak contact face number of the distribution curves, and this is more prominent with higher porosity values. 9. The contribution of contact face number to bed porosity reduction is more pronounced in a mono system than in a binary system. 10. The porosity reduction in a binary bed is more due to the contact face area increase, presumably of the lower melting point particles. 11. The mono system has a single peak contact face number distribution pattern while the binary system exhibits a bimodal distribution pattern once the higher melting point material starts to deform. 12. In a binary system, an increase in deformation condition severity tends to reduce the contact face number of the higher melting point material without having to increase the contact face number of the lower melting point material accordingly to achieve a given porosity.
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Chen, Xiaolin. "Particle packing, compaction and sintering in powder metallurgy." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0014/NQ34746.pdf.

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4

Caulkin, Richard. "Applications of the DigiPac Model for Particle Packing." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491658.

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5

Che, Lida. "Numerical constitutive laws for powder compaction using particle properties and packing arrangement." Thesis, University of Leicester, 2017. http://hdl.handle.net/2381/40677.

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Numerical studies, calibrated and validated using experiments, were carried out to develop a constitutive law for powder compaction. In order to simulate powder compaction at particle level, single particle compression/breakage test is used to characterise the mechanical properties, which include elastic modulus, Poisson’s ratio and yield strength. Finite Element Analysis (FEA) of single particle compression was carried out and validated vs. single particle compression testing and then used to establish a suitable hardening law. The particle size, shape and packing arrangement were obtained using X-ray computed tomography. This information was transferred to FEA. Due to the presence of complex geometrical structures, Meshlab and Solidworks were chosen to deal with the arrangement of particles in the structure. The multi-particle finite element method (MPFEM) was implemented into the finite element software package Abaqus/EXPLCIT v6.14 and used to simulate the powder compaction process. The model input parameters include mechanical properties (of the single particle) and interactions between particles (e.g. friction). The stress-strain curves predicted by MPFEM were validated experimentally using compaction tests performed in a die instrumented with radial stress sensors. The method proposed was used for constitutive model development for powder compaction as an alternative to bulk powder characterisation. The stress-strain curves MPFEM were analysed using the deformation plasticity framework. Contours of constant complementary work in Kirchhoff stress space were established and a model consistent with the behaviour of the materials was identified in order to capture the materials response under conditions experienced in practical die compaction processes.
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Chellappah, Kuhan. "A study of the filtration of fibre/particle mixtures." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/6323.

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This thesis investigates the constant pressure cake filtration of interacting cellulose fibre/TiO2 (rutile) mixtures, and involved experimental studies using an automated pressure filtration apparatus. The influence of suspension composition, filtration pressure and solution environment on filtration has been discussed in relation to cake properties such as average cake porosity and specific resistance. To help interpret the filtration results, sedimentation data were also obtained. The average porosities of filter cakes formed from pure rutile and fibre suspensions in deionised water were approximately 0.6 and 0.75, respectively, and a steady and progressive increase in porosity with fibre fraction was generally observed. With filtrations at 450 kPa, the average specific cake resistances for pure fibre and rutile in deionised water were approximately 9.4x1013 and 4.2x1012 m kg-1 respectively, with the variation of specific resistance with solids composition showing a minimum. Similar trends were observed at other tested filtration pressures with suspensions in deionised water but not with filtrations of suspensions in 0.2 M NaCl and 0.1 M CaCl2 solutions. The minima in average specific cake resistance with solids composition for feeds in deionised water was attributed to rutile-fibre interactions. Abrupt transitions in cake structure were evident part way through some filtrations, and resulted in unexpected filtrate flow behaviour. This is an interesting phenomenon, and not only were the changes in cake structure relatively reproducible, but also the nature of the change could be altered by changes in filtration pressure, solids composition and/or solution environment. The study of fibre/particle binary filtration behaviour, in particular the porosity and specific cake resistance trends, were substantiated by relevant theoretical treatment and modelling analysis. With the porosity trends, an additive porosity concept seemed to represent the data better than interparticle penetration models. With the specific cake resistance trends, a semi-empirical equation was proposed which appeared to represent a wide range of binary mixture filtration data. A mathematical framework was also developed in an attempt to understand the underlying physical mechanisms which led to filter cake restructuring, and possible explanations were postulated.
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Chao, Chien-Wei. "An Improved Dynamic Particle Packing Model for Prediction of the Microstructure in Porous Electrodes." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5632.

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The goal of this work is to develop a model to predict the microstructure of Li-ion batteries, specifically focusing on the cathode component of the batteries. This kind of model has the potential to assist researchers and battery manufacturers who are trying to optimize the capacity, cycle life, and safety of batteries. Two dynamic particle packing (DPP) microstructure models were developed in this work. The first is the DPP1 model, which simulates the final or dried electrode structure by moving spherical particles under periodic boundaries using Newton's laws of motion. The experience derived from developing DPP1 model was beneficial in making the final model, called DPP2. DPP2 is an improved version of DPP1 that includes solvent effects and is used to simulate the slurry-coating, drying, and calendering processes. Two type of properties were used to validate the DPP1 and DPP2 models in this work, although not every property was used with the DPP1 model. First are the structural properties, which include volume fraction, and electronic and ionic conductivities. Experimental structural properties were determined by analyzing 2D cross sectional images of the battery cathodes. These images were taken through focused ion beam (FIB) planarization and scanning electron microscopy (SEM). The second category are the mechanical properties, which include film elasticity and slurry viscosity. These properties were measured through experiments executed by our group. The DPP2 model was divided into two submodels : active-free and active-composite. The 2D cross sectional images of the simulated structure of the models have a similar particle arrangements as the experimental structures. The submodels show reasonable agreement with the experimental values for liquid and solid mass density, shrink ratio, and elasticity. For the viscosity, both models show shear-thinning behavior, which is a characteristic of slurries. The volume fractions of the simulated structures of the active-free and active-composite models have better agreement with the experimental values, which is also reflected in the 2D cross sectional images of the structure.
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Lohmander, Sven. "The influence of particle shape of coating pigments on their packing ability and on the flow properties of coating colours." Doctoral thesis, KTH, Pulp and Paper Technology, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3044.

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The influence of particle shape of coating pigments on theirpacking ability and on the flow properties of coating colourshas been investigated. The particle shapes considered werespherical, flaky and acicular (needle-shaped). In the case ofsuspensions containing monodisperse spherical polystyreneparticles, a concentration gradient appeared in the filter cakeforming during filtration under static conditions. Such agradient, monitoredby non-destructive magnetic resonanceimaging (MRI), is not accounted for in the traditionalfiltration theory used in coating technology. Good agreementwas found between a literature model describing filtrationthrough a compressible filter cake and the concentrationgradients measured by MRI. According to this model, the scaledconcentration gradient was the same at all times.

For flaky (mainly kaolin) and acicular (aragonite)particles, a rapid method was evaluated to estimate a shapefactor of the pigment particle. Generalised mathematical modelsof oblate and prolate spheroids were applied to reduce thethree geometrical dimensions of the particle to two, the majoraxis and the minor axis. The shape factor, which is mass-based,was derived from a comparison between the results obtained bytwo different size-assessment instruments, viz. the Sedigraphand an instrument using light scattering. This yields a shapefactor distribution as a function of equivalent sphericalparticle size, but the results are uncertain for small particlediameters, below 0.2 µm. Good agreement was obtainedbetween the shape factor and a mass-based aspect ratio obtainedby image analysis, but the rapid method is generally moreaccurate for flaky than for acicular particles.

Results obtained by capillary viscometry showed that therewas a relationship between the viscosity at high shear rates(>105s-1) and the shape factor, but that it was notsufficient to use the median value of the shape factor toachieve proper information. A more complete evaluation requiresknowledge of the shape factor distribution, which is also givenin part by the method mentioned above. However, a large medianshape factor was related to a high high-shear viscosity.Non-Newtonian entrance pressure losses were sometimessignificant in capillary viscometry, indicating that it wasinappropriate to measure the shear viscosity with only onecapillary. Such effects were however relatively much morepronounced in slit die viscometry, especially in the case ofacicular particles, where the aspect ratio was a crucialparameter. The influence of the shape factor of kaolinparticles on the non-Newtonian entrance pressure losses over aslit die was surprisingly small. The high-shear viscosity ofcoating suspensions based on different pigments correlated withthe median pore size of the corresponding coating layer ratherthan with the porosity.

Keywords: Aspect ratio, capillary viscometry, coatingcolour, filtration, particle packing, pigment, pore structure,rheology, shape factor, slit die viscometry, spheroid.

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Ng, Priscilla, Priscilla Ng, and Priscilla Ng. "Simulating Particle Packing During Powder Spreading For Selective Laser Melted Additive Manufacturing Using The Discrete Element Method In Abaqus." DigitalCommons@CalPoly, 2020. https://digitalcommons.calpoly.edu/theses/2162.

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Metal additive manufacturing allows for the rapid production of complex parts that are otherwise impractical using conventional subtractive manufacturing techniques. Applications for additive manufacturing span across a broad array of industries including aerospace, automotive, and medical, among many others. One metric of printing success is material properties, including part density. While there has been extensive research completed for the density of printed parts, there is little published work concerning powder packing density on the build plate associated with powder spreading. In this thesis, a Discrete Element Method (DEM) model was created in Abaqus to simulate the spreading behavior of particles through a single sweep of a spreader blade . Spreading behavior was investigated for three different build plate configurations: a flat build plate, a build plate with a small protruding feature, and a build plate with the same protruding feature split into quarters. For each configuration, the 2D packing behavior of the particles were analyzed during the powder spreading process. Different packing patterns seen in the 2D packing behavior were further analyzed to determine particle packing density, analogous to unit cell packing, and to predict 3D packing behavior and packing density. Additionally, particle packing density was measured following simulation using 2D image analysis to quantify powder spreading around, and interaction with, previously fused structures on the build plate. We found that the local packing fraction is measurably disrupted when particles interact with build plate features, providing insights into part density and short loading during part fabrication.
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Conceição, Edilene de Souza. "Influência da distribuição granulométrica no empacotamento de matérias-primas na formulação de porcelânicos." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-04112011-150732/.

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Materiais complexos como porcelanas e porcelanatos tem suas propriedades maximizadas quando atingem altas densidades finais após a sinterização. Contudo, a sua formulação contém no mínimo quatro matérias- primas diferentes, sendo o caulim a maior parte, mas também contendo quartzo e feldspatos. A granulometria final da mistura é controlada por uma única etapa de moagem de todos os materiais misturados. O objetivo deste trabalho foi obter combinações de diferentes granulometrias de ortoclásio, albita e quartzo com uma única granulometria de caulim através de cálculos de máximo empacotamento com o objetivo de alcançar a máxima densidade a cru, mantendo-se uma única composição química final. Os resultados mostraram que utilizando o conceito de empacotamento de partículas e otimizando a distribuição granulométrica foi possível obter corpos de prova com maiores densidades finais, menor retração final, além de reduzir a temperatura de queima, o que impacta diretamente no custo de produção.
Complex materials such as porcelain and porcelain stoneware have maximized their properties when they reach high final densities after sintering. However, formulations contain at least four different raw materials, where the kaolin is the major constituent, but also quartz and feldspars. The final particle size of the mixture is controlled by a single step milling of all materials. The attempt of this paper is to make different combinations of particles size distributions of orthoclase, albite and quartz with a single particle size of kaolin by calculation of maximum packing in order to achieve maximum density crude keeping same final chemical composition. The results showed that using the concept of particle packing and optimizing the particle size distribution was possible to obtain specimens with higher density end, the lower total shrinkage, in addition to reducing the firing temperature, which directly impacts the cost of production.
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Rodrigues, Andre Montes. "Modelagem e visualização de microestruturas digitais de materiais policristalinos monofásicos." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-25062014-132720/.

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Neste trabalho se buscou criar uma base tecnológica para síntese digital e visualização virtual de microestruturas de materiais policristalinos monofásicos, visando disponibilizar software e metodologias de baixo custo aos pesquisadores da área ou de áreas correlatas. Para isso foram levantados e testados métodos, sistemas, bibliotecas e algoritmos computacionais pertinentes ao problema em questão. A técnica de síntese escolhida adotou uma simulação física de empacotamento de partículas seguida por tesselação espacial baseada no diagrama Voronoi. Para testar a abordagem uma amostra de um material real foi reconstituída digitalmente. O modelo reproduziu com grande precisão a distribuição de tamanhos de grão, o número de faces por grão e o número de vizinhos imediatos da referência. Na frente de visualização virtual buscou-se definir um modelo capaz de lidar com grandes quantidades de dados e baseado em princípios cognitivos sólidos, que permitisse maior extração de conhecimento de modelos microestruturais. A técnica de visualização em múltiplas escalas foi considerada a mais apropriada aos modelos cujos objetos e detalhes abrangem diversas escalas espaciais, permitindo ao computador lidar com vastas quantidades de dados ao alternar entre qualidade e quantidade no processo de geração de imagens. Técnicas de visualização tradicionais também foram testadas e a técnica de corte se mostrou fundamental, principalmente para a exploração direta do interior do modelo, mas também para a extração de dados voltados a análise microestrutural estereológica.
The main goal of this work is to create a technological foundation for digital synthesis and virtual visualization of single-phase polycrystalline materials microstrutures, aiming to offer low cost software and methodologies to materials science researchers and alike. Several methods, applications, libraries and algorithms were tested and the most appropriate were selected for further exploration. The chosen microstructural synthesis technique uses newtonian particle packing simulation, followed by a Voronoi-based tesselation. This simple approach were put to test using a real material sample. The sample were digitally built and meaningfull parameters like grain size distribution, edges per face and mean number of neighbours were replicated with acceptable precision. Regarding visualization, the most relevant issue was the specification of a computationally scalable method based on proven cognitive principles, capable to deal with a huge amount of information and to support efficient knowledge extraction from microstructural models. The multiscale approach has proved to be the most suited for models that spans several scales in space, allowing computers to store and display large quantities of data and to manage the tradeoff between quality and quantity in the rendering process. Traditional visualization techniques were tested as well and section visualization has proved to be paramount for internal model visualization, as it is for stereological microstructural analysis.
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Ghasemi, Yahya. "Aggregates in Concrete Mix Design." Licentiate thesis, Luleå tekniska universitet, Byggkonstruktion och -produktion, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-61659.

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The importance of studying the behaviour and properties of concrete can be highlighted by considering the fact that concrete is the most used man-made material in the world. The very first step in making concrete is its mix design and deciding the type and amount of constitutes used in the production of concrete which should fulfil the requirements of the final product. Mix design models are commonly used for the purpose of proportioning concrete ingredients while anticipating the properties of the final product.  The current document deals with the commonly used principals in mix design models namely particle packing theory and excess water/paste layer theories. The conducted studies includes an investigation on accuracy of particle packing models (Toufar, 4C, CPM) and also tries to address the issue with measurement of specific surface area of particles as an essential input to water/paste layer theories.  It has been observed that the particle packing models can predict the packing density with acceptable margin. However, it should be mentioned that the particle packing models by themselves are not mix design models but should be rather used as a part of a mix design. In addition, it was found that the accuracy of calculating the specific surface area of particles based on their size distribution curve can be further improved by assuming angular platonic solids as uniform shape of aggregate instead of traditional approach of assuming spheres for aggregates’ shape.
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Lu, Ye. "Reconstruction, characterization, modeling and visualization of inherent and induced digital sand microstructures." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37176.

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Strain localization, the phenomenon of large shear deformation within thin zones of intensive shearing, commonly occurs both in-situ and in the laboratory tests on soils specimens. The intriguing mechanism of strain localization and how it will affect the general behavior of soil specimens have been investigated by many researchers. Some of the efforts have focused on finding the links between material properties (void space, fabric tensor) and mechanical behavior (stress, strain, volumetric strain). In the last ten years, several extensive studies have been conducted at Georgia Tech to investigate the mechanism of strain localization and link the microstructural properties with the engineering behavior of Ottawa sands. These studies have included 2-D and 3-D characterization of soil microstructures under either triaxial or biaxial shearing conditions. To extend and complement these previous studies, the current study focuses particularly on 3-D reconstruction, analysis and modeling of specimens of Ottawa sand subject to triaxial or biaxial loading. The 3-D microstructure of biaxial specimens was reconstructed using an optical microscopy based montage and serial sectioning technique. Based on the reconstructed 3-D digital volumes, a series of 2-D and 3-D characterizations and analyses, including local void ratio distributions, extent of shear bands, influence of soil fabrics and packing signature effects, were conducted. In addition to the image analysis based reconstruction and characterization, the 3-D discrete element method (DEM) code, PFC3D, was used to explore both biaxial and triaxial shear related soil behaviors at the global and particulate scale. Void ratio distributions, coordination numbers, particle rotations and displacements, contact normal distributions and normal contact forces as well as global stress and strain responses were investigated and analyzed to help understand the mechanism of strain localization. The microstructures of the numerical specimens were also characterized in the same way as the physical specimens and similar strain localization patterns were identified. Combined with the previous related studies, the current study provides new insights into the strain localization phenomenon of Ottawa sands subject to triaxial and biaxial loading. In addition, the reconstructed digital specimens were subject to a series of dissection studies which revealed exciting new insights into "microstructure signatures" which exist at both meso and micro scales within the real and simulated specimens.
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Hafid, Hamid. "Influence des paramètres morphologiques des granulats sur le comportement rhéologique des bétons frais : étude sur systèmes modèles." Thesis, Paris Est, 2012. http://www.theses.fr/2012PEST1026/document.

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Les granulats naturels alluvionnaires sont utilisés actuellement à hauteur de 70 à 80% en volume dans la composition d'un béton et représentent désormais une ressource non renouvelable dont l'accessibilité diminue. Les formulations actuelles de béton visent à augmenter la part de granulats de roche massive concassés. Ces matériaux, de par leur histoire de fabrication, n'ont pas du tout la même morphologie. La substitution des granulats roulés par des granulats concassés affecte considérablement la mise en œuvre du matériau. Dans un premier temps, nous étudions spécifiquement l'influence de la morphologie des granulats sur les propriétés d'empilement des grains. Nous montrons que, le facteur d'aspect des grains affecte fortement la compacité dense et lâche aléatoire. À l'inverse, pour des grains de facteur d'aspect identique, l'impact de la convexité sur la mesure de la compacité dense est faible. Nous étendons, dans un deuxième temps, notre étude au comportement rhéologique de nos systèmes composés d'émulsion inverse et de sables monodisperses. Pour cela, nous construisons des courbes d'écoulement à l'échelle locale grâce à un imageur à résonance magnétique. Nous montrons que cette méthode est, de nos jours, la plus précise pour des mesures de viscosités, car elle prend en compte la migration et la localisation du matériau durant l'écoulement. Nous montrons également que le facteur d'aspect contrôle tout d'un point de vue rhéologique dans le régime où il n'y a pas de réseau percolé de contacts entre grains
Natural alluvial aggregates compose up to 70 at 80% of the volume of today's concrete and now represent for a non-renewable resource whose accessibility is reduced. Actually, concrete mix designs tend to increase the share of aggregate crushed rock mass. These materials have a very different morphology because of their manufacturing process. The substitution of rolled aggregates by crushed aggregates affects the concrete workability. At first, we study specifically the influence of the morphology of the aggregates on the packing properties. We show that the aspect ratio strongly affects the dense and random loose packing. However, for particles of the same aspect ratio, the impact of the convexity of the measure of dense packing is low. In a second step, we go further in our study by measuring the rheological behavior of our systems composed of inverse emulsion and monodisperse sands. To that purpose, we construct flow curves at the local scale thanks to a magnetic resonance imager. We show that this method is, nowadays, the most accurate for viscosity measurements because it takes into account the migration and location of the material during flow. We also show that the aspect ratio control everything of a rheological point of view in the regime where there is no percolated network of contacts between particles
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De, Freitas Macedo Hian. "Concrete Made with Fine Recycled Concrete Aggregate (FRCA): A Feasibility Study." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39619.

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In the process of crushing concrete waste, significant amounts of fine by-products, the so called fine recycled concrete aggregates (FRCA), are generated and excluded from potential use. Limited research has thoroughly investigated the performance of concrete mixes with FRCA, very likely due to the complexity in analysing non-negligible amounts of adhered residual cement paste (RCP). Although some studies have proposed promising sustainable mix-design procedures accounting for the different microstructure when using coarse recycled concrete aggregates (CRCA), no similar approach exists for FRCA concrete. In this work, two promising procedures for mix-designing eco-efficient concrete with 100% FRCA are proposed accounting for the presence of RCP to reduce cement content in new mixtures. First, built on top of the existing procedure for CRCA mix-design, modifications to the Equivalent Volume (EV) method were introduced toconsider full replacement of fine natural sand by FRCA. Second, based on the concept of continuous Particle Packing Models (PPM), an optimized procedure was proposed to allow maximum packing density of FRCA mix linked to a given level of measured RCP content. Results verified the feasibility of producing eco-efficient concrete mixes with 100% FRCA, emphasizing the PPM mixes to report superior rheological and mechanical performance along with suitable durability-related properties. Yet, results also indicated the influence of simple or multistage crushed FRCA on the overall performance of mixes.
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Klement, Nathalie. "Planification et affectation de ressources dans les réseaux de soin : analogie avec le problème du bin packing, proposition de méthodes approchées." Thesis, Clermont-Ferrand 2, 2014. http://www.theses.fr/2014CLF22517/document.

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Les travaux de thèse présentés s’intéressent à l’optimisation des systèmes hospitaliers. Une solution existante est la mutualisation de ressources au sein d’un même territoire. Cela peut passer par différentes formes de coopération dont la Communauté Hospitalière de Territoire. Différents problèmes sont définis en fonction du niveau de décision : stratégique, tactique ou opérationnel ; et du niveau de modélisation : macroscopique, mesoscopique et microscopique. Des problèmes de dimensionnement, de planification et d’ordonnancement peuvent être considérés. Nous définissons notamment le problème de planification d’activités avec affectation de ressources. Plusieurs cas sont dissociés : soit les ressources humaines sont à capacité infinie, soit elles sont à capacité limitée et leur affectation sur site est une donnée, soit elles sont à capacité limitée et leur affectation sur site est une variable. Ces problèmes sont spécifiés et formalisés mathématiquement. Tous ces problèmes sont comparés à un problème de bin packing : le problème du bin packing de base pour le problème où les ressources humaines sont à capacité infinie, le problème du bin packing avec interdépendances dans les deux autres cas. Le problème du bin packing avec incompatibilités est ainsi défini. De nombreuses méthodes de résolution ont déjà été proposées pour le problème du bin packing. Nous faisons plusieurs propositions dont un couplage hiérarchique entre une heuristique et une métaheuristique. Des métaheuristiques basées individu et une métaheuristique basée population, l’optimisation par essaim particulaire, sont utilisées. Cette proposition nécessite un nouveau codage inspiré des problèmes de permutation d’ordonnancement. Cette méthode donne de très bons résultats sur les instances du problème du bin packing. Elle est simple à appliquer : elle couple des méthodes déjà connues. Grâce au couplage proposé, les nouvelles contraintes à considérer nécessitent d’être intégrées uniquement au niveau de l’heuristique. Le fonctionnement de la métaheuristique reste le même. Ainsi, notre méthode est facilement adaptable au problème de planification d’activités avec affectation de ressources. Pour les instances de grande taille, le solveur utilisé comme référence ne donne qu’un intervalle de solutions. Les résultats de notre méthode sont une fois encore très prometteurs : les solutions obtenues sont meilleures que la borne supérieure retournée par le solveur. Il est envisageable d’adapter notre méthode sur d’autres problèmes plus complexes par intégration dans l’heuristique des nouvelles contraintes à considérer. Il serait notamment intéressant de tester ces méthodes sur de réelles instances hospitalières afin d’évaluer leur portée
The presented work is about optimization of the hospital system. An existing solution is the pooling of resources within the same territory. This may involve different forms of cooperation between several hospitals. Various problems are defined at the decision level : strategic, tactical or operational ; and at the modeling level : macroscopic, mesoscopic and microscopic. Problems of sizing, planning and scheduling may be considered. We define the problem of activities planning with resource allocation. Several cases are dissociated : either human resources are under infinite capacity, or they are under limited capacity and their assignment on a place is given, or they are under limited capacity and their assignment is a variable. These problems are specified and mathematically formalized. All thes problems are compared to a bin packing problem : the classical problem of bin packing is used for the problem where human resources are under infinite capacity, the bin packing problem with interdependencies is used in the two other cases. The bin packing problem with incompatibilities is defined. Many resolution methods have been proposed for the bin packing problem. We make several propositions including a hierarchical coupling between heuristic and metaheuristic. Single based metaheuristics and a population based metaheuristic, the particle swarm optimization, are used. This proposition requires a new encoding inspired by permutation problems. This method gives very good results to solve instances of the bin packing problem. It is easy to apply : it combines already known methods. With the proposed coupling, the new constraints to be considered need to be integrated only on the heuristic level. The running of the metaheuristic is the same. Thus, our method is easily adaptable to the problem of activities planning with resource allocation. For big instances, the solver used as a reference returns only an interval of solutions. The results of our method are once again very promising : the obtained solutions are better than the upper limit returned by the solver. It is possible to adapt our method on more complex issues through integration into the heuristic of the new constraints to consider. It would be particularly interesting to test these methods on real hospital authorities to assess their significance
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17

Tagliaferri, de Grazia Mayra. "Contribution to the Understanding of Fresh and Hardened State Properties of Low Cement Concrete." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38109.

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Concrete, the major construction material used in the civil industry worldwide, displays remarkable performance and economic benefits. Yet, it also presents a huge environmental impact producing about 7% of the global carbon dioxide (CO2). Given the rise of global warming concerns, studies have been focusing on alternatives to reduce the amount of Portland cement (PC), which is the least sustainable ingredient of the mixture, for example by adopting particle packing model (PPM) techniques. Although a promising alternative, there is currently a lack of studies regarding the efficiently use of PPMs to reduce PC without compromising the fresh and hardened properties of the material. This work appraises the influence of PPMs and advanced mix-design techniques on the fresh (rheological behaviour) and hardened (compressive strength, modulus of elasticity, porosity, and permeability) state behaviours of systems with reduced amount of PC, the so-called low cement content (LCC) concrete. Results show that is possible to produce eco-efficient concrete maintaining and/or enhancing fresh and hardened properties of the material. Nevertheless, further durability and long-term behaviour must be performed on LCC systems.
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18

Zhang, Yuqi. "Comportement mécanique du matériau granulaire en tenant compte de la rupture des particules." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0041/document.

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Le comportement mécanique de matériaux granulaires est intrinsèquement lié aux propriétés individuelles des grains constitutifs ainsi qu’à leur assemblage (texture, distribution des vides, contact entre grains…). Soumis à un chargement extérieur, cet assemblage se déforme incluant le déplacement relatif entre les particules mais également la déformation propre des grains jusqu’à leur rupture si elle se produit. Pour étudier la rupture d'une seule particule, des études expérimentales et numériques ont été réalisées. Quatre particules sphériques formées de billes d’argile expansée légère ont été testées en compression à déplacement contrôlé jusqu’à la rupture (essai brésilien). Des photos ont été prises avec une fréquence d’acquisition de 4 images par seconde pour suivre la déformation des grains durant l’essai. La structure interne d'une particule a une influence significative sur l'initiation de la fissure. Pour approfondir cet effet, une micro-tomographie par rayons X a été utilisé pour scanner une particule afin d'obtenir la structure géométrique réelle en 3D. Ensuite, un modèle numérique 3D basé sur la géométrie des particules incluant la porosité interne a été construit avec Abaqus pour les mêmes conditions de chargement. Une comparaison des résultats des tests de laboratoire et des simulations a été faite. Sur la base des résultats, l’initiation des fissures, leur localisation dans le grain et la classification des ruptures de particules ont été établies. Afin d’étudier le rôle de l’anisotropie et en particulier de la fabrique d’un matériau granulaire soumis à un chargement externe, cinq essais de compression biaxiaux ont été réalisé sur un assemblage de grains quasi-sphériques placés dans une chambre confinée. Des photos ont été prises pendant les tests et ont été enregistrées selon une fréquence définie. Un programme écrit sous Matlab a été utilisé pour traiter les photos, obtenir le champ de déplacement et analyser les résultats. Un intérêt particulier a concerné l’orientation des contacts, le tenseur de fabrique et son évolution durant le chargement. L'impact de certains facteurs clés tels que la densité de compactage, la pression de confinement, la taille des plateaux de chargement, la taille des particules et l’épaisseur des échantillons sur la déformation des échantillons ont été étudiés. Une attention particulière s’est portée sur les grains subissant une rupture. Nous avons déterminé le nombre de contact sur ces grains et les avons reproduits, dans le modèle numérique (grain 3D) soumis à un chargement diamétral, par le biais de contraintes cinématiques
The mechanical behaviour of granular materials is deeply related to both the individual particle properties and to the assembly of grains (fabric, void distribution …). Subjected to an external loading, the assembly deforms which is not only dependent on relative grain displacements but also on the grain deformation and to grain breakage when occurring. Experimental and numerical studies of single particles were performed. Four approximately spherical particles of light expanded clay were tested to investigate the breakage phenomenon under diametric displacement-controlled compression load. Photos were taken with a frame rate of 4 images per second during the testing. Since the interior of a heterogeneous particle has significant influence on the failure initiation, an X-Ray micro tomography system was used to scan particles. Moreover, the post-processing enables us to obtain the real 3D volumetric structure. Then a 3D numerical model including pore structure was built in Abaqus for the same loading conditions. A comparison of results from laboratory tests and simulations was made. Based on the results, the crack initiation process, its location and classification of particle failures were set. For purpose of understanding the anisotropy and in particular fabric of packing of granular material when disturbed under external loading, five biaxial compression tests were performed on an assembly of approximately spherical particles settled in a chamber under confining pressure. During the test, photos were taken by the camera and saved to a computer at periodic intervals. Software written with Matlab codes was used to process the photos, determine the displacement field and analyse the results. Focus on contact orientation, fabric tensor and its evolution during testing were put on. Impact of some key factors such as packing density, confining pressure, sizes of the covers, sizes of the particles and thickness of samples on the packing characteristic were analysed. In order to understand mechanical behaviour and kinematic of multiple particles under external load considering particle breakage, six biaxial compression tests were performed on an assembly of approximately spherical particles. Photos were taken to record the location of each particle during the tests. Software written with of Matlab codes was used to process the photos and trace the displacement of all particles in order to analyze kinematical behaviour of the particles. A particular attention was payed to given particles subjected grain breakage within the assembly. Their contacts and relative displacements were introduced in the numerical model of single grain breakage and conclusions were derived
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19

Damineli, Bruno Luís. "Conceitos para formulação de concretos com baixo consumo de ligantes: controle reológico, empacotamento e dispersão de partículas." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3146/tde-19092014-103459/.

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Devido à demanda dos países em desenvolvimento, a produção de cimento e as emissões de CO2 relacionadas aumenta progressivamente, colocando esta indústria sob pressão devido às preocupações com o aquecimento global. Como diminuir a produção não é uma opção sustentável do ponto de vista social, deve-se primar pela diminuição dos impactos ambientais mantendo-se o aumento da produção. Porém, as principais estratégias de redução das emissões substituição de clínquer por adições, aumento da eficiência de fornos e uso de combustíveis alternativos não são capazes de uma redução que compense o crescimento da produção, mesmo com a disseminação dos maiores esforços industriais possíveis, devido a limites tecnológicos e de disponibilidade de materiais. A captura e sequestro de carbono, por sua vez, pode vir a aumentar significativamente o custo do cimento, prejudicando justamente os países mais necessitados. Novas alternativas são necessárias. Uma delas, ainda pouco desenvolvida, é o aumento da eficiência do uso dos ligantes em materiais cimentícios, como os concretos. Esta tese tem o objetivo de explorar o potencial desta estratégia para contribuir à mitigação das emissões de CO2 da cadeia concreto/cimento. O êxito nesta tarefa tem relação direta com o uso de ferramentas de empacotamento e dispersão de partículas para permitir comportamento reológico adequado à aplicação com uso de menor teor de água na mistura. O trabalho foi dividido em três etapas: 1) levantamento de dados para criação de benchmark da tecnologia atual de concretos com relação e eficiência no uso dos ligantes através de dois indicadores de eficiência Índice de Ligantes (IL) e Índice de CO2 (IC); 2) levantamento da teoria de empacotamento e dispersão de partículas; e 3) estudo experimental demonstrando como a eficiência do uso dos ligantes pode ser aumentada através da aplicação dos conceitos da etapa 2, do controle mais preciso do comportamento reológico e do uso de finos inertes para substituir clínquer para obtenção de parâmetros reológicos. Concluiu-se que o potencial de aumento da eficiência é superior a 50%. Porém, sua implantação em escala comercial dependeria de aumento do controle tecnológico das dosagens de concreto e de profundas modificações na cadeia produtiva e na definição de agregados, fillers, cimento e ligantes.
Due to the increasing demand of developing countries, cement production and related CO2 emissions increases steadily, putting industry under pressure due to global warming constraints. As decreasing production is not a sustainable option from social point of view, environmental loads need to be decreased even maintaining the increase of production. However, current strategies for reducing emissions clinker replacement by mineral additions, increase of kiln efficiency and the use of alternative fuels are not capable of a reduction which could compensate the increasing in production, even with the dissemination of highest industrial efforts due to technological and materials availability limits. Carbon capture and storage, by the time, could increase significantly cement cost, which could harm exactly the neediest countries. New alternatives are needed. One of them, few developed yet, is increasing the efficiency of binder use on cementitious materials, such as concretes. This thesis has the aim of exploring the potential of this strategy for contributing to the mitigation of CO2 emissions of concrete/cement chain. The success in this task is directly related to the use of tools of packing and dispersion of particles for allowing an adequate rheological behavior for the application but with a lower water content in the mixture. The thesis was divided in three main steps: 1) literature research for creating a benchmark of current concrete technology in terms of binder efficiency by two efficiency indexes Binder Intensity (BI) and CO2 Intensity (CI); 2) research of particles packing and dispersion theory; and 3) experimental planning for demonstrating how the binder use efficiency can be significantly increased by the use of concepts from step 2, a more precise rheological behavior control and the use of inert fillers for replacing clinker to obtain rheological parameters. It could be concluded that the potential of efficiency increase is higher than 50%. However, the implantation in commercial scale would depend on the increase of technological control in concrete designs, and also on deep changes in the productive chain and in the definitions of aggregates, fillers, cement and binders.
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20

Eid, Mohd Nabil. "Proposal of a Mix Design Method for Low Cement Fiber Reinforced Concrete." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40586.

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Concrete, the second most used material in the world, presents great performance and economic benefits. Yet, it is often characterized by a brittle behaviour, low tensile strength, and toughness. Fibers are usually added to concrete to counteract its brittle behaviour, increasing ductility and toughness, controlling crack propagation and delaying concrete failure. However, their addition significantly worsens the fresh state performance of the material. To improve fresh state of the so-called Fiber Reinforced Concrete (FRC), conventional mix-design methods recommend the use of high paste content, which results in a significant increase of Portland cement (PC) content and raises the carbon footprint of the material. The latter is responsible for 8% of the global annual carbon dioxide (CO2) anthropogenic emissions. Given the current worldwide concerns on global warming, the construction industry is in a need to lessen the demand, and thus production of PC. Recent studies have been focusing on the use of advanced mix-design techniques (i.e. particle packing models- PPMs) along with Inert Fillers (IF) as an alternative to reduce PC content in concrete. However, the latter was not applied to conventional FRC. In this work, advanced mix design techniques (i.e. PPMs) are used to overcome the aforementioned issues and mix-proportion eco-efficient FRC with low cement content (< 300 kg/m3). Fresh (i.e. VeBe time, slump, rheological behaviour) and hardened (i.e. compressive strength, and flexural behaviour) state tests were performed on the proposed mixtures and compared with control high PC content (375 kg/m3) FRC mixes. Results show that PPM designed mixes presented higher minimum torque (yield stress) but quite comparable apparent viscositiy when compared to conventionally designed mixtures. Moreover, the flowability (i.e. VeBe time, and slump) tends to decrease as fiber content, length, and/or as the amount of fillers increase in the mixtures. In addition, PPM mixes exhibited a shear thinning behaviour following the Herschel-Bulkley model, which enables the design of FRC PPM mix-proportioned mixtures for applications requiring high torque regimes such as vibrated and/or pumped concrete. Finally, results show that the use of PPMs to mix proportion eco-efficient low cement FRC mixtures produced improved hardened (i.e. compressive strength, and flexural performance) state behaviour with lower environmental impact than conventional ACI designed FRC mixtures.
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21

Campos, Renan Serralvo. "Concreto autoadens?vel produzido com res?duos de constru??o e demoli??o: propriedades mec?nicas e reol?gicas." Pontif?cia Universidade Cat?lica de Campinas, 2017. http://tede.bibliotecadigital.puc-campinas.edu.br:8080/jspui/handle/tede/919.

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES
The high consumption of natural resources and energy, coupled with the significant amount of solid waste generated by the construction activities, makes this sector one of the most responsible for environmental impacts. The recycling of mineral fraction of construction and demolition wastes (CDW), in form of aggregates, is seen as an alternative to reduce these impacts. In this way, the aim of this study was to investigate the influence of recycled aggregates on the rheological, mechanical properties, physical indexes and surface finish of self-compacting concrete (SCC). For this, eight compositions of SCC were analyzed, using the Repette-Melo method and Alfred model, which is based on the concept of particle packing, for the mix design of concretes. Thus, two reference mixtures, composed only of natural aggregates, were established. The other mixtures used recycled fine and/or coarse aggregates instead of natural aggregates, at 20% by mass. The properties of fresh concrete were evaluated with respect to the flowability, viscosity (measure of the speed of flow), passing ability and segregation resistance. In hardened state, compressive strength, splitting tensile strength, static modulus of elasticity, water absorption by immersion and by capillarity, density and voids index were determined. In this study, rheological characterization of cement pastes and mortars destined to the production of SCC was also carried out using rotational rheometry. Rheological characterization of pastes, mortars and concretes is a suitable way to evaluate the behavior of these composites in fresh state, providing useful information that will aid in mix design process and quality control. Another property evaluated was the surface finish of concretes and mortars and the possible correlation of this with the rheological parameters. Through the results obtained it was possible to verify the loss of fluidity in mortars and concretes that used recycled aggregates. Regarding the mechanical properties, different behaviors were observed in concretes produced with recycled aggregates: those that were dosed by Repette-Melo method did not show a significant decrease of these properties; while the concretes dosed by the concept of particle packing exhibited a great reduction in mechanical properties. Concretes produced with recycled aggregates still showed an increase in water absorption by immersion, voids index and capillary absorption, when comparing to the respective reference mixtures. It was possible to observe a good linear correlation between surface finish and shear stress of mortars. In the case of concretes, the slump-flow was the property that best correlated with the quality of surface finish.
O elevado consumo de recursos naturais e energia, associado ao expressivo montante de res?duos s?lidos gerados pelas atividades de constru??o civil faz deste setor um dos maiores respons?veis por impactos ambientais. A reciclagem da fra??o mineral dos res?duos de constru??o e demoli??o (RCD), na forma de agregados, ? vista como uma alternativa para a diminui??o destes impactos. Isto posto, o objetivo deste estudo foi investigar a influ?ncia dos agregados reciclados nas propriedades reol?gicas, mec?nicas, ?ndices f?sicos e no acabamento superficial de concretos autoadens?veis (CAA). Para isso, foram analisadas oito composi??es de CAA, sendo empregados o m?todo de Repette-Melo e o modelo de Alfred, que tem por base o conceito de empacotamento de part?culas, para a dosagem dos concretos. Assim, foram estabelecidos dois tra?os de refer?ncia, compostos apenas por agregados naturais. As demais misturas utilizaram agregados mi?dos e/ou gra?dos reciclados em substitui??o aos agregados naturais, no teor de 20%, em massa. As propriedades do concreto fresco foram avaliadas no que diz respeito ao espalhamento, tempo de escoamento, habilidade passante e resist?ncia ? segrega??o. No estado endurecido foram determinadas as resist?ncias ? compress?o e ? tra??o por compress?o diametral, o m?dulo de elasticidade est?tico, a absor??o de ?gua por imers?o e por capilaridade, a massa espec?fica e o ?ndice de vazios. Neste estudo tamb?m foi realizada a caracteriza??o reol?gica das pastas de cimento e das argamassas destinadas ? produ??o dos CAA?s, por meio de reometria rotacional. A caracteriza??o reol?gica de pastas, argamassas e concretos ? uma forma adequada para avaliar o comportamento destes comp?sitos no estado fresco, podendo prover informa??es ?teis que auxiliar?o no processo de dosagem e controle de qualidade. Outra propriedade avaliada foi o acabamento superficial dos concretos e argamassas e a poss?vel correla??o deste com os par?metros reol?gicos. Atrav?s dos resultados obtidos foi poss?vel constatar perda de fluidez nas argamassas e concretos que empregaram agregados reciclados. No que tange as propriedades mec?nicas, foram observados comportamentos distintos nos concretos produzidos com agregados reciclados: ?queles dosados pelo m?todo de Repette-Melo n?o apresentaram decr?scimo significativo destas propriedades; enquanto que, os concretos dosados com base no conceito de empacotamento de part?culas exibiram grande redu??o nas propriedades mec?nicas avaliadas. Os concretos produzidos com agregados reciclados ainda apresentaram aumento na absor??o de ?gua por imers?o, no ?ndice de vazios e na absor??o capilar, quando comparados aos respectivos tra?os de refer?ncia. Foi poss?vel observar boa correla??o linear entre o acabamento superficial e a tens?o de cisalhamento das argamassas. No caso dos concretos, o di?metro de espalhamento foi a propriedade que melhor se correlacionou com a qualidade do acabamento superficial.
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22

Montenegro, Ana M. C. "Studies of column packings for polymer separations by size exclusion and interactive chromatography." Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/11754.

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The chromatographic behaviour of a new column packing for high performance size exclusion chromatography based on crosslinked polyacrylamide particles was studied. Experimental retention data for poly(ethylene glycol)and poly(ethylene oxide) standards in water and water-methanol mixtures showed that the separation mechanism is size exclusion, since a universal calibration plot based on hydrodynamic volume was obtained. For polysaccharide standards in water and water-methanol (80/20), the universal calibration was valid for molecular weights above 4 * 10~. Below this value, secondary mechanisms appear to be taking part in the separation since water-methanol (80/20) is a poor solvent for polysaccharides. Crosslinked polyacrylamide packings showed an interactive behaviour with tetrahydrofuran and dimethylformamide as eluents with polystyrene and poly( ethylene glycol )/poly(ethylene oxide) standards and the universal calibration was not valid.
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23

Weyers, Megan. "Optimised mix composition and structural behaviour of Ultra-High-Performance Fibre Reinforced Concrete." Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/73097.

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The overall objective of this study was to develop an optimised Ultra-High-Performance Concrete (UHPC) matrix based on the modified Andreasen and Andersen optimum particle packing model by using available South African materials. The focus of this study was to determine the optimum combined fibre and superplasticiser content for UHPC by using a response surface design. The UHPC was appropriately designed, produced and tested. Various changes in mechanical properties resulting from different combinations of steel fibre and superplasticiser contents was investigated. The flowability, density and mechanical properties of the designed UHPC were measured and analysed. Both the fibre and superplasticiser content play a significant role in the flowability of the fresh concrete. The addition of fibres significantly improved the strength of the concrete. The results show that the superplasticiser content can be increased if a more workable mix is required without decreasing the strength significantly. The statistical analysis of the response surface methodology confirms that the designed models can be used to navigate the design space defined by the Central Composite Design. The optimum combined fibre and superplasticiser content depend on the required mechanical properties and cost. Using the modified Andreasen and Andersen particle packing model and surface response design methodology, it is possible to efficiently produce a dense Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC) with a relatively low binder amount, low fibre content and good workability. The effect of heat curing on the mechanical properties was investigated. It was concluded that heat curing is not recommended when considering the long-term strength development. The estimated strength development of concrete obtained by using the fib Model Code 2010 (2013) does not incorporate the detrimental effect of high curing temperatures on long-term strength and therefore overestimate the long-term strengths. The strength estimates for both early and long-term ages can be improved by considering this effect in the strength development functions obtained from fib Model Code 2010 (2013). The effect of specimen size on the compressive and flexural tensile strength of UHPFRC members were established. It was found that the specimen size has a significant effect on the measured cube compressive strength. Smaller beam specimens showed higher ductility compared to those of the larger beam specimens. The crack width decreased as the beam’s depth decreased. A lower variability was experienced in the beams with limited depth (< 45 mm). Further testing is required to determine whether a span-to-depth ratio of 10 would yield optimum results. The utilisation of by-products, such as undensified silica fume and fly ash, as cement replacement materials makes UHPFRC sustainable, leading to a reduced life-cycle cost. The calculated Embodied Energy per unit strength (EE/unit strength) and Embodied Carbon per unit strength (EC/unit strength) values for the UHPFRC mixture yield lower values compared to that of the 30 MPa concrete mixture, indicating that UHPFRC can be used to reduce the environmental footprint of the concrete industry. The inverse analysis method used was successful in providing an improved simplified stress-strain response for the UHPFRC. The analysis provided valuable information into the stress-strain, load-deflection and moment-curvature responses of the UHPFRC. Standard material test results were used to theoretically calculate moment-curvature responses and were then compared to the experimental results obtained. The study demonstrated that it is possible to efficiently produce a dense and workable UHPFRC with relatively low binder amount and low fibre content. This can result in more cost-effective UHPFRC, thus improving the practical application thereof.
Dissertation (MEng)--University of Pretoria, 2020.
Civil Engineering
MEng (Structural engineering)
Unrestricted
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24

Champagne, Victor K. III(Victor Kenneth). "Energy dissipation in shape memory zirconia particles, packings, and composites." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123621.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 47-49).
This research project lies at the intersection of two classes of materials, namely superelastic materials and granular materials, each known for their ability to dissipate large amounts of kinetic energy. Because of their energy-absorbing properties, superelastic granular materials are of interest for development into applications involving force protection. Quasi-static, closed-die compression tests were conducted on granular packings of ceria-doped zirconia, a material which is well-known to exhibit shape memory and superelastic behavior. The doping level of ceria in the zirconia system was controlled to experimentally determine the mole percent for optimal energy dissipation in a granular packing. Various particle size distributions were selected to study mechanisms of energy dissipation in a granular packing including particle friction, fracture, and martensitic phase transformation. To study the behavior of encapsulated shape memory and superelastic zirconia particles, composites were fabricated using polyurea as a matrix material, and the bonding between the zirconia particles and polyurea matrix was studied along with mechanical properties. Finally, the effect of high strain rate impact was observed on ceria-doped zirconia pellets using laser induced particle impact testing (LIPIT) which launches single, micron-sized particles at high velocities. This thesis provides further insight into the mechanical behavior of granular superelastic ceramics under different constraints and loading conditions while optimizing for energy dissipation.
by Victor K. Champagne III.
S.M.
S.M. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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25

Carleen, Bradford J. "Hydrothermal Synthesis Process for the Production of Silicalite-1 Crystal Aggregate Packing Particles." Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-theses/137.

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Methyl Tertiary-Butyl Ether (MTBE) contamination of groundwater and surface waters has become a relevant environmental and public safety concern in recent years. This anthropogenic compound is now persistent at low concentrations in several valuable ground and surface water locations within the United States due largely to the widespread production of MTBE for use as a fuel oxygenate in conjunction with negligent underground storage practices during the 1980's and 1990's. Though there are several treatment strategies for the remediation of MTBE spill sites, the most efficient strategy may be adsorption of MTBE by a packed column of silicalite-1 adsorbent. Effective adaption of this technology requires cheap production of silicalite-1 sorbent packing particles on the order of 3 millimeters diameter. This work entails the development of a new synthesis process which results in sufficient in-situ crystallization of silicalite-1 aggregates within a 3 millimeter spherical amorphous silica gel source. The crystal aggregates sizes can be tuned from 5 to 70 µm, depending on synthesis parameters, and the finished silicalite-1 aggregate particle takes the shape of the amorphous gel source. These aggregate particles, when containing a small amorphous core, should be suitable for packed adsorption column applications. Multiple hydrothermal synthesis experiments were performed by batch methods featuring silica gel spheres as the sole silica source for the batch. Zeolite nucleation and crystal growth were demonstrated throughout the amorphous bead. Synthesis parameters were optimized both for short synthesis times, optimal mechanical properties, and cost effectiveness. The influence of product crystal size on particle hardness was also investigated. The packing production process is sufficiently ready for supporting pilot scale adsorption studies.
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26

Joo, Sung Chul. "Adhesion mechanisms of nano-particle silver to electronics packaging materials." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31730.

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27

Bjorklund, Chad Christopher. "The effects of nucleosome core particle packaging on DNA charge transport." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Fall2006/c_bjorklund_120606.pdf.

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28

Karimi, Kamran. "Quenched Stresses And Linear Elastic Response Of Random Packings Of Frictionless Particles Near Jamming." Research Showcase @ CMU, 2014. http://repository.cmu.edu/dissertations/356.

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We study stress correlations and elastic response in large-scale computer simulations of particle packings near jamming. We show that there are characteristic lengths in both the stresses and elastic response that diverge in similar ways as the confining pressure approaches zero from above. For the case of the stress field, we show that the power spectrum of the hydrostatic pressure and shear stress agrees with a field-theoretic framework proposed by Henkes and Chakraborty [15] at short to intermediate wavelengths (where the power is flat in Fourier space), but contains significant excess power at wavelengths larger than about 50 to 100 particle diameters, with the specific crossover point going to larger wavelength at decreasing pressure, consistent with a divergence at p=0.These stress correlations were missed in previous studies by other groups due to limited system size. For the case of the elastic response, we probe the system in three ways: i) point forcing, ii) constrained homogeneous deformation where the system is driven with no-slip boundary conditions, and iii) free periodic homogeneous deformation. For the point force, we see distinct characteristic lengths for longitudinal and transverse modes each of which diverges in a different way with decreasing pressure with ET⇠p-1/4 and EL⇠p -0.4 respectively. For the constrained homogeneous deformation we see a scaling of the local shear modulus with the size of the probing region consistent with E⇠p-1/2 similar to the EL⇠p-0.4 observed in the longitudinal component of the point response and in perfect agreement with the rigidity length discussed in recently proposed scenarios for jamming. Finally, we show that the transverse and longitudinal contributions to the strain field in response to unconstrained deformation (either volumetric or shear) have markedly different behavior. The transverse contribution is surprisingly invariant with respect to p with localized shear transformations dominating the response down to surprisingly small pressures. The longitudinal contribution develops a feature at small wavelength that intensifies with decreasing p but does not show any appreciable change in length. We interpret this pressure-invariant length as the characteristic shear zone size.
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29

Brown, Eric L. "A quadratic partial assignment and packing model and algorithm for the airline gate assignment problem." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-07212009-040541/.

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30

Olmedilla, González de Mendoza Antonio. "Grain motion and packing : application to metallic alloy solidification." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0265/document.

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La modélisation multi-échelle multi-physique de la solidification d'alliages métalliques demande de combiner des phénomènes à l'échelle macroscopique du produit et microscopiques à l'échelle des structures de solidification. Dans cette thèse, l'empilement aléatoire des grains équiaxes avec des morphologies typiques de solidification est étudié. Nous mettons tout d'abord en évidence les paramètres hydrodynamiques adimensionnels qui régissent l'empilement de grains équiaxes : le nombre de Stokes, St, le nombre d'Archimède, Ar, et le rapport entre le temps caractéristique de la croissance et le temps caractéristique du mouvement, Γ. Un dispositif expérimental a été conçu par similitude hydrodynamique avec le phénomène réel de l'empilement de la solidification afin d'étudier l'influence de la géométrie des grains équiaxes et l'influence des conditions hydrodynamiques sur la fraction d'empilement. En outre, un outil numérique basé sur le méthode des éléments discrets a été développé pour compléter le travail expérimental de détermination de : la fraction d'empilement locale, le nombre de particules voisines en contact et l'orientation des particules. Des fractions d'empilement entre environ 0,53 et 0,67 ont été mesurées et calculées pour les grains sphériques non-cohésifs, alors que des valeurs allant jusqu'à environ 0,30 sont trouvées pour les grains dendritiques non-cohésifs. Enfin, nous étudions la dynamique de l'empilement, qui est la transition d'un régime de sédimentation à l'équilibre mécanique. L'évolution des variables comme la fraction locale de solide, le nombre de particules voisines en contact et l'orientation du grain en fonction du temps est présentée
Solidification multiphase multiscale modeling of metal alloys is based on the combination of the phenomena at the macroscopic scale of the product and at the microscopic scale of the solidification structures. In this thesis, the random packing of the typical equiaxed grain morphologies in metal alloy solidification is investigated. Firstly, we highlight the hydrodynamic dimensionless parameters governing the grain packing in the melt: the Stokes number, St, the Archimedes number, Ar, and the growth-to-motion ratio, Γ. Subsequently, an experimental setup is designed by hydrodynamic similarity with the actual solidification packing phenomenon in order to investigate the influence of the equiaxed grain geometry and the hydrodynamic conditions on the average solid packing fraction. Additionally, a numerical Discrete Element Method tool is developed to complement the experimental work by accessing to those granular variables which result difficult to be experimentally obtained such as the local packing fraction, the contacting neighbors and the particle orientation. Packing fractions between approximately 0.53 and 0.67 are measured and computed for the spherical noncohesive grains, for different hydrodynamic, frictional and polydispersity conditions, whereas values down to approximately 0.30 are found for noncohesive dendrite envelopes. Finally, we investigate the packing dynamics, which is the transition from a sedimentation regime to the mechanical equilibrium (packing). The evolution of the local solid fraction, contacting neighbors, mechanical contacts and grain orientation are given
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31

Elfmarková, Veronika. "Vliv jemnozrnných příměsí na charakter pórového systému betonu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-225906.

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Literature does not provide a satisfactory answer to maximum and minimum particle size or the particle size of the mortar phase especially for optimal porosity of concrete. To overcome the shortcomings of the design methods were thought to design a new method for design of concrete mix. This idea is based on a complex analysis of powder materials (determination of granular properties, shape factor of fillers, porosity, packing of powder materials, surface area, etc.) and subsequently to assess the influence to pore system of concrete and physical and mechanical properties in hardened state of concrete. In this work are presented and analyzed two types of fillers – fly ash and limestone dust.
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32

Peña, Olarte Andrés Alfonso. "Influence of particle shape on the global mechanical response of granular packings : micromechanical investigation of the critical state in soil mechanics /." Stuttgart : IGS, 2008. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016794124&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.

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33

Pizzato, Massimo. "Retroviral vectors for gene therapy : characterisation of vector particle-cell interaction and development of novel packaging cell lines." Thesis, Institute of Cancer Research (University Of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313365.

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34

Cerqueira, Alex da Silva. "Uso de planejamento granulométrico para a preparação de dispersões aquosas para colagem em fitas de alumina." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-15072013-154810/.

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Este trabalho apresenta o uso de planejamento granulométrico na preparação e caracterização de suspensões concentradas de alumina em meio aquoso, que posteriormente deverão ser utilizadas para a conformação por colagem em fitas - processo de tape casting. A suspensão foi preparada utilizando-se duas ou mais distribuições granulométricas diferentes na sua formulação, a fim de promover a otimização do empacotamento de partículas. As condições para estabilização das suspensões preparadas foram obtidas por meio de estudos de comportamento reológico e através de curvas isotermas de adsorção, por meio de medidas de viscosidade em função da concentração de aditivo dispersante e de medidas de mobilidade eletroforética dinâmica, respectivamente. Os valores mostram a qualidade dos dados obtidos nas simulações quanto aos valores de IPS calculados, em função de uma quantidade de água pré estabelecida de 35% em volume, ficando em média próximo do valor de 0,150µm, para as formulações simuladas. Desta forma foi possível preparar uma suspensão concentrada com empacotamento de partículas otimizado podendo chegar a um valor máximo de 60% em volume de sólidos, com possibilidades de minimizar os possíveis efeitos adversos da retração durante a secagem e queima dos filmes.
This paper presents the use of grain size in the pack planning for preparation and characterization of a concentrated suspension of alumina in aqueous medium, which subsequently will be used for the conformation by tape casting process. The suspension was prepared using two or more different particle size distributions in the formulation to promote the optimization of particle packing. The definitions of stability and rheological behavior of dispersion curves were made by adsorption isotherms, by measuring electrokinetic mobility and viscosity curves as a function of concentration of additives, respectively. The results show the quality of data obtained in the simulations as the maximum values of IPS for each formulation. Then, it is possible to prepare a concentrated suspension with optimized particle packing and may reach a maximum value of 60% by volume of solids, with opportunities to minimize the possible adverse effects of shrinkage during drying of the films.
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35

Nguyen, Thanh Hai. "Modélisation numérique et rhéologie des matériaux à particules déformables." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT273/document.

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Les matériaux à particules hautement déformables sont des formes complexes de matière avec de nombreuses applications en chimie, pharmacie, cosmétique et agro-alimentaire. L’effet conjugué du désordre et des grandes déformations des particules conduit à des propriétés mécaniques nouvelles par rapport aux matériaux à particules indéformables. En particulier, la compressibilité et la résistance au cisaillement sont contrôlées par une combinaison de réarrangements et de changement de forme des particules. Dans ce travail de thèse, nous avons développé une approche numérique originale pour la simulation de ces systèmes. Pour permettre aux particules de se déformer indéfiniment, nous avons modélisé chaque particule par un agrégat de particules primaires sans frottement qui interagissent par une force d’attraction de type Lennard-Jones et une contrainte de non-interpénétration. La dissipation d’énergie par collisions inélastiques entre les particules primaires confère un caractère plastique aux déformations des particules. Nous avons utilisé ce modèle pour étudier les propriétés de compaction et de cisaillement de ces systèmes. Nos résultats ont permis de mettre en évidence le caractère non-linéaire de la compressibilité lorsque la compacité progressivement augmente au-delà de celles des assemblages de particules indéformables. Sous cisaillement, un état critique est atteint avec une dilatance contrôlée par la pression de confinement. Dans cet état, nous avons exploré les distributions des formes des particules, les textures et les distributions des forces pour différentes valeurs de la pression. Nous avons également comparé la compressibilité simulée par l’approche développée avec celle obtenue par la Méthode de Points Matériels (MPM) en utilisant des particules élastiques
Soft-particle materials are complex forms of matter that occur in numerous applications in chemical, pharmaceutical, cosmetic and food products. Joint effects of disorder and large particle deformations lead to novel mechanical properties that differ from those of rigid-particle materials. In particular, the compressibility and shear resistance depend on both particle rearrangements and their shape change. In this doctoral work, we developed an original approach for numerical simulation of these systems. To allow the particles to deform without breakage, each particle is modeled as an aggregate of frictionless primary particles interacting via a Lennard-Jones attraction force and impenetrability constraints. Energy dissipation by inelastic collisions between primary particles leads to the plastic nature of particle deformations. This model was used to investigate the compaction and shear behavior of soft-particle systems. We find that the compressibility is strongly nonlinear as the packing fraction increases beyond that of a random close packing of rigid particles. In continuous shearing, a critical state is reached with a dilatancy that depends on the confining pressure. In this state, we investigate the shear resistance, distributions of particle shapes, fabric properties and inter-particle forces as a function of the confining pressure. We also compare our results with those obtained by using the Material Point Method (MPM) with elastic particles
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36

Olivarez, Nicholas Paul. "Role of the Small Terminase Subunit Encoded by Staphylococcus Aureus Pathogenicity Island SaPI1 in Formation of SaPI1 Transducing Particles." VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/934.

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Staphylococcus aureus pathogenicity island SaPI1 is a genomic element that is mobilized and transduced at high frequency by helper phage 80α. SaPI1 encodes a small terminase protein that belongs to the phage small terminase subunit family. The presence of SaPI1-encoded small terminase suggests that it plays a role in SaPI1-specific packaging into transducing particles by complexing with the 80α large terminase subunit and redirecting recognition to a pac site on SaPI1 DNA from 80α DNA. The effects of deleting the small terminase genes in SaPI1 and in a prophage copy of 80α are consistent with this hypothesis. Induction of the 80α small terminase deletion mutant produces wild type levels of SaPI1 transducing particles, demonstrating that SaPI1 small terminase can replace that of 80a in SaPI1 packaging. Southern blot analysis of virion DNAs isolated from the deletion mutants confirms that SaPI1 redirects packaging of its DNA into SaPI1-sized capsids.
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37

Hegron, Lise. "Suivi par émission acoustique de la compaction de particules fragiles d' UO2." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4740/document.

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Une option à l'étude pour le recyclage des actinides mineurs consiste à en incorporer environ 10% à une matrice d'UO2. La présence de pores ouverts interconnectés au sein de ce combustible devrait permettre d'évacuer l'hélium et les gaz de fission pour prévenir le gonflement de la pastille et in fine son interaction avec la gaine qui l'entoure. La mise en oeuvre des actinides mineurs oblige à travailler en cellule blindée, à minimiser leur rétention et à proscrire les ajouts de produits organiques. L'emploi de particules fragmentables de quelques centaines de micromètres paraît une solution intéressante pour contrôler la microstructure des comprimés crus et ainsi maîtriser la porosité ouverte après frittage. L'étude consiste à suivre par émission acoustique la compaction de particules fragiles d'UO2 et à relier leurs caractéristiques à la porosité ouverte obtenue après frittage des compacts. Le signal acquis lors d'essais de cisaillement sur des granulés individuels et sur des compacts montre que l'émission acoustique autorise la détection de la fragmentation et permet l'identification d'une forme d'onde caractéristique. Les influences de la contrainte de compaction, de la distribution granulométrique initiale et de la cohésion interne des granulés, sur la tenue mécanique des compacts et sur la microstructure des frittés, en particulier sur la porosité ouverte sont analysées. Moyennant quelques précautions, l'émission acoustique, par sa capacité à déterminer le domaine de fragmentation des granulés pendant la mise en forme, paraît une technique prometteuse pour suivre la compaction de particules fragiles en vue de la fabrication de combustibles à porosité maîtrisée
One of the options considered for recycling minor actinides is to incorporate about 10% to UO2 matrix. The presence of open pores interconnected within this fuel should allow the evacuation of helium and fission gases to prevent swelling of the pellet and ultimately its interaction with the fuel clad surrounding it.Implementation of minor actinides requires working in shielded cell, reducing their retention and outlawing additions of organic products. The use of fragmentable particles of several hundred micrometers seems a good solution to control the microstructure of the green compacts and thus control the open porosity after sintering.The goal of this study is to monitor the compaction of brittle UO2 particles by acoustic emission and to link the particle characteristics to the open porosity obtained after the compact sintering.The signals acquired during tensile strength tests on individual granules and compacts show that the acoustic emission allows the detection of the mechanism of fragmentation and enables identification of a characteristic waveform of this fragmentation.The influences of compaction stress, of the initial particle size distribution and of the internal cohesion of the granules, on the mechanical strength of the compact and on the microstructure and open porosity of the sintered pellets, are analyzed.By its ability to identify the range of fragmentation of the granules during compaction, acoustic emission appears as a promising technique for monitoring the compaction of brittle particles in the manufacture of a controlled porosity fuel
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38

Cairnie, Mark A. Jr. "Bayesian Optimization of PCB-Embedded Electric-Field Grading Geometries for a 10 kV SiC MOSFET Power Module." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/103566.

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A finite element analysis (FEA) driven, automated numerical optimization technique is used to design electric field grading structures in a PCB-integrated bus bar for a 10 kV bondwire-less silicon-carbide (SiC) MOSFET power module. Due to the ultra-high-density of the power module, careful design of field-grading structures inside the bus bar is required to mitigate the high electric field strength in the air. Using Bayesian optimization and a new weighted point-of-interest (POI) cost function, the highly non-uniform electric field is efficiently optimized without the use of field integration, or finite-difference derivatives. The proposed optimization technique is used to efficiently characterize the performance of the embedded field grading structure, providing insights into the fundamental limitations of the system. The characterization results are used to streamline the design and optimization of the bus bar and high-density module interface. The high-density interface experimentally demonstrated a partial discharge inception voltage (PDIV) of 11.6 kV rms. When compared to a state-of-the-art descent-based optimization technique, the proposed algorithm converges 3x faster and with 7x smaller error, making both the field grading structure and the design technique widely applicable to other high-density high-voltage design problems.
M.S.
Innovation trends in electrical engineering such as the electrification of consumer and commercial vehicles, renewable energy, and widespread adoption of personal electronics have spurred the development of new semiconductor materials to replace conventional silicon technology. To fully take advantage of the better efficiency and faster speeds of these new materials, innovation is required at the system-level, to reduce the size of power conversion systems, and develop converters with higher levels of integration. As the size of these systems decreases, and operating voltages rise, the design of the insulation systems that protect them becomes more critical. Historically, the design of high-density insulation system requires time-consuming design iteration, where the designer simulates a case, assesses its performance, modifies the design, and repeats, until adequate performance is achieved. The process is computationally expensive, time-consuming, and the results are not easily applied to other insulation design problems. This work proposes an automated design process that allows for the streamlined optimization of high-density insulation systems. The process is applied to a 10 kV power module and experimentally demonstrates a 38\% performance improvement over manual design techniques, while providing an 8 times reduction in design cycle time.
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39

Cao, Hong Ha. "The fabrication process of microfluidic devices integrating microcoils for trapping magnetic nano particles for biological applications." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112150/document.

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Le but de cette étude est de concevoir, fabriquer et caractériser une puce microfluidique afin de mettre en oeuve la capture de nanoparticules magnétiques fonctionnalisées en vue de la reconnaissance d’anticorps spécifiques (couplage d’une très grande spécificité et sensibilité). Après avoir modélisé et simulé les performances de la microbobine intégrée dans le canal de la puce microfluidique en prenant soin de limiter la température du fluide à 37°C, la capture devant être effective, le microsystème est fabriqué en salle blanche en utilisant des procédés de fabrication collective. La fabrication du microdispositif en PDMS a aussi donné lieu à l’optimisation de procédés de modification de surface afin d’assurer la ré-utilisation du microdispositif (packaging réversible) et la limitation de l’adsorption non spécifique. L’immobilisation des anticorps su les billes (300 nm) a été menée à l’intérieur du canal en utilisant un protocole de type ELISA éprouvé. Le procédé a montré qu’il était également efficient pour cet environnement puisque nous avons pu mettre ne évidence la capture de nanoparticules
In this study, a concept of microfluidic chip with embedded planar coils is designed and fabricated for the aim of trapping effectively functionalized magnetic nanobeads and immobilizing antibody (IgG type). The planar coils as a heart of microfluidic chip is designed with criterion parameters which are optimized from simulation parameters of the maximum magnetic field, low power consumption and high power efficiency by FE method. The characterization of microcoils such as effectively nanobeads (300 nm) at low temperature (<37oC) is performed and confirmed. The channel network in PDMS material is designed for matching with entire process (including mixing and trapping beads) in microfluidic chip. A process of PDMS’s surface modification is also carried out in the assemble step of chip in order to limit the non-specific adsorption of many bio substances on PDMS surface. The microfluidic chip assemble is performed by using some developed techniques of reversible packaging PDMS microfluidic chip (such as stamping technique, using non-adhesive layer, oxygen plasma combining with solvent treatment). These packaging methods are important to reused microchip (specially the bottom substrate) in many times. The immobilization of antibody IgG-type is performed inside microfluidic chip following the standard protocol of bead-based ELISA in micro test tube. The result showed that IgG antibodies are well grafted on the surface of carboxyl-beads (comparing to result of standard protocol); these grafted antibodies are confirmed by coupling them with labeled second antibody (Fab-FITC conjugation)
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40

Kamp, William Hermanus Michael. "Redundant Number Systems for Optimising Digital Signal Processing Performance in Field Programmable Gate Array." Thesis, University of Canterbury. Electrical and Computer Engineering, 2010. http://hdl.handle.net/10092/4623.

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Speeding up addition is the key to faster digital signal processing (DSP). This can be achieved by exploiting the properties of redundant number systems. Their expanded symbol (digit) alphabet gives them multiple representations for most values. Utilising redundant representations at the output of an adder permits addition to be performed without carry-propagation, yielding fast, constant time performance irrespective of the word length. A resource efficient implementation of this fast adder structure is developed that re-purposes the fast carry logic of low-cost field programmable gate arrays (FPGAs). Experiments confirm constant time addition and show that it outperforms binary ripple carry addition at word lengths of greater than 44 bits in a Xilinx Spartan 3 FPGA and 24 bits in an Altera Cyclone III FPGA. Redundancy also provides other properties that can be exploited for performance gain. Some redundant representations will have more zero-symbols than others. These maximise the opportunities to exploit the multiplicative absorbing and additive identity properties of zero that when exercised reduce superfluous calculations. A serial recoding algorithm is developed that generates a redundant representation for a specified value with as few nonzero symbols as possible. Unlike previously published methods, it accepts a wide specification of number systems including those with irregularly spaced symbol alphabets. A Markov analysis and analysis of the elementary cycles in the formulated state machine provides average and worst case measures for the tested number system. Typically, the average number of non-zero symbols is less than a third and the worst case is less than a half. Further to the increase in zero-symbols, zero-dominance is proposed as a new property of redundant number representations. It promotes a set of representations that have uniquely positioned zero-symbols, in a Pareto-optimal sense. This set covers all representations of a value and is used to select representations to optimise the calculation of a dot-product. The dot-product or vector-multiply is a fundamental operation in DSP, since it is employed in filtering, correlation and convolution. The nonzero partial products can be packed together, substantially reducing the calculation time. The application of redundant number systems provides a two-fold benefit. Firstly, the number of nonzero partial products is reduced. Secondly, a novel opportunity is identified to use the representations in the zero-dominant set to optimise the packing further, gaining an extra 18% improvement. An implementation of the proposed dot-product with partial product packing is developed for a Cyclone II FPGA. It outperforms a quad-multiplier binary implementation in throughput by 50% . Redundant number systems excel at increasing performance in particular DSP subsystems, those that are numerically intensive and consist of considerable accumulation. The conversion back to a binary result is the performance bottleneck in the DSP algorithm, taking a time proportional to a binary adder. Therefore, redundant number systems are best utilised when this conversion cost can be amortised over many fast redundant additions, which is typical in many DSP and communications applications.
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41

Rebmann, Markus Samuel. "Durabilidade de concretos estruturais com baixo consumo de cimento Portland e alta resistência." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-10062011-150726/.

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Este trabalho apresenta um estudo sobre a confecção de concretos estruturais com baixo consumo de cimento Portland e avalia algumas das suas propriedades no estado fresco e endurecido, tanto em termos mecânicos como de durabilidade. O uso de concretos de baixo consumo de cimento Portland tem por objetivo possibilitar maior sustentabilidade da indústria da construção baseada no concreto, como maior longevidade de jazidas, reduções na emissão de \'CO IND.2\' e no consumo de energia e menores custos de transporte. Possibilita também diversas melhorias técnicas, como menor retração, fissuração e calor de hidratação. Com base em conceitos de empacotamento e dispersão de partículas, uso de adições minerais e fílers e escolha adequada dos materiais, obtiveram-se concretos com baixo consumo de cimento e alta resistência, com consumo relativo de materiais aglomerantes inferior a 5 kg/\'M POT.3\' para produzir 1 MPa de resistência à compressão. Avaliaram-se diversos parâmetros relacionados à durabilidade destes concretos com base em ensaios de absorção de água por imersão, absorção de água por capilaridade, permeabilidade, abrasão, carbonatação e potencial de corrosão. Os resultados obtidos indicam que os concretos de baixo consumo de cimento obtidos podem ter durabilidade comparável ou até superior a concretos usualmente considerados como de bom desempenho. Observou-se que a durabilidade é dependente do tipo de cimento empregado e que deve ser avaliada especificamente com relação ao tipo de ação agressiva a que o concreto estará exposto.
This dissertation presents a study on the development of structural concrete with low Portland cement consumption and evaluates some of its fresh and hardened properties, in mechanical and durability terms. The use of low concrete Portland cement consumption is intended to enable greater sustainability of the construction industry based on concrete, as increased longevity of deposits, reductions in \'CO IND.2\' emissions and energy consumption and lower transportation costs. It also allows several technical improvements, such as reduced shrinkage, cracking and hydration heat. Based on particle packaging and dispersion, use of mineral additives and fillers and appropriate choice of material, concrete with low cement content and high strength was obtained, with relative consumption of binder materials below 5 kg/\'M POT.3\' to produce 1 MPa compressive strength. Various durability parameters were evaluated based on tests such water absorption by immersion, water absorption by capillarity, permeability, abrasion, corrosion potential and carbonation. The results indicate that the low cement consumption concretes may have achieved comparable or superior durability to concrete usually regarded as good performance. It was observed that the durability is dependent on the type of cement used and that durability should be assessed specifically with regard to the type of aggressive action that the concrete will be exposed.
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42

Hernando, Louis. "Sédimentation de suspensions non-colloïdales poly-dispersés et concentrées." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14490/document.

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De la pâte à dentifrice au moût de fermentation en passant par la peinture, le lit d’une rivière, le propergol d’un réacteur de fusée et le sang, les suspensions sont présentes dans de nombreux usages de notre vie courante. La maîtrise de leur mise en œuvre notamment nécessite la compréhension de leur comportement et constitue un des challenges de la recherche. Dans le présent travail de thèse, nous nous sommes intéressés au processus de sédimentation de suspensions concentrées de particules non-colloïdales et inertes dont la distribution de taille est mono, bi ou tri-disperse. Deux types de sédimentation ont été étudiés : la décantation et l’alimentation continue. L’objectif est de mener une étude expérimentale et dans une moindre mesure numérique pour caractériser de la façon la plus complète possible la sédimentation avec une attention particulière à la structure de l’écoulement et du dépôt, aux profils de concentration et à la détermination des modes de sédimentation. Les moyens expérimentaux utilisés sont les techniques usuelles de mesure bidimensionnelle (vélocimétrie laser et visualisation directe) qui autorisent l’acquisition de données d’intérêt pour des configurations où les particules évoluent dans le plan. Ces techniques laser ont été améliorées pour permettre le suivi simultané de populations de différentes particules et l’accès à des grandeurs diverses telles que le champ de vitesse de l’écoulement, la fraction volumique locale, et les vitesses des divers fronts de sédimentation. En parallèle, un outil numérique simple a été construit, utilisant la Dynamique Stokesienne et saisissant l’essentiel des phénomènes physiques mis en jeu menant à la modélisation des interactions hydrodynamiques
From toothpaste to must of fermentation passing by painting, bed of a river, propellant of an rocket engine and blood, suspensions are present in many uses of our everyday life. The control of their implementation requires comprehension of their behavior and constitutes one of the challenges of nowadays research. In this work of thesis, we were interested in the sedimentation process of concentrated suspensions of non-colloidal and inert particles whose size distribution is mono, bi or tri-disperse. Two types of sedimentation were studied: decantation and thickening. The objective is to do an experimental and in a lesser way numerical study to characterize sedimentation the most completly possible with a detailed attention to flow and deposit structure, concentration profiles and determination of sedimentation modes. Used experimental means are the usual techniques of two-dimensional measurement (laser velocimetry and direct visualization) which authorize the data acquisition for configurations where particles evolve in the plan. These laser techniques were improved to simultaneously follow various particles populations and access to various outpouts such as velocities field, local volumic fraction, and velocities of various sedimentation fronts. A simple numerical tool was also built using Stokesian Dynamics and seizing the main part of the physical phenomena driving sedimentation leading to the modeling of the hydrodynamic interactions
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43

Reynes, Hugo. "Conception d'un module électronique de puissance pour application haute tension." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI035.

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Satisfaire les besoins en énergie de manière responsable est possible grâce aux énergies renouvelables, notamment éoliennes et solaires. Cependant ces centres de captation d’énergie sont éloignés dans zones de consommation. Le transport de l’énergie via des réseaux HVDC (haute tension courant continu) permet un rendement et une flexibilité avantageuse face au transport HVAC (haute tension courant alternatif). Ceci est rendu possible grâce aux convertisseurs utilisant l’électronique de puissance. Les récents développements sur les semi-conducteurs à large bande interdite, plus particulièrement le carbure de silicium (SiC) offrent la possibilité de concevoir ces convertisseurs plus simples, utilisant des briques technologiques de plus fort calibre (≤ 10 kV). Cependant le packaging, essentiel à leur bon fonctionnement, ne suit pas ces évolutions. Dans cette thèse, nous explorons les technologies actuelles ainsi que les limites physique et normatives liées au packaging haute tension. Des solutions innovantes sont proposées pour concevoir un module de puissance haute tension, impactant que faiblement les paramètres connexes (résistance thermique, isolation électrique et paramètres environnementaux). Les éléments identifiés comme problématiques sont traités individuellement. La problématique des décharges partielles sur les substrats céramiques métallisés est développée et une solution se basant sur les paramètres géométriques a été testée. Le boitier standard type XHP-3 a été étudié et une solution permettant de le faire fonctionner à 10 kV à fort degré de pollution a été développée
The supply of carbon-free energy is possible with renewable energy. However, windfarms and solar power plants are geographically away from the distribution points. Transporting the energy using the HVDC (High Voltage Direct Current) technology allow for a better yield along the distance and result in a cost effective approach compared to HVAC (High Voltage Alternative Current) lines. Thus, there is a need of high voltage power converters using power electronics. Recent development on wide bandgap semiconductors, especially silicon carbide (SiC) allow a higher blocking voltage (around 10 kV) that would simplify the design of such power electronic converters. On the other hand, the development on packaging technologies needs to follow this trend. In this thesis, an exploration of technological and normative limitation has been done for a high voltage power module design. The main hot spot are clearly identified and innovative solutions are studied to provide a proper response with a low impact on parasitic parameters. Partial Discharges (PD) on ceramic substrates is analyzed and a solution of a high Partial Discharge Inception Voltage (PDIV) is given based on geometrical parameters. The XHP-3 like power modules are studied and a solution allowing a use under 10 kV at a high pollution degree (PD3) is given
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44

SYU, HUAN-TING, and 徐煥庭. "Feasibility Study on Building Well-Made Particle Packing Using Compressible Packing Model." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/03131194756052739967.

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碩士
國立臺灣科技大學
營建工程系
103
The volume of aggregates occupies by more than 70 vol. % of concrete. The packing problem of aggregates has a decisive influence on concrete quality, The concrete which is made by a good packing condition will have a better performance on all aspects of strength, permeability and economy, etc. . Most previous researches use experimental method to get the mixing proportion with maximum packing density of aggregates in order to reach the goal of dense grading. This study, used the compressible packing model (CPM) which has proposed by the scholar de Larrard in 1999 to calculate the packing density of aggregates, and compare that from the analysis of Fuller's curve with two different parameters. Simultaneously, the local sand and gravel were sieved into five different combinations of aggregate packing, including five-phase aggregates (all of fine aggregate), six-phase aggregates (five-phase aggregates +#4 coarse aggregate, +3/8" coarse aggregate and +3/4" coarse aggregate), eight-phase aggregates (all of fine aggregate +3 kinds of coarse aggregate),together with three kinds of gradation mode to conduct a total of 15 different sets of experiments for packing density test in order to verify the results of numerical analysis. The results show that, in consideration of the wall effect and loose effect, the mean packing densities for five different combinations of aggregate mixtures calculated by the CPM were higher than those of ten groups of aggregate mixtures obtained by the Fuller's curve by 2% ~ 10%. In the meantime, most experimental results of packing density for those fifteen groups of mixtures were located between two analytical results. The difference of packing density obtained by two kinds of Fuller's curve was less than 7%. The mean packing density of 8-phase aggregate with three packing modes were between 0.677 and 0.721. On the other hand, the mean experimental packing densities of 5-phase aggregate were between 0.770 and 0.827, were between 0.715 and 0.724 for 5-phase aggregate. It indicates that, under the premise of no excessive interference among aggregates that proposed CPM can have the usability and feasibility to build the well-made article packing with different combinations of aggregates.
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45

Wong, Vivian, and 黃暉然. "A 3-parameter particle packing model for spherical and non-spherical particles." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/09100505588370585222.

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46

Yang, Cheng-Tao, and 楊承道. "Simulation System for Three Dimensional Particle Packing." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/75292581717371457894.

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碩士
國立成功大學
土木工程學系
87
In this thesis we present a 3-D model that is able to simulate the packing process of granular particles. We use 3-D ellipsoids as well as polyhedra as the surrogate to simulate natural particle. Assuming mechanical forces non-existant, we model and solve the packing of granular particles as an optimum problem. The research is presented in two aspects. First we use the model to estimate of the maximum packing density for a set of given particles, which has application in determinating the maximum density of granular soil. Secondly we attempt to estimate the particle composition based on cross section information. This technique has application in estimating aggregate composition in cemented materials such as concrete. This thesis can be divided into four parts: (1) Formulation of 3-D system of particles, including mathematical techniques in particle manipulating such as shifting, rotation, and contact testing of particles. Models for ellipsoid and polyhedra are both developed. (2) A model to simulate the packing process. Procedures involved are particle filling, followed by position and attitude adjusting in order to reach a higher density. (3) Theories to link ellipsoids and the elliptical slices obtained by slicing an ellipsoid with planes. (4) A linear system to solve for a set of composition that can be best represented by the cross sections observed. We verify the effectiveness of the model by testing the model against analytical results for some special cases, and also with particle distribution derived from a real life standard sand. All results are reasonable, and we verify that the system can serve as the foundation for further partical research.
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47

Chen, Jen Chang, and 陳仁彰. "The Study of Particle Packing using 2-D Computer Simulation." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/75175783739121851921.

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碩士
國立海洋大學
材料工程研究所
90
The particle packing structure affects the properties of particulate materials. This study is to simulate the 2-D packing structure by using computer simulation. The four simulation programs were developed to simulate different packing structure: (1) 2-D mono-sized sphere ordered packing; (2) 2-D mono-sized sphere random packing; (3) 2-D mono-sized sphere random close packing; (4) 2-D multi-sized sphere random packing. The programs were written by Java programming language. The advantage of Java is web-based programming. All of the simulation programs were uploaded to the server. The user can use browser to run the programs on the net. The basic inputs of program are the container size, particle size, and thickness of matrix film. The outputs are packing structure, packing density, porosity, numbers of the specified particle, and connective paths of matrix film. Computational results show that the remainder of the container size/net length of two particles affects the packing density of ordered packing. For the random packing, the key factors are the particle size distribution, filling order, numbers of iteration and total particles, and thickness of matrix film.
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48

"Structural Characteristics and Applications of Hard-particle Packings via Event-driven Molecular Dynamics Simulations." Master's thesis, 2014. http://hdl.handle.net/2286/R.I.26868.

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abstract: In this dissertation, the results of our comprehensive computational studies of disordered jammed (i.e., mechanically stable) packings of hard particles are presented, including the family of superdisks in 2D and ellipsoids in 3D Euclidean space. Following a very brief introduction to the hard-particle systems, the event driven molecular dynamics (EDMD) employed to generate the packing ensembles will be discussed. A large number of 2D packing configurations of superdisks are subsequently analyzed, through which a relatively accurate theoretical scheme for packing-fraction prediction based on local particle contact configurations is proposed and validated via additional numerical simulations. Moreover, the studies on binary ellipsoid packing in 3D are briefly discussed and the effects of different geometrical parameters on the final packing fraction are analyzed.
Dissertation/Thesis
Masters Thesis Materials Science and Engineering 2014
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49

Zi-JieLin and 林子傑. "Particle Packing in Green Bodies Formed through Slip Casting with Fine Alumina Powders." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/j97rz3.

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50

Tai, Chih-Yuan, and 戴志遠. "Study of particle concentration and metallic compositions in the packing area of a power manufacturing plant." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/v22ae9.

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碩士
元培科技大學
環境工程衛生研究所
98
This study conducted the particle sampling in a pigment TiO2 production factory using different sampling devices. This study also investigated the particle mass concentration and the metal content in particles by different aerosol samplers. The sampling devices include the IOSH cyclone, 10 mm Nylon cyclone, porous foam impactor, inhalable dust sampler(IOM) and the MOUDI sampling devices. This study used polytetrafluoroethylene, mixed cellulose ester filtering paper and polyvinyl chloride filtering paper to obtain samples. Six sampling points were established according to the locations inside the TiO2 pigment factory. According to sampling design of the cut size of the sampler, partices were divided into respirable dust and total dust. The samples collected by the filter were then processed according to standard procedures; afterwards, they were analyzed for metal content using inductively coupled plasma - optical emission spectrometer. Results showed the particles generally fell in the range of 1~10 μm, and the concentration was not high for the diameter less than 1 μm. For comparing the mass concentrations of different samplers, results show IOSH cyclone was greater than the concentration of porous foam impactor, Nylon cyclone had the lowest concentrations. For the comparison of manual instruments and automatic instruments. IOSH cyclone was compared with the Dust Trak, the concentration of Dust Trak was about 1.45 times to that of IOSH cyclone. For the composition analysis of metal parts, results showed that using the mixed cellulose ester filtering paper could analyze more metal elements. In the workplace, the TiO2 levels were lower than the levels suggested by NIOSH. The concentration of dust was influenced mainly by seasonal factors, on-site work environment, working conditions and the use of diesel forklifts.
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