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Huan, Xun. "Numerical approaches for sequential Bayesian optimal experimental design." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101442.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 175-186).
Experimental data play a crucial role in developing and refining models of physical systems. Some experiments can be more valuable than others, however. Well-chosen experiments can save substantial resources, and hence optimal experimental design (OED) seeks to quantify and maximize the value of experimental data. Common current practice for designing a sequence of experiments uses suboptimal approaches: batch (open-loop) design that chooses all experiments simultaneously with no feedback of information, or greedy (myopic) design that optimally selects the next experiment without accounting for future observations and dynamics. In contrast, sequential optimal experimental design (sOED) is free of these limitations. With the goal of acquiring experimental data that are optimal for model parameter inference, we develop a rigorous Bayesian formulation for OED using an objective that incorporates a measure of information gain. This framework is first demonstrated in a batch design setting, and then extended to sOED using a dynamic programming (DP) formulation. We also develop new numerical tools for sOED to accommodate nonlinear models with continuous (and often unbounded) parameter, design, and observation spaces. Two major techniques are employed to make solution of the DP problem computationally feasible. First, the optimal policy is sought using a one-step lookahead representation combined with approximate value iteration. This approximate dynamic programming method couples backward induction and regression to construct value function approximations. It also iteratively generates trajectories via exploration and exploitation to further improve approximation accuracy in frequently visited regions of the state space. Second, transport maps are used to represent belief states, which reflect the intermediate posteriors within the sequential design process. Transport maps offer a finite-dimensional representation of these generally non-Gaussian random variables, and also enable fast approximate Bayesian inference, which must be performed millions of times under nested combinations of optimization and Monte Carlo sampling. The overall sOED algorithm is demonstrated and verified against analytic solutions on a simple linear-Gaussian model. Its advantages over batch and greedy designs are then shown via a nonlinear application of optimal sequential sensing: inferring contaminant source location from a sensor in a time-dependent convection-diffusion system. Finally, the capability of the algorithm is tested for multidimensional parameter and design spaces in a more complex setting of the source inversion problem.
by Xun Huan.
Ph. D.
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Duthil, Eric Patxi. "Thermoacoustic heat pumping study : experimental and numerical approaches /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?MECH%202003%20DUTHIL.
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Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 122-129). Also available in electronic version. Access restricted to campus users.
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CONTI, BRUNO. "Solid Oxide Fuel Cells: Numerical and Experimental Approaches." Doctoral thesis, Università degli studi di Genova, 2019. http://hdl.handle.net/11567/943177.
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Solid oxide fuel cell (SOFC) is a promising electrochemical technology that can produce electrical and thermal power with outstanding efficiencies. A systematic synergetic approach between experimental measurements and modelling theory has proved to be instrumental to evaluate performance and correct behaviour of a chemical process, like the ones occurring in SOFC. For this purpose, starting from SIMFC (SIMulation of Fuel Cells) code set-up by PERT-UNIGE (Process Engineering Research Group) for Molten Carbonate Fuel Cells [1], a new code has been set-up for SOFCs based on local mass, energy, charge and momentum balances. This code takes into account the proper reactions occurring in the SOFC as well as new geometries and kinetics thanks to experiments carried out on single cells and stack in ENEA laboratories of C.R. Casaccia and VTT Fuel Cell Lab in Finland. In particular using an innovative experimental setup it has been possible to study experimentally the influence of a multicomponent mixtures on the performance of SOFC and also validate locally a 2-D model developed starting from SIMFC code. The results obtained are good, showing a good agreement between experimental and numerical results. The obtained results are encouraging further studies which allow the model validation on a greater quantity of data and under a wider range of operating conditions.
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Fliegans, Jérôme. "Coercivity of NdFeB-based sintered permanent magnets : experimental and numerical approaches." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY071.
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Les aimants permanents Nd-Fe-B sont actuellement les plus puissants du marché. Ils sont indispensables pour des applications telles que les moteurs des véhicules électriques ou les générateurs des éoliennes. Leurs propriétés exceptionnelles viennent des propriétés magnétiques intrinsèques de la phase Nd2Fe14B et de leur microstructure. Cependant, les machines électriques fonctionnent entre 120 et 180°C et les propriétés magnétiques extrinsèques telles que la coercitivité et la rémanence diminuent avec la température. Un moyen d’améliorer la coercitivité des aimants frittés Nd-Fe-B est la substitution du Nd par des terres rares lourdes comme le Dy, afin d’augmenter l’anisotropie magnétocristalline. Néanmoins, le Dy est un matériau critique et un objectif majeur de la recherche est actuellement de développer des aimants possédant d’excellentes propriétés magnétiques extrinsèques et contenant peu de Dy. Cela nécessite une meilleure compréhension du lien entre microstructure et coercitivité. Dans les aimants frittés Nd-Fe-B, un des points-clés est le contrôle de la taille de grain et de la répartition des phases secondaires aux joints de grains de façon à limiter la nucléation du retournement de l’aimantation et à garantir un bon découplage magnétique des grains. La première partie de la thèse est une étude comparative des caractérisations magnétiques en circuit ouvert et fermé réalisées sur des aimants frittés Nd-Fe-B. Les différences de coercitivité observées sont expliquées par les phénomènes de viscosité magnétique et d’effets de champ démagnétisant. La deuxième partie traite du procédé de diffusion aux joints de grains appliqué aux aimants frittés Nd-Fe-B et utilisant des alliages Dy-Co. Des caractérisations microstructurales ont été réalisées en complément de mesures magnétiques afin de déterminer les profils de diffusion et de coercitivité, et ainsi d’établir le lien entre les variations locales de composition chimique et le champ coercitif. De plus, des simulations micromagnétiques ont permis de décrire le retournement de l’aimantation à l’échelle nanométrique dans un modèle simplifié cœur-coquille. Enfin, la dernière partie de la thèse constitue une discussion sur la coercitivité des aimants diffusés au Dy-Co (à gradient de champ coercitif) à l’aide d’un modèle de diffusion et de simulations sur un modèle polycristallinNd-Fe-B permanent magnets are the most powerful among all commercially available magnets. They play a significant role in energy applications, such as motors of electric vehicles and generators of windmills. Their outstanding properties come from the excellent intrinsic magnetic properties of the Nd2Fe14B phase and from their microstructure. However, electrical machines operate at about 120-180°C and extrinsic magnetic properties such as coercivity and remanence decrease rapidly with temperature. One way of improving coercivity of Nd-Fe-B sintered magnets is to substitute Nd with a heavy rare earth such as Dy, so as to increase the magnetocrystalline anisotropy. However, Dy is a strategic element and a major objective of the research community is therefore to develop Nd-Fe-B magnets that possess excellent extrinsic magnetic properties with a reduced content of Dy. This requires a better understanding of the link between microstructure and coercivity. The key point is the control of the grain size and the distribution of secondary phases at grain boundaries to prevent magnetization reversal and magnetic coupling. The first part of this thesis concerns a comparison of open-circuit and closed-circuit magnetization measurements carried out on Nd-Fe-B sintered magnets. The observed differences in coercivity values are discussed in terms of magnetic viscosity and demagnetizing field effects. The second part deals with the grain boundary diffusion process performed on Nd-Fe-B sintered magnets using Dy-Co alloys. Microstructural observations and magnetic measurements have been carried out to characterize the diffusion and coercivity profiles and to establish the link between local variations in composition and coercivity. Moreover, micromagnetic simulations have been performed to describe magnetization reversal at the nanoscale in a simple core-shell model. The last part constitutes a discussion about coercivity in graded magnets via a diffusion model and further simulations on a polycrystalline model
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Jrad, Wassim. "Dynamic behavior of thin-walled beams : Analytical, numerical and experimental approaches." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0271.
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Les poutres à parois minces à sections ouvertes sont des éléments de base des ouvrages courants en génie civil, de l'automobile et de l'aéronautique. En raison de leur élancement et la forme des sections, elles sont très sensibles à la torsion et aux instabilités aussi bien en statique qu’en dynamique. En dynamique, les modes de vibration en torsion sont plus dominants par rapport au modes de flexion classiques. Pour ces raisons, les défaillances planaires de telles structures sont connues pour être une exception plutôt qu'une règle. Dans ce travail de thèse, on s’intéresse au comportement dynamique de poutres à parois minces et à section ouvertes arbitraires. En se basant sur le modèle de Vlasov qui prend en compte de la torsion et du gauchissement, les équations de mouvement 3D sont dérivées à partir du principe d’Hamilton. Des solutions analytiques originales pour différentes conditions aux limites sont dérivées pour des modes supérieurs en vibrations libres. Dans ces solutions, les effets des termes de rotation inertiels en flexion et torsion sont pris en compte. Pour des cas généraux, un modèle élément fini de poutre 3D est décrit et implémenté. Dans le modèle, un degré de liberté (ddl) est affecté au gauchissement. Toutes les matrices de rigidité masse de base sont calculées par intégration numérique (intégration de Gauss). Dans le modèle, les calculs en vibrations libres et forcées sont possibles. Le modèle est validé par comparaison aux solutions numériques et expérimentaux de la littérature. Une comparaison aux simulations des codes commerciaux est aussi suivie. Afin de valider le modèle théorique et numérique utilisé, une campagne d’essais a été suivie au LEM3 à Metz. Des essais de vibration libre et forcée sont effectués sur des poutres à parois minces avec différentes conditions aux limites. Les solutions analytiques, numériques et les mesures expérimentales sont comparées et validées. Un bon accord entre les différentes solutions est constaté. Le modèle est étendu aux poutres 3D retenues latéralement par des entretoises. Des ressorts élastiques et visqueux 3D sont ajoutés dans le modèle numérique. L'effet des entretoises est étudié dans le but d’améliorer le comportement des poutres à parois minces vis-à-vis des modes indésirables de type flexion latérale et torsionThin-walled beams with open section constitute main elements in engineering applications fields as in civil engineering, automotive and aerospace construction. Due to slenderness and cross section shapes, these elements are very sensitive to torsion and instabilities in both statics and dynamics. In dynamics, the torsional and flexural-torsional modes of vibration are often lower frequencies compared to the classical plane pure bending modes. Thus, planar failures of such structures are known to be an exception rather than a rule. In torsion, warping is important and governs the behavior. In this thesis work, we are interested with the dynamic behavior of thin-walled beams with arbitrary open cross sections. Based on the Vlasov’s model accounting for warping, the 3D motion equations are derived from the Hamilton’s principle. Original analytical solutions for different boundary conditions are derived for higher free vibration modes. In these solutions, the effects of the inertial rotation terms in bending and torsion are taken into consideration. For more general cases, a 3D beam finite element model is described and implemented. Compared to conventional 3D beams, warping is considered as an additional Degree Of Freedom (DOF). The mass and stiffness matrices are obtained by numerical integration (Gauss method). In the model, free and forced vibration analyses are possible. The model is validated by comparison with benchmark solutions available in the literature and other numerical results obtained from simulation on commercial codes. In order to validate the present model, laboratory test campaign is undertaken at the LEM3 laboratory in Metz. Tests are carried out on thin-walled beams with different boundary conditions. Free and forced vibration tests are performed using impact hammer and shaker machine. In the presence of arbitrary sections, flexural-torsional vibration modes are observed. The analytical, the numerical and the experimental solutions are compared and validated. Moreover, the numerical and experimental dynamic response spectra are compared. A good agreement between the various solutions is remarked. The model is extended to 3D beams in presence of lateral braces. 3D elastic and viscous springs are added in the finite element model. The effect of the springs is studied in order to improve the behavior of thin-walled beams against undesirable lateral bending and torsion modes
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BOIGUES, MUNOZ CARLOS. "Computational Simulation of Solid Oxide Fuel Cells – Integrating numerical and experimental approaches." Doctoral thesis, Università Politecnica delle Marche, 2015. http://hdl.handle.net/11566/242989.
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Le celle a combustibile ad ossido solido (Solid Oxide Fuel Cells - SOFCs) sono una tecnologia promettente in grado di produrre potenza elettrica e termica con un’efficienza eccezionale. Tuttavia, è necessaria una comprensione più approfondita dei processi fisico-chimici che si verificano all’interno della cella per risolvere la maggior parte dei problemi di degradazione che attualmente impediscono la maturità della tecnologia. Un approccio sistematico e sinergico tra misure sperimentali, l’uso di strumenti di analisi e techniche innovative – con particolare attenzione alla deconvoluzione degli spettri di impedenza elettrochimica (Electrochemical Impedance Spectroscopy - EIS) mediante il metodo della distribuzione dei tempi di rilassamento (Distributed Relaxation Times - DRT) – e teoria modellistica ha dimostrato di essere importante per la stima dei parametri che descrivono le caratteristiche microstrutturali ed elettrochimiche di due tipi di SOFC planari anodo-supportate, una progettata per funzionare ad una temperatura intermedia (750ºC) e l’altra per farlo a bassa temperatura (650ºC). Un macro-modello CFD (Computational Fluid Dynamics) dei campioni testati, che incorpora i parametri ottenuti dalla procedura menzionata, è stato convalidato confrontando le curve di polarizzazione simulate con quelle sperimentali. Questo modello ha dimostrato di essere un valido strumento per ottimizzare la microstruttura delle celle e per stabilire le basi per analizzare gli effetti di potenziali fenomeni di degrado nella cella e, infine, prevedere la generazione di elettricità a lungo termine in condizioni di funzionamento predeterminate. Inoltre, un modello CFD di una cella di tipo tubolare all’interno di un generatore di potenza (cioè, stack SOFC) di 500 Wel ha permesso di apprezzare come un singolo elemento dello stack si comporta in condizioni operative quasi realistiche.Solid oxide fuel cell (SOFC) is a promising electrochemical technology that can produce electrical and thermal power with outstanding efficiencies, however, a more profound understanding of the physicochemical processes occurring within the cell is necessary to overcome most of the degradation issues currently impeding the maturity of the technology. A systematic synergetic approach between experimental measurements, the use of novel analysis tools and techniques – with special attention to the deconvolution of electrochemical impedance spectroscopy (EIS) spectra by means of the distribution of relaxation times (DRT) method – and modelling theory has proved to be instrumental for the estimation of parameters describing the microstructural and electrochemical properties of two types of planar anode-supported SOFCs, one designed to operate at intermediate temperatures (750ºC) and the other at low temperatures (650ºC). A comprehensive macro-scale computational fluid dynamics (CFD) model of the tested samples incorporating the aforementioned parameters has been validated by confronting the simulated polarization curves with the experimental ones. This model has demonstrated to be a compelling tool to optimize the microstructure of the cells whilst establishing the bases to monitor and analyse the effects of potential degradation phenomena in the cell and predict the electrical output of the cell in the long run under pre-determined operating conditions. Additionally, a CFD model of a tubular-type cell comprised in the power module (i.e. SOFC stack) of a characterised 500Wel power generator has enabled to appreciate how a singular element of the stack behaves under nearly realistic operating conditions.
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Cescatti, Elvis. "Combined experimental and numerical Approaches to the Assessment of historical Masonry Structures." Doctoral thesis, Università degli studi di Trento, 2016. https://hdl.handle.net/11572/368102.
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The assessment and the conservation of historical masonry structures are very challenging issues. According to the actual methodology, all the phases of the entire process of assessment require efforts and reciprocal comparison in order to understand reliably the structural behaviour and to design effective interventions. This thesis goes through such phases (anamnesis, diagnosis and treatment), introducing some innovations in each step and connecting the experimental experiences to models with the support of some real cases. Three techniques are developed about the knowledge phase, namely sonic test, flat jacks and dynamic identification. Deeper studies have been dedicated to vault systems by means of an extended experimental campaign with five full scale vaults tests and a reverse analysis to better understand the behaviour of structures and, at the same time, the limits of models. Sometime this comparison suggests a lack between model parameters and physical meaning due to modelling approaches (mesh, element type) and parameters (material properties and constitutive laws) and this gap may be fulfil by both local and global tests.
From the experimental point of view this work presents a wide range of tests from the local to the global behaviour and varying among non-destructive, minor destructive and destructive tests. On the other hand for models, both linear and non-linear approaches have been adopted looking as well to local and global phenomena. Finally, about the deepest analysis on vaults even the scale of modelling was evaluated with the comparison between macro and meso-scale modelling. In this framework some proposal in kinematic analysis of strengthened vaults were provided. The work carried out allows therefore to compare traditional and more used tools for structural assessment purposes with real and measured experiences helping to validate the current methodology in the safety evaluation of existing buildings.
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Cescatti, Elvis. "Combined experimental and numerical Approaches to the Assessment of historical Masonry Structures." Doctoral thesis, University of Trento, 2016. http://eprints-phd.biblio.unitn.it/1742/1/PhD_th_Cescatti.pdf.
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The assessment and the conservation of historical masonry structures are very challenging issues. According to the actual methodology, all the phases of the entire process of assessment require efforts and reciprocal comparison in order to understand reliably the structural behaviour and to design effective interventions. This thesis goes through such phases (anamnesis, diagnosis and treatment), introducing some innovations in each step and connecting the experimental experiences to models with the support of some real cases. Three techniques are developed about the knowledge phase, namely sonic test, flat jacks and dynamic identification. Deeper studies have been dedicated to vault systems by means of an extended experimental campaign with five full scale vaults tests and a reverse analysis to better understand the behaviour of structures and, at the same time, the limits of models. Sometime this comparison suggests a lack between model parameters and physical meaning due to modelling approaches (mesh, element type) and parameters (material properties and constitutive laws) and this gap may be fulfil by both local and global tests.
From the experimental point of view this work presents a wide range of tests from the local to the global behaviour and varying among non-destructive, minor destructive and destructive tests. On the other hand for models, both linear and non-linear approaches have been adopted looking as well to local and global phenomena. Finally, about the deepest analysis on vaults even the scale of modelling was evaluated with the comparison between macro and meso-scale modelling. In this framework some proposal in kinematic analysis of strengthened vaults were provided. The work carried out allows therefore to compare traditional and more used tools for structural assessment purposes with real and measured experiences helping to validate the current methodology in the safety evaluation of existing buildings.
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Khoueiry, Nicole. "Study of granular platforms behaviour over soft subgrade reinforced by geosynthetics : Experimental and numerical approaches." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI027.
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Les géosynthétiques sont utilisés depuis les années 70 dans le renforcement des plateformes granulaires reposant sur des sols de faible portance pour des applications de routes non revêtues. La complexité des mécanismes développés et la diversité des produits de renforcement nécessitent encore d’étudier ces plateformes renforcées. Un essai au laboratoire permettant de tester des plateformes à échelle réelle a été développé. Une plateforme granulaire non revêtue reposant sur un sol de faible portance a été reproduite. Un protocole de mise en place de ce sol a été élaboré pour assurer son homogénéité et la répétabilité des essais. Une instrumentation spécifique a été développée pour collecter le maximum de mesures utiles pour l’interprétation du transfert de charge et du comportement des géogrilles utilisées. Trois types de géogrille ont été testées : une géogrille extrudée et deux géogrilles tricotées de rigidité différente. Après de nombreux essais de faisabilité, dix essais ont été effectués sous un chargement cyclique sur plaque circulaire, la plateforme testée a été placée dans un banc d’essai de 1,8 m de large, 1,9 m de long et 1,1 m de haut. Sur la base du même protocole de mise en œuvre, des essais de circulation avec un Simulateur Accélérateur de Traffic (SAT) ont été effectués. Ce simulateur a été spécifiquement conçu et construit pour cette application. Pour ces essais, la plateforme testée a été placée dans le banc d’essai allongé à 5 m. La plateforme a été soumise à deux types de sollicitations : un chargement cyclique sur plaque et un chargement de circulation. Des essais de répétabilité ont permis de vérifier le protocole mis en place. A partir des essais, plusieurs observations ont pu être faites sur le comportement des plateformes granulaires, le sol peu porteur, et sur l’efficacité du renforcement. De plus, ces essais ont permis de montrer que le chargement de circulation est beaucoup plus endommageant que le chargement sur plaque. Parallèlement à ces essais, un modèle numérique a été développé en se basant sur la méthode des différences finies avec le logiciel FLAC 3D. Cette modélisation a permis de prédire le comportement de la plateforme sous le premier chargement de plaqueGeosynthetics were used since 1970 in the base course reinforcement supported by soft subgrade in unpaved road application. The various factors and parameters influencing the dominant mechanism and its relative contribution on the platform improvement explain the need of more investigations in this topic. In this research work, large-scale laboratory test was developed to study the reinforcement contribution in the unpaved road improvement. Therefore, an unpaved platform was built of 600 mm of artificial subgrade supporting a base course layer. A detailed experimental Protocol was established regarding the soil preparation, the installation and the soils compaction procedure to reproduce the site conditions and insure the platform repeatability for each test. Three geosynthetics were tested first under a cyclic plate load test. Cyclic load was performed on the prepared platform, with a maximum load of 40 kN resulting in a maximum applied pressure of 560 kPa. The platform was subjected to 10,000 cycles with a frequency of 0.77 Hz. An advanced and complete soil instrumentation was provided in order to collect the maximum data needed for thorough analysis. Quality control tests were performed before each test to verify the soil layers homogeneity and properties. Two base course thicknesses were tested under this test condition, 350 and 220 mm. Once the developed protocol was confirmed under the circular plate load tests, further tests using the Simulator Accelerator of Traffic (SAT) were performed. Indeed, the laboratory prepared platform was placed in a larger box of 1.8 m in large, 5 m in length and 1.1 m in height. The prepared platform was subjected to two solicitations: a particular plate and traffic load. The Simulator Accelerator of Traffic was developed specially for this application. A machine that simulates the traffic load under an effective length of 2 m and a velocity of 4 km/h. The two areas were instrumented: the area under the circulation load, and the area under the plat load, located aside. In addition, a numerical model based on the differential element method using FLAC 3D was developed. The model simulated the circular plate load test with the same platform configuration under monotonic load. The results were compared to the first monotonic load applied on the rigid plate experimentally
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Ding, Zhongman. "Numerical and experimental analysis on Resin Injection Pultrusion (RIP) Process - using macroscopic and microscopic approaches /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486399160105717.
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Murillo, Carlos. "Experimental and numerical approaches to particles dispersion in a turbulent flow : application to dust explosions." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0040/document.
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Les caractéristiques d’un nuage de poussières avant l’activation de la source d’inflammation ont une grande influence sur la sensibilité et la sévérité de son explosion. Pour cette raison, le procédé de dispersion d’une poussière combustible qui se développe à l’intérieur des chambres d’explosion standardisés telles que le tube de Hartmann modifié et la sphère 20 L a été décrit par deux approches complémentaires. Dans un premier temps, une caractérisation expérimentale de l’évolution du nuage de poussière a identifié les niveaux de turbulence de l’écoulement de gaz, ainsi que les principales variations de la distribution de la taille des particules combustibles. Ces résultats ont été complétés par l’identification des niveaux de ségrégation de la poudre dispersée à l’intérieur des chambres d’explosion. Par la suite, une série de simulations CFD basée sur une approche Euler-Lagrange a été développée pour prédire le comportement du nuage. Cette étude a été réalisée grâce à la caractérisation des principaux mécanismes d’interaction tels que le transfert de quantité de mouvement (couplage bidirectionnel) et le phénomène de fragmentation des poudres. Deux types de particules microniques ont été spécifiquement étudiés : une poussière métallique, l’aluminium et un composé organique, l’amidon de blé. Ces résultats ont démontré qu’il est possible de définir ab initio, par simulation numérique, les conditions de tests les plus pertinentes (les plus réalistes ou les plus pénalisantes) en vue de la quantification de ces risques majeursThe pre-ignition stage of an explosibility test determines the ignitability of a dust cloud as well as the main characteristics of the flame propagation. For this reason, the dispersion process of a combustible dust that develops inside the explosion chambers of the modified Hartmann tube and the 20 L sphere has been described by two complementary approaches. Initially, an experimental characterization of the evolution of the dust cloud identified the evolution of the turbulence levels of the gas flow along with the main variations of the particle size distribution of the combustible dust. These results were complemented by the identification of the segregation levels of the dispersed powder inside the explosion chambers. Thereafter, a set of CFD simulations based on the Euler-Lagrange formulation was developed to predict the behavior of the combustible dust cloud. This study was accomplished through the characterization of the main interaction mechanisms such as the momentum exchange (two-way coupling) and the dust fragmentation phenomenon. In this manner, the research work constituted for this thesis allowed determining the most appropriate conditions to ignite a dust cloud formed by a metallic (Aluminum micro-Al 42) or organic powders (wheat starch) in a case study. Thus, this research work presents a methodology that can be extended for the analyses of combustible dusts and the further development of the standard test methods
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Donkelaar, Corrinus Cornelis van. "A numerical and experimental approach to spatial phenomena." [Maastricht : Maastricht : Universiteit Maastricht] ; University Library, Maastricht University [Host], 1999. http://arno.unimaas.nl/show.cgi?fid=6828.
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Lee, Jinkee. "Developing microfluidic routes for understanding transport of complex and biological fluids : experimental, numerical and analytical approaches." View abstract/electronic edition; access limited to Brown University users, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3319102.
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Cheng, Xiaomin. "Experimental and numerical approaches for improving rolling contact fatigue of bearing steel through enhanced compressive residual stress." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1166828432.
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FARZAD, TALEBI. "STUDY ON BEHAVIOR OF BURIED PIPELINES SUBJECTED TO EARTHQUAKE FAULT MOVEMENT BY ANALYTICAL NUMERICAL AND EXPERIMENTAL APPROACHES." Kyoto University, 2020. http://hdl.handle.net/2433/259023.
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Soufri, Ayoub. "Multi-impact behavior of composite structures : experimental and numerical approach." Electronic Thesis or Diss., Bourgogne Franche-Comté, 2023. http://www.theses.fr/2023UBFCK038.
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Les matériaux composites sont largement utilisés dans le domaine des transports en raison de leurs propriétés mécaniques spécifiques élevées. Cependant, au cours de leur cycle de vie, ils peuvent subir une dégradation significative de leurs propriétés mécaniques lorsqu'ils sont soumis à des chargements d'impacts. Les dommages induits par des impacts se manifestent sous différentes formes telles que la rupture des fibres, la fissuration matricielle, la décohésion fibres/matrice et le délaminage. L'étude du comportement aux impacts des structures composites a suscité une attention importante dans la littérature. Cependant, ces études se rapportent généralement au cas d'un seul impact ou d'impacts répétés. Peu de travaux se sont intéressés au cas d'impacts multiples, même s'ils sont plus proches des conditions réelles de service, comme dans les cas de chute de grêlons ou de projection d'objets externes tels que les gravillons présents sur les routes, les impacts d'oiseaux, etc. Dans cette thèse, nous présentons des méthodes expérimentales et numériques robustes pour le suivi in-situ et post-mortem des endommagements suite aux différents cas d'impacts possibles : mono-impact, impacts répétés, séquentiels, simultanés, etc. Ce travail a consisté dans un premier temps à développer un banc d'essai unique « canon à air comprimé ». Ensuite, un dialogue (essais expérimentaux-calculs numériques) a été assuré afin de mieux comprendre les phénomènes en jeu dans les cas de multi-impacts, pour finalement atteindre les performances maximales des matériaux compositesComposite materials are widely used in the transportation field due to their high specific mechanical properties. However, during their life cycle, they can undergo significant degradation of their mechanical properties when subjected to impact loading. Impact-induced damage occurs in various forms, such as fiber breakage, matrix cracking, fiber/matrix decohesion and delamination. The study of the impact behavior of composite structures has attracted considerable attention in the literature. However, these studies generally relate to the case of a single impact or repeated impacts. Few studies have focused on the case of multiple impacts, even though these are closer to actual service conditions, as in the case of falling hailstones or the projection of external objects such as road gravels, bird strikes, etc. In this thesis, we present robust experimental and numerical methods for in-situ and post-mortem monitoring of damage following the various possible impact cases: single-impact, repeated, sequential, simultaneous impacts, etc. The first phase of the project involved the development of a unique "compressed air cannon" test bench. Then, a dialogue (experimental tests-numerical computations) was ensured to better understand the phenomena involved in multi-impact cases, to finally reach the maximum performance of composite materials
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Jolibois, Alexandre, and Alexandre Jolibois. "A study on the acoustic performance of tramway low-height noise barriers : gradient-based numerical optimization and experimental approaches." Phd thesis, Université Paris-Est, 2013. http://pastel.archives-ouvertes.fr/pastel-00965168.
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Noise has become a main nuisance in urban areas to the point that according to the World Health Organization 40% of the European population is exposed to excessive noise levels, mainly due to ground transportation. There is therefore a need to find new ways to mitigate noise in urban areas. In this work, a possible device to achieve this goal is studied: a low-height noise barrier. It consists of a barrier typically less than one meter high placed close to a source, designed to decrease the noise level for nearby pedestrians and cyclists. This type of device is studied both numerically and experimentally. Tramway noise barriers are especially studied since the noise sources are in this case very close to the ground and can therefore be attenuated efficiently. The shape and the surface treatment of the barrier are optimized using a gradient-based method coupled to a 2D boundary element method (BEM). The optimization variables are the node coordinates of a control mesh and the parameters describing the surface impedance. Sensitivities are calculated efficiently using the adjoint state approach. Numerical results show that the shapes generated by the optimization algorithm tend to be quite irregular but provide a significant improvement of more than 5 dB (A) compared to simpler shapes. Utilizing an absorbing treatment on the source side of the barrier is shown to be efficient as well. This second point has been confirmed by scale model measurements. In addition, a full scale low height noise barrier prototype has been built and tested in situ close to a tramway track in Grenoble. Measurements show that the device provides more than 10 dB (A) of attenuation for a close receiver located at the typical height of human ears. These results therefore seem to confirm the applicability of such protections to efficiently decrease noise exposure in urban areas
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Trinh, Van Hai. "Effect of membrane content on the acoustical properties of three-dimensional monodisperse foams : experimental, numerical and semi-analytical approaches." Thesis, Paris Est, 2018. http://www.theses.fr/2018PESC1016/document.
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Ce travail concerne principalement la détermination des propriétés acoustiques de mousses. Il s’agit d’un projet mené dans le cadre d’une collaboration entre une équipe de physico-chimie des mousses chargée de l’élaboration de matériaux modèles (laboratoire Navier UMR 8205 CNRS) et une équipe d’acousticiens chargée de l’étude de leurs propriétés acoustiques (laboratoire MSME UMR 8208 CNRS). Cette thèse s’articule essentiellement autour de trois parties principales, dont le contenu est résumé ci-dessous. 1) La première partie porte sur la génération de surfaces de réponse par des approximations polynomiales, dans le but de disposer d'un modèle intermédiaire entre le modèle éléments finis micro-macro et la réponse macroscopique. Au lieu d'appeler le modèle éléments finis systématiquement dans un travail d'optimisation, on a recourt à la surface de réponse qui contient l'information associée aux points de calcul éléments finis ainsi que les interpolations correspondantes. Ce manuscrit a été publié dans le journal AAA sous forme de communication rapide. 2) La deuxième partie porte sur la mise au point d'un modèle semi-analytique définit à partir d'une formule disponible pour prédire la perméabilité d'une plaque infinie percée par un trou de surface connue. Ce modèle, utilisé de manière appropriée, permet de calculer la perméabilité de mousses dont la taille de bulles est constante et le taux de fermeture de membranes variable. Des validations numériques par éléments finis et expérimentales sont proposées. L'article a été accepté pour publication dans la revue Physical Review E. 3) La troisième partie, porte sur un calcul éléments finis dans lequel un grand nombre de réalisations sont menées de manière à prendre en compte l'ensemble des combinaisons possibles lorsque on dispose de caractérisation expérimentales fines à l'échelle de la microstructure et que l'on souhaite connaitre la réponse de la mousse avec précision. Le manuscrit est en préparation et la revue visée pour ce dernier manuscrit est le journal Materials and Design. Une introduction et une conclusion générale complètent ces trois parties, et permettent de mettre en perspectives ces contributions par rapport à la littérature existante sur le sujetThis work mainly concerns the determination of the acoustic properties of foams. This is a project carried out as part of a collaboration between a team of physico-chemistry of foams in charge of the development of model materials (Navier laboratory UMR 8205 CNRS) and a team of acousticians responsible for the study of their acoustic properties (MSME laboratory UMR 8208 CNRS). This thesis is structured around three main parts, the content of which is summarized below. 1) The first part deals with the generation of response surfaces by polynomial approximations, in order to have an intermediate model between the micro-macro finite element model and the macroscopic response. Instead of calling the finite element model systematically in an optimization work, we use the response surface that contains the information associated with finite element calculation points and the corresponding interpolations. This manuscript was published in the AAA journal as a fast track publication. 2) The second part focuses on the development of a semi-analytical model defined from an available formula to predict the permeability of a circular orifice in a thin plate. This model, used in an appropriate way, makes it possible to calculate the permeability of foams with a constant bubble size but a tuned membrane content. Numerical validations by finite element computations are proposed. The article has been accepted for publication in the journal Physical Review E. 3) The third part deals with a finite element calculation in which a large number of realizations are carried out in order to take into account all the possible combinations when one has fine experimental characterization at the microstructure scale and that one seek to determine the properties of the foam with precision. The manuscript is in preparation and a possible journal for the publication of this manuscript is the journal Materials and Design. An introduction and a general conclusion complete these three parts, and make it possible to discuss these contributions
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Jolkin, Alexei. "EHL investigations using a hybrid technique : an experimental and numerical approach." Licentiate thesis, Luleå tekniska universitet, 1999. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25826.
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This licentiate thesis deals with a hybrid experimental and numerical method, the so-called Hybrid Technique, to study film thickness and pressure distribution and to investigate the behaviour and properties of lubricants in highly loaded EHL conjunctions. The Hybrid Technique combines experimental studies and advanced numerical calculations. In the experimental part of the hybrid approach Optical interferometry and a Ball & Disc system are applied to obtain the colour intensity images of the EHL contact. The images that captured by a colour video system are then subjected for image analysis to evaluate the film thickness maps from the colour interferograms. The pressure distribution is obtained numerically by solving the equation of elastic deformation. Using the Hybrid Technique the pressure and lubricant film thickness in the contact are obtained without having made any assumptions regarding rheological behaviour of the lubricant. This makes the described approach to a very useful tool in investigations of EHL conjunctions under extreme conditions or in the study of multi-phase lubricants. A detailed description of the Hybrid Technique is given. Method is tested out on oil lubricated and grease lubricated contacts. Results are presented and discussed.Godkänd; 1999; 20070403 (ysko)
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Singh, Raj Laxmi. "Strong radiative shocks relevant for stellar environments : experimental study and numerical approach." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066092/document.
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Les chocs forts sont présents dans des phénomènes astrophysiques variés. De tels chocs sont fortement influencés par le rayonnement par son couplage avec l’hydrodynamique. Par suite, leur topologie et leur dynamique sont assez complexes. Générer de tels chocs hypersoniques en laboratoire, dans des conditions contrôlées, est ainsi un outil pertinent pour étudier l’influence du rayonnement et pour comparer aux résultats des simulations numériques. Ces chocs sont générés par des lasers intenses et par des moyens électromagnétiques. La première partie du texte est consacré à l’étude numérique et expérimentale de l’interaction de deux chocs induits par laser se propageant en sens contraires. Les expériences ont été menées sur l’installation laser kJ PALS, qui permet de former deux chocs avec des vitesses propres différentes ($\sim$ 30-55 et 10-25 km/s respectivement) dans des gaz rares à pression faible (moins de 1 bar). Des diagnostics ont été installés : interférométrie visible, spectroscopie visible à résolution spatiale et temporelle, spectroscopie XUV intégrée en temps. Nos expériences montrent une forte interaction entre les deux précurseurs radiatifs. Les paramètres physiques du plasma ont été déduits de ces diagnostics et comparés aux résultats de simulations monodimensionnelles. La seconde partie est consacrée à la conception d’une expérience où le choc est généré de façon électromagnétique. L’optimisation de ce générateur est présentée ainsi que l’environnement expérimental permettant d’étudier des chocs jusqu’à 30 km/s dans des gaz rares peu denses (1 mbar)Strong shocks are present in various astrophysical phenomena. Such shocks are strongly influenced by the radiation through its coupling with hydrodynamics. Thus their topology and dynamics are quite complex. Generating such hypersonic shocks in the laboratory, with controlled conditions, is thus an adequate tool to study the influence of radiation and to compare them with numerical simulations. Such shocks can be generated by intense lasers and electromagnetic devices.The first part of this dissertation concerns the numerical and experimental study of the interaction of two counter propagating laser-driven shocks. The experiments, performed at the kJ PALS laser facility allowed to generate shocks with different speeds ($\sim$ 30-55 km/s and 10-25 km/s), in noble gases and low pressure (less than 1 bar). Several diagnostics were implemented: visible interferometry, time- and space-resolved visible spectroscopy, and time integrated XUV spectroscopy. Our experiment shows a strong interaction of one radiative precursor onto the second one. The physical parameters of the plasma were deduced from the diagnostics and compared with 1-D simulation results. The second part is devoted to the design of an experiment where the shock is generated electromagnetically. The optimization of this generator is presented and also the full experimental set up which allows studying shock $\sim$ 30 km/s in noble gas at $\sim$ 1 mbar
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Follett, S. "Blast analysis of composite V-shaped hulls : an experimental and numerical approach." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7300.
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During armed conflicts many casualties can be attributed to incidents involving vehicles and landmines. As a result mine protective features are now a pre-requisite on all armoured vehicles. Recent and current conflicts in Iraq and Afghanistan have shown that there is a requirement for vehicles that not only provide suitable protection against explosive devices but are also lightweight so that they may travel off-road and avoid the major routes where these devices are usually planted. This project aims to address the following two topics in relation to mine protected vehicles. 1. Could composite materials be used to replace conventional steels for the blast deflector plates located on the belly of the vehicle, and 2. How effective and realistic is numerical analysis in predicting the material response of these blast deflectors. It also looks into the acquisition and support of new equipment into the armed services, where the equipment itself is but one small element of the system involved. The first topic has been addressed by conducting a number of experimental tests using third scale V-shaped hulls manufactured from steel and two types of composite, S2 glass and E glass. These experiments found that, on a weight-for-weight equivalency, the S2 glass was by far the superior material, with very little damage to the outside shape of the hull. The steel was significantly deformed after testing and the E glass, although also did not deform as such, did experience a severe amount of matrix cracking leading to significant loss of structural integrity in that the hull could be easily flexed by hand after the tests. One S2 glass hull was also subjected to a further two explosive tests and although the amount of delamination was severe at the base of the hull there was very little geometry lost to the outside of the shape. The numerical modelling work consisted of the modelling of the mine blast phenomenon in autodyn and comparisons with published experimental and numerical work, with the results in reasonably good agreement. The second part consisted of comparing flat S2 glass plates subjected to varying charge sizes both experimentally and numerically in order to validate the material model, with good agreement. The final stage involved using the validated material model and re-creating the tests done on the V-shaped hulls. The results here at first were not in agreement, but with development of the model and the limitations from the experimental data collection methods applied a model that, when viewed with the experimental results, gave a reasonable representation of the experimental work was created. The management section of the thesis considers previous equipment purchases and what went wrong during their implementation. The Through Life Capability Management model is assessed in relation to an all composite vehicle and identifies some key questions and areas of concern, such as how the management of the DLOD trade-off process should be conducted.
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Williams, Randolph T. "A Combined Experimental and Numerical Approach to Understanding Quartz Cementation in Sandstones." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1339354653.
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Siedel, Benjamin. "Analysis of heat transfer and flow patterns in a loop heat pipe : Modelling by analytical and numerical approaches and experimental observations." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0092/document.
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La miniaturisation toujours plus poussée des composants électroniques génère des contraintes thermiques de plus en plus importantes. Les boucles diphasiques à pompage thermo-capillaire ou LHP suscitent actuellement un intérêt croissant en raison de leurs bonnes performances thermiques, de leur fiabilité et de leur géométrie permettant une grande souplesse d’implantation. Cependant, une meilleure compréhension des phénomènes en jeu dans ces systèmes est essentielle pour optimiser leur conception et prédire leur comportement de manière fiable. Dans ce travail, un modèle analytique est développé qui intègre les paramètres de fonctionnement d’une LHP, afin d’étudier leur influence en fonction des conditions opératoires. Son originalité principale réside dans la détermination précise de la répartition des différents flux thermiques dans l’évaporateur. Une étude de sensibilité est menée pour évaluer les influences de la résistance de contact entre la structure capillaire poreuse et l’enveloppe de l’évaporateur, de la conductivité thermique équivalente du matériau poreux, du coefficient d’accommodation lié aux transferts de chaleur par évaporation et des coefficients de transfert thermique entre la paroi et le milieu ambiant ou la source froide. Cette analyse montre que les paramètres mentionnés ci-dessus peuvent être estimés individuellement, en comparant le modèle à des données expérimentales judicieusement choisies. Un banc expérimental a également été conçu et fabriqué. Partiellement transparent, il permet l’observation de la position des phases liquide et vapeur au cours du fonctionnement. Les influences de la puissance thermique appliquée, de la présence de gaz incondensables et de la température de la source froide sont analysées. Aux puissances thermiques élevées, un régime d’ébullition nucléée est observé dans le réservoir, qui se traduit par une augmentation des flux parasites vers le réservoir donc une dégradation des performances de la LHP. Plusieurs phénomènes oscillatoires sont également observés et corrélés aux observations visuelles des écoulements. Enfin, différents régimes de condensation sont observés et les mécanismes conduisant au détachement des bulles dans le condenseur sont décrits. Un modèle numérique a été développé, afin de simuler le comportement du banc expérimental en se rapprochant au plus près de ses caractéristiques géométriques et thermophysiques. La comparaison entre les prédictions du modèle et les données expérimentales montre les carences des modèles de pertes de charges dans les écoulements diphasiques, pour la configuration étudiée. Les transferts de chaleur et de masse dans l’évaporateur sont analysés, ainsi que l’influence de l’apparition de l’ébullition dans le réservoir et celle de la conductivité thermique de l’enveloppe de l’évaporateur. Les résultats mettent également en évidence l’importance de la conduction thermique longitudinale dans les canalisations dans le cas d’un matériau conducteurThe increasing development of electronics leads to higher constraints regarding their thermal management. Loop heat pipes (LHP) become more and more attractive because they offer thermal efficiency, reliability and large implementation flexibility. However, a better understanding of the physical phenomena involved within them is required in order to optimise their design and predict accurately their operation. An analytical model is developed to highlight the main parameters of a LHP and their influence depending on the operating conditions. Its main originality lies in a thorough consideration of heat transfer in the evaporator. A sensitivity analysis is conducted to study the influence of the contact thermal resistance between the wick and the body of the evaporator, of the effective thermal conductivity of the wick, of the accommodation coefficient linked to the evaporation heat transfer and of the heat transfer with the ambient and with the heat sink. This analysis shows that these parameters can be individually and separately estimated by comparing the model to a set of well-chosen experimental data. An experimental setup is designed and built. It is partially transparent, to observe the location of the liquid and vapour phases in operating conditions. The effects of the heat input, non-condensable gases and of the heat sink temperature are discussed. Nucleate boiling is observed inside the reservoir for high heat fluxes. This phenomenon increases significantly the parasitic heat flux towards the reservoir and therefore decreases the performance of the LHP. Several oscillating phenomena are also observed and correlated to the flow patterns. Finally, distinct condensation regimes are investigated and the mechanisms leading to the bubble detachment in the condenser are discussed. A numerical model is developed in accordance with the geometrical and thermophysical characteristics of the experimental setup. The model is compared with the experimental data. The comparison shows the lack of accuracy of the two-phase pressure drops models in this configuration. Heat and mass transfer in the evaporator are discussed and the effects of boiling in the reservoir and of the thermal conductivity inside the evaporator casing are investigated. The results highlight the importance of the longitudinal thermal conduction inside the tube in the case of conductive materials
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Chaparala, Satish Chandra. "Die stress analysis in plastic encapsulated electronic packages an experimental and numerical approach /." Diss., Online access via UMI:, 2006.
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Ahmad, Yousef. "Oxidation of Graphite and Metallurgical Coke : A Numerical Study with an Experimental Approach." Thesis, KTH, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193604.
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At the royal institute of technology (KTH) in the department of applied process metallurgy, a novel modelling approach has been developed which allows a dynamic coupling between the commercial thermodynamic software Thermo-Calc and the commercial computational fluid dynamic (CFD) software Ansys Fluent, only referred to as Fluent in the study. The dynamic coupling approach is used to provide numerical CFD-models with thermodynamic data for the thermo-physical properties and for the fluid-fluid chemical reactions occurring in metallurgical processes. The main assumption forthe dynamic coupling approach is the existence of local equilibrium in each computational cell. By assuming local equilibrium in each computational cell it is possible to use thermodynamic data from thermodynamic databases instead of kinetic data to numerically simulate chemical reactions. The dynamic coupling approach has been used by previous studies to numerically simulate chemical reactions in metallurgical processes with good results. In order to validate the dynamic coupling approach further, experimental data is required regarding surface reactions. In this study, a graphiteand metallurgical coke oxidation experimental setup was suggested in order to provide the needed experimental data. With the experimental data, the ability of the dynamic couplings approach to numerically predict the outcome of surface reactions can be tested.By reviewing the literature, the main experimental apparatus suggested for the oxidationexperiments was a thermo-gravimetric analyzer (TGA). The TGA can provide experimental data regarding the reaction rate, kinetic parameters and mass loss as a function of both temperature and time. An experimental setup and procedure were also suggested.In order to test the ability of Fluent to numerically predict the outcome of surface reactions, without any implementation of thermodynamic data from Thermo-Calc, a benchmarking has been conducted. Fluent is benchmarked against graphite oxidation experiments conducted by Kim and No from the Korean advanced institute of science and technology (KAIST). The experimental graphite oxidation rates were compared with the numerically calculated graphite oxidation rates obtained from Fluent. A good match between the experimental graphite oxidation rates and the numerically calculated graphite oxidation rates were obtained. A parameter study was also conducted in order to study the effect of mass diffusion, gas flow rate and the kinetic parameters on the numerically calculated graphite oxidation rate. The results of the parameter study were partially supported by previous graphite oxidation studies. Thus, Fluent proved to be a sufficient numerical tool for numerically predicting the outcome of surface reactions regarding graphite oxidation at zero burn-off degree.
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Wagner, Pinto Fábio. "An experimental and numerical approach to investigate the machining performance of engineered grinding tools /." Zürich : ETH/ IWF, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17666.
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Jahromi, Ashkan S. "Analysis of orthogonal edge trimming of uni-directional composites: numerical, analytical, and experimental approach." Diss., Wichita State University, 2010. http://hdl.handle.net/10057/3282.
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As the use of composites increases, more problems arise with processing and manufacturing of this type of material in order to make it a more durable and reliable for today’s applications. One of the most important problems in the cutting of composites is the poor quality of the machined surface and unknown status of the machining forces. Knowing the status of forces during the final machining process helps reduce such defects as delamination and fiber-matrix debonding. This research attempted to develop a fully theoretical model for edge trimming of composites for fiber orientations greater than 90 degrees. The energy method was used as the approach, and the machining forces were compared to the experimental results. A series of experiments were conducted to validate the theoretical foundations.
Composite coupons with different fiber orientations and tool rake angles were prepared for the machining experiments, and the cutting forces were measured using a four-component dynamometer. In addition, a finite element model (FEM) was built to model the depth of damage along the fibers. The theoretical depth of damage compared to the FEM analysis showed that they were in good agreement. The parameters affecting the machining forces of composites can be divided into three categories: tool geometry, material properties, and machining conditions. The effect of all of these parameters is reflected in the formula. In addition to the thrust and cutting forces, the depth of damage along the fibers can be calculated.
It was concluded that the material properties and machining conditions, more than the geometry of an orthogonal cutting tool, are more influential in affecting the processing and manufacturing of composite materials.Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering
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Mehdizadeh-Kafash, Mehdi. "Deformation and fracture behaviour of high-density polyethylene pipe materials : experimental and numerical approach." Thesis, Lille 1, 2009. http://www.theses.fr/2009LIL10116.
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L'utilisation des matériaux polymères dans les applications de l'ingénierie augmente de plus en plus da part le monde. L'utilisation du polyéthylène (PE) dans la construction de canalisations est l'un des exemples les plus courant. Ceci exige de nouvelles méthodes afin d'évaluer la capacité du matériau à supporter des chargements mécaniques. Dans la présente thèse, le comportement contrainte-déformation en grandes déformations du PE haute densité (PEHD) a été examinée dans différentes configurations de triaxialité. Un large domaine de conditions de chargements (traction, compression et cisaillement simple) a été exploré. L'investigation a été réalisée à partir d'échantillons découpés dans des canalisations en PEHD. Les essais de traction ont été faits à partir d'échantillons sabliers présentant plusieurs rayons de courbure afin de fixer différents états de contrainte dans la section médiane. Une attention particulière a été portée à l'évolution de la déformation volumique résultant de l'endommagement par cavitation. L'effet de la triaxialité sur la déformation à rupture a pu également être dégagé. La méthode des éléments finis (EF) a été utilisée pour simuler le comportement en grandes déformations du PEHD. De plus, le phénomène d'endommagement par croissance de vide a été étudié à partir de cellules unitaires soumises à différentes conditions de triaxialité. Afin d'évaluer le comportement à la rupture du PEHD, une méthode expérimentale basée sur l'hypothèse de la séparation de la charge a été élaborée. En outre, une analyse numérique par EF a été réalisée pour le calcul des paramètres de rupture. L'investigation a été réalisée dans les directions longitudinale et radialeThe use of thermoplastic materials in engineering applications is growing more and more all over the world. The use of polyethylene (PE) in pressure vessels and pipelines is one of the most common examples. This issue demands new methodologies in order to assess the material capability to withstand loads. In the present thesis, the stress-strain response under large plastic deformation of high density PE (HDPE) was investigated in different triaxiality frameworks. A wide range of loading conditions (tension, compression and simple shear) was explored. Investigation was performed using specimens cut from HDPE pipes. The tensile tests were achieved on hourglass-shaped specimens with different curvature radii in order to set different stress states in the median cross-section. The tests were achieved by means of an optical measuring system. A particular attention was given on the evolution of volumetric strain resulting from cavitation damage. The effect of stress triaxilality on the fracture strain was also examined. The finite element (FE) method was used to simulate the large deformation bahaviour of HDPE material when subjected to tensile loading. Moreover, the damage phenomenon by void growth was studied using an axisymmetric representative volume element with different triaxiality conditions. In order to evaluate the fracture behaviour of HDPE pipe, an experimental method based on load separation assumption was developed. Furthermore, a numerical analysis using FE method has been conducted for calculating the fracture parameters. The investigation of fracture parameters and bahaviour of HDPE was performed in longitudinal and radial directions
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Schley, Dan R. "Symbolic-Number Mapping in Judgments and Decisions: A Correlational and Experimental Approach." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1448802342.
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Honzawa, Takafumi. "Numerical and Experimental Investigations on Reduction of NO and CO Emissions in City Gas Combustion." Kyoto University, 2020. http://hdl.handle.net/2433/259038.
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Sarrado, Molina Carlos. "Experimental characterization and numerical simulation of composite adhesive joints using the cohesive zone model approach." Doctoral thesis, Universitat de Girona, 2015. http://hdl.handle.net/10803/384001.
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The present thesis aims at developing robust numerical and experimental methods for the simulation of composite adhesive joints. Firstly, a new method for the experimental characterization of adhesive joints is presented. The proposed method widens the range of applicability of the existing methods at the same time that lowers the uncertainty of the results. By means of this method, a critical study on the validity of the existing experimental methods is presented, as well as the thorough characterization of an adhesive in terms of the cohesive laws of the material. The experimental evidences are analyzed to obtain a guideline for the simulation of adhesive joints and a formulation of a new cohesive elements is presented. The proposed formulation allows the simulation of the elastic response, damage and failure of adhesive layers by using experimentally measurable material properties, with no further calibrations required.L’objectiu de la present tesi és el desenvolupament de mètodes numèrics i experimentals robustos per a la simulació de la fractura en unions adhesives de material compòsit. En primer lloc es presenta un nou mètode per a la caracterització experimental d’unions adhesives que amplia el rang d’aplicació dels mètodes existents i en disminueix la incertesa. A partir d’aquí, es realitza un estudi crític sobre la idoneïtat dels mètodes de caracterització d’unions adhesives existents i es presenta la caracterització exhaustiva d’un adhesiu en termes de la llei cohesiva del material. Les evidencies experimentals obtingudes s’analitzen per tal de proporcionar les directrius necessàries per a la simulació d’unions adhesives i es presenta la formulació d’un nou element cohesiu per modelar la resposta elàstica, el dany i la fallada d’adhesius. El model proposat permet l’ús de propietats del material mesurables experimentalment, sense la necessitat de dur a terme ajustaments o calibratges addicionals.
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Eklund, Gustav. "Experimental and Numerical Investigation of Ratcheting Effects in 316L Stainless Steel - The Two-Rod approach." Thesis, KTH, Hållfasthetslära (Inst.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-178802.
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This Master’s Thesis was conducted during spring 2014. An experimental and numerical investigation was conducted on the austenitic 316L stainless steel. The main focus of the study was the investigation of ratcheting effects. Experimentally, the main focus was the two-rod test, which had not been conducted previously. The two-rod test resembles a structure and a load case where ratcheting effects may be produced, although being less complicated than structures used in prior studies. Furthermore, the stress state in the structure is uniaxial. Other tests were also performed to characterize the material. Based on results from uniaxial tensile tests and fully reversed strain cycling of 316L, four material models were calibrated. The four material models were Bi-linear kinematic hardening model Multilinear kinematic hardening model (Mróz) Armstrong-Frederick non-linear kinematic hardening model Chaboche non-linear kinematic hardening model with three superimposed back-stress tensors. The two-rod test was then numerically simulated with different material models. The results from the FE simulations were then compared to the test results obtained from the two-rod tests. The goal, apart from investigating the ratcheting effects in 316L steel, was to evaluate the material models’ ability to reproduce the two-rod test results. The results from the comparison suggest that the bi-linear and the multilinear material model agreed with the test results to a larger extent than the Armstrong-Frederick and Chaboche model. The two non-linear hardening material models predicted in most cases a constant ratcheting rate which did not agree with the test results. Even though the predictions of the two-rod tests with the bilinear and the multilinear models generally was better than predictions with the two non-linear hardening material models, the bilinear and the multilinear models predicted plastic shakedown in certain cases which was not observed in the tests. The employment of an isotropic part in the non-linear kinematic hardening material models might have improved the simulations’ agreement to experimental results. The setup for the two-rod test proved robust and reliable. The results suggest that structural ratcheting effects dominate the two-rod test results. Furthermore, the comparison between simulations and the two-rod tests suggest that a more advanced material model does not necessarily yield in a better prediction.Det här examensarbetet utfördes under våren 2014. En experimentell och numerisk undersökning genomfördes på det austenitiska rostfria stålet 316L. Huvudområdet för studien var att undersöka fenomenet ratcheting (progressiv plastisk deformation). Experimentellt var huvudfokus på det så kallade tvåstångstestet, vilket tidigare inte hade utförts. Tvåstångstestet utgör en struktur och ett lastfall vari ratcheting kan skapas, samtidigt som strukturen är mer renodlad än de som undersökts i tidigare studier för samma ändamål. Dessutom är spänningstillståndet enaxligt i strukturen. Utöver tvåstångsprovning gjordes även ytterligare provning för att karaktärisera materialet. Utgående från resultat från enaxligt dragprov och fullt reverserad töjningsstyrd cykling anpassades fyra materialmodeller efter materialet. Dessa fyra materialmodeller var Bi-linjär kinematiskt hårdnande modell Multilinjär kinematiskt hårdnande modell (Mróz) Armstrong-Frederick icke-linjärt kinematiskt hårdnande modell Chaboche icke-linjärt kinematiskt hårdnande modell med tre superponerade back stress- tensorer. En FEM-modell över tvåstångsprovet användes för att simulera de olika materialmodellernas respons. Resultaten från dessa jämfördes sedan med resultaten från tvåstångsprovningen. Målet, bortsett från att karaktärisera ratchetingeffekterna i 316L-stålet, var att utvärdera materialmodellernas förmåga att återskapa resultaten från tvåstångsprovningen. Resultaten från jämförelsen mellan simuleringarna och tvåstångsprovningen pekar på att den bi-linjära och den multilinjära materialmodellen förmår återskapa provresultaten bättre än Armstrong-Frederick-modellen och Chaboche-modellen. De två sistnämnda materialmodellerna predikterade i de flesta fall konstant ratchetinghastighet, vilket inte överensstämde med provresultaten från tvåstångsprovningen. Även om predikteringen av tvåstångsprovningen med den bi-linjära och multilinjära materialmodellen överlag var bättre än för de icke-linjärt hårdnande materialmodellerna predikterade den bi-linjära och multilinjära materialmodellen i vissa fall plastisk shakedown, vilket inte sågs i provresultaten. Införandet av isotropt hårdnande i de icke-linjärt kinematiskt hårdnande materialmodellerna kan ha förbättrat simuleringarnas överensstämmande med provresultaten då materialet visar på omfattande plastiskt hårdnande, både i monotont dragprov såväl som cykliskt hårdnande. Metoden som utvecklades för tvåstångsprovningen visade sig robust och pålitlig. En slutsats som kan dras är att effekter från materialratcheting förmodligen är små i jämförelse med effekter från strukturratcheting i tvåstångsprovningen. Dessutom kan från jämförelsen mellan simuleringarna och tvåstångsprovningen sägas att en mer avancerad materialmodell inte nödvändigtvis resulterar i en prediktering som överensstämmer bättre med provningen.
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Dauti, Dorjan. "A combined experimental and numerical approach to spalling of high-performance concrete due to fire." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI062/document.
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Le béton est un matériau très utilisé dans l'industrie de construction. Une limite essentielle à un usage de ce matériau est sa dégradation par écaillage lorsqu’il est exposé au feu. Le phénomène d'écaillage consiste en une éjection du béton sous forme d'écailles à la surface du béton exposée à l'incendie. La section de béton s'en trouve progressivement réduite. De plus, ce phénomène expose les armatures et peut conduire à une rupture prématurée de structures telles que les tunnels, les gratte-ciels, les centrales nucléaires etc. De nombreuses recherches ont été consacrées à la mise au point de méthodes de prévention de l'écaillage et à la détermination des paramètres qui ont une influence sur ce phénomène. Cependant, la physique qui contrôle l'écaillage n'est pas encore entièrement comprise. L'objectif principal de la thèse est de fournir une meilleure compréhension des mécanismes impliqués dans l’écaillage du béton en utilisant une approche numérique-expérimentale, i.e., la tomographie neutronique couplée à la modélisation numérique avancée à une échelle adéquate.Dans ce travail, les premières mesures 3D de la teneur en eau du béton (grandeur locale indispensable au suivi du processus de déshydratation potentiellement responsable de l’écaillage) soumis à un chargement thermique sévère ont été réalisées à l'aide de tomographies neutroniques rapides. Le suivi de la déshydratation rapide du béton a été possible en réalisant un scan 3D toutes les minutes grâce à la source neutrons de l'Institut Laue Langevin (leader mondial), à Grenoble, France. Cette vitesse d'acquisition est dix fois plus rapide que toute autre étude tomographique rapportée dans la littérature. Un dispositif, adapté à l'imagerie neutronique et aux essais à haute température, a été développé pour réaliser de telles expériences. L'influence de la taille des agrégats sur la distribution de l'humidité au sein de l'échantillon est présentée. Les résultats quantitatifs sur l'accumulation d'humidité derrière le front de déshydratation, connue sous le nom de 'moisture-clog" et considérée comme un des facteurs principaux engendrant un excès de pression, sont également présentés et discutésEn parallèle, un modèle thermo-hydro-mécanique (THM) entièrement couplé a été mis en œuvre sur le logiciel élément fini Cast3M afin d'étudier et prédire le comportement du béton à haute température. Le code nouvellement implémenté est remarquablement plus rapide (20-30 fois) que le code existant sur lequel il est basé. Une approche mésoscopique a été adaptée au modèle pour prendre en compte l'hétérogénéité du béton. D'abord, le modèle est appliqué à des expériences de la littérature, qui étu-dient les paramètres standards tels que la température, la pression du gaz et la perte de masse. En-suite, des profils d'humidité 1D obtenus à partir d'expériences de radiographie neutronique sont utili-sés pour vérifier et améliorer le modèle en termes de lois de comportement critiques telles que les courbes de déshydratation et de rétention d'eau. Enfin, le modèle est utilisé pour prédire la distribution d'humidité 3D mesurée dans ce travail de doctorat par tomographie neutronique. Entre autres, des simulations THM mésoscopiques sont effectuées pour étudier l'influence d'un agrégat sur le front de séchageConcrete has been extensively used in the construction industry as a building material. A major drawback of this material is its instability at high temperature, expressed in the form of violent or non-violent detachment of layers or pieces of concrete from the surface of a structural element. This phenomenon, known as fire spalling, can lead to the failure of concrete structures such as tunnels, high rise buildings, nuclear power-plants, underground parkings etc. because the reinforcement steel is directly exposed to high temperature and the designed cross section of the concrete elements (e.g., columns, beams, slabs) is reduced. A lot of research has been dedicated on developing preventing methods for spalling and also on determining the parameters that have an influence on it. However, the physics behind this phenomenon is not yet fully understood.In this doctoral, the first 3D measurements of moisture content in heated concrete, which is believed to be one of the processes directly related to spalling, have been performed using in-situ neutron tomography. In order to follow the fast dehydration process of concrete, one 3D scan (containing 500 radiographs) per minute was captured thanks to the world leading flux at the Institute Laue Langevin (ILL) in Grenoble France. This acquisition speed, which is ten times faster than any other experiment reported in the literature, was sufficient to follow the dehydration process. A dedicated setup, adapted to neutron imaging and high temperature, has been developed for performing such kind of experiments. Concrete samples with different aggregate size have been tested. Quantitative analysis showing the effect of the aggregate size on the moisture distribution is presented. Results on the moisture accumulation behind the drying front, known as the moisture-clog, are also presented and discussed.In parallel, a numerically-efficient coupled thermo-hydro-mechanical (THM) model has been implemented in the finite element software Cast3M for understanding and predicting the complex behavior of concrete at high temperature in the context of spalling. The newly implemented code is remarkably faster (20-30 times) than an existing one, on which it is based. A mesoscopic approach has been adapted to the model for taking into account the heterogeneity of concrete. First the model is applied to experiments from literature monitoring standard parameters such as temperature, gas pressure and mass loss. Then, 1D moisture profiles obtained from neutron radiography experiments are used for verifying and improving the model in terms of some critical constitutive laws such as dehydration and water retention curves. Finally, the model is employed for predicting the 3D moisture distribution measured in this doctoral work via neutron tomography. Among others, mesoscopic THM simulations are performed for investigating the influence of an aggregate on the drying front
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Xing, Changhu. "Analysis of the Characteristics of a Squeeze Film Damper by Three-Dimensional Navier-Stokes Equations: A Numerical Approach and Experimental Validation." Akron, OH : University of Akron, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1247355998.
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Dissertation (Ph. D.)--University of Akron, Dept. of Mechanical Engineering, 2009."August, 2009." Title from electronic dissertation title page (viewed 9/2/2009) Advisor, Minel J. Braun; Committee members, Fred K. Choy, Alex Povitsky, Subramaniya I. Hariharan, Robert C. Hendricks, Gerald W. Young; Department Chair, Celal Batur; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
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Tan, Zhi Bin. "Post-Welding Cooling Rate in TCW Joints: An Experimental and Numerical Approach to Understand its Effects." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21889.
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Thermoset Composite Welding (TCW) is a patented technology developed by CRC-ACS that can be used to build structural aircraft assemblies, potentially with a significant cost savings compared to the conventional methods. In TCW, a thermoset prepreg layup is surfaced with an integrated layer of thermoplastic before being welded together to form a welded assembly. As PVDF is a semi-crystalline polymer, its mechanical performance can be affected by post-welding cooling rate. This investigation focused on TCW joints treated with different cooling rates while FEA was used to complement the experimental section by providing strength predictions. Single lap joint was chosen as the main specimen type for its simplicity in manufacturing. Joints with different laminate configurations were tested in a variety of temperatures to study the effect of temperature on joint strength. Across all lay-ups and temperatures, a clear trend emerges where specimens with slower rate produced joints with higher strength. Investigation using DSC and SEM revealed that while percentage of crystallinity between slow and fast cooling rate are relatively similar, the observed spherulite size between two cooling rates are quite different. This indicates that slower cooling rate allows the crystallites to form slowly and grow to a larger size, which strengthen the PVDF material. In a novel approach to study TCW joints from the fracture perspective, a moment loading methodology was adopted and implemented with a custom designed rig to load the DCB specimen using pure equal moment on both sides to simulate a Mode I fracture. The measured G_IC value portrayed a similar picture with the strength-based test where slowly cooled specimen exhibits higher fracture toughness. It is worth noting that the rig design allows specimens to be tested in a mixed-mode configuration, which can be expanded in future work.
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Cumbunga, Judice. "Modeling and optimization of the thermomechanical behavior of metal partsobtained by sintering : Numerical and experimental approach." Electronic Thesis or Diss., Bourgogne Franche-Comté, 2024. http://www.theses.fr/2024UBFCA006.
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Le procédé de frittage sans pression à l'état solide est un traitement thermique appliqué pour améliorer ou ajuster les propriétés du matériau en fonction de son domaine d’application, compte tenu de sa capacité à traiter des pièces à géométrie complexe, de sa grande précision dimensionnelle, de ses petites dimensions et de son adéquation aux matériaux doux et durs. Cependant, la modélisation de ce type de procédé s’avère une tâche difficile, car un modèle approprié doit prendre en compte différents aspects, à savoir le caractère multi-échelle et multiphysique du problème, la forte non-linéarité du matériau, la complexité des géométries et enfin la nature des conditions aux limites, etc. Sur le plan industriel, les paramètres de traitement thermiques appropriés sont principalement obtenus par essais. La simulation numérique permet de réduire les coûts de ces essais et de fournir des prévisions ou des recommandations plus utiles pour la production réelle, que les essais de frittage proprement dits. De nombreux travaux de recherche ont été consacrés aux développements de modèles mathématiques et numériques avec des approches adaptées à différents niveaux ou échelles, tels que la petite échelle (niveau atomique), la méso-échelle (niveau des particules, des grains et des pores), et l'échelle du continuum (niveau des composants). La capacité et la maitrise de pouvoir prédire l'évolution de la microstructure ont placé le modèle mésoscopique (au niveau des particules, des grains et des pores) devant les autres.Sur le plan recherche, la question posée serait donc "Étant donné une pièce brute obtenue par MExAM, comment simuler numériquement l'évolution de la microstructure (à partir d’un état microstructural initial) pour contrôler les changements dans les propriétés thermomécaniques pendant le processus de frittage à l'état solide ?"Un modèle de calcul robuste, basé sur une approche multiphysique et multiéchèle, a été développé, testé et validé. Il permet la prédiction des évolutions de la microstructure et des grandeurs thermiques et mécaniques du matériau. Le modèle repose sur la méthode des éléments finis et prend en compte de manière progressive les couplages multiphysiques (thermique, mécanique et microstructure) influant sur le comportement du matériau. Un traitement particulier a été étudié pour la prise en compte des phénomènes non linéaires. Les résultats des différentes simulations ont montré que le modèle développé est capable de prédire avec une précision correcte le comportement du processus de frittage. Le cas particulier du comportement du matériau pour le MExAM a été présentée, ainsi que la manière d'utiliser le modèle pour optimiser ses propriétés thermomécaniques. L'optimisation a été réalisée en couplant les résultats des différentes simulations avec la méthode Taguchi. Il faut souligner que les résultats obtenus à partir de l'analyse des propriétés des matériaux témoignent de la réussite de l'application du modèle, tant du point de vue de la prévision du comportement microstructural et thermomécanique du matériau, que du point de vue de l'optimisation de ses propriétésThe pressureless solid-state sintering process is a thermal treatment applied to improve or adjust material properties according to its field of application, given its ability to handle parts with complex geometries, high dimensional accuracy, small dimensions and suitability for soft and hard materials. However, modeling this type of process proves to be a difficult task, as an appropriate model needs to take into account various aspects, namely the multi-scale and multi-physics character of the problem, the high non-linearity of the material, the complexity of the geometries and, last but not least, the type of boundary conditions. From an industrial point of view, the appropriate heat treatment parameters are mainly obtained by trial and error. Numerical simulation makes it possible to reduce the cost of these tests and to provide more useful predictions or recommendations for actual production, than sintering tests themselves. Numerous research projects have been devoted to the development of mathematical and numerical models with approaches adapted to different levels or scales, such as the small scale (atomic level), the meso-scale (particle, grain and pore level), and the continuum scale (component level). The ability to predict the evolution of microstructure has put the mesoscopic model (at particle, grain and pore level) ahead of the others.In research terms, the question posed would therefore be "Given a untreated part obtained by MExAM, how can we numerically simulate the evolution of the microstructure (from an initial microstructural state) to control changes in thermomechanical properties during the solid-state sintering process ?"A robust computational model, based on a multiphysics and multi-scale approach, has been developed, tested and validated. It enables us to predict the evolution of the material's microstructure, thermal and mechanical properties. The model is based on the finite element method, and progressively takes into account the multiphysical couplings (thermal, mechanical and microstructure) that influence the material's behavior. Special considerations have been given to the integration of non-linear phenomena. The results of the various simulations have shown that the model developed is capable of predicting the behavior of the sintering process with correct accuracy. The special case of material behavior for MExAM was presented, as well as how to use the model to optimize its thermomechanical properties. Optimization was achieved by coupling the results of the various simulations with the Taguchi method. It should be noted that the results obtained from the analysis of material properties confirm the successful application of the model, both in predicting the microstructural and thermomechanical behavior of the material, and in optimizing its properties
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Bazin, Clément. "Numerical and experimental studies of two-phase flows interacting with a bundle of tubes." Electronic Thesis or Diss., Institut polytechnique de Paris, 2023. http://www.theses.fr/2023IPPAX106.
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Les générateurs de vapeur (GV) des centrales nucléaires sont composés de faisceaux de tubes soumis à des écoulements diphasiques eau-vapeur. Les vibrations liées à cette interaction peuvent induire des dommages (fatigue et usure par frottement et chocs) pouvant entraîner de graves conséquences pour la sûreté nucléaire.Dans le cadre de la prévention des risques vibratoires des tubes de GV des études expérimentales sont réalisées à l'aide de faisceaux analytiques de tubes droits soumis à un écoulement transverse diphasique.En parallèle, il est également important de développer un outil de simulation numérique permettant d'accéder à des données et des informations difficilement mesurables.L'objectif de cette thèse est donc de simuler l’interaction entre un fluide diphasique et une structure rigide (tube unique ou faisceau de tubes), à l'aide du code NEPTUNE_CFD. Ces simulations doivent permettre de reproduire le chargement mécanique exercé par le fluide sur les tubes. La modélisation employée dans cette thèse repose sur un modèle à deux-fluides - trois-champs, comprenant un champ liquide continu, un champ de gaz dispersé, composé de bulles peu déformées, et un champ hybride dispersé-continu pour tenir compte des bulles très déformées et des poches de gaz. La première partie de ce travail s'est concentrée sur la validation du couplage diphasique-turbulence liquide ainsi que sur la modification et l'adaptation de la modélisation pour mieux prendre en compte la présence d'une structure immergée. De nouvelles modélisations pour la force de dispersion turbulente, les termes sources de coalescence et fragmentation, la masse ajoutée et le critère d'activation du champ continu ont été proposées. Dans la deuxième partie de ce travail, nous avons simulé l’écoulement diphasique autour d’un tube unique fixe, afin d'en extraire une physique sous-jacente et d'identifier ses limites et lacunes. Enfin, dans la dernière partie de ce travail, nous avons simulé l’interaction d’un écoulement diphasique avec un faisceau de tubes rigides. Les résultats numériques ont été comparés aux mesures expérimentales. Cette approche nous a permis de justifier l'intérêt de notre modélisation, de trouver des similitudes entre les résultats numériques et expérimentaux, tout en proposant des pistes d'améliorationThe steam generators (SG) in nuclear power plants are made up of bundles of tubes subjected to two-phase water-steam flows. Vibrations related to this interaction can cause damage (fatigue, wear due to friction and shocks) that can lead to serious consequences for nuclear safety.In the context of preventing vibrational risks in SG tubes, experimental studies are conducted using analytical bundles of straight tubes subjected to transverse two-phase flow. In parallel, it is also important to develop a numerical simulation tool to access data and information that are difficult to measure.The goal of this work is to simulate the interaction between a two-phase fluid and a rigid structure (single tube or bundle of tubes) using the NEPTUNE_CFD code. These simulations aim to reproduce the mechanical loading exerted by the fluid on the tubes. The modeling used in this work is based on a two-fluid - three-field model, including a continuous liquid field, a dispersed gas field made up of slightly deformed bubbles, and a dispersed-continuous hybrid field to account for highly deformed bubbles and gas pockets. The first part of this work focused on the validation of the two-phase liquid-turbulence coupling as well as the modification and adaptation of the modeling to better account for the presence of an immersed structure. New models for turbulent dispersion force, source terms of coalescence and break-up, added mass, and the activation criterion of the continuous field were proposed. In the second part of this work, we simulated the two-phase flow around a fixed single tube to extract underlying physics, and identify its limitations and shortcomings. Finally, in the last part of this work, we simulated the interaction of a two-phase flow with a bundle of rigid tubes. The numerical results were compared to experimental measurements. This approach allowed us to justify the relevance of our modeling, find similarities between numerical and experimental results, while also suggesting areas for improvement
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Bütehorn, Steffen [Verfasser]. "Experimental and Numerical Investigation of the Hydrodynamics of Microfiltration Processes Using a Multi-Scale Approach / Steffen Bütehorn." Aachen : Shaker, 2011. http://d-nb.info/1072592649/34.
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Tecle, Amanuel Sebhatu. "Evaluation of Wind-Induced Internal Pressure In Low-Rise Buildings: A Multi Scale Experimental and Numerical Approach." FIU Digital Commons, 2011. http://digitalcommons.fiu.edu/etd/529.
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Hurricane is one of the most destructive and costly natural hazard to the built environment and its impact on low-rise buildings, particularity, is beyond acceptable. The major objective of this research was to perform a parametric evaluation of internal pressure (IP) for wind-resistant design of low-rise buildings and wind-driven natural ventilation applications. For this purpose, a multi-scale experimental, i.e. full-scale at Wall of Wind (WoW) and small-scale at Boundary Layer Wind Tunnel (BLWT), and a Computational Fluid Dynamics (CFD) approach was adopted. This provided new capability to assess wind pressures realistically on internal volumes ranging from small spaces formed between roof tiles and its deck to attic to room partitions. Effects of sudden breaching, existing dominant openings on building envelopes as well as compartmentalization of building interior on the IP were systematically investigated.
Results of this research indicated: (i) for sudden breaching of dominant openings, the transient overshooting response was lower than the subsequent steady state peak IP and internal volume correction for low-wind-speed testing facilities was necessary. For example a building without volume correction experienced a response four times faster and exhibited 30-40% lower mean and peak IP; (ii) for existing openings, vent openings uniformly distributed along the roof alleviated, whereas one sided openings aggravated the IP; (iii) larger dominant openings exhibited a higher IP on the building envelope, and an off-center opening on the wall exhibited (30-40%) higher IP than center located openings; (iv) compartmentalization amplified the intensity of IP and; (v) significant underneath pressure was measured for field tiles, warranting its consideration during net pressure evaluations. The study aimed at wind driven natural ventilation indicated: (i) the IP due to cross ventilation was 1.5 to 2.5 times higher for Ainlet/Aoutlet>1 compared to cases where Ainlet/AoutletCFD based IP responses. Comparisons with ASCE 7-10 consistently demonstrated that the code underestimated peak positive and suction IP.
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Jasim, Alia. "Exploring the complexity of groundwater flow in volcanic terrains : a combined numerical, experimental and field data approach." Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.702894.
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Eichheimer, Philipp [Verfasser], and Gregor J. [Akademischer Betreuer] Golabek. "Fluid flow in porous media : A combined numerical and experimental approach / Philipp Eichheimer ; Betreuer: Gregor J. Golabek." Bayreuth : Universität Bayreuth, 2020. http://d-nb.info/1213348897/34.
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Mishra, Brijes. "Analysis of cutting parameters and heat generation on bits of a continuous miner using numerical and experimental approach /." Morgantown, W. Va. : [West Virginia University Libraries], 2007. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5514.
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Thesis (Ph. D.)--West Virginia University, 2007.Title from document title page. Document formatted into pages; contains ix, 104 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 94-96).
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Thomaidis, Konstantinos. "Do mantle xenoliths preserve water signature from the lithospheric mantle and how ? : An analytical, experimental and numerical approach." Electronic Thesis or Diss., Université de Lille (2022-....), 2022. http://www.theses.fr/2022ULILR008.
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L'eau sous forme de défauts ponctuels dans la structure des pyroxènes (pxs) des xénolites du manteau est fréquemment utilisée pour tracer la teneur en eau du manteau lithosphérique. Cependant, on sait peu de choses sur le mécanisme qui permet aux xénolites de conserver les signatures hydrogène (H) profondes et si l'on peut éviter une réinitialisation complète ou partielle par réaction avec le magma hôte pendant le transport. En particulier, on ne sait pas : 1) comment la teneur en eau des xénolites est modifiée par le mode d'éruption et pendant le refroidissement de la lave en surface 2) comment les joints de grains (gb) peuvent affecter l'échange H du xénolite avec le magma. L'objectif de cette thèse est de mieux comprendre ces deux aspects de la préservation de la signature de l'eau dans les xénolites mantelliques.La première question est abordée à travers une étude des xénolites de péridotites de deux localités du Massif Central, Allègre et Ray Pic. Nous avons effectué environ 1000 analyses ponctuelles par FTIR et mesures de profil dans des cristaux ol, cpx et opx provenant de 16 xénolites collectés sur les deux localités. Les deux localités ont des structures de coulée de lave différentes, Allègre est un lac de lave figé et a une structure verticale tandis que Ray Pic est une coulée de lave typique allongée/horizontale. Les deux études montrent qu'il n'y a aucune preuve que le refroidissement et la solidification des coulées basaltiques affectent la teneur totale en eau des pxs dans les xénolites du manteau. Cependant, la comparaison des xénolites du dépôt pyroclastique avec ceux de la coulée de lave à Ray Pic montre que la concentration en eau est fortement affectée par le degré de dégazage du magma avant l'éruption. Par contre, des xénolites avec de pxs présentant différentes signatures spectrales, coexistent dans la même coulée de lave. La mise en place et le dégazage n'affectent donc pas les signatures spectrales, suggérant des signatures antérieurement peuvent être conservées.Pour la deuxième question, nous nous sommes concentrés sur l'étude du rôle des gb sur l'échange isotopique de H des xénolites avec leur environnement. Nous avons utilisé une approche combinant expérimentation et numérique. Nous présentons les résultats d'expériences d'échange hydrogène/deutérium réalisés dans monocristaux d'opx et des morceaux cubiques de taille centimétrique provenant d'un même xénolite. Les expériences ont été réalisées entre 600-900°C dans un gaz enrichi en deutérium (D), à pression ambiante. Nous avons comparé les profils de diffusion mesurés dans les monocristaux et les opx situés au bord des cubes avec les profils de diffusion dans les opx à l'intérieur des cubes. Les profils de diffusion ont été analysés grâce à un logiciel de modélisation numérique 2D (Idefick) original. Nos lois de diffusion H-D pour la diffusion intra-cristalline dans les opx mantelliques sont légèrement plus lentes mais comparables à celles proposées dans la littérature pour l'enstatite synthétique pure. Les profils OH-OD enregistrés dans les opx à l'intérieur des cubes ne sont que légèrement plus courts que ceux enregistrés dans les opx au bord des cubes. Ces résultats montrent que la diffusion isotopique de H dans les gb est suffisamment rapide pour équilibrer rapidement les cristaux d'opx à l'intérieur d’échantillons centimétriques. La diffusion aux gb impliquant l'échange H-D dans les xénolites est au moins 3 ordres de grandeur plus rapide que la diffusion intra-cristalline dans l'opx. C’est une première preuve que dans la nature, la signature δD des xénolithes est très probablement contrôlée par l'équilibre avec le magma hôte, même dans le cas de xénolithes de taille conséquentes. Ceci explique pourquoi les pxs de la plupart des xénolithes du manteau ont des signatures δD appauvries. Celles-ci reflètent plutôt un équilibre avec un magma dégazé qu'une signature originale du manteauWater in the form of hydrous point defects in the crystal structure of pyroxenes (pxs) from mantle xenoliths is frequently used to trace the water content in the lithospheric mantle. However, little is known on the mechanism that allows xenoliths to preserve deep hydrogen (H) signatures and if we can avoid complete or partial reset by reaction with the host magma during transport. Especially, it is unknown: 1) how much water content of xenoliths is modified by the eruption mode (effusive versus explosive) and during lava emplacement 2) how grain boundaries (gb) can affect H exchange in the xenolith with the surrounding melt. The aim of this thesis is to provide better understanding on these two aspects of the preservation of water signature in mantle xenoliths. The first question is approached through an analytical study of peridotite xenoliths from two localities in the French Massif Central, Allègre and Ray Pic. We performed around 1000 FTIR point analysis and profile measurements in ol, cpx and opx crystals derived from 16 xenoliths collected on both localities. The two localities have different lava flow structures, Allègre is a frozen lava lake and has a vertical structure while Ray Pic basaltic lava flow is a typical elongated/horizontally one. In Allègre, we studied xenoliths from different heights in the 30 m lava body. In Ray Pic we sampled xenoliths along the 20 km lava flow and in a pyroclastic deposit at the volcanic edifice. Both studies show that there is no evidence that cooling and solidification of basaltic flows affect the total water content of pxs in mantle xenoliths. However, the comparison of the xenoliths from the pyroclastic deposit and the lava flow at Ray Pic shows that the water concentration is strongly affected by the degree of degassing of the magma prior the eruption. In addition, xenoliths with different spectral signatures of pxs coexist with the same lava flow suggesting that the emplacement and degassing does not affect spectral signatures, suggesting that they may preserve signatures acquired earlier.For the second question, we concentrated on the study of the role of gb on the H isotopic exchange of the xenoliths with its surrounding. We used a combine experimental and numerical approach. In our experimental approach, we present results from hydrogen-deuterium exchange experiments performed in cm-size cubic pieces of a natural xenolith, a spinel lherzolite aggregate. Experiments were performed between 600-900oC in a deuterium (D) enriched gas, at room pressure. We used single crystals of opx from the same xenolith, as sensors of the progress of the exchange within the polycrystalline aggregates. We compared diffusion profiles measured in single crystals and opx located at the edge of the cubes with diffusion profiles in opx inside the cubes, not directly in contact with the gas. Diffusion profiles were analysed through a 2D numerical modelling software (Idefick). Our H-D diffusion laws for intra-crystalline diffusion in mantle opx are slightly slower but comparable to the ones in literature for synthetic pure enstatite. OH-OD profiles recorded by FTIR in opx inside the cubes are only moderately shorter than the ones recorded in opx at the edge of the cubes (i.e. apparent diffusion inside the cubes are only moderately slower). These results indicate that the isotopic diffusion of H in gb is fast enough to equilibrate rapidly the opx crystals inside the cube xenoliths. It shows that grain boundary diffusion involving H-D exchange in xenoliths is at least 3 orders of magnitude faster than intra-crystalline diffusion in opx. This can be a first-evidence that in nature the δD signature of xenoliths is very likely controlled by the equilibrium with the host magma even in the case of xenoliths with large grain size. It provides explanation why pxs from most mantle xenoliths have depleted δD signatures. These rather reflect equilibrium with a degassed magma than an original mantle signature
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Massaoudi, Imane. "Domain Decomposition Approach for Deterministic/Stochastic EMC Time-Domain Numerical and Experimental Applications. Alleviating the Curse of Dimensionality." Electronic Thesis or Diss., Université Clermont Auvergne (2021-...), 2023. http://www.theses.fr/2023UCFA0150.
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Cette thèse introduit une nouvelle méthode de décomposition de domaine (DD) pour résoudre des problèmes électromagnétiques stochastiques linéaires dans le domaine temporel. Les approches de décomposition temporelles sont déjà largement utilisées pour gérer la complexité des modèles en effectuant des calculs à un niveau local, mais elles nécessitent souvent l'échange d'informations et de résultats de simulation pour chaqueitération temporelle. La technique proposée consiste à diviser un système linéaire global en sous-systèmes qui ne se chevauchent pas via une ou plusieurs interfaces d'échange ponctuelles. Elle est basée sur l'évaluation des réponses impulsionnelles de chaque sous-système indépendamment (solutions partielles) et sur leur combinaison linéaire par le biais de produits de convolution. Comme aucune information sensible ou propriétairede chaque sous-système n'est requise pour l'échange, la confidentialité des modèles est préservée. La méthode a été extensivement appliquée à plusieurs configurations de réseaux de lignes de transmission sur la base de simulations numériques et de set-ups expérimentaux afin d'évaluer ses performances et ses limites. Cette validation complète a démontré l'efficacité de la méthode et son potentiel pour des problèmes CEM linéairesplus complexes. Cependant, un autre niveau de complexité, traduit par la dimension d'incertitude, s'ajoute aux problèmes du monde réel. Bien que l'efficacité de la technique DD soit démontrée pour l'analyse stochastique en propageant l'incertitude dans les sous-modèles, le coût de calcul croît de manière exponentielle avec l'augmentation du nombre de variables aléatoires dans le système. Pour relever ce défi, connu sous le nom demalédiction de la dimensionnalité, la méthode de collocation stochastique a été associée à l'approche de décomposition de domaine, basée sur une stratégie hors ligne et en ligne motivée par la nature asynchrone de la technique DD permettant la séparation des variables aléatoires. Les validations numériques obtenues pour des applications de réseaux de lignes de transmission soulignent l'intérêt de cette approche originale avec laréduction spectaculaire du coût d'évaluation du modèleThis thesis introduces a novel domain decomposition (DD) method to solve linear stochastic electromagnetic problems in time-domain. Temporal decomposition approaches are already widely used to manage models' complexity by performing computations at a local level, however, they often require the exchange of information and simulation results for each time iteration. The proposed technique consists of splitting a global linear systeminto non-overlapping sub-systems via one or several one-point exchange interfaces. It is based on the evaluation of impulse responses of each sub-system independently (partial solutions) and their linear combination through convolution products. As no sensitive or proprietary information of each sub-system is required for exchange, the confidentiality of the models is preserved. The method was extensively applied for several configurations oftransmission line networks based on computational simulations and experimental set-ups to assess its performance and limitations. This comprehensive validation demonstrated the method's efficiency and potential for more complex linear EMC problems. However, another level of complexity, translated by the uncertainty dimension, adds to real-world problems. Although the efficiency of the DD technique is demonstrated forstochastic analysis by propagating the uncertainty in the sub-models, the computational cost grows exponentially with the increasing number of random variables in the system. To tackle this challenge, known as the curse of dimensionality, the stochastic collocation method was associated with the domain decomposition approach, based on an offline-online strategy motivated by the asynchronous nature of the DD technique allowing random variable separation. Numerical validations obtained for transmission line networkapplications highlight the interest of this original approach with the dramatic reduction of the evaluation cost of the model
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Zebian, Samar. "Influences of cultural artifacts and social practices on number conceptualisation, experimental and ethnographic approaches to everyday numeric cognition." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58249.pdf.
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Kim, Eui-Jong. "Development of numerical models of vertical ground heat exchangers and experimental verification : domain decomposition and state model reduction approach." Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0026/document.
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Dans le contexte énergétique actuel, les pompes à chaleur (PAC) géothermiques sont parmi les technologies les plus performantes pour augmenter l’efficacité énergétique des bâtiments. Par contre le coût initial et l’encombrement des capteurs enterrés traditionnels peuvent être un obstacle à sa diffusion sur le marché des énergies renouvelables. Pour réduire ces coût et encombrement, une réflexion sur l’adjonction d’un système d’appoint et/ou de recharge thermique du sol aux capteurs enterrés est actuellement en cours de tests. Les outils actuels de modélisation des capteurs enterrés obtiennent en effet de bons résultats mais seulement pour un dimensionnement classique en régime permanent. Les modèles existants ne permettent donc pas de représenter correctement les dynamiques rapides des échanges entre le sol et les tubes et cela est d’autant plus vrai si l’on adjoint le système de recharge solaire. Par conséquence, cette thèse a pour objectif de développer les modèles fins et dynamiques nécessaires à l’analyse des phénomènes transitoires dans les capteurs enterrés eux-mêmes. Un maillage fin, sur les bases de la triangulation de Delaunay, est choisi pour le forage ainsi que pour le sol avoisinant. Une approche numérique en 3D (FVM + FEM) peut être obtenue sur les bases de la discrétisation spatiale du domaine. Cette approche appliquée brutalement induirait des temps de calcul très élevés et de toute façon incompatible avec les moyens informatiques ordinaires. Afin de répondre à l’ensemble de ces problèmes, différentes techniques ont été utilisées afin d’accélérer le temps de calcul: décomposition de domaine, emboîtement des pas de temps de calcul pour chaque sous-domaine, réduction des modèles d’états de chaque sous-domaine et finalement couplages temporels et spatiaux des équations de transferts de l’ensemble du problème. Ce dernier est développé particulièrement sur les bases de la méthode des éléments finis. Par ailleurs, un modèle hybride est développé en combinaison de différentes approches. Une approche numérique est adoptée pour la modélisation du puits et la modélisation des transferts de chaleur dans le sol environnant est faite par l’utilisation de solutions analytiques. Ainsi, ce modèle est implanté dans TRNSYS. Une plate-forme expérimentale comprenant trois puits verticaux couplés à une pompe à chaleur géothermique est également présentée. Les résultats expérimentaux sont comparés avec les résultats de la simulation aussi bien au niveau de la température du fluide qu’à la température à différentes profondeurs dans les puits. Le modèle développé donne des résultats très similaires avec ceux qui sont obtenus grâce à l’expérimentation même lors que les pas de temps sont très petits. Il y a des choses à améliorer dans ce modèle développé, mais cela concerne essentiellement l’accélération du temps de calcul. Nous avons constaté que les modèles que nous avons dévéloppés donnent des résultats meilleurs à pas de temps courts que les modèles classiques. Il faut donc bien préciser le domaine d’utilisation de chacun des modèles: consommation sur le long terme, stratégie de contrôle de la PAC, les transferts de chaleur à l’intérieur du puits et etc. De plus, une application du modèle dans le dimensionnement d’échangeurs ainsi que l’investigation de son impact sur le sol avoisinant est également envisagée. Finalement, la méthodologie de modélisation présentée dans ce travail pourrait être aussi utilisé pour différents types d’échangeurs, ouvrant aussi la porte à une analyse fine dans le domaine géothermiqueGround-source heat pump systems with vertical ground heat exchangers (GHE) are gaining popularity worldwide for their higher coefficients of performance and lower CO2 emissions. However, the higher initial cost of installing the borehole GHEs is a main obstacle to spread the systems. To reduce the required total GHE length and efficiently operate the systems, various systems such as hybrid ones (e.g. solar heat injection) have recently been introduced. Accurate prediction of heat transfer in and around boreholes of such systems is crucial to avoid costly overdesigns or catastrophic failures of undersized systems as it is for typical GCHP systems. However, unlike the traditional sizing methods, it is increasingly required to take into account detailed borehole configuration and transient effects (e.g. short circuit effects between U-tubes). Many of the existing GHE models have been reviewed. Some of these models have serious limitations when it comes to transient heat transfer, particularly in the borehole itself. Accordingly, the objective of this thesis is to develop a model that is capable to accurately predict thermal behaviors of the GHEs. A precise response to input variations even in a short time-step is also expected in the model. The model also has to account for a correct temperature and flux distribution between the U-tubes and inside the borehole that seems to be important in the solar heat injection case. Considering these effects in 3D with a detailed mesh used for describing the borehole configurations is normally time-consuming. This thesis attempts to alleviate the calculation time using state model reduction techniques that use fewer modes for a fast calculation but predict similar results. Domain decomposition is also envisaged to sub-structure the domain and vary the time-step sizes. Since the decomposed domains should be coupled one another spatially as well as temporally, new coupling methods are proposed and validated particularly in the FEM. For the simulation purpose, a hybrid model (HM) is developed that combines a numerical solution, the same one as the 3D-RM but only for the borehole, and well-known analytical ones for a fast calculation. An experimental facility used for validation of the model has been built and is described. A comparison with the experimental results shows that the relatively fast transients occurring in the borehole are well predicted not only for the outlet fluid temperature but also for the grout temperatures at different depths even in very short time-steps. Even though the current version of 3D-RM is experimentally validated, it is still worth optimizing the model in terms of the computational time. Further simulations with the 3D-RM are expected to be carried out to estimate the performance of new hybrid systems and propose its appropriate sizing with correspondent thermal impacts on the ground. Finally, the development of the model 3D-RM can be an initiation to accurately model various types of GHE within an acceptable calculation time
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KIM, Eui-Jong. "Development of numerical models of vertical ground heat exchangers and experimental verification : domain decomposition and state model reduction approach." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00684138.
Full textAbstract:
Ground-source heat pump systems with vertical ground heat exchangers (GHE) are gaining popularity worldwide for their higher coefficients of performance and lower CO2 emissions. However, the higher initial cost of installing the borehole GHEs is a main obstacle to spread the systems. To reduce the required total GHE length and efficiently operate the systems, various systems such as hybrid ones (e.g. solar heat injection) have recently been introduced. Accurate prediction of heat transfer in and around boreholes of such systems is crucial to avoid costly overdesigns or catastrophic failures of undersized systems as it is for typical GCHP systems. However, unlike the traditional sizing methods, it is increasingly required to take into account detailed borehole configuration and transient effects (e.g. short circuit effects between U-tubes). Many of the existing GHE models have been reviewed. Some of these models have serious limitations when it comes to transient heat transfer, particularly in the borehole itself. Accordingly, the objective of this thesis is to develop a model that is capable to accurately predict thermal behaviors of the GHEs. A precise response to input variations even in a short time-step is also expected in the model. The model also has to account for a correct temperature and flux distribution between the U-tubes and inside the borehole that seems to be important in the solar heat injection case. Considering these effects in 3D with a detailed mesh used for describing the borehole configurations is normally time-consuming. This thesis attempts to alleviate the calculation time using state model reduction techniques that use fewer modes for a fast calculation but predict similar results. Domain decomposition is also envisaged to sub-structure the domain and vary the time-step sizes. Since the decomposed domains should be coupled one another spatially as well as temporally, new coupling methods are proposed and validated particularly in the FEM. For the simulation purpose, a hybrid model (HM) is developed that combines a numerical solution, the same one as the 3D-RM but only for the borehole, and well-known analytical ones for a fast calculation. An experimental facility used for validation of the model has been built and is described. A comparison with the experimental results shows that the relatively fast transients occurring in the borehole are well predicted not only for the outlet fluid temperature but also for the grout temperatures at different depths even in very short time-steps. Even though the current version of 3D-RM is experimentally validated, it is still worth optimizing the model in terms of the computational time. Further simulations with the 3D-RM are expected to be carried out to estimate the performance of new hybrid systems and propose its appropriate sizing with correspondent thermal impacts on the ground. Finally, the development of the model 3D-RM can be an initiation to accurately model various types of GHE within an acceptable calculation time.
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Pachera, Paola. "Integrated experimental and numerical approach to the biomechanics of surgical meshes evaluating interaction phenomena with regard to abdominal wall repair." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424314.
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The research activity performed is addressed to the evaluation of the interaction phenomena between surgical meshes and native biological tissues and structures, with the aim to assess the biomechanical compatibility, which represents a mandatory factor for successful adoptions in different surgical procedures. The mechanical characterization of meshes for repairs is performed by means of an integrated experimental-numerical approach, in direct correlation with the surgical techniques.
Surgical grafts can origin from different sources and they can be classified as synthetic or biological, characterized by peculiar biochemical and mechanical properties and, consequently, by different biomechanical performances. Biological grafts are derived from collagen-rich tissues and can be drawn from animal (xenografts) or human (allograft) sources, the latter are usually obtained from the fascial system. For this reason, the mechanical characterization of fascial tissues is performed, evaluating the in situ functional role in the interaction with surrounding biological structures. With the purpose to interpret fascial tissues mechanical behaviour, which is characterized by anisotropy, coupled geometric and material non-linearity and time-dependent phenomena, a specific fiber reinforced visco-hyperelastic model is provided. The constitutive parameters evaluation is performed through the minimization of a cost function that defines the discrepancy between experimental data and results from the model of the tensile tests. The optimization technique, based on the Simulated Annealing optimization algorithm, leads to the definition of the set of constitutive parameters to be adopted within the constitutive formulation and implemented in the model, with the purpose to achieve a suitable description of tissue in situ mechanical behaviour.
The preliminary phase of fascial tissues performances is investigated through numerical analysis of the anterior compartment of the leg. The response in this region allow for a definition of the characteristic facial tissues behaviour and is of clinical interest in the several painful syndrome, as the compartment syndrome, also offering the possibility of several references in literature.
As an example of xenograft, Permacol ™ is characterized through experimental analysis and constitutive modelling. It is derived from decellularized and cross-linked porcine skin and it is a graft commonly used in abdominal wall surgery.
As far as synthetic meshes is concerned, Bard® Soft mesh is studied, as a lightweight, large pore monofilament polypropylene mesh, following the above mentioned procedure.
The mechanical investigation of different kinds of surgical meshes is fundamental for the definition of the numerical model of the herniated and repaired human abdominal wall. The reconstruction of the abdominal region is based on MR images integrated with data from literature. Constitutive formulations of the different biological tissues of the anatomical region are provided. The numerical model allows the analysis of different configurations, firstly considering the healthy abdomen to assess its overall mechanical behaviour in physiological conditions. Then a hernia defect is introduced in the abdominal wall, with size and position defined in accordance with clinical evidences, virtually repaired by means of different kinds of grafts (biologic and synthetic). The purpose is to evaluate the mechanical interaction between native abdominal wall tissues and structures and surgical meshes, to assess the mechanical functional response and compatibility. The analysis allows the comparison between physiological and pathological conditions and between different kinds of meshes, by means of the estimation of the stress and strain fields within biological tissues and prosthesis. Attention is paid to the interaction at tissue-implant interface, providing a useful computational tool for the evaluation of surgical strategies in dependence on prosthesis configuration.
The investigation entails a relevant experimental effort, essential for the extensive numerical analysis of the anatomical district considered, providing a result evaluation by direct correlation with surgical competences.Lo scopo della presente ricerca consiste nella valutazione dei fenomeni di interazione che si vengono a creare nell’accoppiamento di mesh chirurgiche e tessuti e strutture biologiche. La valutazione della compatibilità meccanica tra tessuti e impianto rappresenta un fattore fondamentale per il buon esito dell’intervento. In quest’ottica, risulta necessaria la caratterizzazione meccanica delle mesh chirurgiche che viene condotta attraverso un approccio numerico-sperimentale integrato, in diretta correlazione con le tecniche chirurgiche. Le mesh chirurgiche hanno differente origine e possono essere classificate come sintetiche o biologiche, caratterizzate da particolari proprietà biochimiche e meccaniche e, conseguentemente, da differenti prestazioni. Le mesh biologiche sono ricavate da tessuti ricchi di collagene e possono essere di origine animale (xenograft) o umana (allograft), queste ultime sono principalmente ottenute dal sistema fasciale. Per questo motivo i tessuti fasciali vengono caratterizzati meccanicamente, valutandone il ruolo funzionale in situ in interazione con le circostanti strutture biologiche. Uno specifico modello visco-iperelastico e fibrorinforzato viene utilizzato allo scopo di interpretare il comportamento meccanico dei tessuti biologici, caratterizzati da proprietà di anisotropia, grandi deformazioni e fenomeni dipendenti dal tempo. I parametri costitutivi vengono definiti attraverso la minimizzazione di una funzione costo che esprime la differenza tra dati sperimentali e dati numerici. La tecnica di ottimizzazione, basata sull’algoritmo di ottimizzazione del Simulated Annealing, porta all’individuazione di un set di parametri costitutivi che vengono adottati nella formulazione costitutiva, successivamente implementata nel modello numerico, allo scopo di ottenere un’adeguata descrizione del comportamento meccanico del tessuto in situ. Analisi numeriche sul compartimento anteriore della gamba vengono utilizzate per lo studio della meccanica dei tessuti fasciali di questo distretto. Il compartimento anteriore è di particolare interesse clinico a causa delle diverse patologie a carico di tale regione come, ad esempio, la sindrome compartimentale. La mesh chirurgica Permacol™ viene studiata come esempio di xenograft e caratterizzata attraverso analisi sperimentale e modellazione costitutiva. Tale mesh, comunemente utilizzata nella ricostruzione della parete addominale, è ottenuta da derma suino debitamente decellularizzato e trattato al fine di ottenere cross-links. La mesh Bard® Soft viene studiata in quanto esempio di mesh sintetica leggera in polipropilene, caratterizzata da elevata porosità. L’analisi meccanica di diversi tipi di mesh è fondamentale per la definizione del modello numerico della parete addominale erniata e virtualmente riparata. La ricostruzione della geometria della regione addominale viene effettuata attraverso immagini diagnostiche (MR) e dati di letteratura. Nel testo viene specificata la formulazione costitutiva adottata per la descrizione dei diversi tessuti componenti la regione addominale. Il modello numerico permette una prima valutazione del comportamento meccanico globale della parete addominale integra in condizioni fisiologiche. Successivamente, nel modello, viene introdotta una porta erniaria di posizione e dimensioni compatibili con le evidenze cliniche. Tale difetto viene virtualmente riparato con mesh chirurgiche caratterizzate in diverso modo (biologica e sintetica). Lo scopo consiste nella valutazione dell’interazione meccanica tra mesh chirurgiche e i tessuti biologici, considerandone la compatibilità della risposta meccanica funzionale. Le analisi numeriche permettono di valutare il comportamento della parete addominale sana con quello della parete riparata confrontando i campi di tensione e deformazione di tessuti biologici e mesh chirurgica. Il modello numerico proposto fornisce una prima valutazione degli effetti, indotti dalla presenza della protesi, sul comportamento meccanico globale della parete addominale e fornisce gli strumenti per future valutazioni utili alla pianificazione chirurgica e alla configurazione della protesi. Lo studio proposto si fonda su una forte base sperimentale, essenziale per lo svolgimento delle successive analisi numeriche.
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Jönsson, Anders. "Modelling, Simulation and Experimental Investigation of a Rammer Compactor Machine." Licentiate thesis, Luleå : Luleå University of Technology, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-00211.
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This licentiate thesis considers the modelling, simulation and experimental investigation of a rammer compactor machine. The purpose is to develop an efficient and verified method for simulation of rammer compactor machines to be used in the product development process. The experience gained through this work is also intended to be useful for studying other types of dynamic compactor machines. Rammer compactor machines perform impact soil compaction. This is more efficient than static compaction. The machines are often used in places where a high degree of compaction is needed, and where the space for operation is limited. The complexity of this type of machine makes design optimisation through traditional prototype testing impractical. This has pointed to the need for a theoretical model and simulation procedure for predicting the dynamic behaviour of the machine. To be useful for optimisation the theoretical model and simulation procedure must be verified. By concurrently working with theoretical modelling, simulations, experimental verifications, and optimisation an efficient analysis support for product development is achieved. This co-ordination works both ways in an iterative manner: experimental investigations are used to verify theoretical models and simulations; and theoretical models and simulations are used to design good experiments. This Complete Approach concept enables better decisions to be made earlier on in the development process, resulting in a decrease in time-to-market and improved quality. In this thesis, the Complete Approach concept is applied to a rammer soil compactor machine. An introductory iteration is described. The good agreement between theoretical and experimental results indicates that the theoretical model and simulation procedure should prove useful in introductory optimisation studies. The thesis discusses reasons for the remaining discrepancy and suggests improvements in both the theoretical model and the experimental set-up for future iterations.I arbetet studeras det dynamiska beteendet av en jordpackningsmaskin. Syftet är att bygga upp en verifierad modell som kan ligga till grund för vidare produktutveckling. Ett samordnat arbetsätt, Complete Aproach
http://epubl.luth.se/1402-/02/index.html
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Blanc, Ludovic. "Caractérisation expérimentale et numérique du chargement généré par une explosion sur un bâtiment." Thesis, Bourges, INSA Centre Val de Loire, 2016. http://www.theses.fr/2016ISAB0001.
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Les travaux présentés dans ce mémoire s'inscrivent dans le cadre de deux projets, l'un européen, BASIS (Blast Actions on Structure In Steel), et l'autre français BATIRSÛR (Bâtiment en acier en zone PPRT de surpression), qui visent à mieux appréhender la vulnérabilité des bâtiments à ossature métallique face à un aléa de surpression. En particulier, ce travail a consisté à étudier les interactions entre une onde de souffle et une structure afin de caractériser le chargement global induit par une explosion. À partir de la génération d’ondes de souffle par détonation ou déflagration d'une charge gazeuse de propane oxygène, des campagnes expérimentales à petite échelle ont été conduites. Elles ont permis de mettre en défaut pour les faibles niveaux de surpressions étudiés (< 200 mbar) certaines approches simplifiées existantes. Des alternatives ont alors été proposées. Les coefficients de réflexion, caractérisant le chargement, ont été mesurés. De nouvelles valeurs sont proposées, notamment pour caractériser la diffraction d'une onde issue d'une déflagration. Les données du chargement résultant d’une déflagration et d’une détonation ont été comparées dans des configurations identiques. La propagation en champ libre de l’onde de souffle issue d’une déflagration a été reproduite au moyen du modèle du piston sphérique. Pour une de détonation, un modèle prédictif de ballon d'air comprimé, reposant sur la donnée de la masse volumique et l’énergie interne spécifique de l’explosif, a été développé et validé en champ lointain par comparaison avec les essais expérimentaux. Son utilisation a permis de mettre en évidence les atouts et les limites des simulations numériques pour reproduire le chargementThe work presented in this thesis fall within two project, one European, BASIS (Blast Actions on Structure In Steel), and the other French BATIRSÛR (steel building in PPRTs area overpressure), which both aimed at better understanding the vulnerability of metal framed buildings against an overpressure hazard. In particular, our objective was to study the interaction between a shock wave and a structure in order to characterize the overall loading induced by an explosion. From the generation of blast wave by deflagration or detonation of an oxygen propane mixture, small-scale experimental campaigns were conducted. These experimental campaigns highlighted for low levels of overpressure (<200 mbar) some limitations in the existing simplified approaches. Alternatives have then been given. Reflection coefficients, characterizing the loading, were measured. New values were obtained, especially to characterize the diffraction. Data resulting from deflagration and detonation we recompared under identical configurations. The free field propagation of the blast wave generated by a deflagration was reproduced by using the model of the spherical piston. For a detonation, a predictive model of compressed balloon based on the data of the density and the specific internal energy has been developed and validated in far-field range using comparison with experimental tests. Its use has helped highlight the assets and limits of numerical simulation in order to reproduce the loading induced by a detonation