Dissertations / Theses on the topic 'Anodes – Méthodes de simulation'
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Fortin, Hugues. "Modélisation du comportement thermo-électro-mécanique de l'anode de carbone utilisée dans la production primaire de l'aluminium." Thesis, Université Laval, 2009. http://www.theses.ulaval.ca/2009/26702/26702.pdf.
Full textMajidi, Behzad. "Discrete element method simulation of packing and rheological properties of coke and coke/pitch mixtures." Doctoral thesis, Université Laval, 2018. http://hdl.handle.net/20.500.11794/30959.
Full textGlobal aluminum production now is around 60 000 metric tonnes, annually, which is produced by the Hall-Héroult process. The process has mostly kept the original concept developed in 1886. Pre-baked carbon anodes are an important part of the design of aluminum smelting cells. Anodes are part of the chemical reaction of alumina reduction and are consumed during the process. Thus, quality and properties of anodes have direct effects on the performance and economy of the aluminum production in today’s highly competitive market. Although the design of anodes goes back to 130 years ago, effects of raw materials properties on final quality of anodes still need to be investigated. Anodes are composed of granulated calcined coke, binder pitch and recycled anode butts. Pitch at temperatures of mixing and forming steps is a liquid. Hence the mixture is a paste of coke and butts aggregates with pitch acting as binder. Flow and compaction behavior of this mixture, because of the co-existence of a variety of physical, chemical and mechanical parameters are complicated phenomena. Given the importance of high quality and long lasting anodes in performance and so the economy of the reduction cells, understating and predicting the final properties of anodes are very important for smelters. Numerical modeling in such complicated problems can provide a virtual laboratory where effects of different materials or process parameters on anode quality index can be studied without risking the pot performance. However, the choice of the numerical framework is a critical decision which needs to be taken according to the physics of the problem and the geometrical scale of the investigated problems. Discrete Element Method (DEM) is used in this research work to model the anode paste. In the first step, DEM models of coke aggregates are used to simulate the vibrated bulk density test of coke particles and to reveal the parameters involved. As a micromechanical model, DEM provides a unique opportunity to investigate the particle-particle contacts. The developed DEM models of coke aggregates were then used to propose a new dry aggregates recipe exhibiting higher packing density. Packing density of coke aggregates has direct effect on the baked density of anodes. High density is a very favorable anode quality index as it has positive effects on mechanical strength, and consumption rate of anodes in the cell. Electrical resistivity of bed of particles was experimentally measured. Particle-particle contacts information obtained from numerical models were used to explain the electrical resistivity of samples with different size distribution. Results showed that the increase in the number of contacts in volume unit of a sample increases, the electrical resistivity of the particle bed. Packing density also influences the electrical current transfer in granular systems. According to the obtained results, keeping the contacts density as low as possible is beneficial for electrical conductivity if it does not have a negative effect on packing density. Pitch is a viscoelastic material at elevated temperatures. In the present work, rheological properties of pitch and binder matrix (pitch+fine coke particles) were experimentally measured using a dynamic shear rheometer at 135, 140, 145 and 150 ºC. Four-element Burger’s model is then used to model the mechanical behavior of pitch and binder matrix. The verified model is then used to investigate the rheological properties of pitch and coke/pitch mixtures at 150 ºC. Calibrated Burger’s model showed to have a good prediction of viscoelastic properties of pitch and binder matrix at different temperatures. Obtained numerical results showed that available empirical equations in the literature fail to predict the complex modulus of mixtures of pitch and coke particles. As pitch has viscoelastic response and coke particles have irregular shapes, rheology of this mixture is more complicated and needs well-tailored mathematical models. Complex modulus of pitch decreases by increasing the temperature from 135 to 150 ºC, this makes easier the coke/pitch mixtures to flow. DEM modeling showed that the mixture gets a better compaction and so lower porosity by vibro-compacting at higher temperatures. The ability of pitch to penetrate to inter-particle voids in the porous structure of bed of coke particles was also shown to be improved by temperature. Final anode structure with less porosity and so high density is favorable for its mechanical strength as well as its chemical reaction in the cell as Based on the obtained results and considering the physics of the problem, it can be said that discrete element method is an appropriate numerical simulation technique to study the effects of raw materials and the anode paste formulation on mechanical and physical properties of coke/pitch mixtures. The platform created in the course of this research effort, provides a unique opportunity to study a variety of parameters such as size distribution, shape and content of coke particles, content and rheological properties of pitch on densification of coke/pitch mixtures in vibro-compaction process. Outputs of this thesis provide a better understanding of complicated response of anode paste in the forming process.
Vu, Anh Quang. "Etude des mécanismes de corrosion - cicatrisation d'aciers revêtus par des alliages d'aluminium : sur tranche et en zone confinée : approche expérimentale et numérique." Thesis, Dijon, 2012. http://www.theses.fr/2012DIJOS062/document.
Full textThe objective of this work was to study the self healing mechanisms of aluminium based alloy coated steels on cut-edge specimens in confined condition. In situ chemical and electrochemical probe techniques have been used to study the behaviour of two types of sacrificial coatings: one is consisting on an Al alloy containing 55% of Zn (Aluzinc) and the other one contains about 11% of Silicon (Alusi). The results showed that the aluminium based coatings have a sacrificial behaviour which depends strongly on their composition and on the environment concerned. In a corrosive environment containing chlorides it is easier to initiate and / or stabilize the sacrificial behaviour. This is clearly illustrated by the behaviour of the Alusi coating which remains passive in a neutral sulphate solution and therefore does not protect the steel. On the opposite, for 55% Al-Zn coatings, a very stable sacrificial effect has been demonstrated in chloride medium (steel is cathodically protected) which is confirmed in sulphate medium but only for short periods of immersion (t <1 h). An experimental setup allowing pH measurements inside a confined volume representing a lapped joint was designed. The pH evolution over steel and galvanized steel surfaces in confined conditions was monitored. This experimental pH was compared with that calculated using a two-dimensional transport-reaction model only in the case of a confined iron surface. The difference between the experimental and calculated pH in the steady state was attributed to the limitation of the modelling approach, more especially concerning solid phases precipitation inside the cavity
Paris, Adéline. "Contrôle de qualité des anodes de carbone à partir de méthodes statistiques multivariées." Master's thesis, Université Laval, 2020. http://hdl.handle.net/20.500.11794/40352.
Full textPrimary aluminum is produced through the Hall-Héroult process. Carbon anodes are used in this electrolytic process to provide the carbon source for the reaction and to distribute electrical current across the cells. Anode quality influences cell performance. However,increasing raw material variability has rendered the production of high-quality anodes more difficult. The objective of this project is to improve carbon anode quality control before baking by using anode electrical resistivity measurements. Multivariate statistical methods were applied to create two types of models: predictive and explanatory. For a given aggregate, the optimum pitch demand (OPD) is the amount of pitch that yields the best anode properties. High raw material variability causes the OPD to change more frequently, which makes it difficult to add the correct amount of pitch. This can lead to post-baking sticking problems when the optimum is exceeded. A soft sensor was developed based on a principal component analysis (PCA). The integrity of the correlation structure,as measured by the Squared Prediction Error (SPE), appears to break down during high-risk periods for anode sticking. The soft sensor was also tested on data collected during pitch optimization experiments.A sequential multi-block PLS model (SMB-PLS) was developed to determine which parameters influence anode resistivity. Raw material properties, anode formulation and process parameters collectively explain 54 % of the variability in the anode resistivity measurements.The model shows that coke and pitch properties have the greatest impact on green anode electrical resistivity. In addition, the main relationships between process variables implied by the model agree with the relevant literature and process knowledge.
Youn, Lee Kyong Yee. "Simulation mathématique d'un four de cuisson des anodes pour l'électrolyse de l'aluminium." Châtenay-Malabry, Ecole centrale de Paris, 1988. http://www.theses.fr/1988ECAP0219.
Full textLee, Kyong-Yee. "Simulation mathématique d'un four de cuisson des anodes pour l'électrolyse de l'aluminium." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb376150850.
Full textKidd, Jr Michael Scott. "Al-Ga Sacrificial Anodes: Understanding Performance via Simulation and Modification of Alloy Segregation." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/89066.
Full textMaster of Science
Ships must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum has properties which could allow a plate of it to rust instead of a ship it is attached to, thus protecting the ships from rusting. However, because aluminum usually does not rust, gallium can be added to aluminum to allow it to rust. Currently, aluminum-gallium alloys are used commercially to protect ships, but their performance is not consistent. In this research, various aspects of the aluminum-gallium system were simulated in an attempt to understand and potentially correct this reliability issue. Simulations showed that the gallium concentration may not be uniform in the alloy, and various conditions can cause the gallium concentration to be inconsistent. A set of aluminum-gallium alloy plates were cast in molds from liquid aluminum. Some of the plates were cooled quickly, and some cooled slowly. Some samples were later heated in an oven at high temperatures in an attempt to even out the gallium concentration. Samples were subjected to tests to observe corrosion behavior. The corrosion performance of samples was found to be best when subjected to quick cooling rates followed by the oven heating. Testing the samples in cold temperatures seemed to remove the desired corrosion behavior, suggesting that there are multiple reasons for the inconsistent corrosion behavior of aluminum gallium.
Kidd, Michael Scott Jr. "Al-Ga Sacrificial Anodes: Understanding Performance via Simulation and Modification of Alloy Segregation." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/89066.
Full textMaster of Science
Ships must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum has properties which could allow a plate of it to rust instead of a ship it is attached to, thus protecting the ships from rusting. However, because aluminum usually does not rust, gallium can be added to aluminum to allow it to rust. Currently, aluminum-gallium alloys are used commercially to protect ships, but their performance is not consistent. In this research, various aspects of the aluminum-gallium system were simulated in an attempt to understand and potentially correct this reliability issue. Simulations showed that the gallium concentration may not be uniform in the alloy, and various conditions can cause the gallium concentration to be inconsistent. A set of aluminum-gallium alloy plates were cast in molds from liquid aluminum. Some of the plates were cooled quickly, and some cooled slowly. Some samples were later heated in an oven at high temperatures in an attempt to even out the gallium concentration. Samples were subjected to tests to observe corrosion behavior. The corrosion performance of samples was found to be best when subjected to quick cooling rates followed by the oven heating. Testing the samples in cold temperatures seemed to remove the desired corrosion behavior, suggesting that there are multiple reasons for the inconsistent corrosion behavior of aluminum gallium.
Poncet, Philippe. "Méthodes particulaires pour la simulation des sillages tridimensionnels." Phd thesis, Université Joseph Fourier (Grenoble), 2001. http://tel.archives-ouvertes.fr/tel-00004699.
Full textXiao, Yi-Jun. "Contribution aux méthodes arithmétiques pour la simulation accélérée." Marne-la-vallée, ENPC, 1990. http://www.theses.fr/1990ENPC9031.
Full textViseur, Sophie. "Simulation stochastique basée-objet de chenaux." Vandoeuvre-les-Nancy, INPL, 2001. http://www.theses.fr/2001INPL036N.
Full textStoltz, Gabriel. "Quelques méthodes mathématiques pour la simulation moléculaire et multiéchelle." Phd thesis, Ecole des Ponts ParisTech, 2007. http://tel.archives-ouvertes.fr/tel-00166728.
Full textOuld, Salihi Mohamed Lemine. "Couplage de méthodes numériques en simulation directe d'écoulements incompressibles." Phd thesis, Université Joseph Fourier (Grenoble), 1998. http://tel.archives-ouvertes.fr/tel-00004901.
Full textStoltz, Gabriel. "Quelques méthodes mathématiques pour la simulation moleculaire et multiéchelle." Marne-la-vallée, ENPC, 2007. http://www.theses.fr/2007ENPC0708.
Full textThis work presents some contributions to the theoretical and numerical study of models used in practice in the field of molecular simulation. In particular, stochastic techniques to compute more efficiently ensemble averages in the field of computational statistical physics are presented and analyzed. An important application is the computation of free energy differences using nonequilibrium or adaptive dynamics. Some stochastic or deterministic techniques to solve approximately the Schrödinger ground state problem for high dimensional systems are also studied. Finally, some reduced models for shock and detonation waves, relying on an average stochastic dynamics reproducing in a mean sense the high dimensional deterministic hamiltonian dynamics, are proposed
Gillyboeuf, Jean-Philippe. "Diverses méthodes chimère pour la simulation numérique d'écoulements stationnaires." Toulouse, INPT, 1996. http://www.theses.fr/1996INPT127H.
Full textPapadopoulos, Christos. "Méthodes de simulation stochastiques rapides et applications en fiabilité." Compiègne, 1999. http://www.theses.fr/1999COMP1213.
Full textMinvielle-Larrousse, Pierre. "Méthodes de simulation stochastique pour le traitement de l’information." Thesis, Pau, 2019. http://www.theses.fr/2019PAUU3005.
Full textWhen a quantity of interest is not directly observed, it is usual to observe other quantities that are linked by physical laws. They can provide information about the quantity of interest if it is able to solve the inverse problem, often ill posed, and infer the value. Bayesian inference is a powerful tool for inversion that requires the computation of high dimensional integrals. Sequential Monte Carlo (SMC) methods, a.k.a. interacting particles methods, are a type of Monte Carlo methods that are able to sample from a sequence of probability densities of growing dimension. They are many applications, for instance in filtering, in global optimization or rare event simulation.The work has focused in particular on the extension of SMC methods in a dynamic context where the system, governed by a hidden Markov process, is also determined by static parameters that we seek to estimate. In sequential Bayesian estimation, the determination of fixed parameters causes particular difficulties: such a process is non-ergodic, the system not forgetting its initial conditions. It is shown how it is possible to overcome these difficulties in an application of tracking and identification of geometric shapes by CCD digital camera. Markov Monte Carlo Chain (MCMC) sampling steps are introduced to diversify the samples without altering the posterior distribution. For another material control application, which mixes static and dynamic parameters, we proposed an original offline approach. It consists of a Particle Marginal Metropolis-Hastings (PMMH) algorithm that integrates Rao-Blackwellized SMC, based on a bank of interacting Ensemble Kalman filters.Other information processing works has been conducted: particle filtering for atmospheric reentry vehicle tracking, 3D radar imaging by sparse regularization and image registration by mutual information
Demogeot, Thierry. "Développement de l'environnement de simulation Gaspe." Vandoeuvre-les-Nancy, INPL, 1992. http://www.theses.fr/1992INPL064N.
Full textBonithon, Gaël. "Méthodes numériques innovantes pour la simulation thermique de composants électroniques." Phd thesis, Paris, ENSAM, 2010. http://pastel.archives-ouvertes.fr/pastel-00547880.
Full textApraez, Camilo. "Étude comparative de méthodes de simulation de la stabilité transitoire." Mémoire, École de technologie supérieure, 2012. http://espace.etsmtl.ca/1000/1/APRAEZ_Camilo.pdf.
Full textSilva, lopes Laura. "Méthodes numériques pour la simulation d'évènements rares en dynamique moléculaire." Thesis, Paris Est, 2019. http://www.theses.fr/2019PESC1045.
Full textIn stochastic dynamical systems, such as those encountered in molecular dynamics, rare events naturally appear as events due to some low probability stochastic fluctuations. Examples of rare events in our everyday life includes earthquakes and major floods. In chemistry, protein folding, ligandunbinding from a protein cavity and opening or closing of channels in cell membranes are examples of rare events. Simulation of rare events has been an important field of research in biophysics over the past thirty years.The events of interest in molecular dynamics generally involve transitions between metastable states, which are regions of the phase space where the system tends to stay trapped. These transitions are rare, making the use of a naive, direct Monte Carlo method computationally impracticable. To dealwith this difficulty, sampling methods have been developed to efficiently simulate rare events. Among them are splitting methods, that consists in dividing the rare event of interest into successive nested more likely events.Adaptive Multilevel Splitting (AMS) is a splitting method in which the positions of the intermediate interfaces, used to split reactive trajectories, are adapted on the fly. The surfaces are defined suchthat the probability of transition between them is constant, which minimizes the variance of the rare event probability estimator. AMS is a robust method that requires a small quantity of user defined parameters, and is therefore easy to use.This thesis focuses on the application of the adaptive multilevel splitting method to molecular dynamics. Two kinds of systems are studied. The first one contains simple models that allowed us to improve the way AMS is used. The second one contains more realistic and challenging systems, where AMS isused to get better understanding of the molecular mechanisms. Hence, the contributions of this thesis include both methodological and numerical results.We first validate the AMS method by applying it to the paradigmatic alanine dipeptide conformational change. We then propose a new technique combining AMS and importance sampling to efficiently sample the initial conditions ensemble when using AMS to obtain the transition time. This is validatedon a simple one dimensional problem, and our results show its potential for applications in complex multidimensional systems. A new way to identify reaction mechanisms is also proposed in this thesis.It consists in performing clustering techniques over the reactive trajectories ensemble generated by the AMS method.The implementation of the AMS method for NAMD has been improved during this thesis work. In particular, this manuscript includes a tutorial on how to use AMS on NAMD. The use of the AMS method allowed us to study two complex molecular systems. The first consists in the analysis of the influence of the water model (TIP3P and TIP4P/2005) on the β -cyclodextrin and ligand unbinding process. In the second, we apply the AMS method to sample unbinding trajectories of a ligand from the N-terminal domain of the Hsp90 protein
Agouzoul, Asmaâ. "Nouvelles méthodes numériques pour la simulation de l’impression 3D métallique." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0004.
Full textSelective Laser Melting offers new perspectives in terms of part design and simplification of complex assemblies. However, severe thermo-mechanical conditions arise and are responsible for local plastic deformation, residual stresses and distortion of the manufactured component. Numerical simulation is an interesting tool for process understanding the physical phenomena and their impact on the quality of the part. In this thesis, we propose different approaches to perform simulations at a lower cost, by using model reduction algorithms. The results are compared with those obtained by the finite element method. A reverse analysis in order to identify the inherent strain responsible for the measured elastic springback makes possible to build offline numerical abacus. Therefore, we use a multi-parametric reduced order model using the so called Proper Generalised Decomposition (PGD) to construct this abacus. We also explore the benefits of an implementation of PGD on GPU
El, Haddad Rami. "Méthodes quasi-Monte Carlo de simulation des chaînes de Markov." Chambéry, 2008. http://www.theses.fr/2008CHAMS062.
Full textMonte Carlo (MC) methods are probabilistic methods based on the use of random numbers in repeated simulations to estimate some parameter. Their deterministic versions are called Quasi-Monte Carlo (QMC) methods. The idea is to replace pseudo-random points by deterministic quasi-random points (also known as low-discrepancy point sets or sequences). In this work, we propose and analyze QMC-based algorithms for the simulation of multidimensional Markov chains. The quasi-random points we use are (T,S)-sequences in base B. After recalling the principles of MC and QMC methods and their main properties, we introduce some plain financial models, to serve in the following as numerical examples to test the convergence of the proposed schemes. We focus on problems where the exact solution is known, in order to be able to compute the error and to compare the efficiency of the various schemes In a first part, we consider discrete-time Markov chains with S-dimensional state spaces. We propose an iterative QMC scheme for approximating the distribution of the chain at any time. The scheme uses a (T,S+1)-sequence in base b for the transitions. Additionally, one needs to re-order the copies of the chain according to their successive components at each time-step. We study the convergence of the scheme by making some assumptions on the transition matrix. We assess the accuracy of the QMC algorithm through financial examples. The results show that the new technique is more efficient than the traditional MC approach. Then, we propose a QMC algorithm for the simulation of Markov chains with multidimensional continuous state spaces. The method uses the same re-ordering step as in the discrete setting. We provide convergence results in the case of one dimensional chains and then in the case of multidimensional chains, by making additional assumptions. We illustrate the convergence of the algorithm through numerical experiments. The results show that the new method converges faster than the MC algorithm. In the last part, we consider the problem of the diffusion equation in a spatially nonhomogeneous medium. We use a random walk algorithm, in conjunction with a correction of the Gaussian Steplength. We write a QMC variant of the algorithm, by adapting the principles seen for the simulation of the Markov chains. We test the method in dimensions 1, 2 and 3 on a problem involving the diffusion of calcium ions in a biological medium. In all the simulations, the results of QMC computations show a strong improvement over MC outcomes. Finally, we give some perspectives and directions for future work
MAHMOUD, AHMAD. "Simulation numérique d'écoulements par des méthodes de transformation de domaines." Grenoble INPG, 1999. http://www.theses.fr/1999INPG0102.
Full textSaleh, Susi. "Méthodes de simulation des erreurs transitoires à plusieurs niveaux d'abstraction." Grenoble INPG, 2005. https://tel.archives-ouvertes.fr/tel-00009587.
Full textThe nowadays miniaturization of the electronic components increases considerably the sensitivity of the integrated circuits face to transient faults (SEU) or (SET). The analysis of the transient faults sensitivity for combinational logic and sequential circuits is an essential task today. The analytical methods based on probabilistic calculation of the generation of transient pulses SET or SEU, and of the propagation and the transformation of these transients faults into errors, published in the literature are not complete because a certain number of parameters are not taken into account. In this thesis, we propose a fast and accurate multi levels methodology to simulate transient faults. This methodology is a collection of simulation methods, a method for each level of abstraction (physical level, transistor level, and gate level). At the physical level, we use a physical simulation at the components level for any elementary logical gates which consists in the characterization of each type of transistor of a given technology face of SET by taking into account several parameter (the energy or the LET of the particle, the angle of incidence, the impact localization and the dimensions of the transistors where the particle strike occurs). After this characterization, a family of current curves is obtained for each transistor and a domain of the current amplitude values and the current pulses duration is established. The transformation of the current pulse obtained at the physical level into voltage pulses is done by electrical simulations by taking into account the output impedance of each gate. A family of transient voltage pulse curves is also established for each gate. Furthermore, a logical pulse model is defined for these pulses which will be then used in a numerical simulations, which are much faster, and which are finally used in the sensitivity analysis phase for complex circuit. The results of this analysis are used in order to realize a cartography of a complex circuit sensitivity which allow us to determine the most significant zones of a studied circuit and, if required, to decide a hardening solution of the sensitive gates
Labeau, Pierre-Etienne. "Méthodes semi-analytiques et outils de simulation en dynamique probabiliste." Doctoral thesis, Universite Libre de Bruxelles, 1996. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212439.
Full textNavarro, Barragan Alberto. "Etude d'un procédé de séparation chromatographique en continu : modélisation et mise en oeuvre d'un séparateur à trois sorties fonctionnant en simulation de lit mobile." Toulouse, INPT, 1997. http://www.theses.fr/1997INPT040G.
Full textLucas, Philippe. "Modélisation et simulation du régime transitoire d'unités de séparation d'un procédé chimique avec leur système de régulation : Application à la conduite d'un atelier industriel." Châtenay-Malabry, Ecole centrale de Paris, 1988. http://www.theses.fr/1988ECAP0083.
Full textDubos, Samuel. "Simulation des grandes échelles d'écoulements turbulents supersoniques." Rouen, INSA, 2005. http://www.theses.fr/2005ISAM0007.
Full textTurati, Pietro. "Méthodes de simulation adaptative pour l’évaluation des risques de système complexes." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLC032/document.
Full textRisk assessment is conditioned on the knowledge and information available at the moment of the analysis. Modeling and simulation are ways to explore and understand system behavior, for identifying critical scenarios and avoiding surprises. A number of simulations of the model are run with different initial and operational conditions to identify scenarios leading to critical consequences and to estimate their probabilities of occurrence. For complex systems, the simulation models can be: i) high-dimensional; ii) black-box; iii) dynamic; and iv) computationally expensive to run, preventing the analyst from running the simulations for the multiple conditions that need to be considered.The present thesis presents advanced frameworks of simulation-based risk assessment. The methods developed within the frameworks are attentive to limit the computational cost required by the analysis, in order to keep them scalable to complex systems. In particular, all methods proposed share the powerful idea of automatically focusing and adaptively driving the simulations towards those conditions that are of interest for the analysis, i.e., for risk-oriented information.The advantages of the proposed methods have been shown with respect to different applications including, among others, a gas transmission subnetwork, a power network and the Advanced Lead Fast Reactor European Demonstrator (ALFRED)
Perot, Thomas. "Quel est le niveau de détail pertinent pour modéliser la croissance d'une forêt mélangée ? Comparaison d'une famille de modèles et application aux peuplements mélangés chêne sessile - pin sylvestre." Paris, AgroParisTech, 2009. http://tel.archives-ouvertes.fr/docs/00/43/25/73/PDF/ManuscritTheseTPerotVF.pdf.
Full textAppropriate tools and models are needed for the management of mixed forests. The aim of this thesis is to show how the construction and the comparison of models with different levels of detail can help us to choose the most appropriate level to model the growth of a mixed stand. We developed a family of models at different levels of detail from data collected in mixed stands of sessile oak (Quercus petraea L. ) and Scots pine (Pinus sylvestris L. ) : a tree distance independent model (MAID), a tree distance dependent model (MADD), three stand models and an intermediate model bridging the MAID and the MADD. We ensured consistency between models using several approaches in order to make relevant comparisons. These models have given us some knowledge on the growth and dynamics of these forests, in particular on the spatial and temporal interactions between oaks and pines. Thus, we showed a compensatory growth phenomenon between the two species using the MAID. The MADD made it possible to show that, in these stands, the intraspecific competition was stronger than interspecific competition. A stand model developed from the MADD helped us to study the influence of mixing rate on production. To assess the quality of models predictions, we used an independent data set obtained by splitting our data. For example, we have shown that the MAID was more efficient than the MADD to predict individual increments. The models were also compared on examples of applications with short or medium term simulations. The proposed approach is of interest for both understanding the studied phenomenon and developing predictive tools. The different results of this work, allowed us to assess the relevance of a type of model for different contexts of use. This very general approach could be applied to the modeling of other processes such as mortality or regeneration
Turinici, Gabriel. "Analyse des méthodes numériques de simulation et contrôle en chimie quantique." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2000. http://tel.archives-ouvertes.fr/tel-00377187.
Full textMinjeaud, Sebastian. "Raffinement local adaptatif et méthodes multiniveaux pour la simulation d'écoulements multipĥasiques." Phd thesis, Université Paul Cézanne - Aix-Marseille III, 2010. http://tel.archives-ouvertes.fr/tel-00535892.
Full textZoghaib, Maria. "Étude et simulation de méthodes de refroidissement des bandes d'acier défilantes." Paris, ENMP, 2010. http://www.theses.fr/2010ENMP0032.
Full textThe main scope of this dissertation is to ameliorate the cooling process of the steel strips in continuous annealing and galvanizing lines. Cooling in continuous annealing and galvanizing lines is of great metallurgical interest. Insufficient cooling capacity can result in inadequate steel grades. Cooling by impinging gas jets over the steel surface is first investigated. The heat transfer rates of this process are limited on one side by the blowing device power consumption and on the other by the occurring non stationary phenomena for high impingement velocities. On one side, the blowing device configuration and blown gas properties are analyzed in order to increase the cooling rates while keeping the power consumption at its lowest. The study is undertaken throughout literature, experimental measurements, and numerical results. An optimized configuration is defined. On the other, a numerical model is developed to simulate the fluid-structure interaction that generates the detrimental oscillations of the strip. A configuration of oblique jet impingement is compared to normal impingement. It was proven to confer more stability. However, the maximum cooling rates reached by gas convection are insufficient regarding the cooling rates to obtain special steel grades. A more efficient technique based on boiling heat transfer is investigated. Due to phase change that occurs in boiling heat transfer, high heat fluxes are dissipated for small flow velocities. In order to sidestep the oxidation problems encountered with water, another liquid coolant is chosen, Pentane. For homogenous cooling patterns and savings in flow requirements, spray nozzles are used to impinge Pentane over the hot surface. An experimental bench is then set-up to characterize the cooling rates of a pentane spray for high surface temperature, i. E. Film boiling regime. The effect of the spray hydrodynamic parameters on the heat transfer process is analyzed and a correlation is developed. T he correlation predicts the evacuated heat flux from the hot surface as a function of the surface temperature and spray hydrodynamic parameters. The developed correlation is implemented in a simulation model in order to predict the cooling rate of a Pentane spray cooling section. The latter is then compared to gas jet cooling section for the same terms of reference. Aside from yielding higher cooling rates, Pentane spray cooling results in savings in power consumption
Marquez, Bernard. "Simulation des grandes échelles d'écoulements compressibles par des méthodes éléments finis." Toulouse, INPT, 1999. http://www.theses.fr/1999INPT0184.
Full textChoquin, Jean-Philippe. "Simulation numérique d'écoulements tourbillonaires de fluides incompressibles par des méthodes particulaires." Paris 6, 1987. http://www.theses.fr/1987PA066308.
Full textCasarin, Roberto. "Méthodes de simulation pour l'estimation bayésienne des modèles à variables latentes." Paris 9, 2007. https://portail.bu.dauphine.fr/fileviewer/index.php?doc=2007PA090056.
Full textLatent variable models are now very common in econometrics and statistics. This thesis mainly focuses on the use of latent variables in mixture modelling, time series analysis and continuous time models. We follow a Bayesian inference framework based on simulation methods. In the third chapter we propose alfa-stable mixtures in order to account for skewness, heavy tails and multimodality in financial modelling. Chapter four proposes a Markov-Switching Stochastic-Volatility model with a heavy-tail observable process. We follow a Bayesian approach and make use of Particle Filter, in order to filter the state and estimate the parameters. Chapter five deals with the parameter estimation and the extraction of the latent structure in the volatilities of the US business cycle and stock market valuations. We propose a new regularised SMC procedure for doing Bayesian inference. In chapter six we employ a Bayesian inference procedure, based on Population Monte Carlo, to estimate the parameters in the drift and diffusion terms of a stochastic differential equation (SDE), from discretely observed data
Minjeaud, Sebastian. "Raffinement local adaptatif et méthodes multiniveaux pour la simulation d’écoulements multiphasiques." Aix-Marseille 3, 2010. http://www.theses.fr/2010AIX30051.
Full textThis manuscript describes some numerical and mathematical aspects of incompressible multiphase flows simulations with a diffuse interface Cahn-Hillliard/Navier-Stokes model (interfaces have a small but a positive thickness). The space discretisation is performed thanks to a Galerkin formulation and the finite elements method. The presence of different scales in the system (interfaces have a very small thickness compared to the characteristic lengths of the domain) suggests the use of a local adaptive refinement method. The algorithm, that we introduced, allows to implicitly handle the non conformities of the generated meshes to produce conformal finite elements approximation spaces. It consists in refining basis functions instead of cells. The refinement of a basis function is made possible by the conceptual existence of a nested sequence of uniformly refined grids from which “parent-child” relationships are deduced, linking the basis functions of two consecutive refinement levels. Moreover, we show how this method can be exploited to build multigrid preconditioners. From a composite finite elements approximation space, it is indeed possible to rebuild, by “coarsening”, a sequence of auxiliairy nested spaces which allows to enter in the abstract multigrid framework. Concerning the time discretization, we begin by the study of the Cahn-Hilliard system. A semi-implicit scheme is proposed to remedy to convergence failures of the Newton method used to solve this (non linear) system. It guarantees the decrease of the discrete free energy ensuring the stability of the scheme. We show existence and convergence of discrete solutions towards the weak solution of the system. We then continue this study by providing an inconditionnaly stable time discretization of the complete Cahn-Hilliard/Navier-Stokes model. An important point is that this discretization does not strongly couple the Cahn-Hilliard and Navier-Stokes systems allowing to independently solve the two systems in each time step. We show the existence of discrete solutions and, in the case where the three fluids have the same densities, we show their convergence towards weak solutions. We study, to finish this part, different issues linked to the use of the incremental projection method. Finally, the last part presents several examples of numerical simulations, diphasic and triphasic, in two and three dimensions
Legoll, Frédéric. "Méthodes moléculaires et multi-échelles pour la simulation numérique des matériaux." Paris 6, 2004. http://www.theses.fr/2004PA066203.
Full textFaure, Frédéric. "Nouvelles méthodes pour la simulation numérique du soudage des structures élancées." Paris 6, 2004. http://www.theses.fr/2004PA066111.
Full textFréret, Lucie Viviane Françoise. "Méthodes particulaires en vue de la simulation numérique pour la plasturgie." Châtenay-Malabry, Ecole centrale de Paris, 2007. http://www.theses.fr/2007ECAP1058.
Full textThe framework of this thesis is the simulation of injection processes of thermoplastic materials. The aim is to simulate numerically fluid flows with free boundaries where transition of phase can occur. More precisely, in this work, we have considered bidimensionnal incompressible viscous flows with Lagrangian meshless methods. The lack of consistency of discetrized partial derivatives operator for the MPS method (Moving Particle Semi-implicit) is shown. By using approximated consistent meshless techniques close to MLS approximation (Moving Least Square), we then propose an original Lagrangian meshless method which discretize incompressible Navier-Stokes equations in a purely Lagrangian formulation. Concerning the semi-discretization in time, we use the classical projection method. The resultant fractionnal step method consists in three stages: a prediction step of position and velocity field, a correction step of position particles and a correction step of velocities field. Such a discretization keeps the particle repartition regular and do not need to create or destroy particles. An original numerical treatment to track or capture free surfaces and computation of surface tension force are proposed. We compare numerical results to experiments showing the capability of our method to calculate mono-fluid free surface flows. In a second part, we present a bi-fluid extension using a melt model. The Rayleigh-Taylor results are compared to these obtained by other methods. Because of the limitations of such model, we focus on a bifluid model where each fluid is calculated. This model needs first the non-constant coefficient operator div( a grad) to be discretized. We the use an integral representation ans a quadrature formulae with Gauss's points. The numerical model obtained is a previously three step method adaptation. Precise numerical results show the significance of the approach
Rosiello, Immacolata. "Méthodes de simulation, analyse de la complexité, utilisation de modèles, interdisciplinarité." Aix-Marseille 1, 2009. http://www.theses.fr/2009AIX10111.
Full textVenet, Cédric. "Méthodes numériques pour la simulation de problèmes acoustiques de grandes tailles." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2011. http://www.theses.fr/2011ECAP0019.
Full textThis thesis studies numerical methods for large-scale acoustic problems. The parallelization of the numerical acoustic methods is the main focus. The manuscript is composed of three parts: ray-tracing, optimized interface conditions for domain decomposition methods and asynchronous iterative algorithms
Daubas, Bruno. "Modélisation et simulation des procédés continus et discontinus." Toulouse, INPT, 1994. http://www.theses.fr/1994INPT023G.
Full textMulton, Stéphane. "Évaluation expérimentale et théorique des effets mécaniques de l'alcali-réaction sur des structures modèles." Marne-la-Vallée, 2003. http://www.theses.fr/2003MARN0181.
Full textA large scale experimental program has been carried out at the Laboratoire Central des Ponts et Chaussées (LCPC), with Electricité de France (EDF) as a partner, in order to validate methodologies of mechanical reassessment of real structures damaged by Alkali-Silica Reaction (ASR) and thus answer to the needs of owners of civil engineering structures (bridges, dams, pavements). The final aim is to improve calculation tools in order to determine the evolution of ASR affected structures. Major features of this study were to point out the water driving effect and the compressive stresses consequences on swellings due to ASR. Thus, the hydro-chemo-mechanical behaviour of six instrumented laboratory structures has been monitored during a two years experimentation. Three specific devices have been designed to achieve the numerous measurements, in order to evaluate water movements in concrete and structural behaviours of the six structures : -the weighing device allows to measure the mass variations of the 900 kg beams, with a 10 g accuracy, -the gammadensitometry equipment is used to determine the relative mass variations along the height of the beams, -specific stiffness vibrating wire sensors achieve deformation measurements in the beams. Other current or improved techniques have been also used in order to complement the characterisation of the behaviour of the beams, and to quantify chemo-mechanical data related to the two concrete mixtures during two years. This laboratory experimental survey has collected numerous results to document both moisture and chemo-mechanical deformations, which builds a useful data bank in order to validate models. At last, measurements have increased knowledge useful for expert evaluation of ASR-affected structures about : -mechanical properties evolution of concrete mixture damaged by ASR, -methodology of residual expansion tests, -effects of moisture gradient in ASR-damaged structures, -consequences of late water supply on ASR progress in structures already damaged, -range and time-evolution of ASR swellings under specific stress states, due to mechanical loads, reinforcement or various environmental conditions, and, at last, the effect of this chemical reaction on the mechanical strength of damaged structures
Di, Benedetto Hervé. "Modélisation du comportement des géomatériaux : application aux enrobés bitumineux et aux bitumes." Grenoble 1, 1987. http://www.theses.fr/1987GRE10096.
Full textDascalu, Daniel. "Méthodes probabilistes pour la modélisation de la maintenance préventive." Compiègne, 2002. http://www.theses.fr/2002COMP1386.
Full textNomine, Jean-Philippe. "Etude d'outils de simulation du comportement de robots." Paris 6, 1991. http://www.theses.fr/1991PA066596.
Full textDesbenoit, Brett. "Modélisation et simulation de scènes naturelles complexes." Lyon 1, 2006. http://www.theses.fr/2006LYO10214.
Full textIn this thesis, we address the modelling realistic natural sceneries. We focus on the modelling of details and their distribution in a complex scene. Details have a great impact over the overall realism of the final scene. Our approach consists in modeling details such as mushrooms, lichens, leaves or fractures and storing them in an atlas of shapes. Those details are distributed in the scene according to specific physically and biologically based dispersion and propagation algorithms, which are controlled by the parameters of the environment such as the wetness, the temperature or the amount of direct and indirect lighting. Our approach enables us to add a vast variety of details without the burden of editing them by hand
Gabella-Latreille, Céline. "Le modele quinquin-fret : un modele de simulation a l'horizon 2015 des flux nationaux de transport de marchandises." Lyon 2, 1997. http://www.theses.fr/1997LYO22024.
Full textThe quinquin fret model is an instrument helping the decision making. It allows is evaluate ex-ante the long term effects of transport policies measures expected by public authorities as to the sncf. The national ton kilometre obtained by road, transport, rail transport or inland navigation can be simulated at a long term toking into account different asseptions related to industrial growth and to modal split factors