Dissertations / Theses on the topic 'Régime de lubrification mixte'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 44 dissertations / theses for your research on the topic 'Régime de lubrification mixte.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
Marsault, Nicolas. "Modélisation du régime de lubrification mixte en laminage à froid." Paris, ENMP, 1998. http://www.theses.fr/1998ENMP0831.
Full textNogueira, Isabel. "Transformations des couches superficielles des matériaux induites par la phase de rodage lors de régimes de lubrification mixte et limite." Paris, ENSAM, 2004. http://www.theses.fr/2004ENAM0001.
Full textDuring certain working stages of mechanical components such as guiding parts or gear-wheels, the thickness of the oil film can not be sufficient to separate totally the surfaces. The summits of the asperities can be in contact, increasing wear and friction. This situation with a discontinuous film is classically defined as mixed or limited lubrication. In that case, the forces are supported partially by the solids and by the lubricant film. Such situations can occur during the starting and stopping stages, accidental overloads and especially during the running-in. These situations are critical for the mechanical components in particular for their working life and performance in service. The contact problem between solid surfaces has been studied in this work in order to clarify the complexity of the running-in in contact working in mixed lubrication. Firstly, a study of dry contact without sliding has been carried out analysing the geometrical variation of the rough surface and the physical alterations caused by a normal load. Secondly, the influence of the lubricant and the sliding motion on the friction and wear are introduced to study the mixed and boundary lubrication. The tests have been conducted using a pin-on-disc tribometre. The influence of a friction modifier added in to the base oil has been analysed depending on the friction, the wear and the superficial alterations
Havet, Laurent. "Caractérisation tribologique de biolubrifriants." Compiègne, 1998. http://www.theses.fr/1998COMP1170.
Full textAyadi, Khouloud. "Optimisation de la modélisation des régimes de fonctionnement des garnitures mécaniques d'étanchéité : analyse théorique et expérimentale." Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2325/document.
Full textMechanical face seals are sealing components for rotating shafts. It basically consists of two annular flat surfaces lubricated with a very thin film of sealed fluid.The "Seals lubrication" group of the Pprime institute has developed different modeling tools of mechanical face seals behavior by analytical, semi analytical and numerical methods. The objective of this thesis is to define a preliminary methodology to optimize the modeling of the mechanical seal taking into account the seal design. This analysis provides a suggestion of modeling tools among the existing types. A set of indicators and criteria are developed to determine the dominating physical phenomena during the operation of the seal under given conditions. The selected modeling tools should take into account the identified phenomena. Experimental validations were performed for a mechanical seal working in different operating conditions. Studies of the evolution of the friction faces topography, the friction torque, the leakage rate and the thermal effect were carried out. Experiments have shown that the behavior of the mechanical seal strongly depends on the lubrication regime: mixed, hydrodynamic and thermo-elasto-hydrodynamic.Theoretical models were compared with experimental results. A good correlation is obtained into their range of validity defined with preliminary analysis. Larger differences are observed when the models are used in conditions where unconsidered physical phenomena occur. This comparison showed that the indicators and criteria of the proposed method of choice are relevant and allows a good identification of the physical phenomena that should be taken into account
Loehle, Sophie. "Understanding of adsorption mechanism and tribological behaviors of C18 fatty acids on iron-based surfaces : a molecular simulation approach." Phd thesis, Ecole Centrale de Lyon, 2014. http://tel.archives-ouvertes.fr/tel-00999372.
Full textMinet, Christophe. "Lubrification Mixte des Etanchéités dynamiques : application aux garnitures mécaniques d'étanchéité." Phd thesis, Université de Poitiers, 2009. http://tel.archives-ouvertes.fr/tel-00441030.
Full textMinet, Christophe. "Lubrification mixte dans les étanchéités dynamiques : application aux garnitures mécaniques d'étanchéité." Poitiers, 2009. http://theses.edel.univ-poitiers.fr/theses/2009/Minet-Christophe/2009-Minet-Christophe-These.pdf.
Full textMechanical face seals are commonly used in industrial applications. The main purpose of these components is to insure the sealing of rotating shafts. A mechanical seal is basically a set of two rings whose contact is lubricated by the sealed fluid. The optimal point of operation is reached by minimizing both leakage and wear. The average film thickness is then about one micrometer and the seal is operating in mixed lubrication conditions. In this case, the faces are not completely separated by the fluid film and asperity contact occurs. The choice of a deterministic approach was justified from a detailed bibliographical analysis. An accurate description of the surfaces roughness was required, as well as the development of a numerical modelling tool able to simulate it. A metrological study was realised on samples of mechanical seal surfaces at several stages of operation. The statistical parameters obtained from the surfaces roughness could thus be evaluated and used in a numerical model enabling the generation of non Gaussian surfaces. A deterministic flow model for mixed lubrication in mechanical seals is then presented. It takes the cavitation effects and normal hertzian asperity contact into account. The equation of flow rate conservation in the contact was solved using finite volume method. A parametric study was carried out on four statistically equivalent simulated surfaces. The model highlights the increase in load capacity due to the roughness, although the mean surfaces are flat and parallel. Stribeck curves have been obtained for each studied case. The standard deviation of the roughness is the major parameter influencing the coefficient of friction. Furthermore, the development of microcavitation, which mostly depends on the roughness distribution, influences the results to a great extent
Monmousseau, Pascal. "Etude thermoélastohydrodynamique des paliers à patins oscillants en régime transitoire." Poitiers, 1997. http://www.theses.fr/1997POIT2332.
Full textNyemeck, André Parfait. "Modélisation de la lubrification mixte et du comportement thermique des garnitures mécaniques." Poitiers, 2011. http://nuxeo.edel.univ-poitiers.fr/nuxeo/site/esupversions/2ece3128-ba75-4399-ac23-1f1d5f66069b.
Full textMechanical seals are sealing components used in rotating shafts. They are basically a set of two rings (the rotor and the stator), separated by a lubricant film that must be impervious. The optimum operation is obtained by minimizing both leakage and wear. This corresponds to a film thickness of approximately one micrometer and to a mixed lubrication regime. The literature review justified the choice of a multiscale approach to model a mixed lubrication process. A part of this literature allowed identifying the thermal models to use. A model of a mixed lubrication in mechanical seals based on a multiscale approach is presented. This uses numerical surface roughness and consists in dividing the studied area into sub-domains. The Reynolds equation, which takes into account the fluid cavitation is solved by mean of finite volumes method, at fine scale of the sub-domains, as the hertzian contact asperities. The macroscale is introduced to connect the boundaries conditions of the sub-domains. Then, the macroscale pressure distribution is obtained insuring the mass conservation law. The model also takes into account, at the macroscale step, the Thermo-Elasto-Hydro-Dynamic (TEHD) behaviour in mechanical seals. The discretization of heat and elasticity equations is performed using the finite element method for axisymmetric geometry. The multiscale model is first validated by comparing in to a deterministic model, and then to the TEHD model previously developed at the Pprime laboratory. The influence of the parameters characterizing the mechanical seal behaviour is analyzed through the parametric study. In this study, the different lubrication regimes are identified. The lubricant film thickness is controlled by the roughness or by the thermoelastic deformation of the faces
Boirlaud, Matthieu. "Contribution à l'étude de la convection mixte en régime turbulent." Phd thesis, ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2012. http://tel.archives-ouvertes.fr/tel-00784210.
Full textErnesto, André. "Lubrification colloïdale de contacts DLC : du régime stationnaire au régime transitoire : application à la zone segments - piston - chemise." Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0035/document.
Full textEcological issues related to global warming, and more generally the reduction of pollution, have lead to a major revolution in the field of transport. Considerable research work has been carried out during the past decades in order to improve the mechanical efficiency of internal combustion engines. In Diesel engines, almost 40 % of total engine energy losses due to mechanical friction occur in the Piston rings-Piston-Cylinder contact (PPC). The overall framework of this PhD thesis is Diesel engine lubrication in presence of soot and this work focuses more particularly on Diamond-Like Carbon (DLC) lubricated contacts for PPC region. Unique tribometry tools are used to reproduce the particular contact kinematics involved in the piston assembly. This thesis aims to identify the influence of an aged lubricant on the lubrication and friction mechanisms of DLC hard coatings for all lubrication regimes in steady-state and transient conditions. DLC coatings developed during this thesis significantly reduce the boundary friction in steady-state and transient conditions. The lubricant destructuring due to aggregate formation, generated by the passage of soot, or by a temporary vanishing of the entrainment speed, are governed by the triplet, lubricant, surface and contact kinematics. Finally, the analysis of the tribological response of the lubricated interface in steady-state and transient conditions leads to the theoretical modeling of the friction during a complete cycle of sliding at variable velocities
Nyemeck, André Parfait. "Modélisation de la Lubrification Mixte et du Comportement Thermique dans les Garnitures Mécaniques." Phd thesis, Université de Poitiers, 2011. http://tel.archives-ouvertes.fr/tel-00683412.
Full textMolimard, Jérôme. "Etude expérimentale du régime de lubrification en film mince : application aux fluides de laminage." Lyon, INSA, 1999. http://www.theses.fr/1999ISAL0121.
Full textIn the cold rolling process, the strip's quality deeply depends on the contact between the strip, the lubricant and the rolls. This quality -requirement leads to favor the mixed lubrication regime. In this case, important interactions between surface asperities are expected. The lubricant and overall the additives have the important task to protect surfaces. This work suggests studying the lubricant behavior when film thickness is very small in order to bring the additives influence to light. A new film thickness measurement method coupling the classical white light interferometry on a point contact to original image analysis software is designed. First tests on a static smooth contact, then on a rough static on~, and last on a dynamic smooth one show the possibility to obtain a precise film thickness map in a range from 1 to 800 nm. At first, this technique is used with laboratory lubricants in elastohydrodyna. Mic lubrication or thin film lubrication. Results are compared to literature, numerical models and another image analysis software. This shows proof of the method's capacity to study thin film regime. In a second time, studies are performed, on two industrial lubricants. The behavior in thin film lubrication is different whether additives are placed or not in the lubricants. If they are some, a low thickness limit appears (2 or 3 nm) and the film thickness can be more important in a low thickness range (typically under 40 nm), preventing surfaces diseases. A model is proposed. It takes into account adsorption and segregation phenomena. Results are consistent to other studies for various lubricants on surface force apparatus or by spectral analysis methods
Bouard, Ludovic. "Etude thermohydrodynamique des paliers à patins oscillants en régime turbulent." Poitiers, 1995. http://www.theses.fr/1995POIT2311.
Full textDupuy, Florence. "Etude tribologique d'une butée aérodynamique en régime supersonique." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0124.
Full textThe improvement of turbomachines requires to increase their rotational speeds and can leads components to be in presence of a supersonic regime, particularly their air bearing systems. This manuscript deals with a study of an aerodynamic thrust bearing in a supersonic regime. This work belongs to the research field on the high-speed thrust bearings, but very few studies are focused on this subject. This problem is at the boundary between two scientific fields: lubrication and aerodynamic. The aim of this study is to develop models transcribed as a FORTRAN code, able to capture phenomenon related to the supersonic regime (shock, expansion wave) and adapted to the thin film geometry. For this, two models have been developed as well as computer codes related to these models using the finite difference method: the Modified Reynolds equations and the Navier-Stokes equations adapted to thin films. The first model is an extension of the generalized Reynolds equation, taking into account inertia effects. It is a model already used in lubrication studies. The second model was developed from the Navier-Stokes and has their shape. This system has the advantage of using numerical schemes for shock capturing (WENO). The comparison of the two models shows that the Modified Reynolds equations are not appropriate to the study of a supersonic air thin film. Numerical results show the presence of an expansion wave at the end of the sloping region of the tapper flat geometry which depends on speed, on temperature and on the angle of the geometry. This expansion wave, under severe conditions, does not have much influence on the overall static behavior of the thrust bearing. The results also show that, contrary to the supersonic flow theory, a shock is not observed in a supersonic thin film. A geometrical transition obtained by homothetic, between a flow containing a shock and another with no shock, is observed at a given value of the characteristic length ratio for a given speed and geometry. Extrapolation of these results for a realistic case shows that a shock occurs from 5500 m/s for a film thickness of 40 μm with epsilon = 0.001. It is therefore unlikely that a shock occurs in a supersonic thrust bearing in industrial settings
Bouchoule, Christophe. "Optimisation de paliers en régime thermohydrodynamique : application aux réducteurs et multiplicateurs de vitesse à engrenages." Poitiers, 1994. http://www.theses.fr/1994POIT2359.
Full textGherca, Andrei. "Modélisation de la lubrification des surfaces texturées - Application à la butée en régime hydrodynamique." Phd thesis, Université de Poitiers, 2013. http://tel.archives-ouvertes.fr/tel-00943143.
Full textGyan, Philippe. "Etude expérimentale du comportement thermique des moteurs en régime transitoire." Ecully, Ecole centrale de Lyon, 2003. http://www.theses.fr/2003ECDL0023.
Full textPassenger vehicles are mostly used on short distances, in transient thermal conditions for the engine, inducing significant increase in fuel consumption and pollutant emissions. The duration for heating the passenger cabin is also increased, especially for direct injection diesel engines, which have better efficiencies. The present study aims at developing a tool for engine transient thermal behavior simulation, from an existing software THERMOT1, based on the nodal method. The pressure of the gas in the cylinder, the torque and the engine speed are the main imputs. A critical analysis has been conducted on THERMOT1, showing its weaknesses, with the input of bibliographical analysis, some new physical models for heat sources by friction based on tribology have been developed, especially for crankshaft bearings and piston rings assembly
Dragomir, Fatu Ramona. "Étude et modélisation de la lubrification mixte et des modes d'avaries associés dans les paliers moteur." Poitiers, 2009. http://theses.edel.univ-poitiers.fr/theses/2009/Dragomir-Fatu-Ramona/2009-Dragomir-Fatu-Ramona-These.pdf.
Full textControl of mixed lubrication conditions is a complex challenge to meet since it requires understanding of several coupled phenomena: fluid flow between rough surfaces, elasto-plastic deformation of asperities, surface wear. The goal of this study is to propose an approach of mixed lubrication conditions in the context of ICE bearings. The first part gives an overview of key theoretical and numerical modeling dedicated to the analysis of bearings in hydrodynamic and mixed conditions. The second chapter is dedicated to the phenomenon of flow between two rough surfaces. Starting from the model proposed by Cheng and Patir, a new definition of flow factors is proposed. This model takes into account the direction of surface textures. Several parametric calculations have identified selection criteria for rough surfaces used to determine the new flow factors coefficients. The purpose of Chapter 3 is to detail three existing statistical contact models of rough interface asperities. Several comparisons permit to extract the advantages and disadvantages of each model and especially to see their applications in the study of mixed lubrication in ICE bearings. To a better understanding of their limits, the statistical models were compared to a deterministic finite element model. Chapter 4 is dedicated to the study of wear. Three wear models based on Archard's law are detailed. Finally, the different flow, contact and wear models are integrated in a numerical prediction tool and used to simulate the behavior of a big-end connecting rod bearing
Dobrica, Mihai-Bogdan. "Prise en compte de la lubrification mixte lors de l'évaluation des performances des paliers très chargés." Poitiers, 2007. http://www.theses.fr/2007POIT2310.
Full textThis thesis studies the behavior of journal bearings functioning in the mixed lubrication regime. Deterministic numerical models are proposed, which take into account the roughness effects using very fine meshes. Four aspects related to the mixed lubrication regime are studied in detail: numerical generation of rough surfaces, modeling of mechanical deformations, modeling of the elasto-plastic contact between rough and smooth surfaces, and modeling of the lubricant flow between a rough surface and a smooth surface in relative movement. Mechanical deformations are computed with a fast two-mesh approach and compliance matrices computed by structural simulations. Contact is modeled using an active-set / contact-set iterative method. Lubricant flow is modeled using the Reynolds equation, with the finite volumes method. A simulation code for mixed-lubricated partial journal bearings is proposed, which includes deformation calculus, contact modeling and thin-film lubrication modeling components. Piezo-viscosity, plasticity and cavitation are taken into account in a simplified manner. This code was applied in numerical simulations of severely loaded bearings (specific pressures up to 55 MPa), using meshes of 3. 6 million nodes. A study on the influence of three types of roughness (longitudinal, isotropic and transversal), bearing material and lubricant piezo-viscosity over bearing behavior was subsequently conducted. Discussed results include: film thickness, attitude angle, viscous friction torque and contact (dry) friction torque, contact area, plasticity percentage, etc. Stribeck curves showing the evolution of the global friction coefficient are also presented
Mongoin, David. "La doctrine constitutionnelle du Federaliste : La question d'institutions libérales après le régime mixte." Paris 2, 2007. http://www.theses.fr/2007PA020082.
Full textMichaux-Leblond, Nathalie. "Étude du comportement dynamique du sillage à l'aval d'un cylindre chauffé en régime mixte." Le Havre, 1994. http://www.theses.fr/1994LEHA0006.
Full textGros, Nicolas. "Contribution à l'étude expérimentale du jet d'air plan en régime de convection mixte favorable." Poitiers, 1998. http://www.theses.fr/1998POIT2330.
Full textRoussel, Mélanie. "Du "bon régime"." Thesis, Paris 2, 2014. http://www.theses.fr/2014PA020020.
Full textReflecting on the concept of « good political regime » means reflecting on the best suited political organisation for the imperfect nature of man. This nature, combined with the contingency in which human action occurs, makes all tentative of perfect theoretical constructions illusionary. The « good political regime » is a fair regime and a moderate one oriented towards common good. But it is above all a government adapted to the community it intends to organise. Pragmatism and prudence are necessary in order to organise the most suitable constitution for the political community. Its sociological composition, its history, its customs and traditions are for a large part responsible in determining the constitutional solutions that can be implemented. The political regime occurs in fact in a political system which determines it in return. A “mixed” constitution has appeared for a long time as the most adequate institutional form, as it enables the fairest representation of the diversity of its interest, and the adhesion of the majority to the constitution. Its apparent disappearance in modern times is deceiving since its most distinctive features, among which moderation and equilibrium, have evolved and been transformed to adapt to new realities. Modern constitutionalism, by its attachment to the mechanisms of power distribution constitutes a perfect illustration of this phenomenon of adaptation. But it is above all the paradoxical persistence of different forms of heteronomy – sociological, moral, natural – that best exposes how the modern man has not definitively broken with the « good political regime » so dear to the Ancients
Himmel, David. "Application de la microspectrometrie Raman à la mesure in situ de paramètres physiques régnant dans un contact sphère/Plan en régime de lubrification élastohydrodynamique@." Antilles-Guyane, 2005. http://www.theses.fr/2005AGUY0134.
Full textPhysical parameters characterising an elastohydrodynamically lubricated sphère/plane contact are studied by means of in situ Raman microspectrometry using polyphenyl ether (5P4E) as Raman probe and lubricant. Spectroscopic images, also called spectrum images, are acquired point by point in the dynamic contact and are analysed in order to obtain simultaneous high spatial resolution (10µm) mapping of pressure, lubricant film thickness and temperature in the contact and in its vicinity. For pressure, Raman band shifts of the 5P4E band are extracted from spectrum images and are converted into absolute pressure experienced by the lubricant. After a systematic calibration procedure the Raman band intensity of the lubricant film allows us to deduce the distribution of the film thickness. The Antistokes/Stokes intensity ratio is used to determine the temperature values. The experimental distributions of pressure and lubricant film thickness are compared to the theoretical calculations and are in good agreement. The temperature profiles also agree well with the results of previous works
Jacquemard, Pascale. "Tribologie des joints a faces radiales : cas du fonctionnement en lubrification mixte et de premiers corps en carbone et carbure de silicium." Lyon, INSA, 1997. http://www.theses.fr/1997ISAL0014.
Full textRadial-face seals are mechanisms which fulfill the tribological functions of velocity accommodation and leakproofing between a rotating shaft and its fixed housing. They do this by the contact of two annular faces, or first bodies. Depending on the tightness and the operating parameters of such mechanisms, the first bodies are separated by a fluid third body consisting of particles detached from the first bodies. This defines the mixed lubrication studied. In the literature the contribution of the fluid third body to the load capacity and the separation of the first bodies is well modeled by the Reynolds equation, while the contribution of the solid third body is at best included as an obstacle to leakage of the fluid third body. In order to quantify that contribution, this study uses an approach based on phenomena rather than parameters. The contributions of the mechanism and the third body to the tribology of the seal are identified first and only then is the influence of the materials parameters taken into account. This procedure, which can be applied generally to other contacts, relies on the evaluation (qualitative at first) of the flows of the solid third body. These flows are reconstructed from the morphologies of the fust and third bodies after various running times and visualization tests which are also applied glass fust body. The results obtained for the radial-face seal also show that the analysis of tribological functions from the point of view of materials exclusively is valid only after the parity between mechanism and materials has been identified. From the flows of third body, then, the functions of the seal in mixed lubrication can be modeled
Makala, Jérôme. "Modélisation d'un variateur toroidal ; études théorique et expérimentale des contacts de traction en régime élastohydrodynamique." Poitiers, 2000. http://www.theses.fr/2000POIT2257.
Full textNinove, François Pierre. "Texturation de surface par LASER femtoseconde en régime ElastoHydroDynamique et limite : application au contact Segment / Piston / Chemise d'un moteur thermique à combustion." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00688051.
Full textGiraudeau, Célia. "Influence des discontinuités géométriques sur les performances des paliers en régime thermoélastohydrodynamique (TEHD)." Thesis, Poitiers, 2016. http://www.theses.fr/2016POIT2298/document.
Full textDuring various maintenance operations in power plants, some new issues have come to light. One of these issues is the degradation of the supporting and guiding components for the rotating shafts. The degradation has resulted in scratches on bearings which leads to discontinuities of the oil film. The operator of the plant should provide a fast diagnosis of the influence of these scratches. The aim of the work is to examine these issues, to acquire a better understanding of physical phenomenon and to improve numerical predictions. Theoretical and experimental studies have been done for plain journal bearings. The numerical model is based on a thermoelastohydrodynamic (TEHD) resolution that allows to take into account solid deformations induced by the pressure and temperature fields. A computer code has been developed to solve the hydrodynamic (HD) problem. An experimental study has been performed on a two lobe journal bearing with a scratch on the rotating shaft at two scratch locations and for several scratch depth. For all of these configurations, local pressures and temperatures have been measured for different rotational speeds and applied loads. The scratch depth is one parameter that affects the most the journal bearing behavior. It influences more significantly the pressure field, with a drop of pressure near the scratch, than the temperature field. Those results have been compared to the numerical results obtained with an internal EDF software that can provide TEHD solutions
Brunetière, Noël. "Les garnitures mécaniques : Etude théorique et expérimentale." Habilitation à diriger des recherches, Université de Poitiers, 2010. http://tel.archives-ouvertes.fr/tel-00506535.
Full textThomas, Lionel. "Contribution à l'étude et au contrôle passif du mélange d'un jet d'air plan, immergé, en régime de convection mixte favorable." Poitiers, 2002. http://www.theses.fr/2002POIT2267.
Full textThis thesis presents an experimental study of a plane jet in aiding mixed convection regime. A method to modify in a passive way the dynamical mixing in the establishing region is proposed: it consists in introducing small cylinders where the mixing layers are just born, generating a periodical wake. The mean velocity fields, obtained through LDV allow a global characterisation of the jet. The laser tomography visualisations, associated with personal image processing, give access to the instantaneous edge of the jet. Its dynamical behaviour is studied, by detection of the spirals responsible for entrainment and by frequential analysis. The coherent structures are extracted from the instantaneous velocity fields, resulting from PIV. A statistical study of this vortices population is carried out. With all these analyzing tools, it is possible to quantify the impact of obstacles on the global and local mixing: their presence reduces the transverse rollers, amplifies the longitudinal ribs, without modifying notably the mixing
Lecocq, Yannick. "Contribution à l'analyse et à la modélisation des écoulements turbulents en régime de convection mixte - Application à l'entreposage des déchets radioactifs." Phd thesis, Université de Poitiers, 2008. http://tel.archives-ouvertes.fr/tel-00375441.
Full textDans un premier temps, lorsque le régime de convection mixte est dominant, ces calculs, réalisés par le modèle bas-Reynolds k-w SST, et complétés par un calcul isotherme, mettent en évidence de nombreuses structures tourbillonnaires recensées par la bibliographie. Un calcul avec le modèle haut-Reynolds Rij-epsilon SSG est aussi effectué. Avec le modèle k-w SST, l'échange thermique est convenablement reproduit par rapport à l'expérience VALIDA, conduite par le CEA, alors qu'avec le modèle Rij-epsilon SSG celui-ci est fortement sous-estimé, certainement en raison de l'utilisation de lois de paroi.
Dans un second temps, lorsque la convection naturelle est prépondérante, la topologie des écoulements est alors complètement différente et le transfert thermique est bien moins fidèle à l'expérience VALIDA.
Le modèle à pondération elliptique EBRSM, issu de l'approche de Durbin, consiste en la prise en compte des effets de paroi, et en particulier le blocage à la paroi. D'après ce formalisme, un modèle algébrique des flux thermiques avec pondération elliptique est développé, l'EBAFM. Avec ce modèle, des tests a priori dans les trois régimes de convection puis les simulations sur les mêmes cas montrent une nette amélioration dans la prédiction des différents écoulements faisant place à une perspective intéressante d'un modèle intermédiaire entre une formulation SGDH et des équations de transport.
Lecocq, Yannick. "Contribution à l'analyse et à la modélisation des écoulements turbulents en régime de convection mixte : application à l'entreposage des dechets radioactifs." Poitiers, 2008. http://theses.edel.univ-poitiers.fr/theses/2008/Lecocq-Yannick/2008-Lecoq-Yannick-These.pdf.
Full textIn the frame of radioactive waste management, this work aims to study the flow around a heating wall-mounted cylinder in cross flow in URANS approach. Well-known limitations of first order turbulence models lead us to consider second order turbulence modelling. In that frame, a heat transfer model is developed and validated on academic test cases. To begin with, when mixed convection regime is dominant, these simulations, completed by an isotherm one, all performed with low-Reynolds k–w SST model, give prominence to several eddy structures registered by the bibliography. One simulation is also performed with the high-Reynolds Rij–epsilon SSG model. With the k–w SST model, the heat transfer is correctly reproduced compared to the VALIDA experiment lead by the CEA, though with the Rij–epsilon SSG model, it is strongly under-estimated. It is supposed that it comes from the use of wall functions. Subsequently, when natural convection is predominant, flow topology becomes completely different and the heat transfer becomes less accurate to the VALIDA experiment. Following Durbin’s approach, the Elliptic Blending-Reynolds Stress Model EB–RSM, consists in accounting for wall effects, and in wall blockage in particular. Following this formalism, an Elliptic Blending-Algebraic Flux Model is developed, the EB-AFM. With this model, a priori tests in the three convection regimes and then simulations on the same test cases show major improvements in flow predictions. This leads to an interesting perspective to an intermediate model between SGDH and transport equations
Chereches, Nelu Cristian. "Contribution à l'optimisation de circuits thermoconvectifs." Reims, 2006. http://theses.univ-reims.fr/exl-doc/GED00000236.pdf.
Full textThe fluid flow as well as the heat transfer by mixed convection are analysed within a thermoconvection circuit with several cooling channels of a three - phase power transformer with columns immersed in a mineral oil bath inside a tank. The objectives of this work are the heat transfer optimisation and the hot spots temperature limitation insuring a good comprehension of the thermal and dynamic phenomena that occurs inside the power transformer. Initially, different geometrical configurations were conceived and studied in order to choose the best solution for cooling the power transformer when it is constrained to a steady state functioning. The comparative study of the results showed that the redirected flow of oil by an obstacle placed at the entry of the fluid is a good solution in a multichannel system. Then, the approximations made in modelling were validated by the measurements taken on an actual power transformer working in steady state. The study carried out in transient state highlighted that the assumption of an imposed heat flux on the walls of the core and of the windings is no longer valid and the use of an internal heat source is necessary. Second, for a deeper analysis, based on a semi-analytical calculation, a study was made on only one channel between two vertical parallel plates in order to determine the optimal spacing and to find criteria to distinguish among the different convection regimes
Omara, Abdeslam. "Étude de la convection mixte transitoire conjuguée dans une conduite verticale épaisse." Besançon, 2008. http://www.theses.fr/2008BESA2050.
Full textThe proposed survey in this thesis appears in the setting of the conjugated laminar and transient mixed convection in a thick vertical conduct submitted to a constant and uniform heat flux. The fluid penetrates to the top of the conduct to head downwards, therefore one is in presence of opposed mixed convection flow. The governing transport equations were solved using the finite volume formulation and the simple algorithm is adopted. We study the effect of physical and geometrical properties of the physical system on the transient evolution of the thermal magnitudes (interfacial heat flux and radial distribution of the temperature) and the hydrodynamic magnitudes (friction coefficient and vector velocities)
Bonaventure, Julien. "Influence of random surface roughness on friction in elastohydrodynamic, mixed and boundary lubrication." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC038/document.
Full textMost mechanical systems include lubricated contacts submitted to important strengths. The present work deals with the influence of surface roughness on friction in the elastohydrodynamic (EHD), mixed and boundary lubrication regimes, with operating conditions that are typically those found in an internal combustion engine. Most of the surfaces used in the experiments are machined steel, with or with a Diamond-Like Carbon (DLC) coating. Given the friction in boundary and mixed lubrication being higher than in EHD lubrication, it is crucial to predict the transitions between these regimes. These strongly depend on surface roughness. There are very few experimental works that deal with this issue, and the theoretical attempts to include the influence of random surface roughness are based on roughness parameters that are difficult to measure because of their dependence towards the sampling conditions and their non-stationarity. Based on numerous topographical surveys (using interferometry and AFM), a method is implemented to ensure the representativeness of roughness statistical parameters in order to characterize a range of surface roughnesses within the interval [0.001 ; 1] μm. Then, these surfaces are rubbed against each other using Stribeck procedures in order to correlate their morphology to their friction behaviour. The high-pressure rheology of poly-α olefins is measured in smooth contacts with respect to the pressure and the temperature. This not only allows to quantify the friction force for any contact operating in EHD lubrication, but also to set a criterion to spot the onset of mixed lubrication. At high entrainment speed, the viscous shear stress vanishes, which is often attributed to shear heating. It is shown that thermal effects can not explain such a drop of friction for our own experiments. However, the widening of the pressure profile — which becomes significant when the film thickness becomes comparable to a tenth the contact length — is more likely to explain this behaviour. Our results show that the product of the inlet viscosity with the entrainment speed, spotted at the mixed-EHD transition, follows a super linear power law with the RMS roughness, whatever the materials involved, which allows to predict whether a contact operate in mixed lubrication or not. The transition from mixed to boundary lubrication reveals material and roughness-dependent with a clearly different behaviour between DLC/DLC contacts and contacts involving at least one steel body. Regarding the DLC/DLC contacts, the boundary friction is due to the plastic shearing of the lubricant, which explains why surface roughness has no influence on boundary friction for these contacts. With Steel/DLC and steel/steel contacts, the boundary friction presents two monotonous trends versus the composite RMS roughness. Eventually, a mixed bearing model based on the Greenwood-Willimason assumptions was implemented and allowed to reproduce quite closely the experimentally obtained Stribeck curves. This implementation indicates in particular the sampling conditions that are optimal to capture relevant asperity parameters
Vagne, Constance. "Rôle des effets épistatiques dans l’évolution d’une population à régime de reproduction mixte, et dans la régulation de l’expression des gènes homéologues chez une espèce autogame allotétraploïde, le blé dur (Triticum turgidum)." Thesis, Montpellier, SupAgro, 2014. http://www.theses.fr/2014NSAM0063/document.
Full textEpistasis has long been neglected, but it is currently subject to a renewed interest with the development of high-throughput sequencing technologies and of genome-wide association studies (GWAS). It is virtually ubiquitous, having been detected on many traits and in many species. It plays an important evolutionary role, since it is one of the sources of Dobzhansky-Muller incompatibilities, explaining reproductive isolation between related lineages. Moreover, it can enable to fix heterosis in disomic polyploids (mostly allopolyploids). The objective of this thesis was to study epistasis in this evolutionary context. The study material was a broad genetic basis population of a self-pollinating allopolyploid species, durum wheat (Triticum turgidum), having two genomes: A and B genomes. This population was composed from different taxa: durum wheat (T. t. durum), domestic emmer (T. t. dicoccum) and wild emmer (T. t. dicoccoides). Therefore, there are probably combinations of coadapted genes in this population, and thus epistasis generating Dobzhansky-Muller incompatibilities.The first part presents different models to estimate epistasis. These models have advantages and drawbacks, depending on the overall objective. In a second part, we used one of these models on RNA-seq data (expression and genotyping data) of the population of durum wheat to detect regulatory effects of expression, including epistasis between homoelogous genes. This analysis is unique in durum wheat, and probably in polyploid species. We did not detect first-order epistasis, but interactions with genetic background were observed. We found more eQTL on the B genome than on the A genome, which may be due to the fact that the diploid progenitors of durum wheat did not have the same mating system. Furthermore, we showed that the expression levels of homoelogous genes were frequently (80%) positively correlated, indicating that homoelogous genes often belong to the same complex of coregulated genes. Finally, trans regulations are more common among pairs of homoelogous genes, which also supports the idea that homoelogous genes belong to the same gene networks. In the third part, the evolving role of epistasis was examined. First, we showed how epistasis influences the parent-offspring covariance, and thus the short-term evolution of a population. Then we studied the impact of a particular type of epistasis (the one which can generate Dobzhansky-Muller incompatibilities, with combinations of co-adapted genes) on the evolution of a population subjected to truncation selection (as in pre-breeding populations), using a haploid bilocus model, based on the recombination rate and selection intensity. We have shown that if the optimal genotype is not present in the initial population, a high rate of recombination may lead to the fixation of the sub-optimal genotype. However, some recombination is needed to create this optimal genotype and fix it.In perspective, we propose to adopt a network-based method to further the regulation mechanisms of expression in durum wheat. We also propose to make the model more complex, in order to study the effect of recombination on the evolution of an epistatic trait selected by truncation, and complete these modelling works by experimental studies
Herisson, Damien. "Méthode de dimensionnement à l'usure de systèmes de transmission." Phd thesis, Ecole Polytechnique X, 2009. http://pastel.archives-ouvertes.fr/pastel-00006103.
Full textSalcedo, Robledo Manuela. "Amours suspectes : couples binationaux de sexe différent ou de même sexe sous le régime de I'« immigration subie »." Paris, EHESS, 2015. http://www.theses.fr/2015EHES0171.
Full textFrench immigration policy is not limited to the control of foreigners; it also targets French citizens who choose to marry or enter civil unions with a foreign national. Based on research conducted in the lle-de France region, this dissertation studies the experiences of same-sex and different-sex bi-national couples. First, it analyzes how state policies against "inflicted immigration" frame bi-national couples as suspect. In France, since the 2000s, policymakers and bureaucrats created an apparatus of suspicion through categories such as sham marriages [manages blancs] and quasi-sham marriages [mariages gris], the genealogies of which this research traces. These categories have been accompanied by love policing practices in which couples must perform like "real" couples. To prove the authenticity of their love, they reproduce the dominant normative distinction at the heart of relationship discourse between convenience and love. Second, based on ethnographic fieldwork, composed of interviews and observation at organizations helping bi-national couples (Ardhis for same-sex couples and Amoureux au ban public for different sex couples), this dissertation proposes a sociology of bi-national couples drawing on their experiences, demands, and social characteristics (age, nationality, sex, and socioeconomic status). This analysis reveals that, contrary to governmental portrayals of "emotional cheating" on the one hand, and association representations of love unadulterated by economic interests on the other, their relationships are often based on material domination and emotional dependency-between men and women as well as between French citizens and foreigners. Conceptualized as exchanges, the circumstances of these bi-national couples make the mechanisms of these dependencies clear and reveal how they also operate in the relationships of ordinary couples
Badri, Karim. "Légitimité religieuse et transition démocratique : le cas du Maroc." Nantes, 2012. http://www.theses.fr/2012NANT4015.
Full textThe Moroccan political system is characterized by its complexity and specificity. It is a system that tries to reconcile, on the one hand, religious legitimacy and, on the other hand, modern institutions. Hassan II, dedicated craftsman of a democracy Moroccan-style, used this specificity to refute the accusations of international organizations and Western countries about violations of human rights, considering that a universal system of Government would only be possible if men and morals were similar the world over. At the end of the 1980s, pressed by internal social movements on the one hand and an international environment conducive to a democratic opening and respect for human rights on the other hand, the monarchy had undertaken an institutional and constitutional opening while still attempting to manage the design and the consequences of this process. These controlled openings finally resulted in the undermining of the Moroccan political class. Under the pressure of the protest of February 20, 2011, spurred by the Arab spring, King Mohamed VI launched a new constitutional reform. This initiative raised high hopes of a true democratic transition but disappointment was great when considering the advances and stumbling blocks which it carried with it. Indeed, the new Constitution endorsed, as usual, the primacy of the institution of the Monarchy in the Moroccan political system. Mohamed VI’s Morocco has certainly evolved toward a less authoritarian system, nevertheless, it is far from a constitutional, democratic, parliamentary or social monarchy
Dubuc, Julien. "Coopération interlocale et gestion des eaux transfrontalières entre le Canada et les États-Unis le cas du site d'enfouissement de Coventry." Mémoire, Université de Sherbrooke, 2011. http://hdl.handle.net/11143/5638.
Full textFerrier, Jean-Louis. "Contribution à l'étude de la conjugaison de phase, en régime d'excitation picoseconde, dans les milieux liquides et cristallins : faisabilité, caractérisation et applications." Angers, 1986. http://www.theses.fr/1986ANGE0003.
Full textCristea, Alex Florian. "Analysis of thermal effects in circumferential groove journal bearings with reference to the divergent zone." Thesis, Poitiers, 2012. http://www.theses.fr/2012POIT2313/document.
Full textThe main objective of the thesis is to study the thermal effects in steadily loaded circumferential groove journal bearings (CGJBs), including cavitation phenomena occurring in the divergent zone of such bearings. Experimental research conducted at University of Poitiers – Institut Pprime – France enabled a thorough determination of film pressure and temperature fields for the front land of a CGJB plus its mid-groove section, and several performance parameters. Measurements of film pressure and temperature fields under steady-state regime surpassed existing works, regardless of journal bearing design, through: sheer number of land measurement locations, 180 for pressure and for 144 temperature; high precision state of art instrumentation; broad range of operating conditions, 0.125 … 2 MPa specific bearing pressure and 5.25 … 21 m/s shaft speeds. Transient start-up to steady-statestabilization regimes have been investigated at low loads. Experiments at University "Politehnica" of Bucharest – Romania showed a correlation between the downforce thrust and film rupture for a Rayleigh step pin (RSP), important in evaluating divergent zone cavitation phenomena. Theoretical research consisted in developing simple models for evaluating CGJBs performance in steady-state and transient start-up regimes. Several theoretical models were employed for assessing start-up seizure, catastrophic transient thermoelastic instability and damage risk. The major result is a reliable experimental data collection that: enables development of advanced theoretical models; disprove flat film pressure distributions in divergent zones, and constant pressure and temperature in the bearing supply groov
Cremieux, François. "Rousseau et l'histoire." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0136.
Full textIt is customary to mention the report of J.-J. Rousseau to History to enunciate his anthropological optimism to which, like a chiaroscuro, opposes a historical pessimism. Rousseau is above all a humanist, his work is mainly oriented on man and he finds a modern man under the irons, bending under drowsy regimes, with a few exceptions. In the (disastrous) dynamic of history, the citizen perceives only a linear, increasing and secularized degradation, far from any theodicy, the man is the main artisan of his misfortune. However, one cannot conclude to a pessimism without appeal, the citizen hopes in a providential man who can circumscribe this tendency. The historical productions of Jean-Jacques are few and focused mainly on public law. But in the sketch of the history of his republic, Jean-Jacques proved a formidable historian. But History does not interest him much and assigns many faults to him, even if he remains acquainted with ancient history. Rousseau is convinced that history reveals only a denatured man to whom "crutches" are necessary and the author of the Contrat social thinks of the primacy of politics or recourse to mediation. In the relations maintained by the citizen, in three stages, he is first of all the historian of a happy socialization, then evokes his anthropological optimism to which echoes a true process instructed in history; in the end, the last step, the citizen ideologizes History, especially ancient, with a view to a possible and beneficent socialization of man