Dissertations / Theses on the topic 'GHz régime'
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Thomas, Catherine. "Mesures du gradient accélérateur maximum dans des cavités supraconductrices en régime impulsionnel à 3 GHz." Phd thesis, Université Paris Sud - Paris XI, 2000. http://tel.archives-ouvertes.fr/tel-00006564.
Bonamis, Guillaume. "Conception et réalisation d’une source laser femtoseconde GHz et applications au régime d’ablation très haute cadence." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0293.
These last two decades, femtosecond laser technology has gained considerably in terms of maturity and reliability. These laser pulses enable materials micro-machining with minimal thermal collateral effects, thus allowing to work with an outstanding precision, even on materials highly sensitive to temperature. Nevertheless, the penetration of femtosecond processing into the industrial manufacturing market is limited due to an insufficient productivity. The current strategies consist of optimizing the processes on the one hand and increasing the average power of these laser sources on the other hand. Another way suggests increasing the femtosecond ablation process efficiency by delivering bursts of low-energy pulses instead of one highly energetic pulse.Recent works showed that using bursts of pulses at repetition rates on the order of GHz allows to reach ablation rates one order of magnitude higher than the ones obtained by standard femtosecond pulse machining. Nevertheless, these promising results are controversial, as other works point out levels of efficiency lower than expected, added to collateral thermal damages on the machined materials. A thorough study of this new ablation regime is thus necessary to ensure that its interest is justified on the one hand, and to point out the optimal configurations of its use on the other hand. Several optical oscillators delivering bursts of femtosecond pulses at GHz-level repetition rates and laser amplifiers have been developed to this purpose. These innovating laser systems benefit from great flexibility in terms of reachable laser parameters (pulse repetition rate and energy, number of pulses per burst notably). This flexibility allowed us to perform a thorough study of the GHz-ablation regime by numerous machining experiments on several materials of industrial interest. This study points out the influence of the different laser parameters and thus to explain the variety of results related to GHz-ablation and to guide the use of this regime under favorable conditions to reach an efficient and high-quality machining
Lai, Ngoc Diep. "Etude théorique et expérimentale des lasers solides bi-fréquences dans les domaines GHz à THz, en régime continu ou impulsionnel." Phd thesis, Rennes 1, 2003. https://tel.archives-ouvertes.fr/tel-00410958.
Belloni, Valeria. "Spatial and temporal pulse shaping for ultrafast laser materials processing." Electronic Thesis or Diss., Bourgogne Franche-Comté, 2023. http://www.theses.fr/2023UBFCD055.
Ultrafast laser processing has gained significant attention in industrial applications due to its ability to achieve precise and high-quality material ablation. However, laser constraints such as pulse energy and repetition rates have limited the throughput of ultrafast laser processes, especially in industrial settings.In this framework, customizing the spatial and temporal profiles of laser beams can enhance the interaction between the laser and the material. Beam shaping techniques play a crucial role in optimizing the performance of ultrafast laser materials processing and reaching previously inaccessible regimes. In parallel, ultrafast lasers operating at GHz repetition rates deliver a significantly higher number of pulses per unit of time compared to conventional laser sources. Splitting a single pulse into several sub-pulses with high repetition rate seems to be an effective method to increase the ablation rate in laser processing.This thesis explores the possibility of ultrafast laser systems with GHz repetition rates and advanced beam shaping techniques to improve ultrafast laser processing. The Bessel beam is particularly beneficial in processing transparent materials thanks to its robustness to non-linear distortions. A high-order Bessel beam is used in this thesis to generate, for the first time, positive nanopillars with a single laser pulse across the surface of sapphire. In addition, a new setup for highly focused Bessel beams has been developed to investigate new opportunities in silicon processing. Finally, a GHz repetition laser source, in a new regime up to 15 GHz, has been used to process silicon. Promising results were obtained with this very high repetition rate with a Gaussian beam and top-hat beam shaping
Beaussart, Stéphane. "Contribution à l'étude du fonctionnement et à l'optimisation des oscillateurs A. T. T. Au silicium de forte puissance en régime d'impulsions courtes à 94 GHz." Lille 1, 1997. http://www.theses.fr/1997LIL10202.
Richard, Edwis. "Etude du bruit de fond basse-fréquence de 1 Hz à 100 kHz et haute-fréquence de 50 MHz à 4 GHz en régime de porteurs chauds dans des structures n+nn+AlxGa1-xAs." Montpellier 2, 1995. http://www.theses.fr/1995MON20157.
Ewart, Timothée. "Etude des écoulements gazeux isothermes en microconduits : du régime hydrodynamiques au proche régime moléculaire libre." Aix-Marseille 1, 2007. http://www.theses.fr/2007AIX11053.
This Ph. D work involves experimental, numerical and theoretical studies on the isothermal ows in the microtubes and the microchannels using different gases. The experimental part is devoted to the measurements of the mass ow rates. It is completed by a numerical simulation based on the Monte Carlo method, that gives the velocity profile in a section of the microdivice. The results were compared to the following approaches : the NS equations in the slip regime and thevarious kinetic approaches (linearized Boltzmann equation, BGK) in the transitional and the free molecular regime. Comparing our experiments to these numerical or theoretical approaches , we determine the field of validity of the slip regime (using first and second order boundary conditions), the values of the tangential accommodation coefficient, the values of the coefficient of second orderand its parameter dependences. Finally, we analyze the asymptotic behavior of the mass ow rate in the free molecular regime
Aufrère, Loi͏̈c (19. "Etude de l'interaction gaz-paroi en régime hypersonique." Aix-Marseille 1, 2000. http://www.theses.fr/2000AIX11027.
Lusseyran, François. "Caractéristiques cellulaires du régime à poches en écoulement gaz-liquide co-courant vertical, transition vers le régime déstructuré." Vandoeuvre-les-Nancy, INPL, 1990. http://docnum.univ-lorraine.fr/public/INPL_T_1990_LUSSEYRAN_F.pdf.
Plagnol, Vincent. "Modélisation de la colonne positive d'une décharge mercure-argon basse pression : analyse du régime stationnaire et étude de l'influence de la fréquence d'alimemtation en régime sinusoi͏̈dal." Toulouse 3, 1992. http://www.theses.fr/1992TOU30036.
Bataille, Dominique. "Analyse du fonctionnement en régime permanent et en régime transitoire d'un échangeur de chaleur gaz-solide multiétagé à lits fluidisés." Toulouse, INPT, 1986. http://www.theses.fr/1986INPT001G.
Mawlana, Abdulrahman. "Étude en régime permanent et transitoire du transfert liquide-gaz : cas d'un réacteur fluidisé gaz-liquide-solide." Toulouse, INPT, 1987. http://www.theses.fr/1987INPT026G.
Gadoin, Émilie. "Régime intermittent "gaz-liquide" en conduite horizontale : écoulements non établis et transitoires." Toulouse, INPT, 1993. http://www.theses.fr/1993INPT152H.
Girardin, Mathieu. "Méthodes numériques tout-régime et préservant l'asymptotique de type Lagrange-Projection : application aux écoulements diphasiques en régime bas mach." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066377/document.
Two-phase flows in Pressurized Water Reactors belong to a wide range of Mach number flows. Computing accurate approximate solutions of those flows may be challenging from a numerical point of view as classical finite volume methods are too diffusive in the low Mach regime. In this thesis, we are interested in designing and studying some robust numerical schemes that are stable for large time steps and accurate even on coarse meshes for a wide range of flow regimes. An important feature is the strategy to construct those schemes. We use a mixed implicit-explicit strategy based on an operator splitting to solve fast and slow phenomena separately. Then, we introduce a modification of a Suliciu type relaxation scheme to improve the accuracy of the numerical scheme in some regime of interest. Two approaches have been used to assess the ability of our numerical schemes to deal with a wide range of flow regimes. The first approach, based on the asymptotic preserving property, has been used for the gas dynamics equations with stiff source terms. The second approach, based on the all-regime property, has been used for the gas dynamics equations and the homogeneous two-phase flows models HRM and HEM in the low Mach regime. We obtained some robustness and stability properties for our numerical schemes. In particular, some discrete entropy inequalities are shown. Numerical evidences, in 1D and in 2D on unstructured meshes, assess the gain in term of accuracy and CPU time of those asymptotic preserving and all-regime numerical schemes in comparison with classical finite volume methods
Chabut, Emmanuel. "Simulation aérothermodynamique en régime d'écoulement raréfié par méthode de Monte-Carlo." Orléans, 2005. http://www.theses.fr/2005ORLE2017.
Cherradi, el Fadili Ibrahim. "Simulation numérique directe d'écoulements gazeux par la méthode de Monte-Carlo : application à l'étude de mélanges gazeux entre le régime continu et le régime moléculaire libre." Paris 11, 1987. http://www.theses.fr/1987PA112401.
Gherendi, Florin. "Etude de la transition d'un régime diffus à un régime anodique du plasma du disjoncteur sous vide : spectroscopie, imagerie et autres diagnostics." Orléans, 2001. http://www.theses.fr/2001ORLE2028.
Agayeva-Le, Nouail Tamilla. "Le régime juridique des hydrocarbures de la mer Caspienne." Nantes, 2011. http://www.theses.fr/2011NANT4003.
The Caspian Sea is the largest enclosed body of water on Earth by area, which is currently the heart of a strategic zone representing tremendous reserves of hydrocarbon. According to the estimations, professionals expect between 17 and 44 billion barrels of petrol and around 232 billion of m3 of natural gas. The rediscovery of such a potential of the Caspian Sea leads straightaway to two legal problems. The fist problem concerns the questioning of the status of this sea, which still remains uncertain following the multiplication of the number of bordering states, and which determines the international regime on hydrocarbon resources. Each of the bordering states wishes to get one part in the exploration of the energetic resources that demands adaption of a new convention. The question of division of the sea is the object of regional multilateral and bilateral negotiations. These negations were successful in formation of borders sui generis dividing the sea floor between three northern Caspian states. But the uncertainties of the legal status and the delimitation of the Caspian Sea persist and augment the instability in the region. The second problem is regarding the study of the regime formation for hydrocarbon resource extraction. Since their independency the Caspian states have created legislation which foresees the principles of access to the hydrocarbon resources. This regime, however, has not been accomplished yet and constantly suffers important modifications. Furthermore, an intense extraction of the hydrocarbon resources provokes in the first place the question of the environmental protection. The situation of the environment of the Caspian Sea is currently alarming and a formation of a framework for its protection is very urgent
Belenguer, Philippe. "Modélisation des décharges radiofréquence en régime collilsionnel." Nancy 1, 1990. http://www.theses.fr/1990NAN10064.
Bonifacie, Stéphane. "Etude théorique et expérimentale d'un gaz bidimensionnel d'électrons désordonné en régime d'effet Hall quantique." Montpellier 2, 2003. http://www.theses.fr/2003MON20188.
Ewart, Timothée. "Etude des écoulements gazeux isothermes en microconduit : du régime hydrodynamique au proche régime moléculaire libre." Phd thesis, Université de Provence - Aix-Marseille I, 2007. http://tel.archives-ouvertes.fr/tel-00396378.
Truffin, Karine. "Simulation aux grandes échelles et identification acoustique des turbines à gaz en régime partiellement prémélangé." Phd thesis, Toulouse, INPT, 2005. http://oatao.univ-toulouse.fr/7719/1/truffin1.pdf.
Magnifotcham, François. "Ecoulements diphasiques gaz-liquide. Dynamique et thermique des réacteurs ouverts en régime stationnaire ou transitoire." Perpignan, 1994. http://www.theses.fr/1994PERP0174.
Portier, Stéphane. "Modélisation du comportement des gaz de fission en régime transitoire dans le combustible à plaques." Châtenay-Malabry, Ecole centrale de Paris, 2003. http://www.theses.fr/2003ECAP0938.
Enjalbert, Nicolas. "Modélisation avancée de la combustion turbulente diphasique en régime de forte dilution par les gaz brûlés." Phd thesis, INSA de Rouen, 2011. http://tel.archives-ouvertes.fr/tel-00735875.
Bondavalli, Paolo. "Microsystèmes optomécaniques à base d'InP pour l'analyse de gaz." Lyon, INSA, 2000. http://theses.insa-lyon.fr/publication/2000ISAL0009/these.pdf.
In this PhD thesis we talk about the optical-mechanical design and the realization of an optical sensor for hydrocarbon gas concentration measurement (methane, butane, benzene…) performing line-shape absorption analysis around the 1. 665 micrometer spectral region. This device is composed by an InP based opto-mechanical micro-cavity. The cavity is a part of Fabry-Pérot filter which can be turned changing electrostatically the starting thickness of the cavity. In this way we can select the different parts of the absorption line shape of a natural gas mixture and so carry out its composition. The advantages of this kind of device are the measures reproducibility, the fast response (the time response can be less than 1 second), the selectivity (around 10 nanometers) and the possibility of performing a large spectral analysis (around 200 nanometers). In this work we have realized the opto-mechanical design of tunable Fabry-Pérot filters and a tunable resonant photo-detectors with an original approach to the mechanical model which permites to obtain the device performances with a good precision. Finally we shall present some preliminary results obtained on a first generation of tunable filters
He, Jun. "Modélisation des écoulements gaz-solides en régime dilué : influence des collisions entre particules et de l'anisotropie de leur mouvement fluctuant." Compiègne, 1994. http://www.theses.fr/1994COMPD698.
Desruelle, Bruno. "Evaporation par radio-fréquence et condensation de bose-Einstein d'un gaz d'alcalins en régime de champ fort." Phd thesis, Université Paris Sud - Paris XI, 1999. http://pastel.archives-ouvertes.fr/pastel-00716029.
Nafa, Malik. "Spectroscopie DRASC en régime hybride fs/ps à haute cadence (kHz) appliquée à la thermométrie des gaz." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD001/document.
Coherent spectroscopy such as Coherent Anti-Stokes Raman Scattering (CARS) is commonly used for the study of reactive media.Following the recent progress encountered in laser sources and detectors, this thesis work proposes an adaptation of the technique for temperature measurements that exploits the ultra-short pulse regime (femtosecond, picosecond) to operate at high repetition-rate.The developed hybrid fs/ps-CARS setup delivers a 30-ps probe pulse using a femtosecond laser source and a Volume Bragg Grating. The obtained spectral resolution is 0,7 cm-1, which represents, within this pulse generation framework, the state of the art. This setup is applied to ro-vibrational spectroscopy of several molecular species.The interaction in the hybrid regime is described through a CARS simulation model that has been implemented. The modelling takes into account both the amplitude and the phase profiles of the probe pulse, and its delay to the femtosecond excitation. Influence of molecular collisions in the hybrid regime is also discussed.This modelling has been validated by fitting calculated spectra on experimental spectra recorded in ambient air, and in a premixed CH4/air flame. Temperature has been then measured at atmospheric pressure in these media. The precision is similar to the hybrid fs/ps-CARS thermometry state of the art.This work validates our N2 thermometry approach based on both the developed CARS setup and simulation model. Short term perspectives of this work are measurements on real combustion chambers at ONERA, by extrapolating our simulation model at high pressure
Chaussard, Frédéric. "Effets collisionnels homogènes et inhomogènes dans les spectres Raman rovibrationnels de H2, du régime Doppler au régime collisionnel : applications au diagnostic optique de la température dans les milieux en combustion." Dijon, 2001. http://www.theses.fr/2001DIJOS045.
Soulem, Nicolas. "Application de l'interaction laser-gaz à l'étude des régimes de fonctionnement d'une décharge électrique." Orléans, 1996. http://www.theses.fr/1996ORLE2052.
Llamas, Juan-David. "Etude expérimentale de la maldistribution des fluides dans un réacteur à lit fixe en écoulement co-courant descendant de gaz et de liquide." Phd thesis, Institut National Polytechnique de Lorraine - INPL, 2008. http://tel.archives-ouvertes.fr/tel-00376283.
Gobron, Thierry. "Modèles de gaz sur réseau appropriés à l'étude de systèmes de particules en régime de saut sous-amorti." Paris 11, 1986. http://www.theses.fr/1986PA112040.
This thesis set out a lattice gas model which describes the transport properties of classical particle systems in the underdamped hopping régime (superionic conductors, diffusion of adsorbed particles. . . ) in a simple way. On each site, the state of a particle is described by a multicomponent vector [P(x,t)˃ each possible kinetic state for the particle being associated with one of the components. A master equation. That describes the evolution of probability distribution in an independent particle model is established. Although the operator m describes the evolution of the system on a long time scale, it is constructed by determining its matrix elements as the jump probabilities for the particle between times t- τ and t+ τ, τ being a microscopic time scale. Lt is shown that this operator can be factorised into a shifting operator G, diagonal, and a state transition operator Mσ. From the master equation and with the help of the symmetry group that leaves M invariant, several physical quantities such as the diffusion constant, the A. C. Conductivity and the structure factor are explicitly calculated for several lattices in 1 ,2 and 3 dimensions. Even though the model does not allow for a detailled balance, fluctuation and dissipation can be related with a Kubo formula. The influence of a magnetic field and external constraints applied to the system is examinated. Finally, a Boltzmann equation is established and compared to the one that have been proposed in an empirical approach by Rice and Roth
Charton, Sophie. "Étude et modélisation en régime transitoire d'un écoulement de gaz à haute pression dans un milieu poreux réactif." Vandoeuvre-les-Nancy, INPL, 1997. http://www.theses.fr/1997INPL012N.
Ben, Gadri Rami. "Modélisation numérique du régime luminescent d'une décharge contrôlée par barrière diélectrique et établie à pression atmosphérique." Toulouse 3, 1997. http://www.theses.fr/1997TOU30057.
Boucker, Marc. "Modélisation numérique multidimensionnelle d'écoulements diphasiques liquide-gaz en régimes transitoire et permanent : méthodes et applications." Cachan, Ecole normale supérieure, 1998. http://www.theses.fr/1998DENS0032.
Zaabout, Abdelghafour. "Contribution expérimentale à l'étude du comportement hydrodynamique de l'écoulement gaz-particules dans les lits fluidisés : régimes et mécanismes de transitions." Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22094/document.
The aim of this thesis is to characterize the solid phase behavior marking the turbulent fluidization regime in the dilute zone of a circulating fluidized bed riser and set its upper limit, which marks the transition to the fast fluidization regime. A series of experiments were conducted in this direction, especially to determine the particle velocities and their standard deviations using laser Doppler velocimetry technique. The study is divided into two main parts, the first was to determine the average solid phase behavior and the macroscopic structure of the bed in this region and its fluctuating behavior from the analysis of axial and transversal particle motions with and without separation of particles according to their movement direction (up / down, directed toward the center of the column / wall). The second part consists of studying the transition between the turbulent and fast fluidization regime from the analysis of the evolution of mean and fluctuating flow quantities locally in the center riser and in the wall (especially the particle velocity, their standard deviations, and the particle flow rate). Based on the results observations, we have identified a new intermediate regime between the turbulent and the fast fluidization regime that we called "Pre-fast fluidization" regime which shares many characteristics with the fast fluidization regime, but without any significant change in the solid flow rate collected on the column exit
Ginestet, Alain. "Contribution à l'étude des régimes d'écoulement en transport pneumatique vertical et incliné." Compiègne, 1992. http://www.theses.fr/1992COMPD499.
Amara, Salah. "Elaboration et validation d'un modèle de transferts thermiques instationnaires gaz-paroi dans la chambre de combustion d'un moteur." Ecully, Ecole centrale de Lyon, 1994. http://bibli.ec-lyon.fr/exl-doc/TH_T1547_samara.pdf.
Araoud, Zouhour. "Etude du régime dynamique d'un plasma de décharge électrique dans la vapeur de mercure." Toulouse 3, 2009. http://thesesups.ups-tlse.fr/651/.
The present work deals with the modelling of the high-pressure-mercury lamp during the last phase of the warm-up period. Simulation is carried out in the frame of Local Thermodynamic Equilibrium using a time-dependent two-dimensional computational fluid model. After validation from comparison with literature results, this model is used to analyse the dynamic behavior of a high pressure mercury discharge lamp, to describe the evolution of various results during this phase and to measure the effect of the convection. Two models have been compared. The first takes into account of the convection and the second neglects it. We proved that the convection slows down the warm-up phase while increasing mercury losses behind the electrodes and the time of evaporation of the quantity of mercury. In the electric discharge, the influences of several parameters such as the current and the geometry of the burner are studied. Their incidences on the thermalisation of the discharge were examined. It was found, in one hand, that the warm-up of a high pressure mercury lamp is accelerated by amplifying the current or the inter-electrodes length with constant current. On the other hand, an increase in the diameter slows down it
Lam, Van Trien. "Les enjeux juridiques de l'intégration des pays en développement dans le régime climatique de "l'après Kyoto"." Rouen, 2013. http://www.theses.fr/2013ROUED012.
Bourgeois, Pierre-Louis. "Modélisation de sources X générées par interaction laser-plasma en régime relativiste." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX073.
When an ultra-short ultra-intense laser impulsion propagates through a low density gas jet, a plasma is created and a bunch of electrons can be accelerated through laser wakefield acceleration to Gev energies in only a few centimetres. Those accelerated electrons then emit what is called Betatron radiation: a highly focused X-ray source with extremely good spatial and temporal properties, which has a lot of possible applications including ultra-high resolution imaging.In this thesis, we investigate possible improvements to one of the main numerical tools used to simulate those phenomenons: the Particle-In-Cell codes (CALDER). We have especially studied a numerical artefact called the numerical Cherenkov radiation, that occurs when relativistic particles move at speeds aproaching the speed of light in a vaccuum.We show that this artefact has a negative impact on the behaviour of the accelerated electron beam, especially on its transverse motion, which leads to important errors on the betatron radiation calculated using PIC simulations.We then introduce a new approach to mitigate the impact of this numerical Cherenkov radiation on laser wakefield acceleration simulation with a simple modification of the electromagnetic field interpolation method used in PIC codes. The results obtained with this new technique show a meaningful improvement on the electron motion wich becomes close to the theoretically expected behaviour.We then explore other possible applications for this new technique, notably improving the modelization of betatron sources, vacuum laser acceleration or direct laser acceleration.The improvement of the computation of the particles transverse motion thanks to this new method leads to more accurate results but also enables us to study physical phenomenon with subtle effects that would otherwise be hidden among the numerical noise of the simulation
Taha, Bouchra. "Comportement de particules dans des lits fluidisés gaz-solide avec une grille multijets : régimes hydrodynamiques, ségrégation et mélange." Lille 1, 1989. http://www.theses.fr/1989LIL10010.
Bonhomme, Gérard. "Instabilités des systèmes faisceau d'ions-plasma - I) Expériences et simulations numériques en régime non linéaire pour le cas non magnétisé - II) Étude numérique du régime linéaire des instabilités cyclotron ioniques." Nancy 1, 1989. http://www.theses.fr/1989NAN10386.
Volkov, Aleksandr. "Le régime juridique des relations gazières entre la Russie, l'Union Européenne et les pays membres de l'Union Européenne." Thesis, Tours, 2017. http://www.theses.fr/2017TOUR1004/document.
The current legal rules restrain the development of both frameworks now existing – that is, long-term contracts and opened-up markets. The solution to this problem could be the maintain of the first group of relations and the development of the second group. Therefore, it is important to suggest an alternative framework. The basis of such alternative framework could be fixed in an international treaty between Russia, EU and the member-states. This new regulation will also require the adjustment of the local legislation
Olmos, Eric. "Étude expérimentale et numérique des écoulements gaz-liquide en colonne à bulles." Vandoeuvre-les-Nancy, INPL, 2002. http://www.theses.fr/2002INPL045N.
Kuwahara, Takuya. "Caractérisation des régimes d'écoulement diphasique gaz-liquide par fluide magnétique : appareillage, mesures, traitement du signal et analyse de données." Châtenay-Malabry, Ecole centrale de Paris, 2008. http://www.theses.fr/2008ECAP1064.
Llamas, Juan David. "Étude expérimentale de la maldistribution des fluides dans un réacteur à lit fixe en écoulement à co-courant descendant de gaz et de liquide." Thesis, Vandoeuvre-les-Nancy, INPL, 2008. http://www.theses.fr/2008INPL006N/document.
Three different measuring techniques were used to study the fluid distribution inside a trickle-bed reactor: the wire mesh tomography, the liquid collector and a set of thermistors. The liquid collector and specially the wire mesh tomography, whose first application in trickle bed reactors is described here, yielded interesting results concerning the influence of variables such as the initial liquid distribution, the loading method and the fluid flow rates on liquid maldistribution. Among the main observations, the study illustrates the importance of well defining liquid maldistribution in terms of the measured quantity and prompts to some caution when referring to some “normally accepted facts” like the advantages in terms of liquid distribution obtained when increasing the gas flow rate (which depends, according to this study, on the quality of initial liquid distribution) or when using a dense loading of the catalyst (the hypothesis according to which, compared with a sock loading, dense loading favors radial dispersion was not verified by the study). Also, a study performed under high interaction conditions showed the intimate relationship between the inlet distribution and the flow regime observed inside the reactor
Sollier, Arnaud. "Etude des plasmas générés par interaction laser-matière en régime confiné : application au traitement des matériaux par choc laser." Phd thesis, Université de Versailles-Saint Quentin en Yvelines, 2002. http://tel.archives-ouvertes.fr/tel-00089243.
Afin de mieux comprendre les phénomènes physiques mis en jeu dans ce régime d'interaction particulier, une modélisation originale du procédé a été développée. Un code numérique traitant les processus de claquage dans l'eau de confinement permet dans un premier temps de déterminer les caractéristiques (intensité crête et durée à mi-hauteur) de l'impulsion laser transmise à travers la fenêtre de confinement. Un modèle hydrodynamique auto-consistant traitant les plasmas confinés (plasmas froids et denses, corrélés et partiellement dégénérés) utilise ensuite ces paramètres pour calculer les chargements mécaniques et thermiques induits à la surface de la cible traitée. Pour terminer, ces chargements sont utilisés en entrée du code aux éléments finis ABAQUS afin de simuler les contraintes résiduelles d'origine mécanique et thermique induites par le traitement.
Les résultats de ces simulations ont été validés par comparaison avec différentes mesures expérimentales réalisées pour des conditions d'irradiation laser (longueurs d'ondes de 1064 nm et de 532 nm, durées d'impulsion de 3 ns et 10 ns) typiques des conditions opératoires réelles utilisées au niveau industriel.
Ces résultats montrent que les petites taches focales permettent de limiter fortement le chauffage de la cible par le plasma confiné, et donc de s'affranchir des effets thermiques induits par le traitement. Ils ouvrent donc de nouvelles perspectives quant à la réalisation du traitement par choc laser sans utiliser de revêtement thermo-protecteur. Par ailleurs, ils permettant d'expliquer les résultats obtenus avec la configuration de traitement développée par Toshiba (très petites taches focales, haute cadence, pas de revêtement protecteur), qui demeuraient incompris jusqu'alors.
Diaz, Romain. "Métrologie de l'endommagement laser des composants optiques en silice en régime nanoseconde." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4390/document.
In this thesis, laser-induced damage phenomenon in fused silica components is investigated in the nanosecond regime. This material is one of the most widely used in optics, particularly on high-energy laser facilities such as the Laser MégaJoule. In order to ensure the nominal operation of this kind of laser facility, laser-induced damage on optical components has to be understood and controlled. This phenomenon consists in an irreversible modification of the material. In the nanosecond regime, laser-induced damage is tightly correlated to the presence of precursor defects which are a consequence of the synthesis and the polishing of the components. The interaction between these precursor defects and the laser pulses strongly depends on the laser characteristics. The first study focuses on the metrology of the laser beam used in laboratory to study laser-induced damage. The second one consists in a parametric study of the initiation mechanism on the rear surface of fused silica components. The last part deals with the influence of nonlinear propagation on laser induced damage on the surface and in the volume of thick fused silica samples