A otimização da formulação do óleo lubrificante empregado em motores de combustão interna é uma importante maneira de se reduzir o atrito e assim aumentar a eficiência energética. É também uma forma de assegurar proteção ao sistema, mantendo a taxa de desgaste em um nível adequado. O óleo de motor é uma mistura de óleos básicos selecionados com aditivos, entre os quais podem ser encontrados os modificadores de atrito, que são compostos com capacidade de aderir às superfícies metálicas, proporcionando melhoria da lubrificação em condições mista e limítrofe. O dialquilditiocarbamato de molibdênio (MoDTC) está entre os mais importantes redutores de atrito empregados em óleos lubrificantes. Ésteres sintéticos podem ser usados como óleos básicos em algumas formulações. Visto que ésteres são mais polares que hidrocarbonetos, essas moléculas podem atuar modificando propriedades do óleo na região próxima à superfície metálica. Podem também interferir com filmes adsorvidos, limitando sua efetividade. O objetivo do trabalho é a comparação dos efeitos do MoDTC em diferentes misturas contendo hidrocarboneto e éster. Para isso, formulações lubrificantes contendo uma polialfaolefina, um diéster e um aditivo à base de MoDTC foram preparadas, caracterizadas e ensaiadas em tribômetro oscilatório SRV usando configuração esfera-­disco. Foram empregadas esferas de aço AISI 52100 e discos de aço AISI H13. Foi estudada a influência da variação da temperatura e da força normal aplicada. Empregando-­se mistura de hidrocarboneto e éster como lubrificante, o aumento da temperatura causou leve aumento do coeficiente de atrito. Em ausência de MoDTC, a presença de éster aumentou a capacidade de suportação de carga das formulações. Os testes com óleos contendo MoDTC foram marcados pela ocorrência de dois fenômenos: ativação e depleção do aditivo. Estes fenômenos se mostraram dependentes da carga normal e da composição do óleo. O efeito de redução do atrito pelo MoDTC tende a ser menos duradouro com óleos mais ricos em éster e em condições de carregamento mais severo. O comportamento tribológico do éster em mistura com polialfaolefina, medido através do coeficiente de atrito, seguiu a isoterma de adsorção de Frumkin, com alguma atração entre as moléculas do éster, e energia livre da ordem de -­4 kJ/mol, típica de fisissorção. Óleos envelhecidos artificialmente foram testados e não apresentaram diferenças significativas com relação aos mesmos óleos novos. A adição de etanol aos óleos envelhecidos causou uma leve diminuição no coeficiente de atrito a 40 °C; tal efeito não foi perceptível em temperaturas mais altas, provavelmente devido à perda por evaporação do álcool. / The optimization of the lubricant oil formulation used in internal combustion engines is an important way of reducing friction, thus increasing energetic efficiency. It is also a way of protecting the system, maintaining wear rate in an adequate level. The engine oil is a blend of selected base oils with additives, amongst which are the friction modifiers substances able to adhere to the metal surfaces, thus providing better lubrication at the mixed and boundary regimes. Molybdenum dialkyldithiocarbamate (MoDTC) is amongst the most important friction reducers used in lubricant oils. Synthetic esters may be employed as base oils in some formulations as well. Given that esters are more polar than hydrocarbons, these molecules can actuate by modifying oil properties in the near-­surface region. They can also interfere with adsorbed films, preventing their effectiveness. The objective of this work is the comparison of the effects of MoDTC in different mixtures containing hydrocarbon and ester. With this aim, lubricating formulations containing a polyalphaolefin, a diester and a MoDTC-­based additive were prepared, characterized and tested in a reciprocating SRV tribometer using ball-­on-­disc configuration. AISI 52100 steel balls and AISI H13 steel discs were employed. The influences of the temperature and of the normal load were both studied. Employing a mixture of hydrocarbon and ester as lubricant, a higher temperature caused a slightly higher coefficient of friction in the lubricant free of additive. In the absence of MoDTC, the ester increased the load-­carrying capacity of the lubricant formulations. Tests with MoDTC-­containing oils were characterized by two phenomena: activation and depletion of the additive. These phenomena showed to be dependent on the normal load and on the oil composition. The MoDTC friction reducing effect tends to be less sustainable with higher ester concentrations and at higher loads. The tribological behavior of the ester in the presence of polyalphaolefin, as measured by the coefficient of friction, followed the Frumkin adsorption isotherm, with some attraction between ester molecules, and free energy in the order of -­4 kJ/mol, typical of physisorption. Artificially aged oils were tested and did not show differences when compared with the results of the fresh oils. Adding ethanol to the aged oils caused a slightly reduction in the coefficient of friction at 40 °C, but this effect was not observed at higher temperatures, probably due to evaporation loss of the alcohol.

Lorsqu'un liquide mouillant touche un solide, on observe un ménisque de taille millimétrique. Si le solide est rugueux à une échelle submillimétrique, le liquide peut progresser le long des aspérités sur une distance qui est potentiellement illimitée si le solide est horizontal. Nous modélisons la rugosité avec des piliers cylindriques et montrons que quelques cylindres seulement suffisent à transporter et guider précisément un liquide. Nous étudions la dynamique macroscopique et microscopique de l'invasion. Nous examinons ensuite combien de liquide s'accumule dans une variété de textures et proposons un nouveau type de détergence pour extraire le liquide de la rugosité. Nous prenons aussi la gravité en compte et l'utilisons d'abord pour démontrer que plusieurs fronts liquides peuvent être observés simultanément dans des porosités multi-échelles. Nous nous intéressons enfin aux ponts capillaires millimétriques et nous dédions notre dernier chapitre à leur dynamique de croissance radiale. / When a wetting liquid contacts a solid, we observe a liquid meniscus of millimetric size. If the solid is rough at a submillimetric scale, the liquid may progress along the asperities for a potentially unlimited distance if the solid is horizontal. We model the roughness with a regular texture and show that a low number of surface features is sufficient to transport and precisely guide a liquid. We study the macroscopic and microscopic dynamics of the invasion. We examine then how much liquid accumulates in a variety of texture and propose a new kind of detergency to remove the liquid from the roughness. We also consider the influence of gravity and use it to demonstrate that multiple liquid fronts can be observed simultaneously in porosities of different scales. Then we turn our attention to millimetric capillary bridges and dedicate our last chapter to explain their dynamics of radial growth with the Cox-Voinov model.

O objetivo principal deste trabalho de Mestrado é avaliar compensadores que tentam diminuir o efeito do atrito estático existente em válvulas de controle. Os compensadores de atrito utilizados neste trabalho foram: CR1, CR2 Knocker, Two-move, controle por modos deslizantes e controle por modos deslizantes integrador. Estes compensadores são implementados em um ambiente industrial (SDCD). Devido ao atrito, o sistema tem um comportamento não-linear, o qual pode afetar o bom rendimento de um controlador PID, sendo que o sistema em malha fechada pode ter oscilações. Então, para obter uma diminuição do efeito do atrito, empregam-se compensadores de atrito. Para implementá-los, é necessário conhecer os parâmetros do atrito existente. Portanto, a primeira parte deste trabalho consiste em uma explicação dos diferentes modelos e métodos que se vai usar neste trabalho. Também foram realizadas simulações das estratégias de controle utilizadas. Após estes tópicos, vai se identificar o modelo do sistema que conta com uma malha de controle de vazão, com o objetivo de auxiliar na sintonia do controlador PID. Depois, introduzem-se os compensadores de atrito, os quais tentam minimizar os índices ITAE (Integrated Time Absolute Error) e IAE (Integrated Absolute Error), bem como o desgaste que se produz nos equipamentos, devido ao uso (excessiva movimentação da haste das válvulas). O objetivo assumido é implementar as estratégias de controle em um software industrial. Os resultados mostraram que os compensadores CR1 e CR2 obtiveram os melhores índices de desempenho e conseguiram compensar o atrito na haste da válvula de controle. / The main objective of this work is to evaluate compensators that try to decrease the static friction effect existent in control valves. The friction compensaters used in this work were: CR1, CR2, Knocker, Two-move, sliding mode control and sliding mode control with integrator. These compensators are implemented in an industrial environment (DCS). Due to friction, the system has a nonlinear behavior, which may affect the good performance of a PID controller, wherein the closed loop system can have oscillations. So to get a decrease in the effect of friction, friction compensators are employed. To implement them, it is necessary to know the parameters of the friction existent. So the first part of this work consists of an explanation of the different models and methods that will be use in this work. Also, simulations were made of the control strategies used. After these topics, it will be identify the system model which has a own control loop, in order to help the PID controller tuning. Then it will be introduced friction compensators, which attempt to minimize the ITAE (Integral Time Absolute Error) and IAE (Integrated Absolute Error), and wear that occurs on the equipment due to the use (excessive movement of the valve stem). The assumed objective is to implement control strategies in industrial software. The results show that the compensators CR1 and CR2 have the best performance indexes and they compensate for the friction in the control valve stem.

Le thème central de la thèse est l'interférométrie atomique et la réduction du bruit de phase lié aux vibrations de l'environnement. Les interféromètres atomiques sont des instruments pouvant permettre des mesures fondamentales de grande précision et cette précision est fortement liée à la vitesse des atomes. L'interféromètre qui était utilisé à Toulouse travaillait alors avec des atomes de lithium aux énergies thermiques et le projet était de pouvoir utiliser des atomes fortement ralentis. Les vibrations du sol (bruit sismique) deviennent alors un inconvénient majeur et il est indispensable de s'en affranchir le plus possible. La première partie du travail fut de prévoir une isolation vis à vis du bruit sismique. Un premier filtre est réalisé en plaçant l'ensemble de la manipulation sur un pendule suspendu par 3 fils. Celui ci atténue les vibrations de fréquence supérieure à sa fréquence propre mais amplifie celles de fréquences voisines de celle-ci. Il faut donc un pendule asservi et cela implique un sismomètre sensible pouvant fonctionner sous ultravide. Nous avons développé une stabilisation des mouvements horizontaux en nous appuyant tout d'abord sur des sismomètres simples mais peu sensibles, puis nous avons cherché à améliorer les performances en réalisant un capteur de déplacement basé sur un interféromètre de Michelson à coins de cube. Nous avons suivi en cela les travaux de l'équipe de M.Zumberge qui utilise une détection de deux signaux en quadrature ce qui permet une mesure de déplacement avec une sensibilité meilleure que 4.10-13 m/vHz à 1 Hz et entrepris d'adapter cette technologie à un fonctionnement sous ultravide. Mais les difficultés rencontrées et l'abandon de l'interféromètre tel qu'il était pour en developper un nouveau ne nous ont pas permis d'atteindre complètement notre but et de pouvoir tester le sismomètre in-situ.Cependant, la mise au point et l'optimisation du sismomètre nous a amené à nous pencher sur la théorie des pendules à lame élastique, lesquels sont largement utilisés dans ce genre de capteurs. Il nous est apparu que cette théorie était très incomplète et nous avons entrepris une étude plus systématique de tels pendules ce qui a donné lieu à une publication et fait l'objet de la seconde partie de la thèse. [...] / The main theme of my thesis is atomic interferometry and in particular the reduction of the phase noise induced by vibrations. Atomic interferometers are good devices to achieve accurate and fundamental measuring. The sensibility of these devices is related to the flying time of the atoms inside the apparatus. At Toulouse, our interferometer worked with atoms at thermal velocity and to increase the sensibility we wanted slower atoms. However, this will at the same time increase the effect of vibrations, witch result in a larger phase noise and a jamming of the fringes. In order to reduce this effect, I've put the core of the interferometer on a 3 wires pendulum. A pendulum attenuates the vibrations of frequencies much higher than its resonant frequencies but amplifies those with frequencies close to its resonances. To avoid this phenomenom, we have to enslave the pendulum on the signal given by seismometers. With a first realisation, I was able to stabilize 2 horizontal movements with 2 low sensibility seismometers. To increase the performances, I needed high sensibility seismometer and the possibility to operate under ultra vacuum. I've made a deplacement sensor based on the Michelson interferometer with cube corners, following the works of Zumberge's team. By choosing cleverly the polarisation of the laser beam, we can detect 2 signals in quadrature and the sensibility achieved is better than 4x10-13 m/vHz at 1 Hz. The next step was to migrate this seismometer in ultra vacuum but the retirement of the interferometer using slow down lithium atoms at the benefit of an atomic fountain of rubidium stopped this project. However, this work on the seismometer led me to think about elastic blade pendulums, widely used in such sensors. I've complete the theory, showing the presence of 2 resonance frequencies and, as a test, I've build a such pendulum, for witch I've measured the caracteristics with some position and velocity sensors I've developped for this purpose. I was able to measure precisely the damping of the oscillations of the pendulum and study more precisely the different origins of the damping. Two of them have given some additionnal work : a)the coupling with the resonances of the frame witch support the pendulum may have an effect on the quality factor of the pendulum. [...]

This thesis focuses on identifying hard material pairs with low roughness, high coefficient of static friction, high wear resistance and high modulus of elasticity, suitable for sliding in dry friction conditions under a normal load. A wide range of materials including various steels, various coatings on tool steels deposited by various deposition techniques and different ceramics were examined and considered for tribological testing. Procedures and sequences were developed for conducting tribology tests on the material pairs. High endurance - low cycle tests were conducted and based on the performance of material pairs with respect to friction, wear and surface roughness a small set of material pairs and coatings was selected for further testing. High endurance - high cycle tests were performed on an additional seventeen pairs of material pairs selected for long term sliding. Material pairs were selected for low endurance tests based on high corrosion resistance along with all the above specified design parameters. Low endurance tests were conducted to identify material pairs sliding for a short distance in humid environments. Results are tabulated and pictures of the material pairs after wear tests are presented. It was found that four material pairs for high endurance applications and two pairs for the low endurance applications performed very well in regard of design specifications. These material pairs find a major application in friction clamps of an Inchworm motor resulting in enhancement of force output of the motor.

Friction-induced oscillations occur in many engineering systems, often resulting in noise, vibration, and excessive or uneven wear. This research addresses the suppression of such oscillations, especially with application to braking systems, through the use of high-frequency dither signals. Brake squeal is an annoying and elusive problem too often present in braking systems of automobiles, trucks and aircraft. In previous work, the effectiveness of high-frequency dither to eliminate squeal in an automotive disc brake assembly was demonstrated experimentally. The main features of the dither-squeal cancellation system was the application of a high frequency variation in the brake pressure force accomplished by means of a piezoelectric stack placed behind one of the brake pads. This thesis contains a theoretical and numerical treatment of the application of dither to frictional systems. Two types of systems are investigated. The first is a classic, mass-on-a-moving belt problem, which experiences friction-induced oscillations similar to those encountered in brake applications. The system is first studied using an analytical technique based on the method of averaging. It is shown that, depending on the system, friction, dither-waveform, and belt-speed parameters, dither can stabilize an unstable system. However, in some cases, dither can destabilize an initially stable system. These results are verified numerically using time integration. The second type of system analyzed in this thesis is an annular plate with a rotating frictional device. The method of multiple scales is used to predict subcritical regions of instability; the results are validated using Floquet theory. The thesis treats both tangential and normal dither, the latter being closer to the brake application. It is found that normal dither, in addition to being harder to analyze, is much less effective than tangential dither.

Pulse Tube Cryocoolers (PTC) is widely used in aerospace and missile guiding systems where extreme reliability and ruggedness are crucial. PTCs, in particular, are a class of rugged refrigeration systems that are capable of maintaining temperatures as low as 4 K, without a moving part in their cold end. The operation of PTCs is based on complicated and poorly-understood solid-fluid interactions involving periodic flows of a cryogenic fluid in micro porous structures. Currently, PTCs is often modeled as one-dimensional flow fields using methods whose relevance to cryocoolers is at best questionable. Furthermore, recent CFD-based investigations have underscored the need for adequate closure relations representing periodic flows in anisotropic micro porous media, and have shown that multi-dimensional effects can be significant in PTCs. The objectives of this investigation were to experimentally measure and correlate the anisotropic hydrodynamic parameters for typical micro porous structures that are used in the regenerators of PTCs fillers; perform modeling and CFD-based simulations to elucidate the component and system-level thermo-fluidic processes in modern pulse tube cryocooler designs; and perform a preliminary CFD-based assessment of the effect of miniaturization on the thermal performance of a current PTC design. In the experiments, the measurement and correlation of the directional (axial and radial) permeabilities and Forchheimer s inertial coefficients of meshed screen, sintered mesh, foam metal, and stacked micro-machined plate regenerator fillers were of interest. Hydrodynamic parameters under steady-state conditions were addressed first. Pressure drops were measured for purely axial flow in cylindrical test sections and predominantly radial flows in annular test sections that contained regenerator fillers of interest, under steady-state conditions. The permeabilities and Forchheimer s inertial coefficients were then obtained in an iterative process where agreement between the data and the predictions of detailed CFD simulations addressing the entire test sections and their surroundings were sought. Periodic flows were then addressed. Using high frequency pressure transducers and hot wire anemometry, instantaneous pressures and mass fluxes are measured under periodic purely axial flow conditions. CFD simulations of the experiments were then performed, whereby permeabilities and Forchheimer coefficients that bring about agreement between data and simulation results were calculated.

In this study, a novel inserted type of friction welding tool was proposed, where the circular rod was embedded in its central axis using the material same as the workpiece, so that it could effectively promote the friction heat quickly and enhance the welding quality. The welding tool was made of the high-speed steel, the workpiece with its embedded material 6061-T6 aluminum alloy. A vertical milling machine equipped with dynamometer, which could measure the power during the friction stir welding, was employed as the experimental apparatus. During the welding process, the K-type thermocouple was used simultaneously in measuring the welding temperature at the interface of joint. The operating conditions of welding were as followings: the welding speed of 800 rpm, the tool inclination of 1¢X and the clamping force 2kN, the tool with 12mm in diameter and 0.21mm in depth under the downward force about 2 kN. The experiment was conducted into two stages. The first stage was a spot welding to investigate the effect of the ratio of the diameter of embedded material (d) to the diameter of welding tool (D) on the temperature of the interface of joint, the thickness of plastic flow, and the failure load of weld. Experimental results revealed that the interface temperature, the plastic flow thickness, and the failure load of weld are directly proportional to d/D. In comparison with the welding tool without insert (d/D = 0), the maximum interface temperature increased about 1.12 times at d/D = 0.83, the plastic flow thickness increased about 1.52 times, and the failure load of weld increased about 1.45 times. In the second stage, the feeding process was included to investigate the influence of the diameter and the thickness of embedded material on the interface temperature, the plastic flow thickness, and the failure load of weld. Experimental results revealed that the plastic flow thickness was less than 2 mm when the thickness of embedded material was less than 3 mm. However, when the thickness of embedded material was larger than 5 mm, the plastic flow thickness could achieve to 3 mm. Hence, the thickness of embedded material should be larger than 5mm. Moreover, the effect of the diameter of embedded material on the interface temperature and the plastic flow thickness using the feeding process was almost the same as the spot welding. However, in comparison with the welding tool without insert, the failure load of weld increased about two times.

In the last 35 years, several researchers have proposed, developed and tested different friction devices for seismic control of structures. Their research has demonstrated that such devices are simple, economical, practical, durable and very effective. However, research on passive friction dampers, except for few instances, has not been given appropriate attention lately. This has caused some of the results of old studies to become out-of-date, lose their validity in the context of today's design philosophies or to fall short on the expectations of this century's structural engineering. An analytical study on the behavior of friction devices and the effect they have on the structures into which they are incorporated has been undertaken to address the new design trends, codes, evaluation criteria and needs of today's society. The present study consists of around 7,000 structural analyses that are used to show the excellent seismic performance and economic advantages of Friction Damped Braced Frames. It serves, at the same time, to improve our understanding on their dynamic behavior. Finally, this thesis also sets the basis for future research on the application of this type of seismic energy dissipating systems.

Annular gas seal clearances were simulated with closely spaced parallel plates using a Flat?Plate tester. The device is designed to measure the pressure gradient along the test specimen. The main function of the Flat?Plate tester is to provide friction factor data and measure dynamic pressure oscillations. A detailed description of the test facility is described, and a theory for determining the friction factor is reviewed. Three clearances were investigated: 0.635, 0.381, and 0.254 mm. Tests were conducted at three different inlet pressures (84, 70, and 55 bars), producing Reynolds numbers range from 50,000 to 700,000. Three surface configurations were tested including smooth?on-smooth, smooth?on?hole, and hole?on?hole. The Hole?pattern plates are identical with the exception of the hole depth. The results indicate that, for the smooth?on?smooth and smooth?on?hole configurations, the friction factor remains constant or increases slightly with increasing Reynolds numbers. Moreover, the friction factor increases as the clearance between the plates increases. However, the results from the hole?on-hole configurations are quite different. A "friction?factor jump" phenomenon was observed, and the Helmholtz frequency was detected on the frequency spectra.