Este trabalho apresenta uma discussão sobre o estudo dos efeitos térmicos e elásticos decorrentes da pressão de sustentação presentes nos mancais. Para tanto, propõe-se um modelo matemático baseado nas equações para mancais curtos considerando a região de cavitação e utilizando o princípio da continuidade de massa. Com isto, deduzem-se as equações para o mancal a partir das equações de Reynolds e da energia, aplicando uma solução modificada para a solução de Ocvirk, sendo as equações resolvidas numericamente pelo Método das Diferenças Finitas. Somado o tratamento de mecânica dos fluidos, o trabalho discute dois modelos térmicos de previsão de temperatura média do fluido e sua influência no campo de pressão, apresentando gráficos representativos do campo de pressão e de temperatura, assim como as diferenças e implicações das diferenças. Para o cálculo de deformação da estrutura, utiliza-se um Modelo de Elementos Finitos para uma dada geometria, fazendo-se uma avaliação da variação do campo de pressão e o quanto essa diferença afeta as demais propriedades do fluido. Por fim, com o modelo completo, calcula-se o quanto esse modelamento para mancais curtos se aproxima de soluções para mancais finitos, com base em resultados da literatura, chegando a desvios quase oito vezes menores que os previstos pela literatura. Além disso, pode-se estabelecer a abrangência do modelo, ou seja, prever as condições em que suas propriedades são válidas e podem ser utilizadas para estudos iniciais. / This work presents a study on thermal and elastic effects resulting from support bearings. It proposes a mathematical model based on short bearing equations within the cavitation region, using the principle of mass continuity. Then, the used equations are deduced from Reynolds and energy equations applying a modified solution for the Ocvirks solution. All the equations are numerically solved by the Backward Finite Difference Method. In addition to the treatment of fluid mechanics, this work discusses two thermal models to predict the average temperature of the fluid and its influence on the pressure field; it also presents the representative charts for pressure and temperature fields, as well as the differences and implications of these ones. To calculate the deformation of the structure, a Finite Element Model is used, considering a specific geometry and an evaluation of the variation of the pressure field is conducted to determinate how this difference affects other properties of the fluid. Finally, the full model is applied to analyse how this modeling for short bearing solutions can be used as an approach for finite bearings. Analysis reaches deviations nearly eight times smaller than predicted by literature data. Furthermore, it was possible to establish the range of the model in which its properties are valid and can be used for initial studies.

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.

The present study has the objective of evaluating the effect of lubricant features on the friction coefficient by using three different lubricants (two synthetics and one mineral), which are used in automotive transmissions. In order to perform experiments, it was used a ball-on-disc system. The disc was manufactured with the same mechanical properties as transmission gears and the ball was made of 52100 SAE steel. The test parameters were defined based on a dynamic analysis conducted using \"ISOCAD\" which takes into account the geometry of the gear and vehicle dynamics (applied force and speed) during the tribological experiments. In order to set the temperature parameter, the lubricant testing temperature of a standard fuel economy was used. Experiments were conducted in two different lubrication conditions: i (starved) and ii (fully flooded). After the parameters were defined, it was possible to calculate the oil film thickness and, thus define the lubrication regime reached in each condition. Mixed and/or boundary lubrication was obtained in all the tests. Results showed the relationship between the speed and the specific oil film using a Khonsari and Masjedi formulation (2014), which takes into account the effect of surface roughness and, it is based on Downson and Higginson\'s (1981) formulation. The chemical analysis of the lubricant showed a relationship between friction coefficient and the additives used in lubricants. These results also showed the oil performance under different temperatures, speeds and loads. The best results were obtained for a synthetic lubricant. / O presente estudo tem o objetivo de avaliar o efeito de propriedades dos lubrificantes sobre o coeficiente de atrito. Para tanto foram testados três lubrificantes diferentes (dois sintéticos e um mineral), que são utilizados em transmissões automotivas. Os experimentos foram conduzidos utilizando um sistema tribológico denominado \"ball-on-disc\". Os discos foram fabricados com as mesmas propriedades mecânicas das engrenagens de transmissão, já as esferas foram fabricadas com aço SAE 52100. Os parâmetros de teste foram definidos com base na análise dinâmica conduzida utilizando o software \"ISOCAD\", que leva em conta a geometria da engrenagem e a dinâmica do veículo (força aplicada e velocidade) durante os ensaios tribológicos. Para definir os parâmetros de temperatura, foram utilizadas as mesmas temperaturas encontradas durante o ensaio de economia de combustível padronizado. Experimentos foram realizados em duas condições de lubrificação diferentes: i) fornecimento limitado de lubrificante, ou \"Starved\" e ii) condição de lubrificação imersa, ou \"Fully flooded\". Depois dos parâmetros definidos, foi possível calcular a espessura de filme de óleo, de forma a definir o regime de lubrificação alcançado em cada condição. Lubrificação mista e limítrofe foi obtida todas as condições de testes. Os resultados mostraram a relação entre a velocidade e o filme de óleo específico usando uma formulação de Khonsari e Masjedi (2014), que leva em conta o efeito da rugosidade da superfície e baseia-se na formulação de Downson e Higginson (1981). A análise química do lubrificante mostrou que existe uma relação entre o coeficiente de atrito e os aditivos utilizados nos lubrificantes. Estes resultados também mostram o desempenho dos lubrificantes em diferentes temperaturas, velocidades e cargas. Os melhores resultados foram obtidos para um lubrificante sintético.

No description available.

This is a phd thesis

<div>Gerotor units are widely used in low-pressure (up to 30 bar) </div><div>fluid power applications, injection and lubrication systems, due to their compact package and low cost. Their performance in terms of volumetric efficiency, flow pulsations, internal pressure peaks or localized cavitation depends on many parameters, such as the rotors profiles and the manufacturing tolerances. In this work, a multi-domain simulation approach for the numerical analysis of the performance of Gerotor units is proposed. The model can be used for analysis and virtual prototyping of units considering the actual geometry of the rotors, their geometrical tolerances and the properties of the working fluid and materials.</div><div><br></div><div><div>The approach is based on the coupling of different models: a numerical geometric model evaluating the instantaneous volumes and flow areas inside the unit; a lumped parameter fluid dynamic model describing the displacing process of the tooth space volumes; and a mechanical model evaluating the internal micro-motions of the rotors axes according to their tolerances. In this way, the model determines the actual loading of the rotors, considering also the actual location of the points of contact. Advanced 2D CFD models for the analysis of lubricated interfaces have been developed to study the axial and the radial gaps. This approach allows an accurate prediction of the power losses and radial micro-motion of the rotors taking into account fluidstructure interaction effects. A line contact model is used to describe the contact interface using an elastohydrodynamic approach and non-Newtonian fluid behavior for the prediction of the friction between the rotors.</div></div><div><br></div><div><div>Specic experiments were performed by connecting the pump outlet to a variable loading orifice and by measuring the delivered flow, pressure ripple and required torque under dfferent operating conditions of speed and outlet pressure. These experiments allowed a detailed model validation through the comparisons with simulation data in terms of signicant steady-state as well as transient pressure, flow and torque features. After the model validation, gaps compensation solutions to minimize the volumetric losses are developed and studied showing the potential improvements on the performances of a prototype unit by reaching up to 55% volumetric effciency at high pressure (pmax > 100bar).</div><div><br></div><div>The approach used in the current work along with its proven accuracy through experiments can be considered a valuable tool when studying the impact of real-life technological clearances and gears geometry on the fluid-dynamic performance of the pump.</div></div>

La thèse vise à prédire l’adhérence des chaussées contaminées par des particules fines. Ces particules se déposent sur la chaussée pendant les périodes sèches et agissent, seules ou se mélangeant avec l’eau de pluie, comme un lubrifiant à l’interface pneu/chaussée. La démarche de recherche est basée sur l’approche du troisième corps en distinguant les phases de dépôt et de lessivage des particules par la pluie. Les particules sont caractérisées par leur distribution granulométrique et leurs compositions chimique et minéralogique. L’étude est menée à trois échelles : globale, par des mesures de frottement et de masses du troisième corps (particules pendant le dépôt et le mélange eau/particules pendant le lessivage) ; dans l’aire de contact par des analyses de flux du troisième corps ;et au niveau des particules par des observations au MEB. Les flux de particules pendant la phase de dépôt sont identifiés par des visualisations avec une caméra rapide. L’interaction entre les particules et la texture de la chaussée est mise en évidence par des observations microscopiques. La modélisation des flux permet d’estimer le taux de recouvrement d’une surface qui, à son tour, est utilisé comme un facteur de pondération pour calculer le coefficient de frottement pendant la phase de dépôt. En présence d’eau, la fraction volumique des particules est utilisée pour estimer la viscosité du mélange. Le coefficient de frottement pendant la phase de lessivage dépend de cette viscosité et du taux de recouvrement de la surface. Les résultats sont discutés en termes d’influence des caractéristiques des particules(concentration, taille) et de la texture de la chaussée. / The thesis aims to predict the skid resistance of road surfaces contaminated by fine particles. These particles are deposited on the road during dry periods and act, alone or mixing with rainwater, as a lubricant at the tire / road interface. The research methodology is based on the third body approach by distinguishing the phases of deposit and washing of particles by rain. Particles are characterized by their size distribution and their chemical and mineralogical compositions. The study is conducted at three scales: global, by measurements of friction and third body masses (particles during the deposit phase and the water / particles mixture during the washing phase); in the contact area by analyses of third body flows; and at the particle level by SEM observations. Particle flows during the deposit phase are identified by visualizations with a high-speed camera. The interaction between the particles and the road surface texture is highlited by microscopic observations. Flow modeling is used to estimate the coverage rate of a surface that, in turn, is used as a weighting factor to calculate the coefficient of friction during the deposit phase. In the presence of water, the volume fraction of the particles is used to estimate the viscosity of the mixture. The coefficient of friction during the washing phase depends on this viscosity and the coverage rate of the surface. Results are discussed in terms of the influence of particle characteristics (concentration,size) and road surface texture.

This thesis aims at contributing to the characterization of the dynamics of bubbles in microfluidics through modeling and experiments. Two flow regimes encountered in microfluidics are studied, namely, the bubbly flow regime and the Taylor flow regime (or slug flow).In particular, the first part of this thesis focuses on the dynamics of a bubbly flow inside a horizontal, cylindrical microchannel in the presence of surfactants using numerical simulations. A numerical method allowing to simulate the transport of surfactants along a moving and deforming interface and the Marangoni stresses created by an in-homogeneous distribution of these surfactants on this interface is implemented in the Level set module of the research code. The simulations performed with this code regarding the dynamics of a bubbly flow give insights into the complexity of the coupling of the different phenomena controlling the dynamics of the studied system. Fo example it shows that the confinement imposed by the microchannel walls results in a significantly different distribution of surfactants on the bubble surface, when compared to a bubble rising in a liquid of infinite extent. Indeed, surfactants accumulate on specific locations on the bubble surface, and create local Marangoni stresses, that drastically influence the dynamics of the bubble. In some cases, the presence of surfactants can even cause the bubble to burst, a mechanism that is rationalized through a normal stress balance at the back of the bubble. The numerical method implemented in this thesis is also used for a practical problem, regarding the artisanal production of Mezcal, an alcoholic beverage from Mexico.The second part of the thesis deals with the dynamics of a Taylor flow regime, through experiments and analytical modeling. An experimental technique that allows to measure the thickness of the lubrication film forming between a pancake-like bubble and the microchannel wall is developed. The method requires only a single instantaneous bright-field image of a pancake-like bubble translating inside a microchannel. In addition to measuring the thickness of the lubrication film, the method also allows to measure the depth of a microchannel. Using the proposed method together with the measurment of the bubble velocity allows to infer the surface tension of the interface between the liquid and the gaz. In the last chapter of this thesis, the effect of buoyancy on the dynamics of a Taylor flow is quantified. Though often neglected in microfluidics, it is shown that buoyancy effects can have a significant impact on the thickness of the lubrication film and consequently on the dynamics of the Taylor flow. These effects are quantified using experiments and analytical modeling. This work was performed at Princeton University with Professor Howard A. Stone during an eight month stay. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Um dos possíveis modos de falha em engrenagens é relacionado com o carregamento cíclico e, por consequência, a ocorrência de fadiga. O início da falha por fadiga ocorre devido à intensificadores de tensão e é geralmente observado no pé do dente (fadiga de flexão) ou na região de contato na superfície do dente (fadiga de contato). Experimentos para avaliação da fadiga de contato em engrenagens são geralmente conduzidos em bancadas de teste e tem custos elevados. Um método alternativo de experimentação de fadiga de contato em engrenagens é avaliado neste trabalho, consistindo no rolamento de esferas sobre um plano (corpo de prova). Dois grupos de corpos de prova foram fabricados com características e propriedades superficiais semelhantes às da superfície do dente de engrenagens nas condições: a) sem shot-peening e b) com shot-peening. As diferentes características dos corpos de prova foram testadas utilizando um equipamento desenvolvido em trabalho anterior para avaliar a fadiga de contato de rolamento, que ocorre no diâmetro primitivo das engrenagens. Resultados indicaram a ocorrência de dois mecanismos de falha comumente encontrados em engrenagens: pitting e spalling, entretanto, o equipamento se mostrou incapaz de monitorar a ocorrência de pitting. Ademais, os corpos de prova com shot-peening apresentaram menor resistência à fadiga para as condições testadas, em desacordo com ensaios de bancada anteriores. Algumas hipóteses foram discutidas para prover justificativas relacionadas aos resultados obtidos. / One of the possible mechanisms of gear failure is related to the cyclic loading and, consequently, the fatigue occurrence. The onset of fatigue failure occurs due to stress intensifiers and it is generally observed on the fillet (bending fatigue) or on the tooth surface contact region (contact fatigue). Gear fatigue evaluation is usually carried out by test rigs, which are expensive. An alternative method of contact fatigue test of gears is evaluated in this work, which consists of balls rolling on a plane (specimen). Two groups of specimens were manufactured to obtain surface characteristics and properties like gears tooth\'s surface: a) without shot-peening and b) with shot-peening. The different features of specimens were tested by using an in house developed equipment to evaluate the rolling contact fatigue, which occurs on gears on its diametral pitch. Results indicate the occurrence of two failure modes: pitting and spalling, however, the equipment showed to be unable to monitor the occurrence of pitting. Also, the shot-peened group specimens presented lower fatigue life resistance for the analyzed conditions, which are not in agreement with previous rig tests. Some hypotheses were discussed to provide justifications related to the obtained results.

Horizontally mounted compressors offer the advantage of reduced height in central air-conditioning units but prove difficult to produce economically due to costs associated with the manufacture of acceptable lubrication systems for the compressors. This study develops an effective, affordable oil pump for use on a horizontal compressor. Concepts are proven through testing of prototype assemblies. Test results drive modifications for future prototypes, and prototypes demonstrating adequate performance are modified for ease of manufacture. Research in this study proves that the most suitable design results from a modification of a rotating vane pump. The pump’s modifications enable it to pump oil in the same direction, regardless of the direction of shaft rotation and to prime itself when totally dry of oil. However, extensive use of horizontal compressors hinges upon the development of a satisfactory suspension system.