Influence du maillage sur la convergence de la solution d'un modèle numérique de lubrification hydrodynamique en présence de textures

Cette étude a pour objectif de déterminer l’influence du maillage sur la convergence de la solution d’un modèle numérique de lubrification. Ce dernier résout l’équation de Reynolds entre les faces d'une garniture mécanique texturée. La présence des textures engendre des zones de discontinuité qui peuvent augmenter les pertes de précision dues à une insuffisance dans la discrétisation. L’utilisation d’un maillage très fin devrait minimiser ces imprécisions, mais le temps de calcul devient dans ce cas très grand. De plus, l’erreur de convergence obtenue avec un maillage dépend de la variable significative qui est observée (portance, débit, etc…). Afin d’estimer de manière quantitative l’erreur engendrée par le maillage, nous avant utilisé la méthode GCI (Grid Convergence Index). Cette méthode est basée sur la théorie de l’extrapolation généralisée de Richardson. Elle permet d’estimer l’erreur du maillage sans avoir besoin d’une solution analytique du problème. Pour une densité de textures donnée (30% de la surface de la cellule est occupée par la texture), le facteur de forme (profondeur des textures/épaisseur du film) étant maintenu dans un premier temps constant à 5/2, l’influence de la forme de la texture sur les résultats (hémisphère, carré et triangle) est analysée. Ensuite, l’effet du facteur de forme est étudié pour une texture triangulaire, toujours avec une densité de 30%. Tous les calculs sont réalisés avec trois niveaux de maillage (grossier, intermédiaire et fin). Les résultats obtenus sont présentés sur une plage du paramètre hydrodynamique adimensionné, qui est une fonction des paramètres usuels de la lubrification

Enhanced performance of optimised partially textured load bearing surfaces

Textured surfaces have been shown to provide enhanced tribological performance in a variety of contacts. Numerical analysis and optimisation methods are combined for application-oriented texture optimisation. However, an analytical approach is advantageous in providing more generic in-depth understanding of the nature of the relationships between texture parameters and objective functions, such as enhanced load carrying capacity and reduced friction. The paper outlines such an approach to obtain a set of global optimum design parameters for partially textured surfaces. The optimised results are expressed in dimensionless form, which enables their use for a variety of applications. The performance of optimised partially textured sliding surfaces is compared with the other conventional bearing geometries in their optimum state

Theoretical and experimental study of lubrication between textured surfaces. Application to mechanical seals

L'objectif principal de cette thèse est de conduire, à travers une étude théorique et expérimentale, vers une meilleure compréhension des différents effets induits par la texturation de surface dans un contact lubrifié. Le but ultime est de proposer un motif de texture qui permette de réduire le frottement et le niveau de fuite d'une garniture mécanique. L'étude bibliographique a permis d'identifier les différents travaux théoriques et expérimentaux réalisés sur la lubrification en présence de textures, les phénomènes physiques interagissant avec les textures et les différentes méthodes utilisées pour leur mise en forme. Une étude théorique utilisant un modèle conservatif basé sur l'équation de Reynolds est ensuite présentée. Dans la première partie de cette étude, les faces de frottement sont supposées parfaitement parallèles et les effets thermoélastiques sont négligés. Dans la seconde partie, les échanges de chaleur avec les anneaux et les déformations thermoélastiques sont pris en compte. Une étude paramétrique a permis de mieux comprendre l'influence des paramètres géométriques des textures, des défauts de formes et des déformations thermoélastiques des faces sur le fonctionnement de la garniture. En outre, cette étude a permis de définir une texture capable d'améliorer significativement les performances d'une garniture mécanique. Des essais expérimentaux ont ensuite été réalisés avec une garniture mécanique texturée et une garniture mécanique non texturée. Des mesures de couple de frottement et des relevés de température effectués par thermographie infrarouge ont montré que l'utilisation des textures permet de réduire de manière significative la température et le couple de frottement par rapport à une garniture à surfaces lisses. Enfin, une comparaison théorie/expérimentation a permis de valider le modèle développé qui prédit de façon correcte le comportement de la garniture texturée.The main objective of this thesis is to lead, through a theoretical and experimental study, to a better understanding of the various effects induced by surface texturing in lubricated contacts. The ultimate goal is to provide a texture pattern that reduces friction and leakage of a mechanical seal. The literature review identified different theoretical and experimental works performed on lubrication in the presence of textures, physical phenomena interacting with textures and the different methods used for their manufacturing. A theoretical study using a conservative model based on Reynolds equation is then presented. In the first part of this study, the friction surfaces are assumed perfectly parallel and thermoelastic effects are neglected. ln the second part, heat transfer to the rings and thermoelastic deformations are taken into account. A parametric study then allows bettering our understanding of the influence of geometrical parameters of textures, defects and thermoelastic deformations of the faces on the performance of a mechanical seal. In addition, this study has identified a texture capable of significantly improving the performance of a mechanical seal. Experimental tests were then carried out with bath textured and untextured mechanical seals. Friction torque measurements and temperature measurements achieved by means of infrared thermography have shown that the use of textures allows to significantly reduce heat and friction torque compared with a seal with smooth surfaces. Finally, a comparison theory/experiment validated the developed model that predicts correctly the behavior of the textured mechanical seal

Réflexions rétrospectives sur la peste de 1720 en Provence

AIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Friction and Temperature Reduction in a Mechanical Face Seal by a Surface Texturing: Comparison between TEHD Simulations and Experiments

International audienceMechanical face seals are used to avoid fluid leakage from pressurized zones to the environment in many rotating machineries. The initial research into the lubrication mechanism of these components was initiated several decades ago and numerous studies, both theoretical and experimental, have been carried out on the subject. Surface texturing has been of growing interest in recent years, but only a few studies have been devoted to textured mechanical face seals. Thus, the aim of the present work is to provide experimental, as well as theoretical, results with a comparison of smooth and textured seals. The temperatures of the seals are measured by means of infrared thermography. A 50% reduction in friction for the whole speed range and a reduction in the temperature rise of the sealing interface, attaining 40% at the highest speed values, are reported. Because it is not possible to measure the film thickness experimentally, a numerical thermoelastohydrodynamic model is used, taking into account the seal face deformations. A comparison between the experimental and theoretical temperatures allows the model to be validated. It is shown that, as expected, the film thickness increases with speed as a result of the pressure generated in the dimples. However, after a threshold, it starts to decrease because of the detrimental effect of thermal deformation. These results show that fluid solid coupling must be considered when designing the surface texture for a mechanical seal

Surface texturing to reduce temperature in mechanical seals

International audienceMechanical seals are composed of two annular flat rings in contact and relative motion to ensure sealing of a rotating shaft. Because of friction in the sealing interface, a significant temperature rise can be experienced in the contact. Two decades ago, it has been shown that creating a network of shallow dimples on one sealing surface can help to create a lubricant film in the interface and thus reduce friction. Since then, many research works have been carried out on the socalled surface texturing, showing the interest of surface modification for mechanical seals. In the present work, several surface patterns, defined by numerical simulations and machined by plasma etching on stainless steel rings were tested. The rings were mounted on a test bench in which they slide against a sapphire disk counter face. This disk is transparent to infrared radiation and allows interface temperature measurements by infrared thermography. It is shown that all the tested surface texture patterns exhibit a temperature rise at least 2 times lower than with flat smooth surfaces. A slight difference between the different dimple shapes is obtained indicating that the temperature and friction are more controlled by texture area and surface roughness rather than by the texture pattern

Overestimation of Hypoglycemia Diagnosis by FreeStyle Libre Continuous Glucose Monitoring in Long-Term Care Home Residents With Diabetes

International audienceno abstrac

Influence of the real dimple shape on the performance of a textured mechanical seal

International audienceSurface texturing the friction faces of a mechanical seal reduces friction as well as leakage and wear, where dimples machined on the surface enhance the formation of a full lubricating film in the seal interface. Numerical simulation is used to determine the optimal surface texturing for the investigated operating conditions of the seal. The geometry of the dimples introduced in the model assume a perfect shape, but machining causes the dimple shapes to be imperfect in terms of the roughness in the dimples, absence of sharp angles, deformed boundaries, and so on. The effect of the real geometry must be considered to confirm that surface texturing will provide the desired results. In the present work, surface texturing is performed using low-temperature plasma coupled with a thermo-chemical surface treatment on stainless steel sealing rings. The real dimple shapes are analysed and considered within the hydrodynamic lubrication model. The influence of different types of defects is studied. It is shown that there is a limit above which surface imperfections dispel the texture's positive effects. Controlling the dimple shapes is important when performing surface texturing