In this work, the combined effects of couple-stresses and piezo-viscosity on the dynamic behavior of a compression ignition engine big-end connecting-rod bearing with elastic layer are investigated using the V. K. Stokes micro-continuum theory. It is assumed that the journal (crankpin) is rigid and the big-end bearing consists of a thin compressible elastic liner fixed in an infinitely stiff housing. The governing Reynolds' equation and the viscous dissipation term appearing on the RHS of energy equation are modified using the V. K. Stokes micro-continuum theory. The non-Newtonian effect is introduced by a new material constant η, which is responsible for couple-stress property, and the piezo-viscosity effect by the pressure–viscosity coefficient α appearing in the well-known Barus' law. In the proposed model, the nonlinear transient modified Reynolds equation is discretized by the finite difference method, and the resulting system of algebraic equations is solved by means of the subrelaxed successive substitutions method to obtain the fluid-film pressure field as well as the film thickness distribution. The crankpin center trajectories for a given load diagram are determined iteratively by solving the nonlinear equilibrium equations of the journal bearing system with the improved and damped Newton–Raphson method for each time step or crankshaft rotation angle. According to the obtained results, the effects of couple-stresses and piezo-viscosity on the nonlinear dynamic behavior of dynamically loaded bearings with either stiff or compliant liners are significant and cannot be overlooked.

The proposed work is concerned with the theoretical and numerical investigation of the lubricant rheology effects on the steady-state behavior of a plain finite compliant journal bearing operating under isothermal conditions. In the present investigation, the couple-stresses due to the presence of improving viscosity index (VI) additives, the viscosity-pressure (piezoviscosity effect) as well as the density-pressure (compressibility effect) variations are considered. The hydrodynamic lubrication theory is based on the V.K. Stokes micro-continuum mechanics which takes into account the size of macro-molecular chains added to the basic oil. The Barus and Dowson-Higginson laws were used to express the viscosity-pressure and density-pressure variations. Using the classical assumptions of lubrication, a modified Reynolds' equation is derived and solved numerically by the finite difference method. The displacement field at the fluid film bearing liner interface due to pressure forces is determined using the elastic thin liner model. The proposed work is concerned with the theoretical and numerical investigation of the lubricant rheology effects on the steady-state behavior of a plain finite compliant (elastic liner) journal bearing operating under isothermal conditions and laminar flow. The obtained results show that the couple-stresses have significant effects on the hydrodynamic performance characteristics such as the pressure field, the carrying capacity, the attitude angle and friction number especially when the viscosity-pressure variation is considered. Moreover, it is also shown that the compressibility of lubricant doesn't affect the hydrodynamic characteristics.

Aerodynamic bearings have received considerable attention in recent decades and are increasingly being used in applications where high speed, low loads and high precision are required. Aerodynamic applications mainly concern auxiliary power units (APU) and air-conditioning machines (ACM). From the industrial point of view, the static and dynamic characteristics of these bearings rotating at very high speed must be determined. According to the literature, studies carried out on this type of bearing consider the elastic deformations of the foils due to the pressure generated in the air film. The linear approach is from time to time adopted for the prediction of the dynamic behavior of these bearings, which is not always justified. This paper aims to present a step towards a better mastery of the non-linear dynamic behavior of a flexible rotor-air bearing system. We will focus on finite element modeling (FEM) of the non-linear isothermal elasto-aerodynamic lubrication problem in the case of a radial bearing operating in a dynamic regime. We will present the effects of rotational speed, unbalance eccentricity, and rotor mass on the non-linear response of rigid and compliant bearings. We use a partitioned approach which treats fluid and structure as two computation domains solved separately; reducing the development time needed for a monolithic code which is difficult to manage when the geometries or the physical properties of the problem to be treated become complex.

This paper presents an original theoretical investigation of the steady‐state and dynamic characteristics of foil journal bearings lubricated with contaminated air taking into account couple stresses because of the presence of pollutant substances. The substance can be solid particles (eg dust, ash, pollen, and smoke). In aerodynamic lubrication theory, a fluid with couple stresses so‐called couple stress or polar fluid may be considered as one characterised by the 2 physical constants μ and η, which are the absolute viscosity assumed to be independent of the particle volume fraction and the new material constant responsible for couple stress or polar property. The effects of couple stresses on the oil‐lubricated sliding bearings are usually studied by defining the parameter 0.25eml=η/μ12 or its normalised form truel~=l/C . The couple‐stress parameter l, which has the dimension of length, can be thought of as a fluid property depending on the size of the particle contained in the base fluid (solvent). To determine the aerodynamic pressure and the power loss, the governing modified Reynolds' equation and the viscous dissipation term appearing on the right‐hand side of the modified energy equation are derived by using the Vijay Kumar Stokes micro‐continuum theory. The system of partial differential equations resulting from analytical perturbation of the transient modified Reynolds' equation is solved for the steady‐state and dynamic pressures by means of the finite difference method considering both the static and dynamic deformations of the bump foil. Using the complex variable technique, the analytical perturbation process leads to 2 first‐order uncoupled partial differential equations instead of 4 coupled equations as it is usually found in the technical literature. On the other hand, the 2 Cartesian coordinates of the equilibrium position for a given applied static load are iteratively determined by solving the nonlinear equilibrium equations of the journal bearing system with the improved Newton‐Raphson method. According to the obtained results, the effects of couple stresses on the steady‐state and dynamic behaviour of foil self‐acting gas bearings are significant and cannot be overlooked. The results also show that the dynamic deformation of the bump foil should be included in calculating the dynamic performance characteristics of foil journal bearings.

Dans cet article, les effets combinés de la rugosité de surface et de la rhéologie du lubrifiant additivé sur les performances hydrodynamiques d'un patin plan incliné sontétudiés au moyen de la méthode d'homogénéisation. La surface du patin contiguë au film est supposée fixe et rugueuse tandis que la surface inférieure mobile est parfaitement lisse. Le modèle de fluide polaire ouà couple de contrainte de V.K. Stokes est adopté pour décrire le comportement rhéologique du lubrifiant s'écoulant entre les deux surfaces. Leś etudes de simulation sont effectuées en considérant trois formes de rugosités (transversales, longitudinales et anisotropes) et différentes valeurs du paramètre de couple de contrainte. La comparaison des solutions obtenues par les méthodes déterministe et d'homogénéisation a permis de conclure que la méthode d'homogénéisation est efficace pour les trois formes de rugosité envisagées. Les résultats de l'étude paramétrique effectuée montrent que les rugosités de surface et les couples de contraintes dusà la présence des additifs polymériques dans le lubrifiant ont des effets non négligeables sur les performances hydrodynamiques du contact,à savoir : le champ de pression, la capacité de charge, le nombre de frottement et la puissance dissipée.