Raghuvir B Pai

Analysis of water-lubricated journal bearings with multiple axial grooves

Abstract The steady state and dynamic characteristics including whirl instability of water-lubricated journal bearings having three axial grooves are obtained theoretically. The Reynolds equation is solved numerically by the finite difference method satisfying the appropriate boundary conditions. The dynamic behaviour in terms of stiffness and damping coefficients of film and stability are found using a first-order perturbation method. It has been shown that both load capacity and stability improve when smaller groove angles are used.

Lamellar lubrication in vivo and vitro: friction testing of hexagonal boron nitride.

Phospholipid molecules (PLs) in vivo and graphite, molybdenum disulfide, tungsten disulfide and hexagonal boron nitride (h-BN) in vitro are good examples of frictionless lubricants. PLs and solid materials have the ability to form multi-bilayer or layered structures similar to lamellate solid. It has been confirmed experimentally that PLs as lamellar lubricants protect the surface of joints against wear while acting as frictionless lubricant. An experimental study has been conducted on the friction properties of h-boron nitride on porous non-full journal bearings. The porous non-full journal bearings were a mixture of 97.5 wt.% Fe and 2.5 wt.% Cu powder, and compressed to a density of 5.9 g/cm(3). The porosity of non-full journal bearings were 15.5 and 27.8 wt.% and were impregnated with vaseline and vaseline+5 wt.% h-BN. Additionally, the two additives SFR NLGI #2 (or SFR 2522) grease and graphite grease were used for comparison to h-BN. The tribological tests were performed on a four-ball machine under load of 49 daN, and a friction tribotester. The above experiment strongly suggested that h-BN has the ability to lubricate under load with very low friction coefficient comparable to phospholipids. Relatively low surface energy and low adhesion between the crystallites are giving the additives low friction coefficient. The results of the experimental studies showed that h-BN as an additive in vaseline possesses friction reducing properties, and excellent anti-wear properties.

Water lubricated bearings

The increasing ecological awareness and stringent requirements for environmental protection have led to the development of water lubricated bearings in many applications where oil was used as the lubricant. The chapter details the theoretical analysis to determine both the static and dynamic characteristics, including the stability (using both the linearised perturbation method and the nonlinear transient analysis) of multiple axial groove water lubricated bearings. Experimental measurements and computational fluid dynamics (CFD) simulations by the Tribology research group at Queensland University of Technology, Australia and Manipal Institute of Technology, India, have highlighted a significant gap in the understanding of the flow phenomena and pressure conditions within the lubricating fluid.

Repulsive surfaces and lamellar lubrication of synovial joints

Surface-active phospholipid (SAPL) secreted in the synovial joint plays an important role in cartilage integrity. In healthy joints, phospholipid multibilayers coat the cartilage surface, providing boundary lamellar-repulsive hydration lubrication. Current mechanism for lubrication of synovial joints, as well as the physical and chemical nature of the cartilage surface is discussed. Friction between phospholipid (PL) bilayers attached to cartilage surfaces is considered including a discussion on the recent observation of an extreme friction reduction as a consequence of a less charged hydrophilic cartilage surface. It is proposed that the highly efficient lubrication occurring in natural joints arises from the presence of negatively charged cartilage surfaces. The lamellar-repulsive mechanisms for the reduction of friction is supported by phospholipid lamellar phases and charged macromolecules residing between contacting cartilage surfaces at pH ∼7.4.

Study of the Influence of Normal and High Blood Pressure on Normal and Stenosed Carotid Bifurcation Using Fluid-Structure Interaction

Atherosclerosis (stenosis) is a common cardiovascular disease in which the blood vessel restructures by narrowing, thickening and gets hardened due to the deposition of plaque. A detailed study of narrowing of arteries applying computational aspects which leads to better findings in order to know the underlying mechanics of development and progression of such diseases. Such kind of analysis can be a useful tool for the medical professionals to study the realistic physiological conditions. They can simulate and observe the blood flow in arteries. In the present study, a case of normal and stenosed carotid bifurcation is simulated. The models are generated in CATIA based on the clinical data obtained from a patient using Ultrasound Doppler. A transient FSI analysis considering Newtonian behavior is performed to compare the significance of High Blood Pressure (HBP) and Normal Blood Pressure (NBP) on carotid bifurcation. The FSI simulation is carried out for both HBP and NBP conditions for several pulse cycles on normal and stenosed models using ANSYS13.0 to demonstrate the changes in flow behavior at various sections of the model. The computed results agree well with clinical observations and available literature as seen in case of NBP.

Mathematical formulation of a modified film thickness equation for multipad externally adjustable fluid film bearing

Abstract High-speed turbomachinery applications demand a highly stable spindle support system with a need for hydrodynamic bearings with better performance and stability characteristics. The multipad adjustable bearing geometry proposed in this study offers a unique attribute of altering the film thickness in the bearing clearances. The adjustability principle is applied to the four circumferentially spaced bearing pads or elements to translate in radial and tilt directions. The proposed bearing design provides an efficient alternative in the field of active journal bearings. This paper presents a geometrical approach employed in formulating a theoretical equation for film thickness variation under different pad adjustments. The mathematical relation for film thickness is derived using certain trigonometric relations by considering both the radial and tilt adjustment parameters. The present approach provides an accurate approximation of circumferential film thickness variation for an adjustable bearing in comparison with other film thickness models.