STATIC AND DYNAMIC ANALYSIS OF CIRCULAR AND NON-CIRCULAR BEARINGS HAVING NON-NEWTONIAN LUBRICANTS BY A FINITE ELEMENT METHOD

Abstract

The characteristics of lubricants, to meet the specific requirements of many engineering applications, are often controlled by using additives in the lubricating oil. The polymer thickened oils behave as pseudoplast ic or di.latant fluids. The viscosity of these lubricants loaded with additives is not constant and usually follows some nonlinear relation between shear stress and shear strain rate. The nonlinear behavior of lubricants can be described by various non-Newtonian models. To study the non-Newtonian behavior in the bearings, seven models have been taken. The static and dynamic performance characteristics of hydrodynamic be arings using non Newtonian lubricants are different as compared to those for the same be aring with Newtonian lubricant. Some investigators have studied the performance characteristic s of hydrodynamic circular journal bearings using non-Newtonian lubricants by modifying the Reynolds equation and solving it by the finite difference and the perturbation techniques. As the Reynolds equation has to be derived for each non-Newtonian model, it will be quite cumbersome to study the bearing performance characteristics with Reynolds equation as the starting point. In this dissertation, the momentum equations and the continuity equation in cylindrical coordinates have been used. The cylindrical coordinates have been chosen because they are most conformal to the journ al be aring configuration • The V finite element method employing Galerkin's technique is used to solve the momentum equations for Newtonian lubricants and the continuity equation. The non-Newtonian effect is intro-duced by modifying the viscosity term for the non-Newtonian model in each iteration till the required convergence is achieved. The study includes the, circular and non-circular hydrodynamic journal bearings with journal and bearing axes parallel as well as skewed. The static performance characteristics have been studied in terms of load support, attitude angle, friction force, co-efficient of friction, end leakage and temperature rise para-meter. For studying the dynamic performance characteristics, the journal bearing system is considered to have four degrees of freedom, two for the lateral motion and two for the angular motion of the journal. For the general motion of the journal, each of the stiffness and damping coefficient matrices has sixteen coefficients, which have been computed for different values of eccentricity ratio. Using Routh's criteria, the stability margins represented by the threshold speed and the critical mass moment of inertia have been obtained for the lateral and angular motions of the journal independently. The stability study for the combined lateral and angular motions of the journal, has been made by obtaining the roots of the corresponding characteristic equation • The performance charwteristics of the bearings have been obtained for both Newtonian and non-Newtonian lubricants.