T.V.V.L.N. Rao

Rapid performance evaluation of journal bearings

This paper describes a rapid method for evaluating the significant design parameters such as load capacity, maximum pressure, flow, power loss, and maximum temperature in the oil film. The proposed analytical pressure expression is a modification of that given by Reason and Narang. An analytical expression for maximum pressure is presented. The accuracy of the proposed modification is validated up to an eccentricity ratio of 0.99. The effective temperature rise, which depends on the fraction of heat generation carried away by lubricant, is chosen to be a function of the eccentricity ratio. An expression for maximum temperature, based on existing experimental findings, is given. A journal bearing design table is provided to help the designer without the involvement of numerical and mathematical complexities.

An Analytical Approach to Evaluate Dynamic Coefficients and Nonlinear Transient Analysis of a Hydrodynamic Journal Bearing

The objective of this work is the development of analytical expressions for accurate evaluation of dynamic coefficients and prediction of post whirl orbits (transient journal center motion above instability critical speed) by computation of nonlinear journal trajectory for a cylindrical journal bearing.

An integrated approach to design and analysis of lean manufacturing system: a perspective of lean supply chain

The objective of this research is to provide an integrated approach to the design and analysis of lean manufacturing system from the perspective of lean supply chain. The research focuses on four key dimensions: 1 pricing, investment and order quantity decisions; 2 Just-in-Time (JIT) integrated inventory with investments; 3 optimal cycle length and number of inspections in deteriorating production processes with investments; 4 optimal batch size in a single-stage and optimal number of kanbans in a multistage JIT production-delivery system with rework consideration. The goal of this research is to provide insights to organisations that are designing lean supply chains. It provides a framework for using an integrated approach to the analysis of lean supply chains. The research findings indicate the need for an integrated approach to the lean manufacturing system in order to achieve total leanness along the supply chain to gain significant competitive advantages.

Stability Characteristics of Herringbone Grooved Journal Bearings Incorporating Cavitation Effects

Stability characteristics of the herringbone grooved journal bearings (HGJBs) are analyzed taking into account cavitation of the fluid flow. The perturbed values of pressure and film thickness from a given equilibrium position are substituted into the Eirods universal equation, which considers mass conservation in the complete bearing geometry. In order to analyze the herringbone groove configuration, the governing equations under steady and perturbed states are transformed to a rectangular domain using the grid transformation techniques. It is assumed that under perturbed conditions, the cavitation extent in the bearing remains unchanged and the pressure gradients are computed in the full film region. The linearized stiffness and damping coefficients are evaluated in the complete bearing geometry from the predicted values of pressure gradients. The threshold speed parameter and whirl frequency ratio are computed using the linearized stability analysis. Results are generated for various eccentricity ratios and groove angles. The results of this study validate the use of HGJBs at the very higher operating speeds (at concentric journal operation) in rotating machinery.

Analysis of Single-Grooved Slider and Journal Bearing With Partial Slip Surface

In this paper, pressure and shear stress are derived under steady state using one-dimensional analysis of the single-grooved slider bearing and journal bearing with partial slip on the stationary surface. The Reynolds boundary conditions are used in the analysis of journal bearing to predict the extent of the full film region. In the cases of partial slip slider and journal bearing, the pressure distribution is higher compared with the conventional bearing with no slip. In the case of partial slip on both slider and journal bearing surfaces, the single-groove, immediately followed by the partial slip region, results in the increase in pressure distribution. The results also show that in comparison to the conventional bearing with no slip, in the cases of parrial slip slider and journal bearing, the shear stress increases before the region of slip/no slip interface, while the shear stress decreases in the region of no slip. In the case of the partial slip region on bearing surfaces, the shear stress distribution is lower in the region immediately after the groove. Significant pressure distribution is obtained due to the influence of partial slip on the slider bearing with uniform film thickness and the concentric journal bearing. The maximum pressure occurs at the end of the region of groove, immediately followed by the region of the partial slip. It is found that the pressure distribution of the slider and journal bearing with partial slip surface are not influenced with the further increase in the nondimensional slip coefficient (A) from 10 to 100.

Linear Stability Analysis for a Hydrodynamic Journal Bearing Considering Cavitation Effects

The purpose of this paper is to present the two-dimensional linear stability analysis considering the fluid flow in both full film and cavitation regions for a plain cylindrical journal bearing. The Lunds infinitesimal perturbation procedure is applied to Elrods universal equation for evaluation of unsteady pressure gradients. Based on JFO theory, the pressure distribution, film rupture, and reformation boundaries can be obtained using Elrods universal equation, for a given operating position of the journal. In this work, it is assumed that for infinitesimal perturbation of a journal about the equilibrium position, the film rupture and film reformation boundaries are the same as those obtained for steady state. However, the unsteady pressure gradients in the full film region are evaluated taking into consideration the perturbed flow parameters in the cavitation region, i.e., at both rupture and reformation boundaries. The linearized stiffness and damping coefficients, whirl frequency ratio, and threshold speed for various values of eccentricity and L/D ratios are obtained for a plain cylindrical journal bearing with an axial groove along the load line. Measured data of dynamic coefficients for a 120° partial arc bearing are chosen for comparison with this work. Results show good agreement between the theoretical and experimental results. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002

Analysis of Journal Bearing with Double-Layer Porous Lubricant Film: Influence of Surface Porous Layer Configuration

This article presents an analysis of a long journal bearing with a double-layer porous lubricant film using couple stress and Newtonian fluids. The porous layer with infinite permeability analyzed in this study simulates the surface layer. The Brinkman model was utilized to model the flow in the porous region. The effects of couple stresses were analyzed based on Stokes microcontinuum theory. A double-layer porous lubricant film configuration, with a low-permeability porous layer on top of a high-permeability bearing adherent porous layer, improved the journal bearing performance characteristics. A surface porous layered lubricant film configuration increased the load-carrying capacity and reduced the coefficient of friction in a journal bearing.

A Nonlinear Model for Prediction of Dynamic Coefficients in a Hydrodynamic Journal Bearing

This paper investigates the variation of nonlinear stiffness and damping coefficients in a journal orbit with respect to equilibrium position. The journal orbit is obtained by the combined solution of equations of motion and Reynolds equation. In the linearized dynamic analysis, dynamic pressure is written as a perturbation of static pressure and pressure gradients at equilibrium position. However, in order to obtain nonlinear dynamic coefficients about equilibrium position, the dynamic pressure gradients in the orbit are also written as the first order perturbation of static pressure gradients and higher order pressure gradients for displacement and velocity perturbations. The dynamic coefficients are functions of bearing displacement and velocity perturbations. The higher order pressure gradients at equilibrium position are evaluated at various eccentricity ratios and L/D ratios of 0.5 and 1.0. The variation of nonlinear dynamic coefficients is analyzed for three Sommerfeld numbers of a two-axial groove journal bearing under the action of an external synchronous load along and perpendicular to the radial journal load. Results indicate that the oil film nonlinearities affect the journal motion at lower eccentricity ratios (higher Sommerfeld numbers) with wide variation in stiffness and damping coefficients.

A Methodology for Dynamic Coefficients and Nonlinear Response of Multi-Lobe Journal Bearings

A methodology for prediction of dynamic coefficients and nonlinear simulation of multi lobe bearings is developed. This simple formulation that is an extension of Reason and Narang (1982) approach. An easy to implement finite perturbation method is used to evaluate stiffness and damping coefficients. In order to obtain the fluid film forces, the oil film pressure generated in the bearing is solved using a semi analytical pressure model. Four multi lobe journal bearings, namely: two-axial groove, elliptical, three-lobe and offset bearings are studied in terms of non dimensional stiffness and damping coefficients. The parameters are: L/D ratios of 0.5 and 1.0, pre-load factor of 0.5 and offset factor of 0.5; except for the offset bearing, for which the offset factor is 1.0. The results are provided in graphical form and compared with existing numerical techniques. All the coefficients show the influence of Sommerfeld (long) bearing solution at high eccentricity ratios. Results also indicate the applicable range of reciprocal relationship combining the Ocvirk (short) and Sommerfeld bearing solutions for all multi lobe bearing configurations. The journal center trajectories obtained are compared with numerical results and the effect of stability on rotor bearing system is studied for both balanced and unbalanced rotor. It is concluded that the approximate bearing solutions which are predominantly applied to cylindrical bearing configuration, can also be successfully implemented for noncircular profiles.

Optimal batch sizing, quality improvement and rework for an imperfect production system with inspection and restoration

This paper incorporates the effect of process inspection and restoration (Ben-Daya and Rahim, 2003) in an imperfect production process while considering three different scenarios (Ojha et al., 2007): 1) single lot of raw material–multiple lot of finished product–multiple delivery of the product, 2) single lot of raw material–multiple lot of finished product–single delivery of the product, 3) single lot of raw material–single lot of finished product–single delivery of the product. A numerical algorithm is proposed, and an illustrative example is provided. The optimal number of inspections, ordering quantities and expected total cost of the illustrative example are evaluated for each of the three models along with a sensitivity analysis to show the impact of the model parameters on the solution. The analysis shows that incorporating the inspection and restoration in the imperfect production process results in larger batch sizes and lower total costs. The implementation of inspection and restoration in imperfect production processes is good in cases of higher percentage of defective items produced (α), as it results in higher savings on total cost. [Submitted 03 October 2007; Revised 22 May 2008; Revised 10 November 2008; Accepted 11 November 2008]