Dynamic Coefficients of Finite Length Journal Bearing. Evaluation Using a Regular Perturbation Method

A set of simple expressions is deduced for static and dynamic parameters associated to hydrodynamic journal bearings (JB). The behavior of this system is governed by two dimensionless numbers, the aspect ratio, L/D, and the eccentricity ratio, η. In a previous work, we presented a regular perturbation method that extended the Ocvirk solution and successfully described isothermal JBs up to L/D and η of ∼1/2. Presently, we extend that methodology, modified using a smaller perturbation parameter, to obtain analytical expressions of the dynamic coefficients, as well as static variables like friction factor, load carrying capacity, lubricant flow rate and phase angle. The deduced expressions successfully describe the static and dynamic behavior of JBs up to L/D and η of ∼3/4.Fil: Merelli, Claudio Ernesto. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química; ArgentinaFil: Barilá, Daniel Oscar. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Vignolo, Gustavo Gabriel. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Quinzani, Lidia Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentin

A bibliography /with abstracts/ on gas-lubricated bearings Interim report

Gas lubricated bearings - annotated bibliograph

Current research in cavitating fluid films

A review of the current research of cavitation in fluid films is presented. Phenomena and experimental observations include gaseous cavitation, vapor cavitation, and gas entrainment. Cavitation in flooded, starved, and dynamically loaded journal bearings, as well as squeeze films are reviewed. Observations of cavitation damage in bearings and the possibility of cavitation between parallel plates with microasperities were discussed. The transcavity fluid transport process, meniscus motion and geometry or form of the film during rupture, and reformation were summarized. Performance effects were related to heat transfer models in the cavitated region and hysteresis influence on rotor dynamics coefficients. A number of cavitation algorithms was presented together with solution procedures using the finite difference and finite element methods. Although Newtonian fluids were assumed in most of the discussions, the effect of non-Newtonian fluids on cavitation was also discussed

Bending vibration of an automotive turbocharger under the influence of rotor imbalance

As one of the most common faults, rotor imbalance in a turbocharger will give rise to the bending vibration, which may cause damage to and even destroy the bearings and impellers. Therefore, it is necessary to detect rotor imbalance as early as possible. The present paper develops a mathematical model for investigating the rotor dynamic characteristics of a commercial automotive turbocharger supported on floating ring bearings. In order to reveal the behaviours of oil film instabilities the model takes into account nonlinear hydrodynamic oil film forces instead of linearization. A two-dimensional elastic collision model is introduced to deal with the rub-impact process between such solid parts as journal, floating ring and the bearing. In addition, the change of clearances in floating ring bearing due to temperature increases are also estimated by ignoring the variation of lubricating oil viscosity. Following model development, a numerical simulation is implemented to study the bending vibration of the turbocharger and floating ring bearing under the influence of rotor imbalance. This study paves a foundation for the monitoring of turbochargers

Lubrication background

Surface topography, including the various physical methods of measuring surfaces, and the various lubrication regimes (hydrodynamic, elastohydrodynamic, boundary, and mixed) are discussed. The historical development of elastohydrodynamic lubrication is outlined. The major accomplishments in four periods, the pre-1950's, the 1950's, the 1960's, and the 1970's are presented

Dynamic response and stability of a gas-lubricated Rayleigh-step pad

The quasi-static, pressure characteristics of a gas-lubricated thrust bearing with shrouded, Rayleigh-step pads are determined for a time-varying film thickness. The axial response of the thrust bearing to an axial forcing function or an axial rotor disturbance is investigated by treating the gas film as a spring having nonlinear restoring and damping forces. These forces are related to the film thickness by a power relation. The nonlinear equation of motion in the axial mode is solved by the Ritz-Galerkin method as well as the direct, numerical integration. Results of the nonlinear response by both methods are compared with the response based on the linearized equation. Further, the gas-film instability of an infinitely wide Rayleigh step thrust pad is determined by solving the transient Reynolds equation coupled with the equation of the motion of the pad. Results show that the Rayleigh-step geometry is very stable for bearing number A up to 50. The stability threshold is shown to exist only for ultrahigh values of Lambda equal to or greater than 100, where the stability can be achieved by making the mass heavier than the critical mass

Topology and Shape Optimization of Hydrodynamically–Lubricated Bearings for Enhanced Load-Carrying Capacity

Bearings are basic and essential components of nearly all machinery. They must be designed to work under different loads, speeds, and environments. Of all the performance parameters, load-carrying capacity (LCC) is often the most crucial design constraint. The objective of this research is to investigate different design methodologies that significantly improve the LCC of liquid-lubricated bearings. This goal can be achieved by either altering the surface texture or the bearing geometrical configuration. The methodology used here is based on mathematical topological/shape optimization algorithms. These methods can effectively improve the design performance while avoiding time-consuming trial-and-error design techniques. The first category of design studied is a micro-scale mechanical self-adaptive type which can provide “flexible surface texturing”. An accurate 3D model based on the classic plate theory and thin film lubrication is developed and a shape optimization analysis is carried out. Special attention is given to the cavitation phenomena and its numerical analysis. Also proposed is a numerical procedure to improve the convergence rate and stability of the Elrod cavitation algorithm. The idea of using self-adaptive mechanism to improve LCC is also adopted for thrust bearings. Novel flexible-pad thrust bearing designs that provide an optimum load-responsive mechanism are presented and an accurate multi-physics model that considers the coupled mechanism between the lubricant pressure and the pad deformation is developed. The optimum shapes for different bearing geometries are given and a detailed design guideline is provided for optimum performance. The second category of design studied focuses on bearing geometrical configuration. The optimum shape of finite width sectorial sliders, which is an open problem in the field, is determined for the first time in this research using topological optimization algorithms. Also three suboptimum solutions for special cases of 2D step profile, constant film thickness in the radial direction and constant film depth with quadrilateral shape are presented. These configurations are particularly attractive because they can be easily manufactured. The optimum shape of bearings with periodic surface grooves is also determined in this research. It is shown that the optimum shape is dependent to the aspect ratio of the grooves and it can change from elongated “heart-like” shapes to spiral-like shapes. A series of laboratory tests to authenticate the theoretical development is carried out. Results show very good agreement with the theory validating the accuracy of the model. Finally, the optimum geometry of spiral grooves that provide the highest LCC in liquid-lubricated parallel flat surface bearings is determined and a detailed design guideline is provided. The thermal effects are also considered and an approximate thermo-hydrodynamic model is developed for a range of seal geometries and operating conditions

Energy dissipation prediction of particle dampers

This paper presents initial work on developing models for predicting particle dampers (PDs) behaviour using the Discrete Element Method (DEM). In the DEM approach, individual particles are typically represented as elements with mass and rotational inertia. Contacts between particles and with walls are represented using springs, dampers and sliding friction interfaces. In order to use DEM to predict damper behaviour adequately, it is important to identify representative models of the contact conditions. It is particularly important to get the appropriate trade-off between accuracy and computational efficiency as PDs have so many individual elements. In order to understand appropriate models, experimental work was carried out to understand interactions between the typically small (1.5–3 mm diameter) particles used. Measurements were made of coefficient of restitution and interface friction. These were used to give an indication of the level of uncertainty that the simplest (linear) models might assume. These data were used to predict energy dissipation in a PD via a DEM simulation. The results were compared with that of an experiment

Aerodynamic Analysis of Compliant Thrust Foil Bearings

In turbo-expanders, the shaft rotates at a very high speed (i.e. 100000 RPM). At this high speeds, normal bearings cannot be used as it results in high friction and wear of the bearings. That is the reason; we are going to use gas foil bearings as a recent and advanced alternative. Here, in this project we are going to design bearings required to support the shaft which runs at a very high speed. Current project concentrate to analyse the load bearing capacity of the thrust bearings. In the analysis Reynolds’ Equation is used to know the pressure distribution of these bearings. The Reynolds’ Equation is solved by using FINITE DIFFERENCE METHOD and using many assumptions to know the pressure distribution of the thrust bearings. Finite Difference Method is a numerical technique by the principle of discretization to find the approximate solutions of engineering problems. The result comes after a many number of iterations based on a convergence condition. We are using MATLAB (Matrix Laboratory) software to implement Finite Difference Method to solve Reynolds’ Equation. A MATLAB program is written which contains multiple loops that solves the Reynolds’ Equation and gives Pressure plots. After the pressure distribution is known, load carrying capacity of the bearing is calculated and their variations with different parametes are presented. The results of this foil thrust bearings are compared with the load carrying capacity of rigid bearings. The analysis was also done for different types for foil bearings by taking different materials of the bump foil

Fluid Compressibility Effects on the Dynamic Response of Hydrostatic Journal Bearings

A theoretical analysis for the dynamic performance characteristics of laminar flow, capillar/orifice compensated hydrostatic journal bearings is presented. The analysis considers in detail the effect of fluid compressibility in the bearing recesses. At high frequency excitations beyond a break frequency, the bearing hydrostatic stiffness increases sharply and it is accompanied by a rapid decrease in direct damping. Also, the potential of pneumatic hammer instability (negative damping) at low frequencies is likely to occur in hydrostatic bearing applications handling highly compressible fluids. Useful design criteria to avoid undesirable dynamic operating conditions at low and high frequencies are determined. The effect of fluid recess compressibility is brought into perspective, and found to be of utmost importance on the entire frequency spectrum response and stability characteristics of hydrostatic/hybrid journal bearings