Showing papers on "Fluid bearing published in 2017"

Analysis of Coupled Poroviscoelasticity and Hydrodynamic Lubrication

Abstract: As the state of the art pushes triboelements toward greater capabilities and longevity, the need for evolving triboelement technology exists. The following work explores a novel coupling of phenomena inspired by biomimetics. A poroviscoelastic substrate coupled to a fluid film load is modeled and compared to its rigid counterpart. It is hypothesized that poroviscoelasticity can improve triboelement properties such as damping and wear resistance and have utility in certain applications where flexibility is desired (e.g., biomechanical joint replacements, flexible rotordynamic bearings, and mechanical seals). This study provides the framework for the analysis of flexible, porous viscoelastic materials and hydrodynamic lubrication.

Effects of surface roughness and porous structure on the hydrodynamic lubrication of multi-layer oil bearing

Abstract: Purpose The purpose of this paper is to discuss the combined effects of the deterministic surface roughness and porous structure on the lubrication property of the multi-layer bearing. Design/methodology/approach Digital filtering technique and Kozeny-Carman equation are used to simulate the random Gauss surface and the internal pore structure of the porous bearing, respectively. Effects of surface morphology, structure and pores on the lubrication property are discussed by using the finite difference method. Findings Results show that the lubrication performance of the multi-layer bearing increased with the increase of the surface roughness. Also, the transverse surface is better than that of the longitudinal surface. Moreover, lubricating property is getting worse with the increase of the height of each layer and the porosity. The lower permeability surface is beneficial to improve the lubrication performance when the total porosity is certain. Originality/value The effect of the Gauss roughness parameters on the detail of lubrication performance are analysed, such as the migration of the oil film rupture point position, the expansion of the pressure distribution region and the fluctuation of the pressure distribution curve with the roughness parameters. The combined effects of surface roughness, multi-layer structure and the internal pore parameters on the hydrodynamic behaviours of multi-layer porous bearing are analysed. This work is beneficial for the analysis of the tribological property and the structural design of multi-layer bearing.

Validation of the in-plane friction behaviour of a ferrofluid bearing

Abstract: The repeatability of precision positioning systems can be improved by reducing the effects of stick-slip in the system. Stick-slip effects introduce a spontaneous jerking motion when overcoming the static friction coefficient, creating accelerations that are hard to predict. Contactless bearing types, such as magnetic levitation or fluid bearings, can be used to prevent stick-slip effects from occurring. Ferrofluid bearings provide a cost-effective alternative to conventional contactless bearing systems. The bearing is created by applying ferrofluid to a permanent magnet. The fluid gathers at the highest magnetic field intensity, resulting in a load-bearing ring at the edges of the magnet. Due to the uncertainty in the modelling of the in-plane friction behaviour of a ferrofluid bearing, the expected friction force is multiplied with a safety factor during design. In this research the model for the in-plane friction behaviour of a ferrofluid bearing is experimentally validated. The experimental validation will be performed on a modified version of the six degrees of freedom demonstrator stage of Cafe(2014). This stage is well-suited for ferrofluid research due to its high accuracy and versatility as a result of the actuation and control in six degrees of freedom.

Actively compensated aerostatic thrust bearing: design, modelling and experimental validation

Abstract: Active compensation is an effective method for increasing air bearing static and dynamic performance. This paper describes the design, modelling and experimental validation of an actively compensated externally pressurized gas bearing. The active compensation is obtained through the support compensation strategy. With this strategy, the system’s initial working position is restored by compensating for air gap variations through adjustments to the bearing vertical dimension. The described bearing consists in a conventional thrust bearing which is integrated with a multilayer piezoelectric actuator, a compliant mechanism and a digital controller. Nevertheless the non-linear nature of the air system, a simple linear model results to be an effective choice for neighbour of equilibrium conditions. Results demonstrate the good accuracy of the model and the system’s good capacity of rejecting external force disturbances.

Experimental Investigation of Frictional Force in a Hydrodynamic Journal Bearing Lubricated with Magnetorheological Fluid

Abstract: Variations in frictional force developed in the journal bearing lubricated with Magnetorheological (MR) fluid was investigated. Also, a comparative study was conducted between MR fluids and SAE15W40 grade engine oil on the performance characteristics. A test bearing set-up was developed to accommodate MR fluid film with provision for varying magnetic field. MR Fluid was formulated by dispersing electrolytic grade micron sized iron particles in silicon oil base fluid in 0.3 volume fraction. The results of the experimental testing indicated an increase in frictional force with increasing excitation current in the electromagnetic cores of journal bearing for similar loads and speeds in comparison to plain engine oil; the presence of MR fluid causes an increase in viscosity in comparison to plain engine oil and thus holds a great potential to increase the load carrying capacity of the journal bearing.

Static characteristics of ferrofluid finite journal bearing considering rotational viscosity effect

Abstract: Considering the rotation of ferromagnetic particles, the present study investigates hydrodynamic lubrication by ferrofluids of finite journal bearings using the Shliomis model. A magnetic field created by displaced finite wire is used. A numerical solution for the modified Reynolds equation using the finite difference method is obtained. Static characteristics of finite journal bearings are analysed using three control parameters: rotational viscosity, magnetization and volume concentration of the ferromagnetic particles. It is shown that the pressure, load capacity, attitude angle and side leakage increase and the friction coefficient decreases when increasing the value of each control parameter. Similar trends are also obtained when increasing values of eccentricity for a fixed value of each control parameter except for the decrease of the attitude angle. Copyright © 2016 John Wiley & Sons, Ltd.

The Experimental Identification of the Dynamic Coefficients of two Hydrodynamic Journal Bearings Operating at Constant Rotational Speed and Under Nonlinear Conditions

Abstract: Hydrodynamic bearings are commonly used in ship propulsion systems. Typically, they are calculated using numerical or experimental methods. This paper presents an experimental study through which it has been possible to estimate 24 dynamic coefficients of two hydrodynamic slide bearings operating under nonlinear conditions. During the investigation, bearing mass coefficients are identified by means of a newly developed algorithm. An impact hammer was used to excite vibration of the shaft. The approximation by means of the least squares method was applied to determine bearing dynamic coefficients. Based on the performed research, the four (i.e. two main and two cross- coupled) coefficients of stiffness, damping and mass for each bearing were obtained. The mass coefficients add up to the complex shaft weight. These values are not required for modeling dynamics of the machine because the rotor mass is usually known, however, they may serve as a good indicator to validate the correctness of the stiffness and damping coefficients determined. Additionally, the experimental research procedure was described. The signals of displacements in the bearings and the excitation forces used for determination of the bearing dynamic coefficients were shown. The study discussed in this article is about a rotor supported by two hydrodynamic bearings operating in a nonlinear manner. On the basis of computations, the results of bearing dynamic coefficients were presented for a selected speed

Performance analysis of a finite noncircular floating ring bearing in turbulent flow regime

Abstract: The present paper investigates the turbulence effect on the steady-state performance of a new variety of journal bearing, i.e. the noncircular floating ring bearing. This particular bearing consist...

Active Gas Thrust Bearing With Embedded Digital Valves and Backpressure Sensors

Abstract: The present article describes a low-cost active aerostatic thrust bearing controlled via an Arduino card and with feedback transducers and valves embedded in it. Efforts were made to design a compact thrust bearing with small overall dimensions, robust behavior, and reduced costs. Two embedded electropneumatic digital valves are controlled with pulse width modulation (PWM) logic and used to modify the thrust bearing supply pressure. The feedback signal for the control comes from two embedded backpressure sensors designed and characterized for this purpose. The test benches required for static and dynamic thrust bearing characterization are described; preliminary experimental tests were carried out in open and closed loop configurations. The closed loop configuration of the system, with a proportional integral (PI) control, shows good behavior and the time needed for the thrust bearing to return to the reference gap value after a force perturbation of 40 N is about 0.1 s.

Experimental identification of an Aerostatic Thrust Bearing

Abstract: Conventional approaches to design aerostatic bearings are based on their static characteristics. However, dynamic predictions are fundamental in order to obtain very precise positioning since air bearings are frequently subjected to dynamic load variations. This paper presents a simple linear time invariant model for aerostatic thrust bearings and the related experimental identification procedure. The experimental procedure identifies the stiffness and damping coefficients of the air gap model. The model validation was obtained comparing the experimental and theoretical bode diagrams of the studied system. The comparison demonstrates that the model leads to good results when neighbours of equilibrium conditions are considered.

Rotordynamic Performance of Hybrid Air Foil Bearings With Regulated Hydrostatic Injection

Abstract: Air foil bearing (AFB) technology has made substantial advancement during the past decades and found its applications in various small turbomachinery. However, rotordynamic instability, friction and drag during the start/stop, and thermal management are still challenges for further application of the technology. Hybrid air foil bearing (HAFB), utilizing hydrostatic injection of externally pressurized air into the bearing clearance, is one of the technology advancements to the conventional AFB. Previous studies on HAFBs demonstrate the enhancement in the load capacity at low speeds, reduction or elimination of the friction and wear during starts/stops, and enhanced heat dissipation capability. In this paper, the benefit of the HAFB is further explored to enhance the rotordynamic stability by employing a controlled hydrostatic injection. This paper presents the analytical and experimental evaluation of the rotordynamic performance of a rotor supported by two three-pads HAFBs with the controlled hydrostatic injection, which utilizes the injections at particular locations to control eccentricity and attitude angle. The simulations in both time domain orbit simulations and frequency-domain modal analyses indicate a substantial improvement of the rotor-bearing performance. The simulation results were verified in a highspeed test rig (maximum speed of 70,000 rpm). Experimental results agree with simulations in suppressing the subsynchronous vibrations but with a large discrepancy in the magnitude of the subsynchronous vibrations, which is a result of the limitation of the current modelling approach. However, both simulations and experiments clearly demonstrate the effectiveness of the controlled hydrostatic injection on improving the rotordynamic performance of AFB.Copyright © 2017 by ASME

Rotordynamic and Friction Loss Measurements on a High Speed Laval Rotor Supported by Floating Ring Bearings

Abstract: Floating ring bearings are the commonly used type of bearing for automotive turbochargers. The automotive industry continuously investigates how to reduce the bearing friction losses and how to create silent turbochargers. Many of these studies involve creating a numerical model of the rotor-bearing system and performing validation on a test bench on which a turbocharger is driven by hot gases. This approach, however, involves many uncertainties which diminish the validity of the measurement results. In this study, we present a test setup in which these uncertainties are minimized. The measurement results show the behavior of the floating ring bearing as a function of oil feed pressure, oil feed temperature, rotor unbalance and bearing clearances. Next to an increased validity, the test setup provides measurement data with good repeatability and can therefore represent a case study which can be used for validation of rotor-bearing models

Elastro-hydrodynamic lubrication model of multi-decked foil thrust bearing with copper wire support

Abstract: Copper wire supported foil thrust bearing (CWFTB), which can be applied in high speed turbo-expander, adopts underlying flat foil as elastic supporting that interconnected with copper wires In this paper, finite element model of the thrust bearing is developed incorporating the fluid film and foil deflections Fluid-structure interaction (FSI) is realized through serial solution of the fluid Reynolds equation and the plate Kirchhoff equation Pressure profile of the gas film and deflections of the top foil and bottom foil are obtained through iteration Static bearing performance such as bearing load and friction torque of the bearing are evaluated concerning bearing configuration such as taper/land ratio, taper height and copper wire arrangements The finite element numerical results are validated with data from experiments

Computational Mixed TEHL Model and Stribeck Curve of a Journal Bearing

Abstract: The aim of this article is to propose a model capable of estimating the friction along a heavily loaded journal bearing under mixed and hydrodynamic lubrication. The finite element analysis–computa...