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The rotor-bearing system is a crucial component of rotating machinery, such as turbines, pumps, compressors, and turbogenerators, which are widely used in various advanced engineering fields. This work presented a methodology for studying the behavior of an elastic Jeffcott rotor supported by two similar fluid film journal bearings. A finite element model using consistent matrix formulation was employed to simulate the shaft, including the external load, with four degrees of freedom per node. The small perturbation method was used to evaluate the second-order bearing coefficients of a journal bearing of finite length. These coefficients were further integrated with the finite element model to evaluate the dynamic response of the flexible rotors. Moreover, the system equations of motion were presented in dimensional form. The results of the second-order bearing coefficients analysis agreed with nonlinear analysis when the speed was less than the threshold speed, while there was a pronounced difference in second-order analysis when the speed was above the threshold speed. The behavior of the rotor-bearing system was studied using dynamic response and orbit diagrams, revealing that changes in rotational speed significantly affected the rotor's stability. [ABSTRACT FROM AUTHOR]

In this paper, a load-sharing performance analysis method of the planetary gear system is proposed considering the coupling effects of double-helical gear and journal bearing. Firstly, the coupling effects between the meshing characteristics of the double-helical gear pair and the dynamic characteristics of journal bearing under the actual operation state are studied, the dynamic model of the double-helical gear planetary transmission system is established, and the load sharing coefficient before and after considering the coupling effects are calculated; secondly, the load sharing characteristic test rig of planetary transmission system is built, and the load sharing coefficient of gear system under the test condition is measured to verify the accuracy of the proposed method; finally, the effects of operating parameters and structural parameters on the load sharing characteristic of gear system are discussed. [ABSTRACT FROM AUTHOR]

Journal bearings are essential machine elements that are widely used in the bearing of rotating or oscillating machine parts. Many studies in the literature examine the tribological properties of journal bearings. Most of these studies focus on polymer journal bearings and testing the tribological performances of different bearing materials with the same surface quality. In this article, radial journal bearings produced from ultra-high molecular weight polyethylene (UHMWPE) material and polyoxymethylene (POM) material in two different surface qualities in the range of N7–N8 and N10–N11 were tested under different load and different speed scenarios and their tribological performances and relationship of this performance between material and surface roughness were investigated. For this purpose, first of all, bearing samples were designed and manufactured. All samples' tribological and physical properties before the tests were measured, and then tests were carried out according to the determined scenarios. Different loads, different speeds, and different sliding distances were used in the scenarios. As a result, 96 tests were carried out by testing each situation three times in eight scenarios, with two different surface qualities from two different materials. In the tests, the friction coefficient, temperature, and weight loss values of all samples were measured, and after the tests, surface roughness measurements and SEM analyses were made. As a result, all the data obtained from the tests and measuring devices were compared with the pre-test conditions and material and surface quality. The results obtained from the comparisons and the evaluations of tribological performance are discussed in the conclusion part. The study results show that the material and the surface quality significantly affect the tribological performance. [ABSTRACT FROM AUTHOR]

In the crankshaft-connecting rod system of the diesel engine, the complicated lubrication and wear mechanisms of journal bearings are comprehensively affected by the elastic deformation effect, the asperity contact effect, the thermal effect as well as the lubricating oil viscosity-temperature effect. This paper proposes an adaptive iterative method based on a mixed thermo-elasto-hydrodynamic (TEHD) lubrication and wear coupling model to investigate the lubrication and wear behaviors of journal bearings in the mixed lubrication. The evolution laws of the oil film thickness, the hydrodynamic pressure, the asperity contact pressure, the friction power loss, and the wear distribution are discussed and compared under different running times, oil temperatures, external loads, and shaft rotational speeds. The three-dimensional surface models based on the asperity contact power loss and the maximum wear depth with the variation of the running time and the oil temperature are fitted under specific external loads and shaft rotational speeds. The simulation results demonstrate that the bearing wear process includes the initial wear stage and the stable wear stage, which has a significant influence on the changing trend and distribution of lubricating parameters. The three-dimensional surface fitting models can provide theoretical guidance for the future performance prediction of journal bearings under time-varying working conditions. [ABSTRACT FROM AUTHOR]

It is important to propose a reasonable nonlinear dynamic model of gas dynamic bearing–rotor system for the stable operation of turbocharger. This paper presents a hybrid gas journal bearing (HGJBs)–rotor system with flexible supporting structure. A fractional-order dynamic model of the symmetrical flexible HGJB–rotor system is established. A tracking–alarming method is proposed to obtain the rotational speed ratio at the bifurcation point. The stable and unstable regions of the rotational speed ratio Ω ω for both the rigid bearing–rotor system and flexible HGJB–rotor system are analyzed. The nonlinear dynamic behaviors of HGJB–rotor system versus the fractional order α d and rotational speed ratio Ω ω are studied. Results show the fractional-order dynamic model can realize the reasonable prediction of nonlinear dynamic behaviors. An increase in the rotational speed ratio Ω ω and the decrease of fractional order α d result in a growth of the vibration amplitude. The adoption of flexible supporting structure is a good strategy to increase the size of stable region. [ABSTRACT FROM AUTHOR]

This paper deals with scale-fullscale models of rotor-bearing systems on rotating condition. The investigation is focused on the gyroscopic effect, which causes forward and backward whirl frequencies. When the rotor-bearing system is scaled proportionally in its dimension (height, length, and width), the scaling factor of whirl frequencies can be derived. It depends on the ratio between a transverse and polar moment of inertia on its rotating axis called the gyroscopic factor. The experimental study is conducted to validate it on three scaled rotor-bearing systems, which shifts its disc from the middle of the shaft on the scale of 1:1, 2:1, and 3:1 to clearly show the gyroscopic effect on first bending natural frequency. The scaling factor is then validated using the Campbell diagram by finding its critical speed. From this critical speed, the whirl frequencies along the range of the full-scale model speed can be obtained. The result also shows that the scaling factor remains the same whether it is at rotation or rest condition. Consideration must be made on the effect of the structural design, that is, blade and support, because of its unsymmetric stiffness that can cause backward whirl frequencies. The bearing stiffness must be ensured to be scaled proportionally, especially on journal bearing cases. This finding can be used by engineers to deal with scaling method implementation on rotating machinery design. [ABSTRACT FROM AUTHOR]

A predictive analytics methodology is presented, utilizing machine learning algorithms to identify the performance state of marine journal bearings in terms of maximum pressure, minimum film thickness, Sommerfeld number, load and shaft speed. A dataset of different bearing operation states has been generated by solving numerically the Reynolds equation in the hydrodynamic lubrication regime, for steady-state loading conditions and assuming isothermal and isoviscous lubricant flow. The shaft has been modelled with four different values of misalignment angle, lying within the acceptable operating range, as defined in the existing regulatory framework. The journal bearing was modelled parametrically using generic geometric parameters of a marine stern tube bearing. The lift-off speed was estimated for each loading scenario to ensure operation in the hydrodynamic lubrication regime and the effect of shaft misalignment on lift-off speed has been evaluated. The generated dataset was utilised for training, testing and validation of several machine learning algorithms, as well as feature selection analysis, in order to solve several classification problems and identify the various bearing operational states. [ABSTRACT FROM AUTHOR]

A thermohydrodynamic model was used to study the influence of partial composite coatings on the behavior of plain journal bearings, considering solid elastic deformations and wall slip occurring at the oil film–polytetrafluoroethylene coating interface, and heat conduction between film, coating, interlayer and basement. The purpose is to design partial polytetrafluoroethylene coating to obtain improved bearing behavior based on analyzing the maximum temperature and minimum film thickness in different coating positions (or slip zones). The influences of coating thickness and coating materials (polytetrafluoroethylene, graphite and diamond-like carbon coatings) at different coating positions are also presented. Results show that polytetrafluoroethylene coatings that are completely located in the film convergent region have a small influence on thermal behavior in both nonslip and slip cases. Without slip, a full polytetrafluoroethylene coating can increase the maximum temperature; however, wall slip occurring on a full polytetrafluoroethylene coating surface is helpful in decreasing the maximum temperature when accompanied by a lower minimum film thickness. A thicker polytetrafluoroethylene coating causes bearing seizures more readily. Unlike polytetrafluoroethylene, graphite and diamond-like carbon coatings improve the thermal behavior. [ABSTRACT FROM AUTHOR]

Spindle rotation accuracy is important in machining process. Indirect compensation of spindle rotation error has been widely adopted in the field of machining accuracy improvement. However, there are some limitations on indirect compensation, and a little research on direct compensation can be found. This article utilizes active lubrication technology to improve the spindle rotation accuracy. Hydrostatic journal bearing with control recesses and servo valve drove by piezoelectric ceramics are adopted to compose the compensation element. The simple control strategy PID is adopted to provide control signal for servo valve. Both simulation and experiment are designed and conducted. The results show that proposed bearing system has the ability to improve the spindle rotation accuracy. [ABSTRACT FROM AUTHOR]

The lubrication of hydrodynamic journal bearings using shear thinning fluids is investigated analytically by comparing three different constitutive models. Whilst journal bearings have been in use for a long time, they are still fundamental components of the most advanced mechanical systems, and will remain so for a long time to come. In particular, the modified Reynolds equations for the power-law (Ostwald-de Waele), the Carreau and the Cross models were derived based on the perturbation method. The three models were used to calculate the pressure distribution and the load carrying capacity, and their results were compared and discussed. It is shown that at high shear rates (i.e., high shaft speeds) the Carreau and Cross models, which better describe the rheology of shear-thinning fluids, yield higher magnitudes of the pressure than the power-law model, while at low shear rates the three models are in better agreement. [ABSTRACT FROM AUTHOR]

Conventional conical hydrostatic bearings are compared with less conventional three-recess and four-recess designs for operation in hybrid hydrostatic/hydrodynamic mode. Design implications are discussed with reference to operation at either low or high speeds. Conical spindle bearings are chosen for this study because they offer a compact arrangement that allows both radial load support and axial load support. While there is wide availability of design data for separate thrust and cylindrical journal bearings, there are very little data for conical bearings. This paper reviews the design of conical bearings and extends from previous knowledge into hybrid performance at high speeds. It is shown that long narrow recesses provide larger radial load support compared to long wide recesses for higher speeds. Sample data are provided for design of single cone bearings and also for opposed cone bearings. The data provide for radial and axial loads applied in combination for a selection of cone angles. Data are also provided as a guide for flowrate in the concentric bearing state and for effects on temperature rise. [ABSTRACT FROM AUTHOR]

In order to obtain rotating machinery with improved energy efficiency, the approach of surface texturing journal bearings has been adopted to reduce the viscous dissipation in the lubricant. A possible reduction in shear viscous forces in the bearings of rotating machines could reduce the amount of heat released along its operation, resulting in a lower operating temperature that tends to improve journal bearings performance and the machine's energetic efficiency. Thus, this work aims to investigate the texturing of journal bearings under dynamic loading conditions, considering the application in rotating systems. For this, computational simulations are performed through a rotating system model constructed by means of the finite element method in which the hydrodynamic journal bearings that support the rotor are modeled by Reynolds' equation using the finite volume method and the full multigrid technique. The numerical results show that textured journal bearings can be applied to rotating machines, providing reductions in shear viscous forces. However, the magnitude of this reduction should be carefully evaluated, as the Reynolds cavitation model was applied to ensure a lower computational spent time and thus enable the simulations involved in this study. The novelty of this study is related to determining the appropriate distributions and geometric parameters of the textures for the journal bearing under dynamic load condition considering its equivalent static load condition what tends to drastically reduce computational time to perform this procedure, representing an important alternative for industrial application. [ABSTRACT FROM AUTHOR]

In recent times, controlling the performance of fluid film bearings smartly has become an important area for the fluid film bearing designers. This study deals with the numerical simulation of a magneto-rheological fluid–lubricated two-lobe hybrid slot-entry journal bearing. To make the operating condition more exact and realistic, the influence of geometric imperfection of the journal arising from manufacturing inaccuracies and thermal effect has been considered. Dave magneto-rheological fluid model, a constitutive relation of the Bingham model, and finite element method have been used in this article to simulate the behavior of the magneto-rheological fluid in a slot-entry bearing. The results indicate that the heat generated because of viscous friction rises the temperature of the magneto-rheological fluid, which changes the bearing performance significantly. Considering barrel-shaped journal and magneto-rheological fluid (applied current, Ic = 4 A), the performance of two-lobe slot-entry bearing is superior in terms of the value of h ¯ min , Q ¯ , C ¯ 11 , C ¯ 22 , S ¯ 11 , and S ¯ 22 approximately by a magnitude of 2%, 41%, 181%, 168%, 75%, and 41%, respectively, as compared to that of the base bearing (smooth ( a ¯ 1 = a ¯ 2 = 0) , two-lobe bearing, operating with a Newtonian fluid, Ic = 0 A). [ABSTRACT FROM AUTHOR]

The research work reported in this article is focused on the use of magnetic fluids as active lubricant for improving the performance of hybrid journal bearings, with application to high-precision machine tools. Prototype design was optimized following numerical computation of Reynolds equation and computational fluid dynamics calculations, in both cases with Herschel–Bulkley model for the magnetorheological fluid. This fluid (LORD Corp. MRF 122-2ED) was experimentally characterized in detail. The improvement of the hydrodynamic effect in journal bearings was demonstrated with 50% higher load capacity and stiffness, mainly at half of shaft eccentricity 0.4 < ε < 0.7. Active hydrostatic lubrication achieved quasi-infinite stiffness within working limits (load and speed), at low frequencies. For high dynamic response, the active lubrication based on magnetorheological valves did not show good response. The feasibility of using magnetic fluids for developing high performance machine tool spindles and the validity of the simulation models was demonstrated experimentally. [ABSTRACT FROM AUTHOR]

A study on the use of innovative journal bearings of adjustable geometry/properties in industrial turbines is presented in this paper. The adjustable bearing geometry is investigated in this work as a bearing function which can resolve issues in rotordynamic performance of industrial steam/gas turbines. The rotordynamic issues that the proposed bearing is supposed to resolve are given shortly as (a) rotor–stator contact and eccentric rotor whirling, (b) non-optimum bearing loading, (c) instability (steam or oil whirl) and (d) structural distortions (in casing, pedestal or other component). The functionality of the proposed journal bearing is presented in results of unbalance response obtained through nonlinear transient analysis. The principle of the adjustable bearing is the quasi-static displacement of the bearing pads to locate the journal centre in the desired position and to configure the optimum bearing bore profile achieving the optimum performance regarding key parameters of operation such as concentricity of rotor and stator, optimum bearing loading, power loss, temperature rise, stability characteristics and others. The inner mechanism for applying the bearing pad displacement is not a topic of discussion in this paper, as in the current work, the adjustable bearing operation is studied on its fundamental operations. The journal bearing model concerns nonlinear bearing impedance forces which are assigned in the rotor nodes after solving numerically the Reynolds equation for the two-partial arc journal bearing lubrication of finite length and the configuration of the bearing is similar the bearing type installed in industrial turbine applications (partial arc bearings). The bearing model enables the development of the oil-whirl/whip phenomenon if there is a trend towards instability (e.g. light loaded bearing, high speeds). The study presented in this paper concerns two steam turbine-generator shaft lines of small (∼50 MW) and medium size (∼200 MW) in which the adjustable bearings are demonstrated on resolving different issues. [ABSTRACT FROM AUTHOR]

A design strategy of a test rig for the dynamic behavior of a rotor supported by two full-scale journal bearings was proposed. A special part, called "intermediate", was set up to allow the convenient changing of the bearing structure. An electromagnetic exciter was used to obtain the natural frequency, and software running on the Microsoft Visual C++6.0 operating platform was programmed for signal acquisition and analysis. Then, the test rig was constructed. The field dynamic balance and natural frequency testing were carried out. The journal orbits and frequency spectrums were used to measure the dynamic response of different structure full-scale journal bearings. The experimental results showed that an acceptable balance effect was achieved after the field dynamic balance. The natural frequency of the rig agreed with the numerical results. Stability was improved through changing the bearing structure. This revealed that this rig can effectively test the dynamic behavior of a rotor supported by a full-scale journal bearing system, which is critical to the design of journal bearings. [ABSTRACT FROM AUTHOR]

This paper focuses on the modeling method and the gravity-induced dynamic response of a spur planetary gear system with journal bearings. The lumped-parameter model of a planetary gear system with journal bearings is established. Both contact on drive-side and back-side of the tooth are considered simultaneously. Linear and nonlinear bearing force models are introduced into the system model separately to take the planet bearing oil-film forces into account. A demonstration is given to show the adopted nonlinear oil-film force model is still valid for the lubrication of support for planet gears. Equilibrium positions of the planet gear are depicted under different input rotational speeds and input torques. Under gravity effect, system responses at different rotational speeds are calculated by employing Newmark integration; tooth wedging at ring-planet meshes is examined with different backlashes. The system responses are presented as vibration spectra, planet bearing forces, orbits of members, tooth forces, and the percentage of tooth wedging in one carrier cycle. The results show that the gravity effect dominates the response at low rotational speeds. The linear bearing force model is not valid in some cases. The fluctuation of the bearing force and the enlargement of the planet orbits are induced by gravity effect. Tooth wedging is the combined effect of gravity, centrifugal force, and planet bearing clearance. [ABSTRACT FROM AUTHOR]

The article aims to investigate the relationship between eccentricity ratio and the Sommerfeld number based on hydrodynamic water-lubricated journal bearings. Considering the differences between water and oil, especially the difference in vapor pressure, the effect of cavitation on pressure distribution of water film is analyzed based on three boundary conditions and a cavitation model by computational fluid dynamics (CFD). The result shows that the three boundary conditions are all not suitable to replace cavitation model in numerical analysis of water-lubricated journal bearings. Then numerical analysis of journal bearings with different dimensions is undertaken with the cavitation model under different working conditions. Based on the analysis, a reference is produced for designing water-lubricated journal bearings under hydrodynamic lubrication. At last, the reference is verified by experiments. [ABSTRACT FROM AUTHOR]

The flow in the clearance heavily influences the lubrication performance of journal bearing. Therefore, it is important to study the flow mechanism in journal bearing. As known, the pressure distribution in bearing clearance can be described with Reynolds equation. In this paper, unsteady form of Reynolds equation was simplified and nondimensionalized at first, based on certain assumptions. Then, the equation was solved with regular perturbation method, obtaining the analytical solution. At the end, the results of our work were compared with the results of “infinitely short journal bearing” model, Vignolo et al. (Approximate analytical solution to Reynolds equation for finite length journal bearings. Tribol Int 2011; 44: 1089–1099), and numerical simulations. The comparison implies that our results show more coincidence with the numerical results in a wider range. [ABSTRACT FROM AUTHOR]

By considering the effects of multiple grooves, rubber deformation, and actual boundary conditions, the steady elastohydrodynamic lubrication mathematical model and the dynamic Reynolds equation of water-lubricated rubber bearings are presented. The Reynolds equation is solved numerically by the finite difference method, and the stiffness and damping coefficients are calculated from the real and imaginary parts of the integrated pressure. Analysis results suggest that angular velocity, eccentricity ratio, groove configuration, and radial clearance have significant effects on the steady state and dynamic stiffness as well as damping characteristics, which also help in designing proper structure parameters of water-lubricated rubber bearings to obtain better dynamic performance. [ABSTRACT FROM AUTHOR]

A proportional–integral–derivative (PID) control model of an active hydromagnetic journal bearing (AHJB) is presented here and its design guidelines are explicitly described. The nonlinear rotor equations of motion, is introduced. Then, the linearization of these equations in the bearing specific equilibrium point is performed and presented along with the appropriate PID gains. Consequentially, the linear equation is transformed via Laplace method and the control model of the AHJB is finally developed. The multiphysics module of Ansys is used to calculate the forces that the hydrodynamic lubrication applies to the rotor, in every position of the rotor, during its movement inside the bearing. This has been done, in order not to have linear equations of the hydrodynamic forces, but the real, nonlinear equations. The nonlinear equations are used for the electromagnetic forces too. The Matlab software is used to simulate the components that the AHJB is consisted of. The P, I, and D gains are the obtained results of this simulations, which are produced via robust control method, in single-input-single-output tool module. Finally, the Simulink module of Matlab is energized to check the control characteristics of the developed AHJB system, taking into account the nonlinear equations of motion of the system, in combination with the rotor unbalance and gyroscopic effects and the saturation of the coils. The rotor response, the overshoot, the rotor center vibration are controlled using the above produced P, I, and D gains. Several plots are constructed and presented, such as the rotor orbits, to show the possibility of the AHJB control. [ABSTRACT FROM AUTHOR]

A nonlinear dynamic model of a short journal bearing is used to predict the steady-state motion of the journal and its successive bifurcations in the neighbourhood of the stability critical speed. Numerical continuation is applied to determine the branch of equilibrium point and its bifurcation into stable or unstable limit cycles. It has been found that the unstable limit cycles undergo a single limit point bifurcation whereas the stable limit cycles undergo two successive limit point bifurcations. Thus, the bi-stability domain, the potential jumping from small to large motion and the hysteresis loop motion are predicted. [ABSTRACT FROM PUBLISHER]

A novel tilting three-wheeled vehicle was developed at the University of Bath as part of a project funded by the European Union. The space and weight savings provided by this type of vehicle could be a solution to the pollution and congestion problems seen in urban environments. The direct tilt control method originally implemented on the prototype was shown to perform well in the steady state, but rapid transients were shown to lead potentially to rollover instability. To investigate this phenomenon and to design an improved controller, a multi-body model was combined with a lateral dynamics single-track model to predict both the steady-state behaviour and the transient behaviour. With this model, it was possible to obtain an accurate representation of the kinematic and dynamic roll motions of the vehicle and the resultant weight transfer across the rear axle, together with the lateral dynamics of the vehicle. The simple lateral dynamics model provided an easily understood physical representation of the system which can often be hidden in a complex multi-body model. This paper presents the development of the model and its validation against data from static and dynamic tests. [ABSTRACT FROM PUBLISHER]

The performance of hydrodynamic journal bearings is affected by the conditions under which the lubricant is fed to the bearing gap. Axial grooves are often used and, depending on their location relatively to the load line, they might substantially interfere with the hydrodynamic pressure generation and the thermal behaviour of the bearing. However, many of the existing tools for predicting bearing performance are not able to suitably predict bearing behaviour under varying load angle given the oversimplified way under which they treat lubricant feeding conditions. The present work proposes a detailed thermohydrodynamic approach which realistically incorporates these conditions into the bearing analysis. Special care is put on the mass and energy-conserving models of the ruptured film region and on a detailed treatment of lubricant mixing within the vicinity of grooves. This includes the first full modelling of the effect of negative flow rate in a groove, a phenomenon originally described experimentally in detail by the authors in previous publications, and which happens for a broad range of load/groove angles. An extensive investigation on the influence of loading direction on the performance of twin groove journal bearings has been performed. This parameter is found to affect deeply all major performance parameters due to the interference of groove regions in the hydrodynamic pressure generation and in the flow rates at each groove. [ABSTRACT FROM PUBLISHER]

Under severe operating conditions, the thermal effects and various deformations play an important role in determining the performance of misaligned plain journal bearings. However, the thermal effects and various deformations are rarely considered simultaneously in most studies on the misaligned plain journal bearings. In this article, a comprehensive thermoelastohydrodynamic model of the misaligned plain journal bearings is developed that involves the synthetic solution of the generalized Reynolds equation, three-dimensional energy equation, and heat conduction equations of the solids. Based on this model, series of simulation results are provided to examine the influence of the thermal effects and deformations on the behavior of the misaligned plain journal bearings. In addition, the comparisons between the thermohydrodynamic and complete thermoelastohydrodynamic model are also presented for different misalignment angle and magnitude. Results show that the thermal effects and various deformations should not be ignored because of their significant influence on the film thickness, film pressure as well as other bearings characteristics. [ABSTRACT FROM PUBLISHER]

The hydrodynamic lubrication theory founded by Osborne Reynolds in 1886 is based on several assumptions, including that the contact surfaces are perfectly smooth, and the lubricant flow regime is laminar. However, in certain special cases these hypotheses may not be valid, and it is seen that surface roughness and turbulence affect bearing performance. The approach adopted in the present work is based on the application of the homogenization method to the turbulent Reynolds equation. In homogenization, multiscale expansion of the fluid pressure terms leads to a system of four partial differential equations governing two types of problems (local and global). The solutions are, respectively, periodic functions, and the homogenized pressure. As an illustrative example, a journal bearing with a rough surface operating in the turbulent regime is analyzed. Numerical simulations are performed by imposing periodic isotropic roughness patterns over the stationary outer cylinder surface. The homogenized solutions are compared to direct solutions of the deterministic problem. Homogenization is shown to be a powerful but practical method to attack problems of rough surfaces and is applied to turbulent lubrication for the first time. In the plain journal bearing example, the effect of roughness is to increase the load significantly in many cases. The effect of turbulence is to greatly increase the load, in both the rough and smooth cases. [ABSTRACT FROM PUBLISHER]

An overhang rotor with two discs supported by a couple of tilting-pad journal bearings is investigated in this paper. The active lubrication based on injecting pressurized oil into the bearing gap through orifices machined in the bearing sliding surface is utilized to suppress the shaft vibrations. A fuzzy proportional-integral-derivative (PID) controller is designed for the active lubrication to adjust the rotor-bearing equilibrium position. The finite difference method is applied to solve the pressure distribution on each tilting pad surface of the active lubricated system. Numerical simulation and experiment results show that the actively lubricated system presents effective vibration reduction of unbalance response of a flexible rotor and the fuzzy PID controller exhibits good performance. Finally the superiorities in employing the active lubricated system with regard to extending the stable operational speed ranges and manage to put off the instabilities (whirl) of the rotor-bearing system are also investigated, and clearly illustrate one of its most promising applications. [ABSTRACT FROM PUBLISHER]

This article describes a calculation model for the simulation of the transient wear characteristics of journal bearings subjected to mixed friction. For predetermined time steps the local wear is calculated for circumference and width. The resulting changes to the gap geometry then flow directly into the further calculation process. The solid contact load ratio and boundary friction ratio in the mixed friction area are calculated on the basis of real rough surfaces. Modifications to the rough surfaces resulting from the running-in process are taken into consideration. In addition the microhydrodynamic effects, elastic deformations of the bearing environment and mass conserving cavitation are also recorded. The calculation model’s potential is demonstrated by means of an unsteady loaded conrod bearing. [ABSTRACT FROM AUTHOR]

Automotive turbochargers are known to operate into the self-excited unstable region. In the past these instabilities have been accepted as unavoidable, but recent developments in analysis and instrumentation may make it possible to reduce or eliminate them. A test stand has been developed at Virginia Tech to measure the vibrations of a 3.9 liter diesel engine stock turbocharger with both stock floating ring journal bearings and also custom design fixed geometry bearings. Vibration spectrum content clearly identifies the shaft instabilities and provides the basis for additional evaluation of future improved bearing design modifications. The current results, for custom fixed journal bearings, have clearly revealed a distinct jump with associated shift in the spectrum frequency content. This paper will document the recent tests of custom design fluid film bearings that have experienced this nonlinear jump condition. [ABSTRACT FROM PUBLISHER]

Numerical simulation of macro and micro journal bearings is investigated using Lattice Boltzmann Method. Bounce-back boundary condition is applied in macro flow simulation and a combination of diffuse scattering and bounce-back techniques is used in micro calculations. An approximation method which is called ghost boundary is employed to simulate the wall curvature of macro and micro bearings. The Lattice Boltzmann Method solutions of two classic configurations are compared with the numerical solution of the Reynolds equations. Bearing cavitation is approached in a simplified way for a macro journal bearing and the results are compared with a finite element solution. The Lattice Boltzmann Method results are satisfactory for the investigated problem. A computational analysis is also used to simulate the complicated behavior of the micro journal bearings in the slip flow regime with Knudsen number varying between 0.01 and 0.05. The working fluid in micro simulations is gas. In order to model the interaction between gas and solid walls, a local boundary condition which is derived from the kinetic theory of gases using multiple relaxation time method is employed and the static performance of the micro bearing is analyzed. Applying the second-order velocity boundary condition, the pressure distributions obtained from the Lattice Boltzmann Method are successfully compared with the results of spectral collocation method. Results indicate that by increasing Knudsen number the maximum of pressure decreases. [ABSTRACT FROM AUTHOR]

This article presents the applicability of the microcontinuum theories to the fluid in sliding surfaces. The classical continuum mechanics fails to predict the accurate results when the geometric volume under consideration becomes comparable to the material dimensions. The fluid in the presence of microstructures and in the space comparable to the clearance of bearings showed unexpected variations in its properties as per the experimental observations. A general class of micropolar fluid was defined by considering the microrotation vector of its particles. This review critically analyzes the microrotation of lubricant additives and its effects on static and dynamic characteristics of the bearings. [ABSTRACT FROM AUTHOR]

A flexure journal bearing design is proposed that will improve operational behaviour of a journal bearing at pronounced misalignment. Using a thermoelastohydrodynamic model, it is shown that the proposed flexure journal bearing has vastly increased the hydrodynamic performance compared to the stiff bearing when misaligned. The hydrodynamic performance is evaluated on lubricant film thickness, pressure and temperature. Furthermore, the influence of a compliant bearing liner is investigated and it is found that it increases the hydrodynamic performance when applied to a stiff bearing, whereas the liner has practically no influence on the flexure journal bearing's performance. [ABSTRACT FROM PUBLISHER]

The performance of main bearings in a combustion engine affects key functions such as durability, noise and vibration. Thus, with the aim of reducing friction losses and vibrations between the crankshaft and the bearings, the work reported here evaluates different strategies for applying controllable radial oil injection to main crankshaft journal bearings. In an actively lubricated bearing, conventional hydrodynamic lubrication is combined with controllable hydrostatic lubrication, where the oil injection pressures can be modified depending on the operational conditions. In this study, the dynamic behaviour of the main bearing of a medium-size engine is theoretically analysed when the engine operates with controllable radial oil injection and four different injection control rules. The theoretical investigation is based on a single-cylinder combustion engine model. The performance of the actively lubricated bearing is compared with the performance of the conventional lubricated bearing, giving some insights into the minimum fluid film thickness, maximum fluid film pressure, friction losses and maximum vibration levels. [ABSTRACT FROM PUBLISHER]

With the application of sleeve bearing in high speed, super-high speed and narrow-gap conditions, and the emergence of non-metallic bearing materials, the conventional no-slip boundary condition can be broken down. Critical shear stress is a main parameter in the numerical computation of wall slip. The four modified Reynolds equations for the two-dimensional spiral oil wedge sleeve bearing is established based on the critical shear stress model, in which the circumferential and axial wall slip of the sleeve and axial surface are considered. The shear stress angle is used to compute the circumferential and axial shear stress component and slip velocity. The results show the special structure of spiral oil wedge and the increase of eccentricity ratio make slip more difficult to occur. With the decrease of initial limiting shear stress, pressure, carrying capacity and friction drag decrease. Wall slip has an effect on the oil film rupture position, positive pressure area, and pressure peak. Wall slip occurs first in the large shear stress, the small clearance, and the envelop zone. The slip position and area influence each other in the sleeve and axial surface. [ABSTRACT FROM AUTHOR]

Non-linear dynamic performance of rotor–bearing systems supported by plain journal bearings strongly depends on the mathematical oil film force model. In this article, the analytical solution of oil film pressure for finite length plain journal bearing is obtained by employing the separation of variables method to analytically solve the Reynolds equation based on dynamic Gümbel boundary conditions. The analytical expression of oil film force is then derived by applying the integral method. The expression of the pressure is analysed to investigate the pressure distribution. The oil film force of the analytical model is compared with the results from other methods, namely, long bearing approximation, short bearing approximation, as well as the finite difference method. The results clearly validate the current model. The proposed model also proved to be efficient for analysing the dynamic characteristics of a rigid rotor supported by plain journal bearings. [ABSTRACT FROM AUTHOR]

For decades, linear dynamic coefficients of bearings are widely used to evaluate the stability and dynamic response of oil-film bearing-rotor systems. However, there often exist many strong nonlinear excitation sources in rotor systems. Therefore, the linear oil-film forces cannot reflect the nonlinearity characteristics of rotor systems. Some researchers present numerical methods for prediction of bearing nonlinear dynamic coefficients in order to represent nonlinear oil-film forces of bearing, while their methods are closely dependent on the size and shape of journal orbits. This article gives a computational method which is independent on the journal orbit to predict bearing dynamic coefficients using partial derivative method. The reliability of the numerical method is verified by comparing the linear dynamic coefficients of two-axial-groove bearing with the published results. The variation of dynamic coefficients with eccentricity ratios and length-to-diameter ratios of a simple oil-lubricated 360° journal bearing model is discussed. The numerical results indicate that bearing dynamic coefficients are dramatically increasing with the growth of eccentricity ratios and length-to-diameter ratios, especially when eccentricity ratio is larger than 0.8. The numerical model presented in this article will greatly simplify the solution of oil-film forces in nonlinear dynamic analysis of rotor systems. [ABSTRACT FROM PUBLISHER]

A hydrodynamic journal bearing utilizing flexure pads with a compliant liner is studied and its performance enhanced through a parametric study. The main geometrical dimensions are varied and the affect on pad performance is analyzed. This will put more knowledge into the design and function of flexure pads. Guidelines are given to the design of the pads and are also covering the polymer liner. It is found that the use of flexure pads is an attractive alternative to pivoted pads. Pivot contact-related failure modes are eliminated and load capacity is not restricted by the force that can be transferred through the pivot contact. When combined with a polymer liner, the pad performance is enhanced further, especially when operating at thin lubricant films. [ABSTRACT FROM PUBLISHER]

Journal bearing bushing wear and shaft misalignment are the common defects observed in rotating systems. Both defects influence their dynamic behaviour, stability and life time and their detection is a very important task. This article introduces a defect diagnosis approach that uses artificial neural networks. Reynolds equation is solved by finite element method and wear/misalignment data are provided. Then, the proposed model uses values of journal bearing performance characteristics, such as eccentricity, attitude angle and film thickness, and it trains an artificial neural network so that reliable defect identification is performed. The accuracy of the proposed model is demonstrated – for different misalignment angles, wear depths and L/D ratios – for a worn/misaligned journal bearing. The potential use of the artificial neural networks-based model for a real-time condition monitoring system is also discussed. The outcome of this study is to obtain an efficient engineering tool that would be capable of detecting wear and misalignment of journal bearings for different operating conditions using artificial neural networks. [ABSTRACT FROM AUTHOR]

The importance of gross dimensions on the design and operation of hydrodynamic journal bearing system are widely understood, however, the effects of manufacturing tolerances have only been macroscopically analysed. Building on previous theoretical analyses, an experimental investigation on the effect of dimensional manufacturing tolerances is presented. Importantly, the study looks at individual effects and combined effects. The experimental data suggested that the error created by manufacturing tolerances in estimating the onset of oil film instability can be as much as ±20 per cent, depending on the steady state operating position. This finding shows that in order to minimize the effect of manufacturing tolerances on system stability, the hydrodynamic journal bearing system should be designed to operate at a modified Sommerfeld number greater than 0.1, where the effects of manufacturing tolerances on system stability are negligible. [ABSTRACT FROM AUTHOR]

The performance of non-circular bearings, such as multi-lobe bearings is influenced by many bearing parameters such as the number of lobes, the preload factor, and the tilt angle. In this study, the effects of bearing preload factor on the static performance characteristics of micropolar lubricated two-, three-, and four-lobe bearings are investigated. For this purpose, modified Reynolds equation for micropolar fluids is solved by FEM, to find the fluid film pressure.Then, in turn, bearing performance characteristics, namely, load-carrying capacity, attitude angle, frictional force, friction coefficient, and side leakage flow are calculated. Results show that, in general, micropolarity of the lubricant improves the performance of the bearings; however, non-circularity parameter of the lobe of the bearings, preload, has a favourable effect on certain performance characteristics of the bearings, such as the attitude angle which decreases as non-circularity of the bearing increases. The results further show that the rate of influence of preload factor on the performance characteristics of different lobed bearings is not the same. [ABSTRACT FROM AUTHOR]

This article describes two discontinuity effects that can occur when modelling radial tilting pad bearings subjected to high dynamic loads. The first effect to be treated is a pressure build-up discontinuity effect. The second effect is a contact-related discontinuity that disappears when a contact force is included in the theoretical model. Methods for avoiding the pressure build-up discontinuity effect are proposed. [ABSTRACT FROM AUTHOR]

An experimental assessment of the influence of angle between the groove axis and the load line on the thermohydrodynamic behaviour of twin groove hydrodynamic journal bearings has been undertaken. At nine different loading direction angles, the oil—bush interface temperature profiles, oil outlet temperature, maximum bush temperature, total flow rate, and oil flow rate through each groove were measured for variable applied load and oil supply pressure while the feeding temperature was kept constant (40°C). To the authors’ knowledge, this is the first study of the influence of loading direction on the performance of journal bearing with two axial grooves in which the flow rate were measured in each groove for different working conditions under laminar regime. It was found that the variation of loading direction has a strong effect on the bearing performance. Under some running conditions, negative lubricant flow rate (hot oil reflux) at one groove was detected. This seldom-reported phenomenon was found to affect the bearing performance dramatically. Increasing supply pressure yielded a temperature decrease, especially for high loads, and sometimes prevented the occurrence of hot oil reflux. [ABSTRACT FROM AUTHOR]

Results of a study to examine a unique idea of self-levitating journal bearing are presented in this article. The idea represents a radical departure from the current bearing technology. It utilizes acoustic levitation, which relies on the sound energy radiated by an object supporting a load. Acoustic levitation has been demonstrated to support loads of up to 10 kg. In order to support a load the acoustic wave emitted by the radiating surface must be reflected back towards the radiating surface by the levitating object. The radiation pressure increases as the gap between the source of sound and levitating object narrows. Computer simulation and experimental testing of a prototype device were carried out and provided a conclusive proof of the idea. [ABSTRACT FROM AUTHOR]

This article summarizes the work carried out in the development of hydrodynamic lubricated journal bearings with magnetic fluids. Two different fluids have been analyzed: one is the ferrofluid from FERROTEC APG s10n and the other is the magnetorheological (MR) fluid from LORD Corp., MRF122-2ED. Theoretical analysis has been carried out with numerical solutions of Reynolds equation, based on apparent viscosity modulation for ferrofluid and Bingham model for MR fluid. To validate this model, one test bench has been designed, manufactured, and set up, where preliminary results showed in this article demonstrate that magnetic fluids can be used to develop active journal bearings. [ABSTRACT FROM AUTHOR]

Many automotive turbochargers operate in the self-excited unstable region. In the past these instabilities have been accepted as unavoidable, but recent developments in analysis and instrumentation may make it possible to reduce or eliminate them. A test stand being developed at Virginia Tech has been used to measure the vibrations of a 3.9 liter diesel engine stock turbocharger with floating bushing journal bearings. Vibration spectrum content clearly identifies the shaft instabilities and provides the basis for additional evaluation of future bearing design modifications. This paper provides additional experimental vibration data reduction that will be useful for future research direction to fully understand the turbocharger dynamic instability. [ABSTRACT FROM AUTHOR]

In this article, a test methodology of model scale is used to visualize the processes taking place during operation and subsequent breakdown in the boundary layer of journal bearing materials. The investigated materials are alloys of aluminium (Al99.6, AlSn20Cu, AlSn40) and tin (SnSb7.5Cu3.5). The utilized test configuration is based on a ring-on-disc system. The employed seizure test procedure was designed in previous studies. The tribometric results clearly show differences in the tribological behaviour between the materials. A series of tests are carried out to explain the observed differences. The frictional surfaces and microsections are observed using microscopy and microindentation. Pure aluminium is characterized both by a potentially low coefficient of friction and an unforgiving overload behaviour. This is due to the fact that components based on pure aluminium tend to lose system stability spontaneously. As more of the soft-phase Sn is added to the matrix, the emergency running properties improve. The system behaves less erratically and the overload behaviour improves. However, the mechanical strength and the wear resistance drop. Tribological functional models summarize the results of tribometrics and damage analysis. These models are the key to further optimization of the materials. [ABSTRACT FROM AUTHOR]

Measurements of total engine bearing friction have been carried out on a single-cylinder gasoline engine under fired conditions. The bearing friction was measured indirectly by measuring the total engine friction, piston assembly friction, and valve train friction. Total engine friction was measured via pressure--volume (PV) diagram, whereas piston assembly friction measurement was carried out using the indicated mean effective pressure method. Valve train friction was measured using instrumented camshaft drive pulleys. All the engine auxiliaries were independently driven electrically. Engine bearing friction was measured under different engine operating conditions. The hydrodynamic lubrication regime occurred under most of the engine operating conditions, although at lower engine speeds and higher lubricant temperatures a transition from hydrodynamic to boundary/mix lubrication regime occurred. The effect of two different lubricants SAE 0W20 and SAE 5W30 on engine bearing performance was investigated. The adverse effects of viscous oil at low lubricant temperature were notable, as were the benefits at higher lubricant temperature. Predicted results from a number of engine bearing friction mathematical models have been compared with the experimental results. The comparative study showed that the results generated through the short bearing mobility method under cavitation conditions were close to the experimental data. This experimental system can be used to study bearing design parameters, bearing materials, lubricant chemistry, and engine operating conditions on the bearing performance under realistic conditions in its original environment. [ABSTRACT FROM AUTHOR]

'Offset' journal bearings provide an alternate design approach for problematic applications lacking both load reversal and adequate journal angular velocity. More than a quarter century has gone by since the first publication of a dynamic analysis for offset journal bearings (and the concept of such bearings is much older still). Since then it has been found that the 'squeeze film' support crucial to successful operation of these bearings can be extremely sensitive to refilling rate from cavitated film regions, requiring a mass-conservative cavitation analysis that was unavailable earlier. Additionally, the earlier analyses were based on semi-analytic approximate solutions to the Reynolds equation, rather than on later numerically exact full solutions. The present work addresses these shortcomings and attempts thereby to put the design of these unique bearings on a sounder and more reliable footing. Thus, the choice of 'revisited' over 'reviewed' in the title is a deliberate one. Rather than a simple review of previous work, the article is a revisit of the design analysis of offset journal bearings using modern methods not available to previous authors. Included are dimensional sample applications and non-dimensional parametric optimization studies showing an order of magnitude improvement in predicted cyclic minimum film thickness and a modest reduction in cyclic maximum film pressure. [ABSTRACT FROM AUTHOR]

This article considers the effects of non-linearity in the dynamic properties of a journal bearing and presents a method of constructing the calculations needed in the identification of a non-linear dynamic model of the oil film. The new calculation method, together with its background and development is described and illustrated. The method uses frequency-domain descriptions of the test waveforms and accommodates any reasonable oil film model. It can also be used to predict the orbits. It has been applied to both theoretical and experimental results, and a robust procedure based on the new calculation method for the extraction of higher-order dynamic oil film coefficients is proposed and described. [ABSTRACT FROM AUTHOR]

The article presents abstracts of current literature relating to shock and vibration. They include "Active control of noise from a vacuum cleaner," "Hermetically sealed oil-free turbocompressor technology," and "Near field acoustic holography (NAH) theory for cyclostationary sound field and its application."