Model For Journal Bearings Research Articles

Entropy-based fluid–solid–thermal coupled wear prediction of journal bearing during repeated starting and stopping

The novelty of the present study is to construct an Entropy-based wear and fluid-solid-thermal (FST) coupled model for journal bearings, which reveals the transient interaction behavior between wear evolution and FST evolution during repeated starting and stopping. The wear rate is measured experimentally and the contact temperature, friction coefficient and normal contact force are obtained from the validated FST model. Wear tests for the lubricated journal bearing at three constant speeds are used to validate the predicted wear rate. Numerical calculations give the time-varying wear and FST evolution of journal bearings during repeated starting and stopping at the same or different start-stop time, including wear rate, wear depth, temperature, fluid pressure and contact pressure. The effects of the bearing thickness, maximum speed, radial clearance and load on the wear and FST performances are evaluated. The simulation results reveal that the rate of change of wear rate in the start-stop cycle first increases rapidly and then decreases slowly as the number of start-stop cycles increases. The distributions of the contact pressure and the fluid pressure become wider along the circumferential direction with the increase in the number of start-stop cycles while the maximum values become smaller. The maximum wear depth increases with increasing start-stop time for an identical number of start-stop cycles, and the shorter the start-stop time is, the higher the maximum temperature tends to be. Furthermore, the effect on the maximum wear depth and maximum temperature of journal bearings will become significant when the maximum speed and bearing thickness are relatively small or the radial clearance and load are relatively large.

Modeling of Journal Bearings for Wear Diagnosis and Its Verification Using SVM

Recently, deterioration of infrastructure facilities has become problem. To reduce inspection costs, wear diagnosis of journal bearings in operating conditions using machine learning has been studied. However, constructing a highly accurate machine learning model requires training data, and it may be difficult to conduct numerous tests depending on the application. In this study, a mathematical model of a rotor system for wear diagnosis of journal bearings was developed, and the vibration data was obtained when the clearance changed due to wear. Then, changes in the features used for condition monitoring were examined. Furthermore, the important features for wear diagnosis were selected and SVM models were constructed to verify the mathematical model.

Subcritical behaviour of short cylindrical journal bearings under periodic excitation

Rotating machinery supported on journal bearings is affected by forces due to rotating unbalance and pressure gradients in the oil film. The interaction of these forces can evoke nonlinear behaviour, including asynchronous motion and even chaos. This work attempts to characterise the sub-synchronous motion of the rigid rotor supported on cylindrical journal bearings due to the abovementioned interaction. The analysis focuses on the rotor behaviour at the rotor speeds lower than the threshold speed for oil whirl, associated with sub-synchronous vibration of magnitude equaling the bearing clearance. It is shown that the sub-synchronous vibration can occur well before reaching the threshold speed and that the underlying period-doubling bifurcation depends on the amount of the rotating unbalance. The rotor response and stability are analysed using a numerical continuation method employing the infinitely short journal bearing model. Continuation results are further validated by time simulations which utilise the finite difference method to compute the hydrodynamic forces. The validation process employs bifurcation diagrams, Poincaré sections and numerical estimates of the largest Lyapunov exponents.

High-Speed Digital Photography of Vapor Cavitation in a Narrow Gap Flow

Digital photography of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, demands a high time-resolution and a solution to approaching the particular spatial restrictions. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for vapor bubble generation and collapse is about one millisecond, respectively. The authors have developed a Journal Bearing Model Experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. Compared with other methods, e.g., pulsed laser, electrical discharge, tube arrest, applied to produce vapor bubbles, the work on hand applies a dynamic variation of the minimum film thickness to produce suction cavitation, which proves the applicability of this novel approach to study vapor cavitation in fluid films similar to lubricant flows. The results are obtained by means of digital high-speed photography of vapor bubbles from inception to implosion triggered by the dynamic variation of the minimum film thickness of a narrow gap flow. Moreover, the results are set in relation to a general overview of cavitation processes.

Research on Start-Stop Performance of Journal Bearing Based on an Isothermal and Mixed Lubrication Model With Different Acceleration and Deceleration Forms in Consideration

Abstract In order to explore the influence of different acceleration and deceleration forms on the bearing performance during acceleration and deceleration, an isothermal and mixed lubrication model for journal bearings was established. In this model, the fluid mechanics was solved by the Reynolds equation with mass conservation boundary condition, while the contact mechanics was predicted by Greenwood and Tripp (GT) contact model. By the developed model and using different functions of the shaft speed, the start-stop performances of the journal-bearing system under different acceleration scenarios were analyzed. The effects of working conditions, lubrication oil temperature, and bearing structure parameters on the start-stop performance of the journal-bearing system were studied. It was found that the larger starting acceleration can help the journal-bearing system enter the hydrodynamic lubrication faster in the acceleration phase. In the deceleration phase, slow deceleration helps the journal-bearing system maintain hydrodynamic lubrication for a longer time. The higher final speed, lower lubrication oil temperature, and lower bearing clearance can make the journal-bearing system have a better performance in the start-stop process.

CFD Analysis of Journal Bearing by Modifying The Roughness Surface

A journal bearing is a machine part that is used to ensure that the shaft always rotates in the opposite direction of the axis. Journal bearings are chosen because they are well-suited for use in mechanical systems that demand precision, speed, and a high load capacity. Recent years have seen an increase in research on how to improve the tribological performance of bearings by considering the design/architecture of these bearings. Numerous scientists have developed numerous methods for measuring pressure distribution, load-carrying capacity, acoustic power level, force friction, and cavitation phenomena in order to improve the performance of tribology, particularly in journal bearings. As a result, hydrodynamic lubrication was used in the investigation. The investigation was conducted using a computational fluid dynamics (CFD) three-dimensional journal bearing model that took cavitation into account. Additionally,the location of the heterogeneous rough/smooth bearing pattern was modified, as was the shaft rotational speed. The results of this study indicate that when the surface roughness is applied to journal bearings in a variety of locations with heterogeneous rough/smooth bearing patterns, the tribological performance of journal bearings is significantly improved, and that high shaft rotational speed has a significant effect on the tribological performance of journal bearings.

Analytical–numerical modeling of journal bearings with non-Newtonian fluids and cavitation effects

Analytical–numerical modeling of journal bearings with non-Newtonian fluids and cavitation effects

Kriging Approach Dedicated to Represent Hydrodynamic Bearings

Abstract The mathematical modeling of journal bearings has advanced significantly since the Reynolds equation was first proposed. Advances in the processing capacity of computers and numerical techniques led to multiphysical models that are able to describe the behavior of hydrodynamic bearings. However, many researchers prefer to apply simple models of these components in rotor-bearing analyses due to the computational effort that complex models require. Surrogate modeling techniques are statistical procedures that can be applied to represent complex models. In this work, Kriging models are formulated to substitute the thermohydrodynamic (THD) models of three different bearings found in a Francis hydropower unit, namely, a cylindrical journal (CJ) bearing, a tilting-pad journal (TPJ) bearing, and a tilting-pad thrust (TPT) bearing. The results determined by using the proposed approach reveal that Kriging models can be satisfactorily used as surrogate THD models of hydrodynamic bearings.

Transient tribo-dynamic model for journal bearings during start-up considering 3D thermal characteristic

The study presents a transient tribo-dynamic model for journal bearings to reveal the mutual effect between the mixed thermoelastohydrodynamic (mixed-TEHD) performance and the journal dynamic behavior during start-up. In the developed model, the bearing shell, oil film, and journal are considered as a heat conduction coupling system, whose transient 3D thermal characteristic is determined by a general transfer equation. The established model is verified by comparing the numerical predictions, including the transient temperature distribution, maximum temperature, axis orbit and contact time, with the published results. The evolution of the mixed-TEHD performance during start-up is presented. And the impacts of the acceleration time, radius clearance and bearing shell thickness on the transient mixed-TEHD performance are evaluated. The simulation results indicate that the dynamic contact load during start-up may be underestimated when the thermal characteristic is absent. The simulation results also indicate that a maximum temperature can be observed before the hydrodynamic pressure is fully formed. Furthermore, the present study demonstrates that although a short acceleration time can reduce the asperity contact pressure, it leads to a relatively large temperature rise. The present study also demonstrates that a smaller radial clearance and a thinner bearing shell tend to generate a larger maximum temperature and thermal expansion, which leads to the increase in the risk of the thermally induced failure during start-up.

Analysis of a rotor-bearing nonlinear system model considering fluid-induced instability and uncertainties in bearings

In the analysis of rotating systems supported by hydrodynamic bearings, linear models and synchronous responses usually suffice. However, in some respects this type of approach fails to correctly describe these machine’s dynamic behaviour. Fluid-induced instabilities known as “oil whirl” and “oil whip,” in which unstable motion and residual unbalance cause a precessional vibration in the rotor system, are two conditions that point to the shortcomings of linear models. Furthermore, rotor-bearing systems possess inherent uncertainties, which a more reliable model must take into consideration. In this sense, a stochastic solution may be more adequate, and the traditional deterministic model should not be directly applied. Meanwhile, Monte Carlo simulation has a high computational cost, and deterministic problem solution for complex systems—such as rotating machinery modelling—requires a long period of evaluation. Thus, a method able to achieve better computational efficiency while remaining as convergent as Monte Carlo is necessary. Rotating machines under these conditions can be described by means of a nonlinear journal bearing model, and Monte Carlo can still be used to evaluate this stochastic solution, since it allows for the application of deterministic solvers. In this study, generalized polynomial chaos expansion was employed to analyse a rotor-bearing system’s stochastic response, and the stochastic collocation method was used to evaluate expansion coefficients. A convergence comparison between stochastic collocation and Monte Carlo simulations was performed, in order to validate the usage of polynomial approximation. Then, a sensitivity analysis was performed to determine which random parameter had the most effect over the system’s stochastic response. This analysis allowed for the identification of distinct rotational velocity regions of instability. Nonlinear characteristics presented themselves in the stochastic approach as well as in the deterministic models. Difficulties in analysing the sub-synchronous response by means of the proposed approach are discussed.

Effects of restitution coefficient and material characteristics on dynamic response of planar multi-body systems with revolute clearance joint

To study the effects of restitution coefficient and material parameters on the dynamic characteristics of planar multi-body systems with revolute clearance joints, a comprehensive methodology for clearance revolute joints in a planar multibody system is presented and analyzed. A new nonlinear contact force model, which accounts for the axial length of bearing and has a wide suitable range of impact situation, is presented to evaluate the contact force between journal and bearing. Furthermore, a modified Coulomb friction force model also presented to consider the effect of friction in clearance joint. Then, a typical journal-bearing model and a planar slider-crank mechanism has revolute clearance joint are used as examples. From the main numerical results under the different restitution coefficient and material parameters, it can be concluded that coefficient of restitution has significant effects on dynamic response of multi-body systems with revolute clearance joint. Additionally, materials of journal and bearing with smaller Young’s modulus will cause obvious delay on dynamic response of multi-body systems.

Effects of Shaft Axial Motion and Misalignment on the Lubrication Performance of Journal Bearings Via a Fast Mixed EHL Computing Technology

A mixed elastohydrodrynamic (EHL) model for journal bearings considering an axial flow due to shaft axial motion and misalignment is developed for lubrication performance evaluation. A new, faster mixed EHL computing technology utilizing the odd–even successive overrelaxation (OESOR) parallel numerical iterative method is proposed based on the red–black successive overrelaxation (RBSOR) method to minimize the execution time prolonged by the complexity caused by the axial flow and misalignments. The multithreaded computing scheme conducted by the OpenMP directive using different meshes and threads suggests that the OESOR method exhibits better efficiency. A series of transient analyses was conducted to solve the mixed EHL model with the parallel OESOR method. The results show that the axial flow and misalignments significantly affect the average pressure, hydrodynamic and asperity contact pressure, elastic deformation, and other characteristics of the journal bearings.

An approximate solution of oil film forces of turbulent finite length journal bearing

An approximate analytical method is proposed for calculating oil film forces of turbulent finite length journal bearings. The dynamic ‘π’ oil film assumption is usually taken to determine oil film forces in the dynamic analysis of hydrodynamic journal bearing-rotor systems. However oil film field is not in the ‘π’ zone, i.e. the start position of the oil film is not 0, and the termination position of the oil film is not ‘π’. Based on the variational principle, separation of variables is employed to obtain the pressure distribution in this paper. The pressure distribution of the infinitely long journal bearing model is taken as a circumferential separable function of the pressure distribution. The start and termination positions of oil film in the circumferential direction are determined by using the continuity condition. The axial separable function of the pressure distribution is obtained by the variational principle and the circumferential separable function. The results calculated by the proposed method are in good agreement with the oil film forces by the finite element method, and the computing cost is reduced greatly. Meanwhile, the influence of the parameters on the oil film forces is analyzed.

Development and Validation of a Three-Dimensional Multiphase Flow Computational Fluid Dynamics Analysis for Journal Bearings in Steam and Heavy Duty Gas Turbines

The traditional method for hydrodynamic journal bearing analysis usually applies the lubrication theory based on the Reynolds equation and suitable empirical modifications to cover turbulence, heat transfer, and cavitation. In cases of complex bearing geometries for steam and heavy-duty gas turbines, this approach has its obvious restrictions in regard to detail flow recirculation, mixing, mass balance, and filling level phenomena. These limitations could be circumvented by applying a computational fluid dynamics (CFD) approach, resting closer to the fundamental physical laws. The present contribution reports about the state of the art of such a fully three-dimensional multiphase-flow CFD approach, including cavitation and air entrainment for high-speed turbomachinery journal bearings. It has been developed and validated using experimental data. Due to the high ambient shear rates in bearings, the multiphase-flow model for journal bearings requires substantial modifications in comparison to common two-phase flow simulations. Based on experimental data, it is found, that particular cavitation phenomena are essential for the understanding of steam and heavy-duty-type gas turbine journal bearings.

Nonlinear Dynamic of a Geared Rotor System With Nonlinear Oil Film Force and Nonlinear Mesh Force

To investigate the effect of oil film force on a geared rotor system, a short journal bearing model was applied to represent nonlinear oil film force. A dynamic model of the geared rotor oil journal bearing system was presented. The nonlinear gear mesh force and nonlinear oil film force were considered in the model. The nonlinear dynamic responses of the system were investigated by numerical integration method. This article shows that when the rotational speed is relatively low, the vibration of the system is mainly affected by nonlinear mesh force. With the increase of rotational speed, the influence of nonlinear oil film force also increases gradually, and the subsynchronous forward precession phenomena appear. When the speed increases to a certain value, the amplitude of the subsynchronous forward precession exceeds the amplitude of the rotational frequency, and the nonlinear mesh force is greatly affected by the nonlinear oil film force. However, the linear oil film force does not affect the nonlinear mesh force. The subsynchronous forward precession is difficult to be predicted by linear oil film force which was previously applied. This experiment is performed to validate the correctness of the dynamic model presented, and the numerical integration results of low speeds are validated by the experimental data.

A comparison of methods of modelling the bearing surfaces in an internal combustion engine

An existing model for the dynamic analysis of the piston motion in an internal combustion engine has been modified to incorporate a simpler representation of the piston–cylinder interaction, and to represent the main and big-end bearings as lubricated rather than dry journal bearings. The results demonstrate that the differences in calculated bearing forces and output torques are negligible, indicating that the simple dry journal bearing model is sufficient, but show that the modelling of the interaction between piston and cylinder is considerably improved.

The analytical calculation of journal bearing parameters by means of the finite bearing theory

The present paper proposes an original analytical solution of the thermohydrodynamic lubrication and the validation of the model for journal bearings. The validation consists of comparing the hydrodynamic parameters calculated by means of numerical methods with those calculated analytically for the same journal bearing. Besides providing a higher simplicity of calculations in comparison with numerical methods, the new mathematical model ensures a very good precision for journal bearings having finite dimensions. Copyright © 2011 John Wiley & Sons, Ltd.

Balancing of a rigid rotor using artificial neural network to predict the correction masses

This paper deals with an analytical model of a rigid rotor supported by hydrodynamic journal bearings where the plane separation technique together with the Artificial Neural Network (ANN) is used to predict the location and magnitude of the correction masses for balancing the rotor bearing system. The rotating system is modeled by applying the rigid shaft Stodola-Green model, in which the shaft gyroscopic moments and rotatory inertia are accounted for, in conjunction with the hydrodynamic cylindrical journal bearing model based on the classical Reynolds equation. A linearized perturbation procedure is employed to render the lubrication equations from the Reynolds equation, which allows predicting the eight linear force coefficients associated with the bearing direct and cross-coupled stiffness and damping coefficients. The results show that the methodology presented is efficient for balancing rotor systems. This paper gives a step further in the monitoring process, since Artificial Neural Network is normally used to predict, not to correct the mass unbalance. The procedure presented can be used in turbo machinery industry to balance rotating machinery that require continuous inspections. Some simulated results will be used in order to clarify the methodology presented.

Subharmonic vibrations of a roll tube supported by plain journal bearings

This study presents a dynamic model for describing a journal bearing with circumferential waviness of the shaft journal. The journal bearing model is based on an analytical solution of the Reynolds equation and defines the non-linear hydrodynamic forces that act on the journal bearing. The waviness of the shaft journal is modelled through the use of a Fourier cosine series to describe the shape of the film thickness of the bearing. The waviness of the shaft journal can lead to subharmonic vibrations in which the natural vibration mode of the rotor is excited when the rotation speed is a fraction of the natural frequency of the rotor-bearing system. This phenomenon is investigated in this study utilizing the proposed bearing model in a rotor system simulation. The rotor system under investigation consists of a roll tube, two journal bearings and the supporting structure. The proposed journal bearing model can be used in a general multi-body or rotor dynamics computer code as the interface element between the rotor and the bearing housing. In this study, the model of the journal bearing is implemented in a commercial multi-body simulation software application. This approach enables a detailed analysis of the rotor-bearing system in such a way that the dynamic interaction of the rotor with the bearing is taken into consideration. The simulation result agrees with the experimental measurements obtained from a real roll tube system.

A mixed-TEHD analysis and experiment of journal bearings under severe operating conditions

The increasingly high demands for compact design require journal bearings to work under severe operating conditions. A steady-state mixed-TEHD (thermo-elasto-hydrodynamic) model for journal bearings has been developed. The model considers the fluid flow in the gap formed by rough surfaces, asperity contact, surface thermoelastic deformations, and a temperature–pressure–viscosity relationship for the lubricant, as well as an angular misalignment between the journal and the bearing. The model is verified with experimentally measured temperature data. Numerical simulations of the operation of a typical journal bearing are conducted and the importance of several contributing factors in mixed lubrication is discussed. A bearing temperature transition has been experimentally identified and numerically analyzed.