Oil-film Journal Bearings Research Articles

Passive vibration absorbers for vibration reduction in the multi-bladed rotor with rotor and stator contact

Contact phenomena are among the most undesirable incidences in a rotor dynamic system where its emergence could be due to the centrifugal force generated by an unbalance disk. In this work, a Jeffcott rotor supported by oil film journal bearings and with rigid blades is taken into account. The long oil film lubrication is considered where the axial flow is negligible. The rotational speed is taken as a control parameter, and the analysis is performed for two different clearances considering the rotor with three, four, and five blades. To reduce the vibrations of the system with the purpose of contact elimination, a tuned mass damper and a nonlinear energy sink as passive absorbers are utilized. Then, by an optimization process applying a complex averaging method, the optimum parameters for each absorber are calculated. Due to the critical behavior of the system in the lower clearance values, double coupling of the absorbers is suggested. The results demonstrate that single coupling of the absorbers can considerably reduce the vibration of the system. On the other hand, for the lower clearance value single coupling is not efficient, and double coupling could be utilized to mitigate the unwanted vibrations of the system.

Tribo-design of lubricants for power loss reduction in the oil-film bearings of a process industry machine: Modelling and experimental tests

This paper addresses the optimization of the tribological characteristics of lubricating oils used in the process industry. In many cases, the machines are organized in several “stands” to form “lines” and are equipped by spindles supported by oil-film journal bearings that are fed by the same oil. The modelling of a steel roll forming line is presented by using a thermo-elasto-hydro-dynamic model for the calculation of the power dissipated in each journal bearing. The optimal lubricating oil characteristics are defined by means of a multivariate optimization on the parameters of viscosity, temperature and thickness of the oil-film. The results of the experimental tests are shown for the oil used in the real plant and the new oil formulated by simulations. • We investigated the behaviour of all the oil-film bearings of a steel roll forming machine. • We developed a detailed TEHD model for the evaluation of the bearing power loss. • We performed a parametric analysis on the viscosity parameter of the lubricant. • We selected the viscosity properties of a new oil for the reduction of the power loss. • We performed experimental tests on the new oil defined by simulations.

Control of supply oil quantity for suppression of temperature rise in oil film journal bearing under starved lubrication

Control of supply oil quantity for suppression of temperature rise in oil film journal bearing under starved lubrication

Development and Validation of a Three-Dimensional Computational Fluid Dynamics Analysis for Journal Bearings Considering Cavitation and Conjugate Heat Transfer

Computational fluid dynamics (CFD) analysis, which solves the full three-dimensional (3D) Navier–Stokes equations, has been recognized as having promise in providing a more detailed and accurate analysis for oil-film journal bearings than the traditional Reynolds analysis, although there are still challenging issues requiring further investigation, such as the modeling of cavitation and the modeling of conjugate heat transfer effects in the CFD analysis of bearings. In this paper, a 3D CFD method for the analysis of journal bearings considering the above two effects has been developed; it employs three different cavitation models, including the Half-Sommerfeld model, a vaporous cavitation model, and a gaseous cavitation model. The method has been used to analyze a two-groove journal bearing and the results are validated with experimental measurements and the traditional Reynolds solutions. It is found that the CFD method which considers the conjugate heat transfer and employs the gaseous cavitation model gives better predictions of both bearing load and temperature than either the traditional Reynolds solution or CFD with other cavitation models. The CFD results also show strong recirculation of the fresh oil in the grooves, which has been neglected in the traditional Reynolds solution. The above results show conclusively that the present 3D CFD method considering the conjugate heat transfer and employing the gaseous cavitation model provides an efficient tool for more detailed and accurate analysis for bearing performance.

A new nonlinear dynamic analysis method of rotor system supported by oil-film journal bearings

The strong nonlinear behavior usually exists in rotor systems supported by oil-film journal bearings. In this paper, the partial derivative method is extended to the second-order approximate extent to predict the nonlinear dynamic stiffness and damping coefficients of finite-long journal bearings. And the nonlinear oil-film forces approximately represented by dynamic coefficients are used to analyze nonlinear dynamic performance of a symmetrical flexible rotor-bearing system via the journal orbit, phase portrait and Poincaré map. The effects of mass eccentricity on dynamic behaviors of rotor system are mainly investigated. Moreover, the computational method of nonlinear dynamic coefficients of infinite-short bearing is presented. The nonlinear oil-film forces model of finite-long bearing is validated by comparing the numerical results with those obtained by an infinite-short bearing-rotor system model. The results show that the representation method of nonlinear oil-film forces by dynamic coefficients has universal applicability and allows one easily to conduct the nonlinear dynamic analysis of rotor systems.

Effect of unbalanced magnetic pull and hydraulic seal force on the vibration of large rotor-bearing systems

The influence of unbalanced magnetic pull (UMP) and hydraulic seal force on the vibration of large rotor-bearing systems is studied. The UMP caused by rotor eccentricity imposes important effects on rotating machinery, especially for large generators such as water turbine generator sets, because these machines operate above their first critical speed in some instances and are supported by oil film bearings. A magnetic stiffness matrix for studying the effects of the UMP is proposed. The magnetic stiffness matrix can be generated by decomposing the expression of air gap magnetic field energy. Two vibration models are constructed using the Lagrange equation. The difference between the two models lies in the boundary support condition: one has rigid support and the other has elastic bearing support. The influence of the magnetic stiffness and elastic support on the critical speed of the rotor is studied using Lyapunov nonlinear vibration stability theory. The vibration amplitude of the rotor is calculated, taking the magnetic stiffness and horizontal centrifugal force into account. The unbalanced hydraulic seal force is produced because of the asymmetry of seal clearance. This imbalance is one of the factors that causes self-excited vibration in rotating machinery, and is as important as the UMP for large water turbine generator sets. The rotor-bearing system is supported by an oil film journal bearing, whose characteristic also impose considerable influence on vibration. On the basis of the above-mentioned conditions, a three-dimensional finite element model of the rotating system that includes the oil film journal bearing is constructed. The effect of the UMP and unbalanced hydraulic seal force is considered in the construction, and studied in relation to the magnetic parameters, seal parameters, journal bearing stiffness, and outer diameter of the rotating machine critical speed. Conclusions may benefit the dynamic design and optimized operation of large rotating machinery.

1305 給油溝付きジャーナ油膜すべり軸受内流れの可視化(トライボロジー(1))

Oil film journal bearings are used widely in many rotational machines such as engines, turbines, compressors. The oil film in journal bearings had been investigated experimentally and theoretically by many researchers. In this study, we focus on the behavior of the oil film. By using the semiconductor laser unit mounting multi laser elements proposed in this study and high-speed camera, experimental visualization of the oil films are conducted under starved lubrication and flood lubrication conditions. Moreover the video data are analyzed by PIV (particle image velocimetry) and the characteristics of oil flow especially around cavitations in flooded and starved lubrications are compared.

Effect of Supply Oil Quantity on Stability of Oil Film Journal Bearing and Its Hysteresis Characteristics

Effect of Supply Oil Quantity on Stability of Oil Film Journal Bearing and Its Hysteresis Characteristics

Nonlinear dynamic analysis of a rub-impact rotor supported by oil film bearings

A general model of a rub-impact rotor system is set up and supported by oil film journal bearings. The Jacobian matrix of the system response is used to calculate the Floquet multipliers, and the stability of periodic response is determined via the Floquet theory. The nonlinear dynamic characteristics of the system are investigated when the rotating speed and damping ratio is used as control parameter. The analysis methods are inclusive of bifurcation diagrams, Poincare maps, phase plane portraits, power spectrums, and vibration responses of the rotor center and bearing center. The analysis reveals a complex dynamic behavior comprising periodic, multi-periodic, chaotic, and quasi-periodic response. The modeling results thus obtained by using the proposed method will contribute to understanding and controlling of the nonlinear dynamic behaviors of the rotor-bearing system.

Cavitation Mechanism of Oil-Film Bearing and Development of a New Gaseous Cavitation Model Based on Air Solubility

Cavitation phenomenon in lubricants significantly influences the performance of associated machinery. In this paper, the cavitation mechanism of an oil-film bearing is attributed to gaseous cavitation, and a new gaseous cavitation model based on air solubility in the lubricant is presented. The model is validated using the Reynolds equation algorithm for fixed-geometry oil-film journal bearing, and the predicted results at different eccentricity ratios show good agreement with published data. The analyses show that gaseous mechanism can explain the cavitation phenomena that occur in the bearing except for very heavy load cases. In particular, this new model is compatible with the Jakobsson–Floberg–Olsson condition. Therefore, the new model has an explicit physical meaning, can produce good results, can identify whether vaporous cavitation occurs, and more importantly, can provide a novel means of developing cavitation models for low-vapor-pressure lubricants.

Nonlinear Simulation of Rotor Dynamics Coupled with Journal and Thrust Bearing Dynamics under Nonlinear Suspension

This study performs a dynamic analysis of a rotor supported by an oil-film journal and thrust bearings. The analysis of the rotor-bearing system is investigated under the assumptions of an incompressible lubricant, a flexible rotor, and negligible side leakage in the thrust bearing. The numerical results show that the nonlinear dynamics of the system vary with the nondimensional speed ratio and the initial value of the displacements in the horizontal, vertical, and axial directions. Specifically, some routes of periodic responses, subharmonic motions into chaos, out of chaos to subharmonic responses, or suddenly into chaos, suddenly out of chaos to periodic ones were found.

Effects of the Hot Alignment of a Power Unit on Oil-Whip Instability Phenomena

This paper shows the results of the analysis of the dynamic behaviour of a power unit, whose shaft-train alignment was significantly influenced by the machine thermal state, that was affected in operating condition by high subsynchronous vibrations caused by oil-whip instability phenomena. The dynamic stiffness coefficients of the oil-film journal bearings of the generator were evaluated considering the critical average journal positions that caused the instability onsets. By including these bearing coefficients in a mathematical model of the fully assembled machine, the real part of the eigenvalue associated with the first balance resonance of the generator rotor became positive. This paper shows the successful results obtained by combining diagnostic techniques based on mathematical models of journal bearings and shaft train with detailed analyses of monitoring data aimed to investigate the effects of the hot alignment of rotating machines on the occurrence of oil-whip instability onsets.

Development of safety and secure system of high-speed oil film journal bearing using supply oil quantity control

This paper describes the safety operating system of oil film journal bearing using supply oil control system. Journal bearings are widely used for high speed rotating machinery such as turbines, pumps, and compressors because they can support the high speed rotating shaft across the oil lubricating film. However, in higher speed self-excited vibration which is called oil whip is generated and then they cause the seizure of bearing surface or breakdown of the machinery. It is, therefore, important to avoid the oil whip. Hashimoto et. al. suggested the stabilization method of the journal bearing using starved lubrication and the applicability of the method is verified theoretically and experimentally. The next step of the stabilization method is decreasing the several risks such as the contact of the bearing excess of decreasing the supply oil quantity. In this paper, we propose the safety and secure system by controlling the supply oil quantity for stabilization of the journal bearing using the starved lubrication and the effectiveness of the system is verified experimentally.

Chaos and bifurcation of a flexible rub-impact rotor supported by oil film bearings with nonlinear suspension

Abstract The dynamic analysis of the rotor-bearing system is studied in this paper and is supported by oil film journal bearings. An observation of a nonlinearly supported model and the rub-impact between rotor and stator is needed for more precise analysis of rotor-bearing systems. Inclusive of the analysis methods of the dynamic trajectory, the power spectra, the Poincare maps, the bifurcation diagrams and the Lyapunov exponent are used to analyze the behavior of the rotor centre and bearing centre in the horizontal and vertical directions under different operating conditions. The periodic, quasi-periodic, sub-harmonic and chaotic motion are demonstrated in this study. A special phenomenon is occurring at s = 2.27, the motions of the bearing centre and the rotor centre in the horizontal direction are still at chaotic motions but the motions of the bearing centre and the rotor centre in the vertical direction are at 3T-periodic motions. It is concluded that the trajectory of rotor centre and bearing centre have undesirable vibrations. With the analysis of the dynamic behavior of these operating conditions, the theoretical and practical idea for controlling rotor-bearing systems with rub-impact condition can be more precise.

2605 ジャーナルすべり軸受に生じるオイルホイップの慣性効果

The inertia effects of oil-whip generated in full-circular oil film journal bearings were originally found by Pinkus. After this interesting reporting, several research workers tried to develop the theoretical and experimental studies on the phenomena. However, only a few papers can be available on this topics in the past several decades, and it is not yet clear the mechanism of inertia effects of oil-whip even in the present days. This report describes the experimental study of examining the inertia effects in full circular journal bearings lubricated under the submerged conditions relating with the visual observation of cavitation pattern.

Stability of Flexibly Supported Oil Journal Bearings Using Non-Newtonian Lubricants: Linear Perturbation Analysis

The purpose of this paper is to study the effect of non-Newtonian lubricant on the stability of oil film journal bearings mounted on flexible support using linear perturbation technique. The model of non-Newtonian lubricant developed by Dien and Elrod is taken into consideration. The dynamic co-coefficients are calculated for different values of power law index and length to diameter ratio. These are then used to find stability margin for different support parameters to study the effect of the non-Newtonian lubricant.

Effect of fluid inertia on stability of flexibly supported oil journal bearings: linear perturbation analysis

A theoretical analysis to study the effect of fluid inertia on the stability of oil film journal bearings mounted on flexible support using linear perturbation technique is presented. The Navier–Stokes equations have been solved using the parabolic velocity profile. The dynamic coefficients are calculated without neglecting the mass of the oil in the bearing for different length to diameter ratios and modified Reynolds numbers. These are then used to find stability margin for different support parameters to study the effect of fluid inertia.

Measurement of Oil Film Journal Bearing Damping Coefficients—An Extension of the Selected Orbit Technique

This paper describes a novel experimental procedure for measuring the four velocity or damping coefficients of an Oil Film Journal Bearing from imposed dynamic orbits. All four damping coefficients are derived from one imposed journal center dynamic orbit and, therefore, may be regarded as being obtained at the same time. The method requires the production of a “figure of eight” shaped orbit and utilizes the “cross-over” point therein. Coefficients are initially evaluated in a coordinate system which is chosen to align with the designated parts of the measured orbit. Each coefficient is then separately evaluated from single values of instantaneous imposed force and resulting journal center velocity. Coefficients are then converted into any other desired axes system. All the benefits of the original selected orbit technique are retained. The presented method places much less severe demands on experimental procedure. An available example illustrates the technique. A realistic uncertainty analysis for this example is included. Indications are provided which show how the orbit features may be adjusted to substantially reduce uncertainty.

Theoretical Prediction of Journal Center Motion Trajectory in Two-Lobe Hydrodynamic Journal Bearings

In this study, the theoretical prediction of a journal center motion trajectory for high-speed rotors supported by two-lobe hydrodynamic oil film journal bearings is presented for three different values of the noncircular ratios, γ=0, 0.5 and 1.0. In order to obtain values for the oil film forces used in the equations of motion for rotor-bearing systems, the Reynolds equation governing the oil film pressure generated in the bearing gap was solved using the semianalytical finite-element method for each time step. Furthermore, for each time step, the nonlinear equations of motion for a rigid rotor supported by two identical aligned bearings were solved using the improved Euler integration method. From the numerical results, the relations between the journal center motion trajectory and the corresponding pressure distribution were examined theoretically, and the effect of the noncircular ratio on the stability of rotor bearing systems was clarified for the cases of both balanced and unbalanced rotors.

Experimental Investigation of Hybrid Bearings

A new type of bearing test rig has been set up for static and dynamic tests of oil-film journal bearings. Micro pressure and displacement transducers contained in the shaft measure the distribution of oil film pressure and thickness, and two electromagnetic exciters are located under and behind the test bearing to excite the test bearing in order to obtain its eight dynamic stiffness and damping coefficients. A misalignment jig was employed to align or misalign the test bearing with respect to the axis of the shaft