Fluid Film Bearings Research Articles

Comparative analysis on the performance envelope of a three-pad and four-pad active journal bearing

Controllable fluid film bearings with the ability to actively modify the operational conditions of rotor bearing systems possess high demand in the field of rotating machinery. Controllable or active bearing geometries can effectively enhance the performance envelope and life of machine support systems. Alternate forms of an active bearing pad geometry with unique adjustability features having the ability to modify the rotor bearing performance are presented in this study. The adjustability mechanism incorporated in the active pad geometry allows the multiple-bearing pads to translate radially and undergo tilted motions on a real-time basis. These pad adjustments are simulated by incorporating the radial and tilt adjustable functions into the developed theoretical model. In this study, a major focus is on a three-pad active bearing geometry and will further compare its steady state and dynamic performance behavior with a four-pad active bearing model. Effect of varying pad positions, pad angles and number of pads on the steady state and dynamic characteristics are analyzed in this study. For various combinations of operating parameters, pads adjusted to negative radial and negative tilt position were found to provide a notable improvement in the steady state and dynamic performance parameters. Identifying the optimal pad adjustments will further help to develop an active bearing with a feedback control mechanism operated on a real-time basis.

The Advances of Tribology in Materials and Energy Conservation and Engineering Innovation

Tribology has been significantly contributing to materials, energy conservation and engineering innovation. This paper elaborates the development of tribology considering in detail in energy factor, tribological role of efficiency in the society by introducing lubricants which reduces the effective friction while moving the mass which significantly improves overall efficiency of the process all though it was primitive. The objectives of the study of The American Society of Mechanical Engineers (ASME) are working to expand energy conservation, particularly through tribology, by doing things like evaluating the realistic effects of tribological innovation on conserving energy and trying to promote advanced energy technologies, identifying fields the application's location of new or existing Knowledge of tribology is anticipated to result in significant direct or indirect benefits, and so on. The strategy focuses on fluid film and rolling element bearings, consistently sophisticated metal processing, wear and friction reduction, variable power transmission, sealing technologies, automobile engines, and energy technologies. Additionally, the potential savings for various areas are detailed, as is a summary demonstrating the advantages that may be obtained with cutting-edge industrial machinery and processes, and comparing the prospective cost savings with the benefits ratio of the many key program features. road transportation for increasing energy efficiency. It was regarded as the most appropriate and advantageous aspects of tribology at the time to increasing productivity. Since then, numerous studies have focused on the study of industry-based machine and method-specific materials. Also, continuous variable transmissions are now found in many automobiles to enhance vehicle efficiency. Some future challenges were also looked at to plan and see how they can be tackled. The implementation of next level materials in different aspects of technology can lead to growth in the efficiency, quality of engineering parts and machines. This paper is a summary of the improvement in high performance materials both inorganic and organic based. It involves thin hard coverings of their growing importance in tribological improvements for tribo- engineering implementations are looked at and studied. Results from research concerning ceramics and ceramic properties, polymers and polymer properties as well as hard coatings and show the friction and wear attributes and their potential implementation for tribo- engineering. Greasing and friction have a strong relationship with wear. The study of these three topics is essentially what tribology entails. It deals with moving, interacting surfaces in science and technology. To better regulate friction and wear, hard or soft film coating, alloying, and composite structures have all been enhanced. It is accomplished by enhancing the lubricity and wear life of materials and surfaces using novel, modified lubricants and ideas that have been put to the test in challenging tribological applications. The development of new generations of self-lubricating coats with multilayered architecture due to recent advances in thin film deposition methods treatments. The field of tribology is crucial to lowering the levels of emissions from various industries because it is being used to cut down on the amount of unnecessary energy used by mechanisms. Understanding the functions of friction and wear between two surfaces that come into contact has been the domain of tribology for many decades. They have applied this knowledge to make mechanisms more energy efficient by only using what is necessary to power them and reducing the amount of energy lost through wear and friction.

Micro-grooved hybrid spherical thrust bearing with Non-Newtonian lubricant behaviour

Recent tribology research has primarily focused on leveraging engineered grooved surfaces to enhance the lubrication performance of tribo-contacts. The performance of fluid film bearings may be improved by using a properly designed micro-groove on the surface of bearing. This paper deals with the performance of micro-grooved hole-entry hybrid spherical thrust bearing (HSTB) considering Non-Newtonian behavior of the lubricant. To analyse the Non-Newtonian behaviour of lubricant the cubic law model has been used. The solution of the governing Reynold equation in the fluid film domain of the hole-entry hybrid spherical thrust bearing is obtained by the FEM. In this study, the influence of rectangular and circular shaped micro-groves has been analysed. The parametric analysis has also been performed to obtain the optimum attributes (i.e. w¯g,d¯g,l¯gr) of the micro-grooves for both the shapes. The present investigation shows that the performance of the hole-entry hybrid spherical thrust bearing gets enhanced by considering the micro-grooves on the surface of bearing. Furthermore, the bearings performance is affected by the geometry of the micro-groove used. The value of fluid film reaction (F¯y) and stiffness coefficient (S¯) is observed to be increased by 23.33% and 343.98% at εy = 0 and κ¯=1 for the case of rectangular-shaped micro-grooved hole-entry HSTB configuration.

Investigation of stiffness and damping coefficients in fluid film bearing with bio-oils and mineral-based oil

Rotating machinery utilizes fluid film bearings because of their good load carrying capacity and inherent damping properties. Fluid film bearings offer stiffness and damping parameters to ensure dynamic stability. The damping and stiffness characteristics of oil film significantly change the critical speed and unbalance response of the rotor. The damping and stiffness coefficients (direct, cross-coupled) may lead to system instability, also known as self-excited vibrations. Bio-oils have good tribological and physiochemical properties. They are also environment-friendly and bio-degradable. In this work, bio-oils (rapeseed, palm olein, and soybean) are evaluated in terms of their dynamic characteristics to that of mineral-based SAE40 lubricant for journal-bearing applications. The analytical extraction of damping and stiffness coefficients is performed based on the experimental dynamic viscosity data at different temperatures. In comparison to SAE40, the bio-oils have shown improved responsiveness. Bio-oils showed lower cross-coupled stiffness coefficients than SAE40, the primary source of rotor instability. The main contribution of this study is that it provides damping and stiffness coefficients for various bio-oils at different eccentricity ratios and viscosities for different types of oils. This may be used to characterize the dynamic properties of the fluid film bearing under various operating circumstances. It is concluded that the difference in cross-coupled stiffness favors bio-oils. Whereas, the difference in cross-coupled damping favors SAE40 by around 6%. This discrepancy is decreased to less than 2% for all oil’s final eccentricity ratio values (bio-oils and SAE40).

Theoretical and experimental study of motion suppression and friction reduction of rotor systems with active hybrid fluid-film bearings

Active bearings (including fluid film bearing) are efficient in reducing vibration and improving dynamic performances of rotary machinery. The control systems have significant influence in the working processes of rotor-bearing systems, including hydrodynamic and tribological performance. The aim of the study is to investigate the feasibility of the joint controlling of the rotor vibration and simultaneously minimizing friction losses in active hybrid bearing (AHB) – rotor systems. The theoretical and experimental results show the rotor vibrations are reduced at the energy-efficient operating modes under complex loads. The theoretical study is performed by the verified simulation models of rigid rotors with thrust and journal AHB. The artificial neural networks are proposed to calculate the bearing forces to provide a balance of accuracy and computational costs. The controller for the thrust AHB is based on the PI law, while the journal AHB controller implements an adaptive nonlinear proportional law with integrating properties. Both controllers perform well in reducing the vibration magnitudes for the systems under the periodic and constant load forces. Such rotor motion control is also able to reduce power losses caused by the viscous friction in AHB. The theoretical study shows the relations between the position of the rotor with AHBs and the magnitude of the viscou forces of the lubricant film. The minimum friction areas could be used to choose the setpoints for AHBs’ controllers for joint rotor motion and friction control.

Nonlinear Vibration and Stability Analysis of Flexible Rotor Supported on SFD by IHB Method

In this paper, the nonlinear vibration of a flexible rotor supported on squeeze-film dampers (SFDs) with centering springs is analyzed using the incremental harmonic balance (IHB) method, and bifurcation phenomena appeared in the resonance region are investigated. Complex nonlinear phenomena occur in this system due to the interaction of the fluid-film forces and the unbalance forces of the rotor in the SFD. Systems with these complex nonlinearities cannot be solved using the classical IHB methods. To overcome this problem, the classical IHB method and the alternating frequency/time (AFT) method are combined. The processing of linear matrices is performed in the same way as the classical IHB method, and only the processing of nonlinear force matrix caused by fluid–structure interaction is modified (application of transformation matrix). To prove the validity of the proposed method, the results calculated using the proposed method are compared with the results calculated using the Runge–Kutta method and the results presented in reference. Then, frequency response curves according to changes in bearing parameter [Formula: see text], gravity parameter [Formula: see text], stiffness ratio [Formula: see text], mass ratio [Formula: see text], and unbalance parameter [Formula: see text] are constructed. Stability and bifurcation analyses of the calculated solution are performed using the Floquet theory. The proposed method can be effectively applied to the nonlinear vibration analysis of rotor systems supported on fluid-film bearings.

Experimental thermodynamic analysis of automotive turbochargers using fluid film bearings with different groove shapes

Experimental thermodynamic analysis of automotive turbochargers using fluid film bearings with different groove shapes

Dynamic performance and stability characteristics of a multi pad externally adjustable fluid film bearing

ABSTRACT Due to the recent advances in the development of smart rotating machineries, there is a high demand for automated support bearings with efficient integrated control systems. Existing research studies have indicated that high-end performance can be attained from automated bearings through effective control and modification of the bearing performance parameters. In this study, an innovative journal bearing geometry with multi-control operations is presented. The four controllable bearing pads enclosed in the bearing casing have a novel feature to translate radially and undergo controlled tilt motions. The multi-control bearing system with radial and tilt pad motions will significantly influence the stability responses of the rotorsystem, which is theoretically analysed in this study. To predict the variation in film thickness for varied pad adjustments, a modified film thickness equation is incorporated in the linearised perturbed model for dynamic analysis. A notable variation in dynamic coefficients and stability parameters are observed for negative radial adjustment and tilt angles. Results indicate that negatively adjusted radial and pad tilt motion can generate improved stability margins at higher eccentricities. Data generated on stability margins at specific pad adjustments will be helpful while developing the control system for the actuation mechanism in the experimental setup.

Design of actively-controlled oil lubrication to reduce rotor-bearing-foundation coupled vibrations - theory & experiment

This paper gives theoretical and experimental contributions to the field of tribotronics, linking i) tribology of fluid film bearings, ii) flexible rotor and flexible foundation dynamics, iii) sensing systems, iv) fluid power and hydraulic actuator dynamics, and v) control theory in a holistic way. Based on a multi-physical modelling approach, a mathematical model (digital twin) is derived coupling the subsystems from i) till v). The digital twin is employed to design and optimize the feedback control system of an actively-controlled tilting pad journal bearing with the aim of attenuating vibration levels of the rotor-bearing-foundation system. The feedback control system is experimentally implemented and tested on a test rig. Significant reduction of the rotor-bearing-foundation vibrations is achieved in the frequency range of 20 until 250 Hz. Very good agreement between theory and experiment is achieved at the low rotor angular velocity used. The theoretical and experimental outcomes of the paper suggest that vi) the thermal domain needs to be included in the multi-physical modelling approach to accurately represent the bearing properties under thermoelastohydrodynamic conditions and expand the theoretical and experimental approaches to higher angular velocities.

Influence of Fluid Film Bearings with Different Axial Groove Shapes on Automotive Turbochargers: An Experimental Study

Most commercial automotive turbochargers (TC) employ semi-floating ring bearings (SFRB) with axial groove shapes. In order to bring some insights into the role played by the axial groove geometry on the dynamics of TC, this work deals with an experimental study of the rotordynamic behavior of a stock automotive turbocharger operating on SFRB with two different groove shapes, which have the same volume and width, and with the same number of grooves. The rotating machine behavior has been evaluated under different operating conditions using a test bench specially designed to analyze turbochargers. Rotordynamic (RD) characteristics of automotive turbochargers are estimated to evaluate the influence of the axial groove geometry on the machine vibratory behavior. Frequency spectra and orbital plots of the rotor are obtained from accelerometers and proximity probes mounted on the turbocharger. The comparative analysis of the vibrational behavior of automotive turbochargers running on different supporting systems allows the identification of the role played by the axial grooves on the machine rotordynamic performance. The experimental results rendered in this work permit to classify the influence of the axial groove geometry on the turbocharger rotordynamic behavior for several speed and flow conditions.

Misalignment and Surface Irregularities Effect in MR Fluid Journal Bearing

Misalignment is a major issue to hampers the satisfactory operation of the journal bearing system. Perfect alignment of the journal bearing system is rather difficult to achieve due to various reasons. In actual reality, there is always some amount of misalignment that exists. In recent times, smart lubricants have come up in a big way application concerning fluid film journal bearings. The performance of fluid film bearings gets greatly affected due to misaligned journal conditions and bearing surface irregularities. The present study deals with magnetorheological (MR) lubricant behavior fluid in a hybrid slot-entry journal bearing system (SEJBs) operating under misaligned journal conditions with bearing surface irregularities. The numerically simulated result reveals that due to journal misalignment conditions, the fluid film thickness is reduced, whereas, the value of fluid film damping coefficient and frictional torque gets increased. The mutual effect of bearing surface irregularities and MR lubricant enhances the value of minimum fluid film thickness thereby reducing the chances of metal to metal contact. Further, the combined influence of MR lubricant and surface irregularities increases the damping capabilities of bearing system which helps to damp out the oscillating vibration and large excitation under dynamic circumstances.

Balancing of Flexible Rotors Supported on Fluid Film Bearings by Means of Influence Coefficients Calculated by the Numerical Assembly Technique

In this paper, a new method for the balancing of rotor-bearing systems supported on fluid film bearings is proposed. The influence coefficients necessary for balancing are calculated using a novel simulation method called the Numerical Assembly Technique. The advantages of this approach are quasi-analytical solutions for the equations of motion of complex rotor-bearing systems and very low computation times. The Numerical Assembly Technique is extended by speed-dependent stiffness and damping coefficients approximated by the short-bearing theory to model the behavior of rotor systems supported on fluid film bearings. The rotating circular shaft is modeled according to the Rayleigh beam theory. The Numerical Assembly Technique is used to calculate the steady-state harmonic response, influence coefficients, eigenvalues, and the Campbell diagram of the rotor. These values are compared to simulations with the Finite Element Method to show the accuracy of the procedure. Two numerical examples of rotor-bearing systems are successfully balanced by the proposed balancing method.

Effect of lubricant shear thinning behaviour on major functioning parameters of a pad bearing operating in hydrodynamic lubrication region

Type of lubricant used for fluid film bearings is one of the most important factors to consider. Bearing characteristics have to maintain steady throughout a wide range of conditions. However, viscosity, which is one of the primary lubricant properties, highly deviates depending on environmental and operational conditions. Macro-molecular micro-structure of lubricants is strongly correlated to temperature and shear rate, leading to a shear thinning behaviour. This work aims in studying a pad bearing lubricated by a shear thinning oil in hydrodynamic region. Hydrodynamic wedge was modelled for a small fixed pad bearing of 8.5 mm inner radius, 14.5 mm outer radius, 40° angle and 50 μm inlet – outlet film thickness difference. Variety of cases were studied for several runner rotational velocities and minimum film thickness. Lubricant was modelled as a carreau fluid. Load carrying capacity, power losses, friction coefficient, mass flow rate, temperature and viscosity were evaluated. From the aspect of load carrying capacity, this specific pad bearing is optimally operating for rotational velocities of up to 100 krpm. Above this threshold, viscosity highly downgrades due to increase in temperature and shear rate, causing a negative impact in load capacity. Shear thinning behaviour of lubricants is of high importance and should not be considered negligible.

Active Fluid-Film Bearing With Deep Q-Network Agent-Based Control System

Abstract Despite the fact that the hydrodynamic lubrication is a self-controlled process, we designed control systems based on proportional integral (PI) controller, adaptive PI controller, and Deep Q network (DQN)-agent to minimize the friction torque in a conical fluid-film bearing. The bearing construction allows the shaft axial displacement and, as the result, the regulation of the bearing average clearance due to the controlled supply pressure. The main challenge is that the friction torque minimization may lead to the loss of load-carrying capacity and the contact in the shaft-bearing tribocouple. The other challenge is that random events may have an influence on the hydrodynamic lubrication parameters, therefore, changing the load-carrying capacity and the friction torque. So, the proposed control systems were designed and tested under the conditions of limited lateral shaft displacements and the action of a random external force. The tests were performed using simulation models of a controlled rotating machine in matlab software. The rotating machine simulation model includes modules of the rigid shaft, the coupling with linear axial reaction, and the conical bearing. The bearing module is based on the numerical solution of the generalized Reynolds equation and its nonlinear approximation with fully connected neural networks. The obtained results demonstrated that the application of an adaptive PI controller or a DQN agent allows decreasing friction torque in a bearing under the conditions of a random external force. The goal of a DQN agent is self-learning in contrast to an adaptive PI controller that needs to be tuned.

Deep convolutional autoencoder augmented CFD thermal analysis of bearings with inter pad groove mixing

The treatment of thermal mixing in inter pad grooves of a fluid film bearing is essential due to its influence on the heat transfer with the rotating shaft and stationary bearing. Lower fidelity models that either neglect or over approximate thermal groove mixing may lead to premature bearing or machinery failure, most commonly from babbitt thermally induced fatigue. Conventional models rely on bulk flow and thermal analyses yielding a single temperature at the groove outlet into the pad inlet. The high uncertainty of this approach carries over into downstream predictions for bearing life, stiffness and damping, and machinery vibration predictions. Contrary to a uniform temperature, CFD-Conjugate heat transfer studies reveal large gradient temperature distributions varying in both the radial and axial directions at the groove outlet, especially with jet lubrication implemented with multiple nozzles. These distributions vary continuously with time as the spinning shaft and bearing pads vibrate. A direct CFD simulation thus becomes computationally prohibitive.The present work introduces a novel approach which yields highly detailed lubricant temperature distributions at the pad inlets in a computationally economical manner. This is implemented with a surrogate groove model via a deep convolutional autoencoder neural network based on CFD (Computational Fluid Dynamics) data. The trained Convolutional Neural Network (CNN) shows excellent prediction capability for 2D temperature distribution at a circumferential groove outlet. The trained CNN is combined with a rotor-bearing model, and the combined model is verified by full CFD results and experimental data. In addition, this approach is expanded to include various oil injection types, illustrating their detailed heat transfer to the rotating shaft and bearing.

Analysis of nonlinear vibration and stability of Jeffcott rotor supported on squeeze-film damper by IHB method

In this paper, a methodology to analyze the nonlinear vibration of a Jeffcott rotor supported on a squeeze-film damper (SFD) with centering springs, which is widely used in high-speed rotating machines, is proposed using the incremental harmonic balance (IHB) method. In this paper, the IHB method is modified to analyze the dynamic behavior of rotor systems supported on fluid-film bearings, such as SFDs. The processing of the mass matrix, stiffness matrix, and linear force matrix proceeds in exactly the same way as in classical IHB. The nonlinear force generated in the oil film of the SFD is calculated using the alternating frequency/time method and the transformation matrix and incorporated into the computational processing of the classical IHB method. This calculation method is first proposed in this paper. Solutions computed using the proposed method are compared with solutions computed using numerical integration. The results are very close. The stability of the calculated solutions is determined using the Floquet theory. Based on this, frequency–response curves according to the change in various parameters are constructed. The proposed method can be effectively used to analyze the nonlinear vibration characteristics of rotor systems supported on fluid-film bearings, such as SFDs.

Computational Model Development for Hybrid Tilting Pad Journal Bearings Lubricated with Supercritical Carbon Dioxide

Fluid film bearings lubricated with supercritical carbon dioxide (sCO2) eliminate the infrastructural requirement for oil lubricant supply and sealing in turbomachinery for sCO2 power systems. However, sCO2’s thermohydrodynamic properties, which depend on pressure and temperature, pose a challenge, particularly with computational model development for such bearings. This study develops a computational model for analyzing sCO2-lubricated tilting pad journal bearings (TPJBs) with external pressurization. Treating sCO2 as a real gas, the Reynolds equation for compressible turbulent flows solves the pressure distribution using the finite element method, and the Newton−Raphson method determines the static equilibrium position by simultaneously calculating forces, moments, flow rates of externally pressurized sCO2, and pressure drop due to flow inertia. The finite difference method solves the energy equation for temperature distribution. The density and viscosity of sCO2 are converged using the successive substitution method. The obtained predictions agree with the previous and authors’ computational fluid dynamics predictions, thus validating the developed model. Hybrid lubrication increases the minimum film thickness and stiffness up to 80% and 65%, respectively, and decreases the eccentricity ratio by up to 65% compared to those of pure hydrodynamic TPJB, indicating significant improvement in the load capacity. The bearing performance is further improved with increasing sCO2 supply pressure.

Fault diagnosis systems for rotating machines operating with fluid-film bearings

The paper deals with the application of deep learning methods to rotating machines fault diagnosis. The main challenge is to design a fault diagnosis system connected with multisensory measurement system that will be sensitive and accurate enough in detecting weak changes in rotating machines. The experimental part of the research presents the test rig and results of high-speed multisensory measurements. Six states of a rotating machine, including a normal one and five states with loosened mounting bolts and small unbalancing of the shaft, are under study. The application of deep network architectures including multilayer perceptron, convolutional neural networks, residual networks, autoencoders and their combination was estimated. The deep learning methods allowed to identify the most informative sensors, then solve the anomaly detection and the multiclass classification problems. An autoencoder based on ResNet architecture demonstrated the best result in anomaly detection. The accuracy of the proposed network is up to 100% while the accuracy of an expert is up to 65%. A one-dimensional convolutional neural network combined with a multilayer perceptron that contains a pretrained encoder demonstrated the best result in multiclass classification. The detailed fault detection accuracy with the determination of the specific fault is 83.3%. The combinations of known deep network architectures and application of the proposed approach of pretraining of the encoders together with using a block of inputs for one prediction demonstrated high efficiency.

Reducing Rotor Vibrations in Active Conical Fluid Film Bearings with Controllable Gap

Despite the fact that the hydrodynamic lubrication is a self-controlled process, the rotor dynamics and energy efficiency in fluid film bearing are often the subject to be improved. We have designed control systems with adaptive PI and DQN-agent based controllers to minimize the rotor oscillations amplitude in a conical fluid film bearing. The design of the bearing allows its axial displacement and thus adjustment of its average clearance. The tests were performed using a simulation model in MATLAB software. The simulation model includes modules of a rigid shaft, a conical bearing, and a control system. The bearing module is based on numerical solution of the generalized Reynolds equation and its nonlinear approximation with fully connected neural networks. The results obtained demonstrate that both the adaptive PI controller and the DQN-based controller reduce the rotor vibrations even when imbalance in the system grows. However, the DQN-based approach provides some additional advantages in the controller designing process as well as in the system performance.

Two-way Fluid Structure Interaction Analysis of Single Pad Externally Adjustable Fluid Film Bearing

Two-way Fluid Structure Interaction Analysis of Single Pad Externally Adjustable Fluid Film Bearing