Fluid Film Bearings Research Articles

On the continuation of quasi-periodic solutions of rotor systems with fluid-film bearings

On the continuation of quasi-periodic solutions of rotor systems with fluid-film bearings

Intelligent robust controllers for tribotronic conical fluid film bearings

The article presents the results of the development of means for intelligent robust control of the parameters of a tribotronic rotor-support system with a tapered bearing with a removable bush. The proposed controller is implemented on the basis of deep Q-network reinforcement learning (DQN) synthesized on the basis of a numerical model of a rotor support system. The control strategy involved simultaneous control of the shaft position and friction in the lubrication layer. Methods for control synthesis are presented for both a deterministic system and a system with stochastic parameters. In the latter case, a controller synthesis technique is proposed that takes into account uncertainties in the system at the training stage. Testing of the resulting controllers shows the better ability of a controller trained to take into account uncertainties to cope with variable loads, as well as predict possible changes in the system and proactively transfer the system to more advantageous states.

Multi-Objective Deep Q-Network Control for Actively Lubricated Bearings

This paper aims to study and demonstrate the possibilities of using reinforcement learning for the synthesis of multi-objective controllers for radial actively lubricated hybrid fluid film bearings (ALHBs), which are considered to be complex multi-physical systems. In addition to the rotor displacement control problem being typically solved for active bearings, the proposed approach also includes power losses due to friction and lubricant pumping in ALHBs among the control objectives to be minimized by optimizing the lubrication modes. The multi-objective controller was synthesized using the deep Q-network (DQN) learning technique. An optimal control policy was determined by the DQN agent during its repetitive interaction with the simulation model of the rotor system with ALHBs. The calculations were sped up by replacing the numerical model of an ALHB with its surrogate ANN-based counterpart and by predicting the shaft displacements in response to operation of two independent control loops. The controller synthesized considering the formulated reward function for DQN agent is able to find a stable shaft position that reduces power losses by almost half compared to the losses observed when using a passive system. It also is able to prevent the established limit of the minimum fluid film thickness being exceeded to avoid possible system damage, for example, when the rotor is unbalanced during the operation. Analysis of the development process and the results obtained allowed us to draw conclusions about the main advantages and disadvantages of the considered approach, and also allowed us to identify some important directions for further research.

Topological optimization and fatigue life prediction of a single pad externally adjustable fluid film bearing

This work focuses on the prediction and comparison of the fatigue life of topologically optimized pads in an externally adjustable fluid film (EAFF) bearing. It integrates one-way/two-way fluid–structure interaction analysis, topological optimization (TO), and design modifications of the pad of an externally adjustable fluid film bearing. The major goal is to create an optimum pad design that minimizes weight and maintains structural integrity, and then to predict and compare the fatigue life of these alternative designs. The outcomes of the present study are as follows: (i) Two-way FSI results show a decrease of 65.64% in hydrodynamic fluid film pressure when compared to one-way FSI results because they take into account modifications in the fluid region's geometry caused by pad deformation; (ii) even though the maximum pad deformation in optimized pad geometry (Type-4) resulting from oil film pressure is relatively small (0.0036551 mm), the influence of pad deformation on the fluid domain due to hydrodynamic fluid film pressure cannot be understated; and (iii) when comparing the TO technique's results with fatigue life results, four elongated holes in the radial direction (Type-4) are most appropriate.

Transient instability characteristics of fluid film bearings induced by bubble inclusion

Bubble inclusion in the tribo-pair leads to two-phase fluid lubrication. Upon the initial introduction of air bubbles to the tribo-pair, it can lead to instability in the operational state. A numerical model is formulated by coupling the fluid Reynolds equation, bubble dynamics equation, and rotor dynamics equation. Various parameters, such as hydrodynamic pressure, fluid carrying capacity, rotor trajectory, and equilibrium position, are employed to characterize the impact of operational and fluid interface parameters on the bubble entrainment process. The findings reveal that the hydrodynamic pressure plays a crucial role in establishing the correlation between velocity and fluctuations in kinetic parameters. Surface tension predominantly influences bubbles within the dispersion region, while surface dilatational viscosity affects the entire domain. Lower surface dilatational viscosity or neglecting surface tension can trigger larger fluctuations in the rotor trajectory. Changes in liquid-phase viscosity result in fluctuations in bubble behavior and dynamics parameters, influenced by the equilibrium position and the effect of hydrodynamic pressure. Higher initial gas-phase volume fractions lead to a more pronounced reduction in fluid-carrying capacity and increased system instability.

Multi-Objective Optimization of Active Hybrid Fluid Film Bearings Using Heuristic Algorithms

Purpose of research. The design of sliding bearings, especially for heavily loaded rotary machines, is a laborious task. The implementation of control systems for the movement parameters of the rotor further increases the complexity of a design procedure. The study shows a developed approach to the optimal design of active rotor bearings using heuristic optimization algorithms. The approach allows to obtain a set of optimal Pareto solutions and determine the only configuration of the reference node that best meets the given criteria.Methods. The problem of optimal parametric synthesis of an active fluid friction bearing was solved using a numerical model coupled with the model of rotor movement in the support. For the given design problem, objective functions were formulated, design variables were determined, and the necessary restrictions were imposed. Using multicriteria versions of the genetic algorithm and the particle swarm algorithm, procedures for the optimal synthesis of reference nodes were carried out. The solutions obtained by different methods are compared and analyzed based on the results of model tests.Results. As part of the study, algorithmic and software tools were developed for solving problems of optimal parametric synthesis of active hybrid fluid friction bearings. The applied objective functions are conflicting, so the primary result of the solution is a 3D Pareto front. The tested heuristic algorithms showed qualitatively similar solutions, but the genetic algorithm covers a larger range of them. On the whole, the final decisions meet the criteria, but the methods for making final decisions require additional elaboration.Conclusion. The study presents an approach to the automated design of sliding bearings, which allows you to simultaneously take into account the tribological, dynamic aspects of the behavior of the rotary bearing system, as well as ensure readiness for the use of control systems in bearing nodes. The tested heuristic algorithms give comparable solutions to the optimization problem in comparable time as well. Further improvement of the method of parametric synthesis of such supports should be carried out in the direction of decision-making algorithms, refinement of objective functions, as well as acceleration of the applied calculation models.

Propagation of Uncertainty in Experimental Dynamic Coefficients of Fluid Film Journal Bearings

Abstract The stiffness and damping coefficients of fluid film bearings play a key role in predicting levels of vibration and stability margins in high-performance industrial rotating machinery. However, variability in the coefficients calculated by numerical bearing codes creates inaccuracies in the rotodynamic predictions. Therefore, there is a strong need for accurate experimental measurement of bearing coefficients for validation purposes. This work examines new propagation uncertainty strategies in bearing coefficients estimation, and for the first time examines the effect of the nonlinearity of the dynamic coefficients on the experimental uncertainty estimated by the Taylor Series Method. The Montecarlo method is presented as a more accurate approach to estimating experimental uncertainty. The results of the analyses are compared to published values from previously reported studies. This paper also proposes a novel method to convert the random behavior in the output of a sensor in the time domain to the frequency domain. It is found this conversion is quite beneficial for the accuracy of the coefficients; in one example, uncertainty estimations of ±84% are reduced to just ±6%, when using the proposed method. This work also reveals that the uncertainty estimations from the Taylor Series Method are not entirely reliable, without additional checks of nonlinearity, and that converting data to the frequency domain, by using the novel method here, is useful for achieving smaller uncertainty estimations than with traditional methodology.

Experimental study on the feasibility of alternative materials for tilting pad thrust bearings operating in transition to mixed friction

In hydrodynamic bearings traditional bearing alloys: Babbitts and bronzes are most frequently utilized. Polymer sliding layers are sometimes applied as a valuable alternative. Hard diamond-like carbon (DLC) coatings, which are also considered for certain applications may show some advantages, as well. Although material selection is of secondary importance in a full film lubrication regime it becomes important in mixed friction conditions, which is crucial for bearings with frequent starts and stops. Experimental research aimed at studying the performance of fluid film bearings in the specific operating regime, including the transition to mixed friction, is described in the paper. The tests were carried out on four tilting pad bearings of different material compositions: Steel/bronze, DLC/steel, steel/polyether ether ketone (PEEK), and steel/Babbitt. The tests comprised stopping under load and reproduction of the Stribeck curve by decreasing rotational speed to very low values, and observing the changes of friction force during the transition to mixed friction regime. Analysis of the transition conditions and other results showed clear differences between the tested bearings, illustrating the feasibility of less popular material compositions for bearings operating in specific conditions. More specifically, the DLC/steel bearing was demonstrating superior performance, i.e. lower friction, transition to mixed friction occurring at higher load, and more stable performance at start-stop regime over the other tested bearings.

A thermohydrodynamic performance analysis of a fluid film bearing considering with geometrical parameters

Bearing performance characteristics such as stiffness, and load capacity, are related to the lubrication fluid circulating through the gap. In the fluid film bearings, the characteristic of the lubrication film also depends on the journal geometry and the viscosity. This study aimed to research the bearing geometry influences on the thermohydrodynamic performance of a circular journal bearing. The temperature distribution is modeled using a 3-dimensional energy equation. The velocity components are obtained on the pressure distribution governed by Dowson’s equation. Moreover, the heat transfer between the journal and oil is modeled with Fourier heat conduction equation, and the viscosity equation is derived for SAE10W30 commercial oil as a function of the temperature. An algorithm based on the finite difference method is developed, and a serial simulation is performed for different geometrical parame-ters such as bearing clearance, and bearing length-to-diameter ratio (L/D). When the radial clearance decreases from 150 µm to 100 µm, the maximum pressure grows up by 53%, and the maximum temperature decreases by 21%. On the other hand, when the L/D ratio rises from 0.8 to 1, the maximum pressure grows up by 22%, but the temperature distribution does not significantly change. The load capacity, and the stiffness are higher for low radial clearance. The load capacity, and the stiffness increase when the L/D ratio grows up.

Data-driven and physics-informed approaches for improving the performance of dynamic models of fluid film bearings

Conventional numerical models of fluid film bearings (FFB) typically require significant amounts of computations to achieve acceptable calculation accuracy. This may cause many inconveniences, especially for computationally expensive rotor dynamics tasks. The study addresses general issues in building synthetic data-driven dynamic FFB models using machine learning methods, focusing on artificial neural networks (ANNs). In the study, surrogate models predicting journal bearing forces were built using a variety of approaches, including single- and multi-component ANN-based models, as well as so-called physics-informed neural networks (PINN). The work presents a comparative analysis of the considered approaches, primarily in the context of rotor dynamics calculations. It includes an assessment of the accuracy and performance of considered models, as well as the time spent on their creation. The results show that all tested solutions outperform numerical methods by order of magnitude or more, but it is difficult to talk about the overwhelming advantage of any one approach over others. When choosing a methodology for building surrogate FFB models, one should proceed from the requirements for the model, the benefits and shortcomings of certain methods. The work gives an idea of their relationships, including the influence of key hyperparameters of the methods on the properties of the resulting models. The results can be useful both for traditional calculations in the area of rotor dynamics, and for relatively new problems in the rotor systems, such as predictive analytics and optimal design systems, predictive controllers of active components of rotary machines.

Fluid Film Bearings and CFD Modeling: A Review

This paper is a review of the literature about CFD modeling and analysis of journal, thrust, and aerostatic bearings; the advantages and disadvantages of each are specified, and the bearing problems that have been analyzed are discussed to improve their designs and performance. A CFD transient analysis of journal bearings was conducted using the dynamic mesh method together with movement algorithms while keeping a structured mesh of a good quality in the ANSYS Fluent software to determine the equilibrium position of the journal and calculate the dynamic coefficients. Finally, areas of opportunity for analyzing and designing fluid film bearings to improve their performance are proposed.

Effect of bearing shell deformation and ER fluid behavior on two-lobed slot-entry hybrid journal bearing

The present article deals with the effects of deformable bearing shells on the performance of lobed slot-entry hybrid journal bearing systems. The influence of the deformation coefficient [Formula: see text] has been studied using the thin liner elasticity model, which measures the flexibility of the bearing liner. Recently, smart fluid, that is, electrorheological (ER) fluid has been used in various tribological systems to obtain better performance. Therefore, the influence of ER lubricant on the bearing performance characteristics has also been studied in this work. Bingham model constitutive relation has been used to analyze the non-Newtonian behavior of ER fluid. The performance of fluid film bearings is greatly influenced by the noncircularity of the bearings. Therefore, the behavior of deformable bearing shells in a slot-entry journal bearing for lobed conditions has also been studied in the present study. The results reveal that considering deformation in the bearing shell reduces the value of frictional torque, whereas the value of stiffness coefficients and stability threshold speed increases. However, ER lubricant enhances the value of film thickness, stiffness/damping coefficients, and stability threshold speed margin.

Influence of Wear on the Cross-Coupled Dynamic Coefficients and Threshold Speed of Conical Hybrid Fluid Film Bearing

Influence of Wear on the Cross-Coupled Dynamic Coefficients and Threshold Speed of Conical Hybrid Fluid Film Bearing

Machine Learning-Based Optimizer for Tilting Pad Journal Bearing Inlet Flowrate

Abstract In view of the green economy and energy transition, the reduction of the environmental impact of the power generation sector plays a key role. Fluid film bearings are the most common bearing for industrial turbomachinery and new design requirements have a direct impact on bearings operation. In fact, to achieve higher levels of efficiency, bearings must support higher specific loads and higher peripheral speeds. Furthermore, there is great interest in reducing the oil flowrate required for the bearing operation as much as possible. In this work, an optimization strategy for reducing the flowrate fed to tilting pad journal bearings (TPJBs) is proposed. An artificial neural network (ANN) is trained to estimate the static and dynamic performance of the bearings. The training dataset is built with a Reynolds-based thermo-hydrodynamic model. The trained ANN is then used in a constrained optimization that has the goal of minimizing the oil flowrate while ensuring safe bearing operation. Predictions are compared with experimental data from compressor mechanical running tests. The proposed model is an effective tool that can help industry achieve the goals required by the energy transition and can help in the development of optimized fluid film bearings.

Experimental Force Coefficients of a Hydrostatic Thrust Bearing and Comparisons to Predictions

Abstract Reliable fluid film bearings for high-performance turbomachinery provide significantly extended operating life with controllable stiffness and damping force coefficients at low cost. Hydrostatic thrust bearings support thrust loads and control axial motions. This paper reports measurements and predictions of static and dynamic load characteristics of a hydrostatic thrust bearing fed with pressurized air. The current bearing model uses dynamic axial periodic motion amplitudes, that is, models as a function of the initial film thickness, to predict the dynamic force coefficients. Note that, presently, the recorded frequencies and their amplitudes of pneumatic hammer instability along the axial direction are implemented as an external excitation source. The measured and predicted static stiffnesses increase as the film thickness decrease and supply pressure into the bearing increase. The predicted dynamic force coefficients show a favorable agreement with the test data. Analysis reveals the negative damping coefficients and damping ratios as a distinctive onset condition of the present pneumatic hammer instability of the test bearing. A careful recess design and adequate operation conditions along with an accurate prediction can avoid or prevent undesirable pneumatic hammer instability in hydrostatic thrust bearings. This work extends the knowledge database of hydrostatic thrust bearings with pneumatic hammer instability and provides their design guideline for various operating conditions.

Bifurcations and limit cycle prediction of rotor systems with fluid-film bearings using center manifold reduction

Bifurcations and limit cycle prediction of rotor systems with fluid-film bearings using center manifold reduction

Artificial neural network for tilting pad journal bearing characterization

Tilting pad journal bearings (TPJBs) are modeled with Reynold-based models or computational fluid dynamics (CFD) approach. In both cases, the estimation of the dynamic coefficients of the oil-film forces and the static characteristic, can be computationally expensive and time consuming. Artificial Intelligence (AI) is assuming a key role in engineering but is rarely applied in fluid film bearing analysis. A properly trained Deep Learning (DL) model can perform very fast predictions of TPJB behavior with accuracy comparable to more time-consuming models. In this case, the main drawback is the time required to build the training dataset. In this work, an Artificial Neural Network (ANN) is trained to predict the dynamic stiffness and damping coefficients along with the main static quantities of TPJBs, such as minimum oil-film thickness and inlet flowrate. At first, a design of experiment is performed to build an appropriate training dataset. Secondly, a Reynolds-based thermo-hydrodynamic (THD) model is used to populate the training dataset and an appropriate test dataset. Then, a feed-forward ANN is trained with Levenberg–Marquardt backpropagation and its architecture is optimized to increase accuracy. Finally, the accuracy of the ANN is tested using the test dataset and experimental data. The time and computational effort required by the ANN regression are much less than those required by the THD model. Therefore, the trained ANN is an effective and efficient tool for the characterization of TPJBs.

Research on control strategy of an active magnetorheological fluid bearing based on improved gray wolf optimization approach

In order to address the problems of insufficient load capacity and rotor vibration, an active fluid-film bearing lubricated with magnetorheological fluid (MRF) is proposed. First, the geometry of the MRF fluid-film bearing is designed and its intelligent lubrication mechanism is analyzed to clarify its advantages. In addition, mathematical model of MRF fluid-film bearing-rotor system is derived, and FEM model is utilized to obtain stiffness and damping coefficients to supplement mathematical model. Moreover, an improved gray wolf optimization (IGWO) algorithm is developed to tune the PID controller parameters. The validity of the proposed method is verified by numerical simulation. Furthermore, the simulation results show that with the increasing of current magnitude, the orbits of shaft center decrease. Under the presence of magnetic fields, the shaft center orbits of the MRF bearing can converge to a point, and therefore this bearing has ability to suppress rotor vibration. Finally, IGWO-PID controller has better response characteristics than GWO, PSO, and GA algorithms, and hence the IGWO algorithm can find the more appropriate PID controller parameters, that the validity of the improved algorithm is further proved. Therefore, the active bearing and its research findings provide new reference for MRF vibration control in the field of journal bearing lubrication.

Nonlinear vibration analysis and stability analysis of rotor systems supported on SFD by combining DQFEM, CMS and IHB methods

In this paper, the differential quadrature finite element method (DQFEM), component mode synthesis (CMS) method and incremental harmonic balance (IHB) method are combined to propose a methodology to perform vibration analysis and stability analysis of rotor systems supported on fluid-film bearings that exhibit localized nonlinearities such as squeeze-film damper (SFD). In multi-degree of freedom systems with SFD, a method for dynamic analysis of the system by reducing the degrees of freedom is first suggested in this paper. DQFEM are used to create the mass matrix, stiffness matrix, and gyroscopic matrix of the system. Then, the system is divided into linear system and nonlinear system, and the motion equation of the linear system reduces the degrees of freedom using the free interface CMS method, and the motion equation of the nonlinear system is written without reducing the degrees of freedom. By synthesizing the equations of motion of each component, the motion equation of the entire system is created. That is, the motion equation of the whole system uses hybrid coordinates. The motion equation of the system is solved using the modified IHB method. To evaluate the effectiveness of the suggested method, the computed solutions are compared with the results presented in the previous literature, and the results are very consistent. Also, stability analysis of the obtained solutions is performed by the Floquet theory. The method suggested in the paper can be effectively used to analyze the dynamic behavior of rotor systems exhibiting localized nonlinearities such as SFD.

Theoretical and Numerical Investigation of Reduction of Viscous Friction in Circular and Non-Circular Journal Bearings Using Active Lubrication

Reducing friction losses is one of the most common ways to improve fluid film bearings, whose adjustable design provides additional opportunities to improve their dynamic and tribological properties. Previous studies have shown the possibility of reducing viscous friction in actively lubricated bearings by adjusting the rotor position. This work provides a theoretical justification for the mechanism of this effect for the cases of purely laminar lubricant flows in journal bearings. The operating modes connected with the transition to turbulent phenomena and the occurrence of Taylor vortices are beyond the scope of this paper. Conditions that ensure the minimization of friction losses in hydrodynamic and hybrid bearings with hydrostatic parts are determined based on the equations describing viscous friction in a fluid film. In non-adjustable plain hydrodynamic bearings, the minimum of friction is achieved with the centered shaft position that is actually unstable due to the resulting forces configuration. In actively lubricated hybrid bearings, a further reduction in viscous friction is possible by combining film thickness and pressure distributions. Recombining them, along with adjustment of the shaft position, allows the optimization of the distribution of shear stresses in the fluid film. As a result, the shear stresses caused by the rotation of the shaft can be partially compensated by the stresses caused by the pressure gradient, reducing the torque-resisting rotation. In addition, additional benefits can be obtained in the minimum friction state by the reduced lubricant flow and power losses to its pumping. A series of numerical calculations for elliptical, 3-, and 4-lobe bearings show that non-circular bores provide additional variability in film thickness distribution and a premise for optimizing the bearing tribological parameters. Four-lobe bearing demonstrated the best ability for reducing viscous friction among the considered designs. The results obtained can be used as a basis for further optimization of the geometry of fluid film bearings of both active and passive designs by reducing power losses due to viscous friction.