Pad Thrust Bearings Research Articles

Multiscale Mixed Elastohydrodynamics in Inclined Fixed Pad Thrust Bearing Involving Surface Roughness and Low Clearance

The film pressures, surface separation profiles and carried loads of the hydrodynamic inclined fixed pad thrust bearing with the sandwich films were calculated by the multiscale approach when the bearing clearance was low and the combined effects of the adsorbed layer, the surface roughness and the surface elastic deformation were incorporated; The sandwich film consists of two physically adsorbed layers respectively on the coupled bearing surfaces and the intermediate continuum fluid film. The results show that the surface roughness intrinsically generates the film pressure ripples, but the rough surface is somewhat flattened and the film pressure ripples are a bit reduced by the surface elastic deformation. For a given sliding speed and a given original bearing clearance, the surface elastic deformation results in the significant reductions of both the maximum film pressure and the carried load of the bearing especially for a strong fluid-bearing surface interaction. In spite of this, the slope of the increase of the bearing load with the magnitude () of the surface roughness is nearly the same for the elastic surfaces with that for the rigid surfaces. The presence of the surface roughness does not qualitatively alter the influence of the surface elastic deformation on the performance of the bearing.

Influence of 3D surface irregularities on the performance of hydrostatic rectangular tilted thrust pad bearing configurations

Tribological behavior of tribo-pairs is strongly dependent on the surface topography. Further, the structural deformation, manufacturing, and assembly errors cause the hydrostatic thrust pad bearings to tilt slightly. The work in this article is aimed to study the effect of tilt and three-dimensional (3D) surface irregularities on the performance of hydrostatic rectangular thrust pad bearings (HRTPB) compensated with capillary restrictors. The 3D surface irregularities are assumed to follow cosine curve. To perform the analysis, a source code has been developed in MATLAB and the Finite Element Method has been used to solve the governing Reynold's equation. The numerical simulation results indicate that the effect of tilt reduces the value of fluid film reaction, fluid film stiffness, and fluid film damping coefficients. The study reveals that 3D surface irregularities results in a higher value of fluid film stiffness and damping coefficient as compared to that of smooth-bearing surfaces.

Experimental study on scaled-down pads for nuclear main pump thrust bearing

The lubrication performance of thrust bearings is essential for the efficient, economical, and safe operation of nuclear main pumps. In this paper, a test system for scaled-down tilting pad thrust bearings was designed and built, and the feasibility of the scaled-down scheme was verified. The test results show that: with the increase of loading force, the pressure and temperature at different measurement points gradually increase. The influence of lubricant temperature on oil film pressure under the same loading force is small. During the rotor start process, the oil film pressure shows a trend of first increasing and then gradually stabilizing, and the temperature of each pad center gradually increases. During the rotor stop process, the oil film pressure initially increases slightly and then drops sharply with the reduction of speed, while the temperature at the center of the pad gradually decreases and the rate of decrease gradually increases.

Prediction of thrust bearing’s performance in Mixed Lubrication regime

A hydrodynamic thrust bearing could be forced to operate in mixed lubrication regime under various circumstances. At this state, the tribological characteristics of the bearing could be affected significantly and the developed phenomena would have a severe impact on the performance of the mechanism. Until recently, researchers were modeling the hydrodynamic lubrication problem of the thrust bearings either with analytical or with numerical solutions. The analytical solutions are very simple and do not provide enough accuracy in describing the actual problem. To add to that, following only computational methodologies, can lead to time consuming and complex algorithms that need to be repeated every time the operating conditions change, in order to draw safe conclusions. Recent technological advances, especially on the field of computer science, have provided tools that enhance and accelerate the modeling of thrust bearings’ operation. The aim of this study is to examine the application of Artificial Neural Networks as Machine Learning models, that are trained to predict the coefficient of friction for lubricated pad thrust bearings in mixed lubrication regime. The hydrodynamic analysis of the thrust bearing is performed by solving the Average 2-D Reynolds equation numerically. In order to describe the roughness of the profiles, both the flow factors suggested by N. Patir and H.S. Cheng (1978) and the model of J.A. Greenwood and J. H. Tripp (1970) are taken into consideration. Three lubricants, the SAE 0W30, the SAE 10W40 and the SAE 10W60, are tested and compared for a variety of operating velocities and applied coatings. The numerical analysis results are used as training datasets for the machine learning algorithms. Four different ML methods are applied in this investigation: Artificial Neural Networks (ANNs), Multi- Variable Quadratic Polynomial Regression, Quadratic SVM and Regression Trees. The coefficient of determination, R2 is calculated and used to determine the most accurate ML method for the current study. The results showed that ANNs provide very good accuracy in the prediction of friction coefficient compared to the rest of the ML models discussed.

Research on the lubrication performance of circular tilting pad thrust bearings for large wind turbines

AbstractIn view of the large temperature rise and impact load of thrust bearings in the main shaft system of large wind turbines, this article takes the circular tilting pad thrust bearings in large wind turbines as the research object, and analyses the basic theory of bearing lubrication. The lubrication performance calculation model established for this bearing includes the Reynolds equation, energy equation, film thickness equation, and elastic deformation equation. Theoretically analysing and calculating the lubrication performance of the circular tilting pad thrust bearing, the key performance parameters have identified such as minimum film thickness (hmin), temperature rise (ΔT), power consumption (W), and flow rate (Q). The calculation results show that the eccentricity ratio has a significant impact on the lubrication performance of the circular tilting pad thrust bearing. When both radial and circumferential eccentricity ratios are around 0.5, the bearing exhibits a high temperature rise, leading to a potential risk of bearing burnout. The results also show that at a radial eccentricity ratio of approximately 0.54, the minimum film thickness reaches its maximum value of 10.34 μm. Similarly, at a circumferential eccentricity ratio of about 0.60, the minimum film thickness reaches its peak value of 21.89 μm. This indicates that the eccentricity ratio plays a crucial role in the lubrication performance. In addition, the lubrication performance of the bearing under varying loads has been calculated at a speed of 9.5 r/min. The results demonstrated that the applied load significantly impacts the thrust bearing's performance. The findings elucidate the critical role of considering the eccentricity ratio and operational external load during the bearing design process. This study validates the potential of replacing rolling bearings with sliding bearings in wind turbine main shafts. It also provides a theoretical reference for the future design of sliding bearings.

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.

Effect of Surface Elastic Deformation in Hydrodynamic Inclined Fixed Pad Thrust Bearing with Low Clearance

The paper analytically studies the effect of surface elastic deformation in hydrodynamic inclined fixed pad thrust slider bearing with low clearances by the multiscale approach considering the physically adsorbed layer on the bearing surface. The numerical calculation results show that the bearing surface elastic deformation has significant influences on both the hydrodynamic pressure and the surface clearance in the bearing especially for a strong fluid-bearing surface interaction. For given load, sliding speed and bearing geometrical sizes, the surface elastic deformation considerably reduces the minimum bearing clearance, which exists on the exit of the bearing. It also significantly reduces the hydrodynamic film stiffness and the load-carrying capacity of the bearing especially for a strong fluid-bearing surface interaction and low bearing clearances. The increasing proportionality of the carried load of the bearing with the sliding speed is also significantly reduced by the surface elastic deformation particularly for a strong fluid-bearing surface interaction.

Performance analysis of tilting pad thrust bearing incorporating the surface roughness, texture and turbulence effect

In order to improve the lubrication performance of the friction pair, the effect of composite micro-texture on the lubrication performance of the tilting pad thrust bearing is studied. Based on the structural model of tilting pad thrust bearing considering composite micro-texture, the lubrication characteristics of thrust bearing with composite micro-texture parameters and tilting pad parameters are analyzed. At the same time, the theoretical model of tilting pad composite micro-texture bearing considering roughness and turbulence effect is established, and the performance of thrust bearing considering roughness and turbulence effect is studied. The results show that the performance of composite micro-textured bearings is better than that of single micro-textured bearings, the performance of tilting pad bearings is better than that of parallel pad bearings, and the performance of circular composite fish-shaped micro-textured tilting pad bearings is the best. The optimal bearing fulcrum position is near the inner diameter, and the optimal fulcrum circumferential inclination angle is about 27.5°. Considering the roughness and turbulence effect, the maximum pressure and bearing capacity of the bearing improves, and the friction coefficient significantly reduces.

A Thermal Hydrodynamic Model for Emulsified Oil-Lubricated Tilting-Pad Thrust Bearings

On maritime vessels, external factors such as explosions, collisions, and grounding can cause the emulsification of lubricating oil by seawater pollution, which can affect the lubrication of a ship’s thrust bearing. To explore the influence of the mixed emulsification of lubricating oil and seawater on the lubrication performance of thrust bearings, this study conducted an emulsification experiment, from which the viscosity equation of the oil–water mixture was obtained. A thermal hydrodynamic model (THD) of bearings considering oil–water mixed emulsification was established, and the Finite Difference Method (FDM) was used for analysis. The results show that according to the characteristics of the manifold, the mixture is divided into water-in-oil (W/O) and oil-in-water (O/W). In the W/O flow with higher viscosity, the film thickness becomes higher, but the power loss increases. In the O/W manifold with low viscosity, the thin film easily causes mixed friction. In the demulsification stage of the mixed liquid, the thickness loss of the film is huge, and the collision between the thrust-bearing pad and the inference plate may cause the pad to be ablated. The influence of specific heat capacity on temperature is greater than the temperature rise caused by viscosity.

Tribo-behavior of a spiral-grooved annular pocket hybrid tilted thrust pad bearing

Tribo-behavior of a spiral-grooved annular pocket hybrid tilted thrust pad bearing

Numerical and Experimental Studies on Performance Enhancement of Thrust Pad Bearing Employing Surface Texture: A Review

Numerical and Experimental Studies on Performance Enhancement of Thrust Pad Bearing Employing Surface Texture: A Review

A Mixed Lubrication Deterministic Model of an Elastic Support Water-Lubricated Tilting Pad Thrust Bearing

In order to study the effect of surface roughness on lubrication performance of an elastic support water-lubricated tilting pad thrust bearing, a mixed lubrication (ML) deterministic model is hereby presented based on a unified Reynolds equation model. This very model incorporates the elastic–plastic deformation of asperities and polymer matrix of the thrust pad, as well as the elastic deformation of the rubber support. The randomly distributed surface roughness of the thrust pad is generated by a mathematical model and shares the same distribution characteristics as the measured surface roughness. The Greenwood and Williamson asperity contact model and thin plate deformation model are combined to solve the asperities contact stress and deformation. Meanwhile, the bearing ML performance is compared with the results calculated by a thermohydrodynamic (THD) lubrication model and a thermo-elasto-hydrodynamic (TEHD) lubrication model, while the film thickness is also compared with measurements. The results show that the water film thickness calculated by the ML model is smaller than that by the THD model and the TEHD model, but the water film temperature is higher. The roughness has a great influence on the contact area ratio and the lubrication state, but little effect on the average film thickness. A higher roughness indicates a higher rotational speed required for the bearing to achieve full hydrodynamic lubrication. The film thickness calculated by the mixed lubrication model is closer to the measured results. Overall, it is proved that the mixed lubrication model can more accurately predict the lubrication performance of bearings. Compared to the thin plate deformation model, the elastic deformation simulation based on the half-infinite space model severely overestimates the elastic deformation of the pad surface, making it unsuitable for calculating the elastic deformation of the polymer matrix of the thrust pad under contact force or water film pressure. This ML deterministic model provides an effective means for high-precision prediction of the lubrication performance of the elastic supported water-lubricated thrust bearings coupled with multi-layer soft materials.

The effect of misalignment on the performance of tilting pad thrust bearing with TEHD coupling model and turbulence model

A thermoelastohydrodynamic (TEHD) coupling model is developed to study the static performance of a heavy-duty tilting pad thrust bearing (TPTB) under the effect of axis misalignment. To ensure the validity in calculating thermoelastic deformation, the calculation accuracy of the mechanical and thermal deformations used in the TEHD model is verified by the finite element method (FEM). The influence of the TEHD model on the flow state prediction is determined using different axial loads, and the numerical analysis of turbulence model and centrifugal inertia term on the bearing pad temperature is conducted at various operating rotation speeds. Compared with the aligned bearing performance, the characteristic distribution of each bearing pad under different misaligned angles is obtained. The effect of misalignment will cause local overheating of the thrust-bearing pads, especially for the heavy-duty TPTD. The results of this study can help to improve the prediction accuracy of heavy-duty TPTB characteristics and avoid harmful misalignment effects. Therefore, it is necessary to consider the effects of misalignment, turbulence, and thermoelastic deformation in the design and analysis of thrust bearings.

Performance of electro-rheological (ER) lubricant operated hybrid circular thrust pad bearing considering 3D surface irregularities

This paper describes the behaviour of ER lubricated hybrid circular thrust pad bearing (HCTB) having three-dimensional (3D) surface irregularities. Finite element analysis has been used to solve the Reynolds equation and the orifice restrictor equation to analyze the behaviour of hybrid circular thrust pad bearing with irregular surface. The use of ER lubricant and consideration of 3D surface irregularities results in improved load capacity, and damping coefficient, but reduces the stiffness coefficient of HCTB. The dynamic stiffness S̅ and damping C̅ coefficients gets altered around − 98% and 44.45% respectively due to the synergic effect of ER lubricant (V=800volt) and 3D surface irregularity (h̅a=0.2) in comparison to smooth surface (h̅a=0) HCTB lubricated with Newtonian Fluid (V=0volt).

Analysis of Second-Order Thrust Bearing Coefficients Considering Misalignment Effect

PurposeThrust bearings play a critical role in high-speed rotating machinery, such as turbines, pumps, compressors, and turbogenerators, by transferring axial loads between the collar and the bearing pads. The lubricating fluid prevents contact, friction, and wear between solid parts and acts as a cooling medium. The purpose of this study is to evaluate the first- and second-order bearing coefficients of an inclined pad hydrodynamic thrust bearing, which have not been previously investigated, to improve the accuracy of modeling thrust bearings.MethodsIn the analysis of thrust bearing systems, the lubricating fluid film is modeled as a massless spring-damper system. The finite perturbation method for the governing Reynolds equation is used to calculate the dynamic coefficients of the thrust bearing. This is done using the finite difference method (FDM) in polar coordinates.ResultsThis study investigates the influence of misalignment, rotating speed, and mesh size on the bearing coefficients of the thrust bearing. The results show that misalignment angle and film thickness have a clear effect on the dynamic coefficients, while changing the rotational speed has no effect on the damping coefficients. The study also investigates the axial force and moments and dynamic coefficients of an inclined pad thrust bearing.ConclusionThis study concludes that evaluating the first- and second-order bearing coefficients of the thrust bearing using the finite perturbation method can improve the accuracy of modeling thrust bearings. The study also highlights the significant influence of misalignment and film thickness on the dynamic coefficients of the thrust bearing. The results presented in this study provide valuable data that can be used as input for rotor dynamics analyses in high-speed rotating machinery.

Performance Prediction Model for Hydrodynamically Lubricated Tilting Pad Thrust Bearings Operating under Incomplete Oil Film with the Combination of Numerical and Machine-Learning Techniques

Pivoted pad thrust bearings are common machine elements used in rotating mechanisms in order to support axial loads. The hydrodynamic lubrication of such bearings has been a major subject of many investigations over the years. However, the majority of these investigations are based on full film lubrication models, when, in fact, incomplete oil film profiles appear during various operating conditions, such as startups and shutdowns. The lack of lubricant during operations can have severe impact on the bearing’s performance, affecting its ability to carry the applied axial load. The scope of the current investigation is to combine numerical analysis and machine-learning techniques in order to create a model that predicts the thrust bearing’s performance in terms of the pad’s load-carrying capacity. For this purpose, the 2-D Reynolds equation is solved numerically for a variety of angular velocities and three different lubricants: SAE 20, SAE 30 and SAE 10W40. The position of the lack of lubricant within the oil film’s control volume is studied and evaluated, together with the percentage of oil film coverage in the inlet of the pad. The results of the numerical analysis are used as input, in order to train and evaluate three different machine-learning models: Quadratic Polynomial Regression, Quadratic SVM Regression and Regression Trees. The results showed that the position of the film incompleteness affects the ability of the bearing to carry the axial load. At the same time as less lubricant entered the domain, the pressure drop could reach lower values, up to 93%. From the studied lubricants, SAE 10W40 was the one that showed the best performance results during incomplete oil film operation. Finally, the Quadratic Polynomial Regression model showed the best fit and 99% accuracy in predicting the pad’s load-carrying capacity.

Nonlinear vibration phenomena in hydrodynamically supported rotor systems

It is a well-known fact, that hydrodynamically supported systems are prone to nonlinear vibrations. Their exact simulative prediction with respect to frequency and amplitude is complicated by the fact that different system properties interact. The paper at hand outlines an approach that takes all relevant influences like rigid body motions, elastic deformations, nonlinear relation between fluid film pressure and bearing kinematics as well as temperature increase due to power loss or adjacent heat sources into account as detailed as necessary. Both journal and thrust bearings are considered as they contribute to the system's stiffness and damping capabilities. The approach is applied to self-excited pad vibrations of tilting pad thrust bearings as well as the run-up simulation of a turbocharger rotor under different axial loads. Both models are validated against measurements.

Multiscale analysis and numerical simulation of hydrodynamic inclined fixed pad thrust bearing with ultra low surface separation

In the hydrodynamic inclined fixed pad thrust bearing, when the surface separation is ultra low, there will be the special hydrodynamic mode where in the inlet zone occur both the adsorbed boundary layer flows and the intermediate continuum fluid flow i.e. the multiscale flow and in the outlet zone only occurs the physical adsorbed boundary layer flow. This new mode of hydrodynamic bearing has not been addressed before. Here, we present the corresponding multiscale hydrodynamic analysis for this bearing. The inlet zone flow is described by the closed-form explicit multiscale flow equations. The outlet zone flow is described by the nanoscale flow equation. First, the analytical derivations for the pressure distribution and carried load of the bearing were feasibly made by making a reasonable assumption. Then, full numerical solutions to the bearing were obtained to verify the analytical solution. It was found that there are significant differences between the analytically calculated pressure distribution and the numerically solved pressure distribution for the same operating condition; however for the studied different fluid-bearing surface interactions, when the surface separation is relatively large, the analytically derived load equation can be used to calculate the carried load of the bearing. Numerical solutions clearly show that stronger the fluid-bearing surface interaction, higher the generated hydrodynamic pressure in the bearing, and larger the carried load of the bearing. The study not only provides the mathematical tools for studying the bearing but also gives the indication of the strong adsorbed boundary layer effect in this bearing.

Design of Hydrodynamically Lubricated a New Micro-pocketed Tilting Pad Thrust Bearing Based on Simulated Performance Parameters

Design of Hydrodynamically Lubricated a New Micro-pocketed Tilting Pad Thrust Bearing Based on Simulated Performance Parameters

Investigation of the synergism on distribution parameters of micro dimples in partially textured thrust pad bearing

Partially surface texturing is a promising technology to improve the performance of thrust pad bearing. Moreover, how to design the distribution parameters of local textures is a crucial issue of the amelioration of lubrication and anti-friction. Hence, the synergistic effect of micro dimples’ distribution parameters was systematically investigated by numerical and experimental approaches. The textured region area ratio (TRAR) was defined to analyze the synergy of radial and circumferential parameters. Then, a series of frictional tests were conducted with different positions and proportions. The results showed that the CPP and RPP directly determined the efficacy of the ‘equivalent Rayleigh step’ which could enhance the cumulative response of hydrodynamic lubrication. Meanwhile, there was an optimal TRAR (about 0.8) according to the favorable fitting curve with R Square (R2) being 0.9013. And circumferential proportion parameter (CPP) and radial proportion parameter (RPP) exhibit an interactive relationship which was dependent on the optimal TRAR. On the other hand, for generating the ‘inlet roughness’ and ‘open pocket’, the circumferential location parameter (CLP) of local textures needed to keep close to the inlet without consideration of the radial location parameter (RLP) due to the negligible influence.