Porous Bearings Research Articles

Effect of Variation in Viscosity on Static and Dynamic Characteristics of Rough Porous Journal Bearings with Micropolar Fluid Squeeze Film Lubrication

In the present study, an effort was made to determine the effects of a porous matrix with different viscosities on the dynamic and static behaviors of rough short journal bearings taking into account the action of a squeezing film under varying loads without journal rotation. The micropolar fluid was regarded as a lubricant that contained microstructure additives in both the porous region and the film region. By applying Darcy’s law for micropolar fluids through a porous matrix and stochastic theory related to uneven surfaces, a standardized Reynolds-type equation was extrapolated. Two scenarios with a stable and an alternating applied load were analyzed. The impacts of variations in viscosity, the porous medium, and roughness on a short journal bearing were examined. We inspected the dynamic and static behaviors of the journal bearing. We found that the velocity of the journal center with a micropolar fluid decreased when there was a cyclic load, and the impact of variations in the viscosity and porous matrix diminished the load capacity and pressure in the squeeze film and increased the velocity of the journal center.

Opportunities to Enhance sCO2 Power Cycle Turbomachinery with Bearingless Motor/Generators

Thermal power cycles using sCO2 as a working fluid place extreme demands on their turbomachinery components and their electric motors/generators. In this paper, new system topologies for sCO2 turbomachinery are proposed which take advantage of “bearingless” electric machine technology to improve performance. Bearingless motors/generators are a new type of electric machine which integrate the functionality of active magnetic bearings into the existing hardware of an electric motor/generator. The existing electromagnetic surfaces and materials are reused to enable controllable production of radial forces on the machine shaft. This is envisioned to improve hermetic direct-drive turbomachinery systems by either augmenting existing bearings (i.e., bearing assist) or replacing existing bearings (i.e., bearing removal). The state-of-the-art technologies for several bearing types (gas foil bearings, externally pressurized porous (EPP) gas bearings, and active magnetic bearings) and electric machines are reviewed to motivate the introduction of bearingless technology. Two system designs using bearingless machines are proposed and compared against existing commercial solutions in terms of maximum shaft weight, number of passthroughs into the hermetic environment, cost, and complexity. A case-study bearingless motor/generator is assessed via simulations and a hardware prototype to investigate practical considerations for using bearingless technology in sCO2 turbomachinery. The proposed bearingless solutions have potential to enable a new generation of sCO2 turbomachinery with improved reliability, reduced complexity, and lower cost. This paper shows that by transforming the motor/generator already present in turbomachinery into a bearingless motor/generator, the technical challenges involved with sCO2 can be overcome without adding significant cost.

Integrating experimental and theoretical investigations of porous graphite materials with scanning electron microscope image processing

Accurate determination of fractal dimension (FD) and permeability of porous graphite materials (PGM) is essential for applications like porous aerostatic bearings (PABs). This study addresses the need for improved measurement methods by employing image processing and computer vision (IPCV) techniques to enhance FD and permeability accuracy. We aimed to refine these measurements by analysing the effects of image size and magnification on accuracy. The research developed theoretical models based on fractal theory, Darcy's law, and a modified Hagen-Poiseuille gas equation to evaluate these effects. A dual-path X-ray imaging detection system was used for experimental validation. The gauge pressure was varied across the surface of the PGM and volume flow rate was measured. MATLAB was utilized for IPCV, enabling precise FD determination and underscoring the importance of image parameters. Results showed that FD values stabilize at specific image sizes and magnifications, improving accuracy. Linear relationships between pressure gradient and volume flow rate were observed, with permeability stabilizing at high pressures. Porosity values varied among materials: Toyo Carbon (15 %), SGL Graphite (17 %), Super Carbon Graphite (27 %), and poplar porous (30 %). FD obtained through theoretical and scanning electron microscope (SEM) methods had a maximum error of 0.08. The study also found a positive correlation between relative density and image grayscale at the macroscopic level. The findings emphasize the importance of optimizing image size and clarity for accurate PGM analysis, providing crucial insights for PAB design and other advanced applications.

On the dynamics and wear properties of dry friction bearings in motor rotor system considering rough surface contact damping

Maintaining rotor stability and reducing bearing wear hold practical significance for the rotor system. However, the dynamic properties of rotor system supported by dry friction bearings are unknown, hindering effective bearing optimization. To tackle this issue, a 5-degree-of-freedom dynamics model is established for the motor rotor system of the outdoor unit supported by porous bearings. The rough surface damping contact model is employed to calculate the contact performance of the dry friction bearings. The effects of bearing edge modification on system dynamics and bearing wear properties are investigated and compared with well-lubricated bearings. The results demonstrate that an appropriate amount of edge modification can decelerate the impact between the rotor and the bearings and reduce wear under dry friction conditions.

On the static performance of aerostatic elements

Porous aerostatic bearings and seals offer several advantages in precision engineering applications. The static performance of aerostatic elements, i.e., bearings and seals, is investigated both experimentally and numerically. This study presents a method, a test setup, and a measurement of the air gap pressure distribution with high spatial and temporal resolution. This study presents experimental and numerical results of the load capacity, air gap height, static stiffness, air consumption, and air gap pressure distribution. The experimental results are compared to a numerical model based on the modified Reynolds equation. Furthermore, boundaries for the operating parameter space of the investigated seal are determined by stiffness and leakage. The experimental results and the numerical model showed good correlation, providing corroborative evidence for the accuracy of the measurement setup and the feasibility of the pressure measurement method.

Analysis of Lubrication Regimes for Porous Sliding Bearing

The purpose of this paper is to analyze the lubrication quality of porous sliding bearings, starting from the bearing model and in combination with experimental results aimed at analyzing the lubrication regimes of different working conditions. The separation between the surfaces by the lubricant layer is what determines the regime. The quality and type of lubrication regime are determined by parameters in the mathematical model including typically speed, load, motion, materials, environment, etc., which have an impact on friction. Besides those elements, important parameters such as coefficient of friction (COF) and working temperature are to be measured due to experimental investigations to detect an equilibrium working state. The self-lubrication mechanism in porous metal bearings improves their service life and lubrication processes; however, the COF still varies within a wide interval. This variability can be understood, considering that during bearing operation it operates within a broad range of lubrication regimes. Those findings are explained in the paper by using a combination of calculated parameters according to the bearing model and in combination with our own results of experimental investigations. With the obtained results for particular working conditions, the authors are trying to explain, in the form of a diagram with the limit line as an important outcome of the work, that the lubrication regime for porous metal bearings could arise from boundary lubrication (BL) close to hydrodynamic lubrication (HDL).

Pressure evaluation in highly porous medium hydrodynamic bearings

This paper presents an experimental investigation into lift generation during the tangential motion of an inclined surface over a compressible porous layer, focusing on an exceptionally slow sliding speed, a condition that has not been considered in previous studies. Specifically, we validated Pascovici's one-dimensional lubrication model for an inclined slider under the above condition. Additionally, we explore the use of woven fibrous material for soft porous lubrication, broadening the range of media for future studies.

Multifunctional silicon carbide/cement-based composites for porous aerostatic bearings

Multifunctional silicon carbide/cement-based composites for porous aerostatic bearings

Evaluation of the performance characteristics of aerostatic bearing with porous alumina (Al2O3) membrane using theoretical and experimental methods

Instruments with high levels of precision commonly use aerostatic bearings. Moreover, the use of porous (Al2O3 membrane) material validates that the pressure is spread uniformly throughout the air film region. The impression of applied load on the thickness of the air film of the aerostatic bearings was evaluated using a certain experimental technique. As the applied load rises, the thickness of the air film expands, and as the compressive stress rises, it contracts. The theoretical model parameters were set using the experimental stipulations. It was discovered that the theoretical model and the experimental data were consistent. The pressure gradient induced in the air film and the air bearings’ capacity for carrying loads were calculated using a theoretical simulation. The results of theoretical modeling and experimental comparison of the different characteristics of porous (Al2O3 membrane) aerostatic bearings based on stiffness and load-carrying capacity are graphically illustrated in this study. Porous aerostatic bearings with Al2O3 membranes have a number of potential applications, including high-speed spindles, precision instruments, microelectromechanical systems, vacuum pumps, cryogenic applications, etc.

Universal accuracy model for three different types of precision bearings with three basic structures under quasi-static conditions

A universal accuracy model is established under quasi-static conditions to predict motion accuracies and directly compare error averaging abilities among three different types of precision bearings (including fluid hydrostatic, porous air, and cylindrical roller bearings) with three basic structures (including linear (i.e., guideway), journal, and thrust bearing structures) used widely in precision and ultra-precision machine tools. To introduce the universal accuracy model, three types of precision guideways are taken as examples. Uniform generalized coordinate systems are used to evaluate error motions and uniform averaging coefficients are defined to assess error averaging abilities. It is found that the total error averaging abilities consist of basic and layout error averaging abilities characterized by corresponding averaging coefficients. The total averaging coefficients are the products of basic and layout averaging coefficients which are independent of each other. The porous air bearings have strongest basic error averaging abilities, followed by the fluid hydrostatic bearings, and finally followed by the cylindrical roller bearings. The layout averaging coefficients are related to the number and layout of pads or rollers which are working like some structural filters for a certain kind of error motion. A summary of accuracy experiments based on previous studies provides evidence of the existence of layout error averaging abilities. The content discussed in this paper is of significant importance for the selection and design of precision bearings.

Permeability prediction of porous aerostatic bearings through 3D morphology and fractal calculation method

AbstractPorous ceramics for aerostatic bearing restrictors were fabricated using carboxymethyl cellulose and polystyrene microspheres as pore formers. The three‐dimensional morphology of the porous ceramics was nondestructively obtained using laser scanning confocal microscopy, and the processing information was eliminated by fitting the pore area fractal dimensions at different heights. A mathematical model was developed based on the assumption of elliptical tortuous capillaries to relate microstructural pore parameters to permeability by combining fractal theory, Darcy's law, and the gas conservation equation. The calculated permeability closely matched the experimental results, with an error of less than 3.5%. This method has promising potential as an alternative to pressure drop experiments. Moreover, the capacity of the fractal calculation model to establish a correlation between microstructural parameters and permeability paves a new way to design future porous aerostatic bearings.

A novel transient computational fluid dynamics-fluid–structure interaction model for the pad adaptive motion and rotordynamic coefficients of hybrid porous tilting pad bearings

Hybrid porous tilting pad bearings with the advantages of gas porous bearings and tilting pad bearings exhibited excellent rotor-supporting performance with high accuracy and stability. Under hybrid lubrication, the transient adaptive motion of the tilting pads was important for the rotordynamic characteristics. A novel fluid–structure interaction model of hybrid porous tilting pad bearings was developed to investigate the transient hydro forces and the pad's adaptive motion. The rotordynamic coefficients of the hybrid porous tilting pad bearings were identified using the rotor harmonic trajectory. The computational fluid dynamics-fluid–structure interaction model was validated with the experimental data. The effects of eccentricity ratios, rotor speeds, supply pressures, pivot radial stiffnesses, and dampings on the pad adaptive motion and the rotordynamic coefficients were evaluated. The pad self-adaption motions significantly influenced the supporting and vibration-absorbing characteristics of hybrid porous tilting pad bearings.

Semi-analytical approach-based studies of the squeeze film lubrication between rough porous annular discs: Rabinowitsch fluid model

In recent years, there has been much interest in the effects of porosity and surface roughness (SR) or geometric irregularities between two moving plates under hydrodynamic lubrication. Porous bearings are used extensively in wide range of equipment, including computers, office equipment, home appliances, electric motors, and vehicles. In light of the importance of the aforementioned applications, we explored how SR and porous materials affect annular discs under the condition of a squeeze film. A five-point Gauss quadrature integral formula has been used to examine the characteristics of annular discs and a small perturbation method has been used to discretise the governing Rabinowitsch fluid flow (RFF) equations. The impact of nonlinear parameters on the behaviour of porosity and SR have been visualised in terms of film pressure (FP), load carrying capacity (LCC), and squeeze response time (SRT) of annular discs. Under the conditions of pseudoplastic and dilatant fluids, the effects of SR and porous materials between annular discs have been estimated in the form of the film pressure, LCC, and SRT and are presented in this manuscript as tables and graphs. According to the findings, the performance of an annular disc is significantly affected by porous material and radial roughness patterns. In addition, when RFF is carried through a rough surface and porous media, the performance is found to improve for dilatant fluids but suffer for pseudoplastic fluids.

Numerical Modeling and Simulation of a Poroelastic Journal Bearing Lubricated By Nanofluids with Couple-Stresses

In this paper we present a numerical simulation of a porous journal bearing considering the fluid film – poroelastic matrix interaction and the non-Newtonian rheological behavior of nanolubricant consisting of base fluid and nanoparticles (NPs). The flow of nanolubricant in the bearing clearance space is described by the Vijay Kumar Stokes micro-continuum theory which considers the characteristic size of nanoparticles such as fullerenes dispersed in a base oil. The flow of the nanolubricant in the porous medium is modeled by the modified Darcy’s law where the Beavers–Joseph slip conditions are applied at the fluid film-porous matrix interface. The deformation of the fluid-film porous matrix interface due to hydrodynamic pressure is calculated by using a simplified analytical thin elastic liner model. The hydrodynamic behavior of lubricating film is governed by the modified Reynolds equation obtained from the momentum, moment of momentum, and mass conservation laws using the classical Reynolds derivation process. The bearing porosity is introduced into the governing modified Reynolds equation by means of the Morgan-Cameron approximation. The steady-state analysis shows that for an imposed operating eccentricity, the load capacity increases with the characteristic size and the concentration of NPs while the attitude angle, the leakage flow rate, and the coefficient of friction decrease. On the other hand, the permeability decreases the hydrodynamic pressure, the load capacity, and the leakage flow rate, and increases the attitude angle and the coefficient of friction.

Hybrid ANFIS-PSO algorithm for estimation of the characteristics of porous vacuum preloaded air bearings and comparison performance of the intelligent algorithm with the ANN

Air bearings are commonly used in systems requiring high precision, including semiconductor manufacturing, optical and electronic devices, and aerospace systems, and the usage of vacuum preloading and porous material provides a homogeneous pressure distribution on the bearing surface. The prediction of the characteristics of these air bearings, such as air film thickness and location, is crucial for designing and optimizing the performance of the systems. They exhibit highly nonlinear behavior and are challenging to accurately predict their characteristics using conventional analytical or numerical techniques. In this study, the characteristics of vacuum preloaded porous air bearings are estimated using a hybrid ANFIS-PSO predictor soft computing method with a certain pressure (410 kPa), vacuum (50.8 kPa), and with three different diameters (50, 75 and 90 mm). The usage of different algorithms in the characteristics and selection and design criteria of air bearing has been applied. Six different cases are simulated with different input and output parameters to predict the air film thickness and location of the air bearing. The location of the air bearing has been determined with two angle parameters, α, and β. The dataset required for training and testing the algorithm was obtained through experimental study. In the training and testing process, 40 and 20 datasets were used, respectively. Before the starting analysis, a sensitivity analysis was executed to find optimum PSO parameters such as the number of particles, acceleration coefficients, number of membership functions, and inertia weight. The proposed hybrid ANFIS-PSO method was compared with classical ANFIS and ANN, and it showed better performance and a more accurate solution to estimate the characteristics of vacuum preloaded porous air bearings in both training and testing phases with the R2 of 0.9958 and MSE value of 0.102. The maximum training performance of the ANFIS-PSO is better than ANFIS and ANN with the ratio of 6.8% and 8.5%, respectively. On the other hand, the maximum testing performance of the ANFIS-PSO algorithm is higher than ANFIS and ANN, with the ratio of 22.2% and 24.1%, respectively.

Evaluation of the steady-state performance characteristics of a two-layered porous journal bearing under turbulent regimes

Evaluation of the steady-state performance characteristics of a two-layered porous journal bearing under turbulent regimes

Research on dynamic characteristics and structural optimization of porous gas bearings in linear compressors

In order to study the influence of structural parameters of porous gas bearing and operating parameters of linear compressor on the static and dynamic performance of porous gas bearing, based on gas lubrication theory, Darcy's law and Reynolds equation, the mathematical model and simulation model of porous gas bearing of linear compressor are derived and established. The static and dynamic characteristics of the porous gas bearing of the linear compressor are studied by using Fluent software simulation. According to the simulation results, the effects of inlet pressure, porous material thickness and gas gap on the gas consumption and bearing capacity of the porous gas bearing under different eccentricities are analyzed. The results show that the higher the inlet pressure is, the larger the gas consumption and bearing capacity; the thicker the porous material is, the smaller the gas consumption and the larger the bearing capacity, the thicker the gas gap is, the larger the gas consumption and the smaller the bearing capacity. On the basis of simulation research, considering the difficulties of processing and assembly, multi-objective optimization of porous gas bearings is carried out based on response surface methodology. Taking the bearing capacity and gas consumption as the objective functions, the intake pressure is set between 0.3 and 0.5 MPa, the thickness of porous materials is set between 3 and 5 mm, and the thickness of gas gaps is set between 10 and 20 μm. While ensuring the stable operation of the linear compressor, the optimal combination of design parameters is provided for the optimal design of gas bearings used in linear compressors.

A novel parallel capillary-cavity model for the analysis of pneumatic hammer vibration in porous aerostatic bearings

Porous aerostatic bearings (PABs) are widely used in high-speed applications and ultra-precision machinery owing to their frictionless motion and remarkable stability. In this paper, a novel parallel capillary-cavity model based on the intricate pore structure characteristics is established to characterize air flow in PABs and analyze the pneumatic hammer vibration. An experimental setup is constructed to measure the pneumatic hammer vibration of PABs. The experimental results exhibit a strong agreement with the predictions. The effects of various factors, including different loads, air pressures and porosities on the pneumatic hammer vibration are thoroughly discussed. The results show that higher air supply pressures, larger loads, and increased porosity are more likely to trigger pneumatic hammer vibration in PABs.

Manufacturing and static performance of porous aerostatic bearings

According to the common body of knowledge, aerostatic bearings invariably need narrow manufacturing tolerances to ensure maximal load capacity and high stiffness. This study experimentally investigates the manufacturing of porous material aerostatic bearings and the effect of manufacturing parameters on the performance properties of the bearings. During the study, samples were manufactured using different methods, and the geometrical and performance properties of each sample were inspected. The bearing performance measurement device developed during the study is introduced. The results present the dependence between manufacturing parameters and bearing properties under varying load and operating pressure conditions. The results clearly suggest that effect of bearing surface roughness on load capacity is small; meanwhile, surface planarity has a major impact on load capacity.

Wavelet lifting method for the numerical solution of micropolar lubrication problem of porous journal bearing

The pivotal aim of this paper is to develop the wavelet lifting method for the numerical solution of the micropolar lubrication problem of porous journal bearings. To ensure the applicability of the proposed method initially, test problems are considered and the numerical findings are presented in figures and tables elucidate that, the proposed method is more efficient and promising with the consumption of lesser computational CPU time. Subsequently, the effect of micropolar fluid on the porous journal bearing is analyzed by solving the corresponding non-dimensional Reynolds equation of the lubrication problem is considered. The obtained results for pressure distribution and load carrying capacity with varied parameters show that the squeeze film pressure and load carrying capacity are significantly increased by the micropolar fluid effect as compared to the Newtonian case.