High Eccentricity Ratios Research Articles

Performance of a Small Hydrodynamic Journal Bearing Involving Adsorbed Layer and Surface Elastic Deformation

The load and friction performances of a small elastohydrodynamic journal bearing with the shaft radius 1mm have been computationally studied. The effect of the adsorbed layer is incorporated and the multiscale hydrodynamic flow theory is used. It is shown that the multiscale performance of this bearing occurs in the wide eccentricity ratio range from 0.3 to nearly unity because of the influence of the adsorbed layer, and thus the generated pressures and carried load of this bearing are significantly greater than the classical hydrodynamic theory calculations. The effect of the adsorbed layer is more stronger for rigid bearing surfaces than for elastic bearing surfaces especially for a strong fluid-bearing surface interaction, and it is strong for the high eccentricity ratios over 0.9. In this bearing, when the effect of the adsorbed layer is incorporated, the friction coefficients on both bearing surfaces are reduced in the wide eccentricity ratio range as compared to the classical calculation; Stronger the fluid-bearing surface interaction, greater the reduction of the friction coefficient, showing the pronounced non-continuum effect of the adsorbed layer. However, for elastic surfaces the friction coefficient is a bit higher than that for rigid surfaces especially for high eccentricity ratios and strong fluid-bearing surface interactions.

Numerical studies on low-temperature eccentric-compression behaviours of UHPC-filled Q690E high-strength steel tubes

This paper numerically studied the compression behaviours of ultra-high performance concrete - filled square high strength steel tubes (UFSHTs) at low temperatures. Firstly, finite element models (FEMs) were developed to simulate the ultimate strength behaviours of UFSHTs under bending and compression, which were extensively validated by bending and compression test results. Then, extensive FEM analysis were carried out to investigate the low-temperature eccentric-compression behaviours of UFSHTs at low temperatures. The studied parameters in this numerical analysis included low temperatures, eccentricities, and slenderness ratios. The FEM parametric studies showed that (1) reducing low temperatures improved the eccentric-compression capacities; (2) The load-displacement curves exhibited a more protracted hardening stage with higher eccentricity ratios; (3) the normalized N-M curves were shrunk inward with slenderness ratios increasing. Finally, modified code equations were proposed to estimate the N-M interactions of UFSHTs under low-temperature eccentric-compressions, and validations of the predictions against the test and numerical results confirmed that the modified Eurocode 4 code equations provided more reasonable estimations than AISC360 and GB50936.

Long-term creep behavior of glulam member under compression and bending moment

ABSTRACT In this study, 12 glulam members were designed and tested, considering the effects of stress ratio and relative eccentricity. After the 180-day test period, the results showed that increasing the stress ratio and relative eccentricity led to large initial elastic deformation and creep deformation, and the creep coefficients at 180 days for the glulam members under higher stress ratio and relative eccentricity were lower than those for the glulam members under lower stress ratio and relative eccentricity. Typical empirical and mechanical models and a modified model were chosen to fit the creep coefficient curves. The fitting analysis indicated that the values of the R 2 for all creep models were larger than 0.90, reflecting the goodness of fit. Employing the modified model, the prediction of the creep coefficient for the compressive-bending glulam member over 50 years was conducted. The results found that the glulam members under high relative eccentricity and stress ratio exhibited low creep coefficients, of which values approached to 0.7. Compared to creep coefficients specified in current standards and literature, the creep coefficient of 1.5 at a 50-year period for the compressive-bending glulam members was recommended, aiming to provide a reference to the long-term design of the compressive-bending glulam member in practice.

Thermal effect induced by viscous dissipation on characteristics of aerodynamic foil journal bearing with aero-thermo-elastic coupling

In aero–thermo–elastic analysis, aerodynamic foil bearings are one of the most representative components that involve strong coupling among microscale shear flow, aerodynamic heating, and elastic foil deformation. Researches on the role of aerodynamic heating in bearings are really inadequate. This study clarifies the effect of thermal behavior induced by viscous dissipation on the characteristic of an aerodynamic foil journal bearing (AFJB) with a rotational speed of 4 × 104–8.0 × 104r/min and an eccentricity ratio of 0.4–0.8. The results indicate that the thermal effect induced by viscous dissipation significantly affects the aerodynamics of shear flow and the dynamic response of elastic foils in the AFJB. The inherent thermal effect induced by viscous dissipation strengthens the inherent viscosity-temperature effect and weakens the pulsation of static pressure while intensifying the temperature increase of the shear flow. The dynamic response of the elastic foils in the solid domain is closely associated with the behavior of shear flow in the fluid domain. The static pressure and temperature elevation increase with the rotational speed and eccentricity ratio owing to strengthened hydrodynamic effects. The effect of thermal behavior induced by viscous dissipation on the aerodynamic and thermal characteristics of the shear flow becomes significant at high rotational speeds and eccentricity ratios. The load capacity and peak temperature elevation increase with the rotational speed and eccentricity ratio. In the solid domain, the thermal effect induced by viscous dissipation negligibly affects the deformation of the elastic foils because the variation in the temperature increase is insignificant, thus resulting in insignificant variations in the properties of the gas film. This study elucidates the impact of aerodynamic heating, especially the thermal effect induced by viscous dissipation, on the aero–thermo–elastic field in bearings and the performance of the bearings. The results of this study serve as basic design guidelines for AFJBs and can be used to optimize the operation security.

Thermo-hydrodynamic Analysis of Multistep Journal Bearing using Computational Fluid Dynamics Simulation

Journal bearing is a machine element that is used to maintain the continuous rotation of the shaft on its axis. The rising demand for efficient and economical journal bearing applications has resulted in increased demand for high-speed machines. An increase in engine speed raises the distribution of pressure, temperature, and vapor volume fraction. Most of the research still only focuses on increasing pressure distribution and load-carrying capacity. However, the value of friction force, temperature distribution, and vapor volume fraction must also be considered such that the lubrication of the journal bearing is close to the real situation. Therefore, the research was conducted by varying the geometry modelling through multistep textures using viscous boundaries and thermo-hydrodynamic lubrication. Owing to the high load and speed usage on multistep journal bearings, research on the effect of eccentricity ratio and inlet and outlet temperatures on the tribological performance of multistep journal bearings was conducted. The analysis has been performed using a multistep journal bearing modelling 3D computational fluid dynamics considering the effect of cavitation on temperature. The results of this study indicate that the use of multistep textures on journal bearings can reduce friction force, temperature, and vapor volume fraction. The variation of the eccentricity ratio shows that a high eccentricity ratio leads to a high three parameters (i.e., friction force, temperature, and vapor volume fraction). Finally, for variations of inlet and outlet temperatures, such parameters are high when the inlet and outlet temperatures are high.

Performance analysis of journal bearing having surface waviness operating under misaligned condition

In this present study, the effect of surface waviness on the performance of journal bearing operating in misaligned conditions has been investigated. The journal’s misaligned conditions in the present analysis are taken about the circumferential, the axial, and both axes. For computing the pressure of lubricant inside the bearing, the finite element method has been applied to solve the Reynolds equation and thus static parameters are obtained. The static parameters, that is, load carrying capacity and coefficient of friction are evaluated at different waviness variables and are compared with misaligned journal bearing without surface waviness. It is observed that misalignment considered in both axes has the most severe effect on static performance parameters as compared to misalignment only in the circumferential or axial axis. With the increase in circumferential waviness number up to n = 5, the load-carrying capacity increases, and the coefficient of friction decreases under high eccentricity ratios. Change in waviness amplitude also impacts the bearing performance. Axial waviness always deteriorates the bearing performance. Combined waviness increases the load carrying capacity and decreases the coefficient of friction when circumferential waviness number n = 5 and axial waviness number m = 2. The highest performance enhancement ratio is attained at an eccentricity ratio of 0.8 with a circumferential waviness number n of 5, axial waviness number m of 2, and dimensionless waviness amplitude [Formula: see text] of 0.075.

Fatty liver disease, heart rate and cardiac remodelling: Evidence from the UK Biobank.

Growing evidence supports an association between fatty liver disease (FLD) and cardiac dysfunction and remodelling, leading to cardiovascular disease and heart failure. Herein, we investigated the independent contribution of FLD to cardiac dysfunction and remodelling in participants from the UK Biobank with cardiac magnetic resonance (CMR) data available. A total of 18 848 Europeans without chronic viral hepatitis and valvular heart diseases, with liver magnetic resonance imaging and CMR data were included in the analyses. Clinical, laboratory and imaging data were collected using standardized procedures. Multivariable regression models were used to test the association between FLD and CMR endpoints, after adjusting for several cardiometabolic risk factors. Linear regression models with regularization (Least Absolute Shrinkage and Selection Operator [LASSO], Ridge and Elastic Net) were used to generate predictive models for heart-related endpoints. FLD was independently associated with higher average heart rate, higher cardiac remodelling (higher eccentricity ratio and lower remodelling index), lower left and right ventricular volumes (end-systolic, end-diastolic and stroke volumes) as well as with lower left and right atrial maximal volumes (p < 0.001). FLD was the strongest positive predictor for average heart rate, followed by age, hypertension and type 2 diabetes. Male sex was the strongest positive predictor for eccentricity ratio followed by FLD, age, hypertension and BMI. For LV volumes, FLD was the strongest negative predictor along with age. FLD is an independent predictor of higher heart rate and early cardiac remodelling associated with reduced ventricular volumes.

Effects of geometrical parameters on thermohydrodynamic performance of a bearing operating with nanoparticle additive oil

PurposeBearing performance characteristics, such as stiffness and load capacity, are related to the viscosity of the fluid circulating through the gap. Nanoparticle additives in lubricant are one way to enhance of the viscosity. This study aims to investigate the effect of nanoparticle additives on the thermohydrodynamic performance of journal bearing with different bearing parameters.Design/methodology/approachThe temperature distribution is modeled using a three-dimensional energy equation. The velocity components are calculated on the pressure distribution governed by Dowson’s equation. Moreover, the heat transfer between the journal and lubricant is modeled with Fourier heat conduction equation. On the other hand, the viscosity equation is derived for Al2O3 nanoparticles as a function of the volume ratio and the temperature. An algorithm based on the finite difference method is developed, and a serial simulation is performed for different parameters and different volume ratio of nanoparticle.FindingsWith the increase in the nanoparticle volume ratio, the maximum temperature decreases for the lower clearance values, but the addition of the nanoparticle influence on the maximum temperature reverses when the clearance grows up. The nanoparticle additives increase further the maximum temperature for higher values of L/D ratios. Moreover, the effects of the nanoparticle additives on the pressure are stronger at high eccentricity ratios for all bearing parameters.Originality/valueThis paper provides valuable design parameters for journal bearing with lubricant containing the nanoparticle additives.

CFD Analysis of the Eccentricity Ratio on Journal Bearing due to Differences in Lubrication Type

Lubrication on journal bearings plays a vital role in reducing metal-to-metal friction, separates the reliable components. Often there is a decrease in lubrication conditions, which will cause failure or a change in roughness to the inner surface. Direct metal-to-metal contact between the bearing's inner and journal surface will gradually deform the bearing. In diesel engine applications, lubrication is aiming to minimize failure or damage to the journal bearing. This paper investigates a 3D CAD model of a journal bearing using the ANSYS Computational Fluid Dynamics software. The effect of eccentricity ratio is analyzed for semisynthetic lubricating oil R3 10W-30 and synthetic oil. The result shows that synthetic oil has a considerable pressure compared to R3 10W-30, especially at a higher eccentricity ratio.

Impact of partial surface waviness on the tribological performance of hydrodynamic journal bearing

AbstractIn this paper, the static performance analysis of journal bearing having full and partial surface waviness has been presented. The surface waviness is to be considered in the full, first half, second half, and pressure‐increasing and decreasing regions of the bearing for analysis. The effect of surface waviness is considered by modifying the lubricant flow governing Reynolds equation with the film thickness equation and it is solved with the finite element method to get performance parameters like bearing load capacity, friction coefficient, and so forth operating under eccentricity ratios range of 0.2–0.8. The waviness geometrical parameters like waviness numbers and amplitudes are also considered in circumferential, axial, and both directions in the selected regions. The maximum performance has been found for waviness in the full and pressure‐increasing region in the circumferential direction at a high eccentricity ratio.

Computational fluid dynamics-based investigation of the static and dynamic characteristic of hydrostatic bearing with nanolubricant: A theoretical method

The objective of this work is to study the characteristics of the hydrostatic bearing with nanolubricant. To investigate the effect of nanoparticle additives on the performance of hydrostatic bearings, a coupled heat transfer finite-element model of the hydrostatic bearing is developed, and the results of the static and dynamic performance of the hydrostatic bearing with lubricant and nanolubricant are evaluated based on computational fluid dynamics methods at different eccentricity ratios. The results show that the rotation error of the bearing–rotor system is reduced by using nanolubricant at a high eccentricity ratio.

Performance behavior of pocketed journal bearing employing non-newtonian lubricant

This paper reports the improvement in the performance behaviors of non-Newtonian fluid lubricated journal bearings employing a rectangular pocket. Coefficient of friction and load carrying capacity of pocketed and non-pocketed bearings are reported and discussed. In the numerical approach, non-Newtonian behavior of lubricant is simulated employing the power law model. Various cases of bearings having different axial length to diameter ratios [(L/D) in the range 0.5–2.0] are considered. Lubricants of different rheology viz. pseudoplastic, Newtonian and shear thickening were employed for lubricating the bearings. Rheology of lubricant is controlled by varying the power law index n in the range 0.9–1.1. Based on the investigation, it is found that the pocketed bearing yields significantly reduced coefficient of friction and higher load carrying capacity in comparison to the non-pocketed bearing. Also, the performance of pocketed bearing improves with the increase in the power law index. Best performance of the pocketed bearing is observed for the bearing having L/D value of 0.5 at high eccentricity ratio when lubricated with the shear thickening fluid (n=1.1).

Analysis of static and dynamic characteristics of aerostatic bearing with reflux orifices

Purpose The purpose of this paper is to provide a solution for Reynolds equation with both throttling term and reverse throttling term and provides a reference for changing damping of hydrostatic bearing. Design/methodology/approach The reverse throttling term is introduced into the Reynolds equation, and the adaptive damping factor is used in the Newton iteration method to improve convergence of numerical calculations. The static and dynamic performances of this bearing are numerically investigated by the finite-element method. Findings The results indicate that the reflux orifices lead to a decrease in load capacity at a high eccentricity ratio. Additionally, the mass inflow rate is increased; however, the additional inflow increase can be controlled by enhanced backpressure of the reflux orifice. Nevertheless, the bearing with the reflux orifice shows superiority in resisting high-frequency disturbances and enhances direct damping by 20% under a high backpressure. Originality/value This work presents an adaptive Newton damping iterative method for solving Reynolds equation with both throttling term and reverse throttling term. This work also provides a new idea for bearing structure design in improving damping.

Static and dynamic characteristics and stability analysis of high-speed water-lubricated hydrodynamic journal bearings

The purpose of this paper is to analyze the influence of turbulent, inertia, and misaligned effects on the static and dynamic characteristics and stability of high-speed water-lubricated hydrodynamic journal bearings. Based on the Navier–Stokes equation, the mixing-length theory, and the essential assumption that the velocity profile is not strongly affected by inertia force, the fluid lubrication model with turbulent, inertia, and misaligned effects is established, and then the stability analysis of bearings is carried out based on the equation of motion with four degrees of freedom. The model is solved by the finite difference method and the numerical results are compared under different operating conditions. The results show that the turbulent effect greatly increases the load capacity, power consumption, stiffness and damping coefficients, and stability of bearings, and the inertia effect significantly increases the volume flow rate of bearings, and the misaligned effect increases the load capacity, stiffness and damping coefficients, and stability of bearings. In high rotary speed and moderate eccentricity ratios, the influence of the inertia effect on the load capacity, stiffness coefficients, and stability cannot be neglected.

The Static Instability Characteristics of Labyrinth Seals: Experiments and Computational Fluid Dynamics Verification

Abstract The paper proposed an experimental measurement to identify the fluid-induced force and static stiffness coefficients. A three-dimensional fluid model of the labyrinth seals was also established. And the static characteristics under different eccentricities and inlet pressure were studied. Theoretical results show a good agreement with the experiment results. The labyrinth seal with different eccentricity ratios produces a de-centered fluid-induced force and a negative direct static stiffness, which cause the rotor deviating from the geometric center of the stator. Both the fluid-induced force and negative direct static stiffness coefficient with a value of −13.5 kN/m to −72 kN/m increase with increasing eccentricity and inlet pressure. Particularly, the direct static stiffness coefficient shows a relatively significant increase with a high eccentricity ratio (∼&amp;gt;40%). The static instability is mainly due to the fact that the fluid velocity in the small clearance increases more rapidly along the leakage path. The inertial force is increased significantly and the pressure decreases. This results in a greater pressure distribution in the larger clearance. The fluid force and direct static stiffness coefficient that tend to push the rotor away from the stator center are produced, and eventually lead to the static instability of the labyrinth seal.

Optimization performance of plain journal bearings with partial wall slip

In present work, in order to optimize partial slip zone for heavily loaded journal bearings, an isothermal hydrodynamic model considering wall slip occurring at oil-bush interface is built. Two-component slip model is utilized to calculate slip velocity. The performances of the journal bearing in different slip zone shapes and eccentricity ratios are evaluated. The optimal slip parameters in a range of eccentricity ratios are selected by considering their effects on hydrodynamic behavior, such as load carrying capacity and friction coefficient/torque. In addition, the application of optimal partial slip zone is presented. Results show that the optimal range of slip zone in high eccentricity ratio is quite restricted. The slip zone should be located at the convergent region of the film. The circumferential end of slip zone should locate at the convergent region and be close to the position of minimum film thickness. It is better to widen the axial length of slip zone, i.e. maximum rectangular shape could better improve bearing performance.

Computational investigation on the performance of hydrodynamic micro-textured journal bearing lubricated with micropolar fluid using mass-conserving numerical approach

The tribological characteristic of journal bearing systems can be enhanced with the integrating of textures in the contact interfaces, or using the lubricating effect of non-Newtonian fluids. In this study, the combined effects of bearing surface texturing and non-Newtonian lubricants behavior, using micropolar fluid model, on static characteristics of hydrodynamic circular journal bearings of finite length are highlighted. The modified Reynolds equation of micropolar lubrication theory is solved using finite differences scheme and Elrod's mass conservation algorithm, taking into account the presence of the cylindrical texture shape on full and optimum bearing surfaces. The optimization textured area is carried out through particle swarm optimization algorithm, in order to increase the load lifting capacity. Preliminary results are in good agreement with the reference ones, and present an enhancement in the performances of micro-textured journal bearings (load carrying capacity and friction). The results suggest that texturing the bearing convergent zone significantly increases the load carrying capacity and reduce friction coefficient, while fully texturing causes bad performances. It is also shown that the micropolar fluids exhibit better performances for smooth journal bearings than a Newtonian fluid depending on the size of material characteristic length and the coupling number. The combined effects of fully surface textured with micropolar fluids reduce the performance of journal bearing, especially at lower eccentricity ratios. Considering the optimal arrangement of textures on the contact surface, a significant improvement in terms of load capacity and friction can be achieved, particularly at high eccentricity ratios, high material characteristic lengths and high values of the coupling numbers of micropolar fluids.

Dynamic behavior analysis of a rigid rotor supported by hydrostatic squeeze film dampers compensated with new electrorheological valve restrictors

PurposeThis paper aims to propose a new hydrostatic squeeze film damper compensated with electrorheological valve restrictors to control the nonlinear dynamic behavior of a rigid rotor caused by high unbalance eccentricity ratio. To investigate the effect of electrorheological valve restrictors on the dynamic behavior of a rigid rotor, a nonlinear model is developed and presented.Design/methodology/approachThe nonlinear results are compared with those obtained from a linear approach. The results show good agreement between the linear and nonlinear methods when the unbalanced force is small. The effects of unbalance eccentricity ratio and electric field on the vibration response and the bearing transmitted force are investigated using the nonlinear models.FindingsThe results of simulation performed that the harmonics generated by high unbalance eccentricities can be reduced by using hydrostatic squeeze film damper compensated with electrorheological valve restrictors.Originality/valueThe numerical results demonstrate that this type of smart hydrostatic squeeze film damper provides to hydrostatic designers a new bearing configuration suitable to control rotor vibrations and bearing transmitted forces, especially for high speed.

Analysis of Magneto Rheological Fluid Journal Bearing

Magneto Rheological (MR) fluids are a class of smart materials where the shear stress is not directly proportional to rate of shear. The viscosity of fluid changes as magnetic field changes and hence this phenomenon is very useful in bearing-rotor system for attenuating the vibrations. In the present study the application of MR fluid as lubricant instead of Newtonian fluid in the journal bearing is explored through steady state, dynamic characteristics and stability. MR fluid film has been modeled as per Bingham rheological model. FEM with three node triangular elements has been used to solve the Reynolds equation both for the Newtonian fluid film and MR fluid film. The results show the load carrying capacity in the case of MR fluid journal bearing is higher than that of using the Newtonian fluid. The load carrying capacity increases with the increasing magnetic field for all eccentricity ratios. The results also show better stability of the bearing using MR fluid at higher eccentricity ratios. The unbalance response of the rotor mounted on the journal bearing using MR fluid is also estimated to be lower than that of with the Newtonian fluid.

Multiphase Computational Fluid Dynamics Analysis of Hydrodynamic Journal Bearing Under the Combined Influence of Texture and Slip

The drive to maintain the environmental sustainability and save the global energy consumption is urgent, making every powertrain system component a candidate to enhance efficiency. In this work, the combined effects of the slip boundary and textured surface in hydrodynamic journal bearing as one of the critical components in industrial powertrain and engine systems are assessed using a multiphase computational fluid dynamic analysis that allows for phase change in a cavitation process and arbitrary textured geometry. The texture studied consists of regularly spaced rectangular dimples through two-dimensional (infinitely long) journal bearing. The modified Navier–slip model is employed to describe the slip boundary condition. A systematic comparison is made for various textured configurations varying the texture depth and the length of the texturing zone with respect to the performance of a smooth (untextured) bearing for several eccentricity ratios. The effectiveness of the texture with or without slip at enhancing the load support over a corresponding smooth bearing is investigated with the parameters. The detrimental or beneficial effect of surface texturing as well as the slip promotion is explained in terms of the mechanisms of pressure generation for several eccentricity ratios. The results of the present work indicate that journal bearing textured by a proper texturing zone and dimple depth are characterized by substantial load support levels. However, in the range of high eccentricity ratios, the promotion of texturing and slip can significantly degrade the performance of the load support.