Search

The Brownian dynamics of a colloidal particle is consistently modified by the presence in the solvent of other particles of comparable size, whose effects on the particle diffusion coefficient cannot be attributed to a change of the effective solvent viscosity. So far, despite their impact on subjects ranging from microrheology to phoretic transport in crowded environments, a detailed experimental survey of these effects is still lacking. By exploiting the peculiar properties of fluorinated colloidal particle, we have performed an extensive dynamic light scattering (DLS) investigation of short-time self-diffusion in binary colloidal mixtures, focusing on systems where one of the two species (the "tracer" particles) is very diluted compared to the other one (the "host" particles). From the dependence on the host concentration of the DLS correlation function, we have obtained the first-order correction h s 1 s to the tracer single-particle diffusion coefficient, varying the tracer-to-host size ratio q in the range 0.2 ≤ q ≤ 2. Our results support the functional relation of h s 1 s on q proposed to account for the theoretical and numerical results for hard-sphere mixtures. However, h s 1 s seems to have a weaker dependence on the size ratio than theoretically predicted, possibly because of an imperfect matching of the suspensions we used for an ideal hard-sphere mixture. This may be due to the presence of a stabilizing surfactant layer on the particle surface that, although very thin, has significant effects on hydrodynamic lubrication forces. [ABSTRACT FROM AUTHOR]

This study presents a model of starved mixed Elastohydrodynamic Lubrication (EHL) in point and line contact to investigate the lubrication performance and material response. In formulating the governing equations for the lubrication, the dimensional Reynolds equation is discretized to involve all possible regimes from the boundary lubrication to fully hydrodynamic lubrication, and an additional algorithm is provided to determine the fractional film content based on the profiles of pressure distribution and film thickness. Solutions of the point contact from the present model are compared with those reported by the previous studies and good consistency can be found. The three-dimensional line contact is used to predict the load carrying capabilities of the film thickness at the interface of mating spur gear teeth. A return mapping method is implemented to take the plastic revolution into account. The solution at the initial stage of a startup process with the lubricant entrainment velocities of u x = u y = 0 is compared with that from a dry contact to validate the elasto-plastic solutions. Sample cases are presented to reveal the effects of inlet oil supply condition and material plasticity on lubrication starvation. [ABSTRACT FROM AUTHOR]

The need for bearings in a variety of heavily loaded machines, including the influence of pressure and temperature, is generating increasing interest in studying the operating environment for magazine bearings. The purpose of this work is to develop a semi-analytical solution by introducing a new delta profile concept of the location of zero velocity gradients to obtain the simplest form of the equation of energy and Reynolds. In the journal bearing, assuming that journal is rotating and bearing is fixed, a hydrodynamic lubrication is modelled with the Power Law fluid. The lubricant temperature effect is examined under isothermal limits and the results obtained are much more realistic with the experimental results. [ABSTRACT FROM AUTHOR]

The utilization of water glycol as a working medium represents a significant advancement in the realm of deep-sea hydraulic transmission systems. The viscosity of water glycol is a crucial parameter for hydrodynamic lubrication, yet it is profoundly influenced by the environmental conditions of the deep sea. This study employs the TIP4P/2005 water molecule model in conjunction with the optimized potentials for liquid simulations all-atom force field, and non-equilibrium molecular dynamics method to predict the viscosity of water glycol hydraulic fluids with varying compositions under deep-sea conditions. The simulation values agree well with the experimental results. Furthermore, this study introduces a fitting equation that accounts for the effects of composition, temperature, and pressure, enabling the prediction of the viscosity of water glycol hydraulic fluids within the 0–11 000 m sea water environment. [ABSTRACT FROM AUTHOR]

In this paper, the friction properties of the port pair with non‐smooth surface in the pump were studied. The lubrication film was modelled and simulated to analyse dynamic pressure, velocity vector and friction coefficient. Tests were made for studying the effects of pit shape and revolution speed on friction properties of glass fibre epoxy resin (GFER) samples under seawater lubrication, with the wear of the surface and friction coefficient discussed. The results show that GFER is mainly manifested as adhesive and abrasive wear during the tests. The simulations and tests suggest that the hydrodynamic lubrication effect is improved by increasing revolution speed and using non‐smooth surfaces, with the friction coefficient being decreased. Moreover, a roughness test was conducted, and it was found that the Ra value of the 316L sample decreased, whereas the Ra value of the GFER sample increased. [ABSTRACT FROM AUTHOR]

This article presents an experimental study about boundary slippage on the film thickness of hydrodynamic lubrication (HL) using a custom‐made slider‐on‐disc bearing testing apparatus. The interfaces with different affinity were obtained by surface energy modification of sliders with various oleophobic coatings, which are characterised by their contact angle (CA) and contact angle hysteresis (CAH). To study the mechanism of interfacial slip on HL under different wettability constraints, the film thickness and velocity profiles under shear were measured using interference and fluorescence photobleached method, respectively. The results showed that the CAH could better characterise the influence of interface effect on the film thickness of HL, which was explained by the correlation between CAH and the interface potential barrier. Furthermore, it was found that the slip velocity increased with lubricant viscosity and shear rate, which can be explained by the spatial heterogeneity of the flow in conformal contact and the critical shear stress slip model. [ABSTRACT FROM AUTHOR]

Planar lamination is a ubiquitous component of modern and ancient fine‐grained sediments deposited by subaqueous sediment gravity flows. These sediments commonly exhibit alternating sub‐millimetre‐thick, sharply bounded silt‐rich and clay‐rich layers that change little in thickness or sediment texture over lateral distances that range up to at least several tens of metres. Silt‐rich layers are moderately to well‐sorted and a few tens to hundreds of microns to a single silt‐grain thick. In contrast, clay‐rich layers are more poorly sorted, and a few tens to hundreds of microns thick. The thickness and regular alternation of these texturally differentiated interlayers, in addition to the absence of features suggesting transport bypass or deposition by migrating rugged bed forms, suggest alternating physical processes and related modes of deposition in the near‐bed region immediately above the bed. Previous interpretations have focussed on clay flocculation, which is difficult to reconcile with the high fluid shear conditions in the near‐bed region. Here it is suggested that in the millimetre to sub‐millimetre‐thick viscous sublayer at the base of a hydraulically smooth turbulent flow, a combination of high fluid shear and sediment concentration initially leads to shear thinning and enhanced mobility in the lower part of the flow, and for silt to continue settling to the bed forming a well‐sorted silt lamina. As silt settles and clay‐size sediment increases in concentration, hydrodynamic lubrication forces strengthen and reduce mobility of the near‐bed part of the flow. This condition is then perturbed by a bedward‐directed outer flow disturbance that dramatically increases frictional stresses and effective fluid viscosity and ultimately shear jamming that causes gelling and deposition of a poorly sorted clay‐rich layer. This process is then repeated multiple times to build up a deposit composed of alternating silt‐rich and clay‐rich laminae overlain by structureless mud deposited directly from suspension. [ABSTRACT FROM AUTHOR]

The transition to electric vehicles (EVs) has introduced new challenges in lubrication, demanding innovative solutions to ensure consistent performance. One promising approach is the use of nanoparticle additives, which have the potential to improve lubrication performance significantly. However, achieving a stable suspension of these nanoparticles in lubricating oils remains a critical challenge, as suspension stability is essential for maintaining consistent performance and maximizing the benefits of these advanced additives. In this study, carbon nanoparticles (CNPs) were modified with dodecylamine (DDA) to achieve stable suspension in nonpolar fluids. The successful functionalization was confirmed by the FTIR results, which showed characteristic peaks of various bonding. The suspension stability tests demonstrated that DDA-CNPs remained suspended for over 60 days in the Polyalphaolefin (PAO) oil, whereas unmodified CNPs were sedimented within 3–7 days. The rheological behavior was measured under different shear rates and temperatures. Viscosity measurements indicated that DDA-CNPs maintained a lower value compared to base PAO. The lubricants' friction coefficient (COF) was also determined under various speeds and loads. The addition of DDA-CNPs at a concentration of 0.05 wt.% resulted in a significant reduction in COF, with values decreasing by 26% compared to base PAO oil under a load of 1 N. Additionally, the COF for DDA-CNPs was consistently lower than that of PAO, with reductions ranging from 15% to 18% across all tested speeds. The Stribeck curve further highlighted the improved performance of DDA-CNPs across boundary, mixed, and hydrodynamic lubrication regimes. These findings suggest that DDA-CNPs significantly improve the lubrication performance of PAO oil, making them suitable for advanced lubrication applications in automotive and industrial systems. [ABSTRACT FROM AUTHOR]

Gaining insight into tribological systems is crucial for optimizing efficiency and prolonging operational lifespans in technical systems. Experimental investigations are time-consuming and costly, especially for reciprocating seals in fluid power systems. Elastohydrodynamic lubrication (EHL) simulations offer an alternative but demand significant computational resources. Physics-informed neural networks (PINNs) provide a promising solution using physics-based approaches to solve partial differential equations. While PINNs have successfully modeled hydrodynamics with stationary cavitation, they have yet to address transient cavitation with dynamic geometry changes. This contribution applies a PINN framework to predict pressure build-up and transient cavitation in sealing contacts with dynamic geometry changes. The results demonstrate the potential of PINNs for modeling tribological systems and highlight their significance in enhancing computational efficiency. [ABSTRACT FROM AUTHOR]

The article contains a description of the design solutions proposed by the authors for a hybrid wind turbine bearing, in which the sliding part takes over the load to the turbine shaft after reaching the shaft rotation speed, ensuring hydrodynamic lubrication of the plain bearing and relieving the rolling bearing. This allows for low starting resistance of the power plant and ensures quiet operation during use. Two conceptual solutions of a hybrid bearing were presented, differing in the shape of the plain bearing journal. A mechanism for automatic switching of the load between a rolling and a plain bearing was developed. A solid simulation model of this mechanism was built in the Autodesk Inventor—Dynamic Simulation software Inventor Professional 2023 environment, and its operation was simulated. The results confirmed the usefulness of using this design in shaft-bearing systems of wind turbines with a vertical axis of rotation. Based on the simulation, the speed at which the thrust roller bearing will be released was determined. Technical parameters of a plain bearing with a spherical journal shape were calculated. The height of the lubrication gap and the shaft rotational speed at which the bearing load capacity index reaches a critical value were determined. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Mechanical systems are expected to operate under various load conditions, and it is necessary to use a lubrication system to achieve reliability and stable performance. Journal bearings, which are used to achieve such stable lubrication, are representative of hydrodynamic lubrication bearings. In this study, groove-shaped structures and rubber were applied to the ends of the bearings to ensure stable lubrication performance under conditions where, for various reasons, shock loads are applied in addition to static loads under misaligned conditions. The groove structure and rubber contribute to stable lubrication performance by preventing contact between the shaft and bearing as well as absorbing shock loads through elastic deformation of the groove's end due to oil film pressure. This novel design, which utilizes groove-type flexible structures and rubber, led to journal bearings that exhibited improved lubrication performance under various shock load conditions. When a shock load is applied to a mechanical system, the design proposed in this study contributes to improving the reliability of the mechanical system by enhancing its lubrication performance. [ABSTRACT FROM AUTHOR]

Stick–slip is a standard friction-induced self-excited vibration that usually occurs in the boundary or mixed lubrication regimes. Broadening of the hydrodynamic lubrication regime is conducive to suppressing stick–slip motion. In this paper, the load carrying capacity of a magnetic fluid (MF) film in the presence of a magnetic field is derived based on the modified Reynolds equation. An additional lifting force produced by MF under the magnet was applied between the tribopairs to achieve the full fluid lubrication. Thus, the stick–slip is expected to be inhibited in a lower speed scope. The effect of magnet thickness on the lifting force is investigated experimentally and theoretically. Special attention is given to the influence of the lifting force on the friction and the critical transition speed of the hydrodynamic lubrication regime. Results demonstrate that the lifting force increases with the increment of the magnet thickness. The presence of the additional lifting force expands the hydrodynamic lubrication and makes the critical transition speed move left, as shown by the friction transitions on the Stribeck curve. Therefore, stick–slip motion can be suppressed at a lower sliding speed. Such beneficial effects are more pronounced in thicker magnets. It can be confirmed that, so long as the lifting force is higher than the normal load, the friction will invariably operate in the full film lubrication and the stick-slip motion may be eliminated theoretically. [ABSTRACT FROM AUTHOR]

Introduction: The demand to increase reliability and reduce maintenance costs drives the search for new condition monitoring solutions of machines. Bearings are of special interest in this matter as they are main contributors to machine downtime. Therefore, this article investigates the electric behavior of a hydrodynamic journal bearing using impedance measurement. Methods: For that purpose measurements are taken in boundary lubrication, mixed lubrication and hydrodynamic lubrication of a hydrodynamic journal bearing. In order to interpret the behaviour observed in these measurements, a phenomenological model is developed using the quantitative working space model. The measurement results are also interpreted using analogies to the Stribeck curve as a known tribological model. Additionally, measurements in mixed lubrication are analysed in detail. Results: These measurements show that the electric behaviour of journal bearings changes significantly within the mixed lubrication regime. This change in behaviour shows three distinct states within mixed lubrication which helps to identify destructive operating conditions. Furthermore, the measurements potentially allow the detection of deformation or damage of the bearing in mixed lubrication. Discussion: The quantitative analysis of the electric behaviour of journal bearings is possible in the mixed lubrication regime and can be used in future to extract condition and operating information from a system during operation. [ABSTRACT FROM AUTHOR]

The friction pair gap affects not only the temperature increase of the multi-disc wet clutch, but also the efficiency of the helicopter transmission system. Consequently, a rotational–axial engagement and disengagement-coupled kinetic model of a wet multi-disc clutch considering asperity contact, hydrodynamic lubrication, spline resistance, and a separating spring model are developed in this paper. The effects of operating conditions on the dynamic characteristics of the wet clutch are investigated. Further, the gap deviation coefficient is proposed to characterize the dynamic behavior of the friction pair gap. As the control oil pressure increases from 1.3 MPa to 1.7 MPa, the gap deviation coefficient increases by 8.6%. Moreover, as the rotation speed increases from 888 rpm to 2488 rpm and the lubricant oil temperature increases from 25 °C to 85 °C, the gap deviation coefficient decreases by 1.1% and 4.44%, respectively. Therefore, an appropriate increase in lubricant oil temperature and rotation speed can facilitate the friction pair gap to be more uniform. These results are useful for the development of optimal control strategies for aviation wet clutch systems. [ABSTRACT FROM AUTHOR]

This study reports on the tribological behaviour of sliding surfaces having cross-shaped micro-dimples on a surface. One wall is smooth and moving at a constant speed against the other fixed wall with dimples. The laser machine helps to create the desired dimples on the surface of the fixed wall. For the purpose of generating hydrodynamic pressure and tribological behaviour, the effects of cross-shaped dimples and oriented cross-shaped dimples have been compared with circular-shaped dimples. Additionally, the impact of sliding speed, dimple area density and depth on tribological behaviour was examined. The findings show that compared with a circular-shaped dimple, an unconventional cross-shaped and orientated cross-shaped dimple generates a higher net hydrodynamic pressure in the fluid domain and offers superior stability between the sliding surfaces. It has been demonstrated that geometrical factors like dimple depth and area density as well as operational factors like sliding speed have a substantial impact on the hydrodynamic average pressure and tribological behaviour of sliding surfaces. The experimental findings indicate that, for the same geometric and operating parameters, cross- and orientated cross-shaped dimples have a 20%–25% lower friction coefficient between the sliding surfaces than circular dimples. The results of the experiment support those of the analysis and CFD. [ABSTRACT FROM AUTHOR]

This paper studies the effect of the dimple cross-sectional profile on the behavior of gas parallel slider bearings using the numerical method. The numerical method is performed in MATLAB software. The influence of geometrical parameters of dimples on the dimensionless average pressure is studied for different dimple cross-sectional profiles. The geometrical parameters of dimples include dimple depth, dimple area density, transversal textured ratio, and longitudinal textured ratio. It is found that the hydrodynamic lubrication of dimple-textured gas parallel slider bearings is controlled by the dimple depth, dimple area density, transversal textured ratio, longitudinal textured ratio, and dimple cross-sectional profile. Furthermore, the impact of sliding speed on the hydrodynamic lubrication is studied for different dimple cross-sectional profiles. The results indicate that the optimum sliding speed for maximizing the hydrodynamic pressure is controlled by the dimple cross-sectional profile. [ABSTRACT FROM AUTHOR]

Friction between the rake face of the tool and the chip is a primary contributor to tool rake face wear. Hence, reducing the friction coefficient between the tool's rake face and the chip proves to be an effective method for wear mitigation. To minimize the friction coefficient of cutting tools, distinctive microtextures were laser-engraved onto the rake face, employing hydrodynamic lubrication principles. To minimize the adverse impact of microtextures on the tool and simultaneously achieve hydrodynamic lubrication, a sparse matrix arrangement method was introduced for microtexture placement. For further enhancement of the hydrodynamic lubrication effect, finite element analysis was utilized to optimize both the depth and arrangement of microtextures. Friction and cutting experiments were performed to validate the lubrication efficiency of biomimetic microtextures, with an accompanying analysis of the lubrication mechanism. In summary, biomimetic microtextures successfully diminish friction between the tool's rake face and the chip, resulting in a significant reduction in three-dimensional cutting forces, notably decreasing the main cutting force and accomplishing the objective of reducing tool wear. [ABSTRACT FROM AUTHOR]

Given the friction and drag reduction effects observed in various biological hexagonal structures in nature, a new design was implemented on the rubber surface of the stator of a submersible screw pump. This design featured a multilayer concentric hexagonal groove structure. Furthermore, a composite multilayer hexagonal structure integrating grooves and pits was also developed and applied. This study investigated the influence of groove layer number, groove depth, pit depth, and multilayer hexagonal groove texture arrangement on the rubber surface flow characteristics. Additionally, the pressure field state, the degree of influence on the oil film-bearing capacity, and the biomimetic and hydrodynamic lubrication theories were tested using the finite element analysis method. Tribological experiments were conducted on nanosecond laser-processed rubber textures under simulated liquid lubrication conditions, reflecting actual shale oil well experiments. These experiments aimed to investigate the influence of multilayer hexagonal shape parameters on the tribological characteristics of the stator-rotor friction pair of a submersible screw pump. The results indicated that with a constant overall size, a multilayer hexagonal structure with ~0.1 mm groove depth enhanced the oil film-bearing capacity, providing significant friction and drag reduction. For composite textures, a deeper pit depth within the study area enhanced the oil film-bearing capacity. Furthermore, a gradient arrangement of groove textures featuring wider outer grooves and shallower depth exhibited superior performance in terms of bearing capacity. [ABSTRACT FROM AUTHOR]

As the transmission component in mechanical systems, hydrodynamic journal bearing is widely used in large electromechanical equipment. The instability of the hydrodynamic journal bearing often results in mechanical wear and damage, which may cause maintenance shutdowns and significant financial losses. Accordingly, assessing the hydrodynamic journal bearing online is a highly effective approach to guaranteeing reliability. To analyze oil film thickness distribution under various assembly characteristics, this paper proposes a Fluid–Solid coupling analysis method based on hydrodynamic lubrication theory and Hertzian elastic deformation theory. The novelty is that the difference between the oil film thicknesses at the same measuring angle within the two opposing faces of the bearing shell is taken as the assessment parameter, which can directly indicate the deviation degree of the stator axis. Comparison of simulation and experimental results validated that the proposed method exhibits exceptional accuracy in practical applications. [ABSTRACT FROM AUTHOR]

The article discusses the factors affecting the operation of sliding bearings. It is shown that based on the fundamental principles of hydrodynamic lubrication theory, transitioning from the formula characterizing the load-carrying capacity of the lubricant layer in sliding bearings to the parameters of oil film thickness and clearance allows for the derivation of expressions to determine functional clearances within which the bearing will operate under conditions of hydrodynamic friction. As a result of the calculations conducted for the sliding bearing of the conveyor drive reducer the limiting functional clearances were defined for the use of bushings of various lengths in accordance with GOST ISO 4379–2006. A rational length for the sliding bearing trunnion is justified based on the value of the maximum functional clearance and its influence on the deviation of the center distance in the gear transmission of the reducer. A new H8/f7 fit is proposed instead of the recommended H8/g7 and H8/e7 fits according to GOST ISO 4379–2006, as this will ensure the presence of a hydrodynamic wedge at the beginning of operation and provide the most rational material reserve for wear. The practical significance of the research lies in the applicability of the proposed approach in the design of sliding bearings operating under conditions of hydrodynamic lubrication, aimed at determining the rational length and fit of the mating elements in the bearing assembly. [ABSTRACT FROM AUTHOR]

Hydrodynamic linear guides in machine tools offer a high load capacity and excellent damping characteristics, improving stability, precision, and vibration reduction. This study builds on previous research where floating heights were verified with a simulation model limited to measured floating heights. Advancements include incorporating pressure sensors into a fixed steel rail, enabling simultaneous measurement of oil film pressure and floating heights for a comprehensive understanding of lubrication conditions within the lubrication gap. The experimental results explore the effects of different lubrication methods, providing valuable insights into cavitation and lubrication adequacy. The results demonstrate the feasibility of utilizing pressure sensors to measure oil film pressure within the lubrication gap, providing a nuanced understanding of lubrication dynamics. By measuring both floating heights and pressure measurement, distinctions between hydrodynamic lubrication, mixed friction regions, and instances of lubricant deficiency become readily discernible. The variations in real-time oil film pressure and floating heights help to optimize the lubrication cycle for hydrodynamic linear guides, enhancing system performance and longevity. [ABSTRACT FROM AUTHOR]

Piston–cylinder pairs are very common in industrial mechanisms. While a piston is primarily designed for axial reciprocating motion, the occurrence of secondary motions—lateral and rotational—due to the small clearance between the piston and the cylinder may lead to frictional contact, energy loss, wear and an increase in unwanted leakage. This study focuses on mitigating the secondary motion of a ringless piston. The influence of a Rayleigh step bearing and partial surface texturing with numerous micro-dimples on the dynamic stability of the secondary motion is studied. A linear model was used to obtain the trajectory of the secondary motion and Floquet theory was applied to analyze the stability and draw stability maps. The influence of various texturing and step parameters, including the dimple area density and aspect ratio for partial texturing, as well as the length and depth of treatment for both partial texturing and step profiles, on the stability of the secondary motion was examined. The normalization method is presented, enabling the expansion of the results for various operating conditions and geometries. Conclusions and guidelines regarding the optimal parameters, in terms of a wider stability range and higher decay rate, are formulated. [ABSTRACT FROM AUTHOR]

Performance behaviours of oil-lubricated sector shape pad thrust bearings incorporating the variable depth’s pockets/textures have been presented. The variable depth texture comprises of combination of grooves and pockets. Fixed depth pocket, variable depth pocket (depth of the pocket reducing towards the exit) and combination of fixed and variable depth pocket with the fixed and variable depth grooves have been considered in the present investigation. With the aim to improve the performance parameters of fixed pad thrust bearing, the effect of texture parameters such as pocket/groove depth, the circumferential extent of texture and different combinations of variable depth’s pocket and grooves have been investigated. Substantial improvement in the performance parameters (minimum film thickness and coefficient of friction) has been achieved in the presence of proposed textures having variable depths of micro-geometries.

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of AIN Journal is the property of Arab Institute of Navigation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cavitation in micro-scale lubricating film could be determined by the fluid's thermal properties, which impacts the hydrodynamic lubrication capacity dramatically. This study aimed to novelly investigate the impact of the thermal cavitation effect on the hydrodynamic performance of liquid face seals, employing the compressible cavitation model, viscosity–temperature effect, and energy equation. The finite difference method was adopted to analyze the thermal cavitation by calculating the pressure and temperature profiles of the lubricating film. The working conditions and geometric configuration of liquid face seals under different thermal cases were further studied to explore their effects on sealing performance. The results showed that thermal cavitation could reduce the temperature difference of liquid film at high speeds, and cavitation would be weakened under temperature gradients, which further dropped off the hydrodynamic performance. Contrary to the leakage rate, the opening forces tended to be lower with the increasing seal pressure and film thickness under high-temperature gradients. Furthermore, apart from the spiral angle of grooves, the hydrodynamic performance exhibited significant variation with increasing groove depth, number, and radius at high-temperature gradients, which meant that the thermal cavitation effect should be considered in the design of geometric grooves to obtain better hydrodynamic performance. [ABSTRACT FROM AUTHOR]

This study proposed a unique texture type with parabolic grooves inspired by the parabolic grooves on the surface of a cuttlebone to improve the load-carrying capacity of lubricated sliding bearings. A hydrodynamic lubrication model was used to systematically analyze the effect of parabolic groove parameters on the lubrication properties. The load-carrying capacity of the grooved texture was determined by a precise balance between hydrodynamics and cavitation effects. Parabolic grooves exhibited a higher load-carrying capacity than that of conventional straight grooves owing to the fluid collection effect of the parabolic shape texture and narrowing cavitation region around the divergent wedge; the optimal groove depth was typically in the range 5–7 μm. The load-carrying capacity increased at greater sliding velocities and thinner initial film. Consequently, this study provides valuable insights into a new shape configuration and design guidelines for surface texture in sliding bearings, offering potential advancements in the lubrication technology. [ABSTRACT FROM AUTHOR]

The longevity of prosthetic hip implants is significantly influenced by wear. Surface textures of various length scales can reduce the friction coefficient and wear of lubricated bearing surfaces. The optimization of multiscale texture parameters, aimed at maximizing lubricant film thickness, was achieved through hydrodynamic lubrication simulations that solve the Reynolds equation with a mass-conserving cavitation model under various operating conditions. The outcomes indicate that adding "interstitial" texture features to a pattern of microscale texture features can further increase the lubricant film thickness. Additionally, the lubricant film thickness increases as the interstitial texture feature aspect ratio and texture density decrease. Pin-on-disc experiments align with simulation findings, demonstrating that multiscale texturing with ultra-fast laser ablation on Ti6Al4V discs significantly improves wettability and reduces the friction coefficient of ultra-high molecular weight polyethylene pins when compared to untextured and microscale textured surfaces. The multiscale surface texturing also changes the evident wear mechanisms on the pins, reducing the incidence of abrasive scratches and adhesive wear compared to both untextured and just microscale textured surfaces. [ABSTRACT FROM AUTHOR]

A dry gas seal (DGS) is one of the key basic components of natural gas transmission pipeline compressors, and the sealing performance of a DGS dealing with complex multi-component pipeline natural gas is different from that dealing with conventional nitrogen medium. In this paper, a spiral groove DGS of the compressor in natural gas transmission pipeline systems is taken as the research object. The thermal hydrodynamic lubrication model of the DGS is established considering turbulence effect and choking effect. Based on the finite difference method, the temperature and pressure distributions and the steady-state performance of the DGS are obtained by simulating. The influence of unitary impurity compositions such as light hydrocarbon, heavy hydrocarbon, non-hydrocarbon, and their contents on the steady-state performance of the DGS is analyzed. The steady-state performance of the DGS dealing with multi-impurity natural gas such as in the West-East gas transmission is investigated under different operating conditions. The results show that turbulence had a significant effect on the DGS, while choking had a weak effect. Increasing the content of light hydrocarbon such as C2H6 and heavy hydrocarbon such as C5H10 resulted in an increase in the gas film stiffness, leakage rate, and the temperature difference between the inlet and outlet, while non-hydrocarbon, such as N2, reduced the temperature difference between the inlet and outlet. The greatest impact on seal performance was produced by the heavy hydrocarbon, followed by the light hydrocarbon, and the least was produced by the non-hydrocarbon. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

This paper presents two novel artificial intelligence-based approaches for evaluating the performance of heavily loaded marine journal bearings including shaft misalignment. Traditionally, the Sommerfeld number has been used as a key parameter to evaluate the performance similarity between different bearings. However, this method has limitations, particularly when dealing with complex elastic geometries, heavily loaded journal bearings and shaft misalignment. The first proposed approach leverages neural networks to analyze key bearing performance parameters and provide a more accurate and comprehensive assessment of bearing performance similarity, including additional parameters beyond the Sommerfeld number limitations. The second method utilizes artificial intelligence convolutional networks to assess the bearing similarity based on their simulated pressure profiles under isoviscous and isothermal hydrodynamic lubrication regime. The effectiveness of the proposed methods is demonstrated and compared to the traditional Sommerfeld number method, discussing various potential applications and extensions of this concept. [ABSTRACT FROM AUTHOR]

A variety of simple and complex components made of metal, as well as non-metals, can be fabricated by machining. Generally, the machining process produces enormous heat at the metal cutting interface. Coolants are more often used to lessen the amount of heat generated during machining. However, it has been found that cutting fluid produces environmental risks and health risks to the operators such as skin cancer, respiratory diseases, cough, etc. and it also increases machining costs. Therefore, several researchers are working in this field to mitigate these problems without compromising the quality of machined parts produced. Manufacturing processes should be optimised without affecting the environment. Researchers are shifting towards environmental sustainability and adopting various novel machining processes like dry machining, MQL, cryogenic machining, etc. thereby curtailing the usage of cutting fluid up to certain extent. Micro-nano textured surfaces eventually reduces wear, and it will also help in reducing the cutting temperature through effective lubrication and cooling. This article aims to provide comprehensive information on different prospects of surface textured cutting tools in the field of machining. [ABSTRACT FROM AUTHOR]

General reductions in lubricant viscosities and increasing loads in machine components highlight the role of tribofilms in providing surface protection against scuffing. However, the relationship between the scuffing process and the growth and removal of tribofilm is not well understood. In this study, a multiphysics coupling model, which includes hydrodynamic lubrication, asperity contact, thermal effect, tribochemistry reaction, friction, and surface wear, was developed to capture the initiation of surface scuffing. Simulations and experiments for a piston ring and cylinder liner contact were conducted following a step-load sequence under different temperature conditions. The results show that high temperature and extreme load could induce the lubricant film collapse, which in turn triggers the breakdown of the tribofilm due to the significantly increased removal process. The failures of both lubricant film and tribofilm progress instantaneously in a coupling way, which finally leads to severe scuffing. [ABSTRACT FROM AUTHOR]

In this paper, we consider experimental data available for graphene-based nanolubricants to evaluate their convective heat transfer performance by means of computational fluid dynamics (CFD) simulations. Single-phase models with temperature-dependent properties are employed for this purpose. The base fluid is a polyalkylene glycol, and we show the effect of the addition of carbon nanohorns and graphene nanoplatelets (GNPs), in different volume fractions, on the convective heat transfer coefficient between two parallel plates. Then, an application to hydrodynamic lubrication is discussed. The extreme in-plane thermal conductivity of graphene allows a smaller temperature rise of the GNP-based nanolubricant, i.e., a more effective heat removal. To the best of our knowledge, this work represents the first application of single-phase nanofluid models to hydrodynamic lubrication. [ABSTRACT FROM AUTHOR]

Hydrodynamic lubrication is definitely one of the foremost factors upon which the load carrying capacity within journal bearing mainly rely. Therefore, maintaining journal bearing lubrication away from boundary and transient lubrication regions is so instrumental in avoiding journal bearing wear. Accordingly, Universal Journal Bearing Test Rig (UJBTR) was specifically used for conducting wide range tests related to the versatile operational parameters utilizing different oil grades. Those were examined at the variable shaft speeds from 300 rpm up to 600 rpm, under the different applied loads from 50 〖kg〗_f up to 510 〖kg〗_f. The derived results were verified theoretically, where the error percentage hasn't exceeded 5.9 %. In light of the conducted study, oil film pressure was assured to rise with the increase of oil viscosity, loads, and speeds. For more detailed discussion, a dimensionless analysis was carried out to identify the impact percentage for viscosity, speed, and load on the hydrodynamic lubrication. It is observed that increasing load by 60 % had a considerable impact regarding the coefficient of friction where it reduced by 89 %. However, it turned out to have very negative impacts on hydrodynamic lubrication, where the hydrodynamic lubrication has moved into the hazardous boundary lubrication region. Based on the derived outcomes, operational factors are crucial impacts that shape journal bearing behavior considerably in real operating conditions either positively or negatively. Consequently, much consideration must be given to the selection of such factors so as to maintain and possibly enhance journal bearing performance.

In this article, a comprehensive methodology has been developed to study the lubricity of oils with solid micro/nanoadditives, including mathematical models that allow estimating the temperature during shear and variable speed in the layer. The dynamic temperature gradient across the thickness, the variable thickness, the friction moment, and the temperature are calculated. [ABSTRACT FROM AUTHOR]

Porous materials impregnated with lubricants can be used in conditions where limited lubricant is desirable. In this work, three porous polyimides (PPI) with different densities were prepared. Polyalphaolefin (PAO) impregnated PPI (iPPI) discs were rubbed against steel and sapphire balls. In operando observations of the iPPI–sapphire contacts show that oil is released under an applied load, forming a meniscus around contacts. Cavitation at the outlet is created at high sliding speeds. The amount of released oil increases with increasing PPI porosity. Contact moduli, E*, estimated based on the actual contact size show that trapped oil in iPPIs contributes to load support. At higher speeds, tribological rehydration of the contact occurs in low density iPPI, with that E* rises with speed. For high density PPIs, high speeds give a constantly high E* which is limited by the viscoelastic properties of the PPI network and possibly the rate of oil exudation. Friction of iPPI–steel contacts is governed by the mechanical properties of the PPI, the flow of the lubricant, and the roughness of the PPI surfaces. For low- and medium- density (highly porous, high roughness) PPIs, large amount of oil is released, and lubrication is mainly via lubricant restricted in the contact in the pores and possibly tribological rehydration. For high density (low porosity) PPI, with lower roughness, hydrodynamic lubrication is achieved which gives the lowest friction. Our results show that polymeric porous materials for effective lubrication require the optimization of its surface roughness, stiffness, oil flow, and oil retentions. [ABSTRACT FROM AUTHOR]