Search

Moving contact line dynamics calculations include two models: precursor film models and slip models. The lubrication approximation method is used to establish a three-dimensional mathematical model to analyze the droplet thermocapillary migration behavior on a non-uniformly heated solid substrate with a wettability track. The contact line dynamics in the slip model and the disjoining pressure effect in the precursor model are proposed to regulate the substrate wettability. Both models are numerically implemented to investigate droplet spreading for three cases: free spreading on an isothermal substrate, thermocapillary migration on a uniform wettability substrate, and thermocapillary migration on a wettability-confined track. For the case of free spreading on an isothermal substrate, the three-dimensional results of the slip and precursor contact line models are essentially consistent with two-dimensional slip model results. For the case of thermocapillary migration on a uniform wettability substrate, the results of the two models essentially agree with the experimental results. Decreasing the thermal gradient reduces the discrepancies between the two models that result from the coordinate transformation method used in the slip model, which reduces the contact angles measured in the y-direction and enlarges the advancing contact angle in the migration direction. For the case of thermocapillary migration on a wettability-confined track, the slip model gradually shows a "dynamic-pinning" behavior with increasing equilibrium contact angle in the hydrophobic region. By contrast, the precursor film model maintains a stationary pinning behavior but separates a residual liquid outside the track. The precursor film model is preferred over the slip model in lubrication approximations for three-dimensional fluids when calculating complex moving contact dynamics caused by wettability differences. However, the precursor film model must be further optimized to prevent numerical instability. [ABSTRACT FROM AUTHOR]

We consider a cylinder immersed in viscous fluid moving near a flat substrate covered by an incompressible viscoelastic fluid layer, and study the effect of the fluid viscoelasticity on the lift force exerted on the cylinder. The lift force is zero when the viscoelastic layer is not deformed, but becomes non-zero when it is deformed. We calculate the lift force by considering both the tangential stress and the normal stress applied at the surface of the viscoelastic layer. Our analysis indicates that as the layer changes from the elastic limit to the viscous limit, the lift force decreases with the decrease of the Deborah number (De). For small De, the effect of the layer elasticity is taken over by the surface tension and the lift force can become negative. We also show that the tangential stress and the interface slip velocity (the surface velocity relative to the substrate), which have been ignored in the previous analysis, give important contributions to the lift force. Especially for thin elastic layers, they give dominant contributions to the lift force. [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]

This work focuses on the evolution of lubrication wedge shaping in internal combustion piston engines, taking into account liquid microflows on curved surfaces and coating microgeometries. It introduces a new approach to the analysis of friction losses by simulating the microflow of lubricating oil between the surfaces of piston rings cooperating with the cylinder surface. The models used take into account three types of microgeometry and material expansion. Key results indicate that microirregularities with a stereometry of 0.1–0.2 µm significantly influence the distribution of oil film thickness in the phase of maximum working pressure, which is critical for the functioning of the seal ring. The innovation of the work consists of demonstrating that, despite small changes in the friction force and power in the piston rings, changes in the minimum values of the oil film thickness are significant. The work highlights the failure to take into account microgeometry parameters in friction models, which leads to significant errors in the simulation results, especially in terms of oil film continuity and the contribution of mixed friction. The simulations also indicate that advanced geometric models with high mesh resolution are necessary only for the assessment of changes in oil film thickness during the highest pressure increase in the combustion chamber and taking into account various mixed friction conditions. The results suggest significant progress in engine design and performance, confirming the importance of advanced fluid and mixed friction models in piston engine lubrication research. [ABSTRACT FROM AUTHOR]

To improve the reliability and lifespan of wind turbines, this paper takes the two-stage fixed shaft gearbox experimental platform of wind turbines as the research object. Based on Hertz contact theory, the oil film pressure and thickness in the contact area are solved by combining the equations of elastohydrodynamic lubrication and the Newton Raphson method; And the lubrication characteristics of the transmission system were analyzed to verify the correctness of the method; At the same time, in response to partial load phenomenon caused by system coupling deformation, genetic algorithm was selected to modify the gear teeth. The results show that the max unit load on the tooth face and the maximum stress of tooth root decreased by up to 26.48 % and up to 20.35 % respectively after modification which can improve the uneven distribution of oil film and the lubrication performance of the tooth surface. [ABSTRACT FROM AUTHOR]

Analyzing Phan-Thien Tanner fluid film behavior on a vertically upward moving tube can help predictive models in engineering, notably in coating and lubrication operations. This paper provides a theoretical analysis of the dynamics of stagnant rings and uniform Phan-Thien Tanner fluid film adhered to a vertically upward moving tube. Formulated ordinary differential equations are solved to get exact analytic expressions for velocity, flow rate, average velocity, shear stress components, and stagnant rings. Highly nonlinear algebraic equations are solved using Newton's method in MAPLE to find the linear and exponential Phan-Thien Tanner film thicknesses. The uniform film thickness widens with increasing constant tube velocity, while it decreases with increasing Deborah number, Stokes number, and elongation parameter. The analysis delineates that stagnant rings shrink around the tube as the Stokes number, Deborah number, and elongation parameter increase. The minimal Stokes condition for the existence of a realistic stagnant ring is also determined. It has been established that whenever the Stokes number is less than the minimal Stokes condition, stagnant rings do not form. A comparison between the exponential Phan-Thien Tanner, linear Phan-Thien Tanner, upper convected Maxwell, and Newtonian fluids is also provided for stagnant rings and fluid film thickness. Following the application of an efficient approximation on tube geometry, plate geometry is approximated, and the outcomes are consistent with existing literature. The results of this research are significant for a wide range of biofluid applications, including agrochemical uses, paint and surface coating flow behavior, thin films on the cornea and lungs, and chemical and nuclear reactor design. [ABSTRACT FROM AUTHOR]

Wax is a prevalent lubrication material extensively employed in various engineering applications. Understanding the degradation characteristics of the waxy lubrication layer under diverse stress variables and levels is crucial for ensuring system security and reliability. Due to the unclear mechanism governing the degradation of the waxy lubrication layer under different stress variables, existing degradation models are unsuitable for modeling waxy lubrication layer degradation data. To address this challenge, we propose a functional data‐driven method leveraging dense observations of waxy degradation. Through extensive simulations and a case study, we demonstrate the superior performance and effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Friction and wear are the main failure sources of face seals. When the surfaces of sealing rings exhibit greater roughness, the level of friction might increase and lead to sealing failure. Therefore, in this paper, based on the elastic contact hypothesis of rough and wavy surfaces and the influence of temperature on the elastic modulus of materials, a thermoelastic contact lubrication model of a gas-lubricated end seal is established. The novelty and advantage of this study is that it takes the effect of surface roughness into consideration during thermoelastic analysis of gas-lubricated seals. The film pressure, temperature, contact force and deformation of a gas spiral groove-faced seal are numerically determined. The influence of surface roughness on the contact distribution, deformation and temperature of the end-face seal at different speeds and pressures is analyzed. The film thickness increases as the rotational speed increases from 1 rpm to 2000 rpm, while the contact pressure sharply decreases from 0.25 kPa to 0. The analysis shows that the roughness contact mainly happens on the inner side of the rings due to convergent distortion of the seal faces, which easily causes partial wear of the seal faces. Moreover, it can also be found that the spiral grooves on the sealing surface can produce obvious hydrodynamic pressure effect due to the function of shear speed when the speed increases to 2000 rpm, while the film temperature increases from 293.3 K to about 306 K. The greater surface roughness results in a larger temperature rise under low-rotational-speed and lower-seal-pressure conditions, which further increases the risk of severe wear or even failure of the seal faces. [ABSTRACT FROM AUTHOR]

Rolling element bearings are widely used in aero engines, high-speed trains, precision machine tools, and other technical fields due to their high rotational accuracy and strong carrying capacity. With the development of rotating machinery in the direction of high speed, the working conditions of rolling element bearings are becoming more and more harsh, resulting in thermal problems that will seriously affect the mechanical properties of the bearing and the stability of the rotor system. In this paper, the four-degrees-of-freedom quasi-static model of cylindrical roller bearings was established based on the elastohydrodynamic lubrication theory combined with slicing technology. The local thermal approach and the thermal resistance network method were adopted to calculate the frictional heat generation and the transient temperature field of bearings. So the thermal-mechanical coupling model was obtained considering the correction of the thermal effect. On this basis, the influences of temperature on the vibration of the bearing-rotor system were researched. Finally, the temperature and stiffness of the bearings under various operating conditions were discussed. The coupling theory of thermal characteristics and mechanical properties of such bearing-rotor systems was improved. Practical Applications: Cylindrical roller bearings generally play a supporting role in rotating machinery and are widely used on high-speed occasions. For example, aero engines work under high-speed conditions, and high speeds in mechanical systems often bring serious thermal problems. As one of the core components, the spindle bearing must be able to overcome such a complex working environment. In this paper, cylindrical roller bearings and bearing-rotor systems are mathematically modeled for this feature in order to study their thermal and dynamic characteristics. The conclusions of this paper can provide relevant references for the design theory of this type of bearings applied in the fields of aero engines, high-speed precision machine tools, high-speed trains, etc., as well as theoretical guidance for the evaluation of their actual service performance. [ABSTRACT FROM AUTHOR]

The following study investigates the effects of Rabinowitsch fluid on journal bearing lubrication under the influence of velocity slip and variable viscosity. The finite difference method is used to produce a numerical solution to the 2D Modified Reynolds equation. The findings verify the previous results, which indicate that the dilatant (shear-thickening) fluid pressure is higher than the Newtonian and pseudo-plastic (shear-thinning) fluids. The results show that in the presence of slip, the pressure distribution rises with the piezo- viscosity parameter (variable viscosity) by up to 75%. Compared to the Newtonian, and pseudo-plastic (shear thinning) fluid, the dilatant (shear-thickening) fluid produces the highest pressure. A higher eccentricity ratio, slip-velocity, piezo-viscosity parameter, and dilatant fluid enhances the load-carrying capacity. The reduction in the attitude angle plays an integral part in the load-carrying capacity of the journal bearing. The attitude angle decreases for all values of the bearing ratio; the dilatant fluid has the most significant reduction in attitude angle compared to the Newtonian and pseudo-plastic fluids. Slip effects reduce the attitude angle, and a further reduction occurs when the piezo-viscosity and slip factors are combined. The slip-velocity, lower values of the bearing's length to diameter ratio, greater piezo-viscosity, higher values of the eccentricity ratio, and the dilatant fluid minimize friction. The Rabinowitsch fluid properties and the addition of both slip and variable viscosity increase bearing performance by increasing the pressure distribution, load-carrying capacity of the journal bearing and reduction of the frictional parameter, and should be considered when optimizing pressure, load, and friction for the creation of the ideal journal bearing. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to understand the vibration characteristics of full ceramic ball bearings under grease lubrication, reduce the vibration of the bearings and improve their service life. Design/methodology/approach: The Hertz contact stiffness formula for full ceramic ball bearings is constructed; the equivalent comprehensive stiffness calculation model and vibration model of full ceramic ball bearings are established. The dynamic characteristic test of full ceramic ball bearing under grease lubrication was carried out by using the bearing life testing machine, and its vibration was measured, and its vibration acceleration root-mean-square was obtained by software calculation and compared with the simulation results. Findings: At the rotational speed of 12,000 r/min, the root-mean-square value of vibration acceleration is maximum 10.82 m/s2, and the error is also maximum 7.49%. As the rotational speed increases, the oil film stiffness decreases. In the radial load of 600 N, the vibration acceleration root-mean-square is minimum 6.40 m/s2, but its error is maximum 6.56%. As the radial load increases, the vibration of the bearing decreases and then increases, so under certain conditions increasing the radial load can reduce the bearing vibration. With different types of grease, the best preload is also different; low-speed heavy load should be used when the viscosity of the grease is large, and high-speed light load should be used when the choice of smaller viscosity grease is made. Originality/value: It provides a theoretical basis for the application of full ceramic ball bearings under grease lubrication, which is of great significance for reducing the vibration of bearings as well as enhancing the service life of bearings. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0094/ [ABSTRACT FROM AUTHOR]

We numerically investigate the pressure drop reduction (PDR) performance of microchannels equipped with liquid-infused surfaces, along with determining the shape of the interface between the working fluid and lubricant within the microgrooves. The effects of different parameters, such as the Reynolds number of working fluid, density and viscosity ratios between the lubricant and working fluid, the ratio of the thickness of the lubricant layer over the ridges to the depth of the groove, and the Ohnesorge number as a representative of the interfacial tension, on the PDR and interfacial meniscus within the microgrooves are comprehensively studied. The results reveal that the density ratio and Ohnesorge number do not significantly affect the PDR. On the other hand, the viscosity ratio considerably affects the PDR, and a maximum PDR of 62% compared to a smooth non-lubricated microchannel is achieved for a viscosity ratio of 0.01. Interestingly, the higher the Reynolds number of the working fluid, the higher the PDR. The meniscus shape within the microgrooves is strongly affected by the Reynolds number of the working fluid. Despite the insignificant effect of interfacial tension on the PDR, the interface shape within the microgrooves is appreciably influenced by this parameter. [ABSTRACT FROM AUTHOR]

Present analysis deals with the impact of nonlinear convection on MHD non-Newtonian fluid flow considering exponentially stretched sheet through porous media. Additionally, the effects of radiation, Joule heating and energy dissipation have been taken into account. The considered flow situation of nonlinear PDEs is transmuted to nonlinear ODEs using similarity analysis. The numerical computations are derived using a fourth-order Runge–Kutta scheme with a shooting technique. Meaningful observations are discussed for velocity and energy profiles. Further, the impact of pertinent parameters considering pseudoplastic fluids (n = 0. 6) and dilatant fluids (n = 1. 3) is briefed through graphs. It is noted that the escalation in the values of the power-law index declines the velocity and energy profile. Higher values of the nonlinear parameter decline the energy profile. [ABSTRACT FROM AUTHOR]

In mixed elastohydrodynamic lubrication (EHL), the load distribution between the gear meshing surfaces is shared by the oil film and the asperities of the gear's rough surface. Based on the load‐sharing concept, this paper proposes a time‐varying meshing stiffness (TVMS) model for gears with mixed EHL. The initial step involves the utilization of the Greenwood‐Williamson model to calculate the contact stiffness of surface asperities, while the lubricating film is assessed using a curve‐fitting formula to investigate the influence of gear surface morphology on TVMS. Subsequently, the incorporation of gear fillet foundation deformation and friction enables accurate TVMS determination. The proposed method is employed to examine the meshing stiffness of the gear pair under both dry lubrication and EHL conditions. Comparative analysis reveals favorable agreement between the proposed model and experimental results obtained under dry lubrication, thereby highlighting the superior performance of the proposed approach. Moreover, the time‐varying friction coefficient under EHL is computed, and the impacts of gear surface morphology parameters, temperature, speed, and load on lubrication conditions and TVMS are investigated. The findings presented in this paper contribute significantly to advancements in gear design and performance. [ABSTRACT FROM AUTHOR]

The lubricating medium of the aerostatic spindle is gas, with relatively low rigidity, which is easy to cause rotor offset and additional vibration under the action of external load, thus affecting the processing accuracy of the spindle. To solve the problem of unbalanced vibration of the spindle, a new type of controllable radial aerostatic bearing is designed by combining piezoelectric ceramics, which use the inverse piezoelectric effect of piezoelectric ceramics to squeeze the air film to produce corresponding control force, and the radial unbalanced vibration of the spindle is suppressed. A bearing–rotor–piezoelectric ceramic coupling model was established, and the control method of feedforward combined with feedback was used to reduce the hysteresis characteristics of piezoelectric ceramics. On this basis, the sliding mode controller of the entire system, and through research, it is found that the sliding mode controller based on the extended observer has the best vibration suppression effect compared with other sliding mode controllers in the article; this research results can improve the rotation accuracy of the spindle system and the machining accuracy of ultra-precision machine tools. [ABSTRACT FROM AUTHOR]

This study aims to investigate the mechanical characteristics of contact between mating surfaces in the state of mixed lubrication, with a specific focus on the distribution of surface asperity heights in mechanical precision machining parts, which deviates from a Gaussian distribution. To achieve this, a normal contact model is developed for mating surfaces experiencing mixed lubrication, incorporating the non-Gaussian contribution nature of surface asperities and accounting for relative motion between mating surfaces. This model allows us to derivate the stiffness information in both solid and liquid domains to comprehend the contact behavior of mating surfaces under mixed lubrication conditions. The investigation results reveal that several key factors including normal load, viscosity, relative motion velocity, and non-Gaussian roughness parameters influence the normal contact stiffness of non-Gaussian rough surfaces in mixed lubrication mating surfaces significantly. These findings provide valuable insights that enhance our understanding of the performance of mating surfaces under mixed lubrication, and serve as a reference for the optimization design of mechanical equipment. [ABSTRACT FROM AUTHOR]

• Dynamic loaded tooth contact analysis (DLTCA) for computing entrainment speed. • Accurate solution to elastohydrodynamic lubrication (EHL) governing equation. • Discrete convolution and fast Fourier transformation (DC-FFT) for flank elastic deformation. • A separation flow method for iteration of EHL governing equation. • Accurate entrainment effect-based EHL forecasting model for hypoid gears. In full consideration of time-varying meshing performance and oil film characteristics, entrainment effect on elastohydrodynamic lubrication (EHL) is developed for establishing accurate forecasting model of the complex hypoid gears. Firstly, dynamic loaded tooth contact analysis (DLTCA) is employed to determine the meshing interface kinematics, load distribution and entrainment speed under dynamic load condition. Then, entrainment speed is introduced into the EHL governing equation and accurate forecasting model is established. With accurate discretization of EHL governing equation, discrete convolution and fast Fourier transformation (DC-FFT) method is employed to compute the flank elastic deformation. Finally, a hypoid gear set in automotive industrial application is exercised to verify entrainment effect on EHL assessment in the proposed model. [ABSTRACT FROM AUTHOR]

The oil film lubrication performance of a large hydrostatic turntable operating at the model of constant surface cutting speed is studied. Firstly, the rotary speed equation which is bound by the constant surface cutting speed is established. According to the fluid lubrication theory, the gap flow equation, the oil film temperature rise equation and the double‐rectangular‐cavity oil pad bearing capacity equation are derived. Further, a prediction model of oil film lubrication performance in the operating mode is established. The change rules of temperature, pressure and other performance indexes of the film with time are obtained by numerical simulation. And, the above laws are verified by design experiments. It is found that the cutting speed, feed rate leaves a significant impact on the law of variations of oil film performance with time. According to the conclusions, it will be beneficial to improve the bearing capacity of the hydrostatic turntable and further improve the machining accuracy by using cutting parameters reasonably to control the speed within a certain range. [ABSTRACT FROM AUTHOR]

In order to predict the spiral bevel gear churning power loss, based on the Computational Fluid Dynamics (CFD) method, the computational model for the splash lubrication of the spiral bevel gear pair is established and validated by experiments. The churning power loss of spiral bevel gears is obtained and the corresponding flow field distribution in the gearbox with a pair of spiral bevel gears is analysed under a standard operating condition. For the churning power loss of spiral bevel gears, the loss of teeth surface is mainly caused by pressure while the loss of gear side is mainly generated by the viscous force. The effects of the gear rotational speed, oil level, oil temperature and oil shroud on the churning loss are also investigated and analysed. Ultimately, an optimisation method is proposed for the original spiral bevel geared transmission. [ABSTRACT FROM AUTHOR]

The locally oriented roughness is a common feature of surface finished by a machining process, such as the surface of the cylinder liner, and may significantly influence lubrication characteristic. A homogenised transient Reynolds equation for the locally oriented roughness is derived. The Jacobsson–Floberg–Olsson (JFO) boundary conditions was implicitly incorporated into the transient Reynolds equation to ensure the mass flow conservation. On this foundation, a model for the transient lubrication in the cylinder liner‐piston ring considering the effects of the surface roughness and cavitation is established. Then, the results of model developed here are compared with those from the stochastic model by Patir and Cheng. and the effect of the direction of roughness on the lubrication properties is analysed. The homogenised transient Reynolds equation and the lubrication model developed here have great potential for understanding and optimising the transient lubrication considering the surface local roughness orientation, cavitation and starved lubrication. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to propose an optimization framework using deep neural networks (DNN) coupled with nondominated sorting genetic algorithm II and technique for order preference by similarity to an ideal solution method to improve the tribological properties of camshaft bearing pairs of internal combustion engine. Design/methodology/approach: A lubrication model based on the theory of elastohydrodynamic lubrication and flexible multibody dynamics was developed for a V6 diesel engine. Setting DNN model as fitness function, the multi-objective optimization genetic algorithm and decision-making method were used to optimize the bearing pair structure with the goal of minimizing the total friction loss and the difference of the average values of minimum oil film thickness. Findings: The results show that the lubrication state corresponding to the optimized bearing pair structure is elastohydrodynamic lubrication. Compared with the original structure, the optimized structure significantly reduces the total friction loss. Originality/value: The optimized performance and corresponding structural parameters are obtained, and the optimization results were verified through multibody dynamics simulation. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2023-0417/ [ABSTRACT FROM AUTHOR]

The application of elliptical injector will not only increase the atomization quality, but also reduce spray tip penetration, which has the potential to avoid wall wetting. However, so far the research on the effect of elliptical GDI nozzle on impinging spray is seldom reported. In this study, A GDI nozzle with circular and elliptical cross section shapes was employed to study the spray impingement characteristics through VOF-spray one way coupling method. The results revealed that the elliptical spray has shorter penetration as compared to circular spray, and the circular spray impingement time is earlier than the elliptical spray. Additionally, the spray rebound height of the circular spray was larger than that of the elliptical spray at the initial injection progress, while the elliptical spray rebound height became higher at the end of the injection. Furthermore, the elliptical spray impingement wall film mass and area were always smaller as compared with circular spray, and the injection pressure showed a negative influence on wall film mass. Finally, the average film thickness of the spray-wall impingement for an elliptical nozzle is observed to be reduced by 10.3% compared to that of a circular nozzle. Increasing the injection pressure is helpful to decrease the average wall film thickness. [ABSTRACT FROM AUTHOR]

Background: Speculum lubrication may help to reduce the pain experienced during Pap-smear collection and hence increase uptake of cervical cancer screening and repeat testing, but there are fears of its interference with cytological results. Aim: To determine and compare the adequacy of cervical cytology smears and the mean pain scores of women undergoing cervical cancer screening with or without speculum lubrication. Methods: This was a randomised controlled study of 132 women having cervical cancer screening at a tertiary hospital in Nigeria. Sixty-six participants were randomly assigned to the 'Gel' and 'No Gel' groups, respectively. Pap smears were collected from each participant with a lubricated speculum ('Gel group') or a non-lubricated speculum ('No Gel group'). The primary outcome measures were the proportion of women with unsatisfactory cervical cytology smears and the mean numeric rating scale pain scores, while the secondary outcome measures were the proportion of women who were willing to come for repeat testing and the cytological diagnosis of Pap-smear results. Results: The baseline socio-demographic variables were similar in both groups. There was no significant difference in the proportion of unsatisfactory cervical smear results between the two groups (13.6% vs. 21.2%, p = 0.359). However, the mean pain scores were significantly lower in the gel group than in the no gel group (45.04 vs. 87.96; p<0.001). An equal proportion of the participants in each group (90.9% vs. 90.9%; p > 0.999) were willing to come for repeat cervical smears in the future. Conclusion: Speculum lubrication did not affect the adequacy of cervical smears but significantly reduced the pain experienced during pap smear collection. Also, it did not significantly affect the willingness to come for repeat cervical smears in the future. Trial registration: The trial was registered with the Pan-African Clinical Trial Registry with a unique identification and registration number: PACTR2020077533364675. [ABSTRACT FROM AUTHOR]

In Compression ignition engines combustion occurs at higher temperatures that leads to a rapid rise in combustion pressure and amount of heat released. This may lead to lesser emissions during engine cycle. Moreover, occurrence of combustion takes place for a very small crank angles duration resulting in better thermal efficiency. On the other hand, the oil used for lubrication in IC engines is responsible for a significant amount of pollution and particles emitted into the environment. In order to comply with increasingly strict pollution standards, manufacturers make considerable efforts to minimize the impact of oil consumption on engine emissions. The purpose of this study is to develop a one-dimensional numerical simulation method using GT-Suite software to assess how the engine speed and load affect the oil film thickness, frictional force, and power losses during the operating engine cycle. The results obtained in this simulation were validated using experimental data, and there is good agreement between the numerical and experimental results. It was found in this paper that the maximum friction power losses were found to be 1.6 kW at middle of strokes and the minimum Oil film thickness was obtained in range of 9-38 μm. [ABSTRACT FROM AUTHOR]

Polymer based additives with long chain of suspended particles in oil retain polarity effect in the presence of couple stresses. Further, at high speed of journal bearing, the oil film experiences substantial agitation due to pressure-viscosity interaction which evolve piezo-viscous dependency of the lubricant. The present article addresses the combined effects of piezo-viscous dependency and couple stresses of lubricant on the characteristics of multi-recessed hybrid journal bearing under misaligned operation. To govern the flow of piezo-viscous-polar lubricant in clearance space of the journal bearing, a piezo-polar function is used to obtain the modified form of Reynolds equation. Galerkin's technique is employed to obtain the finite element formulation in the form of algebraic equation, which is solved to determine the unknown pressure field in the bearing system. The present results reveal that the use of piezo-viscous-polar lubricant offers an enhancement in performance characteristics of bearing system, i.e., a significant hike of 13–36%, 27–30% and 7–10% in the values of S ¯ ij , C ¯ ij and ω ¯ th respectively vis-à-vis Newtonian lubricant. The numerically simulated non-dimensional results presented in the article may be useful to generate the bearing design data of the hybrid journal baring system functioning in realistic and stringent operating conditions. [ABSTRACT FROM AUTHOR]

• An EHL model considering imperfect transversely isotropic coating was developed. • Imperfect of normal interfacial displacement has a great influence on lubrication. • Coating thickness under cooperative bearing capacity is recommended about 0.03 a to 4 a. Lubricated contact characteristics of transversely isotropic coating considering imperfect interface is of great importance in engineering to provide guidance on tribological design and optimization of tribo-pairs. The current investigation reports an elastohydrodynamic lubrication (EHL) contact model for transversely isotropic coating of imperfect interface. The interface is described by dislocation-like condition, i.e., displacement across it is transmitted discontinuously and such discontinuity is controlled by an imperfect index changing from 0 to 1. Based on this interfacial condition, frequency response functions (FRFs) of elastic field of imperfect transversely isotropic coating were derived, which was further used to establish the EHL contact model combined with the lubrication theory. The proposed model can be reduced to the one without coating, whose calculation results are consistent with those from literatures, providing a good verification. Finally, effects of imperfect index of interfacial displacement, coating thickness on film thickness, surface pressure, stress for transversely isotropic coating were investigated using the proposed model. [ABSTRACT FROM AUTHOR]

Understanding droplet migration in stenosed microchannels is crucial for various applications. This study explores how droplet properties (viscosity, surface tension, density, and diameter) and channel characteristics (stenosis degree and wall elasticity) affect droplet movement and blockage in deformable stenosed microchannels. Higher viscosities lead to lubrication film formation between droplet and wall, reducing viscous resistance, while increased surface tension enhances wall adherence, amplifying Laplace pressure. Droplet entry is primarily influenced by viscosity, while passage is governed by surface tension and curvature effects at the droplet–wall interface. Surface tension dominates pressure generation in the channel and within the droplet, influencing wall deformation and hydrodynamic resistance. The study examines the relationship among droplet viscosity, density, surface tension, channel wall elasticity, and the maximum capillary number (C a max ) on the lubrication film thickness between the droplet and the channel wall. A lubrication film exists for C a max ≥ 0.095 , reducing blockage chances. A critical range of the modified Ohnesorge number O h * × 1000 ≤ 132 and the capillary number (C a max < 0.095) indicates higher chances of droplet blockage. The blockage prediction method based on the modified Ohnesorge exhibits a sensitivity of 100%, specificity of 92.6%, and accuracy of 95.9%. Additionally, the study explores the impact of channel wall elasticity on droplet entry, transit, and hydrodynamic resistance. Higher wall elasticity facilitates faster entry but introduces curvature during passage, increasing frictional resistance and blockage likelihood as the wall softens. [ABSTRACT FROM AUTHOR]

The current paper is aimed to investigate the deformability effects of the bearing surface on the lubrication performance of cylindrical journal bearing with finite length under turbulent conditions. The bush is coated with a thin resilient layer with a smooth surface, the radial distortions of which are of the same order of magnitude as the film thickness. The elastohydrodynamic problem is studied under elasticity conditions in accordance with the plain strain hypothesis (Winkler model). The modified Reynolds equation is carried out on the base of the turbulent lubrication model of Hirs (bulk flow model). The partial differential equation is solved numerically by successive over-relaxation technique on a finite difference grid, considering different values of coating materials, lubricant viscosity, and journal speed. Results for the performance characteristics of the bearing are given for several selected values of Reynolds number and elasticity parameters of the soft liner on the bush. [ABSTRACT FROM AUTHOR]

In this paper, the cycloidal pin wheel drive mechanism of the secondary drive component of the rotary vector (RV) reducer is studied. Under the condition of grease lubrication, considering tooth profile modifications and machining errors, we established a three-dimensional load-bearing contact analysis model of a cycloid pinwheel transmission mechanism. We studied the time-varying contact characteristics of the gear teeth and dynamic joint surfaces of the inner and outer races of a crankshaft bearing. Considering the thermal effects, we proposed an analysis model of the lubrication characteristics of cycloid pinwheel transmission mechanisms. We also studied the thermal lubrication properties, such as load de-formation, lubrication film thickness, contact pressure and temperature increase at the lubrication contact area. The accuracy of the model was verified by temperature experiments on the inner raceway of an RV reducer bearing and the evolution law of the dynamic thermal lubrication characteristics of the inner and outer races of the crankshaft bearing, the meshing gear tooth pair and the whole process of single pin tooth meshing were revealed. This study provides an effective method for analyzing the temperature increases of the key joints of RV reducers. [ABSTRACT FROM AUTHOR]

Demand for micro-deep-drawn complex-shaped parts in biomedical, chemical analysis and microsystem technologies has been growing. Micro-deep drawing is a micro-plastic forming used to produce micro-parts from different materials. Researchers have worked upon several aspects of micro-deep drawing (MDD), namely the scaling effects, handling of micro-parts and process intermittency. The present work reviews some of these experimental and numerical studies on the MDD considering the size effects, forming limit diagram, parametric effect, lubrication and coating on punch and die surfaces. The topology modification of the deep drawing tool surface using macro/microstructured coated tool shows substantial potential for the lubricant-free micro-deep drawing. Further, micro-structuring of the blank via laser has emerged as another approach in the MDD process to reduce the effective contact area between tool and sheet and, hence, the friction forces. Finally, challenges and scope for further research in MDD are listed to implement these processes commercially. [ABSTRACT FROM AUTHOR]

In this research, an angular contact ball bearing with two‐half inner rings is used as a carrier. Considering the two‐phase flow characteristics of oil and air in the bearing, the flow characteristics of lubricating oil inside the bearing with under‐race lubrication are studied. Based on the volume of fluid (VOF) method and the standard k–ε turbulent flow model, the characteristics of oil and air two‐phase flow inside the ball bearing are analysed. The bearing internal pressure field distribution, streamline distribution, and other flow properties for the different radial working clearances, pocket clearances and guide clearances are determined. The distribution of the lubricating oil in key areas is observed. The oil phase volume fraction of the key lubrication areas, such as the cage pocket surface and the inner and outer ring surfaces is used to evaluate the influence of different structural parameters on the bearing lubrication performance. The lubrication influences of the inner and outer guides of the cage are evaluated, and the internal flow characteristics of the bearing are analysed with different guide clearances. The results show that with the radial working clearance range from 0.100 to 0.145 mm, the pressure in the working contact area of the bearing decreases 26%. The pocket clearance ranges from 0.48 to 0.28 mm, and the pressure in the working contact area of the bearing significant increases from 0.642 to 1.165 MPa. From this perspective, the larger the radial working clearance and pocket clearance are, the more favourable it is for bearing lubrication. For bearings with under‐ring lubrication, when the bearing adopts outer guidance, the distribution of lubricating oil in the key areas of the bearing is worse than that for internal guidance. However, the pressure in the working contact area of the bearing slightly increases from 0.642 to 0.759 MPa with the inner guide clearance increasing from 0.4 to 0.8 mm. [ABSTRACT FROM AUTHOR]

The transient mixed lubrication behaviors in thermal elastohydrodynamic lubrication (TEHL) contacts during startup and stop are investigated. A transient mixed TEHL model for point contacts under time-varying speed conditions is proposed with comprehensive consideration of surface roughness, thermal effect, and transient behavior. The model is validated by the comparison to available published data. Based on the developed model, significant differences have been found compared with transient EHL and steady TEHL models. In addition, the transient mixed TEHL performance during start–stop with different acceleration rates and surface roughness is investigated. It shows that the lubrication behaviors during start–stop have an irreversible process. The roughness can significantly enhance the transient behavior. The roughness effect has a remarkable impact on lubrication performance in mixed lubrication. The evolution of lubrication behaviors during start–stop is highly related to the acceleration rate and surface topography. [ABSTRACT FROM AUTHOR]

The interaction of temperature variations and viscoelastic deformation is critical in dynamically loaded journal bearings, especially under fluctuating heavy load conditions. Previous studies have not fully explored the coupling of these two factors. Addressing this gap, this research introduces a novel transient mixed lubrication model that simultaneously considers thermal and viscoelastic effects. This model reveals intricate dynamics influencing the lubrication performance of journal bearings. The findings show that the combined impact of thermal and viscoelastic factors significantly alters the amplitude and phase of lubrication performance parameters. Notably, thermal effects tend to decrease oil film pressure while increasing asperity contact pressure, whereas viscoelastic effects enhance the oil film pressure peak and adjust its phase, concurrently reducing asperity contact pressure. Moreover, varying the eccentric speed profoundly influences the interplay between bearing thermal and viscoelastic effects. This study contributes to a deeper understanding of mixed lubrication in journal bearings and provides technical support for more accurate and predictive reliability improvement in complex mechanical systems. [ABSTRACT FROM AUTHOR]

A time-varying meshing stiffness (TVMS) model that includes oil film stiffness in the elastohydrodynamic lubrication (EHL) line contact is proposed for tooth root cracking. This model employs the oil film thickness to estimate the stiffness of the oil film in gear contact by considering the profile variation of the oil film induced by tooth root cracks, to provide the evolution principle of TVMS in EHL line contact to study the effects of oil film stiffness of cracked gear on the TVMS. The results of the analysis reveal that the overall result of TVMS decreases owing to the stiffness of the oil film, whereas the combined TVMS depends mainly on the rotation speed of the gear system because the thickness of the oil film in the tooth crack is affected by the velocity of the entrainment. Furthermore, a six-degree-of-freedom (DOF) dynamic model is introduced to analyze the vibration behavior of the gear system using the combined TVMS results for different crack levels, and the influence of the combined TVMS on the vibration response of the tooth root crack is exhibited from the time-domain analysis, frequency-domain analysis, and statistical indicator analysis. [ABSTRACT FROM AUTHOR]

Lubricants are usually utilized to decrease wear, reduce friction, and release heat. Although the lubrication approximation originated from thin-film studies, it has limitations because of continuum mechanics assumptions. To overcome these limitations, for the first time, this article employs a hierarchical multiscale approach to study the frictional sliding contact considering elastohydrodynamic lubrication. This multiscale model consists of a molecular model of lubricant and a continuum model of sliding contact components. Specifically, the molecular dynamics method is used at the nanoscale to model the lubricant and analyze the friction coefficient in contacted surfaces. Through MD simulation, the effects of hydrocarbon chain lengths, temperature, and sliding velocity on a constant friction coefficient are studied in this article. The calculated friction coefficients from the molecular model are passed to the continuum model, in which the finite element method is employed to conduct stress and strain analysis of the sliding contact components. Although variations in the frictional sliding response are invariably coupled with the friction coefficients, the molecular-to-continuum hierarchical approach enables us to isolate the relative contributions from the chemical formulation of the lubricant and the temperature. This approach has further potential implications for the evaluation of tribological damage. The results demonstrate that an increase in temperature or the chain length of lubricant hydrocarbon molecules can significantly decrease the friction coefficient and, as a result, reduce contact shear stress, plastic deformation, and pile-up height. [ABSTRACT FROM AUTHOR]

In this paper, the tribological characteristics of an oil-soluble magnetic fluid additive under mixed lubrication are studied by experiments and numerical simulation. [bmim][FeCl4] is dissolved in CF10W-40 lubricating oil as a magnetic liquid additive, and its friction coefficient is tested by a point contact friction tester at different temperatures, rotational speeds and magnetic field intensities. The transition condition of lubrication state is obtained through analyzing the Stribeck curves based on the experiments, and the strength model of boundary film is established accordingly. A mixed lubrication model is established by substituting the boundary film strength model and the surface roughness model into the hydrodynamic lubrication model based on Reynolds equation. The results show that the magnetic solution as an additive can obviously reduce friction and wear, and the effect is more obvious under the condition of magnetic field. The boundary film strength model can accurately reflect the transition characteristics of lubrication state in the presence of boundary film, and the mixed lubrication model based on boundary film strength model can more precisely reflect the tribological characteristics of friction pairs, so this study provides a new theoretical method for the related research on the influence of boundary film on lubrication characteristics. [ABSTRACT FROM AUTHOR]

Heat transfer from the solidified shell to the mold, especially in the meniscus region, significantly affects the surface quality of the strand and the stability of the continuous casting process. The mold slag film serves as the sole heat transfer medium between the shell and the mold, and its performance and structure have a substantial impact on the heat transfer efficiency. Thus, since the 1980s, various testing methods are developed to investigate the heat transfer performance of the slag film, including the pouring method, immersion method, parallel plate method, and mold experiment. In this article, the principles, characteristics, and main study results of these methods are reviewed, and the existing issues are highlighted in these methods. Furthermore, specific requirements that shall be satisfied in future research on the heat transfer of slag film are presented. The new approach for testing heat transfer in slag film necessitates ensuring consistency in the heat flux, surface temperature of the shell, interfacial thermal resistance, and thickness and cooling rate of the slag film, aligning with those observed in a mold. This consistency is crucial to ensure the comparable structure and heat transfer characteristic between the experimental and industrial slag films. [ABSTRACT FROM AUTHOR]

Wheel‐rail adhesion is important to the traction and braking of railway vehicles. This paper develops a three‐dimensional numerical model considering surface roughness and temperature to investigate water‐contaminated adhesion characteristics. A simplified elastohydrodynamic lubrication model considering the thermal effect is developed to obtain the normal load carried by liquid film and asperities. Meanwhile, a third body layer (3BL) model, which considers the effects of pressure and temperature on 3BL, is used to calculate the tangential stress and friction coefficient of asperity contact. To verify the numerical model, firstly, the results are compared with the existing experimental results at low and high speeds. In addition, the effects of surface roughness and temperature on adhesion coefficient are investigated. Furthermore, the elastoplastic behaviour of the tangential stress and the adhesion characteristics for large creepages are studied. The obtained adhesion‐creepage curve can represent the decreasing trend after reaching saturation because of temperature. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the application of non-destructive testing methods in measuring bearing oil film thickness to ensure that bearings are in a normal lubrication state. The oil film thickness is a crucial parameter reflecting the lubrication status of bearings, directly influencing the operational state of bearing transmission systems. However, it is challenging to accurately measure the oil film thickness under traditional disassembly conditions due to factors such as bearing structure and working conditions. Therefore, there is an urgent need for a nondestructive testing method to measure the oil film thickness and its status. Design/methodology/approach: This paper introduces methods for optically, electrically and acoustically measuring the oil film thickness and status of bearings. It discusses the adaptability and measurement accuracy of different bearing oil film measurement methods and the impact of varying measurement conditions on accuracy. In addition, it compares the application scenarios of other techniques and the influence of the environment on detection results. Findings: Ultrasonic measurement stands out due to its widespread adaptability, making it suitable for oil film thickness detection in various states and monitoring continuous changes in oil film thickness. Different methods can be selected depending on the measurement environment to compensate for measurement accuracy and enhance detection effectiveness. Originality/value: This paper reviews the basic principles and latest applications of optical, electrical and acoustic measurement of oil film thickness and status. It analyzes applicable measurement methods for oil film under different conditions. It discusses the future trends of detection methods, providing possible solutions for bearing oil film thickness detection in complex engineering environments. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to design and process the optimal V-shaped microstructure for 7075 aluminum alloy and reveal its wear resistance mechanism and performance. Design/methodology/approach: The hydrodynamic pressure lubrication models of the nontextured, V-shaped, circular and square microtextures are established. The corresponding oil film pressure distributions are explored. The friction and wear experiments are conducted on a rotating device. The effects of the microstructure shapes and sizes on the wear mechanisms are investigated via the friction coefficients and surface morphologies. Findings: In comparison, the V-shaped microtexture has the largest oil film carrying capacity and the lowest friction coefficient. The wear mechanism of the V-shaped microtexture is dominated by abrasive and adhesive wear. The V-shaped microtexture has excellent wear resistance under a side length of 300 µm, an interval of 300 µm and a depth of 20 µm. Originality/value: This study is conductive to the design of wear-resistant surfaces for friction components. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to enhance the lubrication performance of thrust bearings. The influence of columnar convex–concave compound microtexture on bearing performance is investigated Design/methodology/approach: Based on the compound microtexture model of thrust bearings, considering surface roughness and turbulent effect, the variation of lubrication characteristics with the change in the compound microtexture parameters is studied. Findings: The results indicate that, compared with circular microtexture, the maximum pressure of compound microtexture of thrust bearings increases by 7.42%. Optimal bearing performance is achieved when the internal microtexture depth is 0.02 mm. Turbulent flow states and surface roughness lead to a reduction in the optimal depth. The maximum pressure and load-carrying capacity of the bearing decrease as the initial angle increases, whereas the friction coefficient increases with the increase in the initial angle. The lubrication performance is best for bearings with a circumferential parallel arrangement of microtexture. Originality/value: The novel composite microtexture with columnar convex-concave is proposed, and the computational model of thrust bearings is set. The influence of surface roughness and turbulent flow on the bearing performance should be considered for better conforming with engineering practice. The effect of microtexture depth, arrangement method and distribution position on the lubrication performance of the compound microtexture thrust bearing is investigated, which is of great significance for improving tribology, thrust bearings and surface microtexture theory. [ABSTRACT FROM AUTHOR]

The dynamic behavior of the pump-turbine thrust bearing is important to the safety operation of the unit. This paper analyzed the lubrication and energy dissipation mechanism of pump-turbine thrust bearing during load-rejection based on the thermo-hydrodynamic model. The results show that the variation of the axial force and the maximum pad surface pressure is basically consistent with that of the inclination of the pad surface. The change of the friction loss is consistent with the change of rotational speed, while the change of pad surface temperature is affected by the combination of pad inclination and rotational speed. The chaotic flow in the oil tank is accompanied by different forms of vortices, such as Taylor vortices, vortex pairs, and Karman vortices, and results in a significant asymmetry in the pressure distribution. The flow in the bearing pad groove has an effect on the energy dissipation in the oil film. This paper provides a theoretical basis for the design and optimization of thrust bearings, and provides a reference for solving the problems of wear, oil mist, and other related problems of thrust bearings in engineering. [ABSTRACT FROM AUTHOR]

The long-term wear of the piston/cylinder pair is the main failure reason for axial piston pumps. In this paper, the dynamics of textured films to enhance the lubrication performance of piston/cylinder pairs is investigated systematically. The oil film is divided into three regions: the head region, the texture region, and the tail region. The Reynolds equation is used to predict the dynamics, which includes the carrying capacity and the friction. Influences of the texture geometries and the working conditions are presented in sequence. The results show that the texture enhances the lubrication performance by the collective effect. A shorter head length and a larger area ratio always benefit the lubrication performance, while increasing the texture region length does not always lead to positive effects, and the cell length is found to have negligible influences. The texture effect is found to be enhanced with larger shearing velocities and to be restrained with higher inlet pressures. It is also shown that the texture is effective for small inclination angles. Furthermore, a one-dimensional model is performed to unravel the mathematical mechanism, and an explicit expression is given for the texture region length. [ABSTRACT FROM AUTHOR]

In this article, we investigate the complex drainage behavior of liquid ("dimple") films entrapped between hydrophilic glass substrates and air bubbles in water and aqueous suspensions of polystyrene (PS) particles. The film drainage was monitored by capturing the evolution of spatial-temporal thicknesses using interferometry. Faster drainage of the entrapped film is observed in the PS colloid suspensions compared to the water. The film drainage strongly depends on the interface boundary conditions. Our experiments reveal that the air–liquid interface of the entrapped film becomes partially mobile in the PS suspensions, which results in faster drainage. The hydrophobic PS particles tend to migrate toward the air–water interface and form an ordered layer. We argue that the adsorbed layer of PS particles makes the bubble surface elastic, delaying the formation of the immobile interface. [ABSTRACT FROM AUTHOR]

A reduction in wake effects in large wind farms through wake-aware control has considerable potential to improve farm efficiency. This work examines the success of several emerging, empirically derived control methods that modify wind turbine wakes (i.e., the pulse method, helix method, and related methods) based on Strouhal numbers on the O (0.3) . Drawing on previous work in the literature for jet and bluff-body flows, the analyses leverage the normal-mode representation of wake instabilities to characterize the large-scale wake meandering observed in actuated wakes. Idealized large-eddy simulations (LES) using an actuator-line representation of the turbine blades indicate that the n = 0 and ± 1 modes, which correspond to the pulse and helix forcing strategies, respectively, have faster initial growth rates than higher-order modes, suggesting these lower-order modes are more appropriate for wake control. Exciting these lower-order modes with periodic pitching of the blades produces increased modal growth, higher entrainment into the wake, and faster wake recovery. Modal energy gain and the entrainment rate both increase with streamwise distance from the rotor until the intermediate wake. This suggests that the wake meandering dynamics, which share close ties with the relatively well-characterized meandering dynamics in jet and bluff-body flows, are an essential component of the success of wind turbine wake control methods. A spatial linear stability analysis is also performed on the wake flows and yields insights on the modal evolution. In the context of the normal-mode representation of wake instabilities, these findings represent the first literature examining the characteristics of the wake meandering stemming from intentional Strouhal-timed wake actuation, and they help guide the ongoing work to understand the fluid-dynamic origins of the success of the pulse, helix, and related methods. [ABSTRACT FROM AUTHOR]