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Through the analysis of hot oil carrying theory, the problem of oil film heat accumulation in hydrostatic bearing can be revealed, so as to avoid serious lubrication failure caused by heat accumulation. In this paper, the hot oil carrying factor is defined and the mathematical model of the thermal oil carrying characteristics of the oil film is established by taking the beveled double rectangular oil pad hydrostatic bearing as the object, and the hot oil carrying law under different working conditions is obtained by changing the inclination angle of the beveled oil pad at 0.0230°, 0.0250° and 0.0280°, respectively. Theoretical calculations and simulation studies show that within the range of the circumferential inclination of the oil pad with better dynamic pressure effect of the bearing, the inclination has little effect on the oil film hot oil carrying. When the speed of the workbench is lower than 10r/min, no oil film hot oil carrying phenomenon occurs. When the speed is in the range of 10r/min-100r/min, a part of the load will cause the phenomenon of oil film hot oil carrying. And when the speed exceeds 100r/min, the heat accumulation of the oil film is the most serious at this time. There are many reasons for the lubrication failure of hydrostatic bearings, and hot oil carrying is a new research direction, this paper starts from the oil film heating mechanism of beveled oil pads hydrostatic bearings, and describes the phenomenon of hot oil carrying. [ABSTRACT FROM AUTHOR]

In order to explore the crater characteristics of droplet impacting on the oil film floating above the deep pool, experimental study and theoretical analysis were used to investigate cavity dynamics,, and a multi-interfaces model was proposed. The results show that that the immiscible properties of the droplet-oil film-liquid pool leads to a more complex cavity evolution process. It is concluded that for a smaller Froude number Fr, the daughter droplets are mainly generated by the Rayleigh-Plateau instability of the downward jet. For large Fr, the Rayleigh-Plateau instability due to the shrinkage of deformed droplets is the main reason of daughter droplets formation. Due to the effect of shear stress on the immiscible interfaces, the initial expansion rate of the cavity decreases with the increase in the number of deformed interfaces. For the thin liquid film, since the interfacial energy of the oil film-deep pool interface deformation is incorporated, the dimensionless depth of the cavity d′ and Fr does not satisfy the classical relationship with d′~Fr1/4. In contrast, for the thick liquid film, its impact process can be regarded as a droplet impacting the oil deep pool, and the experimental observation satisfies the classical relationship. Moreover, the relationship between the effective cavity depth d′e and Fr obtained by using the multi-interfaces model roughly meets the scaling law d′e~ Fr1/4. [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]

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.)

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]

Copyright of Bearing is the property of Bearing Editorial Office 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 Bearing is the property of Bearing Editorial Office 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.)

Pilot-ignition Otto marine engines are known for greatly reduced emissions of air pollutants (sulphur oxides, nitrogen oxide, particulates) compared to marine diesel engines. However, lubricating oil emissions still are about one order of magnitude higher than in land-based systems. To identify reduction potentials, a better understanding of oil emission mechanisms has to be gained. For this purpose, mass spectrometric oil emission measurements and fluorescence lubricating film thickness measurements were performed on a medium-speed marine engine. With the fluorescence measuring system, the varying lubricating oil film on the cylinder wall can be visualised and analysed in sub-crank-angle resolution. By applying the developed calibration method to the measurement data, the oil film thickness can be determined in µm. It is shown that the oil film left by the piston rings on the liner as it moves down is almost halved after ignition compared to during intake stroke. The authors have further been able to detect and time operating point dependent ring rotation and investigations show a connection between ring rotation and cylinder liner temperature distribution. Aligning ring gaps allow blow-by to happen. This and other high intensity events such as engine knock, load shedding or the transition from diesel-mode to gas-mode, heavily disturb the oil layer and cause peaking oil emissions. [ABSTRACT FROM AUTHOR]

The floatability of low-rank coal is poor because of its low metamorphosis, and the oily bubble flotation is an effective means to collect coal particles. In this paper, adhesion angles and forces between watery/oily bubbles and coal surfaces were measured to analyze the influence of oil film on adhesion behavior between bubble and particle. The properties of watery/oily bubbles were analyzed by dynamic foam analyzer (DFA) to reveal the influence of oil film on the bubbles further. The results showed that in the dynamic environment, the maximum adhesion angle of the oily bubble was 36.55°, while the angle of the watery bubble was 31.29°, and the adhesion kinetic constant for oily bubble-particle and watery bubble-particle were 0.0295 and 0.0174, respectively. The measured maximum adhesion forces of the watery bubble and oily bubble were 19.2 μN and 86.8 μN, respectively, indicating that oily bubbles were more prone to attach to the coal surface and were beneficial to flotation. The calculated normalized contact line indicated that the oil film could squeeze a lot of water out from the coal surface, increasing the actual contact area and strengthening the attachment. The results of DFA showed that with the oil film, the oily bubbles could be more stable with a smaller size and lower liquid content than the watery bubbles. The results of the above study show that the oil film covering the watery bubble could improve the adhesion between bubble and particle and reduce the bubble size, which is conducive to promoting the sorting efficiency and thus enhancing the flotation of lignite. [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.

Utilizing the average Reynolds equation, lubrication friction theory, metal rolling deformation theory, and temperature energy theory, a multi-parameter-coupling mixed lubrication model considering the influence of surface roughness with Gaussian distribution characteristics under rolling conditions was established. The results show that the stress distribution of the lubricating oil at the rolling interface conforms to the typical characteristics of line contact stress distribution. The oil film pressure does not increase significantly with the increase in the reduction ratio. A second peak pressure appears before the outlet. The second peak pressure reaches its maximum when ε = 0.2. The rolling speed has little effect on oil film pressure, but greatly affects oil film thickness. The influence of rolling speed mainly occurs in the outlet zone and at the second peak pressure location. The oil film thickness increases with rolling speed. During rolling, the temperature rise in the rolls exhibits two peak values. The first peak appears near the neutral point, and the second peak appears near the outlet, which is also where the second peak pressure is located. The influence of temperature will reduce the peak stress on the rolls. The overall stress on the rolls will also decrease. [ABSTRACT FROM AUTHOR]

Herein, organic–inorganic hybrid sulfur-containing carbon nanospheres (SCNs) were successfully prepared by one-pot chemical oxidation polymerization of a thiophene monomer and then rigorous carbonization. On account of the good structural strength and organic phase derived from the precursor polythiophene, the as-prepared SCNs manifested remarkable oil-dispersing and tribological properties as lubricant nanoadditives. Subsequently, the friction mechanism of SCNs was deduced; the as-prepared SCNs had the capacity to take the shape of a strong protective film on the surface of friction pairs by intricate physical deposition and tribochemical reaction. So, the SCNs exhibited excellent tribological performance, including a high extreme pressure (950 N), an ultralow friction coefficient of less than 0.06, and a significant reduction in abrasion by 90%. [ABSTRACT FROM AUTHOR]

Healthy coasts have a high ecological service value. However, many coastal areas are faced with oil spill risks. The Synthetic Aperture Radar (SAR) remote sensing technique has become an effective tool for monitoring the oil spill risk in coastal areas. In this study, taking Jiaozhou Bay in China as the study area, an innovative oil spill monitoring framework was established based on Polarimetric SAR (PolSAR) images and deep learning theory. Specifically, a DeepLabv3+-based semantic segmentation model was trained using 35 Sentinel-1 satellite images of oil films on the sea surface from maritime sectors in different regions all over the world, which not only considered the information from the PolSAR images but also meteorological conditions; then, the well-trained framework was deployed to identify the oil films in the Sentinel-1 images of Jiaozhou Bay from 2017 to 2019. The experimental results show that the detection accuracies of the proposed oil spill detection model were higher than 0.95. It was found that the oil films in Jiaozhou Bay were mainly concentrated in the vicinity of the waterways and coastal port terminals, that the occurrence frequency of oil spills in Jiaozhou Bay decreased from 2017 to 2019, and that more than 80 percent of the oil spill events occurred at night, mainly coming from the illegal discharge of waste oil from ships. These data indicate that, in the future, the PolSAR technique will play a more important role in oil spill monitoring for Jiaozhou Bay due to its capability to capture images at night. [ABSTRACT FROM AUTHOR]

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.)

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.)

Axial piston pumps are widely used in construction machinery due to the high power density. The leakage performance of the spherical valve plate pair is of great significance to the large displacement pumps' volumetric efficiency. However, the model and calculation of leakage are unclear. This paper proposed a cylinder block dynamic and oil film lubrication based leakage model of the spherical valve plate pair for axial piston pumps. Numerical solutions on the leakage performance under different working conditions were carried out. The tilt behavior of the cylinder block, thickness, and longitude velocity of the oil film were solved. In addition, the effects of central spring stiffness on leakage performance were analyzed and experiments were conducted. Results show that the pump is with poor volumetric efficiency for operation at low speed and high pressure, and ± 5% adjustment of spring stiffness leads to a 237% maximum leakage gap for spherical valve plate pair.

The thrust bearing, as the only part bearing the axial load, is extremely important in vertical hydroelectric generating units. Its working condition directly affects the safe and reliable operation of the hydroelectric generating unit. However, during operation, the oil film is easily damaged under the influence of complex factors. Installation deviation is a key point that can cause temperature and pressure changes in the oil film, affecting the force on the bearing. This article takes the thrust bearing model of the 1000 MW Francis turbine unit of the Baihetan Power Station as the research object. Based on the fluid–solid coupling theory and CFD technology, the oil film characteristics of thrust bearings are analyzed, and the influence of inclination angles and installation deviation on the oil film flow performance of thrust bearings is discussed. The results show that as the inclination angle changes from 0.0030° to 0.0048°, the axial force changes from 856 t to 368 t, and there is an approximate linear correlation between them. The radial installation deviation has an effect on the axial force. Under the optimal working condition of an inclination angle of 0.0039°, when the radial deviation of the pad changes from 0 mm to 1 mm, the axial force changes from 1573 t to 1275 t. In the process of unit installation, it is necessary to pay attention to the installation deviation of the pad. The results provide guidance for the installation of the bearing, which helps to ensure the safe and stable operation of the station. [ABSTRACT FROM AUTHOR]

Copyright of Bearing is the property of Bearing Editorial Office 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.)

This article studies the tribological behavior of the lubricant film when the Q1-224 hydrostatic turntable is operated at constant cutting speed. First, the rotational speed equation of the worktable under the constraint of constant cutting speed is derived. Based on the lubrication mechanism of hydrostatic turntables, the flow-rate equation of the oil film, the temperature-rise equation of the oil film, and the bearing-capacity equation of the double rectangular cavity are deduced. Furthermore, the prediction model of the lubrication performance of hydrostatic turntable operating at constant cutting speed is established. Meanwhile the quasi-steady-state analysis is carried out by numerical simulation to obtain the change law for the lubricating oil film temperature, pressure, and other performance indicators with time under the different loads. Finally, these laws are verified by designed experiments. It is found that the load has a large effect on the change of oil film performance; it affects the temperature rise of the oil film by influencing the dissipation capacity, and there is a nonlinear relationship between the increase of the load and the average temperature rise of the oil film. [ABSTRACT FROM AUTHOR]

The oil film thickness of the piston ring at the sliding surface affects oil consumption, friction loss and wear of the ring and liner in internal combustion engines. It is important to know the oil film thickness on the piston ring sliding surface in order to improve the engine efficiency. Accurate measurement of oil film thickness on the piston rings is difficult because the oil film thickness is extremely thin. A modified method is proposed for measuring thin oil film. The authors have measured the oil film thickness on the piston skirt and land to contribute. The optical measurement system and analytic method are improved. The presented method present the oil film thickness on the sliding surface of the top ring from the oil film visualization images. The verification of the measured oil film thickness carried out by comparing with the data obtained from the numerical calculation. For evaluating the effect of the oil characteristics, 0W-20 oil and #8 oil were tested with different engine speeds and different crank angle where different ring loads. It was confirmed that the top ring oil film thickness became thick due to the high engine speed. A large load on the top ring reduces the oil film thickness. The oil film became thick when the oil viscosity was high. The effect of oil viscosity on the oil film thickness of the top ring was clarified. The effect of the viscosity index improver was also discussed. It is shown from the experimental results that the present measurement system for the top ring oil film thickness has enough accuracy.

The performance of tooth-sum altered (ATS) gears is determined by the factors influenced by their profile geometry. This study aims to explore the influence of gear geometry modification on tribological aspects that affect surface wear in ATS spur gears. A computer code is developed to simulate surface wear numerically, using Archard's wear model, Greenwood-Williamson micro-asperity contact model, and Johnson’s load-sharing approach. The outcomes of the study indicate that the low contact ratio ATS gears promote the formation of thick oil film owing to reduced specific sliding and increased speed. However, high contact ratio ATS gears create unfavorable operating conditions resulting in extreme boundary lubrication. The effectiveness of lubricant oil film in reducing wear in ATS gears is associated with its modified profile, sliding velocities, load bearing, operating temperature, and oil viscosity.

Oil film characteristics are critical to the high-reliability operation of high-pressure aviation piston pumps (APPs). However, there is still a lack of research on oil film modeling and characteristic analysis of high-pressure APPs. This paper takes the oil film at the cylinder block/valve plate interface of a 35 MPa high-pressure APP as the research object. By introducing a full oil film computational fluid dynamics (CFD) model considering non-isothermal and cavitation effects under multi-field coupling conditions, a cylinder block/valve plate interface oil film model is established, which includes a viscous wedge geometric model, multi-body dynamics model, and full oil film CFD model. The mesh independence test and force balance error analysis ensure the accuracy of the model calculation. Based on the established model, the oil film's lubricating, sealing, load-bearing, and overturning characteristics are comprehensively and systematically analyzed, and the evolution law of different oil film characteristics with pressure changes is revealed. Moreover, suggestions for improving the structure and operating conditions of a 35 MPa high-pressure APP are proposed to optimize the oil film characteristics of the cylinder block/valve plate interface. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology 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.)

The relationship between clutch thermodynamic characteristics and contact states of friction components is explored numerically and experimentally. The clutch thermodynamic numerical model is developed with consideration of the contact state and oil film between friction pairs. The clutch bench test is conducted to verify the variation of the clutch thermodynamic characteristics from the uniform contact (UCS) to the intermittent contact (ICS). The results show that the oil film decreases gradually with increasing temperature; the lubrication state finally changes from hydrodynamic lubrication to dry friction, where the friction coefficient shows an increasing trend before a decrease. Thus, the friction torque in UCS gradually increases after the applied pressure stabilizes. When the contact state changes to ICS, the contact pressure increases suddenly and the oil film decreases rapidly in the local contact area, bringing about a sharp increase in friction torque; subsequently, the circumferential and radial temperature differences of friction components expand dramatically. However, if the contact zone is already in the dry friction state, friction torque declines directly, resulting in clutch failure. The conclusions can potentially be used for online monitoring and fault diagnosis of the clutch. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study the oil film and friction characteristics of valve plates with a micro-textured surface and to explore the influence of textures of different shapes and sizes on the valve plates. Firstly, on the basis of thermohydrodynamic theory, this paper established the lubrication model of the oil film on the valve plate pair of swashplate axial piston pumps, according to the Reynolds equation. Secondly, the micro-texture was added to the mathematical model of the valve plate pair's oil film. A combination of the energy equation, oil-film-thickness equation, elastic deformation equation, viscosity–pressure and viscosity–temperature equation, the finite difference method, as well as the relaxation iteration method, was used to solve the problem, and the textured and non-textured valve plate surfaces were simulated. The nephogram of the oil-film-thickness distribution, elastic deformation distribution, oil-film-pressure distribution and oil-film-temperature distribution were generated. Then, the control variable method was used to change the cylinder rotational speed, tilt angle, oil viscosity, initial oil film thickness and other parameters to analyze their effects on oil film characteristics. In addition, the friction characteristics of non-textured surfaces, square textured surfaces, triangular textured surfaces and circular textured surfaces were compared and analyzed. It was found that the textured surface of valve plates can obviously improve friction efficiency under the same operating conditions. The square texture, especially, is the preferable shape, rather than the triangular texture and the circular texture, and the friction performance is at its best when the texture depths are between 20 μ m and 50 μ m . The results provide a theoretical basis for the design and improvement of the valve plate. [ABSTRACT FROM AUTHOR]

This research aims to evaluate the effect of surface texturing on the cylinder liner on tribological characteristics such as minimum oil film thickness, power losses, and dynamic forces (asperity contact force, hydrodynamic force, and total friction force). The research covers the study of two lubrication conditions: (a) starved and (b) fully flooded. The surface texturing on the cylinder liner was produced by dimpling. For the development of the study, a numerical model was used with MATLAB® software. The analysis of the dynamic forces demonstrated that dimples in the cylinder liner led to a 10.10% decrease in the asperity contact force between the piston ring and the cylinder liner. On the other hand, surface texturing allows a 4.32% increase in the minimum oil film thickness, which results in a 6.05% decrease in power loss. The surface texturing improves the engine's energy efficiency by 3.11%. The fully flooded lubrication condition leads to higher estimates of the frictional force present in the combustion chamber. In general, the mathematical model allows estimating the tribological behavior between the compression ring and the cylinder liner, which is a useful tool for evaluating strategies to minimize the power lost due to surface friction. [ABSTRACT FROM AUTHOR]

Copyright of Large Electric Machine & Hydraulic Turbine is the property of Large Electric Machine & Hydraulic Turbine Editorial Office 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.)

The oil film between the friction disks of the hydro-viscous clutch is taken as the research object. Considering the groove structure of the friction disks, the mathematical model of the oil film flow field is established. The finite difference algorithm is utilized to solve the velocity, the pressure, and the pressure coefficient of the oil film. The incipient position of oil film shear cavitation under different groove structure parameters is carried out. The numerical results indicate that the groove has a great influence on the oil film velocity and pressure. The oil film cavitation inception occurs first in the upstream position of the groove area. The area fraction of cavitation inception is directly proportional to the width and depth of the groove and inversely proportional to the section parameter and inclination angle of the groove. This research provides an efficient and accurate method for predicting the oil film shear cavitation inception. [ABSTRACT FROM AUTHOR]

Featured Application: This research presents the novelty in establishing the true dynamic bending moment using only one bridge of strain gauge. This is achieved by using the actual measured bending stress combined with phase lag stress at an angle of 90 degrees. The measurement of shaft bending (whirling) moment can be performed via a telemetry system including strain gauges which can obtain the bending stress. By using a single bridge of strain gauge, it was possible to obtain only the nominal bending moment. However, in case of the propeller shaft vibration measurement, the true dynamic bending moment is needed to evaluate the effect of propeller forces on the stability of the bearings. To deal with this, typically two bridges of strain gauge at 90 degrees are needed. This research presents a novel reliability assessment method in establishing the true dynamic bending moment using only one bridge of strain gauge. This is achieved by using the actual bending stress measured by strain gauge combined with its own phase lag stress at an angle of 90 degrees. To validate this technique, the experiments were performed under the rapid turning transient states during a sea trial of a 50,000 DWT oil/chemical tanker. As a result, great fluctuations in propeller force were detected, resulting in a non-uniform oil film in the bearings. The displacement sensor was also installed and confirmed the established true dynamic bending moment. [ABSTRACT FROM AUTHOR]

Oil pollution is today one of the main factors of the technogenic impact on the environment. Emergency oil spills are the main source of the oil pollution. The causes, scales, and environmental consequences of emergency spills are considered. The advantages and drawbacks of methods for eliminating the spills of crude oil and petroleum products on the surface of water bodies are discussed. The features of the sorption method for oil collection from the water surface, which is the most widely used method, are described in detail. Requirements to petroleum sorbents are analyzed, and classes of the sorbents are described. Synthetic polymer sorbents have a set of advantages over other types of oil-absorbing materials. Fighting emergency oil spills should include the activity aimed at their prevention. This is particularly topical for Russia, which starts active operation of the Northern Sea Route and of shelf deposits of fossil fuels in seas of the Russian Arctic. [ABSTRACT FROM AUTHOR]

The thrust bearing, as the only part bearing the axial load, is extremely important in vertical hydroelectric generating units. Its working condition directly affects the safe and reliable operation of the hydroelectric generating unit. However, during operation, the oil film is easily damaged under the influence of complex factors. Installation deviation is a key point that can cause temperature and pressure changes in the oil film, affecting the force on the bearing. This article takes the thrust bearing model of the 1000 MW Francis turbine unit of the Baihetan Power Station as the research object. Based on the fluid–solid coupling theory and CFD technology, the oil film characteristics of thrust bearings are analyzed, and the influence of inclination angles and installation deviation on the oil film flow performance of thrust bearings is discussed. The results show that as the inclination angle changes from 0.0030° to 0.0048°, the axial force changes from 856 t to 368 t, and there is an approximate linear correlation between them. The radial installation deviation has an effect on the axial force. Under the optimal working condition of an inclination angle of 0.0039°, when the radial deviation of the pad changes from 0 mm to 1 mm, the axial force changes from 1573 t to 1275 t. In the process of unit installation, it is necessary to pay attention to the installation deviation of the pad. The results provide guidance for the installation of the bearing, which helps to ensure the safe and stable operation of the station.

In this study, the optical flow method for the skin-friction-stress estimation from the unsteady oil film distribution was reformulated based on the variational method, and the validity of the proposed method was verified in comparison with the conventional method. The regularization is proposed to be added directly to the skin-friction-stress field in the proposed method while the regularization is added to the amount of oil movement in the conventional method. As a result, the smoothness of the skin-friction-stress field can be controlled by adjusting the regularization parameter in the proposed method whereas it was difficult in the conventional method. The performance of the proposed method was evaluated to be superior to the previous method through the numerical and experimental data. [ABSTRACT FROM AUTHOR]

In this work, the physical phenomenon of the formation of an oil film containing fullerenes was further developed, on the friction surface of tribosystems, which, in contrast to the known ones, takes into account the structural viscosity and structure of the formed film under the action of the electrostatic field of the friction surface. An increase in load significantly increases the structural viscosity of the gel structure, 13 - 20 times. The concentration of fullerenes in the base lubricant does not significantly affect the dynamic viscosity of aggregates in the composition of the liquid and the structure of the gel. An increase in the tribological properties of the base lubricant medium reduces the value of the structural viscosity of the gel on the friction surface by a factor of 3. At the same time, the concentration of fullerenes in the range of 0.5 - 1.5% does not have a large effect on these indicators. This phenomenon can be explained by the presence or absence of an additive package in the base lubricating medium. For those oils where the additive package is absent or present in a small amount J/m3, the introduction of a fullerene composition promotes the formation of clusters and micelles, which increase the structural viscosity and, consequently, form a film on the friction surface in the form of a gel structure. Conversely, if fullerenes are introduced into a base oil that contains a large and balanced additive package, where tribological properties are high J/m3, interaction at the molecular level does not occur. Fullerenes to a lesser extent will form stable aggregates in the form of micelles. The effect of reducing the coefficient of friction, equal to 96 %, is typical for low and medium loads of operation of tribosystems and base lubricants with average values of tribological properties. With increasing loads or tribological properties of base oils, the effect of the use of fullerenes decreases

The thermal effect of the viscous oil film of hydrostatic bearings is the key factor causing bearing errors, and the hydrostatic bearing working surface with microgroove structures can potentially inhibit the thermal effect and effectively ensure the bearing accuracy. In this study, a modeling method for oil film heat generation of hydrostatic bearings with a rectangular microgroove working surface is established, and the influence of microgroove design scales onto oil film heat generation is studied. First, the flowing field numerical simulation model of the hydrostatic bearing oil film is established and verified by the published analytical model. Based on the simulation method, oil film flowing behaviors of hydrostatic bearings with a rectangular microgroove working surface are studied. Then, by combining the analytical calculation of viscous heat generation of the hydrostatic oil film and its flowing field simulation, a modified oil film thermal modeling of hydrostatic bearings with the rectangular microgroove working surface is established. On this basis, the influence of the microgroove design scale onto oil film heat generation is studied. It can be concluded that with the appropriate scales of the rectangular microgroove, the working surface with microgrooves can reduce the average velocity of the viscous flow field of the hydrostatic bearing oil film and restrain its energy loss and heat generation.

The paper presents theoretical studies of changes in the structural viscosity of oil films on the friction surface with fullerene compositions in the field of action of electrostatic forces of the friction surface and the base lubricant. A feature of the use of fullerene additives in lubricants is that fullerenes are readily soluble in a wide class of organic and inorganic solvents. At the same time, poor solubility of fullerenes in technical oils (mineral, semi-synthetic and synthetic). The purpose of this work is to carry out theoretical studies of changes in the structural viscosity of oil films on the friction surface with fullerene compositions in the field of action of electrostatic forces of the friction surface and the base lubricant. On the basis of the working hypothesis, it was theoretically established that for a thin oil film, located in the field of action of electrostatic forces of the friction surface, it is necessary to consider the structural dynamic viscosity of the lubricant, which at the friction surface has a gel structure, and as the electrostatic forces from the friction surface decrease, the gel structure transforms into the sol structure. It is shown that the value of the structural viscosity of the considered aggregates is comparable with the viscosity of polymers or bitumen. Moreover, the viscosity of the gel structure is four orders of magnitude higher than the viscosity of the sol structure. An increase in the concentration of fullerenes leads to an increase in the dynamic viscosity of aggregates. It is theoretically shown that the structure of the oil film, which corresponds to the structure of the gel, belongs to the class of non-Newtonian fluids. With an increase in the sliding speed, the dynamic viscosity of such structures decreases by a factor of 4, which explains the destruction of micelle clusters and the appearance of rotational motions of elastic flocks. It is assumed that this will lead to a decrease in the value of the coefficient of friction. It is shown that for the gel structure, the concentration of fullerenes in the bulk of the base lubricant does not have a large effect on the structural viscosity. Conversely, for the structure of a sol, the concentration of fullerenes has a significant effect on the value of the structural dynamic viscosity

To study the dynamic characteristics of the slipper pair with the complex surface structure of the valve distribution piston pump, the Least Square Method was combined with the TRD(Trust Region Dogleg) optimization method, and then dynamically coupled with the FVM(Finite Volume Method) and introduced into the solution of the slipper pair lubrication model. Then the mathematical analytical model of lubrication and friction of single-support belt and multi-support belt slipper pair of the valve distribution piston pump based on the FVM-TRD coupling method was established. The lubrication performance of slipper pairs was analyzed by combining the proposed slipper overturning rate and Efficiency Reference Value. Finally, relevant experimental research was conducted. The results show that the oil film dynamic pressure effect of the slipper with multi-support belt is stronger. The influence laws of working condition parameters on the three types of slipper pairs is basically the same, and the slippers are more prone to overturning wear in the low pressure area. Besides, the anti-overturning performance of S3 slipper is the best, S1 is slightly worse, and S2 is the worst. However, the power efficiency of S3 slipper is the lowest, followed by S2, and S1 is the highest. The accuracy of theoretical calculation is verified by experiments.The research results lay a theoretical and technical foundation for the optimal design of slipper pairs of valve distribution piston pump. [ABSTRACT FROM AUTHOR]

The study considered the known hydrodynamic friction model based on the generalized Eyring equation and taking into account the phenomenon of oil film self-heating. The concept of effective friction coefficient is introduced the use of which makes it possible to perform bearing dynamic simulation taking into account the dependence of friction coefficients on cyclically changing contact forces without increasing the calculation time. The effective friction coefficients of the contacts with the inner and outer rings are calculated for the range of specified slip values. As a result, dependences of the effective friction coefficients on slippage of both the cage and the rolling elements are obtained. These dependences have the same form as conventional friction curves: as slip increases, the effective friction coefficient first increases and reaches a certain maximum value, and then decreases, which is caused by self-heating of the oil film and a decrease in its viscosity. A decrease in the friction coefficient during bearing operation, in turn, leads to even greater slippage. A process with such a "positive feedback," if not interrupted, leads to an increase in heating of the oil, a decrease in the thickness of the oil film and, as a result, to its rupture, the occurrence of boundary friction, intense wear, and seizure. The amount of cage slip that achieves the maximum effective friction coefficient on the inner ring is critical. In the example considered in the paper, the critical slip of the cage is 11%. The slip allowed during operation of the bearing must be determined taking into account the margin in relation to its critical value. [ABSTRACT FROM AUTHOR]

Oil film characteristics are critical to the high-reliability operation of high-pressure aviation piston pumps (APPs). However, there is still a lack of research on oil film modeling and characteristic analysis of high-pressure APPs. This paper takes the oil film at the cylinder block/valve plate interface of a 35 MPa high-pressure APP as the research object. By introducing a full oil film computational fluid dynamics (CFD) model considering non-isothermal and cavitation effects under multi-field coupling conditions, a cylinder block/valve plate interface oil film model is established, which includes a viscous wedge geometric model, multi-body dynamics model, and full oil film CFD model. The mesh independence test and force balance error analysis ensure the accuracy of the model calculation. Based on the established model, the oil film’s lubricating, sealing, load-bearing, and overturning characteristics are comprehensively and systematically analyzed, and the evolution law of different oil film characteristics with pressure changes is revealed. Moreover, suggestions for improving the structure and operating conditions of a 35 MPa high-pressure APP are proposed to optimize the oil film characteristics of the cylinder block/valve plate interface.

The relationship between clutch thermodynamic characteristics and contact states of friction components is explored numerically and experimentally. The clutch thermodynamic numerical model is developed with consideration of the contact state and oil film between friction pairs. The clutch bench test is conducted to verify the variation of the clutch thermodynamic characteristics from the uniform contact (UCS) to the intermittent contact (ICS). The results show that the oil film decreases gradually with increasing temperature; the lubrication state finally changes from hydrodynamic lubrication to dry friction, where the friction coefficient shows an increasing trend before a decrease. Thus, the friction torque in UCS gradually increases after the applied pressure stabilizes. When the contact state changes to ICS, the contact pressure increases suddenly and the oil film decreases rapidly in the local contact area, bringing about a sharp increase in friction torque; subsequently, the circumferential and radial temperature differences of friction components expand dramatically. However, if the contact zone is already in the dry friction state, friction torque declines directly, resulting in clutch failure. The conclusions can potentially be used for online monitoring and fault diagnosis of the clutch.

The purpose of this paper is to study the oil film and friction characteristics of valve plates with a micro-textured surface and to explore the influence of textures of different shapes and sizes on the valve plates. Firstly, on the basis of thermohydrodynamic theory, this paper established the lubrication model of the oil film on the valve plate pair of swashplate axial piston pumps, according to the Reynolds equation. Secondly, the micro-texture was added to the mathematical model of the valve plate pair’s oil film. A combination of the energy equation, oil-film-thickness equation, elastic deformation equation, viscosity–pressure and viscosity–temperature equation, the finite difference method, as well as the relaxation iteration method, was used to solve the problem, and the textured and non-textured valve plate surfaces were simulated. The nephogram of the oil-film-thickness distribution, elastic deformation distribution, oil-film-pressure distribution and oil-film-temperature distribution were generated. Then, the control variable method was used to change the cylinder rotational speed, tilt angle, oil viscosity, initial oil film thickness and other parameters to analyze their effects on oil film characteristics. In addition, the friction characteristics of non-textured surfaces, square textured surfaces, triangular textured surfaces and circular textured surfaces were compared and analyzed. It was found that the textured surface of valve plates can obviously improve friction efficiency under the same operating conditions. The square texture, especially, is the preferable shape, rather than the triangular texture and the circular texture, and the friction performance is at its best when the texture depths are between 20 μm and 50 μm. The results provide a theoretical basis for the design and improvement of the valve plate.