Measurements of frictional resistance play an important role in engineering practice. There are several types of air resistance acting on an aircraft, for example. One of them, frictional resistance, accounts for half...Measurements of frictional resistance play an important role in engineering practice. There are several types of air resistance acting on an aircraft, for example. One of them, frictional resistance, accounts for half of the air resistance. Oil film interferometry is one of methods for measuring the frictional resistance. Oil dropped on an object is thinly stretched by the frictional resistance. The bright and dark fringe pattern is generated when monochromatic light is applied to the oil film. The gradient of the oil thickness decreases with the lapse of time, and thus the spacing between neighboring the dark lines increases. The rate at which the spacing increases is proportional to the frictional resistance. In this study, the frictional resistance acting on a small area on a plate was measured and compared with the theoretical value. As a result, these results qualitatively agree well with each other.展开更多
Based on the principles of heat transfer,an oil film model in the engine cylinder was established.Under the condition of cold state,the influence of factors such as engine fuel injection,fuel drop point,cylinder inne...Based on the principles of heat transfer,an oil film model in the engine cylinder was established.Under the condition of cold state,the influence of factors such as engine fuel injection,fuel drop point,cylinder inner wall temperature,and inlet fluid on the oil film is comprehensively considered to establish an oil film quality prediction model.Based on the measurement of the compensation oil quantity in the transition conditions,the variation of the oil film during the transition is analyzed.The experimental results show that the velocity of the air-flow in the intake port and the temperature and pressure on the wall of the intake port are the main factors affecting the oil film in the cylinder.Based on the abovementioned experimental and theoretical studies,an oil film distribution model for each cycle of the transition condition was established based on the engine inlet oil film model.The experimental measurement curve and model prediction curve for the fuel compensation per cycle in the transition condition from 10%load to 30%load.The model established can be in good agreement with the experimental results and meet the fuel compensation trend in the transition condition.While realizing the fuel compensation for the transient conditions,this work is definitely helpful to achieve accurate control of the air-fuel ratio.展开更多
It is of a vital importance to reduce the frictional losses in marine diesel engines. Advanced surface textures have provided an e ective solution to friction performance of rubbing pairs due to the rapid development ...It is of a vital importance to reduce the frictional losses in marine diesel engines. Advanced surface textures have provided an e ective solution to friction performance of rubbing pairs due to the rapid development of surface engineering techniques. However,the mechanisms through which textured patterns and texturing methods prove beneficial remains unclear. To address this issue,the tribological system of the cylinder liner?piston ring(CLPR) is investigated in this work. Two types of surface textures(Micro concave,Micro V?groove) are processed on the cylinder specimen using di erent processing methods. Comparative study on the friction coe cients,worn surface texture features and oil film characteristics are performed. The results demonstrate that the processing method of surface texture a ect the performance of the CLPR pairs under the specific testing conditions. In addition the micro V?groove processed by CNCPM is more favorable for improving the wear performances at the low load,while the micro?con?cave processed by CE is more favorable for improving the wear performances at the high load. These findings are in helping to understand the e ect of surface texture on wear performance of CLPR.展开更多
Lubrication failure is one of the main failure forms of gear failure.Time varying meshing stiffness is an important factor affecting the dynamic behavior of gears.However,the influence of oil film stiffness is usually...Lubrication failure is one of the main failure forms of gear failure.Time varying meshing stiffness is an important factor affecting the dynamic behavior of gears.However,the influence of oil film stiffness is usually ignored in the research process.In this paper,according to the meshing characteristics of double involute gears,based on the non-Newtonian thermal EHL theory,a new calculation method of normal and tangential oil film stiffness for double involute gears is established by the idea of subsection method.The oil film stiffness difference between double involute gears and common involute gears is analyzed,and the influence of tooth waist order parameters,working conditions,and thermal effect on the oil film stiffness are studied.The results reveal that there are some differences between normal and tangential oil film stiffness between double involute gears and common involute gears,but there is little difference.Compared with the torque,rotation speed and initial viscosity of the lubricating oil,the tooth waist order parameters have less influence on the oil film stiffness.Thermal effect has a certain influence on normal and tangential oil film stiffness,which indicates that the influence of thermal effect on the oil film can not be ignored.This research proposes a calculation method of normal and tangential oil film stiffness suitable for double involute gears,which provides a theoretical basis for improving the stability of the transmission.展开更多
The research on the oil film characteristic of piston pair is beneficial to the design and optimization of friction pair,which can improve the performance of piston pump.The fluid pressure of piston cavity is accurate...The research on the oil film characteristic of piston pair is beneficial to the design and optimization of friction pair,which can improve the performance of piston pump.The fluid pressure of piston cavity is accurately obtained by AMEsim simulation.Oil film thickness field model of piston pair under the slanting state of piston is established,and the distribution law is numerically analyzed under different speed and pressure by Matlab.The experiment model pump for oil film characteristic of piston pair is designed to measure oil film thickness under the pressure of 18 MPa.The experiment results show that oil film thickness varies greatly under high pressure,and oil film thickness fluctuates sharply under low speed.The minimum oil film thickness increases with spindle speed increasing and oil film characteristic of piston pair based on the numerical analysis method is verified.This method lays a foundation for studying the friction performance of piston pair in the axial piston pump.展开更多
Bearings are key components in rotating machinery,which is widely used in many fields,such as CNC machines,wind turbines and induction machines.The increasingly harsh operation environment can lead to wear and tear on...Bearings are key components in rotating machinery,which is widely used in many fields,such as CNC machines,wind turbines and induction machines.The increasingly harsh operation environment can lead to wear and tear on raceways and reduce the precision and reliability of bearing or even machinery.Lubrication could relieve the wear to some degree,which is benefit to prolong the bearing’s life.Thus,investigation on the vibration responses under the influence of oil film is of great significance.However,for mechanism analysis,how to include the oil film into the bearing dynamic model affects the result and efficiency of solution.To address this problem,this study proposed a fast algorithm through load distribution and interpolation when calculating oil film stiffness and thickness during the solution of bearing vibration model.Analysis of oil film on vibration is carried out and a bearing test rig is designed to verify the proposed model.Numerical simulation result shows that rotational speed and load have vital effect on oil film and vibration.The experimental result is consistent with the simulation,which shows that the proposed model has a better performance on modeling bearing vibration and the method of considering oil film is reasonable.展开更多
In combination with a wave action balance equation,a damping model for sea waves covered by oil films of a finite thickness is proposed. The damping model is not only related to the physical parameters of the oil film...In combination with a wave action balance equation,a damping model for sea waves covered by oil films of a finite thickness is proposed. The damping model is not only related to the physical parameters of the oil film,but also related to environment parameters. Meanwhile,the parametric analyses have been also conducted to understand the sensitivity of the damping model to these parameters. And numerical simulations demonstrate that a kinematic viscosity,a surface/interfacial elasticity,a thickness,and a fractional filling factor cause more significant effects on a damping ratio than the other physical parameters of the oil film. From the simulation it is also found that the influences induced by a wind speed and a wind direction are also remarkable. On the other hand,for a thick emulsified oil film,the damping effect on the radar signal induced by the reduction of an effective dielectric constant should also be taken into account. The simulated results are compared with the damping ratio evaluated by the 15 ENVISAT ASAR images acquired during the Gulf of Mexico oil spill accident.展开更多
The technique of non stationary oil film force database for hydrodynamic bearing is introduced and its potential applications in nonlinear rotor dynamics are demonstrated. Through simulations of the locus of the shaft...The technique of non stationary oil film force database for hydrodynamic bearing is introduced and its potential applications in nonlinear rotor dynamics are demonstrated. Through simulations of the locus of the shaft center aided by the database technique, nonlinear stability analysis can be performed and the natural frequency can be obtained as well. The easiness of "assembling" the individual bush forces from the database to form the bearing force, makes it very convenient to evaluate the stability of various types of journal bearings. Examples are demonstrated to show how the database technique makes it possible to get technically abundant simulation results at the expense of very short calculation time.展开更多
Oil film forces are usually obtained for dynamic analysis of a journal bearing system by using the approximate analytical formula or solving the Reynolds equation. None of them is suitable for rotor system bifurcation...Oil film forces are usually obtained for dynamic analysis of a journal bearing system by using the approximate analytical formula or solving the Reynolds equation. None of them is suitable for rotor system bifurcation analysis because they are either of poor accuracy or time consuming. Oil film forces database is proposed is to transform the journal speed variation range in radial and circumferential directions from (-∞,+∞) to (-1, +1). The numerical results show the suggested method is much more effective. And sub harmonic, quasi periodic and chaotic vibrations are predicted for a range of speed and unbalance parameters.展开更多
With the rapid development of the steel industry, to keep pace with the current trend of high speed, continuous, and large-scale production that focuses on automation and high levels of efficiency, many state-owned st...With the rapid development of the steel industry, to keep pace with the current trend of high speed, continuous, and large-scale production that focuses on automation and high levels of efficiency, many state-owned steel companies are being equipped with oil film bearings. Through long-term on-spot inspection and research on the fatigue failure of oil film bearing, three segments of annulated fatigue breakage were found axially along the inner surface of the bearing sleeve. In order to elucidate the reason for the three-segment annulated damage under rolling load, numerical boundary element method was adopted to analyze the contact behaviors between the sleeve and rollneck. Failure mechanism was discussed in detail, the distributions of contact stress were analyzed, and the service lives of the sleeve for different positions on the inner surface were quantitatively described, which provided an effective means to decrease wear and adhesive damage of the sleeve and to increase the load capacity of oil film bearing and its service life as well.展开更多
To study the mechanism of burnt damage of oil film bearing in high-speed wire rolling mill,reasonable tempera- ture sensors are designed and calibrated,pressure block of rolling mill has been transformed into pressure...To study the mechanism of burnt damage of oil film bearing in high-speed wire rolling mill,reasonable tempera- ture sensors are designed and calibrated,pressure block of rolling mill has been transformed into pressure sensors.Online tempera- ture and load of oil film bearing in a domestic precision rolling F15 have been tested.Consequently,a large sum of valuable test data was obtained.The distributions rules of pressure and temperature under continuous online rolling state are recorded in detail. Theoretical and experimental results are beneficial to damage mechanism of oil film bearing,thus its service life could be pro- longed.Moreover,such results could provide an important reference for online test and control.展开更多
The effectiveness of variable parameter squeeze oil film damper (VPSFD) in the steady and transient unbalance response control of flexible rotors is examined.First, a preliminary property design of VPSFD is presente...The effectiveness of variable parameter squeeze oil film damper (VPSFD) in the steady and transient unbalance response control of flexible rotors is examined.First, a preliminary property design of VPSFD is presented on the improved finite length bearing theory.VPSFD is different from the conventional squeeze film damper, and is designed to possess continuous changeable oil film clearance and land length. These parameters can be exactly adjusted on a computer by sending commends to a special control device. Then, a simple rotor system with VPSFD is investigated. The experimental results show that VPSFD can attenuate the rotor system resonance peak due to unbalance.展开更多
Through optimizing the eletric parameters of the resistance-capacitance (R-C)oscillation,a measuring instrument is developed for measurement of EHL oil filmthickness.Actual measurement was made with space bearings and...Through optimizing the eletric parameters of the resistance-capacitance (R-C)oscillation,a measuring instrument is developed for measurement of EHL oil filmthickness.Actual measurement was made with space bearings and actual measurements arein good agreement with theoretical calculations.展开更多
In order to analyze the stress and deformation of different permeability of residual oil film in the complex pore, which are affected by the viscous-elasticity of the fluid, the hydrodynamic displacement mechanism is ...In order to analyze the stress and deformation of different permeability of residual oil film in the complex pore, which are affected by the viscous-elasticity of the fluid, the hydrodynamic displacement mechanism is explored from the stand-point of hydrodynamics, that is, the residual oil film displaced by alternating injection of different concentrations of the polymer solution, viscous-elastic fluid flow equation is established in the complex pore by choosing continuity equation, motion equation and the upper convected Maxwell constitutive equation. The flow field is computed by using the method of numerical analysis. Not only the stress and deformation of residual oil film on the different permeability of micro pores, but also the analysis of the flooding mechanism of alternating injection of different concentrations of the polymer solution is got. The results show that the larger the viscous-elasticity of polymer solution is, the bigger the normal deviatoric stress acting on the residual oil film is;the distribution of normal deviatoric stress has the abrupt change. The stronger the viscous-elasticity of the polymer solution is, the bigger the horizontal stress difference acting on the residual oil film is and the more obvious the deformation is;the high-concentration polymer solution is suitable for high-permeability micro pores. Low-concentration polymer solution is suitable for medium and low-permeability micro pores. Alternating injection of polymer solution can improve Volumetric Sweep Efficiency and increase the deformation of residual oil film, which is conducive to enhancing oil recovery.展开更多
Bearing chamber is one of important components that support aero-engine rotors and research on oil droplet and oil film motions is an important part of bearing chamber lubrication and heat transfer design. Considering...Bearing chamber is one of important components that support aero-engine rotors and research on oil droplet and oil film motions is an important part of bearing chamber lubrication and heat transfer design. Considering the pressure of sealing air is an important operating condition that affects the oil droplet and oil film motions,the effect of sealing air pressure on airflow in bearing chamber is investigated in this paper firstly; and then based on the air velocity and air / wall shear force,the oil droplet moving in core air,deposition of oil droplet impact on wall as well as velocity and thickness of oil film are analyzed secondly; the effect of sealing air pressure on oil droplet velocity and trajectory,deposition mass and momentum,as well as oil film velocity and thickness is discussed. The work presented in this paper is conducive to expose the oil / air two phase lubrication mechanism and has certain reference value to guide design of secondary air / oil system.展开更多
The lubrication effectiveness of MoS_(2) nanoparticles as an oil additive remains unclear,restricting its application in industry to reduce friction.The goal of this work was to explore the lubrication mechanism of Mo...The lubrication effectiveness of MoS_(2) nanoparticles as an oil additive remains unclear,restricting its application in industry to reduce friction.The goal of this work was to explore the lubrication mechanism of MoS_(2) nanoparticles as an oil additive.In this study,the oil film thickness behaviors of MoS_(2) nanoparticles in poly-alpha olefin(PAO4)base oil,PAO4 with 3 wt%dispersant(polyisobutyleneamine succinimide,PIBS),and 0W20 engine oil were investigated using an elastohydrodynamic lubrication(EHL)testing machine.Following the EHL tests,the flow patterns around the contact area and the tribofilm covering rate on contact area were studied using optical microscopy to understand the lubrication mechanism.The results indicate that both the dispersant and nanoparticle aggregation significantly affected the oil film thickness.The expected oil film thickness increase in the case of 0.1 wt%MoS_(2) in PAO4 base oil was obtained,with an increase from 30 to 60 nm over 15 min at a velocity of 50 mm/s.Flow pattern analysis revealed the formation of particle aggregation on the rolling path when lubricated with 0.1 wt%MoS_(2),which is associated with a tribofilm coverage rate of 41.5%on the contact area.However,an oil film thickness increase and particle aggregation were not observed during the tests with 0.1 wt%MoS_(2) blended with 3 wt%PIBS as the dispersant in PAO4 base oil,and for 0.75 wt%MoS_(2) in 0W20 engine oil.The results suggest that nanoparticles responsible for tribofilm formation originated from aggregates,but not the well-dispersed nanoparticles in point contact.This understanding should aid the advancement of novel lubricant additive design.展开更多
In this paper,the oscillatory oil squeeze film is taken as a research object,and a coupled cavitation model based on the theory of bubble dynamics and hydrodynamic lubrication is used and a specific method of numerica...In this paper,the oscillatory oil squeeze film is taken as a research object,and a coupled cavitation model based on the theory of bubble dynamics and hydrodynamic lubrication is used and a specific method of numerical calculation is given.Then the parallel-plate squeeze film test apparatus is used to validate the coupled cavitation model.The pictures of the cavitation were captured by a high-speed camera and then processed to obtain the variation of the cavitation area in experiments.Compared with the experimental results,the model can successfully predict the process of generation and development of cavitation.At the same time,the pressure variation calculated by the model is in good agreement with the experimental data and the value of negative pressure is close to the experiment.On this basis,three new parameters that are related to bubble dynamics are studied by comparing the pressure and cavitation area variation in an oscillating squeeze oil film.The results show that surface dilatational viscosity,initial radii of cavitation nuclei and number of bubbles per unit area have a significant influence on the generation time of the cavitation,the maximum tensile stress that the oil film can withstand,and the speed of the cavitation collapse respectively.展开更多
The lubrication design and heat transfer determination of bearing chambers in aeroengine require a sufficient understanding of the oil droplet-film interaction and physical characteristic in an oil/air two-phase flow ...The lubrication design and heat transfer determination of bearing chambers in aeroengine require a sufficient understanding of the oil droplet-film interaction and physical characteristic in an oil/air two-phase flow state.The analyses of oil droplet movement,mass and momentum transfer during the impingement of droplet/wall,as well as wall oil film thickness and flow velocity are very important for the bearing chamber lubrication and heat transfer calculation.An integrated model in combination with droplet movement,droplet/wall impact and film flow analysis is put forward initially based on the consideration of droplet size distribution.The model makes a contribution to provide more practical and feasible technical approach,which is not only for the study of droplet-film interaction and physical behavior in bearing chambers with oil/air two-phase flow phenomena,but also useful for an insight into the essence of physical course through droplet movement and deposition,film formation and flow.The influences of chamber geometries and operating conditions on droplet deposition mass and momentum transfer,and wall film thickness and velocity distribution are discussed.The feasibility of the method by theoretical analysis is also verified by the existing experimental data.The current work is conducive to expose the physical behavior of wall oil film configuration and flow in bearing chamber,and also significant for bearing chamber lubrication and heat transfer study under oil/air two-phase flow conditions.展开更多
Oil film bearing,which works on thin film between sleeve and bush,is widely used in steel industry due to the characteristics of high efficiency and low noise,etc. The backup roll of 1 580PC hot strip mill invested by...Oil film bearing,which works on thin film between sleeve and bush,is widely used in steel industry due to the characteristics of high efficiency and low noise,etc. The backup roll of 1 580PC hot strip mill invested by some steel corporation has been equipped with such bearing. During the process of setup&disassembly and usage period,the sleeve has been dramatically damaged,which results in production accidents and decreases its service life,thus heavily influencing steel production. Aimed at such puzzles,under specific loadcase,mechanical properties of bearing sleeve,as well as estimation of contact status and adhesive force of sleeve by interference fit,are quantitatively simulated by finite element method,which establishes an mechanical foundation for improving the load capacity of bearing and decreasing its wear and adhesion damages. Finally,some measures and conclusions are drawn.展开更多
文摘Measurements of frictional resistance play an important role in engineering practice. There are several types of air resistance acting on an aircraft, for example. One of them, frictional resistance, accounts for half of the air resistance. Oil film interferometry is one of methods for measuring the frictional resistance. Oil dropped on an object is thinly stretched by the frictional resistance. The bright and dark fringe pattern is generated when monochromatic light is applied to the oil film. The gradient of the oil thickness decreases with the lapse of time, and thus the spacing between neighboring the dark lines increases. The rate at which the spacing increases is proportional to the frictional resistance. In this study, the frictional resistance acting on a small area on a plate was measured and compared with the theoretical value. As a result, these results qualitatively agree well with each other.
文摘Based on the principles of heat transfer,an oil film model in the engine cylinder was established.Under the condition of cold state,the influence of factors such as engine fuel injection,fuel drop point,cylinder inner wall temperature,and inlet fluid on the oil film is comprehensively considered to establish an oil film quality prediction model.Based on the measurement of the compensation oil quantity in the transition conditions,the variation of the oil film during the transition is analyzed.The experimental results show that the velocity of the air-flow in the intake port and the temperature and pressure on the wall of the intake port are the main factors affecting the oil film in the cylinder.Based on the abovementioned experimental and theoretical studies,an oil film distribution model for each cycle of the transition condition was established based on the engine inlet oil film model.The experimental measurement curve and model prediction curve for the fuel compensation per cycle in the transition condition from 10%load to 30%load.The model established can be in good agreement with the experimental results and meet the fuel compensation trend in the transition condition.While realizing the fuel compensation for the transient conditions,this work is definitely helpful to achieve accurate control of the air-fuel ratio.
基金Supported by National Natural Science Foundation of China(Grant No.51422507)Hubei Provincial Natural Science Foundation of China(Grant No.2015CFB372)+1 种基金Fundamental Research Funds for the Central Universities of China(Grant No.2015IVA010)Tribology Science Fund of State Key Laboratory of Tribology of China(Grant No.SKLTKF14B03)
文摘It is of a vital importance to reduce the frictional losses in marine diesel engines. Advanced surface textures have provided an e ective solution to friction performance of rubbing pairs due to the rapid development of surface engineering techniques. However,the mechanisms through which textured patterns and texturing methods prove beneficial remains unclear. To address this issue,the tribological system of the cylinder liner?piston ring(CLPR) is investigated in this work. Two types of surface textures(Micro concave,Micro V?groove) are processed on the cylinder specimen using di erent processing methods. Comparative study on the friction coe cients,worn surface texture features and oil film characteristics are performed. The results demonstrate that the processing method of surface texture a ect the performance of the CLPR pairs under the specific testing conditions. In addition the micro V?groove processed by CNCPM is more favorable for improving the wear performances at the low load,while the micro?con?cave processed by CE is more favorable for improving the wear performances at the high load. These findings are in helping to understand the e ect of surface texture on wear performance of CLPR.
基金Supported by National Natural Science Foundation of China(Grant No.52075279)。
文摘Lubrication failure is one of the main failure forms of gear failure.Time varying meshing stiffness is an important factor affecting the dynamic behavior of gears.However,the influence of oil film stiffness is usually ignored in the research process.In this paper,according to the meshing characteristics of double involute gears,based on the non-Newtonian thermal EHL theory,a new calculation method of normal and tangential oil film stiffness for double involute gears is established by the idea of subsection method.The oil film stiffness difference between double involute gears and common involute gears is analyzed,and the influence of tooth waist order parameters,working conditions,and thermal effect on the oil film stiffness are studied.The results reveal that there are some differences between normal and tangential oil film stiffness between double involute gears and common involute gears,but there is little difference.Compared with the torque,rotation speed and initial viscosity of the lubricating oil,the tooth waist order parameters have less influence on the oil film stiffness.Thermal effect has a certain influence on normal and tangential oil film stiffness,which indicates that the influence of thermal effect on the oil film can not be ignored.This research proposes a calculation method of normal and tangential oil film stiffness suitable for double involute gears,which provides a theoretical basis for improving the stability of the transmission.
基金Supported by the National Natural Science Foundation of China(No.51975164)the Fundamental Research Foundation for Universities of Heilongjiang Province.
文摘The research on the oil film characteristic of piston pair is beneficial to the design and optimization of friction pair,which can improve the performance of piston pump.The fluid pressure of piston cavity is accurately obtained by AMEsim simulation.Oil film thickness field model of piston pair under the slanting state of piston is established,and the distribution law is numerically analyzed under different speed and pressure by Matlab.The experiment model pump for oil film characteristic of piston pair is designed to measure oil film thickness under the pressure of 18 MPa.The experiment results show that oil film thickness varies greatly under high pressure,and oil film thickness fluctuates sharply under low speed.The minimum oil film thickness increases with spindle speed increasing and oil film characteristic of piston pair based on the numerical analysis method is verified.This method lays a foundation for studying the friction performance of piston pair in the axial piston pump.
基金supported by Key Program of National Natural Science Foundation of China (52035002)National Natural Science Foundation of China (51805353).
文摘Bearings are key components in rotating machinery,which is widely used in many fields,such as CNC machines,wind turbines and induction machines.The increasingly harsh operation environment can lead to wear and tear on raceways and reduce the precision and reliability of bearing or even machinery.Lubrication could relieve the wear to some degree,which is benefit to prolong the bearing’s life.Thus,investigation on the vibration responses under the influence of oil film is of great significance.However,for mechanism analysis,how to include the oil film into the bearing dynamic model affects the result and efficiency of solution.To address this problem,this study proposed a fast algorithm through load distribution and interpolation when calculating oil film stiffness and thickness during the solution of bearing vibration model.Analysis of oil film on vibration is carried out and a bearing test rig is designed to verify the proposed model.Numerical simulation result shows that rotational speed and load have vital effect on oil film and vibration.The experimental result is consistent with the simulation,which shows that the proposed model has a better performance on modeling bearing vibration and the method of considering oil film is reasonable.
基金The Young Scientists Fund of the National Natural Science Foundation of China under contract No.41106153China Postdoctoral Science Foundation Funded Project under contract No.2012M521293
文摘In combination with a wave action balance equation,a damping model for sea waves covered by oil films of a finite thickness is proposed. The damping model is not only related to the physical parameters of the oil film,but also related to environment parameters. Meanwhile,the parametric analyses have been also conducted to understand the sensitivity of the damping model to these parameters. And numerical simulations demonstrate that a kinematic viscosity,a surface/interfacial elasticity,a thickness,and a fractional filling factor cause more significant effects on a damping ratio than the other physical parameters of the oil film. From the simulation it is also found that the influences induced by a wind speed and a wind direction are also remarkable. On the other hand,for a thick emulsified oil film,the damping effect on the radar signal induced by the reduction of an effective dielectric constant should also be taken into account. The simulated results are compared with the damping ratio evaluated by the 15 ENVISAT ASAR images acquired during the Gulf of Mexico oil spill accident.
文摘The technique of non stationary oil film force database for hydrodynamic bearing is introduced and its potential applications in nonlinear rotor dynamics are demonstrated. Through simulations of the locus of the shaft center aided by the database technique, nonlinear stability analysis can be performed and the natural frequency can be obtained as well. The easiness of "assembling" the individual bush forces from the database to form the bearing force, makes it very convenient to evaluate the stability of various types of journal bearings. Examples are demonstrated to show how the database technique makes it possible to get technically abundant simulation results at the expense of very short calculation time.
基金SponsoredbytheNationalNaturalScienceofFoundationofChina (No .19990 5 10 )andNaturalScienceFoundationofHeilongjiangprovince
文摘Oil film forces are usually obtained for dynamic analysis of a journal bearing system by using the approximate analytical formula or solving the Reynolds equation. None of them is suitable for rotor system bifurcation analysis because they are either of poor accuracy or time consuming. Oil film forces database is proposed is to transform the journal speed variation range in radial and circumferential directions from (-∞,+∞) to (-1, +1). The numerical results show the suggested method is much more effective. And sub harmonic, quasi periodic and chaotic vibrations are predicted for a range of speed and unbalance parameters.
基金Item Sponsored by National Natural Science Foundation of China (50575155)
文摘With the rapid development of the steel industry, to keep pace with the current trend of high speed, continuous, and large-scale production that focuses on automation and high levels of efficiency, many state-owned steel companies are being equipped with oil film bearings. Through long-term on-spot inspection and research on the fatigue failure of oil film bearing, three segments of annulated fatigue breakage were found axially along the inner surface of the bearing sleeve. In order to elucidate the reason for the three-segment annulated damage under rolling load, numerical boundary element method was adopted to analyze the contact behaviors between the sleeve and rollneck. Failure mechanism was discussed in detail, the distributions of contact stress were analyzed, and the service lives of the sleeve for different positions on the inner surface were quantitatively described, which provided an effective means to decrease wear and adhesive damage of the sleeve and to increase the load capacity of oil film bearing and its service life as well.
基金Funded by the Natural Science Foundation of China(50575155)Shanxi younger science foundation(20031041).
文摘To study the mechanism of burnt damage of oil film bearing in high-speed wire rolling mill,reasonable tempera- ture sensors are designed and calibrated,pressure block of rolling mill has been transformed into pressure sensors.Online tempera- ture and load of oil film bearing in a domestic precision rolling F15 have been tested.Consequently,a large sum of valuable test data was obtained.The distributions rules of pressure and temperature under continuous online rolling state are recorded in detail. Theoretical and experimental results are beneficial to damage mechanism of oil film bearing,thus its service life could be pro- longed.Moreover,such results could provide an important reference for online test and control.
文摘The effectiveness of variable parameter squeeze oil film damper (VPSFD) in the steady and transient unbalance response control of flexible rotors is examined.First, a preliminary property design of VPSFD is presented on the improved finite length bearing theory.VPSFD is different from the conventional squeeze film damper, and is designed to possess continuous changeable oil film clearance and land length. These parameters can be exactly adjusted on a computer by sending commends to a special control device. Then, a simple rotor system with VPSFD is investigated. The experimental results show that VPSFD can attenuate the rotor system resonance peak due to unbalance.
基金The Project is supported by the doctoral foundation of the National Education Committee of China
文摘Through optimizing the eletric parameters of the resistance-capacitance (R-C)oscillation,a measuring instrument is developed for measurement of EHL oil filmthickness.Actual measurement was made with space bearings and actual measurements arein good agreement with theoretical calculations.
文摘In order to analyze the stress and deformation of different permeability of residual oil film in the complex pore, which are affected by the viscous-elasticity of the fluid, the hydrodynamic displacement mechanism is explored from the stand-point of hydrodynamics, that is, the residual oil film displaced by alternating injection of different concentrations of the polymer solution, viscous-elastic fluid flow equation is established in the complex pore by choosing continuity equation, motion equation and the upper convected Maxwell constitutive equation. The flow field is computed by using the method of numerical analysis. Not only the stress and deformation of residual oil film on the different permeability of micro pores, but also the analysis of the flooding mechanism of alternating injection of different concentrations of the polymer solution is got. The results show that the larger the viscous-elasticity of polymer solution is, the bigger the normal deviatoric stress acting on the residual oil film is;the distribution of normal deviatoric stress has the abrupt change. The stronger the viscous-elasticity of the polymer solution is, the bigger the horizontal stress difference acting on the residual oil film is and the more obvious the deformation is;the high-concentration polymer solution is suitable for high-permeability micro pores. Low-concentration polymer solution is suitable for medium and low-permeability micro pores. Alternating injection of polymer solution can improve Volumetric Sweep Efficiency and increase the deformation of residual oil film, which is conducive to enhancing oil recovery.
基金supported by the Natural Science Foundation of China under Grant No.51275411
文摘Bearing chamber is one of important components that support aero-engine rotors and research on oil droplet and oil film motions is an important part of bearing chamber lubrication and heat transfer design. Considering the pressure of sealing air is an important operating condition that affects the oil droplet and oil film motions,the effect of sealing air pressure on airflow in bearing chamber is investigated in this paper firstly; and then based on the air velocity and air / wall shear force,the oil droplet moving in core air,deposition of oil droplet impact on wall as well as velocity and thickness of oil film are analyzed secondly; the effect of sealing air pressure on oil droplet velocity and trajectory,deposition mass and momentum,as well as oil film velocity and thickness is discussed. The work presented in this paper is conducive to expose the oil / air two phase lubrication mechanism and has certain reference value to guide design of secondary air / oil system.
基金This work was supported by the Fundamental Research Funds for the Central Universities(31020195C001,3102019QD0413,3102019ZD0403)The suggestions from Q.Jane Wang at Northwestern University are appreciated.Hongxing Wu also acknowledges the scholarship support from the China Scholarship Council(CSC,No.201606280181).
文摘The lubrication effectiveness of MoS_(2) nanoparticles as an oil additive remains unclear,restricting its application in industry to reduce friction.The goal of this work was to explore the lubrication mechanism of MoS_(2) nanoparticles as an oil additive.In this study,the oil film thickness behaviors of MoS_(2) nanoparticles in poly-alpha olefin(PAO4)base oil,PAO4 with 3 wt%dispersant(polyisobutyleneamine succinimide,PIBS),and 0W20 engine oil were investigated using an elastohydrodynamic lubrication(EHL)testing machine.Following the EHL tests,the flow patterns around the contact area and the tribofilm covering rate on contact area were studied using optical microscopy to understand the lubrication mechanism.The results indicate that both the dispersant and nanoparticle aggregation significantly affected the oil film thickness.The expected oil film thickness increase in the case of 0.1 wt%MoS_(2) in PAO4 base oil was obtained,with an increase from 30 to 60 nm over 15 min at a velocity of 50 mm/s.Flow pattern analysis revealed the formation of particle aggregation on the rolling path when lubricated with 0.1 wt%MoS_(2),which is associated with a tribofilm coverage rate of 41.5%on the contact area.However,an oil film thickness increase and particle aggregation were not observed during the tests with 0.1 wt%MoS_(2) blended with 3 wt%PIBS as the dispersant in PAO4 base oil,and for 0.75 wt%MoS_(2) in 0W20 engine oil.The results suggest that nanoparticles responsible for tribofilm formation originated from aggregates,but not the well-dispersed nanoparticles in point contact.This understanding should aid the advancement of novel lubricant additive design.
基金support from Ford motor company,under Ford University Project 2014-2175R.
文摘In this paper,the oscillatory oil squeeze film is taken as a research object,and a coupled cavitation model based on the theory of bubble dynamics and hydrodynamic lubrication is used and a specific method of numerical calculation is given.Then the parallel-plate squeeze film test apparatus is used to validate the coupled cavitation model.The pictures of the cavitation were captured by a high-speed camera and then processed to obtain the variation of the cavitation area in experiments.Compared with the experimental results,the model can successfully predict the process of generation and development of cavitation.At the same time,the pressure variation calculated by the model is in good agreement with the experimental data and the value of negative pressure is close to the experiment.On this basis,three new parameters that are related to bubble dynamics are studied by comparing the pressure and cavitation area variation in an oscillating squeeze oil film.The results show that surface dilatational viscosity,initial radii of cavitation nuclei and number of bubbles per unit area have a significant influence on the generation time of the cavitation,the maximum tensile stress that the oil film can withstand,and the speed of the cavitation collapse respectively.
基金National Natural Science Foundation of China (50975233)
文摘The lubrication design and heat transfer determination of bearing chambers in aeroengine require a sufficient understanding of the oil droplet-film interaction and physical characteristic in an oil/air two-phase flow state.The analyses of oil droplet movement,mass and momentum transfer during the impingement of droplet/wall,as well as wall oil film thickness and flow velocity are very important for the bearing chamber lubrication and heat transfer calculation.An integrated model in combination with droplet movement,droplet/wall impact and film flow analysis is put forward initially based on the consideration of droplet size distribution.The model makes a contribution to provide more practical and feasible technical approach,which is not only for the study of droplet-film interaction and physical behavior in bearing chambers with oil/air two-phase flow phenomena,but also useful for an insight into the essence of physical course through droplet movement and deposition,film formation and flow.The influences of chamber geometries and operating conditions on droplet deposition mass and momentum transfer,and wall film thickness and velocity distribution are discussed.The feasibility of the method by theoretical analysis is also verified by the existing experimental data.The current work is conducive to expose the physical behavior of wall oil film configuration and flow in bearing chamber,and also significant for bearing chamber lubrication and heat transfer study under oil/air two-phase flow conditions.
基金Supported by the Natural Science Foundation of China (50575155) The authors would like to thank for the support of National Natural Science Foundation (50575155)
文摘Oil film bearing,which works on thin film between sleeve and bush,is widely used in steel industry due to the characteristics of high efficiency and low noise,etc. The backup roll of 1 580PC hot strip mill invested by some steel corporation has been equipped with such bearing. During the process of setup&disassembly and usage period,the sleeve has been dramatically damaged,which results in production accidents and decreases its service life,thus heavily influencing steel production. Aimed at such puzzles,under specific loadcase,mechanical properties of bearing sleeve,as well as estimation of contact status and adhesive force of sleeve by interference fit,are quantitatively simulated by finite element method,which establishes an mechanical foundation for improving the load capacity of bearing and decreasing its wear and adhesion damages. Finally,some measures and conclusions are drawn.
