Volume 49,2024 Issue 9

• Molecular Dynamics Study on Boundary Lubrication Properties of N-octane with Nano ZnO
  HOU Xianjun; AN Heng; JIANG Hua
  Abstract:In order to study the mechanism of improving the boundary lubrication performance n-octane by nano ZnO,by considering boundary roughness,a molecular dynamics boundary lubrication model with convex peaks was established.The density distribution and radial distribution function of base liquid and ZnO nano-fluid under a loading condition of 25 MPa to 400 MPa,and the friction characteristics of the base liquid and ZnO nano-fluid under different positive pressures were analyzed.The results show that the density layers occur in both base liquid and nano-fluid under different positive pressures,the greater the positive pressure,the more obvious the layering.The addition of nano ZnO will change the structure of the base liquid and enhance its bearing capacity.Nano-fluids can reduce the stress and strain of friction surface and reduce the degree of lattice distortion during shearing.The friction coefficient of the interface model of the nano-fluid with a mass fraction of 1.636% ZnO is 0.078 1,which is reduced by 47.4% compared with the interface model of base liquid interface,indicating that nano ZnO has a significant friction reducing effect on the n-octane boundary lubrication interface.

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• Modelling of Stiffness and Damping of EHL Friction Pair in Line Contact
  XIA Boqian; WANG Shuangmeng; ZHANG Zebin
  Abstract:Elastohydrodynamic lubricating (EHL) oil film has remarkable elasticity and damping effect,which has great impact on the dynamic performance of high pair contact parts such as gear,rolling bearing,cam etc.However,the mechanism,especially the mathematical formulation on the stiffness and damping of EHL friction pairs remains unclear.A numerical method was used to solve the tribology and dynamics coupling model of line contact EHL friction pair,and the hysteresis loop of the EHL friction pair under harmonic excitation was obtained.Through the hysteresis loop,the stiffness and damping of line contact EHL friction pair were identified.The effects of load,entrainment speed,material parameters on the stiffness and damping of line contact EHL friction pair were studied by means of variable control,and the influence mechanism of load and entrainment speed on the stiffness and damping of EHL friction pairs was analyzed.The results show that the stiffness and damping of the line contact EHL friction pair increase with the increase of load and decrease with the increase of entrainment speed.The stiffness and damping formulas of line contact EHF friction pair were fitted based on a large number of numerical solutions.It is found that the load has the most significant impact on the stiffness and damping of the EHL friction pair,and the change amplitude of the stiffness of EHL friction pair is greater than that of the damping with changes in load,speed,and material parameters.The accuracy test of the fitting formula shows that the relative error between the calculated results of the fitting formula and the numerical solutions is less than 10% in a wide range of parameters.

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• Study on the Relationship Between Friction Characteristics of Textured Surface and 3D Topography Parameters
  LI Zhi; DU Yiyuan; XU Zhiming; QIAO Xuqian; LIU Kun
  Abstract:In order to study the effect of surface texture on the friction characteristics of oil-lubricated interface,the relationship between the friction characteristics of textured surfaces and the change trend of three-dimensional morphology parameters was established.Based on Navier-Stokes equation and cavitation model,Fluent was used to simulate smooth surface model and three textured surface models with different area occupancy,and the influence of textured surface morphology on pressure distribution and flow field distribution under different entrainment speeds was studied.According to ISO25178,the 3D topography parameters of textured surfaces were calculated,and the change trend of the 3D topography parameters and friction and lubrication characteristics of different textured surfaces was analyzed.The results show that under the high speed condition,the effect of texture on the maximum oil film pressure is obvious.The existence of texture disturbs the flow of oil,and with the increase of texture area occupancy,the synergy between unit textures becomes more obvious.In order to display the texture advantage more efficiently,the texture surfaces with 3D topography parameters such as smaller absolute value of absolute skewness Ssk and kurtosis Sku,larger valley void volume Vvv and smaller loading area ratio Smr can be selected to achieve ideal friction characteristics.

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• Research on the Performance of W-shaped Seal Structure Based on Metal Packer
  FENG Ding; ZHANG Yiduo; ZHAN Hongyun; HOU Lingxia; ZHANG Hong; ZENG Yinghui
  Abstract:In view of the shortcomings that the rubber packer is difficult to adapt to the working conditions above 150 ℃ and 70 MPa,a metal packer with W-shaped sealing structure was designed,which was suitable for the working conditions of 230 ℃ and 70 MPa,with load transmission at both ends and a hollow in the middle to promote radial deformation,and its sealing performance was studied.According to the requirements of working conditions,β-NiTi alloy was selected as the W-shaped sealing structural material based on the temperature-dependent and superelastic transformation stress,the sealing performance of the W-shaped structure was evaluated by the contact stress generated after setting,and the unsetting performance was evaluated by the elastic-superelastic strain rate of the W-shaped structure under working pressure.The effects of the size radius,wall thickness and wall thickness ratio of the W-shaped sealing structure on its sealing performance were analyzed.The results show that the size radius has little effect on the sealing performance and unsetting performance of the W-shaped sealing structure,while the wall thickness and wall thickness ratio significantly affects the sealing and unsetting performance.With the increase of wall thickness,the sealing performance of the W-shaped sealing structure gradually decreases,but the unsetting performance gradually increases.With the increase of the wall thickness ratio,the sealing performance gradually decreases,and the unsetting performance first increases and then decreases.The sealing performance of the optimized W-shaped structure was simulated and analyzed.It is found that the W-shaped sealing structure metal packer with β-NiTi alloy material can be fully applied to the high temperature and high pressure environment.Under the working conditions of 230 ℃ and 70 MPa,the load required for the structural setting is 220 kN,and the elastic-superelastic strain rate is more than 90%.

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• Research on the Influence of Impurity Particle on Lubrication Characteristics of Needle Roller Bearings
  SONG Qi; WANG Youqiang; ZHU Junjie; MA Jinyue; XU Ying
  Abstract:In order to investigate the influence of impurity particles mixed in oil on the lubrication performance of needle roller bearings,a line contact lubrication model considering individual impurity particles was established based on the lubrication model of line contact needle roller bearings.The multi grid method was used to calculate the oil film pressure,the multi grid integration method was used to calculate the elastic deformation of the oil film,and the column by column scanning method was used to calculate the oil film temperature.The oil film pressure,film thickness,flow velocity,and temperature changes of particles flowing in the contact area under different entrainment speeds,loads,and particle sizes were obtained.The results indicate that the presence of solid particles can cause an increase in oil film pressure and temperature near this location,a decrease in film thickness,and fluctuations in fluid flow rate.A decrease in the suction speed,an increase in load,and an increase in the size of impurity particles will significantly increase the pressure and temperature at the location of the particles in the contact area,leading to adverse working conditions and causing adhesion or pitting between the roller needle and the raceway at that location.

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• Molecular Dynamics Simulation of Mechanical and Tribological Properties of Molybdenum Disulfide/Nitrile Butadiene Rubber under High-temperature Swelling
  QIAN Cheng; ZHAO Jing; LI Yunlong; LIU Zhongqiang; WANG Shijie
  Abstract:To investigate the effect of molybdenum disulfide (MoS2) on the mechanical and tribological properties of nitrile butadiene rubber (NBR) composites under high-temperature cyclohexane (C6H12) swelling,Monte Carlo method and Forcite module were used to establish models for Pure NBR,swollen NBR,NBR/MoS2,and swollen NBR/MoS2,respectively.The effect of MoS2 on the high-temperature swelling,mechanical and tribological properties of NBR was studied,and the mechanism of MoS2 improving the high-temperature swelling of NBR was explored.The results show that the C6H12 swelling leads to the decrease of mechanical properties of NBR,but after adding MoS2,the mechanical properties of the composite material are improved.The molecular chain migration and movement rate inside NBR are accelerated by C6H12 swelling,but the addition of MoS2 effectively inhibits the C6H12 swelling.The C6H12 swelling can increase the surface molecular chains of NBR composite materials,leading to the decrease of tribological properties of NBR.However,the addition of MoS2 improves the tribological properties of the composite materials.Due to the larger specific surface area of MoS2 and the stronger van der Waals forces and electrostatic force adsorption,the addition of MoS2 can improve the mechanical and tribological properties of the NBR composites under high-temperature C6H12 swelling.

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• CFD Numerical Simulation of the Performance of Floating Ring Seals with Variable Inclination Groove
  YANG Xiqing; WANG Yufei; MA Gaofeng
  Abstract:In order to further improve the sealing performance of floating ring gas film seal,the floating ring seals with variable inclination groove were proposed.Three kinds of groove structures,the divergent groove with unfixed depth,the groove with fixed depth and the convergent groove with unfixed depth were selected as the research objects.FLUENT software was used to numerically simulate the dynamic pressure of the gas film model,and the influence of different working parameters on the sealing performance of the floating ring gas film in the micro-scale clearance was compared and analyzed.The results show that the introduction of medium gas into the micro-groove results in a pronounced localized high-pressure zone at the minimum clearance and at the base of the spiral groove.Among the three groove structures,the convergent groove with unfixed depth has the best sealing performance,the maximum opening force,and a more prominent leakage control.The opening force and leakage of the three types of groove structures increase with the increase of the rotational speed,pressure and eccentricity.

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• Molecular Dynamics Simulation of Friction Behavior of Nano-ZrO2 Reinforced PEEK/PTFE Composites
  DANG Yapeng; TANG Henan; WANG Minghui; LIU Lin
  Abstract:In order to explore and reveal the effect of nanometre zirconium dioxide (ZrO2) on the friction behavior of polyetheretherketone (PEEK)/polytetrafluoroethylene (PTFE) composites from the microstructure,four kinds of nano-ZrO2 filled PEEK/PTFE composites were prepared by adding mass fraction 4%,6%,8%,and 10% nano-ZrO2 to 10% PEEK/PTFE composite materials,respectively.Based on the molecular dynamics (MD) method,the friction models of PEEK/PTFE composites with different mass fractions of nano-ZrO2 sliding against iron were constructed.The results show that an appropriate amount of nano-ZrO2 can enhance the shear deformation resistance of PEEK/PTFE composite molecular chains,form strong van der Waals force between polymer molecular chains,and improve the friction properties of PEEK/PTFE composites.Nano-ZrO2 can effectively inhibit interlayer slip during friction,play a role in adsorbing polymer molecular chains in composites,so as to enhance interatomic interactions,and hinder internal slip of molecular chains during friction.The composites with mass fraction 6% nano-ZrO2 show the best friction performance.

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• Study of Magnetron Polishing Performance of Magnetorheological Elastic Polishing Pads for Single-Crystal SiC
  LI Huilong; LU Jiabin; HU Da; LUO Ziyuan
  Abstract:Intelligent controllable material magnetorheological elastomers (MRE) were used as polishing pads in chemical-mechanical polishing.The magnetron polishing effect of MRE polishing pads with different magnetron parameters(particle type,particle mass fraction,particle size,and solidified magnetic field strength) on single-crystal SiC was investigated,and the magnetron material removal mechanism of MRE polishing pads was analyzed.The results show that compared to Fe3O.4 magnetic particles,MRE polishing pad prepared with carbonyl iron powder (CIP) magnetic particles shows a 52.2% increase in material removal rate (MRR) during SiC polishing.The larger the CIP mass fraction,the larger the MRR of polishing,the smaller the surface roughness,and the better the surface quality of polishing due to a larger material modulus and more CIP particles in contact when the CIP mass fraction is higher.The difference in magnetron polishing effect of MRE polishing pads with different magnetic particle grain sizes is not significant.The grain size influences the removal effect of the polishing process through the size of the particles and the contact probability,which is related to the contact state of the surface.Compared to isotropic MREs,anisotropic MRE prepared by applying curing magnetic field can obtain better magnetron polishing effect.The MRE polishing pad prepared at a curing magnetic field of 140 mT has the best polishing effect,which can increase the MRR of SiC by 31.0% and reduce surface roughness by 50.0% under a polishing magnetic field of 335 mT compared to non magnetic field polishing.The material removal mechanism of magnetic control polishing by MRE polishing pad is that the applied magnetic field increases the mechanical properties of the MRE polishing pad,and the abrasive has a greater cutting force and positive pressure on the SiC surface,thereby achieving greater material removal.

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• Research on the Performance of Magnetic Fluid Sealing Structure for Large Geocentrifuge
  MIN Ziqiang; ZHU Weibing; YAN Zhaoqiang; WANG Heshun
  Abstract:Due to the large spindle diameter and high linear speed,the existing magnetic fluid sealing structure is difficult to meet the requirements of installation and heating of large-scale geotechnical centrifuges.A new type of split magnetic fluid sealing device was designed,and the finite element numerical analysis method was used to study the influence of the split structure deformation,the structural parameters of the pole shoe assembly on the sealing performance and the temperature distribution of the sealing device.Considering the actual processing capacity,orthogonal experiments were used to optimize the structural parameters.The results show that the degree of influence of structural parameters on sealing performance is as follows,the sealing clearance,the permanent magnet height,the permanent magnet width,the slot width,the tooth width,and the tooth height.The parameters of the optimized sealing device are sealing gap 0.5 mm,tooth width 2 mm,tooth height 2 mm,slot width 2.8 mm,permanent magnet width 11 mm,and permanent magnet height 22 mm.The optimized sealing pressure value is 0.97 MPa,which is higher than the pressure value of 0.54 MPa before optimization,and higher than the pressure value of 0.1 MPa required by the operating conditions.During the operation of the large diameter magnetic fluid seal,there is a problem of heat accumulation in the shaft sleeve,and a cooling chamber needs to be set up in the shaft sleeve area.

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• The Investigation on Fretting Wear Performance of UHMWPE Reinforced with MoS2/CF
  XIN Xiaocui; SU Yujie; LIU Hao; QI Zhentao
  Abstract:A series of ultra high molecular weight polyethylene(UHMWPE) composites with different relative contents of carbon fiber(CF) and MoS2 were prepared by hot pressing sintering method.The distribution of fillers in the matrix was studied,and the effects of CF and MoS2 on the thermal properties of UHMWPE composites were investigated.The effects of CF and MoS2 on the fretting wear properties of UHMWPE composites were studied by SRV-IV fretting wear testing,and wear mechanism of the composites was explored.The effects of dry friction and deionized water lubrication on the frictional properties of the composites were investigated.The results show that the addition of CF is conducive to the improvement of the thermal properties of composites.Compared with single CF modification,the simultaneous modification of UHMWPE with appropriate amount of CF and MoS2 is more conducive to improving the tribological properties of composites.The UHMWPE composite reinforced with mass fraction of 10% CF and 10% MoS2 can form a uniform and compact transfer film on the friction surface during the friction process,and MoS2 is uniformly distributed in the transfer film,which makes the composite presents the best friction and wear properties.The composite shows a lower friction coefficient in the water-lubricated medium,and the friction coefficient increases with the increase of load.

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• Study on the Effect of Nano-CaCO3 Particles on the Performance of Lubricating Greases
  WANG Yu; ZHANG Bin; ZHANG Xiangjun; HU Zhihong; WANG Zhe
  Abstract:Two lubricating greases were prepared by adding nano calcium carbonate and a certain amount of base oil to lithium based grease.One of them only added base oil,while the other added both base oil and nano calcium carbonate simultaneously.The physical and chemical properties of the two lubricating greases,including dispersibility,drop point,cone penetration,oxidation induction period,and apparent viscosity,were tested.Friction tests were also conducted to observe and study the tribological properties of the two lubricating greases,and the effect of the addition of nano calcium carbonate on the performance of the lubricating grease was explored.The results show that the distribution size of nano calcium carbonate in soap base is basically less than 1 μm,and the majority of particle sizes are between 150 nm to 300 nm.After adding base oil and nano calcium carbonate additives to lithium based grease,the droplet point and cone penetration of the grease have little change,while the oxidation performance decreases.The thixotropy of the two lubricating grease is basically the same as that of the base grease.The addition of nano calcium carbonate does not damage the strength of the lubricating grease network structure and does not change the stability of the lubricating grease.At a load of 200 N and a temperature of 50 ℃,the nano calcium carbonate lubricating grease can exhibit good anti-wear performance only after a certain period of running in.However,when the temperature is 100 ℃,the addition of nano CaCO3 may cause an increase in friction pair wear.

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• Development and Performance Test of a Fast Measuring Device for Oil Supply Rate of Shafting Core Valve for Space Use
  DOU Zhaoliang; LIU Wanning; DU Yue; ZHOU Gang; ZHANG Shaohua; CHEN Wenbin; SI Lina; YANG Ye; YAN Hongjuan; LIU Fengbin
  Abstract:Passive micro oil supply is one of the main forms of achieving micro lubrication in space shafting,and the appropriate supply of lubricating oil is a key link to ensure the stable operation of space shafting.In response to the problems of long time consumption and high cost in traditional running-in screening technology for porous material core valves used in space shafting,an equivalent method was proposed to quickly detect the oil supply rate of core valves with air instead of aerospace lubricating oil as the fluid medium.A core valve gas permeability detection device was developed on the basis of underwater bubble method and LabVIEW image recognition technology.The results of testing the detection performance of the device show that the gas permeability detection time for the porous material core valve is less than 5 minutes,the detection error is less than 0.5%,and the prediction error of the oil supply rate is less than 6.0%.

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• Optimization Simulation Analysis and Experimental Research of Hydraulic Rubber Seal Ring
  WANG Yanan; GUO Fei; XIANG Chong; HOU Pingan; CHEN Wei; WEI Li; SUO Junying
  Abstract:The optimization research on the rotating dynamic seal O-ring in the hydraulic transmission system was conducted,and the final optimization results through simulation analysis and experiments were obtained.The O-ring model based on ABAQUS was established,and two kinds of nitrile rubber materials with the same hardness level and different mechanical properties were compared and analyzed.The contact stress and initial sealing performance of O-rings with different materials under medium load were studied.The test was employed to optimize the size of the O-ring.The results show that the size has little effect on the static hydraulic sealing performance,low-temperature sealing performance and high-temperature sealing performance of the O-ring,but has a greater impact on the dynamic sealing wear performance of the O-ring.The cross-sectional diameter is controlled within the lower limit of the design tolerance,the O-ring made of NBR material with good mechanical properties shows the best sealing performance.The research results obtained by combining simulation analysis and verification test provide technical support for the design and application of high-performing O-rings.

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• Health Status Assessment of Cylinder Liner-piston System Based on CPA-FM-MEM Wear Debris Analysis
  DING Letian; CAO Wei; WU Jiajun; YAN Yang; WU Jianfeng; SU Rui; SUN Jing
  Abstract:Taking the typical friction pair cylinder liner-piston system of internal combustion engine as the research object,the condition monitoring test bench of cylinder liner-piston system of internal combustion engine was designed and built.Aiming at the shortcomings of the traditional maximum entropy method in analyzing the monitoring data of wear debris in oil,an improved fractional moment maximum entropy method (FM-MEM) was proposed,and the key parameters were optimized by combining the carnivorous plant algorithm (CPA).The threshold division of the monitoring data of wear debris in oil was carried out to evaluate the health status of the internal combustion engine.Combining theory with experiments,with online wear debris monitoring as the main focus,the running state of the cylinder liner-piston system of the internal combustion engine was monitored from three aspects,wear debris in oil,physical and chemical indexes,and surface morphology.The wear health status and the change trend of wear debris concentration in each time period of the cylinder liner-piston system under low speed condition were analyzed.Through the on-line wear debris monitoring test of the internal combustion engine,it is proved that this method can realize the on-line real-time condition monitoring of the cylinder liner-piston system of the internal combustion engine.

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• Design and Experimental Research of Sealing Structure of Large Diameter High Temperature and High Pressure Sleeve Control Valve
  YU Ruiming; MA Yunyan; ZHANG Yujin; XU Weiming
  Abstract:To improve the sealing grade of the large diameter high temperature and high pressure sleeve control valve,a new type of large diameter high temperature and high pressure sleeve control valve with new sealing structure was designed.The valve sealing structure is divided into upper and lower parts.The upper part adjusts the sealing position through the spring pre-tightening force and automatically adjusts the sealing coincidence.The lower part is sealed by the spool and the lower seat.The upper and lower parts are structurally coordinated to seal at the same time.The simulation analysis of static strength shows that the maximum stresses of the control valve is 204.1 MPa,the local stress of pressure plate,spring and the upper valve seat structure is 40.26 MPa.Both of which are less than the yield strength of the material,and the static strength meets the requirements.The simulation analysis of fatigue strength shows that the fatigue strength of the control valve meets the requirements in the life time.The fluid flow simulation analysis shows that under the small opening 30% working condition,the maximum fluid velocity in the valve cavity is 554.240 m/s,the maximum pressure is 1.706 MPa,and the maximum temperature is 252.50 ℃.Under the large opening 80% working condition,the maximum fluid velocity of the valve cavity is 501.736 m/s,the maximum pressure is 1.717 MPa,and the maximum temperature is 259.99 ℃.The results are consistent with the fluid flow characteristics.The pressure test of the valve body and the high pressure sealing test of the valve seat show that there is no visible leakage or deformation in the valve body.The leakage grade of the high pressure sealing of the valve seat is VI,which meets the requirements for the pressure strength of the valve body and the sealing performance of the valve seat.

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• Influence Analysis of Piston Pump Inlet Size on Grease Flow
  AILIXIATI Yilihamu; HUANG Heng; XIE Xiaopeng; ZHANG Wenliang; YI Shibao
  Abstract:In order to have a theoretical design basis for the size design of inlet section of plunger pump,the flow rate and resistance along the path of grease under different size conditions of pipeline were calculated.According to the theory of rheology and fluid mechanics,flow state of grease in pipeline was analyzed,the flow equation of grease in inlet section was derived,and critical conditions of laminar flow of grease pipeline were determined.The results show that for the studied plunger pump,the flow rate decreases sharply when the length of the inlet section increases from 0 to 15 mm,and the flow rate is relatively stable when the length is greater than 15 mm.The flow rate shows a gradual increase when the radius increases from 0 to 30 mm,and sharply increases when the radius exceeds 30 mm.The results of finite element simulation are consistent with those of numerical analysis,and have similar variation rules,which proves the accuracy of pipeline flow equation.Therefore,the derived flow equation of grease in pipeline is applicable to the engineering design of lubrication pumps.

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• Influence of Tungsten Content on the Tribological Performance of Ni-W Alloy Coatings
  GAO Qiang; BAI Xiao; MOU Yi; ZHANG Dejian; WAN Yong
  Abstract:To investigate the effect of W content on the tribological properties of Ni-W alloy coatings,Ni-W alloy coatings were prepared on the surface of 45 steel substrate using pulse electro-deposition technique.The influence of tungsten content on the microstructure,mechanical,and tribological properties of the Ni-W alloy coatings was investigated.The results show that the grain size of the Ni-W alloy coatings is uniform and dense,and the bond between the coating and the substrate is tight.Compared with the 45 steel substrate,the Ni-W alloy coatings have higher hardness,and the hardness increases with the increase of tungsten content.The wear behavior of the 45 steel substrate is mainly abrasive wear,while the Ni-W coating is mainly adhesive wear and abrasive wear,and with the increase of W content,the wear resistance of the coatings gradually improves.Under dry friction and PAO6 oil lubrication conditions,Ni-W alloy coating can significantly reduce the wear of the material,especially under oil lubrication conditions,there is almost no wear on the coating surface.Therefore,the pulse electro-deposited Ni-W alloy coatings demonstrate excellent tribological performance,and the mechanical and tribological properties can be effectively improved by adjusting the tungsten content in the coatings.

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• Study on the Variation Law of Oil Groove Leakage in Multi-groove Sliding Bearings
  DONG Duo; LI Chao; ZHU Jibin; LIU Quan; ZHANG Jinfang
  Abstract:The excessive oil leakage in the oil groove of multi-groove sliding bearings may lead to low lubrication system pressure.To optimize the structural design of multi-groove sliding bearings,the influence of working conditions and oil groove structural design changes on the oil groove leakage was analyzed.STAR-CCM+ software was used for transient CFD calculation,and by adjusting the speed of the sliding bearing,the oil supply pressure,the number of oil grooves and galleries,and the depth of the axial oil groove,the variation law of oil groove leakage was studied.The results show that the rotating speed of the sliding bearing has little effect on the average oil groove leakage.The average oil groove leakage decreases with the decrease of oil supply pressure,and the decreasing rate gradually accelerates.Reducing the number of oil grooves or galleries can both reduce the average oil groove leakage,and the former has a large impact and the latter has a small impact.As the axial groove depth decreases,the average oil groove leakage decreases approximately linearly at first,and then slows down gradually after reaching a certain depth value.It is a better design scheme to retain only one axial oil groove and reducing its depth to 0.4 mm.The research results provide reference for the low oil leakage design of multi-groove sliding bearing.

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• Nonlinear Regression Analysis of Erosion Rate of Spatial Pipeline Based on Orthogonal Design
  WU Zebing; HE Xiaolin; HU Shiyao; JIANG Wen; SHEN Fei
  Abstract:In response to the serious erosion and wear damage caused by solid particles carried in fracturing fluid to pipelines and the failure of pipe fittings,ANSYS Fluent software was used to numerically simulate the erosion and wear of pipelines under different fluid and structural parameters,and the optimal nonlinear curve fitting equation for inlet flow rate,particle diameter,mass flow rate,viscosity,and the maximum erosion rate of spatial pipelines with the elbow diameter was obtained.It is found that the relationship between the flow velocity,particle diameter and viscosity is a quadratic function with the maximum erosion rate,respectively.The relationship between the mass flow rate and the diameter of the elbow is powered functions with the maximum erosion rate,respectively.The comprehensive influence of various parameters on the maximum erosion rate was studied by orthogonal test,and SPASS software was used to perform multiple nonlinear regression analysis on the fitting equation,a predictive model for erosion wear was obtained.The results indicate that the obtained nonlinear regression equation has a high degree of fitting and can well reflect the influence of various factors on the maximum erosion rate of spatial pipelines.

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• Research on Key Reliability Design Factors of Rotary Shaft Lip Seal Based on Likelihood Function Screening Method
  ZHANG Fuying; HAN Zhao; YANG Pengwei; WU Jihao
  Abstract:Based on the finite element and numerical calculation models of oil seals,the influence of design parameters of oil seals on the static and dynamic sealing reliability was analyzed.Standardized data of 8 design parameters,including initial installation interference,oil side lip angle,air side lip angle,waist thickness,waist length,theoretical contact width,elastic modulus of clamping spring,and hardness of the main rubber of the oil seal,were used as input vectors,and standardized data of maximum contact pressure,pump suction rate,and friction torque of the oil seal lip were used as output vectors to establish a response surface model.The likelihood function value of each design factor obtained from the variance of output vector was used as the evaluation index to determine the influence of each design parameter on the reliability of oil seal.The results show that rubber hardness,theoretical contact width,spring elastic modulus,interference amount,and waist length have a significant impact on the reliability of oil seal dynamic sealing.The maximum contact pressure of the oil seal lip is more sensitive to spring elastic modulus,theoretical contact width,rubber hardness,waist thickness,and oil side lip angle.Taking into account the static and dynamic reliability of the rotating shaft lip shaped oil seal,the key design factors affecting its reliability are the theoretical contact width,spring elastic modulus,and rubber hardness.

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• Dynamic Mesh Technology Analysis of Labyrinth Seal Leakage Rate of Layered Oil Pump
  XIAO Yang; LIU Xuhui; GAO Cheng; MEI Yixuan
  Abstract:As a common equipment in the middle and late stages of oilfield exploitation,the seal between the plunger and the pump barrel of the layered oil production pump often adopts a labyrinth seal.Due to the high temperature and high pressure working environment underground,the leakage of seal gap has become the main problem affecting pump efficiency.In order to explore the influence of differential pressure flow and shear flow on seal leakage rate,the simulation experiment of seal clearance flow field was carried out based on computational fluid dynamics and Fluent dynamic mesh technology.The method of grid elastic smoothing and grid reconstruction in dynamic grid was used to avoid grid distortion caused by moving wall surface,and the characteristics of clearance flow field were further revealed.The results show that the shear flow caused by the moving wall is more obvious in the transient simulation.The increase of the shear flow velocity makes the boundary layer thickness thinner,which affects the leakage rate.The gap width,the pressure difference at both ends and the relative plunger velocity have a positive correlation with the leakage rate.The leakage rate is mainly affected by the gap width and the pressure difference flow,and is less affected by the shear flow.

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• Analysis on Lubrication Performance and Reliability of Sliding Bearing of Wind Power Gearbox
  WANG Zhou; WU Miaojie; TAO Yourui
  Abstract:The use of sliding bearings instead of rolling bearings in wind power gearboxes is the mainstream trend in future development.However,due to the complex and variable service conditions,the lubrication law of wind turbine sliding bearings is still needs further research.The lubrication analysis model of sliding bearings of wind power gearboxes was established,the lubrication state of sliding bearings under various working conditions was simulated and analyzed,and the empirical formula of the minimum film thickness of the sliding bearings was fitted.Combined with the lubrication reliability theory,the lubrication reliability model was established based on the minimum film thickness formula,and this model was used to study the lubrication performance of gearbox sliding bearings of fans under starting and stopping conditions of the fan.A lubrication reliability analysis method for sliding bearings of wind power gearbox was proposed,and the lubrication reliability of the gearbox sliding bearing was analyzed.The results show that the minimum film thickness of the bearing during the startup process increases rapidly at first,and then decreases rapidly until it is stable,while the minimum film thickness decreases rapidly during shutdown.The lubrication failure time of sliding bearing in shutdown condition is longer than that in start-up condition.The direction of external load has a significant impact on the probability of lubrication failure during start-up conditions,but has a relatively small impact on shutdown conditions.

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• Research Progress in Application of Variational Mode Decomposition Method in Bearing Fault Diagnosis
  LU Zhijie; WANG Zhiliang; YAN Xiaoan; LIU Deli; SUN Jianjun; MA Chenbo
  Abstract:As the core and fault prone part of rotating machinery,rolling bearing and its fault diagnosis are the focus and frontier of current research.The effective feature extraction method is very important for the fault diagnosis of rolling bearing,and the variational mode decomposition algorithm (VMD) has a good application potential because of its strong analysis ability and adaptability to complex signals.The basic principle and advantages of VMD,the application of VMD in bearing fault feature extraction,VMD parameter optimization methods and the latest progress were summarized.A new solution to the VMD parameter optimization problem was proposed from the aspects of fitness function construction and group intelligence algorithm improvement.The shortcomings of VMD in diagnosing early weak fault and compound fault of rolling bearing were discussed.The future development direction of VMD was prospected from the perspective of theoretical research and engineering application,which can provide reference for relevant researchers in fault diagnosis of rolling bearing.

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• Research Progress and Prospect of Copper-Carbon Composites for Current-Carrying Friction
  SONG Yingjian; YANG Zhenghai; JIAO Jinlong; LI Wenbo; SHANGGUAN Bao
  Abstract:Copper-carbon(carbon material mainly includes graphite,carbon fiber,carbon nanotubes,graphene,etc.) composite materials are widely used as current-carrying friction pairs in the field of aerospace,rail transit,power electronics,weapons and other fields due to their excellent electrical conductivity,thermal conductivity,lubrication and other properties.With the increasingly stringent service conditions of current carrying friction pairs,the performance requirements for copper-carbon composite materials are becoming higher.The types and compositions of copper-carbon composite materials were introduced,the problems existing in copper-carbon composite materials were pointed out,such as low strength,non wetting between copper matrix and carbon material reinforcement phase.The interface improvement and preparation methods of copper-carbon composite materials were reviewed,and the development direction of copper-carbon composites in the future was prospected.

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