As the unique power entrance,the pantograph-catenary electrical contact system maintains the efficiency and reliability of power transmission for the high-speed train.Along with the fast development of high-speed rail...As the unique power entrance,the pantograph-catenary electrical contact system maintains the efficiency and reliability of power transmission for the high-speed train.Along with the fast development of high-speed railways all over the world,some commercialized lines are built for covering the remote places under harsh environment,especially in China;these environmental elements including wind,sand,rain,thunder,ice and snow need to be considered during the design of the pantograph-catenary system.The pantograph-catenary system includes the pantograph,the contact wire and the interface—pantograph slide.As the key component,this pantograph slide plays a critical role in reliable power transmission under dynamic condition.The fundamental material characteristics of the pantograph slide and contact wire such as electrical conductivity,impact resistance,wear resistance,etc.,directly determine the sliding electrical contact performance of the pantograph-catenary system;meanwhile,different detection methods of the pantograph-catenary system are crucial for the reliability of service and maintenance.In addition,the challenges brought from extreme operational conditions are discussed,taking the Sichuan-Tibet Railway currently under construction as a special example with the high-altitude climate.The outlook for developing the ultra-high-speed train equipped with the novel pantograph-catenary system which can address the harsher operational environment is also involved.This paper has provided a comprehensive review of the high-speed railway pantograph-catenary systems,including its progress,challenges,outlooks in the history and future.展开更多
A theoretical model for calculating the stress and strain states of cabling structures with different loadings has been developed in this paper. We solve the problem for the first- and second-stage cable with tensile ...A theoretical model for calculating the stress and strain states of cabling structures with different loadings has been developed in this paper. We solve the problem for the first- and second-stage cable with tensile or bending strain. The contact and friction forces between the strands are presented by two-dimensional contact model. Several theoretical models have been proposed to verify the results when the triplet subjected to the tensile strain, including contact force, contact stresses, and mechanical loss. It is found that loadings will affect the friction force and the mechanical loss of the triplet. The results show that the contact force and mechanical loss are dependent on the twist pitch. A shorter twist pitch can lead to higher contact force, while the trend of mechanical loss with twist pitch is complicated. The mechanical loss may be reduced by adjusting the twist pitch reasonably. The present model provides a simple analysis method to investigate the mechanical behaviors in multistage-structures under different loads.展开更多
Collisions between multibody systems are irreversible processes which cause loss of internal energy by a stress wave that propagates in the impacting bodies away from the region of impact. A coefficient of restitution...Collisions between multibody systems are irreversible processes which cause loss of internal energy by a stress wave that propagates in the impacting bodies away from the region of impact. A coefficient of restitution relating to approach velocity is introduced to denote the losses of translational kinetic energy. A parameter β involved in internal energy losses has been obtained to calculate the coefficient of restitution. As a result, the internal energy losses caused by elastic stress waves and the contact duration in metals can be calculated numerically for the collision between circular cylinder and half plane. The metals include aluminum alloys, steel-mild 1020, steel-stainless austenitic 304, tungsten alloys, copper alloys, nickel alloys and titanium alloys. By introducing a coefficient of velocity-frequency, an exponential aggression equation related the normalized oscillating frequency and normalized approach velocity has been obtained by the numerical method.展开更多
目的:利用T-Scan定量分析单颗后牙种植修复体在牙尖交错位(intercuspal position,ICP)时咬合接触情况,并探讨其对种植体周围垂直骨吸收的影响。方法:选取第一磨牙常规种植修复的40例无咬合高点等不良修复现象和磨牙症等不良习惯的患者。...目的:利用T-Scan定量分析单颗后牙种植修复体在牙尖交错位(intercuspal position,ICP)时咬合接触情况,并探讨其对种植体周围垂直骨吸收的影响。方法:选取第一磨牙常规种植修复的40例无咬合高点等不良修复现象和磨牙症等不良习惯的患者。T-Scan记录种植修复体及对侧同名牙咬合接触情况的差异,分别按照咬合延迟时间、牙合力百分率比、咬合力峰值及咬合接触面积比进行分组,用影像学测量技术评估种植体周围骨组织的变化,从而分析咬合因素对种植体周围垂直骨吸收(vertical bone loss,VBL)的影响,并建立多元线性回归模型。结果:在咬合延迟时间和咬合力峰值分组比较中,平均VBL均存在显著性差异(P<0.05)。同时得出预测方程:Y=1.060-0.734X1+0.248X2-0.589X3,其中Y为平均VBL、X1为咬合延迟时间、X2为咬合力峰值、X3为咬合接触面积比。结论:在单颗后牙缺失常规种植修复时除考虑适当的咬合设计外,在调整种植修复体的咬合接触或定期咬合检查时,推荐应用T-Scan进行定量分析以确保ICP时咬合力峰值尽可能降低(即轻咬合接触),和适当延迟种植修复体首次咬合接触时间,对维持种植体周围骨的稳定性极为有益。展开更多
A good contact between the pantograph and catenary is critically important for the working reliability of electric trains, while the basic understanding on the electrical contact evolution during the pantograph--caten...A good contact between the pantograph and catenary is critically important for the working reliability of electric trains, while the basic understanding on the electrical contact evolution during the pantograph--catenary system working is still ambiguous so far. In this paper, the evolution of electric contact was studied in respects of the contact resistance, temperature rise, and microstructure variation, based on a home-made pantograph-catenary simulation system. Pure carbon strips and copper alloy contact wires were used, and the experimental electrical current, sliding speed, and normal force were set as 80 A, 30 km/h, and 80 N, respectively. The contact resistance presented a fluctuation without obvious regularity, concentrating in the region of 25 and 50 mf~. Temperature rise of the contact point experienced a fast increase at the first several minutes and finally reached a steady state. The surface damage of carbon trips in microstructure analysis revealed a complicated interaction of the sliding friction, joule heating, and arc erosion.展开更多
Mono-crystalline silicon solar cells with a passivated emitter rear contact(PERC)configuration have attracted extensive attention from both industry and scientific communities.A record efficiency of 24.06%on p-type si...Mono-crystalline silicon solar cells with a passivated emitter rear contact(PERC)configuration have attracted extensive attention from both industry and scientific communities.A record efficiency of 24.06%on p-type silicon wafer and mass production efficiency around 22%have been demonstrated,mainly due to its superior rear side passivation.In this work,the PERC solar cells with a p-type silicon wafer were numerically studied in terms of the surface passivation,quality of silicon wafer and metal electrodes.A rational way to achieve a 24%mass-production efficiency was proposed.Free energy loss analyses were adopted to address the loss sources with respect to the limit efficiency of 29%,which provides a guideline for the design and manufacture of a high-efficiency PERC solar cell.展开更多
CNTs-Ag-G electrical contact composite material was prepared by means of powder metallurgical method. The influence of the graphite content on sliding wear characteristics of electrical contact levels was examined. In...CNTs-Ag-G electrical contact composite material was prepared by means of powder metallurgical method. The influence of the graphite content on sliding wear characteristics of electrical contact levels was examined. In experiments, CNTs content was retained as 1% (mass fraction), and graphite was added at content levels of 8%, 10%, 13%, 15% and 18%, respectively. The results indicate that with the increase of graphite content, the contact resistance of electrical contacts is enhanced to a certain level then remains constant. Friction coefficient decreases gradually with the increase of graphite content. Wear mass loss decreases to the minimum value then increases. With the small content of graphite, the adhesive wear is hindered, which leads to the decrease of wear mass loss, while excessive graphite brings much more worn debris, resulting in the increase of mass loss. It is concluded that wear mass loss reaches the minimum value when the graphite mass fraction is about 13%. Compared with conventional Ag-G contact material, the wear mass loss of CNTs-Ag-G composite is much less due to the obvious increase of hardness and electrical conductivity, decline of friction surface temperature and inhibition of adhesive wear between composites and slip rings.展开更多
Superconducting TF and PF coils have been measured in SULTAN test facility. Segregated copper strands are included in four NbTi CICC and this is a technical innovation. Two AC losses measurement methods, calorimetric ...Superconducting TF and PF coils have been measured in SULTAN test facility. Segregated copper strands are included in four NbTi CICC and this is a technical innovation. Two AC losses measurement methods, calorimetric and electromagnetic methods, have been used in the experiments, and a broad frequency range (from 0.05 Hz to 6 Hz) is covered in sample test. The purpose of this experiment was to investigate AC losses of TF and PF CICC conductor including segregated copper and to check the design of PF and TF CICC coated with different resistive barriers (Pb-30Sn-2Sb and Ni plating on NbTi strands).展开更多
With the continuous increase of train speed,undulations of catenary and vibrations of the pantograph head result in generating pantograph- catenary arc frequently,intensifying the abrasion between pantograph strip and...With the continuous increase of train speed,undulations of catenary and vibrations of the pantograph head result in generating pantograph- catenary arc frequently,intensifying the abrasion between pantograph strip and catenary wire,which has seriously influenced the current collection and safety of electric multi units(EMU). It is necessary to study the pantographcatenary arc in immediately. Some researchers develop a few pantograph- catenary arc testing equipment,which couldn’t really reflect the operating condition of pantograph-catenary system. In this paper,the pantograph-catenary arc test apparatus was developed,which simulated the flexible and straight contact of pantograph strip and catenary wire,based on the coupling relationship between pantograph and catenary. The equipment was used to research the electrical parameters of the pantograph-catenary arc and the dynamic contact resistance.展开更多
基金supported by the National Natural Science Foundation of China(Nos.U19A20105,51837009,51807167,51922090,U1966602 and 52077182)the Scientific and Technological Funds for Young Scientists of Sichuan(No.2019JDJQ0019)。
文摘As the unique power entrance,the pantograph-catenary electrical contact system maintains the efficiency and reliability of power transmission for the high-speed train.Along with the fast development of high-speed railways all over the world,some commercialized lines are built for covering the remote places under harsh environment,especially in China;these environmental elements including wind,sand,rain,thunder,ice and snow need to be considered during the design of the pantograph-catenary system.The pantograph-catenary system includes the pantograph,the contact wire and the interface—pantograph slide.As the key component,this pantograph slide plays a critical role in reliable power transmission under dynamic condition.The fundamental material characteristics of the pantograph slide and contact wire such as electrical conductivity,impact resistance,wear resistance,etc.,directly determine the sliding electrical contact performance of the pantograph-catenary system;meanwhile,different detection methods of the pantograph-catenary system are crucial for the reliability of service and maintenance.In addition,the challenges brought from extreme operational conditions are discussed,taking the Sichuan-Tibet Railway currently under construction as a special example with the high-altitude climate.The outlook for developing the ultra-high-speed train equipped with the novel pantograph-catenary system which can address the harsher operational environment is also involved.This paper has provided a comprehensive review of the high-speed railway pantograph-catenary systems,including its progress,challenges,outlooks in the history and future.
基金supported by National Natural Science Foundation of China (Grants 11202087, 11472120, 11421062)the National Key Project of Scientific Instrument and Equipment Development (Grant 11327802)+1 种基金the National Key Project of Magneto-Constrained Fusion Energy Development Program (Grant 2013GB110002)New Century Excellent Talents in University of Ministry of Education of China (Grant NCET-13-0266)
文摘A theoretical model for calculating the stress and strain states of cabling structures with different loadings has been developed in this paper. We solve the problem for the first- and second-stage cable with tensile or bending strain. The contact and friction forces between the strands are presented by two-dimensional contact model. Several theoretical models have been proposed to verify the results when the triplet subjected to the tensile strain, including contact force, contact stresses, and mechanical loss. It is found that loadings will affect the friction force and the mechanical loss of the triplet. The results show that the contact force and mechanical loss are dependent on the twist pitch. A shorter twist pitch can lead to higher contact force, while the trend of mechanical loss with twist pitch is complicated. The mechanical loss may be reduced by adjusting the twist pitch reasonably. The present model provides a simple analysis method to investigate the mechanical behaviors in multistage-structures under different loads.
文摘Collisions between multibody systems are irreversible processes which cause loss of internal energy by a stress wave that propagates in the impacting bodies away from the region of impact. A coefficient of restitution relating to approach velocity is introduced to denote the losses of translational kinetic energy. A parameter β involved in internal energy losses has been obtained to calculate the coefficient of restitution. As a result, the internal energy losses caused by elastic stress waves and the contact duration in metals can be calculated numerically for the collision between circular cylinder and half plane. The metals include aluminum alloys, steel-mild 1020, steel-stainless austenitic 304, tungsten alloys, copper alloys, nickel alloys and titanium alloys. By introducing a coefficient of velocity-frequency, an exponential aggression equation related the normalized oscillating frequency and normalized approach velocity has been obtained by the numerical method.
文摘目的:利用T-Scan定量分析单颗后牙种植修复体在牙尖交错位(intercuspal position,ICP)时咬合接触情况,并探讨其对种植体周围垂直骨吸收的影响。方法:选取第一磨牙常规种植修复的40例无咬合高点等不良修复现象和磨牙症等不良习惯的患者。T-Scan记录种植修复体及对侧同名牙咬合接触情况的差异,分别按照咬合延迟时间、牙合力百分率比、咬合力峰值及咬合接触面积比进行分组,用影像学测量技术评估种植体周围骨组织的变化,从而分析咬合因素对种植体周围垂直骨吸收(vertical bone loss,VBL)的影响,并建立多元线性回归模型。结果:在咬合延迟时间和咬合力峰值分组比较中,平均VBL均存在显著性差异(P<0.05)。同时得出预测方程:Y=1.060-0.734X1+0.248X2-0.589X3,其中Y为平均VBL、X1为咬合延迟时间、X2为咬合力峰值、X3为咬合接触面积比。结论:在单颗后牙缺失常规种植修复时除考虑适当的咬合设计外,在调整种植修复体的咬合接触或定期咬合检查时,推荐应用T-Scan进行定量分析以确保ICP时咬合力峰值尽可能降低(即轻咬合接触),和适当延迟种植修复体首次咬合接触时间,对维持种植体周围骨的稳定性极为有益。
基金supported by the National Natural Science Foundation of China (Nos. U1234202 and 51577158)the National Science Foundation for Distinguished Young Scholars of China (No. 51325704)the Fundamental Research Funds for the Central Universities (No. A0920502051505-19)
文摘A good contact between the pantograph and catenary is critically important for the working reliability of electric trains, while the basic understanding on the electrical contact evolution during the pantograph--catenary system working is still ambiguous so far. In this paper, the evolution of electric contact was studied in respects of the contact resistance, temperature rise, and microstructure variation, based on a home-made pantograph-catenary simulation system. Pure carbon strips and copper alloy contact wires were used, and the experimental electrical current, sliding speed, and normal force were set as 80 A, 30 km/h, and 80 N, respectively. The contact resistance presented a fluctuation without obvious regularity, concentrating in the region of 25 and 50 mf~. Temperature rise of the contact point experienced a fast increase at the first several minutes and finally reached a steady state. The surface damage of carbon trips in microstructure analysis revealed a complicated interaction of the sliding friction, joule heating, and arc erosion.
基金supported by the National Natural Science Foundation of China(No.61504155)。
文摘Mono-crystalline silicon solar cells with a passivated emitter rear contact(PERC)configuration have attracted extensive attention from both industry and scientific communities.A record efficiency of 24.06%on p-type silicon wafer and mass production efficiency around 22%have been demonstrated,mainly due to its superior rear side passivation.In this work,the PERC solar cells with a p-type silicon wafer were numerically studied in terms of the surface passivation,quality of silicon wafer and metal electrodes.A rational way to achieve a 24%mass-production efficiency was proposed.Free energy loss analyses were adopted to address the loss sources with respect to the limit efficiency of 29%,which provides a guideline for the design and manufacture of a high-efficiency PERC solar cell.
基金Project(50271021) supported by the National Natural Science Foundation of ChinaProject(ZD2008003) supported by Key Science Foundation of the Education Department of Anhui Province, China+2 种基金Project(CF07-10) supported by the Innovation Center for Postgraduates at HFNL (USTC), ChinaProject(KF0702) supported by the Open Project Program of Ministry of Education of ChinaProject supported by Nippon Sheet Glass Foundation of Japan for Materials Science and Engineering
文摘CNTs-Ag-G electrical contact composite material was prepared by means of powder metallurgical method. The influence of the graphite content on sliding wear characteristics of electrical contact levels was examined. In experiments, CNTs content was retained as 1% (mass fraction), and graphite was added at content levels of 8%, 10%, 13%, 15% and 18%, respectively. The results indicate that with the increase of graphite content, the contact resistance of electrical contacts is enhanced to a certain level then remains constant. Friction coefficient decreases gradually with the increase of graphite content. Wear mass loss decreases to the minimum value then increases. With the small content of graphite, the adhesive wear is hindered, which leads to the decrease of wear mass loss, while excessive graphite brings much more worn debris, resulting in the increase of mass loss. It is concluded that wear mass loss reaches the minimum value when the graphite mass fraction is about 13%. Compared with conventional Ag-G contact material, the wear mass loss of CNTs-Ag-G composite is much less due to the obvious increase of hardness and electrical conductivity, decline of friction surface temperature and inhibition of adhesive wear between composites and slip rings.
文摘Superconducting TF and PF coils have been measured in SULTAN test facility. Segregated copper strands are included in four NbTi CICC and this is a technical innovation. Two AC losses measurement methods, calorimetric and electromagnetic methods, have been used in the experiments, and a broad frequency range (from 0.05 Hz to 6 Hz) is covered in sample test. The purpose of this experiment was to investigate AC losses of TF and PF CICC conductor including segregated copper and to check the design of PF and TF CICC coated with different resistive barriers (Pb-30Sn-2Sb and Ni plating on NbTi strands).
基金supporting program of the National Science Foundation for Distinguished Young Scholars of China(Project No.51325704)the State Key Program of National Natural Science of China(Project No.U1234202)。
文摘With the continuous increase of train speed,undulations of catenary and vibrations of the pantograph head result in generating pantograph- catenary arc frequently,intensifying the abrasion between pantograph strip and catenary wire,which has seriously influenced the current collection and safety of electric multi units(EMU). It is necessary to study the pantographcatenary arc in immediately. Some researchers develop a few pantograph- catenary arc testing equipment,which couldn’t really reflect the operating condition of pantograph-catenary system. In this paper,the pantograph-catenary arc test apparatus was developed,which simulated the flexible and straight contact of pantograph strip and catenary wire,based on the coupling relationship between pantograph and catenary. The equipment was used to research the electrical parameters of the pantograph-catenary arc and the dynamic contact resistance.