The 20,000-ton combined train running has greatly promoted China’s heavy-haul railway transportation capability. The application of controllable train-tail devices could improve the braking wave of the train and brak...The 20,000-ton combined train running has greatly promoted China’s heavy-haul railway transportation capability. The application of controllable train-tail devices could improve the braking wave of the train and braking synchronism, and alleviate longitudinal impulse.However, the characteristics of the controllable train-tail device such as exhaust area, exhaust duration and exhaust action time are not uniform in practice, and their effects on the longitudinal impulse of the train are not apparent,which is worth studying. In this work, according to the formation of the Datong-Qinhuangdao Railway, the train air brake and longitudinal dynamics simulation system(TABLDSS) is applied to establish a 20,000-ton combined train model with the controllable train-tail device, and the braking characteristics and the longitudinal impulse of the train are calculated synchronously with changing the air exhaust time, exhaust area, and action lag time under initial braking. The results show that the maximum coupler force of the combined train will decrease with the extension of the continuous exhaust time, while the total exhaust time of the controllable train-tail device remains unchanged;the maximum coupler force of the combined train reduces by32.5% with the exhaust area increasing from 70% to 140%;when the lag time between the controllable train-tail device and the master locomotive is more than 1.5 s, the maximum coupler force of the train increases along with the time difference enlargement.展开更多
针对模块化多电平换流器(modular multilevel converter,MMC)高压直流输电技术(high voltage direct current,HVDC)受端交流系统故障引起的直流过电压问题,文中提出一种基于晶闸管的模块化组合式直流泄能装置拓扑及协调控制方法。该直...针对模块化多电平换流器(modular multilevel converter,MMC)高压直流输电技术(high voltage direct current,HVDC)受端交流系统故障引起的直流过电压问题,文中提出一种基于晶闸管的模块化组合式直流泄能装置拓扑及协调控制方法。该直流泄能拓扑包括模块化分布式泄能部分、限流电抗器和集中式泄能电阻3部分,对子模块工作模式进行设计,提出可避免直流泄能装置反复投切的弹性调节泄能的协调控制策略,推导直流泄能装置功率控制及其内部电气耦合关系,给出泄能装置元件参数的设计方法。最后,基于PSCAD/EMTDC搭建MMC-HVDC及所提出的直流泄能装置模型,研究单相和三相接地故障下直流泄能装置的特性及直流过电压抑制效果。结果表明,所提直流泄能装置在协调控制策略下能够分阶段弹性调节泄能功率,有效抑制直流过电压,并有利于故障后的快速恢复。展开更多
To improve the characteristics of wet multi-disc brakes (WMDBs), the WMDBs of the drive axles of mining trucks were studied. A model was established to predict the phenomenon of drag characteristics during wet brake n...To improve the characteristics of wet multi-disc brakes (WMDBs), the WMDBs of the drive axles of mining trucks were studied. A model was established to predict the phenomenon of drag characteristics during wet brake non-engagement by considering the combined effect of surface grooves, film shrinkage, and laminar Navier-Stokes (N-S) equations. The model was used to study drag torque and temperature variation of the wet brakes for different volume flows, dynamic viscosities, and friction pair clearances. The simulation results indicated that the peak torque decreased when the clearance of the friction pair increased. Additionally, the peak torque increased when the volume flow increased and when the cooling liquid dynamic viscosity increased. The model was more accurate than a traditional forecasting system when considering the role of surface grooves and oil film shrinkage in actual working conditions.展开更多
Roadways in Wyoming are characterized by challenging horizontal profiles,vertical profiles,a combination of the two and adverse weather conditions,all of which affect vehicle stability.In this study,we investigated th...Roadways in Wyoming are characterized by challenging horizontal profiles,vertical profiles,a combination of the two and adverse weather conditions,all of which affect vehicle stability.In this study,we investigated the impact of different operating speeds when negotiating combined horizontal and vertical curves under unfavorable environmental conditions on Wyoming’s interstates via vehicle dynamics simulation software.The simulation tools provided the acting forces on each tire of the vehicle and the side friction(skidding)margins.This allowed for examining the interaction between vehicle dynamics and road geometry in such alignments.Also,linear regression analysis was implemented to investigate the skidding margins based on the simulation results to demonstrate when a vehicle is more likely to deviate from its desired trajectory.Specifically,this examines the contributing factors that significantly influence the skidding margins.The results indicated that:1)the skidding margins are dramatically decreased by adverse weather conditions even with lower degree of curvature and gradient values of combined curves and more particularly at higher operating speeds conditions.Increasing the vehicle speed on the curve by 10%,the skidding margin dropped by 15%.2)Compared to heavy trucks and sports utility vehicles(SUVs),passenger cars require the highest side friction demand.3)The effect of applying brakes on vehicle stability depends on the road surface condition;applying the brakes on snowy road surfaces increases the potential of vehicle skidding especially for heavy trucks.This study assessed the curve speed limits and showed how important to assign safe and appropriate limits speed since the skidding likelihood is significantly sensitive to the vehicle speeds.This study is beneficial to Wyoming’s roadway agencies since hazardous sections having combined horizontal and vertical curves are identified.Also,critical situations that require additional attention from law enforcement agencies are pinpointed.Finally,recommendations that are valuable to roadway agencies are made based on this study’s findings.展开更多
基金China National Railway Group Co.,Ltd(N2020J037).
文摘The 20,000-ton combined train running has greatly promoted China’s heavy-haul railway transportation capability. The application of controllable train-tail devices could improve the braking wave of the train and braking synchronism, and alleviate longitudinal impulse.However, the characteristics of the controllable train-tail device such as exhaust area, exhaust duration and exhaust action time are not uniform in practice, and their effects on the longitudinal impulse of the train are not apparent,which is worth studying. In this work, according to the formation of the Datong-Qinhuangdao Railway, the train air brake and longitudinal dynamics simulation system(TABLDSS) is applied to establish a 20,000-ton combined train model with the controllable train-tail device, and the braking characteristics and the longitudinal impulse of the train are calculated synchronously with changing the air exhaust time, exhaust area, and action lag time under initial braking. The results show that the maximum coupler force of the combined train will decrease with the extension of the continuous exhaust time, while the total exhaust time of the controllable train-tail device remains unchanged;the maximum coupler force of the combined train reduces by32.5% with the exhaust area increasing from 70% to 140%;when the lag time between the controllable train-tail device and the master locomotive is more than 1.5 s, the maximum coupler force of the train increases along with the time difference enlargement.
文摘针对模块化多电平换流器(modular multilevel converter,MMC)高压直流输电技术(high voltage direct current,HVDC)受端交流系统故障引起的直流过电压问题,文中提出一种基于晶闸管的模块化组合式直流泄能装置拓扑及协调控制方法。该直流泄能拓扑包括模块化分布式泄能部分、限流电抗器和集中式泄能电阻3部分,对子模块工作模式进行设计,提出可避免直流泄能装置反复投切的弹性调节泄能的协调控制策略,推导直流泄能装置功率控制及其内部电气耦合关系,给出泄能装置元件参数的设计方法。最后,基于PSCAD/EMTDC搭建MMC-HVDC及所提出的直流泄能装置模型,研究单相和三相接地故障下直流泄能装置的特性及直流过电压抑制效果。结果表明,所提直流泄能装置在协调控制策略下能够分阶段弹性调节泄能功率,有效抑制直流过电压,并有利于故障后的快速恢复。
基金Supported by the National Natural Science Foundation of China(51375519)the Chongqing Graduate Education Innovation Fund Project(CYS18223)the Chongqing University of Arts and Sciences Graduate School Research Project(M2018ME16)
文摘To improve the characteristics of wet multi-disc brakes (WMDBs), the WMDBs of the drive axles of mining trucks were studied. A model was established to predict the phenomenon of drag characteristics during wet brake non-engagement by considering the combined effect of surface grooves, film shrinkage, and laminar Navier-Stokes (N-S) equations. The model was used to study drag torque and temperature variation of the wet brakes for different volume flows, dynamic viscosities, and friction pair clearances. The simulation results indicated that the peak torque decreased when the clearance of the friction pair increased. Additionally, the peak torque increased when the volume flow increased and when the cooling liquid dynamic viscosity increased. The model was more accurate than a traditional forecasting system when considering the role of surface grooves and oil film shrinkage in actual working conditions.
基金the generous financial support of the Wyoming Department of Transportation (WYDOT)Mountain-Plains Consortium (MPC) (Grant number: 69A3551747108 (FAST Act)) for this study
文摘Roadways in Wyoming are characterized by challenging horizontal profiles,vertical profiles,a combination of the two and adverse weather conditions,all of which affect vehicle stability.In this study,we investigated the impact of different operating speeds when negotiating combined horizontal and vertical curves under unfavorable environmental conditions on Wyoming’s interstates via vehicle dynamics simulation software.The simulation tools provided the acting forces on each tire of the vehicle and the side friction(skidding)margins.This allowed for examining the interaction between vehicle dynamics and road geometry in such alignments.Also,linear regression analysis was implemented to investigate the skidding margins based on the simulation results to demonstrate when a vehicle is more likely to deviate from its desired trajectory.Specifically,this examines the contributing factors that significantly influence the skidding margins.The results indicated that:1)the skidding margins are dramatically decreased by adverse weather conditions even with lower degree of curvature and gradient values of combined curves and more particularly at higher operating speeds conditions.Increasing the vehicle speed on the curve by 10%,the skidding margin dropped by 15%.2)Compared to heavy trucks and sports utility vehicles(SUVs),passenger cars require the highest side friction demand.3)The effect of applying brakes on vehicle stability depends on the road surface condition;applying the brakes on snowy road surfaces increases the potential of vehicle skidding especially for heavy trucks.This study assessed the curve speed limits and showed how important to assign safe and appropriate limits speed since the skidding likelihood is significantly sensitive to the vehicle speeds.This study is beneficial to Wyoming’s roadway agencies since hazardous sections having combined horizontal and vertical curves are identified.Also,critical situations that require additional attention from law enforcement agencies are pinpointed.Finally,recommendations that are valuable to roadway agencies are made based on this study’s findings.
