Purpose-With the rapid advancement of China’s high-speed rail network,the density of train operations is on the rise.To address the challenge of shortening train tracking intervals while enhancing transportation effi...Purpose-With the rapid advancement of China’s high-speed rail network,the density of train operations is on the rise.To address the challenge of shortening train tracking intervals while enhancing transportation efficiency,the multi-objective dynamic optimization of the train operation process has emerged as a critical issue.Design/methodology/approach-Train dynamic model is established by analyzing the force of the train in the process of tracing operation.The train tracing operation model is established according to the dynamic mechanical model of the train tracking process,and the dynamic optimization analysis is carried out with comfort,energy saving and punctuality as optimization objectives.To achieve multi-objective dynamic optimization,a novel train tracking operation calculation method is proposed,utilizing the improved grey wolf optimization algorithm(MOGWO).The proposed method is simulated and verified based on the train characteristics and line data of CR400AF electric multiple units.Findings-The simulation results prove that the optimized MOGWO algorithm can be computed quickly during train tracks,the optimum results can be given within 5s and the algorithm can converge effectively in different optimization target directions.The optimized speed profile of the MOGWO algorithm is smoother and more stable and meets the target requirements of energy saving,punctuality and comfort while maximally respecting the speed limit profile.Originality/value-The MOGWO train tracking interval optimization method enhances the tracking process while ensuring a safe tracking interval.This approach enables the trailing train to operate more comfortably,energy-efficiently and punctually,aligning with passenger needs and industry trends.The method offers valuable insights for optimizing the high-speed train tracking process.展开更多
Communicating on millimeter wave(mmWave)bands is ushering in a new epoch of mobile communication which provides the availability of 10 Gbps high data rate transmission.However,mmWave links are easily prone to short tr...Communicating on millimeter wave(mmWave)bands is ushering in a new epoch of mobile communication which provides the availability of 10 Gbps high data rate transmission.However,mmWave links are easily prone to short transmission range communication because of the serious free space path loss and the blockage by obstacles.To overcome these challenges,highly directional beams are exploited to achieve robust links by hybrid beamforming.Accurately aligning the transmitter and receiver beams,i.e.beam training,is vitally important to high data rate transmission.However,it may cause huge overhead which has negative effects on initial access,handover,and tracking.Besides,the mobility patterns of users are complicated and dynamic,which may cause tracking error and large tracking latency.An efficient beam tracking method has a positive effect on sustaining robust links.This article provides an overview of the beam training and tracking technologies on mmWave bands and reveals the insights for future research in the 6th Generation(6G)mobile network.Especially,some open research problems are proposed to realize fast,accurate,and robust beam training and tracking.We hope that this survey provides guidelines for the researchers in the area of mmWave communications.展开更多
BACKGROUND The early acquisition of skills required to perform hemostasis during endoscopy may be hindered by the lack of tools that allow assessments of the operator’s viewpoint.Understanding the operator’s viewpoi...BACKGROUND The early acquisition of skills required to perform hemostasis during endoscopy may be hindered by the lack of tools that allow assessments of the operator’s viewpoint.Understanding the operator’s viewpoint may facilitate the skills.AIM To evaluate the effects of a training system using operator gaze patterns during gastric endoscopic submucosal dissection(ESD)on hemostasis.METHODS An eye-tracking system was developed to record the operator’s viewpoints during gastric ESD,displaying the viewpoint as a circle.In phase 1,videos of three trainees’viewpoints were recorded.After reviewing these,trainees were recorded again in phase 2.The videos from both phases were retrospectively reviewed,and short clips were created to evaluate the hemostasis skills.Outcome measures included the time to recognize the bleeding point,the time to complete hemostasis,and the number of coagulation attempts.RESULTS Eight cases treated with ESD were reviewed,and 10 video clips of hemostasis were created.The time required to recognize the bleeding point during phase 2 was significantly shorter than that during phase 1(8.3±4.1 seconds vs 23.1±19.2 seconds;P=0.049).The time required to complete hemostasis during phase 1 and that during phase 2 were not significantly different(15.4±6.8 seconds vs 31.9±21.7 seconds;P=0.056).Significantly fewer coagulation attempts were performed during phase 2(1.8±0.7 vs 3.2±1.0;P=0.004).CONCLUSION Short-term training did not reduce hemostasis completion time but significantly improved bleeding point recognition and reduced coagulation attempts.Learning from the operator’s viewpoint can facilitate acquiring hemostasis skills during ESD.展开更多
Currently,the design of high-temperature superconducting(HTS)maglev trains adopts a U-shaped track operation mode,and the height of the side track significantly impacts the train’s aerodynamic characteristics.In this...Currently,the design of high-temperature superconducting(HTS)maglev trains adopts a U-shaped track operation mode,and the height of the side track significantly impacts the train’s aerodynamic characteristics.In this study,we used computational fluid dynamics(CFD)methods,based on the 3D Reynolds-averaged Navier-Stokes(RANS)method and shear stress transport(SST)k-ωturbulence model,to deeply investigate the effects of the presence or absence of a U-shaped track and different side track heights(800,880,and 960 mm)on the pressure distribution,velocity distribution,and flow field structure of HTS maglev trains at a speed of 400 km/h under crosswinds.The numerical methods were verified using a scaled ICE-2 model wind tunnel test.First,the aerodynamic characteristics of the train under different wind direction angles with and without side tracks were studied.We found that the aerodynamic performance of the train is the most adverse when the wind direction angle is 90°.The presence of a U-shaped track can effectively reduce the lateral force,lift,and yawing moment of the train.The aerodynamic performance of the first suspension bogie at the bottom,which is the worst,will also be effectively improved.Next,the aerodynamic effects of different side track heights on the HTS maglev train were studied.An increase in side track height will reduce the lift and lateral force of the train,while the increase in drag is relatively small.Under the premise of ensuring passengers can conveniently alight,we found that a U-shaped track with a side track height of 960 mm has the best aerodynamic performance.The research findings offer a valuable reference for the engineering application and design of the track structure of HTS maglev train systems.展开更多
Subgrade settlement is a common issue in soil ground within earthquake-prone regions,posing a threat to the safe operation of train-slab track coupled system(TSCS)in high-speed railways(HSRs).This study aims to analyz...Subgrade settlement is a common issue in soil ground within earthquake-prone regions,posing a threat to the safe operation of train-slab track coupled system(TSCS)in high-speed railways(HSRs).This study aims to analyze the mechanical behavior evolution of TSCS under subgrade settlement and earthquake excitation.The refined numerical model of slab track under subgrade differential settlement is established.The short settlement wavelength of 10 m causes the separation between the base and subgrade.The dynamic model of TSCS under subgrade settlement and earthquake excitation is developed.The dynamic response of TSCS exhibits more pronounced fluctuations under the combined effects of subgrade settlement and earthquake excitation than under the effects of settlement or earthquake alone.The evaluation indexes for the running safety of train on slab track under different settlement wavelengths exhibit varying degrees of increase with settlement amplitude and are particularly sensitive to the short settlement wavelength of 10 m.The wheel unloading rate and derailment coefficient of TSCS increase with earthquake intensity.Under the settlement wavelength of 10 m and amplitude of 20 mm,the wheel unloading rate of TSCS exceeds the allowable limit when the earthquake intensity exceeds 0.17g,and the derailment coefficient exceeds the allowable limit when the earthquake intensity surpasses 0.29g.展开更多
High-speed rail trains have a very complex system. Because the signals used by high-speed rails in the sections are mobile blocking systems, this can ensure the safety of the trains in the process of running. However,...High-speed rail trains have a very complex system. Because the signals used by high-speed rails in the sections are mobile blocking systems, this can ensure the safety of the trains in the process of running. However, in the actual operation of high-speed rail, trains cannot directly obtain the information and location of nearby trains. In this way, once the ground control system or signal equipment fails, the trains that are close to each other cannot obtain the information of each other in time and may collide. Therefore, a system has been developed to enable the train to track the nearest train in real time during the course of the train, and to accurately determine the speed and position of the train, which is very necessary for the safety of the train. Based on the Beidou satellite positioning technology, this paper designs a real-time tracking and early warning system suitable for high-speed rail through the analysis of its working principle and workflow, and realizes the real-time tracking of the high-speed rail train position and the collision distance between two high-speed rail trains. Early warning plays a role in improving the precise positioning of high-speed trains.展开更多
There exist three problems in the calculation of lateral vibration of the train-track time-variant system athome and abroad and the method to solve them is presented. Spatially coupling vibration analysis model of tra...There exist three problems in the calculation of lateral vibration of the train-track time-variant system athome and abroad and the method to solve them is presented. Spatially coupling vibration analysis model of train-track time-variant system is put forward. Each vehicle is modeled as a multi-body system with 26 degrees of freedomand the action of coupler is also considered. The track structure is modeled as an assembly of track elements with 30degrees of freedom, then the spatially coupling vibration matrix equation of the train-track time-variant system is es-tablished on the basis of the principle of total potential energy with stationary value and the "set-in-right-position"rule. The track vertical geometric irregularity is considered as the excitation source of the vertical vibration of thesystem, and the hunting wave of car bogie frame is taken as the excitation source of lateral vibration of the system.The spatially coupling vibration matrix equation of the system is solved by Wilson-θ direct integration method. Theapproximation of the calculated results to the spot test results demonstrates the feasibility and effectiveness of thepresented analysis method. Finally, some other vibration responses of the system are also obtained.展开更多
Bridges crossing active faults are more likely to suffer serious damage or even collapse due to the wreck capabilities of near-fault pulses and surface ruptures under earthquakes.Taking a high-speed railway simply-sup...Bridges crossing active faults are more likely to suffer serious damage or even collapse due to the wreck capabilities of near-fault pulses and surface ruptures under earthquakes.Taking a high-speed railway simply-supported girder bridge with eight spans crossing an active strike-slip fault as the research object,a refined coupling dynamic model of the high-speed train-CRTS III slab ballastless track-bridge system was established based on ABAQUS.The rationality of the established model was thoroughly discussed.The horizontal ground motions in a fault rupture zone were simulated and transient dynamic analyses of the high-speed train-track-bridge coupling system under 3-dimensional seismic excitations were subsequently performed.The safe running speed limits of a high-speed train under different earthquake levels(frequent occurrence,design and rare occurrence)were assessed based on wheel-rail dynamic(lateral wheel-rail force,derailment coefficient and wheel-load reduction rate)and rail deformation(rail dislocation,parallel turning angle and turning angle)indicators.Parameter optimization was then investigated in terms of the rail fastener stiffness and isolation layer friction coefficient.Results of the wheel-rail dynamic indicators demonstrate the safe running speed limits for the high-speed train to be approximately 200 km/h and 80 km/h under frequent and design earthquakes,while the train is unable to run safely under rare earthquakes.In addition,the rail deformations under frequent,design and rare earthquakes meet the safe running requirements of the high-speed train for the speeds of 250,100 and 50 km/h,respectively.The speed limits determined for the wheel-rail dynamic indicators are lower due to the complex coupling effect of the train-track-bridge system under track irregularity.The running safety of the train was improved by increasing the fastener stiffness and isolation layer friction coefficient.At the rail fastener lateral stiffness of 60 kN/mm and isolation layer friction coefficients of 0.9 and 0.8,respectively,the safe running speed limits of the high-speed train increased to 250 km/h and 100 km/h under frequent and design earthquakes,respectively.展开更多
The motor and trailer cars of a high-speed train were modeled as a multi-rigid body system with two suspensions. According to structural characteristic of a slab track, a new spatial vibration model of track segment e...The motor and trailer cars of a high-speed train were modeled as a multi-rigid body system with two suspensions. According to structural characteristic of a slab track, a new spatial vibration model of track segment element of the slab track was put forward. The spatial vibration equation set of the high-speed train and slab track system was then established on the basis of the principle of total potential energy with stationary value in elastic system dynamics and the rule of ＂set-in-right-position＂ for formulating system matrices. The equation set was solved by the Wilson-θ direct integration method. The contents mentioned above constitute the analysis theory of spatial vibration of high-speed train and slab track system. The theory was then verified by the high-speed running experiment carried out on the slab track in the Qinghuangdao-Shenyang passenger transport line. The results show that the calculated results agree well with the measured rcsults, such as the calculated lateral and vertical rail displacements are 0.82 mm and 0.9 mm and the measured ones 0.75 mm and 0.93 mm, respectively; the calculated lateral and vertical wheel-rail forces are 8.9 kN and 102.3 kN and the measured ones 8.6 kN and 80.2 kN, respectively. The interpolation method, that is, the lateral finite strip and slab segment element, for slab deformation proposed is of simplification and applicability compared with the traditional plate element method. All of these demonstrate the reliability of the theory proposed.展开更多
A high-speed train-track coupling dynamic model is used to investigate the dynamic behavior of a high-speed train operating on a curved track with failed fasteners. The model considers a high-speed train consisting of...A high-speed train-track coupling dynamic model is used to investigate the dynamic behavior of a high-speed train operating on a curved track with failed fasteners. The model considers a high-speed train consisting of eight vehicles coupled with a ballasted track. The vehicle is modeled as a multi-body system, and the rail is modeled with a Timoshenko beam resting on the discrete sleepers. The vehicle model considers the effect of the end connections of the neighboring vehicles on the dynamic behavior. The track model takes into account the lateral, vertical, and torsional deformations of the rails and the effect of the discrete sleeper support on the coupling dynamics of the vehicles and the track. The sleepers are assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. The train model couples with the track model by using a Hertzian contact model for the wheel/rail normal force calculation, and the nonlinear creep theory by Shen et al. (1984) is used for wheel/rail tangent force calculation. In the analysis, a curved track of 7000-m radius with failed fasteners is selected, and the effects of train operational speed and the number of failed fasteners on the dynamic behaviors of the train and the track are investigated in detail. Furthermore, the wheel/rail forces and derailment coefficient and the wheelset loading reduction are analyzed when the high-speed train passes over the curved track with the different number of continuously failed fasteners at different operational speeds. Through the detailed numerical analysis, it is found that the high-speed train can operate normally on the curved track of 7000-m radius at the speeds of 200 km/h to 350 km/h.展开更多
The dynamic responses of a slab track on transversely isotropic saturated soils subjected to moving train loads are investigated by a semi-analytical approach. The track model is described as an upper Euler beam to si...The dynamic responses of a slab track on transversely isotropic saturated soils subjected to moving train loads are investigated by a semi-analytical approach. The track model is described as an upper Euler beam to simulate the rails and a lower Euler beam to model the slab. Rail pads between the rails and slab are represented by a continuous layer of springs and dashpots. A series of point loads are formulated to describe the moving train loads. The governing equations of track-ground systems are solved using the double Fourier transform, and the dynamic responses in the time domain are obtained by the inverse Fourier transform. The results show that a train load with high velocity will generate a larger response in transversely isotropic saturated soil than the lower velocity load, and special attention should be paid on the pore pressure in the vicinity of the ground surface. The anisotropic parameters of a surface soil layer will have greater influence on the displacement and excess pore water pressure than those of the subsoil layer. The traditional design method taking ground soil as homogeneous isotropic soil is unsafe for the case of RE 〈 1 and RG 〈 1, so a transversely isotropic foundation model is of great significance to the design for high train velocities.展开更多
The process of strength-power training and the subsequent adaptation is a multi-factorial process. These factors range from the genetics and morphological characteristics of the athlete to how a coach selects, orders,...The process of strength-power training and the subsequent adaptation is a multi-factorial process. These factors range from the genetics and morphological characteristics of the athlete to how a coach selects, orders, and doses exercises and loading patterns. Consequently, adaptation from these training factors may largely relate to the mode of delivery, in other words, programming tactics. There is strong evidence that the manner and phases in which training is presented to the athlete can make a profound difference in performance outcome. This discussion deals primarily with block periodization concepts and associated methods of programming for strength-power training within track and field. 2015 Production and hosting by Elsevier B.V. on behalf of Shanghai University of Sport.展开更多
By taking cross-wind forces acting on trains into consideration, a dynamic analysis method of the cross-wind and high-speed train and slab track system was proposed on the basis of the analysis theory of spatial vibra...By taking cross-wind forces acting on trains into consideration, a dynamic analysis method of the cross-wind and high-speed train and slab track system was proposed on the basis of the analysis theory of spatial vibration of high-speed train and slab track system. The corresponding computer program was written by FORTRAN language. The dynamic responses of the high-speed train and slab track under cross-wind action were calculated. Meanwhile, the effects of the cross-wind on the dynamic responses of the system were also analyzed. The results show that the cross-wind has a significant influence on the lateral and vertical displacement responses of the car body, load reduction factor and overturning factor. For example, the maximum lateral displacement responses of the car body of the first trailer with and without cross-wind forces are 32.10 and 1.60 mm, respectively. The maximum vertical displacement responses of the car body of the first trailer with and without cross-wind forces are 6.60 and 3.29 mm, respectively. The maximum wheel load reduction factors of the first trailer with and without cross-wind forces are 0.43 and 0.22, respectively. The maximum overturning factors of the first trailer with and without cross-wind forces are 0.28 and 0.08, respectively. The cross-wind affects the derailment factor and lateral Sperling factor of the moving train to a certain extent. However, the lateral and vertical displacement responses of rails with the crnss-wind are almost the same as those without the cross-wind. The method presented and the corresponding computer program can be used to calculate the interaction between trains and track in cross-wind.展开更多
Planning training programs for strength-power track and field athletes require an understanding of both training principles and training theory. The training principles are overload, variation, and specificity. Each o...Planning training programs for strength-power track and field athletes require an understanding of both training principles and training theory. The training principles are overload, variation, and specificity. Each of these principles must be incorporated into an appropriate system of training. Conceptually, periodization embraces training principles and offers advantages in planning, allowing for logical integration and manipulation of training variables such as exercise selection, intensification, and volume factors. The adaptation and progress of the athlete is to a large extent directly related to the ability of the coach/athlete to create and carry an efficient and efficacious training process. This ability includes： an understanding of how exercises affect physiological and performance adaptation （i.e., maximum force, rate of force development, power, etc.）, how to optimize transfer of training effect ensuring that training exercises have maximum potential for carryover to performance, and how to implement programs with variations at appropriate levels （macro, meso, and micro） such that fatigue management is enhanced and performance progress is optimized.展开更多
Due to the fact that ballastless tracks in highspeed railways are not only subjected to repeated train–track dynamic interaction loads,but also suffer from complex environmental loads,the fundamental understanding of...Due to the fact that ballastless tracks in highspeed railways are not only subjected to repeated train–track dynamic interaction loads,but also suffer from complex environmental loads,the fundamental understanding of mechanical performance of ballastless tracks under sophisticated service conditions is an increasingly demanding and challenging issue in high-speed railway networks.This work aims to reveal the effect of train–track interaction and environment loads on the mechanical characteristic variation of ballastless tracks in high-speed railways,particularly focusing on the typical interface damage evolution between track layers.To this end,a finite element model of a double-block ballastless track involving the cohesive zone model for the track interface is first established to analyze the mechanical properties of the track interface under the loading–unloading processes of the negative temperature gradient load(TGL)followed by the same cycle of the positive TGL.Subsequently,the effect of wheel–rail longitudinal interactions on the nonlinear dynamic characteristics of the track interface is investigated by using a vehicle-slab track vertical-longitudinal coupled dynamics model.Finally,the influence of dynamic water pressure induced by vehicle dynamic load on the mechanical characteristics and damage evolution of the track interface is elucidated using a fluid–solid coupling method.Results show that the loading history of the positive and negative TGLs has a great impact on the nonlinear development and distribution of the track interface stress and damage;the interface damage could be induced by the wheel–rail longitudinal vibrations at a high vehicle running speed owing to the dynamic amplification effect caused by short wave irregularities;the vehicle dynamic load could produce considerable water pressure that presents nonlinear spatial–temporal characteristics at the track interface,which would lead to the interface failure under a certain condition due to the coupled dynamic effect of vehicle load and water pressure.展开更多
Fault detection and isolation of high-speed train suspension systems is of critical importance to guarantee train running safety. Firstly, the existing methods concerning fault detection or isolation of train suspensi...Fault detection and isolation of high-speed train suspension systems is of critical importance to guarantee train running safety. Firstly, the existing methods concerning fault detection or isolation of train suspension systems are briefly reviewed and divided into two categories, i.e., model-based and data-driven approaches. The advantages and disadvantages of these two categories of approaches are briefly summarized. Secondly, a 1D convolution network-based fault diagnostic method for highspeed train suspension systems is designed. To improve the robustness of the method, a Gaussian white noise strategy(GWN-strategy) for immunity to track irregularities and an edge sample training strategy(EST-strategy) for immunity to wheel wear are proposed. The whole network is called GWN-EST-1 DCNN method. Thirdly, to show the performance of this method, a multibody dynamics simulation model of a high-speed train is built to generate the lateral acceleration of a bogie frame corresponding to different track irregularities, wheel profiles, and secondary suspension faults. The simulated signals are then inputted into the diagnostic network, and the results show the correctness and superiority of the GWN-EST-1DCNN method. Finally,the 1DCNN method is further validated using tracking data of a CRH3 train running on a high-speed railway line.展开更多
Train–track–substructure dynamic interaction is an extension of the vehicle–track coupled dynamics.It contributes to evaluate dynamic interaction and performance between train–track system and its substructures.Fo...Train–track–substructure dynamic interaction is an extension of the vehicle–track coupled dynamics.It contributes to evaluate dynamic interaction and performance between train–track system and its substructures.For the first time,this work devotes to presenting engineering practical methods for modeling and solving such large-scale train–track–substructure interaction systems from a unified viewpoint.In this study,a train consists of several multi-rigid-body vehicles,and the track is modeled by various finite elements.The track length needs only satisfy the length of a train plus boundary length at two sides,despite how long the train moves on the track.The substructures and their interaction matrices to the upper track are established as independent modules,with no need for additionally building the track structures above substructures,and accordingly saving computational cost.Track–substructure local coordinates are defined to assist the confirming of the overlapped portions between the train–track system and the substructural system to effectively combine the cyclic calculation and iterative solution procedures.The advancement of this model lies in its convenience,efficiency and accuracy in continuously considering the vibration participation of multi-types of substructures against the moving of a train on the track.Numerical examples have shown the effectiveness of this method;besides,influence of substructures on train–track dynamic behaviors is illustrated accompanied by clarifying excitation difference of different track irregularity spectrums.展开更多
The uneven frost heave of frost-susceptible subgrade soil causes track irregularity,which highly enhances train vibration and affects the comfort and safety of railway transportation.This paper presents a coupled ther...The uneven frost heave of frost-susceptible subgrade soil causes track irregularity,which highly enhances train vibration and affects the comfort and safety of railway transportation.This paper presents a coupled thermo-hydro-mechanical(THM)analysis for the freezing behavior of railway located above a box culvert.The vertical acceleration of the vehicle,an indicator of riding comfort,is predicted through a vehicle dynamic model.The results reveal that the existence of a box culvert changes the subgrade thermal pattern,leading to a deeper frost penetration depth.The frost heave amount above the box culvert is larger than the adjacent section,resulting in uneven track structure upheave and track irregularity.This frostinduced track irregularity highly affects train vibration.展开更多
Automatic modulation classification is the process of identification of the modulation type of a signal in a general environment. This paper proposes a new method to evaluate the tracking performance of large margin c...Automatic modulation classification is the process of identification of the modulation type of a signal in a general environment. This paper proposes a new method to evaluate the tracking performance of large margin classifier against signal-tonoise ratio （SNR）, and classifies all forms of primary user＇s signals in a cognitive radio environment. For achieving this objective, two structures of a large margin are developed in additive white Gaussian noise （AWGN） channels with priori unknown SNR. A combination of higher order statistics and instantaneous characteristics is selected as effective features. Simulation results show that the classification rates of the proposed structures are well robust against environmental SNR changes.展开更多
基金funded by the China Academy of Railway Sciences Corporation Limited Scientific Research Project(No:2023YJ080).
文摘Purpose-With the rapid advancement of China’s high-speed rail network,the density of train operations is on the rise.To address the challenge of shortening train tracking intervals while enhancing transportation efficiency,the multi-objective dynamic optimization of the train operation process has emerged as a critical issue.Design/methodology/approach-Train dynamic model is established by analyzing the force of the train in the process of tracing operation.The train tracing operation model is established according to the dynamic mechanical model of the train tracking process,and the dynamic optimization analysis is carried out with comfort,energy saving and punctuality as optimization objectives.To achieve multi-objective dynamic optimization,a novel train tracking operation calculation method is proposed,utilizing the improved grey wolf optimization algorithm(MOGWO).The proposed method is simulated and verified based on the train characteristics and line data of CR400AF electric multiple units.Findings-The simulation results prove that the optimized MOGWO algorithm can be computed quickly during train tracks,the optimum results can be given within 5s and the algorithm can converge effectively in different optimization target directions.The optimized speed profile of the MOGWO algorithm is smoother and more stable and meets the target requirements of energy saving,punctuality and comfort while maximally respecting the speed limit profile.Originality/value-The MOGWO train tracking interval optimization method enhances the tracking process while ensuring a safe tracking interval.This approach enables the trailing train to operate more comfortably,energy-efficiently and punctually,aligning with passenger needs and industry trends.The method offers valuable insights for optimizing the high-speed train tracking process.
基金supported in part by the National Natural Science Foundation of China(NSFC)under Grant 92267202in part by the Municipal Government of Quzhou under Grant 2023D027+2 种基金in part by the National Natural Science Foundation of China(NSFC)under Grant 62321001in part by the National Key Research and Development Program of China under Grant 2020YFA0711303in part by the Beijing Natural Science Foundation under Grant Z220004.
文摘Communicating on millimeter wave(mmWave)bands is ushering in a new epoch of mobile communication which provides the availability of 10 Gbps high data rate transmission.However,mmWave links are easily prone to short transmission range communication because of the serious free space path loss and the blockage by obstacles.To overcome these challenges,highly directional beams are exploited to achieve robust links by hybrid beamforming.Accurately aligning the transmitter and receiver beams,i.e.beam training,is vitally important to high data rate transmission.However,it may cause huge overhead which has negative effects on initial access,handover,and tracking.Besides,the mobility patterns of users are complicated and dynamic,which may cause tracking error and large tracking latency.An efficient beam tracking method has a positive effect on sustaining robust links.This article provides an overview of the beam training and tracking technologies on mmWave bands and reveals the insights for future research in the 6th Generation(6G)mobile network.Especially,some open research problems are proposed to realize fast,accurate,and robust beam training and tracking.We hope that this survey provides guidelines for the researchers in the area of mmWave communications.
基金Supported by the Japan Society for the Promotion of Science Grant-in-Aid for Scientific Research,No.23K11902.
文摘BACKGROUND The early acquisition of skills required to perform hemostasis during endoscopy may be hindered by the lack of tools that allow assessments of the operator’s viewpoint.Understanding the operator’s viewpoint may facilitate the skills.AIM To evaluate the effects of a training system using operator gaze patterns during gastric endoscopic submucosal dissection(ESD)on hemostasis.METHODS An eye-tracking system was developed to record the operator’s viewpoints during gastric ESD,displaying the viewpoint as a circle.In phase 1,videos of three trainees’viewpoints were recorded.After reviewing these,trainees were recorded again in phase 2.The videos from both phases were retrospectively reviewed,and short clips were created to evaluate the hemostasis skills.Outcome measures included the time to recognize the bleeding point,the time to complete hemostasis,and the number of coagulation attempts.RESULTS Eight cases treated with ESD were reviewed,and 10 video clips of hemostasis were created.The time required to recognize the bleeding point during phase 2 was significantly shorter than that during phase 1(8.3±4.1 seconds vs 23.1±19.2 seconds;P=0.049).The time required to complete hemostasis during phase 1 and that during phase 2 were not significantly different(15.4±6.8 seconds vs 31.9±21.7 seconds;P=0.056).Significantly fewer coagulation attempts were performed during phase 2(1.8±0.7 vs 3.2±1.0;P=0.004).CONCLUSION Short-term training did not reduce hemostasis completion time but significantly improved bleeding point recognition and reduced coagulation attempts.Learning from the operator’s viewpoint can facilitate acquiring hemostasis skills during ESD.
基金supported by the National Natural Science Foundation of China(No.U23A20681)the S&T Program of Hebei Province,China(No.23567602H).
文摘Currently,the design of high-temperature superconducting(HTS)maglev trains adopts a U-shaped track operation mode,and the height of the side track significantly impacts the train’s aerodynamic characteristics.In this study,we used computational fluid dynamics(CFD)methods,based on the 3D Reynolds-averaged Navier-Stokes(RANS)method and shear stress transport(SST)k-ωturbulence model,to deeply investigate the effects of the presence or absence of a U-shaped track and different side track heights(800,880,and 960 mm)on the pressure distribution,velocity distribution,and flow field structure of HTS maglev trains at a speed of 400 km/h under crosswinds.The numerical methods were verified using a scaled ICE-2 model wind tunnel test.First,the aerodynamic characteristics of the train under different wind direction angles with and without side tracks were studied.We found that the aerodynamic performance of the train is the most adverse when the wind direction angle is 90°.The presence of a U-shaped track can effectively reduce the lateral force,lift,and yawing moment of the train.The aerodynamic performance of the first suspension bogie at the bottom,which is the worst,will also be effectively improved.Next,the aerodynamic effects of different side track heights on the HTS maglev train were studied.An increase in side track height will reduce the lift and lateral force of the train,while the increase in drag is relatively small.Under the premise of ensuring passengers can conveniently alight,we found that a U-shaped track with a side track height of 960 mm has the best aerodynamic performance.The research findings offer a valuable reference for the engineering application and design of the track structure of HTS maglev train systems.
基金Project(52078501)supported by the National Natural Science Foundation of ChinaProject(2022-Major-14)supported by the Science and Technology Research and Development Program Project of China Railway Group LimitedProject(2023ZZTS0342)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Subgrade settlement is a common issue in soil ground within earthquake-prone regions,posing a threat to the safe operation of train-slab track coupled system(TSCS)in high-speed railways(HSRs).This study aims to analyze the mechanical behavior evolution of TSCS under subgrade settlement and earthquake excitation.The refined numerical model of slab track under subgrade differential settlement is established.The short settlement wavelength of 10 m causes the separation between the base and subgrade.The dynamic model of TSCS under subgrade settlement and earthquake excitation is developed.The dynamic response of TSCS exhibits more pronounced fluctuations under the combined effects of subgrade settlement and earthquake excitation than under the effects of settlement or earthquake alone.The evaluation indexes for the running safety of train on slab track under different settlement wavelengths exhibit varying degrees of increase with settlement amplitude and are particularly sensitive to the short settlement wavelength of 10 m.The wheel unloading rate and derailment coefficient of TSCS increase with earthquake intensity.Under the settlement wavelength of 10 m and amplitude of 20 mm,the wheel unloading rate of TSCS exceeds the allowable limit when the earthquake intensity exceeds 0.17g,and the derailment coefficient exceeds the allowable limit when the earthquake intensity surpasses 0.29g.
基金supported by the National Natural Science Foundation of China(61203129,61174038,61473151,51507080)the Fundamental Research Funds for the Central Universities(30915011104,30920130121010,30920140112005)
文摘High-speed rail trains have a very complex system. Because the signals used by high-speed rails in the sections are mobile blocking systems, this can ensure the safety of the trains in the process of running. However, in the actual operation of high-speed rail, trains cannot directly obtain the information and location of nearby trains. In this way, once the ground control system or signal equipment fails, the trains that are close to each other cannot obtain the information of each other in time and may collide. Therefore, a system has been developed to enable the train to track the nearest train in real time during the course of the train, and to accurately determine the speed and position of the train, which is very necessary for the safety of the train. Based on the Beidou satellite positioning technology, this paper designs a real-time tracking and early warning system suitable for high-speed rail through the analysis of its working principle and workflow, and realizes the real-time tracking of the high-speed rail train position and the collision distance between two high-speed rail trains. Early warning plays a role in improving the precise positioning of high-speed trains.
基金Project (50078006) supported by the National Natural Science Foundation of China Project (2001G029) supported by the Foundation of the Science and Technology Section of the Railway Bureau
文摘There exist three problems in the calculation of lateral vibration of the train-track time-variant system athome and abroad and the method to solve them is presented. Spatially coupling vibration analysis model of train-track time-variant system is put forward. Each vehicle is modeled as a multi-body system with 26 degrees of freedomand the action of coupler is also considered. The track structure is modeled as an assembly of track elements with 30degrees of freedom, then the spatially coupling vibration matrix equation of the train-track time-variant system is es-tablished on the basis of the principle of total potential energy with stationary value and the "set-in-right-position"rule. The track vertical geometric irregularity is considered as the excitation source of the vertical vibration of thesystem, and the hunting wave of car bogie frame is taken as the excitation source of lateral vibration of the system.The spatially coupling vibration matrix equation of the system is solved by Wilson-θ direct integration method. Theapproximation of the calculated results to the spot test results demonstrates the feasibility and effectiveness of thepresented analysis method. Finally, some other vibration responses of the system are also obtained.
基金Project(51378050) supported by the National Natural Science Foundation of ChinaProject(B13002) supported by the “111” Project,China+2 种基金Project (8192035) supported by the Beijing Municipal Natural Science Foundation,ChinaProject(P2019G002) supported by the Science and Technology Research and Development Program of China RailwayProject(2019YJ193) supported by the State Key Laboratory for Track Technology of High-speed Railway,China。
文摘Bridges crossing active faults are more likely to suffer serious damage or even collapse due to the wreck capabilities of near-fault pulses and surface ruptures under earthquakes.Taking a high-speed railway simply-supported girder bridge with eight spans crossing an active strike-slip fault as the research object,a refined coupling dynamic model of the high-speed train-CRTS III slab ballastless track-bridge system was established based on ABAQUS.The rationality of the established model was thoroughly discussed.The horizontal ground motions in a fault rupture zone were simulated and transient dynamic analyses of the high-speed train-track-bridge coupling system under 3-dimensional seismic excitations were subsequently performed.The safe running speed limits of a high-speed train under different earthquake levels(frequent occurrence,design and rare occurrence)were assessed based on wheel-rail dynamic(lateral wheel-rail force,derailment coefficient and wheel-load reduction rate)and rail deformation(rail dislocation,parallel turning angle and turning angle)indicators.Parameter optimization was then investigated in terms of the rail fastener stiffness and isolation layer friction coefficient.Results of the wheel-rail dynamic indicators demonstrate the safe running speed limits for the high-speed train to be approximately 200 km/h and 80 km/h under frequent and design earthquakes,while the train is unable to run safely under rare earthquakes.In addition,the rail deformations under frequent,design and rare earthquakes meet the safe running requirements of the high-speed train for the speeds of 250,100 and 50 km/h,respectively.The speed limits determined for the wheel-rail dynamic indicators are lower due to the complex coupling effect of the train-track-bridge system under track irregularity.The running safety of the train was improved by increasing the fastener stiffness and isolation layer friction coefficient.At the rail fastener lateral stiffness of 60 kN/mm and isolation layer friction coefficients of 0.9 and 0.8,respectively,the safe running speed limits of the high-speed train increased to 250 km/h and 100 km/h under frequent and design earthquakes,respectively.
基金Project(2007CB714706) supported by the National Basic Research Program of ChinaProject (50678176) supported by the National Natural Science Foundation of ChinaProject(NCET-07-0866) supported by the Program for New Century Excellent Talents in University
文摘The motor and trailer cars of a high-speed train were modeled as a multi-rigid body system with two suspensions. According to structural characteristic of a slab track, a new spatial vibration model of track segment element of the slab track was put forward. The spatial vibration equation set of the high-speed train and slab track system was then established on the basis of the principle of total potential energy with stationary value in elastic system dynamics and the rule of ＂set-in-right-position＂ for formulating system matrices. The equation set was solved by the Wilson-θ direct integration method. The contents mentioned above constitute the analysis theory of spatial vibration of high-speed train and slab track system. The theory was then verified by the high-speed running experiment carried out on the slab track in the Qinghuangdao-Shenyang passenger transport line. The results show that the calculated results agree well with the measured rcsults, such as the calculated lateral and vertical rail displacements are 0.82 mm and 0.9 mm and the measured ones 0.75 mm and 0.93 mm, respectively; the calculated lateral and vertical wheel-rail forces are 8.9 kN and 102.3 kN and the measured ones 8.6 kN and 80.2 kN, respectively. The interpolation method, that is, the lateral finite strip and slab segment element, for slab deformation proposed is of simplification and applicability compared with the traditional plate element method. All of these demonstrate the reliability of the theory proposed.
基金Project supported by the National Natural Science Foundation of China (No. U1134202)the National Basic Research Program (973) of China (No. 2011CB711103)the Program for Changjiang Scholars and Innovative Research Team in University (Nos. IRT1178and SWJTU12ZT01), China
文摘A high-speed train-track coupling dynamic model is used to investigate the dynamic behavior of a high-speed train operating on a curved track with failed fasteners. The model considers a high-speed train consisting of eight vehicles coupled with a ballasted track. The vehicle is modeled as a multi-body system, and the rail is modeled with a Timoshenko beam resting on the discrete sleepers. The vehicle model considers the effect of the end connections of the neighboring vehicles on the dynamic behavior. The track model takes into account the lateral, vertical, and torsional deformations of the rails and the effect of the discrete sleeper support on the coupling dynamics of the vehicles and the track. The sleepers are assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. The train model couples with the track model by using a Hertzian contact model for the wheel/rail normal force calculation, and the nonlinear creep theory by Shen et al. (1984) is used for wheel/rail tangent force calculation. In the analysis, a curved track of 7000-m radius with failed fasteners is selected, and the effects of train operational speed and the number of failed fasteners on the dynamic behaviors of the train and the track are investigated in detail. Furthermore, the wheel/rail forces and derailment coefficient and the wheelset loading reduction are analyzed when the high-speed train passes over the curved track with the different number of continuously failed fasteners at different operational speeds. Through the detailed numerical analysis, it is found that the high-speed train can operate normally on the curved track of 7000-m radius at the speeds of 200 km/h to 350 km/h.
基金the National Basic Research Program of China under Grant No.2013CB036405the Key Research Program of the Chinese Academy of Sciences under Grant No.KZZD-EW-05the Natural Science Foundation of China under Grant Nos.41402317,51209201 and 51279198
文摘The dynamic responses of a slab track on transversely isotropic saturated soils subjected to moving train loads are investigated by a semi-analytical approach. The track model is described as an upper Euler beam to simulate the rails and a lower Euler beam to model the slab. Rail pads between the rails and slab are represented by a continuous layer of springs and dashpots. A series of point loads are formulated to describe the moving train loads. The governing equations of track-ground systems are solved using the double Fourier transform, and the dynamic responses in the time domain are obtained by the inverse Fourier transform. The results show that a train load with high velocity will generate a larger response in transversely isotropic saturated soil than the lower velocity load, and special attention should be paid on the pore pressure in the vicinity of the ground surface. The anisotropic parameters of a surface soil layer will have greater influence on the displacement and excess pore water pressure than those of the subsoil layer. The traditional design method taking ground soil as homogeneous isotropic soil is unsafe for the case of RE 〈 1 and RG 〈 1, so a transversely isotropic foundation model is of great significance to the design for high train velocities.
文摘The process of strength-power training and the subsequent adaptation is a multi-factorial process. These factors range from the genetics and morphological characteristics of the athlete to how a coach selects, orders, and doses exercises and loading patterns. Consequently, adaptation from these training factors may largely relate to the mode of delivery, in other words, programming tactics. There is strong evidence that the manner and phases in which training is presented to the athlete can make a profound difference in performance outcome. This discussion deals primarily with block periodization concepts and associated methods of programming for strength-power training within track and field. 2015 Production and hosting by Elsevier B.V. on behalf of Shanghai University of Sport.
基金Project (2007CB714706) supported by the Major State Basic Research and Development Program of ChinaProject (50678176) supported by the National Natural Science Foundation of ChinaProject (NCET-07-0866) supported by the New Century Excellent Talents in University
文摘By taking cross-wind forces acting on trains into consideration, a dynamic analysis method of the cross-wind and high-speed train and slab track system was proposed on the basis of the analysis theory of spatial vibration of high-speed train and slab track system. The corresponding computer program was written by FORTRAN language. The dynamic responses of the high-speed train and slab track under cross-wind action were calculated. Meanwhile, the effects of the cross-wind on the dynamic responses of the system were also analyzed. The results show that the cross-wind has a significant influence on the lateral and vertical displacement responses of the car body, load reduction factor and overturning factor. For example, the maximum lateral displacement responses of the car body of the first trailer with and without cross-wind forces are 32.10 and 1.60 mm, respectively. The maximum vertical displacement responses of the car body of the first trailer with and without cross-wind forces are 6.60 and 3.29 mm, respectively. The maximum wheel load reduction factors of the first trailer with and without cross-wind forces are 0.43 and 0.22, respectively. The maximum overturning factors of the first trailer with and without cross-wind forces are 0.28 and 0.08, respectively. The cross-wind affects the derailment factor and lateral Sperling factor of the moving train to a certain extent. However, the lateral and vertical displacement responses of rails with the crnss-wind are almost the same as those without the cross-wind. The method presented and the corresponding computer program can be used to calculate the interaction between trains and track in cross-wind.
文摘Planning training programs for strength-power track and field athletes require an understanding of both training principles and training theory. The training principles are overload, variation, and specificity. Each of these principles must be incorporated into an appropriate system of training. Conceptually, periodization embraces training principles and offers advantages in planning, allowing for logical integration and manipulation of training variables such as exercise selection, intensification, and volume factors. The adaptation and progress of the athlete is to a large extent directly related to the ability of the coach/athlete to create and carry an efficient and efficacious training process. This ability includes： an understanding of how exercises affect physiological and performance adaptation （i.e., maximum force, rate of force development, power, etc.）, how to optimize transfer of training effect ensuring that training exercises have maximum potential for carryover to performance, and how to implement programs with variations at appropriate levels （macro, meso, and micro） such that fatigue management is enhanced and performance progress is optimized.
基金the National Natural Science Foundation of China(Nos.51708457,11790283,and 51978587)the Fund from State Key Laboratory of Traction Power(2019TPL-T16)+1 种基金the Young Elite Scientists Sponsorship Program by CAST(2018QNRC001)the 111 Project(Grant No.B16041)。
文摘Due to the fact that ballastless tracks in highspeed railways are not only subjected to repeated train–track dynamic interaction loads,but also suffer from complex environmental loads,the fundamental understanding of mechanical performance of ballastless tracks under sophisticated service conditions is an increasingly demanding and challenging issue in high-speed railway networks.This work aims to reveal the effect of train–track interaction and environment loads on the mechanical characteristic variation of ballastless tracks in high-speed railways,particularly focusing on the typical interface damage evolution between track layers.To this end,a finite element model of a double-block ballastless track involving the cohesive zone model for the track interface is first established to analyze the mechanical properties of the track interface under the loading–unloading processes of the negative temperature gradient load(TGL)followed by the same cycle of the positive TGL.Subsequently,the effect of wheel–rail longitudinal interactions on the nonlinear dynamic characteristics of the track interface is investigated by using a vehicle-slab track vertical-longitudinal coupled dynamics model.Finally,the influence of dynamic water pressure induced by vehicle dynamic load on the mechanical characteristics and damage evolution of the track interface is elucidated using a fluid–solid coupling method.Results show that the loading history of the positive and negative TGLs has a great impact on the nonlinear development and distribution of the track interface stress and damage;the interface damage could be induced by the wheel–rail longitudinal vibrations at a high vehicle running speed owing to the dynamic amplification effect caused by short wave irregularities;the vehicle dynamic load could produce considerable water pressure that presents nonlinear spatial–temporal characteristics at the track interface,which would lead to the interface failure under a certain condition due to the coupled dynamic effect of vehicle load and water pressure.
基金supported by the National Nature Science Foundation of China(No.71871188)the Fundamental Research Funds for the Central Universities(No.2682021CX051)supported by China Scholarship Council(No.201707000113)。
文摘Fault detection and isolation of high-speed train suspension systems is of critical importance to guarantee train running safety. Firstly, the existing methods concerning fault detection or isolation of train suspension systems are briefly reviewed and divided into two categories, i.e., model-based and data-driven approaches. The advantages and disadvantages of these two categories of approaches are briefly summarized. Secondly, a 1D convolution network-based fault diagnostic method for highspeed train suspension systems is designed. To improve the robustness of the method, a Gaussian white noise strategy(GWN-strategy) for immunity to track irregularities and an edge sample training strategy(EST-strategy) for immunity to wheel wear are proposed. The whole network is called GWN-EST-1 DCNN method. Thirdly, to show the performance of this method, a multibody dynamics simulation model of a high-speed train is built to generate the lateral acceleration of a bogie frame corresponding to different track irregularities, wheel profiles, and secondary suspension faults. The simulated signals are then inputted into the diagnostic network, and the results show the correctness and superiority of the GWN-EST-1DCNN method. Finally,the 1DCNN method is further validated using tracking data of a CRH3 train running on a high-speed railway line.
基金This work was supported by the National Natural Science Foundation of China(Grant No.52008404)the National Natural Science Foundation of Hunan Province(Grant No.2021JJ30850).
文摘Train–track–substructure dynamic interaction is an extension of the vehicle–track coupled dynamics.It contributes to evaluate dynamic interaction and performance between train–track system and its substructures.For the first time,this work devotes to presenting engineering practical methods for modeling and solving such large-scale train–track–substructure interaction systems from a unified viewpoint.In this study,a train consists of several multi-rigid-body vehicles,and the track is modeled by various finite elements.The track length needs only satisfy the length of a train plus boundary length at two sides,despite how long the train moves on the track.The substructures and their interaction matrices to the upper track are established as independent modules,with no need for additionally building the track structures above substructures,and accordingly saving computational cost.Track–substructure local coordinates are defined to assist the confirming of the overlapped portions between the train–track system and the substructural system to effectively combine the cyclic calculation and iterative solution procedures.The advancement of this model lies in its convenience,efficiency and accuracy in continuously considering the vibration participation of multi-types of substructures against the moving of a train on the track.Numerical examples have shown the effectiveness of this method;besides,influence of substructures on train–track dynamic behaviors is illustrated accompanied by clarifying excitation difference of different track irregularity spectrums.
基金supported in part by Grant-in-Aids for Scientific Research (A) (16H02360) and Research (C) (15K06214) from Japan Society for the Promotion of Science (JSPS) KAKENHI
文摘The uneven frost heave of frost-susceptible subgrade soil causes track irregularity,which highly enhances train vibration and affects the comfort and safety of railway transportation.This paper presents a coupled thermo-hydro-mechanical(THM)analysis for the freezing behavior of railway located above a box culvert.The vertical acceleration of the vehicle,an indicator of riding comfort,is predicted through a vehicle dynamic model.The results reveal that the existence of a box culvert changes the subgrade thermal pattern,leading to a deeper frost penetration depth.The frost heave amount above the box culvert is larger than the adjacent section,resulting in uneven track structure upheave and track irregularity.This frostinduced track irregularity highly affects train vibration.
文摘Automatic modulation classification is the process of identification of the modulation type of a signal in a general environment. This paper proposes a new method to evaluate the tracking performance of large margin classifier against signal-tonoise ratio （SNR）, and classifies all forms of primary user＇s signals in a cognitive radio environment. For achieving this objective, two structures of a large margin are developed in additive white Gaussian noise （AWGN） channels with priori unknown SNR. A combination of higher order statistics and instantaneous characteristics is selected as effective features. Simulation results show that the classification rates of the proposed structures are well robust against environmental SNR changes.
