The influence of ramps on the transient rolling contact characteristics and damage mechanisms of switch rails remains unclear,presenting substantial challenges to the safety of railway operations.To this end,this pape...The influence of ramps on the transient rolling contact characteristics and damage mechanisms of switch rails remains unclear,presenting substantial challenges to the safety of railway operations.To this end,this paper constructs a transient rolling contact finite element model of the wheel-rail in switch under different ramps using ANSYS/LSDYNA method,and analyzes the tribology and damage characteristics when the wheel passes through the switch at a uniform speed.Our research findings reveal that the vibration induced in the switch rail during the wheel load transfer process leads to a step-like increase in the contact force.Moreover,the interaction between the wheel and the rail primarily involves slip contact,which may significantly contribute to the formation of corrugations on the switch rail.Additionally,the presence of large ramps exacerbates switch rail wear and rolling contact fatigue,resulting in a notable 13.2%increase in switch rail damage under 40‰ramp conditions compared to flat(0‰ramp)conditions.Furthermore,the large ramps can alter the direction of crack propagation,ultimately causing surface spalling of the rail.Therefore,large ramps intensify the dynamic interactions during the wheel load transfer process,further aggravating the crack and spalling damage to the switch rails.展开更多
In this study,samples obtained from 1.3343 high-speed steel punches with TiN coatings were tested.The samples were subjected to heat treatment at different cryogenic temperatures(<196℃)and durations(12,24 and 36 h...In this study,samples obtained from 1.3343 high-speed steel punches with TiN coatings were tested.The samples were subjected to heat treatment at different cryogenic temperatures(<196℃)and durations(12,24 and 36 h),followed by tempering at two different temperatures(200,500℃).For performance testing,a ball-on-disk wear test setup was utilized and a total of 6 groups of samples were examined.The effects of cryo-treatment and tempering on microstructure were revealed through microstructural analysis with scanning electron microscopy(SEM),X-ray(XRD diffraction),and Rietveld analysis.Additionally,the hardness of the punches was measured with microhardness measurements.The optimal wear resistance was observed in the 36 h deep cryo-treated and 200℃tempered samples.The characterization study indicates that by cryogenic treatment a significant portion of the retained austenite transformed into martensite and secondary carbides formed,resulting in improved wear resistance and a slight increase in hardness.展开更多
Following the fundamental characteristics of the porosity windbreak,this study suggests a new numerical investigation method for the wind field of the windbreak based on the porous medium physical model.This method ca...Following the fundamental characteristics of the porosity windbreak,this study suggests a new numerical investigation method for the wind field of the windbreak based on the porous medium physical model.This method can transform the reasonable matching problem of the porosity and windproof performance of the windbreak into a study of the relationship between the resistance coefficient of the porous medium and the aerodynamic load of the train.This study examines the influence of the hole type on the wind field behind the porosity windbreak.Then,the relationship between the resistance coefficient of the porous medium,the porosity of the windbreak,and the aerodynamic loads of the train is investigated.The results show that the porous media physical model can be used instead of the windbreak geometry to study the windbreak-train aerodynamic performance,and the process of using this method is suggested.展开更多
A high-speed train travelling from the open air into a narrow tunnel will cause the“sonic boom”at tunnel exit.When the maglev train’s speed reaches 600 km/h,the train-tunnel aerodynamic effect is intensified,so a n...A high-speed train travelling from the open air into a narrow tunnel will cause the“sonic boom”at tunnel exit.When the maglev train’s speed reaches 600 km/h,the train-tunnel aerodynamic effect is intensified,so a new mitigation method is urgently expected to be explored.This study proposed a novel asymptotic linear method(ALM)for micro pressure wave(MPW)mitigation to achieve a constant gradient of initial c ompression waves(ICWs),via a study with various open ratios on hoods.The properties of ICWs and MPWs under various open ratios of hoods were analyzed.The results show that as the open ratio increases,the MPW amplitude at the tunnel exit initially decreases before rising.At the open ratio of 2.28%,the slope of the ICW curve is linearly coincident with a supposed straight line in the ALM,which further reduces the MPW amplitude by 26.9%at 20 m and 20.0%at 50 m from the exit,as compared to the unvented hood.Therefore,the proposed method effectively mitigates MPW and quickly determines the upper limit of alleviation for the MPW amplitude at a fixed train-tunnel operation condition.All achievements provide a ne w potential measure for the adaptive design of tunnel hoods.展开更多
The majority of the projectiles used in the hypersonic penetration study are solid flat-nosed cylindrical projectiles with a diameter of less than 20 mm.This study aims to fill the gap in the experimental and analytic...The majority of the projectiles used in the hypersonic penetration study are solid flat-nosed cylindrical projectiles with a diameter of less than 20 mm.This study aims to fill the gap in the experimental and analytical study of the evolution of the nose shape of larger hollow projectiles under hypersonic penetration.In the hypersonic penetration test,eight ogive-nose AerMet100 steel projectiles with a diameter of 40 mm were launched to hit concrete targets with impact velocities that ranged from 1351 to 1877 m/s.Severe erosion of the projectiles was observed during high-speed penetration of heterogeneous targets,and apparent localized mushrooming occurred in the front nose of recovered projectiles.By examining the damage to projectiles,a linear relationship was found between the relative length reduction rate and the initial kinetic energy of projectiles in different penetration tests.Furthermore,microscopic analysis revealed the forming mechanism of the localized mushrooming phenomenon for eroding penetration,i.e.,material spall erosion abrasion mechanism,material flow and redistribution abrasion mechanism and localized radial upsetting deformation mechanism.Finally,a model of highspeed penetration that included erosion was established on the basis of a model of the evolution of the projectile nose that considers radial upsetting;the model was validated by test data from the literature and the present study.Depending upon the impact velocity,v0,the projectile nose may behave as undistorted,radially distorted or hemispherical.Due to the effects of abrasion of the projectile and enhancement of radial upsetting on the duration and amplitude of the secondary rising segment in the pulse shape of projectile deceleration,the predicted DOP had an upper limit.展开更多
The seismic damage to ancillary facilities on high-speed railway(HSR)bridges can affect the normal movement of trains.To propose the bridge deck acceleration response spectra of the typical HSR simply-supported girder...The seismic damage to ancillary facilities on high-speed railway(HSR)bridges can affect the normal movement of trains.To propose the bridge deck acceleration response spectra of the typical HSR simply-supported girder bridge for simplifying the seismic responses analysis of the facilities on bridges,the finite element models of the HSR multi-span simply-supported girder bridges with CRTSII track were established,and the numerical model was validated by tests.Besides,the effects of the span number,peak ground acceleration(PGA),pier height on the seismic acceleration and response spectra of the bridge deck were investigated.Afterward,the bridge acceleration amplification factor curves and bridge deck response spectra with different PGAs and pier heights were obtained.The formula for bridge deck acceleration amplification factor,with a 95%guarantee rate,was fitted.Moreover,the finite element models of the overhead contact lines(OCL)mounted on rigid base and bridges were established to validate the fitted formula.The results indicated that the maximum seismic acceleration response is in the midspan of the beam.The proposed formula for the bridge deck acceleration response spectra can be used to analyze the earthquake response of the OCL and other ancillary facilities on HSR simply-supported girder bridges.The bridge deck acceleration response spectra are conservative in terms of structural safety and can significantly improving the analysis efficiency.展开更多
The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In th...The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In this study,computational fluid dynamics(CFD)based on three-dimensional steady incompressible Reynolds-average Naiver-Stokes(RANS)equations and Realizable k-εturbulence model were utilized for numerical simulations.Inspired by the concept of streamlined design and the idea of bottom flow field control,this study iteratively designed the bogies in a streamlined shape and combined them with the bottom deflectors to investigate the joint drag reduction mechanism.Three models,i.e.,single-bogie model,simplified train model,and eight-car high-speed train model,were created and their aerodynamic characteristics were analyzed.The results show that the single-bogie model with streamlined design shows a noticeable drag reduction,whose power bogie and trailer bogie experience 13.92%and 7.63%drag reduction,respectively.The range of positive pressure area on the bogie is reduced.The aerodynamic drag can be further reduced to 15.01%by installing both the streamlined bogie and the deflector on the simplified train model.When the streamlined bogies and deflectors are used on the eight-car model together,the total drag reduction rate reaches 2.90%.Therefore,the proposed aerodynamic kit for the high-speed train bottom is capable to improve the flow structure around the bogie regions,reduce the bottom flow velocity,and narrow the scope of the train’s influence on the surrounding environment,achieving the appreciable reduction of aerodynamic drag.This paper can provide a new idea for the drag reduction of high-speed trains.展开更多
Sudden earthquakes pose a threat to the running safety of trains on high-speed railway bridges,and the stiffness of piers is one of the factors affecting the dynamic response of train-track-bridge system.In this paper...Sudden earthquakes pose a threat to the running safety of trains on high-speed railway bridges,and the stiffness of piers is one of the factors affecting the dynamic response of train-track-bridge system.In this paper,a experiment of a train running on a high-speed railway bridge is performed based on a dynamic experiment system,and the corresponding numerical model is established.The reliability of the numerical model is verified by experiments.Then,the experiment and numerical data are analyzed to reveal the pier height effects on the running safety of trains on bridges.The results show that when the pier height changes,the frequency of the bridge below the 30 m pier height changes greater;the increase of pier height causes the transverse fundamental frequency of the bridge close to that of the train,and the shaking angle and lateral displacement of the train are the largest for bridge with 50 m pier,which increases the risk of derailment;with the pier height increases from 8 m to 50 m,the derailment coefficient obtained by numerical simulations increases by 75% on average,and the spectral intensity obtained by experiments increases by 120% on average,two indicators exhibit logarithmic variation.展开更多
Highly efficient organic solar cells(OSCs)are normally produced using the halogenated solvents chloroform or chlorobenzene,which present challenges for scalable manufacturing due to their toxicity,narrow processing wi...Highly efficient organic solar cells(OSCs)are normally produced using the halogenated solvents chloroform or chlorobenzene,which present challenges for scalable manufacturing due to their toxicity,narrow processing window and low boiling point.Herein,we develop a novel high-speed doctor-blading technique that significantly reduces the required concentration,facilitating the use of eco-friendly,non-halogenated solvents as alternatives to chloroform or chlorobenzene.By utilizing two widely used high-boiling,non-halogenated green solvents-o-xylene(o-XY)and toluene(Tol)-in the fabrication of PM 6:L 8-BO,we achieve power conversion efficiencies(PCEs)of 18.20%and 17.36%,respectively.Additionally,a module fabricated with o-XY demonstrates a notable PCE of 16.07%.In-situ testing and morphological analysis reveal that the o-XY coating process extends the liquid-to-solid transition stage to 6 s,significantly longer than the 1.7 s observed with Tol processing.This prolonged transition phase is crucial for improving the crystallinity of the thin film,reducing defect-mediated recombination,and enhancing carrier mobility,which collectively contribute to superior PCEs.展开更多
During high-speed flight,both thermal and mechani-cal loads can degrade the electrical performance of the antenna-radome system,which can subsequently affect the performance of the guidance system.This paper presents ...During high-speed flight,both thermal and mechani-cal loads can degrade the electrical performance of the antenna-radome system,which can subsequently affect the performance of the guidance system.This paper presents a method for evalu-ating the electrical performance of the radome when subjected to thermo-mechanical-electrical(TME)coupling.The method involves establishing a TME coupling model(TME-CM)based on the TME sharing mesh model(TME-SMM)generated by the tetrahedral mesh partitioning of the radome structure.The effects of dielectric temperature drift and structural deformation on the radome’s electrical performance are also considered.Firstly,the temperature field of the radome is obtained by tran-sient thermal analysis while the deformation field of the radome is obtained by static analysis.Subsequently,the dielectric varia-tion and structural deformation of the radome are accurately incorporated into the electrical simulation model based on the TME-SMM.The three-dimensional(3D)ray tracing method with the aperture integration technique is used to calculate the radome’s electrical performance.A representative example is provided to illustrate the superiority and necessity of the pro-posed method.This is achieved by calculating and analyzing the changes in the radome’s electrical performance over time dur-ing high-speed flight.展开更多
In the realm of high-speed railway bridge engineering,managing the intricacies of the track-bridge system model(TBSM)during seismic events remains a formidable challenge.This study pioneers an innovative approach by p...In the realm of high-speed railway bridge engineering,managing the intricacies of the track-bridge system model(TBSM)during seismic events remains a formidable challenge.This study pioneers an innovative approach by presenting a simplified bridge model(SBM)optimized for both computational efficiency and precise representation,a seminal contribution to the engineering design landscape.Central to this innovation is a novel model-updating methodology that synergistically melds artificial neural networks with an augmented particle swarm optimization.The neural networks adeptly map update parameters to seismic responses,while enhancements to the particle swarm algorithm’s inertial and learning weights lead to superior SBM parameter updates.Verification via a 4-span high-speed railway bridge revealed that the optimized SBM and TBSM exhibit a highly consistent structural natural period and seismic response,with errors controlled within 7%.Additionally,the computational efficiency improved by over 100%.Leveraging the peak displacement and shear force residuals from the seismic TBSM and SBM as optimization objectives,SBM parameters are adeptly revised.Furthermore,the incorporation of elastoplastic springs at the beam ends of the simplified model effectively captures the additional mass,stiffness,and constraint effects exerted by the track system on the bridge structure.展开更多
This study investigates the influence of different pantograph parameters and train length on the aerodynamic drag of high-speed train by the delayed detached eddy simulation(DDES) method. The train geometry considered...This study investigates the influence of different pantograph parameters and train length on the aerodynamic drag of high-speed train by the delayed detached eddy simulation(DDES) method. The train geometry considered is the high-speed train with pantographs, and the different versions have 3, 5, 8, 10, 12, 16 and 17 cars. The numerical results are verified by the wind tunnel test with 3.6% difference. The influences of the number of cars and the position, quantity and configuration of pantographs on flow field around high-speed train and wake vortices are analyzed. The aerodynamic drag of middle cars gradually decreases along the flow direction. The aerodynamic drag of pantographs decreases with its backward shift, and that of the first pantograph decreases significantly. As the number of pantographs increases, its effect on the aerodynamic drag decrease of rear cars is more significant. The engineering application equation for the aerodynamic drag of high-speed train with pantographs is proposed. For the 10-car and 17-car train, the differences of total aerodynamic drag between the equation and the simulation results are 1.2% and 0.4%, respectively. The equation generalized in this study could well guide the design phase of high-speed train.展开更多
The influence of enlarged section parameters on pressure transients of high-speed train passing through a tunnel was investigated by numerical simulation.The calculation results obtained by the structured and unstruct...The influence of enlarged section parameters on pressure transients of high-speed train passing through a tunnel was investigated by numerical simulation.The calculation results obtained by the structured and unstructured grid and the experimental results of smooth wall tunnel were verified.Numerical simulation studies were conducted on three tunnel enlarged section parameters,the enlarged section distribution along circumferential direction,the enlarged section area and the enlarged section distribution along tunnel length direction.The calculation results show that the influence of the different enlarged section distributions along tunnel circumferential direction on pressure transients in the tunnel is basically consistent.There is an optimal enlarged section area for the minimum value of the pressure variation amplitude and the average pressure variation in the tunnel.The law of the pressure variation amplitude and the average pressure variation of the enlarged section distribution along tunnel length direction are obtained.展开更多
A proven beam-track contact model was used to analyze the track-structure interaction of CWR (continuously welded track) on bridge. Considering the impact of adjacent bridges, the tower-cable-track-beam-pier-pile fini...A proven beam-track contact model was used to analyze the track-structure interaction of CWR (continuously welded track) on bridge. Considering the impact of adjacent bridges, the tower-cable-track-beam-pier-pile finite element model of the cable-stayed bridge was established. Taking a bridge group including 40-32m simply-supported beam and (32+80+112)m single-tower cable-stayed bridge and 17-32m simply-supported beam on the Kunming-Shanghai high-speed railway as an example, the characteristics of CWR longitudinal force on the cable-stayed bridge were studied. It is shown that adjacent bridges must be considered in the calculation of the track expansion force and bending force on cable-stayed bridge. When the span amount of adjacent bridges is too numerous, it can be simplified as six spans; the fixed bearing of adjacent simply-supported beams should be placed on the side near the cable-stayed bridge; the track expansion device should be set at the bridge tower to reduce the track force near the bridge abutment.展开更多
The effects of the different landforms of the cutting leeward on the aerodynamic performance of high-speed trains were analyzed based on the three-dimensional, steady, and incompressible Navier-Stokes equation and k-e...The effects of the different landforms of the cutting leeward on the aerodynamic performance of high-speed trains were analyzed based on the three-dimensional, steady, and incompressible Navier-Stokes equation and k-e double-equation turbulent model. Results show that aerodynamic forces increase with the cutting leeward slope decreasing. The maximum adding value of lateral force, lift force, and overturning moment are 147%, 44.3%, and 107%, respectively, when the slope varies from 0.67 to -0.67, and the changes in the cutting leeward landform have more effects on the aerodynamic performance when the train is running in the line No. 2 than in the line No. 1. The aerodynamic forces, except the resistance force, sharply increase with the slope depth decreasing. By comparing the circumstance of the cutting depth H=-8 m with that of H=8 m, the resistance force, lateral force, lift force, and overturning moment increase by 26.0%, 251%, 67.3% and 177%, respectively. With the wind angle increasing, the resistance force is nonmonotonic, whereas other forces continuously rise. Under three special landforms, the changes in the law of aerodynamic forces with the wind angle are almost similar to one another.展开更多
Serviceability and running safety of the high-speed train on/through a bridge are of major concern in China.Due to the uncertainty chain of the train dynamic analysis in crosswinds originating mainly from the aerodyna...Serviceability and running safety of the high-speed train on/through a bridge are of major concern in China.Due to the uncertainty chain of the train dynamic analysis in crosswinds originating mainly from the aerodynamic assessment,this paper primarily reviews five meaningful progresses on the aerodynamics of the train-bridge system done by Wind Tunnel Laboratory of Central South University in the past several years.Firstly,the flow around the train and the uncertainty origin of the aerodynamic assessment are described from the fluid mechanism point of view.After a brief introduction of the current aerodynamic assessment methods with their strengths and weaknesses,a new-developed TRAIN-INFRASTRUCTURE rig with the maximum launch speed of 35 m/s is introduced.Then,several benchmark studies are presented,including the statistic results of the characterized geometry parameters of the currently utilized bridge-decks,the aerodynamics of the train,and the aerodynamics of the flat box/truss bridge-decks.Upon compared with the foregoing mentioned benchmarks,this paper highlights the aerodynamic interference of the train-bridge system associated with its physical natures.Finally,a porosity-and orientation-adjustable novel wind barrier with its effects on the aerodynamics of the train-bridge system is discussed.展开更多
Using three-dimensional, unsteady N-S equations and k-ε turbulence model, the effect of ambient wind on the pressure wave generated by a high-speed train entering a tunnel was studied via numerical simulation. Pressu...Using three-dimensional, unsteady N-S equations and k-ε turbulence model, the effect of ambient wind on the pressure wave generated by a high-speed train entering a tunnel was studied via numerical simulation. Pressure changes of the train surface and tunnel wall were obtained as well as the flow field around the train. Results show that when the train runs downwind, the pressure change is smaller than that generated when there is no wind. When the train runs upwind, the pressure change is larger. The pressure change is more sensitive in the upwind condition than in the downwind condition. Compared with no wind condition, when the wind velocity is 10 m/s and 30 m/s, the pressure amplitude on the train head is reduced by 2.8% and 10.5%, respectively. The wall pressure amplitude at 400 m away from the tunnel entrance is reduced by 2.4% and 13.5%, respectively. When the wind velocity is-10 m/s and-30 m/s, the pressure amplitude on the train head increases by 3.0% and 17.7%, respectively. The wall pressure amplitude at 400 m away from the tunnel entrance increases by 3.6% and 18.6%, respectively. The pressure waveform slightly changes under ambient wind due to the influence of ambient wind on the pressure wave propagation speed.展开更多
An investigation of the effect of simplifying bogie regions on the aerodynamic performance of a high-speed train was carried out by studying four train models,to explore possible ways to optimise the train underbody s...An investigation of the effect of simplifying bogie regions on the aerodynamic performance of a high-speed train was carried out by studying four train models,to explore possible ways to optimise the train underbody structure,improve the underbody aerodynamic performance,and reduce the aerodynamic drag.The shear stress transport(SST)k-ωturbulence model was used to study the airflow features of the high-speed train with different bogie regions at Re=2.25×10^(6).The calculated aerodynamic drag and surface pressure were compared with the experimental benchmark of wind tunnel tests.The results show that the SST k-ωmodel presents high accuracy in predicting the flow fields around the train,and the numerical results closely agree with the experimental data.Compared with the train with simplified bogies,the aerodynamic drag of the train with a smooth surface and the train with enclosed bogie cavities/inter-carriage gaps decreases by 38.2%and 30.3%,respectively,while it increases by 10.8%for the train with cavities but no bogies.Thus,enclosing bogie cavities shows a good capability of aerodynamic drag reduction for a new generation of highspeed trains.展开更多
This paper investigates the main scale analysis of the aerodynamic noise in the foremost bogie area by the large-eddy simulation(LES)and the Ffowcs Williams-Hawkings(FW-H)analogy.The mechanism of the aerodynamic noise...This paper investigates the main scale analysis of the aerodynamic noise in the foremost bogie area by the large-eddy simulation(LES)and the Ffowcs Williams-Hawkings(FW-H)analogy.The mechanism of the aerodynamic noise in this area has been excavated.The aerodynamic excitation results show that the bogie divides the bogie compartment into two cavities,each of which contains a large circulating flow and presents multi-peak characteristics in the frequency domain.The far-field noise results suggest that in the speed range of 200−350 km/h,the aerodynamic noise mechanism in the bogie area is the same.Cavity noise is the main noise mechanism in the foremost bogie area,and the bogie divides the bogie cabin into two cavities,thereby changing the aerodynamic noise in this area.展开更多
Based on the construction bridge of Xiamen-Shenzhen high-speed railway(9-32 m simply-supported beam + 6×32 m continuous beam),the pier-beam-track finite element model,where the continuous beam of the ballast trac...Based on the construction bridge of Xiamen-Shenzhen high-speed railway(9-32 m simply-supported beam + 6×32 m continuous beam),the pier-beam-track finite element model,where the continuous beam of the ballast track and simply-supported beam are combined with each other,was established.The laws of the track stress,the pier longitudinal stress and the beam-track relative displacement were analyzed.The results show that reducing the longitudinal resistance can effectively reduce the track stress and the pier stress of the continuous beam,and increase the beam-track relative displacement.Increasing the rigid pier stiffness of continuous beam can reduce the track braking stress,increase the pier longitudinal stress and reduce the beam-track relative displacement,Increasing the rigid pier stiffness of simply-supported beam can reduce the track braking stress,the rigid pier longitudinal stress and the beam-track relative displacement.展开更多
基金Project(2023YFB2604304)supported by the National Key R&D Program of ChinaProjects(52122810,51978586,51778542,U23A20666,52472458)supported by the National Natural Science Foundation of China+1 种基金Project(K2022G034)supported by the Technology Research and Development Program of China National Railway Group Co.Ltd.Projects(2020JDJQ0033,2023NSFSC0884)supported by Sichuan Province Science and Technology Support Program,China。
文摘The influence of ramps on the transient rolling contact characteristics and damage mechanisms of switch rails remains unclear,presenting substantial challenges to the safety of railway operations.To this end,this paper constructs a transient rolling contact finite element model of the wheel-rail in switch under different ramps using ANSYS/LSDYNA method,and analyzes the tribology and damage characteristics when the wheel passes through the switch at a uniform speed.Our research findings reveal that the vibration induced in the switch rail during the wheel load transfer process leads to a step-like increase in the contact force.Moreover,the interaction between the wheel and the rail primarily involves slip contact,which may significantly contribute to the formation of corrugations on the switch rail.Additionally,the presence of large ramps exacerbates switch rail wear and rolling contact fatigue,resulting in a notable 13.2%increase in switch rail damage under 40‰ramp conditions compared to flat(0‰ramp)conditions.Furthermore,the large ramps can alter the direction of crack propagation,ultimately causing surface spalling of the rail.Therefore,large ramps intensify the dynamic interactions during the wheel load transfer process,further aggravating the crack and spalling damage to the switch rails.
基金Project supported by the Haier GroupProject supported by the Eskisehir Osmangazi University,Türkiye。
文摘In this study,samples obtained from 1.3343 high-speed steel punches with TiN coatings were tested.The samples were subjected to heat treatment at different cryogenic temperatures(<196℃)and durations(12,24 and 36 h),followed by tempering at two different temperatures(200,500℃).For performance testing,a ball-on-disk wear test setup was utilized and a total of 6 groups of samples were examined.The effects of cryo-treatment and tempering on microstructure were revealed through microstructural analysis with scanning electron microscopy(SEM),X-ray(XRD diffraction),and Rietveld analysis.Additionally,the hardness of the punches was measured with microhardness measurements.The optimal wear resistance was observed in the 36 h deep cryo-treated and 200℃tempered samples.The characterization study indicates that by cryogenic treatment a significant portion of the retained austenite transformed into martensite and secondary carbides formed,resulting in improved wear resistance and a slight increase in hardness.
基金Projects(52302447,52388102,52372369)supported by the National Natural Science Foundation of China。
文摘Following the fundamental characteristics of the porosity windbreak,this study suggests a new numerical investigation method for the wind field of the windbreak based on the porous medium physical model.This method can transform the reasonable matching problem of the porosity and windproof performance of the windbreak into a study of the relationship between the resistance coefficient of the porous medium and the aerodynamic load of the train.This study examines the influence of the hole type on the wind field behind the porosity windbreak.Then,the relationship between the resistance coefficient of the porous medium,the porosity of the windbreak,and the aerodynamic loads of the train is investigated.The results show that the porous media physical model can be used instead of the windbreak geometry to study the windbreak-train aerodynamic performance,and the process of using this method is suggested.
基金Project(24A0006)supported by the Key Project of Scientific Research Fund of Hunan Provincial Department of Education,ChinaProject(2024JJ5430)supported by the Natural Science Foundation of Hunan Province,ChinaProjects(2024JK2045,2023RC3061)supported by the Science and Technology Innovation Program of Hunan Province,China。
文摘A high-speed train travelling from the open air into a narrow tunnel will cause the“sonic boom”at tunnel exit.When the maglev train’s speed reaches 600 km/h,the train-tunnel aerodynamic effect is intensified,so a new mitigation method is urgently expected to be explored.This study proposed a novel asymptotic linear method(ALM)for micro pressure wave(MPW)mitigation to achieve a constant gradient of initial c ompression waves(ICWs),via a study with various open ratios on hoods.The properties of ICWs and MPWs under various open ratios of hoods were analyzed.The results show that as the open ratio increases,the MPW amplitude at the tunnel exit initially decreases before rising.At the open ratio of 2.28%,the slope of the ICW curve is linearly coincident with a supposed straight line in the ALM,which further reduces the MPW amplitude by 26.9%at 20 m and 20.0%at 50 m from the exit,as compared to the unvented hood.Therefore,the proposed method effectively mitigates MPW and quickly determines the upper limit of alleviation for the MPW amplitude at a fixed train-tunnel operation condition.All achievements provide a ne w potential measure for the adaptive design of tunnel hoods.
基金the National Natural Science Foundation of China(Grant No.12102050)the Open Fund of State Key Laboratory of Explosion Science and Technology(Grant No.SKLEST-ZZ-21-18).
文摘The majority of the projectiles used in the hypersonic penetration study are solid flat-nosed cylindrical projectiles with a diameter of less than 20 mm.This study aims to fill the gap in the experimental and analytical study of the evolution of the nose shape of larger hollow projectiles under hypersonic penetration.In the hypersonic penetration test,eight ogive-nose AerMet100 steel projectiles with a diameter of 40 mm were launched to hit concrete targets with impact velocities that ranged from 1351 to 1877 m/s.Severe erosion of the projectiles was observed during high-speed penetration of heterogeneous targets,and apparent localized mushrooming occurred in the front nose of recovered projectiles.By examining the damage to projectiles,a linear relationship was found between the relative length reduction rate and the initial kinetic energy of projectiles in different penetration tests.Furthermore,microscopic analysis revealed the forming mechanism of the localized mushrooming phenomenon for eroding penetration,i.e.,material spall erosion abrasion mechanism,material flow and redistribution abrasion mechanism and localized radial upsetting deformation mechanism.Finally,a model of highspeed penetration that included erosion was established on the basis of a model of the evolution of the projectile nose that considers radial upsetting;the model was validated by test data from the literature and the present study.Depending upon the impact velocity,v0,the projectile nose may behave as undistorted,radially distorted or hemispherical.Due to the effects of abrasion of the projectile and enhancement of radial upsetting on the duration and amplitude of the secondary rising segment in the pulse shape of projectile deceleration,the predicted DOP had an upper limit.
基金Project(HNTY2022K03)supported by the Hunan Tieyuan Civil Engineering Testing Co.,Ltd.,ChinaProject(52478573)supported by the National Natural Science Foundation of China。
文摘The seismic damage to ancillary facilities on high-speed railway(HSR)bridges can affect the normal movement of trains.To propose the bridge deck acceleration response spectra of the typical HSR simply-supported girder bridge for simplifying the seismic responses analysis of the facilities on bridges,the finite element models of the HSR multi-span simply-supported girder bridges with CRTSII track were established,and the numerical model was validated by tests.Besides,the effects of the span number,peak ground acceleration(PGA),pier height on the seismic acceleration and response spectra of the bridge deck were investigated.Afterward,the bridge acceleration amplification factor curves and bridge deck response spectra with different PGAs and pier heights were obtained.The formula for bridge deck acceleration amplification factor,with a 95%guarantee rate,was fitted.Moreover,the finite element models of the overhead contact lines(OCL)mounted on rigid base and bridges were established to validate the fitted formula.The results indicated that the maximum seismic acceleration response is in the midspan of the beam.The proposed formula for the bridge deck acceleration response spectra can be used to analyze the earthquake response of the OCL and other ancillary facilities on HSR simply-supported girder bridges.The bridge deck acceleration response spectra are conservative in terms of structural safety and can significantly improving the analysis efficiency.
基金Project(2020YFA0710901)supported by the National Key Research and Development Program of ChinaProject(2023JJ30643)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(12372204)supported by the National Natural Science Foundation of ChinaProject(2022ZZTS0725)supported by the Self-exploration and Innovation Project for Postgraduates of Central South University,China。
文摘The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In this study,computational fluid dynamics(CFD)based on three-dimensional steady incompressible Reynolds-average Naiver-Stokes(RANS)equations and Realizable k-εturbulence model were utilized for numerical simulations.Inspired by the concept of streamlined design and the idea of bottom flow field control,this study iteratively designed the bogies in a streamlined shape and combined them with the bottom deflectors to investigate the joint drag reduction mechanism.Three models,i.e.,single-bogie model,simplified train model,and eight-car high-speed train model,were created and their aerodynamic characteristics were analyzed.The results show that the single-bogie model with streamlined design shows a noticeable drag reduction,whose power bogie and trailer bogie experience 13.92%and 7.63%drag reduction,respectively.The range of positive pressure area on the bogie is reduced.The aerodynamic drag can be further reduced to 15.01%by installing both the streamlined bogie and the deflector on the simplified train model.When the streamlined bogies and deflectors are used on the eight-car model together,the total drag reduction rate reaches 2.90%.Therefore,the proposed aerodynamic kit for the high-speed train bottom is capable to improve the flow structure around the bogie regions,reduce the bottom flow velocity,and narrow the scope of the train’s influence on the surrounding environment,achieving the appreciable reduction of aerodynamic drag.This paper can provide a new idea for the drag reduction of high-speed trains.
基金Projects(52022113,52278546)supported by the National Natural Science Foundation of ChinaProject(2020EEEVL0403)supported by the China Earthquake Administration。
文摘Sudden earthquakes pose a threat to the running safety of trains on high-speed railway bridges,and the stiffness of piers is one of the factors affecting the dynamic response of train-track-bridge system.In this paper,a experiment of a train running on a high-speed railway bridge is performed based on a dynamic experiment system,and the corresponding numerical model is established.The reliability of the numerical model is verified by experiments.Then,the experiment and numerical data are analyzed to reveal the pier height effects on the running safety of trains on bridges.The results show that when the pier height changes,the frequency of the bridge below the 30 m pier height changes greater;the increase of pier height causes the transverse fundamental frequency of the bridge close to that of the train,and the shaking angle and lateral displacement of the train are the largest for bridge with 50 m pier,which increases the risk of derailment;with the pier height increases from 8 m to 50 m,the derailment coefficient obtained by numerical simulations increases by 75% on average,and the spectral intensity obtained by experiments increases by 120% on average,two indicators exhibit logarithmic variation.
基金Project(2022YFB3803300)supported by the National Key Research and Development Program of ChinaProjects(U23A20138,52173192)supported by the National Natural Science Foundation of China+1 种基金Project(GZC20233148)supported by the Postdoctoral Fellowship Program of CPSF,ChinaProject(140050043)supported by the Central South University Postdoctoral Research Funding,China。
文摘Highly efficient organic solar cells(OSCs)are normally produced using the halogenated solvents chloroform or chlorobenzene,which present challenges for scalable manufacturing due to their toxicity,narrow processing window and low boiling point.Herein,we develop a novel high-speed doctor-blading technique that significantly reduces the required concentration,facilitating the use of eco-friendly,non-halogenated solvents as alternatives to chloroform or chlorobenzene.By utilizing two widely used high-boiling,non-halogenated green solvents-o-xylene(o-XY)and toluene(Tol)-in the fabrication of PM 6:L 8-BO,we achieve power conversion efficiencies(PCEs)of 18.20%and 17.36%,respectively.Additionally,a module fabricated with o-XY demonstrates a notable PCE of 16.07%.In-situ testing and morphological analysis reveal that the o-XY coating process extends the liquid-to-solid transition stage to 6 s,significantly longer than the 1.7 s observed with Tol processing.This prolonged transition phase is crucial for improving the crystallinity of the thin film,reducing defect-mediated recombination,and enhancing carrier mobility,which collectively contribute to superior PCEs.
文摘During high-speed flight,both thermal and mechani-cal loads can degrade the electrical performance of the antenna-radome system,which can subsequently affect the performance of the guidance system.This paper presents a method for evalu-ating the electrical performance of the radome when subjected to thermo-mechanical-electrical(TME)coupling.The method involves establishing a TME coupling model(TME-CM)based on the TME sharing mesh model(TME-SMM)generated by the tetrahedral mesh partitioning of the radome structure.The effects of dielectric temperature drift and structural deformation on the radome’s electrical performance are also considered.Firstly,the temperature field of the radome is obtained by tran-sient thermal analysis while the deformation field of the radome is obtained by static analysis.Subsequently,the dielectric varia-tion and structural deformation of the radome are accurately incorporated into the electrical simulation model based on the TME-SMM.The three-dimensional(3D)ray tracing method with the aperture integration technique is used to calculate the radome’s electrical performance.A representative example is provided to illustrate the superiority and necessity of the pro-posed method.This is achieved by calculating and analyzing the changes in the radome’s electrical performance over time dur-ing high-speed flight.
基金Project(2022YFC3004304)supported by the National Key Research and Development Program of ChinaProjects(52078487,U1934207,52178180)supported by the National Natural Science Foundation of China+2 种基金Project(2022TJ-Y10)supported by the Hunan Province Science and Technology Talent Lifting Project,ChinaProject(2023QYJC006)supported by the Frontier Cross Research Project of Central South University,ChinaProject(SKL-IoTSC(UM)-2024-2026/ORP/GA08/2023)supported by the Science and Technology Development Fund and the State Key Laboratory of Internet of Things for Smart City(University of Macao),China。
文摘In the realm of high-speed railway bridge engineering,managing the intricacies of the track-bridge system model(TBSM)during seismic events remains a formidable challenge.This study pioneers an innovative approach by presenting a simplified bridge model(SBM)optimized for both computational efficiency and precise representation,a seminal contribution to the engineering design landscape.Central to this innovation is a novel model-updating methodology that synergistically melds artificial neural networks with an augmented particle swarm optimization.The neural networks adeptly map update parameters to seismic responses,while enhancements to the particle swarm algorithm’s inertial and learning weights lead to superior SBM parameter updates.Verification via a 4-span high-speed railway bridge revealed that the optimized SBM and TBSM exhibit a highly consistent structural natural period and seismic response,with errors controlled within 7%.Additionally,the computational efficiency improved by over 100%.Leveraging the peak displacement and shear force residuals from the seismic TBSM and SBM as optimization objectives,SBM parameters are adeptly revised.Furthermore,the incorporation of elastoplastic springs at the beam ends of the simplified model effectively captures the additional mass,stiffness,and constraint effects exerted by the track system on the bridge structure.
基金Projects(2018YFB1201801-4,2018YFB1201804-2)supported by National Key R&D Program of China。
文摘This study investigates the influence of different pantograph parameters and train length on the aerodynamic drag of high-speed train by the delayed detached eddy simulation(DDES) method. The train geometry considered is the high-speed train with pantographs, and the different versions have 3, 5, 8, 10, 12, 16 and 17 cars. The numerical results are verified by the wind tunnel test with 3.6% difference. The influences of the number of cars and the position, quantity and configuration of pantographs on flow field around high-speed train and wake vortices are analyzed. The aerodynamic drag of middle cars gradually decreases along the flow direction. The aerodynamic drag of pantographs decreases with its backward shift, and that of the first pantograph decreases significantly. As the number of pantographs increases, its effect on the aerodynamic drag decrease of rear cars is more significant. The engineering application equation for the aerodynamic drag of high-speed train with pantographs is proposed. For the 10-car and 17-car train, the differences of total aerodynamic drag between the equation and the simulation results are 1.2% and 0.4%, respectively. The equation generalized in this study could well guide the design phase of high-speed train.
基金Project (2016YFB1200602-11) supported by National Key R&D Plan of China
文摘The influence of enlarged section parameters on pressure transients of high-speed train passing through a tunnel was investigated by numerical simulation.The calculation results obtained by the structured and unstructured grid and the experimental results of smooth wall tunnel were verified.Numerical simulation studies were conducted on three tunnel enlarged section parameters,the enlarged section distribution along circumferential direction,the enlarged section area and the enlarged section distribution along tunnel length direction.The calculation results show that the influence of the different enlarged section distributions along tunnel circumferential direction on pressure transients in the tunnel is basically consistent.There is an optimal enlarged section area for the minimum value of the pressure variation amplitude and the average pressure variation in the tunnel.The law of the pressure variation amplitude and the average pressure variation of the enlarged section distribution along tunnel length direction are obtained.
基金Project(51178469) supported by the National Natural Science Foundation of China
文摘A proven beam-track contact model was used to analyze the track-structure interaction of CWR (continuously welded track) on bridge. Considering the impact of adjacent bridges, the tower-cable-track-beam-pier-pile finite element model of the cable-stayed bridge was established. Taking a bridge group including 40-32m simply-supported beam and (32+80+112)m single-tower cable-stayed bridge and 17-32m simply-supported beam on the Kunming-Shanghai high-speed railway as an example, the characteristics of CWR longitudinal force on the cable-stayed bridge were studied. It is shown that adjacent bridges must be considered in the calculation of the track expansion force and bending force on cable-stayed bridge. When the span amount of adjacent bridges is too numerous, it can be simplified as six spans; the fixed bearing of adjacent simply-supported beams should be placed on the side near the cable-stayed bridge; the track expansion device should be set at the bridge tower to reduce the track force near the bridge abutment.
基金Project(U1134203) supported by the National Natural Science Foundation of ChinaProject(132014) supported by Fok Ying Tong Education Foundation,ChinaProject(2011G006) supported by the Technological Research and Development Program of the Ministry of Railways,China
文摘The effects of the different landforms of the cutting leeward on the aerodynamic performance of high-speed trains were analyzed based on the three-dimensional, steady, and incompressible Navier-Stokes equation and k-e double-equation turbulent model. Results show that aerodynamic forces increase with the cutting leeward slope decreasing. The maximum adding value of lateral force, lift force, and overturning moment are 147%, 44.3%, and 107%, respectively, when the slope varies from 0.67 to -0.67, and the changes in the cutting leeward landform have more effects on the aerodynamic performance when the train is running in the line No. 2 than in the line No. 1. The aerodynamic forces, except the resistance force, sharply increase with the slope depth decreasing. By comparing the circumstance of the cutting depth H=-8 m with that of H=8 m, the resistance force, lateral force, lift force, and overturning moment increase by 26.0%, 251%, 67.3% and 177%, respectively. With the wind angle increasing, the resistance force is nonmonotonic, whereas other forces continuously rise. Under three special landforms, the changes in the law of aerodynamic forces with the wind angle are almost similar to one another.
基金Project(2017YFB1201204)supported by National Key R&D Program of ChinaProjects(51925808,U1934209)supported by the National Natural Science Foundation of China。
文摘Serviceability and running safety of the high-speed train on/through a bridge are of major concern in China.Due to the uncertainty chain of the train dynamic analysis in crosswinds originating mainly from the aerodynamic assessment,this paper primarily reviews five meaningful progresses on the aerodynamics of the train-bridge system done by Wind Tunnel Laboratory of Central South University in the past several years.Firstly,the flow around the train and the uncertainty origin of the aerodynamic assessment are described from the fluid mechanism point of view.After a brief introduction of the current aerodynamic assessment methods with their strengths and weaknesses,a new-developed TRAIN-INFRASTRUCTURE rig with the maximum launch speed of 35 m/s is introduced.Then,several benchmark studies are presented,including the statistic results of the characterized geometry parameters of the currently utilized bridge-decks,the aerodynamics of the train,and the aerodynamics of the flat box/truss bridge-decks.Upon compared with the foregoing mentioned benchmarks,this paper highlights the aerodynamic interference of the train-bridge system associated with its physical natures.Finally,a porosity-and orientation-adjustable novel wind barrier with its effects on the aerodynamics of the train-bridge system is discussed.
基金Projects(U1134203,51575538)supported by the National Natural Science Foundation of ChinaProject(2014T001-A)supported by the Technological Research and Development Program of China Railways CorporationProject(2015ZZTS210)supported by the Fundamental Research Funds for the Central South Universities of China
文摘Using three-dimensional, unsteady N-S equations and k-ε turbulence model, the effect of ambient wind on the pressure wave generated by a high-speed train entering a tunnel was studied via numerical simulation. Pressure changes of the train surface and tunnel wall were obtained as well as the flow field around the train. Results show that when the train runs downwind, the pressure change is smaller than that generated when there is no wind. When the train runs upwind, the pressure change is larger. The pressure change is more sensitive in the upwind condition than in the downwind condition. Compared with no wind condition, when the wind velocity is 10 m/s and 30 m/s, the pressure amplitude on the train head is reduced by 2.8% and 10.5%, respectively. The wall pressure amplitude at 400 m away from the tunnel entrance is reduced by 2.4% and 13.5%, respectively. When the wind velocity is-10 m/s and-30 m/s, the pressure amplitude on the train head increases by 3.0% and 17.7%, respectively. The wall pressure amplitude at 400 m away from the tunnel entrance increases by 3.6% and 18.6%, respectively. The pressure waveform slightly changes under ambient wind due to the influence of ambient wind on the pressure wave propagation speed.
基金Project(2020YFF0304103-03) supported by the National Key Research and Development Program of ChinaProject(2020JJ4737) supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project (202045014) supported by the Central University Financial Funds,ChinaProject(P2019J023) supported by the Science and Technology Research Program of China National Railway Group Co.,Ltd。
文摘An investigation of the effect of simplifying bogie regions on the aerodynamic performance of a high-speed train was carried out by studying four train models,to explore possible ways to optimise the train underbody structure,improve the underbody aerodynamic performance,and reduce the aerodynamic drag.The shear stress transport(SST)k-ωturbulence model was used to study the airflow features of the high-speed train with different bogie regions at Re=2.25×10^(6).The calculated aerodynamic drag and surface pressure were compared with the experimental benchmark of wind tunnel tests.The results show that the SST k-ωmodel presents high accuracy in predicting the flow fields around the train,and the numerical results closely agree with the experimental data.Compared with the train with simplified bogies,the aerodynamic drag of the train with a smooth surface and the train with enclosed bogie cavities/inter-carriage gaps decreases by 38.2%and 30.3%,respectively,while it increases by 10.8%for the train with cavities but no bogies.Thus,enclosing bogie cavities shows a good capability of aerodynamic drag reduction for a new generation of highspeed trains.
基金Project(2017YFB1201103)supported by the National Key Research and Development Plan of ChinaProject(2019zzts540)supported by the Graduate Student Independent Innovation Project of Central South University,China。
文摘This paper investigates the main scale analysis of the aerodynamic noise in the foremost bogie area by the large-eddy simulation(LES)and the Ffowcs Williams-Hawkings(FW-H)analogy.The mechanism of the aerodynamic noise in this area has been excavated.The aerodynamic excitation results show that the bogie divides the bogie compartment into two cavities,each of which contains a large circulating flow and presents multi-peak characteristics in the frequency domain.The far-field noise results suggest that in the speed range of 200−350 km/h,the aerodynamic noise mechanism in the bogie area is the same.Cavity noise is the main noise mechanism in the foremost bogie area,and the bogie divides the bogie cabin into two cavities,thereby changing the aerodynamic noise in this area.
基金Project(50678176) supported by the National Natural Science Foundation of China
文摘Based on the construction bridge of Xiamen-Shenzhen high-speed railway(9-32 m simply-supported beam + 6×32 m continuous beam),the pier-beam-track finite element model,where the continuous beam of the ballast track and simply-supported beam are combined with each other,was established.The laws of the track stress,the pier longitudinal stress and the beam-track relative displacement were analyzed.The results show that reducing the longitudinal resistance can effectively reduce the track stress and the pier stress of the continuous beam,and increase the beam-track relative displacement.Increasing the rigid pier stiffness of continuous beam can reduce the track braking stress,increase the pier longitudinal stress and reduce the beam-track relative displacement,Increasing the rigid pier stiffness of simply-supported beam can reduce the track braking stress,the rigid pier longitudinal stress and the beam-track relative displacement.
