Prediction of high-speed train induced ground vibration based on train-track-ground system model

The development of analysis on train-induced ground vibration is briefly summarized. A train-track- ground integrated dynamic model is introduced in the paper to predict the ground vibration induced by high-speed trains. Representative dynamic responses of the train-track-ground system predicted by the model are presented. Some major results measured from two field tests on the ground vibration induced by two high-speed trains are reported. Numerical prediction with the proposed train-track-ground model is validated by the high-speed train running experiments. Research results show that the wheel/rail dynamic interaction caused by track irregularities has a significant influence on the ground acceleration and little influence on the ground displacement. The main frequencies of the ground vibration induced by high-speed trains are usually below 80 Hz. Compared with the ballasted track, the ballastless track structure can produce much larger train-induced ground vibration at frequencies above 40 Hz. The vertical ground vibration is much larger than the lateral and longitudinal components.

An improved algorithm for fluid-structure interaction of high-speed trains under crosswind

Based on the train-track coupling dynamics and high-speed train aerodynamics, this paper deals with an improved algorithm for fluid-structure interaction of high-speed trains. In the algorithm, the data communication between fluid solver and structure solver is avoided by inserting the program of train-track coupling dynamics into fluid dynamics program, and the relaxation factor concerning the load boundary of the fluid-structure interface is introduced to improve the fluctuation and convergence of aerodynamic forces. With this method, the fluid-structure dynamics of a highspeed train are simulated under the condition that the velocity of crosswind is 13.8 m/s and the train speed is 350 km/h. When the relaxation factor equals 0.5, the fluctuation of aerodynamic forces is lower and its convergence is faster than in other cases. The side force and lateral displacement of the head train are compared between off-line simulation and co-simulation. Simulation results show that the fluid-structure interaction has a significant influence on the aerodynam- ics and attitude of the head train under crosswind conditions. In addition, the security indexes of the head train worsen after the fluid-structure interaction calculation. Therefore, the fluid-structure interaction calculation is necessary for high-speed trains.

Analysis of vibration reduction characteristics and applicability of steel-spring floating-slab track

A coupled dynamics computation model for metro vehicles, along with a steel-spring floating-slab track, is developed based on the theory of vehicle-track coupled dynamics. Using the developed model, the influences of the thickness, length and mass of floating-slab, spring rate and its arrangement space, running speed, etc. on the time and frequency domain characteristics of steel-spring fulcrum force are analyzed. The applicability of steel-spring floatingslab track is discussed through two integrated example cases of metro and buildings possessing distinct natural vibra- tion characteristics. It is concluded that, it is quite significant, in the optimization modular design of the parameters of steel-spring floating-slab track, to take the matching relationship of both the amplitude-frequency characteristics of steel-spring fulcrum force and natural vibration characteristics of integrated structures into comprehensive consideration. In this way the expensive steel-spring floating-slab track can be economically and efficiently utilized according to the site condition, and at the same time, the economic losses and bad social impact resulted from the resonance during usage of steel-spring floating-slab track can be avoided.

Friction and wear of 7075 aluminum alloy induced by torsional fretting

The torsional fretting wear tests of 7075 aluminum alloy flat against 52100 steel ball in dry condition were carried out on a new high-precision torsional fretting-wear tester.The kinetics behaviors and damage mechanism of 7075 aluminum alloy under different angular displacement amplitudes were investigated in detail.The results show that the torsional fretting running behaviors of 7075 aluminum alloy can be defined by three fretting regimes(i.e.partial slip regime(PSR),mixed fretting regime(MFR) and slip regime(SR)) with the increase of angular displacement amplitudes.In PSR,the damage occurs at the lateral portion of the contact zone with a slight annular shape.However,in MFR and SR,more severe damages are observed and the debris layer covers the wear scars.Friction torque and dissipation energy which are strongly dependent upon the imposed angular displacement amplitudes and presented in three stages were discussed in detail.The mechanisms of torsional fretting wear of aluminum alloy are mainly oxidative wear,abrasive wear and delamination in the three fretting regimes.In addition,the oxidative debris plays an important role during the torsional fretting wear processes.

Impact Fretting Wear Behavior of Alloy 690 Tubes in Dry and Deionized Water Conditions

The impact fretting wear has largely occurred at nuclear power device induced by the flow-induced vibra- tion, and it will take potential hazards to the service of the equipment. However, the present study focuses on the tangential fretting wear of alloy 690 tubes. Research on impact fretting wear of alloy 690 tubes is limited and the related research is imminent. Therefore, impact fretting wear behavior of alloy 690 tubes against 304 stainless steels is investigated. Deionized water is used to simulate the flow environment of the equipment, and the dry envi- ronment is used for comparison. Varied analytical tech- niques are employed to characterize the wear and tribochemical behavior during impact fretting wear. Char- acterization results indicate that cracks occur at high impact load in both water and dry equipment; however, the water as a medium can significantly delay the cracking time. The crack propagation behavior shows a jagged shape in the water, but crack extended disorderly in dry equip- ment because the water changed the stress distribution and retarded the friction heat during the wear process. The SEM and XPS analysis shows that the main failure mechanisms of the tube under impact fretting are fatiguewear and friction oxidation. The effect of medium（water） on fretting wear is revealed, which plays a potential and promising role in the service of nuclear power device and other flow equipments.

RESEARCH AND DEVELOPMENT OF VIRTUAL PROTOTYPE OF RUNNING GEARS FOR RAILWAY VEHICLE

Virtual prototype is an important idea to resolve design problems of railway vehicle. A different development method, which is based on national product and autonomous development, and would like to reflect the specialty of railway vehicle development in China, is presented. According to the developing process of railway vehicle, the research contents and developing method are pointed out. The integration between CAD and performance analysis software on dynamics and strength is mainly considered. In CAD environment, the properties for dynamics computing are extracted directly from the model and exported with model. This method can avoid data losing caused by model rebuilding in CAE software, and increase the direct dependence of product CAD. Then the vehicle model with properties will be used for real-time dynamics and kinematics analysis and simulation. Therefore, the strength of the parts can be analyzed. The results of dynamics and strength analysis will be fed back to optimize the design model. All operations are dispatched by a control platform, and all data are managed according to the principle of PDM. Testing results show this method is correct.

Pantograph and catenary system with double pantographs for high-speed trains at 350 km/h or higher

The paper is aimed at developing an optimized design of the pantograph and catenary system with double pantographs at a speed of 350 km/h for the Wuhan-Guangzhou high-speed railway. First, the pantograph and catenary system for the Beijing-Tianjin high-speed railway was analyzed to verify whether its design objective could be fulfilled. It shows that the system is not able to satisfy the requirement of a sustainable running speed of 350 km/h. Then a new scheme for the pantograph and catenary system is proposed through optimization and renovation of the structure and parameters of the pantograph and catenary system, including the suspension type of the catenary, tension of the contact wire, and space between two pantographs. Finally, the dynamic performance of the new system was verified by simulation and line testing. The results show that the new scheme of the pantograph and catenary system for the Wuhan- Guangzhou high-speed railway is acceptable, in which the steady contact between the rear pantograph and the catenary at the space of 200 m can be maintained to ensure the current-collection quality. A current collection with double pantographs at a speed of 350 km/h or higher can be achieved.

RESEARCH PROGRESS ON STRUCTURAL FATIGUE RELIABILITY DESIGN AND ANALYSIS METHODS OF CHINESE RAILWAY VEHICLES

A state-of-art review is given to the new advances on fatigue reliability design and analysis methods of Chinese railway vehicle＇s structures. First, the structures are subject to a complicated random fatigue stressing history and this history should be determined by combining dynamic simulation and on-line inspection. Second, the random fatigue constitutions belong to an intrinsic fatigue phenomenon and a probabilistic model is developed to well describe them with two measurements of survival probability and confidence, similar model is also presented for the random stress-life rela- tions and extrapolated appropriately into Song fatigue life regime. Third, concept of the fatigue limit should be understood as the fatigue strength at a given fatigue life and a so-called local Basquin model method is proposed for measuring the random strengths. In addition, drawing and application methods of the Goodman-Smith diagram for integrally characterizing the random fatigue strengths are established in terms of ten kilometers. Fourth, a reliability stress-based method is constructed with a consideration of the random constitutive relations. These new advances form a new frame work for railway fatigue reliability design and analysis.

Dynamic behavior of frozen soil under uniaxial strain and stress conditions

The split Hopkinson pressure bar （SHPB） method is used to investigate the dynamic behavior of the artificial frozen soil under the nearly uniaxial strain and uniaxial stress conditions. The tests are conducted at the temperatures of -3 ℃, -8 ℃, -13℃, -17℃, -23℃, and -28℃ and with the strain rates from 900 s^-1 to 1500 s^-1. The nearly uniaxial stress-strain curves exhibit an elastic-plastic behavior, whereas the uniaxial stress-strain curves show a brittle behavior. The compressive strength of the frozen soil exhibits the positive strain rate and negative temperature sensitivity, and the final strain of the frozen soil shows the positive strain under the nearly uniaxial strain is greater rate sensitivity. The strength of the frozen soil than that under the uniaxial stress. After the negative confinement tests, the specimens are compressed, and the visible cracks are not observed. However, the specimens are catastrophically damaged after the uniaxial SHPB tests. A phenomenological model with the thermal sensitivity is established to describe the dynamic behavior of the confined frozen soil.

Fretting Wear Behavior of Medium Carbon Steel Modified by Low Temperature Gas Multi-component Thermo-chemical Treatment

The introduction of surface engineering is expected to be an effective strategy against fretting damage. A large number of studies show that the low gas multi-component （such as carbon, nitrogen, sulphur and oxygen, etc） thermo-chemical treatment（LTGMTT） can overcome the brittleness of nitriding process, and upgrade the surface hardness and improve the wear resistance and fatigue properties of the work-pieces significantly. However, there are few reports on the anti-fretting properties of the LTGMTT modified layer up to now, which limits the applications of fretting. So this paper discusses the fretting wear behavior of modified layer on the surface of LZ50 （0.48%C） steel prepared by low temperature gas multi-component thermo-chemical treatment （LTGMTT） technology. The fretting wear tests of the modified layer flat specimens and its substrate （LZ50 steel） against 52100 steel balls with diameter of 40 mm are carried out under normal load of 150 N and displacement amplitudes varied from 2 μm to 40 μm. Characterization of the modified layer and dynamic analyses in combination with microscopic examinations were performed through the means of scanning electron microscope（SEM）, optical microscope（OM）, X-ray diffraction（XRD） and surface profilometer. The experimental results showed that the modified layer with a total thickness of 60 μm was consisted of three parts, i.e., loose layer, compound layer and diffusion layer. Compared with the substrate, the range of the mixed fretting regime（MFR） of the LTGMTT modified layer diminished, and the slip regime（SR） of the modified layer shifted to the direction of smaller displacement amplitude. The coefficient of friction（COF） of the modified layer was lower than that of the substrate in the initial stage. For the modified layer, the damage in partial slip regime（PSR） was very slight. The fretting wear mechanism of the modified layer both in MFR and SR was abrasive wear and delamination. The modified layer presented better wear resistance than the substrate in PSR and MFR; however, in SR, the wear resistance of the modified layer decreased with the increase of the displacement amplitudes. The experimental results can provide some experimental bases for promoting industrial application of LTGMTT modified layer in anti-fretting wear.

Progress in high-speed train technology around the world

This is a review of high-speed train development in the sense of technology advances all over the world. Three generations of high-speed trains are classified according to their technical characteristics and maximum operating speed. Emphasis is given to the newly developed high-speed train in China, CRH380. The theoretical foundations and future development of CRH380 are briefly discussed.

Fretting wear of micro-arc oxidation coating prepared on Ti6Al4V alloy

Micro-arc oxidation(MAO)coating was prepared on Ti6Al4V alloy surface and its characterizations were detected by Vickers hardness tester,profilometer,scanning electric microscope(SEM),energy dispersive X-ray spectrometer(EDX)and X-ray diffractometer(XRD).Fretting wear behaviors of the coating and its substrate were comparatively tested without lubrication under varied displacement amplitudes(D)in a range of 3-40μm,constant normal load(Fn)of 300 N and frequency of 5 Hz.The results showed that the MAO coating,presenting rough and porous surface and high hardness,mainly consisted of rutile and anatase TiO2 phases.Compared with the substrate,the MAO coating could shift the mixed fretting regime(MFR)and slip regime(SR)to a direction of smaller displacement amplitude.In the partial slip regime(PSR),lower friction coefficients and slight damage appeared due to the coordination of elastic deformation of contact zones.In the MFR,the friction coefficient of the coating was lower than that of the substrate as a result of the prevention of plastic deformation by the hard ceramic surface.With the increase of the displacement amplitude,the degradation of the MAO coating and the substrate increased extremely.The fretting wear mechanisms of the coating were abrasive wear and delamination with some material transfer of specimen.In addition,the coating presented a better property for alleviating fretting wear.

A cellular automata model of traffic flow with variable probability of randomization

Research on the stochastic behavior of traffic flow is important to understand the intrinsic evolution rules of a traffic system. By introducing an interactional potential of vehicles into the randomization step, an improved cellular automata traffic flow model with variable probability of randomization is proposed in this paper. In the proposed model, the driver is affected by the interactional potential of vehicles before him, and his decision-making process is related to the interactional potential. Compared with the traditional cellular automata model, the modeling is more suitable for the driver＇s random decision-making process based on the vehicle and traffic situations in front of him in actual traffic. From the improved model, the fundamental diagram （flow^tensity relationship） is obtained, and the detailed high-density traffic phenomenon is reproduced through numerical simulation.

Influence of blasting on the properties of weak intercalation of a layered rock slope

A precondition for correctly analyzing the stability of a slope and designing its bracing structure is to study and determine the influence of excavation blasting on the properties of weak intercalation in the layered rock slope. On the basis of in-situ stratification-cracking blasting tests, the properties of weak intercalation were investigated using the LS-DYNA3D program. The displacement distribution and compactness of weak intercalation at different positions away from the charge center and their various laws are discussed. The critical displacement of stratification-cracking （0.1 mm） was obtained, and an approximate expression of compactness were deduced. Furthermore, through the simulation of a layered rock blasting under the same geological conditions, the stratification-cracking effect of deep-hole blasting on the properties of weak intercalation was compared with that of short-hole blasting, and the influencing differences, in addition to their causes, were analyzed. The results indicated that the blasting cavity of weak intercalation in short-hole blasting with a radius of 40 mm was nearly a circle, whose radius was about 28.7 cm; whereas in deep-hole blasting with a radius of 150 mm, the shape of the blasting cavity was different from that in short-hole blasting, the radius of the cavity behind the charge （89.1 cm） was further smaller than those of the other three （138.7 cm）, and there were sharp crinkles on the surface of weak intercalation. When the distance from the charge center （DCC） was less than 40 and 150 cm in short-hole and deep-hole blasting, respectively, the displacement of weak intercalation was reduced remarkably with the increase in DCC.

Stabilizing Mechanism and Running Behavior of Couplers on Heavy Haul Trains

Published studies in regard to coupler systems have been mainly focused on the manufacturing process or coupler strength issues. With the ever increasing of tonnage and length of heavy haul trains, lateral in-train forces generated by longitudinal in-train forces and coupler rotations have become a more and more significant safety issue for heavy haul train operations. Derailments caused by excessive lateral in-train forces are frequently reported. This article studies two typical coupler systems used on heavy haul locomotives. Their structures and stabilizing mechanism are analyzed before the corresponding models are developed. Coupler systems models are featured by two distinct stabilizing mechanism models and draft gear models with hysteresis considered. A model set which consists of four locomotives and three coupler systems is developed to study the rotational behavior of different coupler systems and their implications for locomotive dynamics. Simulated results indicate that when the locomotives are equipped with the type B coupler system, locomotives can meet the dynamics standard on tangent tracks; while the dynamics performance on curved tracks is very poor. The maximum longitudinal in-train force for locomotives equipped with the type B coupler system is 2000 kN. Simulations revealed a distinct trend for the type A coupler system. Locomotive dynamics are poorer for the type A case when locomotives are running on tangent tracks, while the dynamics are better for the type A case when locomotives are running on curved tracks. Theoretical studies and simulations carried out in this article suggest that a combination of the two types of stabilizing mechanism can result in a good design which can significantly decrease the relevant derailments.

Aerodynamic performances and vehicle dynamic response of high-speed trains passing each other

Based on the aerodynamics and vehicle dynamics, the aerodynamic performances and vehicle dynamic characteristics of two high-speed trains passing each other on the ground, embankment and bridge are studied. Firstly, a train aerodynamic model and a vehicle dynamic model are established. Through the simulation of the two models, the pressure waves, aerodynamic forces, and vehicle dynamic responses are obtained. Then, the pressure waves and aero- dynamic forces on different foundations are compared. The results show that the variation trends of pressure wave and aerodynamic forces of trains passing each other on different foundations are almost similar. The peak-to-peak differ- ences in pressure wave and aerodynamic force are below 4% and 3% in three cases in open air. Besides, the differences of security indexes, including coefficient of derailment, wheel unloading rate, the wheelset lateral force, and the wheel- rail vertical force, are below 2% among the three cases; the differences of comfort indexes, including the lateral acceleration and the vertical acceleration, are also below 2%. It is concluded that the dynamic performances of trains pass- ing each other are influenced little by different foundations in open air.

Lateral Stability Analysis of Heavy-Haul Vehicle on Curved Track Based on Wheel/Rail Coupled Dynamics

Being viewed from the standpoint of whole system, the hunting stability of a heavy-haul railway vehicle on a curved track is investigated in this paper. First, a model to simulate dynamic performance of the heavy-haul vehicle on the elastic track is developed. Secondly, the reason of the hunting motion is analyzed, and a bifurcation diagram for the vehicle on the curved track is put forward to simulate the nonlinear critical speed. Results show that the hunting motion of the heavy-haul vehicle will appear due to the larger conicity, the initial lateral shift and the wheelset angle of attack. With the hunting motion appearing, the lateral shift and force of the wheelset are changed sharply and periodically with a wave of circa 3.6 m. There is obvious difference in the bifurcation diagram between on a curved track and on a tangent track. Relative to the centerline of the track, each vehicle body on the curved track has two stable cycles. As for the curved track with a radius of 600 m and a superelevation of 55 mm, the nonlinear critical speed of the heavy-haul vehicle is 76.4 km/h.

Simulation of unsteady aerodynamic loads on high-speed trains in fluctuating crosswinds

To study the unsteady aerodynamic loads of high-speed trains in fluctuating crosswinds, the fluctuating winds of a moving point shifting with high-speed trains are calculated in this paper based on Cooper theory and harmonic superposition method. The computational fluid dynamics method is used to obtain the aerodynamic load coefficients at different mean yaw angles, and the aero- dynamic admittance function is introduced to calculate unsteady aerodynamic loads of high-speed trains in fluctuating winds. Using this method, the standard deviation and maximum value of the aerodynamic force （moment） are simulated. The results show that when the train speed is fixed, the varying mean wind speeds have large impact on the fluctuating value of the wind speeds and aerodynamic loads; in contrast, when the wind speed is fixed, the varying train speeds have little impact on the fluctuating value of the wind speeds or aerodynamic loads. The ratio of standard deviation to 0.SpKU2, or maximum value to 0.5pKU2, can be expressed as the function of mean yaw angle. The peak factors of the side force and roll moment are the same （ - 3.28）, the peak factor of the lift force is - 3.33, and the peak factors of the yaw moment and pitch moment are also the same （- 3.77）.

Influence of dynamic unbalance of wheelsets on the dynamic performance of high-speed cars

With further increasing in running speed of newer high-speed EMUs（electric multiple units）,higher demand for wheelset dynamic balance is required.In order to study the influence of the dynamic unbalance of wheelset on the stability,ride quality,and curving performance for a high-speed car,a detailed dynamic model of a high-speed EMU car is established using the software SIMPACK.The analysis results indicate that the dynamic unbalance of the wheelset significantly influences the dynamic performance of the high-speed car.The increase in dynamic unbalance of the wheelset will decrease the hunting critical speed,worsen the vertical ride quality,and increase the wheelset lateral force,derailment coefficient,and wheel unloading ratio.Therefore,in order to improve the stability,ride quality,and running safety of high-speed car,the values of dynamic unbalance of wheelset should be strictly controlled in manufacturing,and periodically monitored in operation.

Assessment of the curving performance of heavy haul trains under braking conditions

To study the curving performance of trains, 1D and 3D dynamic models of trains were built using nu- merical methods. The 1D model was composed of 210 simple wagons, each allowed only longitudinal motion; whereas the 3D model included three complicated wagons for which longitudinal, lateral, and vertical degrees of freedom were considered. Combined with the calculated results from the 1D model under braking conditions, the behavior of draft gears and brake shoes were added to the 3D model. The assessment of the curving performance of trains was focused on making comparisons between idling and braking conditions. The results indicated the following： when a train brakes on a curved track, the wheel-rail lateral force and derailment factor are greater than under idling conditions. Because the yawing movement of the wheelset is limited by brake shoes, the zone of wheel contact along the wheel tread is wider than under idling conditions. Furthermore, as the curvature becomes tighter, the traction ratio shows a nonlinear increasing trend, whether under idling or braking conditions. By increasing the brake shoe pressure, train steering becomes more difficult.