Parametric investigation of railway fastenings into the formation and mitigation of short pitch corrugation

Short pitch corrugation has been a problem for railways worldwide over one century.In this paper,a parametric investigation of fastenings is conducted to understand the corrugation formation mechanism and gain insights into corrugation mitigation.A three-dimensional finite element vehicle-track dynamic interaction model is employed,which considers the coupling between the structural dynamics and the contact mechanics,while the damage mechanism is assumed to be differential wear.Various fastening models with different configurations,boundary conditions,and parameters of stiffness and damping are built up and analysed.These models may represent different service stages of fastenings in the field.Besides,the effect of train speeds on corrugation features is studied.The results indicate:(1)Fastening parameters and modelling play an important role in corrugation formation.(2)The fastening longitudinal constraint to the rail is the major factor that determines the corrugation formation.The fastening vertical and lateral constraints influence corrugation features in terms of spatial distribution and wavelength components.(3)The strengthening of fastening constraints in the longitudinal dimension helps to mitigate corrugation.Meanwhile,the inner fastening constraint in the lateral direction is necessary for corrugation alleviation.(4)The increase in fastening longitudinal stiffness and damping can reduce the vibration amplitudes of longitudinal compression modes and thus reduce the track corrugation propensity.The simulation in this work can well explain the field corrugation in terms of the occurrence possibility and major wavelength components.It can also explain the field data with respect to the small variation between the corrugation wavelength and train speed,which is caused by frequency selection and jump between rail longitudinal compression modes.

Multi-Body Dynamics Modeling of Heavy Goods Vehicle-Rail Interaction

Based on the principle of vehicle-track coupling dynamics, SIMPACK multi-body dynamics software is used to establish a C80 wagon line-coupled multi-body dynamics model with 73 degrees of freedom. And the reasonableness of the line-coupled dynamics model is verified by using the maximum residual acceleration, the nonlinear critical speed of the wagon. The experimental results show that the established vehicle line coupling dynamics model meets the requirements of vehicle line coupling dynamics modeling.

Influence of the Randomness of Longitudinal Resistance of Ballast Bed on Track-Bridge Interaction

To get the influence of the randomness of longitudinal resistance of ballast bed (LRBB) on track-bridge interaction, the statistical law of LRBB was studied with existing test data and the Shapiro-Wilk test. Based on the principle of track-bridge interaction, a rail-sleeper-bridge-pier integrated simulation model that could consider the randomness of LRBB was established. Taking a continuous beam bridge for the heavy-haul railway as an example, the effect of the randomness of LRBB on the mechanical behavior of continuous welded rail (CWR) on bridges under typical conditions was carefully examined with a random sampling method and the simulation model. The results show that the LRBB corresponding sleeper displacement of 2 mm obeys a normal distribution. When the randomness of LRBB is considered, the amplitudes of rail expansion force, rail bending force, rail braking force and rail broken gap all follow normal distribution. As the standard deviations of the four indexes are small, which indicates the randomness of LRBB has little effect on track-bridge interaction. The distributions of the four indexes make it possible to design CWR on bridges with the limit state method.

Generation of breathing solitons in the propagation and interactions of Airy–Gaussian beams in a cubic–quintic nonlinear medium

Using the split-step Fourier transform method, we numerically investigate the generation of breathing solitons in the propagation and interactions of Airy–Gaussian（AiG） beams in a cubic–quintic nonlinear medium in one transverse dimension. We show that the propagation of single AiG beams can generate stable breathing solitons that do not accelerate within a certain initial power range. The propagation direction of these breathing solitons can be controlled by introducing a launch angle to the incident AiG beams. When two AiG beams accelerated in opposite directions interact with each other,different breathing solitons and soliton pairs are observed by adjusting the phase shift, the beam interval, the amplitudes,and the light field distribution of the initial AiG beams.

State-of-Arts of Mechanics of Rolling Contact and Its Application to Analysis of the Interactions between Wheel and Rail

A few typical models of theory on rolling contact of bodies are reviewed, and the advantages and disadvantages in the applications to the dynamics of railway vehicles and the wheel/rail rolling contact are discussed in detail in the present paper.

Resistive field generation in intense proton beam interaction with solid targets

The Brown-Preston-Singleton(BPS)stopping power model is added to our previously developed hybrid code to model ion beam-plasma interaction.Hybrid simulations show that both resistive field and ion scattering effects are important for proton beam transport in a solid target,in which they compete with each other.When the target is not completely ionized,the self-generated resistive field effect dominates over the ion scattering effect.However,when the target is completely ionized,this situation is reversed.Moreover,it is found that Ohmic heating is important for higher current densities and materials with high resistivity.The energy fraction deposited as Ohmic heating can be as high as 20%-30%.Typical ion divergences with half-angles of about 5°-10°will modify the proton energy deposition substantially and should be taken into account.

The role of charge-exchange processes in probing hydrogen plasma with a heavy ion beam

Charge-changing processes of low-charged ions,used in hydrogen plasma probing by the heavy ion beam probe method,are considered.Along with the ionization of beam ions by plasma electrons and protons,the charge-exchange processes of ions on H atoms and protons are also studied.It is shown that charge exchange of beam ions on plasma protons and H atoms,which is rarely taken into account,plays an important role in beam–plasma interaction.New data on the cross sections and rates of ionization and charge-exchange processes are presented for Tl+and Tl2+ions,which are frequently used for plasma diagnostics.Calculations are performed for hydrogen plasma temperatures Te=1 eV–10 keV and densities Ne=1012–1014 cm−3 at relatively low and high ion-beam velocities vb=0.2 and 1.0 a.u.,respectively.Special attention is paid to the determination of the electron temperatures at which the charge-exchange processes on H atoms and protons are important.Multiple ionization of beam ions by plasma electrons and protons is briefly discussed.

Beam-track interaction of high-speed railway bridge with ballast track

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.

Spatial Interaction and Network Structure Evolvement of Cities in Terms of China's Rail Passenger Flows

Cities separated in space are connected together by spatial interaction (SI) between them. But the studies focusing on the SI are relatively few in China mainly because of the scarcity of data. This paper deals with the SI in terms of rail passenger flows, which is an important aspect of the network structure of urban agglomeration. By using a data set consisting of rail O-D (origin-destination) passenger flows among nearly 200 cities, intercity rail distance O-D matrixes, and some other indices, it is found that the attenuating tendency of rail passenger is obvious. And by the analysis on dominant flows and spatial structure of flows, we find that passenger flows have a trend of polarizing to hubs while the linkages between hubs upgrade. However, the gravity model reveals an overall picture of convergence process over time which is not in our expectation of integration process in the framework of globalization and economic integration. Some driven factors for the re-organization process of the structure of urban agglomeration, such as technique advance, globalization, etc. are discussed further based on the results we obtained.

Effects of Powder Feeding Rate on Interaction between Laser Beam and Powder Streamin Laser Cladding Process

A theoretical model was presented to calculate the laser intensity distribution and the particle temperatures at different sites of the workpiece in the laser cladding process. By using this model, the effects of the powder feeding rate on the laser intensity distribution and the particle temperatures were investigated, the calculated results under the condition of different injection angles were also plotted. It is shown that with increasing the injection angle, the laser intensity distributions are similar but the peak value of the laser intensity decreases. Simultaneously, the peak value of the particle temperature increases and the distribution of the particle temperatures gets central symmetrical gradually. These tests results should be considered in model of laser cladding due to their subtle effects on the dynamic processes in laser molten pool.

An experimental study on the effects of friction modifiers on wheel-rail dynamic interactions with various angles of attack

By modifying friction to the desired level,the application of friction modifiers(FMs)has been considered as a promising emerging tool in the railway engineering for increasing braking/traction force in poor adhesion conditions and mitigating wheel/rail interface deterioration,energy consumption,vibration and noise.Understanding the effectiveness of FMs in wheel–rail dynamic interactions is crucial to their proper applications in practice,which has,however,not been well explained.This study experimentally investigates the effects of two types of top-of-rail FM,i.e.FM-A and FM-B,and their application dosages on wheel–rail dynamic interactions with a range of angles of attack(AoAs)using an innovative well-controlled V-track test rig.The tested FMs have been used to provide intermediate friction for wear and noise reduction.The effectiveness of the FMs is assessed in terms of the wheel–rail adhesion characteristics and friction rolling induced axle box acceleration(ABA).This study provides the following new insights into the study of FM:the applications of the tested FMs can both reduce the wheel–rail adhesion level and change the negative friction characteristic to positive;stick–slip can be generated in the V-Track and eliminated by FM-A but intensified by FM-B,depending on the dosage of the FMs applied;the negative friction characteristic is not a must for stick–slip;the increase in ABA with AoA is insignificant until stick–slip occurs and the ABA can thus be influenced by the applications of FM.

Comparative study on wheel-rail dynamic interactions of side-frame cross-bracing bogie and sub-frame radial bogie

Improving freight axle load is the most effective method to improve railway freight capability; based on the imported technologies of railway freight bogie, the 27 t axle load side-frame cross-bracing bogie and sub-frame radial bogie are developed in China. In order to analyze and compare dynamic interactions of the two newly developed heavy-haul freight bogies, we establish a vehi- cle-track coupling dynamic model and use numerical calculation methods for computer simulation. The dynamic performances of the two bogies are simulated separately at various conditions. The results show that at the dipped joint and straight line running conditions, the wheel-rail dynamic interactions of both bogies are basically the same, but at the curve negotiation condition, the wear and the lateral force of the side-frame cross-bracing bogie are much higher than that of the sub-frame radial bogie, and the advantages become more obvious when the curve radius is smaller. The results also indicate that the sub- frame radial bogie has better low-wheel-rail interaction characteristics.

Linear theory of beam–wave interaction in double-slot coupled cavity travelling wave tube

A three-dimensional model of the double-slot coupled cavity slow-wave structure （CCSWS） with a solid round elec- tron beam for the beam-wave interaction is presented. Based on the ＂cold＂ dispersion, the ＂hot＂ dispersion equation is derived with the Maxwell equations by using the variable separation method and the field-matching method. Through numerical calculations, the effects of the electron beam parameters and the staggered angle between adjacent walls on the linear gain are analyzed.

Diagnosis for the Interaction of Supersonic Molecular Beam with Plasma

Supersonic Molecular Beam Injection (SMBI) is a new fuelling method for Tokamaks and has recently been improved to enhance the flux of the beam and to make a survey of the cluster effect within the beam. There are a series of new phenomena, which implicate the interaction of the beam (including clusters) with the toroidal plasma of HL-1M Tokamak. The Ha signals from the edge show a regular variation around the torus. Around the injection port, the edge Hα signals are positive rectangular wave, which is consistent with that of the injection beam pulses. The edge electron temperature, measured with movable Langmuir probes, decreases by an order of magnitude and the density increases by an order of magnitude. Hα emission at the beam injection port, measured with CCD camera at an angle of 13.4 degrees to the SMBI line, shows many separate peaks within the contour plot. These peaks may show the strong emission produced by the interaction of the hydrogen clusters with the plasma. Hydrogen clusters may be produced in the beam according to the empirical scaling (Hagena) law of clustering onset, * = .here d is the nozzle diameter in μm, Po the stagnation pressure in mbar, To the source temperature in K, and k is a constant related to the gas species. If * > 100, clusters will be formed. In present experiment * is about 127.

Mechanism analysis of radiation generated by the beam-plasma interaction in a vacuum diode

When we were studying the vacuum switch,we found that the vacuum diode can radiate a broadband microwave.The vacuum diode is comprised of a cathode with a trigger device and planar anode,there is not a metallic bellows waveguide structure in this device,so the radiation mechanism of the vacuum diode is different from the plasma filled microwave device.It is hard to completely imitate the theory of the plasma filled microwave device.This paper analyzes the breakdown process of the vacuum diode,establishes the mathematical model of the radiating microwave from the vacuum diode.Based on the analysis of the dispersion relation in the form of a refractive index,the electromagnetic waves generated in the vacuum diode will resonate.The included angle between the direction of the electromagnetic radiation and the initial motion direction of electron beam is 45 degrees.The paper isolates the electrostatic effect from the beam-plasma interaction when the electromagnetic radiation occurs.According to above analyses,the dispersion relations of radiation are obtained by solving the wave equation.The dispersion curves are also obtained based on the theoretical dispersion relations.The theoretical dispersion curves are consistent with the actual measurement time-frequency maps of the radiation.Theoretical deduction and experiments indicate that the reason for microwave radiating from the vacuum diode can be well explained by the interaction of the electron beam and magnetized plasma.

DESIGN OF BEAM-WAVE INTERACTION BASED ON HIGH EFFICIENCY OF A HIGH-POWER BROADBAND KLYSTRON

The paper mainly presents the design of beam-wave interaction of a C-band high-peakpower high-efficiency broadband klystron.The beam-wave interaction section is designed based on considerations of efficiency and bandwidth synthetically.As a part of beam-wave interaction section,buncher section is simulated by Particle-In-Cell(PIC) code to observe the bunching process of electron beam to achieve high conversion efficiency of electron beam and RF field.When it comes to the other part,output circuit is designed as a three-section filter by an output cavity loaded with Chebyshev filter,and the cold test results are given.The beam-wave interaction is simulated by EGUN code and Arsenal-MSU code respectively.The simulated results indicated that,the existence of power dips in the operating bandwidth is verified by Arsenal-MSU code,comparing proper results by EGUN code.Then,the method that design parameters are not adjusted except parameters of buncher cavities to remove potential power dips is described.What is more,the simulated results of electron optics system are given by EGUN code and Arsenal-MSU code respectively.The further hot test results of klystron prove that the whole design of beam-wave interaction is effective.

Separation Method in the Problem of a Beam-Plasma Interaction in a Cylindrical Warm Plasma Waveguide

The stabilization effect of a strong HF electric field on beam-plasma instability in a cylindrical warm plasma waveguide is discussed. A mathematical technique “separation method” applied to the two-fluid plasma model to separate the equations, which describe the system, into two parts, temporal and space parts. Plasma electrons are considered to have a thermal velocity. It is shown that a HF electric field has no essential influence on dispersion characteristics of unstable surface waves excited in a warm plasma waveguide by a low-density electron beam. The region of instability only slightly narrowing and the growth rate decreases by a small parameter and this result has been reduced compared to cold plasma. Also, it is found that the plasma electrons have not affected the solution of the space part of the problem.

Sensitive factors research for track-bridge interaction of Long-span X-style steel-box arch bridge on high-speed railway

X-style arch bridge on high-speed railways(HSR)is one kind of complicated long-span structure,and the track-bridge interaction is essential to ensure the safety and smoothness of HSR.Taking an X-style steel-box arch bridge with a main span of450 m on HSR under construction for example,a new integrative mechanic model of rail-stringer-cross beam-suspenderpier-foundation coupling system was established,adopting the nonlinear spring element simulating the longitudinal resistance between track and bridge.The transmission law of continuous welded rail(CWR)on the X-style arch bridge was researched,and comparative study was carried out to discuss the influence of several sensitive factors,such as the temperature load case,the longitudinal resistance model,the scheme of longitudinal restraint conditions,the introverted inclination of arch rib,the stiffness of pier and abutment and the location of the rail expansion device.Calculating results indicate that the longitudinal resistance has a significant impact upon the longitudinal forces of CWR on this kind of bridge,while the arch rib’s inclination has little effect.Besides,temperature variation of arch ribs and suspenders should be taken into account in the calculation.Selecting the restraint system without longitudinally-fixed bearing and setting the rail expansion devices on both ends are more reasonable.

Theoretical analysis and numerical simulation of the impulse delivering from laser-produced plasma to solid target

A plasma is produced in air by using a high-intensity Q-switch Nd：YAG pulsed laser to irradiate a solid target, and the impulses delivering from the plasma to the target are measured at different laser power densities. Analysing the formation process of laser plasma and the laser supported detonation wave （LSDW） and using fluid mechanics theory and Pirri＇s methods, an approximately theoretical solution of the impulse delivering from the plasma to the target under our experimental condition is found. Furthermore, according to the formation time of plasma and the variation of pressure in plasma in a non-equilibrium state, a physical model of the interaction between the pulse laser and the solid target is developed. The plasma evolutions with time during and after the laser pulse irradiating the target are simulated numerically by using a three-dimensional difference scheme. And the numerical solutions of the impulse delivering from the plasma to the target are obtained. A comparison among the theoretical, numerical and experimental results and their analyses are performed. The experimental results are explained reasonably. The consistency between numerical results and experimental results implies that the numerical calculation model used in this paper can well describe the mechanical action of the laser on the target.

Numerical optimisation and experimental validation of divided rail freight brake disc crown

In this study, numerical optimisation and experimental validation of a divided rail freight brake disc crown made of grey cast iron EN-GJL-250 is presented.The analysed brake disc is used in rail freight wagons and possesses a load capacity of 22.5 tons per axle. Two of the divided rail freight brake discs are mounted on each axle.With the aid of numerical analysis, the thermal dissipation properties of the brake disc were optimised and ventilation losses were reduced, and the numerical results were compared with experimental results. A one-way fluid–structure interaction analysis was performed. A computational fluid dynamic model of a divided rail freight brake disc, used to predict air flow properties and heat convection, was incorporated into a finite element model of the disc and used to evaluate the temperature of the disc. A numerical parametrical optimisation of cooling ribs of the brake disc was also performed, and novel optimised cooling ribs were developed. A transient thermal numerical analysis of the brake disc was validated using temperature measurements obtained during a braking test on a test bench. The ventilation losses of the brake disc were measured on a test bench specifically designed for the task, and the losses were compared to the simulation results. The experimentally obtained ventilation losses and temperature measurements compared favourably with the simulation results, confirming that this type of simulation process may be confidently applied in the future. Through systematic optimisation of the divided rail freight brake disc, ventilation losses were reduced by 37% and the mass was reduced by 21%, resulting in better thermal performance that will bring with it substantial energy savings.