Rigid Track Research Articles

Genetic Algorithm Tuned Super Twisting Sliding Mode Controller for Suspension of Maglev Train With Flexible Track

The suspension air-gap of Maglev train needs controller for it is inherently unstable and highly nonlinear. To maintain a high quality of ride, comfort and safety for the passengers the train suspension controller must maintain the suspension air-gap. During operation the suspension air-gap of a Maglev train is only in millimeters. This easily causes instability under excitation of nonlinear load and track tiny deformation. Additionally, a track with a low stiffness will experience larger bending displacement and result in high vibrations. A high stiffness track experience minor bending displacement, which will diminish the vibration and improve riding quality. Unfortunately, using high stiffness guideway track is expensive. Instead, by designing a good controller the low stiffness material can be used. In this paper genetic algorithm tuned super twisting sliding mode control is proposed for it offers a good controlling ability since it is insensitive to external disturbance, parameter variation and has a fast dynamic response. The proposed controllers are tested under different circumstances, i.e., Maglev train with rigid track and with flexible track under variable load and external random disturbance.

Assessment of Dynamics of a Rail Vehicle in Terms of Running Properties While Moving on a Real Track Model

Simulation computations represent a very effective tool for investigating operational characteristics and behaviours of vehicles without having a real product. The rail vehicles sector is typical, in that simulation computations including multibody modelling of individual vehicles (i.e., wagons) as well as entire trainsets are widely used. In the case of designing rail vehicles, running safety and ride comfort are two of the most important assessment areas. The presented work is focused on the research of the dynamical effects of a rail vehicle while running on a railway track created in a commercial multibody model. There is a lot of research focused on the investigation of dynamic performances while a rail vehicle is running on a flexible railway track. The real operation of a rail vehicle meets problems on track, where the stiffness-damping parameters of a railway track vary in transient sections (e.g., the exit of a tunnel). This work brings a contribution to research related to the assessment of the dynamic response of a rail vehicle on a chosen track section. A passenger railway vehicle is chosen as a reference multibody model. Simulation computations were performed for three different railway track models, i.e., for a rigid track model and for a flexible track model defined in two different manners. The stiffness-damping parameters of the rail vehicle are defined symmetrically in relation to the longitudinal axis of the vehicle, e.g., they are the same values for the left and right side. The centre of gravity is not located symmetrically, but it is partially shifted in the lateral direction. This can be observed in the results of wheel forces and their waveforms. There are evaluated values and waveforms of the vertical wheel forces, the lateral wheel forces and the derailment quotient. The obtained results have revealed the influence of the railway track formulation in the model on the output parameters.

Vibration analysis and multi-state feedback control of maglev vehicle-guideway coupling system

<abstract> <p>Due to the existence of elastic modes in the track, the suspension system of maglev train is prone to vehicle-track coupling vibration, which has become an important problem restricting the further development of maglev train technology. In view of the limitation of the existing rigid track suspension model, this paper establishes an electromagnet-controller-elastic track coupling system model. And then, the nonlinear maglev system is transformed into a linear system by Hartman-Grobman theorem. Since the elastic deformation of the track is difficult to measure, a tracking differentiator is presented to filter out the interference of the displacement signal and obtain the differential signal of the gap between the electromagnet and the track. In order to suppress the vehicle-track coupling vibration, a four-state feedback control method is proposed by introducing the gap differential feedback signal. According to the Hurwitz algebraic criterion, the stability of four-state feedback control system is compared with that of three-state feedback control system. Simulation results show that, the four-state feedback control method can provide the elastic deformation information of the track, and can suppress the coupling vibration between the vehicle and the elastic track effectively.</p> </abstract>

In-situ performance assessment of track superstructure on fouled railroad

This paper assesses the performance of a class I railroad superstructure due to track fouling. Instrumentation comprised rails and cross-ties’ industry standard circuits in the crib and above the cross-tie to quantify vertical load, digital cameras, and ballast embedded moisture content probes. Normalized maximum rail-tie tensile force was employed to analyse uplift resistance. The longitudinal range of influence of distant wheels was then evaluated by correlating the distance of wheel load peaks on the induced rail-tie force. Moisture analysis showed that water-storage capacity of fouled ballast bed decreased for typical and rigid track stiffness. Results indicate that as the fouled track stiffness increased the influence range of wheels on superstructure increased, for concrete cross-tie supported railroad. The tie-load ratio may misrepresent the superstructure efficiency in fouled ballast beds. Alternatively, the range of influence of distant wheels along with the uplift ratio may be used to assess fouled railroad performance. For this purpose, empirical models are proposed to evaluate the longitudinal range of influence of wheels on the superstructure and uplift ratio.

Modelling and ride comfort analysis of a coupled track-train-seat-human model with lateral, vertical and roll vibrations

A coupled track-train-seat-human model with lateral, vertical and roll vibrations was developed to investigate the ride comfort of high-speed trains. The ride comfort was assessed by the total equivalent acceleration defined according to ISO 2631-1. It was found that the track flexibility had a minor influence on the lateral, vertical and roll floor vibrations below 20 Hz, while the total equivalent acceleration was overestimated by over 10% at high speed using a rigid track. The flexibility of the carbody generated dramatic floor vibration in lateral, vertical and roll directions above 7.5 Hz, so the rigid carbody model significantly underestimated the total equivalent acceleration. The total equivalent acceleration tended to increase with the increase of speed. The equivalent accelerations for two symmetric seat positions illustrated analogous trends with the increasing speed. The ride comfort was the worst close to the carbody ends, followed by the carbody centre at high speed. The vertical acceleration on the seat pan was the most severe whatever the seat position and speed are. The neighbouring subject brought about a reduction of the total equivalent acceleration for the subject under evaluation. The carbody damping can reduce the total equivalent acceleration effectively in the whole speed range.

A Track-Based Molecular Synthesizer that Builds a Single-Sequence Oligomer through Iterative Carbon-Carbon Bond Formation

Summary We report an artificial molecular machine that moves along a track, iteratively joining building blocks to form an oligomer of single sequence with a continuous backbone of carbon-carbon bonds. The rotaxane features a macrocycle bearing an aldehyde-terminated chain and an axle containing different phosphonium ylides separated by rigid spacers. Each ylide is large enough to block the passage of the macrocycle, trapping the ring between the stopper at the terminus of original threading and the next ylide along the track. Once a building block is reachable, it is removed from the track through a Wittig reaction that adds it to the terminus of the growing chain. Operation on a four-barrier tetra(phosphonium salt) track produces a tetra(diphenylpropane) of single sequence linked through alkene bonds. The prototype extends the principle for molecular machines that build polymers by moving along tracks to the synthesis of sequence-encoded chains with continuous carbon backbones.

Study on track–soil traction using discrete element method simulation and soil bin test

The soil ground with low moisture content has the mechanical properties of low viscosity and high friction, which have a great influence on the traveling of a tracked vehicle. In this paper, a movement model of the rigid track on low moisture soil is established based on the discrete element method (DEM) simulation. The soil simulation model was verified by the triaxial compression test. The traction simulation of the track under different vertical stress was carried out, and the traction performance of the track was analyzed by combining with the results of the soil bin test. The analysis shows that the tractive effort increases with the increase in vertical stress. The tractive effort distribution of the track is basically the same as the shape of the bottom of the track, and the tractive effort on both sides of the track cannot be ignored. The average error of tractive effort in simulation is 3.94%. DEM simulation can reproduce the mechanical properties and the discontinuous nature of low moisture soil particles under dynamic load, which is suitable for the numerical study of the interaction between the track and soil.

Vertical track irregularity analysis of high-speed railways on simply-supported beam bridges based on the virtual track inspection method

Understanding the relationship between the static and dynamic track geometry irregularities is crucial for the proper maintenance of rail infrastructures and the reduction of on-site workload. This paper focuses on the analysis of the dynamic and static track irregularities on simply-supported beam bridges for high-speed railways. Based on the simulation of three-dimensional vehicle–track–bridge dynamics, a virtual track inspection method is proposed according to the measurement principle with the inertial reference. With the static irregularity provided as the initial input to the simulation model, the virtual track inspection of dynamic track irregularities is carried out considering different supporting structures, i.e. subgrade and bridges. Furthermore, the characteristics and advantages of the proposed model are investigated in the “rigid track structure”. Then, using the virtual track inspection method, this paper analyzes the relationship between the dynamic and static track irregularities (in the vertical direction) on the simply-supported beam bridge in both the time and frequency domains with respect to different train speeds, and the simulation results are validated by real-world measurements. Numerical results show that the stiffness irregularity in the vertical direction is periodical, with the cycle length equal to the span of the bridge. Furthermore, there is an obvious linear relationship between the dynamic and static irregularities. Also, the regression coefficient increases with increasing vehicle speed.

Sliding Mode Robust Adaptive Control of Maglev Vehicle’s Nonlinear Suspension System Based on Flexible Track: Design and Experiment

The suspension system of Maglev vehicle needs strong robustness and anti-jamming ability in the process of operation and fluctuation control. In order to solve the open-loop instability and strong nonlinearity of the mechanical equation of the suspension system of the Maglev vehicle, the non-linear dynamic equation is established. At present, the research based on the single electromagnet and the rigid track is the most common. However, based on this method, it is impossible to study the coupled vibration caused by track factors. Therefore, based on the dynamic equation of a single span simply supported beam of flexible track and the non-linear equation of the suspended electromagnet itself, an overall control model is needed to discuss the control strategy. Based on this dynamic model, the singularities of the system are solved according to Hurwitz criterion, and the characteristic equation corresponding to the Jacobian matrix is obtained. The stability analysis shows that the system is unstable. At the same time, the necessity of using a feedback control method to control the air gap has been proved. On this basis, a sliding mode adaptive state feedback controller for the maglev system is designed based on the RBF network approximation principle. The corresponding simulation and experimental results are given. The simulation and experimental results show that the controller can ensure the vehicle's stable suspension and effectively suppress external interference. Compared with the traditional PID and fuzzy controllers, the controller can guarantee a faster dynamic response, stronger robustness, and smaller overshoot while considering the flexible track and external disturbances.

Online prediction model for wheel wear considering track flexibility

The objective of this study is to develop a new online model for wheel wear that takes into account the track flexibility. The proposed model consists of two parts that interact with each other, namely, (a) a locomotive/track coupled dynamics model considering the track flexibility, which is validated by field measurement results, and (b) a model for the wear estimation. The wheel wear prediction model can be employed in online solutions rather than in post-processing. The effect of including the track flexibility on the wear estimation is investigated by comparing the results with those obtained for a rigid track. Moreover, the effect of the wheel profile updating strategy on the wheel wear is also examined. The simulation results indicate that the track flexibility cannot be neglected for the wheel wear prediction. The wear predicted with the rigid track model is generally larger than that predicted with the flexible track model. The strategy of maintaining unchanged wheel profiles during the dynamic simulation coincides with the online updating strategy in terms of the predicted wear.

Analysis of Tracked Vehicle Vibration Response Considering the Track Circuit Vibration

To accurately describe the vehicle vibration, the vibration response of the vehicle operation system affected by the track was studied. Through the analysis of the topological structure of vehicle operation system, the flexible track model and the rigid track model was built up. The track circuit model was established by simplifying the rigid track, and its inherent vibration was calculated by eigenvalue analysis. Power spectrum method was used to compare the dynamic model of flexible track and the dynamic model of rigid track and verify the effect of track on the vibration of vehicle. The results show that the effect of track on the vibration of vehicle mainly include the inherent vibration of track circuit and the high frequency vibration related to track pitch; the computing result provides a reference basis for describing the effect of track quantitatively.

On the stick-slip vibration in the suspension of a freight wagon

Damping based on the dry friction is frequently in suspensions of the freight wagons. The paper presents some aspects of vertical vibration of freight wagons. It uses a simple model considering that the vehicle was reduced to a mass suspended on a wheel, moving at constant speed on a rigid track with harmonic irregularity. Stick-slip vibration can occur due to the friction and it is characterized by sudden changes in the wheel acceleration affecting the ride quality. The paper shows the influence of stick-slip vibration on the wheel-rail dynamic force.

中医阴阳循行的量子元素

量子生物学以微观的波粒二重性突破古典力学对于粒子受制于热力学定律的局限，赋予人类遗传物质得以稳定实现演化的规则性和可预测性。在此之前，去相干的古典物理特性明显遮蔽了我们对量子行为的观察，乃至于面对病理表症的解决之道因为缺少分子尺度的微观考虑，从而限制许许多多医学上重大的发现。巨大个体的生长发育过程会遭遇热力学干扰，最终呈现的是我们所熟悉的古典力学样貌，这现象在物理学上称为去相干，在人类则称为老化。换句话说，当生命体呈现古典定律的粒子性僵硬轨迹，而原本具有波顺应性的量子特性被过滤掉了，这是生命先在性的老化宿命。显现出肌肉皮肤萎缩、弹性下降、皱纹产生、粒线体功能失衡、自由基氧化压力、慢性发炎反应等表症。中医《内经》：「营卫阴阳，如环无端。」依照这个规律而有顺序的循行振动，实现生趣盎然的生命现象。此一生生不息的波、粒二重性，在于法阴阳，和术数，饮食有节，起居有常，不妄作劳，故形与神俱，而终其天年，度百岁乃去。这个源自黄帝内经的组件当可以为人类逆转老化的议题提供值得思考的可能性。 Quantum microscopic biological systems with duality are concerned with the influence of non-trivial quantum phenomena, as opposed to the so-called trivial quantum mechanics present in all biology by reduction to fundamental physics and the law of thermodynamics. These characteristics give the human genetic DNA stable evolution and are able to predictive property. Because the lack of molecular microscopic scale and classical physics of gravity theory interfere with objects wave-like behavior, it limits many of the medical intervention and achievement about human diseases. Quantum phenomena present in the processes of individual biological development system will interfere with an entanglement of physics of gravity theory and thermodynamics. This phenomenon is called de- coherent in physics, and it is also illustrated as ageing in human beings. In other words, when the living environment full with the rigid track of the particles characterization could be considered as a class of quantum phenomena in biological systems are excluded, which may illustrate as the fate of life on aging. Manifestations include muscle and skin atrophy, loose skin elasticity, wrinkling production, mitochondria dysfunction, free radical oxidative stress, chronic inflammation and body function imbalance. This can lead to accelerating ageing. And, of course, it is eventually as scene of death. The yellow Emperor’s classic of Chinese medicine said that yin and yang are interdependent and transform as a circle that is always round endless. Following the yin and yang rhythm, integrated technol-ogy and culture, we will have a regular diet, and not be tired and exhausted in a routine living style. In addition, people should remain calm and avoid excessive desires and fantasies, maintaining the natural purity and clarity of the mind, thus illness and disease can be avoided. The concept supporting the yin-yang-pair model is potentially based on fundamental quantum effects. In ancient times, yin- yang theory advised people to guard themselves against disease-causing factors, and the role of yin-yang recurrence can be subtle as quantum microscale mechanisms. We may consider a biological system that exploits coherent superposition of states of yin-yang recurrence for some practical purposes and provide the possibility for mankind reversing ageing issues, making people happy and have healthy life.

Development of quick-hardening infilling materials for composite railroad tracks to strengthen existing ballasted track

Abstract A composite railroad track is a rigid track system that is developed using quick-hardening infilling materials, and has the advantages of a reduced maintenance cost compared to a conventional ballasted track. Quick-hardening infilling materials were developed in this study, which does not require the processes of cleaning the aggregates crushed due to the repeated load imposed by rolling stock, and thus the materials can strengthen existing ballasted tracks with an enhanced level of efficiency and speed. Theoretical reviews of pore size, permeability, pore channel length and tortuosity depending on the size of the aggregate in ballasted tracks were conducted first to predict the influence of filling parameters of infilling materials for composite railroad tracks. Based on the theoretical filling performance analysis of ballasted tracks, a thermosetting polymer was developed, which is a 3D cross linking agent that performs redox radical polymerization reaction at room temperature. The polymer was used as a primary filling material to fill the lower ballast layer, which could not be filled by conventional cement-based filling materials. A double-layered composite was formed by filling the upper ballast layer with the ceramic-based secondary filling material using the reaction between dead-burned magnesia and acid ammonium phosphate. The performance of infilling materials was validated through strength measurement and microscopic analysis.

Study on Wheel-Rail Coupled Vibration of Metro with Co-Simulation of Finite Element Analysis and Multi-Body Dynamics Simulation

Based on the multi-body dynamics theory and modal-reduction analysis, finite element method and multi-body dynamics were combined to establish the flexible track model. The rigid-flexible coupled dynamics model can reflect the features of coupled vibration accurately. When the flexibility of the rail, damping and stiffness of support layers under the rail are taken into consideration, the whole track structure acted as a buffer while wheel and rail is interacting with each other. Compared with rigid track model, the wheel-rail vibration is less in the flexible track model. The proposed method in this paper is simple and effective, which makes the calculation of vehicle-track dynamic response more convenient and quick.

Effects of Track Elasticity on Wheel-Rail Dynamic Performance of Heavy Haul Railway

Two vehicle-track dynamics models on heavy haul railway are established in two conditions of rigid track and elastic track. And the impact of track elasticity on the wheel-rail dynamics performance was analyzed using models. The results show that the critical speed of heavy vehicles and wheel-rail dynamic indexes, such as wheel-rail lateral force and wheel-rail vertical force decreased on elastic track compared with rigid track. However, other dynamic indexes, including derailment coefficient and lateral displacement of wheelsets increased on elastic track. And the wheel-rail wear indexes are some differences on two tracks.

Active Elastic Dimers: Cells Moving on Rigid Tracks

Experiments suggest that the migration of some cells in the three-dimensional extra cellular matrix bears strong resemblance to one-dimensional cell migration. Motivated by this observation, we construct and study a minimal one-dimensional model cell made of two beads and an active spring moving along a rigid track. The active spring models the stress fibers with their myosin-driven contractility and alpha-actinin-driven extendability, while the friction coefficients of the two beads describe the catch/slip bond behavior of the integrins in focal adhesions. In the absence of active noise, net motion arises from an interplay between active contractility (and passive extendability) of the stress fibers and an asymmetry between the front and back of the cell due to catch bond behavior of integrins at the front of the cell and slip bond behavior of integrins at the back. We obtain reasonable cell speeds with independently estimated parameters. We also study the effects of hysteresis in the active spring, due to catch bond behavior and the dynamics of cross-linking, and the addition of active noise on the motion of the cell. Our model highlights the role of alpha-actinin in three-dimensional cell motility and does not require Arp2/3 actin filament nucleation for net motion.

Active elastic dimers: cells moving on rigid tracks.

Experiments suggest that the migration of some cells in the three-dimensional extracellular matrix bears strong resemblance to one-dimensional cell migration. Motivated by this observation, we construct and study a minimal one-dimensional model cell made of two beads and an active spring moving along a rigid track. The active spring models the stress fibers with their myosin-driven contractility and α-actinin-driven extendability, while the friction coefficients of the two beads describe the catch and slip-bond behaviors of the integrins in focal adhesions. In the absence of active noise, net motion arises from an interplay between active contractility (and passive extendability) of the stress fibers and an asymmetry between the front and back of the cell due to catch-bond behavior of integrins at the front of the cell and slip-bond behavior of integrins at the back. We obtain reasonable cell speeds with independently estimated parameters. We also study the effects of hysteresis in the active spring, due to catch-bond behavior and the dynamics of cross linking, and the addition of active noise on the motion of the cell. Our model highlights the role of α-actinin in three-dimensional cell motility and does not require Arp2/3 actin filament nucleation for net motion.

Modelling of a free rail wheelset using non-linear creep force

This paper presents a bond graph model of a free railway wheelset rolling on flexible curved track. A module-based approach is used here. A model of a wheelset considering six degrees of freedom without linearity approximation is created using subsystem models called capsules. Capsules represent various analytical aspects of wheelset dynamics. Different subsystem models are combined to develop a complete bond graph model of a wheelset for simulation on a rigid railway track. For the rail-wheel contact forces (creep forces), a heuristic non-linear formulation is used, which can also be used with slight modification as a linear model for comparative study. Kinematic analysis of the wheelset is done to find out velocities of the contact points on the wheelset. The bond graph is created on the bond graph software SYMBOLS 2000 and simulated for a set of parameter values.

Study of the effect of the spiral geometry on wheel/rail contact forces

Spiral sections are used in the construction of railroad tracks in order to achieve a smooth change in the curvature. In order to satisfy the kinematic conditions at the position, velocity, and acceleration levels in railroad vehicle dynamics computational algorithms based on the constraint contact formulations; third-order derivatives of the wheel/rail contact constraint functions with respect to the wheel and rail geometric surface parameters must be evaluated. Discontinuities in these higher derivatives can produce jumps in the wheel/rail contact forces at the spiral entries and exits. This paper develops a simple procedure that can be applied online to ensure that the curvature and its derivative of the rail space curve are continuous at the spiral entries and exits. Because continuity of the space curve geometric variables does not ensure continuity of these variables on the rail surface, the effect of the proposed procedure on the contact forces is examined. The constraint and elastic wheel/rail contact formulations are first reviewed in order to show the degree of continuity required and the basic kinematic conditions used to search online for the wheel/rail contact points. The rigid track geometry is described using the absolute nodal coordinate formulation (ANCF), which employs a geometric description that ensures the continuity of the position and gradient vectors at the track nodes. In order to ensure the continuity of the curvature vector and its derivative at the intersection of the spirals with the tangent and curve segments, a set of linear conditions are developed and solved online, allowing for implicit elimination of track nodal variables. These conditions are not considered as kinematic constraints imposed on the system motion since they are mainly used to improve the rigid track geometric description and do not involve the system generalized coordinates or their time derivatives. The procedure described in this investigation does not require making changes in the description of the track geometry and does not require the use of higher order derivatives of the track node angles in order to achieve the desired degree of continuity. Because higher degree of continuity achieved for the rail space curve does not ensure a similar degree of continuity on the surface where the wheel/rail contact occurs; the effect of the change of the degree of continuity of the space curve at the spiral entries and exits on the rail surface geometry is also discussed in this paper. The results presented in this study show that the proposed procedure can lead to improvement in the wheel/rail contact force results in some simulation scenarios. The results, obtained using the proposed procedure, are compared with the results obtained using local mesh refinements.