Flexible Railway Research Articles

Multi-objective online driving strategy optimization for energy storage tram considering battery life

Compared with the traditional overhead contact grid or third-rail power supply, energy storage trams equipped with lithium batteries have been developed rapidly because of their advantages of flexible railway laying and high regenerative braking energy utilization. However, trams may face expensive battery replacement costs due to battery degradation. Therefore, this paper proposes a multi-objective optimization method for the tram's driving strategy to reduce operational energy consumption and extend battery life. The method describes the optimization problem as second-order cone programming (SOCP). It uses the interior point algorithm for fast solving, thus obtaining the theoretical optimal speed trajectory in real-time. This feature enables the method to be applied online. To verify the effectiveness and robustness of the proposed method, we conducted simulations under actual operating conditions. The simulation results show that the proposed multi-objective optimization method can extend the battery life by 40 % compared to the single-objective optimization method for energy saving. As a result, the total cost of the whole life cycle is reduced by 6.54 %. Furthermore, this online optimization driving strategy method can effectively deal with unexpected conditions during the actual operation of the tram to ensure the secure operation, punctual arrival, and precise parking of trams. Finally, the effectiveness of the proposed method is further verified by a hardware-in-the-loop (HIL) test.

Research on Symmetric Bipolar MMC-M2Tdc-Based Flexible Railway Traction Power Supply System

Research on Symmetric Bipolar MMC-M²Tdc-Based Flexible Railway Traction Power Supply System

Adaptive optimal control of pneumatic suspensions for comfort improvement of flexible railway vehicles using Monte Carlo simulations

ABSTRACT This paper presents an adaptive optimal control strategy focused on improving ride comfort by minimising the frequency-weighted acceleration measured at three locations on a flexible carbody floor. Front and rear suspensions adapt the restriction orifice, which connects each pneumatic spring to its auxiliary air reservoir, thus conferring different dynamic stiffness and damping depending on train speed and track quality. In this work, as opposed to previous publications by our group, the optimal control problem aims at the particular frequency range which affects passenger comfort in accordance to standard UNE-EN-12299. In addition, a rigorous statistical analysis based on Monte Carlo and Bootstrap sampling techniques has been used to deal with the stochastic nature of track irregularities. Results prove that focusing on the comfort frequency range improves the performance of the adaptive suspension, and that the proposed statistical analysis of optimisation results guarantees the appropriate selection of optimal diameters.

Combined Active and Reactive Power Flow Control Strategy for Flexible Railway Traction Substation Integrated With ESS and PV

This paper proposes a combined active and reactive power flow control strategy for the flexible traction substation (FTSS). It fully uses the active and reactive power flexibility of FTSS to maximize regenerative braking energy (RBE) and photovoltaic (PV) energy utilization and improve power quality comprehensively. First, the active power flow optimization layer coordinates the active power outputs of the back-to-back converter (BTBC) and energy storage system to maximize the utilization of the available RBE and PV energy and balance the active power outputs of the traction transformer. Meanwhile, it controls PV output to limit the surplus energy injected into the utility grid further. Then, the model predictive control (MPC)-based reactive power flow optimization layer employs the spare capacity of BTBC to optimize the reactive power flow to improve the multiple power quality issues further, including negative sequence current (NSC), effective power factor (EPF), and traction network voltage fluctuations. To establish the MPC optimization problem, the NSC, EPF, and traction network incoming voltage sensitivity matrices with respect to the reactive power outputs of the traction transformer are first derived. Finally, the hardware-in-the-loop experiments, based on the data measurement from a high-speed railway traction substation, verify the effectiveness of the proposed strategy.

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.

A finite element methodology to model flexible tracks with arbitrary geometry for railway dynamics applications

The dynamic analysis of railway vehicles requires an accurate representation of the vehicle, the track geometry and structure, and their interaction. Generally, flexible track models with curved geometries represent the rails with straight beam elements, which results in a piecewise linear representation of the rails. Consequently, the wheel-rail contact mechanics are not properly captured, and the wheel-rail contact forces present spurious high-frequency oscillations. This work proposes a novel approach to model flexible railway tracks with arbitrary geometries, in which the correct geometry in the wheel-rail contact mechanics is assured by modeling the rails as Timoshenko curved beam elements. This approach improves both the geometric representation of the rails and the accuracy of the wheel-rail contact forces calculation. A realistic operation scenario in which a multibody model of a railway vehicle runs on a flexible track with a curved geometry is used here to demonstrate the novel aspects of this work and then discuss the improvements over the conventional approaches. The results show that the proposed methodology greatly improves the computation of the wheel-rail interaction forces and prevents spurious oscillations from propagating to the vehicle.

Multitime-Scale Optimal Dispatch of Railway FTPSS Based on Model Predictive Control

The flexible traction power supply system (FTPSS) integrates back-to-back converter, and hybrid energy storage system (HESS) and photovoltaic (PV) generation system will be an important part of the smart railway. The FTPSS not only cancels the neutral zone but also facilitates the utilization of regenerative braking (RB) and renewable energy, but the random fluctuation of PV and the sudden change of traction load will exert influence on the safe and efficient operation of the FTPSS. To improve the benefits of FTPSS and compensate for the imbalance between supply and demand in short-term operation, a multitime-scale optimal dispatch method is proposed for flexible railway energy management (FREM), which integrates day-ahead dispatch and intraday feedback correction. During the day-ahead dispatch, the minimizing operating costs problem is formulated as a mixed linear programming model by coordination between HESS, RB, and PV output. For intraday energy adjustment dispatch, a rolling optimization based on model predictive control combined with the feedback correction method is proposed, with aim of minimum operation deviation of FTPSS because of adjusting the HESS dispatch plan drew up at day-ahead. Finally, the effectiveness of the proposed FREM control strategy is verified by the detailed real case study of a railway line in China.

Critical points numerical analysis of ride comfort of the flexible railway carbody

Ride comfort is one of the criteria for evaluating the dynamic behaviour in railway vehicles, through which the complex sensation triggered by the vibrations in the railway vehicle carbody upon passengers is being described. The behaviour of vibrations along the vehicle carbody is not uniform and the point where the ride comfort is the least convenient can be considered as the carbody critical point. The paper examines the ride comfort along the carbody and the position of the ride comfort critical points in correlation with the speed, carbody flexibility and suspension damping. To this purpose, there are used the results from numerical simulations regarding the ride comfort index calculated along the carbody and the ride comfort index in three points deemed relevant in terms of evaluating the ride comfort at the center of carbody and above the bogies.

A co-simulation approach to the wheel–rail contact with flexible railway track

The standard approach to railway vehicle dynamic analysis includes running the vehicle multibody models in rigid railway tracks. The wheel–rail contact, independently of the rolling contact model used, is either handled online or via lookup tables. This traditional approach disregards the coupling effects between the railway vehicle dynamics and the railway track flexibility. In this work the assumption of rigidity of the railway track is relaxed and a finite element model of the complete track, i.e. rails, pads, sleepers, ballast and infrastructure, is used to represent the track geometry and flexibility. A rail–wheel contact model that evaluates the contact conditions and forces is used online. The dynamics of the railway vehicle is described using a multibody methodology while the track structure is described using a finite element approach. Due to the fact that not only the multibody and the finite element dynamic analysis use different integration algorithms but also because the vehicle and track models are simulated in different, codes a co-simulation procedure is proposed and demonstrated to address the coupled dynamics of the system. This approach allows us to analyze the vehicle dynamics in a flexible track with a general geometry modeled with finite elements, i.e. including curvature, cant, vertical slopes and irregularities, which is another novel contribution. The methodology proposed in this work is demonstrated in an application, in which the railway vehicle–track interaction shows the influence of the vehicle dynamics on the track dynamics and vice versa.

On the resonant vibration of a flexible railway car body and its suppression with a dynamic vibration absorber

The geometric filtering phenomenon is first analyzed with a simplified vertical vehicle model. Analytical solutions obtained with this model show that geometric filtering phenomenon consists of ‘wheelbase filtering’ and ‘bogie spacing filtering’ effects. The wheelbase filtering effect occurs when there is neither car body bounce nor pitch response at certain track wavelengths, whereas the bogie spacing filtering effect occurs when there is a null in either the car body bounce or pitch response at particular track wavelengths. Then, the correlated frequency response function for railway vehicles is defined to assess the effect of geometric filtering upon the resonant frequencies of a flexible car body. It is found that if the car body’s first bending frequency coincides with the peak values of bounce acceleration transmissibility, that is, it is near the null pitch response frequencies, resonant vibration of the flexible car body will happen. Finally, to suppress the resonant vibration of the flexible car body, it is proposed to use a dynamic vibration absorber (DVA) suspended under the car body underframe. The DVA parameters are optimized according to car body bending frequency and the null pitch frequency. The optimal DVAs show very good performance and robustness in suppression of the car body resonant vibration.

Comfort enhancement by an active vibration reduction system for a flexible railway car body

In order to improve the ride comfort of lightweight railway vehicles, an active vibration reduction system using piezo-stack actuators is proposed and studied in simulations. The system consists of actuators and sensors mounted on the vehicle car body. Via a feedback control loop, the output signals of the sensors which are measuring the flexible deformation of the car body generate a bending moment, which is directly applied to the car body by the actuators. This bending moment reduces the structural vibration of the vehicle car body. Simulations have shown that a significant reduction in the vibration level is achieved.

MATEMATICAL MODEL OF DYNAMIC INTERACTION BETWEEN WHEEL-SET AND RAIL TRACK

The main goal of this paper is to show how the effects of maximum bending tensions at different locations in the track caused by simultaneous changes of various parameters can be estimated in a rational manner. The dynamics of the vertical interaction between a moving rigid wheel and a flexible railway track is investigated. An asymmetric linear three-dimensional beam structure model of a finite length of the track is suggested. The influence of eight selected track parameters on the dynamic behaviour of the track is investigated. A two-level fractional factorial design method is used in the search for the combination of numerical values of these parameters minimizing themaximum bending tensions.

MATHEMATICAL MODEL OF DYNAMIC INTERACTION BETWEEN WHEEL-SET AND RAIL TRACK

The main goal of this title is to show how the effects on maximum bending tensions at different locations in the track caused by simultaneous changes of the various parameters can be estimated in a rational manner The dynamic of vertical interaction between a moving rigid wheel and a flexible railway track is investigated. A round and smooth wheel tread and an initially straight and non-corrugated rail surface are assumed in the present optimisation study. Asymmetric linear three-dimensional beam structure model of a finite length of the track is suggested including rail, pads. sleepers and ballast with spatially non-proportional damping. Transient bending tensions in sleepers and rail are calculated. The influence of eight selected track parameters on the dynamic behaviour of the track is investigated. A two-level fractional factmial design method is used in the search for a combination of numerical levels of these parameters making the maximum bending tensions the minimum. Finally, the main conclusions are given.

Dynamic Interaction between Wheel and Track - A Parametric Search towards an Optimal Design of Rail Structures

SUMMARY The dynamic vertical interaction between a moving rigid wheel and a flexible railway track is investigated. A round and smooth wheel tread and an initially straight and noncorrugated rail surface are assumed in the present optimization study. A symmetric linear three-dimensional beam structure model of a finite portion of the track is suggested including rail, pads, sleepers and ballast with spatially nonproportional damping. The full interaction problem is numerically solved by use of an extended state-space vector approach in conjunction with a complex modal superposition for the track. Transient bending stresses in sleepers and rail are calculated. The influence of seven selected track parameters on the dynamic behaviour of the track is investigated. A two-level fractional factorial design method is used in the search for a combination of numerical levels of these parameters making the maximum bending stresses a minimum.

BODY STRUCTURE AND VEHICLE DYNAMICS

SUMMARY This paper is a presentation of aspects on car body design for mass transit vehicles and methods which has been evolved for the analysis of non-linear flexible railway vehicles by use of normal modes. In the end of the paper results from an experimental modal analysis are shown.

Steering a Flexible Railway Truck on Curved Track

This paper gives a linear analysis for the steady motion of a flexible two-axle railway truck on curved track. Most existing truck designs are too rigid to be self-steering, but provided that the primary suspension is sufficiently flexible, it is shown that a truck can negotiate main line curves without slipping or flange contact. Results are obtained for the maximum rolling displacement of the wheelsets (the tracking error), Fig. 8, and the minimum radius of curvature for no slipping, Fig. 10, expressed as a function of the suspension stiffness. It is shown that lateral loads due to superelevation deficiency have only a small effect on the motion of the truck, which is mainly determined by creep forces arising from the geometric inability of the four wheels to roll freely on curved track.

Flexible Railway Freight Rates

Flexible Railway Freight Rates

Flexible Railway Freight Rates

(1935). Flexible Railway Freight Rates. Journal of the American Statistical Association: Vol. 30, No. 191A, pp. 537-548.