Locomotive Dynamics Research Articles

Suppression of carbody hunting for a locomotive caused by low wheel–rail contact conicity by optimising yaw damper location

This study addresses the issue of carbody hunting in an electric locomotive induced by low wheel-rail contact conicity. The main objective is to mitigate this unstable motion by optimising the location of yaw dampers while ensuring bogie stability under high conicity conditions. A field test was first conducted to observe the carbody hunting behaviour, and a detailed locomotive dynamics model was then developed and validated using experimental data. The impact of yaw damper locations on locomotive stability was investigated, taking into consideration different carbody modes. The findings reveal the mechanism behind the deterioration of carbody stability due to the yaw damper installation angle and two installation layouts were proposed to enhance the carbody stability. Comparisons were then made with traditional solutions using both linear and nonlinear analysis, and experimental validation confirmed the effectiveness of the optimised yaw damper locations in improving carbody stability. This research highlights the importance of optimising the yaw damper's location to suppress carbody hunting, providing valuable insights for railway engineers and offering a promising solution for enhancing stability in high-speed train.

Bacteria-inspired magnetically actuated rod-like soft robot in viscous fluids

This paper seeks to design, develop, and explore the locomotive dynamics and morphological adaptability of a bacteria-inspired rod-like soft robot propelled in highly viscous Newtonian fluids. The soft robots were fabricated as tapered, hollow rod-like soft scaffolds by applying a robust and economic molding technique to a polyacrylamide-based hydrogel polymer. Cylindrical micro-magnets were embedded in both ends of the soft scaffolds, which allowed bending (deformation) and actuation under a uniform rotating magnetic field. We demonstrated that the tapered rod-like soft robot in viscous Newtonian fluids could perform two types of propulsion; boundary rolling was displayed when the soft robot was located near a boundary, and swimming was displayed far away from the boundary. In addition, we performed numerical simulations to understand the swimming propulsion along the rotating axis and the way in which this propulsion is affected by the soft robot’s design, rotation frequency, and fluid viscosity. Our results suggest that a simple geometrical asymmetry enables the rod-like soft robot to perform propulsion in the low Reynolds number (Re ≪ 1) regime; these promising results provide essential insights into the improvements that must be made to integrate the soft robots into minimally invasive in vivo applications.

Integrated simulation platform for a locomotive braking system

We used a locomotive and a rail car to examine the working principle of a locomotive braking system. We established models of the locomotive braking system, the locomotive dynamics, and the brake disc thermodynamics and, based on the correlation parameters for each subsystem, built an integrated simulation platform for the locomotive braking system based on Simulink and AMESim. Using this platform, we simulated the characteristics of the pneumatic braking unit, the locomotive braking, and temperature increase in the brake disc under emergency braking conditions. We compared our simulation results with experimental data and the results showed that the integrated simulation platform for the locomotive braking system could successfully be used to study locomotive braking control on the vehicle level. We provide a design optimization method for the development of a braking system, the setting of the anti-skid criterion, and early warning of an increase in the brake disc temperature.

Fatigue life prediction for locomotive bogie frames using virtual prototype technique

Current research papers use simulated load spectrums to assess bogie frames’ fatigue life but seldom consider traction and braking loads. Traction and braking loads play important roles in predicting fatigue life in high-speed and heavy haul operational scenarios. Hence, there is a research gap in terms of the consideration of longitudinal load spectrums while assessing bogie frames’ fatigue life. This paper presents research about this topic. A virtual prototype technique available in literature has been extended for this purpose; it uses multibody dynamics and finite element techniques to simulate the behaviour of bogie frames under real operational service loads. As a result, the special simulation methodology has been developed in this work and it includes the unique integration of simulation approaches that includes train dynamics, locomotive dynamics with the consideration of a traction control algorithm and the adopted fatigue life calculation method. This paper gives numerical examples of a rigid-flexible coupled dynamic railway vehicle model subjected to longitudinal forces. Road Environment Percent Occurrence Spectrum (REPOS) load spectrums of the bogie frame were developed from a whole-trip train simulation on a real route. The spectrums are then used to predict locomotive the bogie frame’s fatigue life. The results of the bogie frame fatigue life evaluation performed in this paper show that fatigue lives at the roots of traction rod seats under longitudinal load spectrums are shorter than their fatigue life under vertical load spectrums.

Isoflurane Exposure in Juvenile Caenorhabditis elegans Causes Persistent Changes in Neuron Dynamics.

Animal studies demonstrate that anesthetic exposure during neurodevelopment can lead to persistent behavioral impairment. The changes in neuronal function underlying these effects are incompletely understood. Caenorhabditis elegans is well suited for functional imaging of postanesthetic effects on neuronal activity. This study aimed to examine such effects within the neurocircuitry underlying C. elegans locomotion. C. elegans were exposed to 8% isoflurane for 3 h during the neurodevelopmentally critical L1 larval stage. Locomotion was assessed during early and late adulthood. Spontaneous activity was measured within the locomotion command interneuron circuitry using confocal and light-sheet microscopy of the calcium-sensitive fluorophore GCaMP6s. C. elegans exposed to isoflurane demonstrated attenuation in spontaneous reversal behavior, persisting throughout the animal's lifespan (reversals/min: untreated early adulthood, 1.14 ± 0.42, vs. isoflurane-exposed early adulthood, 0.83 ± 0.55; untreated late adulthood, 1.75 ± 0.64, vs. isoflurane-exposed late adulthood, 1.14 ± 0.68; P = 0.001 and 0.006, respectively; n > 50 animal tracks/condition). Likewise, isoflurane exposure altered activity dynamics in the command interneuron AVA, which mediates crawling reversals. The rate at which AVA transitions between activity states was found to be increased. These anesthetic-induced effects were more pronounced with age (off-to-on activity state transition time (s): untreated early adulthood, 2.5 ± 1.2, vs. isoflurane-exposed early adulthood, 1.9 ± 1.3; untreated late adulthood, 4.6 ± 3.0, vs. isoflurane-exposed late adulthood, 3.0 ± 2.4; P = 0.028 and 0.008, respectively; n > 35 traces acquired from more than 15 animals/condition). Comparable effects were observed throughout the command interneuron circuitry, indicating that isoflurane exposure alters transition rates between behavioral crawling states of the system overall. These effects were modulated by loss-of-function mutations within the FoxO transcription factor daf-16 and by rapamycin-mediated mechanistic Target of Rapamycin (mTOR) inhibition. Altered locomotive behavior and activity dynamics indicate a persistent effect on interneuron dynamics and circuit function in C. elegansafter developmental exposure to isoflurane. These effects are modulated by a loss of daf-16 or mTOR activity, consistent with a pathologic activation of stress-response pathways.

Train energy simulation with locomotive adhesion model

Railway train energy simulation is an important and popular research topic. Locomotive traction force simulations are a fundamental part of such research. Conventional energy calculation models are not able to consider locomotive wheel–rail adhesions, traction adhesion control, and locomotive dynamics. This paper has developed two models to fill this research gap. The first model uses a 2D locomotive model with 27 degrees of freedom and a simplified wheel–rail contact model. The second model uses a 3D locomotive model with 54 degrees of freedom and a fully detailed wheel–rail contact model. Both models were integrated into a longitudinal train dynamics model with the consideration of locomotive adhesion control. Energy consumption simulations using a conventional model (1D model) and the two new models (2D and 3D models) were conducted and compared. The results show that, due to the consideration of wheel–rail adhesion model and traction control in the 3D model, it reports less energy consumption than the 1D model. The maximum difference in energy consumption rate between the 3D model and the 1D model was 12.5%. Due to the consideration of multiple wheel–rail contact points in the 3D model, it reports higher energy consumption than the 2D model. An 8.6% maximum difference in energy consumption rate between the 3D model and the 1D model was reported during curve negotiation.

Vibration characteristics of railway locomotive induced by gear tooth root crack fault under transient conditions

Dynamic interactions between wheel and rail are becoming more intensified under the development of locomotive towards high-speed, heavy-haul and high-power directions, which are more likely to cause failures in gear transmission system of high-power heavy-haul electric locomotive. The dynamic impact of the locomotive gear transmission system becomes more drastic, especially for the extreme operation conditions, such as traction/braking process. Gear fault diagnosis under unsteady conditions has always been a hot and difficult research spot, and revealing of the gear fault vibration characteristics under the transient conditions is the premise and basis for effective fault detection and diagnosis. In order to reveal the gear fault vibration characteristics of railway locomotive dynamics system, a spatial dynamic model of a heavy-haul electric locomotive considering the dynamic coupling effect of gear transmission system is proposed based on the multibody dynamics theory in this paper. Then the dynamic responses of the locomotive under transient condition are obtained by considering the complicated excitations induced by the wheel-rail nonlinear contact, gear mesh and tooth root crack. The time-frequency analysis and angular synchronous average method are adopted to investigate the fault vibration feature of the tooth root crack. Finally, the distribution and variation of vibration characteristics of the gear tooth root crack fault evolution are revealed by condition indicators such as the Crest Factor (CF), Kurtosis (K), Fourth Order Figure of Merit (FM4), M6A, and M8A. The results indicate that: (1) the time-frequency analysis results of vibration acceleration of wheelset and bogie frame and dynamic mesh force could reflect the fundamental mesh frequency and its harmonics, however, only the vertical and longitudinal vibration acceleration of the wheelset and the gear dynamic mesh force could reflect the fault vibration characteristics in time-frequency analysis results; (2) the FM4, M6A and M8A values of locomotive system vibration signal could effectively reflect the crack propagation on the dynamic features of the locomotive system after being processed by angular synchronous averaging method.

Influence of wheel diameter difference on surface damage for heavy-haul locomotive wheels: Measurements and simulations

Fatigue damage of wheel surface is a common problem in railway field, leading to significant operational disturbances and maintenance costs due to frequent wheel turning. After wheel lathe turning, the initial wheel diameter difference (WDD) also accelerates the initiation and propagation of wheel surface cracks. Combined with a practical case in heavy-haul locomotives, the paper presents an investigation of the effects of initial WDD on wheel surface damage, including extensive field observations, statistical analysis of measured data, and numerical simulation of locomotive dynamics. By observing the crack characteristics, and measuring the wear and diameter of wheels, it is found that the large initial WDD caused by unqualified lathe turning is mainly responsible for the observed wheel damage. From the statistics of 53 heavy-haul locomotives in the depot, large WDD commonly exists even in the new turned wheelsets (more than 4 mm). Cracks and partial wear are both developed quickly on the wheelsets with large initial WDD, and always occurred on the wheels with smaller diameter, whereas the other side wheels are in good condition. Moreover, the wheel surface cracks are mainly located on a band of 65–120 mm from the wheel flange back. In addition, the numerical simulations show that the initial large WDD first causes the wheel partial wear, and further exacerbate the initiation of surface cracks.

Locomotive wheel wear simulation in complex environment of wheel-rail interface

Affected by the traction/braking, creep control and wheel-rail interface environment, wheel wear of locomotives is more complicated than that of other rolling stock. A locomotive wheel wear simulation model is developed, which includes a 3D locomotive track coupling dynamics model, a rolling contact model for rail traction vehicles based on Kalker's simplified theory, a PI-based creep control model and a wheel material wear model based on frictional power. The advantages of the dynamics model built in this paper are evaluated through two typical simulation cases. The effects of traction/braking and creep control on wheel wear are comprehensively investigated. The results indicate that the natural vibration characteristics of the locomotive/track system can be well reflected, and their influence on wheel wear can be taken into account. Traction and braking have a great influence on wheel wear, which should be considered for locomotive wheel wear simulation. It is a better way to control creep by using a control mode with variable creep threshold value.

A spatial dynamics model for heavy-haul electric locomotives considering the dynamic coupling effect of gear transmissions

A locomotive is usually powered by the electromagnetic torque which is transmitted from the traction motor to the wheelset by gear transmission. In order to investigate the dynamic coupling effects from the gear transmission subsystems on the entire locomotive dynamics system, a comprehensive spatial locomotive dynamics model that considers the dynamic coupling effect of the gear transmissions is developed based on the multibody dynamics theory. In this model, the moved Marker technique is employed to calculate the dynamic mesh force of the gear pairs through which more accurate time-varying gear mesh stiffness excitations could be imported, which is the core of this dynamic model. Then, the established locomotive dynamics model is validated by comparing with the experimental test results. Finally, the dynamic effects of the gear transmissions are revealed by comparing with the results from the traditional locomotive dynamics model without considering the dynamic excitations from the gear transmissions. The results indicate that the gear transmissions have negligible effects on the vibrations of the carbody and the bogie frame, and on the lateral vibrations of the motor and the wheelset. However, the gear transmissions have significant effects on the vertical and, in particular, the longitudinal vibrations of the motor and the wheelset. Thus, it is suggested that the dynamic effects of the gear transmissions are considered in the locomotive dynamics modeling, especially when the vibrations of the motors and the wheelsets are taken into account.

A Condition for Singular Optimal Control Formulation for a Tandem Pair of Gravity Fed Linear DC Machine Powered Mine Locomotives

Abstract The key focus in this study is on gravity fed linear DC machines used to drive mine locomotives. A case for optimal control singularity analysis for this tandem pair of gravity fed linear DC machines on a slope is thus presented. The key operational feature is for a generator locomotive to drive a motor locomotive with gravity providing the machine disparity for generator and motor action. Optimal control formulation is extended in this study, particularly optimal control singularity formulation. The optimal controller should be able to minimize the relative displacement between the machines. Mine locomotive dynamics results are also presented to show that the differential velocity and displacement are minimized. The performance index and Lagrangian are also minimized. The optimal control formulation is demonstrated via switching function differential calculus. The solution is shown to improve mine locomotive energy performance.

Effect of the drive system on locomotive dynamic characteristics using different dynamics models

Based on the theory of vehicle-track coupled dynamics and gear system dynamics, a locomotive-track coupled spatial dynamics model is established by considering the dynamic effects of the gear transmission system. The vibration responses of a locomotive’s major components are then simulated using three locomotive-track models, namely the proposed dynamics model with the gear transmissions, a locomotive-track coupled dynamics model that considers the traction motor, and the classical Zhai’s model. The locomotive dynamic responses of the three models are extracted and compared to reveal discrepancies between them so as to explore the dynamic effects of the power transmission system and clarify potential applications of these models. The results indicate that the dynamic effects of the gear transmissions have a negligible influence on the lateral vibrations of the locomotive components. However, they have obvious effects on the vertical and longitudinal vibrations of the wheelset and the traction motor. Another advantage of the locomotive dynamics model that considers the dynamic effects of the gear transmissions is that the dynamic performance of the drive system can be assessed in the vehicle vibration environment. This study provides theoretical references that can assist researchers in choosing the most appropriate locomotive dynamics model according to their specific research purpose.

Identification and characterization of the out-of-plane resonance in a dielectric elastomer to drive an agile robotic cube

A dielectric elastomer (DE) vibrates and resonates mechanically under an alternating voltage and the vibrations undergo a transition from the in-plane to the out-of-plane state. In this study, a phase diagram was established experimentally to illustrate this transition and an electromechanical model was proposed to predict the transition using the boundary conditions. The resonance frequencies were calculated and were shown to be consistent with the experimentally obtained values. A novel vibration-driven robotic cube was then designed and powered by the dielectric elastomer at the 1st order out-of-plane resonance. The agile robotic cube is ultralight and demonstrated a speedy response of 125 mm/s (1.8 body length/s), which is superior to the locomotive dynamics of the existing DE-based robotic devices.

Modeling, simulation and re-adhesion control of an induction motor–based railway electric traction system

Increasing the traction force is a complex problem in the design of railway vehicles; therefore, effective traction systems and algorithms have to be developed. During the traction process, the verification of traction algorithms and control strategies are based on simulations covering all locomotive dynamics. In this article, traction model of a railway vehicle and re-adhesion control method based on simulation approach are investigated to obtain more effective results. The longitudinal dynamic of a railway vehicle having traction system, which comprises two parallel motor groups, each of which has two field-oriented induction motor connected in series, is simulated to examine time-dependent changes in motor stator currents, traction torque, adhesion and resistance forces according to a given speed reference. The interaction between the adhesion force and the slip ratio is established according to the Burckhardt adhesion model, and a modified super-twisting sliding mode slip control is implemented in a computer simulation under various contact conditions so that simulation results approve the presented control method works under the maximum adhesion force. The comparison between the classical and modified version of the proposed control strategy was made to better evaluate the performance of the control system and to better optimize the traction system.

Modelling, simulation and applications of longitudinal train dynamics

ABSTRACTSignificant developments in longitudinal train simulation and an overview of the approaches to train models and modelling vehicle force inputs are firstly presented. The most important modelling task, that of the wagon connection, consisting of energy absorption devices such as draft gears and buffers, draw gear stiffness, coupler slack and structural stiffness is then presented. Detailed attention is given to the modelling approaches for friction wedge damped and polymer draft gears. A significant issue in longitudinal train dynamics is the modelling and calculation of the input forces – the co-dimensional problem. The need to push traction performances higher has led to research and improvement in the accuracy of traction modelling which is discussed. A co-simulation method that combines longitudinal train simulation, locomotive traction control and locomotive vehicle dynamics is presented. The modelling of other forces, braking propulsion resistance, curve drag and grade forces are also discussed. As extensions to conventional longitudinal train dynamics, lateral forces and coupler impacts are examined in regards to interaction with wagon lateral and vertical dynamics. Various applications of longitudinal train dynamics are then presented. As an alternative to the tradition single wagon mass approach to longitudinal train dynamics, an example incorporating fully detailed wagon dynamics is presented for a crash analysis problem. Further applications of starting traction, air braking, distributed power, energy analysis and tippler operation are also presented.

Assessing steam locomotive dynamics and running safety by computer simulation

Steam locomotives are preserved on heritage railways and also occasionally used on mainline heritage trips, but since they are only...

Modelling of track wear damage due to changes in friction conditions: A comparison between AC and DC electric drive locomotives

The locomotive traction motor electric dynamics and its impact on the rail and vehicle have not been investigated deeply in transient wheel–rail contact conditions. Such transient traction behaviour could be more significant to dynamic traction performance and track degradation (i.e. corrugation formation, fatigue, wear, etc.) than steady state behaviour. In order to study this, detailed numerical simulations are performed to investigate the locomotive multi-body dynamic response to a change in contact conditions with an AC and DC electrical traction motor respectively. In particular, creep response, locomotive vibration, and dynamic normal and tractional forces are determined using a developed full scale locomotive dynamics model. The model includes the detailed AC and DC motor dynamics. Further investigation has been undertaken to understand the wear caused during and after the change of friction conditions from dry to wet and wet to dry. The result shows the GT46Ace locomotive AC drive can achieve higher traction efficiency compared to the equivalent DC drive running under notch 8, especially in the wet condition. It is also demonstrated that the AC drive produces slightly lower wear on average than the DC drive after the transient. However, the transient dynamic oscillation of wear caused by the AC drive is significantly higher than the DC drive.

Simplified and advanced modelling of traction control systems of heavy-haul locomotives

Improving tractive effort is a very complex task in locomotive design. It requires the development of not only mechanical systems but also power systems, traction machines and traction algorithms. At the initial design stage, traction algorithms can be verified by means of a simulation approach. A simple single wheelset simulation approach is not sufficient because all locomotive dynamics are not fully taken into consideration. Given that many traction control strategies exist, the best solution is to use more advanced approaches for such studies. This paper describes the modelling of a locomotive with a bogie traction control strategy based on a co-simulation approach in order to deliver more accurate results. The simplified and advanced modelling approaches of a locomotive electric power system are compared in this paper in order to answer a fundamental question. What level of modelling complexity is necessary for the investigation of the dynamic behaviours of a heavy-haul locomotive running under traction? The simulation results obtained provide some recommendations on simulation processes and the further implementation of advanced and simplified modelling approaches.

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.

Analysis of the Deterioration of Harmonic Local Irregularity on Locomotive Wheel-Rail Vertical Force

By the MATLAB software the article simulated the local irregularity, the new harmonic excitation superimposed on the initial harmonic to simulate track settlement deterioration, the new uplift excitation superimposed on the initial harmonic to simulate track raised deterioration, as the locomotive model external excitation, using the SIMPACK multi-body dynamics simulation software to analyze the influences of the deterioration of harmonic local irregularity on locomotive wheel-rail vertical force, on the basis of the locomotive wheel-rail interaction dynamics index by the locomotive vehicle dynamics theory. The simulation results show that when the deterioration of harmonic local irregularity occurs, even if the amplitude of deterioration is small, which will cause serious deterioration of wheel-rail dynamic response and strong shock and vibration of wheel-rail .The larger amplitude of harmonic local irregularity, the greater of the maximum wheel-rail vertical force. When deterioration of the amplitude exceeds a certain value, the maximum of the wheel-rail vertical force exceedes the limit, which will cause derailment. The wheel-rail dynamic interaction increases with the speed increasing. At the same speed (such as 120km/h), harmonic local irregularity settlement deterioration compareing to harmonic local irregularity raised deterioration, the maximum of the wheel-rail vertical force increases 14.4%. Therefore, local irregularity deterioration or the speed of the locomotive should be strictly controlled.