The rise in wheel rail equivalent conicity after wheel reprofiling leads to an increase in bogie hunting frequency, elastic vibration modes of carbodies are easily excited, which may induce abnormal carbody vibrations. A modal optimisation design framework for high-speed train carbodies is proposed from the perspective of structural design. A specific high-speed train carbody exhibiting abnormal elastic vibration during service is taken as the research object, and the vibration mechanism is first identified based on operational test data. A convolutional neural network (CNN)-based surrogate model is constructed to establish the nonlinear mapping between sectional thickness parameters, carbody mass, and the first-order diamond modal frequency. The Covariance Matrix Adaptation Evolution Strategy (CMA-ES) is then employed to carry out high-dimensional size optimisation of the sectional profiles. The optimised carbody is further evaluated through static strength verification, free modal analysis, and rigid-flexible coupled dynamic simulations under equivalent operating conditions. The results show that the proposed optimisation framework achieves significant weight reduction while effectively increasing the first-order diamond modal frequency, thereby suppressing abnormal elastic vibrations and substantially improving passenger comfort. The proposed method provides a practical and effective solution for the lightweight and modal optimisation design of high-speed train carbodies.

The complex vibration of high-speed railway track systems under seismic excitation greatly increases the derailment risk of electric multiple units (EMUs). To clarify the derailment mechanism and evaluate the performance of derailment protection devices, a comprehensive dynamic model incorporating seismic input, bridge response, vehicle multibody dynamics, and 3D multi-point contact among the wheelset, gearbox, traction motor, protection device, rail, and slab track was developed. Numerical simulations were performed under different train speeds and seismic intensities. Results show that the seismic-induced derailment of high-speed EMUs exhibits strong nonlinearity and frequent multi-point collisions, with wheelset lateral displacement being the key indicator for derailment evaluation. The protection device effectively limits lateral displacement and delays complete derailment under low- and medium-speed conditions but shows reduced effectiveness under high-speed operation or strong earthquakes, where failure may occur. Although the brake disc and gearbox provide limited buffering, they cannot replace the dedicated device. Working-domain analysis further indicates that the device remains functional when train speed is below 150 km/h and track lateral acceleration is under 10 m/s2. These findings offer theoretical support for seismic safety assessment and optimization of derailment protection devices for high-speed railway vehicles.

A co-simulation model incorporating bogie active yaw control (BAYC) was initially developed using Simpack and Simulink. Subsequent investigation into the active steering control mechanism of railway vehicles, facilitated by this model, delineated the distinctions and interconnections between the two targets of mitigating wheel-rail wear and balancing wheelset lateral force. This elucidation aimed to clarify the preferred control target of the BAYC system. To realize this target, an evaluation of the merits and demerits of two control strategies was conducted across various dimensions. The control effects, control efforts, stability, robustness, and vibration transmission characteristics of different control strategies were then demonstrated. Additionally, discussions ensued concerning the alignment between actuator drifting mode characteristics and the running safety of vehicle, thus furnishing an engineering framework for the implementation of passive fault-tolerant control (FTC). Ultimately, the active FTC following actuator failure was effectuated leveraging the over-drive characteristics inherent to the BAYC system.

With the increase in train load and longer train formations, wheel-rail wear and contact fatigue issues in heavy-haul trains continuously emerge. However, the impact mechanisms of wheel wear in heavy-haul trains on rail Rolling Contact Fatigue (RCF) remain unclear. Therefore, this paper establishes a dynamic model of a C80 freight vehicle, and the advanced discrete elastic contact method is used to calculate the contact parameters. Then, the fatigue index with shakedown diagrams and damage function is used to evaluate the contact fatigue of the rail. This approach analyzes the extent of rail RCF damage under various levels of wheel wear and different wheel diameter differences (WDD), along with its lateral distribution on the rail. Finally, the paper analyzes curve resistance through a curve resistance model. The results showed that the fatigue index and damage under discrete elastic contact are larger than the equivalent elasticity. For worn wheels, the damage to both inner and outer rails increases sharply when the wear depth exceeds 2 mm. Under different WDD values, the maximum damage amount on the larger wheel side increased from 1.42 x 10-5 to 4.33 x 10-5. Wheel wear increased the probability and amount of rail RCF, with a more significant increase on the outer rail than the inner rail. The curve resistance increases with wheel wear and decreases with the increase of curve radius, with particularly significant changes between 300 m and 500 m. The findings provide a reference for train operation and the mitigation of rail fatigue.

To explore rail corrugation's influence on high-speed train gearbox housing dynamic characteristics, this paper investigates the correlation between gearbox housing vibration acceleration energy and rail corrugation, proposing corresponding safety limits. Using vehicle-track coupling dynamics and multibody dynamics theories, a rigid-flexible coupling model for CRH3 vehicle-track systems was established. With rail corrugation and Wuhan-Guangzhou track spectrum as excitation, three gearbox housing vibration sensors analyzed effects of varying corrugation wavelengths/depths at different speeds on vibration energy. The vibration energy-rail corrugation correlation was explored, with vibration energy limits and maintenance safety limits proposed. Results show rail corrugation significantly increases gearbox housing vibration energy: points A and C exhibit stronger regularity (A's maximum is 86.3% higher than C's), with B most affected. For point A, mixed-wavelength high-frequency responses include single-wavelength components and harmonics, exciting gearbox housing high-frequency resonance. A power model (R2 = 0.9437) characterizes the correlation. A vibration energy threshold of 1.44 & times; 104 m2/s4 and corresponding rail corrugation maintenance limits are proposed. Practically, maintenance strategies should integrate operational conditions, track structure, and gearbox housing status, with timely maintenance when corrugation depth exceeds safety limits.

As the speed of high-speed trains increases, hunting motion has become a critical issue threatening vehicle stability and safety. This paper proposes an active anti-yaw damper control strategy based on an Electro-Hydrostatic Actuator (EHA). A high-speed train vehicle dynamic model and a simplified mathematical model of the EHA were established on the Simpack and Simulink platforms. The EHA was employed as an active anti-yaw damper actuator, controlled by a fractional-order proportional-integral-differential (FOPID) controller. The weighted sum of the root-mean-square (RMS) values of the lateral accelerations of the carbody and bogie was used as the optimisation objective. The Particle Swarm Optimisation (PSO) algorithm was applied to obtain the optimal parameters. Through co-simulation, the vibration suppression effect of this control strategy under primary and secondary hunting motions, and its robustness under various track excitations, were validated. Under the active control, the RMS value of the bogie lateral acceleration decreased from 5.61 m/s2 to 4.22 m/s2, and the nonlinear critical speed of the vehicle increased from 556 km/h to 652 km/h. This paper demonstrates the potential of EHA-based active anti-yaw damper control to improve the hunting stability of high-speed trains, and provides a reference for high-speed train stability control.

To address the deterioration of wheel-rail contact conditions caused by severe rail wear in small-radius curved sections of heavy-haul railways, this paper proposes a new rail grinding profile design method based on the Chi-Square Distribution Function (CDF). By introducing three adjustable parameters to control the grinding area and depth, and integrating the Kriging Surrogate Model (KSM) with the Particle Swarm Optimization (PSO) algorithm, this study established a multi-body dynamic model of a heavy-haul freight vehicle for simulation analysis. The wheel-rail wear index and derailment coefficient were adopted as multi-objective optimization functions. The results show that the optimized grinding profile significantly improves the wheel-rail contact relationship: the contact patch area increases and the equivalent conicity decreases from 0.3 to 0.2. The lateral wheel-rail forces and wear depths are notably decreased. The wear depths of the left and right rails are reduced by 30.39% and 74.09%, respectively. The wear depths on the left wheel and right wheel of the first wheelset decrease by 76.18% and 74.09%, respectively. Additionally, rolling contact fatigue (RCF) evaluation based on the shakedown diagram indicates that the probability of the rail fatigue index entering the ratcheting zone is significantly reduced after grinding, demonstrating improved resistance to fatigue damage. This method enhances the efficiency and engineering applicability of optimized grinding profile design, and effectively improves the curve passing performance and operational safety of heavy-haul trains.

To investigate the dynamic response and instability mechanisms of urban rail vehicles under extreme collision and derailment scenarios, a high-fidelity dynamic simulation model of a metro train system was developed based on the ADAMS/Rail platform. The model integrates three-dimensional nonlinear contact mechanics and structural topological evolution, enabling the simulation of the complete process from normal operation to post-collision derailment. Two representative collision scenarios were designed and analysed: frontal collision and oblique collision. The study systematically evaluated the influence of operating speed (20-40 km/h) and collision angle (90 degrees-70 degrees) on the dynamic behaviour of the train. Simulation results show that train derailment is governed by both speed and collision angle. Frontal collisions at speeds exceeding 40 km/h cause excessive lateral and vertical displacement of the leading wheelsets, triggering derailment, as the energy-absorbing components fail to fully mitigate the impact. Under oblique collision conditions at 30 km/h, derailment probability increases significantly when the collision angle is below 85 degrees, and continuous derailments of multiple wheelsets are observed at an angle of 80 degrees. The wheelset response exhibits marked temporal and spatial sensitivity, with the front wheelsets of the leading car identified as the primary source of instability. The findings offer theoretical insights and engineering guidance for derailment protection structure design, energy absorption system optimization and safety assessment of metro trains under extreme operating conditions.

High-frequency wheel-rail vibrations (300-1000 Hz), induced by transient impacts, periodic excitations, and structural resonances, pose significant threats to the fatigue life of vehicle-track systems and exacerbate wheel-rail noise. This study proposes a novel dynamic vibration-absorbing fastener (DVAF) that integrates vibration suppression and rail support functions. By optimising the stiffness of upper/lower rubber pads and the mass of the iron plate, the DVAF is tuned to target critical rail local bending modes (e.g. 500-700 Hz). Analysis demonstrates the DVAFs' efficacy: under wheel flats, 27-43% vibration reduction at 300-1000 Hz and 36-64% at 500-700 Hz; under wheel polygons, 49-86% at 300-1000 Hz and 50-87% at 500-700 Hz. Long-term assessments confirm DVAF suppresses wheel polygonization via 550-650 Hz energy dissipation with stable performance. After 350,000 km (normal roughness), it reduces wheel roughness by 15.9 dB (FS660), maintaining >97% vibration reduction. After 150,000 km (wheel flats), it reduces wheel roughness by 11.9 dB (FS631), with >97% vibration reduction. The DVAF offers a cost-effective, space-efficient solution that combines static rail support with dynamic vibration absorption, requiring minimal infrastructure modifications while ensuring long-term durability and performance stability.

Fatigue cracking occurred in the spring-cap sleeve of a metro bogie frame after long-term service. This study aimed to identify the most probable engineering mechanism of the cracking and evaluate a practical mitigation strategy for in-service vehicles. Field inspection, field testing, modal analyses of the primary steel springs and bogie frame, in-service stress measurements, and validation tests on a high-frequency vibration test bench were conducted. The results identified a stable hazardous frequency band of 70–100 Hz associated with 12th-order wheel polygonization and rail corrugation. Within this band, the first two modes of the primary steel springs and the first two local bending modes of the bogie frame showed clear frequency-domain overlap with the measured excitation peaks. In-service stress measurements and fatigue assessment based on the measured stress spectrum identified the crack-prone side as the fatigue-controlling location, where the cumulative fatigue damage exceeded 1 under a target service mileage of 3.6 × 10⁶ km. These findings indicate that the cracking was a local high-cycle fatigue problem associated with resonance-coupled wheel–rail excitation transmitted through the primary suspension and amplified by modal interaction between the steel springs and the bogie frame. Bench-based tests showed that the hydraulic damper did not shift the dominant hazardous frequency band, but modulated the local resonant response and the associated fatigue-damage accumulation within this band. Among the tested damping cases, 6.5 kN·s/m showed the best mitigation performance under the present controlled bench-test conditions.

In response to the vertical abnormal shaking phenomenon observed in a certain type of high-speed electric multiple unit (EMU) during operation, this study aims to reveal its vibration mechanism and propose improvement measures to enhance train running quality. Dynamic on-track tests were conducted under four operating conditions, with acceleration sensors installed on the carbody, bogie frame, traction motor, and gearbox. Vibration signals were analyzed using time-frequency methods, and a rigid-flexible coupled dynamic model incorporating finite element-based flexibility of bogie and carbody was developed using condensation and Lanczos techniques. Results show that shaking occurs only during acceleration or deceleration when the traction motor is operating, with a dominant frequency consistently around 38 Hz and independent of blower status. Near 50 km/h, motor excitation triggers the bogie's first torsional mode, amplifying vibrations at the frame ends and transmitting them to the carbody roof through the secondary suspension. This frequency coincides with local carbody bending modes, forming a dual resonance effect. The findings, validated by simulations and experiments, reveal the amplification path of traction-induced vibration and provide guidance for vibration isolation, modal optimization, and resonance-avoidance strategies in high-speed trains.

With the increase in operating speed of high-speed electric multiple units (EMUs), the regulatory role of anti-yaw dampers in vehicle operational stability has become critical. This paper establishes a dynamic model of a high-speed EMUs to investigate the influence of installation angles and anti-yaw damper layouts on dynamic performance. A root locus analysis was conducted by linearizing the vehicle system and the wheel rail interaction to reveal the modal characteristics under different wheel rail matching conditions and rail deviations. The results show that increasing the installation angle can significantly reduce the critical speed. When the installation angle increases from 0 degrees to 25 degrees, the nonlinear critical speed under worn wheel rail contact conditions decreases with increasing angle, resulting in a 13.63% reduction. The inner high rail, combined with worn wheels with higher equivalent conicity, tends to induce secondary hunting instability. Reducing the installation angle enhances stability. The symmetrical layout with upward openings demonstrates superior performance under worn wheel rail conditions, with higher nonlinear critical speeds and improved ride indexes than other layouts. This paper provides theoretical guidance for optimizing anti-yaw damper installation angles and arrangement modes.

Abnormal vibration of gear transmission systems is one of the key factors affecting the operational reliability of tram vehicles. However, the vibration characteristics and excitation mechanisms of gearbox systems under actual operating conditions are not yet fully understood. In this study, field vibration tests were conducted on a tram gearbox system to investigate the characteristics of abnormal vibration. The vibration signals were analyzed using spectral analysis and operational modal analysis methods, and the relationship between gear meshing excitation and structural vibration was examined through theoretical analysis and simulation. The results show that the abnormal vibration is closely related to gear meshing excitation, and significant vibration amplification occurs when the meshing excitation frequency approaches the natural frequencies of the drivetrain structure. The identified modal characteristics reveal that structural resonance plays an important role in the vibration response of the gearbox system. The findings provide useful insights for the diagnosis of abnormal vibration in tram drivetrain systems and offer a reference for vibration control and maintenance of railway gear transmission equipment.

With the rapid development of intercity railways in China, issues such as wheel rail wear and excessive lateral forces during the negotiation of small-radius curved tracks have emerged. This paper proposed a method of integrating Electro-Hydrostatic Actuator (EHA)-based active radial steering dynamic modeling. The method integrates vehicle dynamic modeling, fractional-order Proportional-Integral (PI) control, and wear analysis. An EHA model integrating permanent magnet synchronous motors, gear pumps, and hydraulic cylinders was developed in Simulink. To address the poor curve-negotiation performance of conventional passive bogies, two EHA configuration schemes (longitudinal and lateral arrangements) were proposed based on theoretical analysis. Parameter analysis has been conducted, and the longitudinal EHA configuration has been demonstrated to be superior in the simulation environment. The results show that active radial steering technology significantly improves curve-negotiation performance through optimized wheelset alignment, with the longitudinal EHA configuration achieving superior reductions in attack angles, wear, and lateral forces. The longitudinal EHA arrangement demonstrates superior performance in suppressing wheelset attack angle and comprehensive wear control. Under standard conditions, it reduces wheelset attack angle by 35% and wear number by 30% in a small radius curved track. This technology enhances operational safety and reduces maintenance costs, providing critical technical support for efficient intercity railway operations.

For high-speed bogie, the traction motor contributes to a large mas to the bogie system then influences the running stability. This study proposed to actively control the suspension parameters of the traction motor to enhance the running performance of the high-speed bogie. A simplified vehicle dynamics model was firstly built with nonlinear wheel/rail contact integrated, then a root locus analysis was performed to examine the relationship between the motor suspension frequency and critical speed of the vehicle system. Based on this, the necessity of active control on the motor suspension was elaborated, and it was pointed out that the active suspension control can adjust the suspension frequency of traction motor to increase the critical speed of the vehicle system under different wheel/rail conicity states. Furtherly, bifurcation analysis is carried out to show that the active control may affect the vehicle bifurcation characteristics. According to the calculations, with fixed lateral damping ratio of the motor, the linear critical speed of the system has increased by 4.8% -24.6%, with fixed lateral damping of the motor, the linear critical speed of the system has increased by 1.9% -30.9%, and possible impact of time delay and countermeasures were explained. Furtherly, optimization can be performed using the nonlinear control laws with the cubic terms concerned.

After two decades of leapfrog development, China has built the world's largest 350 km/h high-speed railway operation system. CR400 high-speed train, as the core equipment of this system, its wheel-rail dynamic characteristics directly affect the operational quality of the railway network. Based on a four-month in-service tracking test covering over 230,000 km on the Beijing-Shanghai high-speed line, this study identifies fixed-frequency peaks in vertical axlebox acceleration around 45 Hz, 350 Hz, 580 Hz, and 820 Hz, amplitudes of which surge nonlinearly with speed. Wheel roughness measurements reveal a distinctive "dual-peak order" polygonization pattern: dominated by the 10 similar to 12th order (similar to 350 Hz, wavelength 240 similar to 290 mm) with a co-developing 17 similar to 18th order (similar to 580 Hz, 160 similar to 170 mm), markedly different from the existing CRH380 trains. Through finite element simulations and wear evolution analyses, we establish that these frequencies correspond to intrinsic wheel-rail coupling modes (P2, B2, B3, B4), with the low-damping and frequency-stable B2 and B3 modes acting as the physical origins driving periodic wheel wear. To explain why low-order polygons become dominant despite the presence of both B2 and B3 excitations, we propose PolyFilter, a novel spatial convolution-based model that, for the first time, abstracts the abrasive block as a mechanical low-pass filter. The analysis reveals that the current 125-mm-long abrasive block operates in a severely ineffective trace-grinding mode against the 10-12th-order polygon at 350 km/h, nullifying their intended suppression effect while allowing the B3-excited high-order components to be partially suppressed. This geometric selectivity, rooted in the fundamental mismatch between block length and polygon wavelength, provides the first quantitative explanation for the selective evolution of polygon orders observed in field tests. Accordingly, two targeted countermeasures are proposed: (1) frequency-shifted arrangement of high-frequency vibration-absorbing fasteners to detune resonant excitation; and (2) increasing abrasive block length to achieve effective "span-grinding". These countermeasures offer both theoretical insight and practical pathways for ensuring safe, reliable, and cost-efficient operation of high-speed trains exceeding 350 km/h, including the CR400 and the under-development CR450.

Wheel polygonal wear is a critical form of non-uniform tread degradation in metro systems, leading to abnormal vibration, noise, and accelerated deterioration of wheel-rail components. This study aims to clarify the underlying mechanism of polygonal wear formation from the perspective of vehicle-track coupling dynamics. A comprehensive investigation combining field measurements, dynamic modelling, and finite element modal analysis is conducted. Field data reveal that polygonal wear is primarily concentrated in the 7~9th orders, corresponding to a dominant vibration frequency band of 50~70 Hz. A vertical vehicle-track coupling dynamic model is established to analyze the frequency response characteristics, while finite element models of different track structures are employed to identify intrinsic modal properties. The results indicate that the P2 resonance of the coupling system, occurring at approximately 63.36 Hz for floating slab track, closely coincides with the characteristic frequency of the 8th-order polygonal wear. This frequency matching condition leads to significant dynamic amplification at the wheel-rail interface, initiating initial geometric irregularities. Subsequently, a self-reinforcing feedback mechanism is formed, in which polygonal wear acts as a periodic excitation source that continuously excites the system near resonance. Meanwhile, local rail bending modes at higher frequencies further modulate the contact force distribution, promoting the growth and stabilization of polygonal patterns. In contrast, for trapezoidal sleeper track, the P2 resonance frequency shifts to approximately 126.91 Hz, which is significantly separated from the dominant excitation band. This frequency mismatch suppresses resonance amplification and inhibits the formation of low-order polygonal wear. In addition, it was found during investigation that periodic irregularities in rail joints are the external cause of wheel-rail P2 force resonance. These findings demonstrate that wheel polygonal wear is governed by a resonance-driven coupling mechanism controlled by frequency matching among track excitation, system resonance, and wear-induced vibration. The study provides a theoretical basis for vibration mitigation through track design optimization and wheel maintenance strategies.