Longitudinal resistance is critical for ballasted track stability. An innovative X-shaped sleeper was developed to enhance this performance. A coupled DEM-MBD model of a full-scale ballast-sleeper-subgrade system was established to investigate the effect of sleeper geometry on longitudinal resistance and mechanisms. Results show a single X-shaped sleeper increases longitudinal resistance by approximately 27.2% over double I-shaped sleepers. Both types exhibit comparable end and bottom resistance, but the X-shaped sleeper's V-shaped arms significantly improve ballast interlocking, nearly doubling side frictional resistance. Microscopic analysis indicates the X-shaped sleeper mobilizes a broader range of particles, engaging more ballast in resisting movement. Stress analysis reveals stress under I-shaped sleepers concentrates beneath the crib, whereas the X-shaped sleeper transfers stress into shoulder ballast and deeper subgrade, enabling subballast and subgrade layers to enhance trackbed stability through compaction and disturbance. These findings support the application and optimization of X-shaped sleepers in ballasted tracks.
The casting of self-compacting concrete (SCC) is crucial for the safe operation of China Railway Track System type III (CRTS III) slab tracks. To elucidate the track structure's mechanical behavior during construction, a full-scale experiment was conducted, and a coupled discrete element method (DEM) and multi-flexible body dynamics (MFBD) model was established. SCC flow, alongside track slab buoyancy, displacement, and deformation, was systematically analyzed. It was revealed that SCC flow involves four distinct stages. Track slab mechanical responses were observed to peak at the end of casting, resulting in an upward arching, with measured buoyancy of 42.99 kN and maximum vertical displacement of 0.88 mm. Furthermore, SCC fluidity is significantly influenced by aggregate morphology and gradation, which directly affects these mechanical indicators and casting time. To optimize construction quality and efficiency, reducing flaky aggregate content and balancing coarse aggregate proportions are recommended.
The flow field and far-field aerodynamic noise of 1:8 scaled high-speed trains with three-carriage running on the slab tracks are investigated by wall-adapting local eddy viscosity large eddy simulation and Ffowcs Williams-Hawkings equation. The agreement of pressure coefficient and sound pressure level between the simulations and measurements suggests the accuracy of the current approach. Doppler effect affecting the far-field noise radiation can be observed through the simulations on moving train cases. Compared with the static train cases, the far-field noise spectra are consistent except that the sound pressure level at high frequency is larger with the difference in overall sound pressure level around 1 dB for the moving train cases. The fastener supports of slab track exert periodic disturbances on the near-ground flow, resulting in the pressure fluctuations at discrete frequencies of 1234 Hz and 881 Hz occurring near the train head at the train running speeds of 350 km/h and 250 km/h. There is a strong correlation between the flow near the train head and the aerodynamic noise at the characteristic frequencies whereas the overall energy is small. As the airflow convects downstream, the airflow energy becomes higher, thus the complex vortex structure weakens gradually the influence of the over-track phenomenon.
Polyurethane (PU) grouting is widely used to remediate settlement in ballastless track subgrades. The expansion force generated during this process is a key parameter for lifting the track. Generally, a larger grouting volume produces a greater expansion force and a higher lifting capacity. However, in practice, the grouting volume faces two main constraints. First, the allowable track uplift restricts the maximum lifting height. Second, the physical properties of the grouting medium restrict the injection volume. Therefore, a better understanding of the relationship between PU grouting volume and expansion force is needed. Based on traditional slurry diffusion and uplift theories, this paper develops a mechanical model for expansion force in ballastless track subgrades. Custom-designed tests were then conducted to obtain empirical equations for predicting expansion force and consolidation density. Using these equations, we propose a coupled model that links grouting volume to expansion force for track uplift. To verify this model, we performed physical lifting tests on graded crushed stone layers. The theoretical grouting volumes calculated by the coupled model closely match the experimental results. This agreement validates the proposed theoretical model.
Friction heat will aggravate plastic deformation and performance degradation in wheel-rail system. In this study, a three-dimensional (3D) thermo-mechanical coupled finite element (FE) model of wheel-rail cyclic rolling contact was developed, incorporating strain hardening, strain-rate strengthening and thermal softening effects. The evolution of temperature, stress and strain during wheel-rail rolling-sliding contact was examined, and influences of creepage, train speed and rail corrugation-induced impact were evaluated. The results indicate that contact temperature and residual stress/strain accumulate progressively after four wheel passages. For a corrugated rail under train speed of 400 km/h and 20% creepage, the surface temperature can reach 748.8 degrees C, which may trigger phase transformation of rail material. Thermal effect will significantly enhance the residual stress/strain amplitudes and accelerate wheel/rail damage under higher creepage, and creepage exerts a more pronounced effect on wheel-rail thermo-mechanical response than train speed. These findings will support wheel-rail design and safety assessment in extreme conditions.
When a high-speed maglev train passes through a platform at 600 km/h, the intense train-induced wind field generates significant aerodynamic impact on platform personnel, compromising their safety. Therefore, it is imperative to define a safe evacuation distance suitable for platforms of 600 km/h-class high-speed maglev lines to ensure the aerodynamic safety of waiting passengers and staff. This study employs a combined approach of moving model tests and numerical simulations to investigate the train-induced wind and the surface pressure distribution on personnel mannequins caused by a high-speed maglev train passing a platform. The influence of key parameters such as train speed, evacuation distance, and personnel height on the train-induced wind and personnel surface pressure distribution is examined. The evolution of the flow field structure around the train during both open-track and platform-side operation is explored, revealing the interactive flow mechanism of the coupled high-speed maglev train/platform personnel system. The spatiotemporal distribution characteristics of the train-induced wind and personnel surface pressure in the platform area during train passage are obtained, clarifying the influence patterns of train speed, evacuation distance, and personnel height. The research results indicate that when the train passes the platform, the lateral force increases, the lift difference between the head, middle, and tail cars increases, and the aerodynamic performance deteriorates. Under the platform condition, the amplitude of the train-induced wind when the head and tail cars pass is greater than without a platform. The platform restricts the development of the train's wake vortices, preventing them from reaching the platform and thus reducing the train-induced wind when the tail car passes. Under the platform condition, a vortex is generated on the platform side when the head car passes, which gradually develops and moves upward as the train passes. Using a wind speed of 14 m/s as the safety criterion, the safe evacuation distance is determined to be 3.99 m at a train speed of 600 km/h, 3.53 m at 500 km/h, and increases to 4.18 m when the train speed reaches 650 km/h.
With the rapid development of rail transit in China, elevated bridge lines have been widely adopted due to their high space utilization efficiency. However, the associated environmental noise issues have become increasingly prominent. Particularly in steel box girder bridges, the noise from the track system and the structure-borne noise from the bridge exhibit high similarity in both spectral characteristics and sound pressure levels, with comprehensive sound levels reaching 80-90 dB or above. This makes traditional single-method noise control strategies less effective. This paper focuses on the 'Vehicle-steel bridge-noise barrier' coupled system. Using an integrated approach of field tests, theoretical modelling, and numerical simulation, it systematically investigates the system's noise radiation mechanisms, energy transfer paths, and spatial distribution characteristics. A vehicle-track-bridge coupled dynamics model and a statistical energy analysis (SEA) noise prediction model were established and validated. The results indicate that bridge structure-borne noise plays a dominant role in the overall noise emission, and the noise barrier provides significant insertion loss of 16-20 dB, particularly in the mid-to-high frequency range. The findings of this study can serve as a theoretical basis for noise prediction and the optimized design of noise barriers in rail transit steel bridge applications.
As a core component of power transmission in high-speed trains, traction motor bearings are subjected to long-term and frequent overvoltage impulses, which may lead to electrochemical corrosion occurring, accompanying with the dramatic reduction of bearings' service life. To investigate the electrical corrosion characteristics of these bearings under the combined action of common-mode voltage and transient operational overvoltage, a 'train-converter-motor' equivalent circuit model is constructed, meanwhile an experimental platform for observing the electrical damage of bearings is established for simulating different operational conditions of the traction power supply system. Via a series of simulating tests, it indicates that the insulation layer capacitance is a key tenable parameter directly correlating the bearing voltage, as its variation exhibits opposing regulating patterns on the bearing voltage under common-mode voltage versus transient vacuum circuit breaker (VCB) operational overvoltage impulse. Further coupled 'electrical-thermal' finite element simulations reveal that voltage superposition leads to highly concentrated electric fields within the bearing, with a maximum field strength reaching 4.42 & times; 107 V/m and a local temperature rise peak exceeding 3750 degrees C. Experimental results indicate that under the combined action of both voltage types, the size of electrical corrosion pits increases significantly. The microscopic morphology shows signs of molten accumulation and electrically eroded, flattened surfaces. Energy-dispersive X-ray spectroscopy (EDS) analysis confirms the presence of oxidation and carbonization in the damaged areas. Herein, these works elucidate the electrical corrosion evolution mechanism in traction motor bearings, providing a theoretical basis for the optimization of insulation design and engineering protection measures.
This paper proposes a multifunctional barrier that can integrate anti-glare, noise reduction, and wind resistance functions on highway-railway bridges. A cross-river cable-stayed bridge is used as a representative case to evaluate multifunctional barrier performance. Optical simulations shows that the barrier effectively reduces the glare of the train headlights and reduces the maximum threshold increment of the inner and outer lanes to 3.77% and 4.26%, respectively, far below the limit of 10%. COMSOL acoustic simulations and experimental measurements confirmed that the barrier achieves an insertion loss of 7 similar to 8 dB(A), meeting design expectations. Parametric analysis identified optimal configurations with a barrier height of 3.0 m, a shielding angle of 8 degrees, and an opening rate of 40%. The results demonstrate that the proposed barrier effectively balances anti-glare, noise reduction, and wind resistance, providing a technical reference for the integrated design of multifunctional barriers on road-rail same-deck bridges.
This study proposes a novel analytical approach to assess the impact of time-varying deformation of long-span railway bridges on track irregularity and train dynamic responses. Track irregularities are decomposed into a dynamic trend component and a fluctuating component using a Gaussian kernel moving average method. Temperature effects on both components are analyzed. Results show that the trend component represents large-scale bridge deformation, is mainly temperature-driven, and exhibits nonlinear behavior with short-wavelength features, resembling conventional track profiles but evolving dynamically. The fluctuating component remains stable short-term but shows seasonal amplitude variations due to stochastic irregularity evolution. Train-track-bridge coupled vibration analysis indicates that, from summer to winter, deterioration in the fluctuating component and increased short-wavelength amplitudes in the trend component degrade train performance. This study supports integrated track-bridge assessment and early warning of train operation safety.
The article presents an original method for the ex-ante design of a robust railway timetable, namely the method of reconfiguring the planned timetable that accounts for the robustness of the rail transport system against disturbances. The framework combines a multi-indicator robustness assessment with a transparent, step-wise procedure for modifying an already feasible timetable. Robustness is quantified using synthetic indicators evaluated under stochastically generated disturbances and aggregated into the train-level indicator Wzbj and the system-wide indicator Wzbs. The timetable is iteratively reconfigured using dedicated algorithms: train shifts, buffer relocation, adjustment of connection times for connected trains, and addition of time buffers, until the predefined critical value is satisfied. A microscopic simulation model serves exclusively for ex post evaluation in the planning stage. The method is validated in OpenTrack with archival disturbance data and achieves Wzbs increasing from 0,57 to 0,75.
Due to the combined effects of material properties, manufacturing tolerances, and complex operational conditions, the wheel-rail interface and suspension parameters of high-speed trains exhibit significant stochasticity, which fundamentally shapes dynamic performance distributions. To capture this stochasticity over a full reprofiling cycle, this study integrates multi-condition wear simulations with measured data to establish a stochastic wheel-profile database. A method combining Monte Carlo simulation, Latin hypercube sampling, and Kullback-Leibler divergence is proposed to predict dynamic performance distributions while balancing sampling efficiency and convergence control. Analysis of the coupled effects of stochastic wheel-rail and suspension parameters shows that dynamic performance distributions evolve significantly with mileage. In the later service stage, key indicators such as the lateral Sperling index exhibit left-skewed and heavy-tailed distributions, with broader spreads and increased tail risk as mileage accumulates. The proposed method enables quantitative evaluation of long-term dynamic performance evolution and operational safety risk.
Derailment safety is critical for railway vehicle validation. Although most standards and institutions rely on wheel-rail contact force criteria, these methods become fail during instantaneous wheel-rail separation, where geometric assessment serves as an essential complement. This paper presents and validates novel measurement methodologies for wheel lift and wheelset angle of attack, based on EN 14363 twisted track tests. The proposed wheel lift measurement accounts for axle box nodding and wheelset side-rolling. Test results indicate a maximum wheel lift of 3.34 mm-well below the 5 mm limit-and a maximum angle of attack of 1.51 degrees. Through an integrated analysis combining geometric measurements with wheel-rail contact force indicators, the entry and exit sections are identified as critical zones with elevated safety risks when a vehicle traverses a twisted track at low speed. In contrast, the twist section itself exhibits a comparatively lower operational hazard due to the increased vertical wheel loads.
The theoretical correlations have been employed so far in 1D models to estimate train drag inside the tunnel, but verifying their accuracy is essential. This study uses 3D numerical models to compare drag coefficients inside a tunnel with theoretical predictions. Two train models (cubic and realistic) are examined with two uniform and accelerated velocity profiles. Findings demonstrate that the train drag significantly increases at the tunnel entrance. However, the nose and side drag will gradually decrease in the middle and exit of the tunnel, while base drag remains almost constant. Results also show that theoretical model predictions for side drag are acceptable, but there are significant discrepancies in estimating local nose and base drag. The model underestimates the nose drag at the tunnel entrance and overestimates it in the middle and exit, resulting in a lower mean error. For base drag, the model significantly underestimates values during train movement inside the tunnel.
This paper investigated the distortion of the compression waves and the acoustic features of sonic booms through field tests in a 10.0-km tunnel. Results indicated a steeper waveform and a faster growth of the pressure gradient when the wave propagating distance exceeds 3500 m. The peak pressure gradient produced by Train A is twice that of Train C. The train with a larger body cross-section area and a shorter nose produces a greater value of the amplitude of micro-pressure wave. The peak pressure gradient, corresponding to the hat-oblique-cutting hood, is nearly half of that induced by the straight-cutting hood. The sonic boom is classified as a low-medium-frequency noise since its frequency mainly ranges within 20-500 Hz. The minimum and maximum value of sonic booms are respectively obtained as 60 and 98.3 dBA. Loudness of the sonic boom ranges from 50 to 80 phon, which is far below the feeling threshold.
Identifying the combined wheel-track irregularity power spectral density (PSD) from the vibration response at the tunnel wall (vibration source) has been demonstrated as an efficient approach. However, there is currently no model-driven analytical framework available for this inversion problem. This paper proposes an efficient approach to quantify the combined wheel-track irregularity spectrum from the vibration source. By integrating the periodic train-track and Pipe-in-Pipe (PiP) analytical models with the pseudo-excitation method (PEM), the relationship between the wheel-track combined PSD and the PSD of the vibration source is effectively established. Subsequently, an objective function is formulated within specific frequency bands and minimized to accurately identify the combined PSD. Finally, the proposed method is validated through two theoretical examples and one experimental case. The results demonstrate that the proposed inversion process is both accurate and efficient in identifying the wheel-track combined PSD whether derived from calculated or measured vibration sources while also maintaining robustness against white noise. A single identification event takes approximately 2 min while solving the optimization function requires only 10 s. The proposed method for identifying the combined wheel-track irregularity spectrum holds significant potential for practical application in actual engineering scenarios.
Rail pods are an emerging concept of modular self-propelled rail vehicles which can interchangeably move freight and passengers to provide a more customer-oriented rail service. Pods are envisaged to operate on demand with the possibility of forming platoons either physically (e.g. mechanical or digital couplers) or virtually (e.g. by radio communication) coupling at stations. This study addresses the need to understand how rail pod platoons affect rail corridor capacity by analysing the actual infrastructure occupation under different platoon compositions, taking into account train movement dynamics and signalling constraints. First, this study extends the consolidated rail capacity assessment method (UIC Code 406) by applying the blocking time theory to assess the infrastructure occupation of the rail pod platoons. Based on this extension, a nonlinear optimization model is developed to determine coordinated speed profiles that are structurally consistent with the platoon configuration, aiming to minimize rail capacity utilization. The model is applied to a case study considering the ETCS Level 2 signalling system. The results obtained for the case study illustrate the ability of the proposed model to identify operational speeds and composition of rail pod' platoons that lead to the effective capacity use of the existing infrastructure. This capacity assessment framework provides a theoretical foundation for flexible allocation of modular rail cars in dynamically structured platoons.
