Search Results (5,244)

This study investigates an SAC-type injector nozzle used in a diesel high-pressure common-rail fuel-injection system. The mixture multiphase-flow model, RNG k-ε turbulence model, and Schnerr–Sauer cavitation model were employed to compare the internal flow characteristics of circular and elliptical nozzle orifices under different operating and geometric parameters. The results show that, as the inlet pressure increased from 110 to 170 MPa, the outlet velocity and mass flow rate of the elliptical orifice reached 495.80 m/s and 27.28 g/s, respectively, while the outlet vapor volume fraction increased to 0.161. As the outlet back pressure increased from 5 to 20 MPa, the outlet vapor volume fraction of the elliptical orifice was 41.32–46.49% lower than that of the circular orifice, whereas its mass flow rate was 4.84–23.54% higher. The geometric-parameter analysis indicated that superior internal flow performance was obtained at a nozzle-orifice angle of 75° and an inlet rounding radius of 0.03 mm. The converging elliptical orifice increased the outlet velocity and mass flow rate by 18.3% and 23.29%, respectively. These results demonstrate that the converging elliptical orifice can effectively mitigate flow separation and cavitation while improving outlet-flow uniformity and fuel-delivery performance. Full article

In this study a transient finite element model was developed to examine the temperature evolution of continuous casting blooms during reheating prior to rail rolling. The simulation was carried out using COMSOL Multiphysics 5.6, incorporating convective and radiative heat transfer mechanisms under a three-zone furnace (preheating, heating and soaking) temperature schedule. The temperature distribution and soaking uniformity were evaluated over a 7200 s heating cycle. The results indicate that proper adjustment of furnace setpoints enables the bloom center to reach approximately 1220 °C while maintaining acceptable temperature uniformity $∆T\le 50 ℃$. This study shows how numerical modeling can be used to improve thermal homogeneity prior to hot rolling and optimize reheating furnace performance. Full article

Camera and LiDAR sensors in safety-critical autonomous systems suffer undetected distributional shifts that silently corrupt downstream perception. Out-of-distribution (OOD) detection is the established sensor-data-integrity primitive, but no single post hoc detector covers every shift type, and existing detectors lack guarantees on their false-positive rate (FPR). This paper asks when calibrated score fusion helps and provides a distribution-free finite-sample FPR certificate. Four post hoc scores—Maximum Softmax Probability (MSP), Energy, Mahalanobis distance and k-nearest-neighbour (KNN) distance—are calibrated to p-values by the empirical cumulative distribution function (ECDF) and combined by Fisher’s method or cross-backbone z-score averaging, then wrapped in a conformal predictor with Hoeffding-based Probably Approximately Correct (PAC) bounds. On the full-split PUG camera benchmark (215,040 images), uniform same-backbone p-value fusion does not beat the best single detector (Mahalanobis); the gain comes from cross-backbone diversity: a z-score average of Mahalanobis distances over ResNet-50 and frozen DINOv2 reaches a mean area-under-the-ROC-curve (AUROC) of $0.9258$ ($+0.0199$), rising to $0.9292$ ($+0.0233$) with added spectral and dropout signals (DeLong $p<{10}^{-9}$). On the nuScenes LiDAR sensor (256,873 frames), uniform fusion yields only a small, calibration-sensitive gain over the best single detector (MSP), so the substantial fusion gain is confined to cross-backbone averaging on the camera. The distribution-free PAC certificate, by contrast, transfers across both sensors with margins below $1.5\%$ ($0.96\%$ camera, $0.25\%$ LiDAR), giving evidence usable in ISO 26262 and EASA CoDANN safety cases. Full article

The reliability of traction systems in urban rail transit vehicles is critical to safe and efficient operations. However, existing reliability assessment methods face challenges such as state space explosion, computational complexity, and difficulties in modeling fault interdependencies and imperfect maintenance. This paper proposes an integrated framework that combines dynamic fault trees with fault dependency models and Monte Carlo simulation. The method captures fault dependencies through functional dependency gates incorporating fault impact factors, models component degradation using a two-parameter Weibull distribution, and accounts for imperfect maintenance through a age reduction factor. The simulation efficiency of three random number generators—LCG, MT, and PCG64—was compared. A Monte Carlo simulation of 100,000 trials under maintenance-free conditions yielded a system MTBF of 29.9 months. A mode significance analysis identified the pantograph control unit and the traction control unit as the most critical components. Under targeted maintenance based on component criticality, the MTBF increased to 39.77 months—a 33% improvement—while the peak failure rate was maintained at approximately 3%. The MT generator exhibited the fastest convergence, achieving stability within 1% after 3000 iterations. This framework provides a practical foundation for optimizing preventive maintenance strategies for urban rail transit systems, and sensitivity analysis confirmed the robustness of weak link identification to parameter variations. This method is applicable to other complex systems with interdependent failures and multiple maintenance schedules. Full article

This paper addresses the challenge of maintaining low current stress and high efficiency in dual-active-bridge (DAB) microinverters, where the voltage conversion ratio and instantaneous transferred power vary continuously over the line-frequency cycle. A mode-switching, four-degree-of-freedom, variable-frequency modulation strategy with analytical parameter calculation is proposed. Four representative low-current-stress operating modes are selected for the $G<1$ and $G>1$ regions. Under unity-power-factor and sinusoidal grid-current-tracking constraints, analytical switching-frequency expressions are derived for each mode, enabling coordinated control of the primary-side duty ratio, secondary-side duty ratio, external phase-shift ratio, and switching frequency without iterative online optimization. Duty-ratio limits, switching-frequency bounds, ZVS commutation-current requirements, and an SPS-based hysteresis transition near $G=1$ are incorporated. A 500 W experimental prototype was built for validation. The proposed strategy achieved a peak efficiency of 97.2% at 300 W and an efficiency of 96.5% with a grid-current THD of 2.8% at 500 W. Compared with a fixed-frequency minimum-current-stress TPS strategy, the measured peak leakage-inductor current at 500 W was reduced from 8.23 A to 7.42 A. The results validate the proposed modulation method under the reported experimental conditions. Full article

Highway–rail grade crossing (HRGC) incidents in the United States declined substantially for several decades before stabilizing in recent years. Understanding this persistence is important because future safety improvements may depend on identifying locations where incident occurrence remains resistant to further reduction. This study developed an integrated framework to characterize persistent HRGC incident environments using 50 years (1976–2025) of Federal Railroad Administration incident records. Trend, structural-break, variance, and stationarity tests were first applied to determine whether the historical decline transitioned into a distinct persistence regime. A county-level persistence index (PI) was then developed to quantify the combined effects of incident burden and resistance to decline during the plateau period. Distributional analysis characterized the statistical behavior of the PI, while global and local Moran’s I statistics evaluated its spatial organization. Explainable machine learning methods were subsequently used to identify incident characteristics associated with elevated persistence. The results identified a statistically significant regime change around 2010. Prior to 2010, incidents exhibited a strong declining trend, whereas the subsequent period displayed a statistically significant but substantially weaker decline, lower variance, and behavior consistent with a persistence regime characterized by a markedly attenuated rate of improvement. The PI followed a strongly right-skewed distribution that was best represented by a bounded heavy-tailed unit log-logistic model, indicating that persistence is concentrated within a relatively small subset of counties. Spatial analysis revealed significant positive spatial autocorrelation (Moran’s I = 0.180, p = 0.001) and geographically coherent clusters concentrated primarily in the southeastern United States and several major freight-oriented regions. Explainable machine learning models identified train-operating characteristics, warning device contexts, movement patterns, and temporal conditions as key attributes associated with high-persistence counties. The findings demonstrate that the post-2010 incident plateau is sustained disproportionately by a limited number of geographically concentrated environments and provide a framework for supporting more targeted safety interventions. Full article

Ultra-wideband (UWB) and inertial measurement unit (IMU) fusion is an effective scheme for train and rail-guided target localization because UWB provides absolute ranging results and the IMU provides high-rate motion prediction. In practical rail transportation systems, UWB anchors are usually deployed along the track with large longitudinal intervals and limited lateral separation to reduce installation and maintenance costs. This anchor deployment leads to a large condition number of the observation matrix, so slight ranging errors caused by non-line-of-sight (NLoS) propagation may be amplified into large localization errors. To mitigate LoS/NLoS interference, this article proposes a propagation reliability estimation method for track-constrained UWB/IMU fusion localization. First, rail transportation localization along a narrow path is formulated as a one-dimensional track-constrained problem, and each UWB ranging result is converted into a candidate longitudinal coordinate on the known track centerline. Second, the reliability of each anchor–target propagation is estimated in a sliding window by comparing the motion increments solved by UWB observations with the motion prediction by the IMU. Third, the estimated reliability is incorporated into a reliability-weighted track-domain update before a closed-loop position–velocity Kalman correction. The simulation results show that, under the mixed LoS/NLoS scenario, the proposed method achieves an NLoS-interval RMSE of 0.0090 m. Compared with Track-EKF, Track-Gauss-AUKF, Track-Adaptive KF, and Track-SW-FGO, the proposed method reduces the NLoS-interval RMSE by 92.9%, 62.1%, 92.8%, and 92.6%. A supplementary real-data stress test on the public STAR-loc dataset demonstrates an average longitudinal RMSE of 0.0555 m under a strict online calibrated-range protocol, supporting the algorithm’s practical applicability against real-world lateral sway and asynchronous sensor noise. Full article

This study quantifies, based on real-world operational measurements, the energy intensity and greenhouse gas emissions of selected vehicle types in rail and road freight transport on the Brno–Břeclav corridor. Measurements were conducted on several generations of electric locomotives, one upgraded diesel locomotive, and two heavy road freight vehicle combinations. Energy flows were converted to a common basis, and both energy intensity and greenhouse gas emissions were assessed on a well-to-wheel (WTW) basis. Unlike many previous studies, this research focuses on a comparison of specific, currently operated vehicles rather than on an aggregated comparison of transport modes. The results reveal substantial differences not only between rail and road freight transport, but also within rail traction itself, where pronounced differences were identified among individual locomotive generations. At the same time, they confirm that, even when diesel traction is used, rail freight transport remains more energy-efficient and exhibits lower greenhouse gas emissions than heavy road freight vehicle combinations, both per gross and per net tonne-kilometre. Overall, the findings indicate that the environmental performance of freight transport is determined not only by the transport mode itself, but also by vehicle technology, traction type, and the structure of transport performance. Full article

As a paradigm-shifting hypervelocity propulsion technology, electromagnetic rail launch (EMRL) is fundamentally constrained by armature/rail (A/R) interface degradation, which directly erodes its service longevity and operational reliability. Small-caliber circular bore electromagnetic launchers (SCCB-EMRL) offer superior structural integration and ballistic stability over traditional rectangular bores. Their inherently lower self-centering capability imposes strict requirements on interfacial contact stability. This study investigates the physicochemical evolution of the A/R interface at extreme loading. Consecutive repetitive launch experiments were conducted, and samples were prepared by typical areas of rail according to the current curve. Characterization was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Results revealed a bimodal non-uniform thickness distribution of the deposition layer along the launch direction. The maximum deposition thickness reached 60.6 μm within the acceleration-startup zone. The deposited material comprises transferred Al, oxidized phases (Al₂O₃), Al-Cu intermetallic, and a mixed carbonaceous system containing amorphous and graphitized carbon. Initial launches triggered rapid material accumulation and increased start-up times, after which the interface reached a dynamic equilibrium. This work reveals the evolution patterns of elemental composition and thickness distribution of the deposition layer at the armature/rail interface in small-caliber circular-bore electromagnetic launching and provides experimental reference for the design of anti-deposition coatings to extend the service lifespan of SCCB-EMRL systems. Full article

Cross-border transportation networks show considerable complexity and vulnerability under the influence of geopolitical risks. To identify critical nodes and simulate the propagation paths of failure risk within cross-border transportation networks, this study develops a multilayer cross-border transportation network model that integrates four transport modes: waterway, road, rail, and air transport. First, composite edge weights are calculated using the Criteria Importance Through Intercriteria Correlation (CRITIC) method based on inter-node transport distance, transport time, and geopolitical risk (GPR) exposure score. These weights capture the joint effects of transport efficiency and risk exposure across different transport corridors. Second, an Improved Weighted K-shell (IWKS) model is proposed for critical-node identification by integrating three network topological indicators: degree centrality, weighted degree, and closeness centrality. Third, an edge-risk-based Susceptible–Infected–Recovered (SIR) propagation model is introduced. Monte Carlo simulations are then used to estimate the simulation-based propagation influence of each node. Finally, the identification performance of the IWKS model is compared with that of conventional centrality indicators. The IWKS scores are also significantly correlated with the simulation-based propagation influence under three types of correlation tests. The findings support the applicability of the proposed IWKS model in critical-node identification and system vulnerability research of multilayer cross-border integrated transportation networks. Full article

The absence of overhead catenary systems in contactless trams imposes stringent requirements on onboard energy efficiency and real-time power management. Hybrid energy storage systems combining batteries and supercapacitors provide an effective solution; however, conventional energy management strategies often suffer from limited global optimality under frequent traction–braking conditions. To address this issue, this paper proposes a variable-horizon model predictive control (MPC)-based energy management strategy for a battery–supercapacitor hybrid power supply system in contactless trams. A power-level-matching method is first adopted for capacity configuration, and the MPC prediction horizon is then dynamically adjusted to cover the entire traction phase, enabling global energy loss optimization while satisfying voltage, current, and SOC constraints. Simulation results obtained in MATLAB/Simulink demonstrate that the proposed strategy effectively suppresses excessive battery current and premature supercapacitor depletion. Compared with the conventional single-step MPC, the total energy loss is reduced by 9.88%, indicating improved energy efficiency and operational performance. Full article

Cross-border transport of engineering materials for international railway construction projects is characterized by substantial heterogeneity among material categories, complex intermodal networks, and considerable variability in customs-clearance and cross-gauge transshipment times at border crossings. Route optimization that focuses solely on minimizing deterministic transportation costs is therefore insufficient to ensure continuous operations at overseas construction sites. Unlike existing intermodal-routing models, which generally assume homogeneous cargo and do not represent competition among heterogeneous material categories for shared cross-border capacity under uncertain clearance and transshipment times, the proposed model explicitly incorporates these features. This study develops a route-optimization model for the cross-border intermodal transport of multiple categories of engineering materials under time uncertainty. The model has two objectives—minimizing total transportation cost and minimizing total transportation time—and includes constraints on supply–demand balance, flow continuity, the shared capacities of arcs, border ports, and transshipment nodes, category-specific capacity use, material–mode compatibility, and maximum delivery times. Triangular fuzzy numbers characterize uncertainty in arc travel, transshipment, and customs-clearance times. The α-cut method transforms the fuzzy time constraints into deterministic equivalents, and the augmented ε-constraint method (AUGMECON2) generates the cost–robust-time Pareto frontier. A case study of the China–Thailand Railway corridor on the Central Route of the Pan-Asia Railway validates the proposed model. Moving from the cost-optimal to the time-optimal solution reduces robust transportation time by 23.13% while increasing total cost by 13.74%. The cost–time trade-off also exhibits increasing marginal costs. The cross-gauge transshipment station is the only shared hub operating near full capacity, whereas maritime travel time is the most sensitive source of uncertainty affecting robust transportation time. Tightening the delivery-time limit for rails has the greatest effect on both total cost and network resilience. These findings support differentiated route planning for cross-border engineering materials, capacity expansion at critical hubs, and decisions that balance transportation budgets with project-schedule requirements. Full article

Understanding the non-linear dynamic interaction between tracks and bridge structures is essential for maintaining the safety of continuous rigid-frame bridges. To accurately capture these beam–rail interactions, this study develops a detailed 3D finite element model based on the principle of stationary total potential energy. This framework fully integrates the track, main girders, and piers into a single system. Based on a 4 × 40 m continuous rigid-frame viaduct in an urban transit network, the numerical model accounts for the bilinear mechanical behavior of the rail fasteners. The study compares the transmission of longitudinal forces along the continuously welded rail (CWR) under two fastening layouts. The baseline case uses uniform constant-resistance fasteners across the entire bridge, while the optimized scheme places small-resistance fasteners at the final 20% of each structural segment. Analysis shows that placing low-resistance fasteners in the high-displacement areas near the girder ends creates an effective longitudinal “release zone.” This design effectively interrupts the buildup of longitudinal forces, resulting in a much smoother force distribution along the rails. Quantitative results indicate that this optimized fastener layout has only a minor effect on structural deflection and braking-induced rail stresses, keeping deviations below 11%. At the same time, it significantly reduces the peak expansion stress and broken-rail stress by 43.4% and 22.2%, respectively. By shifting the stress regulation philosophy from “rigid resistance” to dynamic “force channeling,” these findings demonstrate that local low-resistance fastener deployment improves the overall mechanical compatibility of the track–bridge infrastructure. Ultimately, this work offers a solid theoretical basis for the design and maintenance of CWR systems on long-span rigid-frame bridges. Full article

With increasing rail traffic intensity, reliable detection of shallow subsurface rail damage is essential for operational safety. This critical narrative review evaluates non-destructive testing technologies relevant to defects whose active crack front or principal scattering zone lies within the upper approximately 0.5–10 mm of the rail, while treating the 10–15 mm range as a transition to deeper-defect verification. Magnetic flux leakage, magnetic particle inspection, visual inspection, eddy current testing, and conventional ultrasonic testing are first examined as screening or confirmatory comparators. The review then focuses on four ultrasonic surface-wave excitation routes—contact piezoelectric, active air-coupled, electromagnetic acoustic, and laser ultrasonic—and distinguishes source-specific laboratory capability from demonstrated field evidence. Because the cited studies use different defect geometries, rail conditions, sensor configurations, speeds, and decision criteria, their numerical values are reported as source-conditioned evidence rather than as a normalized ranking. An engineering decision matrix links defect depth and size, inspection speed, surface condition, and noise environment to a recommended screening–confirmation workflow. The synthesis identifies contact piezoelectric UT/PAUT as the most mature quantitative confirmation route, while EMAT, air-coupled UT, and laser UT retain method-specific advantages but require stronger natural-defect and in-service validation. Full article

Container sea–rail intermodal transport is pivotal to the low-carbon transformation of global supply chains. However, traditional performance evaluation systems are prone to circular reasoning fallacies due to the nesting of input and output indicators and frequently suffer from spurious regression when analyzing high-dimensional macro time series under small-sample constraints. To address these endogeneity and attribution challenges, this study proposes a four-step progressive causal inference framework. Taking Tianjin Port—a pioneering hub of China’s “road-to-rail” freight restructuring policy—as the empirical subject, we use quarterly operational data covering a complete cycle from 2017Q1 to 2024Q4. First, we construct a strictly exogenous high-quality development index based on turnover efficiency, logistics cost reduction, and carbon emission mitigation, which completely isolates scale input factors. Second, from an initial pool of 35 operational and macroeconomic indicators, 17 candidate variables are rigorously pre-screened according to statistical consistency and logistics system theory. Third, an adaptive Double Machine Learning (DML) model integrated with leave-one-out cross-fitting is applied to disentangle complex collinearity among variables. The results show that DML effectively eliminates confounding noise, accurately identifies 15 true causal drivers, and excludes spurious correlations such as redundant macro-infrastructure investment. Furthermore, a causally weighted composite index reveals that the intermodal system exhibits strong resilience to global supply chain fluctuations and has undergone a four-stage evolution. Its development momentum has fundamentally shifted from extensive scale expansion to a refined mode driven by the synergy of efficiency and service quality. This study provides a robust methodological paradigm for port performance evaluation and targeted decision support for resource allocation. Full article