Abstract:To address the low efficiency and incomplete coverage of conventional ultrasonic testing in detecting weld quality at the fillet welds of shield machine cutterheads, a rapid imaging detection method based on ultrasonic phased array is proposed. Numerical simulations were carried out using finite element software to design the sound beam scanning strategy for weld coverage. Simulation results indicate that when a wedge probe with a center frequency of 1 MHz and an element spacing of 0.5 mm is employed, an effective beam deflection ranging from 45°~70° can be achieved, enabling accurate detection of cracks in fillet welds. On this basis, a coherence factor(CF) weighting algorithm was applied to the traditional total focusing method(TFM) imaging to enhance pixel-level consistency, effectively suppressing artifacts and noise, and improving image contrast and edge clarity. The proposed method is specifically tailored for thick-walled cutterhead structures with complex fillet weld geometries. The results provide a theoretical foundation for the subsequent development of dedicated phased array probes and experimental procedures.

Abstract:Currently, the collapse mechanism and failure mode of tunnel surrounding rock considering the influence of unfavorable structural planes in jointed fractured rock mass are not well understood.To investigate the effect of the unfavorable structural planes on the stability of deep-buried tunnel rock mass, failure mechanisms of the rock mass with unfavorable structural planes existing at roof and spandrel of the tunnel are constructed by using the spatial discretization technique. Based on the Hoek-Brown failure criterion and the upper bound theorem of limit analysis, the objective function of the rock mass safety factor with the consideration of unfavorable structural planes is derived. The upper bound solution of the rock mass safety factor and the collapse range under the limit state are obtained through optimization calculation. Taking Hushan Tunnel as engineering background, a numerical model of the rock mass with unfavorable structural planes is constructed and numerical results of the rock mass safety factor and the collapse range of the rock mass are obtained. By comparing the theoretical results with the numerical results, the validity of the theoretical method proposed in this paper is verified. Parameter analysis indicates that the safety factor of the rock mass with unfavorable structural planes at roof and spandrel increases with the increase of geological strength index GSI and rock material constant m. The collapse range of rock mass increases with the increase of GSI while it decreases with the increase of m.

Abstract:The unsupported structure obtained by topology optimization under conditions of deterministic symmetric load cannot meet the actual engineering requirements. The uncertainty of load direction was incorporated into the structural optimization design. And its influence on the avoidance of unsupported structure was analyzed. In this study interval variables were employed to represent the uncertainty of the load direction, the Taylor formula to solve the sensitivity under the most sensitive loading condition, and the SIMP model and MMA algorithm was applyed to was used achieve the robust design of continuum structure. The optimization results show that the structural optimization considering the uncertainty of load direction can effectively avoid the occurrence of unsupported structures. Under uncertain symmetric loading conditions, the structural compliance shows an upward trend with the increase of the disturbance range. And the structure shows symmetry. Under uncertain asymmetric loading conditions, the influence of asymmetric loading on structural compliance is significant, and the structural asymmetry characteristics tend to be more obvious with the increase in the variability of disturbance ranges.

Abstract:The on-site measured data of short-wave irregularities often exhibit non-stationary on urban rail transit track surfaces. This paper employs the wavelet method with multi-resolution and adaptivity is used to study the local characteristics, defect identification and track irregularity power spectrum of non-stationary track surface shortwave irregularity. Daubechies10 is selected as the wavelet basis function to identify the waveform characteristics of rail surface shortwave irregularity. Using the Daubechies10 wavelet, the signal is decomposed into 10 layers, and the power spectrum analysis of the decomposed detail signal and the approximation signal is carried out to obtain the contribution of different waveforms to the power spectrum. The wavelet power spectrum of short-wave irregularity of the rail surface in the joint area of the straight section and the curve section of the two track types of the elevated line and the underground line are calculated.The results demonstrate that wavelet basis functions can effectively identify local features of short-wave irregularity waveforms. Through the approximation and detail signals obtained from wavelet decomposition, significant irregularities at wavelengths of 20.298 m and 115.98 m were identified. Power spectrum analysis of these decomposed signals revealed the contributions of different waveforms to the power spectrum across various wavelength ranges. The results indicate that the wavelet analysis method can effectively process non-stationary data, providing a robust approach to comprehensively analyze the characteristics of short-wave irregularities on urban rail transit track surfaces.

Abstract:In the rail transit traction system, the operation of the four-quadrant pulse rectifier introduces double grid frequency ripple into the DC bus voltage. This ripple voltage interacts with the fundamental frequency voltage of the inverter, leading to beat-frequency phenomena in the motor stator voltage and current. This phenomenon is particularly pronounced when the motor operating frequency is close to twice the grid frequency. This paper elaborates on the generation mechanism of the beat-frequency phenomenon, and analyzes the rotation direction and frequency of each harmonic component in the motor stator current. To address the beat-frequency problem, a beat-frequency rotating coordinate system is proposed to extract the harmonic currents causing the beat-frequency phenomenon, which are converted into DC quantities in the beat-frequency coordinate system, and the compensation voltage for beat-frequency suppression is generated by a proportional-integral controller. A motor simulation model is built in MATLAB/Simulink, and simulation verification is carried out under three different motor operating conditions. The simulation results show that the proposed method can effectively suppress the beat-frequency phenomenon in a wide frequency range where the motor frequency is close to the double grid frequency.

Abstract:For the location selection problem of urban logistics distribution centers, considering urban dynamic development scenarios and unmanned aerial vehicle (UAV) characteristics is crucial for improving the scientificity and practicality of location schemes. First, three dynamic demand scenarios, namely natural growth, ring expansion, and directional development, were established according to urban development patterns. A full-coverage location model with the objective of minimizing the sum of location cost and operating cost was then constructed. Next, to improve the solution accuracy of the model, the traditional K-means clustering algorithm was improved by using a grid-based method. Finally, numerical simulations verified the feasibility and effectiveness of the model and algorithm. The results show that the improved K-means clustering algorithm achieves better clustering performance; the total cost of distribution centers under the dynamic strategy is lower than that under the static strategy; and except for extremely special scenarios (e.g., abnormally high construction cost or newly added demand completely concentrated in a single year), the dynamic strategy is the better choice.

Abstract:To address the challenge of identifying traveling wave components, including fault point incident waves, reflected waves, and waves reflected by auto-transformer (AT), which complicates fault location in all-parallel AT traction networks, this paper proposes a wave similarity-based fault location method using adaptive projection intrinsically transformed multivariate empirical mode decomposition (APIT- MEMD). The APIT-MEMD algorithm is applied to adaptively decompose fault signals from multi-conductor lines in both directions to extract transient high-frequency characteristics representing different components of fault traveling waves. By constructing the cross-correlation coefficient matrix of different wave mode components to identify traveling waves along different paths and calculating the corresponding maximum time delay, fault location in the traction network is achieved. Experimental results demonstrate that the proposed method, based on time-frequency mode feature extraction, achieves a fault location error within 102 m with an average absolute error of 49 m. Compared with the results of the multivariate empirical mode decomposition (MEMD) algorithm using different projection parameters, the proposed method effectively improves fault location accuracy.

Abstract:To investigate the fatigue performance of Q420qENH welded joints after corrosion, electrolytic accelerated corrosion tests and fatigue experiments were conducted on specimens, combined with numerical simulation. A thermal-mechanical coupled finite element model was established to simulate the welding process. The fatigue life of corroded welded joints was predicted using ABAQUS and FE-SAFE by introducing residual stress fields and stress concentration factors. The results show that all specimens fractured at the corrosion pits in the middle of the weld toe. Residual stress presents tensile stress, and the fatigue life of specimens decreases significantly with the increase of fatigue stress amplitude and corrosion time. The relative errors between test and simulation results are within 15%. The S-N curves with a 95% survival rate were fitted to the fatigue data obtained from experiments and simulations, when the cycle count reaches 2 million, the maximum error between tests and sumulations is merely 4.31%, indicating small errors and good prediction accuracy. It is recommended to adjust the fatigue allowable stress amplitude category of butt joints for railway non-painted Q420qENH weathering steel to category Ⅶ in bridge design.

Abstract:To improve the operational safety of high-speed trains and optimize the wheel reprofiling strategy, this study constructs an iterative model for wheel tread wear based on Archard's wear theory, analyzes the influence patterns of operating speed, friction coefficient, and operating mileage on wear, and explores the influence mechanism of wheel tread wear on train operational performance. The study finds that the wear depth of the wheel tread presents an M-shaped curve within a reprofiling cycle, with wear concentrated in the area around the rolling circle. Increases in operating speed, operation mileage, and friction coefficient all significantly enhance the wear rate, and the width of the wear area shows a non-linear expansion trend. While tread wear has little impact on vertical stability and safety, the nominal equivalent conicity, wheel-axle lateral force, derailment coefficient, and lateral Sperling index all increase significantly with the degree of wear. The research results provide theoretical support for formulating wheel reprofiling cycles and ensuring the safe operation of high-speed trains.

Abstract:To mitigate the impact of sudden sensor faults in traction rectifiers during high-speed train operation, this paper proposes a sensor fault-tolerant control method based on an improved sliding mode observer, which achieves rapid sensor fault diagnosis and fault-tolerant control. Firstly, the topological structure of a two-level traction rectifier is analyzed to establish its mathematical model with unknown disturbances. Subsequently, a novel sensor fault diagnosis strategy employing an adaptive sliding mode observer is developed. The sliding mode observer is designed using linear matrix inequality (LMI) methods, and the sliding mode robust term gain is adjusted online via adaptive laws to obtain voltage and current estimation signals. Residual signals are constructed by comparing these estimated signals with sensor-sampled data, enabling online fault diagnosis through threshold comparison. Furthermore, a voltage outer-loop sliding mode fault-tolerant controller is designed by introducing a novel sliding mode exponential reaching law, complemented by a current inner-loop fault-tolerant controller to enhance system robustness. Finally, a high-power traction rectifier model was constructed on the Simulink platform for simulation verification in this study. The simulation results demonstrate that the proposed fault-tolerant method can diagnose sensor faults within 0.020 s and implement compensation within 0.050 s, with observer state estimation error maintained below 1%. The voltage outer-loop fault-tolerant controller achieves a reduced settling time of 0.035 s under load transient conditions. The proposed methodology effectively enhances system dynamic response performance and operational reliability, providing valuable insights for safety-critical control of high-speed trains.

Abstract:For the welding deformation of rail vehicle thin-plate structures, the traditional flame heating straightening process suffers from issues such as high noise, loose plate body, and unstable straightening effects. This paper proposes the application of a high-frequency induction heat source to the straightening process of vehicle thin-plate structures. Corresponding induction heating power equipment and specialized tooling were designed, and numerical simulations and experimental studies were conducted on the straightening process of the roof and sidewall thin-plate structures. The results indicate that the flatness of the thin plates after induction heating straightening meets the process error requirements. Finally, workshop tests of the induction straightening process for thin-plate structures demonstrated that the induction heat source offers advantages such as a small heating spot diameter, effective plate surface tightening, and no overheating phenomena, which are suitable for correcting welding deformation in vehicle thin-plate structures.

Abstract:To address the issue of single evaluation criterion in time-domain extrapolation threshold selection, a multi-criteria threshold selection method based on CRITIC-VIKOR is proposed. The principal component signals of the dynamic stress data of the vehicle undercarriage are obtained through empirical mode decomposition. The optimal threshold range is preliminarily determined using the exceedance mean function plot method. Within this interval, the optimal threshold is selected using the CRITIC-VIKOR method based on each inspection criterion. Data exceeding the threshold are extracted for generalized Pareto distribution (GPD) fitting, and random loads are generated using the fitting parameters to replace the original threshold-exceeding data for time-domain extrapolation. The damage caused by the extrapolated dynamic stress data is then calculated. The results indicate that compared to actual measurement data, the damage errors calculated by linear extrapolation, rain-flow extrapolation, and time-domain extrapolation are 0.59%, 0.20%, and 0.18%, respectively. This demonstrates the scientific validity and accuracy of the time-domain extrapolation method.

Abstract:Copper matrix composites have serious corrosion issues in complex environments (such as acidic, alkaline, high-salt-spray, high-humidity conditions), but the traditional salt spray tests are time-consuming and cannot effectively simulate diverse corrosive environments. To address this, a rapid evaluation method for interfacial corrosion resistance of copper matrix composites was proposed by adjusting the Al content (0, 1%, 3%, 5%) in the copper alloy and employing electrochemical impedance spectroscopy. In addition, carbon quantum dots (CDs) were added to the corrosive medium to study the enhancement of the corrosion resistance of the adsorbed film. The results show that the alloy containing 5% Al has the best corrosion resistance and the corrosion current density is reduced by about 70%. This study provides a novel strategy for optimizing metal corrosion resistance through compositional adjustment combined with carbon quantum dot strengthening, offering theoretical and technical support for practical applications under complex service conditions.