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Objective Due to the increase of metro operation mileages and track conditions complexity, abnormal bogie vibrations caused by wheel-rail wear often occur. Bogie frame serves as an important load-bearing component, requiring research on its structural integrity and vibration failure mechanism under abnormal vibration conditions. Method Taking a metro bogie frame as example, based on vibration transmission tests and dynamic stress data, a study is conducted on the abnormal vibration and beam fatigue failure causes of metro vehicles on a line during operation, analyzing the source of disturbance and vibration transmission path. Based on the results of frame working modal tests, the vibration acceleration and dynamic stress time-frequency characteristics at beam failure points when vehicle passing typical sections are analyzed. By analyzing influencing factors such as wheel polygon, rail corrugation, and vehicle operating speed, the amplitude and spectrum characteristics of beam dynamic stress are investigated. Result & Conclusion Before wheel reprofiling, the main measuring points where equivalent stress amplitude exceeds the limit are concentrated at the connections between beams and side beams, beams and small longitudinal beams, and the upper cable supports of beams. After wheel reprofiling, the equivalent stress amplitudes at all measuring points significantly decrease, far below the allowable stress amplitude. The main external excitation source causing beam cracking is the 5 to 8 order wheel polygon, and the exacerbated vehicle vibration caused by wheel off-roundness is the direct cause for fatigue failure of beam cable supports.

Nitrous oxide (N2O) emission during the sewage treatment process is a serious environmental issue that requires attention. However, the N2O emission in constructed wetlands (CWs) as affected by different nitrogen forms in influents remain largely unknown. This study investigated the N2O emission profiles driven by microorganisms in CWs when exposed to two typical nitrogen sources (NH4+-N or NO3–-N) along with different carbon source supply (COD/N ratios: 3, 6, and 9). The results showed that CWs receiving NO3–-N caused a slight increase in total nitrogen removal (by up to 11.8 %). This increase was accomplished by an enrichment of key bacteria groups, including denitrifiers, dissimilatory nitrate reducers, and assimilatory nitrate reducers, which enhanced the stability of microbial interaction. Additionally, it led to a greater abundance of denitrification genes (e.g., nirK, norB, norC, and nosZ) as inferred from the database. Consequently, this led to a gradual increase in N2O emission from 66.51 to 486.77 ug-N/(m2·h) as the COD/N ratio increased in CWs. Conversely, in CWs receiving NH4+-N, an increasing influent COD/N ratio had a negative impact on nitrogen biotransformation. This resulted in fluctuating trend of N2O emissions, which decreased initially, followed by an increase at later stage (with values of 122.87, 44.00, and 148.59 ug-N/(m2·h)). Furthermore, NH4+-N in the aquatic improved the nitrogen uptake by plants and promoted the production of more root exudates. As a result, it adjusted the nitrogen-transforming function, ultimately reducing N2O emissions in CWs. This study highlights the divergence in microbiota succession and nitrogen transformation in CWs induced by nitrogen form and COD/N ratio, contributing to a better understanding of the microbial mechanisms of N2O emission in CWs with NH4+-N or NO3–-N at different COD/N ratios.

The traction drive system of a high-speed train is the key subsystem of a high-speed train, which controls the driving and braking of the train through electromechanical coupling, and determines the running speed, power quality, and comfort of the train. The traction drive system is subjected to many internal and external excitation sources and frequency bandwidth, and the dynamic response and dynamic characteristics of the system are extremely complex. The results of the traction motor field vibration test showed that 100Hz vibration frequency occurred during traction and braking of high-speed trains when the inverter output voltage frequency was close to 100Hz, and its vibration amplitude was higher than other frequency bands. When traction power was cut-off, the 100Hz frequency was not significant. Through simulation analysis of fatigue damage, it was found that 100Hz DC-link voltage pulsation would aggravate the fatigue damage of the motor hanger. The line vibration test and bench test of the gearbox showed that there was a natural frequency of the gearbox at about 2500Hz, when the meshing frequency was close to it. Thus, the resonance characteristic became significant., Author(s): Pingbo Wu [1]; Chunyuan Song [1,2]; Xun Wang (corresponding author) [1]; Sheng Qu (corresponding author) [1]; Hao Wu [3] 1. Introduction As an important development direction of China's railway [...]