Reliability-based assessment of high-speed railway subgrade defect

Qingsong Feng,Kui Sun,Hua-peng Chen 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.77 No.2

In this paper, a dynamic response mapping model of the wheel-rail system is established by using the support vector regression (SVR) method, and the hierarchical safety thresholds of the subgrade void are proposed based on the reliability theory. Firstly, the vehicle-track coupling dynamic model considering the subgrade void is constructed. Secondly, the subgrade void area, the subgrade compaction index K30 and the fastener stiffness are selected as random variables, and the mapping model between these three random parameters and the dynamic response of the wheel-rail system is built by using the orthogonal test and the SVR. The sensitivity analysis is carried out by the range analysis method. Finally, the hierarchical safety thresholds for the subgrade void are proposed. The results show that the subgrade void has the most significant influence on the carbody vertical acceleration, the rail vertical displacement, the vertical displacement and the slab tensile stress. From the range analysis, the subgrade void area has the largest effect on the dynamic response of the wheel-rail system, followed by the fastener stiffness and the subgrade compaction index K30. The recommended safety thresholds for the subgrade void of level I, II and III are 4.01m2, 6.81m2 and 9.79m2, respectively.

Environment-dependent Broadband Perfect Absorption of Metal-insulator-metal Metamaterial Systems

Feng Li,Yulong Tang,Qingsong Peng,Guosheng Hu 한국광학회 2023 Current Optics and Photonics Vol.7 No.2

Based on calculations using the macroscopic Maxwell’s equations with mesoscopic boundary conditions, light absorption by a layered metal-insulator-metal (MIM) metamaterial system embedded in three different environments is investigated. Increasing the top metal thickness shifts the broad absorption band to lower dielectric-constant regions and longer wavelengths, for either TM or TE waves. Boosting the dielectric-layer thickness redshifts the broadband absorption to regions of larger dielectric constant. In air, for the dielectric-constant range of 0.86–3.40, the absorption of the system exceeds 98% across680–1,033 nm. In seawater with optimized dielectric constant, ≥94% light absorption over 400–1,200nm can be achieved; particularly in the wavelength range of 480–960 nm and dielectric-constant range of 0.82–3.50, the absorption is greater than 98%. In an environment with even higher refractive index(1.74), ≥98% light absorption over 400–1,200 nm can be achieved, giving better performance. Theinfluence of angle of incidence on light absorption of the MIM system is also analyzed, and the angle tolerance for ≥90% broadband absorption of a TM wave is up to 40° in an environment with large re-fractive index. While the incident-angle dependence of the absorption of a TE wave is nearly the same for different circumstances, the situation is different for a TM wave.

Discussion on the Path of Improving College Students Ideological and Political Quality under the Background of Patriotism Education

Hu Lamei(胡腊,梅),Feng Jieming(冯,洁,铭,),Li Qingsong(李青,嵩),Chen Lu(陈,璐,) 아시아사회과학학회 2022 International Science Research Vol.2 No.1

去年是建党一百周年, 借着开展党史学习教育的契机, 让更多的大学生了解党的历史, 在全校范围内开展爱国主义教育, 对于提升学生的思想政治素质是很有效的。因此在全社会大力开展爱国主义教育的大背景下, 对如何提升大学生思想政治素质进行分析和研究至关重要。本文基于爱国主义教育大背景下, 就如何提升大学生思想政治素质的路径进行探讨, 并提出具体可实施的建议。 Last year is the one hundredth anniversary of the founding, through to carry out the party history study chance in education, let more students understand the party s history, to carry out patriotism education in the school, to improve students ideological and political quality, it is very effective So vigorously carry out patriotism education in the whole society s big background, how to improve college students ideological and political quality is very important to analyze and study Based on the background of patriotism education, this paper discusses how to improve the ideological and political quality of college students, and puts forward concrete feasible suggestions.

3.2-kW 9.7-GHz Polarization-maintaining Narrow-linewidth All-fiber Amplifier

Hang Liu,Yujun Feng,Xiaobo Yang,Yao Wang,Hongming Yu,Jue Wang,Wanjing Peng,Yanshan Wang,Yinhong Sun,Yi Ma,Qingsong Gao,Chun Tang 한국광학회 2024 Current Optics and Photonics Vol.8 No.1

We present a Yb-doped narrow-linewidth polarization-maintaining (PM) all-fiber amplifier that achieves a high mode-instability (MI) threshold, high output power, and 9.7-GHz spectral linewidth. Six wavelength-multiplexed laser diodes are used to pump this amplifier. First, we construct a high-power fiber amplifier based on a master oscillator-power amplifier (MOPA) configuration for experiments. Subsequently, we examine the MI threshold by individually pumping the amplifier with wavelengths of 976, 974, 981, 974, and 981 nm respectively. The experimental results demonstrate that the amplifier exhibits a high MI threshold (>3.5 kW) when pumped with a combination of wavelengths at 974 and 981 nm. Afterward, we inject an optimized phase-modulated seed with a nearly flat-top spectrum into this amplifier. Ultimately, laser output of 3.2 kW and 9.7 GHz are obtained.

Propagation characteristics of ultrasonic guided waves in tram rails

Kui Sun,Hua-peng Chen,Qingsong Feng,Xiaoyan Lei 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.4

Ultrasonic guided wave testing is a very promising non-destructive testing method for rails, which is of great significance for ensuring the safe operation of railways. On the basis of the semi-analytical finite element (SAFE) method, a analytical model of 59R2 grooved rail was proposed, which is commonly used in the ballastless track of modern tram. The dispersion curves of ultrasonic guided waves in free rail and supported rail were obtained. Sensitivity analysis was then undertaken to evaluate the effect of rail elastic modulus on the phase velocity and group velocity dispersion curves of ultrasonic guided waves. The optimal guided wave mode, optimal excitation point and excitation direction suitable for detecting rail integrity were identified by analyzing the frequency, number of modes, and mode shapes. A sinusoidal signal modulated by a Hanning window with a center frequency of 25 kHz was used as the excitation source, and the propagation characteristics of high-frequency ultrasonic guided waves in the rail were obtained. The results show that the rail pad has a relatively little influence on the dispersion curves of ultrasonic guided waves in the high frequency band, and has a relatively large influence on the dispersion curves of ultrasonic guided waves in the low frequency band below 4 kHz. The rail elastic modulus has significant influence on the phase velocity in the high frequency band, while the group velocity is greatly affected by the rail elastic modulus in the low frequency band.

S-I model of horizontal jet grouting reinforcement for soft soil

Zhang, Ning,Li, Zhongyin,Ma, Qingsong,Ma, Tianchi,Niu, Xiaodong,Liu, Xixi,Feng, Tao Techno-Press 2018 Geomechanics & engineering Vol.15 No.5

A superposition-iteration (S-I) model is proposed to simulate the jet grouting pre-reinforcing impact for a shallow-buried tunnel. The common model is deduced by theoretical (force equilibrium) analysis and then transformed into the numerical formulation. After applying it to an actual engineering problem, the most obvious deficiency was found to be continuous error accumulation, even when the parameters change slightly. In order to address this problem, a superposition-iteration model is developed based on the basic assumption and superposition theory. First, the additional deflection between two successive excavation steps is determined. This is caused by the disappearance of the supporting force in the excavated zone and the soil pressure in the disturbed zone. Consequently, the final deflection can be obtained by repeatedly superposing the additional deflection to the initial deflection in the previous steps. The analytical solution is then determined with the boundary conditions. The superposition-iteration model is thus established. This model was then applied and found to be suitable for real-life engineering applications. During the calculation, the error induced by the ill-conditioned problem of the matrix is easily addressed. The precision of this model is greater compared to previous models. The sensitivity factors and their impact are determined through this superposition-iteration model.