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.

A Self-adaptive Workload Balancing Algorithm on GPU Clusters

Jianjiang Li,Yajun Liu,Peng Zhang,Qingsong Miao,Lei Zhang,Wei Chen 보안공학연구지원센터 2016 International Journal of Grid and Distributed Comp Vol.9 No.11

With the wide application of GPU in High Performance Computing, more and more heterogeneous CPU+GPU clusters have been establishedin many fields. But with the comprehensive using of heterogeneous CPU+GPU clusters, workload balancing has become an important problem when the process nodes coordinate with each other, and the execution time of a program on imbalanced clusters resides on the slowest node. Although there are many strategies and algorithms that can solve the problem of workload balancing to some extent, they generally face the problem of high consumption of communication caused by the task migration. In order to make up for the existing deficiencies, this paper proposes a virtual task migration algorithm adapted to GPU clusters on CUDA platform. This algorithm uses virtual task migration to avoid actual data transmission between nodes, so the communication overhead is obviously decreased. At last, this paper performs an actual test using matrix multiplication to verify this algorithm. The experiment results show that compared with static task partitioning, the algorithm proposed in this paper can effectively achieve dynamic workload balancing and reduce the execution time of programs on GPU clusters, thus the algorithm can significantly improve program execution performance of GPU clusters on CUDA platform.

Diagenesis and its controlling factors of Lower Donghetang Formation tight sandstone reservoir in Bachu area, Tarim Basin, China

Hanbing Zhang,Jun Peng,Xiaoxian Lin,Bin Li,Qingsong Xia 한국지질과학협의회 2018 Geosciences Journal Vol.22 No.2

The tight sandstone reservoir of the Donghetang Formation underwent complex diagenetic processes for which the controlling factors remain unknown. Here, we present a case study of the lower member of this formation and show that this part of the reservoir consists mostly of lithic quartz sandstone with poor physical characteristics. Using core observation, thin section identification, electronic microprobe, scanning electronic microscopy, X-ray diffraction, and inclusion fluorescence microscopy, we identified five major diagenetic processes: compaction, cementation, dissolution, metasomatism, and hydrocarbon charging. Compaction and cementation have negative effects on petrophysical properties (referred to porosity and permeability of sandstone in this paper), and dissolution improves these properties. Diagenesis is affected by the depositional environment, and clastic constituents control compaction and dissolution; burial history and the geotemperature field control diagenesis at the macroscopic scale, while hydrocarbon charging affects the degree of cementation and dissolution. As oil saturation increases, the percentage of calcareous cements decreases and the development of secondary dissolved pores improves.

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.

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.

An Improved Energy Recovery Clamp Circuit for PWM Converters with a Wide Range of Input Voltage

Honnyong Cha,Lihua Chen,Fang Z. Peng,Qingsong Tang 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

A full-bridge dc-dc converter employing diode rectifier in the output experiences severe voltage overshoot and oscillation problem across the diode rectifier caused by the interaction between the junction capacitance of the rectifier diode and the leakage inductance of transformer. The pronounced reverse-recovery current of high power diodes enforces these issues significantly by increasing power loss and voltage overshoot. Conventional energy recovery clamping circuits suffer from high voltage overshoot if the input voltage of converter is wide. In this work, a novel energy recovery clamp circuit is proposed to overcome this problem. Performance of the proposed circuit is verified both theoretically and experimentally with a 70 ㎾ dc-dc converter.

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.