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Formability,microstructure evolution and mechanical properties of wire arc additively manufactured AZ80M magnesium alloy using gas tungsten arc welding

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Journal of Magnesium and Alloys 2021年第1期9卷 192-201页

作者： Yangyang Guo Gaofeng Quan Yinglong Jiang Lingbao Ren Lingling Fan Houhong Pan Key Laboratory of Advanced Technologies of Materials Ministry of EducationSchool of Materials Science and EngineeringSouthwest Jiaotong UniversitySichuanChengdu 610031PR China Center for Advancing Materials Performance from the Nanoscale State Key Laboratory for Mechanical Behavior of MaterialsXi’an Jiaotong UniversityXi’an 710049PR China

Wire arc additive manufacturing(WAAM)technology has been used to fabricate the multi-layer single-pass deposited wall of AZ80M magnesium(Mg)alloy by gas tungsten arc *** formability,thermal cycles,microstructural evolution and mechanical properties of the WAAM AZ80M Mg alloy were *** results show that there was significant difference in the temperature variation and the geometries between the original several layers and the subsequent deposited *** to the arc energy input,the interpass temperature rised rapidly and then stabilized at 150℃.As a result,the width of the deposited wall increased and then kept *** were obvious differences in the microstructure of the WAAM AZ80M Mg alloy among the top zone,intermediate zone and bottom zone of deposited *** the arc deposition process,theβphase of the WAAM AZ80M Mg alloy redissolved due to the cyclic heat accumulation,and then precipitated in the grain *** cyclic heat accumulation also led to weakening of dendrite *** the substrate to the top zone,the hardness of the deposited wall decreased gradually,and the intermediate zone which was the main body of deposited wall had relatively uniform *** tensile properties of the WAAM AZ80M Mg alloy were different between the vertical direction and the horizontal *** the maximum ultimate tensile strength of the WAAM AZ80M Mg alloy was 308 MPa which was close to that of the as-extruded AZ80M Mg alloy.

关键词： Wire arc additive manufacturing Magnesium alloy Thermal cycles Microstructure Mechanical properties

An Aerothermal Study of Influence of Blockage Ratio on a Supersonic Tube Train System

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Journal of Thermal Science 2022年第2期31卷 529-540页

作者： SUI Yang NIU Jiqiang YUAN Yanping YU Qiujun CAO Xiaoling WU Dan YANG Xiaofeng School of Mechanical Engineering Southwest Jiaotong UniversityChengdu 610031China School of Architecture and Design Southwest Jiaotong UniversityChengdu 610031China State Key Laboratory of Aerodynamics China Aerodynamics Research and Development CenterMianyang 621000China

Evacuated tube transportation is an important development direction for the high-speed transportation technology of the ***,a train running at supersonic speed in a closed tube can create an unstable aerothermal phenomenon,causing the temperature to rise sharply inside the tube and endangering the safe operation of trains and *** blockage ratio is one of the key factors affecting the aerodynamic characteristics in the *** this paper,a 2 D axisymmetric model and Delayed Detached Eddy Simulation(DDES)based on the Shear Stress Transport(SST)k-ωturbulence model are used to study the aerothermal environment in the *** calculation method used in this paper was verified by a wind tunnel *** aerothermal phenomenon and distribution of the flow field in the tube with different blockage ratios were compared and *** results show that the aerothermal environment is significantly affected by the blockage ratio.A choking limit formed in the flow field will aggravate the aerodynamic phenomenon as the blockage ratio increases,which further deteriorates the aerothermal environment of the ***,the existence of the choking limit,shock wave,and Mach disk make the flow field in the tube more complicated.

关键词： tube train aerothermal environment blockage ratio choking limit numerical simulation

Seismic responses of the steel-strip reinforced soil retaining wall with full-height rigid facing from shaking table test

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Journal of Mountain Science 2018年第5期15卷 1137-1152页

作者： CAO Li-cong FU Xiao WANG Zhi-jia ZHOU Yong-yi LIU Fei-cheng ZHANG Jian-jing Key Laboratory of Transportation Tunnel Engineering Ministry of Education School of Civil Engineering Southwest Jiaotong University Department of Geotechnical Engineering School of Civil Engineering Southwest Jiaotong University Department of Civil Engineering and Architecture Hainan University

To investigate the seismic response of the steel-strip reinforced soil retaining wall with fullheight rigid facing in terms of the acceleration in the backfill, dynamic earth pressure in the backfill, the displacements on the facing and the dynamic reinforcement strain distribution under different peak acceleration, a large 1-g shaking table test was performed on a reduced-scale reinforced-earth retaining wall model. It was observed that the acceleration response in non-strip region is greater than that in potential fracture region which is similar with the stability region under small earthquake,while the acceleration response in potential fracture region is greater than that in stability region in middle-upper of the wall under moderately strong earthquakes. The potential failure model of the rigid wall is rotating around the wall toe. It also was discovered that the Fourier spectra produced by the inputting white noises after seismic wave presents double peaks, rather than original single peak, and the frequency of the second peak trends to increase with increasing the PGA(peak ground amplitude) of the excitation which is greater than 0.4 g. Additionally,the non-liner distribution of strip strain along the strips was observed, and the distribution trend was not constant in different row. Soil pressure peak value in stability region is larger than that in potential fracture region. The wall was effective under 0.1 g-0.3 g seismic wave according to the analyses of the facing displacement and relative density. Also, it was discovered that the potential failure surface is corresponds to that in design code, but the area is larger. The results from the study can provide guidance for a more rational design of reinforced earth retaining walls with full-height rigid facing in the earthquake zone.

关键词： Reinforced soil retaining walls Potentialfailure surface Full-height rigid facing Steel strip Seismic behaviors 1-g shaking table test

Neural FIR adaptive Laguerre equalizer with a gradient adaptive amplitude for nonlinear channel in communication systems

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Science in China(Series F) 2009年第10期52卷 1881-1890页

作者： ZHAO HaiQuan ZHANG JiaShu Key Laboratory of Signal and Information Processing of Sichuan Province Southwest Jiaotong University Chengdu 610031 China

To mitigate the linear and nonlinear distortions in communication systems, two novel nonlinear adaptive equalizers are proposed on the basis of the neural finite impulse response （FIR） filter, decision feedback architecture and the characteristic of the Laguerre filter. They are neural FIR adaptive decision feedback equalizer （SNNDFE） and neural FIR adaptive Laguerre equalizer （LSNN）. Of these two equalizers, the latter is simple and with characteristics of both infinite impulse response （IIR） and FIR filters; it can use shorter memory length to obtain better performance. As confirmed by theoretical analysis, the novel LSNN equalizer is stable （0 〈α〈1）. Furthermore, simulation results show that the SNNDFE can get better equalized performance than SNN equalizer, while the latter exhibits better performance than others in terms of convergence speed, mean square error （MSE） and bit error rate （BER）. Therefore, it can reduce the input dimension and eliminate linear and nonlinear interference effectively. In addition, it is very suitable for hardware implementation due to its simple structure.

关键词： decision feedback nonlinear channel adaptive equalizer neural network Laguerre filter

Analysis of the stability and seismic behavior of the geosynthetic-reinforced embankments under earthquake

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Journal of Mountain Science 2020年第5期17卷 1269-1280页

作者： ZHU Hong-wei YAO Ling-kan XU Guang-xing School of Environment and Resources Southwest University of Science and TechnologyMianyang 621010China MOE Key Laboratory of High-speed Railway Engineering Southwest Jiaotong UniversityChengdu 610031China Research of National Defense Communication Shijiazhuang Tiedao UniversityShijiazhuang 050043

The stability and seismic behavior of geosynthetic-reinforced embankments during the earthquake is not well *** this paper,the damage types of embankments were summarized,and the seismic stability of reinforced embankment were analyzed through an earthquake damage investigation in the Wenchuan earthquake ***,large-scale shaking table model tests were performed on the geosynthetic-reinforced *** results show that the damage level of the reinforced embankment was almost less than that of the unreinforced *** peak seismic earth pressure was nonlinear along the height of the embankment,the largest peak seismic earth pressure was roughly in the middle of the embankment *** peak ground accelerations(PGA)amplification factor first showed an increasing pattern and then a decreasing pattern with the increase of elevation,but there was a final increasing trend along the height of the reinforced *** results can help to establish the proper design of the reinforcement embankments under earthquake conditions.

关键词： Reinforced embankment Stability Seismic behavior Shaking table model test

Study on the operational safety of high-speed trains exposed to stochastic winds

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Acta Mechanica Sinica 2014年第3期30卷 351-360页

作者： Meng-Ge Yu Ji-Ye Zhang Ke-Yue Zhang Wei-Hua Zhang State Key laboratory of Traction Power Southwest Jiaotong University Emei Campus of southwest jiaotong university

The characteristic wind curve （CWC） was com- monly used in the previous work to evaluate the operational safety of the high-speed trains exposed to crosswinds. How- ever, the CWC only provide the dividing line between safety state and failure state of high-speed trains, which can not evaluate the risk of derailment of high-speed trains when ex- posed to natural winds. In the present paper, a more realistic approach taking into account the stochastic characteristics of natural winds is proposed, which can give a reasonable and effective assessment of the operational safety of high-speed trains under stochastic winds. In this approach, the longitudi- nal and lateral components of stochastic winds are simulated based on the Cooper theory and harmonic superposition. An algorithm is set up for calculating the unsteady aerody- namic forces （moments） of the high-speed trains exposed to stochastic winds. A multi-body dynamic model of the rail vehicle is established to compute the vehicle system dynamic response subjected to the unsteady aerodynamic forces （mo- ments） input. Then the statistical method is used to get the mean characteristic wind curve （MCWC） and spread range of the high-speed trains exposed to stochastic winds. It is found that the CWC provided by the previous analyticalmethod produces over-conservative limits. The methodol- ogy proposed in the present paper can provide more signif- icant reference for the safety operation of high-speed trains exposed to stochastic winds.

关键词： High-speed trains Stochastic winds Unsteadyaerodynamic forces Mean characteristic wind curve

Analysis of network traffic flow dynamics based on gravitational field theory

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Chinese Physics B 2013年第6期22卷 670-680页

作者：刘刚李永树张喜平 Faculty of Geosciences and Environmental Engineering Southwest Jiaotong University

For further research on the gravity mechanism of the routing protocol in complex networks, we introduce the concept of routing awareness depth, which is represented by p. On this basis, we define the calculation formula of the gravity of the transmission route for the packet, and propose a routing strategy based on the gravitational field of the node and the routing awareness depth. In order to characterize the efficiency of the method, we introduce an order parameter, η, to measure the throughput of the network by the critical value of phase transition from free flow to congestion, and use the node betweenness centrality, B, to test the transmission efficiency of the network and congestion distribution. We simulate the network transmission performance under different values of the routing awareness depth, ρ. Simulation results show that if the value of the routing awareness depth p is too small, then the gravity of the route is composed of the attraction of very few nodes on the route, which cannot improve the capacity of the network effectively. If the value of the routing awareness depth ρ is greater than the network＇s average distance （l）, then the capacity of the network may be improved greatly and no longer change with the sustainable increment of routing awareness depth p, and the routing strategy performance enters into a constant state. Moreover, whatever the value of the routing awareness depth p, our algorithm always effectively balances the distribution of the betweenness centrality and realizes equal distribution of the network load.

关键词： routing strategy congestion gravitation field complex networks

Simultaneous unidirectional and bidirectional chaos-based optical communication using hybrid coupling semiconductor lasers

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Science China(Information Sciences) 2014年第1期57卷 280-290页

作者： JIANG Ning PAN Wei LUO Bin YAN LianShan XIANG ShuiYing Center for Information Photonics and Communications School of Information Science and TechnologySouthwest Jiaotong University

A simultaneous unidirectional and bidirectional chaos-based optical communication scheme based on a hybrid coupling semiconductor laser system that consists of one center semiconductor laser(CSL)and multiple side semiconductor lasers(SSLs)is proposed *** this scheme,the SSLs oriented in a linear chain mutually couple with the adjacent SSLs and they are subjected to identical unidirectional injections from the CSL which is a chaotic external cavity semiconductor *** theoretically analyze the conditions for diferent types of chaos synchronization based on the symmetry operation mechanism and injection-locking mechanism,and numerically investigate the influences of operation parameters,parameter mismatch robustness,chaos pass filtering efects and communication performance of the hybrid coupling semiconductor laser *** simulation results demonstrate that with proper selection of the unidirectional and mutual coupling conditions,the SSLs can synchronize with each other isochronally and simultaneously synchronize to the CSL completely or laggardly,which enables the proposed system to achieve a unidirectional broadcasting communication from the CSL to the SSLs and a bidirectional communication among the SSLs *** proposed scheme is beneficial to the implementation of optical chaos communication networks.

关键词： semiconductor laser optical communication chaos synchronization chaos communication net-works hybrid coupling

Reversible Data Hiding Based on Run-Level Coding in H.264/AVC Video Streams

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Computers, Materials & Continua 2020年第5期63卷 911-922页

作者： Yi Chen Hongxia Wang Xuyun Zhang School of Information Science and Technology Southwest Jiaotong UniversityChengdu611756China College of Cybersecurity Sichuan UniversityChengdu610064China Department of Electrical Computer and Software EngineeringUniversity of AucklandAuckland1023New Zealand

This paper presents a reversible data hiding(RDH)method,which is designed by combining histogram modification(HM)with run-level coding in H.264/advanced video coding(AVC).In this scheme,the run-level is changed for embedding data into H.264/AVC video *** order to guarantee the reversibility of the proposed scheme,the last nonzero quantized discrete cosine transform(DCT)coefficients in embeddable 4×4 blocks are shifted by the technology of histogram *** proposed scheme is realized after quantization and before entropy coding of H.264/AVC compression ***,the embedded information can be correctly extracted at the decoding ***-signal-noise-to-ratio(PSNR)and Structure similarity index(SSIM),embedding payload and bit-rate variation are exploited to measure the performance of the proposed *** results have shown that the proposed scheme leads to less SSIM variation and bit-rate increase.

关键词： Reversible data hiding run-level coding visual quality bit-rate increase H.264/AVC video streams