西南交通大学学报

MPPT Control of Partial Shadow Photovoltaic Generation System Based on Improved PSO Algorithm

CHEN Weirong, WANG Weiying, ZHENG Yibin, ZHENG Yongkang, LI Qi

2018, 53(6): 1095-1101, 1129. doi: 10.3969/j.issn.0258-2724.2018.06.001

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Under partial shading condition, the traditional MPPT （maximum power point tracking） is suitable for local optimisation, which cannot track to the global MPP. To solve this problem, a maximum power tracking method based on adaptive learning factor particle swarm optimisation is proposed in this study. The learning factor and weight coefficient were constantly changed based on ordinary particle swarm optimisation to improve the speed and precision of the algorithm convergence. It was applied to the maximum power point tracking of photovoltaic system under partial shadow condition. In the RT-LAB environment, two different photovoltaic arrays with different illumination intensities were considered as examples to verify real-time effectiveness. The simulation results indicate that the proposed adaptive learning factor particle swarm algorithm can track to the global maximum power point in 0.298 s in two peaks conditions, while the ordinary PSO （particle swarm optimization） algorithm requires approximately 0.615 s, and the disturbance observation method suitable for local optimisation. These results prove that the proposed algorithm can effectively improve the convergence speed and accuracy and can be applied to multimodal situation. Finally, a simulation example was set up to verify that the algorithm was suitable for light mutation condition.

Reliability Evaluation of Relay Protection for Traction Substation of Urban Rail Transit

LIN Sheng, LIN Xiaohong, FENG Ding

2018, 53(6): 1102-1109. doi: 10.3969/j.issn.0258-2724.2018.06.002

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To understand the reliability and find the weaknesses in the relay protection system of urban rail transit traction substation to provide guidance for failure investigation, a reliability evaluation project of relay protection for urban rail transit traction substation was undertaken. First, the reliability index was determined according to the characteristics of the relay protection system of urban rail transit traction substation. Then, a fault tree model of the relay protection device and different configuration scheme protection systems were set up based on the system structure and failure mode. Finally, based on Markov theory and Monte Carlo method, the reliability index of relay protection of urban rail transit traction substation was calculated considering the self-test function of the microprocessor protection. The results show that the method can obtain sufficient reliability indicators to evaluate the reliability of traction substation relay protection to identify the protection system weaknesses. On the condition that the self-test success rate is 0.9, the relay protection device failure probability caused by the protection maloperation is 17.93% higher than that caused by the protection rejection. Meanwhile, the self-test success rates of maloperation and rejection are 86.09% and 74.37% respectively, and the availability of protection devices is 99.88%. Backup protection can reduce the rejection probability of the protection system, but backup protection caused about 30%–50% of the maloperation of the protection system. Therefore, it is necessary to consider the impact of protection maloperation when selecting the protection configuration.

Study on Impact on Negative Sequence of Single Three-Phase Combined Co-Phase Power Supply System

WANG Pingxiang

2018, 53(6): 1110-1116. doi: 10.3969/j.issn.0258-2724.2018.06.003

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The negative sequence is one of the main power quality issues in the tractive power supply system in our country. The structure and characteristics of a single three-phase combined co-phase power supply system are introduced herein, to study the impact of the negative sequence of a single three-phase combined co-phase power supply system. Negative-sequence currents produced by traction loads of the different phase power supply system and the single three-phase combined co-phase power supply system were calculated with the generalized method. In addition, the impact of a single three-phase combined co-phase power supply system and the different phase power supply system on the negative sequence were analyzed in the situation when traction loads are under traction and regenerative braking. The calculation results indicated that capacity utilization of single three-phase combined-type balanced transformer winding is at least 85.7%. This is higher than the YNvd connected transformer, and the impact of train regenerative braking is lower on the negative sequence.

Analysis of Lightning Breakdown Characteristics of Contaminated Insulators in Parallel Clearance

LIAO Yifan, HU Chuanliang, TANG Jun, YANG Fan, CHEN Zhihao, ZHOU Yu, LU Zhanhui

2018, 53(6): 1117-1122. doi: 10.3969/j.issn.0258-2724.2018.06.004

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To analyse the lightning impulse breakdown characteristics of the parallel gaps of contaminated insulators with different salt densities, the SC-210 porcelain cross-arm insulator was used to conduct the lightning impulse test. Comparing with the electric field simulation results of the clean and contaminated insulators, the phenomenon of flashover along the surface of the insulator was analysed several times during the test. The tests and analysis indicate that in case of the SC-210 porcelain cross-arm installed with parallel gaps, its lightning impulse breakdown voltage U50% decreases with increasing salt density and tends to saturate more readily. The voltage-time characteristics curve of the lightning impulse of the contaminated insulator and the lightning protection gap gradually intersect, and the phenomenon of flashover along the surface of the insulator occurs several times during the test. The results of the study suggest that the effect of contamination on the flashover/breakdown location on the surface of the insulator should be considered in the insulation timing of the parallel gap and the insulator string.

Adaptive Cuckoo Optimization DV-HOP Localization Algorithm Based on Multi-Communication Radius and Error Correction

YU Xiuwu, HU Mufang, LIU Yong, GUO Qian

2018, 53(6): 1123-1129. doi: 10.3969/j.issn.0258-2724.2018.06.005

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An adaptive cuckoo optimization DV-HOP localization algorithm based on multi-communication radius and error correction （MEACS-D）is proposed, aiming at addressing the problem of lager error in wireless sensor networks of range-free DV-HOP algorithms. Using the anchor nodes, which have the ability to broadcast multi-communication radius messages, and to decimalize a counted number of hops （to reduce error caused by different jump lengths）, the virtual intersecting circle geometric method was used to calculate the distance between unknown nodes and anchor nodes in one hop. When the unknown node was used to select the average jump distance, consideration was given to adding each anchor node weight to reduce error. To calculate the node coordinates in order to improve the localization accuracy, the cuckoo algorithm with adaptive search step was introduced instead of the maximum likelihood estimation method. In simulation, by varying the values for the anchor nodes, communication radius, and total node, the localization error of the MEACS-D algorithm was reduced by 39.7% and 10.6%, compared to the DV-HOP algorithm and the original cuckoo DV-HOP （CS-D） algorithm, respectively. These results confirm that the MEACS-D algorithm can reduce the localization error effectively.

Analysis and Testing of Network Security for China Railway Communication Networks and Proposed Architecture Based on Trusted Computing

LI Saifei, YAN Lianshan, LI Hongzhe, GUO Wei, ZHANG Weijun, LIU Qingtao

2018, 53(6): 1130-1136, 1149. doi: 10.3969/j.issn.0258-2724.2018.06.006

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China’s railway communication networks have been deployed throughout the country and have a complex infrastructure. A security architecture based on trusted computing and software-defined networking （SDN） has thus been proposed for ensuring the security of the railway communication system. The security risks for the complete network were investigated and tested through fault tree analysis. A simulation evaluation was subsequently performed and a threat scenario was simulated for analysing possible intrusions into the railway communication network. The obtained results show that the proposed architecture can help address various organised, targeted, and persistent network attacks.

Tunnel Crack Extraction Based on Adaptive Threshold and Connected Domain

LUO Jia, LIU Dagang

2018, 53(6): 1137-1141, 1149. doi: 10.3969/j.issn.0258-2724.2018.06.007

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To solve the problems of traditional tunnel crack detection, such as low efficiency, subjectivity and poor safety, among others, a method of tunnel crack extraction based on adaptive threshold and connected domain marking is proposed using orientation and continuity characteristics. First, according to the orientation characteristics of cracks, an Arabia digital algorithm （Algorithmic） is designed to roughly extract cracks. Adaptive threshold is chosen for threshold selection in the formula, and the improved threshold iteration method is used to automatically obtain the best threshold without manual intervention. Then, according to the continuity characteristics of cracks, the connected region labelling method in mathematical morphology is used to extract the cracks. By controlling the area of the connected domain, the denoising processing after the rough extraction of the crack is realized, and the repair treatment after the rough extraction of the crack is realized by expansion and corrosion operations. Finally, a total of 165 different types of crack images were selected as experimental samples, and simulation experiments were carried out on MATLAB. From the experimental data, we observe that the extraction precision of the adaptive threshold and the connected domain label extraction method can be as high as 94.2%, the average running time is only 35.4 s, the error recognition rate and the rejection rate have been controlled at 2.7% and 1.1%, respectively. Compared with traditional image processing methods, our proposed method demonstrates remarkable improvement and shows promise for future applications.

Quantum Image Encryption Algorithm Based on Chaotic System and DNA Coding

ZHANG Jian, HUO Da

2018, 53(6): 1142-1149. doi: 10.3969/j.issn.0258-2724.2018.06.008

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To ensure the security of quantum information, a quantum image encryption algorithm based on combining a chaotic system and DNA coding is proposed. Firstly, the image is expressed as a quantum superposition state, and the quantum image is then scrambled by a unitary matrix generated by logistic chaos. Next, using Lorenz chaos to generate a natural DNA matrix and selecting DNA addition rules dynamically to perform DNA calculations, the unitary matrix is obtained to encrypt the quantum image. Finally, the quantum image is measured and the classic ciphertext image is obtained. From simulation experiments and histograms, correlation, and number of pixel change rate （NPCR） analysis, results indicated that the image histogram is smoother, grayscales average distribution is approximately 1 000, the correlation of adjacent pixels is low, average correlation coefficient is 0.002, and the NPCR is 99.6%. The conclusion is that the algorithm produces acceptable encryption effects and provides effective security.

Optimization of Endmember Extraction in Mixed Pixel Unmixing in Hyperspectral Images

HUANG Zuowei, ZHANG Suifeng, ZHANG Taoxin

2018, 53(6): 1150-1156, 1172. doi: 10.3969/j.issn.0258-2724.2018.06.009

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Hyperspectral unmixing is a process for unmixing the mixed pixels of a hyperspectral image composed of several substances and their corresponding proportions. Extracting endmembers is a major problem in hyperspectral unmixing. Owing to the goal of achieving a large search range for the endmembers, the efficiency of the traditional algorithm is usually low. Based on an improved ICA（independent component analysis）and optimized endmember extraction method, an improved method of unmixing was proposed. Firstly, endmember extraction was optimized by means of an optimized FastICA algorithm. Thereafter, spatial information and spectral information were considered and combined into a multi-core parallel processing to optimize the candidate endmembers. Lastly, the performance of the proposed algorithm was verified using real hyperspectral data. The method was shown to overcome the shortcomings of the traditional method and obtain more accurate endmembers. In particular, compared to the accuracy of the traditional N-FINDER method, the accuracy of the extracted endmembers increases by 3.55%. The object classification accuracy also improves immensely, and the overall classification accuracy is increased by 2.88%.

Multiscale Modeling of Transition Section with Continuously Welded Rail Based on Homogenization Method

GUO Yishi, YU Zujun, SHI Hongmei, ZHU Liqiang

2018, 53(6): 1157-1165. doi: 10.3969/j.issn.0258-2724.2018.06.010

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To analyse the stress distribution of continuously welded rails at transition sections under the effect of temperature, a multiscale model of the transition section with two-terminal rail lines is proposed. Owing to the structural regularity of the two-terminal bridge and the subgrade extending from the transition section, a simplified macro-scale line model is built based on the macro-equivalent properties of a typical structural unit, which can be evaluated by the asymptotic homogenisation method. As for the transition section, a minor-scale model is built to involve the key details. These sub-models of different scales are connected to each other based on the interface consistency conditions. The homogenised model of the two-terminal extension segments provides a useful boundary condition for the central transition section in the process of solving the multiscale model. Further, the solutions of different-scale models are obtained by model decomposition, which avoids high-dimension matrix operations for the single-scale model. The simulation results show that the multiscale model with the asymptotic homogenisation method has fewer computations than the traditional finite model, which consequently has a faster calculating speed. Comparing the simulation results of the termination cutting off and abutments with measurements from the Xinbianhe bridge of the Beijing–Shanghai high speed railway, the average correlation is approximately 0.8, and the varying trend of simulation results is consistent with the measured data.

Two Simplified Models for Human-Structure Vertical Interaction

CAO Lilin, CAO Dong, YU Guojun

2018, 53(6): 1166-1172. doi: 10.3969/j.issn.0258-2724.2018.06.011

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Based on a mass-spring-damper（MSD）model and a mass-spring-damper-rigid mass（MMSD）model, which are two kinds of pedestrian simplified models, the equations of vertical dynamic interaction pertaining to a simplified human-structure were deduced by the regularization structure modal function. Using the dynamic equation with non-proportional damping characteristics, the state-space method was used to solve the instantaneous frequency and damping ratio of the system equations; the difference between the two coupled dynamic equations and the change regularity of frequency and damping ratio of the structure under walking load were discussed, and the difference in the structural acceleration response in a human-structure coupled state was analysed. The results show that the structural damping ratio between the two kinds of equations is significantly different; however, the instantaneous frequency of the structure is only slightly distinct, considering the vertical interaction between a human and a structure. The instantaneous damping ratio peak increases by an average of 31.67%, and the instantaneous frequency reduces by an average of 0.29%. Human-structure vertical interaction must be considered in response to human-induced structural vibration analysis. The difference in structural dynamic responses between the MSD and MMSD models is very small, and the difference in the root mean square acceleration is only 0.34%.

Non-Linear Analysis of Three-Segment Stiffness Compressive Bar Based on Direct Stiffness Method

ZHANG Junxing, XU Jing, WANG Hongzhi

2018, 53(6): 1173-1178, 1186. doi: 10.3969/j.issn.0258-2724.2018.06.012

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To study the internal forces and displacement of a piecewise stiffness compressive bar with a consideration of the second-order effect, displacement and rotation equations were established based on the displacement governing equation. The displacement coefficients were obtained according to the displacement boundary condition at the ends of the bar and the continuity condition at the variable-stiffness section. The stiffness equilibrium equation in the matrix was established in line with the equations of internal forces. After matrix transformation, a stiffness matrix model for a piecewise stiffness compressive bar was developed. To validate the precision and efficiency of the developed model, the critical load for piecewise stiffness compression was calculated by using the proposed model and the interpolation shape function method. The maximum relative error between the results calculated from the interpolation shape function method and the theoretical solution is 43.24% for one element; as the number of elements increased, the relative error decrease to 0.023%. The results calculated by the stiffness matrix model are consistent with the analytical solutions for a single element. The proposed stiffness matrix model can be applied in non-linear analysis to obtain analytical solutions of internal forces and displacement.

Large Eddy Simulation of Unsteady Downburst Outflow Based on Wall Jet Model

ZHONG Yongli, YAN Zhitao, WANG Lingzhi, YOU Yi

2018, 53(6): 1179-1186. doi: 10.3969/j.issn.0258-2724.2018.06.013

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The feasibility of a large-scale experiment for downburst in a boundary layer wind tunnel was investigated. Large eddy simulation （LES） was employed to investigate the characteristics of stationary and travelling downburst using the impinging jet and wall jet methods, respectively. The velocity profiles from LES were compared with those obtained from the Wood model, the Oseguera model, the Victory model, and the classical wall jet experiment to verify the reasonableness of the two methods. Then, three time functions of the inlet velocity were used to obtain similar time series of the full-scale data. The results show that the fully-developed velocity profiles of the wall jet cohere with those of the three theoretical models and the classical wall jet experiment. When the translational velocity is 15% of the impinging jet velocity, the maximum horizontal wind speed increased by 15.8% compared to that of the stationary impinging jet, while when the velocity of co-flow is 19.2% of the wall jet velocity, the maximum horizontal wind speed increased by 16.9% compared to that of the wall jet without co-flow. The stationary downburst can be appropriately simulated using the wall jet model without co-flow, while the travelling downburst can be effectively simulated using the wall jet model with co- flow. The results from large eddy simulation （LES） and data obtained from Andrews AFB downburst are in good agreement. The unsteady characteristics of downburst outflow can be perfectly reproduced by the time functions of the velocity inlet.

Axial Compressive Experiment on Steel-Jacket Retrofitted Column with Recycled Aggregate Concrete

HE An, CAI Jian, CHEN Qingjun, XUE Hua, ZUO Zhiliang, TANG Xulin, LI Kaiyu

2018, 53(6): 1187-1194, 1204. doi: 10.3969/j.issn.0258-2724.2018.06.014

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To realise the goals of energy saving and emissions reduction in the construction industry, a new retrofitting method of steel-jacket retrofitted columns with recycled aggregate concrete is presented. An unstrengthened column, twelve steel-jacket retrofitted columns, and two concrete-filled steel-tube columns were tested under concentric compressive loading. The axial resistance and deformation capacity were analysed, and the method for calculating the strength of the retrofitted column was evaluated. The experimental results indicated that the strength of the retrofitted columns is 2.19–3.98 times higher than that of the unstrengthened one. In addition, the stiffness and ductility of the steel-jacketed columns increased notably. The strengths of the retrofitted columns with recycled aggregate concrete were 91.8%–97.0% of that of the column with normal infill concrete. As the strength of the infill recycled concrete increased from 27.0 MPa to 32.9 MPa, the strength of the retrofitted column increased by only 2.67%. For specimens with the replacement ratio of recycled coarse aggregate of 50%, the strength of the retrofitted column was enhanced by 34.0% and 77.8% as the thickness of the steel jacket increased from 1.81 mm to 3.84 mm and to 5.84 mm, respectively. After considering the preload of the original column, the strains corresponding to the peak load of the retrofitted column decreased by 47.1%–59.3%. The performance of the steel-jacket retrofitted column was similar to that of the concrete-filled steel-tube columns. Various methods from current design codes were adopted to calculate the axial resistance of the steel-jacket retrofitted column and it was seen that the design code EC4 provides the most accurate and stable predictions.

Analysis of LRB-DSB Three Dimensional Isolation System’s Isolating Effect

GUO Yangzhao, PAN Yi, WU Ti, LI Jingwen, WANG Zichao

2018, 53(6): 1195-1204. doi: 10.3969/j.issn.0258-2724.2018.06.015

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In order to study the isolating effect of the three dimensional laminated rubber bearings-dish spring bearing （LRB-DSB） isolation system, comprehensive analyses for its construction, mechanism, and design theory were performed. On the basis of these analyses, comparative studies of the vibration characteristics and the dynamic response under three dimensional seismic excitation of the three dimensional base of the isolated structure based on LRB-DSB, horizontal isolation structure based on the LRB, and general seismic structure were conducted. The results showed that, in comparison with the LRB horizontal isolation system, the vertical stiffnesses of the three dimensional LRB-DSB isolation systems are properly descended, and the vertical vibration period can be extended by 120%. The LRB isolation system demonstrates good horizontal isolation capacity, but has no vertical isolation effect; it may even amplify any vertical seismic action on the structure. The three dimensional LRB-DSB isolation system can suitably make up for these deficiencies by isolating both the horizontal and vertical effects well.

Mathematical Description and Analysis on Characteristics of Pore Structure for Foam Concrete

LI Fangxian, YU Qijun, LUO Yunfeng, WEI Jiangxiong

2018, 53(6): 1205-1210. doi: 10.3969/j.issn.0258-2724.2018.06.016

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To analyse the characteristics of the pore structure of foam concrete and reveal the relationships between various pore structure parameters, dense and non-dense packing structure models were established. A formula for the calculation of pore structure parameters, including porosity, surface area, and pore wall thickness, was derived based on various theoretical models to analyse the relationships between these parameters. The formula was validated using the measured pore structure parameters and used to analyse the characteristics of the pore structure of foam concrete. The results show that the foam concrete has a dense packing structure when the dry density grade is less than 1 000 kg/m³. The difference in the pore wall thickness according to the experimental data and that obtained via the dense packing structure model is less than 12%, which illustrates that the dense packing structure model is feasible. When the dry density grade was egual or greater than 1 000 kg/m³ foam concrete has a non-dense packing structure. The difference in the pore wall thickness according to experimental data and that obtained via the dense packing structure model is less than 3%, which verifies the feasibility of the non-dense packing structure model. Pore wall thickness increased with increasing pore diame- ter, and decreased with increasing porosity for the same bulk density. The pore surface area can be over 3 000 m² per m³ of foam concrete and the pore wall thickness can be as small as 60 μm. Foam concrete is characterized by a porous structure with thin walls, the coexistence of materials with small volumes and pores with large volumes, and the exposure of materials with small volumes to the gas in pores with a large areas.

Research on Calibration Equipment for Multi-Range Earth Pressure Cell and Calibration Experimentation

YIN Zihong, ZHAO Fengnian, GAO Xue, JIANG Liangwei, SU Qian

2018, 53(6): 1211-1219. doi: 10.3969/j.issn.0258-2724.2018.06.017

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The general problems encountered in obtaining accurate soil pressure test-data are determined by performing a literature review of the research on calibration devices for soil pressure cells. Then, a finite element simulation for the calibration of multi-range soil pressure cell equipment is performed using ABAQUS, revealing how the sizes of bearing plates and calibration barrels affect the bearing surface stresses of the soil pressure cells. The extracted data are used to inform the performance of a rationality analysis to determine the key parameters and sizes of the relevant calibration equipment. On this basis, the single-load-recreating-the-sample scheme, and the cyclic-load-without-disturbing-sand scheme, are adopted to carry out the calibration on four soil pressure cells whose measured pressure ranges are 0.3, 0.6, 1.0 MPa, and 2.0 MPa. The results show that the correlation coefficient of the experimental data, R², is greater than 0.90, showing strong linear correlation. The K values of both the experimental group and the control group have good repeatability, which means the test data is correct and reasonable, and the calibration equipment is reliable. As such, multi-range soil pressure cells can be calibrated effectively using this equipment. Analyzing the repeated loading and hysteresis loops indicates that the data from the cyclic-load-without-disturbing-sand scheme is relatively stable, supporting the recommendation of this scheme as the calibration test program. The test value K₁ in the calibration of sandy soil is less than the factory value of K₂; in order to improve the accuracy of the parameters, soil pressure cells of the resistance strain type should undergo a calibration test appropriate to their intended practical environment before use.

Study of Influencing Factors on Cone Factor for Cone Penetration in Marine Clay

QIU Min, YAO Aiguo, DENG Guoqing, WANG Yanchao

2018, 53(6): 1220-1226. doi: 10.3969/j.issn.0258-2724.2018.06.018

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To study the influence of the rigidity index, strain softening, and strain rate on the cone factor of marine clay, cone penetration in clay is simulated on the basis of the finite element method, and an arbitrary Lagrangian-Eulerian （ALE） technique is adopted to control the quality of mesh under the condition of large strain. The difference between the traditional small-strain analysis and the ALE large-strain analysis under the steady state is discussed, and the influences of the rigidity index on the cone factor and the extension of the plastic zone are analyzed. The strain-softening parameters and the strain-rate-controlling parameter for the strain-rate dependency of soil are introduced to analyze the influence of strain softening （sensitivity） and strain rate on the cone factor. In addition, a cone factor expression is proposed considering the influence of the rigidity index, strain softening, and strain rate of the soft soil. The results show that the traditional small-strain analysis greatly underestimates the bearing capacity of clay, whereas the ultimate bearing capacity under large strain increases with penetration depth to finally reach steady state at 12D depth. Moreover, the cone factor and the plastic zone increase with an increase in the rigidity index, and the radial expansion of the plastic zone around the cone tip is closer to the spherical cavity expansion. The sensitivity of the soil increases and the cone factor decreases slightly with a decrease in the strain-softening parameter. The increase in the strain-rate-controlling parameter causes the cone factor to increase significantly, although the increment is independent of sensitivity. In this study, the influence of the rigidity index, strain softening, and strain rate on the cone factor of marine clay is quantified by this expression, which is helpful in evaluating the shear strength of marine clay using the static cone penetration technique.

Parameters Analysis Based on Simplified Method to Solve Piled Embankment with Geogrid-Reinforcement

LIU Feicheng, ZHANG Jianjing, YAN Shijie, CAO Licong, WU Zuoju

2018, 53(6): 1227-1236. doi: 10.3969/j.issn.0258-2724.2018.06.019

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In order to analyze the influence of parameters on load transfer and deformation mechanisms of piled embankment with geogrid-reinforcement, a simplified method was proposed and employed for parameters analysis. A method including soil arching effect in granular material, subsoil resistance and membrane effect, is deduced and the deformation of the geogrid is expressed by Quadratic parabolic equation. Through comparative analysis with test data and other current design methods, it is found that the proposed method is conceptually and mathematically simple, and the results are reliable. The influence of embankment height, tensile stiffness of the geogrid, soft soil depth and compression modulus of soft soil on the tension of the geogrid, the settlement of soft ground and stress concentration ratio are studied using this method. The influence significance of these factors has been investigated by the evaluation theory of binary variance analysis of non-repeatability tests. The results show that the tension of geogrid is in proportion to embankment height, tensile stiffness of geogrid, soft soil depth, but in inversely proportion to compression modulus of soft soil. The settlement of soft ground is in proportion to embankment height, soft soil depth, but in inversely proportion to tensile stiffness, compression modulus of soft soil. Rsc is in proportion to embankment height, tensile stiffness, soft soil depth, but in inversely proportion to compression modulus of soft soil. Decreasing soft soil depth and improving compression modulus of soft soil are both the effective methods to transfer more load to piles. Larger pile caps and small pile spacing should be prior to adopting the geogrid with high tensile stiffness in promoting transferring more load to piles.

Study of Large Deformation Classification Criterion for Layered Soft Rock Tunnels under High Geostress

CHEN Ziquan, HE Chuan, WU Di, DAI Cong, YANG Wenbo, XU Guowen

2018, 53(6): 1237-1244. doi: 10.3969/j.issn.0258-2724.2018.06.020

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The asymmetric deformation failure characteristics and asymmetric mechanical behaviour of supporting structures in layered soft rock tunnels under high geostress, combined with the anisotropic mechanical properties of carbonaceous phyllite, were investigated. Based on the deformation data of 93 layered soft rock tunnels under high geostress, the relationships between roof settlement, horizontal convergence, largest deformation and geostress, rock compressive strength, and overburden depth were systemically analysed. The results show that the deformations are discretely distributed according to the variations in geostress, rock compressive strength, and overburden depth. Under certain parameters of geostress, rock compressive strength, or overburden depth, the deformations are distributed in both the high- and low-value zones. With increasing geostress and overburden depth, and with decreasing rock compressive strength, the deformations gradually approach the high-value zone. This means that the large deformations of layered soft rock tunnels under high geostress are determined by the combined action of high geostress, weak surrounding rock, and a weak bedding plane. Based on the power exponent variation law between the largest deformation and the strength-stress ratio, a new classification criterion for large deformations is proposed for layered soft rock tunnels under high geostress.

Optimization of Structural Setting Based on Forced Ventilation Method in Tunnel Under Construction

QIAO Liwei

2018, 53(6): 1245-1252, 1277. doi: 10.3969/j.issn.0258-2724.2018.06.021

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Considering the disadvantages of poor air quality and prolonged dust removal caused by the forced ventilation mode in tunnel construction using drilling and blasting methods, the extractive and air curtain ventilation mode was developed by structure optimization and improvement over the traditional ventilation mode. Diversion tunnels I and II of Wujialing second stage hydropower station were used as the research site, with wind speed and characteristics of free SiO₂ dust diffusion monitored and comparatively analysed on site. Moreover, the evolution characteristics of the free SiO₂ dust concentration field were simulated and analysed using Ansys-CFD. The results indicate that the concentration of free SiO₂ dust in the working area can reach the standard after ventilating for 35 min under the extractive and air curtain ventilation mode, with little free SiO₂ dust and a low concentration of dust in the tunnel body area. In addition, the maximum purification rate of SiO₂ dust in the working area is 25.93% higher than that in the forced ventilation mode, and the construction environment in the tunnel is greatly improved.

Automated Lane Marking Identification Based on Improved Canny Edge Detection Algorithm

LUO Wenting, LI Zhongyi, LI Lin, GAN Hong, GUO Jiangang

2018, 53(6): 1253-1260. doi: 10.3969/j.issn.0258-2724.2018.06.022

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Abstract:
In a pavement distress survey, a wandering survey vehicle would reduce the accuracy of lateral position measurement of pavement distress. The errors in the measurement of distress lateral position can be eliminated based on the lane marking identified using an edge detection algorithm. However, the traditional edge detection algorithm has some limitations, such as incomplete and false edge recognition. Therefore, an improved Canny edge detection algorithm is proposed herein, which is composed of three steps: noise elimination using a Wiener filter, adaptive threshold definition using Otsu’s method, and lane marking edge recognition based on offset-allowed area method. The test results show that the total number of edge pixels detected by the proposed algorithm is between 900 and 2 000, which is close to the standard value of 1 352 for existing edge detection algorithms. The ratio of the number of eight-connected domains to the total number of edge pixels ranges from 0 to 0.04, and the ratio of the number of eight-connected domains to the number of four-connected domains ranges from 0 to 0.29, which shows that the improved algorithm demonstrates excellent performance in terms of noise elimination, false edge recognition, consistent edge detection, and single edge response. A validation test based on the manual method shows that the correlation between the test value and reference is up to 99%. The proposed method can be used to detect the lateral position of pavement distress based on 3D laser imaging data.

Cause-based Distribution Models of Affected Trains Account for Primary Delay in High-Speed Rail

WEN Chao, LI Zhongcan, HUANG Ping, TANG Yixiong, JIANG Chaozhe, GAO Lei

2018, 53(6): 1261-1269. doi: 10.3969/j.issn.0258-2724.2018.06.023

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Abstract:
To measure the severity of high-speed train delays, the distributions models of the affected trains, owing to different cause-based primary delays, were established using statistical modeling. First, the train operation records during 2014 and 2015 obtained from China Railway Guangzhou Group Co. Ltd. were considered to train the models, and the goodness of fit of the five candidate models was compared. Subsequently, the inverse regression model was used to model the distributions of the cause-based affected trains, and the parameters of the models were estimated using the R-program. Finally, the chi-square test was performed, and subsequently, the Kolmogorov-Smirnov double sample tests with respect to the models were employed based on the testing data of 2016. The test results indicate that all the cause-based models can pass the accuracy test under the significance level of 0.05, and the established models are identically distributed according to the testing data. The tests also indicate that the matching degree between the prediction results and the observations owing to the delay causes can be higher than 97%.

Multi-Scenario Optimisation Model for Reusable Logistics Resource Allocation

REN Jianwei, CHEN Chunhua, ZHANG Xueyan

2018, 53(6): 1270-1277. doi: 10.3969/j.issn.0258-2724.2018.06.024

[Abstract](474)

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Abstract:
In order to solve the reusable logistics resource（RLR）allocation problem where some uncertain parameters cannot be estimated using historical data, and the types and dimensions of RLR are varied, a multi-scenario optimisation model for RLR allocation was studied using the method of scenario planning. First, the features of RLR and the RLR allocation processes over a pooling system were analysed. Then, a multi-scenario optimisation model for RLR allocation was presented considering that some kinds of resources were capable of being replaced with other kinds while some other kinds of resources were not. The number of demand, recycle, and some other parameters were divided into two parts（certain and uncertain）in the model. Finally, the validity of the model was proved using a case study and the plan for the China-Europe express railway RLR system was proposed based on the results. The results showed that the proposed multi-scenario could make good demand fulfilment and recycling fulfilment. It was also proved that the total expected cost by using multi-scenario model could be reduced by 1.7% and 5.7%, as opposed to the deterministic models considered in both cases.

Logistics Service Composition Based on Multi-Objective Optimization

ZHANG Fei, ZHANG Jin

2018, 53(6): 1278-1285, 1307. doi: 10.3969/j.issn.0258-2724.2018.06.025

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Abstract:
Given the reform in railway freight transportation, the authors developed an end-to-end logistics service to respond more promptly and effectively to customers’ diverse, individual needs. They built a Web-based service model, incorporating all the characteristics of traditional logistics services. This Web-based model dynamically composed the services offered by logistics providers in real time and transformed them into multi-objective optimization problems. Then the authors applied an improved NSGA-Ⅱ（non-dominated sorting in genetic algorithm-Ⅱ） algorithm to the optimization problem. Firstly, in the chromosome encoding and genetic factor of the algorithm, they considered the logical relationship of the logistic services and the associations between the logistics service provider alliances. Secondly, they added customers’ demand for the QoS （quality of service） attribute as a penalty function to the fitness function, effectively avoiding the problem of service re-planning and encouraging the evolution of the chromosomes in the direction of the constraint. The experimental simulation of the algorithm shows that it is a feasible and effective solution to the logistics service composition problem. In an actual railway logistics service, the QoS attribute of specific and composite services meets customer requirements and the composite service is non-inferior for all objectives. The running time of the algorithm meets customer needs even when the number of logistics tasks and candidate services increases. The proposed algorithm offers a better logistics service composition plan compared to the NSGA-Ⅱ algorithm, because the Pareto solution that meets customers’ needs accounts for 100% of the Pareto solution set and also considers the demands of the allied logistics service providers.

Lower Limb Muscle Co-Contraction and Coupling Synergy in Exoskeleton Assistance for Load Carriage Walking

LI Huaixian, CHENG Wenming, LIU Fang, ZHANG Mingkui, YANG Chunmei

2018, 53(6): 1286-1294. doi: 10.3969/j.issn.0258-2724.2018.06.026

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Abstract:
Human-robot interaction performance was evaluated, and better exoskeleton structures and human-robot adaptability control strategies were explored. The muscle activity, paired-muscle contraction index, and synergy coupling of the muscles of nine healthy male subjects carrying loads and walking with and without the exoskeleton prototype were investigated through evaluation of the conducted experiment. The results show that muscle activity significantly increased compared with normal load carrying, especially for the planter flexor muscle peronaeus longus. Some design defects were observed in the foot/ankle area of the current exoskeleton prototype, and the paired-muscle mean co-contraction index decreased. However, the co-contraction index range was greater than in normal load carriage. The module complexities were similar for both load carriage conditions, with total variances of 95% and 96%. Three modules could describe nearly 95% of the variance in electromyography data during normal load carriage. However, the same modules could only describe 83%–91% of the variance in muscle activity while walking with the exoskeleton. These results show that the muscle activities in healthy subjects will not be modulated by the central control strategy in the process of adaption to the assistance of the exoskeleton. The plot shape of the synergy weights and the muscle activation are significantly different from the normal gait. Hence, better human-robot interface designs in the ankle/foot area and human- robot interaction strategies referenced from the kinds of flexible but principle neuromuscular recruitment mechanisms, would improve the usability and the human-robot interaction performance of the exoskeleton.

Analysis of Residual-Stress Test Errors via Ultrasonic Method for Aluminium Alloy Used in High-Speed Trains

LI Minggao, SUN Hairong, GOU Guoqing, YU Jinpeng

2018, 53(6): 1295-1300. doi: 10.3969/j.issn.0258-2724.2018.06.027

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Abstract:
To study the influence of different errors incurred during ultrasonic residual-stress detection on test data concerning key components of high-speed trains, the relationship between the anisotropy of A5083 and 6005A materials, in terms of texture and ultrasonic propagation time, was investigated. The stress coefficient corresponding to the measured depth at different frequencies was also investigated. Results demonstrate a relatively small difference between stress coefficients （a deviation of approximately 4.26%） corresponding to the tensile and compressive stress states of sonic-wave propagation along directions parallel and perpendicular to the rolling direction of the A5083 material. Corresponding deviation in the values of tensile and compressive stress states of the 6005A material equals 13.12%. As such, both materials must be calibrated separately. The depth measured by the sonic probe at different frequencies is different, and the stress coefficient calibrated by the probe at different operating frequencies varies greatly from one region to another. Values of the stress coefficient demonstrate obvious changes under tensile and compressive stress states in the weld zone. The maximum rate-of-change observed measured 30.69%. Change rates corresponding to the heat-affected area and base-metal zone measured 14.03% and 9.66%, respectively.

Effect of Heat Treatment on Microstructures and Properties of Wire and Arc Additive-Manufactured Bainite Steel

FU Youheng, WANG Guilan, YIN Shuang, ZHANG Haiou, LONG Zuohong

2018, 53(6): 1301-1307. doi: 10.3969/j.issn.0258-2724.2018.06.028

[Abstract](507)

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Abstract:
It is difficult to actively control the thermal cycle in wire and arc additive manufacturing（WAAM）, resulting in uneven microstructures and poor mechanical properties. Therefore, an anisothermal quenching and tempering process for bainite steel deposition is presented herein. The microstructures and properties were analysed and optimised after a series of heat treatments. The results show that the annealed microstructures change from tempered sorbite to lower bainite and tempered martensite after posttreatment, and the anisotropy is evidently weakened. After isothermal quenching at 290 ℃/oil cooling followed by tempering at 280 ℃/air cooling, the WAAM bainite steel shows more homogeneous microstructures and better mechanical properties, with increases in the tensile strength, yield strength, elongation, impact toughness, and hardness, by 39%, 61%, 29%, 17%, and 20%, respectively.

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2018 Vol. 31, No. 6