西南交通大学学报

Energy Consumption Optimization Method for Novel Supply Mode in Tram Operation

LI Qi, HUANG Tao, SU Bo, HUANG Wenqiang, ZHAO Zihan, CHEN Weirong

2020, 55(6): 1133-1140. doi: 10.3969/j.issn.0258-2724.20190585

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Aiming at tram energy consumption of contactless power supply, a method is developed to reduce operating energy consumption and improve regenerative braking energy recovery when energy storage capacity is limited. The method can redistribute the three working conditions of traction, coasting and braking and the output of a train in the traction and braking conditions, provided that the running distance between the train stations is constant, the running time between stations is within the feasible range, and the supercapacitor is capable of absorbing braking power. Then it calculates a train target running curve that achieves energy saving and improves braking energy recovery. Finally, the method optimizes the actual running line of a tram. The simulation results show that the proposed method reduces the operating energy consumption by 4% on average during the redundant time. Meanwhile, the supercapacitor increases the energy feedback in brake feedback by 4% and can operate safely during the braking process of the tram.

Construction of Typical Driving Cycle for Tram

CHEN Weirong, LIU Yubei, DAI Chaohua, GUO Ai, AN Qi, SHI Fangli

2020, 55(6): 1141-1146, 1190. doi: 10.3969/j.issn.0258-2724.20190268

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In order to reflect the real driving characteristics and operating parameters of new-energy trams in rail transit, and provide a basis for the design and control of trams, a typical driving cycle was constructed. Firstly, according to the tram operation data and tram lines in the cities of Paris, Budapest and Melbourne, the clustering analysis was used to obtain the driving features with dimensional reduction; and then the typical driving cycle based on Markov chain principle was built. Finally, a comparative analysis was made between the constructed typical tram driving cycle and the existing driving conditions, and the constructed typical driving cycle was validated by simulation. The results show that the average deviation of driving characteristic parameters between the constructed driving cycle and driving database population is 2.63%, which meets the development accuracy requirement, i.e., the deviation should be less than 5%. In addition, the demand power error under the typical driving cycle and actual driving cycle was only 1.78%, which verifies the accuracy of typical driving cycle.

Analysis of Power Tracking Management Strategy for Fuel Cell Hybrid System

LIU Nan, YU Boxuan, GUO Ai, LI Ming, ZHANG Qiumin, CHEN Weirong, DAI Zhaohua

2020, 55(6): 1147-1154. doi: 10.3969/j.issn.0258-2724.20180733

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In order to improve the economical efficiency of the fuel cell hybrid system, the parameters and the adjustment method of state of charge (SOC) in the power following energy management strategy were analyzed, based on the fuel cell hydrogen consumption and the power fluctuation rate. The power fluctuation rate of the fuel cell was defined. Based on the fuel cell-supercapacitor hybrid system model established in the simulation software ADVISOR, the hydrogen consumption and the fluctuation rate were estimated under different SOC limits and charging power parameters. The two methods to adjust SOC , namely the Z-curve and the proportional integral (PI) adjustment , were designed. The hydrogen consumption and the fluctuation rate were compared in the different methods.The results show that the more the lower limit of SOC increases, the more the hydrogen consumption and the fluctuation rate are produced. The hydrogen consumption with the lower limit of SOC 0.5 is more 7.10% than one with 0.25, and its fluctuation rate increases by 3.85%. When the upper limit of SOC increases from 0.75 to 0.95, the fluctuation rate decreases by 3.51%. The change of charging power parameter in a certain range produces a lower hydrogen consumption and a lower fluctuation rate. Among SOC regulation modes, the hydrogen consumption of the PI regulation method are optimal with initial SOC value in the interval [0.28, 0.52], and so is Z-curve method in the interval [0.75, 0.90].

Reliability Evaluation Method for Metro Medium-Voltage Ring-Network Power Supply System

LIN Sheng, CUI Zhen, YANG Qianqian, FENG Ding, ZANG Tianlei

2020, 55(6): 1155-1162. doi: 10.3969/j.issn.0258-2724.20190812

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Metro medium-voltage ring-network power supply system has a complex structure and various devices, which plays a crucial role in the distribution and transmission of electric energy. The analysis of metro medium-voltage ring network supply system is of great significance. In the analysis of its network structure and operation mode, the idea of partitioning is adopted to deal with the medium-voltage ring-network power supply system in a regional and module manner. Thus, the complex system is simplified and the concept of the minimum basic unit is proposed. A universal model is established for system reliability assessment and sequential Monte Carlo method is used to calculate system reliability evaluation indexes. The case study shows that, if the wear of the system equipment is ignored, with the sampling number of 50 000, the steady-state availability of the power supply system for ametro medium-voltage ring network is 99.996%, which verifies the feasibility of the universal model.

Calculation of Urban Rail AC/DC Power Supply with Traction Substation in Multi-Operation Modes

LIU Wei, ZHANG Yangxin, ZHANG Jian, LI Kunpeng, LI Qunzhan

2020, 55(6): 1163-1170. doi: 10.3969/j.issn.0258-2724.20190854

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Traction substations operate in such modes as the rectification, rectifier turn-off, constant voltage operation of inverting-feedback devices, and maximum-power operation of inverting-feedback device. To achieve convergence in power flow calculation when the states of traction substations are uncertain, a calculation algorithm for urban rail AC/DC power supply is proposed while it considers the multi-operation states of traction substation. As for this algorithm, the inverting-feedback devices and onboard resistors on trains are modeled. According to the network voltage of the traction substation in the iterative process, the state of traction substation is determined by hysteretic comparison strategy, and the power flow is solved by AC/DC alternating iteration method. The simulation and field tests of a subway project show that the Pearson correlation coefficient between the simulated and measured load process falls between 0.76 and 0.92; and the errors between the simulation and measured energy-saving rate of the inverting-feedback devices are not more than 1.7%. In the case of high no-load voltage of substations in DC traction power supply system, when the starting voltage of the inverting feedback device is set above 1750 V, the energy consumed by the on-board braking resistor is significantly increased.

Security and Efficiency Enhanced Authentication Scheme Based on Self-Updated Hash Chain for Train-Ground Communication

ZHANG Wenfang, SUN Haifeng, WANG Yu, LIN Wei, WANG Xiaomin

2020, 55(6): 1171-1180, 1206. doi: 10.3969/j.issn.0258-2724.20190205

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Aiming at the special requirement of security and real-time performance in next generation high-speed railway wireless communication system, long term evolution-railway (LTE-R), a security and efficiency enhanced train-ground authentication scheme based on self-updated hash chain is proposed. In the scheme, the master key of home subscriber sever (HSS) is used for encrypting the anonymous variable temporary identity (TID) of the on-board unity (OBU) so as to protect the privacy of OBU and resist the desynchronization attack. In order to realize efficient mutual authentication between the train and the service network, hash chains are used to replace the authentication vectors, and the local updating of hash chains can avoid restarting the full-authentication protocol caused by exhaustion of authentication vectors. Moreover, by using the identity ticket issued by the mobility management entity (MME), seamless handover-authentication can be realized in coordination with base stations. Security and performance analysis shows that compared with the long term evolution (LTE) standard protocols under the same condition, the computation cost of the proposed full-authentication protocol, re-authentication protocol and handover-authentication protocol is reduced by 41.67%, 44.44%, and 45.45% respectively, and the traffic is reduced by 62.11%, 50.91%, and 84.91% respectively, which can meet the security and real-time requirements of LTE-R network.

Resilience Assessment of Urban Road Network Based on Day-to-Day Traffic Assignment

LÜ Biao, GAO Ziqiang, GUAN Xinyi, LIU Yiliu

2020, 55(6): 1181-1190. doi: 10.3969/j.issn.0258-2724.20191214

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In order to effectively evaluate road network performance under major disruptive events, on the basis of a day-to-day traffic assignment (DTA) model, an urban road network resilience assessment model is proposed. With explicit consideration on the dynamic characteristics of traffic flow under a major disruptive event, a DTA model that comprehensively cover the influencing factors including travelers’ cognitive update and behavioral inertia is constructed, and then a heuristic solution algorithm is designed. Based on the DTA model, a road network accessibility index is defined, and a resilience metric as well as an evaluation model are established, which can fully measure the system performance during the disruptive event life cycle. Finally a case study is performed on the Nguyen and Dupuis network. The results show that, after the disruptive event, the road network resilience fluctuates in the first 10 days; then as the traffic flow distribution tends to be stable, it increases monotonically from 0.323 on the 10th day to 0.794 on the 50th day, an increase by 145.77%. Compared to classical stochastic user equilibrium (SUE) model, there are significant differences in both road network accessibility and resilience indicators obtained from DTA model. The road network accessibility index under SUE model monotonically increases with time, while that index under DTA model fluctuates sharply in the first 15 days, after then increasing monotonically. It indicates that, in order to acquire accurate road network resilience metric, travel decision behaviors and corresponding traffic assignment model must be accurately assumed in the first place. All factors including travelers’ behavior inertia, the degradation degree and recovery rate of link capacity, and road network congestion degree have a significant impact on the distribution of traffic flow, which in turn affect road network accessibility index and ultimately result in obvious changes in road network resilience metric. As a result, relevant parameters should be reasonably calibrated under full investigation over practical applications.

GNSS/INS Based Risk Assessment in Train Localization

WU Boqian, CAI Baigen, LU Debiao, WANG Jian

2020, 55(6): 1191-1198. doi: 10.3969/j.issn.0258-2724.20190981

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Risk assessment of global navigation satellite system (GNSS) used in train localization services is essential to fulfilling safety requirements. In this work, GNSS and inertial navigation system (INS) are integrated to build train localization units. The fault detection and identification is realized by the analysis of sensor fusion data, and the horizontal protect level (HPL) is calculated. According to horizontal position error (HPE), horizontal alert limit (HAL) and time to alert (TTA), the states of a train localization unit can be identified. Then the hazardous events caused by risky states are analyzed, the probability of wrong-side failure and the hazard rate are calculated. Finally, the risk assessment method is tested with field data. It is shown that when the false alarm rate and miss detection rate are 1 × 10⁻⁷/h, and the HAL is 20 m, the hazard rate of the train localization unit are calculated as 9.14 × 10⁻⁷/h in open area and 1.52 × 10⁻⁴ /h in constrained environment, respectively. When the railway line requirements on the risk indexes become low, i.e., the false alarm rate, miss detection rate and HAL are all increased, the hazard rate will be reduced. As a result, the hazard rate will be 0 in constrained environment when the false alarm rate and miss detection rate are all 1 × 10⁻⁵/h, and HAL is 100 m. Therefore, it is necessary to cosider requirement difference for railway lines when implementing the risk assessment.

Automatic Volume Calculation System for Sand and Gravel Carried by Ship Based on LiDAR Point Cloud

ZHU Qing, WANG Dengxing, WANG Feng, XIE Xiao, HU Han, HUANG Shuang

2020, 55(6): 1199-1206. doi: 10.3969/j.issn.0258-2724.20181051

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The current volume calculation method of sand and gravel carried by ship mainly relies on manual weighing and waybill transfer, which has the problem of low precision and low efficiency. To deal with this, an automatic volume calculation system of sand and gravel carried by ship is developed on the basis of LiDAR (light detection and ranging) point cloud. It uses the cluster analysis and the octree-based point cloud reduction to realize automatic identification and extraction of the point cloud for the target ship in a complex environment. It adopts the coarse registration based on the improved SK-4PCS (semantic-keypoint-based 4-points congruent sets) and fine registration based on the point-to-plane ICP (iterative closest point) to realize the high-efficient registration of no-load and full-load point clouds from coarse to fine level. The experiment is conducted with the data from the gravel transport ships on the Ganjiang River in Nanchang, Jiangxi, showing that the automatic measurement and calculation time of sand and gravel volume for one ship is less than 2 min, the maximum relative error of multiple calculation results is less than 1.00%, and the maximum error between the volume calculation results and real values is less than 2.00%, which meet practical requirements.

Seismic Damage Evolution Simulation of Long-Span Deck Steel Truss Arch Bridge

LI Xiaozhen, LIU Ming, YANG Dehai, DAI Shengyong, XIAO Lin

2020, 55(6): 1207-1214, 1223. doi: 10.3969/j.issn.0258-2724.20180665

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To evaluate the damage state of a long-span steel arch bridge under multi-dimensional earthquake loadings, a deck steel truss arch bridge was studied. A bridge elastoplastic fiber element model was established by OpenSEES code. Two damage index, i.e., strain and two-parameter damage index were selected for damage evaluation. The damage assessment of both members and the whole bridge were obtained by incremental dynamic analysis (IDA). Moreover, the applicability of two damage index on the main members of the bridge (steel pipe, concrete-filled steel tube, and reinforced concrete member) was compared. The results show that the assessment result by the two-parameter damage index based on deformation and energy may lead to 1−2 damage assessment levels worse than by strain damage index. Less damage is caused when the identical earthquake loading is input in transverse direction than longitudinal direction. The full bridge is still in a slightly damaged state when the peak ground acceleration (PGA) is 1.5g. Among three types of members, the damage quantity of steel tube members is large but damage state is slight. The damage of concrete-filled steel tubular members (arch feet) comes early but damage state is slight. The damage state of reinforced concrete members (joint balance pier) is the most serious. Attention should be paid to the corresponding structural locations in seismic design.

Shaking Table Test and Numerical Simulation of Shield Tunnel Connecting Cross Passage

GENG Ping, YANG Qi, HE Yue, HE Chuan, GUO Xiangyu

2020, 55(6): 1215-1223. doi: 10.3969/j.issn.0258-2724.20180982

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The shield tunnel and cross passage forming a spatial cross structure, is a weak link in the seismic resistance. To study the influence of the rigid and flexible connection forms on the shield tunnels in seismic response, the material parameters and proportions of the similar models in the shaking table test were determined by geotechnical tests based on the similarity theory, then the experimental structure and numerical model were established. The 15.0 Hz predominant frequency obtained from the first test was used as the input earthquake frequency in the other test conditions and numerical calculation. The seismic response of the main tunnel and the connecting crossway was studied by combining the model test and numerical calculation. The results show that the acceleration response of the stratum and structure at the same depth is basically the same, and the amplification effect of stratum acceleration is more obvious when closer to the ground. The maximum strain response occurs at the vault and arch foot of the structure when rigid connection is used in the connecting transverse passage. Flexible connection can better reduce the strain response of the structure, and the larger the input peak acceleration is, the more obvious the reduction effect is. On the cross section of the main tunnel, the position near the connection of the connecting cross-passage is susceptible to stress mutation, which is more affected with rigid connection . Shaking table test and numerical results are basically the same, the influence range of the cross channel on the longitudinal direction of the main tunnel is about 3.0 times as wide as that of the cross channel when rigid connection is adopted, while the influence range is reduced to 1.5−2.0 times when flexible connection is adopted.

Influencing Factors Analysis of Seismic Responses of Water Immersed Tunnel

CUI Jie, LU Yaobo, QÜ Jianxin, LI Yadong

2020, 55(6): 1224-1230. doi: 10.3969/j.issn.0258-2724.20180875

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In order to study the seismic response of immersed tunnels with different joints and under overlying water, large scaled shaking table tests and immersed tunnels seismic response simulations were carried out. The main material of immersed tunnels model was granular concrete. The model scale ratio designed in the tests was 1∶ 30. Laminated shear boxes filled with sand were used in the tests to form the site. The viscous-spring artificial boundary and equivalent load method were adopted in simulation analysis. The results show that acceleration amplification factors of flexible joint immersed tunnels are smaller than rigid joint immersed tunnels in the same layer. The acceleration amplification factor is less than 1 when the soil layer appears liquefied. Under the earthquake, the maximum values of tunnel section shearing stress peak reduce by 20% and 33%, axial stress peak reduce by 16% and 30% and strain peak increase by 60% and 140% when tunnel joint stiffness(G) reduce to 0.10G and 0.01G. Overlying water site makes acceleration amplification factors smaller, because the overlying water makes the site damping increases.Under the vertical earthquake, overlying water increase from 10 m to 40 m, maximum values of tunnel section shearing stress peak, axial stress peak and strain peak increase by 3%−5%, 30%−40% and 12%−17%, respectively.

Effect of Key Block Position on Straight Assembling Segmental Lining Structure under High Water Pressure

LIANG Kun, FENG Kun, XIAO Shu, HE Chuan, ZHANG Xiaoyang, CHEN Songtao, SU Ang

2020, 55(6): 1231-1239. doi: 10.3969/j.issn.0258-2724.20190569

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In order to find out the influence of the key block position on the mechanical behavior of the segmental structure of a shield tunnel, based on the Sutong GIL （gas-insulated transmission） integrated pipe gallery tunnel project, two typical working conditions, i.e., the key block being located at the vault and the waist, are selected to carry out the prototype test of the straight assembling segmental lining structure under high water pressure, and the test results in the two conditions are analyzed from the deformation, stress, crack development and final failure state of the segmental structure. The results show that the influence of different position of key blocks on the segmental structure is generally manifested in the different weakening of the overall stiffness of the structure, and the stiffness-weakening area formed has a stronger ability to resist the deformation outside the tunnel than that inside the tunnel. Compared with the key block at the vault, when the key block is located at the arch waist, the overall rigidity of the structure is greater, the ellipticity of the segmental structure and the maximum single-point displacement are reduced by 39.8% and 38.2%, respectively. When the key block is located at the vault, the bending stiffness of the structure is weakened obviously, and the large longitudinal joint is easy to open; while when the top block is located at the arch waist, the maximum longitudinal joint opening of segment is reduced obviously, which is only 53.3% of the former, and the force of the connecting bolt is reduced by 54.4%. In addition, when the key block is located at the arch waist, the arc surface in the bottom of the segmental structure is more prone to cracks, the cracking load is relatively smaller, and the main reinforcement inside the structure enters the tension state earlier; when the key block is located at the vault, the longitudinal joint opening of the segmental structure is large, and the structural instability is caused by the compressive shear failure of the concrete, which starts from the longitudinal joint in the case of high tensile force.

In-situ Experimental Study on Bearing Characteristics of Deep-Buried Tunnel Anchorage in Fractured Rock Mass

GUO Xifeng, WANG Zhonghao, WU Xiangchao

2020, 55(6): 1240-1246. doi: 10.3969/j.issn.0258-2724.20191077

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In order to study the bearing characteristics of the deep-buried tunnel anchorage in the fractured rock mass, and in the engineering background of Luding Dadu river Bridge, according to the peak shear strength parameters of the contact surface between concrete and rock mass obtained by in-situ test, the safety factor of the anchor plug was obtained. The in-situ test results of the 1∶10 scale model anchor were introduced, and the ultimate load and strength characteristics of the model anchor were studied. Finally, the overall stability of the tunnel anchor was evaluated, and the construction proposal was put forward. The results show that the safety factor of the anchor plug is 3.48, which meets the stability requirements of the specification. The model anchor has a limit load of 7.80P （P is the design load）and the model anchor system yield load characteristic point of 5.25P.

Experimental Study on Discharge and Energy Dissipation of Baffle-Drop Shaft in Deep Tunnel Drainage System

YANG Qian, YANG Qinghua, ZHENG Lining, TIAN Qiang, LIU Yongquan, YAO Jintao, MU Yi, YAO Yuan

2020, 55(6): 1247-1256. doi: 10.3969/j.issn.0258-2724.20190324

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In order to study the transition characteristics with the high-speed air-water flow in the drop shaft of a deep tunnel drainage system, a hydraulic model test was conducted to observe the flow patterns in the process of drop shaft discharge, analyze the relationship between the maximum discharge and the baffle spacing, and calculate the energy dissipation rates of the drop shaft under different conditions. On this basis, the energy dissipation mechanism in the process of drop shaft discharge was revealed. Results show that there are three kinds of flow regimes in the discharge process of drop shaft, i.e., wall-impact confined flow, critical flow, and Free-drop flow. Hydraulic jump is the primary cause of energy dissipation of water on the baffle, and the collision of the water flow with the bottom-drop shaft fluid in the reverse direction and the resulted breakage achieve the ultimate purpose of energy dissipation. The maximum discharge of drop shaft is between 8.7 × 10⁻³ and 14.7 × 10⁻³ m³/s when the shaft diameter D = 0.4 m and the baffle spacing d ranges from 16.02 to 24.56 cm, and there is a linear relationship between the baffle spacing and the maximum discharge (Q_m). The formula of energy dissipation rate is deduced according to the law of conservation of energy, from which the optimal energy dissipation rate of drop shaft is achieved at d = 19.4 cm and inclination angle θ = 10°. The aperture diameter (Ф) of the cover-plate has a great influence on the internal pressure of the drop shaft. When Ф ≥ 4 cm, the internal pressure is nearly 0; the baffle with a certain inclination angle is conducive to accelerating the discharge process of the drop shaft. The impact forces on the upper, middle and lower baffles (denoted by F_u, F_m and F_d, respectively) present a relation of F_u > F_m > F_d; the maximum surface loads of the upper, middle and lower baffles are 42.8, 30.7 and 22.8 kN/m², respectively. The experimental results about the maximum discharge and optimal energy dissipation rate of baffle-drop shaft could provide a reference for the design and operation of the baffle-drop shaft of deep tunnel drainage systems.

Experimental Study on Creep Characteristics of Structural Soft Clay under Lateral Unloading Condition

JIA Mincai, ZHAO Shun, ZHANG Zhen

2020, 55(6): 1257-1263. doi: 10.3969/j.issn.0258-2724.20180718

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Triaxial undrained creep tests under lateral unloading condition were carried out on the soft clay obtained from Ruian, Wenzhou, China to study the influence of lateral unloading path and structural properties on time-strain curves, isochronous curves and other typical creep properties. A creep stabilization time model of soft clay under lateral unloading condition was built to analyze the relationship between strain rate and creep failure criterion of soil, and then applied to structural soft clay soils with different stress paths from different regions to verify its applicability. The results show that creep failure occurred as the ratio of unloading to initial consolidation stress reached 0.2–0.3, and that the deformation of the soft clay can be divided into four stages, i.e., instantaneous deformation, decaying creep, isokinetic creep and accelerated creep. When soil samples under different confining pressures are in the accelerated creep stage, there is a linear relationship between logarithm of strain rate and creep time; the critical line of accelerated creep can be used as a criterion for the unloading creep failure of structural soft clay. The creep stabilization time of structural soft clay is dictated by its structural properties. The axial strain of Wenzhou soft clay increased with an increase in the consolidation confining pressure when the lateral unloading creep failure occurred. Influenced by creep, the cohesion of structural soft clay under unloading condition declined more than 50%, while the internal friction angle remained basically unchanged, resulting in severe attenuation of the long-term strength of shallow structural soft clays and small strains of creep failure, which should be paid more attention to during construction and monitoring.

Gradation of Subgrade Soil and Its Salt-Resistance Effect in Salt Lake Area in Qinghai

ZHANG Wen, LUO Yanzhen, LIU Xin, LI Bin, WANG Longlin, YANG Xiaoxu

2020, 55(6): 1264-1271, 1296. doi: 10.3969/j.issn.0258-2724.20190056

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A subgrade project in Qinghai salt lake area, China was in a cold and dry geotechnical environment with strong concealed salt weathering. Taking the natural saline soil samples of the above subgrade construction project and soil samples of the built subgrade structure in Chaka Salt Lake area of Qinghai, comparative tests were conducted to study the effect of the subgrade structure protection against salt weathering in the saline soil area of Qinghai province. On the basis of soluble salt content measurements, particle analysis and capillary water rising experiment, the maximum height of capillary water rising in subgrade soil layer in Chaka saline soil area was calculated theoretically. The results indicate that the rising height of capillary water in the saline soil was higher than that in the general soil; the content of fine grains (0.250–0.075 mm) was conducive to the increase of water and salt migration, while the content of coarse grains (> 0.250 mm) would inhibit water and salt migration. Under the dual action of water and salt migration and vapor salt migration, secondary salinization occurred in the subgrade soil layer of Chaka saline soil area. It was suggested to set up the gravel salt-blocking layer in the subgrade project of the Chaka saline land area; the grading range of particles should be controlled between 2.0 and 5.0 mm, and the fraction of grains in this size range should be greater than 75%, while the thickness of the gravel salt-blocking layer should be between 300.0 and 1000.0 mm. Besides, the location of the blocking layer should be on the upper part of the embankment, higher than the height specified in the general subgrade code, which can improve the effect of preventing the movement of water-salt and enhancing the effect of vapor-salt leaching.

Temporal and Spatial Variation of Permeability Coefficient of Seasonal Frozen Soil in Western Sichuan

QIN Xiaotong, CUI Kai, MENG Fanyu

2020, 55(6): 1272-1279. doi: 10.3969/j.issn.0258-2724.20200426

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The moisture migration caused by freeze-thaw cycle is the main reason for the instability of seasonal frozen soil slope in western Sichuan Province. It is an important means to master the rule of water migration by studying the spatiotemporal variation characteristics of permeability coefficient of slope soil. In view of the spatiotemporal variation of permeability coefficient of seasonal frozen soil slope under the action of freeze-thaw cycle, permafrost permeability coefficient tests were conducted on a self-developed device using the coarse-grained soil sample from a slope in Xinduqiao area of western Sichuan Province. The test soil columns with different initial moisture contents, fine particle contents and dry densities were prepared with the osmotic solution of 30% ethylene glycol, and then placed into the low constant temperature box for more than 12 h freezing treatment. The permafrost permeability coefficient tests under different freeze-thaw cycles were then carried out and variations of the permafrost permeability coefficient was analyzed. On this basis, combined with the on-site monitoring data of water content of slope in freeze-thaw period, the spatiotemporal variations of permeability coefficient were analyzed. Experimental results show as follows: with the increase of initial water content and dry density, the open porosity and permeability coefficient of frozen soil decrease. The permeability coefficient of frozen soil decreases with an increase in the fine particle content. When the content of fine particle content is more than 20%, the permeability coefficient of frozen soil decreases slightly. The number of freeze-thaw cycles has an inhibitory effect on the permafrost permeability; however, when the number of cycles is more than 3, the effect of freeze-thaw on the permeability of frozen soil is not significant. Within 1 m frozen depth of seasonal frozen soil slope, the permeability coefficient decreases with the increase of depth; in addition, the permafrost permeability coefficient decreases from November to January, and increases from January to March.

Axial Bearing Capacity Analysis of H-Section Steel-Reinforced Recycled Aggregate Concrete Filled Circular Steel Tube Stub Columns

LIU Jian, ZHANG Pengcheng, JIANG Jin, TIAN Yong, LIU Changjiang, CHEN Yuan, ZHANG Shihao, CAO Zhanbin

2020, 55(6): 1280-1286. doi: 10.3969/j.issn.0258-2724.20190244

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In order to investigate the axial compressive properties of H-section steel-reinforced recycled aggregate concrete filled circular steel tube stub columns, the axial bearing capacity calculation formula of this kind of member was theoretically derived. Based on limit analysis and twin shear unified strength theory, bearing capacities of the recycled concrete in H-section steel confined zone and the recycled concrete in steel tube confined zone were calculated, respectively, according to the different restraint effect of H-section steel and steel tube on the recycled concrete in the core area. On this basis, a set of formulas for calculating the axial bearing capacity of H-section steel-reinforced recycled aggregate concrete filled circular steel tube stub columns was put forward, which took into consideration the influences of parameters such as the ratio of inner diameter to thickness of steel tubes, the hoop coefficient, the steel distribution index of H-section steel, and the replacement rate of recycled coarse aggregate on the axial bearing capacity of short columns, and can also be applied to calculate the axial bearing capacity of the recycled aggregate concrete filled circular steel tube stub columns without H-section steel reinforcement. The derived effective binding force of steel tubes is brought into the proposed formula to calculate their axial bearing capacity and compared with test values. Results show that the calculated results agree well with the test values, and the error between them is within 10%, which verifies the validity and accuracy of the proposed calculation formula.

Numerical Simulation of Interior Connections of Precast Concrete Frame with Post-Tensioned Tendons

LIAO Xiandong, HU Xiang, ZHANG Shiqian, LIU Yanan, XUE Weichen

2020, 55(6): 1287-1296. doi: 10.3969/j.issn.0258-2724.20180704

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In order to solve the problem that bond-slip of new and old concrete interfaces and treatment of shear reinforcement bars are challenges for finite element analysis of precast concrete frame joints, different methods in ABAQUS available for simulating the behavior of new and old concrete interfaces were deeply discussed. A new constitutive relation which combines bond-slip between new and old concrete interfaces with shear-slip model of shear reinforcement bar was introduced, and nonlinear finite element models (FEM) were carried out. The calculated results were agreed well with the experimental results of full-scale model test. And then an analysis of parameters was performed, which focused on influences of axial compression ratio, concrete strength, effective stress of prestressed tendon and bonded construction of prestressed tendons (full bond, partial bond and unbonded). The results show that bearing capacity increases by 11% with axial compression ratio increases from 0.2 to 0.4. However, the bearing capacity does not increase significantly when the axial pressure ratio increases from 0.4 to 0.6. Bearing capacity increases with the increasing of concrete strength and effective stress of prestressed tendons. Three types of bonding construction of the prestressed tendons have no obvious influence on the bearing capacity of the connections, but increasing the unbonded length of prestressed tendons may delay the connections yield.

Dynamic Response Analysis of Passive Flexible Protection System under Impact of Rockfalls

LI Huadong, ZUO Mingyu, LI Pu, ZHAO Jinheng

2020, 55(6): 1297-1305. doi: 10.3969/j.issn.0258-2724.20190514

[Abstract](710)

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Abstract:
Finite element program ANSYS/LS-DYNA was applied to study the deformation and energy of passive flexible protection system under rockfalls impact. Using the ANSYS/LS-DYNA explicit analysis, dynamic responses of the passive flexible protection system to impact loads of rockfalls in different motion modes were simulated. According to the time history curves, the displacements, impact forces and energy change of rockfalls in different motion modes were contrasted. Results show that as the initial impact kinetic energy of rockfalls increases, the time required for the protective net to reach the maximum displacement decreases generally, and the impact time is between 0.11 s and 0.14 s. The maximum impact load of rockfalls occur at around 0.04−0.07 s, and increases with an increase in the initial kinetic energy. In the process of rockfall impact, energy dissipation occurs in the passive flexible protective structure, and the energy of steel wire mesh under rolling rocks is greater than that under bouncing rocks. Besides, the maximum peak energy of steel posts under rocks in the rolling state is greater than its counterpart under rocks in the bouncing state; the energy of steel posts increases sharply at the moment the steel wire mesh is broken under the impact of rolling rocks.

Service Performance of High-Speed EMU Axles Made of 30NiCrMoV12 and EA4T

LI Qiuze, ZHANG Yingchun, CHEN Cheng, ZHANG Minnan, ZHANG Qingsong, DAI Guangze

2020, 55(6): 1306-1312, 1336. doi: 10.3969/j.issn.0258-2724.20191211

[Abstract](534)

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Abstract:
In order to gain insight into the mechanical behaviors of China’s high-speed EMU (electric multiple unit) axles made of 30NiCrMoV12 and EA4T, both the in-serving and over-served axles were examined in their chemical composition, conventional tensile strength, fatigue, impact toughness, fracture toughness, the threshold value and rate of fatigue crack growth and the metallographic structure. The final results are shown as follows: (1) The 30NiCrMoV12 axles had 10 times higher Ni element content, 2 times higher Mo and V elements content, and slightly higher C element content than the EA4T axle. The conventional tensile strength, yield strength and fatigue strength were increased by 34%, 54%, and 30%, respectively. (2) Compared with the EA4T axle, the conventional impact energy of the 30NiCrMoV12 axle at room temperature decreased by 12%; however, its fracture toughness increased by 34%. The EA4T axle had a 12% higher threshold value of fatigue crack growth than the 30NiCrMoV12 axle, and as for the two types of the old axis, this feature are quite similar. (3) When the stress intensity factor was less than 50 MPa•m^1/2, the crack growth rate was greater than the EA4T axle; However, when it was larger than 50 MPa•m^1/2, it was on the contrary. (4) The grain size of the full section microstructure of the 30NiCrMoV12 axle was fine bainite and tempered martensite with good hardenability and manufacturing performance. However, the section of the EA4T axle was composed of uniform bainite and tempered martensite within the depth of 30 mm from surface, and the ferrite gradually appeared with depth increasing. When the depth increased to 60 mm, the microstructure consisted of pearlite and ferrite, meanwhile the volume fraction of ferrite was significantly higher than that of pearlite.

Influence of Wheelset Flexibility on Dynamic Response of Linear Induction Motor Vehicles

YANG Yunfan, ZHOU Qing, GONG Lei, LU Wenjiao, WEN Zefeng

2020, 55(6): 1313-1319. doi: 10.3969/j.issn.0258-2724.20180866

[Abstract](481)

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Abstract:
Linear induction motor (LIM) metro vehicles adopt either inside or outside axle boxes. Aiming at two kinds of LIM metro vehicles, the LIM vehicle-track coupling dynamic model was established respectively, in which the wheel axle was modeled as Euler beam, and the effect of the wheelset flexible deformation on the primary suspension force, motor boom force and the wheel-rail spatial dynamic interaction was considered. The flexible response characteristic of the wheelset as well as the influence on the system dynamic response of LIM vehicles with inside and outside axle boxes was analysed comparatively under the excitation of the wheel/rail irregularity. The results show that, compared with the rigid wheelset model, the main vibration frequency of 77 Hz exists in the dynamic response of the flexible wheelset model for these two kinds of LIM vehicles, which corresponds to the first-order bending-mode frequency of the wheelset. With the consideration of the flexibility of wheelset, the LIM vehicles with inside axle boxes has larger wheel-rail vertical force and smaller air gap in comparison to those with outside axle boxes.

KANG Xi, CHEN Guangxiong, LÜ Jinzhou, ZHAO Xiaonan, WU Bowen, ZHU Qi

2020, 55(6): 1320-1327. doi: 10.3969/j.issn.0258-2724.20180898

[Abstract](596)

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Abstract:
In order to study rail corrugation on sharp metro curved tracks, based on the theory that the friction-induced vibration causes rail corrugation, the similarity between a full-scale and a small-scale wheelset-track models was studied. Firstly, to determine if the wheel-rail creep force was saturated, 1∶1 and 1∶5 dynamics models of vehicle-track system were established, respectively. Curve negotiations of these two models were simulated. Secondly, two finite element models were established whose wheel-rail contact parameters were from the dynamic simulation. Finally, using the complex eigenvalue analysis studied the stability of each wheelset-track system.The results show that when 1∶1 and 1∶5 vehicle models negotiate the sharp curved line respectively, creep forces on the inner and outer wheels of leading wheelsets are approximately saturated. Deviations of the vertical suspension force on two axle-ends of the wheelset and the wheel-rail contact angle are less than 3% and 5%, respectively. Frequency deviations of all similar unstable vibration modes are lower than 3%. The small-scale wheelset-track model has good similarity with full-scale model in the dynamic performance and the stability; therefore, the small-scale model can be used to study the formation mechanism of rail corrugation, both theoretically and experimentally.

Laser Visual Dynamic Measurement of Rail Wear on Complete Profile

LI Wentao, WANG Peijun, WANG Meng, CHEN Peng, LI Bailin

2020, 55(6): 1328-1336. doi: 10.3969/j.issn.0258-2724.20180821

[Abstract](912)

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Abstract:
Rail wear directly affects the safety of the railway transportation. To replace the current manual measurement methods and improve the measurement accuracy and efficiency, a laser rail full-profile visual measurement system was researched and designed to realize the dynamic measurement of rail wear. Firstly, the hardware structure of the laser measurement unit was designed by calculating laser vision measurement model. Then, the checkerboard plane calibration method was used to precisely calibrate the laser measurement unit to obtain the projection relationship between the laser plane and the camera plane, so the laser image of rail profile could be converted to the actual profile of rail. Based on the same characteristics of rail head profile on both sides at the same section which could be extracted by Euclidean clustering and distance segmentation, the full profile of rail section could be synthesized by ICP registration method. Finally, the waist contour and characteristic points of the unworn rail on both sides were taken as the datum, the full profile of the measured rail was compared with the standard rail profile, so rail wear was calculated from the difference between them. The laser measurement units were mounted on a self-developed rail measurement trolley for field measurement tests. The results show that the calibration accuracy of the measurement system can reach 4.922 × 10⁻³ mm and the measurement speed can reach 21.6 km/h. Compared with the rail wear gauge, the average deviation of vertical wear and horizontal wear of this system is 0.023 mm and 0.093 mm. The maximum deviation of the system for repeated measurement of the same object is less than 0.05 mm. The new system meets the demand of rail wear measurement, improves the measurement efficiency, and is convenient for the digital management of railway survey.

Finite Element Analysis of Rolling Strengthening Process for Wheel Tread of High-Speed Trains

ZHAO Jizhong, XU Xiang, DING Li, KAN Qianhua, KANG Guozheng

2020, 55(6): 1337-1347. doi: 10.3969/j.issn.0258-2724.20180803

[Abstract](640)

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To improve the wheel tread strength and service life of high-speed trains after reprofiling, the numerical simulation of rolling strengthening for the wheel tread was carried out, and the process parameters of rolling strengthening were optimized. Focusing on the wheel of the CRH3 high-speed train, a three-dimensional rolling contact finite element model was established which combines the roller, wheel, and rail. According to the influences of roller size, rolling pressure and rolling time on the distributions of residual stress and equivalent plastic strain fields of the wheel tread, the rolling strengthening mechanism were numerically investigated. The fatigue crack initiation life of the wheel tread after rolling strengthening in wheel-rail contact were estimated by the Manson-Coffin model modified by Borrow-Miller criterion, and the process parameters of rolling strengthening were optimized. The results show that, with the increase of rolling force, the fatigue crack initiation life of the wheel tread increases at first and then decreases, and it decreases with the increasing rolling time, which implies that the increasing rolling time reduces the fatigue crack initiation life of the wheel tread. Meanwhile, increasing the rolling time has little effect on the residual stress, and the increasing roller radius leads to a small increase of the fatigue crack initiation life. In summary, the optimal rolling strengthening parameters can be considered as the rolling times of 3 times, rolling force of 1 kN and roller radius of 6 mm, which can increase the fatigue crack initiation life of the wheel tread by about 58%.

Transient Impact Behavior Analysis of Rail Broken Gap on High-Speed Continuous Welded Rail

XU Jingmang, WANG Kai, GAO Yuan, MA Qiantao, DONG Zhiguo, LIU Yibin, WANG Ping

2020, 55(6): 1348-1354. doi: 10.3969/j.issn.0258-2724.20190312

[Abstract](671)

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Abstract:
The rail of seamless track may break and form a broken gap at the weld and its heat affected zone under temperature force. In order to study the influence of rail broken gap on train operation, the wheel-rail contact force characteristics and the high-frequency dynamic response of the material is analyzed. First, the ANSYS/LSDYNA three-dimensional wheel-rail transient rolling contact finite element model was established; then, according to the time-domain response of wheel-rail forces at different speeds, the appropriate calculation conditions are selected, and the safety issue in the case of the wheel crossing the broken gap is analyzed by calculating the wheel-rail contact force and the high-frequency dynamic response of the material; finally, when the wheel crosses the gap, the frequency-domain distribution of the wheel-rail force is obtained by wavelet transform. The results show that the peak value of the high-frequency impact force decreases at first and then increases as the length of the rail broken gap increases. The length of the broken gap at the turning point is inversely correlated to the train speed; when the wheel passes through the gap, the maximum shear stress of the rail exceeds the material failure limit, which may cause the brittle fracture of the rail material; there are two special frequency components in the time-frequency diagram of the wheel-rail force, which respectively correspond to the high-frequency impact load (about 1 500 Hz) and secondary impact load (about 450 Hz); the gap length has little effect on the frequency-domain distribution of the wheel-rail force.

Analysis of Rolling Contact between Wheel and Rail in Switch Area

LI Jincheng, DING Junjun, NIU Yuecheng, LI Fu, WU Pengpeng

2020, 55(6): 1355-1361. doi: 10.3969/j.issn.0258-2724.20190199

[Abstract](670)

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Abstract:
In order to study the wheel-rail matching relationship and applicability of the classical wheel-rail contact theory in turnout area, the finite element model of the wheel-rail contact in switch area was established, and several calculation programs of the normal force and tangential force on switch were compiled. By taking the typical section of the No. 18 high-speed switch rail area and the switch frog area as an example, the contact patch area and contact stress in the rolling contact theories of the Hertz, semi-Hertz, Kalker three-dimensional non-Hertz and the finite element model are compared in the normal direction. The creep forces calculated by the FASTSIM algorithm based on Hertz and semi-Hertz, the Polach model and CONTACT are compared under different working conditions. The calculation results show that as the stress-strain characteristics of the wheel-rail material is considered in the finite element model, the result is closer to the actual working conditions. The maximum difference between the contact patch areas of Hertz, semi-Hertz, Kalker non-Hertz and finite element method 50.42%, 17.83% and 24.78%. The maximum difference in contact stress is 60.28%, 25.25% and 32.37%. Under the different working conditions, the creep force of the four tangential force models shows the same trend with the varying creep rate. Under the same working condition, the maximum difference between the creep forces calculated by CONTACT, FASTSIM algorithm based on Hertz and half Hertz and the Polach model are 8.08%, 5.19%, and 9.70%. According to the calculation accuracy of the switch in the normal and tangential directions and computational efficiency, the semi-hertz contact theory combined with the FASTSIM algorithm has advantages in large-scale data processing.

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2020 Vol. 55, No. 6