西南交通大学学报

Energy Management Method for Hybrid Electric Tram Based on Dynamic Programming Algorithm

CHEN Weirong, HU Binbin, LI Qi, YAN Yu, MENG Xiang

2020, 55(5): 903-911. doi: 10.3969/j.issn.0258-2724.20180470

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Aiming at the errors accumulation of traditional dynamic programming algorithm in energy distribution of the fuel cell hybrid electric system, an energy management method for the fuel cell hybrid electric tram was proposed based on improved dynamic programming algorithm, which aims to further improve the durability and fuel economy of the fuel cell hybrid electric tram. The improved dynamic programming algorithm adjusted the state transition equation based on the traditional dynamic programming by discretizing the system state quantities, which avoided the errors accumulation caused by interpolation calculation. At the same time, the equivalent hydrogen consumption of the system, the constraint of the state of charge (SOC) and the durability problems brought from loading and unloading of fuel cells were considered as optimization objectives to constitute a weighted penalty function, which made the system could take into account durability while achieved better fuel economy. The proposed management method was compared with power following and traditional dynamic programming. The results show that the proposed method reduces the final state SOC by 13.3% and the fuel economy by 78% compared with the power-following method. Moreover, the proposed method improves the fuel economy by 3.5%, and both the SOC variation range and the load-carrying condition of the fuel cell have significantly improved compared with the traditional dynamic programming algorithm.

Hierarchical Energy Management for Electric-Hydrogen Island Direct Current Micro-grid

LI Qi, PU Yuchen, HAN Ying, CHEN Weirong

2020, 55(5): 912-919. doi: 10.3969/j.issn.0258-2724.20180457

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In order to realize the control and operation of the electric-hydrogen hybrid energy storage micro-grid, an all-weather energy management method for the kind of island direct current (DC) micro-grid was proposed. The energy management method based on meeting the power demand of the load and controlling the bus voltage, and the method aimed to converse the surplus power from the micro-grid to chemical energy and hydrogen energy and released the energy timely through fuel cells and batteries. By the control of the coordination of the management layer and the DC/DC converter of the power and loading equipment, the energy management was realized. The effectiveness of the energy management method was verified based on the Matlab/Simulink software platform. The results show that the fluctuation of bus voltage is less than 0.33% which is far below the operation requirement of 5.00%, and the differences between the initial and final value of state of charge and state of hydrogen charge is 4.0% and 0.2%, respectively, the storage system operates stably. The energy management method can ensure the stability of the energy storage system and keep all-weather running without additional energy.

Supercapacitor Thermal Behavior of Trams with Different Spatial Structures

DAI Chaohua, FU Xueting, DU Yun, GUO Ai, CHEN Weirong

2020, 55(5): 920-927. doi: 10.3969/j.issn.0258-2724.20190561

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In order to relieve supercapacitor module degradation in trams due to temperatures, the influence of spatial structures on the thermal behavior of the supercapacitor module was studied on the basis of the single unit structure of the supercapacitor. Firstly, the supercapacitor electrochemical-thermal coupling model was established, and the experimental platform was built to validate the model. Secondly, the surface area of natural convection heat transfer was defined. The temperature and volumetric characteristics of supercapacitor modules in the forms of 3 × 6 rectangle, 2 × 9 rectangle, 4 × 4 cube and hexagon, were evaluated by four indexes including the maximum temperature, maximum temperature difference, single temperature fluctuation and space utilization. This work shows that the length of the airflow path, surface area of natural convection heat transfer, and the number of the units with forced convection heat transfer will affect heat dissipation effect. The space structure with short and wide flow path has better cooling effect; the cubic structure is the best choice in terms of cooling effect and temperature uniformity; and the hexagonal structure is the best choice as regard to space utilization and cooling efficiency.

Electric Energy Measurement Method for Traction Loads

ZHANG Liyan, XIE Chen, LIANG Shiwen, LI Xin, BIAN Liding

2020, 55(5): 928-936. doi: 10.3969/j.issn.0258-2724.20190525

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In order to explore the influence of negative sequence from traction loads on electric energy measurement results, the negative-sequence power flow in traction power supply system is analyzed on the basis of the established traction power supply system and three-phase power system models. The shortcomings of the power factor metering method based on the traditional power theory are provided. In this regard, an unbalanced power factor metering scheme for traction load is proposed according to the equivalent apparent power and power factor definitions recommended by the IEEE Std 1459-2010 power theory, in which the limit of the effective power factor is 0.68. Theory analysis and measured data show that the direction of negative-sequence active power is opposite to that of the positive-sequence active power; as a negative-sequence source, traction loads add negative-sequence power to the system, which can eventually be absorbed by the system impedance and balanced load. Finally, algorithm effectiveness and conclusion correctness are analyzed and validated by simulation and statistical analysis on 56 groups of measured data in this paper. The simulation and statistical analysis on 56 groups of measured data are used to validate the algorithm and conclusions. Statistical results of measured data show that the equivalent apparent power and the definition of power factor can account for the effect of nonlinear unbalanced traction load on transmission efficiency, which is more reasonable and accurate.

Mutation Timed Automata with Input and Output-Based Method of Generating Test Suites for Chinese Train Control System Level 3

WEI Baiquan, LÜ Jidong, CHEN Kexing, TANG Tao, WANG Wei

2020, 55(5): 937-945, 962. doi: 10.3969/j.issn.0258-2724.20180078

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In order to design and select the proper set of test cases so that all the known faults can be covered, an automatic test suite generation method was proposed for the Chinese train control system level 3 (CTCS-3) based on timed automata with input and output (TAIO) and mutation analysis. Firstly, according to the characteristics of the fault modes of the system mode transition, kinds of mutation operators (change action, change target, change source, etc.) had been designed, and 15106 mutants were generated. Secondly, based on the timed input and output conformance relation (tioco) and the k-Bounded model checking technique, 10 843 test cases were generated. Finally, the conformance relation score (CRS), average conformance relation score (ACRS) and weighted conformance relation score (WCRS) had been introduced to analyze the coverage of faults domain. The results show that the test cases generated can effectively cover the fault modes of change action, change invariant and sink location, however, the negate guard and invert reset fault modes cannot be effectively covered, which may require additional information of observation for the fault detection.

Two-Stage Optimization Method of Train Energy-Efficient Operation Based on Dynamic Programming

GAO Hao, ZHANG Yadong, GUO Jin, LI Kehong

2020, 55(5): 946-954. doi: 10.3969/j.issn.0258-2724.20191208

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Focusing on the problem of train energy-efficient operation between multi-sections in urban rail transit, a two-stage optimization method was proposed by integrating the processes of energy-efficient driving optimization and timetable optimization. To obtain the optimum train driving strategy between multi-sections, each process was solved with global optimum solutions, respectively. First, to realize energy saving and time saving, a multi-objective energy-efficient driving model was constructed. Utilizing the multistage-based dynamic programming searching approach, a series of sub-stage models that contain multiple objects and constrains were constructed. The Pareto front of the optimum driving strategy was generated by inverse order method. Then, a timetable optimization model was constructed, in which the Pareto front of sections was applied, and the optimum running time allocation of multi-sections was searched by dynamic programming approach. A case study of Yizhuang urban rail line in Beijing was conducted to verify the effectiveness and efficiency of the two-stage optimization method. Compared with the flat-out running strategy, the optimization of two stages resulted in 53.87% and 54.69% energy saving improvement respectively; the calculation time of two process was 258.90 s and 0.08 s respectively.

Integrated Optimum Crew Planning in Fixed Shift System for Subways

JIN Hua, CHEN Shaokuan, LIU Shuang, LIU Gehui

2020, 55(5): 955-962. doi: 10.3969/j.issn.0258-2724.20190952

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In order to globally optimize crew members in commonly used fixed shift system, an integrated optimum scheduling that combines crew scheduling and rostering is proposed with the constraints of shift proportions and candidate shifts. Then, an improved column generation approach is developed for the proposed model in which the suitable shifts are generated according to the type of shifts in a pricing sub-problem. Meanwhile, acceleration techniques are used for solving the proposed model. Finally, the case studies with two metro lines connecting different home stations in Beijing is carried out, focusing on the optimization results under three shifts in four groups and five shifts in six groups and their algorithm efficiency. It is indicated that as for the fixed shift system, the proposed integrated optimum scheduling is able to reduce the number of drivers by 6.67%−14.29% in contrast to the separated optimization, and the computation time by 44.2%−51.4%.

LIRP Joint Collaborative Optimization under Stochastic Demand and Time Constraints

JIAO Yuling, ZHANG Linjing, XING Xiaocui

2020, 55(5): 963-970. doi: 10.3969/j.issn.0258-2724.20190463

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Aiming at improving the overall efficiency of the multi-node, multi-level, and multi-functional supply chain management, a secondary distribution network composed of a single supplier, multiple distribution centers, and multiple retail stores for a chain supermarket wasexplored to establish the multi-objective location-inventory-routing problem (LIRP) integrated planning model with the objectives of the total system cost and supply time. The linear weighting method was used to transform the model into the single-objective programming one. A two-stage heuristic algorithm combining genetic algorithm and mileage saving method was proposed to solve the model. In the first phase, the location-inventory problem was solved by the genetic algorithm, and in the second phase, vehicle routing problem was solved by the mileage saving method. A chain supermarket example was used for the LIRP integration optimization of the distribution network with different decision schemes and total cost weights. Compared the results from a reference, the optimized system scheme reduced the total mileage by 3 606.9 km, the total system cost by 6 526.2 yuan, and the cost of back orders by 124.6 yuan, being 19.7 yuan, which verifies the model and algorithm.

Multi-layer Coded Genetic Algorithm with Collaborative Construction of Two Hub-and-Spoke Networks

HU Jingjing, HUANG Youfang

2020, 55(5): 971-979. doi: 10.3969/j.issn.0258-2724.20190893

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In order to reduce the construction cost of logistics network and make full use of logistics resources, the collaborative construction for hub-and-spoke networks is proposed. We designed the simultaneous construction of two hub-and-spoke logistics networks, in which one hub-and-spoke network selects a group of collaboration hubs from another hub-and-spoke network for each hub, and both networks can use collaboration hubs. The goal is to minimize the sum of the construction costs and collaboration costs of the two hub-and-spoke networks. First, the mixed integer programming model is used to describe the problem. Then, according to the complexity of the problem, a multi-layer coded genetic algorithm is designed to solve the problem. Finally, the parameter sensitivity analysis is carried out with a case to analyze the influences of the parameters on costs, logistics network structure and cooperation hub, in which one chromosome represents two hub-and-spoke networks. The analysis results show that in the collaborative construction of two networks, the amount of traffic transferred from one network to another has a significant impact on the network structure and construction cost of the two networks. Collaborative construction can systematically optimize two hub-and-spoke networks, reduces costs and effectively integrate logistics resources.

Pricing and Quality Decisions of Follower Brands in Presence of Brand Loyalty

XU Xiaolei, ZHOU Jianheng

2020, 55(5): 980-987. doi: 10.3969/j.issn.0258-2724.20200012

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International famous fashion brands usually attract and cultivate many loyal customers with their high quality and unique cultural value. Thus, domestic follower brands have to be confronted with the effect of customer stickiness and strategic behavior. How to break through the existing barriers and attract strategic customers to buy cost-effective follower brands has become an important issue. On the basis of the assumption that fashion products have certain value depreciation, a strategic game model of competitive firms in two-period, is built to analyze how follower businesses decide their product quality and price. It is found that high brand loyalty is benefit to the leader demand, but may be adverse to its profit. Furthermore, given the value depreciation, if the strategic behavior is weak, the followers’ profit may increase with the brand loyalty. The reason is that the positive effect of follower price increasing with customer loyalty is greater than the negative effect of market demand decreasing with it, which promotes the increase of follower brand profit. In addition, a follower’s profit does not monotonically increase with its product similarity; thus it is essential for a follower to own a certain degree of brand originality in order to maximize profits.

Ship Dynamic Collision Avoidance Mechanism Based on Course Control System

HE Yixiong, ZHANG Xiaohan, HU Weixuan, LI Mengxia, GONG Shuai, JIN Yi, MOU Junmin

2020, 55(5): 988-993, 1027. doi: 10.3969/j.issn.0258-2724.20180493

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To explore the relationship between the variation of ship speed vector and the effect of collision avoidance, the static collision avoidance mechanism with the combination of ship domain and velocity obstacle methods was analyzed. Ship speed vector range for the avoidance of all objects without considering the motion process of ship course altering and the external environment was then determined. A course control system based on fuzzy adaptive proportional integral differential (PID) and ship motion equations was developed to reconstruct the nonlinear variation of ship speed vector during course altering process. The dynamic collision avoidance mechanism was then established based on the static collision avoidance mechanism and the course control system. The dynamic course altering range that satisfies the non-linear variation of ship speed was then obtained. The results indicate that in open waters where multiple objects are randomly located, the course altering ranges that satisfy the non-linear speed variation are [−90°, −72°], [31°, 47°], [62°, 79°], under the influence of ship dynamics, the course altering ranges that could cause collision are (−72°, 31°), (79°, 90°]. The obtained results are consistent with the influence of ship motion characteristics on collision avoidance with course altering and can provide a theoretical reference for the development of decision-support for ship collision avoidance, automatic collision avoidance and dynamic ship route planning.

Numerical Simulation of Direct-Current Sand Leakage Wind Tunnel Based on FLUENT

YAN Zhitao, LI Jie, ZHANG Pu, YOU Yi, GONG Bo

2020, 55(5): 994-1000, 1027. doi: 10.3969/j.issn.0258-2724.20180167

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Currently wind-sand tunnels are mainly used for research, protection and management of wind-sand landscape and wind-sand environment, and rarely adopted in structural wind engineering because the stable sections with adjustable wind speeds and wind-sand concentrations at a certain height are difficult to achieve. In order to study the distribution of wind-sand two-phase flow field in the direct-current sand leakage wind tunnel, in this work a wind tunnel model was built using the commercial software FLUENT, and then verified by simulating the existing sand leakage wind tunnel test. Based on the influence of wind speed, sand leakage volume fraction, sand leakage speed, and other parameters on wind-sand flow in the wind tunnel, a new type of sand leakage device for horizontal multi-port wind tunnel was further proposed. Simulation results of the wind-sand tunnel show that the distribution height of sand particles in the same location is higher at a larger wind speed. The quality of the sand particles entering the wind tunnel in unit time is mainly affected by volume fraction and velocity of the sand particles, and is directly proportional to the peak value of the sand particle concentration in the test location. Besides, a test section of about 1/2 wind tunnel height with uniform sand concentration has been realized in the wind-sand tunnel. The required test wind speed field and corresponding sand concentration can be achieved by adjusting the sand leakage volume fraction, sand leakage speed, and test position to complete the wind-sand quantitative tests for wind engineering well.

Mechanical Characteristics Analysis of Toppling Deformation Based on Rheological Tests for Cantilever Beam

ZHENG Da, SU Hang, PANG Bo

2020, 55(5): 1001-1008. doi: 10.3969/j.issn.0258-2724.20190478

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Curved toppling deformation is essentially the rock rheological deformation. In order to clarify its time-dependent characteristics and mechanical properties, the force analysis of anti-dip stratified slope is conducted, in which the force at a certain point of the rock layer is simplified as the gravity stress and horizontal stress. Then, the rheological tests of the bending cantilever beam are performed under this stress condition. The rheological model of the bending cantilever for rock strata is generalized as four stages: instantaneous deformation, attenuated creep, steady creep and accelerated creep. Based on the above tests and analysis, the constitutive equation for the rheological deformation of the bending cantilever beam is deduced. Through the calculation of the equation, assuming that the strain at the position of the ultimate toppling deformation of rock beam is zero lead to the ultimate depth of the toppling deformation. Given that as the beam breaks the strain acceleration is equal to the upper limit acceleration of the steady creep, the toppling fracture depth can be obtained.

Experimental Study on Seismic Performance of Carbon Fibre Reinforced Plastics-Retrofitted Earthquake-Damaged Non-ductile Reinforced Concrete Frames

CHEN Weihong, QIAO Zehui, SHOU Weirong

2020, 55(5): 1009-1016. doi: 10.3969/j.issn.0258-2724.20181068

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To investigate the seismic performance of earthquake-damaged non-ductile reinforced concrete (RC) frames retrofitted with carbon fiber reinforced polymer (CFRP), two pseudo-static tests were conducted on a 1/2 scale two-span and two-story specimen before and after its CFRP reinforcement. After the RC frame was loaded to its peak bearing capacity, specimens with seismic damaged parts strengthened with external CFRP textile were studied experimentally to obtain their failure modes and hysteretic curves. The seismic performance indexes of the CFRP-retrofitted frame, such as stiffness, strength, ductility and energy consumption, were analyzed and compared with the initial intact frame. The results show that the external CFRP reinforcement has no significant influence on the lateral strength and initial stiffness of the earthquake-damaged non-ductile RC frame, but the energy dissipation capacity of the retrofitted RC frame is obviously improved. The average displacement ductility factor of retrofitted RC frame is 2.81. When the maximum story drift ratio reaches 1/50, the retrofitted RC frame still has a large safety margin. The retrofitted earthquake-damage non-ductile RC frames can be used in seismic areas.

Axial Compressive Properties of Prefabricated Circular Steel Tube Confined Concrete Columns

CAO Bing, CHEN Junda, DU Yihan, HUANG Bo, HUANG Jun, XIA Junwu

2020, 55(5): 1017-1027. doi: 10.3969/j.issn.0258-2724.20180867

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A finite element analysis based on test results was carried out to study axial compressive performances of the prefabricated circular steel tube confined concrete columns connected with steel sleeve and straight thread sleeve. First, finite element models of cast-in-situ and prefabricated circular steel tube confined concrete columns were established. Then, axial compressive performances of the cast-in-situ and prefabricated columns were compared in terms of the bearing capacity–average longitudinal strain curves, steel tube stress, rebar stress, and concrete stress; the deformation pattern and mechanism of prefabricated columns were analyzed. Finally, a calculation method of axial compressive capacity of prefabricated columns was proposed. Results show that the cast-in-situ columns and the prefabricated columns both have good mechanical and ductility properties; the steel tube and steel sleeve have strong confinement effect on the core concrete and the axial compressive bearing capacity was increased by 1.94%−6.17%. Increasing the thickness of steel tube can effectively improve the axial compressive bearing capacity by 59.15% at most, while increasing the stirrup spacing has little effect on the axial compressive bearing capacity, merely a reduction of 2.91%. The longitudinal stress of the steel tube is larger in the area near the connection between the steel tube and steel sleeve, while the circumferential stress of the steel tube is larger in the area near the upper and lower circular sutures of steel tube and is also larger at the assembly of steel sleeve. The average ratio of calculated value (N_uc) to finite element value (N_uf) and the average ratio of N_uc to test value (N_ut) is 0.964 and 1.014, with variance of 0.003 5 and 0.002 9, respectively, where N_uc, N_uf and N_ut denote respectively the values from formula calculation, finite element calculation, and test of the prefabricated column axial compressive bearing capacity.

Static Pushover Analysis of Frame Structure Based on Force Analogy Method

HAO Runxia, WANG Mouting, JIA Shuo, LI Gang

2020, 55(5): 1028-1035. doi: 10.3969/j.issn.0258-2724.20180100

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In traditional pushover analysis, solving nonlinear deformation need to update and decompose global stiffness matrix in real time, which costs many computing resources. The static pushover analysis for nonlinear fiber beam element is conducted on the basis of the force analogy method (FAM). Firstly, the elastic displacement under the lateral load was calculated by the factorization of elastic stiffness matrix before the iteration of nonlinear deformation. Secondly, the computational cost of back iteration was decreased by utilizing the factorization result of elastic stiffness matrix and elastic displacement during iterations. Finally, the algorithm complexity theory was utilized to evaluate the efficiency of the proposed algorithm and a classical method. The computational results and algorithm time complexity of the two methods were compared through a numerical results of 2D eight-floor frame structure. Results show that with two methods the vertex displacement-base shear curve basically coincides as well as the story drift curve, and the maximum error of story drift is on the 3rd floor with 3.72%. Compared with the traditional method, the algorithm complexity of the proposed method is decreased about 80%, and its computing efficiency is increased at least five times.

Expansion-Constriction Force Characteristics of Continuously Rails on Bridge under Fracture Condition of CRTS Ⅱ Track Slab Welded

ZHANG Pengfei, GUI Hao, LEI Xiaoyan

2020, 55(5): 1036-1043. doi: 10.3969/j.issn.0258-2724.20180944

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In order to study the longitudinal stress and deformation characteristics and their influences on track and bridge structure under the fracture condition of CRTSⅡ track slab, a spatial coupling model based on the finite element method and bridge-slab-rail interaction mechanism was established. This model can analyze the influences of crack location, width and depth of track slabs, as well as the expansion-constriction stiffness of track slab and bed plate, on distribution rules of the expansion-constriction force of continuously welded rail (CWR) on bridge. Results show that, in order to calculate the expansion-constriction force of CWR on bridge under the fracture condition of CRTSⅡ track slab, a most unfavorable fracture location at track slab should be selected according to the different checking parts. Meanwhile, the crack width and depth of track slab are suggested to be 2 mm and 200 mm, respectively, and the expansion-constriction stiffness of track slab and bed plate should be reduced to 10%−50%, since in this way the calculation result is conservative without losing generality. Track slab fracture increases the fracture risk of cement asphalt mortar screed and bed plate; the longitudinal displacement of rail and the relative displacement between rail and track slab on the side of broken slab are changed dramatically at the crack.

Engineering Characteristics and Road Performance of Cement-Stabilized Expansive Soil for Heavy Haul Railways

SHANG Yonghui, XU Linrong, LIU Weizheng, CHEN Zhaofeng

2020, 55(5): 1044-1051. doi: 10.3969/j.issn.0258-2724.20180871

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In order to explore the engineering characteristics and road performance of cement-stabilized expansive soil filler when it used as the subgrade filler of heavy haul railways, the dynamic triaxial tests, micro-structure tests and in-situ dynamic tests of subgrade were combined to reveal the variation characteristics of static and dynamic indexes when 3%−5% cement was added into expansive soil. The 5% and 3% modified expansive soil was analyzed in terms of their working performances when used as filler of subgrade bottom and embankment of heavy haul railways, and the dynamic stability of the subgrade in service period was evaluated under dynamic train load. The results show that the mix of 3%−5% cement can increase the strength of expansive soil, significantly reduce the swelling and shrinkage, and increase the water stability by 3−4 times. Compared with remolded expansive soil, the critical dynamic stress of the improved expansive soil with 3%−5% cement is increased by 5−6 times. The compaction degree and strength index of the test subgrade meet the standard with moderate margin. The foundation settlement of the middle line for the test subgrade is in the stable state before rail laying. In-situ dynamic tests show that the dynamic stress of subgrade gradually decreases along with the depth under the action of dynamic train load. The maximum attenuation can reach 40% and 80% respectively in the range of the surface layer and the bottom layer of the subgrade. The influence depth of dynamic stress is 1.4−1.8 times the design thickness of the subgrade. The dynamic stress value of roadbed in the influence depth of dynamic stress is far less than the critical dynamic stress of the filler at the same position, demonstrating that the dynamic stability of the subgrade meets the requirements of safe service.

Influence of Freezing-Thawing Cycles on Mechanical Properties of Tailing Soil at Yunnan-Guizhou Plateau

LIU Youneng, HUANG Runqiu, LIU Enlong, LIAO Mengke

2020, 55(5): 1052-1059. doi: 10.3969/j.issn.0258-2724.20180520

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In order to study how the mechanical properties of tailing soil evolve during the freezing-thawing process in open environment, a series of triaxial consolidated undrained (CU) shear tests were carried out with different numbers of freezing-thawing cycles and confining pressures. In the tests, 0, 1, 5, 10 and 15 freezing-thawing cycles were set and the groups of confining pressures including 50, 100, 200 and 300 kPa were applied. Based on test results, the mechanical indexes, including the shear strength, the peak value of shear strength and elastic modulus are finally analyzed. The results indicate that the influence of freezing-thawing on mechanical properties of tailing soils is significant. As the number of freezing-thawing cycles increases, the stress-strain curves gradually transform from the strain-softening type into the work-hardening one, whereas the brittle failure pattern turns into plastic failure, and the negative growth of pore pressure during the shearing process becomes weak till disappears; the peak shear strength, cohesion, internal friction angle and elastic modulus gradually decrease; during the process, tailing soils are affected most by the first cycle of freezing-thawing, of which the effective cohesion and effective internal frictional angle is reduced by 30.55% and 6.33%, respectively; and the average reduction ratios of the peak shear strength and elastic modulus are 42.66% and 33.61%, respectively. The mechanical indexes of tailing soils tend to stabilize after 10 freezing-thawing cycles, and from 10 to 15 cycles of freezing-thawing, the effective cohesion and effective internal frictional angle are reduced by 2.94% and 0.37% respectively; and the average reduction values of the peak shear strength and elastic modulus are 2.53% and 4.03%, respectively. The mechanical indexes of 10 freezing-thawing cycles are proposed as the reference for engineering design.

Analysis of Ultimate Soil Resistance Beneath Cutting Curb Based on Cylindrical Cavity Expansion Theory

ZHOU Hexiang, MA Jianlin, HU Zhongbo, CHEN Wenlong, YANG Bai

2020, 55(5): 1060-1066. doi: 10.3969/j.issn.0258-2724.20181045

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To overcome the shortcomings of the conventional calculation method of the ultimate soil resistance beneath the cutting curb, a theoretical solution for the ultimate soil resistance beneath the cutting curb is proposed based on the theory of cylindrical cavity expansion considering dilation effects. First, characteristics of the unilateral failure of cutting curb foundation are considered and two cutting curbs are symmetrically spliced into an integral foundation for calculation. Then, the ultimate soil resistance beneath the cutting curb is obtained by using the theory of cylindrical cavity expansion and analyzing the vertical force balance of the soil at the bottom of the cutting curb. Finally, centrifugal model test and field monitoring are used to verify the calculation method. Results show that compared with the results of centrifugal model test, the error of the ultimate soil resistance beneath the cutting curb calculated by this method is 6.6% when the sinking depth of caisson is 36 m. Compared with the results of field monitoring, the error of the ultimate soil resistance beneath the cutting curb calculated by this method is 1.36%, 19.5%, and 9.70% when the sinking depth of caisson is 5 m, 10 m, and 15 m, respectively. The calculated values agree well with the centrifuge model test values and field measured values. This study can provide a new idea for calculating the ultimate soil resistance beneath the cutting curb.

Vibration and Noise Measurement of Railway Station Hall Induced by High-Speed Trains

LI Xiaozhen, GAO Wei, LEI Kangning, HU Xuehui, LIANG Lin

2020, 55(5): 1067-1075. doi: 10.3969/j.issn.0258-2724.20190065

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In order to study vibration and noise problems of the integrated transportation hub under train load excitations, a field experiment was carried out taking the Shapingba station of Chengdu–Chongqing high-speed railway as the engineering background. The vibration accelerations were measured in the station waiting hall, platform and track slab, while the radiated sound pressures were measured in the waiting hall, platform and track area. Then, time-domain analysis and one-third octave analysis were applied to the measured signals, and the vibration transmission law and noise characteristics of the station induced by running trains were studied. According to the test analysis results, under the train running load the dominant vibration frequency band of the station and platform is 10.0−80.0 Hz. The vibration decreases with the increase of distance from the vibration source, and the maximum attenuation of the total vibration acceleration level from the platform to the waiting hall is13.5 dB. The maximum vibration acceleration level of track plate appears at 400.0 Hz, which is about 101.0 dB. The dominant frequency band of the sound pressure level in the waiting hall is 20.0−2 500.0 Hz, and the overall sound pressure level of the train entering station is about 0.5−1.3 dB(A) higher than that of the train leaving. The dominant frequency band of the station noise is 125.0−1 000.0 Hz, and the overall sound pressure level of the station during the outbound period is 87.3 dB(A), which is 1.3 dB(A) higher than that of the inbound period. The dominant frequency band of wheel-rail noise is 200.0−2 500.0 Hz, and the overall sound pressure level of the train entering station is 91.1 dB(A), which is higher than that of the train running outward the station by 3.1 dB(A).

Force Transfer and Deformation Mechanism of Single Ring Structure of Prefabricated Subway Station

DING Peng, TAO Lianjin, YANG Xiuren, ZHAO Ji, SHI Cheng, AN Shao

2020, 55(5): 1076-1084, 1110. doi: 10.3969/j.issn.0258-2724.20180719

[Abstract](884)

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In order to study the mechanical and deformation properties of the new prefabricated subway station, took the first prefabricated subway station in Changchun as the background, based on the large-scale general finite element software ABAQUS, the force transfer and deformation mechanism of the single-ring structure of the prefabricated subway station after assembling into a ring were studied.Four numerical models of different structure types and steel bars bracing combination were established. The mechanical, deformation and joint contact surfaces performances of the structure under the action of self-weight were compared and analyzed. The force transfer and deformation mechanism of the type of prefabricated subway station single ring structure were revealed. The results show that the supporting function of steel bars could not be ignored. After added horizontal steel bars to the outside of arch foot, the maximum Mises stress of the structure was reduced by about 40%, the maximum principal stress was reduced by about 80%, the maximum horizontal displacement was reduced by about 90%, and the deflection of the vault was reduced by about 80%, the shear force and bending moment of the structure decreased obviously. The contact state of the joints changed obviously, and the extrusion area ratio of the other joints increased significantly except the D-E joint of the vault, the assembled structure basically met the design requirements of stable and reliable force transmission, safe and controllable deformation, and the overall self-stabilization ability was significantly improved. The cooperative work of steel bars and assembled structure optimized the transmission path of single-ring structure, limited the horizontal and vertical deformation of the structure effectively, the mechanical and deformation performance of this type of fabricated structure was better than the corresponding index of the cast-in-place structure without the steel bar.

Propagation Effect of Passive Flexible Protection System on Rockfall Impact

QI Xin, YU Zhixiang, ZHANG Lijun, XU Hu, ZHAO Lei

2020, 55(5): 1085-1093. doi: 10.3969/j.issn.0258-2724.20180442

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Abstract:
The propagation effect of passive flexible protective system under rockfall impact has an important influence on the energy consumption efficiency of the system, a full-scaled impact test, in which the test model had 3 spans in length, was conducted under a kinetic energy of 1 500 kJ. Based on LS-DYNA, the nonlinear numerical simulation on the whole process of the collision and interception was carried out. The comparative analysis on the system deformation, the displacement of characteristic points and tension in the cables between experimental and numerical results was studied. In particular, the propagation effect of the impact load along the longitudinal direction was investigated. Then the numerical models with 4, 5, 6, and 7 spans were calculated respectively to explore the influence of the number of spans on the ultimate system deformation. The attenuation percentage was introduced to discuss the reduction in the internal forces of the cables and wire-ring net, as well as the impact force according to the increase of span number. An energy dissipation ratio was defined, and the ratios distribute among each component and within the three stages as the span number change were analyzed. The results show that the internal force of the support cable is higher than that of the lateral span significantly. The peak internal force of the wire-ring net appears in the impact area, and the internal forces of the net on both lateral sides are very small, so that it presents a Gauss attenuation distribution. With increase of the span number, the maximum elongation of the system changes little, but the time history values have evident differences. The internal force and the impact force decrease obviously, in the 7-span model, the lower support cable tension, the peak internal force of the wire-ring net, and the impact force reduced by 50%, 40%, and 14%, respectively. With the increase of propagation distance of the impact load due to the bigger length of system, the energy dissipation of the wire ring net, the brake rings and the steel column is reduced, and the energy consumption of cables and other components is increased, the energy dissipation ratio increases within the first and second mechanical stages, and decreases within the third stage.

Track Mechanical Analysis under Strong Cross Wind Based on Fluid-Solid Coupling

ZHANG Moyan, XIAO Hong

2020, 55(5): 1094-1102. doi: 10.3969/j.issn.0258-2724.20180649

[Abstract](595)

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Abstract:
In order to explore the mechanical characteristics of track structure under strong cross wind, the co-simulation of CFD and FEM is used to analyze the force and deformation of track structure. Firstly, SOLIDWORKS is used to establish a model based on the CRH380A high-speed train. Then, the aerodynamic characteristics of the train are calculated by FLUENT and the train-track coupling model is established by finite element software ABAQUS. The aerodynamic force on the surface of the train is completely retained in the model, which has solved the problem of aerodynamic force transfer in the fluid-solid coupling. Finally, based on the established coupling model, the mechanical characteristics of the track structure under strong cross wind are analyzed. The results show that when the train running speed is up to 350 km/h and the wind speed changes from 0 to 15 m/s, the lateral displacement on the leeward side of the rail increases from 0.177 mm to 2.100 mm, which increases by 11.86 times. This indicates that the mechanics of the rail leeward side should be focused. When the wind speed exceeds 15 m/s and the train operation speed is 250 km/h, the rail lateral displacement is beyond the allowable maximum of 2.000 mm, showing that long-term cross wind will lead to track geometry change. However, the rate of wheel load reduction and the coefficient of derailment is not up to the limit of 0.65 and 0.800, respectively. Therefore, it is necessary to consider not only the safety index of train operation, but also the change in the mechanical characteristics of track structure.

Dynamic Planning Method for Indoor-Fire Escape Path Based on Navigation Grid

ZHU Jun, SHE Ping, LI Weilian, CAO Yungang, QI Hua, WANG Bo, WANG Yu

2020, 55(5): 1103-1110. doi: 10.3969/j.issn.0258-2724.20180912

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Abstract:
Existing escape path planning methods for indoor fire in virtual reality (VR) have some deficiencies such as static planning and low efficiency. To solve the these problems, the dynamic planning of indoor-fire escape path was explored with the use of the navigation grid in VR scene. First, a photorealistic visualization method of indoor fire was proposed and a VR scene of indoor fire was constructed. Second, a construction algorithm of initial navigation was created and its dynamic generation algorithm was designed. Then the dynamic planning method for indoor-fire escape path was established. Finally, a prototype system was developed and the exhibition hall in an industrial park was selected for experimental analysis. The experimental results show that the static geographic scene and dynamic fire scene can be combined to construct an indoor-fire VR scene, and the proposed method can dynamically plan escape paths of indoor fire. The navigation grid can be updated within 10 m, and the average time of each escape path planning is about 50 ms.

Smoke Recognition Algorithm Based on Lightweight Convolutional Neural Network

YUAN Fei, ZHAO Xuyan, WANG Yige, ZHAO Zhisheng

2020, 55(5): 1111-1116, 1132. doi: 10.3969/j.issn.0258-2724.20190777

[Abstract](639)

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Abstract:
As smoke images are ambiguous, and the background is complex and variable, it is difficult to capture the effective features, resulting in high false positive rates and false negative rates. In addition, the deep convolutional neural network has a complicated structure and many parameters, and it is difficult to control the calculation time within one millisecond, which becomes a major problem for real-time fire warning. In order to deal with these obstacles, a lightweight convolutional neural network SInception (sequeeze-and-excitation inception) is proposed on the basis of four Inception structures, which significantly reduces the number of network parameters and calculation amount. It adds SE Block (sequeeze-and-excitation block) for smoke so that features are redistributed to make them more representative of smoke images. In order to avoid over-fitting due to insufficient training samples, for the data enhancement techniques on the original dataset and generative adversarial network are used to generate more training samples. Subsequently a strategy of integrating the priori features of dark channels is used in experiments. Finally, the network raises the accuracy rate to 99.65%, while for the dataset GAN-Aug-YUAN it reduces the false alarm rate to 0, and the calculation time is only 0.26 ms.

Effectiveness of Sound Propagation of Hydraulic Noise Suppressor with Expansion Chamber

YANG Fan, DENG Bin

2020, 55(5): 1117-1123. doi: 10.3969/j.issn.0258-2724.20180139

[Abstract](653)

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Abstract:
In order to study the influence of structural parameters of non-coaxial expansion chambers on the accuracy of the one-dimensional (1D) analytical method within cut-off frequency, the validity of the method for two types of inlet/outlet expansion chamber is analyzed on the basis of the higher-order evanescent modes at the area discontinuities. Firstly, the calculation results of the 1D analytic method for the double-tuned extended tube chamber (DTETC) agree well with the experimental ones in the range of cut-off frequency, which proves that the method is feasible for hydraulic noise suppressors. Secondly, two types of inlet/outlet offset expansion chamber structures (configurations 1 and 2), which are widely used in gas silencing system are introduced into hydraulic system to make the corresponding pressure dampers, and their theoretical values are obtained by 1D analytical approach and three-dimensional (3D) finite element method (FEM) respectively. Finally, the effect of structural parameters such as insertion depth, eccentricity and deflection angle on the effectiveness of 1D method is explored in the case of non-planar wave effect in the expansion chamber cavity. The results show that when the eccentricity of configurations 1 and 2 is 40 mm and the deflection angle is 180°, the insertion depth of the inlet and outlet tube has a great influence on the transmission loss (TL) in the high-frequency region of 5000 Hz (cut-off frequency is 5469 Hz); When the insertion depth of configurations 1 and 2 is set, the influence of eccentricity and deflection angle on the accuracy of the 1D method in the range of 0−4000 Hz can be negligible, but it should not be ignored in the range of 4000−5000 Hz.

Assembly Accuracy Analysis of Small Deformation of Flexible Body based on Differential Transformation

ZHAI Xiaochen, DU Qungui, WEN Qi

2020, 55(5): 1124-1132. doi: 10.3969/j.issn.0258-2724.20180480

[Abstract](576)

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Abstract:
Rigid body assumptions were usually used as the premise for assembly accuracy analysis during the product design stage, and the effects of load factors such as external loads and temperature changes were often ignored. In the case of manufacturing errors and assembly errors, the deformation of the part caused by the load factor would further affect the assembly accuracy. Therefore, an assembly accuracy analysis model that considered manufacturing , assembly errors, and part deformations simultaneously was proposed. Firstly, the model made the deformed Tolerance Features discretized along the dimensional chain, and established and consolidated the node coordinate system at each node. Then, the node's deformation information was extracted and differential transformation on each node coordinate system on the target feature was performed to achieve the error synthesis with deformation. Finally, a linearized comprehensive error analysis model was established. The results show that the model overcomes the limitations of the traditional error analysis model based on the assumption of rigid bodies, obtains the effect of the local deformation of parts on assembly accuracy, and also greatly reduce the difficulties and workload of geometric modeling and mechanical analysis.

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2020 Vol. 55, No. 5