2020 Vol. 20, No. 4

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Research status and prospect of unconventional arterial intersection design
AN Shi, SONG Lang, WANG Jian, WANG Ya-qing, HU Xiao-wei
Abstract: To promote the innovative application of unconventional arterial intersection design(UAID) in China, the U-turn, diverging diamond interchange, contraflow left-turn lane, tandem intersection, continuous flow intersection and parallel flow intersection were selected, the geometric layouts, signal phase sequence schemes and control strategies of various types of UAIDs were systematically sorted out. The research results of UAIDs in the recent decade were reviewed from the perspectives of theoretical research and traffic safety benefit. The application feasibilities of various types of UAIDs in China were discussed. Analysis result indicates that there are no difficulties in modelling and solving the signal timing of UAIDs, and most of the literatures adopt accurate algorithms. The benefit evaluation results of UAIDs are different according to the research objects and problems, but on the whole, the U-turn should not be set at the intersection with a high left turn proportion, the diverging diamond interchange is suitable for the freeway and expressway, the contraflow left-turn lane performs better at the intersection with a higher left turn proportion, the tandem intersection has the optimal benefit in the oversaturated state, and the continuous flow intersection and parallel flow intersection have better benefits under the symmetrical demand. In the aspect of traffic safety, setting up the U-turn and diverging diamond interchange can reduce the possibility of accident, but there is no unified conclusion for other types of UAIDs due to the lack of data or no data. Due to the difference between the operation rule of UAID and the driver's cognition, drivers will be confused in the early stage of opening up. It is effective to adopt measures such as the driver training, front vehicle prompt and traffic police on-site guidance. The combination of automatic driving technology and UAID is more hopeful to accelerate the application and promotion of UAID. On the whole, the U-turn, contraflow left-turn lane and tandem intersection have good application prospects in China, the applicability of diverging diamond interchange in China needs to be further discussed in combination with the domestic traffic situation. Due to the complex operation rules of continuous flow intersection and parallel flow intersection, it is necessary to carry on pilot operation first and then gradually popularize.More>
2020, 20(4): 1-20. doi: 10.19818/j.cnki.1671-1637.2020.04.001
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Research progress of anti-friction and anti-wear of piston-cylinder liner system in internal combustion engine
LYU Yan-jun, KANG Jian-xiong, ZHANG Yong-fang, LUO Hong-bo
Abstract: The research findings of friction and wear of piston-cylinder liner system in internal combustion engine were summarized, the developments of research methods and technologies of the system's anti-friction and anti-wear were reviewed from the aspects of lubricating oil improvement, surface modification and dynamics characteristics. The influences of lubrication model, lubrication additive, surface texturing, cylinder liner honing, surface coating and dynamics characteristic on the system's anti-friction and anti-wear were discussed, and the mechanism of friction and wear of the system was studied. Research result indicates that the lubrication characteristic of the piston-cylinder liner system is nonlinear. Lubrication status and additive have a great influence on the system's anti-friction and anti-wear, and the uncertainty of the system's lubrication status leads to the coexistence of multiple lubrication models. It is necessary to establish the comprehensive lubrication model of the system and discuss the optimal dosage and mechanism of anti-wear of lubricant additive in depth. Surface modification technologies(surface texturing, honing and coating) can greatly reduce the friction and wear of the system surface. The comprehensive development of surface modification technologies is relatively slow because of the effect of texture position distribution, processing parameters, processing technology, surface morphology and coating materials on the contact surface, so the anti-wear mechanism and parameter optimization methods of surface modification need to be further studied. Because the piston-cylinder liner system operates under harsh conditions and the components of the system interact and are coupled with each other, it's relatively difficult to deeply discuss the relationship between dynamics characteristics and evolution laws of friction and wear, the relationship should be fully considered under service condition. The improvement of the internal combustion engine performance will force the piston-cylinder liner system to have higher anti-wear and anti-friction performance in future. In order to achieve the goal of economy, energy conservation and emission reduction of the system, the high-efficiency anti-friction technologies need to be further developed.More>
2020, 20(4): 21-34. doi: 10.19818/j.cnki.1671-1637.2020.04.002
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Overview of traffic management of urban air mobility (UAM) with eVTOL aircraft
LI Cheng-long, QU Wen-qiu, LI Yan-dong, HUANG Long-yang, WEI Peng
Abstract: The emergence and development of urban air mobility(UAM) were reviewed, the basic concept of UAM traffic management was defined, and the social and technical factors promoting the UAM industry were analyzed. A nationwide framework of UAM traffic management for the near future was proposed. The UAM traffic management issues based on the electric vertical take-off and landing(eVTOL) aircraft were divided into three aspects for discussion(airspace planning, ground infrastructure, traffic rules and operation control). The representative views put forward by related literatures of UAM traffic management in the past few years were sorted out. The key issues that UAM needs to solve in the near future were summarized, and the development trend of UAM traffic management in the future was prospected. Research result shows that in terms of airspace planning, the UAM needs more refined planning and management of existing low-altitude uncontrolled airspace. The structured airspace demarcation method should be applied in the initial stage of UAM traffic management. The contradiction between the operational safety and airspace capacity can be better balanced by the flight layer airspace structure. In terms of ground infrastructure, the UAM traffic demand predicted by the urban OD data can be used for the location selection of vertiports. Also, the vertiport site management will directly affect the structure of the air route network and the layout of communication, navigation, and surveillance(CNS) stations. In terms of traffic rules and operation control, more complex UAVs and manned aircraft integration operation scenarios will be directly faced by the UAM. The UAM traffic rules need to be innovated and compatible with the existing transportation aviation traffic rules. High-band width communication technology will promote the transformation of the UAM operation control to the direction of air-ground coordinated decision-making and self-pilot. How to deal with the relationship between human and air traffic control system is very important to the future air traffic management. In general, UAM traffic management will likely intersect and gradually integrate with the existing UAS traffic management system. Facing this new mode of transportation, our country will be more likely to adopt the traffic management development route of centralized management, pilot operation, and orderly deregulation.More>
2020, 20(4): 35-54. doi: 10.19818/j.cnki.1671-1637.2020.04.003
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Research review of shipping management
BAO Tian-tian, LIAN Feng, YANG Zhong-zhen
Abstract: In order to systematically analyze and summarize the research status and development trend of shipping management, the co-word cluster analysis of shipping management based on the 628 literatures from WOS Database and CNKI Database was carried out by knowledge map analysis software VOSviewer, and three research hotspots were obtained, including shipping market analysis, shipping operation management and green shipping. According to above three hotspots, the researching areas, objectives and methods of shipping management were summarized, and the main directions of future research were put forward. Research result shows that the time-series model is mainly adopted to analyze shipping market, and the relationship between the supply and demand of freight market and shipping market is studied mainly based on the freight rate. The research of shipping operation management mostly focuses on setting up optimal mathematical model with the objectives of minimizing cost or maximizing profit, and using the heuristic algorithms to deal with the problems at the strategic, tactical and operational decision-making levels.The current research of green shipping mainly solves the practical emission reduction problem, and compares and analyzes the cost-effectivenesses and emission reduction effects of technical measures, operational measures and market-based measures. The future main research directions of shipping management are as follows: the multi-objective and multi-stage mathematical optimization model should be established to meet the various goals of shipping management in order to achieve the collaborative optimization of shipping managements with different scopes and levels; the research of shipping management should be extended from the perspective of shipping supply, and it is necessary to integrally consider the complex relationships among inland transportation, maritime transportation and stakeholders; the issues of shipping management should be investigated under uncertain conditions; the market analysis methods and model solving algorithms with higher accuracy and efficiency should be designed based on the artificial intelligent algorithms and shipping big data; and the shipping management in the new format of intelligent shipping should be researched.More>
2020, 20(4): 55-69. doi: 10.19818/j.cnki.1671-1637.2020.04.004
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Reliability analysis of embedded track continuous welded rail on simply supported beam bridge
FENG Qing-song, SUN Kui, LEI Xiao-yan, CHEN Hua-peng
Abstract: To analyze the influences of key factors on the mechanical characteristics of embedded track continuous welded rail on bridges, and evaluate it based on the reliability theory, the finite element method was used to establish the calculation model of embedded track continuous welded rail on the simply supported beam bridge. The longitudinal resistance of polymer material and the temperature difference of beam body were selected as the random variables, and the distribution types and distribution parameters of random variables were determined according to the actual working conditions. The response surface test was designed by the central composite test design method. The function relationship between the random variable and the response was fitted by the least square method. Thus, the quadratic polynomial response surface model of track-bridge relative displacement with respect to the longitudinal resistance of polymer material and the temperature difference of beam body was established. The correctness of the established model was verified by the variance analysis, and the parameter sensitivities of random variables were carried out through the sensitivity analysis method. The limit state equation of long-term service performance of embedded track continuous welded rail on bridges was constructed. The reliability of embedded track continuous welded rail on the simply supported beam bridge was comprehensively evaluated by using the Monte Carlo method and the response surface model. Analysis result shows that the sensitivity coefficients of temperature difference of beam body and longitudinal resistance of polymer material to the track-bridge relative displacement are 0.99 and-0.08, respectively. Therefore, the influence of temperature difference of beam body on the track-bridge relative displacement is much greater than that of the longitudinal resistance of polymer material. After considering the randomnesses of parameters, the track-bridge relative displacement under the action of temperature has a certain dispersion, mainly distributes in the range of 4.0-6.5 mm, and approximately follows the normal distribution. In the absence of special treatment measures, the embedded track on bridges should not be built in areas with large annual temperature difference. The proposed reliability evaluation method of embedded track continuous welded rail on bridges can provide a theoretical guidance for the design of embedded track structure.More>
2020, 20(4): 70-79. doi: 10.19818/j.cnki.1671-1637.2020.04.005
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Effect of pier temperature gradient on longitudinal force of CRTSⅡslab ballastless track on bridge
ZHANG Peng-fei, LIAN Xi-ni, GUI Hao, LEI Xiao-yan
Abstract: For the longitudinal additional force and deformation of China railway track system(CRTS) Ⅱ slab ballastaless track on bridge caused by the pier temperature gradient, the spatial coupling models of CRTS Ⅱ slab ballastless track continuous welded rails(CWR) on the multi-span simply supported beam bridge and long-span continuous beam bridge were established by using the finite element method based on the beam-slab-rail interacting principle. Both the dimensions and mechanical properties of main and detail structures, such as rail, track slab, cement asphalt(CA) mortar, base plate and bridge, were considered in detail. The longitudinal displacement of pier top caused by the action of longitudinal temperature difference of pier was calculated by the unit load method, to analyze the distribution rules of longitudinal force and displacement of ballastless CWR on the bridge under the influence of displacement of pier top. Analysis result shows that when the uniform displacement of each pier top occurs, the distribution laws and the maximum values of longitudinal force of ballastless track CWR on the multi-span simply supported beam bridge and long-span continuous beam bridge are basically the same, and increase linearly with the increase of uniform displacement of pier top. The peak relative displacement between the rail and track slab appears at the ends of abutment on both sides, the anchorage structures behind the abutments, tops of the second and last spans fixed support piers. When the uniform displacement of pier top is 5 mm, the maximum longitudinal forces of rails on the multi-span simply supported beam bridge and long-span continuous beam bridge are 79.62 and 79.54 kN, respectively, the maximum longitudinal displacements are 4.94 and 4.91 mm, respectively, and the maximum relative displacement between the rail and track slab is 0.23 mm. When the uneven displacement occurs at the top of each pier, the longitudinal force of rail and the relative displacement between the rail and track slab change abruptly at the displacement difference between adjacent piers. The longitudinal force of consolidation mechanism on the multi-span simply supported beam bridge is greater than that of long-span continuous beam bridge. For high pier bridges, it is necessary to pay more attention to the relative displacement between the rail and track slab at the maximum height difference between adjacent piers, the relative displacement between the base plate and bridge and the longitudinal force of consolidation mechanism.More>
2020, 20(4): 80-90. doi: 10.19818/j.cnki.1671-1637.2020.04.006
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Applicability of determination indexes for fatigue failure of modified asphalt
WANG Lin, GUO Nai-sheng, WEN Yan-kai, HOU Yi-lie, YU Chun-hui, YOU Zhan-ping
Abstract: The malvern dynamic shear rheometer was used to conduct the time sweep fatigue tests on the 90# original binder, SBS modified asphalt, rock asphalt modified asphalt, crumb rubber modified asphalt, rock asphalt/SBS composite modified asphalt and rock asphalt/crumb rubber composite modified asphalt(RA/CRCMA) under the stress-controlled and strain-controlled modes. The corresponding fatigue life of modified asphalt was determined according to five fatigue failure definitions. The suitability of fatigue failure determination indexes of modified asphalt was evaluated by using the statistical analysis method. The fatigue performances of modified asphalts were compared and analyzed by using the recommended indexes. Research result shows that the index determined based on the normalized dynamic modulus is not affected by the load control mode and asphalt type. The indexes determined based on the phase angle and cumulative dissipative energy ratio are significantly affected by the asphalt type and load-controlled mode, and are not universal. The index determined based on the dissipated energy change rate is only suitable for the fatigue life judgment of stress-controlled mode. The index determined based on the reduced dissipated energy change rate is less affected by the asphalt type. It exhibits a preferable fatigue life evaluation effect on all asphalts in this study. The correlation coefficients of the indexes determined by the normalized dynamic modulus and the reduced dissipated energy change rate under the stress-controlled and strain-controlled modes are up to 0.94, and the mean absolute error is less than 20%, showing a good correlation and equivalent fatigue life ranking results. Due to the simple calculation and distinct definition, they are recommended to be used as the determination standard for testing the asphalt fatigue failure in time sweep fatigue test. According to the sequence of fatigue life of asphalts tested by the recommended indexes in this study, the RA/CRCMA with 18% crumb rubber and 5% rock asphalt shows the optimal fatigue resistance under the stress-controlled and strain-controlled modes.More>
2020, 20(4): 91-106. doi: 10.19818/j.cnki.1671-1637.2020.04.007
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Temporal and spatial characteristics of moisture migration and instability mechanism of cracked soil slope under rainfall infiltration
ZHOU Zhi, ZHANG Jia-ming, NING Fu-long, LUO Yi, WANG Jian-li
Abstract: To reveal the temporal and spatial characteristics of moisture migration and instability mechanism of cracked soil slope under the rainfall infiltration. The full-scale model test and fiber Bragg grating(FBG) displacement systems were developed independently to conduct the whole-process and multi-physical monitoring of slope progressive failure. The progressive deformation and failure evolution mode of cracked soil slope under the rainfall infiltration were revealed. Based on the progressive failure mode of cracked soil slope, the concept of soil saturation ratio was proposed. The sliding body within the crack depth range was divided into the saturated layer and unsaturated layer. The change of soil saturation degree was used to describe the water transport law of slope with randomly distributed cracks, and the slope instability mechanism controlled by cracks was discussed by combining with the rigid body limit equilibrium method. Research result indicates that the shallow deformation is controlled by the surface matrix suction in the case of continuous light rain for the slope without cracks. After the formation of cracks, the rainwater infiltrates rapidly along the cracks to form a transient saturated zone. It causes a rapid loss of shear strength contributed by the matrix suction with a drop of 82.50%-87.14%, and produces the initial slip flow, sheet erosion and other shallow deformations. After the rainfall stops, the slope is still in the creep process, and the displacements of slope foot and roof increase by 23.40% and 19.39%, respectively. After the evaporation, the development of crack increases the influence range of rainwater on the seepage field and slope failure scale. The soil becomes loose after experienced swelling, shrinking and creep process. The volumetric moisture content of soil at the deep layer of crack zone increases by 205.7% compared with the initial state. Under the same rainfall condition, the deeper the initial crack depth is, the lower the stability coefficient is, and the faster the failure occurs. For a slope with the same crack depth, its stability coefficient decreases with the increase of soil saturation ratio. The faster the soil saturation ratio increases, the wider the connected saturated zone inside the slope is. It is the main reason for the overall instability of cracked soil slope.More>
2020, 20(4): 107-119. doi: 10.19818/j.cnki.1671-1637.2020.04.008
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Triaxial shear mechanical properties of reinforced foam lightweight soil
XU Jiang-bo, WANG Yuan-zhi, LUO Yong-zhen, YAN Zhang-gen, ZHANG Liu-jun, YIN Li-hua, YANG Xiao-hua, QIU You-qiang, LAN Heng-xing
Abstract: Through the triaxial shear test, the shear mechanical properties of polypropylene fiber reinforced foam lightweight soil under different reinforcement ratios and confining pressures were compared. The relationships between the strength parameters of the reinforced lightweight foamed soil and the reinforcement rate and confining pressure were investigated. The crack propagation law of reinforced lightweight foamed soil was obtained, and the stress-strain full curve equation was established. The constitutive equations for the strength parameters of foam lightweight soil in terms of reinforcement ratio and confining pressure were proposed. The experimental results with different reinforcement ratios were analyzed through the data normalization. The stress-strain full curve equation of reinforced foam lightweight soil was obtained. The functional relationships between the parameters of the curve equation and the two variables(reinforcement rate and confining pressure) were obtained. Analysis result shows that the triaxial shear strength and cohesion of reinforced foamed lightweight soil emerge a trend that increases first and then decreases with the increase of the reinforcement rate, and reach the peak values when the reinforcement rate reaches 0.75%. While the reinforcement ratio has limited influence on the internal friction angle of reinforced foam lightweight soil, which indicates that the function of fiber affects the strength of reinforced foam lightweight soil by changing the cohesive force of the material. The strength reduction rate presents an obvious descend trend with the increase of the reinforcement rate, at most, it decreases from about 40% to about 10%, and then keeps stable. When the reinforcement rate is kept constant, the ultimate strength and residual strength of reinforced foamed lightweight soil present an increase trend with the confining pressure. Through analyzing the volume crack curve, it is found that the reinforced lightweight foamed soil is mainly subjected to four stages when it is damaged: compression, cracking, crack restriction because of the fiber tension, and pulling out of fiber due to the large crack extension. When the reinforced foam lightweight soil reaches the yield stage by two crack development processes: the stable and unstable growth of crack. Due to the lack of reinforcement, the failure type of foam lightweight soil belongs to brittle failure, hence, there is no instability growth stage of crack.More>
2020, 20(4): 120-133. doi: 10.19818/j.cnki.1671-1637.2020.04.009
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Effect of hygrothermal aging on transverse impact mechanical properties of BFRP adhesive joints
NEI Jing-xin, TAN Wei, MU Wen-long, LUAN Jian-ze
Abstract: In order to provide a reference for crash safety of vehicle adhesive structure, the BFRP was selected to make single lap joints. According to the service environment of vehicle, the joints were aged for 0, 5, 10 and 15 d in two environments with the temperatures and humidities of 80 ℃/30%(GWCS) and 80 ℃/95%(GWGS), respectively. The change rules of failure load and failure mode with time were tested by using the quasi-static tensile test. The glass transition temperatures of BFRP and adhesive before and after aging were analyzed by using the differential scanning calorimetry. The transverse impact tests with the impact energies of 0, 20, 40 and 60 J were carried out for the joints which were unaged or aged for 15 d. The variation rules of energy absorption, the maximum impact load and the maximum deformation with the impact energy were analyzed, and the change rules of joint failure load and failure mode were also tested. Analysis result shows that after aging in the GWCS environment, the failure loads of joints decrease slightly, and the post-curing reaction of adhesive and the molecular chain fracture of BFRP occur, which makes the joints more prone to the matrix cracking or fiber tearing. In the GWGS environment, aging can obviously accelerate the degradation of joint performance, and easily cause hydrolysis and expansion of the interface between adhesive and BFRP. After 15 d of aging, the failure loads decrease by 54.99%, and the mixed failure of interface and cohesion occurs. After aging in the GWCS environment, the joints have good resistance to the impact load and deformation, and the failure loads change little after impact. After aging in the GWGS environment, the joint is obviously affected by the transverse impact, and its ability to bear the impact load and resist deformation is poor. After the impact of 60 J, the joint surface damages seriously, and the failure load decreases significantly, with the decrement rate of 58.71%. The mixed failure of interface and cohesion occurs, and the damage crack is obvious. It can be seen that in the process of vehicle service, the adhesive structure should avoid the effect of high-temperature and high-humidity environment, especially the influence of transverse impact on the aging adhesive structure.More>
2020, 20(4): 134-144. doi: 10.19818/j.cnki.1671-1637.2020.04.010
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High-speed EMU parking method based on improved fuzzy PID-Smith controller
LI Zhong-qi, XU Jian
Abstract: To solve the problems of control model parameter change when the electric brake and air brake were switched in the EMU braking process and the large delay of air brake system, and improve the parking accuracy of EMU, an improved fuzzy PID-Smith controller was proposed. A second-order pure delay transfer function with respect to the running speed and braking force was established by analyzing the mechanical model of a single carriage in the braking process of EMU and considering the characteristics of braking process of trains. The discretized second-order pure delay transfer function was combined with the mechanical model of a single carriage to establish the multi-particle control model of EMU, and the characteristics of this control model were analyzed. An improved fuzzy PID-Smith controller was proposed. The Smith predicting controller was introduced to solve the large delay problem of air brake system during the braking process of EMU. The recursive least square method was used to identify the model parameters online to solve the problem of model parameter change when the electric brake switching to the air brake during the braking process of EMU. The fuzzy PID controller was used to replace the PID part of Smith predicting controller to solve the problems of PID parameter tuning difficulty and poor robustness. The software MATLAB was used to simulate the CRH380 A high-speed EMU. The controller was used to control the EMU to track the set speed under the conditions of different inbound speeds, different decelerations and different degrees of interferences, and the results were compared with those of fuzzy PID controller. Simulation result shows that the errors between the power unit speed and the set speed obtained by the improved fuzzy PID-Smith controller and fuzzy PID controller are within 0.4 and 1.0 km·h-1, respectively. The parking error obtained by the proposed controller and fuzzy PID controller are within 0.3 and 1.5 m, respectively. Therefore, the proposed controller satisfies the requirement that the parking error during the operation of high-speed EMU should be less than 0.3 m.More>
2020, 20(4): 145-154. doi: 10.19818/j.cnki.1671-1637.2020.04.011
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Load identification and distribution characteristics of high-speed train bogie frame
CHEN Dao-yun, LIN Feng-tao, SUN Shou-guang, MOU Ming-hui, XIAO Qian
Abstract: The bogie frame of a certain model high-speed train was taken as the research object, the load identification and distribution characteristics of high-speed train bogie frame was studied. The principle of identifying frame load based on the dynamic stress response was analyzed, and the frame load was back deduced and identified based on the truncated singular method. The extreme value distribution characteristics of frame load were analyzed by the kernel density estimation method, and the extreme value ranges of frame load under different occurrence probabilities were obtained based on the 3σ criterion. The two-dimensional load spectrum of frame load was compiled by the rain-flow counting method, and the two-dimensional load spectrum was equivalent to one-dimensional load spectrum based on the Goodman equation. Based on the one dimensional load spectrum, the cumulative frequency distribution rule of loads in each load system was analyzed. Analysis result shows that for the object studied in this paper, when the number of truncation is 1, the relative error of load identification result is the smallest. The probability density distributions of the minimum load and maximum load are symmetrical relative to the longitudinal axis of coordinate system. The larger the load range is, the lower the probability density is. The maximum and minimum load ranges of gearbox load system are the largest, the maximum load extremum is 25 kN. The braking load system, lateral rolling load system and transverse load system are the second, the maximum load is 15 kN. The maximum load of floating load system is about 5 kN. The extreme value of torsional load system is the smallest, and the maximum load is about 3 kN. With the increase of occurrence probability, the occurrence range of extreme value of each load system increases gradually. The two-dimensional load spectrums of all load systems have obvious load frequency extremums that appear in the low amplitude region. For the one-dimensional cumulative frequency distribution of load spectrum after the equivalence of two-dimensional load spectrum, the total cumulative frequency time of each load system is almost equivalent. The maximum load amplitude of gearbox load system is significantly greater than those of other load systems. From large to small, the maximum load amplitudes of other load systems are lateral rolling load system, braking load system, floating load system, transverse load system and torsional load system, respectively.More>
2020, 20(4): 155-164. doi: 10.19818/j.cnki.1671-1637.2020.04.012
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Impact characteristics of axle box bearing due to wheel flat scars
CHA Hao, REN Zun-song, XU Ning
Abstract: Taking CRH2 EMU as the research object, the vehicle-track dynamics analysis model including bearing was established. The time histories of wheel-rail impact force, the vibration accelerations of wheelset and axle box, and the contact load between roller and outer ring raceway were obtained by the numerical integration. Combined with the existing wheel flat scar analysis model, the influences of flat scar length and vehicle running speed on wheel-rail impact force were researched. The vibration acceleration response characteristics of wheelset and axle box under flat scar impact, and the contact load response characteristics of outer ring raceway were studied. Research result shows that the impact accelerations of wheelset and axle box increase with the length of flat scar. The impact acceleration of axle box is larger than that of wheelset, and increases faster. The wheel flat scar can affect the contact load of outer ring raceway. In the bearing area of the raceway, when the wheel enters the flat scar area, the effect of the impact load is to reduce the contact load of the outer ring of the roller. When the wheel leaves the flat scar area, the effect of the impact load is to increase the contact load of the outer ring of the roller. In the non-bearing area of the raceway, the roller and the outer ring also have multiple impacts. At 300 km·h-1, when the length of the flat scar is less than 30 mm, the impact load on the outer ring of the roller entering the flat scar area is greater than that on the outer ring of the roller leaving the flat scar area. When the length of the flat scar is longer than 30 mm, the impact load on the outer ring of the roller entering the flat scar area is less than that on the outer ring of the roller leaving the flat scar area. In the whole raceway area, the impact load of the raceway caused by wheel flat scar is symmetrical distribution, and the closer the raceway area is to the symmetrical axis, the greater the impact load is.More>
2020, 20(4): 165-173. doi: 10.19818/j.cnki.1671-1637.2020.04.013
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Noise characteristics in different bogie areas during high-speed train operation
WANG Dong-zhen, GE Jian-min
Abstract: Taking a certain type of high-speed train in China as a research object, the bogie area noise that is one of the major noise sources of high-speed train in operating mode was tested, the noise characteristics and laws of different bogie types and different bogie positions were studied, and the noise values and spectrum characteristics at different speed levels were predicted. Based on certain assumptions, the noise components in the head-car bogie area were separated by using the test data analogy method. Research result shows that the main sources of vehicle noise are concentrated in the bogie area in the speed range of 200-350 km·h-1. The bogie area noise of the head-car is larger than that of the tail-car, and the amplification is approximately 3 dB(A) at the speed of 200 km·h-1. The main reason is that the aerodynamics noise caused by the airflow impact at the head-car bogie is greater than that caused by the eddy flow at the tail-car bogie. The bogie area noise of intermediate motor car is larger than that of the intermediate trailer car, and the amplification is approximately 5 dB(A) at the speed of 200 km·h-1. The main reason is that the traction system noise is generated in the motor bogie compared with the noise of trailer bogie. With the operating speed increasing, the noise in the bogie area significantly increases in the whole frequency band, and the noise-peak frequency also increases, which is mainly due to the wheel rolling noise. When the operating speed becomes higher, the sleeper impact frequency will be higher accordingly. The third-order relationship of noise increasement versus speed increasement in the bogie area of the intermediate trailer conforms with the growth trend of wheel-rail noise increasement versus speed increasement. In terms of the noise in head-car bogie area, the aerodynamics noise is more significant, and its proportion increases with the increase of operating speed.More>
2020, 20(4): 174-183. doi: 10.19818/j.cnki.1671-1637.2020.04.014
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Transportation trend of Chinese expressway
LI Bin, XIAO Run-mou, YAN Sheng-yu, MA Jian
Abstract: The historical data of traffic volume, vehicle structure, vehicle speed, traffic density, empty driving and truck overload of Chinese expressway in 13 years were mined, and the transportation situations of passenger vehicle and freight vehicle on expressway were analyzed. Analysis result shows that the expressway vehicle driving capacity in 2018 was 7.32×1011 veh·km, in which the truck driving capacity was 2.21×1011 veh·km and the bus driving capacity was 5.11×1011 veh·km. The correlation coefficient of expressway vehicle driving capacity and lane mileage was as high as 0.99. In 2018, the passenger turnover volume of expressway was 1.77×1012 people·km, which was three times the value of in 2006 and 1.25 times of railway passenger turnover volume in the same year, respectively. With an increasing number of private car ownership, the total number and proportion of passenger vehicle trips with less than 7 seats increased substantially and continually, from 29.75% of the total passenger turnover of expressway in 2006 to 71.74% in 2018. The freight turnover volume of expressway was 2.99×1012 t·km in 2018, with a year-on-year growth of about 4.25% compared with 2017. The expressway freight turnover volume accounted for 42.00% of the total commercial truck turnover volume in whole society, and its fluctuation basically synchronized with the economic cycle. The passenger and truck transportation of expressway in each province were relatively reasonable. The Gini coefficients of passenger and freight transportation density in each province were 0.36 and 0.30 in 2018, respectively, both within the relatively reasonable range. With a further optimization of expressway freight vehicle structure, the excess freight decreased 1.63% and the empty-truck increased 4.28% in 2018 compared with 2017.More>
2020, 20(4): 184-193. doi: 10.19818/j.cnki.1671-1637.2020.04.015
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Short-term metro passenger flow prediction based on EMD-LSTM
ZHAO Yang-yang, XIA Liang, JIANG Xin-guo
Abstract: To weaken the interference of sample noise to the prediction model of passenger flow, a short-term metro passenger flow prediction model was proposed based on the deep-learning theory, empirical mode decomposition(EMD) and long short-term memory neural network(LSTMNN). The prediction process was divided into three stages.In the first stage, the raw automatic fare collection(AFC) data were preprocessed, and the tap-in(tap-out) passenger flow time series were constructed and decomposed into a series of intrinsic mode functions(IMFs) and a residues by the EMD. In the second stage, the input variables of the LSTMNN were determined by the partial autocorrelation function(PACF). In the third stage, the LSTMNN was developed, trained and predicted through the deep learning library Keras. A case study of Shanghai People's Square Station on metro line 2 was conducted to validate the model performance. Calculation result shows that, compared to the representative prediction models(differential autoregressive integrated moving average model, support vector machine, empirical mode decomposition and back propagation neural network, and LSTMNN), the EMD-LSTM prediction model increases the weekdays' tap-in(tap-out) passenger flow prediction accuracy of peak hour, off-peak hour, and full-day by at least 2.1%(2.5%), 2.7%(3.5%), and 2.7%(3.4%), respectively, and also increases the weekends' tap-in(tap-out) passenger flow prediction accuracy of full-day by at least 3.3%(3.5%). Thus, the EMD-LSTM is effective to predict the short-term metro passenger flow. When the forecasting step gradually increases from 5 minutes to 30 minutes, the weekdays' tap-in(tap-out)average absolute percentage prediction errors of peak hour, off-peak hour, and full-day gradually decreases from 14.8%(13.9%), 16.8%(17.4%), and 16.6%(17.0%) to 7.0%(6.2%), 8.3%(7.5%), and 8.1%(7.4%), respectively. Therefore, the forecasting error of EMD-LSTM is negatively correlated with the forecasting step length.More>
2020, 20(4): 194-204. doi: 10.19818/j.cnki.1671-1637.2020.04.016
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Slot allocation of railway container terminal considering stowage plan
CHANG Yi-mei, ZHU Xiao-ning
Abstract: To enhance the handling efficiency of container yard in container terminal, a slot allocation model of outbound containers was set up to minimize the overlapping amount. Considering the different characteristics of arrival in batches of railway containers and random arrival of road containers and the influence of stowage plan, a heuristic algorithm based on the prediction approach was proposed. According to the arrival characteristics of road containers, the arrival sequence of road containers was predicted by the Markov chain. Considering the characteristics of slot allocation model, a slot allocation solving algorithm was proposed to allocate the railway and road containers. The software MATLAB was used to simulate and test the proposed model and algorithm. The small-scale experiments were conducted to verify the feasibilities and effectivenesses of the proposed model and algorithm, and two large-scale comparison experiments were carried out. One comparison experiment is between the mixed storage mode and the separate storage mode of railway and road containers. Another comparison experiment is between the proposed algorithm and the traditional storage algorithm. Analysis result indicates that the overlapping amount of mixed storage mode is 27.9% less than that of separate mode. The overlapping amount of the proposed algorithm is 37.7% less than that of the traditional storage algorithm. The mixed storage mode can effectively reduce the overlapping amount. The proposed algorithm can both effectively solve the small-scale and large-scale container allocation problems. It effectively enhances the handling efficiency of container yard and facilitates the loading operation of containers.More>
2020, 20(4): 205-216. doi: 10.19818/j.cnki.1671-1637.2020.04.017
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Data cleaning method of ADS-B historical flight trajectories
WANG Bing
Abstract: To effectively solve the various field data anomalies in the automatic dependent surveillance-broadcast(ADS-B) historical flight trajectories affected by the ground station distribution breadth, terrain blocking, electromagnetic interference and so on, an ADS-B data cleaning method was established, and implemented by four steps, such as determining the cleaning object, deleting the duplication of field, cleaning the abnormal point and correcting the time stamp. According to the existing sample ADS-B historical data, the track model was established and the validity was analyzed. The fields such as the time stamp, longitude, latitude, pressure altitude and ground speed were defined as the characteristic fields and cleaning objects. The time stamp, longitude and latitude of ADS-B track point sequence were deduplicated to delete the adjacent track points with repeated data. The outliers of characteristic fields were located through the method based on the density-based spatial clustering of applications with noise(DBSCAN) to improve the cleaning efficiency, detect and correct the abnormality. To make the change of track point state conform to the particle kinematic law, the time stamp was corrected by the field data of longitude, latitude, pressure altitude and ground speed of ADS-B track points, and the extended modified time stamp field was saved. Research result shows that 97.58% of the abnormal track points in the 516 sample flights are effectively identified and cleaned. The cleaned track point state changes more smoothly. The total flight duration before and after correction varies between 10-600 s. The correction effect of time stamp mainly depends on the accuracy of ground speed. The corrected time stamp should be selectively used according to the data characteristics of sample track in practical engineering applications. The established cleaning method of ADS-B data can provide a preliminary data processing platform for the trajectory analysis, evaluation and computing in civil aviation engineering projects.More>
2020, 20(4): 217-226. doi: 10.19818/j.cnki.1671-1637.2020.04.018
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Compression algorithm of ship trajectory based on online directed acyclic graph
ZHANG Yuan-qiang, SHI Guo-you, LI Song
Abstract: To solve the problem of ship trajectory data compression, an online ship trajectory compression algorithm was proposed. An estimation method of multiple sliding reckoning the ship position was used to clean the ship trajectory, and the online directed acyclic graph was used to build the compression path tree on the clean trajectory and to output the sampling points. The Hash table was used to manage the trajectory queue and path tree in memory in order to improve their query speeds. To verify the effect of the proposed algorithm, the compression times and errors of real ship automatic identification system, direction-preserving algorithm and Douglas-Peucker algorithm were compared, and the original trajectory, clean trajectory and compression trajectory were analyzed by the visual method. Experiment result shows that in terms of the compression time, the compression times of direction-preserving algorithm and Douglas-Puck algorithm are about 1.1 and 1.3 times of the proposed algorithm, respectively, indicating that the execution time of the proposed algorithm is shorter than the other two algorithms. The proposed algorithm retains the time information in the compression process, and the average synchronized Euclidean distance error is less than 10 m at any compression rate. The maximum synchronized Euclidean distance error is only 127 m when the compression ratio is 1%, while the average synchronized Euclidean distance errors and the maximum synchronized Euclidean distance errors of the other two algorithms can not be controlled, and change randomly. In terms of perpendicular distance error, both the proposed algorithm and Douglas-Puck algorithm can guarantee that the perpendicular distance errors less than 20 m when the compression rate is not less than 5%, while the perpendicular distance error of direction-preserving algorithm changes randomly. In terms of display effect, the proposed algorithm can effectively remove the noise points of trajectory, and the compression trajectory can better represent the macroscopic traffic flow of original trajectory. Therefore, the proposed algorithm can preserve the shape and time informations of original trajectory more efficiently.More>
2020, 20(4): 227-236. doi: 10.19818/j.cnki.1671-1637.2020.04.019
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