西南交通大学学报

Finite Element Model Updating of Box Girder Bridges with Corrugated Steel Webs

JI Wei, SHAO Tianyan

2021, 56(1): 1-11. doi: 10.3969/j.issn.0258-2724.20191198

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Abstract:
In order to reduce the error between the finite element values and measured values of the box girder bridge with corrugated steel webs, a bridge finite element model updating method using response surface method and Fmincon algorithm was presented, taking a box girder bridge with corrugated steel webs in the connecting line of Jingzhong airport in Gansu province, China as the research object. Firstly, static and dynamic load tests were carried out to obtain the measured values of bending vibration frequency, deflection and strain. Secondly, the calculated values of these parameters were obtained by the finite element modeling using solid and plate-shell elements, respectively. After comparison of the calculated values with the measured values, a more accurate solid finite element model was selected as the updated initial finite element model. Then, on the basis of reasonable selection of design parameters, the corresponding structural response was obtained through the central composite test design, the quadratic polynomial regression equation between the structural response and design parameters was obtained by least square method fitting, and the objective function of the difference between the measured value of the target response and the corresponding response was constructed. Finally, Fmincon algorithm was used to calculate the objective function iteratively, and the updated value of parameters and the baseline finite element model of the bridge were obtained. The results show that it is feasible to modify the finite element model of the composite box girder bridge with corrugated steel webs by combining the response surface method and the Fmincon algorithm, which has the characteristics of simple modification process and fast convergence speed. The calculation time was within 0.25–0.75 s, and the relative error of the first-order bending vibration frequency was updated from 4.85% to 1.62%–2.91% according to different response combinations. Through the comparison between Genetic algorithm and Fmincon algorithm, it was found that Fmincon algorithm improves the model updating efficiency significantly, which can provide reference for the finite element modeling analysis and mechanical performance analysis of this kind of bridges in engineering practices.

Study of Extreme Wave Forces on T-and Box-Types Girder

YANG Zhiying, HUANG Bo, DUAN Lunliang, ZHANG Jiawei, ZHU Bing

2021, 56(1): 12-19. doi: 10.3969/j.issn.0258-2724.20181069

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The extreme wave forces on costal bridges with T-type girder and box-type girder have great differences due to their special geometrical shapes. First, numerical models based on solitary wave theory and cnoidal wave theory were developed to simulate the tsunami waves and hurricane waves, in which the RANS (Reynolds-averaged Navier-Stokes) equations combined with the SST (shear stress transport) k-ω turbulence model were utilized to describe the mean flow motion, and the VOF (volume of fluid) method was used to trace the interface of air and water. Then, the effectiveness of the numerical models was verified. On this basis, the tsunami and hurricane induced wave forces on T-type girder and box-type girder were compared and discussed, considering different wave heights and submergence depths. The results show as follows: Tsunami wave induced horizontal peak forces on T-type girder are greater than those on box-type girder by over 32%; however, the box-type girder suffers greater vertical peak forces than the T-type girder and the maximum difference between them is near 31%. Hurricane induced horizontal peak forces on T-type girder are greater than those on box-type girder by over 31%; meanwhile, the vertical peak forces on T-type girder are also greater than those on box-type girder. Compared with hurricane waves, tsunami waves pose a greater threat to the safety of coastal bridges.

Shaking Table Tests on Seismic Response of Tunnel with Longitudinal Cracking Lining

LI Bingtian, QIU Wenge, QI Xingxin, DENG Zhiheng, HU Hui

2021, 56(1): 20-27, 55. doi: 10.3969/j.issn.0258-2724.20190657

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In order to study the influence of longitudinal cracks in the lining of double track tunnel of high speed railway on the seismic safety of the structure, a large-scale shaking table model test was carried out on class IV surrounding rock in accordance with the Code for design of railway tunnel (TB 10003—2016). The test adopted an improved static-dynamic coupling shear model box to analyze the response rules of seismic strain and structural internal force of tunnel lining, taking into consideration three influencing factors including the tunnel buried depth, the cracking position and the cracking form of lining. The test results showed that under the action of seismic shear wave, the failure mode of the shallow tunnel is tension failure, while that of the deep tunnel is compression failure, both of which occur at the arch waist. The peak acceleration of input wave of the shaking table was 0.8g and 0.9g, respectively, when the crack-free lining was damaged at the two buried depths. Cracks in vault and sidewall have little influence on seismic response of tunnel, while the cracks at the arch waist have significant effect. Under the shallow and deep buried conditions, the peak acceleration of the input wave of the shaking table was 0.5g and 0.6g, respectively, when the lining with cracks at the arch waist was damaged. For deep-buried tunnels, compared with the normal section cracks, inclined section cracks at the arch waist will speed up the deformation of lining structure after failure but have little influence on the critical value of failure acceleration.

Comparative Analysis of Shear Strength Models in Plastic Hinge Region for Concrete Hollow Piers

SHAO Changjiang, QI Qiming, WEI Wang, HU Chenxu

2021, 56(1): 28-36. doi: 10.3969/j.issn.0258-2724.20190196

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Accurate evaluation of shear strength in plastic hinge region is of great significance for seismic design of long-span bridges with tall piers. However, the shear design models for hollow piers are not directly listed in the current codes in China and abroad. The applicability of both the existing formulas for solid piers in the codes and the formulas for solid or hollow columns in literature needs to be further studied. Thus, based on the test results of 25 hollow piers with shear or flexural-shear failure modes, the influencing factors of shear strength in plastic region are analyzed, and the experimental values of shear strength are compared with the calculation results of 15 formulas. The results show that the shear strength of concrete hollow piers increases with an increase in concrete strength, stirrup ratio and axial load ratio, and decreases with an increase in displacement ductility factor and aspect ratio within a certain range, while the influence of the longitudinal reinforcement ratio is not significant. The errors between the test results and the calculated values by formulas of Aschheim, Caltrans, Sezen and Shin are all less than 5%, among which the Sezen model is the most suitable to assess the shear strength in plastic hinge region for hollow piers. The formulas in NZS3101, JRA, JTG/TB 02-01—2008, Eurocode 8, and ACI-318 lead to slightly conservative results, which can be used for shear design of hollow piers; the rest of equations, for overestimation of the shear strength in plastic hinge region, are inappropriate to concrete hollow piers.

Out-of-Plane Stability Analysis Method for Circular Arch Structures

DING Min, WANG Jiajia, JIANG Xiugen, CAO Qiongqiong, WANG Hongzhi

2021, 56(1): 37-46. doi: 10.3969/j.issn.0258-2724.20191158

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In order to analyze the out-of-plane stability behavior of circular arch structures, according to the deformation correlation of circular arch with circular curved beam, the equilibrium equations of circular curved beam were firstly established by taking secondary moment effect into account. Combined with the geometric equation and physical equation of circular curved beam, the deflection control equation and torsion angle control equation of circular curved beam with free torsion were derived by considering large displacement. Both the general formats and corresponding simplified formats of analytical solution for circular curved beam deflection and torsion angle were obtained. Meanwhile, the expressions for deformation and internal force of circular curved beam were also derived. On this basis, the methods to analyze the out-of-plane bifurcation instability and extreme point instability of circular arch structure were presented. Critical load coefficients and their instability modes of four kinds of circular arch structure were calculated when out-of-plane bifurcation instability occurs, and the calculation results between the proposed model and the models from the literature were discussed; their load-displacement curves were calculated, and the extreme point instability of circular arch structures was analyzed. The results show that the critical load coefficient of the circular arch with two ends simply supported can be calculated by this model and has no difference with other models. In addition, this model is also useful to calculate the critical load coefficient of that with single hinge at mid-span or that with two ends inserted supported which are rarely seen in research. The out-of-plane bifurcation instability modes of all kinds of circular arch under in-plane uniformly distributed radial load are in the form of single symmetric wave. The radial load does not change the linear character of the out-of-plane load vs. displacement curve, but reduces the out-of-plane flexural rigidity. When the radial load reaches a certain value, the out-of-plane flexural rigidity becomes 0, and then the out-of-plane instability occurs.

Evolution Characteristics of Indoor Pollutant Concentration in Buoyancy-Driven Natural Ventilation

ZHUANG Jiawei, DIAO Yongfa, ZHANG Li’an, SHEN Henggen

2021, 56(1): 47-55. doi: 10.3969/j.issn.0258-2724.20190582

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Evolution of pollutant concentration at different heights was analyzed to explore the evolution rule of indoor gaseous pollutants during a period from buoyacy-driven natural ventilation to steady state. Firstly, according to the non-uniform three-layer model used to examine the transient flows driven by buoyancy force, two theoretical models that correspond to homogeneous mix and pure displacement were developed for the different mixing characteristics of the inoor lower-layer pollutants. Then, the fourth-order Runge-Kutta method was adopted to find a iterative solution, and the height and concentration variation characteristics of the indoor pollutants during the ventilation process were obtained. Finally, the effects of the effective ventilation area and buoyancy combination coefficient on pollutant concentration was discussed. The results show that, the thermal stratification interface with zero vertical velocity greatly differs from the fresh air layer interface, and the height difference between thermal stratification interfaces will have a larger peak value and a shorter time to reach steady state when the dimensionless effective ventilation area becomes larger. The greater buoyancy combination coefficient is, the greater the height difference between thermal stratification interfaces at any time is, which becomes more obvious with the increase of the dimensionless effective ventilation area. The mixing characteristics of lower-layer pollutants affect the stratification and time evolution, but do not change the concentration distribution in steady state, and the upper layer has the highest pollutant concentration for both models. For the pure-displacement model, the pollutant concentration of the original layer decreases until it reaches stability, and the lower-layer pollutant concentration remains constant, while that of the upper layer increases sharply in the initial stage before decaying. Meanwhile, the average pollutant concentration of the upper and lower layers both slowly decay to a stable value for the homogeneous mix model. Furthermore, a larger dimensionless effective ventilation area can result in a faster decay of the dimensionless pollutant on the pollutant concentration can be almost ignored.

Optimization and Tensile Properties of Composite Insulator at High and Low Temperature

YAN Zhitao, MA Wenjun, ZHANG Pu, QIU Zhe

2021, 56(1): 56-61, 83. doi: 10.3969/j.issn.0258-2724.20181032

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In order to find out the influence of high and low temperature and the crimping process between the core rod and the end fittings on the bearing capacity of composite insulator, and to get the final optimized crimping mode, the finite element simulation analysis was carried out on the high and low temperature tensile test results of the core rod and the end fittings.Firstly, the stress of the fittings and mandrels was simulated at normal temperature, and the results were in good agreement with the experimental data. Then, 10 kinds of crimping conditions were designed to evaluate the optimal preloading conditions of the end fittings of composite insulator. The results show that when the preloading stress is evenly distributed along the radial direction of the fittings and 18% − 25% of the length of the fittings is reserved, the bearing capacity of the composite insulator link is the best, and the elastic limit load of the optimal model is 8.23% higher than that of the existing manufacturers. The simulation method can also be used to simulate the mechanical properties of insulators at high and low temperature, but the compression optimization cannot improve the bearing capacity significantly.

Generation Mechanism of Railway Disc Brake Squeal and Its Suppression Method

QIAO Qingfeng, YANG Weidong, ZHU Qi, CHEN Guangxiong

2021, 56(1): 62-67. doi: 10.3969/j.issn.0258-2724.20190799

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In order to study the generation mechanism of railway disc brake squeal and its influencing factors, the disc brake squeal of a railway brake unit for several different brake conditions in a field test was measured, and the generation mechanism of railway disc brake squeal was obtained. Based on the mechanism of brake friction squeal caused by modal coupling, a full-size prediction model of brake squeal was established, which included a disc, two brake pads, two pad holders, two levers, and several pins. The friction coefficients between the pads and disc from a laboratory test were used in the prediction of brake squeal. The factors affecting brake squeal were studied in the model. The test results show that the characteristic frequencies of disc brake friction squeal are 256.78, 3904.07 Hz and 4320.38 Hz, respectively. When the thrust force is equal to 10.1 kN and 12.3 kN, disc brakes are most likely to produce friction squeal in brake applications, the predicted results of the model are in agreement with the measured frictional squeal. The elastic modulus of the brake pad has an important influence on disc brake squeal, the reasonable elastic modulus of brake pad is helpful to suppress the brake friction squeal.

Research on Multi-Parameter Fitting of Fastener Structures to Suppress Wheel-Rail Friction Self-Excited Vibration

CUI Xiaolu, HUANG Bo, CHEN Guangxiong

2021, 56(1): 68-74. doi: 10.3969/j.issn.0258-2724.20190023

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To study the effect of fastener structure parameters on wheel-rail frictional self-excited oscillation, based on the viewpoint of frictional self-excited vibration of the wheel-rail, a finite element model of the wheelset-track system on a small-radius curve track supporting by the monolithic roadbed was established. Then, the wheel-rail frictional self-excited vibration model was verified by the field test and numerical simulation. Furthermore, the influence of fastener parameters on the wheel-rail frictional self-excited oscillation was studied. Considering the interaction between multiple factors, the occurrence possibility of wheel-rail frictional self-excited oscillation was obtained by the least squares method. The results show that the wheel-rail frictional self-excited oscillation caused by the saturated creep force between the wheel and rail is a key reason that causes rail corrugation on a small-radius curve track supporting by the monolithic roadbed. The frictional self-excited oscillation mainly occurs at 300 Hz and 320 Hz. According to the multi-parameter fitting equation of fastener structure, when the vertical damping of fastener is 1000 N•s/m and the fastener distance is 1.0 m in the appropriate range, the possibility of wheel-rail frictional self-excited oscillation is reduced, thereby the possibility of rail corrugation is reduced.

Experimentation on Vibration Transmission Characteristics of Modern Tram Tracks

ZHANG Xun, LI Xi, HAO Chenxi, YOU Yingchuan, CHEN Weijie, PU Yu, XU Yujin

2021, 56(1): 75-83. doi: 10.3969/j.issn.0258-2724.20200013

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In order to explore vibration transmission characteristics of different tracks in modern tram traffic (MTR), the MTR in a city was selected as the case, three different tracks were measured, i.e., ordinary track without vibration absorption elements, ordinary track with elastic cladding materials, and embedded track. Based on the principle of hammering test, the rail vibration decay rate, frequency response characteristic of each track component and insertion loss were obtained. The test results were compared with other anti-vibration tracks. Results show that the vibration decay rate of the embedded track exhibits frequency dependency, which has a maxima of 5.9 dB/m at 1600 Hz frequency-band. The first rail resonance point of the embedded track appears near 160 Hz, the amplitude of frequency response function and resonant frequency are both lower than that of the ordinary track without vibration absorption elements. Overall, compare to the ordinary track with elastic cladding materials and other anti-vibration tracks, the embedded track demonstrates better vibration reduction effect in longitudinal direction of rails in mid- and high-frequency range, and thus theoretically the wheel-rail noise can be well suppressed.

Effect of Hollow Worn Tread of Electric Multiple Units on Vehicle Stability

WANG Chen, LUO Shihui, WU Pingbo, XU Ziqiang, MA Weihua, FANG Wengwu

2021, 56(1): 84-91. doi: 10.3969/j.issn.0258-2724.20181001

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To solve the issue of frame lateral instability alarm of high-speed EMU (electric multiple units) in the running process, a vehicle dynamics model considering hollow worn tread was established. The wheel-rail relationship between worn treads of different running distance and rail as well as the influence of hollow worn tread on vehicle stability were researched used theoretical analysis, simulation analysis and field tests.The calculation results show that the contact points between turning tread and rail are in uniform distribution. However, for hollow wear tread, contact points distributed on both sides of the depression area. The“False flange effect”initiated by leap metastases of contact point caused severe lateral wheel/rail impact. While the vehicle running at high speed, the lateral vibration frequency is close to the natural vibration frequency of the frame itself, which would induce lateral coupled vibration of bogie and exceed the limit criteria. Through simulation analysis and field test discover hollow worn tread is an important indication for frame lateral alarm. Using wheel re-profiling can improve lateral stability of bogie.

Wheel Tread Wear Characteristics of High-Speed Electric Multi-Units

XU Kai, LI Fu, AN Qi, MAO Wenhui

2021, 56(1): 92-100. doi: 10.3969/j.issn.0258-2724.20190266

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In order to study the wheel tread wear characteristics of different types of high-speed electric multi-units (EMU) vehicles, and to explore vehicle performance evolution in the period of wheel wear, the CRH380A and CRH380B EMU running on Wuhan–Guangzhou passenger dedicated line are targeted. Based on the line data statistics, the high-speed EMU models by SIMPACK and the rail wear program, the wheel wear characteristics of two types of EMU vehicles and wear impact on vehicle running performance are analyzed in a turning repair cycle. The results show that the EMU on this dedicated line mostly show the tread hollow wear, and the wheel tread wear of the CRH380A EMU is more serious. In a turning repair cycle, due to the differences in the design concepts of the two types of EMU vehicles, the CRH380A EMU shows a narrower wear range, greater wear depth, and more obvious hollow wear; however, the CRH380B EMU shows a wider wear range, smaller wear depth, and more uniform wear. Within the operating distance of 250000 km, the running stability of the CRH380A EMU with the new wheels is obviously better than the CRH380B EMU, but when the distance exceeds 100000 km, due to the wheel wear, the running stability of the CRH380A EMU is worse than that of the CRH380B EMU. The maximum vibration acceleration and riding index of CRH380A EMU are 0.52 m/s² and 2.26, respectively, which are better than 0.58 m/s² and 2.38 of CRH380B EMU, but its derailment coefficient and wheel load reduction rate are both 0.35, which are greater than 0.14 and 0.28 of the CRH380B EMU. Therefore, during the entire operation cycle, the riding comfort of the CRH380A EMU is better than the CRH380B EMU, but its operation safety is worse than that of the CRH380B EMU.

Mechanical Performance and Microstructure of Single Component Geopolymer Mortar

YANG Shiyu, ZHAO Renda, JIN Hesong, LI Fuhai, QIAO Yu

2021, 56(1): 101-107, 137. doi: 10.3969/j.issn.0258-2724.20190588

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In order to investigate the strength development rule and microscopic mechanism of fly ash based geopolymer mortar with different NaOH concentrations, cement-sand ratios and solution-cement ratios at various curing temperatures, the mechanical properties test were carried out. The microscopic morphology and pore size distribution were analyzed by scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP), respectively. The results show as follows: For geopolymer mortar specimens prepared using NaOH solution with a concentration of 10%, no significant strength development was observed even at very high curing temperatures. With the increase of NaOH concentration or curing temperature, the compressive strength and flexural strength of single component geopolymer mortar can obtain their best value, and the location of the value is determined by both curing temperature and NaOH concentration. The pore size distribution differential curve of the geopolymer is a unimodal distribution. Controlling the concentration of can greatly reduce the peak value of the pore diameter differential curve and significantly reduce the porosity of the geopolymer. Fly ash particles dissolve gradually under the action of NaOH and form cementitious material on its surface. When the concentration of Na⁺ is low, the geopolymer polymerization is less; controlling the concentration of NaOH can make the geopolymer become dense and improve their compressive strength. The fractal model based on thermodynamic relation is the best one to describe the structure of the geopolymer pore, followed by the pore axis model, while the spatial filling model and the sponge model can only describe the fractal dimension of the pore structure of gel pores and transition pores. The calculated values of fractal dimension based on thermodynamic relationship and sponge model are between 2.0 and 3.0, which is similar to the results of general cement-based materials. Proper adjustment of the concentration of NaOH can improve the pore structure of the geopolymer.

Low Temperature Rheological Performance Analysis of Rubber Modified Asphalt under Heat Aging Process

YU Jiang, ZHAO Qun, YE Fen, SONG Qingqing

2021, 56(1): 108-115. doi: 10.3969/j.issn.0258-2724.20180987

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In order to explore the low temperature rheological properties of rubber modified asphalt (namely the activated twin-screw extruded rubber (AER) powder modified asphalt) and AER/SBS (styrene-butadiene styrene) composite modified asphalt under aging. The low temperature rheological properties of AER modified asphalt and its composite modified asphalt under different aging conditions and different rubber powder content were studied using conventional performance, low temperature bending test and Burgers model. At the same time, the influence of aging on the functional group of AER rubber modified asphalt was quantitatively analyzed by infrared FTIR method, and the correlation between its functional group index and various low temperature indicators was analyzed. The results show that AER and SBS can improve the low temperature performance of asphalt under different aging conditions; the low temperature performance of AER/SBS composite modified asphalt is better than AER modified asphalt under short-term aging, while the opposite is true under long-term aging. Both AER and SBS modifiers can improve the stiffness modulus of asphalt and AER has a greater impact on asphalt stiffness modulus, while low temperature grading indexes (i.e., stiffness modulus S, creep rate m, and the ratio S/m) and viscoelasticity indexes (i.e., relaxation time λ and dissipation-storage energy ratio a has a strong correlation. The low temperature performance of AER modified asphalt has a high correlation with the fat index I_A and the fat long chain index I_AL: the greater the aliphatic index, the better the low temperature performance, while the aliphatic fat long chain index is the opposite.

Feature Line Extraction from 3D Model of Oblique Photogrammetry Based on Multi-Objective Weighted Shortest Path

ZHU Qing, SHANG Qisen, HU Han, YU Haojia, ZHONG Ruofei, DING Yulin

2021, 56(1): 116-122. doi: 10.3969/j.issn.0258-2724.20180248

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Oblique photogrammetry 3D models suffer from coarse structure, high noise and regularity deficiency in corner or ridge regions, which make it difficult to extract feature lines quickly and accurately from these regions. To deal with this problem, a method of feature line extraction from 3D model of photogrammetry based on multi-objective weighted shortest path is proposed. First, the model is pre-processed to build a complete and continuous topological structure, and organized as a weighted directed graph. Then, considering the distance, direction and the change trend of the triangulation, the weights are calculated; the Dijkstra algorithm is constrained to obtain the shortest path to get the feature lines. Finally, using the feature line extraction results, a method is proposed to repair the regions without distinct features. Results show that compared with the interactive method, the proposed method is efficient and only need select two feature points to specify the target. At the same time, the extraction results do not rely on artificial experience and are highly objective. Compared with the automatic extraction method based on edges and faces, this method is less affected by noise, and can extract the specified feature line under simple interaction.

Optimal Evacuation Model of Parking Vehicles in Dynamic Traffic Flows

GAN Jiahua, MAO Xinhua, ZHAO Jing

2021, 56(1): 123-130. doi: 10.3969/j.issn.0258-2724.20190611

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In order to develop an effective evacuation plan for vehicles in a parking lot and achieve the shortest evacuation time, an optimal evacuation model was built by considering the dynamic traffic flow characteristics of a road network. Firstly, according to queuing theory, the vehicle queue on each exit lane of a parking lot was denoted by an M/M/1/1 queuing system, which was used to simulate how the traffic flow headway on the exit lane affects the vehicle departure rate, and estimate the queue time of the vehicles in the parking lot. Secondly, the traffic flow equilibrium model of road network nodes and link traffic flow equilibrium model were employed to imitate the path selection behavior in vehicle evacuation, and the evacuation time and delay time at intersections were estimated. Finally, a parking lot with 4 exits was selected to conduct an evacuation simulation. The results show that the traffic flow headway on the exit lane has a significant impact on vehicle queue time, travel time and evacuation time, while the optimal route choices are mainly affected by background traffic, demonstrating that the proposed model can simulate the dynamic traffic characteristics and time consumption during the evacuation process and adjust the departure rate to improve the evacuation efficiency according to the traffic flow headway.

Inclusion of Latent Class in Behavior Model of Motorized Travel in City

LIU Zhiwei, LIU Jianrong, DENG Wei

2021, 56(1): 131-137. doi: 10.3969/j.issn.0258-2724.20190945

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To study the preference heterogeneity of travel choice and the influence of psychological factors on travel behavior, the psychological latent variables that influence the travel mode choice are obtained through confirmatory factor analysis. Then, these variables are introduced into latent-class conditional Logit model, which is solved by the expectation-maximization algorithm to obtain the number of latent classes and the utility function. Finally, Guangzhou is used as an example for empirical analysis. The results show that the latent-class conditional Logit model has higher fitness than the traditional conditional Logit model. For three travelers’ groups: the metro-preference, car-preference, and bus-preference groups, which account for 42.5%, 25.0% and 32.5%, respectively. The walking time value of the metro-preference and bus-preference groups is 1.2 Yuan/min and 1.3 Yuan/min, respectively, while t the car-preference group evaluate the walking positively. The time value of the metro-preference and bus-preference groups is 0.7 Yuan/min, which is less than that of the car-preference group of 1.1 Yuan/min. Whether the monthly income is more than 10000 Yuan and whether the travelers commute by car have a significant influence on the latent class classification. Of all psychological factors, flexibility and reliability have a significant influence on the latent class classification, while comfort have no significant influence.

Sensitivity Analysis for Transit Network with Distance Effect

DU Muqing, YU Chunbin

2021, 56(1): 138-146. doi: 10.3969/j.issn.0258-2724.20190453

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In order to accurately analyze the performance of transit network, the amplification effect of distance on the travelers’ perceived travel cost is considered, and a generalized travel cost function is proposed in the sensitivity analysis of transit network. Firstly, as to the influence of distance effect, a transit network model is established. Then the problem of common bus line and the passengers' choice behaviors are coped with the hyperpath theory. Secondly, based on the equilibrium assignment of transit network, a sensitivity analysis method for transit network with distance effect is constructed in the perturbation problem of variational inequality. Finally, an example is used to analyze the changes in each arc and network performance when the transit network is affected by different factors, especially the distance. The results show that along with the demand increasing from 0 to 900 people per hour, the optimal travel strategy under the influence of distance is changed from the original single hyperpath to the multiple hyperpaths. In the identification of critical parameters, the distance factor is a sensitive parameter, which need more accurate calibration in practice. At the same level of demand, when the distance parameter changes from 0 to 0.03, the derivatives of the total travel cost to bus service frequency noticeably declines, which can be utilized for finding the region such that the total travel time is likely to reduce.

Text-Mining Based Risk Source Identification Model for Transportation Safety

LUO Wenhui, CAI Fengtian, WU Chuna, XIA Hongwen, MENG Xingkai

2021, 56(1): 147-152. doi: 10.3969/j.issn.0258-2724.20200140

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In order to solve data deficiency and excessive staff workload in the risk-source identification of road transportation safety, an automatic identification model is proposed from the angle of text mining. Firstly, the model performs feature enhancement preprocessing operation through the causality sentence extraction and extracted sentence segmentation. Secondly, the feature construction adapted to the convolutional neural network (CNN) is conducted, which contains word information and position information. Thirdly, the results of feature construction feed into the CNN to realize the identification of risk sources. Finally, experiments are conducted with the data sets of traffic accidents, demonstrating that the proposed model can identify most of risk sources for road transportation safety with the accuracy of about 77.321%.

Automatic Traffic State Recognition from Road Videos Based on 3D Convolution Neural Network

PENG Bo, TANG Ju, ZHANG Yuanyuan, CAI Xiaoyu, MENG Fanhe

2021, 56(1): 153-159. doi: 10.3969/j.issn.0258-2724.20191169

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In order to directlyextract effective traffic information from videos, a traffic state recognition method based on 3D CNN (3D convolutional neural networks)was put forward. Firstly, with the deep convolutional network C3D (convolutional 3D) as 3D CNN prototype, the number and position of convolutional layers, convolutional kernelsize and 3D convolutional depth were optimized and adjusted; thus 37 candidate models were built. Secondly, video datasets were established to systematically train and test candidate models, and a traffic state recognition model C3D* was proposed. Then, tests and analysis were conducted on traffic state recognition results of C3D* and existing 3D convolutional models. At last, traffic recognition results were compared between C3D* and commonly used 2D convolutional networks. The results show that for video traffic state recognition, the average F value of C3D* reaches 91.32%, which is 12.24%, 26.72% and 28.02% higher than that of C3D, R3D (region convolutional 3D network) and R(2+1)D (resnets adopting 2D spatial convolution and a 1D temporal convolution), respectively, demonstrating that the proposed model C3D* is more accurate and effective. Compared with image recognition results from LeNet, AlexNet, GoogleNet and VGG16, the average C3D* is 32.61%, 69.91%, 50.11% and 69.17% higher respectively, proving that 3D video convolution F value of outperforms 2D image convolution in terms of traffic status recognition.

Design of Airborne Video Dehazing System for UCAV Based on HSV Transmission Weighted Correction

WANG Jian, QIN Chunxia, YANG Ke, REN Ping, ZHENG Jie, ZHAO Yuanpeng, CHEN Guifeng

2021, 56(1): 160-167, 205. doi: 10.3969/j.issn.0258-2724.20190985

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As there is image degradation when the UCAV (unmanned combat air vehicle) captures the real-time image in the haze day, a low power-consumption system is designed on the basis of the HSV (hue, saturation, value) transmission weighted correction. First, the overall design of the dehazing system is completed, which can meet the requests of a low power-consumption and real-time image dehazing. Then, according to the needs of the video acquisition dehazing system, functions are being designed, including digital video BT.656/BT.1120 interlaced and progressive processing, video control, instruction receiving processing, TS1601 video dehazing algorithm processing, H.264 video compression processing and framing, etc. Lastly, the design and implementation are focused in terms of the system dehazing algorithm, platform design, dehazing parameter processing and other functional modules. Also this system and several other methods suggested in references are used to process typical hazy images respectively, and then evaluated after employing three definition evaluation functions (variance function, average gradient function and TenenGrad function) and normalization process. The results indicate that the design of this dehazing system has such merits as low power consumption, easy implementation, and high adaptability. After processing the typical hazy images, the variance function is increased by 46.87%, 1.44% and 12.83%, the average gradient function is increased by 12.54%, 9.26% and 11.15%, that of normalization of TenenGrad function is increased by 53.19%, 3.60% and 8.82%, respectively. The overall operation time of the test algorithm is respectively increased by 4.74 times, 5.41 times and 5.46 times.

Segmentation of Small-Field-of-Viewstar Images Based on Kittler Minimum Error Algorithm

SHI Chunlin, YANG Peizhang, ZHANG Chao, DU Lan, YE Kai, FAN Chengxiao, LI Jian, ZU Anran

2021, 56(1): 168-175. doi: 10.3969/j.issn.0258-2724.20190841

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Compared with conventional images, small-field-of-view star images are more susceptible to the impacts of uneven illumination and measurement noises. Meanwhile, the traditional threshold segmentation algorithm has poor processing effect or efficiency. In terms of the Gaussian distribution of star image gray, the Kittler minimum error segmentation algorithm was used to process star images on the basis of Bayesian minimum error theory. By the use of the video measuring robot, several commonly-used threshold segmentation algorithms and one-dimensional maximum entropy algorithm are compared and analyzed in terms of goodness methods, regional consistency, regional contrast ratio and time complexity. It is indicated that the Kittler minimum error segmentation algorithm can achieve a satisfied segmentation of the small-field-of-view star images, and improves astronomical data processing efficiency significantly withthe average computation timereduced by about 70%. Laboratory experiments for semi-simulation star map and real star mapshow that the proposed algorithm can extract star points and obtain centroid coordinates accurately,whose horizontal and vertical root mean square errors are 0.025 and 0.019 pixels, respectively. Furthermore, extensive field experiments show that the astronomical longitude and latitude calculated by the proposed algorithm can meet first-class astronomical survey accuracy requirements, whose average internal accordant accuracy is better than 0.015 s and 0.22″ respectively, and external accordant accuracy is better than 0.025 s and 0.35″ respectively.

Multi-Discipline Forward Collaborative Design Technology Based on BIM Interaction and Data-Driven

SHI Haiou, YUAN Quan, ZHANG Yunlin, ZENG Wenqu, ZHENG Qing, DING Guofu

2021, 56(1): 176-181. doi: 10.3969/j.issn.0258-2724.20200035

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In order to realize data-driven collaborative design among multiple disciplines and improve design efficiency, with the analysis of the forward collaborative design model of urban rail transits, the data-driven forward collaborative design technology is proposed for multiple disciplines. Firstly, the seven-dimensional building information model (BIM) that conforms to the characteristics of the urban rail transit is adopted. The three-dimensional design model is expressed by industry foundation class (IFC) and parsed to form the model structure tree. Then, the interactive component parameter design is completed through model interaction and data extraction. Finally, based on data-driven and collaborative information, the design parameters of collaborative components are adjusted, and the collaborative design process is completed. The case analysis shows that the data-driven forward collaborative design technology proposed in this work could effectively promote data interaction and coordination among the various disciplines of urban rail transit. It realizes the forward collaborative design among multiple disciplines, and contribute to forming an optimized design scheme and improving collaboration efficiency.

Peak-Current and Peak-Voltage Control Scheme for Single-Inductor Dual-Output Buck Converter

XU Limei, WANG Yao, ZHANG Liuyang, YANG Jiayong

2021, 56(1): 182-189. doi: 10.3969/j.issn.0258-2724.20191067

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In order to reduce the output cross regulation of single-inductor dual-output (SIDO) buck converter in continuous conduction mode (CCM), a peak-current and peak-voltage (PCPV) control method is proposed. The circuit structure and operating principle of the PCPV-controlled SIDO buck converter are analyzed. The gain expressions of input voltage and output voltage are deduced according to the principle of inductor volt-second balance and capacitor ampere-second balance. The state space average model of PCPV-controlled SIDO buck converter is established by using the state space average method. On this basis, the small signal model of PCPV-controlled SIDO buck converter is established, which is compared with traditional peak-current-mode (PCM) controlled SIDO Buck converter in the cross regulation. The research results show that the cross regulation from the higher voltage output branch to lower voltage output branch of PCM controlled SIDO Buck converter is 300 mV, and its transient regulation time of load variation is 12.5 ms. However, the proposed converter can reduce the cross regulation to almost zero and reduce the transient regulation time to 10 ms. Compared to the PCM controlled SIDO buck converter, the proposed PCPV-controlled SIDO Buck converter can effectively reduce the cross regulation and improve the transient performance. Finally, the theoretical analysis of the proposed method is verified by experimental results.

Fault Diagnosis for Track Circuit Based on Interval Type-2 Neural-Fuzzy System

WANG Zicheng, ZHANG Yadong, GUO Jin, SU Lina, YANG Jing, SONG Ci, LI Kehong

2021, 56(1): 190-196. doi: 10.3969/j.issn.0258-2724.20180983

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At present, the threshold method, despite its low efficiency, has still been used to identify the fault of track circuit on site. To handle this, an interval type-2 neural-fuzzy system (IT2NFS) was built by combining neural networks and fuzzy logic. Intelligent identification of failure modes was realized by constructing a diagnostic model. During the construction of the diagnostic model, a preliminary network structure was established through the structure identification. Uniform design method was used to generate the mean values of fuzzy sets. Then the standard deviations and initial consequent parameters were generated through performing a similarity test on training samples. At last, the optimized consequent parameters were obtained by recursive singular value decomposition to reduce the output error. For 8 common failures, a total of 9000 samples were collected from the test platform. Of them, 6300 samples were used for model training, the rest 2700 samples were used for testing. The test results show that when using the IT2NFS model for fault diagnosis, the recognition rate of each fault category was above 82%, the average correct rate was 90.9%, and the simulation time was only 10.59 s.

Power Following Control Strategy of SOC Dynamic Adjustment for Small Fuel-Cell Cars

CHEN Weirong, LI Jincheng, LI Qi

2021, 56(1): 197-205. doi: 10.3969/j.issn.0258-2724.20190552

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An SOC (state of charge)-based energy management method is proposed to dynamically adjust the power following coefficient for the small-vehicle hybrid system that consists of an air-cooled proton exchange membrane fuel cell and a lithium battery. Moreover, a hybrid sightseeing car prototype is developed. Three parts of the prototype vehicle are illustrated, i.e., the hybrid power system, hydrogen storage supply system, and signal control system. How the coefficient of the power following algorithm affects the control under different operating conditions is analyzed. By dynamically adjusting the coefficient, the SOC deviation of the lithium battery and output power fluctuation of the fuel cell in the operation of the power following algorithm is alleviated and the service life of the stack is prolonged. Through the actual running tests on the prototype vehicle, the control method was verified. The average operating efficiency of the fuel cell in operation reached 48.15%, and the theoretical maximum cruising range was 94 km, which is consistent with the practice.

Mechanism of High-Speed Railway Interference on Power Cables of Adjacent Normal-Speed Railway

XIE Shaofeng, SUN Jingdi, LUO Bingxiang, SU Peng, LI Jingwen

2021, 56(1): 206-213. doi: 10.3969/j.issn.0258-2724.20191003

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Due to high speed, large traction power and continuously receiving current in operation, high-speed railways generate obvious electromagnetic interference on the power cables of adjacent normal-speed railways. Based on the analysis of inductive coupling and resistive coupling mechanism, the interference from high-speed railways on the induced voltage of power cables was analyzed, and CDEGS software was used to establish the electromagnetic simulation model of high-speed railway interference to the power cables of adjacent normal-speed railways, and the factors affecting the induced voltage of power cables are summarized. The simulation model was verified on the basis of the calculation results. The results show that the induced voltage of power cables near high-speed railways is related to the traction load, parameters of power cable and soil structure. Of them, the parallel length, load current, soil resistivity and short-circuit current have significant influence on the induced voltage of power cables. The protection distance between high-speed railways and normal-speed railways should be set according to different cable lengths. Middle grounding and single-terminal grounding can effectively reduce the induced current of power cables.

Heat Dissipation Characteristics Analysis of Surface Air-Oil Heat Exchanger Applied in Aircraft Engine

CAI Huikun, SU Lijun, LIAO Yidai, WENG Zeju, XU Chen

2021, 56(1): 214-220. doi: 10.3969/j.issn.0258-2724.20180964

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In order to enhance aircraft engine heat transfer performance in the conditions of ground idle speed or low flying speed, a surface air-oil exchanger was presented using air inlet passage as its dissipation area. Its heat dissipation characteristics, as well as districted simulation equivalence, were investigated through the studies of 4 districted mode, 7 districted mode and the mode of using flat surface to replace arc surface. The numerical results demonstrate that temperature distributions in air side are almost the same in the cases of 4 districted mode, 7 districted mode and the mode used flat surface to replace arc surface in the simulations. All of their temperature differences are smaller than 1 K, and the discrepancies of calculated heat dissipation power are below 5%. The phenomena of heat transfer in oil side are also the same in the three cases. The research validates the feasibility and reliability of the methods of using districted simulation and using flat surface instead of arc surface where the ratio of arc length to diameter is below 0.203, when analyzing thermal characteristics of a large surface heat exchanger.

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2021 Vol. 56, No. 1