Journal of Chongqing Jiaotong University(Natural Science)

Automated Modal Identification Method in Frequency Domain Improved by AR Model Power Spectrum

YAO Xiaojun, YANG Xin

2023, 42(2): 1-7. DOI: 10.3969/j.issn.1674-0696.2023.02.01

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Aiming at the shortcomings of frequency domain decomposition method in automatic modal identification, an improved automated modal identification——AR-AFDD method in frequency domain based on AR model power spectrum was proposed. Firstly, all possible frequency points of physical mode were determined through AR model power spectrum estimation, and the corresponding power spectrum matrix was decomposed by singular value. Secondly, the selected peak value was distinguished by the correlation of time vibration mode to realize the automatic distinction between physical mode and noise mode. Finally, the damping ratio was estimated by the optimal fitting of the self-power spectrum. The AR-AFDD method was verified by the experimental model and the actual bridge respectively. The study shows that the AR-AFDD method can quickly and effectively realize the automatic identification of structural modal parameters, and the identification results can distinguish the physical mode from the noise mode, which has good reliability in the analysis of the actual structural health monitoring data.

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Improved Calculation Method of Lean Busbar Saddles Design Position of Suspension Bridge with Spatial Cables

DENG Xiaokang, LI Xiaobei

2023, 42(2): 8-12. DOI: 10.3969/j.issn.1674-0696.2023.02.02

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Based on the cable space slope as the basic parameter of cable system equation, the calculation method of design position of inclined busbar saddle of spatial cable suspension bridge was discussed. Based on the geometrical and mechanical relations between the main cable and the cable saddle of the spatial cable suspension bridge, a set of binary non-linear equations with the spatial slope of the left and right tangent points of the cable saddle as the unknown parameters were derived, and the design position of the inclined busbar saddle could be obtained by solving the equations with dichotomy method, which simplified the complicated calculation process caused by too many variables in the traditional method. Numerical examples show that the improved method has good accuracy.

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Influence of Multiple Presences of Heavy Traffic on the Reliability of Medium and Small Span Bridges

LIU Lang, YANG Hong,

2023, 42(2): 13-18. DOI: 10.3969/j.issn.1674-0696.2023.02.03

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In order to study the influence of multiple presences of heavy vehicles on the reliability of medium and small span bridges, the measured heavy load data based on the most adverse effect was extracted. The parallel probability of all vehicles and the parallel probability of heavy load were compared and calculated, and a real-time simulation method of multiple presences of heavy vehicles based on random fleet flow was proposed. Furthermore, the finite element models of T-girder bridge, box-girder bridge and hollow slab beam bridge were established respectively. Considering the influence of the random variability of material properties and section geometric dimension on structural resistance, JC method was used to calculate the reliability index of each main beam under the action of different multiple presences of heavy loads and single heavy loading in the main lane, respectively. The research results show that: the reliability indexes of girder component significantly decrease under multiple presences of heavy loads and even decrease by 40% at maximum, compared with single heavy loading, which is only 50% of the target reliability index specified in the code. Meanwhile, the multiple presences of heavy vehicles have the greatest impact on the reliability of box girder bridges. The calculated reliability index of each component is 2.3~3.7, which is 23%~40% lower than that of single vehicle.

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Vertical Random Vibration of Train-Track-Bridge System Considering Dimension-Reduced Simulation of Track Irregularity

YANG Tao1, ZHANG Xinyu1, GAO Qiankun1, WANG Lidong2, WANG Lei2

2023, 42(2): 19-27. DOI: 10.3969/j.issn.1674-0696.2023.02.04

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Based on the probability density evolution method (PDEM), the vertical random vibration of the train-track-bridge system was studied. Combined with the idea of orthogonal random function and the reconnaissance theory of number theory, a dimension-reduced method for simulation of representative samples of track irregularity was proposed. The simulation of random excitation representative samples on the level of probability density was realized through two basic random variables. Based on PDEM, the vertical random vibration equation of the train-track-bridge system was established and was verified by a numerical example. The influence of vehicle speed on the random vibration response of the simply supported beam bridge and the CRH3, CRH2 and ICE3 vehicle was discussed. The results show that under the influence of vehicle-bridge resonance, the mean value and standard deviation of the vertical displacement of the midspan of the bridge have the maximum peak value at the speed of 425 km/h; the mean value and standard deviation of the vertical acceleration of the midspan of the bridge basically increase with the increase of vehicle speed; when the main frequency of track irregularity excitation is close to the first vertical natural frequency of the vehicle, the vertical displacement response of the vehicle body is the most significant; the higher the vehicle speed, the greater the contribution of track random irregularity to the vertical acceleration response of the vehicle body.

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Repair Effect of Beam Joint Flange Combination of Steel Truss Bridge Based on Cutting Reinforcement

LI Chuanxi, JI Bohai, YAO Yue, FU Zhongqiu

2023, 42(2): 28-36. DOI: 10.3969/j.issn.1674-0696.2023.02.05

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A whole bridge model and node sub-model of simply supported steel truss bridge were established by the finite element analysis method. The correctness of the finite element model was verified by comparing the measured values with the calculated values of the finite element method of the key section vertical displacement and the axial stress of the member. The variation rules of stress intensity factors KⅠ, KⅡ, and KⅢ at the crack tip under different crack lengths were analyzed. Aimed at fatigue cracking of web gap in crossbeam joints, the maintenance effects of cutting the upper flange and angle steel reinforcement were analyzed. A combined maintenance method of cutting the upper flange of the beam end and strengthening the angle steel was proposed. The results show that the cracking mode changes from type Ⅱ-Ⅲ crack to type Ⅰ-Ⅱ-Ⅲ crack and then to type Ⅱ-Ⅲ crack during the whole process of crack propagation. The upper flange cutting method and angle steel reinforcement method have good repair effects on both type I and type Ⅱ cracks, and the combined maintenance method of the upper flange cutting and angle steel reinforcement has a good inhibitory effect on composite type cracks. In the proposed model, when the crack propagation length is less than 60% of the web gap length, the equivalent stress intensity factor at crack tip can be reduced by 60% to 90%, and the inhibiting effect is significant.

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Road Performance of Light-Colored Pavement Materials

LI Zhiyong, ZHU Shangshu

2023, 42(2): 37-43. DOI: 10.3969/j.issn.1674-0696.2023.02.06

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Two kinds of light-colored materials, light-colored stones and toughened glass cullet, were used and synthesized to design 10 kinds of light-colored paving materials. Their road performance and lighting performance of the tunnel were studied and analyzed. The results show that the road performance of pavement material with light-colored stones is equivalent to that of AC-13 bituminous mixture. The road performance of the light-colored paving material with glass decreases with the increase of the dosage, and the road performance decreases significantly when the dosage is 15%~20%. Through grey correlation analysis, it is found that the main reason that affects the pavement performance of glass light-colored pavement material is that the addition of glass makes the asphalt film on the aggregate surface thinner, and the glass material has smooth surface and poor adhesion with asphalt. In addition, through the lighting test of the self-made tunnel model, it is found that compared with the ordinary AC-13, the light-colored pavement material can significantly improve the average luminance of the road surface.

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Comparison and Conversion Study on Asphalt Pavement Technical Status Assessment Standards between China, Japan, America, and Canada

DONG Shi1,2, XU Zhuo1,2, WANG Jianwei1,2, LIN Fali3, YANG Dongtao4

2023, 42(2): 44-51. DOI: 10.3969/j.issn.1674-0696.2023.02.07

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The accurate quantification of the technical status indicators of asphalt pavement is an important basis for the accurate evaluation of the pavement service status and the formulation of scientific repair plans. At present, there are conspicuous differences in the evaluation standards for pavement status in various countries in the world, which makes it difficult to compare and convert the results. Through the detailed analysis of the current asphalt pavement technical condition evaluation standard system in China, Japan, the United States and Canada, the evaluation indexes of pavement technical conditions were compared and studied from the aspects of pavement smoothness, pavement damage and pavement skid resistance. Combined with the sample of multiple road sections, the standard systems of various countries were used to calculate the results of each evaluation index, and the results obtained by different calculation standards were converted and analyzed. The research results show that the statistical indicators of pavement performance evaluation have certain similarity in the specifications of various countries, and the statistical indicators involved in the Chinese specifications are more comprehensive. There is correlation between national norms, and some countries have strong linear correlation. The statistical concept of indicator data in Canadian norms has a great impact on the results. The result can provide a reference basis for the conversion of pavement condition evaluation index values under different standards, and provide an optional direction for the further improvement of pavement performance evaluation standards in China; meanwhile, it can promote the updating and progress of different methods and standards, and also promote the application of international advanced research results such as pavement evaluation methods, performance prediction models and restoration decision-making algorithms.

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Expansion Response of Subgrade Caused by Track-Slab Gap in Transition Section of High-Speed Railway Bridge

ZHENG Mingxin1,2,3, XIONG Lang1,3, REN Yongjiang1,3, LI Zhengyang1,3, WU Leyong1,3

2023, 42(2): 52-59. DOI: 10.3969/j.issn.1674-0696.2023.02.08

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Taking the rainfall infiltration caused by the separation of the track-slab of a certain road and bridge transition section of the Shanghai-Kunming high-speed railway as the research object, the transition section rainfall-seepage finite element analysis model was established, which was according to the topography and geomorphology of the road section, hydrogeological conditions and the data obtained from laboratory tests. The deformation characteristics and laws of the transition section between road and bridge were analyzed. The research results show that the subgrade filling of the transition section of the road and bridge has a certain degree of expansion. Under different rainfall infiltration conditions, the subgrade of the transition section will have corresponding expansion. Generally, the expansion at the near abutment is significantly smaller than that at the far abutment. The main reason for the disease of the transition section is that the infiltration of surface water and rainwater causes the subgrade to expand, and the material difference of the transition section causes uneven expansion of the subgrade along the line direction.

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Influence of Chimney Effect on Fire Spread in Cable Tunnel

WU Zhi1, ZHANG Wuchao2, WANG Lang1, PENG Jing1, LI Linjie2

2023, 42(2): 60-66. DOI: 10.3969/j.issn.1674-0696.2023.02.09

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In order to study the development process and law of cable tunnel fire in mountainous terrain, and provide the basis for the prevention and control of cable tunnel fire and the design of tunnel structure, the three-dimensional fire dynamics simulation software (FDS) was used to simulate the fire in cable tunnels with different slope sections. The laws of smoke spread, flame spread speed and temperature distribution in cable tunnel fire were analyzed. The research results show that the slope sections in cable tunnel would form chimney effect in the fire process, and then affect the development of cable tunnel fire. With the increase of the slope of the cable tunnel slope section, the high temperature area in the tunnel decreases and moves towards the side of the slope section. The slope of the tunnel has a positive correlation with the air inlet velocity at the left end of the tunnel.

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Numerical Simulation of Tunnel Shaking Table Test andAnalysis on Vibration Input Meth

LIANG Bo1,2, ZHAO Fengbing1, LIU Tao1, REN Zhaodan3

2023, 42(2): 67-74. DOI: 10.3969/j.issn.1674-0696.2023.02.10

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In view of the numerical simulation of the “model body-model box” system in tunnel shaking table test, the damping realization method of model foam boundary layer was analyzed by summarizing the dynamic finite element damping calculation method. The realization method of the bottom vibration input of the numerical model was discussed, and the calculation processes such as the large mass method and the displacement time-history input method were derived respectively. The calculation accuracy of the large mass method and the displacement time-history input method was compared and analyzed through the single-degree-of-freedom system. The advantages and disadvantages, as well as the feasibility in application of the proposed two methods were respectively analyzed. Taking the numerical calculation of a certain tunnel shaking table test as an example, the large mass method and the displacement time-history input method were respectively adopted to analyze the calculation models comparatively. The results show that the two proposed methods have similar overall accuracy in the numerical analysis of seismic action of the actual test model, but the large mass method is prone to produce cumulative displacement error.

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Dynamic Change and Evolutionary Trend in the Supply and Demand Relationship of Water Supply Services in the Three Gorges Reservoir Area

GUAN Dongjie1, SUN Lingli1, JIANG Laihan1, ZHOU Lilei2

2023, 42(2): 75-85. DOI: 10.3969/j.issn.1674-0696.2023.02.11

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As a very important ecosystem service, water supply service plays an important role in the regulation of water cycle balance and human production, life and ecology. Based on the InVEST model, the water supply in the Three Gorges Reservoir area was evaluated, and the water demand was calculated by using the water consumption indicators of population, industry and ecological agriculture. Then, the supply-demand ratio of water supply services was calculated to reveal the spatial differences in their supply-demand relationship. Finally, the factors influencing the mismatch between supply and demand of water supply services of Three Gorges Reservoir area were analyzed and its spatial autocorrelation and evolutionary trends were clarified. The results show that the total amount of water supply services in the Three Gorges Reservoir area shows decreasing firstly and then increasing slowly, with a total reduction of 1.13×1010 m3, decreasing by 19.68%. The depth of water production in the central region is greater than that in the eastern region. From 2000 to 2015, the total demand for water supply services in the Three Gorges Reservoir area has increased year by year, with a total increase of 11.37×108 m3, with a growth rate of 402.93%. The water demand decreases step by step from west to east. From 2000 to 2015, the ratio of supply to demand in the Three Gorges Reservoir area has decreased from 20.69% to 10.66%, and the supply-demand relationship has tightened year by year. There is always a significantly positive spatial correlation between the supply and demand of water supply services in the Three Gorges Reservoir area, and the agglomeration effect of supply and demand has been strengthened, which is influenced by factors such as land use, economic structure, water resources conditions and climatic precipitation. To maintain the balance of regional water resources, it is necessary to rationally allocate production, living and ecological water to reduce the impact of the mismatch between supply and demand.

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Design and Optimization of Signalized Intersection of Asymmetric Traffic Flow with Shifted Left-Turn Lanes

LIU Xiaojia1,2，LI Zimu1,2

2023, 42(2): 86-92. DOI: 10.3969/j.issn.1674-0696.2023.02.12

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The conventional traffic organization and signal control are not ideal for handling asymmetric traffic flow, which can cause waste of travel time and road resources. In view of the characteristics of asymmetric traffic flow, the signal control optimization scheme of asymmetric traffic flow intersection with shifted left-turn lane is proposed. With the objective of minimizing the delay of both straight and left-turn vehicles, a model for optimizing the spatial and temporal resources of the shifted left-turn intersection and a model for calculating the vehicle delay are established. Experiments were designed to study the effect of traffic flow asymmetry and the length of the shifted turn lane on the delay of left-turning vehicles, to analyze the adaptation of asymmetric traffic flow to the shifted left-turn lane, and to simulate the optimization scheme using VISSIM software. The simulation results show that: compared with the status quo of the intersection, the average delay of vehicles in Scheme 2 is reduced by 27.2% and the average queue length is reduced by 29.7%, which indicates that the signal control scheme of shifted left-turn lane can greatly improve the driving conditions of vehicles at the intersection of asymmetric traffic flow, reduce the average delay time of vehicles and make the traffic flow run more smoothly.

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Path Optimization Model in Vehicle Storage and Retrieval System of Horizontal Circulating Three-Dimensional Garage Based on Improved Dijkstra Algorithm

ZENG Chao1,2, CUI Zihao1

2023, 42(2): 93-98. DOI: 10.3969/j.issn.1674-0696.2023.02.13

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In order to shorten the running time of vehicle access and the average waiting time of users in the horizontal circulating three-dimensional garage, an optimization model of the vehicle access path was proposed, which improved Dijkstra algorithm. Based on the working logic of vehicles access in horizontal circulating three-dimensional garage, the queuing model of three-dimensional garage was established on the basis of constructing the running time model of vehicle access path. Taking the average queue length and waiting time of vehicles as evaluation indexes, the bi-directional sector dynamic Dijkstra algorithm was introduced for optimization in terms of search direction, search range and dynamic node changes. The research results indicate that compared with the traditional Dijkstra algorithm, the improved Dijkstra algorithm improves the search efficiency of the target node and can make up for its lack of dynamic search ability. And the shortest path between the source node and the target node is output, which can effectively shorten vehicle access time and the average waiting time of the user, and improve the service efficiency of the horizontal circulating three-dimensional garage.

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Traffic Capacity of Urban Road Signalized Intersection Work Zone

SHAO Changqiao, WANG Fengjiao

2023, 42(2): 99-105. DOI: 10.3969/j.issn.1674-0696.2023.02.14

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In order to improve the efficiency of traffic organization and management in the work zone of the intersection, the characteristics of traffic flow and the influencing factors of traffic capacity were studied. The characteristics of the parameters such as headway, speed, starting delay time and saturation flow rate in the work zone of the intersection were analyzed by using the measured data. Through comparative analysis, it is found that under construction conditions, the saturation flow rate of straight lane decreases by about 18.9%, and the starting delay time increases by about twice. Based on the measured data, the recommended saturation flow rate of the straight lane in the work zone of the signalized intersection is 1 400 ~1 500 pcu/h, and the recommended saturation flow rate of the left-turn lane is 1 300 ~1 400 pcu/h. Based on the measured and simulated methods, the conversion coefficient of large vehicles in the work zone of the signalized intersection and the correction coefficient of the influence of the mixing ratio of large vehicles on the traffic capacity of the work zone are given, and the influence of the bus stops and lane markings on the traffic capacity is analyzed.

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Evolution of the Competition-Cooperation Relationship between Urban Rail Transit and Conventional Bus Based on the Improved Lotka-Volterra Model

HAN Baorui, PU Haijian, ZHU Zhenjun

2023, 42(2): 106-112. DOI: 10.3969/j.issn.1674-0696.2023.02.15

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In view of the competition-cooperation relationship between rail transit and conventional bus and its development and evolution, combined with the ecological characteristics of the development of the two transportation modes, an adaptive inter-modal competition evolution model was established based on the Lotka-Volterra model of interspecific competition. Through the stability analysis of the equilibrium state of the proposed model, the internal dynamic mechanism of the evolution of the two traffic modes and the evolution path of different equilibrium states were discussed. Taking Shanghai, Nanjing and Xi’an as examples, the feasibility and applicability of the improved model were verified. The research results show that: compared with the standard Lotka-Volterra model, the improved model is closer to the evolution of actual competition between rail transit and conventional bus. The relative errors of the simulation data of Shanghai, Nanjing and Xi’an are reduced by 2.96%, 17.51% and 29.39% respectively. In different traffic environments, the two modes of transportation have different co-opetition effects, causing factors such as competition coefficients to fluctuate, which in turn affects the evolution of the competitive evolution between the two modes of transportation, and makes equilibrium state mutate and transit to a new, more coordinated and orderly state of equilibrium.

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Accident Injury Severity of Two-Wheel Driver with Multi-injury Body Regions

ZHU Tong1, ZHU Zishuo1, LIN Miao2, JING Yunchao1

2023, 42(2): 113-120. DOI: 10.3969/j.issn.1674-0696.2023.02.16

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Previous studies on accident consequences of two-wheeled vehicle accidents mainly focused on discussing the overall injuries of cyclists, while few studies focused on the injuries of specific body parts of cyclists. In order to reveal the correlation and cause of injuries of various body parts, the injury severity of seven main parts such as the head, chest, upper and lower limbs of the two wheel (TW) driver were addressed as the dependent variables, and 44 main independent variables were selected to represent the pre-crash behavior, crash position and other information, which was based on 2799 two-wheeled vehicle accidents sourced from the China in-depth accident study (CIDAS) data. A multivariable model with random parameters was used to better explain the relationship between the severity of each injury site and the heterogeneity that was not observed in the data. The results show that the gender and age of TW driver, TW vehicle characteristics, TW driving behaviors prior to crash and TW collision positions will have a significant impact on the injuries of different parts of TW driver. The head, chest and lower limbs are proven to be three most vulnerable parts during TW crashes, which deserve further study. The middle-aged TW driver is a random parameter obeying normal distribution in the head injury model, indicating that the middle-aged TW driver will have heterogeneous effects on the severity of head injury of TW driver. It is extremely necessary to strengthen the safety design of cars and two-wheeled vehicles to protect the chest and abdomen of two wheeled cyclists. Wearing helmets can not only protect head from injuries, but also play an important role in protecting from upper limb injuries.

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Visual Characteristics of Large Truck Drivers on Small Radius Curved Slope Section Based on Natural Driving Test

HUANG Pingwen1, XIA Haojie2, YU Biao1, LIU Xingliang3, LIU Tangzhi3

2023, 42(2): 121-127. DOI: 10.3969/j.issn.1674-0696.2023.02.17

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A natural driving test of large truck and car drivers on the small radius curved slope section of the G246 highway in Guizhou Province was carried out. Based on Begaze software and statistical methods, the relationship between the distribution characteristics of two types of drivers gaze points and the turning direction, radius, and slope of the small radius curved slope section was analyzed, and the relationship among the pupil diameter, information acquisition ability and speed of drivers when turning left and right was studied. The research results show that the drivers of large trucks mainly focus on the area 15~25m in front of the vehicle when driving in the small radius curved slope section and pay insufficient attention to the vehicles behind. The car driver will pay attention to the farther area, the direction of the oncoming vehicles and the alignment of the road. Steering and curve radius are the main factors affecting the drivers gaze points. When turning left and right, the driver mainly focuses on the central marking of the road and the right side line of the road. Emphasis should be placed on enhancing the effectiveness of visual guidance in curved slope sections with radius less than 30m. The peak position of pupil diameter and information acquisition ability of large truck drivers when turning does not coincide with the center of the curve, therefore, the existing treatment measures of setting the convex mirror and other suggestive facilities in the center of the curve are not suitable for large trucks.

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Control Method of Vehicle Adaptive Cruise System Based on Natural Driving Data

LI Wenli, QIAN Hong, SHI Xiaohui, LI Chao

2023, 42(2): 128-135. DOI: 10.3969/j.issn.1674-0696.2023.02.18

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In conventional adaptive cruise control system based on model predictive control algorithm, the comfort constraint was in the form of fixed acceleration. The problem of range of acceleration extremes at different speeds was not considered in depth, which would lead to excessive changes in system acceleration and impact in the pursuit of safety and speed following, thus reduced the comfort of driving and riding. The NGSIM natural driving data set was used to obtain the speed-acceleration relationship of the vehicle, which was used as the constraint object of acceleration. The constant constraint of the conventional model predictive control was changed to the variable constraint following the change of speed, to improve the following comfort based on natural driving data. The rationality of the proposed method was verified by simulation test. The research results show that the proposed method can make the acceleration and impact fluctuation of ACC system smaller while ensuring safe following and speed following. Compared with the model predictive control with constant acceleration constraint, the maximum impact decreases by 14.96%, which effectively improves the comfort of ACC system.

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High-Speed Lane-Change Stability of the Tractor-Semitrailer Based on the Model Predictive Control

XU Xiaomei, WANG Yuting, CAI Haohao

2023, 42(2): 136-143. DOI: 10.3969/j.issn.1674-0696.2023.02.19

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In view of the lateral stability problem under high-speed lane-change conditions for the tractor-semitrailer, the model predictive controller was designed based on the five-freedom vehicle referenced model and the vehicle model in the Trucksim software. And the selection rules of differential braking target braking wheels were formulated. The effectiveness of the designed control system was verified through simulation tests under the conditions of high-speed single lane-change and double lane-change maneuvers. Research results show that the designed control system can make the tractor-semitrailer have better lane-change stability under the condition of single lane-change or double lane change maneuvers. Under the condition of high-speed single lane-change for the controlled tractor-semitrailer, the peak values of the centroid sideslip angles, the yaw rates and the roll angles have decreased in varying degrees, the time for each state parameter to reach the steady state is obviously shortened and the lateral swing motion of the vehicle during lane changing is obviously suppressed. Under the condition of high-speed double lane-change, the controlled tractor semitrailer avoids the dangerous rollover motion suffered by the uncontrolled tractor-semitrailer, completes the high-speed double lane-change motion safely and smoothly, and improves the high-speed lane-change stability of the tractor-semitrailer.

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Resistance Prediction of Yacht Based on CFD and Profile Deformation of Bulbous Bow

YANG Jingdong, ZHAO Deng, PENG Wei, HUANG Yuntao

2023, 42(2): 144-148. DOI: 10.3969/j.issn.1674-0696.2023.02.20

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Aiming at the optimization of bulbous bow shape of yacht, a ship shape optimization method was established by use of the optimization platform composed of CAESES and SHIPFLOW software. Taking the yacht with a length of 49m as the mother ship, the three-dimensional model of the main hull was established. The relevant hydrodynamic calculation module was realized by SHIPFLOW software, and the optimal ship type of resistance was obtained through comparative calculation. The bulbous bow deformation module realized the automatic transformation of ship shape through CAESES software parametric deformation technology. With the wave making resistance as the optimization goal, the best ship shape of total resistance was obtained through the optimization algorithm and the total resistance calculation program. The optimization results show that for the yacht, the new bulbous bow shape with reduced resistance can be obtained by the proposed method under the condition of meeting engineering constraints.

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