交通运输工程学报

Advances on molecular simulation technique in asphalt mixture

WANG Hai-nian, DING He-yang, FENG Po-nan, SHAO Lin-long, QU Xin, YOU Zhan-ping

Abstract: The basic principle, implementation method and simulation procedure of molecular simulation technique were analyzed.Two main methods of asphalt molecular model construction were researched.Asphaltene structure models in different periods and aggregate models in different occasions were summarized. The problems about asphalt diffusion process, modifier effect on asphalt performance, asphalt-rejuvenator integration, asphalt-aggregate interface simulation factors and adhesion properties were explored.The future research direction of molecular simulation technique in asphalt mixture was discussed. Research result shows that molecular simulation technique can explore the performance change and internal mechanism of road materials from micro-scale, laying the foundation for accurate design and quantitative analysis. Multiple components asphalt model is an important method for asphalt molecular model construction.The construction method characterizes the physical and chemical properties of asphalt. The main construction method for aggregate models is to select and build unit cell according to aggregate chemical composition, to represent the characteristics of aggregate in the macroscopic view.Molecular simulation technique shows the asphalt diffusion process and studies the internal components diffusion rate.Molecular simulation technique analyzes the process of asphalt self-healing behavior and proposes different indicators to characterize the healing rate of each stage. Molecular simulation technique can explain the influences of asphalt internal components and additives on asphalt performance from micro-scale.In terms of asphalt-rejuvenator fusion, molecular simulation technique can characterize diffusion depth, incorporation timing and rejuvenation theory. In terms of asphalt-aggregate interface, molecular simulation technique can characterize the influences of the factors such as chemical compositions, loading mode, model parameters and interface contact.The factors such as water, temperature and aged asphalt will have an important influence on the interface behavior. Moisture model can link microscopic simulation with macroscopic experiment.More>

2020, 20(2): 1-14. doi: 10.19818/j.cnki.1671-1637.2020.02.001

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Application status of steel slag asphalt mixture

HE Liang, ZHAN Cheng-yang, LU: Song-tao, GAO Jie, XIE Jun, , LING Tian-qing

Abstract: The physical properties, chemical composition and mineral phases of different steel slags were summarized. The factors that affect the volume stability and improvement measures were analysed. The mix design method for steel slag asphalt mixtures was discussed. The road performance(high temperature stability, low temperature crack resistance, moisture susceptibility, fatigue resistance, volume stability, and skid resistance) and functional characteristics(conductivity and microwave heating ability) of steel slag asphalt mixture were all investigated. The benefits of steel slag asphalt mixtures in ecology, society and economy were studied, and the engineering applications at home and abroad were introduced. Research result indicates that certain steel slag can be used for asphalt mixtures, and the steel slag for asphalt mixtures should be the basic oxygen furnace and electric arc furnace aged for more than half a year. The steel slag has excellent physical and mechanical properties, whilst the chemical composition and mineral phase composition are different for each slag type and affected by the steel making process. The lack of volume stability of steel slag can be improved with a pre-treatment or aging treatment. The key points of mix design of steel slag asphalt mixture include the mode and proportion of steel slag that can replace traditional aggregates, the gradation correction of asphalt mixture, the determination of effective relative density and the optimum asphalt-aggregate ratio. The pavement performances and functional properties of steel slag asphalt mixtures are better than those of natural aggregate asphalt mixtures. The use of steel slag asphalt mixture is of benefit to the environment and saves cost.The research on the road performance of steel slag asphalt mixture is additional, but the mechanism of action is relatively lacking. The key limiting factors such as the large density, poor volume stability, and the increasing amount of asphalt mixture have not been fundamentally resolved. In the future, the long-term performance and quality control system of steel slag asphalt pavement should be researched, and the whole life cycle research should be carried out to accelerate the application and promotion of steel slag asphalt pavement.More>

2020, 20(2): 15-33. doi: 10.19818/j.cnki.1671-1637.2020.02.002

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Evolution characteristics of flexural fatigue performance of dense concrete consolidated with high frequency vibration applied in airport pavement

QUAN Lei, TIAN Bo, LI Si-li, HE Zhe, HE Kai-han

Abstract: To verify the reliability of slip-form paving technology with high frequency vibration and its influence on the evolution characteristic of flexural fatigue of dry concrete containing large diameter aggregates(maximum to 40 mm), two 40 cm-thick concrete pavement slabs were constructed adopting the small machine construction process(low frequency vibration) and slip-form construction technology(high frequency vibration), respectively, at Xinzheng Airport, Zhengzhou. The flexural tensile strength and fatigue tests were conducted on the specimens(both dimensions are 150 mm×150 mm×550 mm) cut on the field and prepared in the laboratory with the same mixture proportion. The strains and vertical deflections at the mid span bottom of beam were measured. The flexural fatigue life probability distribution characteristics of concrete beams consolidated with different methods were analyzed according to the reliability theory, and the flexural fatigue equations were established. The deteriorations of flexural moduli of specimens and the evolutions of residual strains at the mid span bottom of beam were analyzed as well. Research result shows that the high frequency vibration technology consolidates the concrete denser, and the average fatigue life of specimens is about 27% longer than that consolidated with low frequency vibration. The double logarithmic fatigue equation can well characterize the fatigue behavior of pavement concrete containing large-diameter aggregates. The fatigue life of concrete consolidated with high frequency vibration is 4% longer than that consolidated with low frequency vibration at high stress level, while the fatigue life of concrete consolidated with high frequency vibration is 18% longer than that consolidated with low frequency vibration at low stress level. The flexural tensile modulus of concrete deteriorates linearly with the increase of loading cycle ratio. The flexural tensile moduli of specimens at the failure point are 50%-80% of the initial moduli. The axial residual strain at the bottom of beam increases with the accumulation of loading cycles. The four proposed typical evolutionary morphologies can characterize the complex growth trends of concrete residual strains at different stress levels. The increase of aggregate size mainly leads to the dispersion of the evolution rule of specimen's fatigue performance. The cumulative damage and gradually failure of aggregates under the fatigue load are responsible for the typical step characteristics in the concrete residual strain evolution curves. The research results provide a foundation for the establishment of relation function between the laboratory test and the full scale concrete pavement slab on the field, through the full scale ring track acceleration loading test.More>

2020, 20(2): 34-45. doi: 10.19818/j.cnki.1671-1637.2020.02.003

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Dynamic properties of fused silica sand based on dynamic triaxial test

WEI Ping, BAO Ning, WEI Jing, CHEN Jian-feng

Abstract: To investigate the dynamic deformation and strength of fused silica sand in the process of liquefaction under vibration load, and promote the application of transparent soil technology in the dynamic characteristics visualization model test of geotechnical engineering, the dynamic triaxial tests on the saturated fused silica sand specimens with typical sizes(0.5-1.0 mm) forming the skeleton structure of transparent sand were carried out. The cumulative axial strain, development mode of dynamic pore pressure, attenuation of dynamic stress, and change rules of dynamic elastic modulus and damping ratio of fused silica sand specimens under the working conditions of different confining pressures, loading frequencies and dynamic stress ratios were studied, and the test results were compared with those of standard sand with the same gradation. Analysis result shows that the cumulative axial strain of fused silica sand changes from a stable type to a destructive type with the increase of dynamic stress ratio. The critical dynamic stress ratio is 0.150-0.175 as the loading frequency ranges from 0.5 Hz to 1.5 Hz, which is less than that of standard sand of 0.200-0.225. Increasing the confining pressure and dynamic stress ratio and decreasing the loading frequency will accelerate the accumulation of plastic strain of specimen and shorten the liquefaction failure time. With the increase of confining pressure, the development mode of pore pressure gradually changes from the Seed model to the exponential model. Increasing the dynamic stress will increase the vibration amplitude of pore pressure after the liquefaction failure. Under the same dynamic stress ratio, the dynamic stress changes of fused silica sand and standard sand are linearly correlated with the dynamic strain. When the confining pressure is greater than 200 kPa, the dynamic stress attenuation amplitude decreases with the increase of confining pressure. The relationship between dynamic elastic modulus and damping ratio is linear. The dynamic elastic modulus decreases hyperbolically with the increase of dynamic strain and increases as the confining pressure increases. The damping ratio increases first with the increase of dynamic strain and then basically stabilizes at 0.22, and its development curve is less affected by the confining pressure.More>

2020, 20(2): 46-54. doi: 10.19818/j.cnki.1671-1637.2020.02.004

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Safety evaluation model of excavating rock slope based on entropy-grey correlation method

FENG Zhong-ju, ZHU Yan-ming, GAO Xue-chi, LONG Hou-sheng, WANG Fu-chun, ZHAO Rui-xin, WEN Jun-qiang, WANG Gui-jun, WANG Zheng-bin

Abstract: According to slope stability evaluation system, five evaluation indexes, such as slope rock mass quality score, excavation method adjustment coefficient, height correction coefficient, structural surface adjustment coefficient, and structural surface adjustment value, were selected to reflect the overall stability of slope, and serve as the safety evaluation model sequence variables. The entropy weight-gray correlation safety evaluation model was established. Taking the target slopes as the system characteristic sequence and the 12 rock slopes as the correlation factor sequence, the safety of the typical rock slopes along the reconstruction and expansion project of Beijing-Shanghai Expressway was evaluated, and the engineering advices were provided. FLAC3 D simulation software was used to analyze the stability variation laws of the slopes under different stages of mechanical excavation and static blasting at different blastholes, and the accuracy of the safety evaluation model was verified. Analysis result shows that the evaluation indexes of the slope stability can well reflect the slope stability characteristics. The entropy weight-grey correlation safety evaluation model full plays the advantages of grey correlation method in the analysis of small sample data, and the index weights calculated by entropy weight method improve the defect of the traditional grey correlation analysis that the indexes are weighted by experts or average method, making the evaluation result more objective. The third-grade and first-grade slope excavations reduce the safety factor of the slope K593+260~K593+555 to 1.01 and 1.00, respectively, with decreases of 34.8% and 9.1% respectively compared with the upper grade slope. It shows that the excavation of rock slope with gently inclined bedding slope will cause rock layer slide along structural plane and makes the slope become unstable. Transients dynamic load and load accumulation effect control the stability of the slope under static blasting condition. The occurrence of transients dynamic load reduces the slope safety factor by 7.7%, and the dissipation of the load accumulation effect rises the safety factor by 3.6%. It shows that the blasting has obvious loosening effect on the slope, and the dissipation of load accumulation improves the slope stability.More>

2020, 20(2): 55-65. doi: 10.19818/j.cnki.1671-1637.2020.02.005

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Anti-overturning capacity of straddling monorail vehicle based on factor model

WANG Chao-ran, JI Yuan-jin, REN Li-hui

Abstract: Aiming at the characteristic that factors affecting the anti-overturning capacity of straddling monorail vehicle are numerous and complicated, a comprehensive evaluation method of vehicle anti-overturning capacity was proposed, and the sensitivities of influencing parameters were analysed based on the thought of dimensionality reduction. From the definitions of height of buoyancy center, flexibility coefficient and critical roll angle, the calculation methods for the three indexes of straddling monorail vehicle were deduced, and the differences of three indexes were discussed. Thirteen quantifiable anti-overturning factors were comprehensively proposed. Based on the test and simulation data, the anti-overturning factor model of straddling monorail vehicle was built, and the five main factors and influence weights of parameters were calculated. The anti-overturning coefficient was proposed to comprehensively evaluate the anti-overturning capacity of straddling monorail vehicle, and its convenient calculation method was obtained. The vehicle-track parameterized dynamics model was established based on the multibody dynamics software Universal Mechanism to verify the accuracies of parameter weights and evaluation indexes. Research result indicates that the height of buoyancy center, flexibility coefficient and critical roll angle of straddling monorail vehicle can reflect the anti-overturning capacity of vehicle to some extent, but they cannot reflect the parameter sensitivity. The contact state between the stabilizing wheel and the track beam surface significantly affects the anti-overturning capacity of straddling monorail vehicle. When one side of the stabilizing wheel departs from the track surface, the anti-overturning capacity of vehicle decreases by about 50%. The five main factors affecting the anti-overturning capacity of vehicle are the stabilizing wheel, the second suspension, the lateral span, the first suspension and the car body. Reducing the vertical position of stabilizing wheel and the centroid position of car body and increasing the pre-load of horizontal wheel and the lateral span of running wheel, can effectively improve the anti-overturning capacity of straddling monorail vehicle.More>

2020, 20(2): 66-76. doi: 10.19818/j.cnki.1671-1637.2020.02.006

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Mathematical model of ship motions in regular waves based on Froude-Krylov force nonlinear method

ZHANG Teng, REN Jun-sheng, MEI Tian-long

Abstract: To accurately predict the ship motions in regular waves, the adaptive mesh method based on the quad-tree division was proposed to generate the instantaneous wet hull surface. The Froude-Krylov(F-K) force and hydrostatic restoring force were calculated on the instantaneous wet hull surface. For the F-K force fluctuating violently at the wave profile, the quad-tree division method was adopted to further divide the panels interacted with the wave profile. Based on the linear theory, the perturbation forces were calculated on the mean wet hull surface by using the instantaneous free surface Green function. To avoid the serious numerical error caused by the violent fluctuation of instantaneous free surface Green function near the free liquid surface, the waterline integral term of boundary integral equation satisfied by the perturbation potential was excluded. The numerical computation was carried out for the Wigley Ⅰ hull with a forward speed against waves at a Froude number of 0.2. Calculation result shows that for the hull under the instantaneous wave profile, the quantity of panel required by the F-K force nonlinear method is less, being 1/4-1/8 of the fine mesh method. Except for irregular frequencies, the relative errors of hydrodynamic coefficients obtained by the methods with and without waterline term are less than 33.4% and 54.8%, respectively, comparing with the experimental result. Therefore, the hydrodynamic coefficient computational result obtained with the waterline term is closer to the experimental result. When the incident wave amplitude is 0.018 m, and the ratio of wave length to ship length is 1.25, the pitch response amplitude operators obtained by the F-K force nonlinear method and the linear method are 3.2% and 17.0%, respectively, lower than the experimental value. When the ratio of wave length to ship length is 2.00, the pitch response amplitude operators obtained by the F-K force nonlinear method and the linear method are 6.7% and 13.5%, respectively, lower than the experimental value. Thus, the F-K force nonlinear method can accurately simulate the ship motions in regular waves.More>

2020, 20(2): 77-87. doi: 10.19818/j.cnki.1671-1637.2020.02.007

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Grey box identification modeling for ship maneuverability based on single parameter self-adjustable RM-GO-LSVR

MEI Bin, SUN Li-cheng, SHI Guo-you, MA Wen-yao, WANG Wei

Abstract: To realize the identification modeling of ship maneuverability when the rudder angle is small and the test data were less, a grey box model for the ship maneuverability motion was put forward. The mathematical ship motion models with foregone hydrodynamic coefficients were collected as the alternative reference models(RM). The correlation coefficients between the identified ship and the alternative RMs were calculated to select the appropriate RM. The similitude regulation was applied to map the measurement data to the input range of RM and to build the motion relationship between the identified ship and the RM, and the accelerations of RM were acquired. The linear support vector regression(LSVR) machine was used to compensate the acceleration error between the identified ship and the RM. The mechanism model was analyzed, the suitable LSVR inputs were designed, and the global optimization(GO) algorithm was used to automatically adjust the insensitive band parameter of LSVR. The grey box model was trained by the data of free running model test, and the results were compared with those of the captive model test(CMT) and the computational fluid dynamics to validate the generalization ability and prediction accuracy. Research result shows that for the zigzag test with 20° heading angle and 20° rudder angle, the prediction accuracy of the first overshoot angle from the grey box model is at least 1° higher than those of CMT, virtual captive model test(VCMT) and RM method. The prediction accuracy of the second overshoot angle from the grey box model is at least 0.4° higher than those of CMT and VCMT. For the turning circle test with 35° rudder angle, the prediction accuracy of advance from the grey box model is at least 1% higher than those of CMT, VCMT, numerical circulating water channel test(NCWCT) and RM method. The prediction accuracy of tactical diameter from the grey box model is 4% less than that of CMT, and is 10% higher than that of NCWCT. The RM method is benefited for the grey box modeling. The GO algorithm can optimize the insensitive band parameters of LSVR. The established grey box method with self-adjustable single parameter can realize the identification modeling for the ship maneuverability with small rudder angle and less test data.More>

2020, 20(2): 88-99. doi: 10.19818/j.cnki.1671-1637.2020.02.008

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Evolution of air traffic control system of Chinese civil aviation

ZHAO Yi-fei, XIAO Tong-tong, WAN Jun-qiang

Abstract: In order to research the evolutionary characteristics of air traffic control(ATC) of Chinese civil aviation, an evaluation index system of ATC development was established. The data of 8 indexes, including aircraft number, transport aircraft number, passenger number, passenger turnover, route number, destination city number, total turnover of air traffic, and accident number, were collected during 1950-2018. Two redundant indexes were excluded by conducting correlation analysis, the retained 6 indexes were standardized, the entropy method was used to calculate the weight of each index, finally, dimensionless data were obtained. The dimensionless data were analyzed by Fisher cluster algorithm, and the time points which divide the evolutionary stages were obtained, and the evolution process of ATC was divided into 6 stages. Through the collection of major events in the development of civil aviation in China, the results of quantitative analysis were adjusted. Analysis result shows that the development of ATC in China can be divided into 7 stages, and every stage has its own development characteristics. After the seven stages of development and evolution, China has formed a military and political condominium state ATC system, including the three-level operation management system headed by the Air Traffic Management Bureau of CAAC, the three-level government supervision system headed by the Air Traffic Regulation Office of CAAC, and the civil aviation ATC technical system based on the International Civil Aviation Organization standard. The civil aviation ATC has been developed by both the management system and the technical system. A new generation of integrated ATC system should be established through the new management system and technical system. The intensive degree of the system should be improved, and the responsibility of avoiding collision should be gradually transferred from the ground controller to the aircraft or the pilot.More>

2020, 20(2): 100-120. doi: 10.19818/j.cnki.1671-1637.2020.02.009

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Multi-objective optimization of flight-gate assignment based on improved genetic algorithm

YU Chao-jun, JIANG Ju, XU Hai-yan, ZHU Ping

Abstract: In order to improve the resource utilization efficiency and passenger transfer experience of modern airports, the multi-objective flight-gate assignment problem was studied. Considering the constraints of flight type, aircraft body type and transition time interval, a multi-objective nonlinear 0-1 integer planning model of the flight-gate assignment was established by taking the maximum number of flights allocated at a fixed gate, the minimum number of used fixed gates and the minimum passenger transfer tension as the objective functions. Then a genetic algorithm based on the improved gene coding was designed to improve the solving efficiency of the model. The gene individual adopts two-stage integer coding, and the mapping process from the gene coding method to a feasible solution was designed. Meanwhile, it was theoretically proved that the gene coding method could be mapped to the optimal solution. Different crossover operators and mutation operators were designed for the two stages of gene coding to avoid infeasible individuals. In order to verify the effectiveness of the algorithm, based on the actual operation data of a large-scale airport, the improved genetic algorithm and MATLAB built-in genetic algorithm were compared. Calculation result shows that with the improved genetic algorithm, the number of flights assigned to the fixed gates increases by 5%, the total transfer tension of passenger decreases by 3%, the average transfer tension of passenger decreases by 32%, the number of used fixed gates stays the same, the passengers assigned to the fixed gates increase by 20%, and the running time of the algorithm reduces by 8%, which shows that the improved genetic algorithm has better performance and can improve the gate utilization efficiency and passenger transfer comfort. In the optimization process of the improved genetic algorithm, the number objectives of flights and gates reach the best in 130 iterations, the transfer tension basically converges after 400 iterations, and the flight schedule generated by the optimal solution is reasonable, which indicates that the algorithm has fast iterative convergence speed and reasonable optimization result.More>

2020, 20(2): 121-130. doi: 10.19818/j.cnki.1671-1637.2020.02.010

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Research review on public acceptance of autonomous driving

TANG Li, QING San-dong, XU Zhi-gang, ZHOU Hou-qing

Abstract: The relevant studies in the field of public acceptance of autonomous driving were comprehensively sorted out and summarized. The connotation of acceptance was defined and explained from five aspects such as the possibility and attitude on accepting the autonomous driving, degrees of understanding and trust, perception and focus, willingness to pay and use preference. The data collection and analysis methods used in the existing researches were compared and analyzed from the aspects such as the survey object selection, questionnaire design, survey and sampling schemes, modelling and data analysis methods. The key factors impacting the public acceptance of autonomous driving were summarized. The influences of key factors on the public acceptance were analyzed. The problems and future research directions were pointed out. The research result indicates that most of the existing studies focus on the problems of accepting possibility of autonomous driving, attitude and use preference. The research relating to the willingness to pay is relatively rare. The public is generally positive about the autonomous driving, and have certain knowledges of autonomous driving technology and its related functions. The safety issue is people's primary concern for the autonomous driving, while the concern degrees are significantly different among various groups. People's willingness to pay extra money to enjoy the autonomous driving technology is not strong enough. The willingness to pay of respondents from developed countries is generally lower than that from developing countries. The personal psychological and physiological attributes, social demographic attribute, ethics, legal responsibility and vehicle safety level and related attributes, vehicle automation level and related attributes, travel-related attributes and environmental factor are several key factors influencing the public acceptance of autonomous driving. However, the quantitative analysis on the factors such as ethics and legal responsibility in existing researches is still lacking. The effects of some key factors such as gender, age and income level are still controversial, and further discussion is needed. In-depth research is needed in the aspects of sample representative analysis, refined design of questionnaire and survey, and analysis of specific mechanisms of key factors.More>

2020, 20(2): 131-146. doi: 10.19818/j.cnki.1671-1637.2020.02.011

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Dynamic trajectory planning and tracking control for lane change of intelligent vehicle based on trajectory preview

NIE Zhi-gen, WANG Wan-qiong, ZHAO Wei-qiang, HUANG Zhen, ZONG Zhang-fu

Abstract: To obtain the control for lane change of intelligent vehicle in the actual dynamic traffic environment, the dynamic trajectory planning and tracking control strategy for the lane change of intelligent vehicle based on the trajectory preview was proposed. Aiming at the speed and acceleration changes of vehicles in the target lane in the actual traffic environment, a dynamic planning algorithm for the lane change trajectory of intelligent vehicle was proposed. The maximum longitudinal length of lane change trajectory of intelligent vehicle was obtained to avoid the collision. The optimization objective function considering both the lane change efficiency and the passenger comfort was designed to obtain the real-time dynamic optimal lane change trajectory within the maximum longitudinal length of lane change trajectory. The humanoid steering control method combining the trajectory preview feedforward with the state feedback was used to achieve the optimal controls of dynamic trajectory tracking and passenger comfort for the lane change of intelligent vehicle, and the proposed control strategy was verified on the hardware-in-loop test bench. Research result shows that under the constant speed condition, the lateral displacement and heading angle deviations between the actual and reference trajectories and the maximum lateral acceleration are 1.4%, 4.8% and 0.59 m·s^-2, respectively. Under the constant acceleration condition, the lateral displacement and heading angle deviations between the actual and reference trajectories and the maximum lateral acceleration are 1.1%, 4.6% and 0.48 m·s^-2, respectively. Under the intense condition of variable acceleration, the lateral displacement deviation between the actual and reference trajectories and the maximum lateral acceleration are 1.7% and 0.80 m·s^-2, respectively, and the heading angle can quickly re-track the dynamic trajectory heading angle after the overshooting. Therefore, in the actual traffic environment, the proposed control strategy can well track and control the dynamic lane change trajectory of intelligent vehicle under the conditions that the vehicles in the target lane are in the constant speed, constant acceleration, and variable acceleration. Thus, it can realize the optimal lane change of intelligent vehicle, avoid collisions with vehicles in the target lane during the lane change process, and take into account both the lane change efficiency and the passenger comfort.More>

2020, 20(2): 147-160. doi: 10.19818/j.cnki.1671-1637.2020.02.012

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Packet scheduling scheme for energy-delay tradeoff in self-powered roadside units

DAI Liang, ZHAI Yi-ming, WANG Gui-ping

Abstract: Considering the randomness of energy harvesting, vehicle arrival and vehicle speed in the process of self-powered roadside units' packet transmission, the packet scheduling system was modeled as a constrained Markov decision model to analyze the average packet transmission delay and energy consumption. The optimization problem of the minimum packet average transmission delay under the constraint of energy queue was analyzed, and packets scheduling scheme for energy-delay tradeoff in self-powered roadside unitswas proposed. The performance of the optimal packet scheduling scheme was analyzed by simulation experiments, and compared with the greedy bundle relaying scheme and Q-learning method. Simulation result shows that the packet scheduling scheme has a dual-threshold structure. The decision variables were determined by the energy queue state of the self-powered roadside units and the speed state of the arriving vehicles, so that the system can reduce the average transmission delay of the monitoring data on the premise of considering the energy utilization efficiency, and ensure non-overflow of the self-powered roadside units' energy storage to minimize the average packet transmission delay. In the single packet transmission model, the average transmission delay of the proposed packet scheduling scheme is 15.7% lower than that of greedy bundle relaying scheme, and 13.5% lower than that of Q-learning method. In the batch packet transmission model, the average transmission delay of the proposed packet scheduling scheme is 20.4% lower than that of greedy forwarding scheme, and 11.5% lower than that of Q-learning method.More>

2020, 20(2): 161-171. doi: 10.19818/j.cnki.1671-1637.2020.02.013

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Forward collision warning algorithm optimization and calibration based on objective risk perception characteristic

LU: Neng-chao, ZHENG Meng-fan, HAO Wei, WU Chao-zhong, WU Hao-ran

Abstract: In order to improve the adaptability of advanced driver assistance system(ADAS) warning algorithm in complex driving environments, a comprehensive warning algorithm named the objective risk perception(ORP) algorithm based on the vehicle kinematics and risk perception characteristic was proposed. The analysis and derivation under typical risk conditions show that the proposed warning algorithm is a comprehensive mode of time headway(THW), time-to-collision(TTC) and safety margine(SM) based warning algorithms. In order to calibrate the parameter thresholds of the proposed warning algorithm, a total of 4 500 km natural driving experiments were carried out, and finally 409 valid near-crash events were extracted. The distribution characteristics of objective risk perception parameters when release accelerator and press brake were obtained. The risk warning algorithm parameters were calibrated based on the near-crash events and their parameter characteristics extracted from the natural driving data. The forward collision warning algorithm was developed under a simulated driving environment, and the verification experiments of the algorithm were carried out based on four risk scenarios. Research result shows that based on the parameter calibration of natural driving data, the two-level warning parameter thresholds of the ORP warning algorithm are 1.4 and 0.8 s, respectively. Based on the comparison of driving behavior under typical risk conditions, in terms of warning effectiveness, the ORP warning algorithm is slightly higher than the RP warning algorithm, and the effectiveness of secondary early warnings is significantly higher than that of the TTC warning algorithm. In terms of the average minimum time-to-collision of all driving segments under the warning algorithm, the ORP warning algorithm is 2.02 s, the RP warning algorithm is 1.90 s, and the TTC warning algorithm is 1.65 s, which shows that the ORP warning algorithm can adapt to the risk identification in complex risk environment. Based on a large number of natural driving test based parameter calibration and effect verification, the proposed warning algorithm can be used for the risk identification of advanced driver assistance systems.More>

2020, 20(2): 172-183. doi: 10.19818/j.cnki.1671-1637.2020.02.014

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Longitudinal control model for connected autonomous vehicles influenced by multiple preceding vehicles

WU Bing, WANG Wen-xuan, LI Lin-bo, LIU Yan-ting

Abstract: In order to better simulate the car-following characteristics of connected autonomous vehicles(CAV), based on the longitudinal control model(LCM), the LCM in the connected autonomous environment(C-LCM) was constructed considering the influences of speed and acceleration of multiple preceding vehicles in V2 V environment. The stabilities of LCM and C-LCM were analyzed. The stability regions of two models were compared, and the influence of C-LCM on the traffic flow stable region under different communication distances was determined. Numerical simulation was designed to simulate the common traffic scenarios including acceleration and deceleration, and the car-following behavior characteristics of CAV in V2 V environment were analyzed. The traffic flow safety levels with different communication distances and penetration rates of CAV were analyzed with simulation. A fundamental diagram model of mixed traffic flows with different penetration rates of CAV was constructed. Analysis result shows that the traffic flow stability region increases with the increase of considered preceding vehicles numbers, and when only considering one preceding vehicle, the longer the distance between the preceding vehicle and ego vehicle, the bigger the influence of velocity coefficient on the C-LCM stability region. The C-LCM can respond to the behaviors of multiple preceding vehicles in advance and simulate the dynamics characteristics of connected autonomous vehicles better. In the deceleration scenario, the speed overshoot decreases from 0.15 to 0.08, and the maximum speed delay decreases from 7.5 s to 4.9 s. In the acceleration scenario, the speed overshoot decreases from 0.07 to 0.04 and the minimum speed delay decreases from 3.5 s to 2.6 s. With the increase of CAV penetration rate, the safety level of traffic flow increases. The highest safety level is achieved with four CAVs in communication distance, and the TIT and TET indexes decrease by 57.22% and 59.08%, respectively. With the increase of CAV penetration rate, the highway capacity increases from 1 281 veh·h^-1 to 3 204 veh·h^-1. So the proposed C-LCM can describe the car-following characteristics of different vehicles to achieve the modeling of mixed traffic flow, decrease the complexity of mixed traffic flow, and provide a reference for the impact analysis of CAV on traffic flow.More>

2020, 20(2): 184-194. doi: 10.19818/j.cnki.1671-1637.2020.02.015

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Obstacle avoidance path planning of intelligent electric vehicles in winding road scene

SHENG Peng-cheng, LUO Xin-wen, LI Jing-pu, WU Xue-yi, BIAN Xue-liang

Abstract: In order to study the reliability of obstacle avoidance planning for intelligent electric vehicles in the winding road scene, a method of converting the Cartesian coordinate system into the curvilinear coordinate system was proposed. The quintic Bézier curve was used to approximate the lane line in the winding road scene to obtain the reference path. Through the arc-length parameterization of reference path, a curvilinear coordinate system was established by using the arc-length as abscissa and the lateral offset as ordinate. According to the position of the vehicle and the sub-target points in the curvilinear coordinate system, the candidate paths were generated by the cubic polynomial in real time, and the candidate paths were optimized by using the sequence quadratic planning method. In order to verify the reliability of the proposed algorithm, an electric vehicle was used as a platform to build a test car with monocular cameras, 64-line laser radar, industrial control computers and other equipments. The online simulation of vehicle obstacle avoidance algorithm in the winding road scene was implemented based on Apollo platform. During the real vehicle experiment in the zone, the GPS position error and heading angle cumulative error of the obstacle avoidance algorithm were analyzed. Research result shows that the obstacle avoidance path planning of vehicle in the winding road scene can effectively describe the information of path curvature radius, the offset distance of vehicle center from the lane line, etc, and it is easy to determine the driving area of the vehicle and the obstacle position information ahead, so as to generate the optimal path. During the obstacle avoidance in the zone, the GPS position error occurs at the initial point, turning point and obstacle avoidance point, the maximum error is 0.15 m, and the heading angle cumulative error is 12°. The sudden increase of curve position error is mainly caused by the instantaneous change of vehicle posture and the matching process of obstacles, but the error can be well controlled within a certain range. So it is feasible to solve the obstacle avoidance path planning in the winding road scene by using the curvilinear coordinate system.More>

2020, 20(2): 195-204. doi: 10.19818/j.cnki.1671-1637.2020.02.016

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Longitudinal and lateral coordination control method of high-speed unmanned vehicles with integrated stability

LI Jun, TANG Shuang, HUANG Zhi-xiang, ZHOU Wei

Abstract: A path tracking control method considering longitudinal and lateral coordination control was proposed. The vehicle preview error model and high-speed vehicle equivalent dynamics model considering road surface terrain were established to introduce road curvature terrain factors. The preview distance generator based on the fuzzy rules was designed to solve the problem of fixed preview distance in the preview error model. The function relationship between the time domain and the road curvature was established. The model predictive control algorithm was used to solve the front wheel rotation angle, thereby establishing a path tracking controller. The expected vehicle speed was represented by the exponential model, and the proportion integration differentiation longitudinal controller was designed to improve the path tracking accuracy. The vehicle stability characteristic was represented by phase plane of slip angle, and the proportion integration differentiation stability controller was designed to improve the vehicle stability. Research result shows that the control method can optimize the vehicle tracking performance on the roads with different adhesion coefficients. When driving on a dry asphalt pavement at a speed of 90 km·h^-1, the maximum lateral error reduces by 33% compared with a vehicle that only uses model predictive control algorithm for path tracking control. When driving on a wet asphalt pavement at a speed of 70 km·h^-1, the maximum lateral error reduces by 30% compared with a vehicle that only uses model predictive control algorithm for path tracking control. When driving on an icy and snow pavement at a speed of 55 km·h^-1, the maximum lateral error reduces by 16% compared with a vehicle that only uses model predictive control algorithm for path tracking control. Therefore, the proposed control method can effectively improve the path tracking accuracy.More>

2020, 20(2): 205-218. doi: 10.19818/j.cnki.1671-1637.2020.02.017

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Adaptive sliding mode control for two-wheeled self-balancing vehicle with input delay

XUE Han, SHAO Zhe-ping, FANG Qiong-lin, MA Feng

Abstract: An adaptive sliding mode control algorithm was designed for two-wheeled self-balancing vehicle with input delay. The Lagrange equation was used to establish the dynamic mathematical model of two-wheeled self-balancing vehicle system. In the system model, the input delay in practice environment and the unknown disturbance in dealing with the input delay were considered. After the singular value decomposition of transformed input matrix, an adaptive sliding mode controller with adaptive estimation ability for the disturbance parameters was designed. Based on the Lyapunov stability theory, the robust asymptotic stability of closed-loop system was guaranteed. In the experiment, the gyroscope MPU-6050 and acceleration sensor were used to construct the vehicle attitude detection device.Analysis result shows that when the control parameters are small, the overshoot of the system is small, while the regulation time of the system is long. When the control parameters are large, the system has a more obvious overshoot, while the regulation time of the system is shortened. The velocity range is less than 0.08 m·s^-1 and the angular velocity range is less than 0.6°·s^-1 when the vehicle body is subjected to a small disturbance. The velocity range is less than 0.1 m·s^-1 and the angular velocity range is less than 0.8°·s^-1 when the vehicle body is subjected to a large disturbance. From the initial inclination of 5°, the velocity of vehicle is within 0.005 m·s^-1 and the angular velocity of vehicle is within 0.022°·s^-1. While from the initial inclination of 10°, the velocity of vehicle is within 0.007 m·s^-1 and the angular velocity of vehicle is within 0.031°·s^-1. So the adaptive sliding mode control algorithm can make the vehicle adjust itself and quickly return to a stable state under an appropriate interference and different initial vehicle inclinations.More>

2020, 20(2): 219-228. doi: 10.19818/j.cnki.1671-1637.2020.02.018

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Cell transmission model of mixed traffic flow of manual-automated driving

QIN Yan-yan, ZHANG Jian, CHEN Ling-zhi, LI Shu-qing, HE Zhao-yi, RAN Bin

Abstract: In order to analyze the impacts of automated driving vehicles on the macroscopic traffic flow characteristics, the mixed traffic flow with manual driving vehicles and automated driving vehicles was considered as the study objective, and the cell transmission model(CTM) of mixed traffic flow under different proportions of automated driving vehicles was proposed.The car-following model proposed by Newell was used for the car-following model of manual driving vehicles, while the model calibrated by PATH program used the real vehicle experiments was employed for the car-following model of automated driving vehicles.The function relation of equilibrium space headway-speed was calculated according to the car-following models of manual and automated driving vehicles.The fundamental diagram model of mixed traffic flow was derived under different proportions of automated driving vehicles. In addition, the characteristic quantities such as the maximum capacity, the maximum jam density, and backward wave speed were calculated for the mixed traffic flow under different proportions of automated driving vehicles. Based on the CTM theory of homogenous traffic flow, the CTM of mixed traffic flow was proposed under different proportions of automated driving vehicles. The moving bottleneck problem was selected for example analysis, the influence times of moving bottleneck under different proportions of automated driving vehicles were calculated by using the mixed traffic flow CTM. The car-following models were used for the microcosmic numerical simulation on the moving bottleneck problem. The errors between the calculation results of the mixed traffic flow CTM and the microcosmic simulation results of car-following models were analyzed. The accuracy of mixed traffic flow CTM was validated. Research result shows that the proposed mixed traffic flow CTM can effectively calculate the influence time of moving bottleneck. Under different proportions of automated driving vehicles, the errors between the calculation results of the mixed traffic flow CTM and the microcosmic simulation results of car-following models are all below 52 s, and the relative errors are all below 10%, which indicates the accuracy of the proposed mixed traffic flow CTM in actual application. The mixed traffic flow CTM reflects the study idea from microcosmic to macroscopic. There are relationships between the microcosmic car-following models and the small-scale automated driving vehicle experiments being gradually implemented. The mixed traffic flow CTM can truthfully reflect the evolutionary process of mixed traffic flow on single lane in the background of automated driving under different proportions in the future, which enhances the application value of the model research.More>

2020, 20(2): 229-238. doi: 10.19818/j.cnki.1671-1637.2020.02.019

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