Abstract:Hypersonic flight vehicles (HFVs) have strong penetration and reconnaissance capabilities in military affairs, efficient deployment and space travel capabilities in civil use, making them one of the important ways for countries to construct strategic threats and compete for space resources. Hence, it draws much attention from many countries. The paper firstly reviews the development history and current research status of the HFVs, aiming to reveal the development principle. It is followed by the flight task analysis in different space domains ranging from orbiting space, near-space, and airspace. Then, the flight constraints and guidance methods for the reentry phase are mainly discussed, including offline reference trajectory-based guidance method, online trajectory-based guidance method, and prediction guidance method. Furthermore, the expectation of the future guidance system is given which lies in multi-constraints trajectory-based guidance method with high accuracy, nonlinear programming trajectory optimization-based guidance in real-time, and trajectory re-planning guidance technology with robustness to different tasks. Thirdly, the hypersonic flight control methods on solving the problem of high nonlinearity, uncertainty, time-varying, flexibility, input constraint, and system fault are summarized. Then, looking into the future, three aspects are discussed, including the deep mechanism analysis on system model/disturbance/fault, the control tradeoff when solving multiple problems, controller smooth switching technology, and autonomous hypersonic flight control in the present of the unexpected events. At last, the thinking on the HFV future development including hypersonic missile and reusable launch vehicle is provided, as well as the integrated guidance and control system design.

Abstract:In order to optimize the formation of large-scale unmanned combat aircraft vehicle (UCAV) in complex constraint environment, an algorithm for formation optimization based on bi-level programming model was proposed. According to the existing UCAV formation combat mode of air to ground, the upper-level model of UCAV formation in combat environment was established. The discrete particle swarm optimization and simulated annealing (DPSO-SA) algorithm was used to obtain the number of UCAV and the best formation of each task. According to the existing formation library, the lower-level model of the UCAV location was built, and the UCAV position in the formation was obtained by using the genetic algorithm. The simulation results show that the improved simulated annealing algorithm can solve the problem that the discrete particle swarm optimization is easy to fall into local minimum, and the slow convergence rate of DPSO-SA can be solved with the design of a bi-level programming model. Compared with the single-level programming model, the bi-level programming model has faster convergence speed and better optimization effect on solving large-scale UCAV formation optimization problems.

Abstract:To solve the difficulty of generating magnetic maps in magnetic guidance system and improve the poor applicability of the existing methods on multi-intersection mapping, a method applying the feature of magnetic segment is proposed in this paper. First, IMU, odometer, and magnetic ruler were used to collect the road magnets data, and then the data were divided into magnetic segments based on the signal magnetic segment. After that the features of the magnetic segments were extracted from the sensors data, they were matched and loop closure constraints were established between the segments. Second, by using the improved graph-based optimization algorithm, the influence of error constraints was reduced. Finally, the corrected magnets were obtained from the optimized graph and the magnetic map could be generated. Based on the experimental results of a real road, it can be concluded that the method is simple to operate and the obtained magnetic map is accurate with high global consistency. The guidance experiment also verified the usability of the method. Therefore, this method has a wide applicability on multi-intersection mapping and it can effectively generate magnetic maps.

Abstract:The rated life of an electromagnetic relay is the key to meet the requirements of the whole machine, which has a direct influence on the reliability of the system. According to the large endurance discrepancy between different batches, we analyzed the mechanism that affects the rated life of electromagnetic relays and found that the life failure of electromagnetic relays is mainly caused by contact area, contact pressure, contact gap, and the material of contactors. Without changing the structural design and the materials of contactors, the test design instructed by design of experiment (DOE) for the related influencing factors was carried out to improve the rated life and its consistency, and obtained reasonable contact gap, constant contact pressure, and overrun. Besides, the contact gap, constant contact pressure, and the control range of overrun were optimized by using the tolerance design to enhance the consistency of rated life. The result indicates that the DOE test can disclose the optimization scheme of the factors that influence electromagnetic relays and the control range of the influencing factors can be optimized through tolerance design, which can effectively enhance the rated life and its consistency, thus improve product quality.

Abstract:To deal with the 3D path-following control problem of underactuated autonomous underwater vehicle (AUV) in the presence of current disturbance and model uncertainty, a tracking error model on the basis of virtual target in Serret-Frenet frame was established. Based on the Lyapunov theory and back-stepping method in kinematic controller, the virtual target with adaptive law and an improved integral line-of-sight (ILOS) guidance law were then developed, which can overcome the interference of current and reduce overshoot. Dynamic controller was designed based on the back-stepping adaptive sliding mode control (BASMC) theory, which guarantees the stability and robustness of the system. Finally, the closed loop stability of the system was demonstrated by the nonlinear cascade system theory. The simulation results demonstrate that the control law, which is implemented based on the relative velocity between AUV and fluid, is convenient for engineering application, and the controller can effectively overcome the influence of current and model uncertainty and realize 3D path-following.

Abstract:To investigate the feasibility of industrial preparation of nano-silica process by pretreated rice husk combustion in fluidized bed, the combustion test of pretreated rice husk was carried out in a bench-scale fluidized bed and active rice husk ash (RHA) samples were obtained. Scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray fluorescence spectrometer and specific surface area and pore size analyzer were used to characterize the microstructure and physicochemical properties of bed material and RHA, and then the effects of acid pretreatment on the combustion state of rice husk in fluidized bed and the performance of RHA were deeply studied. The results showed that the pretreated rice husk burned well in the bench-scale fluidized bed and the bed material′s agglomeration was not happened. The obtained RHA consisted of 15-50 nm nanoparticles and had abundant mesoporous pores of about 4 nm, SiO₂ purity of higher than 98 wt.% and ultra-low residual carbon content of less than 0.08wt.%. Acid pretreatment greatly eliminated the limitation of combustion temperature on RHA properties under low temperature condition, however, the temperature constraints gradually appeared when temperature above 800 ℃. In brief, the fluidized bed combustion of acid-pretreated rice husk could achieve the purpose of preparing high purity and high active RHA, and the pretreatment effect of sulfuric acid was better than citric acid.

Abstract:To adapt to the changes in the next generation air transport systems, this research proposed an aircraft collision avoidance method that takes into account pilot’s intentions. An improved aircraft position prediction model was proposed by considering pilot’s intentions. On this basis, conflict probability between aircraft and restricted airspace and that between aircraft pairs were modelled and estimated respectively, and the conflict risks were divided to three levels according to the conflict probability value. Additionally, four important factors that affect the conflict probability were analysed, and the corresponding conflict avoidance strategies for each conflict risk level was proposed. Results show that the conflict probability can be reduced by increasing the distance between two flights route segments or the length of each flight route segment, or by declining the overlapping time of flight plans between two flights or the time duration of each flight plan. The proposed aircraft conflict avoidance method provides a theoretical basis for the improvement of the autonomous decision support system for conflict detection and resolution, which is of great significance for ensuring air traffic safety.

Abstract:In order to investigate the shape characteristics of coarse aggregates in asphalt concrete and their influences on performances of asphalt mixture, asphalt concretes were scanned by industrial CT, and the morphology parameters of the coarse aggregates were obtained from the scanned images by image processing technique and statistical method. The influences of the coarse aggregate level grading on morphology parameters were studied and analyzed. Results showed that CT scanning combined with image processing technique could accurately obtain the coarse aggregate morphology parameters of asphalt concrete. The cumulative distribution probability of the aspect ratio and angularity of coarse aggregate particles obeyed the three-parameter Weibull distribution. Contour fractal dimension, longitudinal/lateral trend parameters, longitudinal declination mean, and area parameters were sensitive to changes in coarse aggregate gradation. The longitudinal/lateral trend parameters, longitudinal declination mean, contour fractal dimension, angularity, and area parameters could significantly characterize changes of the passing rate of the 4.75 mm particle size aggregate.

Abstract:In order to improve the reliability of bus service and reduce the bus bunching phenomenon, this paper presents an optimized method for time control point selection of a bus route based on bus GPS data. First, three basic principles of control points setting were given, which mainly consider position of control points, travel time between control points, and distance between control points. Several factors were selected from the principle of control point setting for quantitative analysis, and the evaluation index of control points setting was determined. Based on the GPS data of buses, the computing methods of the average dwell time, the difference between inter-stop travel time, and the comprehensive evaluation index were established. The overall optimum and the local optimum time control point selection methods were brought forward. The overall optimum method can select the optimal solution from all the alternatives, but the calculation process is cumbersome and time consuming; whereas the local optimum method can save a lot of costs under the premise of ensuring certain optimization effects. Finally, bus route 102 in Suzhou City was taken as an example to analyze the two selection methods and the results show that the two methods can both select an effective time control point scheme.

Abstract:To scientifically monitor and predict the performance of large-scale tower-beam dampers during operation, the longitudinal vibration of the cable-stayed bridge main beam in natural environment was made equivalent to the problem of the single degree of freedom (SDOF) system under random vibration in this study, and the power spectrum under white noises was deduced. Several acceleration gauges were mounted on the bridge and dampers and field tests were performed three times in three years repetitively. Discrete wavelet transform (DWT) was applied to extract the low frequency vibration data of the main beam. With the measured acceleration power spectrum curve fitted to the formula in SDOF system by the least square method, the damping ratio of the tower-beam damper was obtained approximately. Results showed that after the simplification of the cable-stayed bridge, the system damping ratio of longitudinal vibration of the main beam can be precisely identified. Compared with traditional low-pass filters, the DWT method performs better in conserving the low frequency component. The attenuation of the system damping ratio indicates that the tower-beam damper installed at Sutong Bridge degenerates in a slow process. The field monitor of the tower-beam damper should be carried out regularly, which is beneficial for maintenance guidance and the management of dampers without interrupting traffic, which guarantees the normal operation of long-span cable-stayed bridges.

Abstract:To investigate the flexural behavior of steel-concrete composite beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates, a total of five large scale steel-concrete composite beams including one control unstrengthened beam and four strengthened beams were prepared and tested with static load in a simply supported four-point bending setup. Welded I-beam was used for the structural steel section of all specimens. An innovative fabricated anchorage system was developed to prestress the CFRP plates attached to the bottom flange of the steel beams. The connection between the CFRP plates and the steel beams both depended on flat-plate anchors and epoxy resin adhesive. The strengthening effects of the method using CFRP plates of different thicknesses and different prestressing forces were investigated. Experimental results showed that the strain distribution along the cross-section conformed to plane-section assumption during load application. The specimen strengthened with thicker CFRP plate exhibited a higher ultimate bearing capacity. The yield bearing capacity increased and the mid-span deflection slightly decreased with increase of prestressing force. The CFRP plates failed due to rupture or debonding under ultimate condition and a great portion of tensile strength was employed (up to 80% on average). The fabricated anchorage system can provide strong anchoring force and is proved to be feasible and practical. The prestressed CFRP plate for strengthening steel-concrete beams improves the flexural behavior and is an efficient technique in bridge strengthening and rehabilitation.

Abstract:Focusing on the instability of mixed traffic flow including connected vehicles and traditional vehicles, this paper proposes an analytical method for the asymptotic stability of the mixed traffic flow with connected vehicles. Based on the transfer function theory, the car-following models were used to derive the transfer function of disturbances spreading in traffic flow. Then the analytical framework of asymptotic stability of mixed traffic flow was built under different proportions of connected vehicles. The intelligent driver model (IDM) and optimal velocity model (OVM) were selected as car-following models for connected vehicles and traditional vehicles, respectively. Subsequently, case analysis of asymptotic stability of mixed traffic flow was conducted and numerical simulations were performed under small disturbances. Results showed that the proposed analytical framework of asymptotic stability of the mixed traffic flow can be used to calculate the stability region of the mixed traffic flow related to connected vehicle proportion and equilibrium velocity. When the equilibrium velocity was larger than 21.5 m·s^-1, the mixed traffic flow was stable under any connected vehicle proportion. When the connected vehicle proportion was larger than 0.63, the mixed traffic flow was stable under any equilibrium velocity. Moreover, the numerical simulation experiments of mixed traffic flow validated the soundness of the theoretical analysis. The analytical framework of asymptotic stability of mixed traffic flow can be applied to different car-following models. It can also be used to analyze impacts of connected vehicles on traffic flow stability under the condition of real experimental tests.

Abstract:In order to quickly assess bridge scour during operation period, a dynamic-based identification method was proposed based on the measured vibration modes and model updating technique, and was applied to the pylon scour detection of the Hangzhou Bay Bridge. Two field measurements were conducted in 2013 and 2016 respectively to record the acceleration data of the superstructure of the Hangzhou Bay Bridge under ambient vibration. A modal analysis was carried out to obtain the natural frequencies and modes of vibration for each measurement. The superstructure was numerically simulated by a fish-bone finite element model and the pile-soil effect of the substructure was simulated by soil springs. The stiffness of equivalent springs around piles in the simulation model was firstly updated based on the measured natural frequencies of the scour-insensitive modes. Until the simulated natural frequencies corresponded to the measurement, the stiffness of the springs in the simulation could be seen as the identification of the real pile-soil effect of the bridge. Then, the scour depth in the simulation model was updated based on the variation of the measured natural frequencies of the scour-sensitive modes. Until the simulated and the measured variations of the natural frequencies were the same, the scour depth in the simulation model could be regarded as the identification of the real situation of the foundation during the three years. The identification accuracy was finally verified by the results of underwater terrain map around the foundation of the bridge. Results show that it is feasible to update the foundation scour by tracing the measured modal variation of the superstructure to identify a correct scour depth. This method can resolve the long-term difficulty of the traditional scour detection because it does not need underwater operation.

Abstract:To analyze the micromechanical response of asphalt mixture during field compaction, a 3D compaction model was developed based on particle flow code in 3-dimensions (PFC3D) by considering the asphalt pavement properties and compaction temperature. The Burger’s model parameters were obtained by dynamic modulus test with time-temperature superposition (TTS) principle, and were used to describe the contact behavior between aggregate and asphalt. Micromechanical characteristics, such as aggregate migration and motion, evolution of contact force and energy were investigated during field compaction. Results showed that asphalt pavement displacement displayed non-continuity and asymmetry. Meanwhile, aggregate motion and stress were concerned with the load position and orientation of compaction load. The laws of aggregate motion in compacted areas were different from the non-compacted areas, and the analogous whirlpool condition was formed in the transitional zone of the compacted and non-compacted areas. Additionally, the compacted areas were mainly dominated by contact pressure. The work of external force and strain energy increased quickly at the initial stage of compaction, and gradually decreased at the later stage. Due to the unstabilized compaction stress that resulted in a faster speed, the kinetic energy developed abnormally. However, once the compaction model entered a stable stage, the kinetic energy decreased. These results agree with those of preliminary research. It is reasonable to conduct a survey of the microscopic behavior of asphalt mixture with discrete element method (DEM). The DEM can be employed to investigate micromechanical characteristics of asphalt mixture during filed compaction.

Abstract:In order to obtain the wind velocity histories of Hutong rail-cum-road Yangtze River Bridge, an in-situ wind field test of the cable-stayed bridge was carried out. The wind field characteristics were analyzed, and the wind velocity spectra parameters of the experiment were compared with those of the specification. By means of harmonic synthesis method, this paper simplified the 3D turbulence wind field into multi 1D turbulence wind filed, and simulated the turbulence wind velocity histories of two towers, the girders on roadway and on railway deck separately. Results showed that the 3D turbulence wind velocities obtained based on in-situ test records fitted well with the target value, and exhibited differences with the specification values. It indicates that the application of specification spectra values is limited when used in different regions, especially in regions with complex climate conditions. The wind velocity histories of the long-span cable-stayed bridge obtained can be used in bridge aerodynamic analysis, which is pragmatic for engineering purposes.

Abstract:Although the bus lanes could guarantee public transport priority effectively, their great attraction to bus passengers can lead to the transfer of passenger flow in local area of bus network, and has an impact on bus operation. In order to accurately obtain the specific scope and extent of this change, this research put forward an overlapping community structure detection algorithm based on the improved bus transfer network, and used the improved bus station network and Djkstra algorithm to propose an impact model to calculate the specific impact degree. Finally, the rationality of the method was verified in accordance with the actual survey data. Results show that the interconnection among bus lines in the public transport network is the basis of the influence of the bus lanes, and the transfer conditions are the important factors limiting its influence. The set of stations with a maximum of one transfer relationship with the bus lane stations constitutes the scope of the impact of the bus lane, and the impact degree is determined by the resources and environment of the bus. The results can be used to evaluate the existing bus lanes or to further planning.

Abstract:To accurately describe features of passengers’ route choice behaviors of feeder bus lines, this research took the commuting trips during morning peak period under a typical commuting OD as study object, and established a passenger flow assignment model based on Logit-SUE model, which considers the relationship between the actual arrival time of passengers and the arrival time of vehicles. This model proposed a detailed quantitative description of the passengers’ queuing process at bus stations and improved the existing calculation method of waiting time at bus stations in the generalized travel cost measuring. Then the feasibility of the model was verified by comparison with previous studies, and the influences of the time step length t- and passengers’ perception coefficient of the path cost θ on the choice probabilities of different bus lines were analyzed. Results indicated that the modelling results will not have a big change when t- changes. Smaller t- leads to more accurate calculation results of waiting time. If all the commuters start at time t-, the model results in this paper correspond with that of the previous studies. However, when θ is small, there is a certain gap between the passenger perceived route costs and the actual costs. Big θ makes passengers feel closer to the reality of impedance so when θ is bigger, the choice probabilities of feeder bus lines with low costs are bigger.

Abstract:This research focuses on the change rules of solar radiation effects and the relationship between most unfavorable live load effect and temperature effect of suspension bridges under natural environment. The fine model of an under-construction long-span suspension bridge was established, the parameter sensitivity analysis of environmental factors of solar radiation effects was carried out, and the relationship between the solar radiation effects and the most unfavorable live load effect was investigated. Results showed that the solar radiation effects of suspension bridge were mainly affected by ambient temperature, followed by the wind speed, the influence of which is nonlinear. Daily ordinal number and latitude had little influence on the solar radiation effects. The change of solar radiation effects was not consistent with that of latitude, but was affected by many environmental factors. The maximum deflection of the main beam caused by the most unfavorable live load was twice the maximum deflection caused by thermal radiation, and the offset of the tower top was equal to that of thermal radiation. These results could provide theoretical basis and technical support for the error analysis of the construction phase of suspension bridges and eliminate the temperature influence of the health monitoring data.

Abstract:Current normal transit network results in long passenger travel time because it does not consider the particularity of the travel demand in transit network between urban area and suburb. To solve this problem, a novel transit network model was proposed based on principles of milk-run and hub-spoke, which considers the capacity constraint for the travel demand in transit network between urban area and suburb. Then the corresponding genetic algorithm was developed to solve this model. In this model, the number and locations of the hub stops, the route structure of milk-run route, and the vehicle assignment can be determined. Different from normal transit network, decentralized passenger flow can be aggregated at hub stops to form scale effect through milk-run routes in this network. In addition, massive passenger flow can complete their travels by express routes from hub stops, which can reduce their travel time. Finally, the proposed approach was applied to a real network in Tin Shui Wai of Hong Kong to verify its effectiveness. The comparisons of the proposed network and the existing network show that when the proposed network was applied, the total travel time was reduced by 16.26% with existing available fleet size. It suggests that the proposed network can improve the existing transit service level and travel satisfaction, as well as attract more passengers to travel by public transit, thereby mitigating traffic jam.

Abstract:Since most current vulnerability analysis methods are only applicable for one-dimensional seismic analysis, we established three-dimensional (3D) seismic damage index functions of bridge risk components. Based on the reliability theory of engineering structure and the method of probability and statistics, a general 3D seismic vulnerability calculation theory of bridge structure was derived and the corresponding analysis method was developed. A typical rigid frame continuous beam combined railway bridge from the Western region was selected as the research object and the vulnerability analysis of the bridge was carried out. Based on the results of the cloud method, the correctness of the 3D seismic vulnerability analysis method was verified and full-view vulnerability cloud pictures of each bridge risk component were established to evaluate the general seismic performance of the bridge structure in 3D earthquakes. Results show that only analysis of the distribution characteristics of the longitudinal and transverse vulnerability of the bridge is not effective for reflecting its actual seismic capacity, so it is necessary to conduct the 3D vulnerability analysis. The full-view vulnerability cloud pictures of the bridge can be applied to evaluate the seismic performance of the bridge, which provides evidence for 3D bridge seismic design.

Abstract:To take the spatial distribution into account when identifying and processing single outlier continuous compaction quality, the near neighbor weighted estimation and identification method was developed based on autocorrelation distance. Judge index of single outlier was defined as abnormal index α_i. After eliminating the outliers, the original outlier data were estimated using ordinary Kriging interpolation method. Then continuous compaction experiments were carried out in Loudi construction site of Shanghai-Kunming high-speed railway. Results show that the test value can be determined as a single outlier when the abnormal index α_i is greater than 0.2. Compared with the current Pauta criterion recognition method, the near neighbor weighted estimation and identification method based on autocorrelation distance has higher accuracy and recognition efficiency. The ordinary Kriging interpolation method could provide a more accurate estimation of the single outlier data, reduce the coefficient variation of the data, and improve the uniformity of continuous compaction quality measured value.

Abstract:To improve the safety and efficiency of freeway under the management of partition speed limit and reduce drivers’ burden caused by improper speed limit and frequent speed changes, this research optimized and coordinated freeway speed limit sections under the management of partition speed limit. First, the optimal coordination model for freeway speed limit was constructed in three cases on the basis of the principle of minimum loss time. Second, the minimum length of the speed limit section and the number of speed limit sections used in the process of the coordinated optimization were determined based on the theoretical calculation of drivers’ cognitive distance, psychological stability distance, speed limit sign front distance, and a questionnaire survey. Then the risk function and income function were used to characterize the traffic safety and efficiency of freeway and construct the corresponding evaluation model. Finally, the effectiveness of the proposed method was tested by simulating the original setting of the speed limit section and the traffic condition of a project freeway. Results show that after the optimization the comprehensive safety index decreased by 45.51% and the comprehensive efficiency index increased by 26.78%, which means the state of safety and efficiency has come closer to the ideal point (a, b). This feasible and effective method can improve traffic safety and efficiency level, and provides a theoretical basis for the safety and efficiency management of speed limit sections.

Abstract:To improve the control efficiency of the signalized intersection control scheme, the algorithm for optimal intersection signalization scheme was proposed by considering movement lapping. Firstly, the movement compatibility relation in intersections were analyzed and refined, and the phase movements’ combination was determined. Then, the phase movements’ combination was represented and the random samplings were re-arranged. According to the phase setting requirements of intersection signal control scheme, the feasible phase combination (FPC) schemes for intersections were obtained by selecting the phase combination schemes satisfying the condition and consideration of the movement lapping. Finally, the signal phase timing and average vehicle delay were calculated by combining the existing timing model, and the control scheme corresponding to the minimum average delay was selected as the optimal control scheme of the intersection by comparing the average vehicle delay. Analysis results showed that the average delay of movement vehicles under the proposed scheme was reduced by 0.3 s/pcu compared with the ring barrier controller structure phase combination scheme (RBS), 0.5 s/pcu compared with the diffluence phase combination scheme (DS), and 4.5 s/pcu compared with the combination phase combination scheme (CS). Therefore, it showed that the proposed method is feasible.

Abstract:In order to understand the basic law of temperature field, water field, and the coupling effects of airport pavement structure, and to provide theoretical basis and measure suggestions for the prevention and control of uneven frost heave damage of airport pavement structures in seasonal frozen regions, we designed a test box and conducted the test of external water infiltration and a model test of uneven frost heave of an airport pavement structure. The reliability and applicability of the model were verified by the results of on-site frost heave monitoring. Results showed that the model test intuitively simulated the phenomenon of faulting of slab ends between runway and shoulder with the reasons and mechanism clarified. It objectively revealed the law of temperature field, water field, and the coupling effects of airport pavement structure. The external water infiltration exhibited a great impact on water field redistribution. Uneven frost heave of airport pavement structure is the result of the coupling of temperature field and water field inside the airport pavement structure. The cooling rate and temperature gradient impact the moisture migration and accumulation, and in turn, the water field redistribution affects the delivery of temperature. The research method of combining the physical model test and the on-site monitoring test not only provides a theoretical basis for the prevention and control of the uneven frost heave of the buildings in the frozen area, but also enriches ways of exploring the law of hydro-thermal coupling.

Abstract:Existing speed limit strategies cannot reflect the effects of geometric alignments and the road friction condition on vehicle lateral stability precisely. Regarding this issue, the lateral instability of vehicle running on circular curve segment was decoupled into three instability modes. A precise method for calculating the safety boundary of each mode was presented, and the maximum speed which ensures vehicle lateral stability was deduced. Firstly, the drawbacks of the traditional lateral stability indicator, i.e., the side friction factor, were analyzed. The instability status was decoupled as steering instability, losing track-holding capacity, and rollover, and the corresponding safety evaluation indices were proposed. Secondly, a 7 degree-of-freedom (DOF) nonlinear vehicle-circular highway segment coupling model was developed, with which the computational models within the safety boundaries of safety evaluation indices were deduced. Subsequently, the accuracy of the safety boundaries were validated in various road friction conditions through the employment of Carsim. Finally, based on the 7 DOF nonlinear vehicle-road coupling model and the computational models of safety boundaries, the critical safe speeds for circular curves were deduced using MATLAB/Simulink, and the comparisons among the proposed method, the operating speed, and the design speed were made. The results indicate that design speed limit is too conservative on dry and wet pavement, while operating speed often exceeds critical safe speed on wet and icy pavement, which may cause safety issues. The speed limit strategy proposed in this paper fully considers the non-linearity of vehicle’s lateral motion, and could be used as a complement for other speed limit strategies for mountain highway which takes driving expectancy and efficiency into account.

Abstract:In order to ensure the rationality of urban rail transit stations location and avoid low sharing rate after construction, a bi-level model was established based on the selected route and candidate stations. The upper level aimed to achieve maximum ridership, and a GWR model was selected for ridership forecast at candidate stations. The lower level aimed to achieve minimum comprehensive cost per passenger, and the urban rail transit comprehensive transportation cost was defined to include both ridership cost and operating cost. Several heuristic algorithms were compared, and the simulated annealing algorithm was selected to solve the bi-level model. Harbin Metro Line 1 was taken as a case. The established model was used to optimize the location of the stations on this route. Results showed that there were 191 553 passengers per day at the optimized stations. Compared with the ridership of 177 010 at the current stations, there is an increase of 14 543 passengers with an increasing rate of 8.2%. The cost of energy consumption of the optimized stations was 15 972 yuan, which is 1 529 yuan less than that of the current stations with a decreasing rate of 8.7%. Therefore, the established bi-level model of urban rail transit station location can guarantee both social and economic benefits.

Abstract:Urban waterlogging disasters frequently occur in China in recent years, and “Seeing the Sea” is very common in the rainy season. However, there is no unified evaluation index system to assess the degree of urban intrusion. In order to get a more complete evaluation index system of waterlogging degree of sponge city, the concept of the momentum of waterlogging potential energy was introduced based on the dynamic duration characteristics of urban intrinsic temporality. The indexes system for the evaluation of urban intrinsic degree, including the local indicatory instantaneous index, the local indwelling comprehensive index, the regional overall indifference index standard value, and the corresponding calculation and analysis methods were established. The Zhongjiao Future City in Fenghua District of Ningbo City was taken as a case. The SWMM model was used to calculate the intrinsic conditions in the region. Results show that the calculated local indwelling comprehensive index can effectively reflect the degree of internal flaws and the internal flaw design of the city. The value could evaluate the degree of the city’s overall internality. The calculated average of the region’s overall internal level can describe the overall rationality of the flood prevention design of the LID (low-impact development) measures, and the index system can effectively reflect the spatial and temporal distribution characteristics of the internal plutonium. Adopting dimensionless quantity, the evaluation method is proved more scientific.