Abstract:In view of the characteristics of the poor driving comfort for beam bridges, to explore the passing vehicle ride comfort in the process of driving on the highway bridge, a vehicle-bridge coupling vibration differential equation was established with a beam bridge as the analysis object, based on the theory of vehicle bridge coupling vibration. The seat acceleration of the vehicle was calculated by using the self-programmed vehicle bridge coupling MATLAB program, and the ride comfort of the driver and passenger was evaluated by the international standard ISO2631-1 root mean square acceleration value evaluation method. The influences of vehicle type, seat position, vehicle weight, bridge surface roughness, speed and other factors on the ride comfort of the vehicle were analyzed. The results show that the driving comfort of cars is better than that of trucks and buses for different vehicle types. For a two-axle bus with multiple rows of seats, the ride comfort of the front seat is better than that of the back seat in different riding positions, and the farther the seat is from the vehicle centroid, the more comfortable the ride is. If different passengers are in the same row, the comfort of standing passengers is worse than that of seat passengers. Vehicle ride comfort is very sensitive to bridge deck road condition, and it decreases rapidly with the deterioration of bridge deck road condition. For different vehicle weight, vehicle ride comfort increases with the increase of vehicle weight. Vehicle speed has a certain influence on ride comfort with less effect. It is suggested that beam bridge vehicle speed limit measures be taken in order to improve the ride comfort.

Abstract:This paper takes an iron ore project as the engineering background, simulates the mechanical characteristics of the solidified tailings with PFC, determines the meso-mechanical parameters of the solidified tailings, and establishes the uniaxial compression numerical model of solidified tailings. On this basis, the paper studies the influence of particle size distribution and particle number simplification on mechanical characteristics of simulated solidified tailings. According to research findings, the average error between the numerical model and experimental results under uniaxial compression is 5.5%. It proves that the numerical model constructed by this method can effectively predict the uniaxial compressive strength of solidified tailings, and the effect of capturing the flexible and brittle failure mode of the solidified tailings is good. It further indicates that the PFC numerical model is effective and feasible to simulate the solidified tailings. Because of different engineering conditions, the size distribution of tailings is quite different. if the size distribution of tailings is wide, the particle size distribution and particle number of tailings can be simplified when the numerical model of tailings is established. Anal ysis shows that when the selection ratio of model tailings particle group range reaches more than 50%, the simulation of stress-strain curve and failure mode of solidified tailings can be well performed.

Abstract:The effect of geocell on the performance of ordinary subgrade is significant, but the improvement of the bearing capacity of subgrade by adding geocell to the high fill subgrade with two side retaining walls is not clear. To explore the application of the geocell in this structure and mechanical characteristics of geocells between different layers and retaining walls, three different reinforcement spacings and one unreinforced operating condition are set to model test. The results show that: In addition to the significant influence of reinforcement on bearing capacity, it also greatly improves the initial modulus of subgrade. When the allowable load is reached, it can still maintain the integrity of the structure itself.The tensile stress of reinforcement is inversely proportional to the depth. The tensile stress and the lifting rate of the first layer are much greater than those of the other layers.The stress distribution of retaining wall is triangular and increases suddenly at 0.22H.

Abstract:Motion stability of the high-speed maglev vehicle under steady aerodynamic load was studied. The dynamic model of the high -speed maglev vehicle on the curved guideway considering influence of aerodynamic loads was established. The critical speed concept of the maglev vehicle considering aerodynamic loads′ effect based on eigenvalues was presented. Vehicle speed, control parameters, and aerodynamic coefficients to make the critical speed of the high-speed maglev vehicle change in the critical state were also analyzed. The results show that when the system reaches the critical state, it has two critical speeds. Under the conditions in the critical state, the position control parameters vary from 20 000 kN/m to 2 000 kN/m, and aerodynamic coefficients vary from 0.05 to 0.01, the critical speed gets larger. When the real part of the eigenvalue is zero, but the imaginary part is not zero, the first kind of critical velocity occurs. When both the real part and the imaginary part of the eigenvalue is zero, the second kind of critical velocity appears. Instability is caused by the change from the equilibrium position for the curved guideway and wind loads. Aerodynamic downward force and centrifugal wind loads are not good for stability, but aerodynamic upward force and centripetal wind loads improve stability. The horizontal angle can be matched with the centripetal force, but the vertical angle is allowed to be set in a small range.

Abstract:Based on evolutionary game theory, with the introduction of reward and punishment mechanisms, an evolutionary game model between online freight platforms and government regulators is constructed, and the stability of their equilibrium points is analyzed. The results show that under static punishment, there is no equilibrium stability point in the system, no matter whether the reward mechanism is static or dynamic; under the static reward dynamic punishment and dynamic reward and punishment mechanism, both sides tend to reach a stable equilibrium point, and the effect is better under the dynamic reward and punishment mechanism; the online freight platforms' behavior is affected by the government′s reward and punishment mechanism, and the binding effect of the punishment mechanism is more significant.

Abstract:In order to accurately and effectively evaluate the operational efficiency of arrival flights in the terminal area, based on the flight arrival efficiency and the capacity improvement capability of the airport terminal area, an efficiency evaluation index body for different runway operation modes and different types of flight procedures was established. An improved TOPSIS comprehensive evaluation model based on the entropy weight method was established to evaluate the efficiency of arriving flights in the terminal area. For the first time, the arrival efficiency index based on terminal area control load was introduced to evaluate the arrival efficiency of the flight, and the correlation analysis was carried out with the traditional efficiency index, which verified the rationality of the index. Finally, taking Nanjing Lukou Airport as an example, the AirTop software was used to simulate the isolated operation and independent operation of typical daily flights (traditional ILS mode, based on RNP AR technology and PMS technology), and compare and analyze various modes. The experimental results show that the approach efficiency under the PMS technology mode is optimal, with good approach efficiency and the ability to increase capacity. This study provides decision support for the perception of the airport′s operational efficiency and planning management.

Abstract:Research on the problem of frequent failures of the potential transformer in the operation of the rolling stock concludes that the aging of the insulation in the natural environment and the influence of overvoltage and overcurrent on the insulation are the main reasons for the failure of the potential transformer, and the theoretical analysis is proved by simulation based on the finite element method. Finally, the insulation is optimized by adding an electrostatic screen and increasing the insulation distance of the first end of C section winding, and the overload capacity is optimized by increasing the wire diameter of high-voltage winding, the cross-sectional area of the core, and the number of turns of winding. The heat dissipation is optimized by increasing the heat transfer coefficient of the side surface so that the function of increasing the insulation strength, improving the overload capacity and reducing the temperature rise can be realized, and the finite element simulation analysis is carried out. The simulation results show that the maximum field strength of the optimized grid potential transformer is reduced from 2.79 kV/mm to 2.24 kV/mm, which increases the end insulation margin; the saturation degree can be controlled within 110% under 90 kV frequency withstand voltage, and the excitation current can be within the limit capacity, which effectively improves the overload capacity; the hot spot temperature is re-duced from 115.7 ℃ to 108.8 ℃, and the heat dissipation capacity is improved. The simulation results confirm the rationality of the optimized design and provide some reference for engineering applications.

Abstract:To solve the optimal path problem of the traffic network, an improved travel time estimation model was proposed, and an optimal path algorithm based on this model was designed. The travel time estimation model was improved on the basis of the segment truncated quadratic velocity trajectory model by replacing the velocity measured at the same departure moment with the arrival velocity of the road segment nodes, and the travel time was estimated by constructing a velocity trajectory that is continuous in time and space. The optimal path algo-rithm based on travel time estimation firstly solved K shortest paths based on Yen′s KSP algorithm with road section distance as impedance, then estimated the travel time of K shortest paths by the improved travel time es-timation model respectively, and finally selected the optimal path with travel time as cost. The validity and superiority of the model and algorithm were verified by numerical experiments of Sioux falls network. The experimental results show that the improved segmented truncated quadratic speed trajectory model improves the accuracy by an average of 65% compared with the original model and the optimal path results based on the proposed al-gorithm can reduce the number of intersections the path passes through and shorten the total length of the opti-mal path. Moreover, the estimated results of the optimal path's travel time stay within 3% of the real value of MAPE. The results of this study may provide a theoretical basis for the optimal path method for traffic networks.

Abstract:When the mobile robot passes through the dynamic dense crowd, due to the insufficient understanding of environmental information, the robot navigation efficiency is low and the generalization ability is weak. To solve this problem, a double-attention deep reinforcement learning algorithm is proposed. Firstly, the sparse reward function was optimized, and the distance penalty term and comfort distance were introduced to ensure that the robot approached the target while taking into account the safety of navigation. Secondly, a state value network based on double attention was designed to process environmental information to ensure that the robot navigation system has both environmental understanding ability and real-time decision-making ability. Finally, the algorithm was verified in the simulation environment. Experimental results show that the proposed algorithm not only improves the navigation efficiency, but also improves the robustness of the robot navigation system; The main performance is that in 500 random test scenarios, the collision times and timeout times are 0, the naviga-tion success rate is better than the comparison algorithm, and the average navigation time is 2% shorter than the best algorithm; When the number of pedestrians and navigation distance in the environment change, the algo-rithm is still effective, and the navigation time is shorter than the comparison algorithm.

Abstract:Aiming at deflection or loss of high-speed railway fasteners caused by the loose fasteners in the ballastless track of high-speed railway, this paper proposes a high-speed railway fastener detection algorithm based on improved Faster R-CNN. Deformable convolution was introduced in the feature extraction network to build deformable residual convolution block(DRCB), which makes the feature extraction process more focused on the fastener region and achieves the accurate extraction of fastener state; and Alpha-IoU was used as the target regression loss function to improve the regression accuracy of high-speed railway fasteners. The experimental results show that the algorithm proposed improves the detection accuracy of high-speed railway fasteners and can perform fastener localization and state detection more accurately than other algorithms.

Abstract:In order to explore the effect of hysteresis damping on the band gap of periodic track structure, the ballasted track of was taken as an example, and the band gap characteristics were analyzed based on the energy functional variational principle. By introducing hysteretic damping effect into rails, fasteners and track bed, the variation of dispersion characteristics with damping of periodic ballasted track was studied. Furthermore, the vibration transmission characteristics of the track structure under the effect of damping were explored. The results show that the band gap range of the undamped track structure is consistent with the attenuation range of the vibration response; the rail damping is very small and has little effect on the band gap of the track structure, which can be ignored when calculating and predicting vibration; the damping of the fasteners slightly increases the track structural band gap and has little effect on the overall band gap, but for the vibration response, the dissipation effect of the fastener damping increases the vibration attenuation range within 150~500 Hz; the increase of the ballast bed damping increases the first-order band gap range, but it decreases the second-order bandgap range, in the vibration response, increasing the damping of the track bed can dampen the vibration of the rail within 260 Hz.

Abstract:In order to improve the wear resistance of CrN coating, magnetron sputtering technology was used to study the influence of external Cr layer on the wear width of CrN coating. The friction and wear of the surface were studied under different loads, rotational speeds and radius. The results show that the effect of centrifugal force is more obvious with the increase of rotation radius. When the rotation speed is 300 r/min, the average wear width of the CrN coating without sputtering Cr layer reaches 945.7 μm and the outer wear is more serious. Under the same conditions, the wear width of the outer Cr layer is 571.2 μm. It shows that the outer Cr layer can effectively inhibit the increase of surface wear area. When the outer Cr layer is being sputtered, the friction coefficient and the wear area width of the surface increase with the increase of the rotation radius at 200 r/min. The wear marks on the surface are furrowed and the wear mechanism is abrasive.

Abstract:Inspired by the recent experiments of cavity-magnon system and the theories of nonlinear reservoir, a scheme of coupling a cavity-magnon system to a squeezed reservoir is proposed to analyze the magnon blockade effect, thus realizing the manipulation of magnetism at quantum level. An yttrium iron garnet sphere was located in a driven microwave cavity. The Kittel mode in the yttrium iron garnet sphere interacted with the microwave cavity mode, and the cavity field was coupled to a squeezed vacuum reservoir. By numerically solving the quantum master equation of the system, the influence of various factors such as coupling strength, detuning and dissipation rate on the correlation function was analyzed in details. It is proved theoretically that the cavity-magnon system coupled to a squeezed reservoir can induce single-magnon blockade and two-magnon blockade, and the switching among single-magnon blockade, two-magnon blockade and two-magnon tunneling can be flexibly controlled by tuning the driving intensity or the detuning. The magnon blockade effect in the proposed scheme is mainly induced by the nonlinearity of the squeezed reservoir, which provides a possible new method to realize single or double magnon blockade in cavity-magnon system.

Abstract:Density peak clustering(DPC) is a novel clustering algorithm based on density and distance. It is widely used in the field of data mining because of its simple principle, no iteration and the ability to process shape datasets. However, DPC algorithm also has some defects，including the sensitive cutoff distance parameter, nonautomatic selection of initial clustering center, the chain problem in subsequent allocation and high time complexity. This paper summarizes the research status of DPC algorithm. Firstly, it introduces the principle and process of DPC algorithm. Secondly, in view of the deficiencies of DPC algorithm, the optimization of DPC algorithm is summarized and analyzed, and the core technology, advantages and disadvantages of the optimization algorithm are pointed out. Finally, the possible challenges and development trend of DPC algorithm in the future are concluded.

Abstract:The road surface at tram grade crossings has borne combined loads of passing vehicles and trams. The load conditions and distresses of this area are complicated and varied, which becomes relatively weak spots on municipal roads. In order to clarify the distress mechanism of this transition pavement at grade crossings, on the basis of field investigation, the statistics and classification of the distresses were carried out, and a 3D finite element model was established to analyze the mechanical response of the road-rail pavement structure, in which combined vehicle and tram loads were conducted. The field investigation results show that the distresses in this transition area are mainly distributed within 30 cm of the track side, and the settlement of pavement near the track is mostly distributed within 0 ~10 mm. The numerical results show that the poor bearing capacity and strength and the disharmony deformation of pavement structure are the main reasons for the failure of the roadrail transition pavement. Focusing on the mechanism of the distress, the countermeasures of laying high modulus concrete under the pavement structure and adding transitional pavement materials between the road and the track are put forward.