Dai Shi-qiang

Phase transition on speed limit traffic with slope

Through introducing a generalized optimal speed function to consider spatial position, slope grade and variable safe headway, the effect of slope in a single-lane highway on the traffic flow is investigated with the extended optimal speed model. The theoretical analysis and simulation results show that the flux of the whole road with the upgrade (or downgrade) increases linearly with density, saturates at a critical density, then maintains this saturated value in a certain density range and finally decreases with density. The value of saturated flux is equal to the maximum flux of the upgrade (or downgrade) without considering the slight influence of the drivers sensitivity. And the fundamental diagrams also depend on sensitivity, slope grade and slope length. The spatiotemporal pattern gives the segregation of different traffic phases caused by the rarefaction wave and the shock wave under a certain initial vehicle number. A comparison between the upgrade and the downgrade indicates that the value of saturated flux of the downgrade is larger than that of the upgrade under the same condition. This result is in accordance with the real traffic.

The Effect of the Relative Velocity on Traffic Flow

The optimal velocity model of traffic is extended to take the relative velocity into account. The traffic behavior is investigated numerically and analytically with this model. It is shown that the car interaction with the relative velocity can effect the stability of the traffic flow and raise critical density. The jamming transition between the freely moving and jamming phases is investigated with the linear stability analysis and nonlinear perturbation methods. The traffic jam is described by the kink solution of the modified Korteweg–de Vries equation. The theoretical result is in good agreement with the simulation.

Q-Learning for Adaptive Traffic Signal Control Based on Delay Minimization Strategy

The goal of the paper is to test the performance of Q-learning for adaptive traffic signal control. For Q-learning algorithm, the state is total delay of the intersection, and the action is phase green time change. The relationship between phase green time change and action space is discussed. The performance between Q-learning and fixed cycle signal setting for isolated intersection is compared. The computation results show that Q-learning for traffic signal control can achieve lesser delay for variable traffic condition.Incremental multistep Q learning (Q( lambda )) combines Q learning and TD(lambda ). Theoretically, Q(lambda ) has better performance than Q learning. The goal of the paper is to test the performance of Q(lambda ) for adaptive traffic signal control. For Q(lambda ), the state is total delay of the intersection, and the action is phase green time change. The relationship between phase green time change and action space is discussed. The performance between Q(lambda) learning and fixed cycle signal setting for isolated intersection is compared. The computation results show that Q(lambda ) learning for traffic signal control can achieve lesser delay for variable traffic condition.

Subconscious Effect on Pedestrian Counter Flow

We propose an extended lattice gas model with different maximum velocities to simulate pedestrian counter flow by considering the subconscious behaviour of walkers. Four types of walkers including faster right walkers, slower right walkers, faster left walkers and slower left walkers are involved in the simulation. The simulation results show that our model can capture some essential features of pedestrian counter flows, such as the lane formation, segregation effect and phase separation at higher densities. We also find that the subconscious effect can reduce the occurrence of jam cluster evidently compared with the case of un-subconscious effect. At large maximum velocity, the critical density corresponding to the maximum flow rate of the fundamental diagram is in good agreement with the empirical results.

Hamiltonian formulation of nonlinear water waves in a two-fluid system

In this paper, it is dealt with that the Hamiltonian formulation of nonlinear water waves in a two-fluid system, which consists of two layers of constant-density incompressible inviscid fluid with a horizontal bottom, an interface and a free surface. The velocity potentials are expanded in power series of the vertical coordinate. By taking the kinetic thickness of lower fluid-layer and the reduced kinetic thickness of upper fluid-layer as the generalized displacements, choosing the velocity potentials at the interface and free surface as the generalized momenta and using Hamiltons principle, the Hamiltonian canonical equations for the system are derived with the Legendre transformation under the shallow water assumption. Hence the results for single-layer fluid are extended to the case of stratified fluid.

One-dimensional cellular automation model of traffic flow based on car-following idea

An improved one-dimensional CA (Cellular Automaton) traffic model was proposed to describe the highway traffic under the periodic boundary conditions. This model was based on the idea of the car-following model, which claims that the motion of a vehicle at one time step depends on both its headway and the synchronous motion of the front vehicle, thus including indirectly the influence of its sub-neighboring vehicle. In addition, the socalled safety distance was introduced to consider the deceleration behavior of vehicles and the stochastic factor was taken into account by introducing the deceleration probability. Meanwhile, the conditional deceleration in the model gives a better description of the phenomena observed on highways. It is found that there exists the metastability and hysteresis effect of traffic flow in the neighborhood of critical density under different initial conditions. Since this model gives a reasonable depiction of the motion of a single vehicle, it is easy to be extended to the case of traffic flow under the control of traffic lights in cities.

SURFACE EFFECTS OF INTERNAL WAVE GENERATED BY A MOVING SOURCE IN A TWO-LAYER FLUID OF FINITE DEPTH

Based on the potential flow theory of water waves, the interaction mechanism between the free-surface and internal waves generated by a moving point source in the lower layer of a two-layer fluid was studied. By virtue of the method of Greens function, the properties of the divergence field at the free surface were obtained, which plays an important role in the SAR (Synthetic Aperture Radar) image. It is shown that the coupling interaction between the surface-wave mode and internal-wave mode must be taken into account for the cases of large density difference between two layers, the source approaching to the pynocline and the total Froude number Fr close to the critical number Fr2. The theoretical analysis is qualitatively consistent with the experimental results presented by Ma Hui-yang.

A semi-inverse algorithm in application of computer algebra

For the purpose of overcoming the difficulty of the so-called “intermediate expression swell” in applying computer algebra, a semi-inverse algorithm is proposed. The order of seeking solutions for various problems is partly inverted, i. e., the intermediate expressions appearing in computation are “frozen” in the symbolic form at first, and “unfrozen” till the formal expressionsof final solutions are found out. In this way, the overflow due to the shortage of saving space is avoided. The applications of the algorithm in the problems on nonlinear oscillation, dynamical optimization and interfacial solitary waves are described, which show the effectiveness of the semiinverse algorithm.

New insights into traffic dynamics: a weighted probabilistic cellular automaton model

From the macroscopic viewpoint for describing the acceleration behavior of drivers, this letter presents a weighted probabilistic cellular automaton model (the WP model, for short) by introducing a kind of random acceleration probabilistic distribution function. The fundamental diagrams, the spatio-temporal pattern are analyzed in detail. It is shown that the presented model leads to the results consistent with the empirical data rather well, nonlinear velocity-density relationship exists in lower density region, and a new kind of traffic phenomenon called neo-synchronized flow is resulted. Furthermore, we give the criterion for distinguishing the high-speed and low-speed neo-synchronized flows and clarify the mechanism of this kind of traffic phenomena. In addition, the result that the time evolution of distribution of headways is displayed as a normal distribution further validates the reasonability of the neo-synchronized flow. These findings suggest that the diversity and randomicity of drivers and vehicles has indeed remarkable effect on traffic dynamics.From the macroscopic viewpoint for describing the acceleration behaviour of drivers, a weighted probabilistic cellular automaton model (the WP model, for short) is proposed by introducing a kind of random acceleration probabilistic distribution function. The fundamental diagrams, the spatiotemporal patterns, are analysed in detail. It is shown that the presented model leads to the results consistent with the empirical data rather well, nonlinear flow-ensity relationship existing in lower density regions, and a new kind of traffic phenomenon called neo-synchronized flow. Furthermore, we give the criterion for distinguishing the high-speed and low-speed neo-synchronized flows and clarify the mechanism of this kind of traffic phenomenon. In addition, the result that the time evolution of distribution of headways is displayed as a normal distribution further validates the reasonability of the neo-synchronized flow. These findings suggest that the diversity and the randomicity of drivers and vehicles have indeed a remarkable effect on traffic dynamics.更多还原From the macroscopic viewpoint for describing the acceleration behaviour of drivers, a weighted probabilistic cellular automaton model (the WP model, for short) is proposed by introducing a kind of random acceleration probabilistic distribution function. The fundamental diagrams, the spatiotemporal patterns, are analysed in detail. It is shown that the presented model leads to the results consistent with the empirical data rather well, nonlinear flow–density relationship existing in lower density regions, and a new kind of traffic phenomenon called neo-synchronized flow. Furthermore, we give the criterion for distinguishing the high-speed and low-speed neo-synchronized flows and clarify the mechanism of this kind of traffic phenomenon. In addition, the result that the time evolution of distribution of headways is displayed as a normal distribution further validates the reasonability of the neo-synchronized flow. These findings suggest that the diversity and the randomicity of drivers and vehicles have indeed a remarkable effect on traffic dynamics.

Revised MAXBAND Model for Bandwidth Optimization of Traffic Flow Dispersion

MAXBAND model of bandwidth optimization assumes that all the vehicles have the same speed. But there is traffic flow dispersion because of different vehicle performance. Traffic flow dispersion has been described by normal distribution and geometric distribution. The paper integrates traffic flow dispersion model into MAXBAND model to optimize bandwidth of traffic flow dispersion. Revised model will more effectively optimize bandwidth.