In light of previous work [Phys. Rev. E 60 4000(1999)], a modified coupled-map car-following model is proposed by considering the headways of two successive vehicles in front of a considered vehicle described by the optimal velocity function. The non-jam conditions are given on the basis of control theory. Through simulation, we find that our model can exhibit a better effect as p = 0.65, which is a parameter in the optimal velocity function. The control scheme, which was proposed by Zhao and Gao, is introduced into the modified model and the feedback gain range is determined. In addition,a modified control method is applied to a mixed traffic system that consists of two types of vehicle. The range of gains is also obtained by theoretical analysis. Comparisons between our method and that of Zhao and Gao are carried out, and the corresponding numerical simulation results demonstrate that the temporal behavior of traffic flow obtained using our method is better than that proposed by Zhao and Gao in mixed traffic systems.
This paper studies the influence of the accelerated overtaking process on the vehicles' transient aerodynamic characteristics, through 3-D numerical simulations with dynamic meshes and sliding interface technique. Numerical accuracy is verified by experimental results. The aerodynamic characteristics of vehicles in the uniform overtaking process and the accelerated overtaking process are compared. It is shown that the speed variation of the overtaking van would influence the aerodynamic characteristics of the two vans, with greater influence on the overtaken van than on the overtaking van. The simulations of three different accelerated overtaking processes show that the greater the acceleration of the overtaking van, the larger the aerodynamic coefficients of the overtaken van. When the acceleration of the overtaking van increases by 1 m/s2, the maximum drag force, side force and yawing moment coefficients of the overtaken van all increase by more than 6%, to seriously affect the power performance and the stability of the vehicles. The analysis of the pressure fields under different accelerated conditions reveals the cause of variations of the aerodynamic characteristics of vehicles.
Urban tunnels are generally narrow and fire smoke can hardly diffuse.In the present study,numerical simulation is used to analyze the diffusion of high temperature smoke produced by fire inside a specific tunnel(the Kaiyuan tunnel).The results are compared with similar data relating to other tests to determine the validity of the numerical method.Moreover,the critical velocity obtained by numerical simulation of 5 MW,20 MW,and 50 MW fires in curved and linear sections of the considered tunnel is compared with the values obtained using empirical formulas.The results show that,for the tunnel ventilation design,it is necessary to consider the fan pressurization at different sections and the fan pressurization should be higher at curved sections than that at linear sections.The safety of personnel escaping under different critical velocity values in the linear section has also been considered.On the basis of our findings,if only relying on natural ventilation,people can escape safely for the case of small fires,whereas for medium and large fires,it is necessary to turn on mechanical ventilation in time(and in order to avoid the danger caused by rapid diffusion of smoke,the timing of mechanical ventilation should be carefully tuned).
A new car-following model is proposed based on the full velocity difference model(FVDM) taking the influence of the friction coefficient and the road curvature into account. Through the control theory, the stability conditions are obtained,and by using nonlinear analysis, the time-dependent Ginzburg-Landau(TDGL) equation and the modified Korteweg-de Vries(mKdV) equation are derived. Furthermore, the connection between TDGL and mKdV equations is also given. The numerical simulation is consistent with the theoretical analysis. The evolution of a traffic jam and the corresponding energy consumption are explored. The numerical results show that the control scheme is effective not only to suppress the traffic jam but also to reduce the energy consumption.
