Traffic bottleneck characteristics caused by the reduction of lanes in an optimal velocity model

In this paper, the lane reduction bottleneck is investigated using the optimal velocity model, in which two kinds of vehicles (fast and slow) are introduced. The asymmetric lane changing rules in the slowdown section and the lane squeezing behaviors at the bottleneck are taken into account. Under the periodic boundary condition, the numerical simulations are performed. The traffic states change with increasing density. And an interesting phenomenon of ratio inversion appears. When the current saturates, the headway and velocity discontinuously vary with the position. In addition, traffic patterns and the phase transition points depend greatly on the speed limit and the length of the slowdown section.     

Traffic flow behavior at un-signalized intersection with crossings pedestrians

Mixed traffic flux composed of crossing pedestrians and vehicles extensively exists in cities. To study the characteristics of the interference traffic flux, we develop a pedestrian-vehicle cellular automata model to present the interaction behaviors on a simple cross road. By realizing the fundamental parameters (i.e. injecting rates ${\alpha }_1$, ${\alpha }_2$, the extracting rate β and the pedestrian arrival rate ${\alpha }_P$), simulations are carried out. The vehicular traffic flux is calculated in terms of rates. The effect of the crosswalk can be regarded as a dynamic impurity. The system phase diagrams in the $({\alpha }_1,{\alpha }_P)$ plane are built. It is found that the phase diagrams consist essentially of four phases namely Free Flow, Congested, Maximal Current and Gridlock. The value of the Maximal current phase depends on the extracting rate β, while the Gridlock phase is achieved only when the pedestrians generating rate is higher than a critical value. Furthermore, the effect of vehicles changing lane ($P_{\mathrm{ch}1},P_{\mathrm{ch}2}$) and the location of the crosswalk $X_P$ on the dynamic characteristics of vehicles flow are investigated. It is found that traffic situation in the system is slightly enhanced if the location of the crosswalks $X_P$ is far from the intersection. However, when $P_{\mathrm{ch}1}$, $P_{\mathrm{ch}2}$ increase, the traffic becomes congested and the Gridlock phase enlarges.     

准滑模控制应用于行人通道的交通瓶颈

单向行人交通在瓶颈处极易发生堵塞,设置障碍会阻碍行人通行,却能保证瓶颈处通畅.本文将准滑模控制引入LWR模型中,理论推导控制变量.在三车道宏观交通流模型基础上,模拟瓶颈处的障碍对行人流的影响,解释设置障碍的作用.研究表明准滑模控制变量的设置与阈值有关,当阈值对应基本图的流量最大点时,行人流量能保持最大值,达到提高单向行人交通瓶颈处的行人流通过效率. 关键词： 交通瓶颈 准滑模控制 LWR模型     

An interferometric technique for measuring gas flow velocity at large peclet numbers

A technique for determining the gas flow velocity at large Peclet numbers using an interferometric approach has been developed. It is shown that if a heat source is introduced in a uniform gas flow, areas under curves describing shifts of interference maxima are approximately equal to each other and tend to a certain limiting value. The limiting area is inversely proportional to the gas flow velocity and does not depend on the heat conduction and the type of flow. A theoretical expression has been derived that gives the relative error of velocity determinations by the method developed.     

Traffic flow of connected and automated vehicles at lane drop on two-lane highway: An optimization-based control algorithm versus a heuristic rules-based algorithm

This paper investigates traffic flow of connected and automated vehicles at lane drop on two-lane highway. We evaluate and compare performance of an optimization-based control algorithm (OCA) with that of a heuristic rules-based algorithm (HRA). In the OCA, the average speed of each vehicle is maximized. In the HRA, virtual vehicle and restriction of the command acceleration caused by the virtual vehicle are introduced. It is found that (i) capacity under the HRA (denoted as C_H) is smaller than capacity under the OCA; (ii) the travel delay is always smaller under the OCA, but driving is always much more comfortable under the HRA; (iii) when the inflow rate is smaller than C_H, the HRA outperforms the OCA with respect to the fuel consumption and the monetary cost; (iv) when the inflow rate is larger than C_H, the HRA initially performs better with respect to the fuel consumption and the monetary cost, but the OCA would become better after certain time. The spatiotemporal pattern and speed profile of traffic flow are presented, which explains the reason underlying the different performance. The study is expected to help for better understanding of the two different types of algorithm.     

Aerodynamic actuation characteristics of radio-frequency discharge plasma and control of supersonic flow

In this paper, aerodynamic actuation characteristics of radio-frequency(RF) discharge plasma are studied and a method is proposed for shock wave control based on RF discharge. Under the static condition, a RF diffuse glow discharge can be observed; under the supersonic inflow, the plasma is blown downstream but remains continuous and stable.Time-resolved schlieren is used for flow field visualization. It is found that RF discharge not only leads to continuous energy deposition on the electrode surface but also induces a compression wave. Under the supersonic inflow condition, a weak oblique shock wave is induced by discharge. Experimental results of the shock wave control indicate that the applied actuation can disperse the bottom structure of the ramp-induced oblique shock wave, which is also observed in the extracted shock wave structure after image processing. More importantly, this control effect can be maintained steadily due to the continuous high-frequency(MHz) discharge. Finally, correlations for schlieren images and numerical simulations are employed to further explore the flow control mechanism. It is observed that the vortex in the boundary layer increases after the application of actuation, meaning that the boundary layer in the downstream of the actuation position is thickened. This is equivalent to covering a layer of low-density smooth wall around the compression corner and on the ramp surface, thereby weakening the compressibility at the compression corner. Our results demonstrate the ability of RF plasma aerodynamic actuation to control the supersonic airflow.     

Active control of normal particle velocity at a boundary between two media

A spatially one-dimensional model of a plane active double layer between two homogeneous elastic half-spaces is studied analytically. The layer synthesizes a preset smooth trajectory of the controlled boundary between the media without any mechanical support. The outer layer of the coating is a piezoelectric, and the inner layer is a polymer that is transparent for low-frequency sound and opaque for high-frequency sound because of dissipation. An algorithm for controlling the piezoelectric elements of the layer on the basis of signals from surface particle-velocity sensors is proposed, and a method for measuring the particle velocity is developed. Conditions of stability and efficiency of the synthesis are formulated. It is shown that the active layer thickness can be much smaller than the wavelength corresponding to the minimal time scale of the boundary trajectory to be formed. The accuracy of the trajectory synthesis depends on the accuracy of measuring, computing, and actuating elements of the system but does not depend on the vibroacoustic characteristics of the half-spaces separated by the active layer or on the presence of smooth waves in these half-spaces. For the synthesis to be efficient, the operating frequency band and the dynamic range of sensors and actuators should be many times greater than the frequency band and the dynamic range of the trajectory to be formed.     

Dilemma game structure hidden in traffic flow at a bottleneck due to a 2 into 1 lane junction

Following Yamauchi’s study [A. Yamauchi, J. Tanimoto, A. Hagishima, H. Sagara, Dilemma game structure observed in traffic flow at a 2-to-1 lane junction, Physical Review E 79 (2009) 036104], we find that several social dilemma structures are represented by n-person Prisoner’s Dilemma (n-PD) games in certain traffic flow phases at a bottleneck caused by a lane-closing section. In this study, the stochastic Nishinari-Fukui-Schadschneider (S-NFS) model was adopted as a cellular automaton traffic model. In the system, two classes of driver-agents coexist: C-Agents (cooperative strategy) always driving in the first lane, and D-Agents (defective strategy) trying to drive in a lower-density lane, whether the first or the second lane. In relatively high-density flow phases, such as the metastable phase and the high-density phase, we found n-PD games, where D-Agents’ interruption into the first lane from the second just before the lane-closing section creates a heavier traffic jam, which reduces social efficiency. This could be solved by decreasing the interruption probability, which can be realized by a provision where drivers in the first lane firmly refuse interruptions.     

Anisotropic velocity correlation spectrum at small scales in a homogeneous turbulent shear flow

A simple theoretical analysis and direct numerical simulations on 512(3) grid points suggest that the velocity correlation spectrum tensor in the inertial subrange of homogeneous turbulent shear flow at high Reynolds number is given by a simple form that is an anisotropic function of the wave vector. The tensor is determined by the rate of the strain tensor of the mean flow, the rate of energy dissipation per unit mass, the wave vector, and two nondimensional constants.     

Traffic flow behavior at a single lane roundabout as compared to traffic circle

In this paper, we propose a stochastic Cellular Automata (CA) model to study traffic flow at a single-lane urban roundabout (resp. traffic circle) of N   entry points (resp. exit points), the entry points are controlled by rates _α1${\alpha }_1$ and _α2${\alpha }_2$ while the removal rates from the exit points are denoted by β. The traffic is controlled by a self-organized scheme. Based on computer simulation, density profiles, global density and current are calculated in terms of rates. Furthermore, the phase diagrams for roundabout as well as traffic circle are constructed. It has turned out that the phase diagrams consist essentially of two phases namely free flow and jamming. It is noted that the typology of the phase diagrams of the roundabout is not similar to it in the traffic circle. Furthermore, we have compared the performance of the two systems in terms of the geometrical properties and the number of entry points.     

浅海声场垂直振速与水平振速相关特性及应用

基于矢量水听器记录的质点振速信号,研究了浅海声场垂直振速与水平振速的相关特性,理论与仿真结果表明记录的垂直振速与水平振速的相关系数是矢量水听器俯仰角度的函数,矢量水听器不发生俯仰时二者的相关系数约为零。基于上述特点,提出了一种利用矢量水听器记录信号自适应校正矢量水听器俯仰姿态的方法,实验结果表明,该方法能有效校正矢量水听器俯仰姿态。     

Mitigation of congestion at a traffic bottleneck with diversion and lane restrictions

Mitigation of congestion on a two-lane highway with an off-ramp and an on-ramp is simulated with three-phase traffic theory. Advanced travel information-the average velocity of vehicles near the bottleneck at an on-ramp-is used to divert vehicles at an upstream off-ramp. If enough vehicles divert, previously expanding synchronous flow congestion can be stalled and isolated to the region between the ramps. The introduction of lane restrictions (forbidding lane changing on the portion of highway between the ramps) in addition to diversion substantially reduces and essentially eliminates the congestion, restoring flow to nearly free-flow conditions.     

The characteristics of surface arc plasma and its control effect on supersonic flow

The characteristic of surface arc plasma included millisecond and microsecond actuation in supersonic flow is investigated both experimentally and numerically. In the experiment, the discharge characteristic of surface arc plasma in quiescent air and supersonic flow is recorded. The stable oblique shock could be observed with millisecond actuation. And the unstable compressive wave could be also observed with microsecond actuation. In the numerical investigation, plasma actuation is defined as a source term with input power density from discharge V–I characteristic, which is expected to better describe the influence of heating process. The numerical results are coincident with experimental results. In order to confirm the capability of surface arc plasma actuation to control supersonic flow, experimental investigations on control shock induced by ramp and separation of boundary layer induced by impinging shock are performed. All the results demonstrate the control effect of surface arc plasma actuation onto supersonic flow.     

Microfluidic valves for flow control at low Reynolds numbers

Fluidics is a technology of generating and controlling fluid flows — preferably without the action of mechanical moving components. Microfluidics perform these tasks in small, typically micronsized structures. Essential part of almost all microfluidic systems are flow control valves. The basic problem is the low Reynolds numberRe: inertial effects used in large-scale fluidics are too small relative to viscous dissipation. New approaches, such as pressure or electrokinetic driving are required. In the subdynamic, viscosity dominated flow regime, Re ceases to be of importance and for pressure-driven valves a new characterisation number was to be introduced. An example of a diverter valve, developed by the author, is described and the meaning of the new dimensionless parameter is demonstrated.     

光波位相耦合色散效应与固态介质中室温下的光速调控

文章介绍了作者利用光波位相耦合的色散效应调控光速的新机制，并利用光折变位相耦合的色散效应在室温下在Bi12SO20晶体中实现极慢光速和超光速现象．进一步的研究表明，在Bi12SO20晶体中传播的、由位相耦合色散效应引起的慢光和快光由于光折变光强耦合效应而得到了相干放大．     

演示流体压强与流速关系的实验装置

利用有机玻璃管、吸管、泡沫球等简易材料自制了演示流体压强与流速关系的实验装置。该装置有效地解决了小球随意滚动、吹气方向不固定等问题。实验用泡沫球代替乒乓球,并将其放置在玻璃管中放置,使实验过程不受外界空气影响,且较轻的泡沫球更易运动,实验效果更明显。利用该原理还自制了模拟非洲草原犬鼠洞穴的演示装置,有趣且直观地演示了犬鼠洞穴中的气体流向。     

Lubricant film flow and depletion characteristics at head/disk storage interface

The characteristics of lubricant film at head/disk interface(HDI) are essential to the stability of hard disk drives. In this study, the theoretical models of the lubricant flow and depletion are deduced based on Navier–Stokes(NS) and continuity equations. The air bearing pressure on the surface of the lubrication film is solved by the modified Reynolds equation based on Fukui and Kaneko(FK) model. Then the lubricant film deformations for a plane slider and double-track slider are obtained. The equation of lubricant film thickness is deduced with the consideration of van der Waals force, the air bearing pressure, the surface tension, and the external stresses. The lubricant depletion under heat source is simulated and the effects of different working conditions including initial thickness, flying height and the speed of the disk on lubricant depletion are discussed. The main factors that cause the lubricant flow and depletion are analyzed and the ways to reduce the film thickness deformation are proposed. The simulation results indicate that the shearing stress is the most important factor that causes the thickness deformation and other terms listed in the equation have little influence. The thickness deformation is dependent on the working parameter, and the thermal condition evaporation is the most important factor.     

小孔流速实验中的排水时间和流量系数的研究

本文以水作为理想流体,考虑到水头损失和孔口缩流效应,对小孔流速实验涉及的容器排水问题进行了系统的理论和实验研究.从理论上推导得出了圆柱形容器排水时间的解析解,分析了排水时间和自由液面速度、流量系数之间的规律,提出了排水时间的等效性.实验上,加工了底部开有不同小孔的大型圆柱形容器,测量了容器排水时间随液面高度的变化关系,借助实验结果计算了流量系数值,验证了容器排水时间的等效性关系,实验结果与理论计算符合较好.     

Influence of crystal mosaicity on the X-radiation characteristics observed at a small angle to the particle velocity direction

b-class mosaic crystals, including pyrolytic graphite, are widely used as neutron and X-ray mono-chromators in experimental physics and ensure a more intense yield of monochromatic radiation than do perfect crystals. A new technique that has been proposed for calculating the X-ray reflectivity of these crystals via the Monte Carlo method is implemented. According to this technique, repeated reflections of photons inside crystals and the experiment geometry can be correctly estimated for an arbitrary mosaicity distribution.     

Critical velocity for superfluid flow across the BEC-BCS crossover

Critical velocities have been observed in an ultracold superfluid Fermi gas throughout the BEC-BCS crossover. A pronounced peak of the critical velocity at unitarity demonstrates that superfluidity is most robust for resonant atomic interactions. Critical velocities were determined from the abrupt onset of dissipation when the velocity of a moving one-dimensional optical lattice was varied. The dependence of the critical velocity on lattice depth and on the inhomogeneous density profile was studied.