Free Flow Phase Research Articles

A two-dimensional CA model for traffic flow with car origin and destination

Dynamic phase transitions in a two-dimensional traffic flow model defined on a decorated square-lattice are studied numerically. The square-lattice point and the decorated site denote intersections and roads, respectively. In the present model, a car has a finite deterministic path between the origin and the destination, which is assigned to the car from the beginning. In this new model, we found a new phase between the free-flow phase and the frozen-jam phase that is absent from previous models. The new model is characterized by the persistence of a macroscopic cluster. Furthermore, the behavior in this macroscopic cluster phase is classified into three regions characterized by the shape of the cluster. The boundary of the three regions is phenomenologically estimated. When the trip length is short and the car density is high, both ends of the belt-like cluster connect to each other through the periodic boundary with some probability. This type of cluster is classified topologically as a string on a two-dimensional torus.

Jamming of directed traffic on a square lattice

The phase transition from a free-flow phase to a jammed phase is animportant feature of traffic networks. We study this transition in the caseof a simple square lattice network for different values of data posting rate(ρ) by introducinga parameter p which selects a neighbour for onward data transfer depending on queued traffic. For everyρ there is acritical value of p above which the system becomes jammed. Theρ–p phasediagram shows some interesting features. We also show that the average load diverges logarithmicallyas p approaches pc and the queue length distribution exhibits exponential and algebraic nature in differentregions of the phase diagram.

Dynamics of congestion transition triggered by multiple walkers on complex networks

The congestion transition triggered by multiple walkers walking along the shortest path on complex networks is numerically investigated. These networks are composed of nodes that have a finite capacity in analogy to the buffer memory of a computer. It is found that a transition from free-flow phase to congestion phase occurs at a critical walker density fc, which varies for complex networks with different topological structures. The dynamic pictures of congestion for networks with different topological structures show that congestion on scale-free networks is a percolation process of congestion clusters, while the dynamics of congestion transition on non-scale-free networks is mainly a process of nucleation.

Probabilistic Breakdown Phenomenon at On-Ramp Bottlenecks in Three-Phase Traffic Theory

A nucleation model for the breakdown phenomenon at an on-ramp bottleneck is presented. This model is based on Kerner's three-phase traffic theory. In this theory, traffic breakdown is associated with a first-order phase transition from the free-flow phase to the synchronized-flow phase. It is suggested that because of merging of a flow on the main road with an on-ramp inflow, free flow is spatially nonhomogeneous in the neighborhood of a bottleneck. This permanent and motionless nonhomogeneity can be considered a deterministic vehicle cluster localized at the bottleneck. Because of the deterministic cluster, the breakdown phenomenon can also occur if there were no fluctuations in free flow. At a lower flow rate, traffic breakdown nucleation occurs through a random increase in vehicle number within the deterministic vehicle cluster. The mean time delay and the associated nucleation rate of traffic breakdown at the bottleneck were found and investigated. The model and a nucleation rate of traffic breakdown exhibit qualitatively different features compared with previous results.

Probabilistic Breakdown Phenomenon at On-Ramp Bottlenecks in Three-Phase Traffic Theory

A nucleation model for the breakdown phenomenon at an on-ramp bottleneck is presented. This model is based on Kerner's three-phase traffic theory. In this theory, traffic breakdown is associated with a first-order phase transition from the free-flow phase to the synchronized-flow phase. It is suggested that because of merging of a flow on the main road with an on-ramp inflow, free flow is spatially nonhomogeneous in the neighborhood of a bottleneck. This permanent and motionless nonhomogeneity can be considered a deterministic vehicle cluster localized at the bottleneck. Because of the deterministic cluster, the breakdown phenomenon can also occur if there were no fluctuations in free flow. At a lower flow rate, traffic breakdown nucleation occurs through a random increase in vehicle number within the deterministic vehicle cluster. The mean time delay and the associated nucleation rate of traffic breakdown at the bottleneck were found and investigated. The model and a nucleation rate of traffic breakdown ...

Phase transition in a directed traffic flow network

The generic feature of traffic in a network of flowing electronic data packets is a phase transition from a stationary free-flow phase to a continuously growing congested nonstationary phase. In the most simple network of directed oriented square lattice we have been able to observe all crucial features of such flow systems having nontrivial critical behavior near the critical point of transition. The network here is in the shape of a square lattice and data packets are randomly posted with a rate rho at one side of the lattice. Each packet executes a directed diffusive motion toward the opposite boundary where it is delivered. Packets accumulated at a particular node form a queue and a maximum of m such packets randomly jump out of this node at every time step to its neighbors on a first-in-first-out basis. The phase transition occurs at rho(c) = m. The distribution of travel times through the system is found to have a log-normal behavior and the power spectrum of the load time series shows 1/f-like noise similar to the scenario of Internet traffic.

New kind of phase separation in a CA traffic model with anticipation

A cellular automaton model of traffic flow taking into account velocity anticipation is introduced. The strength of anticipation can be varied to describe different driving schemes. We find a new phase separation into a free-flow regime and a so-called v-platoon in an intermediate density regime. In a v-platoon all cars move with velocity v and have vanishing headway. The velocity v of a platoon only depends on the strength of anticipation. At high densities, a congested state characterized by the coexistence of a 0-platoon with several v-platoons is reached. The results are not only relevant for automated highway systems, but also help to elucidate the effects of anticipation that play an essential role in realistic traffic models. From a physics point of view the model is interesting because it exhibits phase separation with a condensed phase in which particles move coherently with finite velocity coexisting with either a non-condensed (free-flow) phase or another condensed phase that is non-moving.

Phase transition and 1/ f noise in a computer network model

Using a simple cellular automaton model of data packets transport in the Internet, the travel times of data packets and transport rates of routers along a fixed path are studied. In this model the additive increasing of transport rates, extraneous random interferences and finite capacity of router are considered. Changing the mean injecting rate of data packets, numerical simulation results show that there exists free flow and congested phase characterized by the different power spectrum of the travel times and the transport rates. While the power spectrum of both the travel times and the transport rates show 1/ f noise (power law) in the free flow, the power spectrum of the travel times is approximately characterized by 1/ f noise at low frequencies and white noise at high frequencies, and that of transport rates of routers only by white noise in the congested phase. These results are in agreement with previous experimental data.

A study on an improved Nagel-Schreckenberg traffic flow -model with open boundary conditions

Using the improved Nagel-Schreckenberg traffic model with open boundary conditions,we present the fundamental diagrams of traffic flow under different parameters by numerical simulation.It turns out that the traffic flow of the improved Nagel-Schrec-kenberg model is greater than that of the Nagel-Schreckenberg model,then we analyse the characters and critical points of the transition from free flow phase to maximum current phase and the transition from jamming phase to free flow phase.

Random walk theory of jamming in a cellular automaton model for traffic flow

The jamming behavior of a single lane traffic model based on a cellular automaton approach is studied. Our investigations concentrate on the so-called VDR model which is a simple generalization of the well-known Nagel–Schreckenberg model. In the VDR model one finds a separation between a free flow phase and jammed vehicles. This phase separation allows to use random walk like arguments to predict the resolving probabilities and lifetimes of jam clusters or disturbances. These predictions are in good agreement with the results of computer simulations and even become exact for a special case of the model. Our findings allow a deeper insight into the dynamics of wide jams occuring in the model.

Critical behavior of a traffic flow model

The Nagel-Schreckenberg traffic flow model shows a transition from a free flow regime to a jammed regime for increasing car density. The measurement of the dynamical structure factor offers the chance to observe the evolution of jams without the necessity to define a car to be jammed or not. Above the jamming transition the dynamical structure factor exhibits for a given k-value two maxima corresponding to the separation of the system into the free flow phase and jammed phase. We obtain from a finite-size scaling analysis of the smallest jam mode that approaching the transition long range correlations of the jams occur.

Jamming transition in a cellular automaton model for traffic flow

The cellular automaton model for traffic flow exhibits a jamming transition from a free-flow phase to a congested phase. In the deterministic case this transition corresponds to a critical point with diverging correlation length. In the presence of noise, however, no consistent picture has emerged up to now. We present data from numerical simulations which suggest the absence of critical behavior. The transition of the deterministic case is smeared out and one only observes the remnants of the critical point.

Multistage centrifugal extractors

With centrifugal extractors recently gaining importance in the extraction technology of nuclear-power materials, the authors have designed the ETs models of multistage centrifugal extractors featuring liquid mixing under gravity and free-flow phase discharge. The specifications are given and the models are shown. The extractors can be used in both fast and slow mass-transfer processes. The mechanical reliability of the centrifugal extractors depends to a large extent on the reliability of the bracket bearing and of the rotor unit and drive as a whole.