2,087 research outputs found
Disorder Effects in CA-Models for Traffic Flow
We investigate the effect of quenched disorder in the Nagel-Schreckenberg
model of traffic flow. Spatial inhomogenities, i.e. lattice sites where the
braking probability is enlarged, are considered as well as particle disorder,
i.e. cars of a different maximum velocity. Both types of disorder lead to
segregated states.Comment: 6 pages, 4 postscript figures, Proceedings of the conference "Traffic
and Granular Flow '97", Duisburg, Germany, October 5-8, 199
A realistic two-lane traffic model for highway traffic
A two-lane extension of a recently proposed cellular automaton model for
traffic flow is discussed. The analysis focuses on the reproduction of the lane
usage inversion and the density dependence of the number of lane changes. It is
shown that the single-lane dynamics can be extended to the two-lane case
without changing the basic properties of the model which are known to be in
good agreement with empirical single-vehicle data. Therefore it is possible to
reproduce various empirically observed two-lane phenomena, like the
synchronization of the lanes, without fine-tuning of the model parameters
Origin of rebounds with a restitution coefficient larger than unity in nanocluster collisions
We numerically investigate the mechanism of super rebounds for head-on
collisions between nanoclusters in which the restitution coefficient is larger
than unity. It is confirmed that the temperature and the entropy of the
nanocluters decrease after the super rebounds by our molecular dynamics
simulations. It is also found that the initial metastable structure plays a key
role for the emergence of the super rebounds.Comment: 8 pages, 10 figures, to be published in Phys. Rev.
Magnetic Actuators and Suspension for Space Vibration Control
The research on microgravity vibration isolation performed at the University of Virginia is summarized. This research on microgravity vibration isolation was focused in three areas: (1) the development of new actuators for use in microgravity isolation; (2) the design of controllers for multiple-degree-of-freedom active isolation; and (3) the construction of a single-degree-of-freedom test rig with umbilicals. Described are the design and testing of a large stroke linear actuator; the conceptual design and analysis of a redundant coarse-fine six-degree-of-freedom actuator; an investigation of the control issues of active microgravity isolation; a methodology for the design of multiple-degree-of-freedom isolation control systems using modern control theory; and the design and testing of a single-degree-of-freedom test rig with umbilicals
Localized defects in a cellular automaton model for traffic flow with phase separation
We study the impact of a localized defect in a cellular automaton model for
traffic flow which exhibits metastable states and phase separation. The defect
is implemented by locally limiting the maximal possible flow through an
increase of the deceleration probability. Depending on the magnitude of the
defect three phases can be identified in the system. One of these phases shows
the characteristics of stop-and-go traffic which can not be found in the model
without lattice defect. Thus our results provide evidence that even in a model
with strong phase separation stop-and-go traffic can occur if local defects
exist. From a physical point of view the model describes the competition
between two mechanisms of phase separation.Comment: 14 pages, 7 figure
Microgravity vibration isolation: An optimal control law for the one-dimensional case
Certain experiments contemplated for space platforms must be isolated from the accelerations of the platforms. An optimal active control is developed for microgravity vibration isolation, using constant state feedback gains (identical to those obtained from the Linear Quadratic Regulator (LQR) approach) along with constant feedforward (preview) gains. The quadratic cost function for this control algorithm effectively weights external accelerations of the platform disturbances by a factor proportional to (1/omega)(exp 4). Low frequency accelerations (less than 50 Hz) are attenuated by greater than two orders of magnitude. The control relies on the absolute position and velocity feedback of the experiment and the absolute position and velocity feedforward of the platform, and generally derives the stability robustness characteristics guaranteed by the LQR approach to optimality. The method as derived is extendable to the case in which only the relative positions and velocities and the absolute accelerations of the experiment and space platform are available
Steady state solutions of hydrodynamic traffic models
We investigate steady state solutions of hydrodynamic traffic models in the
absence of any intrinsic inhomogeneity on roads such as on-ramps. It is shown
that typical hydrodynamic models possess seven different types of inhomogeneous
steady state solutions. The seven solutions include those that have been
reported previously only for microscopic models. The characteristic properties
of wide jam such as moving velocity of its spatiotemporal pattern and/or
out-flux from wide jam are shown to be uniquely determined and thus independent
of initial conditions of dynamic evolution. Topological considerations suggest
that all of the solutions should be common to a wide class of traffic models.
The results are discussed in connection with the universality conjecture for
traffic models. Also the prevalence of the limit-cycle solution in a recent
study of a microscopic model is explained in this approach.Comment: 9 pages, 6 figure
Human behavior as origin of traffic phases
It is shown that the desire for smooth and comfortable driving is directly
responsible for the occurrence of complex spatio-temporal structures
(``synchronized traffic'') in highway traffic. This desire goes beyond the
avoidance of accidents which so far has been the main focus of microscopic
modeling and which is mainly responsible for the other two phases observed
empirically, free flow and wide moving jams. These features have been
incorporated into a microscopic model based on stochastic cellular automata and
the results of computer simulations are compared with empirical data. The
simple structure of the model allows for very fast implementations of realistic
networks. The level of agreement with the empirical findings opens new
perspectives for reliable traffic forecasts.Comment: 4 pages, 4 figures, colour figures with reduced resolutio
Memory effects in microscopic traffic models and wide scattering in flow-density data
By means of microscopic simulations we show that non-instantaneous adaptation
of the driving behaviour to the traffic situation together with the
conventional measurement method of flow-density data can explain the observed
inverse- shape and the wide scattering of flow-density data in
``synchronized'' congested traffic. We model a memory effect in the response of
drivers to the traffic situation for a wide class of car-following models by
introducing a new dynamical variable describing the adaptation of drivers to
the surrounding traffic situation during the past few minutes (``subjective
level of service'') and couple this internal state to parameters of the
underlying model that are related to the driving style. % For illustration, we
use the intelligent-driver model (IDM) as underlying model, characterize the
level of service solely by the velocity and couple the internal variable to the
IDM parameter ``netto time gap'', modelling an increase of the time gap in
congested traffic (``frustration effect''), that is supported by single-vehicle
data. % We simulate open systems with a bottleneck and obtain flow-density data
by implementing ``virtual detectors''. Both the shape, relative size and
apparent ``stochasticity'' of the region of the scattered data points agree
nearly quantitatively with empirical data. Wide scattering is even observed for
identical vehicles, although the proposed model is a time-continuous,
deterministic, single-lane car-following model with a unique fundamental
diagram.Comment: 8 pages, submitted to Physical Review
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