Luis Javier Alvarez

Dynamic Friction Model-Based Tire-Road Friction Estimation and Emergency Braking Control

An adaptive control scheme for emergency braking of vehicles is designed based on a LuGre dynamic model for the tire-road friction. The wheel angular speed and longitudinal vehicle acceleration information are used to design a fast convergence observer to estimate the vehicle velocity and the internal state of the friction model. The unknown parameters of the dynamic friction model are estimated through a parameter adaptation law. A Lyapunov-based state estimator and a stabilizing braking controller are designed to achieve near to maximum braking capability of the vehicle. Underestimation of the maximum friction coefficient, a very desirable feature from the perspective of safety, is guaranteed by a proper choice of adaptation gains and initial values of the estimated friction parameters. fDOI: 10.1115/1.1870036g

Piecewise-Linearized Cell Transmission Model and Parameter Calibration Methodology

This paper studies the development of macroscopic freeway traffic models and parameter calibration methodologies that are computationally efficient and suitable for use in real-time traffic monitoring and control applications. Toward the fulfillment of these objectives, a macroscopic traffic model, the switching-mode model (SMM), is presented; it is a piecewise-linearized version of Daganzos cell transmission model (CTM). The observability and controllability properties of the SMM modes are reviewed because these properties are of fundamental importance in the design of traffic estimators and on-ramp metering controllers. A semiautomated method has been developed for calibrating the CTM and SMM parameters. In this method, a least-squares data-fitting approach is applied to loop detector data to determine free-flow speeds, congestion-wave speeds, and jam densities for specified subsections of a freeway. Bottleneck capacities are estimated from measured mainline and on-ramp flows. The calibration method wa...

Stability of macroscopic traffic flow modeling through wavefront expansion

In this paper, second-order macroscopic vehicle traffic flow models are discussed from the perspective of their capability to reproduce stable and unstable traffic flow behaviors observed in real traffic. To achieve this goal, a nonlinear traffic flow stability criterion is derived using a wavefront expansion technique. Qualitative relationships between traffic flow stability and model parameters are derived for an entire class of second-order macroscopic traffic flow models. The stability criterion is illustrated by numerical results using the CLAWPACK package for the well-known Payne-Whitham (PW) model. The newly derived stability results are consistent with previously reported results obtained using both microscopic models and approximate linearization methods. Moreover, the stability criteria derived in this paper can provide more refined information regarding the propagation of traffic flow perturbations and shock waves in second-order models than previously established methodologies.

Traffic flow control in automated highway systems

Abstract The problem of vehicle traffic flow control in automated highway systems is analyzed. Given desired vehicular density and velocity profiles along a highway, stabilizing velocity controllers are designed so that the real vehicle traffic flow converges to the desired profiles. The controllers are derived using vehicle conservation flow models and Lyapunov stability techniques. A highway topology with a discrete number of lanes is considered. Vehicles can have different destinations and perform diverse maneuvers. The control law obtained is distributed and therefore is suited for implementation on AHS hierarchical multilayer architectures. Simulation results are presented.

Surface models for γ-Al2O3 from molecular dynamics simulations

Molecular dynamics simulations for γ-Al2O3 and La3+-doped γ-Al2O3 crystals have been performed. From bulk simulations a description of the crystal-terminating layers in both doped and pure alumina solids is reported. The molecular dynamics simulations allow us to describe systematically for the first time the surface of the γ-Al2O3 crystal, taking into account the actual stoichiometry of the solid. This description results in a model in which the number of different surface sites is increased with respect to the previously reported models. The number of different surface sites may account for the IR spectra of hydroxy groups adsorbed on γ-Al2O3.

Maximum a posteriori estimation of the daily ozone peaks in Mexico City

Exposure to high levels of pollution is a persistent problem in large cities throughout the world. The ability to predict the occurrence of a high level of a pollutant allows environmental authorities to take preventive measures, such as controlling the emission of pollution. Communities and officials can also take actions to reduce the exposure of susceptible groups in the population. Therefore, being able to estimate the behavior of a given pollutant is of great importance. In this article we use a Markov chain model to study this behavior. In order to do so, we consider the sequence of the daily maximum measurements of a pollutant and let successive intervals containing them follow a Markov chain of order K>-0. The novelty here is that we allow K to be a random variable and estimate it and the corresponding transition probabilities using a maximum a posteriori method. The results are used to perform estimations about the behavior of ozone levels in Mexico City.

REAL-TIME IDENTIFICATION OF MAGNETO-RHEOLOGICAL DAMPERS

Modeling of magneto-rheological dampers to be used in semi-active control of civil engineering structures is addressed. The behavior of this kind of dampers is modeled through a first order Lugre dynamic friction model whose structure is analytically simpler than other dynamic friction models used in the literature. With this structure real-time parametric identification of the magneto-rheological damper is possible. Forces obtained with this modeling approach are in good agreement with those produced by other models.

ADAPTIVE EMERGENCY BRAKING CONTROL WITH OBSERVER-BASED DYNAMIC TIRE/ROAD FRICTION MODEL AND UNDERESTIMATION OF FRICTION COEFFICIENT

Abstract An adaptive control scheme for emergency braking of vehicles is designed based on a LuGre dynamic model for the tire/road friction. The wheel angular speed and longitudinal vehicle acceleration information are used to design an observer-estimator for vehicle velocity, friction internal state and friction parameters. A Lyapunov-based stabilizing controller is designed to achieve near maximum braking capability of the vehicle. Underestimation of the friction coefficient is guaranteed by a proper choice of adaptation gains and initial conditions of the friction parameters. Simulation results show that both the state estimation and the friction parameters converge to the true values and that vehicle stops rapidly.

Studies of LaAlO3 {100} surfaces by molecular dynamics simulations

Abstract Molecular dynamics simulations were used to study the bulk and {100} surface of LaAlO 3 . Bulk and surface structures and vibrational spectra are reported. Both the AlO 2 and LaO surface termination were studied. The LaO termination is clearly more stable than the AlO 2 termination.

Lithium diffusion in γ-LiAlO2, a molecular dynamics simulation

Abstract A set of molecular dynamics simulations in the microcanonical ensemble has been performed in order to study the diffusion of lithium in γ-LiAlO 2 , since this material is considered as candidate material for tritium breeder for fusion reactors. In this system tritium release and diffusion depends on the diffusion of lithium. Radial distribution functions, diffusion coefficient and activation energy for the process were determined from our calculations.