arXiv subjects

J. A. del Rio

Publications and source records attributed to J. A. del Rio.

11 recordsLinked to original sources

arXiv2005

Measurements of the bulk and interfacial velocity profiles in oscillating Newtonian and Maxwellian fluids

We present the dynamic velocity profiles of a Newtonian fluid (glycerol) and a viscoelastic Maxwell fluid (CPyCl/NaSal in water) driven by an oscillating pressure gradient in a vertical cylindrical pipe. The frequency range explored has been chosen to include the first three resonance peaks of the dynamic permeability of the viscoelastic fluid / pipe system. Three different optical measurement techniques have been employed. Laser Doppler Anemometry has been used to measure the magnitude of the velocity at the centre of the liquid column. Particle Image Velocimetry and Optical Deflectometry are used to determine the velocity profiles at the bulk of the liquid column and at the liquid--air interface respectively. The velocity measurements in the bulk are in good agreement with the theoretical predictions of a linear theory. The results, however, show dramatic differences in the dynamic behaviour of Newtonian and viscoelastic fluids, and demonstrate the importance of resonance phenomena in viscoelastic fluid flows, biofluids in particular, in confined geometries.

physics.flu-dyn↗

arXiv2005

Transient situations in traffic flow: Modelling the Mexico City Cuernavaca Highway

In this paper a recent variable anticipation cellular automata model for single-lane traffic flow is extended to analyze the situation of free and congested flow in the Highway from Mexico City to Cuernavaca. This highway presents free flow in standard days; but in the returning day of long weekends or holidays it exhibits congested flow and in rush hours jamming appears. We illustrate how our CA model for traffic flow can deal appropriately with transient situations and can be used to search new alternatives that allow to improve the traffic flow in Mexican highways.

cond-mat.other↗

arXiv2004

Optimal behavior of viscoelastic flow at resonant frequencies

The global entropy generation rate in the zero-mean oscillatory flow of a Maxwell fluid in a pipe is analyzed with the aim at determining its behavior at resonant flow conditions. This quantity is calculated explicitly using the analytic expression for the velocity field and assuming isothermal conditions. The global entropy generation rate shows well-defined peaks at the resonant frequencies where the flow displays maximum velocities. It was found that resonant frequencies can be considered optimal in the sense that they maximize the power transmitted to the pulsating flow at the expense of maximum dissipation.

physics.flu-dyn↗

arXiv2003

Experimental Observation of Differences in the Dynamic Response of Newtonian and Viscoelastic Fluids

In this paper we present an experimental study of the dynamic responses of a Newtonian fluid and a Maxwellian fluid under an oscillating pressure gradient. We use laser Doppler anemometry in order to determine the velocity of each fluid inside a cylindrical tube. In the case of the Newtonian fluid, the dissipative nature is observed and the response obeys the Zhou and Sheng universality (PRB 39, 12027 (1989)). In the dynamic response of the Maxwellian fluid an enhancement at the frequencies predicted by the corresponding theory (PRE 58, 6323 (1998)) is observed.

physics.flu-dyn↗

arXiv2003

Tailoring the photonic bandgap of porous silicon dielectric mirror

A systematic method to fabricate porous silicon one dimensional photonic crystals has been engineered to have a photonic bandwidth up to 2000nm. The observation of the tailorability of the photonic bandgap (PBG) underscores the requirement of the large refractive index contrast for making broad PBG structures. In this letter, we present the fabrication and characteristics of such structures that may be promising structures for a large variety of applications.

cond-mat.mtrl-sci↗

arXiv2003

Platoon formation in a traffic model with variable anticipation

A cellular automaton model of traffic flow taking into account velocity anticipation is introduced. The strength of anticipation can be varied which allows to describe different driving schemes. We find 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.

cond-mat.stat-mech↗

arXiv2002

Possible Gigantic Variations on the Width of Viscoelastic Fingers

We analyze the effect of frequency on the width of a single finger displacing a viscoelastic fluid. We derive a generalized Darcy's law in the frequency domain for a linear viscoelastic fluid flowing in a Hele Shaw cell. This leads to an analytic expression for the dynamic permeability that has maxima which are several orders of magnitude larger than the static permeability. We then follow an argument of de Gennes to obtain the smallest possible finger width when viscoelasticity is important. Using this, and a conservation law, we obtain a lowest bound for the width of a single finger displacing a viscoelastic fluid. Our results indicate that when a small amplitude signal of the frequency that maximizes the permeability is overimposed to a constant pressure drop, gigantic variations are obtained for the finger width.

physics.flu-dyn↗

arXiv2001

Light-scattering spectrum of a viscoelastic fluid subjected to an external temperature gradient

The light-scattering spectrum for a Maxwell fluid in a steady state due to the presence of an external temperature gradient is computed. In such a fluid heat conduction is assumed to be governed by the classical Fourier law. The calculation is carried out through the use of fluctuating hydrodynamics. The effect of the non-Newtonian character of the fluid in the resulting spectrum is discussed.

cond-mat.stat-mech↗

arXiv2001

Two effective temperatures in traffic flow models: analogies with granular flow

We present a model of traffic flow, with rules that describe the behaviour of automated vehicles in an open system. We show first of all that the fundamental diagram of this system collapses to a point, where states of free and jammed traffic can coexist in phase space. This leads us to consider separately the roles of average velocities and densities as better descriptors of the actual state of the traffic. Next, we observe that the transition between free and jammed traffic as a function of the braking parameter R is different for high and low initial densities, in the steady state; it turns out to be 'smeared out' for low densities, a behaviour which is already portended by the transient behaviour of the system. Our results indicate strongly that, at least for such models, two effective temperatures (one related to R, and the other to the density) are needed to describe the global behaviour of this system in statistical mechanical terms. Analogies with granular flow are discussed in this context.

cond-mat.stat-mech↗

arXiv2001

Cellular Automata for One-Lane Traffic Flow Modelling: Safety and Automation

In recent years the modelling of traffic flow using methods from statistical physics, especially cellular automata models have allowed simulations of large traffic networks faster than real time. In this paper, we study a probabilistic cellular automaton model for microsimulations of traffic flow of automated vehicles in highways. This model describes single-lane traffic flow on a ring. We study the equilibrium properties by including a parameter of safe distance in the model and calculate the so-called fundamental diagrams (flow vs. density graph) considering parallel dynamics. This is done numerically by computer simulations of the model and by means of an analysis of speed variance.

cond-mat.soft↗

arXiv1999

Possible Self-Organised Criticality and Dynamical Clustering of Traffic flow in Open Systems

We focus in this work on the study of traffic in open systems using a modified version of an existing cellular automaton model. We demonstrate that the open system is rather different from the closed system in its 'choice' of a unique steady-state density and velocity distribution, independently of the initial conditions, reminiscent of self-organised criticality. Quantities of interest such as average densities and velocities of cars, exhibit phase transitions between free flow and the jammed state, as a function of the braking probability R in a way that is very different from closed systems. Velocity correlation functions show that the concept of a dynamical cluster, introduced earlier in the context of granular flow is also relevant for traffic flow models.

physics.class-ph↗