Antonio Astillero Vivas - Academia.edu (original) (raw)

Papers by Antonio Astillero Vivas

Research paper thumbnail of A granular fluid modeled as a driven system of elastic hard spheres

arXiv (Cornell University), Sep 9, 2003

We explore the possibility of describing the main transport properties of a granular gas by means... more We explore the possibility of describing the main transport properties of a granular gas by means of a model consisting of elastic hard spheres under the action of a drag force that mimics the inelastic cooling of the granular gas. Direct Monte Carlo simulations of the Boltzmann equation show a good agreement between the results for a gas of inelastic hard spheres and those for a gas of driven elastic hard spheres in the simple shear flow state. This approximate equivalence between both systems is exploited to extend known kinetic models for elastic collisions to the inelastic case.

Research paper thumbnail of Velocity distribution and cumulants in the unsteady uniform longitudinal flow of a granular gas

The uniform longitudinal flow is characterized by a linear longitudinal velocity field u x (x,t) ... more The uniform longitudinal flow is characterized by a linear longitudinal velocity field u x (x,t) = a(t)x, where a(t) = a 0 /(1 + a 0 t) is the strain rate, a uniform density n(t) ∝ a(t), and a uniform granular temperature T (t). Direct simulation Monte Carlo solutions of the Boltzmann equation for inelastic hard spheres are presented for three (one positive and two negative) representative values of the initial strain rate a 0. Starting from different initial conditions, the temporal evolution of the reduced strain rate a * ∝ a 0 / √ T , the non-Newtonian viscosity, the second and third velocity cumulants, and three independent marginal distribution functions has been recorded. Elimination of time in favor of the reduced strain rate a * shows that, after a few collisions per particle, different initial states are attracted to common "hydrodynamic" curves. Strong deviations from Maxwellian properties are observed from the analysis of the cumulants and the marginal distributions.

Research paper thumbnail of Estudio mediante la teoría cinética de medios granulares en régimen de flujo rápido

Un modelo reológico sencillo basado en el modelo cinético BGK .

Research paper thumbnail of Transport Coefficients for Inelastic Maxwell Mixtures

Journal of Statistical Physics, 2005

The Boltzmann equation for inelastic Maxwell models (IMM) is used to determine the Navier-Stokes ... more The Boltzmann equation for inelastic Maxwell models (IMM) is used to determine the Navier-Stokes transport coefficients of a granular binary mixture in d-dimensions. The Chapman-Enskog method is applied to solve the Boltzmann equation for states near the (local) homogeneous cooling state. The mass, heat, and momentum fluxes are obtained to first order in the spatial gradients of the hydrodynamic fields, and the corresponding transport coefficients are identified. There are seven relevant transport coefficients: the mutual diffusion, the pressure diffusion, the thermal diffusion, the shear viscosity, the Dufour coefficient, the pressure energy coefficient, and the thermal conductivity. All these coefficients are exactly obtained in terms of the coefficients of restitution and the ratios of mass, concentration, and particle sizes. The results are compared with known transport coefficients of inelastic hard spheres (IHS) obtained analytically in the leading Sonine approximation and by means of Monte Carlo simulations. The comparison shows a reasonably good agreement between both interaction models for not too strong dissipation, especially in the case of the transport coefficients associated with the mass flux.

Research paper thumbnail of A granular fluid modeled as a driven system of elastic hard spheres

arXiv (Cornell University), Sep 9, 2003

We explore the possibility of describing the main transport properties of a granular gas by means... more We explore the possibility of describing the main transport properties of a granular gas by means of a model consisting of elastic hard spheres under the action of a drag force that mimics the inelastic cooling of the granular gas. Direct Monte Carlo simulations of the Boltzmann equation show a good agreement between the results for a gas of inelastic hard spheres and those for a gas of driven elastic hard spheres in the simple shear flow state. This approximate equivalence between both systems is exploited to extend known kinetic models for elastic collisions to the inelastic case.

Research paper thumbnail of Velocity distribution and cumulants in the unsteady uniform longitudinal flow of a granular gas

The uniform longitudinal flow is characterized by a linear longitudinal velocity field u x (x,t) ... more The uniform longitudinal flow is characterized by a linear longitudinal velocity field u x (x,t) = a(t)x, where a(t) = a 0 /(1 + a 0 t) is the strain rate, a uniform density n(t) ∝ a(t), and a uniform granular temperature T (t). Direct simulation Monte Carlo solutions of the Boltzmann equation for inelastic hard spheres are presented for three (one positive and two negative) representative values of the initial strain rate a 0. Starting from different initial conditions, the temporal evolution of the reduced strain rate a * ∝ a 0 / √ T , the non-Newtonian viscosity, the second and third velocity cumulants, and three independent marginal distribution functions has been recorded. Elimination of time in favor of the reduced strain rate a * shows that, after a few collisions per particle, different initial states are attracted to common "hydrodynamic" curves. Strong deviations from Maxwellian properties are observed from the analysis of the cumulants and the marginal distributions.

Research paper thumbnail of Estudio mediante la teoría cinética de medios granulares en régimen de flujo rápido

Un modelo reológico sencillo basado en el modelo cinético BGK .

Research paper thumbnail of Transport Coefficients for Inelastic Maxwell Mixtures

Journal of Statistical Physics, 2005

The Boltzmann equation for inelastic Maxwell models (IMM) is used to determine the Navier-Stokes ... more The Boltzmann equation for inelastic Maxwell models (IMM) is used to determine the Navier-Stokes transport coefficients of a granular binary mixture in d-dimensions. The Chapman-Enskog method is applied to solve the Boltzmann equation for states near the (local) homogeneous cooling state. The mass, heat, and momentum fluxes are obtained to first order in the spatial gradients of the hydrodynamic fields, and the corresponding transport coefficients are identified. There are seven relevant transport coefficients: the mutual diffusion, the pressure diffusion, the thermal diffusion, the shear viscosity, the Dufour coefficient, the pressure energy coefficient, and the thermal conductivity. All these coefficients are exactly obtained in terms of the coefficients of restitution and the ratios of mass, concentration, and particle sizes. The results are compared with known transport coefficients of inelastic hard spheres (IHS) obtained analytically in the leading Sonine approximation and by means of Monte Carlo simulations. The comparison shows a reasonably good agreement between both interaction models for not too strong dissipation, especially in the case of the transport coefficients associated with the mass flux.