arXiv subjects

Pep Español

Publications and source records attributed to Pep Español.

23 records · Page 2Linked to original sources

arXiv1998

Dynamical regimes in DPD

We discuss theoretically the behavior of the velocity autocorrelation function in the Dissipative Particle Dynamics model. Two dynamical regimes are identified depending on the dimensionless model parameters. For low frictions a mean field behavior is observed in which the kinetic theory for DPD provides good predictions. For high frictions, collective hydrodynamic effects are dominant. We have performed numerical simulations that validate the theory presented.

cond-mat.stat-mech↗

arXiv1997

A fluid particle model

We present a mechanistic model for a Newtonian fluid called fluid particle dynamics. By analyzing the concept of ``fluid particle'' from the point of view of a Voronoi tessellation of a molecular fluid, we propose an heuristic derivation of a dissipative particle dynamics algorithm that incorporates shear forces between dissipative particles. The inclusion of these non-central shear forces requires the consideration of angular velocities of the dissipative particles in order to comply with the conservation of angular momentum. It is shown that the equilibrium statistical mechanics requirement that the linear and angular velocity fields are Gaussian is sufficient to construct the random thermal forces between dissipative particles. The proposed algorithm is very similar in structure to the (isothermal) smoothed particle dynamics algorithm. In this way, this work represents a generalization of smoothed particle dynamics that incorporates consistently thermal fluctuations and exact angular momentum conservation. It contains also the dissipative particle dynamics algorithm as a special case. Finally, the kinetic theory of the dissipative particles is derived and explicit expressions of the transport coefficients of the fluid in terms of model parameters are obtained. This allows to discuss resolution issues for the model.

cond-mat.stat-mech↗

arXiv1997

Dissipative Particle Dynamics with energy conservation

Dissipative particle dynamics (DPD) does not conserve energy and this precludes its use in the study of thermal processes in complex fluids. We present here a generalization of DPD that incorporates an internal energy and a temperature variable for each particle. The dissipation induced by the dissipative forces between particles is invested in raising the internal energy of the particles. Thermal conduction occurs by means of (inverse) temperature differences. The model can be viewed as a simplified solver of the fluctuating hydrodynamic equations and opens up the possibility of studying thermal processes in complex fluids with a mesoscopic simulation technique.

cond-mat.stat-mech↗

arXiv1997

Fluid particle dynamics: a synthesis of dissipative particle dynamics and smoothed particle dynamics

We present a generalization of dissipative particle dynamics that includes shear forces between particles. The new algorithm has the same structure as the (isothermal) smoothed particle dynamics algorithm, except that it conserves angular momentum and includes thermal fluctuations consistently with the principles of equilibrium statistical mechanics. This clarifies the connection of dissipative particle dynamics with numerical resolution algorithms of the macroscopic Navier-Stokes equations.

cond-mat.stat-mech↗

arXiv1997

Stochastic differential equations for non-linear hydrodynamics

We formulate the stochastic differential equations for non-linear hydrodynamic fluctuations. The equations incorporate the random forces through a random stress tensor and random heat flux as in the Landau and Lifshitz theory. However, the equations are non-linear and the random forces are non-Gaussian. We provide explicit expressions for these random quantities in terms of the well-defined increments of the Wienner process.

cond-mat.stat-mech↗