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Faculty Publications

Articles 31 - 38 of 38

Full-Text Articles in Other Physics

Direct Simulation Monte Carlo For Thin Film Bearings, Alejandro Garcia, B. Alder, F. J. Alexander Jan 1994

Direct Simulation Monte Carlo For Thin Film Bearings, Alejandro Garcia, B. Alder, F. J. Alexander

Faculty Publications

The direct simulation Monte Carlo (DSMC) scheme is used to study the gas flow under a read/write head positioned nanometers above a moving disk drive platter (the slider bearing problem). In most cases, impressive agreement is found between the particle-based simulation and numerical solutions of the continuum hydrodynamic Reynolds equation which has been corrected for slip. However, at very high platter speeds the gas is far from equilibrium, and the load capacity for the slider bearing cannot be accurately computed from the hydrodynamic pressure.

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Microscopic Simulation Of Dilute Gases With Adjustable Transport Coefficients, Alejandro Garcia, F. Baras, M. Malek Mansour Jan 1994

Microscopic Simulation Of Dilute Gases With Adjustable Transport Coefficients, Alejandro Garcia, F. Baras, M. Malek Mansour

Faculty Publications

The Bird algorithm is a computationally efficient method for simulating dilute gas flows. However, due to the relatively large transport coefficients at low densities, high Rayleigh or Reynolds numbers are difficult to achieve by this technique. We present a modified version of the Bird algorithm in which the relaxation processes are enhanced and the transport coefficients reduced, while preserving the correct equilibrium and nonequilibrium fluid properties. The present algorithm is found to be two to three orders of magnitude faster than molecular dynamics for simulating complex hydrodynamical flows.

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Quantam Wave Turbulence, Alejandro Garcia, M. Haeri, S. Putterman, P. Roberts Jan 1993

Quantam Wave Turbulence, Alejandro Garcia, M. Haeri, S. Putterman, P. Roberts

Faculty Publications

The nonlinear quantum kinetic equation for the interaction of sound waves is solved via analytic and numerical techniques. In the classical regime energy cascades to higher frequency (ω) according to the steady-state power law ω-3/2. In the quantum limit, the system prefers a reverse cascade of energy which follows the power law ω-6. Above a critical flux, a new type of spectrum appears which is neither self-similar nor close to equilibrium. This state of nonlinear quantum wave turbulence represents a flow of energy directly from the classical source to the quantum degrees of freedom.

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Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon Jan 1992

Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon

Faculty Publications

We study the phenomenon of slip length using molecular dynamics and direct simulation Monte Carlo simulations of a dilute gas. Our work extends the range of Knudsen numbers that have been previously studied. In a recent paper, Bhattacharya and Lie [Phys. Rev. 43, 761 (1991)] suggest a logarithmic dependence of slip length on Knudsen number. By a simple redefinition of the mean free path, we obtain good agreement between simulation results and Maxwell theory for slip length. The anomalies seen by Bhattacharya and Lie appear to be due to their definition of the mean free path.

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Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck Jan 1991

Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck

Faculty Publications

A reactiodffusion system of polymers undergoing interchange reactions is studied. The equation that describes the dynamics of the system is similar to the Boltzmann equation for a gas of hard spheres. We consider a one-dimensionsl system in which the average length and the concentrations at the boundaries are fixed. The resulting steady states are obtained analytically and with numerical integration of equations obtained by using a local equilibrium approximation. Monte Carlo simulations of experimentally realizable conditions were performed and compared. The results reveal a nonlinear distribution of molecular concentration and mass. The entropy of the polymer distributions is calculated as …

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Hydrodynamic Fluctuations In A Fluid Under Constant Shear, Alejandro Garcia, M. Malek Mansour, G. Lie, E. Clementi, M. Mareschal Jan 1987

Hydrodynamic Fluctuations In A Fluid Under Constant Shear, Alejandro Garcia, M. Malek Mansour, G. Lie, E. Clementi, M. Mareschal

Faculty Publications

No abstract provided.

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Fluctuating Hydrodynamics In A Dilute Gas, Alejandro Garcia, G. Lie, E. Clementi Jan 1987

Fluctuating Hydrodynamics In A Dilute Gas, Alejandro Garcia, G. Lie, E. Clementi

Faculty Publications

Hydrodynamic fluctuations in a dilute gas subjected to a constant heat flux are studied by both a computer simulation and the Landau-Lifshitz formalism. The latter explicitly incorporates the boundary conditions of the finite system, thus permitting quantitative comparison with the former. Good agreement is demonstrated.

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Nonequilibrium Fluctuations Studied By A Rarefied Gas Simulation, Alejandro Garcia Jan 1986

Nonequilibrium Fluctuations Studied By A Rarefied Gas Simulation, Alejandro Garcia

Faculty Publications

A dilute gas under a constant heat flux is studied with use of a Monte Carlo simulation based on the Boltzmann equation. Results for several spatial correlation functions of equal-time fluctuations are reported and compared qualitatively with previous fluctuating hydrodynamics calculations for liquids.

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