Faculty PublicationsCopyright (c) 2014 San José State University All rights reserved.
http://scholarworks.sjsu.edu/physics_astron_pub
Recent documents in Faculty Publicationsen-usFri, 30 May 2014 01:49:16 PDT3600Nonequilibrium Fluctuations studied by a Rarefied Gas Simulation
http://scholarworks.sjsu.edu/physics_astron_pub/95
http://scholarworks.sjsu.edu/physics_astron_pub/95Wed, 28 May 2014 09:37:20 PDT
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.
]]>
Alejandro GarciaPublicationsEstimating Hydrodynamic Quantities in the Presence of Microscopic Fluctuations
http://scholarworks.sjsu.edu/physics_astron_pub/94
http://scholarworks.sjsu.edu/physics_astron_pub/94Wed, 28 May 2014 09:37:19 PDT
This paper discusses the evaluation of hydrodynamic variables in the presence of spontaneous fluctuations, such as in molecular simulations of fluid flows. The principal point is that hydrodynamic variables such as fluid velocity and temperature must be defined in terms of mechanical variables such as momentum and energy density). Because these relations are nonlinear and because fluctuations of mechanical variables are correlated, care must be taken to avoid introducing a bias when evaluating means, variances, and correlations of hydrodynamic variables. The unbiased estimates are formulated; some alternative, incorrect approaches are presented as cautionary warnings. The expressions are verified by numerical simulations, both at thermodynamic equilibrium and at a nonequilibrium steady state.
]]>
Alejandro GarciaPublicationsComment on ‘‘Stress-density ratio slip-corrected Reynolds equation for ultra-thin film gas bearing lubrication’’
http://scholarworks.sjsu.edu/physics_astron_pub/93
http://scholarworks.sjsu.edu/physics_astron_pub/93Wed, 28 May 2014 09:37:17 PDTAlejandro GarciaPublicationsTime step truncation error in direct simulation Monte Carlo
http://scholarworks.sjsu.edu/physics_astron_pub/92
http://scholarworks.sjsu.edu/physics_astron_pub/92Wed, 28 May 2014 09:37:16 PDTAlejandro Garcia et al.PublicationsA direct simulation Monte Carlo method for the Uehling-Uhlenbeck-Boltzmann equation
http://scholarworks.sjsu.edu/physics_astron_pub/91
http://scholarworks.sjsu.edu/physics_astron_pub/91Wed, 28 May 2014 09:37:14 PDT
In this paper we describe a direct simulation Monte Carlo algorithm for the Uehling-Uhlenbeck-Boltzmann equation in terms of Markov processes. This provides a unifying framework for both the classical Boltzmann case as well as the Fermi-Dirac and Bose-Einstein cases. We establish the foundation of the algorithm by demonstrating its link to the kinetic equation. By numerical experiments we study its sensitivity to the number of simulation particles and to the discretization of the velocity space, when approximating the steady-state distribution.
]]>
Alejandro Garcia et al.PublicationsBurnett Description for Plane Poiseuille Flow
http://scholarworks.sjsu.edu/physics_astron_pub/90
http://scholarworks.sjsu.edu/physics_astron_pub/90Wed, 28 May 2014 09:37:13 PDT
Two recent works have shown that at small Knudsen number ~K! the pressure and temperature profiles in plane Poiseuille flow exhibit a different qualitative behavior from the profiles obtained by the Navier-Stokes equations. Tij and Santos [J. Stat. Phys. 76, 1399 (1994)] used the Bhatnagar-Gross-Kook model to show that the temperature profile is bimodal and the pressure profile is nonconstant. Malek-Mansour, Baras, and Garcia [Physica A 240, 255 (1997)] qualitatively confirmed these predictions in computer experiments using the direct simulation Monte Carlo method (DSMC). In this paper we compare the DSMC measurements of hydrodynamic variables and non-equilibrium fluxes with numerical solutions of the Burnett equations. Given that they are in better agreement with molecular-dynamics simulations [E. Salomons and M. Mareschal, Phys. Rev. Lett. 69, 269 (1992)] of strong shock waves than Navier-Stokes [F. J. Uribe, R. M. Velasco, and L. S. Garcı´a-Colı´n, Phys. Rev. Lett. 81, 2044 (1998)], and that they are second order in Knudsen number suggests that the Burnett equations may provide a better description for large K. We find that for plane Poiseuille flow the Burnett equations do not predict the bimodal temperature profile but do recover many of the other anomalous features.
]]>
Alejandro Garcia et al.PublicationsRectification of Thermal Fluctuations in Ideal Gases
http://scholarworks.sjsu.edu/physics_astron_pub/89
http://scholarworks.sjsu.edu/physics_astron_pub/89Wed, 28 May 2014 09:37:12 PDT
We calculate the systematic average speed of the adiabatic piston and a thermal Brownian motor, introduced by C. Van den Broeck, R. Kawai and P. Meurs [Phys. Rev. Lett. 93, 090601 (2004)], by an expansion of the Boltzmann equation and compare with the exact numerical solution.
]]>
Alejandro Garcia et al.PublicationsHydrodynamic description of the adiabatic piston
http://scholarworks.sjsu.edu/physics_astron_pub/88
http://scholarworks.sjsu.edu/physics_astron_pub/88Wed, 28 May 2014 09:37:11 PDT
A closed macroscopic equation for the motion of the two-dimensional adiabatic piston is derived from standard hydrodynamics. It predicts a damped oscillatory motion of the piston towards a final rest position, which depends on the initial state. In the limit of large piston mass, the solution of this equation is in quantitative agreement with the results obtained from both hard disk molecular dynamics and hydrodynamics. The explicit forms of the basic characteristics of the piston’s dynamics, such as the period of oscillations and the relaxation time, are derived. The limitations of the theory’s validity, in terms of the main system parameters, are established.
]]>
Alejandro Garcia et al.PublicationsNonequilibrium processes in Polymers undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes
http://scholarworks.sjsu.edu/physics_astron_pub/87
http://scholarworks.sjsu.edu/physics_astron_pub/87Wed, 28 May 2014 09:37:09 PDT
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 function of position and shown to be less than the entropy for the distributions without interchange reactions. The diffusion of a square pulse is also considered.
]]>
Alejandro Garcia et al.PublicationsSlip Length in a Dilute Gas
http://scholarworks.sjsu.edu/physics_astron_pub/86
http://scholarworks.sjsu.edu/physics_astron_pub/86Wed, 28 May 2014 09:37:08 PDT
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.
]]>
Alejandro Garcia et al.PublicationsQuantam wave turbulence
http://scholarworks.sjsu.edu/physics_astron_pub/85
http://scholarworks.sjsu.edu/physics_astron_pub/85Wed, 28 May 2014 09:37:07 PDT
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.
]]>
Alejandro Garcia et al.PublicationsMolecular simulations of sound wave propagation in simple gases
http://scholarworks.sjsu.edu/physics_astron_pub/84
http://scholarworks.sjsu.edu/physics_astron_pub/84Wed, 28 May 2014 09:37:06 PDT
Molecular simulations of sound waves propagating in a dilute hard sphere gas have been performed using the direct simulation Monte Carlo method. A wide range of frequencies is investigated, including very high frequencies for which the period is much shorter than the mean collision time. The simulation results are compared to experimental data and approximate solutions of the Boltzmann equation. It is shown that free molecular flow is important at distances smaller than one mean free path from the excitation point.
]]>
Alejandro Garcia et al.PublicationsFluctuating Hydrodynamics in a Dilute Gas
http://scholarworks.sjsu.edu/physics_astron_pub/83
http://scholarworks.sjsu.edu/physics_astron_pub/83Wed, 28 May 2014 09:37:04 PDT
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.
]]>
Alejandro Garcia et al.PublicationsHydrodynamic Fluctuations in a Fluid under Constant Shear
http://scholarworks.sjsu.edu/physics_astron_pub/82
http://scholarworks.sjsu.edu/physics_astron_pub/82Wed, 28 May 2014 09:37:03 PDTAlejandro Garcia et al.PublicationsThree-Dimensional Direct Simulation Monte Carlo Method for Slider Air Bearings
http://scholarworks.sjsu.edu/physics_astron_pub/81
http://scholarworks.sjsu.edu/physics_astron_pub/81Wed, 28 May 2014 09:37:02 PDT
The direct simulation Monte Carlo (DSMC) method is used to solve the three-dimensional nano-scale gas film lubrication problem between a gas bearing slider and a rotating disk, and this solution is compared to the numerical solution of the compressible Reynolds equations with the slip flow correction based on the linearized Boltzmann equation as presented by Fukui and Kaneko [molecular gas film lubrication (MGL) method] [ASME J. Tribol. 110, 253 (1988)]. In the DSMC method, hundreds of thousands of simulated particles are used and their three velocity components and three spatial coordinates are calculated and recorded by using a hard-sphere collision model. Two-dimensional pressure profiles are obtained across the film thickness direction. The results obtained from the two methods agree well with each other for Knudsen numbers as large as 35 which corresponds to a minimum spacing of 2 nm. The result for contact slider is also obtained by the DSMC simulation and presented in this paper.
]]>
Alejandro Garcia et al.PublicationsNumerical Methods for the Stochastic Landau-Lifshitz Navier-Stokes Equations
http://scholarworks.sjsu.edu/physics_astron_pub/80
http://scholarworks.sjsu.edu/physics_astron_pub/80Wed, 28 May 2014 09:37:00 PDT
The Landau-Lifshitz Navier-Stokes (LLNS) equations incorporate thermal fluctuations into macroscopic hydrodynamics by using stochastic fluxes. This paper examines explicit Eulerian discretizations of the full LLNS equations. Several computational fluid dynamics approaches are considered (including MacCormack’s two-step Lax-Wendroff scheme and the piecewise parabolic method) and are found to give good results for the variance of momentum fluctuations. However, neither of these schemes accurately reproduces the fluctuations in energy or density. We introduce a conservative centered scheme with a third-order Runge-Kutta temporal integrator that does accurately produce fluctuations in density, energy, and momentum. A variety of numerical tests, including the random walk of a standing shock wave, are considered and results from the stochastic LLNS solver are compared with theory, when available, and with molecular simulations using a direct simulation Monte Carlo algorithm.
]]>
Alejandro Garcia et al.PublicationsComputational fluctuating fluid dynamics
http://scholarworks.sjsu.edu/physics_astron_pub/79
http://scholarworks.sjsu.edu/physics_astron_pub/79Wed, 28 May 2014 09:36:59 PDT
This paper describes the extension of a recently developed numerical solver for the Landau-Lifshitz Navier-Stokes (LLNS) equations to binary mixtures in three dimensions. The LLNS equations incorporate thermal fluctuations into macroscopic hydrodynamics by using white-noise fluxes. These stochastic PDEs are more complicated in three dimensions due to the tensorial form of the correlations for the stochastic fluxes and in mixtures due to couplings of energy and concentration fluxes (e.g., Soret effect). We present various numerical tests of systems in and out of equilibrium, including time-dependent systems, and demonstrate good agreement with theoretical results and molecular simulation
]]>
Alejandro Garcia et al.PublicationsAlgorithm Refinement for Fluctuating Hydrodynamics
http://scholarworks.sjsu.edu/physics_astron_pub/78
http://scholarworks.sjsu.edu/physics_astron_pub/78Wed, 28 May 2014 09:36:58 PDT
This paper introduces an adaptive mesh and algorithm refinement method for fluctuating hydrodynamics. This particle-continuum hybrid simulates the dynamics of a compressible fluid with thermal fluctuations. The particle algorithm is direct simulation Monte Carlo (DSMC), a molecular-level scheme based on the Boltzmann equation. The continuum algorithm is based on the Landau–Lifshitz Navier–Stokes (LLNS) equations, which incorporate thermal fluctuations into macroscopic hydrodynamics by using stochastic fluxes. It uses a recently developed solver for the LLNS equations based on third-order Runge–Kutta. We present numerical tests of systems in and out of equilibrium, including time-dependent systems, and demonstrate dynamic adaptive refinement by the computation of a moving shock wave. Mean system behavior and second moment statistics of our simulations match theoretical values and benchmarks well. We find that particular attention should be paid to the spectrum of the flux at the interface between the particle and continuum methods, specifically for the nonhydrodynamic (kinetic) time scales.
]]>
Alejandro Garcia et al.PublicationsDiffusive Transport Enhanced by Thermal Velocity Fluctuations
http://scholarworks.sjsu.edu/physics_astron_pub/77
http://scholarworks.sjsu.edu/physics_astron_pub/77Wed, 28 May 2014 09:36:57 PDT
We study the contribution of advection by thermal velocity fluctuations to the effective diffusion coefficient in a mixture of two identical fluids. We find good agreement between a simple fluctuating hydrodynamics theory and particle and finite-volume simulations. The enhancement of the diffusive transport depends on the system size L and grows as ln(L/L0) in quasi-two-dimensional systems, while in three dimensions it scales as L0-1-L-1, where L0 is a reference length. Our results demonstrate that fluctuations play an important role in the hydrodynamics of small-scale systems.
]]>
Alejandro Garcia et al.PublicationsOn the Accuracy of Explicit Finite-Volume Schemes for Fluctuating Hydrodynamics
http://scholarworks.sjsu.edu/physics_astron_pub/76
http://scholarworks.sjsu.edu/physics_astron_pub/76Wed, 28 May 2014 09:36:55 PDT
This paper describes the development and analysis of finite-volume methods for the Landau–Lifshitz Navier–Stokes (LLNS) equations and related stochastic partial differential equations in fluid dynamics. The LLNS equations incorporate thermal fluctuations into macroscopic hydrodynamics by the addition of white noise fluxes whose magnitudes are set by a fluctuation-dissipation relation. Originally derived for equilibrium fluctuations, the LLNS equations have also been shown to be accurate for nonequilibrium systems. Previous studies of numerical methods for the LLNS equations focused primarily on measuring variances and correlations computed at equilibrium and for selected nonequilibrium flows. In this paper, we introduce a more systematic approach based on studying discrete equilibrium structure factors for a broad class of explicit linear finite-volume schemes. This new approach provides a better characterization of the accuracy of a spatiotemporal discretization as a function of wavenumber and frequency, allowing us to distinguish between behavior at long wavelengths, where accuracy is a prime concern, and short wavelengths, where stability concerns are of greater importance. We use this analysis to develop a specialized third-order Runge–Kutta scheme that minimizes the temporal integration error in the discrete structure factor at long wavelengths for the one-dimensional linearized LLNS equations.Together with a novel method for discretizing the stochastic stress tensor in dimension larger than one, our improved temporal integrator yields a scheme for the three-dimensional equations that satisfies a discrete fluctuation-dissipation balance for small time steps and is also sufficiently accurate even for time steps close to the stability limit.
]]>
Alejandro Garcia et al.PublicationsLow Mach Number Fluctuating Hydrodynamics of Diffusively Mixing Fluids
http://scholarworks.sjsu.edu/physics_astron_pub/75
http://scholarworks.sjsu.edu/physics_astron_pub/75Wed, 28 May 2014 09:36:54 PDT
We formulate low Mach number fluctuating hydrodynamic equations appropriate for modeling diffusive mixing in isothermal mixtures of fluids with different density and transport coefficients. These equations eliminate the fast isentropic fluctuations in pressure associated with the propagation of sound waves by replacing the equation of state with a local thermodynamic constraint. We demonstrate that the low Mach number model preserves the spatio-temporal spectrum of the slower diffusive fluctuations. We develop a strictly conservative finite-volume spatial discretization of the low Mach number fluctuating equations in both two and three dimensions. We construct several explicit Runge-Kutta temporal integrators that strictly maintain the equation of state constraint. The resulting spatio-temporal discretization is second-order accurate deterministically and maintains fluctuation-dissipation balance in the linearized stochastic equations. We apply our algorithms to model the development of giant concentration fluctuations in the presence of concentration gradients, and investigate the validity of common simplications neglecting the spatial non-homogeneity of density and transport properties. We perform simulations of diffusive mixing of two fluids of different densities in two dimensions and compare the results of low Mach number continuum simulations to hard-disk molecular dynamics simulations. Excellent agreement is observed between the particle and continuum simulations of giant fluctuations during time-dependent diffusive mixing.
]]>
Alejandro Garcia et al.PublicationsAnomalous Flow Profile due to the Curvature Effect on Slip Length
http://scholarworks.sjsu.edu/physics_astron_pub/74
http://scholarworks.sjsu.edu/physics_astron_pub/74Wed, 28 May 2014 09:36:53 PDTAlejandro Garcia et al.PublicationsMicroscopic simulation of dilute gases with adjustable transport coefficients
http://scholarworks.sjsu.edu/physics_astron_pub/73
http://scholarworks.sjsu.edu/physics_astron_pub/73Wed, 28 May 2014 09:36:51 PDT
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.
]]>
Alejandro Garcia et al.PublicationsComment on 'Simulation of a two-dimensional Rayleigh-Bénard system using the direct simulation Monte Carlo method
http://scholarworks.sjsu.edu/physics_astron_pub/72
http://scholarworks.sjsu.edu/physics_astron_pub/72Wed, 28 May 2014 09:36:50 PDTAlejandro Garcia et al.PublicationsA Simple Model for Nonequilibrium Fluctuations in a Fluid
http://scholarworks.sjsu.edu/physics_astron_pub/71
http://scholarworks.sjsu.edu/physics_astron_pub/71Wed, 28 May 2014 09:36:49 PDT
Presents a train model that shows the long-range spatial correlations of fluctuations in nonequilibrium fluid systems. Illustration of model through analysis of flat-car trains running on parallel tracks; Simulation of train model in computers; Theoretical analysis for fluctuations in the train model; Relationship between train model and the fluctuating hydrodynamic theory of fluids.
]]>
Alejandro Garcia et al.PublicationsInverted velocity profile in the cylindrical Couette flow of a rarefied gas
http://scholarworks.sjsu.edu/physics_astron_pub/70
http://scholarworks.sjsu.edu/physics_astron_pub/70Wed, 28 May 2014 09:36:48 PDT
The cylindrical Couette flow of a rarefied gas is investigated, under the diffuse-specular reflection condition of Maxwell’s type on the cylinders, in the case where the inner cylinder is rotating whereas the outer cylinder is at rest. The inverted velocity profile for small accommodation coefficients, pointed out by Tibbs, Baras, and Garcia [Phys. Rev. E 56, 2282 (1997)] on the basis of a Monte Carlo simulation, is investigated extensively by means of a systematic asymptotic analysis for small Knudsen numbers as well as the direct numerical analysis of the Boltzmann equation, and the parameter range in which the phenomenon appears is clarified.
]]>
Alejandro Garcia et al.PublicationsStochastic Hard-Sphere Dynamics for Hydrodynamics of Non-Ideal Fluids
http://scholarworks.sjsu.edu/physics_astron_pub/69
http://scholarworks.sjsu.edu/physics_astron_pub/69Wed, 28 May 2014 09:36:46 PDT
A novel stochastic fluid model is proposed with a nonideal structure factor consistent with compressibility, and adjustable transport coefficients. This stochastic hard sphere dynamics (SHSD) algorithm is a modification of the direct simulation Monte Carlo algorithm and has several computational advantages over event-driven hard-sphere molecular dynamics. Surprisingly, SHSD results in an equation of state and a pair correlation function identical to that of a deterministic Hamiltonian system of penetrable spheres interacting with linear core pair potentials. The fluctuating hydrodynamic behavior of the SHSD fluid is verified for the Brownian motion of a nanoparticle suspended in a compressible solvent.
]]>
Alejandro Garcia et al.PublicationsA hybrid particle-continuum method for hydrodynamics of complex fluids
http://scholarworks.sjsu.edu/physics_astron_pub/68
http://scholarworks.sjsu.edu/physics_astron_pub/68Wed, 28 May 2014 09:36:45 PDT
A previously developed hybrid particle-continuum method [J. B. Bell, A. Garcia, and S. A. Williams, Multiscale Model. Simul., 6 (2008), pp. 1256–1280] is generalized to dense fluids and two- and three-dimensional flows. The scheme couples an explicit fluctuating compressible Navier–Stokes solver with the isotropic direct simulation Monte Carlo (DSMC) particle method [A. Donev, A. L. Garcia, and B. J. Alder, J. Stat. Mech. Theory Exp., 2009 (2009), article P11008]. To achieve bidirectional dynamic coupling between the particle (microscale) and continuum (macroscale) regions, the continuum solver provides state-based boundary conditions to the particle subdomain, while the particle solver provides flux-based boundary conditions for the continuum subdomain. This type of coupling ensures both state and flux continuity across the particle-continuum interface analogous to coupling approaches for deterministic parabolic partial differential equations; here, when fluctuations are included, a small (< 1%) mismatch is expected and observed in the mean density and temperature across the interface. By calculating the dynamic structure factor for both a “bulk” (periodic) and a finite system, it is verified that the hybrid algorithm accurately captures the propagation of spontaneous thermal fluctuations across the particle-continuum interface. The equilibrium diffusive (Brownian) motion of a large spherical bead suspended in a particle fluid is examined, demonstrating that the hybrid method correctly reproduces the velocity autocorrelation function of the bead but only if thermal fluctuations are included in the continuum solver. Finally, the hybrid is applied to the well-known adiabatic piston problem, and it is found that the hybrid correctly reproduces the slow nonequilibrium relaxation of the piston toward thermodynamic equilibrium but, again, only if the continuum solver includes stochastic (white-noise) flux terms. These examples clearly demonstrate the need to include fluctuations in continuum solvers employed in hybrid multiscale methods.
]]>
Alejandro Garcia et al.PublicationsErratum: "Cell size dependence of transport coefficients in stochastic particle algorithms"
http://scholarworks.sjsu.edu/physics_astron_pub/67
http://scholarworks.sjsu.edu/physics_astron_pub/67Wed, 28 May 2014 09:36:44 PDTAlejandro Garcia et al.PublicationsDirect Simulation Monte Carlo for Thin Film Bearings
http://scholarworks.sjsu.edu/physics_astron_pub/66
http://scholarworks.sjsu.edu/physics_astron_pub/66Wed, 28 May 2014 09:36:42 PDT
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.
]]>
Alejandro Garcia et al.PublicationsCell Size Dependence of Transport Coefficients in Stochastic Particle Algorithms
http://scholarworks.sjsu.edu/physics_astron_pub/65
http://scholarworks.sjsu.edu/physics_astron_pub/65Wed, 28 May 2014 09:36:41 PDT
Using the Green–Kubo theory, the dependence of the viscosity and thermal conductivity on cell size is obtained explicitly for stochastic particle methods such as direct simulation Monte Carlo (DSMC) and its generalization, the consistent Boltzmann algorithm (CBA). These analytical results confirm empirical observations that significant errors occur when the cell dimensions are larger than a mean free path.
]]>
Alejandro Garcia et al.PublicationsA Consistent Boltzmann Algorithm
http://scholarworks.sjsu.edu/physics_astron_pub/64
http://scholarworks.sjsu.edu/physics_astron_pub/64Wed, 28 May 2014 09:36:39 PDT
The direct simulation Monte Carlo method for the Boltzmann equation is modified by an additional displacement in the advection process and an enhanced collision rate in order to obtain the exact hard sphere equation of state at all densities. This leads to consistent thermodynamic and transport properties in the low density (Boltzmann) regime. At higher densities transport properties are comparable to the predictions of the Enskog model. The algorithm is faster than molecular dynamics at low and moderate densities and readily run on a parallel architecture
]]>
Alejandro Garcia et al.Publications