Analogies between dissipative particle dynamics ( DPD) and stochastic dynamics are exploited to derive new algorithm for DPD with an improved temperature control, without recursion or tuneable parameters.
Analogies between dissipative particle dynamics ( DPD) and stochastic dynamics are exploited to derive new algorithm for DPD with an improved temperature control, without recursion or tuneable parameters.
A particle-based model for mesoscopic fluiddynamics is used to simulate steady and unsteady flows around a circular and a square cylinder in a two-dimensional channel for a range of Reynolds numbers between 10 and 13...
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A particle-based model for mesoscopic fluiddynamics is used to simulate steady and unsteady flows around a circular and a square cylinder in a two-dimensional channel for a range of Reynolds numbers between 10 and 130. Numerical results for the recirculation length, the drag coefficient, and the Strouhal number are reported and compared with previous experimental measurements and computationalfluiddynamics data. The good agreement demonstrates the potential of this method for the investigation of complex flows.
Results are described from a two-dimensional numerical model in which a cyclonic monopole that moves due to the beta-effect encounters a north-south oriented ridge or trough, the height and depth of which is varied. T...
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Results are described from a two-dimensional numerical model in which a cyclonic monopole that moves due to the beta-effect encounters a north-south oriented ridge or trough, the height and depth of which is varied. The fate of the monopole depends on its initial north-south position y(0) (or, equivalently, the value of the constant f(0) in the Coriolis parameter): the monopole can be rebounded, destroyed or trapped by the topography. Only for a narrow range of y(0)-positions, depending on the height (depth) of the ridge (trough), can the monopole actually cross the topography, sometimes after being heavily deformed. it is the gradient of the topography-induced vorticity, which deforms the background potential vorticity field due to the beta-effect, that determines the fate of the monopole. This topography-induced vorticity is larger for initial positions more to the north or south, and for higher ridges and deeper troughs. (C) 2000 The Japan Society of fluid Mechanics and Elsevier Science B.V. All rights reserved.
We propose a mean field (MF) theory for a homogeneously driven granular gas of inelastic particles with Coulomb friction. The model contains three parameters, a normal restitution coefficient r(n), a maximum tangentia...
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We propose a mean field (MF) theory for a homogeneously driven granular gas of inelastic particles with Coulomb friction. The model contains three parameters, a normal restitution coefficient r(n), a maximum tangential restitution coefficient r(t)(m), and a Coulomb friction coefficient mu. The parameters can be tuned to explore a wide range of physical situations. In particular, the model contains the frequently used mu --> infinity limit as a special case. The MF theory is compared with the numerical simulations of a randomly driven monolayer of spheres for a wide range of parameter values. If the system is far away from the clustering instability (r(n) approximate to 1), we obtain a good agreement between mean field and simulations for mu = 0.5 and r(i)(m) = 0.4, but for much smaller values of r(n) the agreement is less good. We discuss the reasons of this discrepancy and possible refinements of our computational scheme. (C) 2000 Elsevier Science B.V. All rights reserved.
A thermodynamically consistent lattice Boltzmann scheme for simulating the flow of a binary fluid is extended to allow the fluid components to have different viscosities. The approach is tested for the shear and Poise...
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A thermodynamically consistent lattice Boltzmann scheme for simulating the flow of a binary fluid is extended to allow the fluid components to have different viscosities. The approach is tested for the shear and Poiseuille flow of layered immiscible fluids and for the dispersion relation and the damping of a capillary wave. We then consider the fingering that results when a fluid is displaced by a less viscous fluid in a two-dimensional channel. The finger widths obtained match the results of Reinelt and Saffman [1], but differ somewhat from those of Halpern and Gaver [2] for capillary numbers above 2. A limiting finger width close to 1/2 is obtained for high capillary numbers and high viscosity ratios.
We present a lattice Boltzmann algorithm for the hydrodynamics of liquid crystals in the isotropic and nematic phases. The coupling between the tensor order parameter and the flow is treated consistently allowing inve...
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We present a lattice Boltzmann algorithm for the hydrodynamics of liquid crystals in the isotropic and nematic phases. The coupling between the tensor order parameter and the flow is treated consistently allowing investigation of a wide range of non-Newtonian flow behaviour. To illustrate the use of the method we present results for the effect of hydrodynamics on defect coalescence and demonstrate the occurrence of shear-banding and shear-thinning.
Differential equations for continuum fields describe many macroscopic phenomena. Hydrodynamics, for example, is described by the Navier-Stokes equations, and their solutions depend on boundary conditions. However, bou...
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Differential equations for continuum fields describe many macroscopic phenomena. Hydrodynamics, for example, is described by the Navier-Stokes equations, and their solutions depend on boundary conditions. However, boundary conditions are set by the interactions at the atomistic or molecular scale. We introduce a "hybrid model" that permits a continuum description in one region to be coupled to an atomistic description in another region. The coupling is symmetric in the sense that the fluxes of the conserved quantities are continuous across the particle-field interface. As an example, we couple a Lennard-Jones liquid and the compressible Navier-Stokes equations and show that the hybrid model is consistent with hydrodynamic predictions.
We study the hydrodynamic properties of polymers and more generally self-similar structures using a new recursion model. The hydrodynamic interaction between monomers is modeled by the standard Green's function of...
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We study the hydrodynamic properties of polymers and more generally self-similar structures using a new recursion model. The hydrodynamic interaction between monomers is modeled by the standard Green's function of Stokes flow in which an ultrametric distance is substituted for the usual Euclidean distance. This leads to a model where the long-range hydrodynamic interactions and the long-range correlations of the polymer conformation can both be accounted for and yet allow for analytical solutions. We explore the asymptotic as well as the finite size corrections to the scaling behavior with this model. In order to compare the results of the present scheme with more conventional techniques a generalized version of the existing mean field results by Kirkwood and Riseman for the hydrodynamic drag is introduced.
The paper presents computations of decaying two-dimensional turbulence in an adaptive wavelet basis. At each time step the vorticity is represented by an adaptively selected set of wavelet functions which adjusts to t...
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The paper presents computations of decaying two-dimensional turbulence in an adaptive wavelet basis. At each time step the vorticity is represented by an adaptively selected set of wavelet functions which adjusts to the instantaneous distribution of vorticity. Essential features are the use of operator-adapted test functions and the adaptive evaluation of the convection term, The results of this new algorithm are compared to a classical Fourier method and a Fourier method supplemented with wavelet compression in each time step. They show that turbulent flows with a multitude of spatial scales can be computed with a reduced number of degrees of freedom. The investigation of diverse spectral and statistical criteria validates the wavelet approach. (C) 1999 Elsevier Science B.V. All rights reserved.
To demonstrate essentials of the mechanism for the onset of turbulence in a pipe at Re = 2000, 48 degrees of freedom are enough. The derivation from the Navier-Stokes equation uses a novel type of modes which guarante...
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To demonstrate essentials of the mechanism for the onset of turbulence in a pipe at Re = 2000, 48 degrees of freedom are enough. The derivation from the Navier-Stokes equation uses a novel type of modes which guarantee linear stability. For the reduction of the nonlinear interactions, the modes are grouped in 3 blocks. Facilitated by these simplifications the interdependence between linear and nonlinear processes is analysed, however, just for a special example. A phenomenon resembling backflow is identified.
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