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Mathematical simulation of one-dimensional dam-collapse flow over wetted bed

EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS 2003年第2期22卷 133-142页

作者： Medkour, D Kadja, M Ben Mhidi Univ Inst Mech Oum El Bouaghi 04000 Algeria Mentouri Univ Dept Mech Constantine 25000 Algeria

A mathematical model is described and applied to simulate sudden total one-dimensional dam-break flow over wetted bed. The dam collapse takes place in a rough sloping non-prismatic channel of various cross-sections. The water parameters to be instantaneously calculated are the height h, the discharge Q, the mean velocity u and the pressure force P. The mentioned. flow is governed by the Saint-Venant shallow water equations and the computation process, on the basis of rectangular grid of points, consists of two complementary solutions: (a) at the first instant after the collapse, an analytical procedure is considered. The calculated parameters are taken as initial values in the water stream embraced by the flood wave. Outside this zone, initial conditions are those which preexist before the rupture. (b) Beyond this time, a numerical computation is carried out by using an iterative explicit method of characteristics. ( c) Every time stage of calculation starts by determining the discontinuity ( wave front) parameters namely its abscissa x(delta), height h(delta), celerity c(delta) and alert delay t(delta). The former is the discontinuity arrival time at considered station. Typical results are obtained and compared with similar ones already published by others in the literature.

关键词： Numerical simulation, solution of equations Hydrodynamic waves computational methods in fluid dynamics

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Correction factor of the Stokes force undergone by a sphere in the axis of a cylinder in uniform and Poiseuille flows

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EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS 2003年第2期24卷 153-165页

作者： Ben Richou, A Ambari, A Naciri, JK EMT ENSAM F-49035 Angers France Fac Sci Ain Chock UFR Mech Casablanca Morocco

To contribute to the existing knowledge of the hydrodynamic force exerted on a spherical particle placed in the axis of a cylinder, at small Reynolds numbers, the influence of the uniform and Poiseuille flows on the wall correction factor are numerically and asymptotically investigated. The Stokes and continuity equations are expressed in the stream function and vorticity formulation and are rewritten in an orthogonal system of curvilinear coordinates. These equations are solved using a finite differences method. The generation of the grid was carried out by the singularities method. The accuracy of the numerical code is tested through comparison with theoretical and experimental results. In both cases we numerically calculated the separate contributions of the pressure and viscosity forces. In concentrated regime these numerical calculations are in very good agreement with those obtained by asymptotic expansions. This analysis allowed us to show the prevalence of the pressure term over the viscosity one in the lubrication regime contrary to what happened for the dilute regime. All our numerical and asymptotical results compared with those of Bungay et al. (Int. J. Multiphase Flow 1, 25-56 (1973)) seem to give a response to this problem argued for a long time.

关键词： Laminar suspensions Low-Reynolds-number (creeping) flows computational methods in fluid dynamics

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Minimal entropic kinetic models for hydrodynamics

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EUROPHYSICS LETTERS 2003年第6期63卷 798-804页

作者： Ansumali, S Karlin, IV Öttinger, HC ETH Dept Mat Inst Polymers ETH Zentrum CH-8092 Zurich Switzerland

We derive minimal discrete models of the Boltzmann equation consistent with equilibrium thermodynamics, and which recover correct hydrodynamics in arbitrary dimensions. A new discrete velocity model is proposed for the simulation of the Navier-Stokes-Fourier equation and is tested in the setup of Taylor vortex flow. A simple analytical procedure for constructing the equilibrium for thermal hydrodynamics is established. For the lattice Boltzmann method of isothermal hydrodynamics, the explicit analytical form of the equilibrium distribution is presented. This results in an entropic version of the isothermal lattice Boltzmann method with the simplicity and computational efficiency of the standard lattice Boltzmann model.

关键词： Nonequilibrium and irreversible thermodynamics computational methods in fluid dynamics Kinetic and transport theory of gases

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An extended dissipative particle dynamics model

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EUROPHYSICS LETTERS 2003年第6期64卷 723-729页

作者： Cotter, CJ Reich, S Univ London Imperial Coll Sci Technol & Med Dept Math London SW7 2AZ England

The method of dissipative particle dynamics (DPD) was introduced by Hoogerbrugge and Koelman (Europhys. Lett., 19 ( 1992) 155) to study meso-scale material processes. The theoretical investigation of the DPD method was initiated by Espanol (Phys. Rev. E, 52 ( 1995) 1734) who used a Fokker-Planck formulation of the DPD method and applied the Mori-Zwanzig projection operator calculus to obtain the equations of hydrodynamics for DPD. A current limitation of DPD is that it requires a clear separation of scales between the resolved and unresolved processes. In this letter, we suggest a simple extension of DPD that allows for inclusion of unresolved stochastic processes with exponentially decaying variance for any value of the decay rate, and give an application of this algorithm to the simulation of the shallow-water equations using the Hamiltonian particle-mesh method. The proposed extension is as easy to implement as the standard DPD methods.

关键词： Markov processes computational methods in fluid dynamics Computer simulation of molecular and particle dynamics

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An advected-field approach to the dynamics of fluid interfaces

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EUROPHYSICS LETTERS 2003年第4期63卷 623-629页

作者： Biben, T Misbah, C Leyrat, A Verdier, C Univ Grenoble 1 LSP Grephe CNRS UJF F-38402 St Martin Dheres France Univ Grenoble 1 Lab Rheol CNRS UJF INPG F-38041 Grenoble 9 France Univ Grenoble 1 CNRS UMR 5520 F-38041 Grenoble 9 France

We present an advected-field model of fluid interfaces at low Reynolds numbers and apply it to the fundamental problem of drop dynamics in an external flow. We focus on the ability of the numerical method to account for topology changes such as breakup, and compare the results obtained with this method to experimental data and theoretical predictions.

关键词： Emulsions and suspensions computational methods in fluid dynamics Multiphase and particle-laden flows

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Hydrodynamic vector potentials

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EUROPEAN PHYSICAL JOURNAL B 2002年第1期26卷 121-132页

作者： Brosa, U Grossmann, S Univ Marburg D-35032 Marburg Germany

Solving the Navier-Stokes equation for incompressible fluids is greatly simplified by the solution of the vorticity equation. To accomplished this for three-dimensional flows requires vector potentials. These potentials are not only useful to take care of the incompressibility. Their modes are suitable also as test functions since the familiar Galerkin procedure does not work. The new method is checked by examples with known results and its relation to the classical approach with the stream function is clarified. The principle, demonstration, however, concerns the transition to turbulence in plane shear flows. A simple layer of long rolls with axes parallel to the basic flow incites the transition.

关键词： Instability of shear flows Transition to turbulence computational methods in fluid dynamics

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Rotationally driven gas of inelastic rough spheres

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EUROPHYSICS LETTERS 2002年第6期60卷 854-860页

作者： Cafiero, R Luding, S Herrmann, HJ Ecole Super Phys & Chim Ind Ville Paris PMMH F-75251 Paris 05 France Inst Comp Applicat 1 D-70569 Stuttgart Germany Delft Univ Technol DelftChemTech NL-2628 CJ Delft Netherlands

We study a gas of inelastic rough spheres confined on a 2D plane, driven on the rotational degrees of freedom. Event-driven molecular dynamics (MD) simulations are compared to mean-field (MF) predictions with surprisingly good agreement for strong coupling of rotational and translational degrees of freedom even for very strong dissipation in the translational degrees. Although the system is spatially homogeneous, the rotational velocity distribution is essentially Maxwellian. Surprisingly, the distribution of tangential velocities is strongly deviating from a Maxwellian. An interpretation of these results is proposed, as well as a setup for an experiment.

关键词： Granular systems Kinetic and transport theory of gases computational methods in fluid dynamics

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Compound waves in a thermohydrodynamic lattice BGK scheme using non-perturbative equilibria

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EUROPHYSICS LETTERS 2002年第5期57卷 690-696页

作者： Dellar, PJ Univ Cambridge Dept Appl Math & Theoret Phys Cambridge CB3 9EW England

A previously proposed thermohydrodynamic lattice BGK scheme using non-perturbative, or non-polynomial, equilibria is found to simulate continuum equations that differ from the Euler equations of gas dynamics at leading order. Shock tube simulations with this BGK scheme coincide with solutions obtained by solving these different continuum equations with conventional methods. Both sets of solutions contain unphysical compound waves, shocks attached to rarefactions, where the Euler equations contain contact discontinuities.

关键词： Compressible flows, shock and detonation phenomena Kinetic theory computational methods in fluid dynamics

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Lattice Boltzmann model for magnetic fluid interfaces

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EUROPEAN PHYSICAL JOURNAL B 2001年第1期20卷 141-149页

作者： Sofonea, V Früh, WG Romanian Acad Ctr Fundamental & Adv Tech Res Lab Numer Simulat & Parallel Comp Fluid Mech Timisoara 1900 Romania Univ Edinburgh Edinburgh Parallel Comp Ctr Edinburgh EH9 3JZ Midlothian Scotland Heriot Watt Univ Dept Mech & Chem Engn Edinburgh EH14 4AS Midlothian Scotland

A Lattice Boltzmann model is developed to account for the competition between surface tension and dipolar interaction in magnetic fluids. The description of the interactions was kept as simple as possible to identify and isolate the nature of the essential interactions in the examined situations. The model is used thereafter in order to simulate the deformation of a magnetic fluid drop under the action of an external magnetic field, as well as the onset of the normal field instability in magnetic fluids. The success of the model, and easily identified deviations, demonstrate that the model is a powerful and versatile tool for the study of magnetic and nonmagnetic fluid systems with interfaces.

关键词： Magnetic liquids computational methods in fluid dynamics Interfacial instability

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Chemical efficiency of reactive microflows with heterogeneous catalysis: a lattice Boltzmann study

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EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS 2001年第1期16卷 71-84页

作者： Succi, S Gabrielli, A Smith, G Kaxiras, E CNR Ist Applicaz Calcolo I-00161 Rome Italy Univ Roma La Sapienza Dipartimento Fis INFM I-00185 Rome Italy Harvard Univ Dept Phys Lyman Lab Cambridge MA 02138 USA

We investigate the effects of geometrical micro-irregularities on the conversion efficiency of reactive flows in narrow channels of millimetric size. Three-dimensional simulations, based upon a Lattice-Boltzmann-Lax-Wendroff code, indicate that periodic micro-barriers may have an appreciable effect on the effective reaction efficiency of the device. Once extrapolated to macroscopic scales, these effects can result in a sizeable increase of the overall reaction efficiency.

关键词： Chemically reactive flows computational methods in fluid dynamics

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