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Herschel-Bulkley rheology from lattice kinetic theory of soft glassy materials

EPL 2010年第1期91卷

作者： Benzi, R. Bernaschi, M. Sbragaglia, M. Succi, S. Univ Roma Tor Vergata Dept Phys I-00133 Rome Italy Univ Roma Tor Vergata Ist Nazl Fis Nucl I-00133 Rome Italy CNR Ist Applicaz Calcolo I-00185 Rome Italy

We provide clear evidence that a two-species mesoscopic Lattice Boltzmann (LB) model with competing, short-range attractive and mid-range repulsive, interactions supports emergent Herschel-Bulkley (HB) rheology, i.e. a power-law dependence of the shear stress as a function of the strain rate, beyond a given yield stress threshold. This kinetic formulation supports a seamless transition from flowing to non-flowing behaviour, through a smooth tuning of the parameters governing the mesoscopic interactions between the two species. The present model may become a valuable computational tool for the investigation of the rheology of soft glassy materials on scales of experimental interest. Copyright (C) EPLA, 2010

关键词： computational methods in fluid dynamics Rarefied gas dynamics computational techniques, simulations

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Nanoflows through disordered media: A joint lattice Boltzmann and molecular dynamics investigation

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EPL 2010年第4期89卷

作者： Russo, J. Horbach, J. Sciortino, F. Succi, S. Univ Roma La Sapienza Dept Fis I-00185 Rome Italy Univ Roma La Sapienza CNR INFM SOFT I-00185 Rome Italy Deutsch Zentrum Luft & Raumfahrt Inst Mat Phys Weltraum D-51170 Cologne Germany Univ Freiburg Freiburg Inst Adv Studies D-79104 Freiburg Germany CNR Ist Applicaz Calcolo I-00185 Rome Italy

We investigate nanoflows through dilute disordered media by means of joint lattice Boltzmann (LB) and molecular dynamics (MD) simulations -when the size of the obstacles is comparable to the size of the flowing particles-for randomly located spheres and for a correlated particle-gel. In both cases at sufficiently low solid fraction, Phi < 0.01, LB and MD provide similar values of the permeability. However, for Phi > 0.01, MD shows that molecular-size effects lead to a decrease of the permeability, as compared to the Navier-Stokes predictions. For gels, the simulations highlights a surplus of permeability, which can be accommodated within a rescaling of the effective radius of the gel monomers. Copyright (C) EPLA, 2010

关键词： Flows through porous media computational methods in fluid dynamics Micro- and nano- scale flow phenomena

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Detrended fluctuation analysis of numerical density and viscous fingering patterns

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EPL 2010年第6期92卷

作者： Baroni, M. P. M. A. de Wit, A. Rosa, R. R. INPE Lab Assoc Computacao & Matemat Aplicada BR-12201970 Sao Jose Dos Campos SP Brazil Univ Libre Brussels Fac Sci Nonlinear Phys Chem Unit B-1050 Brussels Belgium

We study transversely averaged concentration profiles of fingering dynamics from numerical simulations. Such profiles are studied here for a comparative fluctuation analysis between density fingering (DF) and viscous fingering (VF) envolving in a quite similar nonlinear regime. Although many physical properties influence the fingering pattern formation in miscible displacements, there are few measurements obtained from the averaged profiles, as the mixing length, that help to characterize concentration fluctuations due to self-correlations in the interfacial structure. Besides mixing length, scaling exponents (alpha) from detrended fluctuation analysis (DFA) are computed here for DF and VF simulations. The scaling exponent evolution is compared between DF and VF cases providing a specific signature for each kind of process: DF with alpha = 1.93 +/- 0.04 and VF with alpha = 1.82 +/- 0.04. Our analysis, based on DFA, provides a new approach for quantifying the fingering pattern formation and, in particular, the fine fluctuations differences between viscous and density fingering in miscible fluids displacements. Copyright (C) EPLA, 2010

关键词： computational methods in fluid dynamics Pattern selection, pattern formation Fluctuation phenomena, random processes, noise, and Brownian motion

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Non-periodic boundary model with soft transition in molecular dynamics simulation

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EPL 2010年第5期92卷

作者： Huang, Z. G. Guo, Z. N. Yue, T. M. Chan, K. C. Hong Kong Polytech Univ Fac Engn Adv Mfg Technol Res Ctr Hong Kong Hong Kong Peoples R China Guangdong Univ Technol Fac Electromech Engn Guangzhou 510090 Guangdong Peoples R China

The imposition of non-periodic boundary conditions is a challenging issue in molecular dynamics (MD) simulation because of the difficulty in reconstructing the detailed particle dynamics from the few state variables. In this paper, a general scheme for the imposition of this kind of boundary conditions is presented. The complete model includes the imposition of Dirichlet boundary conditions and applying the boundary force to ensure the continuity of flow properties. Both the flux and the boundary force are introduced in a consistent way with the microscopic dynamics of the molecular system. Moreover, a soft constraint mechanism is included to correct the instantaneous deviation of the local state. A uniform flow and a Poiseuille flow of Lennard-Jones fluid is simulated using the boundary model. The results demonstrate that the fluctuation of flow properties near the boundary is kept at a low level, and the model is stable even subject to internal disturbance. Copyright (C) EPLA, 2010

关键词： Molecular dynamics and particle methods Multi-scale methods computational methods in fluid dynamics

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Multiple-relaxation-time lattice Boltzmann approach to compressible flows with flexible specific-heat ratio and Prandtl number

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EPL 2010年第5期90卷

作者： Chen, Feng Xu, Aiguo Zhang, Guangcai Li, Yingjun Succi, Sauro China Univ Min & Technol State Key Lab GeoMech & Deep Underground Engn Beijing 100083 Peoples R China Inst Appl Phys & Computat Math Natl Key Lab Computat Phys Beijing 100088 Peoples R China CNR Ist Applicaz Calcolo I-00161 Rome Italy

A new multiple-relaxation-time lattice Boltzmann scheme for compressible flows with arbitrary specific-heat ratio and Prandtl number is presented. In the new scheme, which is based on a two-dimensional 16-discrete-velocity model, the kinetic moment space and the corresponding transformation matrix are constructed according to the seven-moment relations associated with the local-equilibrium distribution function. In the continuum limit, the model recovers the compressible Navier-Stokes equations with flexible specific-heat ratio and Prandtl number. Numerical experiments show that compressible flows with strong shocks can be simulated by the present model up to Mach numbers M alpha similar to 5. Copyright (C) EPLA, 2010

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

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On the microscopic foundation of dissipative particle dynamics

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EPL 2009年第4期86卷

作者： Eriksson, A. Jacobi, M. Nilsson Nystrom, J. Tunstrom, K. Univ Gothenburg Dept Phys SE-41296 Gothenburg Sweden Chalmers Univ Technol Environm & Energy Dept Complex Syst Grp SE-41296 Gothenburg Sweden

Mesoscopic-particle-based fluid models, such as dissipative particle dynamics, are usually assumed to be coarse-grained representations of an underlying microscopic fluid. A fundamental question is whether there exists a map from microscopic particles in these systems to the corresponding coarse-grained particles, such that the coarse-grained system has the same bulk and transport properties as the underlying system. In this letter, we investigate the coarse-graining of microscopic fluids using a Voronoi-type projection that has been suggested in several studies. The simulations show that the projection fails in de. ning coarse-grained particles that have a physically meaningful connection to the microscopic fluid. In particular, the Voronoi projection produces identical coarse-grained equilibrium properties when applied to systems with different microscopic interactions and different bulk properties. Copyright (C) EPLA, 2009

关键词： computational methods in fluid dynamics Multi-scale methods Complex fluids and colloidal systems

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Continuum free-energy formulation for a class of lattice Boltzmann multiphase models

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EPL 2009年第2期86卷

作者： Sbragaglia, M. Chen, H. Shan, X. Succi, S. Univ Roma Tor Vergata Dept Phys I-00133 Rome Italy Univ Roma Tor Vergata Ist Nazl Fis Nucl I-00133 Rome Italy EXA Corp Burlington MA 01803 USA CNR Ist Applicaz Calcolo I-00161 Rome Italy

It is shown that the Shan-Chen (SC) model for non-ideal lattice fluids can be made compliant with a pseudo-free-energy principle by simple addition of a gradient force, whose expression is uniquely specified in terms of the fluid density. This additional term is numerically simulated and shown to provide fairly negligible effects on the system evolution during phase-separation. To the best of our knowledge, these important properties of the SC model were not noted before. The approach developed in the present work is based on a continuum analysis: Further extensions, more in line with a discrete lattice theory (SHAN X., Phys. Rev. E, 77 (2008) 066702), can be envisaged for the future. Copyright (C) EPLA, 2009

关键词： computational methods in fluid dynamics Rarefied gas dynamics computational techniques, simulations

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Lattice Boltzmann across scales: from turbulence to DNA translocation

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EUROPEAN PHYSICAL JOURNAL B 2008年第3-4期64卷 471-479页

作者： Succi, S. CNR Ist Applicaz Calcolo I-00161 Rome Italy

The capability of the lattice Boltzmann (LB) method to describe complex flow behaviour across a wide range of scales of motion is discussed. This capability is illustrated by means of three examples, straddling across over ten decades of fluid motion, from macroscopic turbulence, to microfluidics, all the way down to nanoscopic flows of biological interest. It is pointed out that each of these applications requires extensions of the original LB scheme, beyond the realm of Navier-Stokes hydrodynamics for which the method was originally designed. The main qualitative ideas behind such extensions are discussed and commented on, with special emphasis on their direct ties with modern non-equilibrium statistical mechanics.

关键词： Kinetic theory computational methods in fluid dynamics Statistical physics and nonlinear dynamics

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Acceleration techniques for reduced-order models based on proper orthogonal decomposition

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JOURNAL OF computational PHYSICS 2008年第16期227卷 7791-7812页

作者： Cizmas, Paul G. A. Richardson, Brian R. Brenner, Thomas A. O'Brien, Thomas J. Breault, Ronald W. Texas A&M Univ Dept Aerosp Engn College Stn TX 77843 USA Dept Energy Natl Energy Technol Lab Morgantown WV 26507 USA

This paper presents several acceleration techniques for reduced-order models based on the proper orthogonal decomposition (POD) method. The techniques proposed herein are: (i) an algorithm for splitting the database of snapshots generated by the full-order model;(ii) a method for solving quasi-symmetrical matrices;(iii) a strategy for reducing the frequency of the projection. The acceleration techniques were applied to a POD-based reduced-order model of the two-phase flows in fluidized beds. This reduced-order model was developed using numerical results from a full-order computational fluid dynamics model of a two-dimensional fluidized bed. Using these acceleration techniques the computational time of the POD model was two orders of magnitude shorter than the full-order model. (C) 2008 Elsevier Inc. All rights reserved.

关键词： proper orthogonal decomposition multiphase flow computational methods in fluid dynamics nonlinear dynamics

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Discrete effects on thermal boundary conditions for the thermal lattice Boltzmann method in simulating microscale gas flows

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EPL 2008年第4期82卷

作者： Zheng, L. Guo, Z. L. Shi, B. C. Huazhong Univ Sci & Technol Natl Lab Coal Combust Wuhan 430074 Peoples R China Huazhong Univ Sci & Technol Dept Math Wuhan 430074 Peoples R China

The lattice Boltzmann equation (LBE) has been shown to be able to describe important rarefied flow phenomena in the nearly continuum limit. However, the specific slip boundary condition for this promising method is still one of the critical issues. In this paper, two kinetic boundary conditions are proposed for simulating thermal microscale gas flows: one is the combination of the equilibrium distribution and specular-reflection scheme, another is the combination of the equilibrium distribution and bounce-back scheme. The two boundary conditions are then analyzed for the Couette flow. It is found that some discrete effects exist in the boundary conditions, which should be considered to ensure an accurate slip boundary condition. A correction method is then proposed to minimize the discrete effects, and numerical results demonstrate that the improved boundary schemes can yield much better results than the original ones. Copyright (C) EPLA, 2008.

关键词： computational methods in fluid dynamics Heat conduction Rarefied gas dynamics

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