scholarly journals Impact of collision models on the physical properties and the stability of lattice Boltzmann methods

2020 ◽  
Vol 378 (2175) ◽  
pp. 20190397 ◽  
Author(s):  
C. Coreixas ◽  
G. Wissocq ◽  
B. Chopard ◽  
J. Latt
Keyword(s):  
Physical Properties ◽  
Lattice Boltzmann ◽  
Soft Matter ◽  
Spectral Element ◽  
Collision Model ◽  
Zero Viscosity Limit ◽  
High Reynolds ◽  
Bgk Approximation ◽  
Moment Spaces ◽  
Collision Models

The lattice Boltzmann method (LBM) is known to suffer from stability issues when the collision model relies on the BGK approximation, especially in the zero viscosity limit and for non-vanishing Mach numbers. To tackle this problem, two kinds of solutions were proposed in the literature. They consist in changing either the numerical discretization (finite-volume, finite-difference, spectral-element, etc.) of the discrete velocity Boltzmann equation (DVBE), or the collision model. In this work, the latter solution is investigated in detail. More precisely, we propose a comprehensive comparison of (static relaxation time based) collision models, in terms of stability, and with preliminary results on their accuracy, for the simulation of isothermal high-Reynolds number flows in the (weakly) compressible regime. It starts by investigating the possible impact of collision models on the macroscopic behaviour of stream-and-collide based D2Q9-LBMs, which clarifies the exact physical properties of collision models on LBMs. It is followed by extensive linear and numerical stability analyses, supplemented with an accuracy study based on the transport of vortical structures over long distances. In order to draw conclusions as generally as possible, the most common moment spaces (raw, central, Hermite, central Hermite and cumulant), as well as regularized approaches, are considered for the comparative studies. LBMs based on dynamic collision mechanisms (entropic collision, subgrid-scale models, explicit filtering, etc.) are also briefly discussed. This article is part of the theme issue ‘Fluid dynamics, soft matter and complex systems: recent results and new methods’.

scholarly journals Efficient supersonic flow simulations using lattice Boltzmann methods based on numerical equilibria

2020 ◽  
Vol 378 (2175) ◽  
pp. 20190559 ◽  
Author(s):  
Jonas Latt ◽  
Christophe Coreixas ◽  
Joël Beny ◽  
Andrea Parmigiani
Keyword(s):  
Supersonic Flow ◽  
Lattice Boltzmann ◽  
Soft Matter ◽  
Compressible Flows ◽  
Relaxation Times ◽  
Boltzmann Distribution ◽  
Low Viscosity ◽  
Flow Past ◽  
Zero Viscosity Limit ◽  
Supersonic Regime

A double-distribution-function based lattice Boltzmann method (DDF-LBM) is proposed for the simulation of polyatomic gases in the supersonic regime. The model relies on a numerical equilibrium that has been extensively used by discrete velocity methods since the late 1990s. Here, it is extended to reproduce an arbitrary number of moments of the Maxwell–Boltzmann distribution. These extensions to the standard 5-constraint (mass, momentum and energy) approach lead to the correct simulation of thermal, compressible flows with only 39 discrete velocities in 3D. The stability of this BGK-LBM is reinforced by relying on Knudsen-number-dependent relaxation times that are computed analytically. Hence, high Reynolds-number, supersonic flows can be simulated in an efficient and elegant manner. While the 1D Riemann problem shows the ability of the proposed approach to handle discontinuities in the zero-viscosity limit, the simulation of the supersonic flow past a NACA0012 aerofoil confirms the excellent behaviour of this model in a low-viscosity and supersonic regime. The flow past a sphere is further simulated to investigate the 3D behaviour of our model in the low-viscosity supersonic regime. The proposed model is shown to be substantially more efficient than the previous 5-moment D3Q343 DDF-LBM for both CPU and GPU architectures. It then opens up a whole new world of compressible flow applications that can be realistically tackled with a purely LB approach. This article is part of the theme issue ‘Fluid dynamics, soft matter and complex systems: recent results and new methods’.

Modelling and simulation of ship collisions in port and coastal waters

2021 ◽  
pp. 147509022198918
Author(s):  
Chien-Chang Chou
Keyword(s):  
Coastal Waters ◽  
Maritime Transportation ◽  
Critical Factors ◽  
Ship Maneuvering ◽  
Collision Model ◽  
The Past ◽  
Sea Current ◽  
Ship Collision ◽  
Comparison Of The Results ◽  
Collision Models

Navigational safety is an important issue in maritime transportation. The most frequent type of maritime accident in the port and coastal waters is the ship collision. Although some ship collision models have been developed in the past, few have taken account of wind and sea current effects. However, wind and sea current are critical factors in ship maneuvering. Therefore, based on the previous collision model without wind and sea current effects, this study further develops a ship collision model with wind and sea current effects. Finally, a comparison of the results for the proposed collision model in this study and the ship maneuvering simulator is shown to illustrate the effectiveness of the proposed mathematical model in this paper, followed by the conclusions and suggestions given to navigators, port managers, and governmental maritime departments to improve navigational safety in port and coastal waters.

scholarly journals Current Research on Polyelectrolyte Nanostructures: From Molecular Interactions to Biomedical Applications

Macromol ◽  
2021 ◽  
Vol 1 (2) ◽  
pp. 155-172
Author(s):  
Aristeidis Papagiannopoulos
Keyword(s):  
Physical Properties ◽  
Molecular Interactions ◽  
Interdisciplinary Research ◽  
Biomedical Applications ◽  
Electrostatic Interactions ◽  
Soft Matter ◽  
Extracellular Polysaccharides ◽  
Polymer Science ◽  
Biological Matter ◽  
Biomedical Field

Polyelectrolytes have been at the center of interdisciplinary research for many decades. In the field of polymer science and soft matter, they have provided the dimensions of electrostatic interactions, which opens a vast variety of opportunities for new physical properties and applications. In biological matter, polyelectrolytes are present in many forms, from extracellular polysaccharides to complex DNA molecules and proteins. This review discusses the recent research on polyelectrolytes covering the fundamental level of their conformations and nanostructures, their molecular interactions with materials that have close relevance to bioapplications and their applications in the biomedical field. This approach is motivated by the fact that the polyelectrolyte research is constantly active in all the aforementioned levels and continually affects many critical scientific areas.

A GENERAL MULTIPLE-RELAXATION-TIME BOLTZMANN COLLISION MODEL

2007 ◽  
Vol 18 (04) ◽  
pp. 635-643 ◽  
Author(s):  
XIAOWEN SHAN ◽  
HUDONG CHEN
Keyword(s):  
Relaxation Time ◽  
Lattice Boltzmann ◽  
Lattice Structure ◽  
Transport Coefficients ◽  
Hermite Polynomials ◽  
Simple Extension ◽  
Relaxation Rates ◽  
Collision Model ◽  
Multiple Relaxation Time ◽  
Lattice Boltzmann Models

We formulate a simple extension to the Bhatnagar-Gross-Krook collision model by expanding the distribution function in Hermite polynomials and assigning a relaxation time to each hydrodynamic moment. By discretizing the velocity space, multiple-relaxation-time lattice Boltzmann models can be constructed. The transport coefficients are analytically calculated and numerically verified. At the lowest order, allowing different relaxation rates for the second and third Hermite components results in a variable Prandtl number. Comparing with the previously proposed multiple-relaxation-time lattice Boltzmann models, the present formulation is general in the sense that it is independent of the underlying lattice structure and does not require a procedure for transformation of base vectors.

scholarly journals Wall-modeled large-eddy simulation of the flow past a rod-airfoil tandem by the Lattice Boltzmann method

2018 ◽  
Vol 28 (5) ◽  
pp. 1096-1116 ◽  
Author(s):  
Emmanuel Leveque ◽  
Hatem Touil ◽  
Satish Malik ◽  
Denis Ricot ◽  
Alois Sengissen
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Lattice Boltzmann ◽  
Early Stage ◽  
Content Type ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbulent Airflow ◽  
High Reynolds ◽  
Boltzmann Method

Purpose The Lattice Boltzmann (LB) method offers an alternative to conventional computational fluid dynamics (CFD) methods. However, its practical use for complex turbulent flows of engineering interest is still at an early stage. This paper aims to outline an LB wall-modeled large-eddy simulation (WMLES) solver. Design/methodology/approach The solver is dedicated to complex high-Reynolds flows in the context of WMLES. It relies on an improved LB scheme and can handle complex geometries on multi-resolution block structured grids. Findings Dynamic and acoustic characteristics of a turbulent airflow past a rod-airfoil tandem are examined to test the capabilities of this solver. Detailed direct comparisons are made with both experimental and numerical reference data. Originality/value This study allows assessing the potential of an LB approach for industrial CFD applications.

scholarly journals Generic theory of the dynamic magnetic response of ferrofluids

Soft Matter ◽  
2020 ◽  
Vol 16 (48) ◽  
pp. 10928-10934
Author(s):  
Angbo Fang
Keyword(s):  
Physical Properties ◽  
Soft Matter ◽  
Magnetic Response ◽  
Important Class ◽  
Generic Theory

Ferrofluids belong to an important class of highly functional soft matter, benefiting from their magnetically controllable physical properties.

Random collision models in oriented graphs

1979 ◽  
Vol 16 (01) ◽  
pp. 36-44 ◽  
Author(s):  
Yoshiaki Itoh
Keyword(s):  
Oriented Graph ◽  
Dominant Type ◽  
Oriented Graphs ◽  
Collision Model ◽  
Dominance Relations ◽  
Different Types ◽  
The Stability ◽  
Collision Models

We investigate a random collision model for competition between types of individuals in a population. There are dominance relations defined for each pair of types such that if two individuals of different types collide then after the collision both are of the dominant type. These dominance relations are represented by an oriented graph, called a tournament. It is shown that tournaments having a particular form are relatively stable, while other tournaments are relatively unstable. A measure of the stability of the stable tournaments is given in the main theorem.

scholarly journals A multi-component lattice Boltzmann approach to study the causality of plastic events

2020 ◽  
Vol 378 (2175) ◽  
pp. 20190403
Author(s):  
Pinaki Kumar ◽  
Roberto Benzi ◽  
Jeannot Trampert ◽  
Federico Toschi
Keyword(s):  
Yield Stress ◽  
Lattice Boltzmann ◽  
Soft Matter ◽  
Scaling Laws ◽  
System A ◽  
Plastic Event ◽  
Glassy Materials ◽  
Couette Cell ◽  
Soft Glassy Materials ◽  
Concentrated Emulsions

Using a multi-component lattice Boltzmann (LB) model, we perform fluid kinetic simulations of confined and concentrated emulsions. The system presents the phenomenology of soft-glassy materials, including a Herschel–Bulkley rheology, yield stress, ageing and long relaxation time scales. Shearing the emulsion in a Couette cell below the yield stress results in plastic topological re-arrangement events which follow established empirical seismic statistical scaling laws, making this system a good candidate to study the physics of earthquakes. One characteristic of this model is the tendency for events to occur in avalanche clusters, with larger events, triggering subsequent re-arrangements. While seismologists have developed statistical tools to study correlations between events, a process to confirm causality remains elusive. We present here, a modification to our LB model, involving small, fast vibrations applied to individual droplets, effectively a macroscopic forcing, which results in the arrest of the topological plastic re-arrangements. This technique provides an excellent tool for identifying causality in plastic event clusters by examining the evolution of the dynamics after ‘stopping’ an event, and then checking which subsequent events disappear. This article is part of the theme issue ‘Fluid dynamics, soft matter and complex systems: recent results and new methods’.

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