2,120 research outputs found
Spatial Coupling of a Lattice Boltzmann fluid model with a Finite Difference Navier-Stokes solver
In multiscale, multi-physics applications, there is an increasing need for
coupling numerical solvers that are each applied to a different part of the
problem. Here we consider the case of coupling a Lattice Boltzmann fluid model
and a Finite Difference Navier-Stokes solver. The coupling is implemented so
that the entire computational domain can be divided in two regions, with the FD
solver running on one of them and the LB one on the other.
We show how the various physical quantities of the two approaches should be
related to ensure a smooth transition at the interface between the regions. We
demonstrate the feasibility of the method on the Poiseuille flow, where the LB
and FD schemes are used on adjacent sub-domains.
The same idea can be also developed to couple LB models with Finite Volumes,
or Finite Elements calculations.
The motivation for developing such a type of coupling is that, depending on
the geometry of the flow, one technique can be more efficient, less memory
consuming, or physically more appropriate than the other in some regions (e.g.
near the boundaries), whereas the converse is true for other parts of the same
system. We can also imagine that a given system solved, say by FD, can be
augmented in some spatial regions with a new physical process that is better
treated by a LB model. Our approach allows us to only modify the concerned
region without altering the rest of the computation.Comment: 10 pages, 2 figure
Competing Species Dynamics: Qualitative Advantage versus Geography
A simple cellular automata model for a two-group war over the same territory
is presented. It is shown that a qualitative advantage is not enough for a
minority to win. A spatial organization as well a definite degree of
aggressiveness are instrumental to overcome a less fitted majority. The model
applies to a large spectrum of competing groups: smoker-non smoker war,
epidemic spreading, opinion formation, competition for industrial standards and
species evolution. In the last case, it provides a new explanation for
punctuated equilibria.Comment: 7 pages, latex, 2 figures include
Bankruptcy Law: a Mechanism of Governance for Financially Distressed Firms.
This paper explores the various governance models for financially distressed firms. We offer a new typology of major bankruptcy models and provide a connection between this bankruptcy law puzzle and the variables depicting the governance of healthy firms in order to shed light on two topics: (1) the factors that the lawyer should consider before removing its national bankruptcy law, and (2) the risks associated with each bankruptcy model according to the economic literature on bankruptcy law. Our final aim is to test whether the various bankruptcy models detailed in the paper perform in separate economic and legal environments.Bankruptcy, Governance, Law and Economics.
Hermite regularization of the Lattice Boltzmann Method for open source computational aeroacoustics
The lattice Boltzmann method (LBM) is emerging as a powerful engineering tool
for aeroacoustic computations. However, the LBM has been shown to present
accuracy and stability issues in the medium-low Mach number range, that is of
interest for aeroacoustic applications. Several solutions have been proposed
but often are too computationally expensive, do not retain the simplicity and
the advantages typical of the LBM, or are not described well enough to be
usable by the community due to proprietary software policies. We propose to use
an original regularized collision operator, based on the expansion in Hermite
polynomials, that greatly improves the accuracy and stability of the LBM
without altering significantly its algorithm. The regularized LBM can be easily
coupled with both non-reflective boundary conditions and a multi-level grid
strategy, essential ingredients for aeroacoustic simulations. Excellent
agreement was found between our approach and both experimental and numerical
data on two different benchmarks: the laminar, unsteady flow past a 2D cylinder
and the 3D turbulent jet. Finally, most of the aeroacoustic computations with
LBM have been done with commercial softwares, while here the entire theoretical
framework is implemented on top of an open source library (Palabos).Comment: 34 pages, 12 figures, The Journal of the Acoustical Society of
America (in press
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