1,659 research outputs found
On the intermittent energy transfer at viscous scales in turbulent flows
In this letter we present numerical and experimental results on the scaling
properties of velocity turbulent fields in the range of scales where viscous
effects are acting. A generalized version of Extended Self Similarity capable
of describing scaling laws of the velocity structure functions down to the
smallest resolvable scales is introduced. Our findings suggest the absence of
any sharp viscous cutoff in the intermittent transfer of energy.Comment: 10 pages, plain Latex, 6 figures available upon request to
[email protected]
A lattice Boltzmann study of non-hydrodynamic effects in shell models of turbulence
A lattice Boltzmann scheme simulating the dynamics of shell models of
turbulence is developed. The influence of high order kinetic modes (ghosts) on
the dissipative properties of turbulence dynamics is studied. It is
analytically found that when ghost fields relax on the same time scale as the
hydrodynamic ones, their major effect is a net enhancement of the fluid
viscosity. The bare fluid viscosity is recovered by letting ghost fields evolve
on a much longer time scale. Analytical results are borne out by
high-resolution numerical simulations. These simulations indicate that the
hydrodynamic manifold is very robust towards large fluctuations of non
hydrodynamic fields.Comment: 17 pages, 3 figures, submitted to Physica
Stochastic Resonance in Two Dimensional Landau Ginzburg Equation
We study the mechanism of stochastic resonance in a two dimensional Landau
Ginzburg equation perturbed by a white noise. We shortly review how to
renormalize the equation in order to avoid ultraviolet divergences. Next we
show that the renormalization amplifies the effect of the small periodic
perturbation in the system. We finally argue that stochastic resonance can be
used to highlight the effect of renormalization in spatially extended system
with a bistable equilibria
Intermittency in Turbulence: computing the scaling exponents in shell models
We discuss a stochastic closure for the equation of motion satisfied by
multi-scale correlation functions in the framework of shell models of
turbulence. We give a systematic procedure to calculate the anomalous scaling
exponents of structure functions by using the exact constraints imposed by the
equation of motion. We present an explicit calculation for fifth order scaling
exponent at varying the free parameter entering in the non-linear term of the
model. The same method applied to the case of shell models for Kraichnan
passive scalar provides a connection between the concept of zero-modes and
time-dependent cascade processes.Comment: 12 pages, 5 eps figure
Universal statistics of non-linear energy transfer in turbulent models
A class of shell models for turbulent energy transfer at varying the
inter-shell separation, , is investigated. Intermittent corrections in
the continuous limit of infinitely close shells () have
been measured. Although the model becomes, in this limit, non-intermittent, we
found universal aspects of the velocity statistics which can be interpreted in
the framework of log-poisson distributions, as proposed by She and Waymire
(1995, Phys. Rev. Lett. 74, 262). We suggest that non-universal aspects of
intermittency can be adsorbed in the parameters describing statistics and
properties of the most singular structure. On the other hand, universal aspects
can be found by looking at corrections to the monofractal scaling of the most
singular structure. Connections with similar results reported in other shell
models investigations and in real turbulent flows are discussed.Comment: 4 pages, 2 figures available upon request to [email protected]
Phase-field model of long-time glass-like relaxation in binary fluid mixtures
We present a new phase-field model for binary fluids exhibiting typical
signatures of self-glassiness, such as long-time relaxation, ageing and
long-term dynamical arrest. The present model allows the cost of building an
interface to become locally zero, while preserving global positivity of the
overall surface tension. An important consequence of this property, which we
prove analytically, is the emergence of compact configurations of fluid
density. Owing to their finite-size support, these "compactons" can be
arbitrarily superposed, thereby providing a direct link between the ruggedness
of the free-energy landscape and morphological complexity in configurational
space. The analytical picture is supported by numerical simulations of the
proposed phase-field equation.Comment: 5 Pages, 6 Figure
Medical Diagnosis and Actual Causation
I suggest that some diagnoses can be seen as causal ex-planations based on \u201cparticulars\u201d \u2013 instead of regularities \u2013 and on the notion of actual causation. Diagnoses based on case-based rea-soning provide a particularly vivid example
Cooperativity flows and Shear-Bandings: a statistical field theory approach
Cooperativity effects have been proposed to explain the non-local rheology in
the dynamics of soft jammed systems. Based on the analysis of the free-energy
model proposed by L. Bocquet, A. Colin \& A. Ajdari ({\em Phys. Rev. Lett.}
{\bf 103}, 036001 (2009)), we show that cooperativity effects resulting from
the non-local nature of the fluidity (inverse viscosity), are intimately
related to the emergence of shear-banding configurations. This connection
materializes through the onset of inhomogeneous compact solutions (compactons),
wherein the fluidity is confined to finite-support subregions of the flow and
strictly zero elsewhere. Compactons coexistence with regions of zero fluidity
("non-flowing vacuum") is shown to be stabilized by the presence of mechanical
noise, which ultimately shapes up the equilibrium distribution of the fluidity
field, the latter acting as an order parameter for the flow-noflow transitions
occurring in the material.Comment: 33 pages, 10 figure
A new scaling property of turbulent flows
We discuss a possible theoretical interpretation of the self scaling property
of turbulent flows (Extended Self Similarity). Our interpretation predicts
that, even in cases when ESS is not observed, a generalized self scaling, must
be observed. This prediction is checked on a number of laboratory experiments
and direct numerical simulations.Comment: Plain Latex, 1 figure available upon request to
[email protected]
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