11,058 research outputs found
An amplitude-frequency study of turbulent scaling intermittency using Empirical Mode Decomposition and Hilbert Spectral Analysis
Hilbert-Huang transform is a method that has been introduced recently to
decompose nonlinear, nonstationary time series into a sum of different modes,
each one having a characteristic frequency. Here we show the first successful
application of this approach to homogeneous turbulence time series. We
associate each mode to dissipation, inertial range and integral scales. We then
generalize this approach in order to characterize the scaling intermittency of
turbulence in the inertial range, in an amplitude-frequency space. The new
method is first validated using fractional Brownian motion simulations. We then
obtain a 2D amplitude-frequency representation of the pdf of turbulent
fluctuations with a scaling trend, and we show how multifractal exponents can
be retrieved using this approach. We also find that the log-Poisson
distribution fits the velocity amplitude pdf better than the lognormal
distribution.Comment: 6 pages with 8 figure
Hilbert Statistics of Vorticity Scaling in Two-Dimensional Turbulence
In this paper, the scaling property of the inverse energy cascade and forward
enstrophy cascade of the vorticity filed in two-dimensional (2D)
turbulence is analyzed. This is accomplished by applying a Hilbert-based
technique, namely Hilbert-Huang Transform, to a vorticity field obtained from a
grid-points direct numerical simulation of the 2D turbulence with a
forcing scale and an Ekman friction. The measured joint probability
density function of mode of the vorticity and
instantaneous wavenumber is separated by the forcing scale into
two parts, which corresponding to the inverse energy cascade and the forward
enstrophy cascade. It is found that all conditional pdf at given
wavenumber has an exponential tail. In the inverse energy cascade, the
shape of does collapse with each other, indicating a
nonintermittent cascade. The measured scaling exponent is
linear with the statistical order , i.e., ,
confirming the nonintermittent cascade process.
In the forward enstrophy cascade, the core part of is changing
with wavenumber , indicating an intermittent forward cascade.
The measured scaling exponent is nonlinear with and
can be described very well by a log-Poisson fitting:
. However, the
extracted vorticity scaling exponents for both inverse
energy cascade and forward enstrophy cascade are not consistent with
Kraichnan\rq{}s theory prediction. New theory for the vorticity field in 2D
turbulence is required to interpret the observed scaling behavior.Comment: 13 pages with 10 figure
Equivalent Effect Function and Fast Intrinsic Mode Decomposition
The Equivalent Effect Function (EEF) is defined as having the identical
integral values on the control points of the original time series data; the EEF
can be obtained from the derivative of the spline function passing through the
integral values on the control points. By choosing control points with
different criteria, the EEF can be used to find the intrinsic mode
function(IMF, fluctuation) and the residue (trend); to fit the curve of the
original data function; and to take samples on original data with equivalent
effect. As examples of application, results of trend and fluctuation on real
stock historical data are calculated on different time scales. A new approach
to extend the EEF to 2D intrinsic mode decomposition is introduced to resolve
the inter slice non continuity problem, some photo image decomposition examples
are presented
Intermittency measurement in two dimensional bacterial turbulence
In this paper, an experimental velocity database of a bacterial collective
motion , e.g., \textit{B. subtilis}, in turbulent phase with volume filling
fraction provided by Professor Goldstein at the Cambridge University UK,
was analyzed to emphasize the scaling behavior of this active turbulence
system. This was accomplished by performing a Hilbert-based methodology
analysis to retrieve the scaling property without the limitation. A
dual-power-law behavior separated by the viscosity scale was
observed for the th-order Hilbert moment . This
dual-power-law belongs to an inverse-cascade since the scaling range is above
the injection scale , e.g., the bacterial body length. The measured scaling
exponents of both the small-scale \red{(resp. ) and
large-scale (resp. )} motions are convex, showing the
multifractality. A lognormal formula was put forward to characterize the
multifractal intensity. The measured intermittency parameters are
and respectively for the small- and large-scale motions. It
implies that the former cascade is more intermittent than the latter one, which
is also confirmed by the corresponding singularity spectrum vs
. Comparison with the conventional two-dimensional Ekman-Navier-Stokes
equation, a continuum model indicates that the origin of the multifractality
could be a result of some additional nonlinear interaction terms, which
deservers a more careful investigation.Comment: 23 pages, 7 figures. This paper is published on Physical Review E,
93, 062226, 201
Multi-level segment analysis: definition and application in turbulent systems
For many complex systems the interaction of different scales is among the
most interesting and challenging features. It seems not very successful to
extract the physical properties in different scale regimes by the existing
approaches, such as structure-function and Fourier spectrum method.
Fundamentally these methods have their respective limitations, for instance
scale mixing, i.e. the so-called infrared and ultraviolet effects. To make
improvement in this regard, a new method, multi-level segment analysis (MSA)
based on the local extrema statistics, has been developed. Benchmark
(fractional Brownian motion) verifications and the important case tests
(Lagrangian and two-dimensional turbulence) show that MSA can successfully
reveal different scaling regimes, which has been remaining quite controversial
in turbulence research. In general the MSA method proposed here can be applied
to different dynamic systems in which the concepts of multiscaling and
multifractal are relevant.Comment: 18 pages with 9 figures, accepted by Journal of Statistical Mechanic
Multidimensional Analytic Signals and the Bedrosian Identity
The analytic signal method via the Hilbert transform is a key tool in signal
analysis and processing, especially in the time-frquency analysis. Imaging and
other applications to multidimensional signals call for extension of the method
to higher dimensions. We justify the usage of partial Hilbert transforms to
define multidimensional analytic signals from both engineering and mathematical
perspectives. The important associated Bedrosian identity for
partial Hilbert transforms are then studied. Characterizations and several
necessity theorems are established. We also make use of the identity to
construct basis functions for the time-frequency analysis
Compressed Sensing for Time-Frequency Gravitational Wave Data Analysis
The potential of compressed sensing for obtaining sparse time-frequency
representations for gravitational wave data analysis is illustrated by
comparison with existing methods, as regards i) shedding light on the fine
structure of noise transients (glitches) in preparation of their
classification, and ii) boosting the performance of waveform consistency tests
in the detection of unmodeled transient gravitational wave signals using a
network of detectors affected by unmodeled noise transientComment: 16 pages + 17 figure
Moment-based cosh-Hilbert Inversion and Its Applications in Single-photon Emission Computed Tomography
The inversion of cosh-Hilbert transform (CHT) is one of the most crucial
steps for single-photon emission computed tomography with uniform attenuation
from truncated projection data. Although the uniqueness of the CHT inversion
had been proved \cite{Noo2007}, there is no exact and analytic inverse formula
so far. Several approximated inversion algorithms of the CHT had been developed
\cite{Noo2007}\cite{You2007}. In this paper, we proposed a new numerical
moment-based inversion algorithm
Lagrangian Statistics and Intermittency in Gulf of Mexico
Due to the nonlinear interaction between different flow patterns, for
instance, ocean current, meso-scale eddies, waves, etc, the movement of ocean
is extremely complex, where a multiscale statistics is then relevant. In this
work, a high time-resolution velocity with a time step 15 minutes obtained by
the Lagrangian drifter deployed in the Gulf of Mexico (GoM) from July 2012 to
October 2012 is considered. The measured Lagrangian velocity correlation
function shows a strong daily cycle due to the diurnal tidal cycle.
The estimated Fourier power spectrum implies a dual-power-law behavior
which is separated by the daily cycle. The corresponding scaling exponents are
close to and respectively for the time scale larger (resp.
) and smaller (resp. )
than 1 day. A Hilbert-based approach is then applied to this data set to
identify the possible multifractal property of the cascade process. The results
show an intermittent dynamics for the time scale larger than 1 day, while a
less intermittent dynamics for the time scale smaller than 1 day. It is
speculated that the energy is partially injected via the diurnal tidal movement
and then transferred to larger and small scales through a complex cascade
process, which needs more studies in the near future.Comment: 8 pages with 5 figure
Synchrosqueezed Curvelet Transform for 2D Mode Decomposition
This paper introduces the synchrosqueezed curvelet transform as an optimal
tool for 2D mode decomposition of wavefronts or banded wave-like components.
The synchrosqueezed curvelet transform consists of a generalized curvelet
transform with application dependent geometric scaling parameters, and a
synchrosqueezing technique for a sharpened phase space representation. In the
case of a superposition of banded wave-like components with well-separated
wave-vectors, it is proved that the synchrosqueezed curvelet transform is
capable of recognizing each component and precisely estimating local
wave-vectors. A discrete analogue of the continuous transform and several
clustering models for decomposition are proposed in detail. Some numerical
examples with synthetic and real data are provided to demonstrate the above
properties of the proposed transform.Comment: 32 page
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