Large-to-small scale frequency modulation analysis in wall-bounded turbulence via visibility networks

Iacobello, Giovanni; Ridolfi, Luca; Scarsoglio, Stefania

doi:10.1017/jfm.2021.279

Cited by 21 publications

(15 citation statements)

References 76 publications

(364 reference statements)

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“…The intensity of the modulation is observed to go hand-in-hand with the intensity of the large-scale outer structures and their footprints, the latter two rising with the Reynolds number [8]. In addition, a few recent studies [9][10][11][12], discussed later, have provided evidence of "frequency modulation" -i.e., the increase and reduction in the time scale of the near-wall turbulence.…”

Section: Introductionmentioning

confidence: 90%

“…[10], Pathikonda and Christensen [11] and Iacobello et al [12], the first three of which are based purely on processing experimental data, while the fourth involves both experimental and computational elements.…”

Section: Introductionmentioning

confidence: 99%

“…Iacobello et al [12] applied the so-called Natural Visibility Graph (NVG) approach, developed by Lacasa et al [32], to the boundary layer at Re τ ≈ 14750, previously examined in [9,10], and to the channel flow of at Re τ ≈ 5200 [33]. The principle of this method is to count how many times a signal at a point (a "node") can be linked to other discrete values by straight lines without crossing any other parts of the signal.…”

Section: Introductionmentioning

confidence: 99%

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Auto-encoder-assisted analysis of amplitude and wavelength modulation of near-wall turbulence by outer large-scale structures in channel flow at friction Reynolds number of 5200

Agostini

Leschziner

2022

Physics of Fluids

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The present paper reports a novel methodology that allows the intensity of, and the underlying mechanism for, the amplitude and length-scale modulation (amplification or attenuation) of the turbulent stresses in the boundary layer of a channel flow at Reτ=5200 to be clarified. A unique aspect of the present framework is the use of an auto-encoder algorithm to separate full-volume extremely large DNS fields into large-scale and small-scale motions. This approach is adopted in preference to the empirical mode decomposition (EMD) previously used by the present authors at the lower Reynolds number, Reτ=1000, because the resource requirements posed by the EMD quickly become untenable due to the extremely large direct numerical simulation (DNS) data set and the large solution box needed to capture the wide spectrum of scales at the present Reynolds number. A second original element is a formalism that derived the modulation, conditional on large-scale fluctuations, from continuous statistical quantities represented as multivariable-joint probability-density functions (\textit{pdfs}), thus obviating the need for any discrete representation or binning beyond that imposed by the discrete DNS solution. A third novel aspect is the use of the length-scale-wise derivative of the second-order structure function to quantify the modulation (increase or decrease) in the length scale, again conditional on the large-scale structures. Apart from illuminating the modulation itself, the study examined the validity of the Quasi-Steady Hypothesis which proposes that the near-wall turbulence is universal when scaled by the spatially and temporally varying large-scale wall shear stress, rather than its time average.

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Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Auto-encoder-assisted analysis of amplitude and wavelength modulation of near-wall turbulence by outer large-scale structures in channel flow at friction Reynolds number of 5200

Agostini

Leschziner

2022

Physics of Fluids

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“…The family of visibility algorithms as graph-theoretic methods for time series were first proposed in [30,31] and since then they have been successfully applied to a range of problems in many scientific disciplines, from purely theoretical analysis [35][36][37], description of nonlinear [38][39][40] and stochastic dynamics [41,42] to applications in physical [43][44][45][46][47], biological [48][49][50] and socio-technical systems [51][52][53][54], even in the arts [55] (see [56,57] for reviews on graph-theoretic methods for signal processing). The methods offer simple and computationally efficient mappings between an ordered sequence -i.e.…”

Section: A Experimental Setup and Data Collectionmentioning

confidence: 99%

Visibility graphs of animal foraging trajectories

Paiva¹,

Alves²,

Lacasa³

et al. 2022

Preprint

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“…The family of visibility algorithms as graph-theoretic methods for time series were first proposed in [30,31] and since then they have been successfully applied to a range of problems in many scientific disciplines, from purely theoretical analysis, description of nonlinear and stochastic dynamics to applications in physical, biological and socio-technical systems [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52], even in the arts [53], (see [54,55] for reviews on graph-theoretic methods for signal processing). The methods offer simple and computationally efficient mappings between an ordered sequence-i.e.…”

Section: The Visibility Algorithm and Associated Network Metricsmentioning

confidence: 99%

Visibility graphs of animal foraging trajectories

et al. 2022

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The study of self-propelled particles is a fast growing research topic where biological inspired movement is increasingly becoming of much interest. A relevant example is the collective motion of social insects, whose variety and complexity oﬀer fertile grounds for theoretical abstractions. It has been demonstrated that the collective motion involved in the searching behaviour of termites is consistent with self-similarity, anomalous diﬀusion and Lévy walks. In this work we use visibility graphs –a method that maps time series into graphs and quantiﬁes the signal complexity via graph topological metrics– in the context of social insects foraging trajectories extracted from experiments. Our analysis indicates that the patterns observed for isolated termites change qualitatively when the termite density is increased, and such change cannot be explained by jamming eﬀects only, pointing to collective eﬀects emerging due to non-trivial foraging interactions between insects as the cause. Moreover, we ﬁnd that such onset of complexity is maximised for intermediate termite densities.

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Large-to-small scale frequency modulation analysis in wall-bounded turbulence via visibility networks

Abstract: Abstract

Cited by 21 publications

References 76 publications

Auto-encoder-assisted analysis of amplitude and wavelength modulation of near-wall turbulence by outer large-scale structures in channel flow at friction Reynolds number of 5200

Auto-encoder-assisted analysis of amplitude and wavelength modulation of near-wall turbulence by outer large-scale structures in channel flow at friction Reynolds number of 5200

Visibility graphs of animal foraging trajectories

Visibility graphs of animal foraging trajectories

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