Application of continuous wavelet transform to the study of large-scale coherent structures

Kanani, Arash; Silva, Ana Maria Ferreira da

doi:10.1007/s10652-015-9428-x

Cited by 10 publications

(9 citation statements)

References 48 publications

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“…A turbulent event may be defined as a series of turbulent fluctuations that contain more energy than the average turbulent fluctuations within a studied data section (KLINE et al 1967, RAO et al 1971, WALLACE 2013. Turbulent event analyses were successfully applied to laboratory open channel flows NEZU 1981, KANANI andDA SILVA 2015), water tunnel investigations (JOHANSSON and ALFREDSSON 1982), wind tunnel studies (OSTERLUND et al 2003), atmospheric boundary layer flows (FINNIGAN 2000, NARASIMHA et al 2007), estuarine flows (TREVETHAN and CHANSON 2010), as well as direct numerical simulation (DNS) investigations of boundary layers (LOZANO-DURAN et al 2012). Such turbulent event analyses were developed for steady flows and were never applied to unsteady rapidly-varied open channel flows like tidal bores ( Fig.…”

Section: Introductionmentioning

confidence: 99%

Turbulence and turbulent flux events in tidal bores: case study of the undular tidal bore of the Garonne River

2017

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The tidal bore of the Garonne River (France) was investigated on 29 August, 31 August and 27 October 2015, during which instantaneous velocity measurements were performed continuously at highfrequency (200 Hz). The tidal bore occurrence had a marked effect on the flow field and turbulent Reynolds stress data, indicating large shear stresses, together with large and rapid fluctuations, during the bore passage and the early flood tide. Like many natural process flows, the tidal bore flow motion was dominated by coherent structure activities and turbulent events, with significant impact on the natural systems including in terms of sediment processes. Herein a new turbulent event analysis was developed for the highly-unsteady rapidly-varied tidal bore flow. The analysis was based upon basic concepts, in which turbulent bursting events were defined in terms of the instantaneous relative turbulent flux, and the method was extended to the rapidly-varied, highly-unsteady tidal bore motion. The turbulent event data showed relatively close results for most fluxes during the tidal bores. The event duration showed some tidal trend, with longer turbulent events immediately after the tidal bore passage, occurring simultaneously with major sediment erosion processes. The field data set and analyses suggested that a turbulent event analysis may be applicable to highly-unsteady rapidly-varied flows, providing quantitative details into the turbulent bursts that are responsible for major mixing and sedimentary processes.

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Section: Introductionmentioning

confidence: 99%

Turbulence and turbulent flux events in tidal bores: case study of the undular tidal bore of the Garonne River

2017

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“…To analyze coherent structure, the CWT power spectrum of a signal is necessary. It can be defined as follows [ 14 , 18 , 29 ]:

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Section: Processing Of Datamentioning

confidence: 99%

“…The exact frequency responsible for the chaotic behavior could be further determined. In addition, the Morlet wavelet is widely used to analyze turbulent or velocity signals [ 14 , 18 , 19 ], which indicates that the Morlet wavelet could be one of the options for the CWT in our study.…”

Section: Introductionmentioning

confidence: 99%

“…The method was successfully utilized in the detection of secondary flow structures in three clinically-relevant blood flow scenarios. CWT was used to detect and establish the length and time scales of the largest horizontal coherent structures existing in a shallow open channel flow by Kanani et al [ 14 ]. They found CWT was particularly well suited to determine the average time and length scales of the structures.…”

Section: Introductionmentioning

confidence: 99%

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Coherent Structure of Flow Based on Denoised Signals in T-junction Ducts with Vertical Blades

Wang

Mei

2019

Entropy

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The skin friction consumes some of the energy when a train is running, and the coherent structure plays an important role in the skin friction. In this paper, we focus on the coherent structure generated near the vent of a train. The intention is to investigate the effect of the vent on the generation of coherent structures. The ventilation system of a high-speed train is reasonably simplified as a T-junction duct with vertical blades. The velocity signal of the cross duct was measured in three different sections (upstream, mid-center and downstream), and then the coherent structure of the denoised signals was analyzed by continuous wavelet transform (CWT). The analysis indicates that the coherent structure frequencies become abundant and the energy peak decreases with the increase of the velocity ratio. As a result, we conclude that a higher velocity ratio is preferable to reduce the skin friction of the train. Besides, with the increase of velocity ratio, the dimensionless frequency St of the high-energy coherent structure does not change obviously and St = 3.09 × 10−4–4.51 × 10−4.

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“…Scanlon and Albertson (2001) applied wavelet transform to describe turbulent transport of carbon dioxide and water vapour within vegetation canopies. More recently, Kanani and da Silva (2015) considered the application of wavelets in the visualisation of coherent structures. The above studies are obviously not exhaustive and more examples will be presented later, while introducing the key components of continuous wavelet transform (CWT) method.…”

Section: Introductionmentioning

confidence: 99%

Wavelet Characteristics of Hydrological and Dissolved Oxygen Time Series in a Lowland River

2016

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A b s t r a c tIn this study, we investigated the temporal variability of dissolved oxygen and water temperature in conjunction with water level fluctuations and river discharge in the Narew lowland river reach. For this purpose, high resolution hydrologic and water quality time series have been used. Spectral analyses of time series using continuous wavelet transform scheme have been applied in order to identify characteristic scales, its duration, and localisation in time. The results of wavelet analysis have shown a great number of periodicities in time series at the inter-annual time scale when compared to the classical Fourier analysis. Additionally, wavelet coherence revealed the complex nature of the relationship between dissolved oxygen and hydrological variables dependent on the scale and localisation in time. Hence, the results presented in this paper may provide an alternative representation to a frequency analysis of time series.

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Application of continuous wavelet transform to the study of large-scale coherent structures

Cited by 10 publications

References 48 publications

Turbulence and turbulent flux events in tidal bores: case study of the undular tidal bore of the Garonne River

Turbulence and turbulent flux events in tidal bores: case study of the undular tidal bore of the Garonne River

Coherent Structure of Flow Based on Denoised Signals in T-junction Ducts with Vertical Blades

Wavelet Characteristics of Hydrological and Dissolved Oxygen Time Series in a Lowland River

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