Application of the time-frequency technique for analysis of velocity fluctuations in the wake of a teardrop profile in the presence of a localized flow inhomogeneity

Abstract Experimental simulation of the inhomogeneity of the incident flow localized in time and space on a bluff tear-drop airfoil is carried out. It is shown that in the region outside the aerodynamic wake of the tear-drop airfoil, the presence of inhomogeneity leads to an increase in the amplitudes of velocity fluctuations in a wide frequency range. In the region inside the wake, the presence of inhomogeneity leads to the suppression of velocity fluctuations at the frequency of vortex shedding by a factor of 2–3 in amplitude. The intensification of fluctuations at frequencies above the main one was also noted, and there was no effect on fluctuations at lower frequencies.

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Simulation of Real-Time Frequency Estimators for Pulsed Doppler Systems

Ultrasonic Imaging ◽

10.1177/016173468600800403 ◽

1986 ◽

Vol 8 (4) ◽

pp. 252-271 ◽

Cited By ~ 37

Author(s):

G.H. van Leeuwen ◽

A.P.G. Hoeks ◽

R.S. Reneman

Keyword(s):

Real Time ◽

Instantaneous Frequency ◽

Wide Frequency Range ◽

Frequency Range ◽

Zero Crossings ◽

Time Frequency ◽

Doppler Signals ◽

Extended Frequency Range ◽

Extended Frequency ◽

Frequency Detector

Four time-domain oriented, real-time frequency estimators, based on the detection of phase, zero-crossings, instantaneous frequency or autocorrelation, were simulated on a digital computer and subjected to computer generated Doppler signals, enabling the investigation of the influence of spectral shape, filtering, frequency shift, noise and quantization. Three estimators, the autocorrelator as well as the instantaneous frequency detector and the autocorrelator, both with extended frequency range, appeared to be very accurate. They exhibit a bias in the estimator output of less than 2 percent over a wide frequency range, the former up to nearly the Nyquist frequency, the latter two beyond, even for skew spectra and under poor signal conditions regarding bandwidth and noise.

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Comparison of near infrared spectroscopy (NIRS) and near-infrared transillumination-backscattering sounding (NIR-T/BSS) methods

Scientific Reports ◽

10.1038/s41598-020-75037-1 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Agnieszka Gruszecka ◽

Marcin Gruszecki ◽

J. Patrick Neary ◽

Jyotpal Singh ◽

Taylor Teckchandani ◽

...

Keyword(s):

Blood Pressure ◽

Healthy Volunteers ◽

Near Infrared ◽

Diagnostic Procedures ◽

Wide Frequency Range ◽

Frequency Range ◽

Time Frequency ◽

Amplitude Spectra ◽

Patient Prognosis ◽

Space Width

Abstract The aim of the study was to compare simultaneously recorded a NIR-T/BSS and NIRS signals from healthy volunteers. NIR-T/BSS is a device which give an ability to non-invasively detect and monitor changes in the subarachnoid space width (SAS). Experiments were performed on a group of 30 healthy volunteers (28 males and 2 females, age 30.8 ± 13.4 years, BMI = 24.5 ± 2.3 kg/m2). We analysed recorded signals using analysis methods based on wavelet transform (WT) for the wide frequency range from 0.0095 to 2 Hz. Despite the fact that both devices use a similar radiation source both signals are distinct from each other. We found statistically significant differences for WT amplitude spectra between both signals. Additionally, we showed different relationships of both signals to blood pressure. Collectively, based on the present findings and those of previous studies, we can conclude that the combination of NIR-T/BSS or NIRS signals and time–frequency analysis opens new frontiers in science, and give possibility to understand and diagnosis of various neurodegenerative and ageing related diseases to improve diagnostic procedures and patient prognosis.

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