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    Wyświetlanie 1-3 z 3
    Tytuł:
    Acoustical Analysis of Enclosure as Initial Approach to Vehicle Induced Noise Analysis Comparatevely Using STFT and Wavelets
    Autorzy:
    Błażejewski, A.
    Kozioł, P.
    Łuczak, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/176551.pdf
    Data publikacji:
    2014
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    modal analysis
    short-time Fourier transform
    wavelet transform
    acoustic signal processing
    Opis:
    It is assumed in the paper that the signals in the enclosure in a transient period are similar to a noise induced by vehicles, tracks, cars, etc. passing by. The components of such signals usually points out specific dynamic processes running during the observation or measurements. In order to choose the best method of analysis of these phenomena, an acoustic field in a closed space with a sound source inside is created. Acoustic modes of this space influence the sound field. Analytically, the modal analyses describe the above mentioned phenomena. The experimental measurements were conducted in the room that might comprise the closed space with known boundary conditions and the sound source Br¨uel & Kjær Omni-directional type 4292 inside. To record sound signals before the field’s steady state was reached, the microphone type 4349 and the 4-channel frontend 3590 had been used. The obtained signals have been analysed by using two approaches, i.e. Fourier and the wavelet analysis, with the emphasis on their efficiency and the capability to recognise important details of the signal. The results obtained for the enclosure might lead to the formulation of a methodology for an extended investigation of a rail track or vehicles dynamics.
    Źródło:
    Archives of Acoustics; 2014, 39, 3; 385-394
    0137-5075
    Pojawia się w:
    Archives of Acoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Short time vibration analysis and parameterisation as a tool for machine prototypes testing
    Autorzy:
    Barczewski, Roman
    Powiązania:
    https://bibliotekanauki.pl/articles/2146636.pdf
    Data publikacji:
    2020
    Wydawca:
    Politechnika Poznańska. Instytut Mechaniki Stosowanej
    Tematy:
    machine vibration
    non-stationarity identification
    short time signal analysis
    drgania maszyn
    identyfikacja niestacjonarności
    krótkoczasowa analiza sygnału
    Opis:
    The paper outlines the idea of using the short-time vibration signal processing for testing machines of a complex design, particularly the machines consisting of many subassemblies with a non-stationary (e.g. cyclic) operation modes. The method presented consists in graphic representation of vibrations of subassemblies in the form of a trace on a plane. It is created by associating instantaneous rms values of vibration acceleration and instantaneous Rice frequency values obtained as a result of short-time signal processing. On the basis of the shape, orientation of the created trajectory and / or dispersion / concentration of points on the Rf - arms plane, the type of non-stationarity of generated vibrations can be identified. The presented methodology can be used for testing machine prototypes. The results in the proposed form can be helpful to determine the type of vibration reduction systems for individual machine subassemblies. It is also possible to detect subassemblies for which an increase in machine capacity results in an increase in the level of generated vibrations. The location of the averaged values of measures obtained for a new machine on the Rf - arms plane can be a reference point for further monitoring of machine vibration and for detection of damage or malfunction of its subassemblies.
    Źródło:
    Vibrations in Physical Systems; 2020, 31, 1; art. no. 2020112
    0860-6897
    Pojawia się w:
    Vibrations in Physical Systems
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Comparison of multiband filtering, empirical mode decomposition and short-time fourier transform used to extract physiological components from long-term heart rate variability
    Autorzy:
    Adamczyk, Krzysztof
    Polak, Adam G.
    Powiązania:
    https://bibliotekanauki.pl/articles/2052173.pdf
    Data publikacji:
    2021
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    heart rate variability
    nonstationary signal analysis
    multiband filtering
    empirical mode decomposition
    short-time Fourier transform
    Hilbert transform
    Opis:
    Heart rate is constantly changing under the influence of many control signals, as manifested by heart rate variability (HRV). HRV is a nonstationary, irregularly sampled signal, the spectrum of which reveals distinct bands of high, low, very low and ultra-low frequencies (HF, LF, VLF, ULF). VLF and ULF components are the least understood, and their analysis requires HRV records lasting many hours. Moreover, there are still no well-established methods for the reliable extraction of these components. The aim of this work was to select, implement and compare methods which can solve this problem. The performance of multiband filtering (MBF), empirical mode decomposition and the short-time Fourier transform was tested, using synthetic HRV as the ground truth for methods evaluation as well as real data of three patients selected from 25 polysomnographic records with a clear HF component in their spectrograms. The study provided new insights into the components of long-term HRV, including the character of its amplitude and frequency modulation obtained with the Hilbert transform. In addition, the reliability of the extracted HF, LF, VLF and ULF waveforms was demonstrated, and MBF turned out to be the most accurate method, though the signal is strongly nonstationary. The possibility of isolating such waveforms is of great importance both in physiology and pathophysiology, as well as in the automation of medical diagnostics based on HRV.
    Źródło:
    Metrology and Measurement Systems; 2021, 28, 4; 643-660
    0860-8229
    Pojawia się w:
    Metrology and Measurement Systems
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
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