Temat: power spectrum - Katalog OPAC zbiorów

Skocz do pozycji: 1.

Tytuł:: Study on Noise Attenuation Characteristics of Hydrofoil with Specific Cavitation Number
Autorzy:: Xiaohui, He
Zhongle, Liu
Chao, Yang
Zhiyong, Yuan
Powiązania:: https://bibliotekanauki.pl/articles/31339799.pdf
Data publikacji:: 2023
Wydawca:: Polska Akademia Nauk. Czasopisma i Monografie PAN
Tematy:: sound pressure spectrum
noise
sound power spectrum
numerical prediction
Opis:: In this study, the modified Sauer cavitation model and Kirchhoff-Ffowcs Williams and Hawkings (K-FWH) acoustic model were adopted to numerically simulate the unsteady cavitation flow field and the noise of a three-dimensional NACA66 hydrofoil at a constant cavitation number. The aim of the study is to conduct and analyze the noise performance of a hydrofoil and also determine the characteristics of the sound pressure spectrum, sound power spectrum, and noise changes at different monitoring points. The noise change, sound pressure spectrum, and power spectrum characteristics were estimated at different monitoring points, such as the suction side, pressure side, and tail of the hydrofoil. The noise characteristics and change law of the NACA66 hydrofoil under a constant cavitation number are presented. The results show that hydrofoil cavitation takes on a certain degree of pulsation and periodicity. Under the condition of a constant cavitation number, as the attack angle increases, the cavitation area of the hydrofoil becomes longer and thicker, and the initial position of cavitation moves forward. When the inflow velocity increases, the cavitation noise and the cavitation area change more drastically and have a superposition tendency toward the downstream. The novelty is that the study presents important calculations and analyses regarding the noise performance of a hydrofoil, characteristics of the sound pressure spectrum, and sound power spectrum and noise changes at different monitoring points. The article may be useful for specialists in the field of engineering and physics.
Źródło:: Archives of Acoustics; 2023, 48, 3; 359-372
0137-5075
Pojawia się w:: Archives of Acoustics
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Spectral analysis by a video camera in a holographic optical tweezers setup
Autorzy:: Drobczynski, S
Dus-Szachniewicz, K
Symonowicz, K.
Glogocka, D
Powiązania:: https://bibliotekanauki.pl/articles/174701.pdf
Data publikacji:: 2013
Wydawca:: Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:: holographic optical tweezers
power spectrum density
video analysis
Opis:: We discuss the basic parameters of the holographic tweezers equipped with a diode laser and cheap video camera. We compare these parameters with the system using a fast camera and high power Nd:YAG laser. The measured parameters are: the power spectra density calculated from tracing the position of the micron polystyrene beads and the trap stiffness. We show that this cheap optical tweezers system is sufficient for experiments in microbiology.
Źródło:: Optica Applicata; 2013, 43, 4; 739-746
0078-5466
1899-7015
Pojawia się w:: Optica Applicata
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Bandgap properties in locally resonant phononic crystal double panel structures with periodically attached pillars
Autorzy:: Qian, D.
Shi, Z.
Powiązania:: https://bibliotekanauki.pl/articles/280927.pdf
Data publikacji:: 2017
Wydawca:: Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:: bandgap property
phononic crystal double panel
band structure
displacement field
transmission power spectrum
Opis:: The locally resonant (LR) phononic crystal double panel structure made of a two-dimensional periodic array of a two-component cylindrical LR pillar connected between the upper and lower plates is proposed, and the bandgap properties of the structure are investigated theoretically in this paper. The band structures, displacement fields of eigenmodes and transmission power spectrums of the corresponding 8×8 finite structure are calculated by the finite element method. Numerical results and further analysis demonstrate that a band gap with a low starting frequency and a wide band width is opened by the coupling between dominant vibrations of the pillars and plate modes of the upper and lower plates when the vibration source and the receiver are considered on different sides of the structure. By comparing the band structures and displacement fields of the double panel and those of the single plate with the same parameters, many common characteristics are displayed. Then, the influence of geometrical parameters on the band gap are studied and understood with the help of a simple ‘spring-mass’ model.
Źródło:: Journal of Theoretical and Applied Mechanics; 2017, 55, 4; 1167-1179
1429-2955
Pojawia się w:: Journal of Theoretical and Applied Mechanics
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: A Study of the Influence of Muscle Type and Muscle Force Level on Individual Frequency Bands of the EMG Power Spectrum
Autorzy:: Bartuzi, P.
Roman-Liu, D.
Tokarski, T.
Powiązania:: https://bibliotekanauki.pl/articles/90164.pdf
Data publikacji:: 2007
Wydawca:: Centralny Instytut Ochrony Pracy
Tematy:: EMG power spectrum
upper limb
muscle type
extensor digitorum
palmaris longus
biceps brachii
Opis:: The aim of this study was to analyse the electromyographic (EMG) power spectrum indicating differences in the frequency bands of the spectrum resulting from differences in muscle type and force level for the extensor digitorum (ED), palmaris longus (PL) and biceps brachii (BB) muscles. The study was performed on 12 young men as 2 tests different in terms of the type of exerted force (30, 15 and 5% MVC, maximum voluntary contraction). The parameters of the EMG power spectrum were obtained as a result of a division of the EMG power spectrum into ranges determined by border frequencies. The results suggest that (a) frequency bands contained in the 30–80 Hz range and over the frequency of 300 Hz depend on muscle force, and (b) the power spectrum in the frequency range of up to 40 Hz and 60–300 Hz indicates muscle type.
Źródło:: International Journal of Occupational Safety and Ergonomics; 2007, 13, 3; 241-254
1080-3548
Pojawia się w:: International Journal of Occupational Safety and Ergonomics
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: Wpływ gradientu odkształcenia światłowodowej siatki Bragga o stałym okresie na jej charakterystyki spektralne
Influence of the strain gradient of a uniform fiber grating on its spectral characteristics
Autorzy:: Kaczmarek, Z.
Detka, M.
Powiązania:: https://bibliotekanauki.pl/articles/153358.pdf
Data publikacji:: 2010
Wydawca:: Stowarzyszenie Inżynierów i Techników Mechaników Polskich
Tematy:: siatka Bragga
gradient odkształcenia
parametry widma mocy
fiber Bragg grating (FBG)
strain gradient
power spectrum parameters
Opis:: W artykule przedstawiono wyniki badań eksperymentalnych i symulacji wpływu gradientu odkształcenia siatki Bragga o stałym okresie na jej charakterystyki widmowe: pasmo 3 decybelowe i współczynnik odbicia mocy. Zakres zmian gradientu odkształcenia wynosił od 0 do š27 žε/mm. Wyniki pomiarów wskazują na liniową zależność pasma 3 dB siatki od stałego gradientu odkształcenia oraz brak jego wpływu na współczynnik odbicia mocy siatki w badanym zakresie jego zmian. Wyniki tych badań mogą być przydatne przy konstrukcji czujników wielkości mechanicznych z siatkami Bragga, w których elementem sprężystym jest belka zginana oraz w pomiarach odkształceń.
Experimental and simulation results of the influence of the strain gradient of a uniform fiber Bragg grating on its spectral characteristics, the 3-dB bandwidth and reflectivity, are presented in the paper. For experiments a 10 mm long grating embedded in a bended cantilever (Fig. 1) was used. The strain and the strain gradient of the cantilever were caused by a concentrated force acting on the cantilever free end. A change of the kind of strain (stretching or compression) and the strain gradient sign was achieved by reversing the cantilever in the holder. The range of the strain gradient equals 0š27 žε/mm. The measurements were taken in a setup shown in Fig. 2. Using the transfer matrix method derived from the coupled mode theory, the changes of the grating reflected spectrum caused by the strain and the strain gradient in it were simulated [5]. The obtained results of measurements and simulations show that increase in the strain gradient causes increase in the 3-dB bandwidth of the grating reflected beam both for a positive and negative strain gradient (Figs. 3-5). The dependence of the 3-dB bandwidth on the strain gradient is linear and symmetric with respected to the y-axis. The measurement results confirm this feature in the range š 8,5 žε/mm. Outside this range, increase in the 3-dB bandwidth for a negative strain gradient is smaller than for a positive one. For the investigated range of the grating strain gradient, its influence on the grating reflectivity was not observed (Fig. 6).This last feature is important in detection of the grating signals by means of optical wavelength discriminators.
Źródło:: Pomiary Automatyka Kontrola; 2010, R. 56, nr 12, 12; 1439-1441
0032-4140
Pojawia się w:: Pomiary Automatyka Kontrola
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Tytuł:: The Combination of Spectrum Subtraction and Cross-power Spectrum Phase Method for Time Delay Estimation
Autorzy:: Bin, Feng
Lei, Xu
Powiązania:: https://bibliotekanauki.pl/articles/177562.pdf
Data publikacji:: 2020
Wydawca:: Polska Akademia Nauk. Czasopisma i Monografie PAN
Tematy:: sound source localization
time delay estimation
generalized cross correlation
phase of cross power spectrum
spectral subtraction
Opis:: In order to solve the problem of large error of delay estimation in low SNR environment, a new delay estimation method based on cross power spectral frequency domain weighting and spectrum subtraction is proposed. Through theoretical analysis and MATLAB simulation, among the four common weighting functions, it is proved that the cross-power spectral phase weighting method has a good sharpening effect on the peak value of the cross-correlation function, and it is verified that the improved spectral subtraction method generally has a good noise reduction effect under different SNR environments. Finally, the joint simulation results of the whole algorithm show that the combination of spectrum subtraction and cross-power spectrum phase method can effectively sharpen the peak value of cross-correlation function and improve the accuracy of time delay estimation in the low SNR environment. The results of this paper can provide useful help for sound source localization in complex environments.
Źródło:: Archives of Acoustics; 2020, 45, 3; 453-458
0137-5075
Pojawia się w:: Archives of Acoustics
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 7.

Tytuł:: Comparison of the efficiency of time and frequency domain descriptors for the classification of selected wind instruments
Porównanie skuteczności deskryptorów wdziedzinie czasu i częstotliwości do klasyfikacji wybranych instrumentów dętych
Autorzy:: Tyburek, Krzysztof
Namli, Ömer Bora
Powiązania:: https://bibliotekanauki.pl/articles/41205950.pdf
Data publikacji:: 2022
Wydawca:: Uniwersytet Kazimierza Wielkiego w Bydgoszczy
Tematy:: power spectrum
MFCC
timbre
Music Instrument Identification
MPEG-7
aerophones
widmo mocy
barwa
identyfikacja instrumentów muzycznych
aerofony
Opis:: By analyzing the physical features of the time domain and the frequency domainof the audio signal, it is possible to determine its source and use appropriate algorithms to automatically classify of it. The issue of sound indexing deals with the analysis ofdifferent classes and sources -including signals from musical instruments. By calculating the values of descriptors and classifying them, we obtain information about the type of instrument and its structure -most often the material from which it was made. During the conducted research, it turned out that a different composition of the feature vector is implemented to describe brass instruments and a different one for wooden instruments. In this case, the key feature may be harmonic highs in the frequency domain. The conducted experiments concern an attempt to parameterize wind instruments (aerophones) in order to compare the classification effectiveness of time and spectral descriptors. Sounds from a tube, a flute and a soprano saxophone were used for research. The sample population for each instrument was 21.
Analizując fizyczne cechy domeny czasu i domeny częstotliwości sygnału audio można okreslić jego źródło i przy pomocy własciwych algorytmów dokonac jego automatycznej klasyfikacji. Kwestia indeksacji dźwięku dotyczy analizy różnych klas i źródeł –także sygnałów wywodzących się z instrumentów muzycznych. Obliczając wartości deskryptorów i dokonując ich klasyfikacji uzyskujemy informację o typie instrumentu oraz jego budowie -najczęściej materiału, z którego zostal wykonany. Podczas prowadzonych badań okazało się, że różna kompozycja wektora cech jest implementowana do opisu instrumentów blaszanych oraz inna dla instrumentów drewnianych. W tym przypadku cechą kluczową mogą być składowe wyże harmoniczne w postaci częstotliwościowej dźwieku. Przeprowadzone eksperymenty dotyczą próby parametryzacji instrumentów dętych (aerofonów) w celu porównania skuteczności klasyfikacyjnej deskryptorów czasowych i widmowych. Do badań przeznaczono dźwieki pochodzace z tuby, fletu oraz saksofonu sopranowego. Populacja próbek dla każdego instrumentu wynosiła 21.
Źródło:: Studia i Materiały Informatyki Stosowanej; 2022, 14, 3; 13-19
1689-6300
Pojawia się w:: Studia i Materiały Informatyki Stosowanej
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 8.

Tytuł:: Wave Propagation in a LRPC Composite Double Panel Structure with Periodically Attached Pillars and Etched Holes
Autorzy:: Qian, D.
Powiązania:: https://bibliotekanauki.pl/articles/176620.pdf
Data publikacji:: 2018
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:: locally resonant phononic crystal
composite double panel structure
band structure
displacement field
transmission power spectrum
“base-spring-mass” simplified model
Opis:: The locally resonant phononic crystal (LRPC) composite double panel structure (DPS) made of a twodimensional periodic array of a two-component cylindrical LR pillar connected between the upper and lower composite plates is proposed. The plates are composed of two kinds of materials and periodically etched holes. In order to reveal the bandgap properties of structure theoretically, the band structures, displacement fields of eigenmodes and transmission power spectrums of corresponding 8 × 8 finite structure are calculated and displayed by using finite element method (FEM). Numerical results and further analysis demonstrate that if the excitation and response points are picked on different sides of the structure, a wide band gap with low starting frequency is opened, which can be treated as the coupling between dominant vibrations of pillars and plate modes. In addition, the influences of filled-in rubber, etched hole and viscidity of soft material on band gap are studied and understood with the help of “base-spring-mass” simplified model.
Źródło:: Archives of Acoustics; 2018, 43, 4; 717-725
0137-5075
Pojawia się w:: Archives of Acoustics
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 9.

Tytuł:: The Influence Of Propagation Environment On The Accuracy Of Emission Source Bearing
Autorzy:: Ziółkowski, C.
Kelner, J. M.
Powiązania:: https://bibliotekanauki.pl/articles/220529.pdf
Data publikacji:: 2015
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:: DF
methodology of bearing measurement
bearing accuracy
measurements in multipath environment
power azimuth spectrum
Opis:: This paper focuses on the radio direction finding (DF) in multipath environments. Based on the measurement results presented in the open literature, the authors analyse the influence of environment transmission properties on the spread of the signal reception angle. Parameters that define these properties are rms delay and angle spreads. For these parameters, the mutual relationship is determined. This relationship is the basis for assessment of the required number of bearings that minimize the influence of the environment on the accuracy of DF procedure. In the presented analysis, the statistical properties of the signal reception angle are approximated by the normal distribution. The number of bearings versus the rms delay spread is presented as the main objective of this paper. In addition, a methodology of the bearings’ spatial averaging that provides better estimation of the reception angle is shown.
Źródło:: Metrology and Measurement Systems; 2015, 22, 4; 591-600
0860-8229
Pojawia się w:: Metrology and Measurement Systems
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 10.

Tytuł:: Power spectrum analysis for determination of the number of Vertical Axis Wind Turbine blades
Autorzy:: Anweiler, S.
Fedak, W.
Gancarski, W.
Ulbrich, R.
Powiązania:: https://bibliotekanauki.pl/articles/95342.pdf
Data publikacji:: 2017
Wydawca:: Politechnika Koszalińska. Wydawnictwo Uczelniane
Tematy:: renewable energy sources
wind turbine
VAWT
power spectrum
hydrodynamic force
odnawialne źródła energii
turbina wiatrowa
turbiny wiatrowe o osi pionowej
widmo mocy
Opis:: Technology of wind exploitation has been applied widely all over the world and has already reached the level in which manufacturers want to maximize the yield with the minimum investment outlays. The main objective of this paper is the determination of the optimal number of blades in the Cup-Bladed Vertical Axis Wind Turbine. Optimizing the size of the Vertical Axis Wind Turbine allow the reduction of costs and increase the output. The target is the maximum power of the rotor. The optimum number of Vertical Axis Wind Turbine blades evaluation is based on analysis of a single blade simulation and its superposition for the whole rotor. The simulation of working blade was done in MatLab environment. Power spectrum graphs were prepared and compared throughout superposition of individual blades in the Vertical Axis Wind Turbine rotor. Some wind tunnel measurements of the hydrodynamic force according to pitch angle of the blade are also shown. The major result of this research is the Vertical Axis Wind Turbine kmax ratiopower characteristic. On the basis of the analysis of the power spectra, optimum number of the blades was specified for the analysed rotor. Power spectrum analysis of wind turbine enabled the specification of the optimal number of blades, and can be used regarding investment outlays and power output of the Vertical Axis Wind Turbine.
Źródło:: Journal of Mechanical and Energy Engineering; 2017, 1, 2; 153-161
2544-0780
2544-1671
Pojawia się w:: Journal of Mechanical and Energy Engineering
Dostawca treści:: Biblioteka Nauki

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