Current Issue : October - December Volume : 2020 Issue Number : 4 Articles : 5 Articles
In this paper, the Chebyshev spectral method is used to solve the normal mode and parabolic equation models of underwater\nacoustic propagation, and the results of the Chebyshev spectral method and the traditional finite difference method are compared\nfor an ideal fluid waveguide with a constant sound velocity and an ideal fluid waveguide with a deep-sea Munk speed profile. The\nresearch shows that, compared with the finite difference method, the Chebyshev spectral method has the advantages of a high\ncomputational accuracy and short computational time in underwater acoustic propagation....
This paper introduces a new usage of piezoelectric poly (vinylidene fluoride) (PVDF)\nelectrospun nanofiber (NF) membrane as a sensing unit for acoustic signals. In this work, an NF mat\nhas been used as a transducer to convert acoustic signals into electric voltage outcomes. The detected\nvoltage has been analyzed as a function of both frequency and amplitude of the excitation acoustic\nsignal. Additionally, the detected AC signal can be retraced as a function of both frequency and\namplitude with some wave distortion at relatively higher amplitudes and within a certain acoustic\nspectrum region. Meanwhile, the NFs have been characterized through piezoelectric responses,\nbeta sheet calculations and surface morphology. This work is promising as a low-cost and innovative\nsolution to harvest acoustic signals coming from wide resources of sound and noise....
The propagation of surface acoustic waves over a solid plate is highly influenced by the\npresence of liquid media on the surface. At the solidâ??liquid interface, a leaky Rayleigh wave radiates\nenergy into the liquid, causing a signification attenuation of the surface acoustic wave amplitude.\nIn this study, we take advantage of this spurious wave mode to predict the characteristics of the\nmedia, including the volume or height. In this study, the surface acoustic waves were generated on\na thick 1018 steel surface via a 5 MHz transducer coupled through an angle beam wedge. A 3Dprinted\ncontainer was inserted on the propagation path. The pulse-echo time-domain responses of\nthe signal were recorded at five different volumes.....................
Due to the heterogeneity of the internal structure and the different external loading conditions, the mechanical and acoustic emission\n(AE) characteristic parameters of coal and rock are discrete in the process of loading until failure, and many repeated and destructive\ntests need to be completed to obtain the performance parameters. It is of theoretical significance to explore the correlation of various\nparameters and to establish multiparameter regression models of coal rock strength and AE characteristics for predicting the strength\nand acoustic emission characteristic parameters of coal rock and reducing the repeated tests. For the coal sample from a coal seam of\nLongde Coal Mine in China, the mass density of coal samples and the acoustic velocity in the samples before loading are measured at\nfirst, and their respective coefficient of variation is analyzed. Then, the stress-strain curve and the time history curve of AE\ncharacteristic parameters are obtained by the uniaxial compression AE test of each coal sample according to the different loading\nrates. Theinfluence of loading rate, mass density, and acoustic velocity on the mechanical and AE energy parameters of coal sample is\nanalyzed by the section morphology of the coal sample after failure, the three-dimensional location map of AE, and the scanning\nmicrograph of the electron microscope. Based on the least-square method, the multiple regression models of compressive strength,\nelastic modulus, and the maximum AE energy are established by mass density, acoustic velocity, and loading rate of coal samples.The\nresults indicate that, for the coal samples from the same geological source, the obtained regression models can, respectively, predict\nthe uniaxial compressive strength, elastic modulus, and the maximum AE energy according to the predesigned loading rate, the\nacoustic velocity, and mass density of coal samples measured before loading, without too many repeated loading failure tests....
In research into various hydrophysical and hydroacoustic wave processes, it is extremely\nimportant to know the regularities of their propagation in the sea at decreasing depths, especially\nin the shelf areas, and also to know the regularities of their transformation into seismoacoustic\nprocesses in the earth crust. In the course of the processing and analysis of the experimental data of\nour complex experiment, in this paper we investigate these regularities. In our experiment, we used\na low-frequency hydroacoustic transmitter that generated harmonic oscillations at the frequency of\n22 Hz and received hydroacoustic systems with a shore laser strainmeter. It was established that\nhydroacoustic waves, propagating at the shelf of decreasing depth, transform into seismoacoustic\nwaves at the depth of the sea equal to or less than a half-length of the hydroacoustic wave. A\ncomparison of the results of this work with earlier-obtained results allows us to state that such\nregularities should be inherent to all hydrophysical and hydroacoustic processes....
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