scholarly journals Reflection of acoustic waves from the boundary or layer of two-phase medium

2018 ◽  
Vol 148 ◽  
pp. 15005
Author(s):  
D.A. Gubaidullin ◽  
D.D. Gubaidullina ◽  
Yu.V. Fedorov
Keyword(s):  
Reflection Coefficient ◽  
Acoustic Wave ◽  
Acoustic Waves ◽  
Finite Thickness ◽  
Low Frequency ◽  
Bubbly Liquid ◽  
Pure Liquid ◽  
Angle Of Incidence ◽  
Two Phase ◽  
Low Frequencies

The inclined incidence of the acoustic wave on a layer of gas-droplet mixture or bubbly liquid of finite thickness is theoretically investigated. In the case of the incidence of the low-frequency acoustic wave to interface between the pure gas and aerosol or to interface between pure liquid and bubbly liquid the basic laws of reflection and transmission of a wave are established. This circumstance allows us to evaluate the transmission and reflection coefficients, depending on the volume content of inclusions and the angle of incidence of the acoustic wave. In particular, for the interface between pure gas and aerosol analytical expressions of the critical angle of wave incidence at which reflection coefficient becomes zero are obtained, i.e. thus there is a complete passage of the acoustic wave through the interface. It is established that the increase of the angle of incidence of the acoustic wave on the boundary or layer of aerosol causes: first, either to increase or to decrease of the reflection coefficient at low frequencies, and second, to appearance of additional minima depending on the reflection coefficient from frequency of disturbances related to the difference of speed of sound and density of the medium.

scholarly journals Acoustic wave propagation in rivers: an experimental study

2018 ◽  
Author(s):  
Thomas Geay ◽  
Ludovic Michel ◽  
Sébastien Zanker ◽  
James Robert Rigby
Keyword(s):  
Acoustic Wave ◽  
Water Depth ◽  
Acoustic Waves ◽  
Cutoff Frequency ◽  
Low Frequency ◽  
Attenuation Coefficients ◽  
Low Frequencies ◽  
River Bed ◽  
Bed Slope ◽  
Passive Acoustic

Abstract. This research has been conducted to develop the use of Passive Acoustic Monitoring (PAM) in rivers, a surrogate method for bedload monitoring. PAM consists in measuring the underwater noise naturally generated by bedload particles when impacting the river bed. Monitored bedload acoustic signals depend on bedload characteristics (e.g. grain size distribution, fluxes) but are also affected by the environment in which the acoustic waves are propagated. This study focuses on the determination of propagation effects in rivers. An experimental approach has been conducted in several streams to estimate acoustic propagation laws in field conditions. It is found that acoustic waves are differently propagated according to their frequency. As reported in other studies, acoustic waves are affected by the existence of a cutoff frequency in the kHz region. This cutoff frequency is inversely proportional to the water depth: larger water depth enables a better propagation of the acoustic waves at low frequency. Above the cutoff frequency, attenuation coefficients are found to increase linearly with frequency. The power of bedload sounds is more attenuated at higher frequencies than at low frequencies which means that, above the cutoff frequency, sounds of big particles are better propagated than sounds of small particles. Finally, it is observed that attenuation coefficients are variable within 2 orders of magnitude from one river to another. Attenuation coefficients are compared to several characteristics of the river (e.g. bed slope, bed rugosity). It is found that acoustic waves are better propagated in rivers characterised by smaller bed slopes. Bed rugosity and the presence of air bubbles in the water column are suspected to constrain the attenuation of acoustic wave in rivers.

scholarly journals Acoustic wave propagation in rivers: an experimental study

2019 ◽  
Vol 7 (2) ◽  
pp. 537-548 ◽  
Author(s):  
Thomas Geay ◽  
Ludovic Michel ◽  
Sébastien Zanker ◽  
James Robert Rigby
Keyword(s):  
Grain Size ◽  
Acoustic Wave ◽  
Water Depth ◽  
Acoustic Waves ◽  
Cutoff Frequency ◽  
Low Frequency ◽  
Attenuation Coefficients ◽  
Low Frequencies ◽  
River Bed ◽  
Bed Roughness

Abstract. This research has been conducted to develop the use of passive acoustic monitoring (PAM) in rivers, a surrogate method for bedload monitoring. PAM consists in measuring the underwater noise naturally generated by bedload particles when impacting the river bed. Monitored bedload acoustic signals depend on bedload characteristics (e.g., grain size distribution, fluxes) but are also affected by the environment in which the acoustic waves are propagated. This study focuses on the determination of propagation effects in rivers. An experimental approach has been conducted in several streams to estimate acoustic propagation laws in field conditions. It is found that acoustic waves are differently propagated according to their frequency. As reported in other studies, acoustic waves are affected by the existence of a cutoff frequency in the kilohertz region. This cutoff frequency is inversely proportional to the water depth: larger water depth enables a better propagation of the acoustic waves at low frequency. Above the cutoff frequency, attenuation coefficients are found to increase linearly with frequency. The power of bedload sounds is more attenuated at higher frequencies than at low frequencies, which means that, above the cutoff frequency, sounds of big particles are better propagated than sounds of small particles. Finally, it is observed that attenuation coefficients are variable within 2 orders of magnitude from one river to another. Attenuation coefficients are compared to several characteristics of the river (e.g., bed slope, surface grain size). It is found that acoustic waves are better propagated in rivers characterized by smaller bed slopes. Bed roughness and the presence of air bubbles in the water column are suspected to constrain the attenuation of acoustic wave in rivers.

scholarly journals Damping and reflection coefficient measurements for an open pipe at low Mach and low Helmholtz numbers

1993 ◽  
Vol 256 ◽  
pp. 499-534 ◽  
Author(s):  
M. C. A. M. Peters ◽  
A. Hirschberg ◽  
A. J. Reijnen ◽  
A. P. J. Wijnands
Keyword(s):  
Experimental Data ◽  
Reflection Coefficient ◽  
Strouhal Number ◽  
Acoustic Waves ◽  
High Frequency ◽  
Nonlinear Behaviour ◽  
Mean Flow ◽  
Frequency Limit ◽  
Low Frequencies ◽  
Open Pipe

The propagation of plane acoustic waves in smooth pipes and their reflection at open pipe terminations have been studied experimentally. The accuracy of the measurements is determined by comparison of experimental data with results of linear theory for the propagation of acoustic waves in a pipe with a quiescent fluid. The damping and the reflection at an unflanged pipe termination are compared.In the presence of a fully developed turbulent mean flow the measurements of the damping confirm the results of Ronneberger & Ahrens (1977). In the high-frequency limit the quasi-laminar theory of Ronneberger (1975) predicts accurately the convective effects on the damping of acoustic waves. For low frequencies a simple theory combining the rigid-plate model of Ronneberger & Ahrens (1977) with the theoretical approach of Howe (1984) yields a fair prediction of the influence of turbulence on the shear stress. The finite response time of the turbulence near the wall to the acoustic perturbations has to be taken into account in order to explain the experimental data. The model yields a quasi-stationary limit of the damping which does not take into account the fundamental difference between the viscous and thermal dissipation observed for low frequencies.Measurements of the nonlinear behaviour of the reflection properties for unflanged pipe terminations with thin and thick walls in the absence of a mean flow confirm the theory of Disselhorst & van Wijngaarden (1980), for the low-frequency limit. It appears however that a two-dimensional theory such as proposed by Disselhorst & van Wijngaarden (1980) for the high-frequency limit underestimates the acoustical energy absorption by vortex shedding by a factor 2.5.The measured influence of wall thickness on the reflection properties of an open pipe end confirms the linear theory of Ando (1969). In the presence of a mean flow the end correction δ of an unflanged pipe end varies from the value at the high-Strouhal-number limit of δ/a = 0.61, with a the pipe radius, which is close to the value in the absence of a mean flow given by Levine & Schwinger (1948) of δ/a = 0.6133, to a value of δ/a = 0.19 in the low-Strouhal-number limit which is close to the value predicted by Rienstra (1983) of δ/a = 0.26.The pressure reflection coefficient is found to agree with the theoretical predictions by Munt (1977, 1990) and Cargill (1982b) in which a full Kutta condition is included. The accuracy of the theory is fascinating in view of the dramatic simplifications introduced in the theory. For a thick-walled pipe end and a pipe terminated by a horn the end correction behaviour is similar. It is surprising that the nonlinear behaviour at low frequencies and high acoustic amplitudes in the absence of mean flow does not influence the end correction significantly.The aero-acoustic behaviour of the pipe end is dramatially influenced by the presence of a horn. In the presence of a mean flow the horn is a source of sound for a critical range of the Strouhal number.The high accuracy of the experimental data suggests that acoustic measurements can be used for a systematic study of turbulence in unsteady flow and of unsteady flow separation.

scholarly journals Inverse Measurement of the Thickness and Flow Resistivity of Porous Materials via Reflected Low Frequency Waves-Frequency Approach

2021 ◽  
Author(s):  
Mustapha Sadouki
Keyword(s):  
Reflection Coefficient ◽  
Direct Problem ◽  
Fluid Model ◽  
Low Frequency ◽  
Low Frequencies ◽  
Reflected Waves ◽  
Two Samples ◽  
Flow Resistivity ◽  
Theoretical Reflection ◽  
Low Frequency Waves

A direct and inverse method is proposed for measuring the thickness and flow resistivity of a rigid air-saturated porous material using acoustic reflected waves at low frequency. The equivalent fluid model is considered. The interactions between the structure and the fluid are taken by the dynamic tortuosity of the medium introduced by Johnson et al. and the dynamic compressibility of the air introduced by Allard. A simplified expression of the reflection coefficient is obtained at very low frequencies domain (Darcy’s regime). This expression depends only on the thickness and flow resistivity of the porous medium. The simulated reflected signal of the direct problem is obtained by the product of the experimental incident signal and the theoretical reflection coefficient. The inverse problem is solved numerically by minimizing between simulated and experimental reflected signals. The tests are carried out using two samples of polyurethane plastic foam with different thicknesses and resistivity. The inverted values of thickness and flow resistivity are compared with those obtained by conventional methods giving good results.

scholarly journals Interaction acoustic waves with a layered structure containing layer of bubbly liquid

2018 ◽  
Vol 148 ◽  
pp. 15006
Author(s):  
Damir Gubaidullin ◽  
Anatolii Nikiforov
Keyword(s):  
Acoustic Waves ◽  
Theoretical Study ◽  
Bubbly Liquid ◽  
Air Bubbles ◽  
Angle Of Incidence ◽  
Natural Oscillations ◽  
Reflection And Transmission ◽  
Transmission Coefficients ◽  
Gel Layer ◽  
Transmission And Reflection

The results of a theoretical study of the effect of a bubble layer on the propagation of acoustic waves through a thin three-layered barrier at various angles of incidence are presented. The barrier consists of a layer of gel with polydisperse air bubbles bounded by layers of polycarbonate. It is shown that the presence of polydisperse air bubbles in the gel layer significantly changes the transmission and reflection of the acoustic signal when it interacts with such an obstacle for frequencies close to the resonant frequency of natural oscillations of the bubbles. The frequency range is identified where the angle of incidence has little effect on the reflection and transmission coefficients of acoustic waves.

Study of Low-Frequency Narrow Bandwidth Surface Acoustic Wave Sensor for Liquid Applications

2019 ◽  
Author(s):  
Kun-Lin Lee ◽  
Ioana Voiculescu
Keyword(s):  
Acoustic Wave ◽  
Surface Acoustic Wave ◽  
Acoustic Waves ◽  
Delay Line ◽  
Water Drop ◽  
Low Frequency ◽  
Polymer Waveguide ◽  
Saw Devices ◽  
A Cell ◽  
Liquid Sensing

Abstract Surface acoustic wave (SAW) devices have been applied as telecommunication filter for decades. Due to its simple interdigitated transducer (IDT) layout and geometry-dependent frequency, the SAW filter operates at the designed frequency and its working bandwidth could be designed to fulfill specific applications. Researchers also use SAW devices for sensing the mass or pressure in air. Furthermore, SAW device can be employed in liquid environments. The main focus of this paper is to present a Love mode device for liquid sensing. The Love mode device included a shear-horizontal surface acoustic wave (SH-SAW) delay-line configuration with a photoresist waveguide, which was deposited on split-electrode IDT and reflectors. The substrate was ST-cut quartz, and the SH-SAW propagated between the waveguide and the piezoelectric substrate. Using the Love mode device, we monitored the frequency shift corresponding to a water drop. We demonstrate that the insertion loss level is not critical for S-parameter transmission signal readout. The signal quality within the resonant narrowband is very important for water sensing. In this study, two types of SH-SAW devices were fabricated and tested; SH-SAW resonator and SH-SAW delay-line. We also demonstrate single and split electrodes electrode configurations to generate acoustic waves. Four different waveguide thickness values were tested to prove the benefit of thick polymer waveguide. This research also offers a standard method to fabricate SAW on ST-quartz for liquid application. In the future, we plan to integrate the Love mode device with a cell-culturing chamber to obtain a biosensor.

Connection between formation factor for electrical resistivity and fluid‐solid coupling factor in Biot’s equations for acoustic waves in fluid‐filled porous media

Geophysics ◽  
1980 ◽  
Vol 45 (8) ◽  
pp. 1269-1275 ◽  
Author(s):  
Robert J. S. Brown
Keyword(s):  
Porous Media ◽  
Electrical Resistivity ◽  
Acoustic Waves ◽  
Low Frequency ◽  
Fluid Viscosity ◽  
Coupling Coefficients ◽  
Formation Factor ◽  
Low Frequencies ◽  
Viscous Forces ◽  
Inertial Coupling

The coefficient of inertial coupling between fluid and solid for elastic waves in fluid‐filled porous media is shown to be equal to or greater than the porosity times the low‐frequency electrical‐resistivity formation factor, being equal to this product when effects of fluid viscosity are minimal, as they may be for high‐frequency measurements on porous materials of high permeability and porosity. At sufficiently low frequencies, the coupling is due primarily to viscous forces. At intermediate frequencies, viscous forces increase inertial coupling, and inertial forces increase viscous coupling. Thus, porosity and formation factor measurements provide lower limits to coupling coefficients that can be used in the interpretation of acoustic data.

scholarly journals Spectrum of the seismic-electromagnetic and acoustic waves caused by seismic and volcano activity

2005 ◽  
Vol 5 (2) ◽  
pp. 203-209 ◽  
Author(s):  
S. Koshevaya ◽  
N. Makarets ◽  
V. Grimalsky ◽  
A. Kotsarenko ◽  
R. Perez Enríquez
Keyword(s):  
Acoustic Wave ◽  
Acoustic Waves ◽  
Low Frequency ◽  
Electromagnetic Emission ◽  
Plasma Waves ◽  
Nonlinear Propagation ◽  
Moving Crack ◽  
Crack Motion ◽  
Down Conversion ◽  
Acoustic Component

Abstract. Modeling of the spectrum of the seismo-electromagnetic and acoustic waves, caused by seismic and volcanic activity, has been done. This spectrum includes the Electromagnetic Emission (EME, due to fracturing piezoelectrics in rocks) and the Acoustic Emission (AE, caused by the excitation and the nonlinear passage of acoustic waves through the Earth's crust, the atmosphere, and the ionosphere). The investigated mechanism of the EME uses the model of fracturing and the crack motion. For its analysis, we consider a piezoelectric crystal under mechanical stresses, which cause the uniform crack motion, and, consequently, in the vicinity of the moving crack also cause non-stationary polarization currents. A possible spectrum of EME has been estimated. The underground fractures produce Very Low (VLF) and Extremely Low Frequency (ELF) acoustic waves, while the acoustic waves at higher frequencies present high losses and, on the Earth's surface, they are quite small and are not registered. The VLF acoustic wave is subject to nonlinearity under passage through the lithosphere that leads to the generation of higher harmonics and also frequency down-conversion, namely, increasing the ELF acoustic component on the Earth's surface. In turn, a nonlinear propagation of ELF acoustic wave in the atmosphere and the ionosphere leads to emerging the ultra low frequency (ULF) acousto-gravity waves in the ionosphere and possible local excitation of plasma waves.

What controls the initial peak of an air-gun source signature?

Geophysics ◽  
2019 ◽  
Vol 84 (2) ◽  
pp. P27-P45 ◽  
Author(s):  
Leighton M. Watson ◽  
Jonatan Werpers ◽  
Eric M. Dunham
Keyword(s):  
New York ◽  
Rise Time ◽  
Acoustic Waves ◽  
High Frequency ◽  
Low Frequency ◽  
Field Tests ◽  
Operating Pressure ◽  
Low Frequencies ◽  
Air Gun ◽  
Initial Peak

Seismic air guns are broadband sources that generate acoustic waves at many frequencies. The low-frequency waves can be used for imaging, whereas the high-frequency waves are attenuated and/or scattered before they can reflect from targets of interest in the subsurface. It is desirable to reduce the amplitude of the high-frequency acoustic waves because they are thought to be disruptive, and potentially damaging, to marine life and are not useful for geophysical purposes. The high-frequency acoustic waves are primarily associated with the initial expansion of the air-gun bubble and associated peak in the acoustic pressure time series, which is commonly referred to as the source signature of the air gun. We have developed a quasi-1D model of a seismic air gun coupled to a spherical bubble that accounts for gas dynamics and spatially variable depressurization inside the firing chamber to investigate controls on the initial peak of the source signature. The model is validated against data collected during field tests in Lake Seneca, New York. Simulations and field data show that the initial peak is primarily dependent on the operating pressure. A lower gun pressure results in a smaller peak amplitude and a slower rise time. The slope, the amplitude of the initial peak divided by the rise time, is used as a proxy for environmental impact and can decrease by as much as 50% when the air-gun pressure is reduced from 2000 to 1000 psi. The low frequencies are controlled by the total discharged mass, which is dependent upon the gun volume and pressure. Decreasing the operating pressure while simultaneously increasing the gun volume will reduce the high frequencies while maintaining the desirable low-frequency signals.

scholarly journals Vibration of a stiffened pipe filled with a bubbly liquid: analysis of resonance frequencies in function of bubble fraction

2021 ◽  
Vol 263 (5) ◽  
pp. 1008-1018
Author(s):  
Sanae Serbout ◽  
Laurent Maxit ◽  
Frédéric Michel
Keyword(s):  
Cylindrical Shell ◽  
Volume Fraction ◽  
Low Frequency ◽  
Acoustic Properties ◽  
Bubbly Liquid ◽  
Low Frequencies ◽  
Stiffened Cylindrical Shell ◽  
Resonance Frequencies ◽  
Gas Volume Fraction ◽  
Gas Volume

The characterization of the presence of bubbles in industrial fluid circuits may be extremely important for many safety issuses. It is well known that the acoustic properties of liquids can be drastically modified by a small amount of gaz content in the liquid. At sufficiently low frequencies, the speed of sound depends primarily on the gas volume fraction. The variation of the gas fraction may then induce some variations in the vibroacoustic behavior of the pipe transporting the liquid. Analysis of the pipe vibrations can then help in the monitoring of the bubble presence. In such a context, the aim of this study is to show how the the presence of bubbles in the liquid could affect the resonance frequencies of the pipe. A numerical vibroacoustical model has been developed to predict the vibroacoustical behavior of a stiffened cylindrical shell filled with a bubbly liquid exhibiting low frequency resonances. The model, experimentally verified with a well-characterized bubbly liquid, is then used to analyse the frequency shifts of the shell resonances in function of the bubble. Keywords : pipe, heavy fluid, numerical modelling, circumferential admittance approach, cylindrical shell, resonance frequency, void fraction

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