Acoustic Field Propagation Research Articles

Time-domain immersed-boundary simulation of acoustic propagation between two spherical gas bubblesa).

Acoustic fields and resonance responses from two spherical gas bubbles are investigated using a time-domain simulation. Interior acoustic fields are obtained simultaneously from the simulation of the entire acoustic field propagation with an immersed-boundary method. The linear resonance responses are obtained and discussed for each of the bubbles with respect to the respective interior gas velocities. Also, these are analyzed in the frequency domain in terms of the coupled interactions. Unlike previous numerical and analytical solutions, the method allows for two bubbles of different sizes and shapes to be in contact with each other, which is representative of applicable underwater scattering targets.

Tow ship interference mitigation in shallow ocean using correlated mode decomposition technique

Passive towed arrays assume great importance in shallow ocean surveillance, owing to their capability to detect long range underwater acoustic targets. The detection and classification performance is severely impacted by the tow ship interference manifestation in the pressure sensor array towed behind the ship. In this work, a robust tow ship multipath interference mitigation algorithm intended for shallow ocean operation is developed, based on the dynamic mode decomposition (DMD) technique, which in turn exploits the coherent structure of the multimode acoustic wave propagation inherent in the shallow ocean scenario. The proposed algorithm effectively identifies the coherent normal mode interference subspace and eliminates its components from the received array data vector. Further, this approach compliments the shallow ocean normal mode acoustic field propagation and ensures simultaneous mitigation of all the multipath generated interferences, making it a superior method to reduce the azimuth spread of the interference and tow ship spectral leakage into the panoramic detection beams. This greatly enhances the detection and classification capability of sonar, especially for distant stealthy targets. The efficacy of the algorithm is validated using Monte Carlo simulations and further ratified by experimental data captured during the field trials in the Arabian Sea.

Analysis of acoustic field characteristics to detect internal pipeline corrosion based on ultrasonic full-focus

Seawater pipelines are an important part of ship structures. After a certain period of service, corrosion becomes a serious problem. Ultrasonic corrosion detection has good applicability in seawater pipeline corrosion detection. Aiming at the focusing problem of ultrasonic arrays in pipeline inspection, the sound pressure characteristics and acoustic field directivity in the propagation process were analyzed. A mathematical model of the acoustic field propagation characteristics was established, and the influence of deflection, focusing of the sound beam, and geometric characteristics of the array element on the characteristics of the ultrasonic acoustic field were analyzed through simulation calculations. An ultrasonic array focusing transducer was used to test the corrosion of a Φ168 pipeline. The results show that the number, size, and focal length of the working array significantly affect the focused acoustic field characteristics of the ultrasonic array. The ultrasonic full-focus method can effectively detect local corrosion of pipelines, and the defect detection accuracy has a nonlinear relationship with the number of working array elements and the focal length of the focus. Within a certain range, with an increase in the number of working elements, the overall tendency of the average error of defect detection gradually decreases. With the increase in focal length, the overall tendency of defect detection error first decreases and then increases, and there is a focal length range with the best detection accuracy. In pipeline inspection, the best working parameters can be selected according to the actual size of the pipeline.

Magnetoacoustic signal analysis of bio-tissue containing liquid metal

As a ‘new organ’ in the human body, an interstitial structure distributes throughout the body and constitutes an operational framework of the interstitial fluid. Research into interstitial structure and its fluid behavior are conducive to revealing the operation law of interstitial fluid and establishing a complete operation system model for life fluid. In this paper, magnetoacoustic tomography with magnetic induction (MAT-MI) with liquid metal as a marker of the interstitial fluid channel is proposed as an imaging research method for the fluid behavior of interstitial structures. For the huge differences in the physical properties between liquid metal and bio-tissue, we studied the distribution characteristics of induction current in liquid metal under pulsed magnetic field stimulation, as well as the acoustic field propagation characteristics and the signal received by the transducer in acoustic inhomogeneous materials. Finally, experimental studies were carried out to verify the theoretical analysis. This work provided a basis for the extraction of effective measurement signals, which is conducive to the identification of acoustic field signals and the position imaging of the liquid metal.

A Numerical Study on the Distribution and Evolution Characteristics of an Acoustic Field in the Time Domain of a Centrifugal Pump Based on Powell Vortex Sound Theory

The acoustic field distribution and evolution characteristics in a time domain inside a centrifugal pump are studied. During the fluid motion process, the acoustic source and acoustic pressure are basically less than 0, and the minimum value of the two parameters is distributed near the tongue. Additionally, the concentration, break, extend, migration and reaggregation phenomena of the minimum acoustic source region exist. Specifically, as the blade passes through the tongue, the minimum acoustic source region concentrates on the tongue firstly, then extends and migrates downstream slightly with the blade motion, and aggregates again around the tongue, which results in the similar evolution characteristics of acoustic pressure. Moreover, the standard deviation (STD) of acoustic source mainly focuses near the pressure side of blade tail and volute tongue, and the maximum STD is located at the tongue. Compared with the source component induced by stretching of the vortex, the source component induced by non-uniformity of fluid kinetic energy is closer to the overall acoustic source. Take the tongue as an example, at various rotational speeds, the STD proportions of the two components are about 5% and 95%, respectively. This study discusses the generation, distribution and evolution characteristics of acoustic field, which lays a foundation to analyze the acoustic field propagation mechanism of centrifugal pumps.

Enseñanza de acústica física con simulaciones en k-wave

Se presenta el uso del toolbox k-wave para apoyar la enseñanza de acústica. Este toolbox permite de modo simple y eficiente la simulación de propagación de ondas en el dominio del tiempo. Es ampliamente utilizado para simular el comportamiento de ondas ultrasónicas en medios biológicos. Mediante el agregado de un limitado número de instrucciones es posible simular la propagación de campos acústicos en dos dimensiones con diversas condiciones de contorno, basadas en una imagen de referencia (archivo BMP) en el cual puntos de diferentes colores representan elementos específicos de la simulación. Esto permite experimentar con diferentes condiciones utilizando el toolbox k-wave con mínimos conocimientos de MATLAB/Octave. Cualquier alteración en la imagen mediante operaciones simples de corte, pegado, desplazamiento o rotación produce nuevas condiciones de simulación.

Apparatus for Physical Modeling of the Electroseismic Effect of the First Kind

The paper describes a modified apparatus for physically modeling the electroseismic effect of the first kind in rocks. The apparatus makes it possible to simulate the effect when a rock sample is exposed to an electric field with and without current in the sample. Two methods can be used for measuring changes in the acoustic field propagation velocity. The first method excites a pulsed acoustic field and measures the time it takes for the field to propagate from the source to the receiver; the second measures the phase modulation of a sinusoidal acoustic field when the sample is exposed to an electric field. The first method has two modifications: in the first, only an electric field without an active current component is generated in a sample; in the second, both an electric field and an active current component are generated. The apparatus includes a signal generator that excites coherent electric and acoustic fields in rock samples. Field coherence makes it possible to apply an interference-immune phase method for measuring the velocity of a sinusoidal acoustic field and to decrease the sensitivity threshold for a change in velocity from 0.2 to 0.02%. The authors present results of modeling the effect using saltwater-saturated limestone and sandstone samples (four each) with a mineralization factor of 1%. When the electric field was switched on, all samples demonstrated an approximately 0.2% decrease in acoustic field velocity. In the 2–200 kHz frequency range, the velocity decrease does not depend on frequency for all limestone and sandstone samples. It is shown that the modified apparatus can reliably detect the electroseismic effect without a current in a sample, despite the fact that its value exceeds the sensitivity threshold by only 20–25 dB. Field coherence makes it possible to measure the relaxation time of the acoustic field velocity after an electric field without a current in a sample is switched on and off. The authors demonstrate that after the electric field is switched on, the relaxation time of the acoustic field velocity does not exceed 2 ms, and after it is switched off, this value is 10–20 ms. The relaxation time difference can be used to assess the nonlinearity of the electroseismic effect of the first kind.

Modeling Breast Ultrasound on the Applicability of Commonly Made Approximations

To design breast ultrasound scanning systems or to test new imaging methods, various computer models are used to simulate the acoustic wave field propagation through a breast. The computer models vary in complexity depending on the applied approximations. The objective of this paper is to investigate how the applied approximations affect the resulting wave field. In particular, we investigate the importance of taking three-dimensional (3-D) spatial variations in the compressibility, volume density of mass, and attenuation into account. In addition, we compare four 3-D solution methods: a full-wave method, a Born approximation method, a parabolic approximation method, and a ray-based method. Results show that, for frequencies below 1 MHz, the amplitude of the fields scattering off the compressibility or density contrasts are at least 24 dB higher than the amplitude of the fields scattering off the attenuation contrasts. The results also show that considering only speed of sound as a contrast is a valid approximation. In addition, it is shown that the pressure field modeled with the full-wave method is more accurate than the fields modeled using the other three methods. Finally, the accuracy of the full-wave method is location independent whereas the accuracy of the other methods strongly depends on the point of observation.

Experimental Model for Data Transmission in the Underwater Environment

Abstract Communications applications in the underwater environment have recently developed a considerable development due to the demand for underwater research with Robot Underwater Vehicle (ROV). The most important aspects addressed by researchers are related to the speed and distance of data transmissions. In most cases, this data signal may be electromagnetic, optical or acoustic. The first two cases have limitations on the distance of the communication channel due to signal attenuation. That is why the acoustic field can be considered the favorite in this choice. In this case, the limitations of use are given by the acoustic field propagation, which depends on the temperature, salinity and pressure of the underwater environment and the result is the variation of the propagation speed. The influence of frequency on attenuation and reverberation are important factors limiting the use of the acoustic field. Based on these considerations, the paper presents an experimental transceiver model of data transmission using Frequency Shift Keying (FSK), modulation with phase discontinuity for transmitting and receiving commands at the speed of 2kbits / s

A fractal approach of the sound absorption behaviour of materials. Theoretical and experimental aspects

In the materials area there are many theoretical and experimental investigations concerning their sound absorption behaviour, covering a wide range of applications. An alternative approach consists in identifying the ensemble acoustic field-propagation environment with a fractal gives its functionality in the form of structure parameters that is dependent on scale resolution. These fractal parameters can be matched with “classical” ones typical for sound absorption experiments in various materials. The mathematical methodology presented here implies the substitution of a dynamics with constraints on continuous but differentiable curves, in an Euclidian space, with “synchronous” dynamics, free from any constraints, on continuous but non-differentiable curves with various fractal dimensions but on a fractal space (i.e. the geodesics of that space). In a very special representation, the external constraints select the fractal geodesics type. In our study this “type selection” refers to the geodesics tunnel effect of fractal (acoustic) type for which we calculate the reflectance and the transparency of an external fractal barrier. An experimental procedure, using a modified impedance tube technique, to determine the sound absorption coefficients for various composite materials was conducted. The procedure uses an anechoic room and the measured sound absorption coefficients also include the sound transmission. The fractal approach of the acoustic behaviour, through the fractal parameters determined (transparency and reflectance) matched the experimental results, in terms of sound absorption, emphasizing the high degree of generality of the fractal theory in the dynamics of physical processes.

Variable-Frequency Ultrasonic Treatment on Microstructure and Mechanical Properties of ZK60 Alloy during Large Diameter Semi-Continuous Casting

Traditional fixed-frequency ultrasonic technology and a variable-frequency ultrasonic technology were applied to refine the as-cast microstructure and improve the mechanical properties of a ZK60 (Mg–Zn–Zr) alloy during large diameter semi-continuous casting. The acoustic field propagation was obtained by numerical simulation. The microstructure of the as-cast samples was characterized by optical and scanning electron microscopy. The variable-frequency ultrasonic technology shows its outstanding ability in grain refinement compared with traditional fixed-ultrasonic technology. The variable-frequency acoustic field promoted the formation of small α-Mg globular grains and changed the distribution and morphology of β-phases throughout the castings. Ultimate tensile strength and elongation are increased to 280 MPa and 8.9%, respectively, which are 19.1% and 45.9% higher than the values obtained from billets without ultrasonic treatment and are 11.6% and 18.7% higher than fixed-frequency ultrasound treated billets. Different refinement efficiencies appear in different districts of billets attributed to the sound attenuation in melt. The variable-frequency acoustic field improves the refinement effect by enhancing cavitation-enhanced heterogeneous nucleation and dendrite fragmentation effects.

Control of cavitation through coalescence of cavitation nuclei

Therapeutic ultrasound in the form of SWL, HIFU, or histotripsy frequently generates cavitation nuclei (bubbles 1–10 um radius), which can persist up to about 1 s before dissolving. These nuclei can attenuate and reflect propagation of acoustic fields reducing SWL efficiency, enhancing HIFU heating, or shifting the location of a histotripsy focal zone making procedures less predictable. Depending on their location, nuclei can also directly cause tissue damage when a high amplitude sound field causes them to undergo inertial cavitation. These undesirable effects can be reduced by using a low amplitude sound field (MI <1) to stimulate coalescence of nuclei through primary and secondary Bjerknes forces. We will show nuclei coalescence significantly reduces sound field attenuation, improves SWL breakup of model kidney stones, and reduces collateral damage in soft tissues. We also show techniques for designing the non-focal acoustic fields for efficient coalescence with 3D printed acoustic lenses. Timothy Hall has a consulting arrangement with Histosonics, Inc., which has licensed intellectual property related to this abstract.

Effects of multiple scattering, attenuation and dispersion in waveguide sensing of fish

An ocean acoustic waveguide remote sensing system can instantaneously image and continuously monitor fish populations distributed over continental shelf-scale regions. Here it is shown theoretically that the areal population density of fish groups can be estimated from their incoherently averaged broadband matched filtered scattered intensities measured using a waveguide remote sensing system with less than 10% error. A numerical Monte-Carlo model is developed to determine the statistical moments of the scattered returns from a fish group. It uses the parabolic equation to simulate acoustic field propagation in a random range-dependent ocean waveguide. The effects of (1) multiple scattering, (2) attenuation due to scattering, and (3) modal dispersion on fish population density imaging are examined. The model is applied to investigate population density imaging of shoaling Atlantic herring during the 2006 Gulf of Maine Experiment. Multiple scattering, attenuation and dispersion are found to be negligible at the imaging frequencies employed and for the herring densities observed. Coherent multiple scattering effects, such as resonance shifts, which can be significant for small highly dense fish groups on the order of the acoustic wavelength, are found to be negligible for the much larger groups typically imaged with a waveguide remote sensing system.

Application of the multicomponent lattice Boltzmann simulation method to oil/water dispersions

We study the propagation of acoustic fields in bounded, two-dimensional, mono-disperse oil/water emulsions using a carefully modified and appropriately calibrated single relaxation time multicomponent lattice Boltzmann equation simulation. Our model is a variant of an algorithm applying both interface forces based on macroscopic surface tensions and a kinematic condition for phase separation, adapted to allow sonic speed variations between its oil and water components. Appropriate second-order accurate acoustic boundary conditions are obtained from a node-based lattice closure with local mass conservation and applicability for varying fluid viscosities. Data from an example simulation of a single oil drop in water interacting with a generated standing acoustic wave are presented and, where appropriate, compared with empirical theories and analogous calculations for a solid object.

Dynamic modeling of the propagation of low-frequency seismic acoustic fields in the oceanic medium

Numerical modeling of the propagation of wave fields in heterogeneous media has developed signifi� cantly in hydroacoustics, seismic prospecting, and other fields. Since modeling of the physical processes is complicated, a number of simplifications are usually introduced. In particular, the energy losses in the medium are neglected and the approximation of liquid bottom is also applied; however, in this case, shear waves and a number of related phenomena disappear. The other usual simplification is the parabolic approx� imation, which applies a stationary harmonic field source, but in this case the dynamics of the wave prop� agation process is lost, and the waves reflected from the inhomogeneities of the medium and other phe� nomena disappear [1, 2]. In this paper, we perform numerical modeling without the simplifications men� tioned above. The problems of propagation of the pulse seismic acoustic fields over the oceanic waveguides water surface–bottom and at the ocean– continent boundary are considered for the first time in the low frequency range from 0.05 to 1 Hz. Long range propagation of storm microseisms and fields of earth� quakes occur in this range [1–5]. A viscoelastic model of the medium and the generalized Hooke law are applied to take damping into account. The differential equations in partial derivatives of the hyperbolic type are used for the mathematical description. The numerical solution of the differential equations in the problem considered here is performed using the grid models that are closest to the physical conditions of the propagation of fields [6].

Effects of multiple scattering, attenuation, and dispersion on fish population density imaging with ocean-acoustic waveguide remote sensing.

Ocean-acoustic waveguide remote sensing (OAWRS) instantaneously images and continuously monitors fish populations distributed over continental-shelf scale regions. It is shown that the areal population density of fish groups can be estimated from their incoherently averaged, broadband matched filtered scattered intensities. A numerical Monte-Carlo model is developed to determine the statistical moments of the scattered returns. It uses the parabolic equation to simulate acoustic field propagation in random range-dependent ocean waveguides. The effects of (1) multiple scattering, (2) attenuation due to scattering, and (3) modal dispersion on fish population density imaging are examined. Results of the model are applied to interpret OAWRS images of shoaling Atlantic herring populations acquired during the 2006 Gulf of Maine experiment. Multiple scattering and attenuation are found to be negligible at OAWRS frequencies employed in the experiment and for the herring densities observed. Coherent multiple scattering effects, such as resonance shifts, are significant for small highly dense fish groups on the order of the wavelength, but negligible for larger groups. Optimal sound speed for charting scattered returns in range within the random waveguide is found to roughly equal the group speed of mode 1.

A sparse‐grid, nonintrusive formulation of acoustic field uncertainty in ocean waveguides.

The inclusion of environmental uncertainty in simulations of acoustic wave propagation in ocean waveguides is important for the development of simulation‐based prediction methods that quantify the influence of multiple sources of incomplete environmental knowledge on the simulation results. Polynomial chaos expansions have been suggested as a natural mathematical framework for describing both environmental and acoustic field uncertainties, their interaction, and propagation through the waveguide [S. Finette, J. Acoust. Soc. Am. 120 (2006)]. Previous research has described the inclusion of these expansions directly into the propagation equation (the intrusive approach), yielding coupled differential equations for the expansion coefficients. The solution for the coefficients contains the statistical properties of the uncertain field. Here we describe an alternative nonintrusive formulation, where existing acoustic propagation codes can be used to estimate the chaos coefficients rather than solve for them via a complex set of coupled differential equations. The nonintrusive formulation involves multiple solutions of an existing deterministic code, e.g., a wide‐angle parabolic equation solver, in conjunction with the Smolyak sparse‐grid interpolation and multidimensional quadrature to obtain uncertainty statistics on the acoustic field. [Research supported by the Office of Naval Research.]

The analysis of diffraction effects of acoustic waves on the crack's top

Diffraction effects and features of acoustic wave propagation in elastic media with microcrack were investigated in detail for pulse probing signals. The crack's plane was oriented across the direction of longitudinal ultrasonic wave incidence so that the detection of such a crack with so "inconvenient" spatial location is difficult enough by using traditional acoustic techniques. By using laser interferometer, the set of instantaneous pictures of acoustic field on the specimen's surface, corresponding to different time moments was obtained what allowed investigating and visualizing of acoustic field propagation and diffraction's effects on the crack's top in dynamics. Using various methods of numerical modeling of diffraction processes of acoustic wave on the crack's edge and top for pulse signals the origin of V‐like structures on the snapshots of acoustic fields was explained and analyzed.

SOLUTION OF PRIDE'S EQUATIONS THROUGH POTENTIALS

In 1994, S. Pride offered a system of equations describing interdependent propagation of acoustic and electromagnetic (EM) fields in porous media saturated by a fluid electrolyte (electrokinetic effect). We proved that the displacement vectors of frame and of pore fluid can be represented as a linear combinations of gradients of two scalar potentials and rotors of two vector potentials provided the coefficients of Pride's equations are independent of spatial coordinates. Each of these potentials satisfies Helmholtz equation with appropriate complex velocity. This representation underlies the computer code created by us for exploring borehole acoustics logging problems in axial-symmetric radially layered medium. Noteworthy, layers can be of any of the following types: uniform porous medium saturated by fluid electrolyte, uniform nonporous elastic medium, compressible nonviscous fluid or compressible viscous fluid. Results of numerical experiments are presented and discussed. The most important of them is that the back influence on acoustic disturbance of EM field excited by this disturbance is negligibly small in usually used frequency band and for realistic formation parameters. The mechanism of generation and propagation of different types of EM waves during acoustic logging is discussed as well.

Uncertainty propagation in ocean acoustic waveguides

This presentation discusses a general method for representing uncertainty in numerical models that describe acoustic field propagation within partially specified ocean waveguide environments. The approach treats uncertainty within a probabilistic framework, representing both the sound speed distribution and acoustic field as stochastic processes. In this talk, environmental uncertainty is linked to incomplete knowledge of the volume sound speed field and is directly incorporated into the mathematical formulation for acoustic propagation in a stochastic ocean waveguide. As an example, equations describing the propagation of uncertainty [Finette, J. Acoust. Soc. Am (in press)] are solved analytically for the special case of a point source in a random, but spatially uniform sound speed field bounded by a pressure release surface and a rigid bottom. Results for the first two moments of the acoustic field are calculated using this approach and compared with an independent estimate of the same moments obtained from Monte Carlo based realizations that are computed from a deterministic parabolic wave equation. [Work supported by ONR.]