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Journal of the Acoustical Society of America

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Jun 1991

Volume 89, Issue 6, pp. 2495-3034

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Aeroacoustics of large wind turbines

Harvey H. Hubbard and Kevin P. Shepherd

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2495-2508 (1991); (14 pages) | Cited 4 times

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This paper reviews published information on aerodynamically generated noise from large horizontal axis wind turbines operated for electric power generation. Methods are presented for predicting both the discrete frequency rotational noise components and the broadband noise components, and results are compared with measurements. Refraction effects that result in the formation of high-frequency shadow zones in the upwind direction and channeling effects for the low frequencies in the downwind direction are illustrated. Special topics such as distributed source effects in prediction and the role of building dynamics in perception are also included. © 1991 Acoustical Society of America.
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43.10.Ln Surveys and tutorial papers relating to acoustics research; tutorial papers on applied acoustics
43.28.Hr Outdoor sound sources
43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.50.Nm Aerodynamic and jet noise

Power flow for sound incident on a solid aluminum sphere in water

Robert Hickling, R. Kirk Burrows, James F. Ball, and Mirjana Petrovic

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2509-2518 (1991); (10 pages)

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Power flow is computed for sound incident on a solid aluminum sphere in water. First, power flow together with kinetic and potential energy distributions are investigated for the standing modes of free vibration of the sphere. The instantaneous power flow excited in the sphere by a continuous train of plane waves is examined next. Finally, time-averaged power flow is investigated. Little has been done so far to compute sound-power flow in structures immersed in a fluid. Computations of this kind provide a new insight into the relation between the elastic waves in the structure and the sound radiated into the fluid. © 1991 Acoustical Society of America.
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43.20.Bi Mathematical theory of wave propagation
43.20.Fn Scattering of acoustic waves
43.20.Ks Standing waves, resonance, normal modes
43.40.At Experimental and theoretical studies of vibrating systems

Characterizing pulses reflected from rough surfaces using ultrasound

Ömür Bozma and Roman Kuc

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2519-2531 (1991); (13 pages) | Cited 2 times

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A model for the scattering of wideband signals from three-dimensional rough surfaces is presented. This development is an extension of the scattering based on the Kirchhoff approximation method for a monochromatic wave source. The usual plane-wave approximation is relaxed and the Kirchhoff method is extended to include spherically diverging waves from the scattering surface. The scattered signal is expressed in terms of the Fourier transform of the acoustic channel. The frequency correlation function of the channel is then derived for a rough surface having the Gaussian spectrum. The coherent and incoherent components of the scattered signal intensity are determined from the frequency correlation function. The theory is applied to the signals produced by the Polaroid transducer operating in air and mounted on a mobile vehicle capable of automatic translation and rotation. Theoretical results are compared with experimental observations from two different rough surfaces. The analytic results are verified over the observable range of incidence angles from 0° to 60°. © 1991 Acoustical Society of America.
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43.20.Fn Scattering of acoustic waves
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Hw Rough interface scattering

Wave-vector-time domain and Kirchhoff integral equation methods to determine the transient acoustic radiation loading on circular cylinders

D. D. Ebenezer and Peter R. Stepanishen

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2532-2544 (1991); (13 pages) | Cited 1 time

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Two new methods are presented to determine the transient acoustic radiation loading on circular cylinders. The acoustic modal forces are expressed as a sum of the convolution of the modal radiation impulse responses and the modal velocities. In the wave-vector-time domain method, the modal radiation impulse responses are obtained by using the radiation impulse responses of an infinite cylinder and the modes in wave-vector space. The approach can thus be easily used for parametric studies on the effects of boundary conditions and normalized lengths on the modal radiation impulse responses. In the Kirchhoff integral equation method, space and time are discretized. The pressure and acceleration in each element are then expressed in the form of a Taylor-series expansion about points at which the pressure is obtained by marching forward in time. The radiation impulse responses of both infinite and simply supported finite cylinders are obtained by the two methods and compared. © 1991 Acoustical Society of America.
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43.20.Fn Scattering of acoustic waves
43.20.Px Transient radiation and scattering
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods

Ray synthesis of the form function for backscattering from an elastic spherical shell: Leaky Lamb waves and longitudinal resonances

Steven G. Kargl and Philip L. Marston

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2545-2558 (1991); (14 pages) | Cited 4 times

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An acoustic ray analysis is employed in synthesizing the form function for backscattering, f(θ = π,ka), from a fluid-loaded evacuated elastic spherical shell where k is the wave number of the incident plane wave and a is the outer radius of the shell. The synthesis contains a component associated with a specular reflection, fsp, and contributions from leaky Lamb waves. The contribution fl of the lth leaky Lamb wave is expressible in a Fabry–Pérot resonator form [P. L. Marston, J. Acoust. Soc. Am. 83, 25–37 (1988)]. A comparison of the ray synthesis for f(ka) with the exact partial-wave series representation for a 440c stainless-steel shell verifies the usefulness of the ray synthesis for the present case of a shell. The present synthesis is also new in that it includes the effects of longitudinal resonances on fsp. A novel ray synthesis of fsp indicates a significant resonance effect near the condition kLh = nπ (n=1,2,…). The thickness of the shell is h, and kL = ω/cL is the longitudinal wave number where cL is the longitudinal speed of sound in the elastic material. The ray synthesis demonstrates that the curvature of the shell is essential to the modeling of longitudinal resonances. Although acoustic ray modeling is generally a high-frequency technique, the ray synthesis of f(ka) for a 440c stainless-steel shell appears to be applicable for ka as small as 7. Certain anomalies in the synthesis are investigated to better understand the limitations of the present ray model. © 1991 Acoustical Society of America.
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43.20.Fn Scattering of acoustic waves
43.30.Cq Ray propagation of sound in water
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions

Acoustic scattering from submerged cylinders. MIIR Im/Re: Experimental and theoretical study

Gérard Maze

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2559-2566 (1991); (8 pages) | Cited 9 times

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To recognize a target submerged in water, a spectroscopy based on the backscattering spectrum or on the resonance spectrum can be used. These spectra are experimentally obtained from the quasiharmonic or short pulse method of isolation and identification of resonances (MIIR). They show sharp amplitude variations that are related to the scatterer’s resonances. These resonances are related to the surface waves that propagate around the target. The backscattering spectrum and the resonance spectrum are power spectra. They are obtained from the computation of the modulus of the Fourier transform of the signal scattered by the target. In this paper, the computation of the phase tangent of the Fourier transform is presented. The spectra obtained are called the Im/Re spectra. The experimental results are compared with the computation of the ratio of the imaginary part over the real part of the complex pressure observed at a large distance from the target center. It is shown that the Im/Re spectra are highly useful for distinguishing resonances in scatterers with large absorptivity, where conventional backscattering or resonance spectra prove insensitive. © 1991 Acoustical Society of America.
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43.20.Fn Scattering of acoustic waves
43.30.Ft Volume scattering
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries

Reconstructing stratified fluid flow from reciprocal scattering measurements

Stephen J. Norton

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2567-2572 (1991); (6 pages) | Cited 2 times

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This paper shows how an inversion formula can be derived for reconstructing the magnitude and direction of stratified fluid flow from two scattering measurements. The measurements are recorded by transmitting an acoustic pulse from a source below the region of stratified flow and then recording the scattered wave at another point horizontally displaced from the source. A second measurement is performed with the source and receiver interchanged and the result is subtracted from the first scattering measurement. This difference is, within the Born approximation, independent of scattering that arises from stationary inhomogeneities and thus solely sensitive to scattering due to flow. As a by-product, the sum of the two scattering measurements with source and receiver interchanged yields a quantity sensitive only to scattering from stationary inhomogeneities. This allows the stationary inhomogeneities to be recovered independently of flow. © 1991 Acoustical Society of America.
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43.20.Fn Scattering of acoustic waves
43.28.Py Interaction of fluid motion and sound, Doppler effect, and sound in flow ducts
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography

Characterization of fiber-matrix interface by guided waves: Axisymmetric case

P.-C. Xu and S. K. Datta

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2573-2583 (1991); (11 pages) | Cited 1 time

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A hybrid method combining the finite-element and eigenfunction expansions is proposed to study the guided waves in composite cylinders. This method is shown to be flexible in modeling generally anisotropic cylinders and computationally efficient. However, most of the analysis is confined to the case of a transversely isotropic cylindrical core surrounded by coaxial isotropic cylinders. The object is to model uniaxial fiber-reinforced materials with interface zones between the fiber (which is anisotropic) and the matrix (which is isotropic). Numerical results are presented for the axisymmetric case for a graphite fiber in magnesium and epoxy matrices. In particular, the measurable and analyzable effects of imperfect bonding are investigated. The reduction of bond stiffness is found to have significant effect on the leaky waves. © 1991 Acoustical Society of America.
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43.20.Fn Scattering of acoustic waves
43.20.Mv Waveguides, wave propagation in tubes and ducts

Propagation of Love waves in an initially stressed medium consisting of a slow elastic layer lying over a liquid-saturated porous solid half-space

M. D. Sharma and M. L. Gogna

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2584-2588 (1991); (5 pages) | Cited 2 times

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The dispersion equation, for Love wave propagation in a slow elastic layer overlying a liquid saturated porous solid half-space, is derived. Both the media are assumed to be under initial stress. The effect of porosity and initial stress on the phase velocity of Love waves has been discussed. Dispersion curves for the phase velocity have been plotted, both with the presence and absence of prestress, for different values of the sandiness parameter. Some special cases have also been deduced. © 1991 Acoustical Society of America.
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43.20.Hq Velocity and attenuation of acoustic waves
43.20.Bi Mathematical theory of wave propagation
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.40.Ph Seismology and geophysical prospecting; seismographs

Generation of fluctuating normal stress in a viscoelastic layer by surface shear stress and pressure as in turbulent boundary-layer flow

David M. Chase

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2589-2596 (1991); (8 pages)

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At low wave numbers, according to recent indications, fluctuating wall shear stress generated by a turbulent boundary layer may be comparable with fluctuating wall pressure. Consideration is given here to the fluctuating normal stress generated within an elastic layer by both shear-stress and pressure excitation on its outer face. The transfer level from surface shear to normal stress is shown to be comparable with or exceed that from surface pressure in a significant range of low to intermediate wave numbers. This transfer from surface shear stress is enhanced by the outer fluid loading and by the imposition of vanishing displacement at an inner rigid surface. Results of computations are presented and analyzed in numerical examples based on a configuration where an elastomer layer is bounded by a fluid half-space at its excited surface and by a thin, damped plate at its inner surface, with a similar fluid half-space below the plate. Results are given also for the limiting cases of a rigid inner surface and of an elastic half-space with and without fluid loading. The transfer level from shear stress is computed also where a concomitant wall pressure is present and related to shear stress as recently determined from a theoretical treatment of the viscous boundary condition at low wave numbers in turbulent boundary-layer flow. It is thus suggested that the contribution of turbulent wall-shear stress to flow noise on recessed hydrophones in the absence of a plate-like element between these and the flow is likely an important one. © 1991 Acoustical Society of America.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.30.Lz Underwater applications of nonlinear acoustics; explosions
43.35.Mr Acoustics of viscoelastic materials

Effects of anisotropy upon the normal modes in a borehole

K. J. Ellefsen, C. H. Cheng, and M. N. Toksöz

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2597-2616 (1991); (20 pages) | Cited 7 times

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Elastic anisotropy affects the modes generated during acoustic logging. To study these effects, the wave equation was solved using a variational method for a model consisting of a fluid-filled borehole through a solid whose anisotropy is defined in the Cartesian coordinate system. The solution for each normal mode includes its phase velocity, group velocity, pressures in the fluid, and displacements in the solid. The most significant findings are: (1) two quasiflexural waves exist and have different phase and group velocities; (2) for the slow quasiflexural wave, the particle displacements in the plane perpendicular to the borehole, when viewed together, are aligned with the polarization of the slow, planar qS wave whose wave-number vector is parallel to the borehole; and (3) for the fast quasiflexural wave, the particle displacements in the plane perpendicular to the borehole, when viewed together, are aligned with the polarization of the fast, planar qS wave whose wave-number vector is parallel to the borehole. © 1991 Acoustical Society of America.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Ks Standing waves, resonance, normal modes

Measurement and calculation of acoustic propagation constants in arrays of small air-filled rectangular tubes

Heui-Seol Roh, W. Patrick Arnott, James M. Sabatier, and Richard Raspet

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2617-2624 (1991); (8 pages) | Cited 11 times

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An experimental and theoretical investigation of sound propagation in a porous sample composed of capillary tubes with rectangular cross sections is described in this paper. An experimental technique valid for low flow resistivity and high porosity porous samples was developed to measure the attenuation and phase velocity in the porous material. This technique uses transmission of a short pulse in a large tube through the porous sample and subsequent frequency domain analysis in the range 200–1300 Hz. Good agreement was obtained if an anomalous tortuosity factor of 1.1 is used in the theory. A scaling factor for relating cylindrical and square tube capillary theories, known as the dynamic shape factor, was investigated. Propagation constants computed from use of a near unity dynamic shape factor in the cylindrical pore theory agree favorably with calculations based on the square pore theory for the frequencies and pore radii used in the experiment. © 1991 Acoustical Society of America.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.50.Vt Topographical and meteorological factors in noise propagation

Numerical errors associated with the method of superposition for computing acoustic fields

Limin Song, Gary H. Koopmann, and John B. Fahnline

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2625-2633 (1991); (9 pages) | Cited 13 times

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The method of “wave superposition” is based on the idea that an acoustic radiator can be approximately represented by the sum of the fields due to a finite number of interior point sources. The accuracy of this representation depends upon how well the velocity boundary condition on the surface of the body is approximated. The ultimate objective of this study, then, is to provide some guidelines for improving the accuracy of the surface velocity reconstruction and, consequently, the accuracy of the superposition solutions. In general, this is dependent upon the particular surface velocity distribution to be reconstructed, as well as other formulation factors such as the acoustic wave number, the number and locations of the surface nodes, and the number and locations of the point sources. Velocity interpolation functions are introduced as a means of quantifying the dependence of reconstruction errors on the acoustic wave number and the placement of the surface nodes and point sources. Numerical experiments on cylindrical radiators with different velocity distributions are performed to further illustrate how the solution accuracy depends on the surface velocity boundary conditions as well as the other formulation factors. © 1991 Acoustical Society of America.
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43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance

Measurements of the effective nonlinearity parameter B/A of water containing trapped cylindrical bubbles

Junru Wu and Zhemin Zhu

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2634-2639 (1991); (6 pages) | Cited 2 times

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The effective nonlinearity paramter B/A of water containing a three-dimensional ensemble of randomly distributed uniform-sized trapped cylindrical bubbles was measured. The experimental results indicate that the dramatic enhancement of the effective nonlinear parameter B/A is due to the nonlinear resonance oscillation of the trapped bubbles. The measured effective B/A for the system is of the magnitude of 104 to 105. © 1991 Acoustical Society of America.
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43.25.Ba Parameters of nonlinearity of the medium
43.30.Lz Underwater applications of nonlinear acoustics; explosions

Plane sound waves of finite amplitude for intermediate Gol’dberg numbers

François Y. Coulouvrat

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2640-2651 (1991); (12 pages)

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Burgers equation provides a good description of the propagation of plane sound waves of finite amplitude for which nonlinear effects are important. Although an exact solution is known, simple asymptotic approximations are useful since they may provide starting points in the case of more general situations for which no exact solution is known. Approximation solutions of Burgers equation are sought by means of a “mixed asymptotic method” involving both the method of multiple scales and the method of strained coordinates. The main point is the introduction of a new slow variable binding the solution in the region before shock formation with the solution in the old age region. For an emitted monochromatic wave, the method yields a simple and complete description for Gol’dberg numbers up to 20, as it is shown by comparison to exact or other approximated solutions. For higher Gol’dberg numbers, the solution is valid up to the shock formation distance and it can be connected with Fay solution beyond. © 1991 Acoustical Society of America.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves

Oblique reflection of a nonlinear P wave from the boundary of an elastic half-space

K. T. Shu and Jerry H. Ginsberg

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2652-2662 (1991); (11 pages) | Cited 4 times

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This paper describes mode conversion effects and subsequent waveform distortion arising when a finite amplitude dilatational (P) wave that has already experienced nonlinear distortion is obliquely incident on a stress-free boundary of an isotropic elastic half-space. A two-term perturbation expansion is first employed to identify the dominant nonlinear effects. The understanding of wave interactions obtained from the perturbation analysis is then exploited to derive a successful solution using the method of characteristics for two-dimensional wave. It is shown that the incident and reflected P waves undergo nonlinear amplitude dispersion along their ray paths. The orientation of the rays for the reflected waves are time dependent, being governed by a modified form of Snell’s law, in which the phase speed incorporates the nonlinear correction for the association particle velocity. The reflection coefficients are shown to resemble those of linear theory, except for the dependence on the variable angles of reflection. The nonlinear propagation and reflection laws are solved to determine temporal waveforms for the reflected P and SV (vertically polarized shear) waves. This requires an iterative procedure in order to trace rays arriving at a specified field point at an arbitrary instant back to their source. © 1991 Acoustical Society of America.
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43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves

Generating eigenray tubes from two solutions of the wave equation

James B. Bowlin

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2663-2669 (1991); (7 pages) | Cited 5 times

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A method is presented for calculating the paths taken by sound between a source and receiver. These paths, which are called eigenray tubes, are obtained from two solutions of the wave equation at finite frequency, one propagated from the source and the other propagated from the receiver. The results are not restricted to the high-frequency limit as is the case with classical ray traces. This generalization of classical ray tracing could be an important new tool in acoustic tomography. A numerical example is included with plots of 11 eigenray tubes. © 1991 Acoustical Society of America.
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43.30.Bp Normal mode propagation of sound in water
43.30.Cq Ray propagation of sound in water
43.30.Dr Hybrid and asymptotic propagation theories, related experiments

A narrow-band approximation to the acoustic pressure field

Kevin J. McCann and Freda Lee-McCann

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2670-2676 (1991); (7 pages) | Cited 2 times

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Broadband theoretical calculations of the acoustic pressure field generally suffer from the need to perform a large number of calculations at each of several frequencies across the frequency band and to, subsequently, construct the required time series through a Fourier synthesis. The computational load for such a series of calculations can be prohibitive especially for high frequencies. This paper presents a theoretical approach within the framework of normal-mode theory that significantly reduces the computational requirements for broadband calculations. The limits of the applicability of this method have been examined, and the technique has been used in comparisons with experimental data. The method is easily extended to accommodate range dependence in the environment. © 1991 Acoustical Society of America.
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43.30.Bp Normal mode propagation of sound in water
43.20.Bi Mathematical theory of wave propagation

A new algorithm for sound speed in seawater

John L. Spiesberger and Kurt Metzger

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2677-2688 (1991); (12 pages) | Cited 6 times

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Travel times of acoustic pulses across a 3000-km section in the northeast Pacific are used to estimate an algorithm for the speed of sound in seawater. This algorithm, derived from tomographic techniques, is inconsistent both with the international standard algorithm derived by Chen and Millero [J. Acoust. Soc. Am. 62, 1129–1135 (1977)] and with the algorithm of Del Grosso [J. Acoust. Soc. Am. 56, 1084–1091 (1974)]. Both previous algorithms were derived from laboratory experiments. The additive correction, δc (m s−1), to Del Grosso’s sound speeds between 0- and 4-km depth is δc(p) = −0.104 189 813 8×10−2p+0.210 143 906 0×10−4p2−0.141 411 578 8×10−6p3+0.317 812 236 0×10−9p4−0.217 806 024 3×10−12p5 with p being pressure-gauge units in kg cm−2. The rms error of δc is about 0.05 m s−1 and 0.1 m s−1 between the intervals of 0 to 2 km and 2 to 4 km, respectively. At about 3-km depth, sound speeds predicted by Chen and Millero and Del Grosso are about 0.7 m s−1 and 0.2 m s−1 too fast, respectively. An accurate algorithm for sound speed is of fundamental importance in acoustics and in tomographic measures of ocean temperature. © 1991 Acoustical Society of America.
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43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography

Modeling compressional wave velocity and attenuation in carbonate sediments

Michael T. Hurley and Murli H. Manghnani

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2689-2695 (1991); (7 pages) | Cited 1 time

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The Biot poroelastic theory is used to model ultrasonic (1 MHz) compressional wave velocity (Vp) and specific attenuation (Qp−1) for carbonate sediment sequences from three Deep Sea Drilling Project (DSDP) sites 288, 289, and 316 on the Ontong–Java Plateau in the western Pacific ocean. The sediments are assumed to be represented by a granular frame containing tortuous capillary tubes of a constant radius. Experimental data for the variation of shear velocity Vs and bulk density ρ with depth are used as input parameters for the model. Assumptions of the frame Poisson’s ratio σb, grain bulk modulus Kg, and tortuosity α are necessary. The low-frequency asymptote of the Biot theory is adequate in modeling the variation of Vp with depth for sites 288 and 289. Modeled velocities agree to within 8% of experimental. The sensitivity of the modeled velocities to the uncertainty in the input parameters is investigated. The equations of motion are partially differentiated with respect to each parameter and the resulting equations are used in conjunction with each parameter’s uncertainty or error. The uncertainty in the modeled velocities is on average 11% and is mostly dependent upon the uncertainties in Kg and σb. The assumption of constant σb for the chalk-limestone sequences from sites 288 and 289 is then tested. It is found to remain constant at a value of 0.2 for the chalk, and decreases to approximately 0.1 for the transition to limestone. Modeled values for Qp−1 are found to be sensitive to σb and ρ, in addition to the pore space parameters, and are considerably smaller than the experimental observations from sites 288, 289, and 316. © 1991 Acoustical Society of America.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

Transmission of sound beams through the interface between two fluids

Rolf J. Korneliussen, Halvor Hobaek, and Gunnar Lien

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2696-2710 (1991); (15 pages)

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In this article, results from an experiment on the transmission of a sound beam at and above critical incidence onto an interface between two fluids, which are chosen to simulate a water/sand interface, are presented. The incident beam is produced from a parametric array that is arranged to intersect the interface either within the absorption limit of the primary waves, or far outside the same, with the aim to discriminate whether linear or nonlinear processes are responsible for the transmission. Postcritical transmission is found to be basically a linear process, and is observed out to about 10° above the angle of critical incidence. Interference between the transmitted field and evanescent waves is observed just beneath the interface. The asymptotic axis of the main penetrating beam is investigated with respect to refraction angle and beam displacement. The field structure becomes markedly different if the primary waves are intersected by the interface, the main difference being the presence of a strong “underlobe” that has no direct counterpart in the incident field as measured in free field. This change in field structure is attributed to nonlinear effects, the candidates of which are discussed in detail. The most likely of these are the effects of primary beam truncation suggested by D. J. Wingham [“A theoretical study of the penetration of a water sediment interface by a parametric beam,” J. Acoust. Soc. Am. 76, 1192–1200 (1984)] and nonlinearity of the boundary conditions at the interface where the primary beams are intersected. © 1991 Acoustical Society of America.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Qd Global scale acoustics; ocean basin thermometry, transbasin acoustics

Vibrational relaxation in gaseous SiF4 by Ar and Ne at 304 K

Robert C. Amme, Bradley Jacobs, and John R. Olson

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2711-2714 (1991); (4 pages)

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A computer-controlled ultrasonic interferometer has been utilized for exploring room-temperature relaxation of gaseous SiF4–Ar and SiF4–Ne mixtures. A single relaxation process was observed for all mixtures, and the relaxation rates, 1/pτ, were found to vary linearly with the mole fraction of added argon or neon. Analysis of the mixture relaxation data shows that collisions between SiF4 molecules and either Ar or Ne atoms are less efficient for V−T transfer than are SiF4 self-collisions. This result can be explained within the Schwartz–Slawsky–Herzfeld formulation if it is assumed that a steep repulsive potential (i.e., the 7:28 function) is operative for SiF4–SiF4 collisions, while the repulsive interaction for SiF4–noble gas collisions is treated as being between a molecule obeying a 7:28 law and an atom characterized by a 6:12 function. © 1991 Acoustical Society of America.
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43.35.Ae Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in gases

Stimulated ultrasound absorption in liquids

T. J. Lewis, C. Barnes, and M. J. van der Sluijs

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2715-2724 (1991); (10 pages)

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It is shown that if two ultrasonic absorption processes, each with a relaxation frequency, exist in a liquid, then under certain conditions a nonlinear quasiresonance equation of state may be derived. If further absorption processes are associated with clusters in the liquid, a cluster being a local aggregation of molecules, then stimulated three-wave combination-frequency interaction is possible when a primary and a secondary pressure wave of different frequencies exist in the liquid. These conditions can occur in resonator and pulse-echo experiments. When the clusters have a significant second-order compressibility, the absorption can be either enhanced or reduced, according to circumstances, with maxima or minima at frequencies much lower than the relaxation frequencies. The theory is used to explain the anomalous resonance-like absorptions that have been reported for toluene, acetic acid, alcohols, and certain biomolecules. © 1991 Acoustical Society of America.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.35.Fj Ultrasonic relaxation processes in gases, liquids, and solids

Ultrasonic velocities in pure hydrocarbons and mixtures

Zhijing Wang and Amos Nur

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2725-2730 (1991); (6 pages) | Cited 2 times

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Ultrasonic velocities were measured in hydrocarbons of n-alkanes, 1-alkenes, and naphthenes as a function of temperature, using the ultrasonic pulse transmission method. The velocities of all the hydrocarbons measured decrease with increasing temperature approximately linearly, although the rate of decrease is different for different hydrocarbons. The data also show that hydrocarbons of the same homologous series with higher carbon content have higher bulk moduli (or lower compressibilities) and the measured velocities V in mixtures of these pure hydrocarbons obey a simple physical mixing law V = Σi = 1nXiVi, where Xi is the volume fraction and Vi is the velocity, respectively, of the ith component. © 1991 Acoustical Society of America.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions

Similarities between various Lamb waves in submerged spherical shells, and Rayleigh waves in elastic spheres and flat half-spaces

G. C. Gaunaurd and M. F. Werby

J. Acoust. Soc. Am. Volume 89, Issue 6, pp. 2731-2739 (1991); (9 pages)

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A variety of resonance features are studied in the back-scattering cross sections (BSCS) of an air-filled metal spherical shell submerged in water and insonified by a plane cw sound wave. Rayleigh (R) and whispering gallery (WG) waves were originally investigated for vibrational purposes for (flat) half-spaces in contact with vacuum. Lamb waves were originally studied in flat plates also in contact with vacuum. These old findings are generalized to the cases of an elastic spherical shell (o.d./i.d.=2a/2b) fluid-loaded on both surfaces, and excited by an incident plane wave. The various (leaky-type) Lamb waves present in the shell are shown to reduce to the earlier R/WG waves as a≫1≫b and ρf→0. The manner in which each one of these various shell waves manifests itself in the various frequency bands of the shell’s BSCS as perceived by a remote sensor is also studied. Dispersion plots for the various phase velocities of the various waves are displayed in very wide (i.e., 0<ka<500) bands, and a number of analogies between Lamb and R/WG waves are obtained as the submerged shell becomes a solid sphere (b≪a), and vice versa (b≲a). The fluid loadings, the finite shell thickness, and the curvatures of the structure all generate novel types of waves in the shell (that manifest their effects in its BSCS) that could have never emerged from earlier models that ignored these effects, and which are analyzed here. © 1991 Acoustical Society of America.
Show PACS
43.35.Mr Acoustics of viscoelastic materials
43.40.Ey Vibrations of shells
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