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Aug 1974

Volume 56, Issue 2, pp. 305-711

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Impulse response and radiation impedance of an annular piston

P. R. Stepanishen

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 305-312 (1974); (8 pages)

Online Publication Date: 12 Aug 2005

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An approach is presented to evaluate the impulse response of an annular piston, which is mounted in an infinite planar rigid baffle. Since the impulse response is defined to be the time‐dependent force on the ring, which results from an impulsive velocity of the ring, the impulse response and radiation impedance of the ring are a Fourier transform pair. A closed‐form expression for the impulse response of a ring of any size is developed from the well‐known double surface integral representation of the radiation impedance. Various integral and asymptotic expressions for the radiation impedance of the ring are derived from the impulse response, and the results are shown to be in agreement with those of earlier investigators. Several numerical results are also presented to show the effect of changing the ring size on the impulse response, and on the radiation resistance and reactance of the ring.

Farfield viscous effects in nonlinear noise propagation

Wesley L. Harris, Sr.

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 313-322 (1974); (10 pages)

Online Publication Date: 12 Aug 2005

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The method of parametric differentiation has been applied to predict the farfield noise propagation in both a lossless and a dissipative medium. The classical nonlinear acoustical problems of calculating the sound field of two rectilinear vortices rotating about an axis between them in a lossless medium and of calculating the sound field generated by a rotating cylinder in a viscous medium have been investigated. Solutions to these classical problems valid for asymptotically small Mach number have been extended to larger values of the Mach number parameter. It is shown that in the lossless medium, the governing equation transformed to parameter space reduces to a wave equation in the farfield. In the dissipative medium, the system of nonlinear partial differential equations transformed to parameter space reduces to a linear partial differential equation of the propagating type which contains a third‐order derivative as well as the wave operator. Pressure distributions in the farfield are obtained in the lossless medium; the results appear reasonable physically and mathematically self‐self‐consistent. The method of parametric differentiation and Newton's method are compared.

Measurements of sonic‐boom overpressures from Apollo space vehicles

David A. Hilton and Herbert R. Henderson

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 323-328 (1974); (6 pages)

Online Publication Date: 12 Aug 2005

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This paper presents representative results of sonic‐boom overpressure data recorded during the launch and reentry of the Apollo 15 and 16 space vehicle systems. Comparisons are made between measured overpressures and those predicted using available theory. The measurements were obtained along the vehicle ground track at 68, 87, 92, 129, and 970 km downrange from the launch site during ascent, and at 9, 13, 55, 185, and 500 km from the splash‐down point during reentry. Also included are tracings of the sonic‐boom signatures along with a brief description of the launch and recovery test areas in which the measurements were obtained, the sonic‐boom instrumentation deployment, flight profiles and operating conditions, and high‐altitude weather information for the general measurement areas.

Measured variations in aircraft noise near Arlanda Airport

Anders R. Kajland

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 329-331 (1974); (3 pages)

Online Publication Date: 12 Aug 2005

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Tape recordings were made of ca 1500 takeoffs at Arlanda Airport by means of an automatically operating recording device. Type of aircraft and destination as well as temperature, air humidity and wind velocity, and direction were registered. Correlation analyses of peak sound levels in dBA and meteorological factors were made. Sound level showed no significant covariation with humidity and temperature, but a positive correlation to the wind velocity from the aircraft towards the measuring station was found. The mean values measured verify theoretical calculation of the sound level from standard noise contours according to ISO Recommendation No. 507 and NASA CR‐767 and also show that calculations are more accurate than occasional measurements. Parts of the data were also analyzed as to the difference among dBA, PNdB, EPNdB, and dBD. High correlations among these different units were found.

Helicopter noise experiments in an urban environment

W. A. Kinney, A. D. Pierce, and E. J. Rickley

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 332-337 (1974); (6 pages) | Cited 1 time

Online Publication Date: 12 Aug 2005

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In two series of helicopter noise experiments, sound‐pressure‐level recordings were made on the ground while a helicopter flew over (i) an array of microphones placed in an open field, and (ii) a similar array placed in the center of a city street surrounded by tall buildings. For given helicopter altitude and airspeed, it was found that the flyover noise recorded in the street, although initially lower, built up rapidly as the aircraft approached such that the peak recorded noise was actually more intense than that recorded in the open field. This result is in qualitative accord with the results of previous laboratory scale‐model experiments performed by Lyon and Pande. The differences between the two sets of field data are attributed in major part to the fact that a reverberant sound field builds up in the street during flyover. This enhancement is less pronounced for higher flight altitudes. A simple theory based on geometrical acoustics and statistical concepts is described that quantitatively explains the sound enhancement found for a helicopter flying over a city street.

Naturally occurring atmospheric acoustical signals

John A. McDonald

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 338-351 (1974); (14 pages) | Cited 2 times

Online Publication Date: 12 Aug 2005

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Atmospheric disturbances located close to microbarograph arrays in north Texas are assumed to be caused by sources of acoustic‐gravity waves and/or infrasound. The sources studied are large storms, hurricanes, tornadoes, and frontal systems. The large‐amplitude long‐period acoustic‐gravity waves are readily found, but detection of infrasound presents problems which are indicated and some possible solutions are suggested.

Hydrodynamic solutions at a sonic‐boom focus

L. W. Parker and R. G. Zalosh

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 352-360 (1974); (9 pages)

Online Publication Date: 12 Aug 2005

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A numerical shock‐following method has been developed and applied to a study of the focusing of sonic‐boom N waves. The focusing occurs subsequent to the formation of converging concave shock fronts which can result from refraction by atmospheric inhomogeneities or from aircraft maneuvers. The geometry is two dimensional, or three dimensional with axial symmetry, leading to a line or point focus, respectively. The computer code used in the calculations employs a moving mesh so that weak N wave shocks (relative overpressures of the order of 1/1000) can be followed for large distances without numerical dissipation. In several sample calculations, overpressures at the focus ranging from two to 20 times the nominal overpressure have been computed. The typical length scale of the high‐pressure region is the order of a wavelength. It is also found that weak shocks tend to cusp at the axis in accord with the geometric‐acoustics description, whereas strong shocks straighten out without cusping.

Reflection from a sinusoidal surface

L. R. Brownlee

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 361-368 (1974); (8 pages)

Online Publication Date: 12 Aug 2005

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A formula, derived for the scattering of the various orders, differs from the results of Eckart and Brekhovskikh in the same way as these results differ from each other—namely, by the term in front of the Bessel function. In our case the term is unity. By deducing a simple geometric formula for the angular distribution of scattered energy in the high‐frequency limit, and by using an asymptotic form for the Bessel function, the three formulations are compared in the high‐frequency limit at various values of height, angle, etc., with the geometric formula. The result is that our formulation agrees best.

Damping of gas bubbles in water from desinent threshold for subharmonic‐1/2

M. Ceschia and G. Iernetti

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 369-373 (1974); (5 pages)

Online Publication Date: 12 Aug 2005

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Threshold for subharmonic‐1/2 emission has been measured in water saturated with different gases in a sound field of 0.7 MHz. Incipient threshold is determined by bubbles of radii smaller than that of resonance at subharmonic‐1/2, the desinent threshold by bubbles resonant at this frequency. The latter can be correlated to the lowest sound pressure for subharmonic‐1/2 emission and to the resonant‐bubble damping constant. The experimental data are in good agreement with the predictions, for He, N2, air, O2, and Ar bubbles in water, but for H2 bubbles the threshold results are about three times the predicted values.

Shallow‐water bottom reverberation under downward refraction conditions

Bernard F. Cole and Eugene M. Podeszwa

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 374-377 (1974); (4 pages) | Cited 1 time

Online Publication Date: 12 Aug 2005

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In 1965, some propagation loss and reverberation level measurements were performed under downward refraction conditions at a location south of Long Island. The reverberation levels measured during those trials are reduced to scattering strength values by considering the details of the propagation to and from the bottom, and the results are shown to be similar to those that Urick derived by ignoring the details of the propagation paths. The manner in which downward refraction conditions facilitate the measurement of bottom scattering strength values for shallow‐water areas is also discussed.

Some considerations in choosing an explosive source and processing filter for the measurement of transmission loss

J. S. Hanna and B. E. Parkins

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 378-386 (1974); (9 pages)

Online Publication Date: 12 Aug 2005

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Explosives are often used as a source of acoustic energy in transmission measurements in the ocean because of the broad‐band spectra of underwater explosions and the wide range of levels that can be generated. At the same time, this broad‐band spectrum can complicate a transmission loss measurement because the spectral character of the shock wave and subsequent bubble pulses of the shot can be very similar to the spectral character of the loss which is due to the multipath structure of the propagation. This complication can be avoided by the proper choice of the detonation depth and the charge weight. When these choices have been made, the properties of the analyzing filter of the data processing system must then be selected; this must be done with regard for the nature of that portion of the multipath structure to be resolved as well as the nature of the charge spectrum. This paper discusses the principles involved in making these choices and gives illustrations of both short‐ and long‐range measurements.

Normal‐mode theory of underwater sound propagation from directional multipole sources

Anton Haug, Ronald D. Graves, and H. Überall

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 387-391 (1974); (5 pages) | Cited 1 time

Online Publication Date: 12 Aug 2005

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Normal‐mode theory of underwater sound propagation, which so far has been established only for omnidirectional point sources, is developed here for the case of sources with arbitrary spatial extent and directionality. This is accomplished by expanding the source in a series of spherical multipole distributions. From the Green's function representation, the sound field is then obtained for arbitrary multipolarity of the source, and it simplifies considerably for a point multipole source. Our results are illustrated by a calculation of range‐focusing effects in a channel with parabolic velocity profile using a dipole source.

On thresholds for surface waves and subharmonics of an oscillating bubble

D. Y. Hsieh

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 392-393 (1974); (2 pages) | Cited 2 times

Online Publication Date: 12 Aug 2005

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A theory of the simultaneous excitation of surface waves and subharmonics of an oscillating bubble is presented. The threshold pressures are computed, discussed, and compared with the available experimental values.

Geographic patterns in volume‐reverberation spectra in the North Atlantic between 33°N and 63°N

Paul T. McElroy

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 394-407 (1974); (14 pages) | Cited 1 time

Online Publication Date: 12 Aug 2005

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Volume‐reverberation observations were made at 34 stations on Cruise 105 of R/V CHAIN during its passage from Newfoundland to the Azores, and thence to Portugal and Ireland. The acoustic returns at each station were analyzed in 16 1/3‐octave bands extending from 1 kHz to 31.5 kHz to yield column strength spectra. Techniques to maximize the accuracy of these spectra are described. Representative spectra are plotted. Using a measure we have called the cross‐standard deviation, we found evidence that the spectra for nearby stations were similar and thus could be classed in geographically‐based groups called pelagic regions. This is reasonable since much volume reverberation is sound scattered from animals which in turn are distributed in pelagic faunal regions. We present a matrix showing the similarity of each pair of stations; a small number indicates similarity, while a large number indicates difference in the two spectra. We have identified many of these regions on the basis of physical‐oceanographic features such as the polar front. These features are used in defining boundaries for the regions.

Intermodal coupling coefficients for a fluid‐loaded rectangular plate

Larry D. Pope and Ralph C. Leibowitz

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 408-415 (1974); (8 pages) | Cited 5 times

Online Publication Date: 12 Aug 2005

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The intermodal coupling coefficients are calculated for a thin, simply supported rectangular plate in an infinite rigid baffle. The coefficients describe the modal auto‐ and cross‐resistive and reactive coupling induced by a dense fluid‐filled half‐space above the plate.

Closed‐form solutions for SOFAR ray caustics in media with bilinear sound‐speed profiles

David Towns Raphael

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 416-426 (1974); (11 pages) | Cited 1 time

Online Publication Date: 12 Aug 2005

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In an unbounded medium with a bilinear sound‐speed profile composed of two constant‐gradient layers separated by an interface at the depth of minimum sound speed, SOFAR rays are generated which are continuously refracted towards the channel axis. The existence conditions for real roots of the acquiring‐ray cubic and quartic equations treated herein facilitate the determination of the caustic equations. When the condition is imposed that the discriminant of the cubic or quartic equation be zero valued, the caustic equation emerges as the boundary line along which repeated roots occur. Two general cases are examined: (a) receiver and source in same layer, and (b) receiver and source in different layers. Explicit, closed‐form solutions are obtained for most of the caustics by exploitation of reciprocity considerations and by reduction‐to‐single reflection or crossing arguments. Only rays which cross the interface without undergoing either a surface or bottom reflection are treated.

Sound radiation from a cylinder immersed in an acoustic fluid bounded by an elastic half‐space

O. Skidan, J. M. Klosner, and M. L. Baron

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 427-439 (1974); (13 pages)

Online Publication Date: 12 Aug 2005

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The problem of the forced steady‐state response of an infinite cylindrical shell immersed in an acoustic fluid bounded by an elastic half‐space is investigated. The solution is obtained by using the Helmholtz integral to express the acoustic velocity potential, utilizing the Fourier transform to determine the influence coefficients for the pressure‐velocity relationship at the boundary of the half‐space, and by using a modal analysis to express the shell response. By enforcing the appropriate boundary conditions at discrete points of the interfaces, a system of simultaneous equations is obtained. The solutions of these equations yield the values of the unknown source strengths which are then used to determine the pressure field.

Long‐range sound fluctuations with drifting hydrophones

R. C. Spindel, R. P. Porter, and R. J. Jaffee

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 440-446 (1974); (7 pages) | Cited 3 times

Online Publication Date: 12 Aug 2005

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Phase fluctuations of underwater sound (406 Hz) transmitted between a fixed source and deep free‐drifting hydrophones have been obtained for transmission ranges of 200 km. Phase variations due to hydrophone drift are removed by a bottom‐moored, CW tracking system that corrects for motion‐induced phase variations of 0.06 rad or larger. Most of the energy traveled along refracted paths, eliminating much of the phase fluctuation due to bottom and surface scatter. Residual surface scatter effects are removed by narrow‐band filtering. Maximum observed phase fluctuations are 15 cycles over 3 h on the deepest hydrophones (1500 m). The mean‐square phase spectrum has a slope of −2 for frequencies between 0.4 and 40 cycles/h. The shallow hydrophone (300 m) data contain half the phase fluctuation of the deep hydrophones. Depth dependence of the fluctuations is attributed to internal gravity waves.

Internal tidal influence on deep‐ocean acoustic‐ray propagation

N. L. Weinberg, J. G. Clark, and R. P. Flanagan

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 447-458 (1974); (12 pages)

Online Publication Date: 12 Aug 2005

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Based upon previous studies of fixed‐system acoustic‐environmental relationships in the Straits of Florida, work on transmission fluctuations has been extended to the deep ocean. The model for the acoustic propagation study employs linear profiles for the sections at the surface and bottom, and hyperbolic cosines for the region about the minimum sound‐velocity axis. Closed‐form solutions are known for each profile segment, and combining these, the initial angles of all ray arrivals which reach a specified receiver from a given source are determined. By calculating travel time, spreading loss, and the boundary effects at the surface and bottom, the amplitude and phase (assuming CW transmission of a known frequency) of each arrival can be found. These arrivals, when summed as a function of time, yield the resultant acoustic time series for sound‐speed profile variations derived from assumed amplitudes of internal tides of 2,4,7, and 10 m. These time series are compared with data. It is shown that the effect of surface tides on acoustic propagation in the deep ocean is minimal.

Ultrasonic holography at the critical angle

B. P. Hildebrand and F. L. Becker

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 459-462 (1974); (4 pages)

Online Publication Date: 12 Aug 2005

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Ultrasonic holography is a recording technique preserving phase and amplitude of a wavefront on a two‐dimensional surface. This paper explores the possibility of using this technique to map phase changes occuring on an otherwise featureless surface by illuminating the surface at the Rayleigh critical angle. Since phase response at the critical angle is extremely sensitive to such things as stress concentrations, subsurface defects, or work hardening, it appears that this technique may offer a way to detect and map such distributions. We present preliminary experimental results that substantiate this claim.

Transient response of multidegree‐of‐freedom linear systems to forcing functions with inequality constraints

C. D. Michalopoulos

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 463-468 (1974); (6 pages)

Online Publication Date: 12 Aug 2005

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Optimal control theory is employed to analyze the transient response of discrete, linear systems to forcing functions, whose dependence on time is not known, but which lie within specified bound. Attention is focused on the complete determination of the forcing function which will induce (a) maximum displacement of any specified mass element, (b) maximum relative displacement of any two adjacent masses, and (c) maximum acceleration of a given mass. Linear mechanical systems with an arbitrary number of degrees of freedom are considered, wherein only a single forcing function acts. In general, the desired forcing function is found to be a bang‐bang‐type function; that is, a function which switches from the upper to the lower bound and vice‐versa at certain instants of time. The general procedure for finding these switching times is presented.

Impact on coaxial circular cylinders of two materials

Patrick M. O'Leary and A. Cemal Eringen

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 469-476 (1974); (8 pages)

Online Publication Date: 12 Aug 2005

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In this paper, the problem of an impulsive load on a bar, composed of two coaxial cylinders of different materials, is investigated. Double integral transforms are used to solve the equations of motion. The exact solution appears as a sum of Fourier integrals, whose integrands are all divided by the generalized version of the Pochammer‐Chree frequency equation. Asymptotic values are obtained by using the saddle‐point method of integration. The displacements and stress functions are plotted for various times at a point far away from the point of impact. These functions are also plotted across the bar to show the effect of the interface surface.

Exact solution to finite amplitude oscillation of an anisotropic thin rubber tube

M. Shahinpoor

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 477-480 (1974); (4 pages)

Online Publication Date: 12 Aug 2005

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Based on the theory of finite deformations of homogeneous anisotropic materials of Ericksen and Rivlin and on the Truesdell theorem on quasi‐equilibrated motions of incompressible, anisotropic materials, the problem of large‐amplitude free and forced oscillations of a longitudinally anisotropic elastic thin rubber tube is analyzed. Exact expressions for the dynamic deformations are given upon solving explicitly the nonlinear, nonautonomous time‐dependent differential equations of motion under the action of a blast load that decays linearly with time.

Numerical evaluation of Rice's integral representation of the probability density function for Poisson impulsive noise

W. J. Richter, Jr. and T. I. Smits

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 481-496 (1974); (16 pages)

Online Publication Date: 12 Aug 2005

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Numerical evaluation of Rice's triple integral representation of the probability density function (pdf) for Poisson impulsive noise has been accomplished for the intermediate pulse repetition rate case with several meaningful waveforms. The technique was applied to (1) a case for which a closed form was available, (2) the low‐pulse repetition rate case where simplifications are possible, and (3) to several cases for which empirical results were available. In all cases, agreement was excellent. The technique consists of numerically computing the characteristic function, and obtaining from this the pdf by subtracting constant from the characteristic function, and transforming the constant analytically and the remainder numerically. The transformation is carried out separately in different regions, depending on the shape of the curve in a particular region, after which the individual integrals are added. This process overcomes some of the difficulties previously encountered in evaluating Rice's integral.

Unified approach to aerodynamic sound generation in the presence of solid boundaries

Marvin Goldstein

J. Acoust. Soc. Am. Volume 56, Issue 2, pp. 497-509 (1974); (13 pages) | Cited 7 times

Online Publication Date: 12 Aug 2005

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See Also: Erratum

Show Abstract
In many cases of technological interest solid boundaries play a direct role in the aerodynamic sound generation process and their presence often results in a large increase in the radiated sound. A generalized treatment of the emission of sound from solid boundaries is presented. It is then shown how the various acoustic analogy theories of aerodynamic sound generation can be obtained as special cases of this equation.
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