bluuebunny/crossref_metadata_2025 huggingface dataset:
Jet Aircraft Noise in Metropolitan Los Angeles under Air Route Corridors
Authors: Hurdle P. , Lane S. R. , Meecham W. C.
Published: October 2005

Airport community noise exposure to jet aircraft takeoff and landing activity at Los Angeles International Airport (LAX) has been extensively measured and documented. However, the noise instrusion problems due to overflights of jet aircraft in the approach and departure air routes over the communities of the Los Angeles metropolitan area have largely been ignored. Preliminary measurements indicate that in at least 10 peripheral residential communities (at distances up to 15 miles from LAX) the noise levels caused by jet aircraft overflights exceed 20 dB(A) above the average ambient-noise levels. There are four major approach and departure corridors to LAX with a total number of 500 commercial jet aircraft overflights each 24 hours. Many communities are thus subjected to about 100 overflights during the peak traffic periods (about three hours duration). As a result, hundreds of thousands of individuals are subjected to a significant noise annoyance every two minutes for sustained periods. In most of these instances, the noise levels exceed the municipal codes on allowable residential noise disturbances. However, these noise ordinances are not enforced against the air carriers. It is estimated that if the aircraft operators were fined accordingly, the total of such fines in the Los Angeles area would be a billion dollars per year.
The Objectives of Structural Analysis System Programming
Authors: Tagg Malcolm
Published: October 2005

The past decade has witnessed the blossoming of many large, all-encompassing structural analysis programs. We have now reached the stage where most self-respecting organizations are using one or more such programs. An enormous amount of effort has been spent on developing these programs. It is, perhaps, time to reflect on the degree to which the original objectives have been achieved. Has the effort expended been justified, and what changes in objectives might now appear desirable? What is the position of the smaller organization with more limited resources? The paper attempts to resolve these questions and to advance suggestions as to what our future objectives should be.
Ultrasonic Absorption in Naphthalene Single Crystals at Low Temperatures
Authors: Wilson J. D. , Yun S. S.
Published: October 2005

The attenuation of ultrasonic waves was measured in single crystals of naphthalene from 23° to −185°C for frequencies from 15 to 45 MHz. A maximum was observed in the absorption coefficient at low temperatures, and from the frequency dependence of the absorption, the result was examined in terms of relaxation phenomena. The experimental results are compared to the relaxation maximum predicted by the Liebermann theory assuming the temperature-cubed term of the transition probability to be the dominant temperature dependence. The transition probability is calculated from the experimental data and compared directly to the theoretical values. Also, a transition probability with exponential temperature dependence is shown to agree equally as well with the experimental results.
Field due to a Point Source in an Inhomogeneous Elastic Medium
Authors: Acharya Hemendra K.
Published: October 2005

Wave propagation in an inhomogeneous elastic half-space is investigated. Integral expressions for vertical and horizontal displacement due to a point source have been obtained in terms of reflection coefficients for a medium in which compressional- and shear-wave velocities increase monotonically with depth. These expressions are further shown to reduce to known expressions in the case of homogeneous solid and stratified liquid.
Surface Wave Dispersion in a Mass-Loaded Half-Space
Authors: Alsop L. E. , Goodman A. S. , Ash E.
Published: October 2005

The effect of a layer on surface wave propagation on a half-space can be separated into terms arising from elastic and from inertial restraining forces. In a number of situations of practical importance, it turns out that the inertial terms are dominant. The period equations governing the dispersion for this pure mass loading are obtained in suitable form and numerical solutions for Rayleigh waves for both solid and fluid loading are obtained. It is shown that by presenting the results in terms of appropriate variables, extremely simple, approximately linear, dispersion characteristics are found. A single computation suffices for substrate materials having the same Poisson ratio. The validity of this approximation is explored for modified Rayleigh waves for both solid and liquid layers, and for Love waves.
Scattering of Sound by Sound
Authors: Berktay H. O. , Al-Temimi C. A.
Published: October 2005

The debate about scattering of interaction-frequency components when two sound waves interact at a non-zero angle has not been resolved because no positive evidence of such scattering outside the interaction volume has been put forward. In this contribution, an attempt is made to review the situation in view of the available experimental evidence relating to interaction between a plane wave and a “collimated” pump wave.
Wave Propagation in a Fluid-Filled Tube
Authors: Rubinow S. I. , Keller Joseph B.
Published: October 2005

A circular cylindrical viscoelastic solid tube filled with a compressible viscous fluid is considered. The outer surface of the tube is assumed to be constrained so that it cannot move freely. Axially symmetric wave solutions are obtained for the linearized equations governing the motion of the fluid and the solid. The solutions lead to a complicated transcendental dispersion equation relating the wave frequency and the propagation constant. This equation is simplified by taking the fluid to be inviscid and the tube to be thin. Then it is studied by both analytical and numerical means. Formulas and graphs are given for the propagation constant, the phase velocity, the group velocity, etc., as functions of the frequency for various sets of parameter values. There are infinitely many modes of propagation, two of which are “tube modes” and the rest of which are acoustic modes. The case of a viscous fluid and a tube of any thickness are to be treated in a subsequent paper.
Waves in a Thin-Walled Tube due to Sudden Release of a Radial Ring Pressure
Authors: Hsu Jamie C. , Clifton R. J.
Published: October 2005

The approximate thin-shell theory of Herrmann and Mirsky is used to study stress wave propagation in a thin-walled cylindrical tube due to sudden release of a concentrated ring pressure. The tube is assumed to be of infinite length, so that the problem is a pure initial-value problem for which the solution can be represented as a superposition of harmonic plane waves. Numerical results are plotted for profiles of strains, stress resultants, and displacements versus distance along the tube axis at several times after the load is released.
Response of a Thin-Walled Cylindrical Duct to Internal Airflow
Authors: Khosrovani H. , Cohen R. , Chanaud R. C.
Published: October 2005

The vibration of a thin cylindrical duct, due to an internal random pressure field caused by airflow, was studied both experimentally and theoretically. The Reynolds number for the experiments was near 105 and the Mach number was less than 0.1, typical of large air handling applications. Although a muffler was used to simulate acoustically a much longer duct, the acoustic pressure was found to be a significant cause of duct vibration. A simple model (white noise) of the pressure field was convolved with the dynamic Green's function of the duct to compute numerically the radial displacement cross covariances. In spite of this simplification, the measured displacement covariances were in good agreement with those calculated. The displacement spectral density was predicted to vary as ω−3 with white-noise excitation. The observed dependence was ω−4.8 and was accounted for by the fact that the forcing function was not white noise, but had a frequency dependence near ω−2.
Axially Symmetric Waves in Transversely Isotropic Rods
Authors: Mengi Y. , McNiven H. D.
Published: October 2005

In this study, a three-mode approximate theory governing axisymmetric motions in transversely isotropic rods is developed. The development of this approximate theory follows closely the method adopted by Mindlin and McNiven when they developed a three-mode theory for isotropic rods. There is, however, one significant departure. After the generalized displacements and generalized strains are defined, the equilibrium and constitutive equations and the kinematic relations are derived using a variational theorem due to Hu and Washizu. The approximate theory is analyzed numerically for two transversely isotropic materials, and spectral lines derived from the theory are compared with those from the exact three-dimensional theory.
A Method of Selecting Element Positions in a Hydrophone Array to Reduce Minor Lobes
Authors: Kendig Paul M.
Published: October 2005

It is shown that, if the sensitivities and resonant frequencies of elements in a hydrophone array can be accurately determined before they are placed in an array, it is possible to select their positions in the array so as to reduce minor lobes significantly. An expression for the sensitivity of an individual element that depends on easily and accurately measured quantities has been derived. The variation in phase depends primarily on the resonant frequencies of the elements, if element positions can be held to sufficiently close tolerances. Comparisons of calculated results are made with experimental measurements and with computed results of random placement of the transducer elements.
Monostatic and Bistatic Backscattering Measurements from the Deep Ocean Bottom
Authors: Schmidt P. B.
Published: October 2005

Monostatic and bistatic backscattering from the ocean bottom was measured at frequencies from 0.5 to 6.3 kHz at four stations in the North Atlantic and North Pacific Oceans. The data can be approximately described by Lambert's law of diffuse reflection at grazing angles below 50°. The average of the scattering constants 10 logμ measured for all frequencies is −29 dB.
The Averaged Impulse Response of a Shallow-Water Channel
Authors: Smith P. W.
Published: October 2005

The averaged impulse response for sound transmission in a shallow-water channel is estimated by a theory based on ray acoustics with lossy specular reflection from the boundaries. Averaging is introduced primarily by strict averaging in depth of the square of the received pressure. Rays need be traced over but a single cycle of their paths. The impulse response contains useful and readily accessible information about environmental loss parameters. The rate of decay of the reverberant tail, which is characteristic of channels with only moderate variations in sound speed, appears to be a particularly valuable measure. Theoretical and experimental data are compared.
The Noise of Melting Icebergs
Authors: Urick R. J.
Published: October 2005

Icebergs seem to have escaped serious attention as sources of underwater sound. The noise of icebergs has been measured by means of sonobuoys dropped by an aircraft at distances between 200 and 10 000 yd. Two isolated icebergs 130 to 150 ft high were measured at a location northeast of Newfoundland. Noise apparently originated by the bergs was found to have a spectrum flat to about 10 kHz, the limit of measurement, with spectrum levels of −37 and −42 dB re 1 dyn/cm2 at 200 yd from the two bergs. Ice sizzle is readily observed with a cube of cloudy ice and a hydrophone in a container of water. It is surmised that this noise is caused by the explosion of tiny air bubbles entrapped in the ice under pressure and released as melting occurs. Alternatively, at deep depths, the process may be one of implosion of the cavities by inrushing water. The level of the noise of icebergs doubtless depends on many factors, such as size, depth, air content, and rate of melting in the surrounding water.
Frequency-Averaged Power Flow into a One-Dimensional Acoustic System
Authors: Scharton Terry D.
Published: October 2005

This work shows the effect of the drive-point impedance of a finite acoustic system on the power delivered by a realistic source. At low frequencies when the modal overlap of the system is small, the frequency-averaged power delivered by the source can be much less than the power which the source would deliver to an equivalent semiinfinite system. An analysis of the power flow into a finite one-dimensional wave tube is used to explain the observation that broad-band high-intensity acoustic drivers deliver less low-frequency power to small reverberation chambers than they deliver to progressive wave tubes. The analysis indicates that the modal overlap also plays a central role in the determination of the ratio of space-averaged to drive-point response.
Generalization of the Boltzmann-Ehrenfest Adiabatic Theorem in Acoustics
Authors: Smith W. E.
Published: October 2005

A generalized adiabatic theorem is obtained for loss-free linear acoustic systems. The theorem includes the usual adiabatic or resonator action theorem (Boltzmann-Ehrenfest theorem) as a special case, but also includes results expressing radiation pressure forces or average radiation energy storage in terms of the phenomenological exterior behavior of the system. Some new interrelations between average energy storage and radiation pressure forces also follow from the theorem.
Acoustics of St. Peter's and Patriarchal Basilicas in Rome
Authors: Shankland R. S. , Shankland H. K.
Published: October 2005

This paper reports on acoustical measurements made with Vatican permission in several large churches, including St. Peter's Basilica and the other three Patriarchal Basilicas in Rome: S. Giovanni in Laterano, S. Paolo fuori le Mura, and S. Maria Maggiore. The observed reverberation times for these large churches are unusually short. This is because of the acoustical coupling of the air volumes making up the structures and also the profusion of architectural detail and decoration, especially sculpture, that produces a very considerable amount of sound diffusion. The measured reverberation times are consistent with standard reverberation theory when the coupled nature of the air volumes is considered.
Multilayer Microwave Acoustic Transducers
Authors: Fahmy A. H. , Adler E. L.
Published: October 2005

The frequency response of a multilayer semiconducting piezoelectric transducer is obtained algorithmically. The multilayer transducer is first reduced to a conventional three-port structure by defining recursively the mechanical impedance loading each face of the piezoelectric layer. Electromechanical power conversion theory is then used to obtain the transducer loss. Computed results for the performance of multilayer transducers composed of a 1.5-μ-thick ZnO film and other metallic layers illustrate the use of this theory in the design of microwave ultrasonic transducers. The effects of finite resistivity, contact resistance, and different tuning conditions are described. The possibility of frequency-response shaping by using a multilayer is demonstrated by showing that an unusually broad-bandwidth transducer is obtained for an Au-ZnO-Au-Al structure.
Signal Velocity in a Duct with Flow
Authors: Eversman Walter
Published: October 2005

The acoustic signal velocities for pressure modes in an infinite rectangular hard-walled duct with a steady flow are investigated for the purpose of clarifying the degeneration of wave propagation which occurs with a low-frequency sinusoidal excitation. It is found that all pressure modes propagate both upstream and downstream at a speed governed by the Doppler effect. All modes other than the plane wave are dispersive and leave a lingering disturbance after passage. In steady sinusoidal excitation, this lingering disturbance gives rise to cancellations and reinforcements which can cause nearly complete attenuation in the cutoff condition or can cause waves with negative phase velocities in the downstream section of the duct even without end reflections.
Speech Intelligibility in the Presence of Time-Varying Aircraft Noise
Authors: Williams Carl E. , Pearsons Karl S. , Hecker Michael H. L.
Published: October 2005

This study concerns the question of whether or not the relation between intelligibility test scores and the Articulation Index (AI) established for steady-state noise can be used to predict speech intelligibility in the presence of time-varying aircraft noise. For various aircraft flyovers, intelligibility scores and several noise measures were obtained as functions of time. In addition, intelligibility scores and measures of AI were obtained for steady-state simulated aircraft noise. The relation between speech intelligibility and AI for time-varying noise was different from the relation obtained for steady-state noise. The various noise measures were almost equally effective in predicting speech intelligibility in the presence of time-varying aircraft noise. There is an appreciable disruption of contextual speech when the peak level of a flyover exceeds 88 PNdB, a speech-interference level of 68 dB, or an A-weighted sound-pressure level of 76 dB.
Resonance versus Resonant
Authors: Hunt F. V.
Published: October 2005

The term resonant frequency embodies both technical and grammatical errors and its use should be deplored and deprecated. The proper form is resonance frequency.
Monaural Temporal Interactions
Authors: Babkoff Harvey , Sutton Samuel
Published: October 2005

The monaural temporal interaction of transients was investigated by using a “mirror-image” paradigm. A pair of unequal monaural clicks in which the less intense click precedes the more intense click by a given interpulse interval (backward masking) was discriminated from an identical pair of clicks in which the more intense click precedes the less intense click by the same interval (forward masking). The functions obtained show an initial rise in discrimination as a function of increasing interpulse interval (Δt) followed by a leveling of the curve at a high discrimination level for Δt's of up to approximately 8–10 msec, followed by a decrease in discrimination to approximately 12–15 msec, followed by a second increase in discrimination at Δt's greater than 15 msec. Comparing the discrimination of mirror-image click pairs to forward masking and to backward masking alone indicates that monaural temporal interactions exist at intermediate interpulse intervals even though forward and backward masking are no longer evident. At these intervals, the discrimination is unrelated to the perception of temporal order. The shape of the functions and the Δt range over which it is evident are dependent upon the relative intensities of the two clicks comprising the pair. At longer intervals (greater than 15 msec), perception of temporal order is the dominant cue. Possible mechanisms are discussed.
Two- versus Four-Tone Masking at 1000 Hz
Authors: Canahl Julius A.
Published: October 2005

The threshold of a 1000-Hz sinusoidal signal masked by two or four tones placed symmetrically around the signal was investigated as a function of the frequency difference (ΔF) between consecutive maskers as well as masker level. The results concur with previous evidence that (1) the masked threshold decreases linearly as ΔF increases for a two-tone masker, and (2) the difference between masked thresholds is much greater than would be predicted on the basis of a simple summation of masking power or intensity. For small ΔF, the size of the difference (6–8.5 dB) did not vary greatly as level changed. At larger frequency separations, the highest levels produced more difference than lower levels. It was concluded that the difference between two- and four-tone masking was (1) dependent upon the level of the maskers and the frequency separation between the maskers, and (2) independent of the masking contributed by the individual maskers.
Two-Frequency Stimulation of a Cutaneous Mechanoreceptor
Authors: Cholewiak R. W. , Hahn J. F.
Published: October 2005

First-order afferent single-unit responses were obtained to sinusoidal one- and two-frequency stimulation of the touch corpuscle in the cat. With two-frequency stimulation, the amount of “masking” varied with the frequency and with the amplitude of the stimuli. In some instances, the addition of a second frequency decreased unit's rate of firing below the rate at which it was responding to a single frequency. The “masked” thresholds in the two-frequency stimulation were predictable from the single-frequency rate-intensity functions for the unit, as were some of the decreased firing rates occurring during two-frequency stimulation.
Effect of Unilateral Masking on the Lateralization of Binaural Pulses
Authors: Dunn Bruce E.
Published: October 2005

Pulsed tones were presented binaurally to subjects. Pure-tone frequencies were 250, 1000, 4000, and 8000 Hz. Loudness was varied in each ear. One ear was continuously stimulated with an octave band of noise. The subject attempted to lateralize the pulsed tones in either the masked or unmasked ear. Results indicate that the pulsed tone in the masked ear had little or no effect on the lateralization until it exceeded masked threshold. Comparison of the loudness levels in the unmasked ear, required for lateralization in that ear with curves for loudness in noise, indicated that there may well have been centrally mediated loudness enhancement in the unmasked ear produced by the masking stimulus.
Some Observations on Underwater Hearing
Authors: Norman Donald A. , Phelps Robert , Wightman Fred
Published: October 2005

We examine the relative role of bone conduction and tympanic conduction in underwater localization and detection by humans. Basically, we placed divers underwater and covered up various parts of the skull and outer ear with neoprene foam (an insulator of sound) and measured thresholds and localization accuracy. Sound conduction through the ear canal (tympanic conduction) appears to play only a minor role in the detection of sounds 1000 Hz and higher. Yet conduction through the canal appears to be very important for localization.
Intracochlear Potential Recorded with Micropipets. I. Correlations with Micropipet Location
Authors: Sohmer H. S. , Peake W. T. , Weiss T. F.
Published: October 2005

Glass micropipets (filled with 2M KCl) were inserted through the round window of anesthetized cats. As the micropipet was advanced through the cochlea, we recorded (1) depth of penetration of the micropipet, (2) resistance of the micropipet, (3) dc potential, (4) magnitude and phase of the fundamental component of the response to tones, and (5) magnitude of response from a stationary electrode. At the end of the experiment, the micropipet was cemented to the temporal bone and kept in place during histological preparation. From examination of 54 sectioned cochleas, we determined which structures in the cochlea had been penetrated by the micropipet. The inaccuracies involved in determining the location of the tip of the micropipet with this technique made it impossible, however, to associate recorded electric events with structures as small as individual cells. The average dc potentials (referred to scala tympani) were scala media, +103 mV; scala vestibuli, −2 mV. Occurrences of large negative dc potential (−50 to −100 mV) were frequently recorded between scala tympani and scala media; these potentials were generally stable for a short time only (<10 sec).
Signal Processing for a Cocktail Party Effect
Authors: Mitchell O. M. Mracek , Ross Carolyn A. , Yates G. H.
Published: October 2005

A binaural listener has the ability to concentrate on speech from a particular location while suppressing speech from other locations (binaural “cocktail party” effect). In some communication situations where sounds are picked up by a microphone system for transmission on a single path to a remote listener, it would be desirable to preprocess the signals to achieve a similar effect. We describe a class of nonlinear processes for the outputs of an array of microphones which emphasize speech coming from a particular (on-center) location in a background of other sounds. These processes completely eliminate any off-center impulsive noise which is nonoverlapping at the four microphones. Results of processing outputs of real and computer-simulated microphone arrays for speech and noise signals are described. Under anechoic conditions, the processing results in reproduction of the on-center speech without change, and in distortion and attenuation of an off-center speech source. The distortion produced by the processing appears to be an important factor in subjective suppression of the off-center source.
Automatic Formant Tracking by a Newton-Raphson Technique
Authors: Olive J. P.
Published: October 2005

A wide range of speech investigation requires natural-sounding synthetic speech whose individual acoustic features—such as pitch, formants, and duration—can be varied independently. This study describes an algorithm for obtaining such synthetic speech by automatically analyzing natural speech to obtain data for the control of a formant synthesizer. The lowest three formants of natural speech were determined by finding simultaneous solutions of the least-square-fit equations by means of a Newton-Raphson technique. The data obtained from this formant analysis, together with pitch data which were also obtained automatically, were used for controlling a computer-simulated formant synthesizer. This algorithm was tested for various sentences and speakers, and the synthesized speech was found to be of good quality.
Estimate of the Inherent Channel Capacity of the Ear
Authors: Corliss Edith L. R.
Published: October 2005

The growth of intelligibility of speech stimuli as a function of level above hearing threshold can be computed from the “circuit parameters” of the hearing mechanism by applying Shannon's concepts of channel capacity, equivocation, and “bits.” In the ear, the unit of response is an effective “least count,” derived from experimental data on hearing by means of the equations for a model resembling a frequency-selective circuit [E. Corliss, J. Acoust. Soc. Amer. 41, 1500–1516 (1967)]. The model predicts that the number of least counts available rises as the one-fourth power of the signal intensity above threshold. Experimentally, this growth rate is observed for the intensity-resolving power of the ear. Approximately the same power law is observed for the sensation of loudness. The model ascribes both effects to the same mechanism. From the observed integration time of the ear, the model predicts the rate at which transitions of single counts can be detected. From the counting rate and the integration time, the channel capacity available at the ear and its increase with level above threshold can be computed. The information content of speech as a source function is evaluated from the rate at which single “distinctive features” of speech phonemes are produced. Intelligibility scores can be predicted from the ratio between the rate at which information is being produced by the source and the rate at which the receptor can accept the source material. The scores predicted agree fairly closely with experimental data on random-word and random-syllable intelligibilities. This agreement shows that the listener need recognize no more than a single distinctive feature of each phoneme to display the recognition functions that have been observed. From a theorem of C. Shannon [Inform. and Control 1, 6–25 (1957)] relating code length and error probability, one can show that the channel capacity required for polysyllabic words is lower than the channel capacity required for monosyllabic words because the duration of correlated utterance may be taken as a code length. Evidently, contextual effects are not prominent in the intelligibility of random-word lists; the hearing process involved is primarily recognition of groups of sounds; meaning is secondary. The results also lead to the inference that a direct relation may exist between channel capacity and perceived loudness when speech is transmitted over a broad-band system, and suggest that loudness functions for impaired ears might prove to be correlated with intelligibility functions.
Auditory Sensitivity and Song Spectrum of the Common Canary (Serinus canarius)
Authors: Dooling Robert J. , Mulligan James A. , Miller James D.
Published: October 2005

The auditory sensitivity of one strain (Belgian Waterschlager) of common canary (Serinus canarius) was measured by behavioral audiometry. Four birds were trained by instrumental avoidance conditioning in a double-grille cage, and their thresholds for pure tones (0.25–9.0 kHz) were measured. Auditory sensitivity is greatest between 2.0 and 4.0 kHz with a possible maximum at 2.8 kHz, declines about 15 dB/oct for frequencies below 2.0 kHz, declines about 25 dB between 4.0 and 8.0 kHz, and 13 dB between 8.0 and 9.0 kHz. The acoustic power in the songs and calls of the Belgian Waterschlager falls primarily in the range 1.8–4.5 kHz as do the critical frequencies of a substantial proportion of the neural units in the cochlear nucleus of the canary. Thus, the auditory sensitivity and the neural machinery of the peripheral auditory system appear to be matched to the long-term-average power spectrum of the songs. In addition, these facts are compared to those for other birds and mammals, and speculations as to some of the selective pressures that influenced the evolution of hearing are presented. Certain relevant problems of the biophysics of hearing are also discussed.
Need for Standardization in the Measurement of Speech Level
Authors: Brady Paul T.
Published: October 2005

A literature survey indicates lack of standardization of a speech-level measure among published experiments. In addition, experiments reported here show that the measure most commonly used, the VU (volume unit), exhibits high variability, especially among nonexpert observers. The possibility of better measures of speech level is demonstrated by a completely objective measure based on an assumed log uniform distribution of instantaneous voltage levels. It is concluded that there is a need to reassess the general problem of speech-level measurement and to propose new approaches.
Statistical Approach to Complex Random Vibration
Authors: Zeman J. L. , Bogdanoff J. L.
Published: October 2005

A statistical approach to response prediction is a method for estimating the gross features of the response of complex structures to random excitation. A method of this type is presented and illustrated by means of two simple examples. In the first example, the mean-square velocity at a specific point of a single homogeneous beam excited by a stochastic point force is considered; in the second, the mean power flow between two homogeneous beams weakly coupled by a spring is considered when one of the two beams is excited by a stochastic point force.
Radiation Resistance of a Small Transducer at a Water Surface near an Oblique Plane Boundary
Authors: Lam Clement Y. , Stumpf F. B.
Published: October 2005

The measured values for the radiation resistance of a small sonar transducer at an air-water surface near an oblique plane brass boundary are presented and compared with the theoretical values calculated from a dipole-image model.
A Comment on Time Variability of Mechanical Impedance Data for a Cylindrical Shell Immersed in Two Anechoic Tanks
Authors: Pallett David S.
Published: October 2005

The radial mechanical driving point impedance for a submerged aluminum shell structure has been studied in two anechoic tanks. One of these tanks is lined with concrete and wood chip (Insulkrete) wedges, while the other is lined with a perforated sound-absorbent coating (SAPER-T). It has been found that the mechanical impedance values obtained in the wedge-lined tank vary with time following immersion, whereas the values obtained in the other tank have a high degree of repeatability. It is postulated that the time dependence is a consequence of a chemical reaction between the aluminum shell and the highly alkaline solution contained within the wedge-lined tank, because of the generation of minute gas bubbles.
Reply to “Comments on ‘Zero-Crossing Shifts as a Detection Method’” [S. RITER AND P. BOATRIGHT, J. Acoust. Soc. Amer. 50, 1036(L) (1971)]
Authors: Bom N. , Conolly B. W.
Published: October 2005

The background of our assumption, that (for practical purposes) the zero-crossing rate can be taken as normally distributed, is explained in more detail. It is also stated that no proof of this proposition has been given in the paper.
Reflection and Refraction Coefficients at a Fluid-Solid Interface
Authors: Mott G.
Published: October 2005

For an infinite plane elastic wave which strikes the plane interface separating two semiinfinite isotropic media, the calculation of the complex reflection coefficient, R*, for varying angles of incidence, θ, is not difficult. In the past, calculations have been made for a number of lossless media and, consequently, an important facet of the R*−θ curve for real materials has been overlooked. The total reflection, |R*|=1, which occurs at the longitudinal- and shear-wave critical angles is well known, but the appearance of a minimum (sometimes a zero) in R* is not and its existence defines a third critical angle, sometimes inappropriately called the Rayleigh-wave angle, at which a wave with large surface components is generated. During experiments with beams of acoustic waves, there is an apparent lateral displacement of the reflected beam at the third critical angle which manifests itself markedly only when there is a near-zero in |R*|. Notwithstanding the calculations of Schoch [Ergeb. Exakt. Naturw. 23, 127–234 (1950)] and the experimental measurements of others apparently to the contrary, it is strongly suggested that no actual lateral displacement occurs and that re-radiation from the region outside that ensonified by the incident beam gives rise to the apparent lateral displacement. Some outcomes of the investigation are discussed and of these the more important are: (1) Rayleigh and other interface and surface waves in real media are degenerate; (2) no interface wave can exist independently at the junction of two nonideal media; (3) Huyghens's principle in its elementary secondary-wavelet form does not apply to lossy media; (4) the usefulness of the sensitivity of R* to minute changes in elastic parameters at the Rayleigh angle as a measuring tool has a wide application; (5) elliptical polarization of both shear and longitudinal waves can occur, owing to boundary influences in lossy refracting media. The real part of the propagation vector lies in the plane of the ellipse.
Velocity Dispersion of Rayleigh Waves Propagating along Rough Surfaces
Authors: Sinclair R.
Published: October 2005

The frequency dependence of the velocity of Rayleigh waves propagating along rough surfaces is examined from the viewpoint of the mass loading of a smooth surface. Predicted values are given for examples of idealized surfaces on a solid of Poisson's ratio 0.29.
Forced Vibration of Internally Damped Circular and Annular Plates with Clamped Boundaries
Authors: Snowdown J. C.
Published: October 2005

Closed-form expressions are presented for the driving-point impedance, transfer impedance, and force transmissibility of circular and annular plates with clamped boundaries. The plates are internally damped and are driven either by a sinusoidally varying central point force or by one or more concentric ring forces of variable radii. The circular plates are mass loaded or elastically restrained at their midpoints, or are loaded by an ideally rigid annular mass (rib) of arbitrary radius. Computed results illustrating the frequency dependence of impedance and transmissibility are described and their physical significance is discussed. Added mass is very effective in increasing plate impedance levels and in blocking force transmission to the plate boundaries, particularly when the mass is positioned directly beneath the driving force.
Equations of Elastic Motion of an Isotropic Medium in the Presence of Body Forces and Static Stresses
Authors: Mott G.
Published: October 2005

By taking account of second-order coupling between stress and strain, modified equations of elastic motion have been derived which include the effects of static surface forces and body forces upon the propagation of elastic waves in isotropic materials. Anisotropy of the kind found in hexagonal crystals is shown to occur when an isotropic substance is acted upon by a uniaxial static stress. A brief discussion of some inferences to be drawn from these results is given.
Longitudinal and Shear Magnetoelastic Behavior of Metals
Authors: Goodrich G. W. , Lange J. N.
Published: October 2005

The magnetic-field dependence of the complex Young's and shear moduli are determined for a variety of nonferromagnetic metals. An experimental technique using capacitive excitation of torsional and longitudinal modes in low-loss systems is described and the criterion for frequency resolution is discussed. Contributions to the magnetic-field dependence of the elasticity due to the charge carriers and dislocations are considered.
Surface-Wave Propagation over an Elastic Cosserat Half-Space
Authors: Koebke R. H. , Weitsman Y.
Published: October 2005

The equations describing an elastic isotropic Cosserat continuum are presented. Solutions of these equations for the various modes of plane harmonic waves in an infinite medium are briefly discussed. The analysis then concentrates on the development and interpretation of the surface-wave solution for straight crested waves on a Cosserat half-space. It is found that a wave analogous to the Rayleigh wave of the classical elasticity theory exists, except that it is a dispersive wave in this theory. The phase velocity of the surface wave may either increase or decrease with frequency, depending on the relative magnitude of the micromaterial moduli.
Early-Time Interaction of Spherical Acoustic Waves and a Cylindrical Elastic Shell
Authors: Huang H. , Wang Y. F.
Published: October 2005

The three-dimensional transient interaction of spherical acoustic waves with a cylindrical elastic shell is investigated using the concept of fictitious Riemann surface. Integral transform techniques are used. The transform double integrals with respect to the two shell coordinates are evaluated asymptotically by the method of “critical points.” Simple expressions for the early-time responses of the shell and the scattered wave are obtained. The results of this investigation show that the effects of the curvature of the incident wave are quite significant with respect to the bending moments of the shell.
Propagation of Acoustic Waves in a Turbulent Medium
Authors: Wenzel Alan R. , Keller Joseph B.
Published: October 2005

A theoretical analysis of the propagation of the coherent, or average, acoustic wave in a turbulent medium is presented. The analysis is based on the smoothing method developed by Keller and others. The dispersion equation is derived for a statistically homogeneous medium for three special cases: waves in a fluid at rest with density and temperature fluctuations, high-frequency waves in a fluid in turbulent motion, and waves in an isentropic irrotational turbulent flow. This equation is solved approximately for the propagation constant of high- and low-frequency waves by assuming that the medium is statistically isotropic. From the propagation constant, the propagation speed and attenuation coefficient are obtained. The results indicate that generally the propagation speed of the coherent wave is less than the average sound speed of the medium. The results also indicate a similarity between the effect of turbulent velocity fluctuations and the effect of inhomogeneities the thermodynamic properties of the medium on the attenuation of high-frequency waves, whereas there is apparently a fundamental difference between the effect of velocity fluctuations and the effect of thermodynamic inhomogeneities on the attenuation of low-frequency waves.
Acoustic Waves Transmitted through Solid Elastic Cylinders
Authors: Brill Donald , Überall H.
Published: October 2005

The acoustic field of a plane wave incident on an elastic cylinder may be decomposed into two parts, one representing circumferential waves that propagate around the cylinder, the other part obeying in the high-frequency limit the laws of geometrical optics. The latter part is studied in this paper, and is decomposed into the specularly reflected wave and into a series of transmitted waves which traverse the cylinder either directly along a secant, or undergo additional internal reflections with and without mode convention (compressional to shear type, or vice versa). Wavefront loci and amplitudes of these waves are calculated using the saddle-point method, and the corresponding reflection and transmission coefficients are shown to reduce, for the case of a large cylinder, to the known expressions for a flat elastic half-space in contact with a liquid.
Volume Backscattering in the South China Sea and the Indian Ocean
Authors: Hall M.
Published: October 2005

Volume backscattering strengths averaged over four depth intervals and at the frequencies 3.5, 6, 8, and 12 kHz were measured at a number of stations in the South China Sea and the eastern region of the equatorial Indian Ocean. Measured values ranged from −91 dB re m−1, which occurred at 3.5 kHz, to −61 dB re m−1, which occurred at 8 kHz. On the average, the scattering was a maximum in the depth interval 0<z<500 m at 3.5, 6, and 8 kHz; but at 12 kHz, the maximum was usually in the interval 350<z<500 m. At one station, a deep scattering layer with a resonant frequency of 3.5 kHz was observed at a depth of 1700 m. In the Indian Ocean, negative correlations existed between the scattering at 8 kHz and the water temperature at a depth of 100 m. It is shown that the conventional sonar equation for volume reverberation is applicable to resonant scattering as well as nonresonant scattering and that it is necessary for the acoustic source to be at a finite depth.
Wood's Refraction Correction Equations for a Constant-Gradient Medium: An Alternate Derivation
Authors: Raphael David T.
Published: October 2005

Closed-form solutions have been developed by Wood [J. Acoust. Soc. Amer. 47, 1448–1452 (1970)] for the exact computation of the true distance d and direction θi of a sound source relative to the observer in an unbounded constant-gradient medium. Wood's solutions are given in terms of the sound speed c at the receiver depth, the apparent direction θ0, the one-way travel time t, and the positive gradient g. All of these quantities are measurable at the receiving point. Wood makes use of the Pekeris triangle formulas to arrive at these solutions; however, it is of interest to know whether and how the refraction correction equations can be derived from the conventional ray propagation and time equations in a constant-gradient medium. Such an alternate derivation is presented in this article. Also, a few applications illustrating the utility of Wood's solutions are presented.
The Transient Response of Arrays of Transducers
Authors: Stepanishen P. R.
Published: October 2005

A general approach is developed to compute the time-dependent velocities of transducers within an array resulting from a set of prescribed electrical inputs. It is noted that the effect of the dynamic response of a transducer of any complexity and the effect of the time-dependent mutual interactions are included within the approach which is based on a Green's function solution to an initial boundary value problem. The solution of the initial boundary value problem is reduced to a set of time-domain-coupled convolution integral equations which can be easily solved on a digital computer. In addition to presenting a clear physical understanding of the transient behavior of arrays, the approach leads to a more basic understanding of array operation and limitations caused by its transient response. Specific application of the approach to the analysis of planar arrays mounted in rigid baffles is discussed and related to earlier work. Finally, a simple numerical example is presented to verify the approach and offer insight into the behavior of coupled systems exhibiting array-type characteristics.
A Continuous-Gradient Curve-Fitting Technique for Acoustic-Ray Analysis
Authors: Weinberg Henry
Published: October 2005

A method of computing acoustic-ray paths is developed. The velocity of sound is approximated by a function of depth that has a continuous gradient and allows one to evaluate the range and travel time integrals in closed form. The advantages of this technique over others are discussed, and some interesting phase effects are illustrated.
Estimation of Wall-Pressure Fluctuations in a Separated Flow
Authors: Fricke F. R. , Stevenson D. C.
Published: October 2005

Wall-pressure fluctuations are estimated from the flow properties in the shear layer of a separated region, using a modified form of Kraichnan's mean-shear-turbulence interaction equation. Experimental and calculated values of the rms wall pressure are presented as well as pressure-correlation measurements and flow properties in a separated flow behind a thin fence mounted normal to the flow boundary.
Null Detection with the Impedance Bridge
Authors: Engelberg Marvin
Published: October 2005

The reliability of two methods in detecting the acoustic null with the Zwislocki bridge using trained listeners was investigated. One method consisted of the subjects listening directly from the bridge with a stethoscopic headset. The other method consisted of the signal being amplified and then detected by an oscilloscope readout and listening combined. There were no significant differences between methods even though the subjects preferred the direct listening method.
Jet-Noise Reduction through Liquid-Base Foam Injection
Authors: Manson Lidia , Burge H. L.
Published: October 2005

An experimental investigation has been made of the sound-absorbing properties of liquid-base foams and of their ability to reduce jet noise. Protein, detergent, and polymer foaming agents were used in water solutions. A method of foam generation was developed to permit systematic variation of the foam density. The investigation included measurements of sound-absorption coefficients for both plane normal incidence waves and diffuse sound fields. The intrinsic acoustic properties of foam, e.g., the characteristic impedance and the propagation constant, were also determined. The sound emitted by a 1-in.-diam cold nitrogen jet was measured for subsonic (300 m/sec) and supersonic (422 m/sec) jets, with and without foam injection. Noise reductions up to 10 PNdB were measured.
Sound Propagation and Absorption in Foam: A Distributed Parameter Model
Authors: Manson Lidia , Lieberman Seymour
Published: October 2005

Liquid-base foams are highly effective sound absorbers. A better understanding of the mechanisms of sound absorption in foams was sought by exploration of a mathematical model of bubble pulsation and coupling and the development of a distributed-parameter mechanical analog. A solution by electric-circuit analogy was thus obtained and transmission-line theory was used to relate the physical properties of the foams to the characteristic impedance and propagation constants of the analog transmission line. Comparison of measured physical properties of the foam with values obtained from measured acoustic impedance and propagation constants and the transmission-line theory showed good agreement. We may therefore conclude that the sound propagation and absorption mechanisms in foam are accurately described by the resonant response of individual bubbles coupled to neighboring bubbles.