bluuebunny/crossref_metadata_2025 huggingface dataset:
The collective acoustic properties of water containing resonating air bubbles, and its effect on the propagation of sound
Authors: Feuillade C.
Published: October 2005

The classic theory of sound propagation in bubbly water incorrectly describes the properties of dense media containing resonating bubbles of uniform size. It assumes that the bubbles oscillate independently. However, resonating bubbles are strongly coupled by acoustic radiation, and acoustic propagation can be fully explained only in terms of the collective action of the medium, which is dominated by the ‘‘symmetric’’ normal mode. In this work, the propagational characteristics of bubbly water are determined by averaging the ensemble behavior of the symmetric mode over distributions of bubble sizes and locations. All orders of multiple scattering are included, and ‘‘shadowing’’ effects incorporated. New theoretical expressions for the phase speed and attenuation are presented. Comparisons between theory and experimental data are made by integrating multiple scattering effects over a ‘‘region of collective interaction’’ around the bubbles. For uniformly size bubbles, a downward frequency shift and suppression of the attenuation peak is observed, which is more pronounced for higher volume fractions. The phase speed is also modified. In water containing many differently sized bubbles, multiple scattering typically plays a much smaller role in determining acoustic properties, and the classic theory of propagation is adequate.
A discussion of the low-frequency resonance scattering of a bubble cloud
Authors: Hwang Paul A.
Published: October 2005

A comparison of four different formulas to compute the lowest mode resonance frequency of a bubble cloud is provided in this presentation. Based on the comparison, it is concluded that only one of the four equations represents the generalized solution, which includes air bubbles as its asymptotic condition, of void traction equals unity. Also shown is the numerical calculation of the scattering of a spherical bubble cloud using the classical solution of acoustic scattering of elastic spheres. With the elastic properties of the bubble cloud approximated by Wood’s formulation, it is found that isothermal conditions exist only at a very low void fraction level (less than 0.0001). Within the range of void fraction from 0.001 to 0.1, the polytropic coefficient of the bubble cloud is approximately 1.2, which is halfway between adiabatic and isothermal conditions. Finally, two simple scaling laws for the resonance characteristics of a spherical bubble cloud are presented: (1) the dimensionless resonance wave number is uniquely determined by the void fraction; and (2) the backscatter cross section at resonance is uniquely determined by the resonance frequency. [Work supported by ARPA.]
Monopole acoustic radiation by a bubble encountering a turbulent flow field
Authors: Kolaini Ali R. , Goumilevski Alexei
Published: October 2005

The acoustical characteristics of an ‘‘adult’’ bubble encountering a turbulent flow are studied both exprimentally and theoretically. By injecting an ‘‘adult’’ bubble in a flow, generated by a submerged axisymmetric water jet, the acoustic reexcitation of the bubble with and without breakup may occur in the shear-induced flow region. Bubbles of various sizes were introduced into jets of various speeds by means of interchangeable hypodermic needles. Results of the role of the turbulent flow characteristics in determining the acoustic bubble response are discussed. The characterizations of both acoustical and the dynamics of bubbles encountering the turbulent flow field depend upon the estimated integral and microlength scales, the corresponding Reynolds numbers, and the cirtical Weber numbers for both bubble distortion and breakup. These parameters are examined both in fresh and salt water. A simple model is given to account for bubble acoustic radiation. The Rayleigh–Plesset equation was altered by incorporating the turbulent pressure fluctuation of the flow as a driving force of the bubble. Some conclusions are given about the nature of the turbulent flow field and conditions under which the bubble acoustic reexcitation may occur. [Work supported by ONR.]
Scattering of sound from laboratory breaking waves
Authors: Mao Yi , Kolaini Ali R. , Hao Xinwei , Dandenault Pat B.
Published: October 2005

Computer-controlled gravity waves were generated to break in an anechoic tank. A sequence of 15 incident bursts was directed at the bubble cloud entrained by each breaking wave. A burst has seven cycles of a sine wave of frequency ranging from 10 to 15 kHz. The interval between adjacent bursts is set at 0.1 s in order to avoid overlapping the bursts. By analyzing the data of the 15 sound scattering events, the fluctuation was significantly reduced. The bubble clouds were observed to be roughly semicylindrical. The bubble size distribution in an entrained cloud was obtained from video images of a bubble cloud. This experimental information of the shape, size, and bubble size distribution of a bubble cloud was employed as the input into the theory adapted from Sarkar and Prosperetti [J. Acoust. Soc. Am. 93, 3128–3138 (1993)] to estimate the theoretical scattering strength. A comparison between the experimentally measured and the theoretically estimated scattering strengths will be shown. [Work supported by ONR.]
Startle reflex in fish
Authors: Rogers Peter H. , Lewis Thomas N. , Gray Michael D.
Published: October 2005

Directional hearing in fish is a poorly understood phenomenon, whose complexity makes it difficult to analyze. The directional, Mauthner cell mediated, startle response, which does not involve the CNS, is considerably simpler and more amenable to analysis but may still provide insight into the algorithms and mechanisms for more general directional hearing tasks. The startle reflex is modeled and studied experimentally in goldfish. The basic model posits that the initial polarity of both the incident acoustic pressure and particle acceleration measured by the fish’s auditory system determines the direction of a threat, and initiates an escape reflex in the appropriate direction. The startle reflex of goldfish is observed experimentally in a large acoustic test tank at Georgia Tech. The subject is placed in the center of the tank, and its behavior is observed using a video camera. The acoustic stimulus is generated using simple spherical sources driven to provide independent control of pressure and velocity waveform, so that, for example, monopole and nearfield dipole fields could be established. A parallel effort was undertaken in order to determine a potentially relevant acoustical stimulus, the field generated by an attacking fish. [Work supported by ONR.]
Acoustic stunning of marine animals
Authors: Hastings Mardi C.
Published: October 2005

Acoustic stunning, a complete physiological shutdown of bodily functions, occurs in some marine animals when exposed to intense sound for a short period of time. Anecdotal evidence of acoustic stunning has been reported in the literature [G. E. MacGinitie and N. MacGinitie, NaturalHistoryofMarineAnimals (McGraw–Hill, New York, 1968); K. S. Norris and B. Mohl, Am. Naturalist 122, 85–104 (1983)], but the physiological mechanisms and threshold values associated with this phenomenon have not been studied. Acoustic stunning of gouramis (Trichogastertrichopterus) was observed in the laboratory when they were exposed to intense pure tones underwater; however, oscars (Atronotusocellatus) and goldfish (Carassiusauratus) exposed to similar tones were not acoustically stunned. This paper examines the characteristics of the sound field that caused the transient stunning. In addition, differences in body size and geometry as well as in structure of the ear and lateral line among the three species are examined in an effort to explain why only the gourami was affected.
Active/passive technique for the creation of a low-frequency traveling wave inside a water-filled tube
Authors: Finneran James J. , Hastings Mardi C.
Published: October 2005

Studies of sound reception in aquatic animals are often complicated by the problem of generating a suitable acoustic stimulus at low frequencies underwater. In this study, active and passive control techniques were used to generate a traveling acoustic wave inside a water-filled acrylic tube, at pure-tone frequencies from 10 to 800 Hz. The compliant walls of the tube reduced the wavelength and increased attenuation, both of which helped to reduce the amplitude of any reflected waves. Above 400 Hz, a traveling wave was present without any active control. Below 400 Hz, a secondary source was used to actively absorb sound at the tube end. The active control system consisted of two hydrophones, two sound projectors, and a personal computer with digital signal processing hardware. A simple pattern search algorithm was used to adjust the secondary source amplitude and phase in order to attain the desired acoustic impedance at the test location. This technique seems well suited for underwater sound tests on fish, since the relationship between pressure and particle velocity may be easily manipulated. [Work supported by ONR Grant No. N00014-94-1-0337.]
Theoretical modeling of the acoustic pressure field produced by commercial lithotripters
Authors: Averkiou Michalakis A. , Crum Lawrence A. , Hamilton Mark F.
Published: October 2005

A theoretical model for the acoustic field produced by commercial lithotripters based on the KZK equation is presented. The KZK equation has been used previously to model high-intensity sound beams in thermoviscous fluids. Both electrohydraulic and piezoelectric lithotripters are considered. To model the acoustic field reflected from ellipsoidal reflectors found in electrohydraulic litho- tripters, geometrical acoustics are used to define a directivity function at the mouth of the reflector. An equivalent focused source with a shading function defined by the directivity function is then assumed as the boundary condition for the KZK equation. A code that solves this equation entirely in the time domain is used to obtain results for the acoustic pressure. The numerical results are compared with previous experiments [Coleman etal., Ultrasound Med. Biol. 13(10), 651–657 (1987)] and good agreement is found. Results for propagation in both water and tissue are presented. Positive pressures of 40–100 MPa and negative pressures of 4–10 MPa are predicted in the focal region. A reflector with a pressure release surface is also considered. In this case the field close to the source is an inverted replica of that of the rigid reflector. However, strong distortion due to nonlinearity affects the rest of field. Negative pressures of 20–30 MPa are predicted in the focal region for this type of reflector. [Work supported by NIH.]
A review of current research on optical techniques for acoustic measurements in lithotripsy
Authors: Coleman Andrew J. , Galloway Peter C. M.
Published: October 2005

This paper reviews some recent research on optical techniques for acoustic pressure measurement along with initial results obtained in the field of a newly developed electromagnetic-type shock wave source. A long-path-difference Michelson interferometer enables direct determination of the Doppler shift from a target to evaluate particle velocity in water in the range 1–100 ms−1. The instrument operates as a high-resolution spectroscope with a 532-nm wavelength laser source and a remote optical-head utilizing fiber links. The aim is to establish measurement standards in lithotripsy where conventional hydrophone-based procedures are inadequate. A second optical fiber ultrasound sensor, orginally developed for the measurement of photoacoustic transients in tissue, is also described [P. C. Beard and T. N. Mills, Proc. SPIE 2388, 446–457 (1995)]. This sensor employs a Fabry–Perot interferometer comprising a 50-μm polymer film acoustically matched to water which is illuminated with light emerging from the fiber. An electromagnetic shock wave source developed recently by the Medical Physics Directorate (Guy’s and St. Thomas’ Hospital, London) has been used to compare measurements from the two interferometer systems with conventional hydrophone measurements.
Stress wave fracturing of biological stones with lithotripter pulses
Authors: Gracewski Sheryl M. , Dahake Girish , Fitzgerald Adam , Burns Stephen J.
Published: October 2005

Stress waves contributions to stone fragmentation during lithotripsy are investigated both theoretically and experimentally. A two-dimensional finite difference scheme is developed to analyze the time evolution of the strain fields inside irregularly shaped solids subjected to ultrasonic pulses that simulate lithotripter shock waves. The reflections and superposition of stress waves inside the stones are analyzed to better understand the effects of stone parameters and geometry on the induced internal strains and fragmentation during lithotripsy. Numerical results show the focusing effect of the concave backsurface of a spherical stone, with the subsequent formation of focal zones (caustics). The focusing is reduced when a section of the back surface of the stone is removed. Principal strain contours depict the time evolution of the stress waves as they refract and reflect at the stone boundaries. Locations of maximum stresses are calculated and compared to locations of crack initiation in experiments with stones of similar geometry. The calculated time evolution of strain at fixed points within a stone is compared to imbedded silicon strain gauge measurements. Fracture characteristics of synthetic stones show internal crack initiation and subsequent propagation to external stone surfaces, indicative of internal stress fragmentation mechanisms. [Work supported by NIH.]
The dependence of ocean acoustic parameter resolution bounds on sample size
Authors: Makris Nicholas C.
Published: October 2005

It is currently common practice in theoretical ocean acoustics to derive ‘‘fundamental’’ parameter resolution bounds for a monochromatic measurement of the temporally fluctuating field received on a hydrophone array. However, a monochromatic measurement corresponds to a single random sample. In applied ocean acoustics, single samples are seldom if ever used for parameter estimation because the associated error can be unnecessarily large. Instead estimates are derived from ensemble averages such as the sample covariance. To bridge the gap between these two approaches, the Fisher information for the sample covariance is examined and found to be equal to the number of independent and stationary samples times the Fisher information for a single sample. Therefore, therearenopracticallimitsonparameterresolution if (1) the bound for a single sample is finite, which is generally the case of interest, (2) a sufficiently large population of independent samples can be found. The parameter resolution issue then becomes one of determining the maximum number of such samples. This number is set by physical variables that do not appear in the monochromatic or instantaneous measurement. A means of determining this number from the temporal coherence of the received field and the measurement time is given.
Coherent wideband matched-field processing in an uncertain environment
Authors: Czenszak Stephen P. , Krolik Jeffrey L.
Published: October 2005

Broadband matched-field processing approaches have centered around incoherent averaging of narrow-band MFP ambiguity surfaces. This technique works well when environmental mismatch results in a frequency-independent shift in the source position. This appears to be true for mismatch in the bottom parameters when the sound speed is constant in the lower half of the water column. In the presence of more general sound-speed profiles, the performance of incoherent averaging techniques is significantly degraded. In this paper, coherent wideband matched-field processing is proposed to exploit statistical dependencies between the signal wavefronts at different frequencies for more general settings. The fourth-order statistics of the data are used to exploit these cross-frequency dependencies. For Gaussian data this fourth-order moment can be expressed in terms of the narrow-band second-order data cross-spectral density matrices. The coherent wideband MV-EPC processor consists of minimizing the squared output power of the beamformer subject to a set of constraints designed to provide robustness over an ensemble of random environmental realizations. In the presence of sound-speed mismatch this processor is shown to yield improved probability of correct localization performance versus incoherently averaged wideband matched-field processors. [Work supported by ONR.]
Experimental demonstration of environmental source tracking
Authors: Fialkowski Laurie T. , Perkins John S. , Collins Michael D. , Kuperman W. A. , Fawcett John A.
Published: October 2005

Environmental source tracking (EST) is a matched-field processing (MFP) technique that exploits source motion in a complex environment [Collins etal., J. Acoust. Soc. Am. 94, 3335–3341 (1993)]. EST involves searching for a source track which provides the best agreement with the data. EST performed using a single receiver and a single frequency can often outperform conventional MFP methods with a fixed source and an array of receivers. In this paper EST performance is discussed, using a data set obtained in shallow water north of Darwin, Australia. In-situ acoustic data from a known source were used to invert for the environmental parameters. Parabolic equation solutions were then used to generate replica fields throughout the region. EST was performed for both radial and nonradial source tracks. In some instances, the source speed was reasonably constrained to eliminate very short tracks from the search space. The performance of several error measures is discussed. Improved EST results were obtained using multiple receivers and frequencies.
Saturated ocean acoustic intensity statistics as a function of temporal coherence and measurement time
Authors: Makris Nicholas C.
Published: October 2005

Coherence theory is used to analyze the statistics of saturated ocean acoustic intensity measurements. The circular complex Gaussian random field assumption has been used to describe saturated multipath propagation in the ocean for many years. However, previous analysis of intensity statistics in the saturated region have implicity been limited to certain special cases for which the time-bandwidth product of the field measured from a given source is unity. In this paper, the intensity statistics in the saturated region are extended and generalized to be a function of measurement time and temporal coherence. As a result, the well-known 5.6-dB transmission loss (TL) standard deviation of Dyer is found to be a special case of a more general TL standard deviation that approximates 4.34√1/μ dB when the time-bandwidth product or number of independent samples μ of the intensity average is large. Therefore, the TL standard deviation is shown to approach zero when the time-bandwidth product becomes large, as it must in this deterministic limit. A similar generalization is obtained for the TL mean. Additionally, asymptotic analysis shows that the log-normal distribution for intensity can provide an excellent approximation to TL statistics, contrary to previous contentions.
Broadband model-based processing for shallow ocean environments
Authors: Candy James V. , Sullivan Edmund J.
Published: October 2005

Most acoustic sources found in the ocean environment are spatially complex and broadband. When propagating in a shallow ocean these source characteristics complicate the analysis of received acoustic data considerably. On the other hand, each of the narrow-band lines composing the broadband source spectrum can be considered multiple observations which can be used to enhance signal levels. The usual approach is to process each line separately and combine the results to achieve more enhancement at the array than that which could be utilized for a single temporal frequency. The enhancement of broadband acoustic pressure-field measurements using a vertical array is discussed. Here the model-based approach is developed for a broadband source using a normal mode propagation model. It is well known from propagation theroy that a different modal structure evolves for each temporal frequency line; thus it is not surprising that the model-based solution to this problem results in a scheme that requires a ‘‘bank’’ of model-based processors—each processing its own underlying modal structure for the narrow frequency band it operates over. It is shown how this broadband processor can be implemented in pseudo-real-time due to its underlying parallel structure.
Prediction of mismatch dependence and source depth dependence of mismatch-induced peak broadening in matched-field processing
Authors: Smith George B. , Gardner Nichalos D.
Published: October 2005

In previous work [Smith and Akundi, J. Acoust. Soc. Am. 95, 2980(A) (1994); Smith, Akundi, and Gardner, J. Acoust. Soc. Am. 97, 3292(A) (1995)] analytic expressions for mismatch-induced range and depth localization error and signal gain degradation for a linear correlator matched-field processor were obtained. Those results agreed with previously obtained results [Shang and Wang, J. Acoust. Soc. Am. 89, 2285–2290 (1991)]. In this work the problems of mismatch-induced peak broadening and the mismatch dependence and the source depth dependence of this peak broadening are addressed. Computer simulations are compared to predictions based on the hypothesis that the peak broadening in range and in depth are related to the variances of the distributions of the range shifts and depth shifts, respectively, predicted by the mode pairs. [This work was supported by the Office of Naval Research and by the Mississippi Alliance for Minority Participation (MAMP) program.]
Effects of signal frequency and ear of input on ICP-determined loudness adaptation
Authors: Tannen Robert S. , Weiler Ernest M. , Warm Joel S. , Dember William N.
Published: October 2005

The ipsilateral comparison paradigm (ICP) uses a monaurally presented base tone punctuated by referent tones of greater or less intensity to reveal magnitude-estimated loudness adaptation. Research with this technique has demonstrated adaptation across a broad spectrum of base-tone intensities [Dange etal., J. Gen. Psychol. 120, 217–274 (1993)]. Given evidence for different coding mechanisms at high and low signal frequencies and ear differences in adaptation [Ivry and Libby, Psychol. Sci. 4, 41–45 (1993); Davis and Weiler, Br. J. Audiol. 12, 59–60 (1978)], the present study examined the generality of ICP-determined loudness adaptation for the two ears at frequencies of 250, 1000, and 4000 Hz. Base tone intensity in all conditions was 50 dBA. Three referent conditions (+10 dB referent, −10 dB referent, and a no referent control) were also employed. The generality of ICP-determined adaptation was demonstrated by similar declines in loudness over time in all ear/frequency combinations when referent tones were present. Adaptation effects were noted for the base and for the referent tones. In addition, adaptation was stronger for the base tone in comparison to the +10 dB referent and for the −10 dB referent in comparison to the base, a result consistent with Hood’s model of loudness adaptation [Weiler and Hood, Audiology 16, 499–506 (1977)].
Loudness-data basis for ‘‘FIG6’’ hearing-aid fitting targets
Authors: Killion Mead C.
Published: October 2005

Loudness data from Pascoe (1988), Hellman etal. (1991), Lippman (1981) and Lyregaard (1988) provide the basis for a hearing-threshold-based set of three frequency-response fitting targets: one each for 40, 65, and 90 dB SPL inputs. Although individual loudness measurements obtained using either the automated LGOB or LGCM loudness-growth tests generally agree with average data, Niemeyer’s (1971) report that subjects with prolonged exposure to intense noise may have loudness discomfort levels elevated by 30 dB or more suggests caution in applying FIG6 to someone who has been wearing powerful linear hearing aids.
Control strategies for neurons modeled by self-exciting point processes
Authors: Irlicht Laurence S. , Clark Graeme M.
Published: October 2005

Experiments demonstrate that electric stimulation of the auditory nerve evokes responses, which are qualitatively different to those of normal hearing. A self-exciting point process model of the neural response is applied to explain and predict responses for both situations. For acoustic stimulation, the model predicts the initial responses to a tone, average firing rate, maximum firing rate, and the shape of the per-stimulus time histogram. The model also predicts the neural response to pulsatile electric stimulation. For applications such as cochlear implants, it would be beneficial if the acoustic and electric responses were more similar. The model is used to parametrize the response differences in each case and based on these parameters to design electrical stimuli, which cause a neuron to respond similarly to the normal hearing situation. Such stimuli should find application in advanced cochlear implants.
Benchmarking the Kirchhoff approximation for specular scatter from a finite length cylindrical scatterer
Authors: LePage Kevin D.
Published: October 2005

Recent work at BBN has been directed toward understanding and parametrizing the low- to mid-frequency, broadband scattered signature of submarines in terms of a small set of physical mechanisms. These mechanisms include parametrized dispersion curves, end-cap reflection coefficients, and end-cap radiation and excitation coefficients. Here, the Kirchhoff approximation is applied to model the early time portion of the backscattered signal. Two issues present themselves with this approach: (1) What is the correct frequency-dependent background impedance of the hull; and (2) for what frequencies and range of bistatic angles does the Kirchhoff approximation provide adequate performance. Here, the later issue is addressed by benchmarking the approximate results against consistent SARA calculations for a locally reacting finite length body of revolution. [Work supported by ONR.]
Scattering of a narrow acoustic beam by a truncated fluid-filled cylindrical shell
Authors: Dodd Stirling S. , Loeffler Charles M. , Griffy Thomas A.
Published: October 2005

Previously a method of describing spherical acoustic waves in cylindrical coordinates was applied to the problem of point source scattering by an elastic infinite fluid-filled cylindrical shell [S. Dodd and C. Loeffler, J. Acoust. Soc. Am. 97, 3284 (A) (1995)]. This method is applied to numerically model monostatic oblique incidence scattering from a truncated cylinder by a narrow-beam high-frequency imaging sonar. The narrow-beam solution results from integrating the point source solution over the spatial extent of a line source and line receiver in the frequency domain. The cylinder truncation is treated by the method of images, and assumes that the reflection coefficient at the truncation is unity. The scattering form functions, calculated using this method, are applied as filters to a narrow bandwidth, high ka pulse to find the time domain scattering response. The time domain pulses are further processed and displayed in the form of a sonar image. These images compare favorably to experimentally obtained images [G. Kaduchak and C. Loeffler, J. Acoust. Soc. Am. 97, 3289 (A) (1995)]. The impact of the s0 and a0 Lamb waves are vividly apparent in the images.
The effect of ribs on the scattering response of a ribbed finite elastic cylinder
Authors: Sarkissian Angie
Published: October 2005

The scattered field is examined from a finite cylindrical shell with ribs for 2.5<ka<25, where k is the wave number and a is the radius of the cylinder. The cylinder contains ribs of two different sizes. Results for the monostatic, forward, and bistatic geometries will be shown where the interaction of the elastic waves with ribs produce extrema in the frequency/angle domain. The rib spacing contains two types of periodicity. The first is representative of the spacing between any two ribs while the second is representative of the spacing between any two long ribs. This gives rise to two types of Bragg diffraction effects produced by the interaction of the acoustic field with the ribs.
Acoustic scattering from a hemicapped cylindrical shell with substructures
Authors: Zhang Weiping , Igusa Takeru , Achenbach Jan D.
Published: October 2005

This paper extends the study on acoustic radiation of axisymmetric submerged shells of finite length to the scattering problem. A modal-based method is developed to determine the scattering from finite shells insounified by plane incident waves. A surface variational principle provides the acoustic impedance relationship between the surface pressure and displacement fields, which are expanded into a series of shape functions. Lagrange multipliers are introduced in a Lagrange formulation of the dynamic analysis to account for the interaction between the shell and internal substructures. Surface and far-field pressures scattered from the elastic shell are calculated. It is found that, at certain angles, the scattered pressure field has pronounced peaks, particularly as the incident frequency increases. A wave number domain analysis is performed on the surface displacement field. A dominant wave number is found which accounts for the high directivity pattern of the far field. The effect of substructures on the far field is also investigated.
A unique boundary integral approach for acoustic radiation of axisymmetric bodies with arbitrary boundary conditions
Authors: Wang W. , Atalla N. , Nicolas J.
Published: October 2005

A boundary integral method for solving the exterior acoustic radiation problem of axisymmetric bodies with arbitrary boundary conditions has been developed. The new formulation derives from the method proposed by Burton and Miller, which uses a linear combination of the Helmholtz integral equation and its normal derivative to ensure the uniqueness of the numerical solution at all frequencies. By taking advantage of the properties of axisymmetric geometry, and using the expansion of the boundary conditions and the surface distribution functions in Fourier series with respect to the angle of revolution, the surface integral is reduced to a line integral along the generator of the body, and Fourier integrals of the Green’s function and its derivatives over the circumferential angle. A main feature of this formulation is that new recurrence formulas of the Fourier coefficients have been developed to evaluate accurately the Fourier integrals with the singular kernels in terms of the complete elliptic integrals. In order to demonstrate the validity and accuracy of the method, numerical results with quadratic isoparametric curvilinear elements are presented for radiation problems of a pulsating sphere, an oscillating sphere, and a finite cylinder with various boundary conditions.
Radiation of sound by a point-excited free-flooded cylindrical shell of finite length
Authors: Kim K. Steven
Published: October 2005

Radiated acoustic pressure is obtained when a free-flooded cylindrical shell of finite length is excited by a time-harmonic point force. Integral equations are formulated for an elastic thin shell with simply supported boundary condition at both ends. Near-field and far-field acoustic pressures are calculated and cases of a short shell and a long shell are discussed.
Interior noise of an aircraft fuselage: Dynamics and structural acoustics with experimentation
Authors: Herdic Peter C. , Houston Brian H. , Williams Earl C.
Published: October 2005

The area of interior noise is of growing interest to the aircraft industry due to recent trends associated with increasing passenger comfort. In an effort to understand the physics of the problem, highly spatially sampled surface motion and interior acoustic measurements of a business jet fuselage section under point excitation were made over a band from 10 to 1000 Hz. Both the cylindrical shell and endcaps were measured using laser Doppler vibrometry and the associated coupling of these structural modes to interior pressure levels is observed and discussed. Superimposed on this interior response are the normal cavity modes of the interior which set up due to the quasirigid boundaries. Localization of the fulselage vibrations with the associated passbands and stop bands are found due to the pseudo- periodic nature of the internal structure of the fulselage. These structural acoustic attributes may be exploited to reduce the interior acoustic levels. a)Also at Sachs/Freeman Associates, Inc., 1401 McCormick Dr., Landover, MD 20785.
Direct global stiffness matrix method for thin cylindrical shell dynamics
Authors: Hayner Mark A. , Fricke J. Robert
Published: October 2005

This paper introduces the direct global stiffness matrix (DGSM) method for analyzing the dynamics of cylindrical shells with axial symmetry. The dynamic stiffness matrix of a straight, circular cross-section cylindrical element is formulated in terms of ring forces and displacements at each end on a per circumferential mode basis. The stiffness matrix is based on an exact wave-type solution of the thin shell Donnell equations. More complicated shell systems are analyzed by assembling any number of cylindrical elements. For example, a cylinder with a gradual variation in radius may be modeled by a series of shell elements welded together at their ends. Total system dynamics are found at any given frequency by inverting the global system matrix formed from the individual stiffness element matrices and summing over circumferential mode number. Results for a test case are presented to demonstrate and verify the implementation. [Research sponsored by ONR.]
Power flow between circular cylindrical shells and flat plates
Authors: Willis Benjamin F. , Burroughs Courtney B.
Published: October 2005

An analytic model for the transmission of power between circular cylindrical shells and flat plates attached along a circumference of the shell is developed. The model includes transverse displacements associated with bending waves and in-plane displacements associated with longitudinal and shear waves. Plates internal and external to both semi-infinite and infinite shells are modeled. Examples of power transmission coefficients for different incident wave types in the plate, circumferential mode numbers and frequencies are presented and discussed.
Active control of vibration transmission in a cylindrical shell
Authors: Pan Xia , Hansen Colin H.
Published: October 2005

Active control of vibratory power transmission in a semi-infinite cylinder, using a circumferential array of control forces and a circumferential array of error sensors, is investigated experimentally and theoretically. The model considered is a semi-infinite cylinder, free at one end, anechoically terminated at the other end, and excited by an array of in-phase primary forces arranged in a line around its circumference. Control is achieved by an array of independent control forces applied downstream from the primary forces. For three or more control forces it is possible to achieve levels of power transmission reduction in excess of 30 dB for both acceleration and power transmission cost functions, provided that the error sensors are in the far field of the primary and control forces. The study also demonstrates how it is possible to simplify power transmission measurement methods for a realistic control force configuration.
Driving a self-oscillating vocal fold model with laryngeal muscle activations
Authors: Titze Ingo R.
Published: October 2005

A self-oscillating model of the vocal folds (with arbitrary numbers of masses in the length, thickness, and depth dimensions) is driven by inputs that closely resemble muscle activations. With this model, EMG recordings and lung pressures can be used to simulate speech. In the present version, adduction-abduction and vocal fold tensing are probed to demonstrate the dynamics of laryngeal posturing and the corresponding phonation regimes.
Bifurcations in excised larynx experiments
Authors: Berry David A. , Titze Ingo R. , Story Brad H. , Herzel Hanspeter
Published: October 2005

Bifurcation analysis is applied to vocal fold vibration in excised larynx experiments. In particular, two-dimensional bifurcation diagrams are generated in a parameter plane spanned by subglottal pressure and asymmetry of vocal fold adduction or elongation. Various phonatory regimes are observed, including single vocal fold oscillations. Selected spectra demonstrate a correspondence between the observed phonatory regimes and vocal registers noted in the literature. Many instabilities or bifurcations are noted in the regions of coexistence, i.e., the regions where the phonatory regimes overlap. Bifurcations are illustrated with spectrograms and fundamental frequency contours. Where possible, results from these studies are related to clinical observations. [This research was supported by Grant No. P60 DC00976 from the National Institute on Deafness and Other Communication Disorders.]
Articulatory kinematics from the standpoint of automatic speech recognition
Authors: Zlokarnik Igor
Published: October 2005

The discriminant power of articulatory movements was evaluated for six subjects on a speaker-dependent continuous speech recognition task using a hidden-Markov-model-based speech recognition system. The articulatory measurements were gathered by means of electromagnetic articulography and describe the movement of small coils fixed to the speakers’ tongue, jaw, and lower lip during the production of 108 German sentences. Four different articulatory representations were evaluated: coil displacements and their first three time derivatives (coil velocities, accelerations, and jerks). From these four representations, the coil accelerations performed by far the best in terms of recognition performance, both with and without acoustic features. The superior performance of acceleration features is surprising from the viewpoint of automatic speech recognition based on acoustics, since in the acoustic domain, acceleration features perform worse than static features on speaker-dependent tasks. From the viewpoint of articulatory phonetics, however, this result confirms the importance of the role articulator forces play in speech production.
Experimental evaluation of matched-field track-before- detect processing in shallow water
Authors: Baxley Paul A.
Published: October 2005

The detection of a moving source at low signal-to-noise ratio can be enhanced by taking advantage of the time evolution of matched-field ambiguity surfaces. By including a track search in the matched-field process, track-before-detect (TBD) techniques extract source track information so that the target signal function can be reconstructed, rendering it more detectable. The detection enhancement produced by a shift-then-average (coherently and incoherently) TBD algorithm [Baxley, J. Acoust. Soc. Am. 90, 1844(A) (1993)] is investigated for multitone source-tow data recorded near San Diego during the first and third shallow-water evaluation cell experiment (SWellEX-1 and 3). The 3-knot source-tow traversed a range-independent radial from a FLIP-mounted vertical line array. Previously masked targets were rendered detectable in ambient noise and in the presence of a single loud interferer. Gains in detectability of up to 5 dB above that obtained by straight averaging (no tracking) were obtained for a 6-min averaging time.
Detection performance of broadband adaptive matched-field beamforming on a vertical array in shallow water
Authors: Booth Newell O. , Schey Philip W.
Published: October 2005

Quantitative estimates of detection performance are presented for a broadband adaptively processed vertical line array with matched-field replicas. The estimates were obtained with broadband and multitone signal data obtained in the shallow water evaluation cell experiment 3 (SWellEx-3). The experiment was carried out in July 1994 west of Point Loma in 200 m deep water of complex bathymetry. The multitone test signal was transmitted from an acoustic source towed at various depths over complex propagation paths and consisted of five sets of ten tones, each set spanned 50–200 Hz. Each set was transmitted at various levels over 22-dB dynamic range. The beamforming used sets of 8 and 16 hydrophones over 80-m vertical aperture. Detection performance is estimated for various input signal-to-noise ratios by processing sets of frequencies corresponding to the various signal levels. Another set of 10 frequencies which excludes the signal frequencies form the noise only estimates. [Work supported by ONR, Code 321US.]
Selective high-resolution environmental parameter estimation using sector-focused matched-field processing
Authors: Chandler Howard A. , Feuillade Christopher , Smith George B.
Published: October 2005

Sector-focusing (SF) has been shown to be effective at enhancing range-depth resolution while minimizing the instability caused by environmental mismatch. It has also been shown that a stable Bartlett type response could be obtained with SF using a small sector in range-depth space. This property is used to advantage when matched-field processing is used for source localization. By extending the sector focusing concept to include environmental parameter variation within the sector, high resolution may be selectively achieved. In this way greater resolution may be realized for a chosen set of search parameters by including in the sector, replicas derived from a set of ‘‘neighboring’’ environmental parameters. Conversely, by not including replicas derived from other ‘‘known’’ parameters, such as source range or depth, a broad Bartlett-like response may be obtained. Thus the estimate will simultaneously attain high resolution only in the selected search parameter while remaining insensitive to measurement errors in all other parameters, including errors in source location. Examples are presented for a simple parametrization scheme using the KRAKEN normal mode model to simulate a canonical shallow-water environment.
Improvement of signal-to-noise ratio at the single-sensor for narrow-band signals in a partially correlated noise field
Authors: Munn D. R. , Stergiopoulos Stergios
Published: October 2005

This paper deals with the development of a processing technique that will improve the signal-to-noise ratio at the single sensor for a received signal that is embodied in a partially correlated noise field. The approach of this study is unique in that the noise will be treated as being nonwhite and partially correlated. The concept of the proposed development is based on the time interval over which the temporal coherence or correlation properties of a noise field are defined. For narrow-band signals, the associated temporal coherence period is much longer than the correlation time interval of the anisotropic noise field. Thus a coherent integration of discontinuous segments of received signals will enhance the signal-to-noise ratio at the sensor by lowering the correlation properties of the associated nonwhite noise. Reconstruction by the proposed technique of the narrow-band signal time series with improved signal-to-noise ratio at the sensor will allow the use of the existing high resolution techniques to be utilized more effectively by lowering their threshold values in order to detect very weak signals. The intention here is to integrate the characteristics of the real anisotropic noise field during the preliminary processing stages of the array-sensor received signals.
Jovian acoustic matched-field processing
Authors: Collins Michael D. , McDonald B. Edward , Kuperman W. A. , Siegmann William L.
Published: October 2005

Hubble Space Telescope images contain evidence of outward propagating waves. Infrared images from the fragment G impact site contain a small circular feature (the inner ring) and a large circular feature (the outer ring). The inner ring (which appears in several images) has been identified as an internal gravity wave based on its observed group speed of about 450 m/s [Hammel etal., Science 267, 1288–1296 (1995)]. The radius of the outer ring (which appears in only a few images) is consistent with the group speeds of acoustic modes trapped in the Jovian sound channel. During a 34-min interval between images, however, the outer ring appears to expand at only 425 m/s, which is about half the minimum group speed of acoustic waves. To properly analyze the expansion of the outer ring, it is necessary to account for the vertical component of propagation. This is not necessary for the inner ring, which is apparently dominated by a single gravity wave mode trapped in the water clouds [Ingersoll and Kanamori, Nature 374, 706–708 (1995)]. Since acoustic waves repeatedly enter and exit the debris cloud as they cycle about the sound channel axis, one would expect the outer ring to spread outward (and vaporize the debris cloud as it goes) at a variable rate. Matched-field processing results are in agreement with the observations for an acoustic source located deep in the water clouds.
A neural model of auditory scene analysis and source segregation
Authors: Grossberg Stephen , Govindarajan Krishna K. , Wyse Lonce L. , Cohen Michael A.
Published: October 2005

In environments with multiple sound sources, the auditory system is capable of teasing apart the impinging jumbled signal into different mental objects or streams. A neural model of auditory scene analysis is presented that groups different frequency components based on pitch and spatial location cues, and selectively allocates the components to different streams. Grouping is accomplished through a resonance that develops between a given object’s pitch, its harmonic spectral components, and (to a lesser extent) its spatial location. Those spectral components that are not reinforced by being matched with the top-down prototype read-out by the selected object’s pitch representation are suppressed, thereby allowing another stream to capture these components. The model simulates data from psychophysical grouping experiments, such as how an upward sweeping tone creates a bounce percept by grouping with a downward sweeping tone due to frequency proximity, even if noise replaces the tones at their intersection point. The model also simulates illusory auditory percepts such as the auditory continuity illusion, and the Deutsch scale illusion whereby downward and upward scales presented alternately to two ears regroup based on frequency proximity. Stream resonances provide the coherence whereby one voice or instrument is tracked through a multiple source environment.
Measurements of passive and active microbubbles in the sea
Authors: Medwin Herman
Published: October 2005

Around 1960 an oceanographer at the Navy Electronics Laboratory dared to question physics laboratory measurements when he wrote an internal memo titled ‘‘Do Invisible Microbubbles Exist at Sea?.’’ Indeed they do! From 1964 to 1974 a series of M.S. students at the Naval Postgraduate School published the first microbubble density distributions at sea. These were measured by several in-situ ocean techniques including: change of transducer impedance; photography; excess attenuation, backscatter and sound-speed dispersion in a small pulse-echo system: Fourier transform of a sawtooth signal propagating between two separated hydrophones. An ‘‘unbelievable’’ immense number of coastal bubbles of radius 15 to 300 μm were found. The 1990s have seen a renaissance in the field. The spatial and temporal variation of bubble numbers have been studied, and acoustical oceanographers now use bubbles as tracers to determine ocean processes near the ocean surface. Sea state noise and rain noise have both been definitively ascribed to the radiation from huge numbers of infant microbubbles. Indeed, the ‘‘noises’’ have now become ‘‘signals.’’ The underwater sound of breaking waves has been inverted to yield the spectrum of ocean wave height and recently the underwater sound of rainfall has been inverted to reveal the real-time rainfall drop size distribution. The distinctive spectrum of underwater sound during rainfall even allows one to describe the clouds from which the rain has fallen. [Work supported by ONR.]