bluuebunny/crossref_metadata_2025 huggingface dataset:
A least-squares spectral element method for computational aeroacoustics
Authors: Lin W. H. , Chan D. C.
Published: October 2005

Because of its relatively small magnitude compared with the carrier flow field variations, an acoustic signal is not easily tracked without distortion and degradation to the phase and amplitude information contained therein. The spurious dispersion and dissipation effects introduced by most numerical methods for computational fluid dynamics are detrimental to an accurate calculation of the acoustic signal. To rectify such deficiency in current codes, a least-squares spectral element method was developed to solve the linearized acoustic field equations derived from the full Navier–Stokes equations. The method solves the first-order partial-differential equations and minimizes the integral of the squares of the residual over the domain of interest. Spatial derivatives are approximated by Legendre polynomials, and temporal discretization is performed by dual-time stepping. The resultant algebraic equations are solved by a Jacobi preconditioned conjugate gradient method. Numerical examples were presented for a Gaussian pulse in a uniform flow of Mach 0.5 above an infinite plate. The computed acoustic pressures on the wall at different time instances were compared against the exact analytical values, and the comparison showed very good agreement. It indicates that the proposed method is indeed suitable for computing the sound generation and propagation in an unsteady flow regime.
A study on effective selection of control points in sound field reproduction based on Kirchhoff’s integral equation
Authors: Takane Shouichi , Suzuki Yôiti , Sone Toshio
Published: October 2005

This paper deals with a method for controlling the sound field using multiple sound sources and sensors. Methods based on Kirchhoff′s integral equation are the effective and promising ones. However, even if the sound pressure on the boundary of the controlled region is given, the sound field inside it cannot be controlled if the frequency of reproduced sound coincides with one of the eigenfrequencies defined by internal Dirichlet problem of the controlled region. For avoiding this problem, a new method using additional control points within the controlled region is proposed in this study. The results of computer simulation showed that sound field can successfully be reproduced by the proposed method. Moreover, a method for distributing the additional control points is discussed. As a result, it is shown that sound field control is properly achieved when the additional control points are so located that a partial area of the region under consideration is controlled based on the sound intensity on the boundary of the area.
Sound field analysis near the surface of the Schroeder diffuser
Authors: Fujiwara F. , Nakai K.
Published: October 2005

Schroeder developed a structure to reflect incident sound in a diffuse manner, which is composed of many wells of different depths. This is the so-called Schroeder diffuser. A practically constructed diffuser, which is named QRD (quadratic residue-type diffuser), showed an unexpectedly high sound absorption at low frequency, especially at a frequency lower than the lower design frequency. In this study, the sound field near the surface of the Schroeder diffuser identifies the reason for this high absorption. The particle velocity distributions near the surface of the diffuser and inside the wells are analyzed theoretically and compared with the measured distributions, which were observed by using small particles sprinkled over the observation area. This method encompasses the same idea as the Kundt experiment. The predicted distribution coincides well with the observed one. The observed data show the intense coupled resonance between the wells of different depth. The particle velocity around the edge of the well was extremely large. Computation predicts that the velocity is more than 17 times larger than the velocity of the incident sound wave at the edge. This intense resonance may cause very high absorption. The observed movement of the particle will be presented by VCR.
Shallow-water high-frequency active situational adaptation
Authors: Di Napoli Frederick R.
Published: October 2005

Situational adaptation as used in this paper is the process of (a) recognizing that a change in the in-situ sonar environment has occurred that could adversely impact system performance and (b) Providing recommendations for system adaptations tailored to the situation that preclude performance degradation. Many diverse types of potential deleterious changes in the situation (e.g., operational constraints on the platform housing the sonar, sonar system state of calibration and readiness, object to be detected and identified, environmental and acoustic, etc.) must be considered. Only those related to the propagation of high-frequency acoustic energy in an active context are addressed. Consideration is further focused (to fit within the allotted time) to ‘‘first-order situational adaptations,’’ such as sonar depth, beam tilt angle, and beam pattern. The impact on detection of these most fundamental of possible situational adaptations can be substantial and will be delineated for a realistic generic high-frequency active sonar system in typical shallow-water environments. Examples will be presented for representative seasonal shallow-water sound-speed profile and boundary conditions comparing the improvements in detection performance with and without the situational adaptations of depth change, beam pattern shape, and tilt.
A model for bistatic scattering into ocean sediments for frequencies from 10 to 100 kHz
Authors: Williams Kevin L. , Jackson Darrell R.
Published: October 2005

A model is presented for bistatic scattering into ocean sediments from an acoustic source located in the water to a receiver buried in the bottom. The model is closely related to that developed previously for a source and receiver that were both located in the water. The model is an applied effort that incorporates the results of more fundamental work that has tested the validity of some components of the model. Bottom scattering is treated as being due to interface roughness and volume inhomogeneity. Kirchhoff theory is used to explain interface scattering near the refracted (Snell’s law) direction, and perturbation theory is used for all other directions. Perturbation theory is also used to treat the scattering due to volume inhomogeneities. Model results are presented for two bottom types. It is shown that it predicts subcritical penetration into sediments with sound speeds greater than that of water. [Work sponsored by Office of Naval Research.]
Determination of ray path probabilities in stochastic media
Authors: Ruppel Timothy H.
Published: October 2005

Modeling the propagation of high-frequency sound in shallow water environments often requires the inclusion of stochastic effects in order to provide realistic results. The inclusion of these effects may cause the model to be more computationally intensive and difficult to run. It is therefore desirable to know when these effects are significant, and when they may be ignored. One method of determining this significance is to determine the probability that the ray paths traced by a deterministic ray tracing model will occur in the stochastic environment; if the probability is low that the deterministic ray path is nearly correct, then stochastic effects must be included. This paper discusses a method for determining these ray path probabilities given an average variability in the sound speed and a correlation length. This paper will concentrate on spatial variations, though a procedure for including variations with time will be discussed. [Work supported by ONR.]
Impact of the environment on energy spreading loss in shallow water at high frequencies
Authors: Tanaka Akira , Wilson James H. , Bourke Robert H.
Published: October 2005

Energy spreading loss (ESL) is qualitatively defined as reduction in peak echo level due to time spreading of the transmitted acoustic pulse. An analysis of the impact of shallow water propagation on ESL was performed using a time domain propagation loss program to compute the spreading of the received pulse due to multipath propagation. Typical sound speeds and a Hamilton geoacoustic model of Area Foxtrot off the U.S. eastern seaboard was used. ESL’s impact on sonar performance was determined as a function of range, depth, sound speed and geoacoustic properties. The impact of shallow water propagation on the correlation of the propagated pulses through the quantitative definition of mismatch loss (MML) was also discussed. Strong ESL existed over a reflective bottom and was generally invariant with range. ESL was correlated with TL. ESL was not as large over absorptive bottoms due to increased absorption of the bottom refracted path, and thus, reduction in the number of multipath modes. Broadband pulses were found to exhibit fewer fluctuations than narrowband signals, and the total TL loss was larger than a single cw case. To overcome the ESL, integration techniques based on an accurate prediction model are required with high temporal resolution of the echo energy.
Effects of aircraft overflights on wilderness recreationists
Authors: Fidell Sanford , Silvati Laura , Howe Richard , Pearsons Karl S. , Tabachnick Barbara , Knopf Richard C. , Gramann James , Buchanan Thomas
Published: October 2005

On-site and telephone opinion surveys were conducted to assess outdoor recreationists’ annoyance with aircraft overflights of wilderness areas. Although current technology for measuring noise exposure does not yet permit accurate and cost-effective estimates of dosage-response relationships in outdoor recreational settings, it was nonetheless possible to construct a rough relationship between estimated aircraft noise exposure and annoyance from the data of the on-site study. In the second survey, telephone interviews were administered to another sample of outdoor recreationists within 2 weeks of their return from visits to 12 wilderness areas. The prevalence of aircraft noise-induced annoyance (in any degree) among respondents in all wilderness areas ranged from 5% to 32%. The prevalence of a consequential degree of aircraft noise-induced annoyance among respondents was less than 5% in all wilderness areas combined. Noise-induced annoyance proved to be a more direct measure of the effects of aircraft overflights on recreationists than more global measures such as visit satisfaction or intent to revisit.
Interfacial waves in an elastic body fractured by periodic cracks
Authors: Danicki E.
Published: October 2005

Two elastic half-spaces are considered bonded to each other and have periodic disbondings (cracks) in the plane of bonding. A new method is presented for analysis of the boundary value problem for interfacial waves propagating obliguely in the plane of cracks. An example is presented for isotropic body. An anisotropic case is discussed, as well as the Bragg reflection of interfacial waves from cracks.
Theory of elastic waves in three-dimensional anisotropic plates
Authors: Tewary V. K. , Fortunko C. M.
Published: October 2005

The delta-function representation of the elastodynamic Green’s function is used to calculate three-dimensional time-dependent waveforms for an elastic pulse propagating in an anisotropic plate of arbitrary thickness for a point source of stress on a surface. The Green’s function includes the effects of mode coupling and mode conversion, and multireflections in the plate. As an example, the method is applied to anisotropic plates exhibiting cubic and orthotropic symmetries. Numerical results are presented for time-dependent waveforms in model cubic plates and in an orthotropic carbon fiber composite plate.
Variational formulation of interior cavity frequencies for spheroidal bodies
Authors: Chen Pei-Tai
Published: October 2005

This paper presents interior cavity frequencies for spheroidal bodies in cases of Neumann and Dirichlet homogenous boundary conditions. The Helmholtz wave equation is expressed in terms of prolate spheroidal coordinates from which a variational formulation is derived for the determination of the interior cavity frequencies. The search of stationarity is performed by means of a Rayleigh–Ritz type expansion of trial functions. The trial functions are expressed as a double summation of basis functions in radial and angular coordinates. A variable transformation is applied to the variational form in order to have homogenous boundary conditions, which are essential for establishing a complete function space of the associated boundary conditions. The present analysis is verified by comparisons of interior frequencies of a spherical body, of prolate spheroidal bodies, and of the interior characteristic functions with the radial and angular functions obtained from prolate spheroidal differential equations. Interior frequencies are tabulated for various aspect ratios of spheroidal bodies in accordance with harmonic orders in azimuthal directions, for both Neumann and Dirichlet conditions.
Displacement-based finite element method for guided wave propagation problems: Application to poroelastic media
Authors: Easwaran V. , Lauriks W. , Coyette J. P.
Published: October 2005

Poroelastic materials are used extensively in the literature for sound absorption and attenuation. Guided wave propagation in these materials is therefore of considerable interest to researchers. In the present paper, a finite element method is presented for guided wave propagation in poroelastic media. For harmonic vibrations, the finite element method gives rise to a quadratic eigenvalue problem in the phase speed. Solution of the standard finite element procedure is shown to excite modes with spurious phase speeds. It is shown that the real and spurious modes can be identified using the penalty constraint approach. For this, one needs to compute the rate of change of phase speed with the penalty constraint constant α. An expression for computing this rate of change of phase speed has been derived. It is shown that in most cases the rate of change of phase speed needs to be evaluated only at α=0. The results apply to a pure fluid and also to poroelastic media. In the process, analytical expressions are also derived for wave propagation in poroelastic cylinders. The use of reduced order integration to eliminate spurious modes is also discussed in this paper. Dispersion curves for the phase speeds are presented for the first few breathing modes of a poroelastic cylinder. Finally, results are presented for the case of a rigid, lined ducted system.
On the reconstruction of the vibro-acoustic field over the surface enclosing an interior space using the boundary element method
Authors: Kim Bong-Ki , Ih Jeong-Guon
Published: October 2005

The vibrational velocity, sound pressure, and acoustic power on the vibrating boundary comprising an enclosed space are reconstructed by the boundary element method based on the measured field pressures. The singular value decomposition is used to obtain the inverse solution in the least-square sense and to express the acoustic modal expansion between the measurement and source fields. In general, such an inverse operation has been considered an ill-posed problem having a divergence phenomenon involved with extremely small measurement errors. The ill-conditioned nature of the acoustic inverse problem is caused by the singularity of the transfer matrix which produces nonradiating wave components. In order to minimize the singularity and to also reduce the number of measurement points, optimal measurement positions are determined by the effective independence method. Regularization methods are used to stabilize the reconstructed field by suppressing nonradiating components resulting in the singular transfer matrix. In order to enhance the resolution of the reconstructed field, the optimal regularization order for yielding the minimum mean-square error is estimated from the known measurement noise variance by virtue of the statistical analysis. A half-scaled automotive cabin is considered an example for validating and demonstrating the proposed reconstruction process. It is noted that the present method can improve the resolution of the reconstructed field; thus vibro-acoustic parameters of the vibrating boundary can be estimated in reasonably good precision.
Comparison of computer codes for the propagation of sonic boom waveforms through isothermal atmospheres
Authors: Cleveland Robin O. , Chambers James P. , Bass Henry E. , Raspet Richard , Blackstock David T. , Hamilton Mark F.
Published: October 2005

A numerical exercise to compare computer codes for the propagation of sonic booms through idealized atmospheres is reported. Ground waveforms are calculated using four different codes or algorithms: (1) weak shock theory, an analytical prediction; (2) SHOCKN, a mixed time and frequency domain code developed at the University of Mississippi; (3) ZEPHYRUS, another mixed time and frequency code developed at the University of Texas; and (4) THOR, a pure time domain code recently developed at the University of Texas. The codes are described and their differences noted. They are then used to calculate propagation for two different source waveforms, for both a uniform and isothermal (varying density) atmosphere, with and without the presence of molecular relaxation. In all cases the results of THOR, SHOCKN, and ZEPHYRUS are in excellent agreement. Because the weak shock theory algorithm does not include the effect of ordinary absorption, it does not predict the shock structure provided by the other codes. This leads to discrepancies particularly for an atmosphere that includes relaxation effects.
Phase-locking condition in the feedback loop of low-speed edgetones
Authors: Kwon Young-Pil
Published: October 2005

The phase criterion of the feedback cycle of edgetones is shown to be p=−1/4 in the equation h/Λ+h/λ=n+p, where n is an integer, h is the distance from the nozzle exit to the edge tip, and Λ and λ are the wavelengths of the downstream-propagating and the upstream-propagating waves, respectively. The present result has been obtained on the basis that the effective source point of jet–edge interaction is located around a quarter wavelength downstream from the edge tip. The proposed criterion p=−1/4 is just the opposite in phase to p=1/4, which has been regarded as an established characteristic of edgetones. However, it is verified substantially by comparison with available experimental data and found to be effective up to a wedge angle of 90°.
Convergence zone feature dependence on ocean temperature structure
Authors: Bongiovanni K. P. , Siegmann W. L. , Ko D. S.
Published: October 2005

A model which provides a connection between deep-ocean temperature data and convergence zone phenomena is presented. Temperature variability below the mixed layer of the thermocline and SOFAR channel is modeled parametrically. A sound-speed profile is used which has closed form ray solutions in a range-independent ocean. By incorporating the environmental parameters into the sound speed and using the ray formulas for acoustic sources below the mixed layer, expressions for convergence zone widths and ranges are developed. Temperature profile data from the Sargasso Sea is used to construct a parameter domain representative of statistically homogeneous deep-water masses. A parabolic equation model is used to assess the accuracy of the convergence zone formulas. Good agreement is seen between the two models over the entire parameter domain. By varying the temperature parameters individually, convergence zone feature sensitivities to the parameters are characterized.
Multifrequency acoustic investigations of juvenile and adult fish in Lake Biwa, Japan
Authors: Trevorrow Mark V.
Published: October 2005

As part of an intensive, multidisciplinary limnological study of Lake Biwa, Japan during 23 August through 15 September 1993, multifrequency acoustic backscatter profiles of small fish were collected at a single location. Estimates of volume scattering strength using calibrated inverted echo sounders at five frequencies (29–198 kHz) were combined with echo statistics and simple scattering models to estimate approximate sizes and population densities. Echo amplitude probability density functions (PDFs) were used to constrain population density estimates in two ways: (1) PDF shape estimates were used to find the critical density among four different beam-width sonars, and (2) an isolated echo convolution model was fit to measured PDFs from the 198-kHz sonar, yielding the scattering cross-section for individual fish. An epilimnion scattering layer was consistently found, bounded below by the 24 °C isotherm at 10- to 15-m depth, likely consisting of juvenile Hasu (Opsariichthys uncirostris) of length 35 to 45 mm, with acoustic cross-sections of 4–9×10−5 m2 (target strengths of −55 to −51 dB re: 1 m2), and mean population densities in the range of 0.2–0.5 per m3. Individuals or small schools of adult fish (likely O. uncirostris, Plecoglossus altivelis, and/or Gnathopogon caerulescens) with typical lengths of 10 to 20 cm were intermittently observed at or above the main thermocline with instantaneous densities of 1 to 25 per m3. The typical depth of occurrence of these adult fish varied from 2.8 m during the day to 15.2 m at night.
Acoustic scattering from cylindrical objects embedded between two half-spaces
Authors: Fawcett John A.
Published: October 2005

In this paper a boundary integral equation method is presented for the computation of the acoustic field scattered from a cylindrical object which is totally within the water column, totally buried in sediment, or partially buried. The unknown field quantities within the cylindrical object (which may have internal cylindrical layering) are represented by a Fourier/Bessel series with unknown coefficients. The pressure field and its radial derivative on the exterior of the cylinder are related to this series and a system of equations for the unknown coefficients derived. This method is used to compute the spectral curves for the backscattered field as a function of cylinder burial. Some two-dimensional full-field computations for scattering from cylindrical objects are also presented.
Application of the finite-element method for modeling backed transducers
Authors: Assaad Jamal , Ravez Martine , Bruneel Christian
Published: October 2005

To model backed transducers by the finite-element method, the main drawback is generally the large size of the numerical problem. Thus, the aim of this paper is to show how the backing mesh can be quite limited. For this purpose, the backing is considered as a lossy transmission line. Then, the equivalent acoustic impedance of the backing is expressed in terms of its thickness TB and the tangent of the phase angle (tan δ). It will be shown that the characteristics of a backed transducer (electrical impedance, acoustic radiated power, etc., ...) can stay unchanged if the thickness TB is scaled down and tan δ is scaled up, keeping the product TB tan δ constant. Finally, finite-element results are successfully compared with measurements results using lithium niobate backed transducer.
New constitutive relations for piezoelectric composites and porous piezoelectric ceramics
Authors: Gómez Alvarez-Arenas Tomás E. , Montero de Espinosa Freijo Francisco
Published: October 2005

This paper deals with a new system of constitutive relations that describe the elastic, dielectric, and piezoelectric behavior of piezoelectric composite materials. Porous piezoelectric ceramics saturated with different fluids and epoxies are an example. These relations are obtained from basic thermodynamic considerations and are applicable to a great number of different cases. This new theoretical approach takes into account the mutual influence between the different components of the composite and provides a novel procedure to analyze this coupled behavior. Experimental results concerning the elastic and dielectric properties of porous piezoelectric ceramics saturated with different polymers and oils are also presented. The influence of the coupling mechanisms on the material parameters is analyzed. The advantages of using this theory as opposed to other averaging approaches to study this type of materials are clearly shown.
The generation, propagation, and detection of Lamb waves in plates using air-coupled ultrasonic transducers
Authors: Castaings M. , Cawley P.
Published: October 2005

Air-coupled nondestructive testing has become feasible following recent improvements in air-coupled transducer design. However, the large acoustic impedance mismatch between air and solid materials does not allow normal incidence pulse-echo inspection. Nevertheless, air-coupled transducers can be used for the generation and detection of Lamb waves, the receiver being outside the field of the specular reflection. A finite element study of the generation of Lamb waves in plates from a finite air-coupled transducer, the interaction of these waves with defects, and their detection using an air-coupled receiver is described. These predictions are compared with experimental results obtained on a variety of specimens using a pair of 1-3 composite, air-coupled transducers. The use of an ideal collimated beam in the model, instead of using the real pressure field generated by the transducers, is demonstrated to have a negligible effect on the predicted Lamb waves. It is shown both theoretically and experimentally that the measured amplitude of the Lamb waves is very sensitive to the alignment of the transducers with respect to the test structure, misalignment of 0.6° reducing the amplitude by around 50%. The detection of notches of various depths in steel plates is investigated, and the sensitivity of the technique with different choices of incident mode and different positions of the receiver with respect to the defect is discussed. It is shown that in metal structures it is most satisfactory to use the a0 mode since it has a large out-of-plane surface displacement and so is easy to excite.
The effect of an undamped finite degree of freedom ‘‘fuzzy’’ substructure: Numerical solutions and theoretical discussion
Authors: Weaver R. L.
Published: October 2005

A single degree of freedom master oscillator attached to a simple undamped N degree of freedom ‘‘fuzzy substructure’’ is studied numerically and theoretically. Results are found to be in accord with the predictions of the Pierce–Sparrow–Russell theory at early times; in particular, the master oscillation manifests an apparent damping. At later times, however, the damping ceases and the energy is returned from the fuzzy to the master. The precise manner in which the energy is returned, and the time taken to do this, depend on the details of the mass and frequency distribution within the fuzzy, and in particular on the distribution of spacings between the fuzzy resonances.
Control strategies for neurons modeled by self-exciting point processes
Authors: Irlicht L. S. , Clark G. M.
Published: October 2005

Experiments demonstrate that electrical stimulation of the auditory nerve evokes qualitatively different responses to those of normal hearing. We apply a self-exciting point process model to explain and predict both responses. For acoustic stimulation, the model predicts the shape of the per-stimulus time histogram (PSTH), the average firing rate, and the maximum possible firing rate. The model also predicts the PSTH for pulsatile electric stimulation. The model is used to parametrize the response differences between electric and acoustic neural stimulation, and to design electrical stimuli which cause single auditory neurons to respond similarly to the normal hearing situation. Such stimuli should find application in advanced cochlear implants.
Two sources of acoustic distortion products from the human cochlea
Authors: Brown Ann M. , Harris Frances P. , Beveridge Hazel A.
Published: October 2005

The amplitude and phase of both stimulus-frequency and distortion-product emissions have been measured in healthy human ears. In some ears it is possible to model acoustic distortion products (DPs) generated by low-to-moderate stimulus levels as the vector sum of two components originating from distinct regions of the cochlea, one from the f2 place and the other, with a longer delay, from the distortion product place. The phase lag of the more delayed DP component is slightly greater than that of stimulus frequency emissions (SFEs) measured in the same ears.
Measures of tuning and suppression in single-fiber and whole-nerve responses in young and quiet-aged gerbils
Authors: Hellstrom Lisa I. , Schmiedt Richard A.
Published: October 2005

Tuning and suppression were examined in the auditory nerves of young-control and quiet-aged gerbils. Tuning curves obtained from single-fiber responses were compared to those obtained with the compound action potential (CAP) using masking procedures. Tuning was measured in terms of the high-frequency slope of the tuning curve and Q values obtained 10 dB and 40 dB (Q10 dB and Q40 dB, respectively) above the threshold at its best frequency. The study had two objectives: first, how CAP measures of tuning and suppression correspond to single-fiber measures in presbyacusic cochleas; and second, how the above measures of tuning change with age without the confounding effects of noise exposure. It was found that measures derived from the CAP responses in aged gerbils remained similar to the trends of the single-fiber data, despite the many morphological changes that are known to occur in the presbyacusic ear. Thus, CAP procedures remain an appropriate alternative to single-fiber recording in aged animals where the stability of the preparation can be tenuous. With regard to tuning and suppression, our results show that single-fiber and CAP tuning curves in quiet-aged animals are similar to those of young controls except for higher thresholds near the best frequency. The tail response remained largely stable with age, and no instances of tail hypersensitivity were found. The slopes of the high-frequency legs of the curves were similar in young and aged animals, and were associated with the presence of two-tone suppression on the high-frequency side. In a few instances high-side suppression was absent in the aged gerbils and was associated with tuning curves with shallow high-frequency slopes and characteristic frequency (CF) threshold shifts of 30 dB or greater. Mean high-frequency slopes and Q values increased with best frequency in young controls, but were fairly constant with best frequency in quiet-aged animals. Thus, in comparison to controls, the frequency selectivity of quiet-aged gerbils tends to decrease somewhat at frequencies above 4 kHz. Many of these changes with age may be ascribed to a chronic decline of the endocochlear potential (EP) acting on an intact hair-cell system in quiet-aged gerbils. With this assumption, CF thresholds are most sensitive to the EP decline, whereas boundaries of tuning and two-tone suppression taken at more intense levels are least affected.
The relative strength of the tone and noise components in iterated rippled noise
Authors: Patterson Roy D. , Handel Stephen , Yost William A. , Jaysurya Datta A.
Published: October 2005

Rippled noise is constructed by delaying a random noise and adding it back to the original. Iterated rippled noise (IRN) is constructed by repeating the delay-and-add process. IRN produces a two-component perception, i.e., a buzzy tone with a pitch equal to the reciprocal of the delay and a background noise that sounds like the original random noise. The perceived tone/noise ratio increases with the number of iterations. The effective tone/noise ratio in IRN sounds with 1–16 iterations was measured in a discrimination matching experiment; each IRN was paired with a range of standard sounds, having varying proportions of a broadband noise and a complex tone, to find the point where their perceived tone/noise ratios are the same. The experiment shows that the tone/noise ratio of the matching standard increases 3.8 dB per doubling of the number of iterations in the IRN stimulus. Spectral models of auditory perception explain the pitch of IRN in terms of peaks in the region of the first five to eight harmonics of the reciprocal of the delay. However, the matching data are unaffected when the sound is high-pass filtered at the twelfth harmonic of the delay—above the region of resolved harmonics. We show that a wide range of time-domain auditory models can explain the discrimination matching data by applying autocorrelation, either to the IRN waveform, or to the neural activity patterns produced by the cochlea in response to IRN waves.
Analogy between the one-dimensional acoustic waveguide and the electrical transmission line for cases with loss
Authors: Wu Junru , Du Gonghuan
Published: October 2005

Analogy between the one-dimensional acoustic waveguide and the electrical transmission line for lossless cases has been generalized to cases with loss.
Characterizing cochlear mechano-electric transduction using a nonlinear systems identification procedure
Authors: Chertoff Mark E. , Steele Timothy , Ator Gregory A. , Bian Lin
Published: October 2005

A nonlinear systems identification technique [J. S. Bendat, Nonlinear System Analysis and Identification from Random Data (Wiley, New York, 1990)] provided the frequency-domain parameters of a third-order system polynomial equation describing cochlear mechano-electric transduction (MET) in Mongolian gerbils. The magnitude of the linear system term was the largest followed by the cubic and quadratic terms. The phase of the linear and cubic system terms differed by approximately 180 deg and the phase of the quadratic term lay between. Between-animal and within-animal variability was smallest for the linear and cubic terms, and largest for the quadratic term. Summing linear and nonlinear coherence functions revealed that the third-order system polynomial equation characterized approximately 83% of MET for low frequencies and 92% for high frequencies. Animals exposed to a 4-kHz pure tone at 100 dB SPL for 20 min showed changes in the magnitude and phase of the parameters of the third-order polynomial equation. An increase in linear coherence and a decrease in nonlinear coherence occurred at frequencies centered at the exposure frequency. Below the exposure frequency, linear coherence decreased and nonlinear coherence increased. Summation of the coherence functions showed that the third-order polynomial equation characterized MET better after exposure to the pure tone.
Sound propagation over screened ground under upwind conditions
Authors: Rasmussen Karsten Bo
Published: October 2005

A screen on an absorbing ground is investigated experimentally and theoretically under upwind conditions. The experimental data are the result of scale model experiments in a 1:25 scale model. The sound propagation is measured using a triggered spark source with signal spectrum averaging in the frequency domain. The meteorological data representing the wind conditions have been determined by means of hot-wire anemometry in positions on both sides of the screen as well as directly over the screen. The theoretical model used for comparison is a hybrid approach. The sound field without a barrier is determined by means of numerical integration of a Hankel transform solution for a stratified atmosphere [like a fast field program (FFP) but taking the near field into account]. This solution is used on both sides of the screen and is combined with a screen diffraction calculation. Results from the calculation model are able to explain the overall tendency in the experimental results.
High resolution adaptive beamforming for three-dimensional acoustic imaging of zooplankton
Authors: Papazoglou Michael , Krolik Jeffrey L.
Published: October 2005

This paper investigates the use of adaptive beamforming techniques to increase the performance of a sonar imaging system developed at the Scripps Institution of Oceanography to monitor the migration of zooplankton. The original system, known as Fish Television (FTV), images a volume using an 8×8 grid of beams in elevation and azimuth. Imaging currently performed with the FTV system is limited by a 2-deg resolution in both azimuth and elevation. In this paper, both a conventional delay-and-sum beamformer and a minimum variance adaptive beamformer are evaluated for use with the FTV sonar system to increase resolution and reduce sidelobe interference. Through simulation it is shown that by using adaptive beamforming, the image resolution can be improved to 1/4 deg in azimuth and elevation for targets with signal-to-noise ratios of at least 20 dB. Results using acoustic data from the Gulf of Eilat are compared to the original images of the FTV sonar system to illustrate the improvement in resolution, accuracy, and dynamic range achieved by adaptive beamforming.
A normal mode model for acousto-elastic ocean environments
Authors: Westwood Evan K. , Tindle C. T. , Chapman N. R.
Published: October 2005

A normal mode method for propagation modeling in acousto-elastic ocean waveguides is described. The compressional (p-) and shear (s-) wave propagation speeds in the multilayer environment may be constant or have a gradient (1/c2 linear) in each layer. Mode eigenvalues are found by analytically computing the downward- and upward-looking plane wave reflection coefficients R1 and R2 at a reference depth in the fluid and searching the complex k plane for points where the product R1R2=1. The complex k-plane search is greatly simplified by following the path along which |R1R2|=1. Modes are found as points on the path where the phase of R1R2 is a multiple of 2π. The direction of the path is found by computing the derivatives d(R1R2)/dk analytically. Leaky modes are found, allowing the mode solution to be accurate at short ranges. Seismic interface modes such as the Scholte and Stonely modes are also found. Multiple ducts in the sound speed profile are handled by employing multiple reference depths. Use of Airy function solutions to the wave equation in each layer when computing R1 and R2 results in computation times that increase only linearly with frequency.
Shear-wave velocity structure of shallow-water sediments in the East China Sea
Authors: Collins John A. , Sutton George H. , Ewing John I.
Published: October 2005

The results of an experiment designed to measure the shear-wave velocity structure of the shallow-water sediments at three locations in the East China Sea, in water depths ranging from 40 m to 150 m, are reported. Both vertically polarized and horizontally polarized shear-wave velocities were measured by placing both source and receiver on the seafloor. The recorded data consist of interface waves of Love wave and Stoneley/Scholte wave type, and both horizontally polarized (SH) and vertically polarized (SV) body waves. With the aid of synthetic seismogram analysis, the travel times and amplitudes of these phases were used to constrain the velocity structure of the seabed to depths of ∼50 m. These results show that velocities range from less than 50 m/s at the seafloor to greater than 400 m/s at subseafloor depths of only 50 m. Vertical velocity gradients of up to 200 and 15 s−1 are required in the upper 1 and 10 m of the seabed, respectively. Comparison of profiles carried out at the same approximate location shows that the velocity structure of the upper 10 m varies by up to 80% over lateral distances of less than a few kilometers. In the data bandwidth of 5–30 Hz, shear Q values range from 10–20 (attenuation factor of 0.07–0.14 m−1 at 20 Hz) at the seafloor to 40 (attenuation factor of 0.004 m−1 at 20 Hz) at depth. The shear velocities immediately below the seafloor differ by less than a factor of 2 from the values predicted by applying the Biot theory to the geotechnical parameters measured on cores taken at the experiment locations. In two of three cases the differences between the predicted and measured values are less than 8%.
Chirp response of a single-plate transducer
Authors: Alwi Hasan A. B. , Carey John R. , Smith Brian V.
Published: October 2005

The chirp response of a thickness-resonant, single-plate transducer is evaluated using a recursive digital-filter method. The theoretical model using the z-form method is most suitable for lossless and simple transducer structures, such as with back and front resistive loads, and with no front layer. The results of the analysis are compared with experimental measurements and are also compared with theoretical results obtained with a simple lumped-element, tuned-circuit model of the plate.
Vibration of moderately thick cylindrical shallow shells
Authors: Lim C. W. , Liew K. M.
Published: October 2005

A first-order shear deformation theory is employed for the vibration analysis of shallow cylindrical shells of rectangular planform. A general method of solution based on the Ritz extremum energy principle and two-dimensional polynomial is developed to examine the effects of thickness and curvature on the vibrating response of shells having various boundary constraints. Convergence and comparison studies are conducted to justify the accuracy of the eigenvalues. Numerical results are presented to demonstrate the capability of the present method and to provide new data for design purposes. Sets of new vibration mode shapes are also presented to illustrate the vibratory characteristics of the shells.
Vibration of arbitrarily laminated plates of general trapezoidal planform
Authors: Lim C. W. , Liew K. M. , Kitipornchai S.
Published: October 2005

This study forms a generalization of the free vibration analysis of thin composite plates. It extends previous analyses and presents benchmark results for the effects of general lamination and geometric unsymmetry parameters on the natural frequencies of general trapezoidal plates. The Ritz extremum energy principle with kinematically oriented pb-2 shape functions, transformed into efficient numerical procedures, have been further exploited to obtained fast-converging and accurate results. Selected new transverse vibration mode shapes are presented to illustrate the effects of boundary constraints, aspect ratio, and fiber orientation.
Diffuse energy propagation on heterogeneous plates: Structural acoustics radiative transfer theory
Authors: Turner Joseph A. , Weaver Richard L.
Published: October 2005

The propagation of diffuse energy on an unwetted flat plate with attached heterogeneities is examined using a statistical, multiple scattering approach. The statistically homogeneous heterogeneities lightly couple the membrane and flexural waves. The problem is formulated in terms of the Bethe–Salpeter equation, which governs the field covariance. It is reduced to a radiative transfer equation in the limit that the attenuations per wave number are small, i.e., when the heterogeneities are weak. This radiative transfer equation governs the diffuse energy propagation as a function of space, time, and propagation direction. Solutions of the radiative transfer equation are presented for the simple case of attached heterogeneities in the form of delta-correlated springs excited by an extensional point source. The results show the evolution of the extensional, shear, and flexural energy densities across the plate as a function of time. A similar approach is expected to apply to the more complicated case of submerged complex structures.
Vibration of circular and annular Mindlin plates with internal ring stiffeners
Authors: Xiang Y. , Liew K. M. , Kitipornchai S.
Published: October 2005

The first-known investigation is reported for free vibration of circular and annular Mindlin plates with intermediate concentric ring stiffeners. The total potential energy functional is first derived for the stiffened circular and annular plates. The Mindlin first-order shear deformation plate theory is used to account for the effects of plate shear deformation and rotary inertia, while the Engesser theory is used to consider the shear deformation and torsional effects in stiffeners. A set of trial functions is proposed for the displacement fields to satisfy the geometric boundary conditions of the plate at outset. Minimizing the energy functional by applying the Ritz procedure, the governing eigenvalue equation is derived. Solving the eigenvalue equation, first-known sets of vibration solutions are obtained for circular and annular Mindlin plates with concentric ring stiffeners. The accuracy of the results is tested using convergence studies. The significant influences of boundary conditions, plate thickness ratio, cut-out ratio and locations of ring stiffeners are highlighted.
The normalized correlation: Accounting for binaural detection across center frequency
Authors: Bernstein Leslie R. , Trahiotis Constantine
Published: October 2005

Bernstein and Trahiotis [L. R. Bernstein and C. Trahiotis, J. Acoust. Soc. Am. 100, 1754–1763 (1996)] recently reported the results of experiments designed to determine the form of interaural correlation that accounts for listeners’ sensitivities to interaural disparities within high-frequency stimuli. Overall, those results demonstrated that listeners’ abilities to discriminate changes in the interaural correlation of the envelope (from a base correlation of 1.0) were well accounted for by the use of the normalized correlation. The purpose of this study was to determine how well the normalized correlation computed subsequent to half-wave rectification and low-pass filtering could account for binaural detection data at low, intermediate, and high frequencies, respectively. In a four-interval, two-alternative task, listeners detected which interval contained a tone (between 500 Hz and 2 kHz) added antiphasically to diotic, 100-Hz-wide, noise (NoSπ). ‘‘Nonsignal’’ intervals contained the tone added homophasically (NoSo). Performance was measured for signal-to-noise ratios between −30 and +30 dB. Results indicated that a low-pass filter function based on physiological measures of synchrony in cochlear nerve fibers in conjunction with the assumption of half-wave, square-law rectification, accounted for typically 80% of the variance in the behavioral data.
Vowel classification in children
Authors: Palethorpe Sallyanne , Wales Roger , Clark John E. , Senserrick Teresa
Published: October 2005

Research into the developing vowel system has assumed greater importance in recent years with growing evidence for a more important theoretical role for vowels in child phonology. One limitation of acoustic studies in child speech has been the practical difficulties associated with formant-based analysis and the experiments reported in this paper compare the reliability of critical bands and formant frequencies as acoustic correlates of vowel identity in children. Gaussian classification of vowels in /CVd/ Australian English words was carried out using data collected from 4-year-old children and male and female adults. The results show that the use of critical bands for the classification of vowels in children is a robust technique which requires less experimenter intervention in the analysis procedure than the use of formant frequencies, while achieving similar results. The ability to utilize an automatic methodology such as critical band analysis can provide a very powerful tool for large-scale studies in this area.