bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of bistatic scattering from two geologically distinct abyssal hills
Authors: Swee Chia Chin , Makris Nicholas C. , Fialkowski Laurie T.
Published: July 2002

The bistatic scattering characteristics of two geologically distinct abyssal hills located on the western flank of the Mid-Atlantic Ridge, known as B′ and C′, are experimentally compared using data acquired with low-frequency towed-array systems at 12 convergence zone (∼33 km) stand-off. The comparison is significant because the abyssal hills span the two classes of elevated seafloor crust that cover the Mid-Atlantic Ridge. The highly lineated B′ feature is representative of abyssal hills composed of outside corner crust, the most commonly occurring category, whereas the domed C′ promontory is representative of the rougher, low-aspect-ratio abyssal hills composed of inside corner crust. The latter are less common and usually restricted to segment valley margins. The mean biazimuthal scattering distributions of the two abyssal hills each exhibit Lambertian behavior with comparable albedos, suggesting that the distinction between abyssal hills composed of differing crust is not significant in modeling long-range reverberation. The adverse effect of using bathymetry that undersamples seafloor projected area in scattering strength analysis is also quantified with data from the B′ ridge. Specifically, the use of undersampled bathymetry can lead to significant overestimates in the strength of seafloor scattering.
A turbulence spectral model for sound propagation in the atmosphere that incorporates shear and buoyancy forcings
Authors: Wilson D. Keith
Published: July 2002

A three-dimensional model for turbulent velocity fluctuations in the atmospheric boundary layer is developed and used to calculate scattering of sound. The model, which is based on von Kármán’s spectrum, incorporates separate contributions from shear- and buoyancy-forced turbulence. New equations are derived from the model that predict the strength and diffraction parameters for scattering of sound as a function of height from the ground and atmospheric conditions. The need is demonstrated for retaining two distinct scattering length scales, one associated with scattering strength and the other with diffraction. These length scales are height dependent and vary substantially with the relative proportions of shear and buoyancy forcing. The turbulence model predicts that for forward-scattered waves the phase variance is much larger than the log-amplitude variance, a behavior borne out by experimental data. A new method for synthesizing random fields, based on empirical orthogonal functions, is developed to accommodate the height dependence of the turbulence model. The method is applied to numerical calculations of scattering into an acoustic shadow zone, yielding good agreement with previous measurements.
Sound localization in a new-world frugivorous bat, Artibeus jamaicensis: Acuity, use of binaural cues, and relationship to vision
Authors: Heffner Rickye S. , Koay Gimseong , Heffner Henry E.
Published: July 2002

Passive sound-localization acuity and its relationship to vision were determined for the echolocating Jamaican fruit bat (Artibeus jamaicensis). A conditioned avoidance procedure was used in which the animals drank fruit juice from a spout in the presence of sounds from their right, but suppressed their behavior, breaking contact with the spout, whenever a sound came from their left, thereby avoiding a mild shock. The mean minimum audible angle for three bats for a 100-ms noise burst was 10°—marginally superior to the 11.6° threshold for Egyptian fruit bats and the 14° threshold for big brown bats. Jamaican fruit bats were also able to localize both low- and high-frequency pure tones, indicating that they can use both binaural phase- and intensity-difference cues to locus. Indeed, their ability to use the binaural phase cue extends up to 6.3 kHz, the highest frequency so far for a mammal. The width of their field of best vision, defined anatomically as the width of the retinal area containing ganglion-cell densities at least 75% of maximum, is 34°. This value is consistent with the previously established relationship between vision and hearing indicating that, even in echolocating bats, the primary function of passive sound localization is to direct the eyes to sound sources.
Propagation of finite amplitude sound through turbulence: Modeling with geometrical acoustics and the parabolic approximation
Authors: Blanc-Benon Philippe , Lipkens Bart , Dallois Laurent , Hamilton Mark F. , Blackstock David T.
Published: July 2002

Sonic boom propagation can be affected by atmospheric turbulence. It has been shown that turbulence affects the perceived loudness of sonic booms, mainly by changing its peak pressure and rise time. The models reported here describe the nonlinear propagation of sound through turbulence. Turbulence is modeled as a set of individual realizations of a random temperature or velocity field. In the first model, linear geometrical acoustics is used to trace rays through each realization of the turbulent field. A nonlinear transport equation is then derived along each eigenray connecting the source and receiver. The transport equation is solved by a Pestorius algorithm. In the second model, the KZK equation is modified to account for the effect of a random temperature field and it is then solved numerically. Results from numerical experiments that simulate the propagation of spark-produced N waves through turbulence are presented. It is observed that turbulence decreases, on average, the peak pressure of the N waves and increases the rise time. Nonlinear distortion is less when turbulence is present than without it. The effects of random vector fields are stronger than those of random temperature fields. The location of the caustics and the deformation of the wave front are also presented. These observations confirm the results from the model experiment in which spark-produced N waves are used to simulate sonic boom propagation through a turbulent atmosphere.
Acoustic radiation force on a spherical particle in a viscous heat-conducting fluid. II. Force on a rigid sphere
Authors: Doinikov Alexander A.
Published: July 2002

The general expression derived in Part I of this study [J. Acoust. Soc. Am. 101, 713–721 (1997)] for the acoustic radiation force on a spherical particle immersed in a viscous heat-conducting fluid is applied here to the case of a rigid sphere. Three types of incident sound field are considered: a plane traveling wave, a plane standing wave, and a diverging spherical wave. To demonstrate dissipative effects on the force clearly, for each of these fields two limiting cases of interest are investigated. In the first of these, the sphere radius is assumed to be large compared with the viscous and thermal wavelengths in the surrounding fluid and the thermal wavelength inside the sphere. In the second case, the sphere radius is assumed to be small compared with the above wavelengths. In addition, in both cases, it is assumed that the sound wavelength is much larger than the above parameters. Since viscous effects have been examined in earlier papers by the present author, in this paper, the main attention is given to thermal effects. It is shown that these can drastically change the radiation force, resulting in, for example, the movement of light spheres both from the sound source and to it in a plane traveling wave and levitation in a diverging spherical wave.
Active control of sound radiation from cylinders with piezoceramic actuators and structural acoustic sensing
Authors: Maillard Julien P. , Fuller Chris R.
Published: July 2002

In this paper, analytical and experimental results of an investigation of active control of sound radiated from cylinders are presented. The aluminum cylinder is 1 m in length, 25 cm in diameter, and 2.4 mm in thickness with two rigid endcaps at both ends. The excitation is a bandlimited random noise encompassing the first five modes of the cylinder and the control actuators are surface mounted piezoceramic transducers. Since it is desired to integrate the error sensors into the structure, the recently developed structural acoustic sensing (SAS) approach is extended to cylindrical coordinates and implemented using 12 accelerometers mounted on the cylinder. The SAS approach provides time-domain estimates of far-field radiated sound at predetermined radiation angles. The controller is a 3×3 filtered-x LMS paradigm implemented on a TMS320C30 DSP. The results show excellent global control of the radiated sound over the frequency bandwidth of excitation. The SAS approach is shown to yield similar performances as error microphones located in the far field. [Work supported by the Office of Naval Research.]
Arabs’ stress placement in English: Intelligibility test
Authors: Mitleb Fares
Published: July 2002

This study was intended to give an impressionistic description of Arabs’ performance in English stress placement. Therefore, two native British English speakers were asked to evaluate six Arabs production of English words. Findings indicated that Arab subjects’ ‘‘conscious knowledge’’ of a stressful speaking situation was less than satisfactory. Listeners reported a great percentage of confusion in stress placement. A number of explanations were attempted for the intelligibility problem which arises from the misplacement of stress in our subjects’ production. It was inferred from confusions Arabs made that suprasegmentals are to be given emphasis in the teaching of foreign languages and should be taught simultaneously with segmental structure of the target tongue. [Research supported by Yarmouk University.]
Temporal gap detection thresholds measured for conditions that minimize off-frequency listening
Authors: Formby C. , Sherlock L. P. , Forrest T. G.
Published: July 2002

Temporal gap detection (TGD) thresholds measured for silent gaps as a function of the frequency separation between a fixed-frequency pre-gap sinusoidal marker (F1) and a variable-frequency post-gap sinusoidal marker (F2) may be confounded by off-frequency listening (Formby et al., Aud. Neurosci. 3, 1–20). Evidence of this confounding role comes from simulation experiments with a single-channel envelope detector model. TGD stimulation results suggest that listeners can improve the signal-to-noise ratio and, in turn, TGD performance by adjusting their optimal auditory filter so that it is centered between F1 and F2 (Forrest and Formby, Aud. Neurosci. 3, 21–33). Off-frequency listening between F1 and F2 may result in underestimates of TGD thresholds that appear as asymmetries in detection performance for F2 markers presented below and above the F1 frequency. To obtain more precise estimates of TGD, unaffected by off-frequency listening, performance has been measured and will be reported for three listeners with markers spaced symmetrically and asymmetrically in linear frequency below and above the center frequencies Fc=500 and 4000 Hz. These new results will be compared with an otherwise comparable set of results that were likely confounded by off-frequency listening (Formby et al., Aud. Neurosci. 3, 1–20). [Research supported by NIH.]
Pulse propagation through continental-shelf internal solitary waves
Authors: Turgut Altan , Wolf Stephen N.
Published: July 2002

A newly developed pseudospectral numerical model is used to study pulse propagation through continental-shelf internal waves. A time-domain mode coupling analysis is performed on plane-wave pulses propagating through a simple internal solitary wave (ISW) described by downward undulation of a thermocline having the shape of hyperbolic secant. Initial acoustic fields made up of eight-cycle Hanning-weighted sine waves with 224- and 400-Hz center frequencies (vertically shaded by desired acoustic mode shapes) are used. Two-dimensional and three-dimensional numerical results were compared to investigate the validity of two-dimensional techniques in the case of nonparallel acoustic-ISW alignment. Similar to the results of Preisig and Duda [IEEE J. Oceanic Eng. 22(2) (1997)], it has been observed that the horizontal refraction and azimuthal scattering seem to be minor for up to 65-deg oblique incidence angle. Results of two-dimensional propagation and mode-coupling analysis for the ISW packets measured during the SWARM95 experiment are also discussed. [Work supported by ONR.]
Observations of attenuation during the Scripps Pier bubble experiment
Authors: Caruthers Jerald W. , Elmore Paul A. , Beben Philip A. , Stanic Stephen J.
Published: July 2002

An experiment that measured the effects of bubbles just offshore from active surf was performed in the spring of 1997 off the pier at the Scripps Institution of Oceanography. A region from a few tens of meters to 1000 m from the beach was instrumented by several researchers. An emphasis was placed on a region approximately 400 m2 in area and about 300-m offshore where most of the instruments were clustered. Located in this area was a triangular-shaped frame called the Delta Frame, which had sources at two vertices and eight hydrophones along the perimeter (each side was 9.4 m long). Eight frequencies, from 39 to 244 kHz, were propagated sequentially from each source and received on each hydrophone. All 16 transmissions occurred within 12 ms and were repeated at a 1-s interval during each of ten 88-min data runs. Bubbles produced in the surf zone were carried out to the experimental region by rip currents and had dramatic effects on all the instruments. This paper discusses their effects on attenuation as measured at the Delta Frame. [Work supported by ONR.]
Attenuation estimates for bubbly sea water
Authors: Goodman R. R. , Elmore P. A. , Caruthers J. W.
Published: July 2002

Acoustic techniques used for determining bubble distributions can be limited because a solution to an ill-conditioned inverse problem is required. Examining cases in which closed-form solutions are possible, however, may give us insight about the inverse procedure. In a previous ASA meeting [Goodman, Caruthers, and Elmore, ‘‘Dispersion estimates for bubbly seawater,’’ J. Acoust. Soc. Am. 100, 3196(A) (1997)], exact solutions for dispersion for the inverse procedure in special cases of bubble distributions were explored. Here some of those special cases are examined in terms of how they apply to attenuation measurements. For cases in which the closed-form solution are not possible, the resonant bubble approximation allows for estimating the bubble population from attenuation measurements. This paper shows that there is observable error in this procedure, but that the error can be reduced by application of an iterative procedure discussed here. [Work supported by ONR.]
Modeling of harmonic generation and shock formation in nonlinear surface acoustic waves in several real crystals
Authors: Kumon R. E. , Hamilton M. F. , Il’inskii Yu. A. , Zabolotskaya E. A.
Published: July 2002

Harmonic generation and shock formation in nonlinear surface acoustic waves that propagate in anisotropic crystals were studied numerically on the basis of a new theoretical model presented earlier [Hamilton et al., Nonlinear Acoustics in Perspective, edited by R. J. Wei (Nanjing University Press, Nanjing, 1996), pp. 64–69]. The theory applies for arbitrary elastic materials, surface cuts, and propagation directions. Numerical simulations were performed for initially sinusoidal signals propagating across the surface of KCl, Ni, and Si crystals for the (001), (110), and (111) cuts, and over the appropriate range of directions for each cut. Waveforms are shown to exhibit asymmetric distortion, well-defined shocks with cusped spikes in the horizontal waveform, and a phase shift in the zero crossings. Solutions for propagation in the (001) plane and in the 〈100〉 direction of KCl are shown to exhibit atypical trapping of energy in the lowest order harmonics. Analytical solutions derived for the fundamental and second-harmonic components for this particular case are in good agreement with the numerical solutions close to the source. Although the phenomenon resembles one observed in nonlinear optics resulting from dispersion, it is due instead to properties of the nonlinearity coefficient matrix. [Work supported by ONR.]
An improved theoretical model for highly nonlinear bubbly liquids
Authors: Zhu Zhemin , Zhao Xiaoliang , Du Gonghuan
Published: July 2002

Strong nonlinearity of bubbly liquids is a most interesting property not only for its theoretical importance in nonlinear acoustics but also for its potential application in, for example, ultrasound imaging technology. A physical model which describes the nonlinear property of liquids containing uniform size bubbles is presented [Ultrasound Med. Biol. 21, 545–552 (1995)]. The theory is successful to some extent but still has some limitations since the sizes of the bubbles are usually not exactly the same. In this paper, a model dealing with more practical situations, i.e., liquids containing many bubbles whose sizes are randomly distributed is extended. The effective nonlinearity parameter B/A (as high as about 104) and attenuation coefficient for these bubbly liquids are given. Calculations and comparisons show that the improved model explains the existent experiments more satisfactorily. [Work supported by the National Science Foundation of China.]
Shock-wave collisions in bubbly liquids: Numerical studies
Authors: Kedrinskii Valery K.
Published: July 2002

The results of numerical investigations of different effects arising in bubbly liquid due to wave interactions are presented. The influence of the gas content on the parameters and the structure of shock waves and of chemical reactions in the gas phase will be considered. The problem is solved within the framework of the two-phase mathematical model including the kinetic equations for the description of the medium-state dynamics, thermoexchange as well as of bimolecular reaction kinetics. The purpose is to estimate the amplification level of the wave intensity as the result of such kinds of interactions. The wave amplitudes in a passive bubbly media turned out to be amplified by one order of magnitude in the collision plane and their amplification depends on the bubble concentration k0 as pmax=2+24.5⋅k01/4. The possibilities of simulating the hot-spot mechanism of liquid explosive detonation ignition and the mechanism of the large-scale explosions of containers filled with a fuel by bubbly detonation wave interactions are discussed. [Work supported by RFFR, Grant 96-02-19369.]
Radiation from small acoustic sources located close to a submerged, compliantly coated cylindrical shell
Authors: Gray Michael D. , Caille Gary W. , Bogle John R. , Rogers Peter H.
Published: July 2002

Measurements were made of the radiation from individual, small acoustic sources located close to a submerged, compliantly coated, thin cylindrical shell in the 1<ka<20 frequency range, where k is the acoustic wavenumber, and a is the radius of the coated cylinder. The behavior of the radiated pressure field is shown to have two distinct frequency regimes. For ka>5, the field is simple, and is well approximated by a source and its negative image. For ka<4, the pressure field is characterized by significant spatial variations, owing to contributions from the elastic response of the coated cylinder. Finite-element model results are compared with the measurements, and are used to provide insight into the interactions between the source and the coated shell. [Work supported by ONR.]
Method for broadband measurement of complex shear modulus and Poisson ratio of viscoelastic materials
Authors: Sheiba L.
Published: July 2002

This method is based on the inverse solution to the vibration problem of a finite elastic cylinder with reinforced torsion surfaces by rigid septa or plates. In all cases the polymer layer to be tested is bonded to rigid plates; therefore, the radial displacement is zero at the boundary between the polymer layer and the septum. The admittance matrix Y of the element with abovementioned boundary conditions is constructed within the framework of the hypothesis for planar cross sections. The dimensionless shear wave number kt(ω)h and compression wave number kλ(ω)h, which are the unknown variables, are obtained by measuring the transfer matrix of a known structure and as a result of solving the transcendental equation in a designated frequency range. Data are attained over a broadband of frequencies and temperatures without dependence on the time-temperature superposition principle. 10:00
Effects of laser stroke parameters on quantitative vibration measurements with stroboscopic shearography
Authors: Bard Benjamin A.
Published: July 2002

Digital shearography is a full-field speckle interferometric technique similar to electronic holography. Traditionally, shearography and holography have been used for vibration measurement with either time averaged or stroboscopic techniques. Time averaging images sinusoidal motion of an object’s surface over many periods of vibration, resulting in a fringe pattern representative of the magnitude of the displacement mode shape. Stroboscopic illumination synchronizes short bursts, or strokes, of laser light with extrema of vibration. This essentially freezes motion of the vibrating surface, allowing it to be studied with techniques normally reserved for static deformation. In particular, phase stepping, an established technique for capturing a series of images and calculating the exact displacement at every point, can be applied to vibration measurement. If displacement amplitudes calculated from laser strobing and phase stepping are to be used for measurement of peak vibration response, corrections are necessary to compensate for errors due to the finite duration of the laser strokes as well as their improper timing due to system impedance. In this presentation, effects of stroke duration will be expressed mathematically and trends demonstrated experimentally. Potential solutions for stroke offset correction will be discussed and experimental validation provided. [Work sponsored by the PSU Applied Research Laboratory.]
Sonar observations of deep ocean hydrothermal flows
Authors: Jackson Darrell R. , Jones Christopher D. , Wen Timothy , Rona Peter A. , Bemis Karen G.
Published: July 2002

A mechanically scanned sonar operating at 330 kHz has been used to image hydrothermal flows on ocean ridges using two different techniques. Scattering from particulates is used to image smoker plumes [Rona et al., Geophys. Res. Lett. 18, 2233–2236 (1991)], and scintillation of seafloor backscatter is used to image diffuse flows. Results will be presented from cruises on the East Pacific Rise and the northern Cleft segment of the Juan de Fuca Ridge. Plume images have been analyzed to extract physical parameters relevant to plume theory. Observations of diffuse flow employ cross correlation of ping doublets. Scattering theory is used to relate the correlation levels to the variance of temperature fluctuations. [Work supported by the NOAA National Undersea Research Program through the West Coast Undersea Research Center.]
Seismoacoustic recordings of a volcanic event on the Mohns Ridge, 1995
Authors: Blackman Donna K. , Orcutt John A.
Published: July 2002

A swarm of earthquakes occurred on an oceanic spreading center north of Iceland in late 1995 and was recorded by U.S. Navy hydrophone arrays in the Norwegian Sea. About two dozen of these events on the Mohns Ridge were detected by onshore seismic arrays. Analysis of the hydrophone array data shows that 7000 events occurred; the greatest number (40/h) took place in a 3-day period in the middle of the 70-day duration of the swarm. Recorded arrivals include P waves, water-borne T waves, PT pairs, and P waves reflected at the seasurface. Separation in arrival times of P and T waves are used to determine relative locations of events and their spatial evolution throughout the swarm. The locus of activity shifts by 30–40 km during the swarm but steady migration of activity is not apparent. This suggests that surface breaks during dike injection did not occur or, at least, did not generate T waves, or that the swarm was not associated with a simple dike emplacement along the ridge. The time history of the activity, on the other hand, is quite similar to that seen associated with two known volcanic events on the Juan de Fuca and Gorda ridges.
Velopharyngeal function in young and older adult speakers: Evidence from aerodynamic studies
Authors: Zajac David J.
Published: July 2002

Intraoral air pressure (P0), nasal airflow, and nasal air volume characteristics were determined from 63 adult speakers during production of oral and nasal consonants. The speakers were categorized into two age groups. Young speakers (21 males, 21 females) ranged in age from 18 to 37 years (mean=24); older speakers (10 males, 11 females) ranged in age from 68 to 83 years (mean=75). Speakers produced the syllables /pi/ and /si/ and the word “hamper” at self-determined loudness levels during reiterant speech tasks. Results indicated similar velopharyngeal function between young and older adults as reflected by nasal airflow and air volume measures. Older adults, however, exhibited significantly higher levels of P0 than younger adults during production of /p/ in “hamper.” In addition, (a) male speakers exhibited higher P0 than females during production of /p/ in “hamper,” (b) all speakers demonstrated declination of P0 during production of /p/ in “hamper” as a function of word position in the utterance, and (c) male and female speakers exhibited different patterns of nasal air volume during production of “hamper” as a function of word position in the utterance. The intraoral air pressure results suggest differences in respiratory function between young and older speakers. The nasal air volume results suggest a gender specific velopharyngeal declination effect. Implications for velar motor control strategies are discussed.
Earthquake studies using under-ice hydrophone data (‘‘Spinnaker’’)
Authors: Sohn Robert A. , Hildebrand John A. , Sotirin Barbara J.
Published: July 2002

Preliminary studies indicate that the Spinnaker array, a network of hydrophones currently deployed in the Arctic Ocean, may be used to monitor seismicity of the Arctic Basin, as well as long distance teleseismic arrivals from the Southern Hemisphere. The Arctic Basin is a tectonically complex region that has seen few seismic studies, and the Spinnaker array has the potential to monitor some of its most interesting features, such as the Nansen–Gekkel Ridge (the slowest spreading ridge in the world), in near real time. In addition, teleseismic arrivals at the array may have raypaths that coincide closely with the Earth’s spin axis. These data may prove useful to current studies of the crystalline alignment and differential spin of the Earth’s inner core.
Fractals, wavelets, and stochastic interface modeling
Authors: Lupien Vincent
Published: July 2002

The seafloor is one of many natural interfaces which, when viewed as a random process, exhibits a power law decay, i.e., the power spectral density (PSD) decays as A/fb, A>0, b>0 as f→∞. Power law spectra are usually taken as evidence that the stochastic process is multiscale or fractal. Multiscale interfaces exhibit features at all scales and their acoustical properties are distinct from those of single-scale interfaces, which contain features closely clustered about a mean size. Thus, determination of the scale structure, or size distribution of component features, is important in characterizing random interfaces for acoustical applications. However, because the PSD is only a second moment characterization, a power law PSD can allow both single-scale and multiscale processes. Only if the process is Gaussian is the PSD a complete description. Wavelet representations succeed where Fourier methods fail, as they are ideally suited for determining scale structure. In the case of fractal interfaces, the wavelet coefficients are Gaussian and independent across scale and space. Single-scale interfaces lead to a dependence of wavelet coefficients across scale for a given spatial location and vice-versa.
Thermoacoustic measurements on a single pore with an applied temperature gradient
Authors: Wilen Larry A. , Petculescu Gabriela , Petculescu Andi G.
Published: July 2002

Previous measurements [L. Wilen, J. Acoust. Soc. Am. 101, 3022(A) (1997)] probed the geometry-dependent thermal coupling between a gas and the walls of single pores over a wide range of ratios of the thermal penetration depth to pore size. A volume modulation method was described which allows one to measure the complex compressibility of the pore directly. The present work extends those results to pores with an applied temperature gradient. Unlike the earlier experiments, the results are sensitive to terms in the thermoacoustic equations which depend on a gradient, and the theoretical predictions can be tested in a direct way. After a brief review of the experimental technique, data for pores of different lengths and gradients will be presented and discussed. Possible new applications of the technique will be proposed. [Work supported by Ohio University Research and Sponsored Programs.]
Numerical investigations of a two stack annular prime mover
Authors: Lin Hsiao-Tseng , Muehleisen Ralph T. , Atchley Anthony A.
Published: July 2002

A numerical analysis of the two-stack thermoacoustic prime mover in an annular resonator has been made. It was found that the addition of a second stack significantly alters the eigenmodes of a single stack annular prime mover such that thermoacoustic growth may be supported. Simulations predict that one mode of the two-stack prime mover could reach onset at a reasonable temperature. The performance of the two-stack prime mover with various spacings between the stacks is presented. The results are compared to the performance of single-stack annular prime mover in a constricted annular resonator. [Work supported by the Office of Naval Research and the American Society for Engineering Education.]
Design of a thermoacoustic refrigerator for visualization measurements
Authors: Wetzel Martin , Herman Cila
Published: July 2002

In previous studies, holographic interferometry (HI) combined with high-speed cinematography was applied to investigate the oscillating temperature field in a thermoacoustic refrigerator model [Wetzel et al., J. Acoust. Soc. Am. 100, 2846(A) (1996)]. While important flow parameters of thermoacoustics could be matched in these experiments, it was not possible to model all length scales because of design requirements imposed by HI. In order to resolve this problem, a novel design algorithm was developed based on the short-stack boundary-layer approximation. The advantage of this algorithm is that all design parameters are presented in normalized form, and therefore, the design optimization can be performed in the normalized multidimensional parameter space without determining the actual dimensions of the device. Once this optimization has been completed, the actual dimensions can be determined according to the design requirements imposed by HI. At the meeting, the design as well as initial measurements with the thermoacoustic refrigerator will be presented. [Work supported by the Office of Naval Research.]
Angle dependence of the meridional leaky-ray backscattering enhancement from the end of a tilted finite cylinder. Convolution analysis and a numerical test for shells
Authors: Marston Philip L. , Morse Scot F.
Published: July 2002

Reflection of a meridional leaky ray from the far end of a tilted cylinder produces a backscattering enhancement when the tilt angle is close to the leaky wave coupling angle. The ray lies in the meridional plane defined by the incident wave vector and the cylinder’s axis. The peak magnitude of this enhancement was related to the end-reflection coefficient by a convolution surface integral [P. L. Marston, J. Acoust. Soc. Am. 102, 358–369 (1997)]. The more difficult integrals descriptive of the dependence on tilt angle are numerically evaluated in the present study. Though the exact analytical solution of the problem considered is unknown, for comparison an approximate partial-wave series description is available where the boundary conditions at the ends of the cylinder are such that the end-reflection coefficients become unimodular. For antisymmetric leaky Lamb waves on long thick and thin shells, the enhancement width, magnitude, and location each agree with the result from the integral when a unimodular reflection coefficient is also assumed in the convolution formulation. The convolution analysis should also apply to meridional leaky Rayleigh waves reflected by the ends of a solid cylinder. [Work supported by the Office of Naval Research.]
Confirmation of the effective coefficient for scattering by turbulent velocity fluctuations
Authors: Smith Makeda J. , Wilson D. Keith , Heyd Michael , Havelock David I. , Auvermann Harry J. , Noble John M.
Published: July 2002

The effective structure-function parameter for scattering by atmospheric, turbulent velocity fluctuations has normally been assumed to be Ceff2=4C2V/c20 However, a new derivation by V. E. Ostashev [Waves Random Media 4, 403–428 (1994)], which takes into account the vectorial nature of the wind velocity field, suggests that Ceff2=22C2V/3c20. An experiment was designed to determine the correct value of the coefficient. Amplitude variances were monitored for several discrete frequencies between 380 and 3500 Hz, at distances up to 675 m. Cup and hot-wire anemometers were used to determine C2V. A theory for scattering by inertial-subrange turbulence was then used to calculate the Ceff2 coefficient from the amplitude variance and C2V. Although there is some tendency in favor of the 22/3 coefficient, the results cannot be considered conclusive. The main difficulty appears to be obtaining a sufficiently accurate measurement of C2V.
Capabilities and limitations of boundary- and finite-element methods for solving noise and vibration problems
Authors: Hamdi M. A. , Mebarek L.
Published: July 2002

Over the last decades the boundary- and finite-element methods (BFEM) have been used in the solution of practical mechanical engineering problems. It is, therefore, appropriate at this time to examine the capabilities and the limitations of these numerical methods to predict, analyze, and solve real-life vibroacoustic problems encountered in several industries such as aerospace, automotive, naval, and railroad. Due to the rapid growth of computer power, several computer-aided engineering tools, based on these BFEM techniques, have been developed and are now commercially available. The purpose of this paper is to review the current state of development of BFEM techniques, and to examine their ability to predict and solve noise and vibration problems. The finite-element method (FEM), will be first analyzed for interior fluid–structure interaction problems, with an extension for exterior radiation problems using the infinite-element method (IEM). Then, the boundary-element method (BEM), will be analyzed for external interaction problems, where the fluid domain is infinite. It will be shown that the combination of these two methods (BFEM) provides a very powerful tool for solving a wide class of vibroacoustic problems, taking advantage of advanced numerical algorithms implemented on modern high-performance computing platforms.
The internal wave spectrum: Evolution, resolution, and inversion
Authors: Pinkel Robert
Published: July 2002

Internal waves scatter low-frequency sound, complicating the interpretation of long-range acoustic transmission experiments. One can now ‘‘invert’’ acoustic data and infer parameters of a modeled internal wave spectrum (S. Flatté, this session). The quality of the result depends, among other things, on the realism of the model spectrum. For many phenomena (surface gravity waves, for example), changes in wave-field energy result in changes in spectral form, as well as level. It is appropriate to investigate this issue with regard to internal waves. Estimates of the vertical wave-number-frequency spectrum of internal waves are presented from six sites around the world (83° N to 2° S). Coded pulse Doppler sonar systems provide the required data. Wave-field energy varies by a factor of 100 in the global sample. The wave-number dependence of the spectrum varies with both wave frequency and overall spectral energy level. These spectral estimates are ‘‘resolved’’ in the sense that ocean velocity profiles are inverted to provide estimates of variance density on a band-by-band basis in the wave-number-frequency domain. The ‘‘model mismatch’’ issue is not escaped, however, since the waves are often nonsinusoidal. The spectrum alone provides an incomplete description of the field.
Long-range tomography experiment in the western equatorial Pacific
Authors: Yuan Gang , Fujimori Hidetoshi , Nakamura Toshiaki , Nakan Iwao
Published: July 2002

An ocean acoustic tomography experiment was performed with a pair of 200-Hz transceivers in the western equatorial Pacific along the longitudinal line of 147.5 °E during April–December 1996. Time series of reciprocal ray travel times were obtained at about the 700-km range for approximately 100 days between the transceivers. The one-direction, resolved-ray travel times were applied to obtain temperature, and differential resolved-ray travel times to obtain barotropic current velocity. The inversions derived from the stochastic inverse method gave a series of snapshots of two-dimensional temperature fields, which showed a pattern similar to that determined from CTD measurements during the transceiver deployment cruise. The range-averaged temperature anomaly, δT(z), agreed almost perfectly with that calculated from the difference between the CTD temperature profile and the NODC reference temperature profile within an estimated error of ±0.5 °C, except for the surface layer. The evolution of acoustically determined range-averaged temperature and temperature anomaly structures agreed well with the concurrent PMEL/TAO array data. A range-averaged barotropic current determined from the difference of the reciprocal ray travel times also agreed with the range- and depth-averaged meridional velocity determined from ADCP measurements during the transceiver deployment cruise in the same order.
Modulation of ultrasound by vibration and its application for flaw detection
Authors: Sutin Alexander , Donskoy Dimitri M.
Published: July 2002

The paper gives an overview of a recent advancement in the development and implementation of an innovative nonlinear modulation technique for nondestructive testing. The theoretical and experimental investigations discovered that a weakly or incompletely bonded interface or contact-type defect causes the modulation of a probing high-frequency ultrasonic wave by low-frequency vibration. The vibration varies the contact area modulating the phase and amplitude of a higher-frequency probing wave passing through the interface. In the frequency domain the result of this modulation manifests itself as sideband spectral components with respect to the frequency of the probing wave. Such a modulation effect was observed experimentally for various materials (metals, composites, concrete, sandstones, glass) with various types of defects such as cracks, debondings, delaminations, and microstructural changes. Two modifications of the technique have been developed: vibromodulation (VM) and impact modulation (IM), employing cw and impact-induced vibrations, respectively. The examples of applications of these methods include crack detection in Boeing 767 steel fuse pins, combustion engine cylinder heads, sandstone, and glass. These methods also proved their effectiveness in evaluating bonding conditions in titanium and composite plates, as well as corrosion in reinforced concrete.
Mesa di voce: An investigation of the symmetry of crescendo and decrescendo in singing
Authors: Titze Ingo , Long Russel
Published: July 2002

Messa di voce (to place the voice) is an often used exercise by professional classical singers. It is a crescendo followed by a decrescendo on a constant pitch and vowel. Difficulty is often encountered in maintaining constant voice quality (register) and a consistent and gradual loudness change, especially at high pitches. Six well-trained singers were studied, three males and three females. Measurements consisted of sound pressure level, electroglottography, oral airflow, subglottal pressure, lung volume change, and ribcage and abdomen movement. Results indicate that symmetry between crescendo and decrescendo portions is effected by variations in subglottal pressure and peak acoustic airflow, and to a lesser extent, by abdominal movement. Subjects also differed greatly in their soft–loud dynamic ranges. [Work supported by NIDCD, Grant No. P60 DC00976.]
Experiments on a recorder with a movable, expandable tone hole
Authors: Kunes Kay C. , Hall Donald E.
Published: July 2002

The pitch produced by a flute-type instrument with a single tone hole depends on the position and size of that hole. Comparisons of theory with reality would be easiest if that tone hole had continuously variable size and position, so that no other holes need be present to complicate matters. A scheme for having such a tone hole has recently been presented [D. Hall and J. Schreiner, Proc. Intl. Soc. Musical Acoustics, Edinburgh (1977)]. A recorder head joint attached to a slotted cylindrical tube fitted with a sleeve with a wedge-shaped hole allows ranges of approximately 5 cm in hole position, a factor of 5 in hole size, and 2.5 semitones in pitch. This makes possible relatively simple experiments for (1) comparing the effect of hole size and position upon fundamental frequency with approximate theories and (2) studying the effect of hole size and position upon departure from harmonicity of the first two natural modes of the instrument. Results of such experiments will be presented.
New techniques for nonlinear system analysis and identification from random data
Authors: Bendat Julius S.
Published: July 2002

Direct and reverse MI/SO (multiple-input/single-output) techniques are new frequency-domain techniques that provide accurate practical methods to analyze and identify the dynamic properties of nonlinear systems. The Dirac MI/SO technique is applicable to nonlinear systems with specified parallel linear and nonlinear transformations. The reverse MI/SO technique is applicable to nonlinear systems that can be reasonably modeled by nonlinear integrodifferential equations of motion. Nonlinear systems are included where the coefficients can be constants or frequency dependent. Simulated or measured data can have arbitrary probability and spectral features. Each of the identified nonlinear components can be evaluated at any desired frequency with separate coherence functions. Thus these techniques represent a significant advance in using real-world data to help improve the design and understanding of nonlinear systems. This presentation will review the analytical basis of these new techniques and illustrate their application from material in the latest book by J. S. Bendat [Nonlinear System Techniques and Applications (Wiley-Interscience, New York, 1998)].
Power flow in structures
Authors: Rasmussen Gunnar
Published: July 2002

Power released in or transferred to a structure will cause noise radiation, fatigue, or mechanical malfunction in the structure or parts connected to the structure. Nonlinear behavior is of great significance to the integrity of any structure and is therefore of fundamental interest. An ideal machine would produce no vibration at all because all energy would be channeled into the job to be done. In practice, vibration occurs as a by-product of the normal transmission of cyclic forces through the mechanism. Machine elements react against each other and energy is dissipated through the structure in the form of vibration and acoustic noise. If the surface area is large compared to an acoustic wavelength, acoustic intensity is a good indicator of dynamic activity. If the area is small compared to a wavelength at the frequencies in question, surface measurements using the vibratory motion on the structure’s surface will be a good indicator. If the energy transfer takes place between two separate structures coupled at points, the point power measurement method should be applied. Two accelerometers, accelerometer and force gauge, two microphones, multi microphone arrays or laser techniques may be used for transduction. Signal processing and interpretation will be discussed.
Spectral function of the shocks of acoustic fluctuation phenomena
Authors: Tran Dat H. , Krasilnikov Alexsandr J.
Published: July 2002

In the description of the acoustic fluctuation phenomena (AFP), for example, sonocavitation noise, the signals of the acoustic emission, scattering on the heterogeneity, reverberation, and others, the model of shot noise is often applied and the principle of distribution is considered to be Gaussian. This model of AFP is proposed and proven with the conjecture that the shape of the impulse depends on the time of its generation, and amplitude of the impulse is subjected to the inhomogeneous Poisson process. It was shown that the characteristic function of the linear process is an unlimited dividend and, therefore, the function of the distribution or the probability density cannot be obtained in the evident mode, even through the mixed function. The spectral function of shocks (SFS) was proposed for the investigation of the principle of distribution and for the determination of the characteristic function. The algorithm was obtained that permits finding the SFS. Komologov, Levin, and some properties of SFS as well and the results of the calculation of SFS of the different AFPs are shown.
The control of beam direction and beamwidth of loudspeaker arrays
Authors: Harrell Jefferson A. , Hixson Elmer L.
Published: July 2002

By the control of time delay and the frequency function of each speaker in an array, the direction and coverage as a function of frequency can be controlled. Beamwidth can be held constant with frequency so that everyone in the coverage area will receive the same spectrum of sound. Examples of one-dimensional beam control will be presented using broadside and endfire line arrays. Then two-dimensional coverage control with crossed broadside and stacked endfire arrays will be demonstrated. Advantages of controlled loudspeaker arrays will be discussed.
Information theory and variance estimation techniques in the analysis of category rating and paired comparisons
Authors: Takayanagi Sumiko , Hasegawa-Johnson Mark , Eisenberg Laurie S. , Martinez Amy Schaefer
Published: July 2002

Speech clarity judgments of bandpass filtered sentences were measured by category rating and paired comparisons in five age groups—4, 5, 6, 7, and 8 years old, and adults [data for children were provided from Eisenberg and Dirks, J. Speech Hearing Res. 38, 1157–1167 (1995)]. The judgment data within each age group were subjected to information theory and variance estimation analytical techniques in order to investigate developmental differences in task performance capability. All response variability was converted into equivalent signal detection ‘‘error’’ components, representing the ability of subjects in a given age group to perform a given psychophysical procedure. Preliminary results revealed a different developmental trend for each psychophysical procedure. For category rating, children 4 to 6 years of age exhibited higher error components in their responses, suggesting reduced capability to extract information compared with adults. In contrast, children as young as 5 years of age were approaching adultlike low error components in the paired comparisons. In this particular study, paired comparisons may provide a greater amount of information with less variance than category rating when subjective judgments of sound quality are measured. [Work supported by NIH.]