bluuebunny/crossref_metadata_2025 huggingface dataset:
The interaction of airborne sound with the poroelastic ground
Authors: Hickey Craig J. , Sabatier James M.
Published: October 2013

An airborne acoustic wave impinging on the surface of the ground provides a good vibrational source for investigating the near surface. Research has been carried out on the use of this type of source for landmine detection, characterization of agricultural soils, and studying the characteristics of snow and ice cover. Since the ground and snow is porous, the impinging sound wave induces motion of the fluid within the pores as well as vibrating the solid framework. Vibrating the solid component of the ground using an airborne sound source is known in the acoustic community as acoustic-to-seismic (a/s) coupling. The most complete understanding of the interaction of airborne sound with the ground is to treat the ground as a poroelastic or poroviscoelastic medium. This treatment predicts three types of waves can propagate in a bulk homogeneous porous material with a deformable framework: two dilatational waves and one rotational wave. The dilatational waves are usually referred to as the fast, or Type I, and slow, or Type II, waves and deform both the solid and fluid constituents. This presentation will discuss the energy partition and impedance at an air-porous medium interface as related to the solid and fluid deformations.
Vibration of submerged prolate spheroidal shells with internal fluid loading
Authors: Boisvert Jeffrey E. , Hayek Sabih I.
Published: October 2013

The equations of motion for nonaxisymmetric vibration of submerged prolate spheroidal shells of constant thickness with internal fluid loading were derived using Hamiltons principle. The shell theory used in this derivation includes shear deformations and rotatory inertias. The shell displacements and rotations were expanded in infinite series of comparison functions. These include associated Legendre functions in terms of the prolate spheroidal angular coordinate and circular functions in the azimuthal angle coordinate. The external and internal fluid loading impedances were computed using expansions of prolate spheroidal wave functions in each domain. The shell was excited by axisymmetric normal surface forces, including a point load at the shell apex and ring load at other locations. Numerical results were obtained for the driving and transfer mobilities for several shell thickness-to-half-length ratios ranging from 0.005 to 0.1, and for various shape parameters, a, ranging from an elongated spheroid shell (a=1.01) to a spherical shell (a=100). Results are presented for various combinations of external and internal fluid loading, and comparisons are made to the in vacuo shell vibration. [Work supported by ONR and the Navy/ASEE Summer Faculty Program.]
Noise radiated from a rotating submerged elastic cylindrical thin shell
Authors: Caspall Jayme J. , Yoda Minami , Rogers Peter H.
Published: October 2013

Although the aeroacoustics of high Reynolds number boundary layers is reasonably well understood, less is known about the hydroacoustics of such flows, and the effect of fluid loading. The noise generated by the turbulent boundary layer around an elastic, thin-walled and cylindrical shell rotating in quiescent water was studied in the Georgia Tech. Underwater Acoustic Tank for Reynolds numbers up to 200000. The steel shell, which is filled with air, has a diameter D of 0.625 m, a wall thickness of 0.004D, and an aspect ratio of unity; the tank dimensions are 19D by 12D by 11D. Extraneous noise sources (e.g., bearing and motor vibration) were isolated from the net signal to estimate flow noise. Radiated noise power was calculated from hydrophone data under a diffuse field assumption. To our knowledge, these results are unique in both their structural acoustics and fluid mechanics scaling.
Vibration of a cylindrical membrane shell subjected to a steady rotational load
Authors: Koral Arthur I. , Pierucci Mauro
Published: October 2013

The vibration of a cylindrical membrane shell is driven by a point source moving along its circumferential direction. The point source is modeled by a Dirac delta function. The shell vibration is governed by the membrane equations. No variation is assumed to take place along the shell axial direction. The coupled partial differential equations for the radial and the tangential displacements w(theta,t) and v(theta,t) are decoupled by decomposition and two sets of coupled ordinary differential equations for the time varying magnitudes of the shell circumferential modes are obtained. The force starts its motion at t=0 and continues at a constant rate omega. The spectrum of the shell vibration, as expected, shows frequencies that are multiples of the rotating forcing frequency, multiples of the propagating wave front frequency as well as other components. For large times these spectra yield vibrations resembling those of broadband noise.
Modeling of wall-pressure fluctuation based on time-mean flow field
Authors: Lee Yu-Tai , Blake William , Farabee Theodore , Tse Michael , Brown Joseph
Published: October 2013

Time-mean flow field and turbulent flow characteristics from solving the Navier–Stokes equations are used to predict the flow direction wave number spectrum of wall-pressure fluctuations. The vertical turbulent velocity is represented by the kinetic energy contained in the local turbulent flow. A redistribution of the turbulent kinetic energy to account for the anisotropic turbulence is implemented based on the equilibrium turbulent shear flow. The spectral correlation model in predicting the wall-pressure fluctuation is obtained through the Green’s function formulation, and the streamwise and spanwise wave number spectrum modelings. Predictions for the equilibrium flow agree well with measurements, and reveal an overlap region of an inverse of the frequency. Predictions for a 2-D reattached flow field after flow separation and a 3-D flow field on an airfoil with focus on the trailing edge and airfoil tip are discussed and compared to measurements. [Work supported by ONR.]
Simulation of the transient behavior of impact machinery using finite elements package a
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Authors: Villalobos-Luna Jose de Jesus , Lopez-Cruz Pedro , Gonzalez-Guajardo Patricia , Elizondo-Garza Fernando J.
Published: October 2013

In this paper the finite elements method is used to simulate the transient behavior of impact machinery and its foundation. Using the software package ansys, two cases are modeled: first, the impact machine directly mounted on the floor, and second, the machine mounted over an inertia block foundation. The results of the modeling permit clear visualization of transient vibrations in the machine and how they are transmitted to the foundation and the floor. How to use this modeling for didactic purposes is discussed.
Analysis of shallow water experimental acoustic bistatic data
Authors: Brothers Richard , Heald Gary , Dugelay Samantha
Published: October 2013

During February 2002, data were collected in controlled experimental conditions in Weymouth Bay, UK. The experimental setup consists in a broadband source with variable depth and variable azimuthal and tilt angles and a 16 element receiver array located on a tower. The tower is placed at 27.4 m or 33 m from the source and the receiver is pointed in various directions for each pulse. Transmitted pulses consist mainly in CW and linear chirps with central frequencies at 150 kHz, bandwidths varying up to 100 kHz, and pulse lengths varying from 67 ms to 15 ms. The primary objectives of the data reported here are: (1) compare and validate the bistatic scattering strength model developed by the Applied Physics Laboratory of University of Washington; and (2) to assess the complexity and practical implementation of bistatic scattering for mine hunting purposes. Data are processed and the bistatic scattering strength is compared to the predicted bistatic scattering strength. Comparisons are discussed for various geometrical configurations and for different pulse types. Results show good concordance of the model and the experimental data despite ambient noise limitations due to difficult sea conditions.
Broadband matched-field tracking with horizontal line arrays in shallow water
Authors: Baxley Paul A. , Abawi Ahmad T. , Brannan Randall
Published: October 2013

The use of three-dimensional matched-field processing to obtain time-dependent range, depth, and bearing estimates with a horizontal line array (HLA) can be computationally restrictive. The problem becomes much more tractable, however, when beam forming is first used to obtain bearing estimates versus time, which are then used to obtain range-depth ambiguity surfaces versus time. For the case of a moving source, matched-field tracking (MFT) compensates for source motion by integrating matched-field correlations over candidate source tracks through the bearing-range-depth space. The true track is determined by the highest integrated correlation, which also results in a gain in detectibility for the true source track. The effectiveness of this approach for the tracking of broadband sources in shallow water is studied via the analysis of HLA data collected during the Shallow Water Evaluation Cell Experiment 1996 (SWellEX-96), which occurred in 200 m water, 6 km southwest of San Diego. Broadband signals in this experiment included a narrowband comb and the broadband signature emanating from the source-tow ship. The MFT methoc can be used as a stand-alone tracker or as a tool to obtain initial track estimates for the initialization of a more efficient conventional tracker. [Work supported by ONR 321US.]
An AUV underwater acoustic array
Authors: D’Spain Gerald L. , Lepper Paul A. , Zimmerman Richard
Published: October 2013

An eight-element hydrophone array has been installed within the shroud of an Odyssey IIb AUV. Each array channel is digitized and recorded with 10-kHz bandwidth by an autonomous, PC-104+ data acquisition system. To determine the effects of the AUV body itself on the acoustic field measured by the array, tones at low (200–800 Hz) and mid- (2–8 kHz) frequencies were transmitted in a large water tank to the AUV by a source continuously varying in azimuth but fixed range. Bartlett beamforming for source azimuth using both plane wave replicas and replicas calculated using a 2-D time domain, finite-difference code that accounts for the scattering from the two glass spheres in the AUV shows that (1) not accounting for scattering results in 2- to 6-dB signal gain degradation, but (2) scattering moves the ambiguity surface sidelobes closer to the main lobe location, thus improving localization capability. The effect of scattering from the AUV on an azimuthally isotropic noise field, estimated by averaging over pings at all azimuths, is a decrease in spatial coherence at low frequencies over that in free space, thus increasing detection capability. [Work supported by ONR.]
A simple method of passive source range measurement
Authors: Juan Zeng , TianFu Gao , ShengMing Guo , Yan Chen
Published: October 2013

In this paper, a simple method of passive range measurement is discussed. The receiver system can be either hydrophone or horizontal array. Unlike earlier methods of passive source range measurement, we mainly consider the phase information of the passive source, rather than the amplitude. The method only uses the simplest principle range=velocity time. The key of the method is how to acquire the partial deviation of the phase with respect to radial frequency and measurement variables. In physics, the former is equal to time, which can be obtained from the spectrum of the source. The latter is equal to group velocity, which can be evaluated according to the environmental variable, such as water depth, sound profiles, bottom quality, etc. In fact, measurement variables can be substituted by the sound speed in water over the bottom; the error is no more than 8 percent.
Effects of size and density of diffusers on scattering coefficients measured in a 1:10 reverberation chamber
Authors: Jeon Jin Yong , Lee Sung Chan
Published: October 2013

The degree of diffusion, or scattering coefficient, in surface materials has been known to be one of the most important aspects of the acoustical qualities of concert halls. It has also been recognized that one of the best methods, which can reduce the errors in calculating the reverberation time and other acoustic parameters through computer modeling, is to calculate the scattering coefficient of surface materials. Based on the suggested ISO method, which measures the random-incidence scattering coefficient of surfaces in a diffuse field, the scattering coefficients of different size and density of wooden hemispheres were measured in a 1:10 reverberation room. As a result, the 17.5 cm hemisphere (real size) has the maximum scattering coefficient. It was also found that the scattering coefficient was growing higher when the coverage area increased from the center of the base plate and when the diffuse density increased until the density reached about 50%. Ceramic tiles designed by the calculations of scattering coefficients have been installed for the sidewalls of a 400-seat concert hall.
Scattering from faceted surfaces in optimized room acoustics computations
Authors: Torres Rendell R. , Svensson U. Peter , de Rycker Nicolas
Published: October 2013

To minimize the computational demands of including scattering in auralization, it is appropriate to study how many orders of scattering are necessary. For this purpose, studying edge diffraction is especially appropriate as an elementary form of surface scattering. In a previous study [Torres et al., J. Acoust. Soc. Am. 109, 600–610 (2001)], it was found that higher orders and combinations of edge diffraction components were not usually as significant as first-order diffraction components. The primary reason was that the reference geometry (a large concert-hall stagehouse) was conservatively composed of large flat walls with dimensions larger than most wavelengths of interest. In that case, significant edge-diffractions occurred at relatively low frequencies (below about 150 Hz). Other realistic reflecting surfaces in rooms, however, also include smaller-scale surface irregularities, e.g., facets for which higher-frequency wavelengths are typically a similar order or larger. This study examines a smaller test geometry consisting of reflector panel arrays similar to those found in concert halls, and we compare computations with various orders of diffraction. Studies of diffraction order are done to determine when inclusion of higher orders is necessary or may be neglected for applications such as interactive auralization.
Room acoustics auralization studies of laterally incident boss-model scattering
Authors: Torres Rendell R. , Kleiner Mendel , Natsiopoulos Georgios
Published: October 2013

Computation of room impulse responses by commercial auralization programs typically employs simplified Lambert models to account for nonspecular scattering. However, Lambert scattering models, developed primarily for diffuse lighting computation, have limited validity in acoustics. Instead, in this study, surface scattering from hemispherical bosses on walls is computed with numerical models based on exact classical solutions. Scattering impulse responses for auralization are calculated with various configurations of bosses on infinite planes on both sides of a binaural receiver (approximately 7–10 m away). The physical sound field is analyzed along with the resulting subjective effects of varying boss size and scatterer density.
Acoustic diffusers III
Authors: Bidondo Alejandro
Published: October 2013

This acoustic diffusion research presents a pragmatic view, based more on effects than causes and 15 very useful in the project advance control process, where the sound field’s diffusion coefficient, sound field diffusivity (SFD), for its evaluation. Further research suggestions are presented to obtain an octave frequency resolution of the SFD for precise design or acoustical corrections.
Sound reduction by simple walls of brick and concrete
Authors: Laranja Rafael A. C. , Tamagna Alberto
Published: October 2013

Sound insulation can be difficult to forecast. In most cases it is necessary to take certain precautions in order to avoid degradation in the acoustical performance of walls. Knowing that sound transmission through walls depends on mass per unit area, bending stiffness, damping, mounting conditions, frequencies, etc., the sound transmission can be explained theoretically by several hypotheses. Even though sound transmission has been investigated for more than 100 years, there still remain a lot of issues to be solved. The purpose of this work is to present a discussion regarding the main analytical models used in sound reduction by simple walls, to help the engineer in noise control projects for industry or homes. Several model cases were analyzed by numerical estimation, and the best results were selected to perform experimental comparisons. Some comparative graphics are presented to compare numerical and experimental results. [Work supported by CAPES.] (To be presented in Portuguese.)
Measurement and simulation of brick wall sound reduction index
Authors: da Paixao Dinara X. , Teodoro Elias B. , Gerges Samir N. Y.
Published: October 2013

This paper presents the procedures and results of an experimental, numerical simulation and analytical model of sound reduction index of solid brick wall. The solid brick used has the following dimensions: 22×10×5 cm and density of 1850 kg/m3. The physic-mechanical characteristics: density, resistance, and elasticity modulus were measured using a set of small walls (0.60×0.63 m). One wall of 4.10×3.20×0.10 m (length/height/thickness) was built between two reverberant rooms, with 60 and 63 cubic meters in volume, respectively. Two kinds of junctions were used between the wall and the concrete walls of the reverberant rooms: elastic junction (with a thin layer of rubber, sealed with silicon rubber on both sides and the top of the wall) and rigid junction (using the normal mortar). The sound reduction index was measured according to ISO 140-3 using airborne transmission. The brick characteristics were used as input data for the statistical energy analysis (SEA) model. The results from SEA, analytical, and measured models are compared.
Bob meets bullfrogs: Love at first croak
Authors: Goldstein Moise H.
Published: October 2013

After graduating from UC Berkeley, young Bob took at job at Bell Labs (BTL) and he and his lovely wife Patricia moved east. Somehow he found himself in a ‘‘wet’’ biological laboratory hidden in a corner of the BTL Murray Hill campus. Here Bob found Larry Frishkopf and the author, a MIT summer visitor at BTL, doing unit recording from bullfrog auditory nerves. Bob was pleased to help with the project. Sometimes, we would speculate about the tie between the electrophysiology and bullfrog behavior. As summer ended, Bob competed for and won a BTL Ph.D. fellowship. Bob chose to do his dissertation research at MIT and to address that question. I was his preceptor. He developed a novel method, sound evoked vocalizations, and skillfully demonstrated the relation of neural coding and behavior in bullfrogs. Soon after competing his dissertation research, Bob accepted a faculty position at Cornell. It is a great pleasure for me to take part in honoring Bob’s brilliant career.
Nonlinearity in central auditory processing
Authors: Feng Albert S.
Published: October 2013

The pioneering work of Robert Capranica in sound communication in bullfrogs revealed that sound pattern recognition involves a nonlinear operation. He showed in 1965 that, for bullfrogs, although the peripheral auditory system exhibits nonlinear properties, nonlinearity of the central auditory system is necessary for sound perception. Researchers studying sound processing in anurans as well as in birds and mammals have since shown that central auditory processing underlying various perceptual tasks (e.g., localization, ranging, and pattern recognition) mostly involves nonlinear operations; these are time- or frequency-dependent or both. Signal detection and discrimination in noise is another example. Frogs exhibit spatial unmasking, a space-dependent phenomenon, i.e., the masking effect is reduced when signal and noise sources are spatially separated. Spatial unmasking allows frogs to communicate effectively by sound in a dense chorus. Recent physiological evidence showed that spatial unmasking is largely attributed to nonlinear binaural processing in the CNS. The auditory periphery contributes to spatial unmasking but the processing therein is largely linear and its role is more limited. [Work supported by NIH/NIDCD.]
A reexamination of the teleost swimbladder as an acoustic source
Authors: Fine Michael L.
Published: October 2013

Classically swimbladders are considered pulsating resonant bubbles that are omnidirectional monopole sources capable of translating acoustic pressure to the ears. Swimbladder sounds are driven by sonic muscles (the fastest in vertebrates), yet high speed would seem unnecessary to excite a resonant structure. Recent studies in the oyster toadfish Opsanus tau and the weakfish Cynoscion regalis suggest that the classic generalizations may not apply to all fishes. The toadfish bladder is a low-Q inefficient (highly-damped) resonator that moves in a quadrupole fashion producing sound amplitude proportional to bladder velocity. Slow movements do not produce audible sound. When the bladder is stimulated artificially, dominant frequency is determined by the waveform of the excitation stimulus and not fish size. The sound field, measured underwater, is mildly directional, and deflation of the bladder does not change auditory thresholds. The dominant frequency of weakfish sounds (pulses produced by individual muscle contractions) appears to be determined by timing parameters of muscle twitches and not the natural frequency of the bladder. [Work supported by NIH.]
Auditory nerve recordings in Xenopus laevis
Authors: Kelley Darcy , Elliot Taffeta , Christiasen-Dahlsgaard Jakob
Published: October 2013

The South African clawed frog X. laevis communicates using a rich repertoire of underwater calls made up of clicks. Two calls, rapping and ticking, differ only by interclick interval [Tobias et al., PNAS (1998)]. To begin to explore rate coding in the auditory system, extracellular recordings were obtained in vivo from the auditory nerve of frogs stimulated with both pure tones and recorded calls. To avoid problems of impedance matching, acoustic stimuli were delivered via vibration-excited probe directly to the frog’s tympanum. Preferred frequencies across the population of 104 recorded fibers (taken from 5 females) fell into 2 or 3 groups: 1500, 600, and 200 Hz. Cells of all preferred frequencies fired in phase with clicks of the various calls. [Work supported by an NSF graduate fellowship to TME.]
Suppression of frog amphibian-papillar (AP) axons
Authors: Lewis Edwin R. , van Dijk Pim , Yamada Water M.
Published: October 2013

In response to white-noise stimuli, AP afferent axons of Rana catesbeiana and R. esculenta exhibit excitation, adaptation, and suppression simultaneously. After eigendecomposition of the second-order Wiener kernel, spectrotemporal properties of suppression and adaptation, in the individual axon, can be reconstructed by short-term averaging taken parallel to the main diagonal of the inhibitory subkernel. The results show suppressive spectra with deep, sharp notches in the vicinity of BEF. Spectral components outside the notch, on both sides of BEF, are effective in eliciting the suppression response; those very close to BEF are not. The results imply that the suppressive response (a negative dc shift in instantaneous spike rate) may occur with or without the presence of excitatory stimuli. It will be visible, however, only if there is background spike activity. The suppressive spectrum on the high side of BEF can extend beyond the highest AP BEF. In other words, AP axons can respond (negatively) to stimuli at frequencies beyond the highest BEF. The results further imply that a brief suppressive stimulus will be most effective if applied toward the end of a brief excitatory stimulus, or slightly after that excitatory stimulus has ended.
Acoustic thermometry along an Arctic Ocean path
Authors: Mikhalevsky Peter , Sperry Brian , Gavrilov Alexander
Published: October 2013

Acoustic thermometry has been shown to be a very effective technique for monitoring average heat content and average temperature in the Arctic Ocean and in particular in the Arctic Intermediate Water (AIW) layer. As part of the U.S./Russian Arctic Climate Observations using Underwater Sound (ACOUS) program a 14-month time series of acoustic transmissions were analyzed along a 1250 km propagation path that extended from the Franz Victoria Strait to the Lincoln Sea from Oct. 1998 through Dec. 1999. The receive array mooring in the Lincoln Sea was recovered in April 2001. Modal travel times were estimated after pulse compression processing and mode filtering of the vertical line array. The interarrival time between mode 1 and modes 2 and 3 show net cooling during the first several months followed by a dramatic warming of the AIW along the propagation path. This warming is consistent with direct CTD measurements made along a central Arctic transect performed by the USS Hawkbill during the Scientific Ice Exercise (SCICEX) 2000. [Work supported by ONR, NSF, the Civilian Research and Development Foundation, and the Ministry of Industry, Science and Technology of the Russian Federation.]
Long-range detection of hydroacoustic signals from large Antarctic icebergs
Authors: Talandier Jacques , Hyvernaud Olivier , Piserchia Pierre F. , Okal Emile A.
Published: October 2013

T-waves are commonly observed on coastal seismographs of the French Polynesian Seismic Network (RSP), when an oceanic earthquake or an underwater explosion occurs, even for small events. T-waves are trapped in the underwater channel and can propagate at very long distances before being converted into seismic waves close to the coastal seismic stations. During the 2000/2001 Austral summer, coastal seismic stations of the RSP detected unique series of T-waves from Antarctica about 60 away in the frequency band 2–15 Hz. Some of them last a few minutes while other wavetrains last several hours; some are broadband while others feature prominent frequencies, occasionally accompanied by overtones. Most of the hydroacoutics sources are relocated using the RSP stations and some Antarctic seismographs. It is shown that observed waves have a very long underwater path but may also propagate in the ice sheet. Satellite monitoring demonstrates that hydroacoustic source locations are very well correlated in space and in time with icebergs B-15B and B-17 moving off the Ross Ice Shelf. These two icebergs appeared after the Iceberg B15 broke from the Ross Ice Shelf in March 2000.
The dynamics of abyssal T-phases
Authors: Stephen Ralph A. , Smith Deborah K. , Williams Clare
Published: October 2013

The characteristics of earthquakes, as revealed by T-phase observations, have the potential to provide important constraints on physical models of crustal processes under the oceans. Although it has been postulated that some form of scattering at or near the seafloor is necessary to convert the compressional and shear body waves from earthquakes into the low grazing angle paths necessary for propagation in the ocean sound channel, there are T-phase observations that cannot be explained by seafloor scattering alone. Water depth above the epicenter, for example, should have a strong effect on T-phase excitation. We use the time domain finite-difference method combined with ray theory to demonstrate these issues and we compare the theory to a series of events that occurred near the mid-Atlantic Ridge at the Kane Fracture Zone (MARK) in 1999 and 2000. There is evidence in this data set which suggests that topographic steering of T-phase locations occurs. Earthquake energy appears to preferentially enter the sound channel at topographic highs and epicentral locations are biased toward shallow bathymetry.
Propagation of sound through a spicy ocean: Analysis
Authors: Munk Walter , Dzieciuch Matthew , Rudnick Daniel
Published: October 2013

We derive some of the parameters for a simple model of spice and internal wave scatter, using the canonical ocean sound channel. A distant goal is for long-range acoustic transmissions to provide a measure of upper ocean stirring from abyssal ocean acoustic signatures.
Discrepancies between ocean-acoustic fluctuations in parabolic-equation simulations and estimates from integral approximations
Authors: Vera Michael D. , Flatté Stanley M.
Published: October 2013

Analytic, line-integral approximations to the acoustic path integral have been used to estimate the magnitude of internal-wave-induced fluctuations in a signal traveling through the ocean. These approximations for the bias and variance of travel time, the length scale of acoustic coherence in depth, and the spreading in time of acoustic intensity peaks are compared, in this discussion, to values from simulations that used the standard parabolic equation. Two different temperate-latitude sound-speed profiles were used in simulated 250 Hz acoustic propagations with a maximum range of 1000 km. The sound speed was perturbed by internal waves conforming to the Garrett–Munk (GM) spectral model with strengths of 0.5, 1, and 2 times the GM reference energy level. Though predictions of the travel-time variance were largely successful, the other quantities examined did not correspond to simulation values. Calculated biases deviated from parabolic-equation results at ranges beyond a few hundred kilometers. The predicted depth-coherence lengths at 1000 km were significantly shorter than those extracted from the simulations. The estimated magnitudes of pulse spreading at 1000 km were much greater than the differences in widths between intensity peaks from simulations with and without internal-wave perturbations.
Calculations of ocean-acoustic fluctuations for use in tomography of internal waves
Authors: Flatté Stanley M. , Vera Michael D.
Published: October 2013

In order to use observations of the bias and variance of travel time, the length scale of acoustic coherence in depth, and the spreading of the acoustic pulse as information about the internal-wave field in the ocean (all for identifiable rays at long range), a reliable method of calculation of these quantities in the presence of a specific internal-wave model must be made. Attempts to use analytical methods having proven unreliable for long range, except for the variance of travel time; there are two possibilities: (1) restrict tomography of identifiable rays to travel-time variance; or (2) use simulation by parabolic equation to calculate expected values. The former is restricted and the latter is computer intensive. The needed resources for the latter will be discussed.
Limitations on perturbation theory applied to ocean acoustic inversion
Authors: McDonald B. Edward , Sperry Brian , Baggeroer Arthur
Published: October 2013

Perturbation theory for ocean acoustic modal group speed responses to small environmental changes is investigated with regard to its applicability in ocean acoustic tomography. Assuming adiabaticity, the inverse problem for each vertical eigenmode is an integral equation whose kernel involves the eigenfunction and its frequency derivative. A new proof is given for the so-called ‘‘third term problem’’ which requires equivalence between two dissimilar forms of the integral equation. Numerical examples are given for the inversion kernel for four types of sound speed profiles, and then the parameter range (amplitude and scale size) in which perturbation theory is accurately examined. It is found that the range of validity is set not only by the amplitude of the perturbations, but also by their vertical scale size. [Work supported by ONR and Saclantcen.]
Horizontal refraction and coherence of acoustic signals propagating over a long-range in the ocean
Authors: Voronovich Alexander G. , Ostashev Vladimir E.
Published: October 2013

The paper is devoted to experimental and theoretical studies of horizontal refraction and coherence of acoustic signals recorded during the NPAL experiment with the use of the billboard acoustic array [The NPAL Group, J. Acoust. Soc. Am. 109, 2384 (2001)]. Both ray- and mode representations of the acoustic field are used for signal-processing. In the first approach, signals at different pairs of hydrophones located at approximately the same depth are cross-correlated. This allows us to obtain the mean horizontal refraction angle, its time-dependence and variance, and the coherence radius of the sound wavefront. The variance and the coherence radius are also estimated using a theory developed. In this theory, the energy of the sound field scattered by internal waves spreads in horizontal directions according to a diffusion law. The diffusion coefficient is evaluated numerically for the Garret–Munk spectrum and canonical Munk profile. It is shown that the variance of the horizontal refraction angle and the coherence radius of the wavefront calculated theoretically agree qualitatively with their values obtained using the NPAL data. [Work supported by ONR.] a)J. A. Colosi, B. D. Cornuelle, B. D. Dushaw, M. A. Dzieciuch, B. M. Howe, J. A. Mercer, R. C. Spindel, and P. F. Worcester.
Origins and evolution of the developments which led to echo-Doppler duplex color flow diagnostic methodology
Authors: Baker Donald W.
Published: October 2013

Research efforts to develop instrumentation for animal physiologic research to better characterize the cardiovascular system in engineering terms ultimately evolved for application on man and led to the Pacific Northwest becoming the current foci of the medical ultrasound industry. This presentation will trace the events from my being a student in Electrical Engineering to heading the Cardiovascular Instrument Development Program originally begun by Dr. Robert Rushmer in 1957. This narrative will range from early instruments for measurements on research animals to their development for noninvasive use on man. The instruments covered will be the transit time flow-meter, CW Doppler, pulsed Doppler, duplex scanner, color flow mapping. The role of collaboration in both engineering and many specialties of medicine will be demonstrated. Many of the original instruments have been in the Smithsonian Museum of American History and will in the near future be on permanent exhibit there.
Measurement and numerical simulation of the changes in the open-loop transfer function in hearing aid as a function telephone handset proximity
Authors: Daigle Gilles A. , Stinson Michael R.
Published: October 2013

The presence of a nearby object (telephone handset, cupped hand, etc.) can cause acoustical feedback to occur in a hearing aid. The object reflects or scatters additional sound energy to the microphone position causing the open-loop transfer function (OLTF) to increase. Feedback can occur when the OLTF>0 dB. To investigate this problem, measurements of the OLTF were made for three hearing aids (BTE, ITC, ITE) mounted on a KEMAR manikin. A telephone handset, positioned initially in a typical user position, was translated to positions between 0 and 100 mm away from the pinna, repeatibly, using a linear translation system. Changes of up to 15 dB or more were observed as the handset moved, particularly for positions within 20 mm of the pinna. In parallel, numerical simulations were made using a boundary element method. Computed changes in OLTF were consistent with the measured changes.
New acoustic test facility at Georgia Tech
Authors: Biesel Van , Cunefare Kenneth
Published: October 2013

Georgia Tech’s Integrated Acoustics Laboratory (IAL) is a state of the art research facility dedicated to the study of acoustics and vibration. The centerpiece of the laboratory is a 24 ft×24 ft×20 ft full anechoic chamber, which has been in operation since 1998. The IAL is currently expanding to include a reverberation room and hemi-anechoic chamber, designed and built by Acoustic Systems. These two chambers will be joined by an 8 ft×8 ft transmission loss opening, allowing for a detailed measurement and analysis of complex barriers. Both chambers will accommodate vehicles and similarly large structures. The reverberation room will have adequate volume for standardized absorption measurements. Each chamber will be equipped with dedicated multichannel data acquisition systems and instrumentation for the support of simultaneous research in all areas of the laboratory. The new test chambers are funded by a grant from the Ford Motor Company and are planned to be completed and fully functional by 1 January 2003.
Education in acoustics and vibration at UFSC—Brazil
Authors: Gerges Samir N. Y.
Published: October 2013

In the 1970s, Brazil invested heavily on postgraduate program of all areas, especially in acoustics and vibration. Several universities achieved benefits from these investments, namely the Federal University of Santa Catarina (UFSC), the Federal University of Rio de Janeiro (UFRJ), and the Federal University of Santa Maria (UFSM). Part of the undergraduate and postgraduate studies at the Mechanical Engineering Department (EMC) of the Federal University of Santa Catarina relates to vibration and noise. On the undergraduate level an optional course called Noise Control, totaling 54 hours, is offered, which covers basic acoustics and noise control concepts. In the postgraduate program Master’s and Doctorate degrees students can attend courses and pursue studies in the area of noise and vibration. This area of concentration is supported by a well equipped laboratory consisting of two reverberation chambers, with a third one, for transmission loss measurements, under construction, together with a hemianechoic room and equipment for the measurement and analysis of noise and vibration. Part of this laboratory, the Industrial Noise Laboratory, is accredited by the Brazilian authorities for measurements of and research on hearing protectors. [Work supported by the Federal Government, and industry.]
Acoustics lecturing in Mexico
Authors: Beristain Sergio
Published: October 2013

Some thirty years ago acoustics lecturing started in Mexico at the National Polytechnic Institute in Mexico City, as part of the Bachelor of Science degree in Communications and Electronics Engineering curricula, including the widest program on this field in the whole country. This program has been producing acoustics specialists ever since. Nowadays many universities and superior education institutions around the country are teaching students at the B.Sc. level and postgraduate level many topics related to acoustics, such as Architectural Acoustics, Seismology, Mechanical Vibrations, Noise Control, Audio, Audiology, Music, etc. Also many institutions have started research programs in related fields, with participation of medical doctors, psychologists, musicians, engineers, etc. Details will be given on particular topics and development.
Engineering acoustics: A pioneer undergraduate program at Rio de Janeiro
Authors: Tenenbaum Roberto A. , Zindeluk Moyses
Published: October 2013

Acoustics, essentially a multidisciplinary subject, still has in Brazil a small but increasing number of professionals with a solid background to deal with various aspects of this area. Since 1970 the faculty of the Acoustics and Vibration Laboratory, COPPE/UFRJ, offers graduate (M.Sc and D.Sc) programs, and some undergraduate courses in acoustics, vibration, and signal processing. In January 2000, this group launched a formal undergraduate engineering acoustics program in the Mechanical Engineering Department of the Federal University of Rio de Janeiro. After three years of mechanical engineering, with a firm foundation in physics, applied mathematics, and engineering basics, the undergraduate student may elect to take the engineering acoustics program for the remaining two years. In this program, a wide number of courses are offered, including basic acoustics, room acoustics, signal processing, musical acoustics, machine diagnosis, etc. Approximately 30 different courses may be chosen from. However, the student is not completely free, since the courses selected must fit within a subject concentration profile, e.g., noise control or musical acoustics. In this paper the programs curriculum are presented and its impact on the students is discussed. A first evaluation of the qualifications achieved by the graduate students in the area is also presented.
Acoustics: A branch of engineering at the Universidad Austral de Chile (UACh)
Authors: Poblete Victor , Arenas Jorge P. , Sommerhoff Jorge
Published: October 2013

At the end of the 1960s, the first acousticians graduating at UACh had acquired an education in applied physics and musical arts, since there was no College of Engineering at that time. Initially, they had a (rather modest) four-year undergraduate program, and most of the faculty were not specialized teachers. The graduates from such a program received a sound engineering degree and they were skilled for jobs in the musical industry and sound reinforcement companies. In addition, they worked as sound engineers and producers. Later, because of the scientific, industrial and educational changes in Chile during the 1980s, the higher education system had massive changes that affected all of the undergraduate and graduate programs of the 61 universities in Chile. The UACh College of Engineering was officially founded in 1989. Then, acoustics as an area of expertise was included, widened and developed as an interdisciplinary subject. Currently, the undergraduate program in acoustics at UACh offers a degree in engineering sciences and a 6-year professional studies in Civil Engineering (Acoustics), having two main fields: Sound and Image, and Environment and Industry.
Acoustic Engineering program at the Universidad Austral de Chile (UACh)
Authors: Sommerhoff Jorge , Poblete Victor , Arenas Jorge P.
Published: October 2013

From the beginning of the acoustics program at UACh in 1968, the studies of Acoustic Engineering have been modified and developed according to the vision and human resources of its developers. Three different stages of growth can be seen. When the program began, it was totally aimed at forming skilled professionals in audio and recording. In this way, the professional title given was Sound Engineer. At that time, each applicant was required to have ‘‘good musical hearing,’’ which had to be demonstrated through a special musical audition test. The second stage was characterized by the incorporation of acoustics subjects which allowed students, with no musical abilities, to competently work on acoustic engineering activities not related to music. Then, the professional title was changed to Acoustic Engineer. Thus, job opportunities were diversified and access was allowed by all types of students. In the last stage, the study plan was modified as a response to the new vision and requirements of the globalized world in which the environmental component has a great importance. In this work the development of a program that dates from 35 years ago is presented and justified.
Using dynamic means to teach a dynamic subject: A new concept for a graduate vibrations course in Mexico
Authors: Echeverria-Villagomez Salvador
Published: October 2013

Mechanical vibrations is a subject that belongs in every undergraduate curricula in mechanical engineering, and to many graduate programs in mechanical design and manufacturing. It is a subject in which many disciplines come in, from mechanics, through materials properties, to mechanisms and special mathematics tools. It is also a most interesting discipline from many points of view: from the theoretical models used to analyze the dynamical behavior of systems, through the modern numerical and computational tools, to the experimental techniques used to measure and test their performance. The paper presents a concept to teach vibrations and acoustics. This concept provides a framework for using the mentioned tools, which is homologous in structure to the subject being taught, thus enhancing the power and effectiveness of teaching and training in the field. The main characteristics of the concept are their systemic approach, fluid logic, use of conceptual virtual maps and dynamic means.
Acoustic outsourcing: New employment possibilities for the specialists
Authors: Perez Patricia , Rios Heriberto , Andrade Armando , Ramirez Mario
Published: October 2013

The need for companies to be more competitive has led them to resort to training, external consultantship, continuous improvement programs, but with the aim of achieving maximum productivity, the big companies go even further: they are opting to focus on their high-priority activities, leaving some nonstrategic functions in the hands of third parties (organizations or individuals). Acoustic outsourcing presents immense business opportunities for the specialists in this area when offering services or completing a production process that the company carries out in an internal way but that is not its main function or activity. Outsourcing contemplates a serious long term commitment between the two parties; a kind of strategic alliance, all with the purpose of increasing efficiency and the quality of the products that the company develops, besides solving acoustic problems related to the production stage. (To be presented in Spanish.)
Spectral modeling, analysis, and synthesis of musical sounds
Authors: Marchand Sylvain , Desainte-Catherine Myriam
Published: October 2013

Spectral models provide general representations for sound well-suited for expressive musical transformations. These models allow us to extract and modify perceptually-relevant parameters such as amplitude, frequency, and spectrum. Thus, they are of great interest for the classification of musical sounds. A new analysis method was proposed to accurately extract the spectral parameters for the model from existing sounds. This method extends the classic short-time Fourier analysis by also considering the derivatives of the sound signal, and it can work with very short analysis windows. Although originally designed for stationary sounds with no noise, this method shows excellent results in the presence of noise and it is currently being extended in order to handle nonstationary sounds as well. A very efficient synthesis algorithm, based on a recursive description of the sine function, is able to reproduce sound in real time from the model parameters. This algorithm allows an extremely fine control of the partials of the sounds while avoiding signal discontinuities as well as numerical imprecision, and with a nearly optimal number of operations per partial. Psychoacoustic phenomena such as masking are considered in order to reduce on the fly the number of partials to be synthesized.
Analysis-synthesis of musical sounds by hybrid models
Authors: Ystad S.
Published: October 2013

Analysis-synthesis consists of constructing synthetic sounds from natural sounds by algorithmic synthesis methods. The models used for this purpose are of two kinds: physical models which take into account the physical characteristics of the instrument and signal models which take into account perceptual criteria. By combining physical and signal models hybrid models can be constructed taking advantage of the positive aspects of both methods. In this presentation I show how hybrid models can be adapted to specific instruments producing both sustained and plucked sounds. In these cases signal models are used to model the nonlinear source signal. The parameters of these models are obtained from perceptual criteria such as the spectral centroid or the tristimulus. The source signal is further injected into the physical model which consists of a digital wave guide model. The parameters of the physical model are extracted from the natural sound by analysis based on linear time-frequency representations such as the Gabor and the wavelet transforms. The models which will be presented are real-time compatible and in the flute case an interface adapted to a traditional flute which pilots a hybrid model will be described.