bluuebunny/crossref_metadata_2025 huggingface dataset:
Beam noise and array gain models for computing ship resolution gain
Authors: Craig D. W. , Tan L.
Published: October 2005

Array gain estimates for horizontal towed array systems in ship-induced noise fields are typically predicated on the assumption of a constant noise power in the horizontal azimuth. Large-aperture arrays operating in such fields are able to resolve individual ship interferers and are capable of enhanced detection gain in regions of reduced noise. This enhanced gain, known as ‘‘ship resolution gain’’ (SRG) [Heitmeyer etal., NRL Report 8863, Feb. 1985] represents an additional term that must be added to the sonar equation. A revised model is presented that computes beam noise distribution functions numerically, without Heitmeyer’s approximation of mainlobe/sidelobe sectors, and illustrates the effects of steering angle, hydrophone shading, sidelobe degradation, and shipping density. This model assumes a Poisson shipping density and computes beam noise as the finite sum of contributions from individual ships. The SRG in the revised beam model is compared with that obtained from a new model that has been developed for computing array gain in resolved noise. Both models indicate that substantial detection gains are possible with large-aperture arrays when individual ship interferers are resolved.
Temperature and sound-speed measurements from diffuse hydrothermal vent plumes at the Southern Juan de Fuca Ridge
Authors: Trivett D. A. , Williams A. J.
Published: October 2005

An array of sensors was deployed for 2 weeks at the Southern Juan de Fuca Ridge during the NOAA VENTS’90 field experiment. The instrument measured temperature at six heights on each of four moorings, and temperature, velocity, sound speed, and Reynolds’ stress on each of two tripods. The instruments were placed close to the seafloor to detect effluent from diffuse hydrothermal flow that was advanced horizontally by ambient currents. Temperature and sound-speed measurements were compared during intervals when no plume was evident, and when effects of plumes were clearly detected. The data showed that energy flux from diffuse vents was approximately 125±75 MW from a source to the north of the instrument array, and 12±8 MW from a small source to the east. The largest error in the data was due to estimation of the plume width. A sensor array that would reduce this error in future work will be described. Such an array could be suitable for a long-term vent field monitor.
Permeability and porosity of clayey sediments in seismo-acoustics
Authors: Bryant William R. , Richardson Michael D.
Published: October 2005

Permeability of fine-grained marine sediments is the most controversial and difficult variable to define for seismo-acoustics. Theoretical formulations of permeability are extremely complex for fine-grained sediments and usually bear small resemblances to real material. Values of permeability from consolidation tests and direct analysis of clayey marine sediments greatly differ from results determined by the Kozeny–Carman equation. These differences are not accountable by deviations from Darcy’s law, electrokinetic coupling, or viscosity but are related to changes in microfabric. Porosities relationship to permeability presents natures largest range between cause and affect. In fine-grained marine sediments permeability changes at a rate from 2 to the 12th power of porosity. A 50% change in porosity, from a mud to mudstone, can result in a change in permeability of 10−3 to 10−12 cm/s, which is analogous of going from the speed of light to 60 mph. The effects of permeability on P-wave velocities of high porosity (85% to 70%) sediments, particularly Pacific red clays, appears minimal. A measured change of permeability from 7×10−4 to 1.2×10−7 cm/s has less of an effect on the velocity (average 1469 m/s) than does a density change from 1.25 to 1.36 g/cc. P-wave velocities of red clays, spanning an age of 45 m.y. with permeabilities of above, are essentially constant over a depth of 60 m while S-wave velocities of the same material increase from 5 to 180 m/s. The best relationship between permeability and porosity of marine clays for seismo-acoustic determinations is k=6.63×10−9 β8.1, where k=permeability (cm/s) and β=decimal porosity.
Choked jet edge tones, continued again: Scattering of evanescent waves as the sound source
Authors: Lin Dan , Powell Alan
Published: October 2005

The early suggestion of monopole sources due to the high-impedance supersonic jet switching above and below the edge resulted in excessive acoustic radiation estimates. It is now proposed that the sound is better attributable to the growing then decaying ‘‘evanescent wave’’ of the sinuous jet instability, estimated by Rayleigh’s formula applied to a plane just outside the jet flow. The wave amplitude, growth and decay rates (both taken as a cosine form), wavelength, and convection speed (Mach number=0.6 for pressure ratio 3.07) are all estimated from schlieren and shadowgraph photographs. For the nozzle aspect ratio of 4.8, the two limiting cases calculated are (i) two-dimensional and (ii) acoustically equivalent line source. The preferred downstream radiation calculated in both cases is consistent with experiment, while the amplitudes calculated appear somewhat high, (ii) being within difficult measurement error (3–4 dB). [Work supported by Texas Advanced Research Program.]
A mechanism of jet-edge interaction and sound radiation
Authors: Kwon Youngpil , Powell Alan
Published: October 2005

A theoretical model is presented to explain the jet-edge interaction and the sound radiation. The aerodynamic response of the edge to the sinuous impinging jet is obtained by regarding the edge reaction as the surface distribution of dipoles necessary to meet the local boundary condition. Then the sound radiation is estimated using these dipoles. The relationship between the jet sinuosity and the sound radiation is quantified: The pressure field on the edge and the directivity of the sound radiation is estimated. It is found that the effective point source is located about a quarter wavelength downstream from the edge tip. The effect of the edge configuration and the jet velocity on the magnitude and directivity of the sound radiation is estimated. This simple model is consistent with available experimental data for low- and high-speed edge tones.
Tomographic measurements of sediment inhomogeneities and determination of statistical parameters critical to sediment volume backscattering
Authors: Turgut Altan
Published: October 2005

A tomographic method was used for measuring sound-speed fluctuations in the top 5 m of sediments in Biscayne Bay, Florida. Sub-bottom porosity and density fluctuations were estimated from measured sound-speed fluctuations by using Gassmann’s [Geophysics 16, 673–685 (1951)] equations. Statistical parameters for volume backscattering calculations such as vertical correlation length, horizontal correlation length, and variance of acoustic impedance were obtained from tomographic measurements. Volume backscattering strengths for the experiment site were calculated using the theoretical results given by Crowther [AcousticsandtheSeabed, edited by N. G. Pace (Bath University, Bath, 1983), pp. 147–155]. Measurements of acoustic backscattering strengths were also conducted at the same site. Comparisons between measured backscattering strengths and calculated volume backscattering strengths indicate that, for this particular location, scattering is mostly due to bottom roughness. [Work supported by ONR and UM-Research Program.]
An artificial neural network model of human sound localization
Authors: Anderson T. R. , Janko J. A. , Gilkey R. H.
Published: October 2005

An artificial neural network was trained to identify the location of sound sources using the head-related transfer functions (HRTFs) of Wightman and Kistler [J. Acoust. Soc. Am. 85, 858–867 (1989)]. The simulated signals were either filtered clicks or pure tones, with speaker placements separated in steps of 15 deg in azimuth of 18 deg in elevation. After the signals were passed through the HRTFs, the inputs to the nets were computed as the difference of left ear and right ear phase spectra or the difference of the power at the output of left and right ear third-octave or twelfth-octave filter banks. Back propagation was used to train the nets. Separate nets were trained for each signal type and for each type of input data. Better than 90% correct identification of the source speakers location can be achieved in either the horizontal or median planes. The results for the horizontal plane are compared to the predictions of the duplex theory of sound localization. [Work supported by AFOSR-91-0289 and AFOSR-Task 2313V3.]
Sensitivity of shallow water transmission loss to source and receiver proximity to a hard bottom under downward refracting conditions
Authors: Herstein Peter D. , Cole Bernard F. , Browning David G. , Groneman Frank L.
Published: October 2005

Under downward refracting conditions, raypaths from a shallow source will tend to have grazing angles at a hard bottom that are greater than the critical angle and therefore suffer a relatively large loss per bounce. As the source depth increases, lower grazing angles can be obtained. When the grazing angle becomes less than the critical angle, bottom loss per bounce is significantly reduced allowing a possible reduction in propagation loss. An analysis is made for a North Atlantic shallow water area south of Long Island under summer conditions to determine the sensitivity of transmission loss to changes in source and receiver depth for ranges up to 50 km. The results are compared to the previous results of Cole and Podeszwa [B. F. Cole and E. M. Podeszwa, J. Acoust. Soc. Am. 41, 1479–1484 (1967)].
Simulation of two-dimensional, fine-scale geomorphology
Authors: Caruthers J. W. , Novarini J. C.
Published: October 2005

Recent experimental work in the Acoustic Reverberation Special Research Program (ARSRP) demonstrated a need for two-dimensional fine-scale geomorphology to help explain observed scattering at 250 Hz in a rugged region just west of the Mid-Atlantic Ridge. Bathymetry resolved in 2-D to 100 m is available for the region, but at this frequency geomorphology at horizontal scales (about 1 m) is required. One-dimensional geomorphology with sufficient resolution has been simulated and molded to regional bathymetry established by a single line bathymetric profile resolved to 1 km by Goff and Jordan [WHOI ARSRP TN♯2 (1992)] based on their earlier work [J. Geophys. Res. 93, 13 589–13 608 (1988)]. While some scattering theories can handle only 1-D geomorphology and produce 2-D scattering fields, others are designed to use 2-D geomorphology and produce 3-D scattering fields. Caruthers and Novarini had earlier developed a 2-D surface simulation technique [TAMU TN♯71-13-T (1971)] that, so far, had been applied only to sea-surface simulation and scattering [J. Acoust. Soc. Am. 53, 876–884 (1973) and J. Acoust. Soc. Am. 91, 813–822 (1992)]. Although the simulation technique presented here is essentially the same as that developed by Caruthers and Novarini and Goff and Jordan, unique features of this current work are (1) the sea floor is simulated in fine-scale detail in 2 D, (2) local spectra of deterministic bathymetry in small regions are use to dictate the form of spectra extended to higher resolution, and (3) the technique for molding the simulated geomorphology to the deterministic bathymetry using a coupling of wave-number bands is new. [This work is supported by ONR.]
Kilohertz Gaussian transducer design and fabrication
Authors: Breazeale M. A. , Huang Dehua
Published: October 2005

The Gaussian distribution of an ultrasonic field has attracted attention and interest because of its unique features: analytic mathematical solution for a sound field in a homogeneous medium; no maxima or minima in Fresnel zone; a single beam free of sidelobes in the Fraunhofer region. Heretofore the mathematical attractiveness of the Gaussian function has been used in many physical theories. It has been used in connection with underwater acoustics, interface problems, medical ultrasonics, nondestructive evaluation, acoustical microscopy, nonlinear acoustics, etc. The Gaussian beam not only is an ideal mathematical model, but it is beginning to be physically realizable. Several methods reported to be successful in the megahertz frequency range have failed to produce a Gaussian distribution in the kilohertz range. This paper presents an improved design that is successful for a kilohertz Gaussian transducer. It has worked in the megahertz frequency range also. Gaussian transducers at 375 kHz (4 in. diam) and at 332 kHz (5 in. diam) have been made in our lab. The frequency–transducer size relation has been set by a 30-dB sidelobe suppression criterion. Theoretical design and experimental verification are presented. A 6-in.-diam Gaussian transducer that works at even lower frequency is in progress. [Work supported by ONT.]
Fabrication of a high-frequency polymer projector
Authors: McLaughlin Elizabeth A. , Kavarnos George J.
Published: October 2005

A high-frequency projector was fabricated using solvent-cast piezoelectric polyvinylidene trifluoroethylene P (VF2/EF3) copolymer film. It has a higher electromechanical coupling factor, (kT∼0.3) [Ohigashi and Koga, Jpn. J. Appl. Phys. 21 (8), L455–457 (1982)], than P (VF2) homopolymer and it does not require stretching to align the polymer chains. 75% P(VF2/EF3) copolymer dissolved in methyl ethyl ketone was cast into a 200-to 300-μm sheet, annealed at 130 °C, and slow cooled. A thin layer of conductive metal was sputtered onto either side of the copolymer. The metalized film was subsequently poled in a heated oil bath in the thickness direction. The samples (6.5 cm2) were tested with and without brass electrodes. The brass brought the resonance frequency down to the 700-kHz range. Measured parameters included coupling, quality factor, piezoelectric constant, and transmit voltage response. The transducer was modeled using a modified Mason equivalent circuit, which is similar to that demonstrated by Brown and Carlson [IEEE Trans. Ultrason. Ferroelec. Freq. Control UFFC-36, 313–318 (1989)]. Measured and calculated parameters are compared with values obtained for representative P(VF2) homopolymer.
The limitation of ultrasonic flaw sizing by a model-based approach
Authors: Cook Bill D. , Johansen Michael
Published: October 2005

A simple model has been developed that accounts for the excitation signal to the transducer, the transducer characteristics, and the diffraction of the sound for the purpose of flaw sizing. The goal has been to seek the ramp response that is the second integral of the impulse response. The ramp response yields volume and cross-sectional area information about the flaw. This research has demonstrated that all of the above mechanisms are high-pass frequency filters whereas the frequency content needed for the ramp response is low, namely ka<2. Unfortunately the physical mechanisms reduce the low-frequency content well below the noise levels and it is impossible to extract the information required even though the transducer is driven with a signal that contains a large amount of low-frequency content.
Acoustic wave propagation in multilayer systems
Authors: Esquivel-Sirvent Raúl , Cocoletzi G. H.
Published: October 2005

Theoretical studies are performed on the propagation of acoustic waves in multilayer systems using a transfer matrix approach similar to that developed for the studies of optical filters [L. I. Epstein, J. Opt. Soc. Am. 42, 806–810 (1952)] and metallic superlattices [E. L. Olazagasti etal. , Solid State Commun. 78, 9–12 (1991)]. The formalism presented here is used to calculate the reflectivity R of sound waves on multilayer structures. Comparisons are made with experimental results [B. G. Martin, J. Acoust. Soc. Am. 91, 1469–1473 (1992)] for a three-layer structure, in the normal incidence case. The calculated resonances are in good agreement with the experimental ones. For the same system, in the non-normal incidence of sound waves, the spectra of R suggests surface waves coupling. Finally, to show the usefulness of the theory, a Kronig–Penney type structure is studied, calculating the dispersion relation of the normal modes of an infinite system and the reflectivity for the semiinfinite case.
Reciprocity and representation theorems for one-way wave fields in fluids and solids
Authors: Wapenaar C. P. A.
Published: October 2005

An acoustical reflection experiment is intuitively based on (i) downward wave propagation from the acquisition surface into the medium, (ii) reflection by inhomogeneities inside the medium, and (iii) upward propagation of the reflected waves to the acquisition surface. The acoustic and elastodynamic wave equations do not explicitly account for this intuitive distinction between downward and upward propagation. These wave equations govern the total wave field, which may be seen as a superposition of downward propagating and upward propagating wave fields. For this reason these equations are referred to as the two-waywaveequations and their solutions are called two-waywavefields. Analogously, the equations that explicitly govern downward and upward propagation are referred to as the one-waywaveequations and their solutions are called one-waywavefields. In this paper reciprocity and representation theorems are developed for one-way wave fields. These theorems are the basis for a systematic discussion of acoustic reflection imaging in inhomogeneous fluids and in inhomogeneous anisotropic solids.
Composite ray-mode approximations for backscattered sound from gas-filled cylinders and swimbladders
Authors: Clay Clarence S.
Published: October 2005

The normal mode solution for sound backscattered by a finite fluid (gas)-filled cylinder in water is replaced by a Kirchhoff approximation for ka>0.15 and the normal mode solution for ka<0.15 where a is cylinder radius and k is the wave number. The composite solution was tested for density and sound-speed ratios g and h in the ranges of 0.0012<g<0.05 and h=0.23. The simplification and approximations have been tested over the range of 0.0005<ka<20. Expressions that include straight and bent cylinders are given. A derivation of the amplitude and phase factor for finite cylinder lengths is given. The amplitude factor is proportional to the length of the cylinder for lengths much less than the Fresnel zone diameter. At larger lengths, the amplitude factor oscillates above and below 1 as the increasing length passes through the Fresnel zones. The phase is −π/4 for very small lengths and oscillates above and below 0 as the increasing cylinder length passes through Fresnel zones. In experimental (laboratory) measurements of sound scattering, the lengths of objects relative to the diameter of the first Fresnel zone must be considered. Fourier transformations of the scattering amplitudes give the time-domain scattered pressures. The time-domain pressure is a negative impulsive function. Bending of the cylinder decreases the amplitude of the backscattered sound pressure. We expect the main applications of the techniques to be in the computation of sound scattering from fish swimbladders. Expressions for numerical computations are given. The expressions are accurate, easier to code than the complete mode solutions, and about two orders of magnitude faster to compute.
High-frequency nonlinear acoustic beams and wave packets
Authors: Norris Andrew N.
Published: October 2005

Gaussian beams and wave packets are formally equivalent to high-frequency solutions of the linear wave equation with complex-valued phase functions. The theory of weakly nonlinear high-frequency waves is extended in this paper to allow for complex phase solutions. The procedure is similar to nonlinear geometrical optics and the nonlinearity causes the phase to vary, leading to the development of weak shocks. However, unlike standard geometrical optics that describes the evolution of wave fronts, complex phase solutions correspond to Gaussian decay away from a central ray, and the associated curvatures are complex valued. Geometrical singularities due to caustics and foci do not occur, and the only singularities in the theory are purely nonlinear. The theory is developed specifically for nonlinear acoustic waves in a homogeneous inviscid fluid. The time taken for nonlinear singularities to develop is compared for a real spherical wave front and a Gaussian beam with Gaussian radius equal to the real radius of curvature of the wave front. The time to blowup for the Gaussian beam is intermediate between the shortest possible, which is for the converging wave front, and the longest possible, for the diverging front.
Acoustic levitation by Oseen drag
Authors: Dyer Thomas W. , Ohkawa Tihiro
Published: October 2005

Acoustic levitation of spherical particle samples was demonstrated using the steady force exerted by a harmonically distorted acoustic wave. The force arises due to a nonlinear dependence of the fluid drag on the velocity of flow around the sphere. The experimentally determined acoustic intensity required for levitation against gravity was found to be proportional to the particle radius and the particle density in agreement with theory. Levitation was demonstrated for samples with particle diameters ranging from 5 μm to 8 mm and in a variety of gases and at several gas pressures.
Broadband modeling of the three-dimensional penetrable wedge
Authors: Westwood Evan K.
Published: October 2005

A ray method for finding the acoustic field due to a point source in a two-dimensional (2-D), penetrable-bottom wedge has been extended to the three-dimensional (3-D) wedge, where the receiver may lie cross slope as well as downslope or upslope from the source. The environment assumed is a simple model for a sand-bottom ocean near a shoreline: The wedge of water and the sand bottom are isovelocity, and the sound speed in the bottom is assumed to be greater than that in the water. The total field in the 3-D wedge is expressed as a sum of ray fields, each of which takes the form of a double integral over plane waves. As in the 2-D wedge method, the integrals are solved using the method of steepest descent, where the plane-wave reflection coefficients are placed in the ‘‘phase function’’ of the integrand and thus allowed to influence the location of the saddle points. The ray method is also extended to model broadband propagation: Eigenrays are found at coarsely spaced frequencies, and the eigenray characteristics are interpolated across frequency. The ray model is used to simulate the propagation of a pulse from a point source to a set of vertical arrays at various cross slope ranges. Mode extractions from the vertical array data demonstrate several interesting phenomena unique to 3-D wedge propagation: multiple mode arrivals, modal shadow zones, and the dependence of the shadow zones on mode number. An example illustrating mode wave-front curvature and mode capture is also given.
Radiation coupling of a transducer–target system using the angular spectrum method
Authors: Fung Clement C. W. , Cobbold Richard S. C. , Bascom Peter A. J.
Published: October 2005

A general approach for analyzing the transmit–receive response of ultrasound transducer systems is presented. It is based on using the plane-wave angular spectrum to represent the radiation characteristics of the transducer and to describe the target in terms of its plane-wave scattering properties. The method is illustrated for continuous wave excitation of a baffled circular piston coupled to: a plane mirror, monopole and dipole scatterers, and a rigid incompressible sphere. For the sphere, numerical results are presented for both on- and off-axis cases, and the effects of target size and transducer radius are examined. The results provide a quantitative basis for describing the influence of using a ball target of nonzero dimensions for measuring the transmit-receive characteristics. In the near-field region, major distortions of the monopole scatterer transmit–receive response can arise even for targets whose radii are significantly less than a wavelength.
Surface pressure and harmonic loading on shells of revolution using an internal source density method
Authors: Stepanishen Peter R. , Chen Huo-Wang
Published: October 2005

An internal source density method is presented to evaluate the surface pressures and hence the fluid loading on a harmonically vibrating shell of revolution. The normal velocity of the shell is specified to be axisymmetric and harmonic. After expressing the normal velocity of the shell in terms of a modal vector expansion, the radial component of the modal vectors is used to define acoustic modal radiation impedances. In order to evaluate the surface pressures and acoustic radiation impedances, an unknown linear monopole source density is positioned along the axis of the shell. The normal components of the specified modal velocities are subsequently used to determine the monopole source distribution via a set of coupled linear algebraic equations. Extensive numerical results are presented to illustrate the spatial and frequency characteristics of the source density for both spherical and spheroidal shells. Numerical results for the modal acoustic radiation impedances for spherical and spheroidal shells are also presented and discussed.
The equilibrium oceanic microseism spectrum
Authors: Webb Spahr C.
Published: October 2005

Microseisms are seismoacoustic waves excited by nonlinear interactions of ocean waves and are evident in the band 0.1 to 5 Hz in measurements of pressure or displacement spectra from the deep seafloor. A remarkable uniformity in microseism amplitudes is observed at the seafloor, despite many orders of magnitude variation in the amplitude of ocean waves overhead. This paper looks at how a balance is established between the excitation of microseisms under large source regions and the dissipation of this energy within a waveguide formed by the ocean, crust, and upper mantle. The excitation functions and dissipation of modes within ocean models are calculated to determine the ‘‘equilibrium microseism spectrum’’ of displacement or pressure for which local excitation is balanced by local dissipation. Efficient propagation of energy within the ocean waveguide also acts to make deep ocean microseism observations homogeneous.
Source imaging and sidelobe suppression using time-domain techniques in a shallow-water waveguide
Authors: Feuillade C. , Clay C. S.
Published: October 2005

Source localization in a shallow-water waveguide, using harmonic (cw) techniques, is typically complicated by the repetitive sidelobe structure of the acoustic field. For this reason, much interest has been shown recently in the development and implementation of time-domain methods, which should achieve better performance because of their additional frequency-averaging capability. In a previous publication [C. S. Clay, J. Acoust. Soc. Am. 81, 660–664 (1987)], the basis for optimum signal transmission and source localization in a waveguide using time-domain techniques was described. In this present work a simple two-layer Pekeris model with shallow water depth (20 m) and short range (1500 m) has been used to compute image resolution and sidelobe suppression as a function of frequency bandwidth, number of modes, and the number of receivers in an array. The results indicate that source localization performance is most strongly dependent upon the bandwidth and number of modes available to carry the signal transmission. The physical mechanism for narrowing the source image and suppressing sidelobes is spatial averaging of the acoustic field due to variation of the horizontal wave numbers for the modes as a function of frequency. Improvements in mode sampling, by increasing the number of receivers, also reduced the level of sidelobes, but did not improve the resolution of the image.
Directional dependence of auditory sensitivity and frequency selectivity in the leopard frog
Authors: White Thomas D. , Schmitz Barbara , Narins Peter M.
Published: October 2005

Direction-dependent changes in frequency selectivity were documented in three populations of neurons in the auditory periphery of the leopard frog: low-, mid-, and high-frequency sensitive fibers. These changes were most pronounced in the mid-frequency (720–1199 Hz) sensitive fibers which exhibited positive shifts in characteristic frequencies (CFs) and concomitant narrowed bandwidths from posterior speaker presentations. Maximum sensitivities were observed for ipsilateral speaker presentations in these fibers. Low-frequency (63–500 Hz) sensitive fibers exhibited mean threshold shifts at their CFs of up to −7 dB with posterior speaker presentations. Low- and high-frequency sensitive fibers whose CFs closely correspond to the peaks of spectral energy of the species’ mating call were the most sensitive (exhibited lowest thresholds) but showed little directional-dependent frequency selectivity. Directional-dependent variation in frequency selectivity and sensitivity in low- and mid-frequency sensitive fibers was attributed to pressure and phase differences impinging on the inner surface of the eardrum.
Experimental investigation of dynamics of transverse-impulse wave propagation and dispersion in steel wire ropes
Authors: Kwun H. , Burkhardt G. L.
Published: October 2005

Results of an experimental investigation of the dynamics of transverse-impulse wave propagation and dispersion in steel wire ropes of two different diameters (4.8 and 25.4 mm) are presented. The dispersion relation determined experimentally was consistent with the theoretical one derived for a stiff string when a suitable adjustment was made in the bending stiffness to account for the rope’s flexibility. Significant behavioral difference also was observed between the wave motions in horizontal and vertical planes.
Hybrid background coefficients to isolate the resonance ‘‘spectrograms’’ of submerged shells
Authors: Gaunaurd Guillermo C.
Published: October 2005

The scattering of sound waves by elastic shells in fluids is considered in the mid-frequency or resonance regime. Background coefficients used in the past for the purpose of extracting resonance features in the backscattering cross sections of solid bodies are known to yield inaccurate results in the case of thin shells. These coefficients are modified here. The new hybrid-type backgrounds resemble those found by the application of an impedance type of boundary condition on the shell’s outer surface. The modal surface admittances (in the coefficients) are proportional to the radiation damping factor (or loss factor) at resonance of the shell’s most efficiently radiating (i.e., monopole or breathing) mode. When these (frequency-dependent) hybrid backgrounds are used in the calculations, the target resonances that are thus isolated, seem quite accurate, look less distorted, and the ‘‘spectrograms’’ that result are optimized. This clearly increases the sensor’s target-identification capabilities. As the damping losses decrease, or as the shell thickness increases, the earlier ‘‘rigid’’ backgrounds are recovered.
Wave-vector analysis of the forced vibrations of cylindrical shells of finite length
Authors: Glandier Christian Y. , Berthelot Yves H. , Jarzynski Jacek
Published: October 2005

The forced vibrations of thin shells of finite length are analyzed from a structural wave viewpoint. The proposed theory is restricted to in-vacuo vibrations and to radial harmonic excitation at a surface point on the shell. The theory is based on Donnell’s equations of motion for thin shells. The solution to the forced problem is obtained by solving a boundary value problem that involves a 16×16 system. The 16 equations that are necessary to solve the system are: 4 boundary conditions at each end of the shell, 7 continuity conditions at the excitation point, and 1 discontinuity condition at the excitation point. The method is based in part on Forsberg’s original paper [AIAA J. 2 (12), 2150–2156 (1964)] on the free vibrations of shells of finite length, and, in part, on a general technique for solving one-dimensional forced vibration problems. The theory can be easily implemented on a microcomputer. Some sample axial mode shapes are calculated. To gain physical insight, all the waves that combine into the given mode shape are presented. The theory is also used to perform a wave-vector analysis of the predicted vibration field on the shell surface to separate the contributions from flexural, shear, and longitudinal waves. It is found that a Prony decomposition algorithm in the axial direction of the shell is more useful than the standard fast Fourier transform because it yields a much finer resolution of the helical wave spectrum. The algorithm developed in this study does not include internal losses in the shell. It appears that, with no internal losses, the amplitude of the helical wave spectrum is very sensitive to the physical parameters of the shell, in particular to its thickness, when the excitation frequency is very close to a natural frequency of the shell.
Vibrations of simply supported cylindrical shells isolated from an ambient acoustic medium by a compliant layer
Authors: Junger Miguel C.
Published: October 2005

The effect of a resilient layer isolating a finite cylindrical shell from a high-impedance acoustic medium, e.g., water, on the predominantly radial modes of the shell is explored. While the submerged, bare shell displays resonances whose natural frequencies are reduced below their in vacuo values by the kinetic energy of the entrained fluid vibrating with the same amplitude as the structure, the coated shell displays two families of radial modes: (1) predominantly structural modes whose natural frequencies are raised above those of the shell in vacuo by the coating stiffness, the coating/fluid interface remaining nearly stationary; (2) low-frequency modes embodying the compliant layer’s spring stiffness and the combined modal masses of entrained fluid and of the shell; for these modes, coating/fluid interface amplitudes are markedly enhanced above those of the coated shell and even those of the bare, submerged shell.
Relations among different measures of speech reception in subjects using a cochlear implant
Authors: Rabinowitz W. M. , Eddington D. K. , Delhorne L. A. , Cuneo P. A.
Published: October 2005

A comprehensive set of speech reception measures were obtained in a group of about 20 postlingually deafened adult users of the Ineraid multichannel cochlear implant. The measures included audio, visual, and audiovisual recognition of words embedded in two types of sentences (with differing degrees of difficulty) and audio-only recognition of isolated monosyllabic words, consonant identification (12 alternatives, /Ca/), and vowel identification (8 alternatives, /bVt/). For most implantees, the audiovisual gains in the sentence tests were very high. Quantitative relations among audio-only scores were assessed using power-law transformations suggested by Boothroyd and Nittrouer [J. Acoust. Soc. Am. 84, 101–114 (1988)] that can account for the benefit of sentence context (via a factor k) and the relation between word and phoneme recognition (via a factor j). Across the broad range of performance that existed among the subjects, substantial order was observed among measures of speech reception along the continuum from recognition of words in sentences, words in isolation, speech segments, and the retrieval of underlying phonetic features. Correlations exceeded 0.85 among direct and sentence-derived measures of isolated word recognition as well as among direct and word-derived measures of segmental recognition. Results from a variety of other studies involving presentation of limited auditory signals, single-channel and multichannel implants, and tactual systems revealed a similar pattern among word recognition, overall consonant identification performance, and consonantal feature recruitment. Finally, improving the reception of consonantal place cues was identified as key to producing the greatest potential gains in speech reception.
Matched-mode processing schemes of a moving point source
Authors: Chen Han-Yang , Lu I-Tai
Published: October 2005

Matched-mode processing schemes are presented to estimate the frequency, velocity, depth, and range information of a time-harmonic point source moving uniformly in stratified oceanic waveguides. Three linear modal filtering approaches (frequency spectral decomposition by a single receiver, spatial spectral decomposition by a horizontal receiving array, and eigenfunction decomposition by a vertical receiving array) are first discussed to provide an overview for possible approaches to localize a moving source. An iterative nonlinear extrapolation algorithm involving only the fast Fourier transform is then employed to reduce the observation time by about an order less than that required by the linear frequency method. Physical insights of the Doppler effect in these inversion procedures are discussed in detail. Based on these insights, practical criteria for choosing processing parameters are established so that they can be applicable to all range-independent waveguides. Numerical results calculated by these methods of both shallow water and deep ocean examples are presented.
Comparative performance of matched-mode and matched-field localization in a range-dependent environment
Authors: Bogart Christopher W. , Yang T. C.
Published: October 2005

Matched-mode localization has been proposed recently as an alternative to matched-field processing for underwater source localization. It involves processing in mode space rather than phone space, and requires much less processing time compared to match-field processing. To date, studies of matched-mode processing have concentrated on single vertical arrays in range-independent environments. In this paper, matched-mode localization of a source in range, depth, and bearing using twin vertical arrays is demonstrated using simulated acoustic data. The environment considered consists of sloping bottoms with a sound speed increasing with depth. Acoustic modeling assumes adiabatic normal modes, neglecting horizontal refraction. Results of source localization are compared for both a range-independent environment and for matched-mode processing versus matched-field processing. It is found that for the cases studied the matched-mode processing is an order of magnitude faster than the matched-field processing for range-depth searches, and the time difference is greater for range-bearing searches. The matched-mode ambiguity surface shows equal or slightly improved (lower) sidelobe levels compared with that of matched-field processing. Results of source localization are compared for arrays of different number of phones, different vertical spacings, and different locations. The arrays that resolve more modes generally have better performance.
Simultaneous ultrasonic velocity and sample thickness measurement and application in composites
Authors: Hsu David K. , Hughes Michael S.
Published: October 2005

Ultrasonic velocity is widely used in the investigation of material properties. In cases where thickness of the test piece is not precisely known or varies spatially, it is desirable to determine the wave velocity and the sample thickness in the same ultrasonic measurements. For tests in an immersion tank or using squirters, both wave velocity and the specimen thickness may be deduced from the time of flight of several ultrasonic pulses. In this paper four different configurations of pulse echo and through transmission are described for the ‘‘simultaneous’’ velocity and thickness determination. The method is then applied to investigate the porosity content in graphite/polyimide and graphite/epoxy composite laminates. Good results were obtained for both the wave velocity and the part thickness, and a clear correlation between velocity and void content is demonstrated.
Internal phonetic category structure depends on multiple acoustic properties: Evidence for within-category trading relations
Authors: Hodgson Philip , Miller Joanne L.
Published: October 2005

Two acoustic properties underlying the distinction between the presence and absence of a stop consonant, as in say vs stay, are silence duration and first-formant (F1) onset frequency: little or no silence and a high F1 onset frequency specify say, whereas a longer silence and a lower F1 onset frequency specify stay. Previous research has established that these two properties enter into a trading relation at the phonetic category boundary. Whether they also enter into a trading relation within the category is explored in the current investigation. Two series of stimuli having low (230 Hz) and high (430 Hz) F1 onset frequencies, respectively, have been created. Silence duration in each series varied from 0 to 996 ms, resulting in stimuli ranging from say through stay to an exaggerated version of stay. A preliminary two-choice study (with just the stimuli between 0 and 136 ms) confirmed the expected trading relation at the say–stay boundary, with the boundary for the high F1 series being located at a longer silence duration than that for the low F1 series. In the main experiment, listeners were presented randomizations of all the stimuli and asked to judge each for its goodness as an exemplar of the word stay, using a rating scale (1–10). It was expected that for each series, only a limited range of stimuli would be given high ratings. At issue was the location of these stimuli. If silence duration and F1 onset frequency trade within the category as well as at the boundary, then the best exemplars for the high F1 series should be displaced towards longer silence durations relative to those for the low F1 series.

The results confirmed the predictions. These findings indicate that the internal structure of phonetic categories is determined by multiple acoustic properties. It is suggested that this complex acoustic-phonetic mapping derives from the common articulatory origin of these properties. [Work supported by NIH.]
A new lattice gas model for 1-D sound wave propagation
Authors: Sudo Yasushi , Sparrow Victor W.
Published: October 2005

The basic idea behind lattice gas methods is that the simple dynamics of lattice gas particles can describe complex systems. In this paper, a new lattice gas model for one-dimensional (1-D) sound wave propagation will be demonstrated. The particles move at either unit or zero velocity, and there is no interaction between them. The present model leads to a 1-D sound wave system with speed of sound M/N (M, N=integers; 0≤M≤=N; with units of [sampling distance]/[sampling time]). The group velocity is also M/N and is independent of frequency, unlike many popular finite difference methods. Allowing the field variables to be real numbers instead of integers, it is easy to incorporate boundary effects and inhomogeneities. One can apply this model to wave propagation in two or three dimensions also.
Global and local partial response of ribbed uniform panels
Authors: Maidanik G. , Dickey J.
Published: October 2005

Two formalisms of the response of a ribbed uniform panel excited by a line drive are considered. In the first, the global response is obtained. In this response, phases among the responses of the bays are preserved and accounted for. (A bay is the portion of the panel that lies between two adjacent ribs.) The preservation of the phases yield responses that exhibit the phenomena of pass and stop bands and of localizations and delocalizations when the separations between adjacent ribs are equal. In the second formalism, the local response is obtained. The response is estimated in terms of the energy densities in the individual bays. In this formalism the phases among the responses of the bays are inconsequential. Therefore, the phenomena of pass and stop bands and of localizations and delocalizations are not manifested in the localized response. It is thus suggested that formalisms that are akin to the statistical energy analysis (SEA) and SEA itself cannot be expected to exhibit some of the features in the response of a complex structure, especially if the structure is composed of a number of regular substructures; e.g., the identical bays in a ribbed panel. Generic examples are presented in this paper to illustrate that in certain situations and for certain purposes the missing features in the local response, as compared with the global response, may be significant.
Testing an auditory streaming hypothesis of the comodulation masking release effect
Authors: Rappold Patrick W. , Mendoza Lee , Cullen John K.
Published: October 2005

An auditory streaming hypothesis has been proposed to explain the comodulation masking release (CMR) effect. This hypothesis suggests that threshold for a masked pure-tone is lower when the temporal envelope of a masker-band fluctuates in synchrony with a flanker-band (s) because of auditory cross-spectrum fusion of the noise-bands. Thus the pure-tone may be ‘‘removed’’ from the stream comprising the noise bands and become perceptually isolated in a stream of its own and ‘‘easier’’ to detect. Two stimulus conditions were created using only synchronously fluctuating noise bands: strongly fused and weakly fused. To investigate a possible relationship between auditory fusion of noise bands and the CMR effect, thresholds were determined for a pure tone while attempting to impair fusion of the noise bands in the weakly fused condition. Fusion was impaired by capturing the single flanker band into a sequential stream with a captor band. In the strongly fused condition, no attempt was made to manipulate fusion of the noise bands. Thresholds did not differ significantly across the two conditions.
The effect of nonsimultaneous off-frequency cues on the detection of a tonal signal masked by narrow-band noise
Authors: Bernstein Leslie R. , Trahiotis Constantine
Published: October 2005

Listeners’ detection thresholds were measured for a 125-ms, 1-kHz tonal signal masked by a similarly gated 50-Hz-wideband of noise. A two-cue, two-interval adaptive, forced-choice procedure was employed and the presence and nature of the cues were varied across conditions. In the baseline conditions, no cues were provided and the maskers were either chosen randomly or were identical within but not across trials. In the conditions of interest, the envelopes and phase-modulations of the maskers were ‘‘frozen’’ across all four intervals of a trial, but were randomly chosen across trials. The center frequency of the bands of noise that served as cues (first and fourth intervals) was either 1 kHz (on-frequency) or 900 or 700 Hz (off-frequency). Detection with 1-kHz cues was greatly improved over baseline conditions and this improvement declined rapidly when the center frequency of the cue was changed to 900 or 700 Hz. Roving-level conditions were also employed to assess the nature of the information used by the listeners. [Work supported by AFOSR and NIH.]
Statistics of Arctic ambient noise
Authors: Sotirin B. , Myers R.
Published: October 2005

Characteristics of Arctic ambient noise include a wide dynamic range, non-Gaussian distributions, nonstationary intervals and a high variability in spectral shape. However, there are times during which these noise fields reflect stationary normally distributed processes. This variability demands that data sets be analyzed for independence, time stationarity, and distribution to verify the assumption of valid statistical ensembles prior to processing, as these properties are prerequisites for many algorithms. A statistical analysis of noise samples at 20 and 75 Hz over a 10-day period during which the omnidirectional levels varied significantly indicate that the change in statistics of the noise field correlates with local ice activity. The quiet intervals are dominated by long-range propagation where the noise exhibits stationary Gaussian characteristics and the noisy intervals are affected by local ice dynamics where the transient nature of the events tend to invoke non-Gaussian as well as nonstationary properties.