bluuebunny/crossref_metadata_2025 huggingface dataset:
Impulse response for backscattering by a thin spherical shell: Measurement and wave interpretation
Authors: Kaduchak Gregory , Kwiatkowski Christopher S. , Marston Philip L.
Published: October 2005

A broadband sheet source was developed to produce a pressure impulse with a planar wave front containing a wide range of frequency components [C. S. Kwiatkowski etal., to be presented at this meeting]. This source is nearly acoustically transparent and was used for backscattering from an empty stainless steel spherical shell where prominent features in the shell’s calculated impulse response are observed over a wide frequency interval. A wideband hydrophone was placed in the far field of the scatterer on the opposite side of the source. Time records reveal a gaussian wave packet associated with the excitation of the subsonic a0− wave responsible for a large backscattering enhancement near the coincidence frequency. Superposed on the same records are large contributions from the low frequency excitation of the breathing mode [G. Kaduchak and P. L. Marston, J. Acoust. Soc. Am. 93, 2700–2706 (1993)]. The shell used in the experiment has a thickness to radius ratio of 2% for which the above scattering phenomena occur for frequencies less than 450 kHz. [Work supported by ONR.]
Nature of the Scholte wave on a cylindrical shell
Authors: Maze G. , Léon F. , Ripoche J. , Überall H.
Published: October 2005

The real parts of the eigenfrequencies of an evacuated, fluid-immersed infinite cylindrical shell can be used to obtain the dispersion curves versus frequency of the phase velocities of families of circumferential waves. These waves are analogous to those of the families of Lamb waves on an elastic plate invacuo, but contain an additional A wave corresponding to the Scholte–Stoneley wave in the fluid loading [see M. Talmant, Ph.D. thesis, Univ. of Paris VII (1987), or M. Talmant etal., J. Acoust. Soc. Am. 86, 278 (1989)], which is approximated by the first Franz wave [B. Clotteau etal., J. Acoust. 3, 213 (1990)]. Near the coincidence frequency, a repulsion phenomenon is obtained between the (Lamb wave) A0 and the A-wave dispersion curves, analogous to that in perturbed, quasidegenerate atomic levels. An analytic explanation is provided, using perturbation theory, for the form of the dispersion curves and the nature of the corresponding waves in the region of repulsion.
Acoustic and syntactic correlates of hesitations in spontaneous speech
Authors: Veilleux Nanette , Schlosser Ahwat , Ostendorf Mari
Published: October 2005

One of the difficulties in modeling the prosody of spontaneous speech is distinguishing hesitations from fluent intonational phrase breaks. The goal of this study is to identify acoustic and syntactic cues that can be used to better model hesitation phenomena. The study is based on a set of several hundred utterances of spontaneous speech from the ATIS corpus, each with prosodic constituents and hesitations labeled by hand and syntactic constituents and phonetic alignments labeled automatically. The first set of analyses compared acoustic correlates for prosodic phrase boundaries with and without hesitations. For constituents below the level of the intermediate phrase, the average duration of a pause is longer when there is a hesitation (mean 270 ms vs 19 ms), as is the mean normalized segment duration in the word-final syllable rhyme (mean 1.8 vs 0.2), both with significance p<10−5. The second set of analyses looked at the differences in syntactic structure at word boundaries with and without hesitations. Again, for constituents below the level of the intermediate phrase, results show that hesitations are likely to occur after a conjunction, auxiliary verb, or preposition, i.e., at locations where the entropy of next-word candidates is relatively high.
Fresnel array method for determining the dispersion curves in plates
Authors: Costley R. Daniel , Berthelot Yves H.
Published: October 2005

Experiments have been conducted on the thermoelastic generation of Lamb waves in plates by a Q-switched ruby laser. Detection was performed both by interferometric laser probe and a miniature piezoelectric pinducer. The long-term objective of this work is to determine various characteristics of the plate such as material properties, plate thickness, flaws, and inhomogeneities, or even bonding between plates by comparing experimentally determined points with the theoretical dispersion curves. The technique consists in forming on the surface of the specimen an array of confocal arc sources by passing the laser beam through a Fresnel lens. The array spacing produces a ‘‘forcing wavelength’’ for which only a few specific frequencies can propagate. Dispersion curves can be obtained by measuring the frequency content of the received signals for a range of wave numbers. Because of the narrow-band nature of the technique, and because of the confocal geometry of the source distribution, this technique offers a relatively high signal-to-noise ratio. Good agreement is obtained between theoretical and experimental dispersion curves especially for the lower modes, thus showing that the proposed technique has potential for the above-mentioned applications. [Work supported by the National Science Foundation.]
Velar coarticulation revisited
Authors: Bell-Berti Fredericka , Krakow Rena A. , Ross Dorothy
Published: October 2005

Several models, embodying fundamentally different assumptions about the nature and organization of speech motor control, have been offered in explanation of observations of coarticulatory phenomena. A series of experiments has been undertaken to test specific predictions about the role of carryover coarticulation in delaying the normally stable onset of a velar gesture for a segment, made by Bell-Berti and Harris’ coproduction model [F. Bell-Berti and K. S. Harris, Phonetica 38, 9–20 (1981); F. Bell-Berti, Phonet. Phonol. 5, 63–85 (1993)]. For example, the onset of velar lowering for a vowel or a nasal consonant following an obstruent will be delayed until near the end of the acoustic period of the obstruent (depending upon its duration), to insure adequate velopharyngeal closure for the obstruent. (That is, the velar gesture for a later segment is modified by the requirements for a preceding one.) Early results encourage the belief that it will be possible to account for anticipatory and carryover effects with a single model. [Work supported by NIDCD Grant No. DC-00121 to the Haskins Laboratories.]
Examination of sonic boom propagation through turbulence with ray theory
Authors: Robinson Leick
Published: October 2005

The properties of sonic boom propagation through turbulence continue to be explored by a ray theory approach. Ray theory is used to model the effects of refraction and subsequent folding of the wave front by an instantaneous realization of the turbulence. Comparison is made with other prediction methods. These results are compared with characteristics observed in sonic boom measurements. The relative contributions of the large and small scale modes of the turbulent field are evaluated.
Application of the CFFP to sound propagation in inhomogeneous media above a ground with an impedance discontinuity
Authors: Li Y. L. , White Michael J.
Published: October 2005

Using the chirp fast field program (CFFP), a systematic method has been developed for numerical computation of sound propagation in an inhomogeneous atmosphere above a ground with an abrupt change in impedance. In situations where a noise is generated above one type of ground surface (say pavement) and travels beyond its edge, onto a second type of surface (e.g., grassy ground), each surface usually controls the rate of attenuation near it. When the air near the ground is refractive, it may emphasize the attenuation during downward refraction and eliminate it in upward refraction. Other effects of the inhomogeneous atmosphere are discussed. Several interesting examples will be presented.
Sound propagation in inhomogeneous media above a ground with a barrier
Authors: Li Y. L. , White Michael J.
Published: October 2005

To study the problem of scattering of acoustic waves from a ground with a barrier, the exact expression of the Green’s function due to a line source embedded in a layered medium has been successfully incorporated into the Helmholtz–Kirchhoff integral equation. An extension of the method of moments, which can solve the Helmholtz–Kirchhoff integral equation for studying the problem of sound scattering in the inhomogeneous medium has been developed. Using the method, the effects of scattering in the region beyond a barrier are studied for situations when the background medium is inhomogeneous. The effects of the inhomogeneous atmosphere are discussed. Several interesting examples will be presented.
Measurements of focused, finite amplitude sound beams reflected from curved targets
Authors: Averkiou Michalakis A. , Makin Inder Raj S. , Hamilton Mark F.
Published: October 2005

The reflection of focused, finite amplitude sound beams from curved targets in water was investigated experimentally and theoretically. Measurements of small signal diffraction effects were used to characterize the effective radius (1.9 cm) and focal length (15 cm) of the source, the center frequency of which is 2.25 MHz. Detailed comparisons are made between measurements of harmonic generation in the incident focused beam and numerical results from a computer code that solves the KZK equation in the frequency domain [Naze Tjo/tta etal., J. Acoust. Soc. Am. 89, 1017–1027 (1991)]. Reflection from both convex and concave target surfaces is considered. The targets are made of nickel with different radii of curvature down to a minimum of 5 cm. Measurements of the reflected beam were obtained with a membrane hydrophone that was placed between the source and the target. Theoretical predictions for harmonic generation in the reflected field were obtained by modifying the computer code to account for the phase shifts introduced by interaction of the incident beam with the target. Theory and experiment are in good agreement for both the incident and reflected beams. [Work supported by the Packard Foundation and the Office of Naval Research.]
The Lookup program for prediction of noise levels outdoors
Authors: White Michael J. , Li Y. L.
Published: October 2005

A rigorous calculation of the noise level away from a broadband source of known characteristics under known meteorological conditions requires considerable computational effort. However, many practical situations fall into easily described classes of meteorological condition, source and receiver height, ground type, etc. Results have been of tabulated full-wave acoustic calculations, systematically changing the source and receiver configuration, frequency, and environmental parameters. The Lookup program accepts a one-third octave source spectrum, source and receiver configuration, ground condition, and meteorological profile, then accesses the Lookup table for the nearest case and estimates the receiver spectrum. It does this in under 1 s on a PC.
SoundProp—Fast, accurate prediction of sound propagation under varying weather conditions and over hard or soft surfaces
Authors: Schomer Paul D. , White Michael J.
Published: October 2005

LOOKUP provides a fast, accurate callable sub-routine to predict the one-third octave band received sound spectrum for an arbitrary combination of source height, receiver height and range, one-third-octave-band source spectrum, and surface impedance (soft or hard). SoundProp is a shell that facilitates the use of LOOKUP. With SoundProp, the user can accurately and quickly perform virtually any sound propagation prediction for a soft or hard surface and a range of sound propagation conditions. Simple barriers can also be included. Future enhancements will include separate specification of the source, path, and receiver surface impedance and additional sound-speed profiles in the LOOKUP library. SoundProp is limited to simple ASCII text file output and must have a VGA monitor. Currently, SoundProp uses about 6 MB of disk space and must be located in drive C. WINSoundProp will be a Windows version of SoundProp and will be able to plot graphical output on any printer supported by Windows. These programs, developed by the U.S. Army Construction Engineering Research Laboratories, are free.
Effective vertical aperture for three-dimensional arrays in shallow waters
Authors: Bogart Christopher W. , Yang T. C.
Published: October 2005

In shallow waters, the effective vertical aperture of an array composed of horizontal and vertical segments may be greater than the water column depth. The extended vertical aperture leads to better decomposition of bottom-interacting normal modes and hence better range-depth localization compared with the performance of the vertical subarray alone. The conditions under which the effective vertical aperture gives improved localization performance over a vertical array spanning the water column are demonstrated. The effect of source frequency, ratio of horizontal to vertical array length, and bottom properties on localization performance are discussed.
Signal-to-noise improvement for higher-order correlators with one-dimensional prefiltering
Authors: Pflug Lisa A. , Ioup Juliette W. , Ioup George E. , Field Robert L.
Published: October 2005

Previous work by the authors has shown that prefiltering when used in conjunction with higher-order correlators possesses potential detection advantages over the ordinary cross-correlation detector for bandlimited transient signals in noise for active (known source) and passive (unknown source) sonar. Preliminary simulation results have been presented [Ioup etal., J. Acoust. Soc. Am. 92, 2417(A) (1992); Ioup etal., Proceedings of the IEEE Signal Processing Workshop on Higher-Order Statistics, 7–9 June 1993]. Additional research has been completed, including a systematic and quantitative study using three different filter levels. Eight test signals are presented in the study: Several very low-frequency signals, a pulse, a 50-Hz sinusoid, a resonating sinusoid, a FM linear sweep, and a nonlinear FM sweep. SNR gain comparisons between the detectors are made for Pd=0.5 and Pfa=0.001. Significant SNR gains are evident for both the known and unknown source models with the tricorrelation detector exhibiting the largest gains. For all the test signals, the tricorrelation detector outperforms the cross-correlation detector for the unknown source model, and outperforms the matched filter for seven of the eight test signals for the known source model. [Research supported by Office of Naval Research, Program Element 61153N, with technical management provided by NRLSSC.]
Cross-spectral matrix estimation effects on adaptive beamforming
Authors: Grant David E. , Gross Jonathan H. , Lawrence Mimi Z.
Published: October 2005

Adaptive beamforming algorithms, which use CSM (cross-spectral matrix) data to calculate optimum weights, are sensitive to the number of unsmoothed CSM samples used in the CSM estimate. Assuming that the samples used in the CSM estimate are independent identically Gaussian distributed with zero mean, it is shown that the output power from the estimated CSM is biased low relative to the output power from the real CSM. Using data from a horizontal line array deployed in a shallow water, high noise environment, the adaptive beamformer output power with various numbers of samples used in the CSM estimate has been measured. The number of CSM samples was varied by changing the time–bandwidth product. The measured median beam noise levels are compared with the theory. Since the data do not fit the assumptions stated above, the agreement is not exact. However, the general trends of the data and theory agree quite well. Conclusions are drawn about the number of samples that should be used for a CSM estimate to be reliable, and about the stationarity of the data within the time-bandwidth integration used in the CSM estimates. [This work is supported by the U.S. Navy Space and Naval Warfare Systems Command.]
Ray acoustic modeling of the surface fields of a submerged elastic cylindrical shell with hemispherical endcaps
Authors: Ho Jin-Meng
Published: October 2005

Combining the available ray acoustic algorithms descriptive of submerged thin cylindrical and spherical shells, this paper formulates the pressure and velocity distributions on a hemispherically capped cylindrical shell insonified by an obliquely incident acoustic plane wave. As the first ray acoustic model for a noncanonical shell geometry of considerable current interest, it neglects wave coupling and diffraction due to curvature discontinuities at the junctures as well as contributions from the leaky waves excited through the endcaps. This might be justifiable, because the junctions are not sharp edges (i.e., the normals are continuous) and because the cylinder under consideration is very long compared to the radius. By matching the surface wave vector along the joints, however, due account is taken of leaky wave propagation on, and radiation from, the hemispheres. The total pressure or velocity—their ray constituents are related to each other by appropriate impedances—on the cylinder is then synthesized by a modified geometrical acoustics field, as developed recently, and a supersonic membrane wave field that accounts for the leaky surface rays successively reaching the observer along helical trajectories and great circles on the cylinder and hemispheres, respectively. Numerical implementation is also performed here. The results are compared with the reference solution generated at NRL by a boundary element code. [Work supported by ONR.]
Structural acoustics of cylindrical shells having multiple layers using the direct global matrix
Authors: Ricks David C. , Schmidt Henrik
Published: October 2005

A method has been developed to compute the response of cylindrically layered viscoelastic systems using the direct global matrix approach (DGM). The numerical stability of the method allows us to model multilayered shells that have viscoelastic layers for damping and compliant coatings for decoupling. In this presentation, the method is applied to a cylindrical shell having external fluid loading and a viscoelastic layer of damping material sandwiched between two solid layers. The model can be excited by ring forces, point forces, and a point source in the fluid. Parameter studies are presented to investigate the effect of the viscoelastic damping layer on the various wave types (flexural, membrane compression, and membrane shear). [Work supported by ONR.]
Forward modeling of midfrequency wave propagation in shells
Authors: Bondaryk Joseph E. , Schmidt Henrik
Published: October 2005

Experimental, bistatic, scattering measurements were made on two, fluid-loaded, cylindrical shells in the frequency range of 2<ka<10. Data were collected for an empty shell and a duplicate shell stiffened with unequally spaced ring stiffeners and resiliently mounted, wave-bearing, internal structural elements. The shells were ensonified by wideband pulses of spatially plane waves at bow incidence and the scattered field was measured by a synthetic array in the transition field regime. Time domain focusing is used to backpropagate the measured field to the shell surface. The specular contribution to the measured field is first estimated and removed to eliminate it in the backpropagated data. The resulting waveforms show the transient, dynamic, structural response of the shell, uncluttered by the specular wave and its sidelobes. The measurement array does not provide enough resolution to allow direct analysis of membrane waves traveling on the shell. Therefore, a forward-modeling technique coupling a transmission-line model of the shell and simulated annealing parameter estimation is used. This procedure provides estimates of wave speeds, decay rates, and reflection and transmission coefficients at shell discontinuities for flexural and compressional waves on the both shells. [The authors acknowledge NRL for acquisition of scattering data. Research supported by ONR.]
Response of submerged cylindrical shells with internals to an impulse line load
Authors: Utschig Michael J. , Igusa Takeru , Achenbach Jan D.
Published: October 2005

An infinitely long cylindrical shell containing internal substructures and submerged in a fluid is excited by a short duration line load. The response of the shell, substructure, and fluid is examined in the frequency and time domains. To gain insight into the response characteristics, two approaches are used. The first is the normal mode approach, where the response is expressed as a Fourier series in the circumferential coordinate [M. C. Junger and D. Feit (1986)]. In the second approach, the shell is unwrapped into a two-dimensional manifold unbounded in both the longitudinal and circumferential coordinates [Pierce and Kil, J. Vib. Acoust. 112, 399–406 (1990)]. The response is expressed as a Fourier transform in the circumferential coordinate. The results of the modal approach are useful in examining resonances between the fluid-loaded shell and the substructures and in interpreting the effects of the substructure connections. The results of the second approach can be visualized as waves propagating around the shell circumference and generating near-field acoustic disturbances. A time sequence of contour plots of the near-field pressure reveals the evanescent and propagating acoustic waves associated with the shell and substructure responses. [Work supported by ONR.]
A psychological experiment on quantitative judgment for transposition of melodies
Authors: Shirado Tamotsu , Yanagida Masuzo
Published: October 2005

Novice musicians have difficulty in judging the interval between a melody and its transpose quantitatively. It is expected that the more one accumulates musical experiences, the more he or she can improve their ability of quantitative judgment for the interval between a melody and its transpose. It is supposed that this ability depends on abilities of absolute pitch. Psychological experiments were conducted to investigate relations among these abilities. Single tones, pairs of single tones, and pairs of melodies and their transposes generated by a synthesizer were used for the experiments. Subjects (students majoring in music) were asked to give pitch names of single tones presented in isolation, to judge intervals between two single tones presented sequentially, and to estimate the interval between a melody and its transpose presented on a continuous rhythm pattern. From the experiments, it can be seen that there are various types of difficulties in judging musical intervals between two single tones and those between melodies and their transposes. Further, weak correlation has been found between the ability to judge intervals between two single tones, and the ability to judge intervals between a melody and its transpose.
The tritone paradox and speakers’ voice range: A dubious connection
Authors: Repp Bruno H.
Published: October 2005

Deutsch and her co-workers [Music Percept. 7, 371–384 (1990); 8, 335–347 (1991)] have proposed that individual differences in the perception of the so-called tritone paradox (i.e., the perceived direction of pitch change in pairs of Shepard tones six semitones apart) derive from listeners’ reference to a template acquired through experience with the pitch range of their own voice. Deutsch has reported a striking difference in tritone perception between American and British listeners, as well as a correspondence with the upper limit of the voice pitch range within an American group. The present study compared groups of Dutch, British, and American listeners. Contrary to Deutsch’s observations, the perceptual results of these three groups were very similar, and there was no correlation with individual differences in vocal range within any group. Instead, there were large and systematic differences as a function of stimulus characteristics (spectral envelope), which further contradicts Deutsch’s findings. These results suggest that, rather than deriving from a language-based pitch template, the perception of tritone stimuli depends on psychoacoustic factors and individual differences in auditory processing whose nature is not well understood at present. [Work carried out at IPO, Eindhoven.]
Retroflective backscattering of sound in water due to leaky waves on facets, plates, and corner truncations: Approximate theory
Authors: Marston P. L. , Dodd S. S. , Loeffler C. M.
Published: October 2005

A leaky Rayleigh (or Lamb) wave is known to be launched on a flat elastic surface (or plate) in water when the surface normal lies near a cone whose symmetry axis gives the k vector of the incident sound. If the surface has a corner with edges meeting at angles of 90°, 45°, 30°,..., the wave vector of the leaky wave is exactly reversed due to repeated reflections at the edges that form the corner. The resulting leaky radiation is backscattered toward the source and depends only weakly on the orientation of the corner. The high-frequency cross section is large since the outgoing wave front is flat. For a suitably cut, randomly oriented facet or metal block, this effect is more likely to be observed than the specular reflection since then the normal must lie on a narrow range of angles. An approximate geometric theory for the amplitude is given. The mechanism also applies to circular cylindrical shells with 90° truncations.
Ultrasonic nondestructive evaluation of thin (subwavelength) coatings
Authors: Zhu C. , Kinra V. K.
Published: October 2005

This paper describes a technique for ultrasonic nondestructive evaluation of a thin coating (subwavelength) on a thick substrate. A plane longitudinal wave which is normally incident upon the coating is considered. Transfer functions have been derived for both the coating-side and the substrate-side insonification. A systematic analysis of the sensitivity of the transfer functions to the thickness and wavespeed has been carried out. An inverse algorithm has been developed to reconstruct the thickness and the phase velocity through a comparison of the theoretical and the measured transfer functions. Using this technique both the thickness and the wave speed of the coating can be extracted from the same measurement, without knowing either. The technique was used to measure the thickness and wave speed of epoxy and Plexiglas coatings (50–100 μm) on an aluminum substrate using low-frequency (10 and 20 MHz) transducers; the ratio of thickness/wavelength was about 1/3. The precision in the measurement of the thickness and the wave speed was found to be ±2 μm and ±3%, respectively. [Work supported by Texas Advanced Technology Program.]
Underwater earthquakes noise levels and its possible effect on marine mammals
Authors: Nishimura Clyde E. , Clark Christopher W.
Published: October 2005

Earthquakes in oceanic regions commonly generate acoustic signals known as T-phases which are similar but not identical, to man-made explosions. As earthquake-producing areas are also regions where marine mammals congregate (e.g., Aleutians and Caribbean margin), knowledge of the characteristics of T-phases may provide some additional information on the possible effect of noise on these animals. T-phases are generally characterized by acoustic energy below 100 Hz with most of its energy in the 10- to 30-Hz range. The duration of the T-phase is, to the first order, linearly related to the source earthquakes magnitude; durations of several minutes are common. The T-phase source signal level, which can exceed 200 dB re: 1 μPa for a magnitude 4–5 earthquake, is a complex function of the source magnitude, focal depth, and the complexity of the bathymetry at the water–rock radiation area. This radiation area is not a point source and can extend over a radius of several tens of km. As part of the Whales ’93 program, analysis has begun as to whether there is any correlation between the occurrence of earthquakes and observable changes in the acoustic signature form, and the positioning of large cetaceans.
The reaction of humpback whales to underwater explosions: Orientation, movements, and behavior
Authors: Lien Jon , Todd Sean , Stevick Peter , Marques Fernanda , Ketten Darlene
Published: October 2005

In 1992, local fishermen reported unusually high net collision rates by humpback whales in Bull Arm, Trinity Bay, Newfoundland (47° 45'N, 53° 50'W), an area of underwater industrial activity. As part of a study to investigate this phenomenon [see also Ketten etal., this meeting], levels and types of noise—including underwater explosions—were sampled. The location and movement of a small group of humpbacks (71 individuals identified over a 19-day period) resident in Bull Arm were monitored; when possible, behavior of individuals was recorded directly. CTD profiles and bait abundance were also noted. Explosions were of high amplitude and low frequency. Measured at 1 mile from source, levels typically reached 150 dB (re: 1 μPa at 1 m, at 350 Hz). Following explosions, residency time and location of individual humpbacks did not change. When individuals could be observed directly, no behavioral reaction to explosions (sudden dives, abrupt movements) were seen. Although not statistically significant, more animals were sighted and resighting rates were higher in the explosion area than in other parts of the bay. However, two animals recollided with fishing gear—such reports of successive entrapments are rare.
Recording, analysis, and verification of low-frequency sounds produced by Arctic offshore drilling equipment
Authors: Brewer Kenneth D. , Hall John D.
Published: October 2005

Digital recordings of underwater sounds produced by anchored and bottom-founded Arctic offshore drilling equipment (drilling rigs) were made during drilling and idle conditions in open water and under sea ice. Sound production was verified by recording the frequencies produced by specific pieces of equipment aboard the rigs using a single axis accelerometer. It was determined that most of the sound energy produced by both the anchored and bottom-founded drilling equipment was in the frequency band from 1 Hz to 1 kHz. The drill turntable and drive equipment on the bottom-founded drilling rig produced sounds as low as 1.8 Hz. The broadband [20 Hz to 20 kHz source level (dB re: 1 μPa2@1 m] of the bottom-founded drilling rig (146.2 dB) was about 30 dB less than the broadband source level of the anchored drilling rig (178.6 dB). Acoustic transmission loss in the inshore areas of the Alaskan Beaufort Sea, where water depths are less than 100 m, was found to be slightly greater than cylindrical spreading (−11.0 to −13.0 log R dB) at the two sites about 350 km apart. [Work supported by ARCO Alaska, Inc.]
Variation in received level from man-made low-frequency underwater noise sources as a function of diving animal depth
Authors: Ellison William T. , Weixel Karen S. , Clark Christopher W.
Published: October 2005

Interest in the effects of low-frequency (<1 kHz man-made noise on marine wildlife highlights the need for accurate knowledge of the spatial distribution of noise levels within a given wildlife habitat. These levels can vary significantly, particularly with respect to depth within the water column. For diving animals, the ability to measure or predict this variation with depth is a necessary factor in assessing the net impact of that noise; i.e., one needs to perform a convolution of diving patterns (depth as a function of time) with the noise pattern as a function of time and depth. Recent advances in range dependent acoustic propagation modeling allow for the ability to predict with some accuracy the transmission loss from a known source of noise as a function of source characteristics (directivity, sound spectrum, location, and depth) to any given location in a hypothetical habitat. Several examples are presented that illustrate how these models might be used to evaluate the net impact of a passing noise source on pelagic whale species. [Work supported by ONR.]
Modeling noise interference with animal communication
Authors: Awbrey Frank T.
Published: October 2005

Regulators are proposing to set simplistic limits for anthropogenic noise in natural environments. These proposed limits specify only SPL, without regard to the method of measurement, frequency or time weighting, normal ambient levels, or spectra. In some cases such limits may be inadequate, but in others they may be much too severe, resulting in unrealistic restrictions on human activities, including scientific investigations, without real benefit to the animals. Realistic limitations on noise level should incorporate information on the time history and spectrum levels of the noise and the animals’ communication signals, with estimates of hearing threshold curves. This paper outlines an initial effort to devise such a model and to estimate how seriously noise of different kinds will limit communication.
Vibration and acoustic monitoring of rotating shafts
Authors: Dimarogonas Andrew D.
Published: October 2005

Vibration and acoustic monitoring of the operating conditions and incipient failures of rotating shafts and other machine members has been used extensively in the past 30 years. The shaft vibration spectrum was used to obtain information about unbalance, bearing, and other instabilities in rotating machinery since the 1920’s. It was further identified in the 1960’s as a source of information for the existence of cracks, misaligned couplings, loose parts, and other unwanted operating conditions. Such conditions would mainly introduce asymmetries of the rotating parts which would result in vibration spectra in the acoustic range which are characterized by the response of parametrically excited systems, including sub- and superharmonics. Such signatures have been used for rotating machinery condition monitoring. It was further observed that field singularities, such as cracks, couple the lateral, longitudinal, and torsional vibration of rotating shafts providing additional monitoring tools. Finally, it was found that the nonlinearities associated with closing cracks and gaps and journal misalignments lead to additional information on the condition of the rotating parts, such as higher harmonics. In recent years, the wealth of accumulated observation on the signatures of abnormal operating conditions in rotating machinery have been incorporated in expert systems for rotating machinery monitoring. Such systems have been developed using predicate logic or artificial neural networks. Further, fuzzy sets and interval analysis have been incorporated to account for nontraditional recording of operating conditions.
Decay of resonances of reinforced concrete beams with cracks
Authors: Wang Zhijing , Pandya Shail , Finch Robert D. , Jansen Ben H.
Published: October 2005

Reinforced concrete beams in practical use always contain cracks. This paper reports a study of the changes in decay rates of resonance frequencies when cracks occur in a vibrating concrete beam. The experiments were performed using model reinforced concrete beams with general end conditions as well as ideal pinned–pinned end conditions. The power spectrum and its time variation were studied. The short time Fourier transform (STFT) technique was used. Theoretical studies were made to establish the effects of damping on the vibration of the beam. A complication exists in that the reinforced concrete beam is in effect a composite material. The results will be compared with the data obtained from a steel beam of homogeneous material [J. Robin, Acoust. Soc. Am. 92, 2441 (A) (1992)]. The changed behavior of decay rates of resonance frequencies could be a feature in the vibration monitoring of reinforced concrete structures such as highway bridges. [Work supported by NSF Grant No. MSS-9024224.]
Necessary accuracy for early reflections in sound field auralization
Authors: Okano Toshiyuki
Published: October 2005

Necessary accuracy for early reflection levels was investigated in order to derive criteria to verify the accuracy of a sound field simulator. Early reflections are the most important in controlling the subjective impression of a room’s sound field. The accuracy of the sound field simulator depends primarily on the accuracy of early reflections. The just-noticeable level difference (jnld) of early reflections defines the maximum of allowable level difference between real and simulated reflections. Also, the masked threshold level (MTL) of early reflections defines the level of the smallest reflections which a simulator should generate. However, jnld and MTL of early reflections depend on the sound field’s configuration. It is desirable that criteria are independent of the configuration of the sound field. The jnld and MTL were measured for lateral and ceiling reflections in various types of rooms with simulated sound fields. Measured jnlds and MTLs were converted into the difference in objective parameters (LE, IACCE, C80, etc.), which correspond to subjective impressions caused by early reflections. Criteria for necessary accuracy were pursued in the domain of rooms with objective acoustic parameters.
An algorithm for generating phrase boundaries for the automatic assignment of prosodic contours in a text-to-speech system for Spanish
Authors: Karn Helen E.
Published: October 2005

Determining phonological and intonational phrase boundaries is an important step in synthesizing natural-sounding prosodic contours in a text-to-speech (TTS) system. An algorithm is presented here that generates phrase boundaries in Spanish texts. The basis for this algorithm is Liberman and Church’s function group (f-group) parser for English [M. Y. Liberman and K. W. Church, ‘‘Text Analysis and Word Pronunciation in Text-to-Speech Synthesis,’’ in AdvancesinSpeechSignalProcessing, edited by S. Furui and M. M. Sondhi (Marcel Dekker, New York, 1992), pp. 791–831]. The Spanish f-group parser produced satisfactory results for shorter sentences and sentences containing a fair amount of punctuation, but the parser tended to overgenerate phrase boundaries in longer sentences and sentences with little punctuation. In addition, the parser generated but did not distinguish different types of sentence and paragraph transitions. To refine the parser in these areas, selections from a Spanish text [E. Sabato, Eltúnel (Editorial Seix Barral, Barcelona, 1982)] were read by adult native Spanish speakers and analyzed for phrase boundaries as evidenced by significant changes in fundamental frequency, tempo, and/or pauses. The acoustic phonetic data and its role in the development of the phrase boundary algorithm are discussed.
Optimal detection and source localization in an uncertain, shallow water environment
Authors: Shorey J. A. , Nolte L. W.
Published: October 2005

An optimal aposteriori probability approach to matched-field processing is implemented using the optimum uncertain field processor (OUFP) [A. M. Richardson and L. W. Nolte, J. Acoust. Soc. Am. 89, 2280–2284 (1991)]. Combining Monte Carlo techniques with this processor results in a fast, efficient method for source localization or environmental parameter estimation when the environmental parameter search space is large. Detection and localization performance is presented using the ROC for detection and the LROC (localization receiver operating characteristic) for source localization. Specific results are presented for a shallow water environment as a function of signal-to-noise ratio and environmental uncertainty. [Research supported by ONR under Contract No. N00014-91-J-1448.]
A nonlinear regression approach to the evaluation of reverberation times using Schroeder’s integrated impulse response method
Authors: Xiang Ning , Ahnert W. , Feistel R.
Published: October 2005

Reverberation decay curves can be obtained by backward integration of room impulse responses [M. R. Schroeder, J. Acoust. Soc. Am. 37, 409–412 (1965)]. The evaluation of reverberation times is often achieved by a regression line fitting the reverberation decay curves. However, the successful application of this method requires either a careful choice of the integration limit or estimation of the mean-square value of background noise where background noise is present in the room impulse responses to be evaluated. In the present paper, an alternative method for evaluating reverberation times from Schroeder’s decay curves using a nonlinear iterative regression approach is proposed. The regression process is based on a nonlinear curve model using the generalized least-square error principle rather than a linear model as used in the linear regression. The present paper will describe the principle of this approach and discuss the advantages and disadvantages involved. Comparison of results obtained using this approach and alternative methods will also be presented.
Wavelet representation of the three-dimensional anisotropic elastodynamic Green’s function
Authors: Tewary Vinod K. , Fortunko Christopher M.
Published: October 2005

A detailed knowledge of waveforms is required for nondestructive ultrasonic characterization of anisotropic materials. The waveforms can be calculated in terms of the elastodynamic Green’s function of solids. The traditional Fourier/Laplace transform methods are computationally inefficient for three-dimensional anisotropic solids since they require four-dimensional numerical integration in the wave vector and the frequency space. A representation of the Green’s function has been developed in terms of highly localized Huygens-type wavelets in which the Green’s function is expressed in the space of slowness vectors rather than that of wave vectors and frequency. The wavelet representation requires only a one-dimensional numerical integration of simple functions and thus saves computational (CPU) time by a factor of about 1000 compared to the Fourier transform method. A solution of the tensorial elastodynamic Cauchy problem and calculation of the retarded Green’s function will be described in terms of these wavelets. Results will be presented for pulse propagation in anisotropic solids.
Waveform-based ultrasonics in anisotropic hemispheres
Authors: Boltz Eric S. , Tewary Vinod K. , Fortunko Christopher M.
Published: October 2005

Conventional ultrasonic materials characterization methods rely heavily upon measurements of acoustic wave velocities and amplitudes which are often ambiguous. Waveform-based ultrasonics, however, seeks to extract valuable information from the actual ultrasonic waveforms. This computational portion of the work seeks to mathematically represent ultrasonic waves propagating in a bounded, three-dimensional, anisotropic hemisphere. An integral representation for the exact solution of the Christoffel equation for wave propagation in anisotropic hemispheres is developed using a wavelet transform developed at NIST. This representation allows the computation of material displacements as a function of both position and time for a given source. This wavelet is a function of the slowness vector, rather than the wave vector, and is better suited to anisotropic solids where the direction of energy flow is parallel to the slowness vector. The source case considered is pencil lead break in the center of the flat side of an anisotropic hemisphere. Surface displacements are computed for various materials. Where possible, comparison with previous work and with experimental data are presented.
An efficient method for designing quiet composite structures via material tailoring
Authors: Oh Jung Bae , Koopmann Gary H.
Published: October 2005

An efficient design method is successfully developed for achieving structures that radiate minimum acoustic power based on a material tailoring. First, the far-field acoustic power of a planar radiator is written as a quadratic expression in terms of the Rayleigh–Ritz formulation. Second, a complete acoustic power design sensitivity is developed analytically that is needed to find a search direction for the improved design. This analytical sensitivity significantly reduces computation time as compared to the finite difference scheme and provides an exact design sensitivity information. The formulations for acoustic power and design sensitivity are coupled together within the numerical optimization code, CONMIN, to minimize acoustic power radiated from a planar surface subject to various excitation conditions via local thickness tailoring. The design of quiet structures for general conditions—harmonic point excitation, uniformly distributed harmonic acoustic loading, and random acoustic loading—in the given frequency band is achieved successfully. Results on various test cases show that the hybrid composite structure is the most promising material for minimizing radiated acoustic power. The optimum hybrid composite plate shows that the radiated acoustic power can be reduced up to 10 dB on various test cases.
Acoustic reflections from acoustically tailored nonhomogeneous viscoelastic coatings
Authors: Burroughs Courtney B. , Beach Kimberly L.
Published: October 2005

An analytic model for acoustic reflections from nonhomogeneous viscoelastic coatings is developed. The model includes variations in the viscoelastic properties of the coating in directions parallel to the surface of the coating. By converting acoustic pressure wave incident on the coating to high wave-number pressure and shear waves in the coating, the nonhomogeneities in the coating convert potentially reflected waves into nonreflecting waves, thereby trapping the energy in the coating where the energy is dissipated by the internal damping in the coating. Examples are presented to show the sensitivity of acoustic reflections from coatings to the nonhomogeneous properties and damping of the coating material.
New fiber-reinforced polyurethane composites as a soft sonar window
Authors: Thompson C. M. , Ting R. Y. , Leimer L. M.
Published: October 2005

A new polyurethane formulation has been developed for use as the acoustical window for a soft sonar dome. The polyurethane is based on a 3000 molecular weight difunctional polybutyleneoxyglycol (PBOG) softblock. In addition, a moderately high trifunctional PBOG was added to increase the cross-link density for improving the polymer toughness. ‘‘Spectra,’’ an extended chain polyethylene fiber, was selected as the reinforcement fiber because it has excellent physical strength and is low in density. The lower density assists in matching the specific acoustical impedance of the composite to that of sea water. Fiber loadings up to 50% in thickness were used. Samples of this new composite were fabricated and their physical and acoustical properties were evaluated. Insertion loss of the test panel was measured in the USRD ATFI facility. The material was found to be acoustically transparent at the operating frequency range, and physically resilient to high impact loadings.
Long-range responses of belugas and narwhals to ice-breaking ships in the Northwest Passage
Authors: Finley Kerwin J. , Greene Charles R.
Published: October 2005

Responses of belugas and narwhals to ice-breaking ships were studied during three spring seasons. The two species reacted differently. Belugas exhibited panic as ships approached at distances of 35–50 km; received noise levels ranged from 94–105 dB re: 1 μPa (20- to 1000-Hz band). Sound spectrographs revealed a tone at 105 Hz from an ore-carrier ship at 130 km. Presumed alarm calls indicated that belugas were aware of the ore carrier at 85 km (101 dB, 20- to 1000-Hz band level); they moved up to 80 km away from ice-breaking operations. In contrast, narwhals showed subtle ‘‘freeze’’ responses and dispersed slowly. Ship approaches caused narwhals to cease vocalizing temporarily whereas belugas emitted noisy alarm calls. Narwhals returned to disturbance areas faster than belugas and resumed normal activities when received noise levels from ice-breaking operations were as high as 120 dB. These responses occurred at unprecedented ranges, but no previous field studies had been conducted in areas with marine mammal populations unaccustomed to industrial noises. The disparity between field observations and theory, based on beluga audiograms, is examined. Results of Finley etal. [Can. Bull. Fish. Aqua. Sci. 224 (1990)] are augmented by additional acoustical analyses. [Work supported by Canadian Dept. of Indian Affairs & Northern Development.] a)Present address: 10232 Summerset Place, Sidney V8L 4X2, Canada.