bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental comparison of dynamic mechanical testing facilities at several Navy laboratories
Authors: Capps R. N. , Ting R. Y. , Quinn M. E.
Published: October 2005

Dynamic mechanical spectroscopy provides valuable information on frequency-dependent relaxation mechanisms in high polymers. The Young's modulus and loss tangent are often measured, due to the relative ease of experimental implementation. A variety of techniques is used, which often gives different results for samples that are supposedly of the same materials. A problem exists in interpreting such results in that one can never be sure if such differences are due to measurement techniques or to actual material property variations. Two systems, an automated resonance technique and the Polymer Laboratories DMTA, are now used at several Navy laboratories. To check the internal consistency of results obtained with these systems, a “round-robin” evaluation was performed. Common batches of materials of several different types of rubbers were used to prepare samples for each of three different Navy laboratories. The results of this test will be presented, and factors that can affect the accuracy and reproducibility of dynamic mechanical property measurements will be discussed. Criteria for the applicability of the method of reduced variables will also be treated. [Work supported by NAVSEA.]
A computer-based system for representation of damping properties of materials
Authors: Burkewitz B. L. , Hamer J. L. , Holmer C. I.
Published: October 2005

The design of a computer-based damping data and design system (DDDS) is described. Important features of the system are: modularity, standardized interfaces between modules based on defined information content, ease of expansion, physically based representation of material dynamic modulus, support for all users from test through analysis, and quality control to treatment design. System architecture and module function are described, followed by a detailed discussion of the material representation module. The input for this module is material test data, and the output is a set of analytic expressions for the frequency and temperature dependence of the material. The software for this module is based on the work of Rogers [J. Rheol. 27, 351–372 (1983)], which provides a rheologically consistent analytic function representation for the dynamic modulus and loss factor. The module is written within RS/1, a table-oriented, scientific software system. Damping treatment design software and approaches to system data quality issues are also addressed.
Seismic anisotropy in the upper oceanic crust—A review
Authors: Stephen R. A.
Published: October 2005

Over the past 10 years, there have been four reported observations of seismic azimuthal anisotropy in the upper 2 km of oceanic crust. The most probable cause of anisotropy in the upper crust is the preferred orientation of large-scale fractures that are created during crustal generation at the ocean ridges. Seismic velocities are slow parallel to the spreading direction and fast perpendicular to it. In some instances, clear azimuthally dependent travel-time anomalies are observed and, in others, there is evidence for shear wave splitting. At one site, both shear wave splitting and travel-time anomalies gave consistent results. The challenge in all studies, however, is to separate the effects of anisotropy from the effects of scattering and lateral heterogeneity. Current modeling capability is inadequate to include the effects of both anisotropy and heterogeneity at the scales observed in the seafloor. A definitive study on the effects of anisotropy and heterogeneity that will determine which observations are best for resolving given parameters is needed. In addition, high-quality three-component seismic stations are required to provide the data for particle motion analysis. This may require borehole seismic installations. [Work supported by NSF.]
The effects of azimuthal anisotropy on seismic shear wave data
Authors: Alford R. M.
Published: October 2005

As a result of seismic field experiments, shear polarization splitting has been identified as a significant impediment to shear wave data quality. The polarization splitting, or shear birefringence, results when a transversely polarized elastic shear wave propagates through an azimuthally anisotropic medium. As a consequence of this observation, the perception of shear wave propagation has been significantly altered and new techniques for acquisition, processing, and interpretation has been developed. In this paper, the anomalous behavior of the data is examined and techniques are developed to compensate for the effects of shear polarization splitting. The corrected data reveal a time-varying delay between two shear polarizations, which is characteristic of shear wave propagation in an azimuthally anisotropic medium. Azimuthal anisotropy may provide another parameter for discriminating rock types and properties, and the possibility of detecting fractures and permeability trends. The realization that shear wave splitting is an important phenomenon helps to explain the erratic and unpredictable nature of shear data quality. New techniques provide an exciting renewal of potential for the exploitation of shear wave seismic data in exploration.
Arctic databuoys—An update
Authors: Buck Beaumont M.
Published: October 2005

A 1983 paper, “Arctic data collection the easy way—Data buoys” [J. Acoust. Soc. Am. Suppl. 1 74, S2 (1983)], presented data buoys as a partial solution to the problems and limitations inherent to manned operations in the Arctic. The present paper describes the successes and failures of these devices, as applied to Arctic underwater acoustics, in the intervening years and what has been done with the large quantities of data that they have generated. This will include wide-area, synoptic collection of ambient noise level data, as well as first-ever measurement of low-frequency propagation during the summertime in the Central Arctic using autonomous cw projector and receiving data buoys. Plans for even more sophisticated devices to be installed in 1988 are discussed. [Work supported by U.S. Navy.]
Some unusual renovation Projects
Authors: Klepper David L.
Published: October 2005

A comparison of several different renovation projects indicates that an acoustical consultant must be very flexible in adopting a particular set of recommendations for the acoustical, architectural, and restoration requirements of a particular project. In one project, sound-reflecting panels may be appropriate, in another, definitely not. In one project, an ideal central cluster loudspeaker system may be appropirate, in a second, it must be supplemented by delayed underbalcony loudspeakers, while a third would best employ vertical line-source loudspeakers, a fourth a horizontal line source, and a fifth a distributed delayed loudspeaker system. By means of slides, the differences between these several projects, which include a university concert hall, the conversion of a motion picture theatre to a multi-use performing arts center with emphasis on symphony concerts, a university theatre, and two 19th century opera houses restored as multi-use performing arts centers will be explored. One common thread runs through all of them, however; all make maximum use of live sound before the use of electronics, with minimum use of sound-absorbing treatment.
Physiology of the female larynx
Authors: Titze Ingo R.
Published: October 2005

The Recording and Research Center, The Denver Center for the Performing Arts, 1245 Champa Street, Denver, CO 80204 Anatomically, the female larynx differs from the male in vocal fold length, thickness, angle of the thyroid laminae, resting angle of the glottis, vertical convergence angle in the glottis, and a number of other ways. The vocal fold tissue itself differs with respect to the thickness of the mucosa and fiber composition, e.g., the ratio of connective tissue to muscle tissue. Biomechanically, it has been found that the stress-strain curves are slightly more linear in females than males. Based on these and other known differences in morphology and viscoelastic properties, a scaling procedure is attempted for fundamental frequency, intensity, and other acoustic properties. Some rationale is give also for why females develop pathology at different sites in the larynx, given what is currently known about mechanical stress in the tissues.
Fact and fiction in the description of female and male pitch
Authors: Henton Caroline G.
Published: October 2005

Female speech has been characterized as high pitched, shrill, overemotional, and swoopy. Pitch is, of course, a relative scale, so it would be equally valid to describe male pitch as low pitched, rumbling, underexpressive, and montonous. But if “swoopiness” is inherent in female speech, it must be asked whether the effect is one of a comparatively wider range, of greater dynamicity, or of a simple arithmetical misinterpretation. It may be the case that previous accounts have been based on absolute (linear) and, therefore, misleading values in Hertz; whereas the use of the semitonal, and thus perceptually more appropriate, scale, indicates that female speech should not be so marked on acoustic bases alone. Reexamination of pitch ranges and dynamicity values reported by others leads to the rejection of some of the elements of the stereotype. New data assembled from five males and five females also indicate that, auditorily, female speech contains similar ratios of pitch range in relation to long-term average pitch, as does male speech. Monotonicity and reduced pitch range, as important ingredients in enhancing stereotypical masculine speech (Terrango, 1974; Bennett and Weinberg, 1974), are reexamined.
Masker envelopes and simultaneous-masking psychophysical tuning curves
Authors: Fortune Todd W. , Nelson David A.
Published: October 2005

Recent reports demonstrate that the temporal envelope of a masking stimulus can influence its effectiveness. To examine the probable effects of masker envelope on psychophysical measures of tuning, simultaneous-masking psychophysical tuning curves (PTCs) were obtained from two normal-hearing listeners. The probe was a 250-ms 1-kHz tone burst presented at 60 dB SPL, which was temporally centered within the 500-ms maskers. Maskers included SAM and QFM tones, narrow-band noise, and pure tones. PTCs were obtained in quiet and in the presence of a continuous broadband noise to mask combination tones. Results indicate that fluctuating envelope maskers are less effective than flat envelope maskers only on the low-frequency side of the PTC. These data suggest that the listener is able to listen for the presence of a probe during periods of low masker energy. Four of the six maskers interacted with the probe producing audible combination tones that could be masked by the broadband noise. Combination tones were most pronounced for the QFM and pure tone maskers, which have similar envelopes. The significance of these data will be discussed in terms of frequency and temporal resolution, particularly with regard to the hearing-impaired population. [Work supported by NINCDS.]
Tuning curve widths of infants and adults in simultaneous and nonsimultaneous masking
Authors: Spetner Nancy Benson , Olsho Lynne Werner
Published: October 2005

Tuning curve widths were estimated using the pulsation threshold (PT) technique for infants, 6-month-olds, and adults. The observer-based psychoacoustic procedure [L. W. Olsho et al., Dev. Psychol., in press (1987)] was the test procedure. Listeners discriminated a train of alternating masker and probe tone bursts from a train of masker tone bursts presented with a continuous probe tone. These stimuli were presented in a background of broadband noise at 20-dB pressure spectrum level. The probe level was 10 dB SL. PTs were obtained at the tuning curve tip and at two points, one above and one below the probe frequency, 10 dB above the tip. The resulting Q10s were compared to those obtained in simultaneous masking for 6-month-olds and adults [L. W. Olsho, Inf. Behav. Dev. 8, 371–384 (1985)]. Adult Q10s were significantly greater for PT tuning curves at 500, 1000, and 4000 Hz. Infant PT Q10s were significantly greater than simultaneous masking Q10s at 500 and 1000 Hz, but not at 4000 Hz. [Work supported by NIH.]
Masking of short tone bursts of frequency sweeps
Authors: Fabry David A. , Cheesman Margaret F. , Viemeister Neal F. , Schei Dean
Published: October 2005

Masked thresholds for a short probe tone are greater for sweep-frequency tonal maskers than for stationary sinusoidal maskers at equal SPL, and greatest for sweep rates of 20–30 oct/s [G. F. Smoorenburg and F. Coninx, Hearing Res. 3, 301–316 (1980)]. The present study examined possible explanations for this surprising phenomenon and concentrated on the effects of masker level on probe threshold. Masked thresholds were obtained for a 10-ms, 1-kHz tone temporally centered in the 100-ms masker. The maskers were swept in frequency at rates of 0–80 oct/s and passed through 1 kHz at 50 ms. At the lower masker levels, maximum masking occurred at sweep rates of 15–25 oct/s. At higher levels, little influence of sweep rate on masked thresholds was seen. Although there were substantial individual differences in slopes, the growth-of-masking functions had slopes less than one with minimum slopes at 20–25 oct/s. The shallow slopes are a distinguishing feature of sweep-frequency masking and may provide a basis for understanding this important phenomenon. [Supported by NINCDS grant NS12125 and SSHRC-Canada.]
Tonal prominence effects on annoyance ratings for business equipment spectra
Authors: Bienvenue G. R. , Nobile M. A. , Balant A. C.
Published: October 2005

While recent researchers have reported Appendix B of ANSI S12.10-1985 to “work well in over 80% of cases” and to be “a vast improvement” over the earlier method, there are two notable difficulties in its implementation. First, when two “audibly prominent” tones occur closely together within a single critical band, they are rated as “not audibly prominent” by the present Appendix, though they produce an audible event. Second, certain sharply falling noise spectra could, by the upward spread of masking, mask a tone that is “audibly prominent.” In this case, an inaudible tone would be rated as prominent. For the present study, 15 subjects were presented with tape recorded sounds of varying tone-noise ensembles designed to explore these phenomena. Subjects rated these sounds for their levels of loudness, tonal prominence, and annoyance. The research data are discussed with special attention to their relevance for implementing Appendix B of ANSI S12.10-1985. [Work supported by IBM Corporation.]
Modeling subject responses in a reproducible noise masking task
Authors: Gilkey R. H. , Meyer T. A.
Published: October 2005

Gilkey and Robinson [J. Acoust. Soc. Am. 79, 1499–1510 (1986)] modeled subject responses to individual reproducible noise samples, randomly selected on each trial from a set of 25, in a diotic tone-in-noise detection task. They found that a detector composed of a 50-Hz-wide single-tuned filter centered at the 500-Hz signal frequency, a nonlinearity, and an integrator with a 100- to 200-ms decay constant predicted the data relatively well. Here, a set of 150 noise samples was used, and a more detailed analysis of the parameter space of the detector was performed. The results of this study are similar to their results, although the bandwidths of the filters are smaller (26–49 Hz) and the decay constants are shorter (39–100 ms). “Spectral weighting functions” were derived from linear combinations of the outputs of seven detectors, each at a different center frequency. These functions are more consistent than those of Gilkey and Robinson and also indicate that subjects compare information across frequency regions. These functions can be described as the difference between two Gaussian-shaped weighting functions. [Supported by NSF and AFOSR.]
Detection of infratonal repetition of frozen noise: Singularity recognition or pattern recognition?
Authors: Brubaker Brad S. , Warren Richard M.
Published: October 2005

Listeners can readily detect iteration of “frozen” Gaussian noise segments with durations up to 1 s [N. Gattman and B. Julesz, J. Acoust. Soc. Am. 35, 610 (1963)]. Is detection of repetition of these complex waveforms based upon recognition of the reoccurrence of unique features or singularities, or upon a more holistic recognition of the pattern formed by these events? To answer this question, frozen noise segments were divided into three sections of equal duration (A, B, C) that were reassembled and then repeated to form two periodic sounds (ABC)n and (ACB)n. This manipulation changed the temporal arrangement between sections but preserved singularities and repetition rate. Untrained listeners heard a series of sequence bursts consisting of either one arrangement [(ABC)n, (ABC)n, (ABC)n,…] or two alternating arrangements [(ACB)n, (ABC)n, (ACB)n,…] and judged whether successive bursts were the same or different. Discrimination was possible when the duration of the entire iterated pattern (A + B + C) was 900 ms or less, indicating that a holistic recognition of patterns operates up to the limit of echoic storage. [Work supported by AFOSR.]
Detection and recognition of complex stimuli
Authors: Ansley David A. , Weber Daniel L.
Published: October 2005

Green et al. [J. Acoust. Soc. Am. 62, 948–954 (1977)] have demonstrated that a subject's ability to detect one of m possible signals in a yes/no task can be used to predict the subject's ability to identify which of the m possible signals was present when the signals are four sinusoids well separated in frequency. This study examines detection and recognition when the signals are four complex stimuli presented against a background of white noise (spectrum level 20 dB SPL). Each complex stimulus consists of a temporal sequence of seven sinusoids. Each sinusold differs in frequency from the others within a pattern, and each is presented for 100 ms at the same sensation level. The patterns differ in the sequence of the frequencies of the component sinusoids. For example, the frequencies in the second pattern are monotonically decreasing, whereas those in the third pattern are monotonically increasing. Six experimental conditions are examined, obtained by varying the frequency separation between components and patterns. The condition with the greatest frequency separation is one in which there is a one-fourth octave gap between patterns; the condition with the least frequency separation is one in which all four patterns are composed from a single set of frequencies. Except for the last condition, successive patterns within each condition are centered around 700, 1000, 1400, and 2000 Hz, respectively. Subjects' performance in the recognition task is at the level predicted on the basis of their detection performance, in those conditions with greater frequency separation between patterns. Recognition performance falls below the predicted level in those conditions with little or no frequency separation. [Research supported by AFOSR.]
Sound radiation from beams under the action of moving line forces
Authors: Keltie R. F. , Peng H.
Published: October 2005

The topic of sound radiation from beams under the action of harmonic line forces moving at subsonic speeds (M < 1) is studied. The nondimensional sound power expressions are obtained through the integration of the surface intensity distribution over the entire beam. An asymptotic expression for the sound power in the low-frequency region is derived depending upon the characteristics of the fluid loading and the spatial extent of the applied forces. Numerical integrations have been performed to determine the effects on the radiated sound power of the Mach number M, the acoustic length of line force K0L, and the wavenumber ratio γ. The results show that: For beams under heavy fluid loading, the effect of the speed of the moving force is not pronounced; while for beams under light fluid loading, the unique coincidence radiation peak at γ ∼ 1 for a stationary force (M = 0) is split into two coincidence peaks (located in the frequency region γ < 1 and γ > 1, respectively) due to the effects of the Doppler shift. The values of K0L that suppress the coincidence peaks are also changed due to the motion of the line force.
A review of noise effects studies from the U.S. west coast
Authors: Chamberlain Dilworth W.
Published: October 2005

Concern over the possibility of effects from geophysical activity on marine organisms has recently generated several research studies in California. Results of effects studies by compressed air releases from airguns (seismic energy releases) on fish dispersion and upon physical effects to fish have been obtained. This information includes the physical effects of a simulated, towed geoseismic array on northern anchovy (Engraulis mordax) eggs, larvae, and adults. Other studies have produced data about the schooling behavior of rockfish (Sebastes spp.) exposed to airgun releases. Additional research addressing the effects of seismic energy releases on Dungenesse crab (Cancer magister) eggs and larvae and on rockfish behavior are being planned for the waters of California and Washington.
Drill-site sounds and bowhead whale calls
Authors: Greene Charles R.
Published: October 2005

Bowhead whales, an endangered species, migrate westward along Alaska's north coast during September to October, when ice conditions are best for oil explorations on the outer continental shelf. Concern exists that marine activity sounds may adversely influence whale behavior. Underwater sounds were measured in the fall of 1986 near two drillship operations 20 and 35 km offshore, northwest of Kaktovik, Alaska, with water depths of 34–35 m. Sound levels at range 0.2 km, 20–1000 Hz, for three support ships underway at 10–12 kn (standard speed) were 130, 137, and 145 dB re: 1 μPa. The level from the strongest ice-breaking source, same frequency band and range, was 148 dB. Corresponding levels from the drillship were 135–136 dB during drilling and cleaning and 130 dB during tripping. For measurements within 0.4 km, sound levels were highest in 13-oct bands from 50–100 Hz. Hourly measurements for 20 days at 11 km from one site revealed a median level of 114 dB in the 20–1000-Hz band, with 5th and 95th percentile levels of 108 and 125 dB, respectively. Dominant sounds at that distance came from the drillship and support ships. Continuous monitoring during 20 days recorded 206 bowhead calls, with 29 of them located 9.5–24 km from the drillship. [Work supported by Shell Western E&P, Inc.]
Random response of a Duffing oscillator: The probability density function
Authors: Liu Qiang , Davies Huw G.
Published: October 2005

A Duffing oscillator excited by narrow-band random noise can exhibit multivalued behavior, with random jumps between two pseudostable states. In this paper, an approximate form of the probability density function of the envelope of the response is obtained. State equations for the response envelope with the random excitation envelope as input are obtained by multiple time-scale analysis. The joint pdf of response envelope and input envelope can be found approximately for certain ranges of the system parameters. The response envelope pdf shows two maxima in the cases where the response is multiple valued. Numerical simulations confirm the results. [Work supported by NSERC Canada.]
Scattering of sound from concentric cylindrical shells
Authors: Akay Adnan
Published: October 2005

An analytical model of sound scattering from concentric, coaxial thin cylindrical shells is developed. The specific model for scattering from three concentric shells is examined in detail, and it is shown that the results can be easily extended for any number of shells. In order to see the effects of the shells and the annular fluid media between them more clearly, the case of scattering from shells of infinite length with a common axis parallel to the wave front of the incident plane wave is considered. The problem is modeled in general terms using radiation and mechanical impedances. The influence of fluid loading of the shells on the resonant scattering from the multiple-shell structure is addressed. Transition from pressure boundary conditions to velocity boundary conditions is discussed and demonstrated with numerical results. Finally, effects of compliant coatings on the shells are examined. [Work supported, in part, by the National Science Foundation.]
Application of diffraction tomography to acoustic intensity measurement
Authors: Gan Woon S.
Published: October 2005

Diffraction tomography is applied to measure acoustic intensity in three-dimensional space. With Rytov's approximation, the homogeneous Helmholtz equation is obtained. The backpropagation algorithm is used to reconstruct the scattered field. Taking the special case of incident plane waves, the image kernel is expressed in convolution form, and reconstruction becomes a deconvolution process. An experimental setup is proposed. The object is a vibrating plate driven at its center. The acoustic pressure is measured from various angles. The pressure measurement acts as a diffraction tomogram. The particle velocity is reconstructed. The structural intensity (SI) is then computed using the finite difference method in terms of particle velocity. A cross-section image of the SI is obtained, which is an advantage over the nearfield acoustic holography method of J. D. Maynard, E.G. Williams, and Y. Lee [J. Acoust. Soc. Am. 78, 1395–1413 (1985)], which can only give the acoustic intensity as contours and three-dimensional plots. From the cross-section image, one will be able to clarify the outstanding theoretical problems of active intensity and reactive intensity.
Diagnostic spectra catalogs—A powerful means for prediction of faults in machinery
Authors: Moustafa M. , Shabara M. , El-Bahloul A. , Fanny M.
Published: October 2005

A well-designed joint will produce low levels of inherent vibration. As the joint wears, however, clearance between mating components increases and this is reflected in an increase in the vibration energy. As this vibration energy is dissipated through the mechanism links, it excites resonances and exerts extra dynamic loads on joints. It is of great interest to the maintenance engineers to predict the occurrence of excessive clearance in joints, regarding its location and magnitude. The fact that vibration signals carry much information relating to the running conditions of joints can be used to solve this problem. In this study, a mathematical model is formulated to simulate the effect of clearance in joints on the vibration spectrum of machines and mechanisms. The equations of motion of the mechanism frame and links are formulated and solved simultaneously using the Runge-Kutta method. In doing so, and with the aid of fast Fourier transform (FFT), the frequency spectra of the frame in the horizontal, vertical, and angular directions are obtained. The spectra obtained for the machine corresponding to various faults with different locations and magnitudes can be used to construct vibration charts which form the “diagnostic spectra catalog.” This DSC can be used to determine the proper times for maintenance and the preparation of spare parts to avoid failure of the machines.
Underwater active array for echo cancellation. Application to reciprocal measurements
Authors: Chatel Gilles , Rohan Thierry , Pasqualini Jean-Pierre , Roure Alain
Published: October 2005

Reciprocal measurement of mechanical-acoustical transfer functions is often used. If the radiating structure is immersed in shallow water, the problem of parasitic reflections arises. A new method has therefore been developed, based on the use of a reciprocal array of acoustic sources. This method allows real-time measurement of free field structure radiation on a wide frequency range. Four acoustic sources are monitored so as to create within an observation volume an acoustic field equivalent to the one generated by a monopolar source placed in the free field. The excitation signals are calculated by a stationarity method, taking into account the intrinsic characteristics of the environment. First, tests carried out in shallow water enabled us to check that the acoustic pressure field measured was the one required. Second, this method was applied to determine by reciprocity the free field mechanical-acoustical transfer functions of an immersed cylinder. The results were compared to measurements made in the free field for the same structure.
Delay-Doppler resolution performance of large time-bandwidth product linear FM signals in a multipath ocean environment
Authors: Hermand Jean-Pierre , Roderick William I.
Published: October 2005

Active sonar systems that transmit large time-bandwidth (TW) product linear frequency-modulated (LFM) waveforms and receive echoes from targets of unknown speed can suffer considerable correlation losses that cannot be predicted from conventional (narrow-band) ambiguity function theory. As is well known, the theory can be modified to include the effects of Doppler distortion on large TW-product signals by correlating the received signal against a reference that is a time-compressed version of the transmitted signal. In this paper, the effects of multipath (or target highlight structure) and Doppler on the correlation process for rectangular weighted large TW-product LFM waveforms are examined. When the received echo contains no multipath, the correlator peak output is a maximum for the reference channel that is closest in Doppler to the target. However, in a multipath environment, the correlator output peak does not generally occur at the correct Doppler reference channel. The spreading of the cross-ambiguity function as a result of Doppler mismatch and multipath is calculated in terms of the delay-Doppler coordinates and magnitude of the extrema. It is shown that, under multipath conditions, correct estimates of target parameters can be recovered through integration of the correlator output.
Effects of correlated noise on broadband conventional and modal matched-field processing
Authors: Smith G. B. , Del Balzo D. R. , Feuillade C.
Published: October 2005

In a recent paper [J. Acoust. Soc. Am. Suppl. 1 82, S73 (1987)], the effect of realistic ambient noise on narrow-band matched-field processing in both hydrophone space and mode space was examined. A significant result of that study was that correlated noise degraded the performance of the matched-field processor in hydrophone space much more than it did in mode space. In this paper, the previous work is extended to broadband in both hydrophone space and mode space. Using computer simulations, the performance of broadband conventional and broadband modal matched-field processing is compared at various bandwidths and various mixtures of correlated and white components in the ambient noise field. Since the averaging of correlated noise (which causes the modal processor to perform better than the conventional processor in realistic noise fields) depends on the number of propagating modes, the effect of varying the center frequency of these processors is also examined.
The sensitivity of experimental, shallow-water, matched-field localization estimates to variation of environmental parameters
Authors: Feuillade C. , Kinney W. A. , Del Balzo D. R.
Published: October 2005

In two recent papers [J. Acoust. Soc. Am. Suppl. 1 80, S113 (1986)], the results of simulation studies to determine the effects of environmental mismatch on the robustness of matched-field processors in shallow water were studied. In this paper, the knowledge gained from those studies is applied to the interpretation of a vertical array shallow-water, matched-field experiment off Panama City, FL. How the ability to localize in range and depth is dependent upon the following factors is discussed: water depth, sound-speed discontinuity at the water/sediment interface, and sediment density and attenuation. Also discussed will be the fact that the results indicate: (a) the limitations of single-frequency, time-independent, matched-field processing and (b) the need for broadband and time-dependent techniques.
Remote sensing of ocean flows with spatial filters
Authors: Crawford Gregory B. , Lataitis Richard J. , Clifford Steven F. , Farmer David M.
Published: October 2005

The complicated scintillation pattern observed when an acoustic wave propagates through refractive index irregularities is due to the “projection” of all the refractive eddies at each path position onto the receiving plane. A current transverse to the acoustic path will advect the eddies and produce a drift in the scintillation pattern. A single transmitter and two receivers can be used to monitor the drift and infer a path-averaged flow speed. Much more localized measurements of the transverse current can be made with multiple sources and receivers that spatially filter the scintillation pattern. Such spatial filter systems can be used to profile the transverse current. Recent results obtained with small transmitter and receiver arrays mounted across a well-mixed, turbulent tidal channel are presented.
The attentuation of dissipative flow duct mufflers with internal mean fluid flow in the absorbent
Authors: Cummings A.
Published: October 2005

In dissipative flow duct mufflers incorporating layers of porous bulk sound absorbent, mean flow within the pores of the material is inevitable because the porous medium is exposed to pressure gradients in the duct flow. The acoustical effects of internal mean flow can be considerable, particularly in the case of internal cumbustion engine exhaust mufflers of the dissipative type. Theoretical treatments are presented here, both to describe the effect of internal flow on the bulk acoustic properties of the porous medium and to find the effect of the absorbent in situ, in the form of the sound transmission loss of the silencer. The measured transmission loss of an experimental silencer is compared to predicted data, and good agreement between the two is obtained. The effects of mean fluid flow in the central passage and internal flow in the absorbent are separately demonstrated.
Perturbations of the acoustic field inside a resonant cavity
Authors: Herzog Philippe , Bruneau Michel
Published: October 2005

A theoretical and experimental study has been made of the acoustic field inside a closed resonant cavity with two axes of resonance under the influence of several perturbations, like an imperfect geometry, the presence of the transducers, and the effects of the motion of the cavity (linear and angular speeds and accelerations). The analytical study is based on a modal decomposition of the pressure, for Cartesian and cylindrical shapes. The influence of geometrical perturbations and the presence of the transducers are taken into account by a perturbation method applied to a matrix formulation of the Helmholtz-Huygens equation. The influence of inertial terms is expressed in a similar form, but one which may be used for greater mode coupling. The experimental work has been done in the Cartesian case for a two-dimensional cavity. The use of a swept-sinusoidal excitation with synchronous demodulation and a custom-made acoustic antenna permitted us to obtain very accurate measurements. Several examples are shown, and the agreement with theory is quite good, leading to discrepancies typically less than 0.1 dB and the detection of modes in a dynamic range of about 50 dB.
Ultrasonic tomography in the field of flow measurement
Authors: Wolf Jörg
Published: October 2005

Ultrasonic tomography is known as a nonintrusive imaging method for static sound attenuating objects in fields such as medical diagnostics or nondestructive testing. A new application of ultrasonic tomography in chemical engineering is presented in this paper, namely, the nonintrusive imaging of the static fluctuating void fraction in a cross section of a gas liquid flow. Here, the attenuation of parallel ultrasonic rays is measured. The set of values obtained from this measurement result in a projection of the flow. Now the spatial distribution of void fraction can be reconstructed from a set of these projections, taken from various directions, by the algorithms of computerized tomography [Proc. IEEE, 21(3) (1983)]. The method was applied to a bubble column as used in chemical engineering. To get a fast and nondisturbed measurement of the projection data, a circular array of 108 piezoceramic transducers was directly integrated in the pipe wall of the column. The transducers are electronically switched and need not be mechanically operated. The control of the array and the reconstruction algorithms are implemented on a microcomputer coupled with an array processor.
Laser Doppler anemometry detection of hydroacoustic particle velocity
Authors: Dubbleday P. S. , Schau H. C.
Published: October 2005

The method of Laser Doppler Anemometry (LDA) is applied to the measurement of particle velocity in a hydroacoustic field. The field is created in a USRD type G19 or G40 calibrator. The LDA results are compared with the values for the velocity obtained from the pressure gradient measured by a USRD standard hydrophone. The anemometer is operated in forward scattering mode, and also in backscattering mode through the use of a fiber-optic transducer. Seeding particles of varying material and size are dispersed in the acoustic medium (water). The influence of these parameters including the particle concentration on the signal quality and detection threshold is discussed. [Work supported by ONR.]
Transmission loss of a piping network
Authors: Stredulinsky D. C. , Craggs A. , Faulkner M. G.
Published: October 2005

This paper describes a numerical procedure developed to analyze piping and duct systems. The procedure combines transfer matrix and finite element methods and was used to predict the transmission loss of a piping network constructed of rigid-walled, square cross-section tubing. The network consisted of one input, one output, and several segments made up of straight pipes and 90° elbows. These were interconnected at several “T” junctions. The junctions and elbows were treated using finite element models that took into account two-dimensional wave propagation. These were connected to straight pipes in which one-dimensional wave propagation was assumed. This led to a much reduced connective matrix for each finite element model. The solution of the entire network was then obtained by solving a relatively small system of linear equations. Experimental measurements of the network transmission loss were made using a two-microphone transfer function technique with random “white” noise and a dual channel FFT analyzer. The resultant sound transmission loss was in good agreement with the predicted transmission loss up to the cut-on frequency of cross modes within the straight pipe sections.
Audio processing for improved detection and recognition of threats in radar warning systems
Authors: Wiseman Charles H.
Published: October 2005

Radar warning receivers (RWR) are systems that alert pilots of military aircraft to imminent danger of attack by missiles and gunfire. These RWRs function to: (a) intercept radar transmissions; (b) detect the radar's pulsed modulations; (c) identify the patterns of pulses as emanating from friend or foe, and, finally, (d) present information as to threat type and direction via alfa numerics and symbols on a video display and, aurally, via a heat set. The aural presentation termed “raw audio” is entirely an analog process. It is used to complement the video display as an aid in the detection and recognition of threats. In order to decrease clutter and distraction to the pilot, modern RWRs incorporated computer analysis to assist in discerning threats from the myriad of PRF patterns. With compter logic, of course, the demodulated pulse data must first be converted to digital form. This process, however, has eliminated the analog raw audio in modern RWRs in favor of “synthetic audio,” reconstituted from digital data. This paper discusses the differences between raw audio and synthetic audio and their advantages and disadvantages. The paper concludes that computer-driven RWRs supplemented with raw audio capability show considerable promise for improved detection and recognition capability and should be expeditiously investigated.
A survey of FORTRAN code generation using MACSYMA
Authors: Steinberg Stanly , Roache Patrick J.
Published: October 2005

This paper presents the underlying symbolic manipulation techniques used by the authors to produce FORTRAN code with the artificial intelligence code MACSYMA. The FORTRAN codes produced use finite difference methods to solve the governing equations for numerical grid generation, including elliptic and variational methods, and to solve the hosted equations, including fluid dynamics, heat transfer, and electro-statics. Consideration will be given to writing the hosted equations in strong conservation form in general nonorthogonal coordinates; high order and conditional differencing schemes; colocated variables versus staggered grids; and code validation procedures.
Application of symbolic computation to singular perturbation problems in physical acoustics
Authors: Thompson Charles
Published: October 2005

Problems in fluid mechanics, and in turn in physical acoustics, often incorporate a large number of length scales and parameters. These scales are the result of local fluid interactions with either boundary surfaces or across discontinuities in the physical properties of the fluid. The art of developing a correct description of any physical situation is in discerning the relative importance of each of the parameters of the solution. One might consider solutions to a problem as a restricted range of values of these parameters. In such a case, these solutions would be locally valid in the parameter space and are an asymptotic representation of the global solution. The integration of locally valid solutions into a global description is the essence of singular perturbation methods. In this paper, the method by which computer algebra can be used to solve problems involving a singular perturbation analysis in physical acoustics will be discussed.
Farfield criteria for vibrating structures: Numerical simulation on plates and cylinders
Authors: Journeau Christophe , Rohan Thierry , Pellegrini François
Published: October 2005

In order to determine practical criteria for the nearfield/farfield transition in the case of underwater vibrating structures, the acoustic field radiated by plates and cylinders is simulated. Various mode shapes of these structures are computed for different frequencies including their resonance frequencies. These calculations are made for radiators of different sizes and are compared with the results of a mechanical simulation for a point-excited ribbed cylinder. Then the distances at which the pressure field is at ± 1 dB of the farfield value, the wave specific impedance is ρc ± 12% (1 dB), and pressure and velocity have a phase difference of less than ± 15° are tabulated as a function of frequency. The envelope of these points is compared with the standard criterion (R ≫ λ and R ≫ L2/λ). Finally, various criteria are proposed depending on which property of the farfield is required.
The Blake threshold of a bubble having a radius-dependent surface tension
Authors: Atchley Anthony A.
Published: October 2005

The Blake threshold is incorporated in most theoretical models of transient acoustic cavitation. In standard derivations, this threshold is calculated for a bubble having constant surface tension. However, such a bubble is unstable against dissolution and not a realistic model for a cavitation nucleus. In this work, the Blake threshold is calculated for a more realistic nucleus—a bubble having a radius-dependent surface tension. A relationship is derived for this dependence, based upon the properties of a surfactant-stabilized cavitation nucleus. Two cases, appropriate for charged and polar surfactants, are examined. The Blake threshold for the former case is identical to that of the standard case by approximately 2%–20% for radii ranging from 3.0 μm down to 0.01 μm. Therefore, it is concluded that both unstabilized and surfactant-stabilized bubbles become mechanically unstable under essentially the same acoustic conditions. Thus the use of the simpler, unrealistic nucleus in theoretical models results in no serious error. [Work supported by NPS Foundation.]
An active acoustic backscattering technique for detecting transient cavitation
Authors: Roy Ronald A. , Madanshetty Sameer , Apfel Robert E.
Published: October 2005

Relatively dirty water is insonified with short pulses (order 10μs) of high-frequency (≈ 1 MHz), focused ultrasound. The subsequent transient cavitation bubble activity is detected by a focused 30-MHz pulse-echo detector confocally positioned relative to the insonifying transducer. The cavitation detector is sensitive enough to observe submicron size bubbles. Transient cavitation thresholds measured using this active detection system are as much as 40% lower than those measured using other techniques (such as passive acoustic detection). Thresholds are measured as a function of various acoustic parameters (e.g., pulse length, pulse repetition frequency, etc.) and the results are compared with previous investigations as well as theoretical predictions. [Work supported by NIH Grant No. 1 R01-CA-39374.]
Brewster angle light scattering from bubbles in water: Observations and potential applications to the acoustics of natural microbubbles
Authors: Bäumer S. M. , Marston P. L.
Published: October 2005

Consider the reflection of light from a clean gas bubble in water such that the light is polarized with its electric field parallel to the scattering plane. The Fresnel reflection coefficient should vanish when the local angle of incidence i is at Brewster's angle iB = arctan (n−1) ≈ 36.9 deg, where n = 1.33 is the refractive index of water. When the scattering angle θ is close to that of the Brewster scattering angle, θB = (180 − 2iB) ≈ 106.2 deg, this Brewster effect should be strongly manifested in the scattering pattern [D. L. Kingsbury and P. L. Marston, Appl. Opt. 20, 2348–2350 (1981)]. In the present research the first laboratory observations described are of Brewster effects in the scattering patterns of bubbles rising through water having radii ≈ 70μm. There is a noticeable reduction in the visibility of fringes in the scattering pattern for scattering angles ≈θB. (The fringes arise from the interference of a farside ray with the reflected ray.) Microbubbles of natural origin can be important in ocean and bioacoustics and Brewster effects may be useful in the optical characterization of such bubbles including the discrimination of optical scattering patterns of bubbles from those of particles or cells. Brewster angle scattering may also be useful for characterization of the surfactant coating that is thought to occur on some microbubbles in nature. [Work supported by ONR.]
Measurement uncertainty assessment of the scanning laser acoustic microscope and application to canine skin and wound
Authors: O'Brien William D. , Steiger Dianne L. , Olerud John E. , Riederer-Henderson Mary Ann , Odland George F.
Published: October 2005

The assessment of measurement uncertainty of the scanning laser acoustic microscope (SLAM) has not been thoroughly evaluated experimentally. It is essential that the uncertainty of any measurement be fully understood. Both accuracy and precision were experimentally evaluated for the SLAM by measurements on homogeneous liquids of known ultrasonic properties. Using aqueous solutions of bovine serum albumin, the attenuation coefficient accuracy and precision are ± 12% and ± 15%, respectively. And from Dew Coming 710, a silicon oil, the speed accuracy and precision are ± 2.9% and ± 0.4%, respectively. Further, an application of the assessment of precision was conducted using duplicate samples of dog skin and wound tissue. From these evaluations of a heterogeneous tissue, the estimated precision in the measurement of the attenuation coefficient and speed was ± 16% and ± 1.7%, respectively. [Work supported by NIH Grant AM 21557 and the Rehabilitation Research and Development Service of the Veterans' Administration.]