bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of noise during glottal vibration: Measurements performed on a mechanical model
Authors: Reis B. Y. , Coker C. H. , Kubli R. A.
Published: October 2005

Speech synthesis and coding schemes commonly incorporate a random noise component during voicing. It is hard to isolate this noise in recorded speech because of the inaccuracy of characterizing a modulated random process from a few nonidentical periods with a strong periodic component. Direct measurement on humans poses many clinical difficulties. Computational hydrodynamic modeling is difficult, and reliable modeling of turbulence is an unsolved problem. Here, direct steady-state measurements are made on a detailed, life-size mechanical model. A molded rubber model of the vocal cords is driven synchronously with the sampling clock so that precise repetitions of pitch periods are generated. The random component of the recording is isolated by subtracting away the periodic component (obtained by ensemble averaging across 1000 pitch periods). The noise power and its spectrum at each point in the pitch period are estimated by ensemble averaging the autocorrelations of the noise. The noise results are well explained in terms of the directly measured transglottal pressure and glottal area. In high-passed human speech, bursts of noise appear to overlap the closed-glottis interval. To explain this, it is necessary to include transit time for glottal air bursts to reach an obstruction 2–3 cm downstream. a)Also a student at MIT.
The normal modes of incompressible vocal fold tissues.
Authors: Berry David A. , Titze Ingo R.
Published: October 2005

Much of the theoretical groundwork for treating vocal fold vibrations as viscoelastic waves in a continuum can be found in earlier publications [Titze and Strong, J. Acoust. Soc. Am. 57, 736–744 (1975) and Titze, J. Acoust. Soc. Am. 60, 1366–1380 (1976)]. Both of these papers are based on small-amplitude vibrations where linearization is assumed to be valid, allowing normal modes and natural frequencies to be calculated. Although vocal fold tissues are known to be nearly incompressible, the first analytic expression for the normal modes of vocal fold tissues were based on the assumption of complete compressibility. The present study shows how the analytic normal modes deform and how the natural frequencies of oscillation shift as the vocal fold tissues are gradually changed from being strictly compressible to absolutely incompressible, leaving all other factors constant. [This research was supported by Grant No. P60 DC00976 from the National Institute on Deafness and Other Communication Disorders.]
Stress-strain response of the human vocal ligament and its effect on F0 control
Authors: Titze Ingo R. , Min Young B. , Alipour-Haghighi Fariborz
Published: October 2005

The longitudinal elastic properties of the human vocal ligament were quantified by stress-strain measurements and by modeling the response mathematically. Human ligaments were obtained from surgery and autopsy cases. They were dissected, mounted, and stretched with a dual-servo ergometer to measure force versus elongation and to convert the results into stress and strain. To calculate a longitudinal Young’s modulus, the stress-strain curves were fitted with polynomial and exponential functions and differentiated. Young’s modulus was separately defined in the low and high strain regions. The mean Young’s modulus for the low strain region was 33.1±10.4 kPa. In the high strain region, A and B parameters for an exponential fit in the high strain portion were 1.4±1.0 and 9.6±1.2 kPa, respectively. The stress-strain and Young’s modulus curves showed the typical hysteresis and nonlinearity seen previously in other vocal fold tissues (muscle and mucosa), but the nonlinearity was most profound for the vocal ligament. The effect of these results on F0 control will be discussed. [Work supported by NIDCD Grant No. DC00976.]
Multiphonic vocalizations: A multifactor analysis of Tibetan monk chanting
Authors: Milstein Claudio F. , Shipp Thomas
Published: October 2005

Multiphonic chanting refers to highly specialized vocal techniques wherein one person is able to sing two or more tones simultaneously. Tibetan chanting is one of these techniques. Five Tibetan monks were studied (two low chanters and three high chanters). Digital recordings, EGG, airflow glottograms, oral fiberoptic laryngoscopy, and perceptual data were analyzed. Spectra from both types of chanters presented a display of extremely well defined F1 and F2 tuned to specific harmonics (harmonics 5 and 9 for low chanters and harmonics 2 and 4 for high chanters). Low chanters showed unusual activity at the vocal fold level and were able to maintain the multiphonic quality and formant tuning despite significant modifications of the vocal tract. It is suggested that the larynx is responsible for the production of the multiple tones in low chanters. Low and high chanters appear to use different strategies to achieve the same multiphonic effect. Our findings corroborate earlier findings by Smith, Stevens, and Tomlinson [J. Acoust. Soc. Am. 41, 1262–1264 (1967)] for low chanters.
Transmitted beam distortion and rotation due to mode conversion between acoustic and shear waves at liquid–solid interfaces
Authors: Landsberger B. J. , Hamilton M. F. , Il’insky Yu. A.
Published: October 2005

An experiment was performed with a pulsed sound beam incident on a 6-cm-thick aluminum block immersed in water. Tone bursts were radiated at 1 MHz by a circular source of radius 1.2 cm, which was positioned 10 cm away from one side of the block. Transmitted acoustic beam patterns were measured in the water beyond the opposite side. Attention was devoted to angles of incidence in the neighborhood of the critical angle for compression waves in the block (∼13.5°). The use of pulses, and the strong refraction of the compression wave in the block, enabled isolation of effects associated with the shear wave. Distortion in the form of multiple beam splitting, and up to 4° increase in the effective propagation direction of the transmitted beam (relative to the angle of the incident sound beam), were observed. Computations based on standard Fourier-transform techniques, but excluding contributions due to the compression wave in the block, yield good quantitative agreement with experiment. For the conditions in this experiment, calculations indicate that the distortion and rotation of the transmitted sound beam are due mainly to the mode conversion at the second interface. [Work supported by AASERT and ONR.]
A new parabolic equation for range-dependent sound speeds
Authors: Dashen Roger , Wurmser Daniel , Orris Gregory
Published: October 2005

A new parabolic equation for range-dependent sound speeds has been developed by modifying a procedure borrowed from quantum mechanics. The forward and backward propagating solutions are decoupled order by order by repeated applications of the Foldy–Wouthuysen transformation. The result includes energy-conserving terms which are proportional to the second range derivative of the sound speed squared. Physically, the technique has identified the terms responsible for heretofore anomalous refractive effects which accumulate during propagation as a result of rapid oscillations between the forward and backward propagating solutions. Moreover, this phenomenon does not result in permanent energy transfer between the two types of solutions. [Work supported by ONR.]
Range-stepping algorithm for the Helmholtz equation
Authors: Dacol Dalcio K.
Published: October 2005

The usual range-stepping algorithms used to obtain an approximate solution to the Helmholtz equation are based on the parabolic approximation and restricted to the forward propagating component of the solution. A complete solution of the Helmholtz equation in an inhomogeneous medium must also include backpropagating waves, that is, waves scattered towards the source by inhomogeneities. The inclusion of such effects in a numerically feasible full-wave approach to acoustic propagation is a problem of continual interest in ocean acoustics. This problem has been studied using the method of coupled amplitudes. Theoretical developments on the application of this technique to ocean acoustics will be discussed as well as numerical applications to the ASA range-dependent benchmark problems. Numerical application of this method involves a fourfold increase in the number of arithmetic operations as compared with that required for solving the same problem using a PE approach. However, one does get the backscattered field and one not does have to approximate square roots of differential operators as one must do in the PE approach. Since an elliptic equation is being solved one encounters numerical instabilities; how to deal with them will be discussed.
A numerical method for random two-way propagation in the Helmholtz equation
Authors: Oba Roger M.
Published: October 2005

Consider a strongly stratified ocean with randomness for which numerical computation of average complex pressure with two-way propagation is to be made. Let depth dependence be piecewise continuously differentiable and sediment be modeled by a fluid bottom. Within a fixed range interval, model uncertainty by an ensemble dependence upon some parameter in a continuously differentiable way, and the range dependence to be piecewise constant over independent intervals. For a single frequency source at a known depth, analysis for one element of the ensemble proceeds via the Helmholtz equation in radial symmetry and satisfies an outward radiation condition at large range. A previously developed modification for finite length range intervals in finite depth of the Kohler–Papanicolaou coupled mode equations in the forward scattering approximation [R. M. Oba, Acoust. Lett. 16, 56–61 (1992)] computes the transmission loss and phase for the average solutions for one-way propagation. This paper presents a reformulation of this method to two-way propagation of average solutions. This analysis will also show the development and computation of averaged scattering type operators. [Work supported by Naval Research Laboratory and ONR.]
Nonparabolic marching algorithm for sound field calculation in the inhomogeneous ocean waveguide
Authors: Voronovich A.
Published: October 2005

A new algorithm is proposed for calculating sound field in the inhomogeneous ocean waveguide. It does not involve parabolic approximation and at least for 2D inhomogeneities can be considered as exact. On the other hand, it is ‘‘marching’’ and can be as easily implemented as a parabolic equation. For inhomogeneity with final horizontal extent, the algorithm calculates, in particular, the scattering matrix for acoustic modes interacting with inhomogeneity. It is significant that the approach is able to calculate not only the acoustic field itself, but propagation times of different modes as well. The cases of uneven boundary and media with losses can be also dealt with. Thus the algorithm is able to provide an exact solution of the Helmholtz equation with 2D inhomogeneities both for shallow- and deep-water situations. The algorithm can be easily generalized for the case of the moving media and/or density variations. The corresponding code does not require great computer memory or speed and can be performed on a conventional PC. Numerical simulations of sound propagation through strong inhomogeneity related to subpolar front will be presented. Two types of mode interaction appearing for two-channel situations will be discussed. [Work supported by ONR.]
Comparing the performance of split-step algorithms for coastal acoustics problems
Authors: King David B. , Chin-Bing Stanley A. , Collins Michael D.
Published: October 2005

The split-step Fourier algorithm [R. H. Hardin and F. D. Tappert, SIAM Rev. 15, 423 (1973); S. M. Flatté and F. D. Tappert, J. Acoust. Soc. Am. 58, 1151–1159 (1975)] has been an important technique for solving range-dependent ocean acoustics problems for more than two decades. Since this algorithm is restricted to leading-order asymptotics, parabolic equation solutions based on finite-difference algorithms have been developed for handling effects that require higher-order asymptotics, such as wide propagation angles, extensive bottom interaction, and elastic and poroelastic waves. The split-step Fourier algorithm has remained in widespread use despite the improved accuracy and capability of finite-difference solutions. The split-step Padé algorithm [M. D. Collins, J. Acoust. Soc. Am. 93, 1736–1742 (1993); M. D. Collins, J. Acoust. Soc. Am. 96, 382–385 (1994)], which includes higher-order asymptotics, is orders of magnitude faster than standard finite-difference solutions. Results will be presented for representative test problems to illustrate that the split-step Padé algorithm is also more efficient than the split-step Fourier solution for the coastal acoustics problems that are currently of interest.
Convergence properties of wide-angle techniques
Authors: Yevick David
Published: October 2005

The relative accuracy of various high-angle propagation methods were examined for the case of a rapidly expanding point source. It was established that the removal of evanescent modes in wide-angle calculations through, e.g., hybrid Fourier/Lanczos or Fourier/Padé algorithms [J. Acoust. Soc. Am. 96, 396 (1994)], greatly improves the numerical predictions of such techniques. Alternatively, procedures in which the imaginary part of the Thomson–Chapman propagation operator is applied after each propagation step may also be employed to increase the rate of convergence of standard unitary methods. Further, it was found that for moderate step lengths and highly divergent fields the errors implicit in rational approximations to the square-root operator are comparable to those associated with analogous approximations to the full propagator as well as with Chebyszev expansions of the exponent of the propagation operator with degree about twice that of the equivalent Padé method. Finally, a heuristic but useful relationship between the rate of convergence of a given Lanczos technique and the Taylor series expansion of the underlying propagation operator is outlined.
High-frequency propagation in a turbulent flow
Authors: Farmer David M. , Di Iorio Daniela , Cartier Ward
Published: October 2005

As part of the new ONR-initiative in moderate-to-high-frequency acoustics, a pilot experiment will be carried out in a shallow tidally forced channel in September 1994 to compare acoustic variability with direct measurements of turbulent velocity and sound-speed fluctuations. The acoustic configuration will consist of a linear array of four sources on one side, and four receivers on the other (f=67.5 kHz, L≊700 m), together with a single source and receiver for reciprocal transmission. Separation of reciprocal transmission from reception of the other four sources allows a repetition rate for all sources of 5 Hz. The spatial filter will be applied to the acoustic data so as to focus the measurement on the central portion of the channel, at which location a moored turbulence sensor (R. Lueck) will be deployed at the same depth as the acoustic path. Supplementary measurements will be acquired with a multiple frequency backscatter sonar, moored current meters, and pressure gauges, and a neutrally buoyant float to measure the larger scale turbulent motions (E. D’Asaro, APL-UW and D. Veenstra, IOS). The experimental work will be discussed in the context of prior studies of forward scattering from turbulence and preliminary results will be presented.
Effect of random volume and surface fluctuations on propagation in shallow water
Authors: Ewart Terry E. , Rouseff Daniel
Published: October 2005

The potential difficulties associated with modeling acoustic propagation in shallow-water environments are well documented. Larger scale deterministic features combine with random fluctuations in the water column, sediment, sea surface, and bottom to produce an extremely complicated propagation regime. The extent to which each of these features needs to be included in realistic propagation models remains to be quantified. Towards this end, results from a series of detailed simulations generated using the parabolic equation (PE) method are presented. Beginning with a deterministic downward refracting sound-speed profile and a known sloping bottom, realizations of the random features are sequentially added to the simulation. Pierson–Moskowitz surface waves, power-law bottom roughness, and representative bottom absorption are used to model the medium. The individual and cumulative effects of these scattering mechanisms on the acoustic wavefront are evaluated. Successive interactions with a random bottom are studied. The results are quantified by using a modal decomposition and also by examining the local arrival angle of energy as a function of depth. [Work supported by ONR.]
Pulse propagation in a range-dependent turbulent ocean
Authors: Chang W. R. , Dong S. H. , Tarng J. H.
Published: October 2005

In this research, an acoustic pulse propagating in a turbulent ocean with slightly range-dependent vertical sound-speed profile is investigated. A numerical approach called the split-step method, based on the parabolic equation, is used to simulate each frequency component of the pulse to propagate through the ocean. A random phase screen is generated to include the effects of random fluctuation of sound-speed profile in each step. The average acoustic pulse profile and root-mean-square pulse width are evaluated for different fluctuation strengths and scale lengths of turbulence. Some results are compared with those computed by theoretical approach. It is found that in each realization the pulse echoes, due to the multipath propagation, are changed in arrival times, pulse shapes, and numbers because of the random fluctuation of the sound-speed profile. The broadening of the pulse width is varied for different depths of the receiving position. An initial Gaussian-shaped pulse is considered. For the simulations, a Gaussian-beam source is used instead of a point source. Here, the sound-speed profile is assumed to be changed uniformly in the range direction.
Intensity statistics of acoustic waves scattered by internal waves
Authors: Dashen Roger , Gerber James
Published: October 2005

Intensity correlations for ocean acoustic propagation show markedly different behavior in the partially saturated regime than in the fully saturated regime. In contrast to the known exponential decay of temporal intensity correlations in full saturation, partial saturation correlations fall off very slowly. This phenomenon is a consequence of the peculiar time dependence of internal waves, and does not occur in other physical situations, such as atmospheric optics. Results of a numerical simulation which demonstrate the effect are presented.
Rethinking the acoustics curriculum
Authors: Raichel Daniel R.
Published: October 2005

R. Bruce Lindsay’s classic ‘‘wheel diagram’’ [Acoustics: HistoricalandPhilosophicalDevelopment (Deaden, Hutchison and Ross, Stroudsburg, PA, 1972), p. 2] remains remarkably relevant today. The manifold categories of acoustics have not increased in number but deepened, rather, under the impetus of current R&D spurred by easy availability of computers. This situation has resulted in more material to cover in undergraduate and graduate courses for students of engineering and natural sciences. The necessity for total mastery of fundamentals remains, but the question arises regarding how much and what should be treated within time constraints. After a basic overview-type course (which must include laboratory experience) at least two additional courses should be provided in order to ensure that the undergraduate student has a sufficiently strong background in acoustics. The second course might deal almost exclusively with the theory and applications of ultrasonics, and the third course could be an independent study, whereby the student can pursue topics of specific interest under professorial guidance. For architecture majors, a special course in building acoustics should be a requisite—not so much for the purpose of making them acoustical experts as to inculcate in them an awareness of the acoustical implications of their work.
A perceived low-frequency sound in Taos, New Mexico
Authors: Mullins Joe H. , Poteet Horace
Published: October 2005

Persistent complaints of an annoying low-frequency sound in Northern New Mexico, particularly in the vicinity of Taos, led to a request by members of the Congressional delegation of NM for an investigation. During the summer of 1993, in Taos, extensive simultaneous measurements were carried out of acoustic, seismic, electric, magnetic, and electromagnetic signals by a team from Sandia and Los Alamos National Laboratories, the Air Force Phillips Laboratory, and the University of New Mexico. Since anecdotal evidence and signal matching tests by the hearers implicated the frequencies between 30 to 100 Hz, special attention was given to that range. However, no signals were found matching the description, and in particular no airborne audio signals in this range were found other than background, even though the acoustical detector was capable of measuring signals less than −50 dB SPL. Subsequent complaints of similar sounds from widely distributed areas in the U.S., and a long history of these in the U.K. [R. N. Vasudevan and C. G. Gordon, Appl. Acoust. 10, 57–69 (1977)] have focused attention on human hearing in the 20–100 Hz range. New instruments are being developed and controlled clinical tests are planned with hearers and nonhearers in the Taos area.
Low-frequency acoustic measurements at Los Alamos
Authors: Whitaker Rodney W.
Published: October 2005

Los Alamos National Laboratory has had an active program of atmospheric infrasonic measurement for the last 10 years, in the frequency region of 0.1–10 Hz. During this time, substantial data have been gathered on acoustic signals from underground nuclear tests, earthquakes, and large conventional explosions, often at long range. Normal operational activity, issues of long-range propagation, and interesting data examples will be discussed. Recent work related to a low level environmental noise problem will also be presented.
Low level, low-frequency sounds: Measurement and analysis challenges
Authors: Bedard Alfred J.
Published: October 2005

Low-frequency sounds from both natural and civilization sources can travel for long distances (tens or hundreds of kilometers), producing local regions of enhanced as well as reduced intensity depending upon range and time. Thus the identification of sources can be difficult, since merely mapping sound level in the direction of increasing intensity may not help to identify distant sources. A brief review of some examples of low-frequency background sounds provides the basis for a discussion of potential methods for identifying sound sources in a complex propagation environment. At low frequencies (<100 Hz) it is more difficult to determine direction with simple, portable systems. Some practical approaches for low-frequency source location are described.
Response of national park visitors to the sounds of aircraft overflights
Authors: Robert William E.
Published: October 2005

The responses of over 750 national park visitors to sounds of aircraft overflights were measured at six study areas in the Grand Canyon, Hawaii Volcanoes, and Haleakala National Parks. Park visitors were observed as they entered each study area, and were asked to participate in a brief survey as they exited the area. The survey included questions about the visitor’s reasons for visiting the park, and asked visitors to rate their responses to aircraft sounds on five-point scales. Simultaneously, in one to three positions representative of the study area, A-weighted sound levels were recorded at 1-s intervals using extremely low noise instrumentation. In addition, human observers maintained time-synchronized logs of aircraft audibility, types of aircraft audible, types of background sounds, and other factors. Several mitigating variables, such as background sound level and visitor expectations, were tested for their ability to improve the dose-response relationships. Logistic regression was used to generate four separate dose-response relationships, relating two visitor responses (annoyance due to aircraft sounds, and interference of aircraft sounds with natural quiet) to two acoustic doses (percentage of time aircraft are audible, and aircraft A-weighted equivalent sound level). [Work supported by National Park Service.]
Automated monitoring of low level ambient noise levels
Authors: Lewis Nelson D. , Russell William A.
Published: October 2005

Automated monitoring of low level ambient noise levels presents many challenges. The obvious challenge is to have a noise monitor with a low noise floor, less than 20 dBA, so that the ambient can be monitored. Other challenges include designing a lightweight system that can be backpacked to the monitoring site, and the site selection. Site selection criteria include protecting the monitor from direct sunlight and heat, and locating the microphone so that the influence on the measurements from rustling leaves and wind will be minimal. This paper presents the results of our learning curve from three studies of low level ambient noise.
Homeowner judgments of the annoyance of individual heavy weapons blasts
Authors: Luz George A. , Lewis Nelson D. , Russell William A.
Published: October 2005

Past studies of the annoyance of heavy weapons noise have shown the relationship between the yearly average exposure and average annoyance as reported by residents. However, no one has reported the relationship between individual weapons blasts and the annoyance reported by homeowners who were experiencing these events inside their own home. As part of a noise and vibration measurement study undertaken in response to community complaints, four homeowners made judgments of the annoyance of heavy weapons noise. When these judgments were plotted against the outdoor measured linear peak SPL, ‘‘moderate annoyance’’ was found to begin just above 115 dB. This finding is consistent with a report by L. L. Pater in 1976 that there was a low probability of complaints from residents living in the vicinity of the Naval Surface Weapons Center, Dahlgren, VA, if weapons blasts were below 115-dB peak at the complainant’s home.
Effect of silent periods having short or long durations on the annoyance of vehicle sounds
Authors: Versfeld Niek J. , Vos Joos , Geurtsen Frank W. M.
Published: October 2005

Two laboratory experiments were performed to study the effect on annoyance of noise concentration in time. The first (rating-scale) experiment dealt with the influence on annoyance of short-time silent periods (varying from 0 to 160 s) in pass-by vehicle noise of 240-s total duration. Results showed that, at a fixed equivalent sound level, and with the number of vehicles kept constant, annoyance hardly depended on the duration and position in time of the silent period. In the second experiment subjects had to compare the annoyance of road traffic sounds with that of sounds from heavy vehicles (such as tanks). In deciding which fragment was more annoying, the subjects had to imagine that they were exposed to the road traffic sounds throughout the year, whereas the sounds of heavy vehicles were only audible during a certain part of the day, week, or year. Results indicate that, at a given equivalent sound level, concentration of the sounds in time reduces annoyance. [Work supported by the Ministry of Defence.]
Evidence for the existence of strong bending modes for signals scattered at oblique incidence from spheroidal shells
Authors: Werby M. F. , Sidorovskaia N. A.
Published: October 2005

In an earlier work [Werby etal., J. Acoust. Soc. Am. 85, 2365 (1989)] it was established that bending (flexing) modes are excited for signals scattering at oblique incidence from solid spheroidal shells. This was accomplished by comparing the exact T-matrix resonance predictions with those predicted from Timoshenko beam theory which accurately predicts the bending modes of a bar. One must then ask, do such modes exist for shells? One would expect that for fairly thick shells such modes do, but do they exist for thin shells too? In this study scattering of acoustical signals from elastic shells of various materials, aspect ratios, and shell thicknesses are examined. The study does indeed demonstrate the presence of bending modes even for very thin shells. It is interesting that for thick shells the resonance’s manifest themselves as maximum amplitude returns while for thin shells they manifest themselves as minimum amplitude returns. The effect with the transitional nature of a rigidlike background is associated to a softlike background for the two extremes so that the return signals vary in their coherence from adding constructively to adding destructively over the thickness variation. The sensitivity of resonance locations as a function of the elastic parameters is also presented. [Work sponsored by NRL and ONR.]
Do pseudo-Scholte resonances exist?
Authors: Werby M. F. , Sidorovskaia N. A.
Published: October 2005

In a pioneering work Talmant etal. [J. Acoust. Soc. Am. 86, 278 (1989)] established the presence of pseudo-Stonely resonances excited when acoustical signals scatter from shells at or near coincidence frequency. This notion was supported by the argument that Stoneley waves exist at the fluid–elastic interface of a plate when water is on one side and the other side is evacuated. It is known that nondispersive waterborne waves are excited at the fluid–water interface for that case in the frequency region around coincidence frequency. This coincided with the bounded shell case in which very narrow strong resonances corresponded with the waterborne waves and a broad envelope function corresponded with the onset of the flexural resonances which become manifest at coincidence frequency when the flexural waves become supersonic and thus radiated into the water. The envelope effect corresponds to an abrupt phase change of pressure at coincidence frequency. An analogous argument predicts the existence of pseudo-Scholte resonances. The analog for that case is a plate in which fluids of like properties exist on both sides. In that case waterborne waves exist over the entire frequency range. The implication is that if one scatters from such an object there should be a proliferation of waterborne waves and thus for closed shells an abundance of resonances associated with waterborne waves circumnavigating the shell should by present. Can the abundance of sharp peaks excited on fluid filled shells be explained in terms of this mechanism? This issue is examined and the question is answered. [Work sponsored by NRL and ONR.]
The study of pulse signals from elastic spheroidal shells near reflecting interfaces
Authors: Sidorovskaia N. A. , Dean Cleon , Werby M. F.
Published: October 2005

A formulation is presented that allows one to describe backscattered echoes from elastic shells near pressure release and rigid interfaces. This formulation is always consistent even at low frequencies and large distances from the interfaces and allows for the rapid reproduction of backscattered echoes over frequency ranges of practical interest. Numerical results are examined for pulse signals scattering from various targets as a function of target material, distance from the interface, and the effect that the two interface extremes have on the detected signals. [Work sponsored by NRL and ONR.]
Large-scale 3D finite-difference simulation of elastic wave propagation in borehole environments
Authors: Liu Qing-Huo , Schoen Eric , Daube François , Randall Curt , Liu Hsui-lin , Lee Ping
Published: October 2005

Elastic wave propagation in realistic borehole environments is very complex because of the presence of borehole, dipping beds, and other irregular scatterers. In order to understand this complex wave propagation phenomenon for sonic logging applications, a three-dimensional finite-difference (FD) method was used to simulate elastic wave propagation on a parallel computing architecture. The FD scheme solves the first-order elastic wave equations with central differencing in both space and time via staggered grids. Liao’s absorbing boundary condition is used to reduce artificial reflections from the finite computational domain. In this work, uniform grids in Cartesian coordinates are used to discretize the inhomogeneous medium. Because of the staircase approximation of the circular borehole, it is observed that the discretization requirement is quite different for monopole and dipole sources. Several methods are suggested to remedy this problem. The results from the FD method were validated by other methods available for several special geometries. Numerical examples will be shown to demonstrate the interaction of elastic waves with borehole and the surrounding geologic structures. Applications to interpretation of sonic logging will be illustrated.
Average acoustic field in shallow water II: Reverberation and its inverse problem
Authors: Zhou Ji-Xun , Zhang Xue-Zhen
Published: October 2005

Average reverberation intensity and the vertical correlation coefficient for reverberation, obtained from Pekeris shallow water, are offered as possible simple test cases for numerical modeling of reverberation and bottom scattering mechanism analysis. Measurements were conducted at three different areas in the Yellow Sea and the East China Sea with water depths of 40, 29, and 52 m. These three locations have very different seabed sediments, with mean grain diameters of 0.35, 0.07, and 0.02 mm, and porosities of 35.5%, 46.2%, and 56.1%, respectively. Wideband explosive sources with 1000-g TNT charges were used to get 1/3-octave reverberation data with center frequencies ranging from 200 to 5000 Hz. Using theoretical results obtained from the angular spectrum method, both small-angle bottom reflectivity and scattering strength are derived from high reverberation-noise ratio data, including reverberation intensity and vertical coherence in shallow water. [Work supported by ONR and IAAS.]
Scattering of seismic interface waves from pointlike obstacles in unconsolidated sediments
Authors: Smith Eric , Atchley Anthony , Behrens John A. , Wilson Preston S. , Wolz Benjamin T. , Muir Thomas G.
Published: October 2005

The concept of an active, bistatic, seismoacoustic interface-wave sonar is investigated theoretically and experimentally. The goal of the theory is to relate the scattering of seismoacoustic interface waves from material inhomogeneities and objects buried beneath an interface to their target strengths. This is done in a multipole scattering expansion, which takes a simple and efficient form in the limit that the inclusions can be treated as pointlike perturbations of the properties of the medium. Experiments were performed in a sandy beach area of the Gulf of Mexico to demonstrate the concept. The experiments included methods for the selective excitation of interface waves, and examined the propagation of seismic interface waves in unconsolidated wet sand, both water-saturated and unsaturated. The boundary conditions and target strengths of a collection of buried objects were measured, using a variety of pulse-echo and continuous-wave sonar configurations.
Numerical simulation of the aerosound from the viscous layer of an impinging jet
Authors: Alexander Hani G. , Meecham William C.
Published: October 2005

Noise generated by a jet impinging on a surface is of interest in itself for such applications as vertical takeoff. Here we consider the image argument [see A. Powell, J. Acoust. Soc. Am. 32, 982 (1960) and W. C. Meecham, ibid. 37, 516 (1965)]. It shows that there can be no dipole sound for a large flat surface, only the volume, quadrupole aerosound. The sound generated by the viscous layer at the surface is neglected, and is examined by us here and shown to be indeed negligible. The simulation was carried out in two separate steps. The first step was to generate the hydrodynamic field which was compared to well-documented experimental results of similar flows. Once an adequate hydrodynamic field was generated, the theoretical treatment of Curle and Lighthill relating surface generated sound and the nature of aeroacoustic sound, respectively, was employed to get order-of-magnitude values for the sound intensity and develop directivity patterns. The source region considered was the viscous region near the surface. The kε turbulence model was employed and did a fair job of depicting the fluid field. Velocity profiles of the free-jet region were very successful, while the model broke down some in the ‘‘wall jet’’ region of the flow. Surface pressure and shear stress distribution was in good agreement with experimental values. The acoustic values were then obtained and the viscous layer was found to generate very low intensity levels, in the neighborhood of 25 dB, much less than the volume sound.
Two-sound-pressures theorem for aerodynamic sound from two-dimensional flows
Authors: Henderson Brenda
Published: October 2005

The three-sound-pressures theorem [A. Powell, J. Acoust. Soc. Am. 34, 902–906 (1962)] applies to sound generated by inviscid, incompressible, free flows when the source region is acoustically compact and shows that the acoustic far field must be reducible to lateral quadrupole radiation only. In two dimensions, the source region is not compact in the third dimension so it is not obvious that the three-sound-pressures theorem directly applies in this case. The two-sound-pressures theorem is developed by integrating Lighthill’s source term over the ‘‘third’’ dimension and is shown to be satisfied by two-dimensional lateral quadrupole radiation. In all known two-dimensional situations, the two-sound-pressures theorem is satisfied. A simple two-dimensional line vortex problem involving the collision of four rectilinear vortices is presented as an illustration.
Symmetrical mode of rectangular choked jet screech
Authors: Lin Dan , Powell Alan
Published: October 2005

The screech and edge tones of rectangular jets had always been considered to be due to asymmetric (sinuous) jet instabilities, with out-of-phase sound fields across the jet plane. Kozu’s 1991 screech measurements showed a discontinuity at 2.12 ≤Rd<2.16, R=pressure ratio, the wavelengths λ below this being about 25% less than the empirical λ/h =k√(R−Rc), h=small dimension of rectangular nozzle, k=constant=5.2 (Powell),=5.0 (Krothapali), Rc=critical value. However, Lin’s 1992 schlieren photographs showed a symmetric (varicose) mode for edge tones at a pressure ratio R=2.36 and small nozzle-to-edge distances for the same nozzle, aspect ratio 4.8, with wavelength about half that for (asymmetrical) screech. Lin’s 1992 investigation of screech for R<Rd showed unambiguous symmetry of the sound field, implying symmetrical (varicose) jet instabilities. The evidence consisted of signals from microphones symmetrically placed in the nozzle plane that showed unambiguous symmetry below the discontinuity and asymmetry above; correlation measurements were consistent with this (though of low coherence). Powell’s phase criterion λ/h=(1+Mcon)/Mcon is satisfied within 10% for 2.5≤R<3.6, with significant discrepancies elsewhere.
Vortex sound: Equivalence of ‘‘vortex-force’’ and ‘‘vorticity-alone’’ forms
Authors: Powell Alan
Published: October 2005

A direct general proof is offered of the equivalence of the source integrals of the ‘‘vortex-force’’ and ‘‘vorticity-alone’’ formulations of aerodynamic dipole and quadrupole sound in both two and three dimensions as given in the previous paper. For the dipole (with solid surfaces replaced by an image system), take the expansion of ∇(a⋅b), a=y, b=(ζΛu), apply Helmholtz’ equation ζ’+∇Λ(ζΛu)=0, then after some manipulation and reduction integrate over 2-D or 3-D space and use Kelvin’s transformations; finally, differentiate w.r.t. t and take the x component. For the quadrupole, form (y⋅x̂)∇y⋅[x̂(a⋅b)] and proceed similarly, introducing ∫y⋅(ζΛu)dV(y)’=(kinetic energy)’=0 in 3D but ∫y⋅(ζΛu)dS(y)’ =(constant or 0)’=0 in 2D. Only kinematic relationships have been used apart from the foregoing hydrodynamic integral relationships for the quadrupole. Most transparently, in 2D for the dipole, if no vorticity is generated, ζ’+∇Λ(ζΛu)=Dζ/Dt=0; so for moving vorti- city ζ=ζ0δ(y−y0), y0=y0(t), and ζ0=constant. Then the vorticity- alone form reduces directly to the vortex force form: ∫yΛ(ζ0δ)‘ dS(y)=∫(y0Λζ0)dS(y0)‘= −∫(ζ0Λu’0)dS(y0).
Active noise control for attenuation of low-frequency broadband jet engine exhaust noise
Authors: Smith Jerome P. , Burdisso Ricardo A. , Fuller Chris R. , Gibson Rob
Published: October 2005

Low-frequency broadband jet engine exhaust noise radiated into the surrounding area has been a problem for facilities that perform ground jet engine run up operations such as military hush-houses. This low-frequency acoustic radiation is capable of propagating over long distances, creating a noise and vibration problem in nearby communities. In this paper, active noise control (ANC) is experimentally implemented to achieve attenuation of low-frequency turbo-fan jet engine exhaust noise in a nearby area. The control method is the feedforward filtered-x LMS algorithm and is implemented for both single-input, single-output and multiple-input, multiple-output systems. The control inputs are generated by filtering a reference signal through adaptive FIR filters before being input to the control loudspeakers, and microphones are used to generate the reference and error signals. Attenuations of up to 15 dB are achieved in the 1/3-octave bands at the error sensor locations. The results also demonstrate a large area of reduction surrounding the error microphones with overall attenuations of up to 7 dB and generally agree with analytical predictions. Results are demonstrated for both a running jet engine in a small scale hush-house facility and an unsuppressed running jet engine. [Work sponsored by the U. S. Air Force.]
Instrumentation to generate a two-phase turbulent (bubble) submerged water jet for flow noise measurements
Authors: Korman Murray S.
Published: October 2005

It has been demonstrated that the near-field pressure spectrum (generated by a turbulent submerged water jet) is enhanced when the turbulent flow is modified to become a two-phase flow containing air bubbles [‘‘Proceedings of the 14th ICA, Beijing, China,’’ Acoustica 76, supplement to No. 4, May (1992), paper B6-1, p. 70]. An amplification factor G =∫p2two-phasedf/∫p2single-phasedf is measured as a function of the gross void fraction β of the air bubbles. Results showed that G∼β2 and G∼20 at β=0.0065. The range of void fraction was limited due to the use of the bubble maker (located at the jet nozzle entrance) which consisted of a fritted ceramic disk that was housed in a glass Buchner funnel and fed compressed nitrogen gas. It is possible to improve this apparatus by using carbonated water at high pressure in a nozzle that consists of an array of small holes in a thin circular plate. This arrangement can be controlled to yield small bubbles with an average diameter of about 100 μm in water. Larger void fractions are possible and the necessary constraint of having the resonant bubble frequencies well above the region of the low-frequency flow noise spectrum (<500 Hz) is obtained. A brief videotape will be shown. [Work supported in part by ONR.]
Approximate diffraction coefficients
Authors: Barbone Paul E.
Published: October 2005

Expressions for diffraction coefficients for canonical shapes, joints, and discontinuities are necessary in applications of the geometrical theory of diffraction to scattering from submerged structures. In many cases of practical interest, however, the diffraction coefficients are either not available or are very difficult to evaluate. The use of perturbation theory and matched asymptotic expansions in obtaining suitable approximations of diffraction coefficients is described. These two methods can yield approximations that are simple to compute, easy to apply, and are valid in complementary parametric ranges. The perturbation method assumes that the properties of the solid or its geometry are nearly homogeneous. Matched asymptotics, on the other hand, is a useful tool when the solid is nearly hard, or the fluid is light. The accuracy of these methods is demonstrated by comparing them to the exact solution for diffraction by an impedance discontinuity. When the effort is made to obtain uniformly valid asymptotic expressions, the results prove to be remarkably accurate even at values of ε=1 (here, ε is a ‘‘small’’ parameter).
Longitudinal wave diffraction generated at curved plate junctions
Authors: Rebinsky Douglas A.
Published: October 2005

A perturbation solution is developed to study diffracted longitudinal membrane waves originating from the junction of two curved plates which are joined so that their tangent is continuous. It is shown that the diffracted longitudinal wave field in the plates is dependent upon or forced by a background solution which characterizes the acoustic interaction between two joined, flat plates and the surrounding fluid. Two forms of background wave fields are used: (1) a simple solution based on the acoustic diffraction from two massive plates, and (2) the solution of acoustic diffraction from two flat plates governed by the classical theory of flexure. Explicit expressions are shown for the longitudinal diffraction coefficients, associated with this fluid/structure interaction. The reciprocal problem of an incoming longitudinal wave to the joint is discussed. Numerical results of the diffraction coefficient will be shown. [Work supported by ONR.]
Structural and acoustic responses of mass-spring loaded elastic cylindrical shells: Numerical implementation
Authors: Ho Jin-Meng
Published: October 2005

An important step in dealing with the mass-spring loaded cylindrical shell is to evaluate the total shell displacements at the attachment points, which determine the strength of the equivalent forces. Through dynamical balance at such points, these displacements satisfy a system of linear equations whose coefficients involve the shell displacements generated by on-surface forces of unit strength, a Green’s-function problem with both source and observer located on the shell surface. It is thus evident that flexural waves, though subsonic, must be accounted for in the ray acoustic solution to the latter problem. Numerical examples show that they produce high Q intense resonances because of their extremely small radiation damping, which would be dominated by structural damping for dissipative shell material, imprinting their signature in the far field through radiation of the induced forces and carrying much of the information on the internal load. By including the flexural as well as membrane waves, the ray model accurately predicts the induced forces, the shell displacements, and the surface and far-zone pressures in the frequency range of interest; 1≤ka≤25 (where k is the fluid acoustic wave number and α is the shell mean radius). [Work supported by ONR.]
The impact of a rigid body of revolution with an elastic layer of finite thickness
Authors: Rossikhin Yu. A. , Shitikova M. V.
Published: October 2005

The problem of the impact of a rigid body of revolution with an elastic isotropic layer is considered in the initial stage of dynamic interaction. The initial stage is characterized by the fact that the velocity of the displacement of the intersection points of the sphere with the upper boundary of the layer is larger than the velocity of longitudinal waves; in so doing the free surface external to the contact domain with the body is undisturbed. The method of successive approximations as well as the ray method, according to which the solution behind the fronts of incident and reflected waves is constructed in terms of power series (ray expansions), are used as methods of solution. In the problem under consideration, use has been made of one-term ray expansions whereby the main characteristics of the shock interaction have been obtained, and the possibility of localized damage of the material of the layer at the points lying along the central ray has been examined.