bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental investigation of minimization of the dynamic response of mass-loaded beams using vibration absorbers
Authors: Manikanahally Dhanesh N. , Crocker Malcolm J.
Published: October 2005

An experimental verification of the theoretical analysis of the use of discrete vibration absorbers consisting of spring–mass–damper systems, to attenuate the response of a mass-loaded cantilever beam, is presented. Ten different beam systems that are similar except for the location of the masses were studied both theoretically and experimentally. Initially, eigenvalues, eigenfunctions, and generalized masses were obtained for each beam system without absorbers. Then, an experimental investigation was conducted on these beam systems without absorbers, to determine the hysteretic damping factor for each system. With this information, two discrete vibration absorbers were designed using theoretical methods to suppress the first and second resonances of the beam systems under consideration in the frequency range below 100 Hz. Absorber I was designed to attenuate the first resonance and absorber II, the second resonance. The interaction of the absorbers was accounted for in the analysis. Ten different sets of absorber parameters, damping coefficients of the viscous damper, and spring stiffnesses of the springs were obtained for both absorbers I and II. Ten different sets of absorbers were designed corresponding to the ten different beam systems described above. The mass of the absorbers was kept constant for all the different beam systems. The stiffness and damping coefficients of absorbers I and II were found to be of the same order of magnitude for all of the ten absorber sets designed for the ten beam systems. Therefore, a single set of vibration absorbers was fabricated and used for each of the ten beam systems. The parameters of the vibration absorbers used for the experiment were similar to the theoretical values.
Active control of power flow from a vibrating rigid body to a flexible panel through two active isolators
Authors: Pan Jiaqiang , Hansen Colin H.
Published: October 2005

Active control of harmonic vibratory power flow from a rigid body through two active isolators to a simply supported flexible panel is investigated theoretically and experimentally. Power flow as a result of moments acting on the rigid body as well as horizontal and vertical forces is taken into account. Both theoretical and experimental results show that over a wide frequency range, an active isolation system consisting of a force actuator in parallel with a passive elastic element can demonstrate substantial performance improvements over the simple passive elastic system acting alone.
Calibration of a distorted towed array using a propagation operator
Authors: Marcos Sylvie
Published: October 2005

In this paper, a new method for array shape calibration is presented. This method can be applied to any antenna distortion, it does not require any a priori knowledge about the sources, and it is relatively simple to implement. A number of unknown remote point sources, propagating plane waves, are required to implement this method. An equal number of sensors having known relative positions are used as a geometric reference. The method relies on a propagation operator, called the propagator, which can be estimated from the cross spectral matrix of the received signals through a simple least-square process. The performances of the proposed method are illustrated through simulations by showing how good accuracy in source bearing estimation, by both the classical beamforming method and MUSIC, can be recovered when the array shape is estimated.
Ratio of variance to mean of action potential counts for an auditory nerve fiber model with second-order refractory behavior
Authors: Gaumond Roger P.
Published: October 2005

Sequences of interval times were generated with the first- and second-order interval probability dependence proposed by Gaumond et al. [J. Neurophysiol. 48, 856–873 (1982)] to characterize cochlear nerve fiber spontaneous action potential (AP) sequences. The ratio F(T) of the variance to the mean of the count of APs in bins of T s was computed for the simulated sequences, and compared to the corresponding measure for cochlear nerve fiber data presented by Lowen and Teich [J. Acoust. Soc. Am. 92, 803–806 (1992)]. The simulations were generally consistent with the data in the range 15<T<100 ms.
Broadband source localization and signature estimation
Authors: Yang T. C.
Published: October 2005

The temporal signature and source location of a broadband impulse propagating in an ocean waveguide are estimated using matched mode processing and illustrated using simulated data in an Arctic sound channel. Matched mode processing provides a simple method for broadband signal detection and localization; the peak-to-sidelobe ratio is significantly improved using broadband data compared with the narrow-band case. The range and depth ambiguity function evaluated at the source location yields directly the source spectrum, which is inverse Fourier transformed to estimate the original signal waveform. For the simulated data, the reconstructed signal, compensated for spreading loss and array signal gain, agrees rather well with the original waveform. The estimated spectrum/waveform is weaker than the original spectrum/waveform due predominantly to the fact that the Arctic wave guide is lossy. A method for coherent broadband processing is proposed to improve signal localization and detection when the original source spectrum is known. Multiplying (correlating) the original spectrum with the range and depth ambiguity function, the product can be coherently summed over the frequency band of the signal. Near theoretical processing gain is achieved for the simulated data. Broadband signal detection is proposed using a frequency versus depth plot in addition to the commonly used frequency versus bearing plot.
A two-way parabolic equation for elastic media
Authors: Collins Michael D.
Published: October 2005

The parabolic equation (PE) method is extended to handle wave propagation and scattering in range-dependent elastic waveguides, which are approximated by a sequence of range-independent regions. The two-way elastic PE involves an efficient PE-based scattering method for computing reflected and transmitted fields at the vertical interfaces separating range-independent regions. The one-way elastic PE is used to propagate the outgoing and incoming fields through the range-independent regions with two-way range marching. In addition to providing the backscattered field, the two-way PE provides a correction to the outgoing field. The self-starter is generalized to handle a source in a solid layer.
A gradient formulation of the Helmholtz integral equation for acoustic radiation and scattering
Authors: Francis David T. I.
Published: October 2005

A method of overcoming the problem of nonuniqueness in the discretized Helmholtz integral equation is described, based on a partial application of the Helmholtz gradient formulation of Burton and Miller [Proc. R. Soc. London, Ser. A 323, 201–210 (1971)]. The numerical implementation is designed to be compatible with a finite-element structural analysis, and uses boundary elements of the quadratic isoparametric type. The method is illustrated for scattering from a sphere, and for radiation by a piston vibrating in the end of a cylinder, with consistent results being obtained across a wide frequency range. The additional computation is of the order of 35% of that required for the standard formulation.
Ray tracing in a moving medium with two-dimensional sound-speed variation and application to sound propagation over terrain discontinuities
Authors: Lamancusa J. S. , Daroux P. A.
Published: October 2005

The development of an efficient method for tracing rays and determining sound pressure levels in a moving medium is described. The medium is specified with horizontal and vertical variations in temperature and vectorial wind velocity. Reflections from a nonlevel ground surface of complex impedance are treated and an adaptive time step numerical integration is implemented for high accuracy. Two integration algorithms are compared for accuracy and computational efficiency. Recommendations are given for improved discretization of the medium and for accurate ray tracing through a ground reflection. This model is used to investigate the effect that terrain discontinuities, such as hills, have on atmospheric sound propagation. The importance of correct inclusion of the vectorial nature of wind is demonstrated.
On the validity of the heuristic ray-trace-based modification to the Weyl–Van der Pol formula
Authors: Li Kai Ming
Published: October 2005

The Weyl–Van der Pol formula from electromagnetic wave propagation theory is known to give tolerable predictions of sound levels over a wide range of ground surfaces in a homogeneous atmosphere. A ray-tracing technique is perhaps the simplest approach to extend the applicability of the Weyl–Van der Pol formula to the inhomogeneous situation. Essentially one uses ray theory to determine the path lengths and the angle of incidence at the ground. These modified parameters are then substituted into the Weyl–Van der Pol formula for the overall sound levels. This heuristic approach may be criticized for its lack of mathematical rigor even though it is physically reasonable. By using a ray theory approximation in the wave equation, a closed-form solution has been obtained for the sound field over an impedance plane in the presence of a sound-speed gradient. It has been shown that the heuristic formula represents an approximation of the solution. The theory also suggests that there is a strong interaction between the sound-speed profile and the ground surface, in particular, when the impedance is high. The solution is limited to a single reflection.
A split-step Padé solution for the parabolic equation method
Authors: Collins Michael D.
Published: October 2005

A split-step Padé solution is derived for the parabolic equation (PE) method. Higher-order Padé approximations are used to reduce both numerical errors and asymptotic errors (e.g., phase errors due to wide-angle propagation). This approach is approximately two orders of magnitude faster than solutions based on Padé approximations that account for asymptotic errors but not numerical errors. In contrast to the split-step Fourier solution, which achieves similar efficiency for some problems, the split-step Padé solution is valid for problems involving very wide propagation angles, large depth variations in the properties of the waveguide, and elastic ocean bottoms. The split-step Padé solution is practical for global-scale problems.
Measurement of acoustic power output in the active control of sound
Authors: Johnson M. E. , Elliott S. J.
Published: October 2005

Active sound control can be used to obtain large global reductions in low-frequency harmonic enclosed sound fields. The secondary sources of sound in such applications have typically been adjusted to minimize practical approximations to the total acoustic potential energy in the enclosure. Minimizing the total acoustic power output of the primary and secondary sources has recently been theoretically shown to give very similar results. In this paper, some of the physical consequences of minimizing total power output are discussed, specifically the implications this has on the power output of the secondary sources. In the single channel case, it is found that the acoustic power output of the secondary source is exactly zero when adjusted to minimize the total power output of both sources. A method of adjusting the secondary source to achieve this objective is presented, in which the volume velocity of the secondary source is adjusted to be out of phase with that of the primary source, and the secondary source amplitude is gradually increased. The amplitude is adjusted using measurements of the acoustic power output of the secondary source only. This initially becomes negative as the amplitude is increased, indicating that the secondary is absorbing power, but then increases until it is exactly zero at the amplitude required to minimize the total power output. This method has been verified by experiments in an enclosure in which the acoustic power output of two loudspeakers acting as the primary and secondary sources were monitored, together with the sum of the squared pressures at 32 microphone locations in the enclosure.
A neural network harmonic family classifier
Authors: Meister James
Published: October 2005

A method of automatic target discrimination and classification for passive sonar applications is obtained using an unsupervised, self-organizing, Kohonen neural network. Utilizing detected, smoothed spectral data, the kth-order frequency differences are histogrammed into constant percentage resolution spectral bins prior to presentation to the network. This nonlinear transformation results in good neural network classification when the input data is topologically close to the training set. Simulations of the algorithm show highly robust performance to missing spectral detections, spurious spectral detections and Doppler shifts.
An insert earphone system for delivery of spectrally shaped signals for physiological studies
Authors: Chan Joseph C. K. , Musicant Alan D. , Hind Joseph E.
Published: October 2005

Acoustic signals arriving at the eardrum in free-space carry directionally dependent temporal and spectral information resulting from the acoustical effects of the body, head, and external ear as well as from differences in the length of the sound path to each ear. Through analysis of the responses of single auditory neurons, the acoustical and neural mechanisms by which sounds in free-space are localized are being studied. The approach involves simulation of free-field signals at the two eardrums of a cat via earphones and a study of the neuronal responses to such a virtual acoustic space. This approach makes it possible to manipulate different stimulus parameters independently in order to examine their role in determining the spatial characteristics of neuronal response. This report describes an insert earphone system designed for the delivery of such simulated signals which are broadband transients having complex spectra that mimic the acoustic transfer function of the external ear for frequency components up to 30 kHz or more.
Speed of sound in pure water as a function of temperature
Authors: Bilaniuk Nykolai , Wong George S. K.
Published: October 2005

In view of the adoption of the International Temperature Scale of 1990 (ITS-90), which defines the International Celsius Temperatures, t90, the dependence on temperature of the speed of sound in pure water is examined. Drawing on the experimental data published previously by Del Grosso and Mader [J. Acoust. Soc. Am. 52, 1442–1446 (1972)], it is found that the change from the previous t68 scale is significant. At 100 °C, the difference between the two scales (t68–t90) is 0.026 °C, resulting in a difference of 0.022 m/s for the speed of sound. The speed of sound is fitted to a new fifth-order polynomial applicable over the t90 range 0–100 °C.
Nonuniqueness of solutions to extended Kirchhoff integral formulations
Authors: Wu Sean F.
Published: October 2005

This paper examines the nonuniqueness of solutions to an extended Kirchhoff integral formulation at certain discrete frequencies corresponding to the eigenfrequencies of the related interior boundary value problem. In particular, effects of surface motion and interaction between turbulence and vibrating surface in motion on nonuniqueness difficulties are investigated. It is shown that surface motion affects nonuniqueness difficulties in two ways: (1) it shifts the eigenfrequencies of the related interior boundary value problem and (2) it excites more eigenfrequencies at which nonuniqueness difficulties occur than the corresponding stationary case. The interaction between turbulence and vibrating surface in motion further shifts the eigenfrequencies. Although changes in these eigenfrequencies are small at low Mach numbers, they increase with the Mach number. It is also demonstrated that although an extended Kirchhoff integral equation fails to yield a unique solution at certain discrete frequencies, a combined extended surface Kirchhoff integral equation and an extended interior Kirchhoff integral equation always yield a unique solution for all frequencies. This is because there is only one set of solutions that satisfy both an extended surface Kirchhoff integral equation and an extended interior Kirchhoff integral equation.
Constrained-layer damping analysis for extensional waves in infinite, fluid-loaded plates
Authors: Dubbelday Pieter S.
Published: October 2005

This study concerns the mathematical analysis of constrained-layer damping of extensional waves in plates of infinite extent, with and without fluid loading. Previous work was mostly limited to flexural waves. Some aspects of fluid loading for flexural waves may be understood by means of thin-plate theory. Therefore, a similar theory was developed for extensional waves. The description and examples presented here are based on three models: The first is an extension of Kerwin’s 1959 model [E. M. Kerwin, J. Acoust. Soc. Am. 31, 952–962 (1959)], the second is a hybrid model in which the base plate is described by exact elasticity theory and the other two layers by Kerwin’s concepts, and the third uses exact elasticity theory for all three layers. It is shown that the extended Kerwin model is useful in the design of constrained-layer damping for extensional waves as well as for flexural waves.
A model for context effects in speech recognition
Authors: Bronkhorst Adelbert W. , Bosman Arjan J. , Smoorenburg Guido F.
Published: October 2005

A model is presented that quantifies the effect of context on speech recognition. In this model, a speech stimulus is considered as a concatenation of a number of equivalent elements (e.g., phonemes constituting a word). The model employs probabilities that individual elements are recognized and chances that missed elements are guessed using contextual information. Predictions are given of the probability that the entire stimulus, or part of it, is reproduced correctly. The model can be applied to both speech recognition and visual recognition of printed text. It has been verified with data obtained with syllables of the consonant–vowel–consonant (CVC) type presented near the reception threshold in quiet and in noise, with the results of an experiment using orthographic presentation of incomplete CVC syllables and with results of word counts in a CVC lexicon. A remarkable outcome of the analysis is that the cues which occur only in spoken language (e.g., coarticulatory cues) seem to have a much greater influence on recognition performance when the stimuli are presented near the threshold in noise than when they are presented near the absolute threshold. Demonstrations are given of further predictions provided by the model: word recognition as a function of signal-to-noise ratio, closed-set word recognition, recognition of interrupted speech, and sentence recognition.
Interaction of lithotripter-generated shock waves with air bubbles
Authors: Philipp A. , Delius M. , Scheffczyk C. , Vogel A. , Lauterborn W.
Published: October 2005

The shock wave-induced collapse and jet formation of pre-existing air bubbles at the focus of an extracorporeal shock wave lithotripter is investigated using high-speed photography. The experimentally obtained collapse time, ranging from 1 to 9 μs for bubbles with an initial radius R0 of 0.15 to 1.2 mm, agrees well with numerical results obtained using the Gilmore model. The collapse time is not linearly dependent on the initial bubble diameter since the temporal profile of the lithotripter wave contains a stress wave. The bubbles, positioned below a thin plastic foil, show strong jet formation in the direction of wave propagation with peak velocities of up to 770 m/s at the moment of collapse. Bubbles of initial radii between 0.3 and 0.7 mm always induce perforation of the foil by the jet (hole diameter 80–300 μm). Averaging the jet flow speed over 5 μs immediately after the collapse results in velocities from nearly zero up to 210 m/s, depending on the initial bubble size, with a maximum at R0=550 μm. This maximum is related to the temporal profile of the shock wave and to the effective cross section of the bubble for shock wave energy transfer. As cavitation bubbles are generated in the focal region of the lithotripter, the results are discussed with respect to the processes in a cavitation bubble field, which are of importance in cavitation erosion as well as in extracorporeal shock wave lithotripsy.
Disturbance caused by residential air conditioner noise
Authors: Bradley J. S.
Published: October 2005

This paper reports the results of a field survey of disturbance caused by outdoor residential air conditioner noise. For 550 subjects, questionnaire responses along with integrated air conditioner and ambient noise levels were obtained. Reported hearing of neighbors’ air conditioners and annoyance to the noise from neighbors’ air conditioners were significantly related to measured noise levels. Responses were most strongly related to the level by which the air conditioner noise exceeded the ambient noise. Residents of noisier neighborhoods were less disturbed by neighbors’ air conditioner noise. Owners of air conditioners were less disturbed by their neighbors’ air conditioner noise by an amount equal to an approximate 7-dBA difference in noise levels. Acceptable limits for air conditioner noise levels can be derived from the dose response curves produced in this study.
On the estimation of source motion parameters by temporal and spatial focusing
Authors: Zugmeyer O. , Le Cadre J. P.
Published: October 2005

This paper deals with the study of focusing methods for moving sources. For numerous applications (e.g., sonar) large integration times are required in order to enhance the array processing performance in terms of detection, tracking, etc. It is then necessary to incorporate the source motion model in its own model and to define array processings using basically this extended source model. The classical array processing separates the sources of (sufficiently) different bearings at a given time. This is the basic ‘‘philosophy’’ not only for classical beamforming but also for high-resolution methods. However, for many practical situations (e.g., passive sonar) a large amount of spatio-temporal data is available. It then seems possible to benefit from all these data in order to separate, detect, and track the sources by considering their respective trajectories. The classical and natural way consists in using a time-varying beamforming method. It is actually a focusing method. However, this method suffers from a main drawback: interferences between sources. This problem is analyzed and a new frame for spatio-temporal analysis is presented. This approach allows one to mix the methods of time series analysis with the spatial analysis. Despite its simplicity, this approach may be applied advantageously to a wide variety of practical problems.
Finite element modeling of active periodic structures: Application to 1–3 piezocompositesa)
Authors: Hladky-Hennion Anne-Christine , Decarpigny Jean-Noël
Published: October 2005

The finite-element approach has been previously used, with the help of the ATILA code, to model the scattering of acoustic waves by single periodic passive structures, such as compliant tube gratings [A.-C. Hennion et al., J. Acoust. Soc. Am. 87, 1861–1870 (1990)], or by doubly periodic passive structures, such as Alberich anechoic coatings [A.-C. Hladky-Hennion et al., J. Acoust. Soc. Am. 90, 3356–3367 (1991)]. This paper presents an extension of this technique to active periodic structures, and describes with particular emphasis its application to the modeling of 1–3 piezocomposites made of parallel piezoelectric connecting strips in a passive matrix. The method can also be applied to many other piezocomposites or to large high-frequency arrays. In the proposed approach, only the unit cell of the active structure and a small part of the surrounding fluid domain have to be meshed, while the acoustic field on both sides of this mesh is described by a plane-wave expansion including progressive and evanescent contributions. Internal losses and anisotropy of the materials as well as normal or oblique incidence of the impinging wave, if this wave exists, can be taken into account in the model. In this paper, the general method is first described, and particularly the aspects related to the piezoelectric elements. Then, one test example is given, for which analytical results exist. This example is followed by a detailed presentation of finite-element results, which are compared with the corresponding measurements (free-field voltage sensitivity or transmitting voltage response), in the case of a given 1–3 composite. The accuracy of the whole approach is thus clearly demonstrated. Finally, the influence of the geometric parameters of a 1–3 composite is studied, while at the same time the limitations of previously published simple analytical models are discussed.
Construction and evaluation of a noise-suppressing hydrophone
Authors: Zain Saadi J. , Thompson William , Kahn Manfred
Published: October 2005

The construction and evaluation of an acoustic sensor is described which consists of two small pieces of piezoceramic bonded together with their poling axes collinear, one piece containing ordered macrovoids, the other solid. Electrical leads attached to each piece allow their outputs to be separately processed. The solid piece has a small hydrostatic voltage coefficient while the voided has a significantly larger voltage coefficient. Both have appreciable responses to vibration excitation along their poling axes. Hence, if the two electrical outputs are appropriately weighted, phase reversed, and then combined, the net response to vibration excitation should be negligible while the net response to an incident pressure wave should be essentially that of the voided piece alone. Hence, the assembly should function simultaneously as a poor accelerometer but a good hydrophone. The data show that at least 10 dB of vibration response cancellation and a large, nearly uniform, free-field voltage sensitivity are achieved over the frequency range from 5 to 20 kHz.
Finite element simulation of glottal flow and pressure
Authors: Guo Chwen-Geng , Scherer Ronald C.
Published: October 2005

Computational studies of laryngeal aerodynamics should help clarify the relationships among configuration, air flow, surface pressure, and vocal fold movement within the larynx, and the acoustic consequences of the output glottal air flow. The penalty finite element method [S. W. Kim, Comput. Fluids 16(4), 429–444 (1988a); NASA CR-179357 (1988b); S. W. Kim and R. A. Decker, Int. J. Num. Meth. Fluids 9, 43–57 (1989)] was adopted to simulate steady air flow and air pressure through the larynx. A total of 133 conditions of different glottal configurations and inflow rates were studied. The computational results were compared to empirical data from earlier experiments. Two cases are reported (1) constant glottal divergence (42°) but variable diameter and (2) constant glottal diameter (0.04 cm) but variable glottal angle. For case (1), the average discrepancy for translaryngeal pressure drop between the computational results and empirical data was 6.8% for pressures between 3 and 15 cm H2O. Flow separation occurred just downstream of the minimal glottal diameter. For case (2), the computational results for translaryngeal pressure drop differed from the empirically derived Scherer–Guo (S–G) equation predictions by an average of 8.9% for pressure between 3 and 13 cm H2O. Pressure recovery in the glottis suggested that the optimal glottal diffuser angle was near 10°. Results suggest that the computational method should be sufficient to study glottal aerodynamics (assuming quasisteady flow).
Response latency, latency-based receiver-operating characteristics, and uncertainty about interaural phase in the detection of in-phase and out-of-phase tones presented in noisea)
Authors: Emmerich David S. , Brown William S. , Thoms James B.
Published: October 2005

Subjects were given the task of detecting tonal signals presented in a continuous background of white noise which was always in phase at the ears (No). The signals were either in phase (So), or phase-reversed (Sπ) at the ears. The analysis of response latencies (for similar levels of performance) indicated that there were consistent differences in the processing of the two types of signals. Latencies were longer, and somewhat more variable, for Sπ than for So signals. It was also found that the theory of signal detectability can contribute to an understanding of what and how decisions are made. Latencies were treated as confidence ratings in order to determine latency-based receiver operating characteristics (LROCs) for the detection task. It was observed that the LROCs for the interaural condition No-So tend to leave the origin at a steeper angle than do those for the interaural condition No-Sπ, presumably reflecting the different sensory and decision processes employed in the two conditions. When the two interaural conditions were intermixed within blocks of trials, performance was slightly impaired in comparison to the situation in which the interaural condition remained constant throughout blocks of trials.
Temporal and spectral basis of the features perceived in repeated noise
Authors: Kaernbach Christian
Published: October 2005

When a half-second segment of a noise is played repeatedly, it initially creates a ‘‘whooshing’’ perception. With longer listening, however, individual features like ‘‘clanks’’ and ‘‘rasping’’ emerge. It is easy to tap the period of the perceived structure. This offers a possibility to investigate the mechanisms underlying the perception of these distinct features. The present study addresses the subject of the temporal and spectral extent of the physical correlates of these percepts. Five subjects participated in this study, and their tapping is in notable, although not perfect correlation. The physical correlate of the features can be confined in time to intervals as small as 100 ms. This segment of the stimulus is processed largely independently from the rest of the noise sample. Spectral processing is, in general, local. Some features, however, are spread over more than one octave. In 3 cases out of 25, across-channel processing is apparent.
Combined evaluation of interaural time and intensity differences: Psychoacoustic results and computer modeling
Authors: Gaik Werner
Published: October 2005

The physical and the psychophysical relationships between interaural time and intensity differences were studied for 24 frequency bands of critical bandwidth covering the full audio range. For the physical investigations a catalogue of outer ear impulse responses for 122 directions of the upper hemisphere was analyzed according to the combinations of interaural time and level differences found in each critical band. From these data curves of ‘‘natural combinations’’ of the interaural parameter differences were determined by the minimum square error method. In a psychoacoustical study it is shown that signals containing ‘‘natural’’ parameter combinations produce response patterns that differ from those produced when signals with contradictory interaural properties have been used. Finally an extension to the powerful binaural model of Lindemann [J. Acoust. Soc. Am. 80, 1608–1622 (1986)] is introduced, taking into account the results of the previous investigations.
Ambient noise measurements in the 200–300-Hz band from the Greenland Sea tomography experiment
Authors: Lynch J. F. , Wu H. X. , Pawlowicz R. , Worcester P. F. , Keenan R. E. , Graber H. C. , Johannessen O. M. , Wadhams P. , Shuchman R. A.
Published: October 2005

Ambient noise in the 200–300-Hz band was measured every four hours from Sept 1988 to Sept 1989 as part of the Greenland Sea tomography experiment (GSP88). Four transceivers, located in the central Greenland Sea gyre, sampled the noise during a wide variety of ice, wind, and wave conditions, revealing large seasonal variations in the noise field. The environmental conditions were obtained mainly from large-scale remote sensing and numerical modeling, i.e., operational meteorological forecast models, surface wave models, and microwave and infrared satellite imaging (for ice). To understand the noise field, a number of analyses were performed on the noise, wind, ice concentration, and wave-time series, including regressions, auto- and cross correlations, spectra, and acoustic propagation modeling. As a result, a number of environmental noise effects, particularly as related to ice edge noise, are observed. The results generally agree well with previous, shorter time period process oriented studies which used remote sensing as well as in situ ice, wind, and wave measurements. It is seen that prediction of the marginal ice zone (MIZ) noise field for a deep ocean region at the acoustic frequencies examined is feasible using large-scale environmental information.
Hole tone generation from highly choked jets
Authors: Umeda Y. , Ishii R.
Published: October 2005

The hole tone generated from the passage of underexpanded jets through a circular hole in a rigid plate and the secondary sound wave emission associated with the strong hole tone generation were investigated experimentally. Flow visualization shows that when the jet passes through a hole whose diameter is less than the nozzle diameter and interacts with the plate around the hole, two immediately succeeding strong hole tones having partially plane and spherical wave fronts are radiated in the upstream direction of the plate. A particular flow condition, where the pressure ratio R=3.90, the nozzle-to-plate distance h/d=2.40, and the hole diameter D/d=1.00, was investigated in detail. In addition to the radiation of two succeeding strong hole tones in the upstream direction, four strong secondary sound waves are radiated downstream of the plate during one cycle of the hole tone generation. Flow visualization confirmed that the six sound waves found for this flow condition are generated by two different generation mechanisms: (a) upstream of the plate, a feedback mechanism consisting of upstream-propagating sound waves in the ambient and downstream-convecting coherent vortical structures surrounding the jet; and (b) downstream of the plate, a radial expansion of the vortical structure due to the interaction with the hole and merging of two succeeding vortices. It is found that the shapes of wave fronts are changed by the refraction of the sound wave due to the vortex-induced flow near the jet boundary. The directionality of the far sound field is consistent with the result of flow visualization.
Assessment of an electromagnetometric system for the investigation of articulatory movements in speech production
Authors: Nguyen Noël , Marchal Alain
Published: October 2005

Electromagnetometry can be used to track articulatory movements during speech production by means of small electromagnetic receivers attached to the articulators. This study was aimed at determining the measurement accuracy of the Movetrack system marketed by Botronic (Sweden). The average difference between a position transduced by Movetrack and the actual position, obtained from a precision mechanical device, was less than 0.4 mm, when the receiver was placed in the midsagittal plane and parallel to the transmitters at a distance of about 25 cm from each transmitter. Higher deviations were observed when the receiver was tilted with respect to the transmitters. Thus the device appears to be capable of delivering accurate measures of position for rigid anatomical structures like the jaw, which are not likely to produce tilt.
An improved procedure for the determination of ground parameters using level difference measurements
Authors: Sabatier James M. , Raspet Richard , Frederickson Carl K.
Published: October 2005

Attenborough has developed a theory to predict the ground impedance from four physical parameters; the flow resistivity (σ), the tortuosity (T), the porosity (Ω), and the pore shape factor (sp). This theory has been used to determine the flow resistivity, tortuosity, and effective flow resistivity (sp2σΩ) by fitting level difference measurements above the soil surface to the theory [Soil Sci. Soc. Am. J. 54, 658–672 (1990)]. Subsequent work indicated that this procedure may be indeterminate. A numerical and analytic study is performed to identify and remove the indeterminacy. A new form of the Attenborough four parameter model which is a function of two independent variables is developed and is shown to be determinate for simulated data and for data published previously. These new variables are the reduced flow resistivity and reduced tortuosity. Since there are only two independent variables, an additional measurement is required to determine σeff, T, and Ω. Two measurements are suggested to remove the indeterminacy.
Sound field computations in a stratified, moving medium
Authors: Wilson D. Keith
Published: October 2005

A numerical method for computing the sound field in a stratified, moving medium is described. The method is quite similar to the well-known fast-field program (FFP), except that the wave equation is modified to account for fluid and/or source motion. The computation requires a two-dimensional horizontal wave-number spectrum rather than a one-dimensional radial wave-number spectrum as required by previous FFPs. As an example, the sound pressure produced by a point source in a neutrally buoyant atmospheric shear layer is calculated. A far-field approximation, which reduces the calculation to a one-dimensional spectrum, is also discussed.
The acoustic pressure waveform from small unconfined charges of plastic explosive
Authors: Ford Roy D. , Saunders David J. , Kerry Geoffrey
Published: October 2005

The pressure waveform has been measured at distances to 1000 m from 125-g and 1-kg unconfined charges of plastic explosive. Pressure waveforms in free air have been compared with other published data and TNT equivalence factors for PE4 are given. Propagation over concrete and water are shown to yield similar waveforms, although the yield factor of the charge appears to be somewhat less over water. Propagation over grass gives waveforms of quite a different character, with much of the high-frequency content being removed. The positive peak overpressure decays more rapidly with distance than it does over concrete. ANSI Standard S2.20-1983 is shown to be more suitable for predicting the peak overpressure over concrete or water than over grass. The sound exposure level (SEL) is calculated and empirical expressions are given in terms of charge size, distance, and surface. The effects of C-weighting are considered, and it is concluded that errors in the application of empirical equations are likely to be increased because of the effects of scaling on the frequency content.
Magnetoelastic surface shear waves due to a momentary point source
Authors: Chattopadhyay A. , Maugin G. A.
Published: October 2005

In this paper, the propagation of shear waves in a layer over a semi-infinite medium, both being conductors, due to a momentary point source has been discussed using Green’s function technique. Two cases have been considered. In the first case, the upper layer is of constant thickness and in the second case, the upper layer is of a slowly variable thickness. It has been shown that the displacement is very large when a certain relation between the thickness of the layer, frequency, and phase velocity holds and this may cause fracture. Dispersion curves have been drawn and the effect of the magnetic field is distinctly marked.
Influence of inharmonicity on the tuning of a piano—Measurements and mathematical simulationa)
Authors: Lattard Jean
Published: October 2005

It is well known that inharmonicities in piano string vibrations and especially any irregularities in their progression, are partially responsible for the difficulties encountered in tuning the instrument. This paper studies the quantitative influence of inharmonicities by including their actions in the mathematical relations governing musical intervals. The measurement of fundamental and rank 2, 3, 4, 5 partial frequencies of the piano strings is discussed, and a method using a relatively simple electronic apparatus is described. Results obtained on a grand piano are given. These values are entered in a mathematical simulation of tuning. The first-hand calculation procedure used successive steps inspired from the classical tuning process: proposed beat rates, verification on other intervals, corrections. A much easier simulation is now obtained with a personal computer using either a commercially available spreadsheet software, or a specifically developed small program written in basic. Results of the simulation are precisely determined fundamental frequencies. Test of tuning the measured piano by zero beating it with calculated frequencies was successful. Several similar experiments were made on other pianos, leading to the idea of a ‘‘personalized tuning’’ for each instrument, provided an adequate electronic generator is available.
Acoustic relaxation of fluid-saturated porous samples
Authors: Zhu Guozhen , Pan Yongdong
Published: October 2005

The acoustic relaxation of fluid-saturated porous samples under flexural vibration is studied experimentally and theoretically. Artificial samples are used for the purpose of avoiding complications of natural samples. The viscosity (controlled by temperature) is selected as the variable for studying the attenuation and elastic modulus of the samples so that the experimental points cover the relaxation peak. Based on Biot’s theory, the modulus of the plate at flexural vibration and the pore pressure distribution along its thickness are derived. The numerically computed theoretical curve agrees with experimental data in two respects: the location of the relaxation peak and the elastic modulus at low viscosity (corresponding to low frequency). The energy dissipation per unit volume along the thickness computed at various viscosity shows that the total dissipation reaches a maximum at a certain viscosity that agrees quantitatively with experimental results. The relaxation mechanism proposed by White [Geophysics 51, 742 (1986)] and Dunn [J. Acoust. Soc. Am. 79, 1709 (1986); 81, 1259 (1987)] is examined and is found to be valid in artificial samples at flexural vibration.
Near-field characteristics of circular piston radiators with simple support
Authors: He Cheng , Hay Alex E.
Published: October 2005

A closed-form expression for the pressure field produced by a circular piston radiator with simply supported boundary condition and continuous-wave excitation is derived. The method of Hasegawa et al. [J. Acoust. Soc. Am. 74, 1044–1047 (1983)], developed for a uniformly vibrating piston, is extended to include the nonuniform case. The resulting expression is valid for all field points and for large ratio of source diameter to wavelength. The average pressure on the surface of a circular receiver as a function of receiver size and distance from the transducer is also calculated.
A simple derivation of the Green’s function for a rectangular Helmholtz resonator at low frequency
Authors: Vandegrift Guy
Published: October 2005

The Green’s function for a Helmholtz resonator is obtained by considering a closed box containing a point source radiator. Using the method of images, a low-frequency approximation is derived for the special case of a rectangular box.
Solution of the Euler field equations for plane-wave scattering by an end-capped cylinder via the uniform geometrical theory of diffraction
Authors: Pitts Todd A. , Selfridge Richard H. , Chabries Douglas M.
Published: October 2005

An approximate solution to the problem of plane-wave scattering by a finite, hemispherically terminated (end-capped) cylinder of circular cross section is found via the uniform geometrical theory of diffraction (UTD). Both Dirichlet and Neumann boundary conditions are considered. A scattering model is applied in which a reduced set of geodesic paths or rays is used to obtain the acoustic pressure field at any point in space where the UTD is valid. A standard method for obtaining transfer functions describing the pressure field changes along the geodesic paths is briefly outlined. This method uses asymptotic expansion of the exact solutions to two related problems (plane wave scattering by a sphere and an infinite cylinder) whose ray sets together comprise the total ray set for the end-capped cylinder problem. An approximation to the total pressure field is then found for the case when an impinging plane wave is scattered by an end-capped cylinder. The predicted scattered fields demonstrate the expected similarities to and differences from the field patterns produced by the infinite cylinder and sphere targets. The origin and significance of a discontinuity in the pressure field predictions is discussed.
Time-domain analysis of transient structural acoustics problems based on the finite element method and a novel absorbing boundary element
Authors: Kallivokas Loukas F. , Bielak Jacobo
Published: October 2005

This paper is concerned with the development of an efficient and accurate finite element procedure for the solution directly in the time domain of transient problems involving structures submerged in an infinite acoustic fluid. The central feature of the procedure is a novel impedance, or, absorbing boundary, element that is used to render the computational domain finite. This element is local in both time and space, and is completely defined by a pair of symmetric stiffness and damping matrices. It thus can be attached directly to the adjoining fluid elements within the computational domain using standard assembly procedures. Due to its local nature, it also preserves the overall structure of the global equations of motion, including symmetry and sparseness. Thus the new impedance element makes it possible to solve complex transient exterior structural acoustics problems via existing finite element software for interior problems by just incorporating this element into current finite element libraries. Standard step-by-step temporal integration techniques can then be used to solve the resulting equations of motion. Even though the focus is in the time domain, the same equations of motion can naturally be used to determine the solution under time-harmonic excitation directly in the frequency domain. In this paper the new methodology is presented in a two-dimensional setting, using as a model an infinite cylindrical thin elastic circular shell submerged in an acoustic fluid. The absorbing element, however, can be used equally well with any arbitrary (possibly nonlinear) two-dimensional structure. Explicit formulas for the element matrices are included, and numerical examples, involving both transient scattering and radiation model problems, are given for the homogeneous shell as well as for a shell with a concentrated mass to illustrate the validity and accuracy of the new procedure.
Transfer functions for acoustic emission transducers using laser interferometry
Authors: Jacobs Laurence J. , Woolsey Craig A.
Published: October 2005

A high-fidelity, broadband laser interferometer is used to develop a transfer function for a piezoelectric, acoustic emission transducer. The transfer function, which converts the relative transducer output to an absolute measurement of surface velocity, uses a methodology that accounts for the transducer’s frequency bias. This technique treats the piezoelectric transducer as a corruptive channel and develops a filter that models this bias on a measured acoustic emission signal. This filter, which is developed with a signal processing software package, is based on comparisons between signals measured with a laser interferometer and those made with a piezoelectric transducer. The accuracy of this filter is verified and it is used to remove the transducer-related features from simulated acoustic emission signals.