bluuebunny/crossref_metadata_2025 huggingface dataset:
Active vibration and structural acoustic control of shape memory alloy hybrid composites: Experimental results
Authors: Rogers Craig A.
Published: October 2005

Shape memory alloy hybrid composites have been shown both by analytical simulations and experiments to be effective adaptive materials for active vibration and structural acoustics control [Rogers and Robertshaw, Engineering Science Preprints 25, ESP25.88027, Society of Engineering Sciences (1988) and ASME Paper 88-WA/DE-9 (1988); Rogers et al., in Proceedings of the 30th Structures, Structural Dynamics, and Materials Conference, AIAA Paper 89-1389 (1989)]. Structural acoustics is the study of how elastic structures radiate or receive sound, and in its most fundamental form involves the simultaneous solution of the differential equations describing the structure and fluid media with appropriate boundary conditions between the two, i.e., a ‘‘fully’’ coupled analysis. This paper will review the state-of-the-art of active control utilizing shape memory alloy hybrid composites and present experimental results showing active dynamic tuning by a method called active strain energy tuning (ASET), active control of sound radiation from a clamped-baffled beam, and transient vibration control of a cantilevered beam.
Replacing tracheoesophageal voicing sources using LPC synthesis
Authors: Qi Yingyong
Published: October 2005

The feasibility of using the linear predictive coding (LPC) technique to replace the voicing sources of tracheoesophageal speech was explored. Four vowels, [i], [a], [e], [u], and one diphthong [ou], produced by two male and two female tracheoesophageal speakers were analyzed by the LPC autocorrelation method. Normalized prediction error functions were used to choose the algorithm and the control parameters of the analysis. Poles of the vocal tract transfer function were selected from frames whose normalized prediction errors were close to minimum with criteria derived from transfer functions of normally produced vowels. Vowels were synthesized with the reconstructed transfer function and a synthesized excitation input. Results of an identification task indicated that the synthesized vowels were highly intelligible, and the gender of the speaker was better identified from the synthesized vowels than from the original tracheoesophageal vowels.
Speechreading sentences with single-channel vibrotactile presentation of voice fundamental frequency
Authors: Eberhardt Silvio P. , Bernstein Lynne E. , Demorest Marilyn E. , Goldstein Moise H.
Published: October 2005

The main goal of this study was to investigate the efficacy of four vibrotactile speechreading supplements. Three supplements provided single-channel encodings of fundamental frequency (F0). Two encodings involved scaling and shifting glottal pulses to pulse rate ranges suited to tactual sensing capabilities; the third transformed F0 to differential amplitude of two fixed-frequency sinewaves. The fourth supplement added to one of the F0 encodings a second vibrator indicating high-frequency speech energy. A second goal was to develop improved methods for experimental control. Therefore, a sentence corpus was recorded on videodisc using two talkers whose speech was captured by video, microphone, and electroglottograph. Other experimental control issues included use of visual-alone control subjects, a multiple-baseline, single-subject design replicated for each of 15 normal-hearing subjects, sentence and syllable pre- and post-tests balanced for difficulty, and a speechreading screening test for subject selection. Across 17 h of treatment and 5 h of visual-alone baseline testing, each subject performed open-set sentence identification. Covariance analyses showed that the single-channel supplements provided a small but significant benefit, whereas the two-channel supplement was not effective. All subjects improved in visual-alone speechreading and maintained individual differences across the experiment. Vibrotactile benefit did not depend on speechreading ability.
Masker fringe and binaural detection
Authors: Gilkey Robert H. , Simpson Brian D. , Weisenberger Janet M.
Published: October 2005

Yost [J. Acoust. Soc. Am. 78, 901–907 (1985)] found that the detectability of a 30-ms dichotic signal (Sπ) in a 30-ms diotic noise (No) was not affected by the presence of a 500-ms dichotic forward fringe (Nπ). Kollmeier and Gilkey [J. Acoust. Soc. Am. 87, 1709–1719, (1990)] performed a somewhat different experiment and varied the onset time of a 25-ms Sπ signal in a 750-ms noise that switched, after 375-ms, from Nπ to No. In contrast to Yost, they found that the Nπ segment of the noise reduced the detectability of the signal even when the signal was temporally delayed well into the No segment of the noise and suggested that the Nπ segment of noise acted as a forward masker. To resolve this apparent conflict, the present study investigated the detectability of a brief Sπ signal in the presence of an No masker of the same duration as the signal. The masker was preceded by quiet or an Nπ forward fringe and followed by quiet, an No, or Nπ backward fringe. The present study differs from most previous studies of the effects of the masker fringe in that the onset time of the signal was systematically varied to examine how masking changes during the time course of the complex fringe–masker–fringe stimulus. The results failed to replicate those of Yost in that an Nπ forward fringe reduced the detectability of the signal, and agreed with those of Kollmeier and Gilkey in that thresholds were elevated well after the offset of the Nπ segment of the noise. The addition of an Nπ backward fringe was also shown to reduce the detectability of the signal. Possible reasons for differences between the results of the present study and those of Yost are evaluated. Results are discussed in the context of models of binaural detection.
Electrically evoked whole-nerve action potentials: Data from human cochlear implant users
Authors: Brown Carolyn J. , Abbas Paul J. , Gantz Bruce
Published: October 2005

This study describes a method for recording the electrically evoked, whole-nerve action potential (EAP) in users of the Ineraid cochlear implant. The method is an adaptation of one originally used by Charlet de Sauvage et al. [J. Acoust. Soc. Am. 73, 615–627 (1983)] in guinea pigs. The response, recorded from 11 subjects, consists of a single negative peak that occurs with a latency of approximately 0.4 ms. EAP input/output functions are steeply sloping and monotonic. Response amplitudes ranging up to 160 μV have been recorded. Slope of the EAP input/output function correlates modestly (approximately 0.6–0.69) with results of tests measuring word recognition skills. The refractory properties of the auditory nerve were also assessed. Differences across subjects were found in the rate of recovery from the refractory state. These findings imply that there may be difference across subjects in the accuracy with which rapid temporal cues can be coded at the level of the auditory nerve. Reasonably strong correlations (approximately 0.74–0.85) have been found between the magnitude of the slope of these recovery curves and performance on tests of word recognition.
Spectral weights in profile listening
Authors: Berg Bruce G. , Green David M.
Published: October 2005

The COSS analysis suggested by Berg [B. G. Berg, J. Acoust. Soc. Am. 86, 1743–1746 (1989)] is applied to a profile listening task. The listener’s task is to detect an increment in the level of the middle component of an n-component spectrum. The overall level of the components is randomly selected from a 20-dB range on each presentation; thus the detection task is essentially one of detecting a change in spectral shape. To implement the COSS analysis, a small perturbation in level is added to each component of the complex. COSS functions are generated from these perturbations, and the spectral weight that the listener assigns to each component is estimated. Data are reported for n=3,5, and 11 components and for perturbations with standard deviations of 0.5, 1, and 2 dB. The estimated weights are similar to those derived for an optimum detector; namely, the level at the signal component is compared with the average level of the nonsignal components. This result supports the view that profile analysis involves an across-channel comparison process. The pattern of weights also provides insight into differences among listeners. In a separate experiment, the spectral weights of a very poor profile listener are estimated, and the pattern of the weights suggests reasons for the inferior detection performance.
Temporal integration in amplitude modulation detection
Authors: Sheft Stanley , Yost William A.
Published: October 2005

Thresholds for detecting sinusoidal amplitude modulation (AM) of a wideband noise carrier were measured as a function of the duration of the modulating signal. The carrier was either: (a) gated with a duration that exceeded the duration of modulation by the combined stimulus rise and fall times; (b) presented with a fixed duration that included a 500-ms carrier fringe preceding the onset of modulation; or (c) on continuously. In condition (a), the gated-carrier temporal modulation transfer functions (TMTFs) exhibited a bandpass characteristic. For AM frequencies above the individual subject’s TMTF high-pass segment, the mean slope of the integration functions was −7.46 dB per log unit duration. For the fringe and continuous-carrier conditions [(b) and (c)], the mean slopes of the integration functions were, respectively, −9.30 and −9.36 dB per log unit duration. Simulations based on integration of the output of an envelope detector approximate the results from the gated-carrier conditions. The more rapid rates of integration obtained in the fringe and continuous-carrier conditions may be due to ‘‘overintegration’’ where, at brief modulation durations, portions of the unmodulated carrier envelope are included in the integration of modulating signal energy.
Restarting the adapted binaural system
Authors: Hafter Ervin R. , Buell Thomas N.
Published: October 2005

Previous experiments using trains of high-frequency filtered clicks have shown that for lateralization based on interaural differences of time or level, there is a decline in the usefulness of interaural information after the signal’s onset when the clicks are presented at a high rate. This process has been referred to as ‘‘binaural adaptation.’’ Of interest here are the conditions that produce a recovery from adaptation and allow for a resampling of the interaural information. A train of clicks with short interclick intervals is used to produce adaptation. Then, during its course, a treatment such as the insertion of a temporal gap or the addition of another ‘‘triggering’’ sound is tested for its ability to restart the binaural process. All of the brief triggers tested are shown to be capable of promoting recovery from adaptation. This suggests that, while the binaural system deals with the demands of high-frequency stimulation with rapid adaptation, it quickly cancels the adaptation in response to stimulus change.
Nonlinear vibration properties of felt pads
Authors: Dunlop J. I.
Published: October 2005

The dynamic modulus and damping loss of felt pads have been measured in the frequency range 50–160 Hz using a reaction mass vibration system. The properties of three different felts of densities 145, 190, and 340 kg/m3 were investigated at pressure loadings of 4.9 and 7 kPa. The values of dynamic compression moduli obtained were in good agreement with those predicted from fiber mass compression theory. The moduli were dependent on the amplitude of the vibration, decreasing by up to 50% at large amplitudes of vibration for one of the felts investigated. The damping loss was observed to be independent of frequency, it being characterized by a constant loss angle, or tan δ which varied from 0.1 at low amplitudes of vibration to 0.4 at high amplitudes. Both of these amplitude-controlled effects have been attributed to the nonlinearity of the elasticity and friction effects resulting from film slippages that occur during compression and rarefaction. The nonlinearity of the system results in the generation of harmonics of the fundamental forcing frequency in its response.
An effective method for solving the hyper-singular integral equations in 3-D acoustics
Authors: Chien C. C. , Rajiyah H. , Atluri S. N.
Published: October 2005

The application of the boundary integral methods to the problem of acoustics, exterior to a three-dimensional surface, suffers, in general, from the nonexistence of nonuniqueness of its solutions at frequencies that are characteristic of the associated interior problem. The formulation that is most suitable for numerical implementation still appears to be that proposed by Burton and Miller [Proc. R. Soc. London Ser. A 323, 201–210 (1971)]. However, the hypersingular kernels present in such a formulation render it computationally unattractive. Previous attempts to regularize such hypersingular kernels involved the use of double surface integrals, or implicit use of tangential operators, or closed-form evaluations of hypersingular integrals. The method of double surface integrals is computationally highly inefficient, even though it allows higher-order interpolation schemes on the surface. The other two approaches are more conducive to the assumption of a constant value for each of the variables (pressure and its normal gradient) over each of the descretized surface subdomains.

The present work is concerned with the development of a procedure to regularize the hypersingular integral found in the Burton and Miller formulation, through a novel method by employing certain identities for the hypersingular integrals arising in an associated integral equation for the Laplace equation in the interior domain. It is feasible to use arbitrary-order C0 interpolations for pressure and its normal derivative on the three-dimensional surface in the present approach. Even in such a case, the contribution to the hypersingular integrals over a small patch near the source point can be evaluated indirectly without using any special quadrature schemes, through a consideration of simple solutions to the associated Laplace equation in the interior domain. It should be noted here that there is no extra effort required in computing the potential kernels since they are a subset of the kernels found in the acoustic problem. In order to demonstrate the simplicity, robustness, and efficiency of the proposed method, numerical results with quadratic isoparametric C0 surface elements are presented for both radiation and scattering problems. Comparisons are made with close-form solutions and other existing formulations.
Resonance scattering from submerged elastic spheroids of high aspect ratios and its three-dimensional interpretation
Authors: Werby M. F. , Gaunaurd G. C.
Published: October 2005

Numerical predictions for the end-on and broadside backscattering cross sections of elastic spheroids submerged in water are obtained. The material composition of the spheroids is aluminum, tungsten carbide (WC), and steel. The (nondimensional) frequency range examined is: 5≤kL/2≤26, where k is the wave number in the water and L is the length of the spheroid. The aspect ratios L/D studied here vary in the range 4≤L/D≤10 for the end-on incidence case, for the three materials. These higher aspect ratios are associated with more relevant shapes and present a substantially higher computational challenge. The broadside form functions are examined only for steel of aspect ratios of L/D=2, 3, 4, and 5. A systematic study of the predicted scattering cross sections suggests in all cases that the resonance features present in them are consistent with a (leaky) Rayleigh-like interpretation of these resonances, and with the underlying Rayleigh wave that causes them.
The Kirchhoff approximation for acoustic scattering from a rough fluid–elastic solid interface
Authors: Dacol Dalcio K.
Published: October 2005

The Kirchhoff approximation for wave scattering from a penetrable surface is applied to the case of acoustic scattering from a rough fluid–elastic solid interface. An approximation to a surface integral yields a simpler expression for the scattering amplitude. It turns out to be similar to an approximation previously introduced by Hagfors [J. Geophys. Res. 69, 3779 (1964); J. Geophys. Res. 71, 379 (1966)] to study radar backscattering from the moon. This simpler version produces results that compare favorably with exact numerical results for the case of periodic fluid–solid interfaces. This approximation is well suited to describe acoustic scattering from a randomly rough fluid–solid interface. To illustrate this point, the coherent field reflection coefficient as a function of angle of incidence and the incoherent scattering coefficient as a function of scattering angle were computed and plotted for the case of a model randomly rough fluid–solid interface with acoustical parameters of a water–granite interface and compared with corresponding results from a previously developed renormalized perturbation theory. The geometrical parameters of the randomly rough interface (i.e., the rms roughness and the correlation length) were chosen so that the perturbation results are expected to be accurate in order to provide another test of the reliability of the approximation developed in this article. Overall this approximation is satisfactory, but since it is a single scattering theory it fails to incorporate multiple scattering effects displayed by the renormalized perturbation theory results. These effects, such as those due to Rayleigh angle phenomena, are small in the domain of validity of the Kirchhoff approximation.
Infrasonic ambient noise in the ocean due to atmospheric pressure fluctuations on the surface
Authors: Buckingham Michael J.
Published: October 2005

The theory of infrasonic ambient noise in a semiinfinite, isotropic ocean due to random wind-pressure fluctuations acting on the sea surface is reexamined. The surface pressure field is modeled as a Poisson distribution of point forces. This provides a boundary condition that must be satisfied by the solution of the homogeneous Helmholtz equation for the resultant acoustic field in the ocean. Using this solution the spatial coherence function of the ambient noise is constructed, from which the directionality in the vertical is derived and shown to be the same as that for the noise field produced by a random distribution of vertical dipoles on the surface. The power spectrum of the noise scales with the point spectrum of the wind-pressure fluctuations, which is determined empirically from published measurements of wind-pressure spectra taken over water, and with the square of the Helmholtz number for the turbulent sources. Since the Helmholtz number is very much less than unity, it is concluded that wind turbulence is an inefficient mechanism for producing sound in the ocean. A comparison of the final result for the ambient noise power spectrum with measured noise spectra, taken by several investigators in various parts of the world, indicates that wind turbulence generally makes an insignificant contribution to the infrasonic ambient noise in the ocean.
Single-hydrophone localization
Authors: Frazer L. Neil , Pecholcs Peter I.
Published: October 2005

It is shown that Clay’s single-hydrophone time-domain localization algorithm is a member of a large class of algorithms {χmn} that require exact knowledge of the source time function w(t). The single-hydrophone Clay algorithm is χ∞2; however, χ∞1 often localizes better than χ∞2. Next, five new families of single-hydrophone localization algorithms are introduced. The first of these, {μmn}, also requires a knowledge of w(t), and is introduced mainly to emphasize that Clay localization is the ratio of norms. The four new localizer families, {φmn}, {θmn}, {βmn}, and {νmn}, require almost no knowledge of w(t). These new algorithms actually yield an estimate of the source spectrum W(ω), as well as the location of the source. The localizers φ, θ and ν work best when ‖W(ω)‖, the amplitude spectrum of the source, is smooth, although w(t) need not be a pulse. The β localizers work best when w(t) is a pulse. If it happens that an estimate of W(ω) is available, then φ, θ, β, and ν can use this information and their performance is enhanced. A similar enhancement is obtained when two hydrophones are available.
Comodulation masking release as a function of bandwidth and time delay between on-frequency and flanking-band maskers
Authors: Moore Brian C. J. , Schooneveldt Gregory P.
Published: October 2005

The threshold for a signal masked by a narrow band of noise centered at the signal frequency (the on-frequency band) may be reduced by adding to the masker a second band of noise (the flanking band) whose envelope is correlated with that of the first band, an effect called comodulation masking release (CMR). This paper examines CMR as a function of masker bandwidth and time delay between the envelopes of the on-frequency and flanking bands. The 1.0-kHz sinusoidal signal had a duration of 400 ms. The on-frequency band was presented alone (reference condition) or with the flanking band. The flanking-band envelope was either correlated or uncorrelated with that of the on-frequency band. Flanking-band center frequencies ranged from 0.25–2.0 kHz. The flanking band was presented either in the same ear as the on-frequency band (monaural condition) or in the opposite ear (dichotic condition). The noise bands had bandwidths of 6.25, 25, or 100 Hz. In the correlated conditions, the flanking-band envelope was delayed with respect to that of the on-frequency band by 0, 5, 10, or 20 ms. For the 100-Hz bandwidth, CMRs were small (typically less than 1 dB) in both monaural and dichotic conditions at all delay times. For the 25-Hz bandwidth, CMRs were about 3.5 dB for the 0-ms delay, and decreased to about 1.5 dB for the 20-ms delay. For the 6.25-Hz bandwidth, CMRs averaged about 5 dB and were almost independent of delay time. The results suggest that the absolute delay time is not the critical variable determining CMR. The magnitude of CMR appears to depend on the correlation between the envelopes of the on-frequency and flanking bands. However, the results do not support a model of CMR that assumes that signal threshold corresponds to a constant change in across-band envelope correlation when the correlation is transformed to Fisher’s z.
Ray synthesis of Lamb wave contributions to the total scattering cross section for an elastic spherical shell
Authors: Kargl Steven G. , Marston Philip L.
Published: October 2005

The optical theorem relates the extinction cross section σe(ka) to the forward-scattering amplitude f (θ=0,ka). Here, θ denotes the scattering angle, k is the wavenumber of the incident sound, and a is the radius of the scatterer. If the absorption by the scatterer is negligible so that the scatterer is elastic, σe is equal to the total scattering cross section σt. By applying this theorem to the partial wave series for f (0,ka), an expression can be obtained for σt for an elastic spherical shell in water. However, the series representation of σt does not facilitate a direct understanding of the rich structure caused by the shell’s elastic response. In particular, the elastic response is attributable to leaky Lamb waves. A generalization of the geometrical theory of diffraction [P. L. Marston, J. Acoust. Soc. Am. 83, 25–37 (1988)] is employed to synthesize f (0,ka). This simple ray acoustic synthesis contains a component for ordinary diffraction by the shell and distinct contributions for the individual Lamb waves that can be excited on the shell. A comparison of numerical computations for σt utilizing the exact partial wave series and the ray synthesis shows good agreement in the description of the resonance structure. The relevant range of ka for this comparison is 7<ka<100. The elastic material of the shell is 440c stainless steel and the inner-to-outer radius ratio is b/a=0.838. Dispersion curves and radiation damping for Lamb waves were calculated by Watson transform methods. The structure in σt(ka) due to Lamb waves may also be depicted as a manifestation of forward glory scattering and experimental evidence for the forward glory is noted.
Longitudinal resonances in the form function for backscattering from a spherical shell: Fluid shell case
Authors: Kargl Steven G. , Marston Philip L.
Published: October 2005

Reverberations of longitudinal waves in a hollow shell can strongly affect the backscattering amplitudes at frequencies associated with a thickness resonance. The phenomena are studied for the idealized case of vanishing shear stresses in the shell material by taking that material to be an inviscid fluid. The sound speed cL for the fluid is taken to be that of longitudinal waves in elastic materials of interest, the surrounding fluid being water. An exact partial-wave series gives the form function  f for backscattering and plots of ‖ f ‖ as a function of ka display resonance features where a denotes the outer radius of the shell. These features are also recovered in a direct geometrical calculation of  f that sums the amplitudes associated with rays multiply reflected within the curved shell. This geometric synthesis shows that the effects of curvature are essential to modeling  f. In addition to numerical comparisons with the partial-wave series, the geometrical calculation is tested by considering several limiting cases and results anticipated from elementary consideration are recovered.
The longitudinal pulse velocity in finite cylindrical cores
Authors: Blair D. P.
Published: October 2005

The dynamic finite-element method (DFEM) was used in order to numerically obtain the velocity of pulse propagation along cylindrical cores. The numerical results show that the velocity of the axial component of the pulse gradually increases from the bar-wave velocity Vb, to the (infinite body) compressional wave velocity Vp, as D/λ goes from zero to approximately 1.0, where D is the diameter of the core and λ is the appropriate pulse wavelength. It is also shown that the velocity of the radial component of the pulse approaches Vp provided that D/λ>1 and L/D>2, where L is the length of the core. The DFEM results agree with three of the four sets of available axial pulse data obtained for aluminum cores, and it is suggested that the fourth set of data may have been influenced by the particular time pick used to obtain the velocity. The present numerical study also shows that any variations in either the spatial or relative spectral distributions of the sources are unlikely to be the cause of any large discrepancies. Since λ is a spectral domain parameter, its appropriate value is not obvious in any pulse test, and thus an alternative parameter is suggested. In this regard, it is shown that condition D/λ>1 may be replaced by DT/(Lτ)>6, where T is the pulse travel time and τ the rise time. Although the numerical results were obtained for two particular elastic materials, they should be applicable to most cylindrical cores provided D/λ>0.5, and imply that the current ISRM and ASTM recommendations for the dynamic testing of rock cores can be relaxed.
The propagation of short pulses of ultrasound from a circular source coupled to an isotropic solid
Authors: Ilan A. , Weight J. P.
Published: October 2005

New finite-difference formulations in cylindrical coordinates are given allowing calculations to be made of the field radiated by a circular source coupled to an isotropic solid. Theoretically predicted results are compared with earlier theoretical and experimental results for the case of a pointlike source. Calculations of the spacial distribution of the field radiated by a finite-sized circular source are compared with stroboscopic visualizations of the field radiated by a transducer typical of those used in nondestructive evaluation using ultrasound. Calculated field-point particle-velocity waveforms are compared with experimentally measured waveforms received using a miniature piezoelectric receiver directly coupled to the solid surface as well as with calculated results obtained using an impulse-response model. Good agreement between theoretical and experimental results is observed. The field radiated into solids is described in terms of plane and edge waves. The results are of particular significance for explaining the limitations of nondestructive evaluation using ultrasonic pulse-echo techniques.
Comment on ‘‘Multiple scattering by finite regular arrays of resonators’’ [J. Acoust. Soc. Am. 8
7, 25–41 (1990)]
Authors: Tolstoy I.
Published: October 2005

Given a sound field incident upon a system of interacting resonant monopoles, the individual response of each scatterer can be measured in the near field.
Bifurcation structure of bubble oscillators
Authors: Parlitz U. , Englisch V. , Scheffczyk C. , Lauterborn W.
Published: October 2005

Methods from chaos physics are applied to a model of a driven spherical gas bubble in water to determine its dynamic properties, especially its resonance behavior and bifurcation structure. The dynamic properties are described in a growing level of abstraction by radius-time curves, trajectories in state space, strange attractors in the Poincaré plane, basins of attraction, bifurcation diagrams, winding number diagrams, and phase diagrams. A sequence of bifurcation diagrams is given, exemplifying the recurrent pattern in the bifurcation set and its relation to the resonances of the system. Period-doubling cascades to chaos and back (‘‘period bubbling’’) are a prominent recurring feature connected with each resonance (demonstrated for period-1, period-2, and period-3 resonances, and observed for some higher-order resonances). The recurrent nature of the bifurcation set is most easily seen in the phase diagrams given. A similar structure of the bifurcation set has also been found for other nonlinear oscillators (Duffing, Toda, laser, and Morse).
Wave motions in some composite, porous, and layered media
Authors: Junger Miguel C.
Published: October 2005

Fluid- and structure-borne waves are governed by the balance between elastic and inertia forces embodied, respectively, in the compliance and density of the wave-bearing medium. This paper is concerned with a class of composite, porous, and layered media where compliance is dominated by one medium and density by another. A number of dilatational and interface wave motions are analyzed, some familiar and others that have received little attention in the literature. The purpose, in all these cases, is to formulate an elementary mathematical model that captures the basic physical phenomenon. Particular emphasis is placed on the interpretation of frequency ranges where certain media, either layered or porous, are unable to sustain wave motions.
Conservation of energy in the oscillations of laser-induced cavitation bubbles
Authors: Ward B. , Emmony D. C.
Published: October 2005

The oscillations of Nd:YAG laser-induced cavitation bubbles close to a free liquid surface are studied using a Mach–Zehnder interferometer and high-speed photography. For an initial bubble depth of 2.6 mm and a laser energy of 5.1 mJ, three complete expansion cycles are observed. During the second cycle, a high-speed liquid jet is directed away from the free surface and the whole bubble is displaced downwards. Particular attention is paid to the production of acoustic transients during the initial and subsequent expansions of the cavitation bubbles. Optical measurements of the changes in refractive index of the liquid yield the pressure profiles of these acoustic waves. The respective energies of the four transients are found to be 101, 59, 55, and 2 μJ; the energies of the three cavity expansions are 640, 350, and 70 μJ. By conservation of energy, it follows that the thermal energies given out during the initial supersonic expansions of the second and third acoustic waves are 230 and 220 μJ, respectively. These are large proportions of the initial shock-wave energies.
On acoustical impulse propagation in a moving inhomogeneous atmospheric layer
Authors: Chunchuzov I. P. , Bush G. A. , Kulichkov S. N.
Published: October 2005

In the present work a solution is obtained by the method of normal modes, which describes the sound field of a point impulse source in the atmosphere with definite temperature and wind velocity profiles and ground impedance. This solution describes the impulse shape transformation in different directions relevant to wind velocity involving the low-frequency case, when the ray approach becomes invalid. The impulse shape evolution during guided and antiguided propagation (in the shadow region) is in good qualitative agreement with the shape observed in the experiment. The change of the impulse shape in time is observed in the experiment during transition of the boundary atmospheric layer from a convective state to one with a stable temperature inversion. The experimental measurements and theoretical estimations show that the nearground acoustical waveguide is formed mainly due to wind stratification in the boundary layer. Solving of the direct problem also shows a principal possibility of inclined sounding of the boundary atmospheric layer.
Further investigation of nonpropagating solitons and their transition to chaos
Authors: Wei Rongjue , Wang Benren , Mao Yi , Zheng Xiaoyu , Miao Guoqing
Published: October 2005

Some new features of the nonpropagating hydrodynamic solitons are investigated experimentally, in particular, the collision dynamics of such solitons, the coexistence of the two dominant nonlinear phenomena, the soliton and chaos, as well as the transition of one to the other. Open questions are raised by this simple experiment.
Inversion of leaky Lamb wave data by simplex algorithm
Authors: Karim M. R. , Mal A. K. , Bar-Cohen Y.
Published: October 2005

A numerical procedure is presented for the inversion of leaky Lamb wave (LLW) data to determine certain material properties of a waveguide, using a modified version of the simplex algorithm. The technique is capable of computing the parameter values that best fit a particular set of data, given an analytical model of the associated phenomenon containing any number of variables and parameters. The basic theoretical concepts involved are reviewed, and the versatility and simplicity of the method are illustrated by examples. The inversion scheme is used to estimate the elastic properties and thickness of an adhesive layer between two aluminum plates and the elastic constants of a unidirectional graphite/epoxy composite laminate. The limitations of the LLW data in the determination of the elastic constants of a composite are discussed.
Scattering by acoustically large corrugated planar surfaces
Authors: Kriegsmann Gregory A.
Published: October 2005

The problem of the scattering of acoustic waves by a large, sound soft (hard), corrugated surface in two dimensions is addressed. The surface undulates periodically up to a characteristic length L beyond which it becomes planar. The height of the corrugation is measured by a characteristic length a and its period by Λ. The ordering of these scales is taken to be λ∼Λ∼a≪L, where λ is the wavelength of the incident plane acoustic wave. The method of matched asymptotic expansions is applied to analyze the problem in the limit as ε=a/L→0. This approach is both mathematically systematic and physically intuitive. The results that are obtained in the far field are identical to those obtained by using a finite beam approximation for a sound hard surface in two dimensions and almost the same for a sound soft case; the only difference being a sine factor that yields correct boundary behavior. Results for three-dimensional scattering problems are also derived and are compared similarly.
Beams and modes for scattering from weak bonding flaws in a layered aluminum plate
Authors: Lu I. T. , Felsen L. B. , Klosner J. M. , Gabay C.
Published: October 2005

Location and identification of faults in multilayer elastic materials by ultrasound is aided by a physically based parametrization of the input, scattered, and detected fields. When the transducer input is beam shaped, the beam-to-mode conversion in the unflawed layered environment suggests a ‘‘good’’ parametrization in terms of a self-consistent hybrid beam-mode format. The scattered field produced by interaction of this beam-mode field with a fault zone should then be parametrized in a similar manner. This strategy guides the present investigation of scattering from a weak bonding flaw in a multilayer aluminum plate. The horizontal and vertical displacements excited by a high-frequency two-dimensional dilatational (P) Gaussian input beam have previously been tracked through successive cross sections in the perfectly bonded material [Lu et al., J. Acoust. Soc. Am. 87, 42–53 (1990)]. This input is now allowed to interact with a smoothly tapered weak-bond zone of moderate length. The equivalent forcing terms induced by the input beam are modeled in the Born approximation, and the scattered field is evaluated accordingly. Depending on the flaw size, its location relative to the input and output transducers, and other variables, the detected response at the plate surface may contain beamlike or modelike features. The beamlike phenomena are explored here with a view toward finding conditions through which the physical observables that should facilitate flaw location and identification are enhanced. Although, for convenience, the numerical data have been generated by normal-mode summation, the results reveal clearly that the hybrid beam-mode format, which remains to be developed, furnishes the proper parametrization for what is observed.
Analysis using variational principles of the surface pressure and displacement along an axisymmetrically excited disk in a baffle
Authors: Ginsberg Jerry H. , Chen Pei-Tai , Pierce Allan D.
Published: October 2005

A discussion of the singularities that arise in a variational principle for the surface pressure resulting from a specified harmonic motion of an arbitrary surface leads to the observation that essentially the same formulation may be employed to study a thin disk in an annular baffle and a disk in an infinite baffle. This variational principle is implemented jointly with Hamilton’s principle for structural displacement to study the response of an axisymmetrically excited flexible disk (membrane or elastic plate) in a baffle. Surface pressure, as well as displacement, are represented in a series of assumed modal functions. The system equations reduce to a set of simultaneous equations for the complex amplitudes of the assumed modes, in which the inhomogeneous terms are the modal generalized forces, whereas the coefficients of the homogeneous terms arise from the isolated responses of the fluid and structural media, and from the fluid–structure coupling. The coefficients associated with surface pressure are obtained from numerical integrations over the surface. The technique for performing such integrations in conjunction with analytical basis functions is reviewed and extended to interpolating functions spanning segments of the surface. Results obtained for the infinite baffle case are shown to be in close agreement with an earlier analytical solution, except for differences stemming from discrepancies in the in vacuo resonant frequencies predicted by conventional and Timoshenko plate theory.
Conformal generalized near-field acoustic holography for axisymmetric geometries
Authors: Borgiotti Giorgio V. , Sarkissian Angie , Williams Earl G. , Schuetz Luise
Published: October 2005

The normal velocity field on the boundary σ of a radiating source is reconstructed with high resolution by using pressure data, measured in the very near field to include evanescent components, fast decaying with the distance. The measurement points belong to a surface conformal to σ. The reconstruction is performed by identifying the boundary normal velocity distribution generating the pressure field best mean-square fitting the measurement data. The ensuing normal equations are solved by resorting to the singular value decomposition (SVD) of the transformation from the boundary normal velocity to the pressure at the measurement points. The reconstructed boundary normal velocity is represented as a linear combination of basis functions, each associated with a singular value (SV). The errors in the estimation of the coefficients of the linear combination are proportional to the inverses of the corresponding SVs. To achieve robustness, the SVD is truncated to retain the terms corresponding to a limited dynamic range, in turn related to the dynamic range of the measurement system. For axisymmetric, but otherwise general, surfaces, the numerical complexity is reduced because separate SVDs of greatly reduced dimensionality must be performed on a number of matrices, each associated with one of the harmonics of the Fourier expansion of the field around the symmetry axis. In a numerical experiment, making use of an available computer model, by processing very-near-field pressure samples, the normal velocity was reconstructed with excellent accuracy on the surface of a finite compliant cylinder with flat endcaps, excited by point forces. The viability of the method was then confirmed in a measurement tank experiment in which the distribution of the boundary normal velocity was reconstructed on a finite compliant cylinder driven by point shakers. Comparison with accelerometer data shows good agreement on a wide frequency band.
Equivalent modal impedance matrix of multiple degree of freedom electroelastic structures
Authors: Johnson Michael P.
Published: October 2005

Most transducer devices used in present day sonar arrays are usefully approximated as single degree of freedom devices. The type of device that dominates the present systems are Tonpilz transducers. As system requirements move to lower frequency regimes, devices such as these become too large to be handled manageably. New types of devices, typically having more than one important vibrational mode and significantly smaller dimensions, are being investigated for future applications. Most of the analysis techniques presently used have been developed to support single degree of freedom devices. New tools are needed to analyze devices that rely on more than one vibrational mode to perform their mission. The technique described here combines finite-element analysis (FEA) methods with tools that have already been developed, providing a bridge to previous analysis techniques. This allows the considerable investment made in the development of previous techniques to be applied to devices where they may not otherwise have been considered sufficiently accurate.
Vibrations of rectangular membranes subjected to shear and nonuniform tensile stresses
Authors: Leissa Arthur W. , Ghamat-Rezaei Amir
Published: October 2005

This work presents the first known results for vibration frequencies and mode shapes of rectangular membranes subjected to shear stresses and/or nonuniform tensile stresses. The tensile stresses are permitted to vary linearly (σx =C1+C2 y, σy =C3+C4x), while the shear stress is constant (τxy =C5). A restriction is placed upon the magnitude of the shear stress so that the normal stress in all directions and at all points does not become compressive, so that the membrane does not wrinkle. The Ritz method is used to solve the vibration problem. Transverse displacements are assumed to be a double series of trigonometric functions. A convergence study is made to establish that solutions retaining 8×8=64 terms in the series are sufficiently accurate for most purposes. Using such solutions, the first ten frequencies are found for a square membrane subjected to uniform and equal tensile stresses with added shear stress. Contour plots of mode shapes are also shown. As C5/C1 approaches unity, the stress field becomes one of diagonal tension, and frequencies and mode shapes change rapidly. Frequencies for rectangular membranes of aspect ratio 2 are also given. Finally, the effects of nonuniformity in the tensile stress upon the frequencies and mode shapes are studied. Either added shear stress or nonuniformity of tensile stress typically causes decreased frequencies, and the changes can become very large.
A study of optoacoustic signal amplitude in weakly absorbing fluids
Authors: Cheyne Stanley A. , Bass Henry E.
Published: October 2005

The optoacoustic effect has been experimentally studied. These results have been compared to existing theoretical predictions based upon linear thermal expansion. The dependence of optoacoustic amplitude on the coefficient of thermal expansion, propagation distance, and laser pulse energy was measured. The experimental observations were found to be in agreement with theory. The signal amplitude was also measured as a function of optical absorption coefficient. It was found that the observed signal agreed with theory so long as the absorption coefficient was small. The absolute magnitude of the optoacoustic signal was also measured and compared to theory.
Calculations of acoustic scattering from the ocean surface
Authors: Dashen Roger , Henyey Frank S. , Wurmser Daniel
Published: October 2005

The problem of acoustic scattering from the ocean surface can be solved using the formalism that has been developed to describe the scattering of a wave off a finite object. A refined version of this formalism is used to generate various approximation schemes. The validity of these approximations are investigated and their relative merits are discussed. The scattering cross section is evaluated numerically and it is concluded that the observed cross section for scattering near the ocean surface cannot be explained by ocean surface scattering alone.
Relating acoustic properties to perceptual responses: A study of Swedish voiced stops
Authors: Krull Diana
Published: October 2005

Perception models based on different kinds of acoustic data were compared with respect to their capacity to predict perceptual confusions between the Swedish stops [b,d,Δ,g] in systematically varied vowel contexts. Fragments of VC:V utterances read by a male speaker were presented to listeners. The resulting confusions were especially numerous between short stimulus segments following stop release, and formed a regular pattern depending mainly on the acute/grave dimension of the following vowel. The acoustic distances calculated were based on: (1) filter band spectra; (2) F2 and F3 at the CV boundary and in the middle of the following vowel; (3) the duration of the burst (=transient + noise section). Both the spectrum-based and the formant-based models provided measures of acoustic distance (dissimilarity) that revealed regular patterns. However, the predictive capacity of both models was improved by including the time-varying properties of the stimuli in the distance measures. The highest correlation between predicted and observed percent confusions, r=0.85, was obtained with the formant-based model in combination with burst length data. The asymmetries in the listeners’ confusions were also shown to be predictable, given acoustic data on the following vowel.
Moments of wave scattering by a rough surface
Authors: Spivack Mark
Published: October 2005

This paper gives the first two moments of a wave field scattered by grazing incidence on a moderately rough surface. The expressions are derived for normally distributed surfaces with arbitrary spectrum, and are valid at depths that are large compared with the surface height. It is demonstrated that the first moment has a weak dependence on the surface fluctuation spectrum. The first moment is compared with Monte Carlo simulations, and gives close agreement. It is also shown that for a given degree of surface roughness the first moment retains the flat-surface reflection property of being determined by the distance from an ‘‘image source,’’ i.e., the sum of the depths of source and receiver.