摘要:

The simplified quasi-one-dimensional model of thermoacoustic devices formulated in Part I [Watanabe et al., J. Acoust. Soc. Am.102, 3484–3496 (1997)] is studied in the nonlinear regime. A suitable numerical method is described which is able to deal with the steep waveforms that develop in the system without inducing spurious oscillations, appreciable numerical damping, or numerical diffusion. The results are compared with some experimental ones available in the literature. Several of the observed phenomena are reproduced by the model. Quantitative agreement is also reasonable when allowance is made for likely temperature nonuniformities across the heat exchangers.

ISSN:0001-4966    

DOI:10.1121/1.420396

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Porous piezoelectric ceramics and 0–3/3–3 connectivity piezoelectric composites are normally characterized following the Standards on Piezoelectricity. Nevertheless, these materials are not homogeneous and losses are significant. New constitutive and wave equations have been obtained recently for these kind of materials. The objective of this paper is to derive new definitions for the electromechanical coupling coefficients and a suitable characterization procedure according to the new constitutive and wave equations previously mentioned. In particular, the case of the length expander bar mode is analyzed in detail. The study of resonant elements requires the use of suitable boundary conditions. In this case the boundary conditions are borrowed from the theory of poroelasticity and extended for a piezoelectric material. Finally the procedure is applied to characterize a commercial porous piezoelectric ceramic.

ISSN:0001-4966    

DOI:10.1121/1.420143

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The vibrational and dynamic response control of cantilevers carrying externally mounted stores is investigated. The cantilevered structure is modeled as a thin-walled beam of arbitrary cross section and incorporates a number of nonclassical effects such as transverse shear, secondary warping, anisotropy of constituent materials, and heterogeneity of the construction. The control is carried out via a dynamic bending moment applied at the tip of the structure. A feedback control law relating the boundary moment with one of the kinematical variables characterizing the response of the beam is implemented, and its results upon the closed-loop eigenfrequencies and dynamic response are highlighted. The obtained numerical results emphasize the efficiency of this control methodology to enhance, without weight penalties, vibrational and dynamic response behavior and inhibit and even suppress the occurrence of the resonance phenomenon.

ISSN:0001-4966    

DOI:10.1121/1.420397

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Acoustic scattering by elastic bodies is usually analyzed in terms of resonances, the frequency, width, and order of which should be determined. In this paper, a simple approach based on a frequency derivative of the scattered pressure is proposed for resonance order identification on bodies of arbitrary shape. The method is applied to the acoustic scattering of a plane wave by a spherical shell for validation and by a cylindrical shell bounded by hemispherical end caps. In both cases, theAandS0wave resonances are identified.

ISSN:0001-4966    

DOI:10.1121/1.420144

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The transmission of plate flexural waves through a reinforcing beam is related to the coupling between the plate flexural waves and the flexural and torsional waves in the beam. The beam–plate coupling and the energy transmission through the beam can be described in terms of the trace wave matching of the flexural waves in the plate with the flexural and torsional waves in the beam. For a given incident flexural wave from the plate to the beam interface, the amount of trace matching is determined by the flexural and torsional wave numbers in the beam. It is shown in this paper that the reinforcing beam of an infinite beam–plate system serves as a good passive device in attenuating wave transmission except at two coincidences corresponding to the optimal wave trace-matching conditions. The maximum power flow across the beam at the optimal trace wave matching conditions can be reduced by a feedforward active control system using the information on the wave numbers at the coincidence conditions. In this paper, the coupling mechanisms involved with the wave transmission in a coupled beam–plate structure is used to explain the coincidence conditions of the wave transmission. The active control is applied to the reinforcing beam to attenuate the transmitted waves at the coincidences. Results demonstrate that it is possible to achieve a significant reduction of the transmitted energy by using an array of point forces and point moments, and the biologically inspired control strategy for the control actions.

ISSN:0001-4966    

DOI:10.1121/1.420145

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Equations for linear piezoelectricity are formulated in a reference frame rotating at a constant angular velocity and are simplified by a perturbation procedure when the angular velocity of the reference frame is small. The equations thus obtained are then employed in the analysis of a rectangular ceramic plate piezoelectric gyroscope operating with thickness shear modes. Approximate analytical solutions to the equations resulted from the perturbation procedure are obtained based on Mindlin’s two-dimensional equations for a piezoelectric plate which are simplified by the thickness shear long wave approximation. Free-vibration frequencies and mode shapes, as well as the condition for double resonance, are obtained. Forced vibration is also studied which leads to a simple expression for the voltage sensitivity of the gyroscope. The analysis is approximate and qualitative mainly with the purpose of exhibiting some most basic characteristics of the gyroscope. Some of the results are compared with finite element numerical method.

ISSN:0001-4966    

DOI:10.1121/1.420398

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

An experimental/numerical technique has been implemented to determine simultaneously the bulk and shear dynamic moduli (and loss factor) of viscoelastic materials of arbitrary shape under low-frequency (0.5–2.5 kHz) harmonic excitation. The method consists of measuring the dynamic response of the sample at several points on the surface with a set of five independent laser interferometers, and matching the response with the predictions from a finite element code in which the two complex elastic moduli are the adjustable parameters. Results are presented for measurements made in air, under standard pressure and temperature conditions, and compared with predictions based on Kerner’s model.

ISSN:0001-4966    

DOI:10.1121/1.420288

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This paper examines the potential improvements in bearing estimation performance of split-beam processing over full-aperture beamforming for broadband signals. It presents theoretical results in order to define the details of the signal flow in a split-beam processor, and it provides theoretical performance predictions by using Cramer–Rao lower bound (CRLB) analysis. The split-beam processing scheme was implemented in a real-time line array system. Good agreement between the theoretical performance predictions and the associated experimental broadband results were obtained. The experimental results indicate that the advantage of improved bearing estimation performance of the split-beamformer over the conventional full-aperture beamformer may be practically insignificant for passive line array applications because of the split-beamformer’s poor performance in detecting very weak broadband signals.

ISSN:0001-4966    

DOI:10.1121/1.420146

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Although many aspects of the mechanisms by which low-frequency sounds exert their powerful masking on responses to high-frequency sounds are well documented and understood, there are few data on thegrowth of maskingfor signal frequencies near, but not necessarily at, auditory-nerve-fiber characteristic frequency (CF). Masking of responses to 6- or 8-kHz tones by a continuous 300-Hz band of noise centered at 500 Hz was measured in single auditory-nerve fibers with various CFs. The growth rate of maskings averaged approximately 2 dB/dB, was typically largest for tones about 10% above fiber CF, and decreased at higher and lower frequencies. This pattern of masking versus frequency relative to CF resembles the pattern of compression of the growth of basilar membrane motion versus frequency at a fixed cochlear place. This correspondence supports the hypothesis that the high growth rate of masking by low-frequency sounds is due to the same mechanisms which produce the compression in the growth of basilar membrane motion.

ISSN:0001-4966    

DOI:10.1121/1.420147

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

There has been little exploration of the mechanisms by which stapedius muscle contractions reduce the masking of responses to high-frequency sounds by low-frequency sounds. To fill this gap in knowledge, controlled stapedius contractions were elicited with direct shocks in anesthetized cats, and measurements were made of the effects of these contractions on the masking of single auditory-nerve fibers and on the attenuation of middle-ear transmission. The results show that the stapedius-induced reductions of masking can be much larger than the attenuations of low-frequency sound. With a 300-Hz band of masking noise centered at 500 Hz, and signal tones at 6 or 8 kHz, unmasking effects over 40 dB were observed for sounds 100 dB SPL or less. The data suggest that much larger unmasking might occur. The observed unmasking can be explained completely by a linear stapedius-induced attenuation of sound transmission through the middle ear and a nonlinear growth rate of masking for auditory-nerve fibers. No central effects are required. It is argued that the reduction of the upward spread of masking is probably one of the most important functions of the stapedius muscle.

ISSN:0001-4966    

DOI:10.1121/1.420399

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP