摘要:

Various reciprocity relations in duct acoustics have been derived on the basis of the spatial reciprocity principle implied in Green’s functions for linear waves. The derivation includes the reciprocity relations between mode conversion coefficients for reflection and transmission in nonuniform ducts, and the relation between the radiation of a mode from an arbitrarily terminated duct and the absorption of an externally incident plane wave by the duct. Such relations are well defined as long as the systems remain linear, regardless of acoustic properties of duct nonuniformities which cause the mode conversions.

ISSN:0001-4966    

DOI:10.1121/1.384314

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Previous studies of the title problem have produced only partial solutions for this classical configuration. The present study shows how complete solutions are readily obtained from simple polynomial expressions. Numerical results in graphical form are presented for a steel shell submerged in water as functions of a parameter related to the shell’s thickness‐to‐radius ratio. It is found that descriptions based upon added‐mass and added‐damping perturbations of the shell’sinvacuofree‐vibration characteristics can be misleading.

ISSN:0001-4966    

DOI:10.1121/1.384315

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Previous investigation concerning the scattering of elastic waves from solid spherical inclusions have furnished expressions for the scattering cross sections which, upon numerical evaluation, exhibited resonancelike features as a function of frequency. In the present work, we study these resonances in a fashion suggested by the resonance theory of acoustic scattering due to Flax, Dragonette, and Überall [J. Acoust. Soc. Am. 63, 723 (1978)]. The resonances of the solid inclusions, exemplified by iron or lucite spheres imbedded in an aluminum matrix, are found numerically in the individual normal‐mode scattering amplitudes, and are interpreted in terms of phase‐matched circumferential waves. Dispersion curves for the phase velocities of the latter are obtained, exhibiting two families of waves of different type. Finally, the connection of these waves with the Stonely waves on the boundary between two flat half‐spaces is noted in high‐frequency limit.

ISSN:0001-4966    

DOI:10.1121/1.384316

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Ultrasonic pulse echo techniques have proven particularly valuable in locating discrete flaws, such as cracks or inclusions, in metal components. It has long been recognized that many factors influence the echo amplitude from a defect. Three factors of particular significance are the angle of incidence between pulse and defect, the shape and size of the defect, and the roughness of its surface. A diffraction model is developed which includes these parameters and successfully accounts for the experimentally observed reflections of ultrasonic pulses from a variety of surfaces. The equations describing reflection in the frequency domain essentially predict the complex frequency spectra of pulses reflected from surfaces of various geometries: by Fourier transforming them, expressions describing the actual pulse waveforms reflected from the surfaces have been obtained. The predicted effects of surface roughness, size, shape, and defect orientation on both the reflected pulse waveform and its frequency spectrum are confirmed by experiment. The converse problem of using the reflected pulse to infer information about the reflecting surface via a deconvolution technique is also demonstrated.

ISSN:0001-4966    

DOI:10.1121/1.384317

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Dispersion and attenuation of acoustic plane‐wave disturbances propagating in a ducted combustion system are studied. The dispersion and attenuation are caused by fuel droplets and soot emission from a jet engine combustor. The attenuation and dispersion are due to heat and mass transfer, and viscous drag forces between the emissions and the ambient gas. Theoretical calculations show sound propagation at speeds below the isentropic speed of sound at low frequencies. Experimental results are in good agreement with the theory.

ISSN:0001-4966    

DOI:10.1121/1.384318

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The problem of sound propagation in a constant‐area duct with compliant walls is studied, including a uniform mean flow. The wall characteristics are assumed to be piecewise constant. Energy conservation leads to a unitary scattering matrix. A second relation of similar type is derived from momentum conservation which is, however, violated at the wall discontinuities, thereby introducing additional dyadic terms into this relation. The rank of the commutator of the scattering matrix and a wavenumber matrix is shown to be related to the number and type of the wall discontinuities. Explicit results are obtained if this rank is one. As an example, sound propagation in a duct with a semi‐infinite splitter plate is discussed.

ISSN:0001-4966    

DOI:10.1121/1.384319

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The method of multiple scales is employed to analyze the wave propagation in a rectangular hard‐walled duct whose walls have weak periodic undulations. Interacting modes traveling in the same direction propagate unattenuated. The energy is continuously exchanged between the two modes. The modes that travel in opposite directions are attenuated and, there, may be cut off. This cutoff will depend upon the geometry of the cross section as well as the phase‐angle differences between the undulations of the opposite walls.

ISSN:0001-4966    

DOI:10.1121/1.384320

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The relationship between the ultrasonic nonlinearity parameter for solids and the acoustic Grüneisen number has been derived for longitudinal ultrasonic wave propagation in the pure mode directions of cubic crystals and isotropic solids. Agreement between the acoustic Grüneisen number and the thermodynamic Grüneisen parameter is best for ultrasonic harmonic generation measurements along the [100] direction of a cubic crystal. Comparison of the temperature curves of the acoustic Grüneisen number of copper shows that the acoustic Grüneisen number generally follows the temperature dependence of the lattice contribution to the thermodynamic Grüneisen parameter.

ISSN:0001-4966    

DOI:10.1121/1.384321

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Intermediate difference frequency directivity for the parametric acoustic array is identified with the transition from narrowbeam (Rutherford scattering) directivity to broadbeam (primary product pattern) directivity. Experimental data are presented in which parametric arrays with intermediate difference frequency directivity were formed for several primary frequency bands, step‐down ratios, primary source configurations, and directivity ratios. The experimental results compare well with theoretical predictions. The difference frequency half‐power beamwidth with intermediate directivity was observed to always be greater than the computed narrowbeam and broadbeam results; and low sidelobes, which are characteristic of intermediate and broadbeam directivity, were observed in the difference frequency beam patterns. Parametric acoustic source performance with intermediate directivity was demonstrated in the nearfield of the parametric array with a modest decrease in directivity and apparent source level as compared to farfield conditions.

ISSN:0001-4966    

DOI:10.1121/1.384322

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A theoretical model of surface waves in equilibrium with acoustic waves at a fluid–fluid interface is developed. Modifications to the usual pressure and particle velocity boundary conditions lead to a dispersion relation for the waves of the coupled system. An expression for the total reflection coefficient is found which consists of the usual term and an additional one which depends on the interfacial surface tension, the surface wave frequency, and wavenumber. The ratio of acoustic energy absorbed due to reflection from the interface to the incident wave energy is calculated making use of the previously obtained reflection coefficient. This ratio is relatively constant except in a wavenumber regime which corresponds to a minimum in the total reflection coefficient, and itself exhibits ’’resonance transmission’’ behavior.

ISSN:0001-4966    

DOI:10.1121/1.384310

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP