摘要:

Experimental and theoretical results are presented for a wall‐mounted cavity in turbulent flow, oscillating at Helmholtz or depth‐mode resonance, where the mouth dimensions are small compared with acoustic wavelength. A new, computerized, hot‐wire method was employed to investigate the oscillating flow field in the cavity mouth. Measured wavelength of the interface wave agrees well with predictions of Michalke, using an equivalent laminar flow model based on the oscillating mean velocity profile. By means of a forward transfer function derived from the theoretical interface wave model and a backward transfer function derived from organ‐pipe theory, a root locus solution of the frequency lock‐in problem has been obtained. Predicted frequencies and sound pressure amplitudes are in good agreement with experimental values at the lower modes. Both resonant and off‐resonant oscillation was investigated. For resonant oscillation, the streamwise slot width is required to beM−1/4 times the disturbance wavelength, whereMis an integer. For situations in which the equations are applicable, the method can be used to predict design parameters for nonoscillating wall cavities in moving vessels.

ISSN:0001-4966    

DOI:10.1121/1.382047

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

We derive the coupled mode equations governing the Thompson–Quate experiment, that is, the parametric interaction of two counterpropagating bulk acoustic waves and a spatially uniform electric field oscillating at the second harmonic of the acoustic frequency. The derivation applies to propagation of any acoustic mode type in any direction in any piezoelectric or pyroelectric crystal. A new result of the derivation is a general but explicit expression for the material interaction coefficient that governs the strength of the process. We also find that the equations differ from the generic equations assumed by Thompson and Quate by the replacement of a phase velocity with the component of the group velocity normal to the crystal surface. As an aid to this derivation we also derive the coupled mode equations governing the parametric interaction of three acoustic waves. This derivation applies to the propagation of any mode types in any directions (consistent with being close to or at phase matching) in any dielectric, piezoelectric, or pyroelectric crystal.

ISSN:0001-4966    

DOI:10.1121/1.382048

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The farfield acoustic scattering by a prolate spheroid with axial point sources near the tip of the body was measured. Data were taken forkabetween 10 and 160, whereais the semimajor axis of the spheroid. Comparisons were made with numerical results obtained by an integral equation based on the simple‐source method, with appropriate coordinate stretching introduced to permit high‐frequency solutions with a minimal number of grid points. Theory and experiment agree within experimental error except for the highest frequencies in the shadow region, where very rapid changes in pressure make precise measurements difficult. The results show that for frequencies of aeroacoustic interest, the scattered field is very large and cannot be ignored.

ISSN:0001-4966    

DOI:10.1121/1.382049

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

We discuss here the diffraction of a normally incident plane acoustic wave by two equal, staggered, parallel, perfectly soft or rigid infinite strips. In each case, expressions are obtained for the first few terms of the series for the farfield amplitude and the scattering cross section when the wave length is much larger than the distance between the outer edges of the strips and the distance between the strips is large. By taking appropriate limits, the corresponding results are derived for two equal, parallel, perfectly soft or rigid infinite strips lying exactly opposite to each other. Numerical calculations of the physical quantities of interest are presented graphically.

ISSN:0001-4966    

DOI:10.1121/1.382050

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The propagation of the Rayleigh surface wave in an isotropic elastic material subjected to a homogeneous strain is studied theoretically. The displacement of the wave is assumed infinitesimally small, and its propagation direction is taken to be arbitrary. By the practical approximation that the second and higher orders of the initial strain are neglected, the formula for the change of the propagation velocity due to the strain is derived. In this analysis, the SH component of the wave cannot be assumed small and plays an important role, but it is finally ascertained that the resultant mode of the wave is almost the same as that in the linear theory of elasticity and the SH component contained in the mode is of the first order of the strain.

ISSN:0001-4966    

DOI:10.1121/1.382051

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

In the present article we give a general three‐dimensional formalism for scattering in two half spaces, one of which contains a bounded inhomogeneity. Our formalism consists of an extension of the transition matrix method which has been given by Waterman, a method which applies equally well to acoustic, electromagnetic, and elastic scattering. The formalism is here developed in detail for the case when the source and inhomogeneity are situated in different half‐spaces. However, the same method works for other source positions as well, and the basic equations are given also for the case when the source and the inhomogeneity lie in the same half space. In the final expression for the total scattered field, that part (the so‐called anomalous scattered field) which depends on the presence of the inhomogeneity, can be separated, and the physical meaning of the various quantities which determine this anomalous scattered field can be identified. The inhomogeneity enters through itsTmatrix, and previous results on various bounded configurations of scatterers can therefore be inserted and used in the present formalism. Numerical results are given for inhomogeneities consisting of one or two spheres.

ISSN:0001-4966    

DOI:10.1121/1.382052

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The effect of a wave scattered back to an oscillating bubble from a nearby object is studied. It is shown that this wave alters the decay rate of the bubble oscillation, but hardly changes its frequency. These results agree with the observations of S. Ayyash.

ISSN:0001-4966    

DOI:10.1121/1.382053

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP