摘要:

Acoustical properties of water saturated and gassy sediments are observed to be significantly different. The present state of knowledge of the acoustical properties of saturated sediments, gassy water, and gassy sediments is reviewed. The dynamics of bubbles in water and in various solid materials, including sediments, are experimentally examined in a companion paper. Pulsation resonance is exhibited by the bubbles in all materials examined. Predictions of bubble resonance frequency and damping are shown to agree with the measurements. Equations for sound speed and attenuation, based on the model of resonating gas bubbles, are shown to agree with published measurements in gassy sediments. Parameters required for predicting gassy sediment acoustical properties are identified. Ranges of values of these parameters for various sediments are discussed.

ISSN:0001-4966    

DOI:10.1121/1.384453

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Acoustical properties of water saturated and gassy sediments are observed to be significantly different. The present state of knowledge of the acoustical properties of saturated sediments, gassy water, and gassy sediments is reviewed in a companion paper. The dynamics of bubbles in water and in various solid materials, including sediments, are experimentally examined here. Pulsation resonance is exhibited by the bubbles in all materials examined. Predictions of bubble resonance frequency and damping are shown to agree with the measurements. Equations for sound speed and attenuation, based on the model of resonating gas bubbles, are shown to agree with published measurements in gassy sediments. Parameters required for predicting gassy sediment acoustical properties are identified. Ranges of values of these parameters for various sediments are discussed.

ISSN:0001-4966    

DOI:10.1121/1.384454

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In the present paper we adapt the transition matrix method to the case of a smooth elastic obstacle. The boundary conditions employed are discussed in some detail and are seen to be responsible for the fact that the rather complicated formal solution in many respects resembles that for an elastic obstacle in a fluid. Comparisons are made between the smooth and the usually employed welded obstacles, and for spheres approximate expressions are given for the transition matrices in the long wavelength limit. Numerical results (cross sections and surface stresses) are given for spheres and spheroids, and it is then seen that often the smooth and welded obstacles, at least qualitatively, show similar features.

ISSN:0001-4966    

DOI:10.1121/1.384455

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The linear acoustic propagation in rigid planar sharp bends and bifurcation ducts is analyzed using a Green’s‐function integral technique often known as the surface element method. The acoustic characteristics of the sharp bend differ substantially from those of a circular bend with identical turning angle, width, and centerline length. The acoustic loading resulting from a duct bifurcation is highly two dimensional beyond the first cutoff frequency.

ISSN:0001-4966    

DOI:10.1121/1.384456

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The linear acoustic propagation in finite rigid three‐dimensional waveguides is determined analytically using an eigenfunction expansion of the Helmholtz equation. The geometry considered consists of straight and circular bends of rectangular cross section with continuous interfaces (branches and sharp corners are excluded). The phenomena of resonance shift and relocation are explained for a bend–straight duct combination.

ISSN:0001-4966    

DOI:10.1121/1.384457

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Experimental results are presented which show a mode selective transfer of energy from sound propagating inside a circular pipe to pipe wall vibration. The experiments utilize broadband noise generated by flow through a restriction in the plastic (PVC) pipe. For each higher acoustic duct mode, the energy transfer occurs in a narrow frequency band located slightly above the higher‐mode cut‐on frequency. A match in axial phase velocity between the higher acoustic duct mode and a compatible pipe wall vibrational mode is proposed as the mechanism for the energy transfer. Theoretical predictions for the frequency at which the axial phase velocity match occurs show good agreement with the experimental results.

ISSN:0001-4966    

DOI:10.1121/1.384458

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Acoustic radiation from a source, here viewed as an immobile point singularity with periodic strength and a given multipolar nature, is affected by the presence of nearly structural elements (e.g., rigid or impedance surfaces) as well as that of a background flow in the medium. An alternative to the conventional manner of calculating the net source output by integrating the energy flux over a distant control surface is described; this involves a direct evaluation of the secondary wavefunction at the position of the primary source and obviates the need for a (prospectively difficult) flux integration. Various full and half‐planar surface configurations with an adjacent source are analyzed in detail, and the explicit result obtained, in particular, for the power factor of a dipole brings out a substantial rise in its output as the source nears the sharp edge of a half‐plane.

ISSN:0001-4966    

DOI:10.1121/1.384459

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Reflection and transmission coefficients for plane elastic waves obliquely incident on the boundary between two isotropic materials have been known for some time. The solution for anisotropic materials, however, has not been fully treated in the literature. Here we derive these coefficients for the case of a piezoelectric ceramic in contact with water. This problem is of significant practical interest, since in a variety of applications, piezoelectric ceramics, which are inherently anisotropic, are used as transducers to radiate acoustic energy into water. Due to the anisotropy, velocities of both compressional and shear waves are functions of the angle of incidence. Piezoelectric equations are solved to find the variations of compressional and shear wave velocities with the angle of incidence. Reflection and transmission coefficients are then obtained and numerical results are presented for four piezoelectric ceramics.

ISSN:0001-4966    

DOI:10.1121/1.384460

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Coupled equations are derived which describe the evolution of harmonic content for quadratic nonlinearity in the presence of arbitrary attenuation and dispersion. The equations are shown to be in agreement with known results of nonlinear acoustics and to describe novel phase locking and parametric phenomena when applied to dispersive systems. They are well suited to a planned computer analysis concerning the existence of solitary waves in systems with topological dispersion.

ISSN:0001-4966    

DOI:10.1121/1.384461

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The status of current research into the relations between thunder and the lightning process is examined. Nonlinear effects near the discharge strongly influence the pressure waveform and hence the nearfield acoustic spectrum. At distances where measurements are typically made, propagation effects strongly influence the shape of the recorded spectrum. Since most measurements do not reliably determine propagation distances or the physical characteristics of the propagation path, they are of little value in deducing the nearfield pressure waveform. Even with these problems, the gross features of thunder can be explained qualitatively and there is hope that future experiments will provide information necessary to correct for propagation effects making the study of thunder a useful tool for testing theoretical models of lightning.

ISSN:0001-4966    

DOI:10.1121/1.384354

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP