摘要:

Measurements are reported of the growth of air bubbles in water by rectified diffusion at 22.1 kHz. Values of the threshold acoustic pressure amplitude were obtained as a function of bubble radius, liquid surface tension, and gas concentration. Measurements of the rate of growth of bubbles by rectified diffusion were also obtained as a function of acoustic pressure amplitude for a range of different values of the liquid–vapor surface tension. It was determined that although both the threshold and the growth rate were in agreement with theory for normal values of the surface tension of water, the addition of a surfactant caused the observed thresholds and growth rates to deviate from the predicted values. Surface wave activity that could increase the diffusion rate by acoustic streaming was not detected at low radii and is not thought to be the principal mechanism for the increased diffusion. Some possible explanations are given for the effect.

ISSN:0001-4966    

DOI:10.1121/1.384624

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Transmission and reflection characteristics at normal incidence have been measured for 1‐cm‐thick foam layers of 98% porosity in the frequency range 10–200 kHz. The ’’boundary frequency’’ is determined from these measurements. Below this frequency, (1) the transmitted field has no irregularity, (2) the transmission loss is proportional to the square root of frequency, (3) the reflection is specular, and (4) the reflected wave consists of two components which are reflected from the front and back surfaces of the layer and interfere with each other. The boundary frequency is 60 to above 200 kHz, for the layers with cell densities of 14 to 50 cells/in. It is found that, for each cell density, the boundary frequency is almost equal to the frequency at which one‐half a wavelength of sound is equal to the average diameter of cells.

ISSN:0001-4966    

DOI:10.1121/1.384625

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A resonant tube has been developed to measure sound absorption in gases, with specific emphasis on the vibrational relaxation peak of N2, over a range of frequency/pressure ratios from 0.1 to 2500 Hz/atm. The experimental background losses, measured in argon, show good agreement with the theoretical wall losses except at a few isolated frequencies. Measures to minimize spurious contributions to the background losses include the use of rigid cavity terminations, external excitation, and a differential technique of background evaluation. Room temperature measurements of sound absorption in binary mixtures of N2–CO2, in which both components are excitable, yield the following results for the locations of the respective vibrational relaxation peaks in Hz/atm: (f/P)max=0.063 + 123mfor the N2peak,m=mole percent of added CO2; (f/P)max=34 500−268mfor the CO2peak,m=mole percent of added N2. The figure 0.063 is an upper bound due to the presence of 2.5 ppm H2O.

ISSN:0001-4966    

DOI:10.1121/1.384626

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The compressional wave speed and attenuation and the shear wave speed and attenuation of unconsolidated artificial laboratory sediments have been measured as a function of temperature. No overburden or pore pressure in excess of that found at a few centimeters depth was applied. The compressional wave speed of the sediment was found to vary approximately as would water. Shear wave speed appears to be independent of temperature within the accuracy of the measurement. Attenuation of both types of acoustic waves was also found to be independent of temperature.

ISSN:0001-4966    

DOI:10.1121/1.384627

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Eckart’s formulation of acoustic wave scattering from a randomly rough surface expresses the average pressure as the Fourier transform of the probability density function [C. Eckart, J. Acoust. Soc. Am. 25, 566–570 (1953)]. This implies a complete independence from the correlation function of the surface, a rather surprising result which does not follow from Eckart’s only assumption of statistical homogeneity. A more detailed derivation which takes into account surface correlation is given here.

ISSN:0001-4966    

DOI:10.1121/1.384629

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

An inverse method for determining the velocity in a stratified medium is described here. The method allows the source and receiver used to probe the medium to be separated both horizontally and vertically. An integral equation for the velocity variation is derived under the assumption of small variations from a known reference velocity. A closed form solution to the integral equation is derived for the case in which the reference velocity is constant. The method is tested on synthetic data.

ISSN:0001-4966    

DOI:10.1121/1.384630

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The farfield pressure radiated by a force‐excited, extensive plate, separated from an ambient liquid by an air bubble swarm, is expressed in closed form in terms of bubble swarm and plate parameters, frequency, and the spherical angle ϑ from the normal to the plate. Comparing the pressure field with that of the plate in the absence of the bubble swarm, a ϑ‐dependent insertion loss is computed. The wavenumber and impedance of the bubble swarm being highly dispersive, simple asymptotic expressions giving the insertion loss are formulated for various frequency ranges.

ISSN:0001-4966    

DOI:10.1121/1.384631

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Resonator measurements in synthetic media show that sound absorption in seawater is caused by chemical relaxations involving B(OH)3and MgCO3in addition to MgSO4. The MgCO3relaxation can be modeled as a two‐step MgCO03ion‐pair association in which a monomolecular step controls the absorption process. The B(OH)3relaxation involves a similar two‐step association of the B(OH)−4ion in which interactions with thepH buffer system play a crucial role. A number of other relaxations are observed, but their contributions are negligible under seawater conditions.

ISSN:0001-4966    

DOI:10.1121/1.384632

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Given a rough interface between two fluids of different densities but similar sound velocities, we assume that the mean dimensionsdand spacinghof the roughness elements is small compared to an acoustical wavelength, i.e.,kd

ISSN:0001-4966    

DOI:10.1121/1.384633

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A concise energy‐flux formulation is used to investigate the range‐ averaged acoustic propagation in ocean ducts. Examples treated have isovelocity, linear, and parabolic sound speed profiles. The results are expressed as the product of a scale factor and, for the latter two examples, a depth factor. The scale factor has a similar form in each case, and remains simple and easy to use even when the profile is asymmetrical and the parameters vary with range. The appropriate solution for transmission from an isovelocity duct to a duct of arbitrary profile is also given. Surprisingly, the depth factor generally has a nominal infinity when receiver depth equals source depth in an unchanging but stratified duct, or when velocity at the receiver equals that at the source, or for scaled depths in a range‐dependent duct. These infinites are discussed from the flux, ray, and mode viewpoints and a ray‐tracing demonstration is provided. For the special case of axial source and receiver, the character of the infinite is different, and an important point is that it occurs only for velocity minima sharper than that of the parabolic profile. The latter profile has in several respects a critical nature.

ISSN:0001-4966    

DOI:10.1121/1.384634

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP