摘要:

The speed of sound in saturated pure water has been measured between 273.16 and 534.69 K at 7.5 MHz using the pulse‐echo‐overlap method. An equation was fitted to our data within the experimental uncertainties of 0.05%. This equation predicts the values of speed of sound over the whole vapor pressure curve with an assigned zero value at the critical point. Our data were combined with available density data to obtain the isentropic compressibilities.

ISSN:0001-4966    

DOI:10.1121/1.391861

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Experimental measurements of sound transmissions in a laboratory waveguide are analyzed. The transmissions were from a single source to a vertical array of receivers that operated as a mode filter. Water waves on the surface caused the sound fields to fluctuate at the receiver. We used theories of coherent mode transmission to describe the experiments. Within a mode, sound field fluctuations have three components: (1) phase fluctuations due to fluctuations of the horizontal component of the wave number, (2) fluctuations of depth‐dependent eigenfunctions at source and receiver positions, and (3) mismatch of the mode filter to the local eigenfunction. Analysis showed that most of the fluctuations of the mode filtered signals were due to components (2) and (3).

ISSN:0001-4966    

DOI:10.1121/1.391862

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The Biot theory of wave propagation in porous, saturated materials contains 13 parameters. We discuss empirical and theoretical ways to predict values of these parameters for natural materials. The self‐consistent theory of composites is used to predict the elastic moduli of the skeletal frame assuming that the inclusions (pore fluid, sediment grains) are needle‐shaped at low concentrations. The Biot theory is then used to predict compressional and shear wave speeds in consolidated materials. In a man‐made material (porous sintered glass), the predictions agree with experimental data to within 3% (experimental uncertainty is also 3%); these samples were distilled‐water‐saturated. The predictions agree with data to within 1% for Berea sandstone, and to within 5% for Bedford limestone; all of these samples were brine‐saturated. The predictions agree with data to within 8% for distilled‐water‐saturated Bedford limestone. In the natural sedimentary rocks, the experimental uncertainty in measured wave speeds is estimated at 5%, and the comparisons apply at high effective pressures (>0.3 kbar), where the experimentally determined wave speeds approach ‘‘limiting velocities.’’ In distilled‐water‐saturated Massilon sandstone, predicted shear wave speeds are about 25% to 35% higher than measured speeds; this may indicate a reduction of the frame shear modulus due to interaction of the pore fluid with the minerals of the rock.

ISSN:0001-4966    

DOI:10.1121/1.391863

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The Biot theory is used to compute compressional wave speeds and attenuation in fluid–solid suspensions. The frame moduli are estimated from the self‐consistent theory of composites, assuming needle‐shaped pores and spherical or ellipsoidal grains of uniform size. The permeability is computed from the Kozeny–Carman equation. The attenuation data are matched by assuming that all losses are caused by viscous absorption in the fluid.For suspensions of kaolinite, polystyrene beads, and glass beads in various fluids, the Biot model agrees with experimental sound speed data at least as well as do other models. For aqueous suspensions of kaolinite, of attapulgite, and of hydrous aluminum silicate pigments, the Biot model generally is in better agreement with attenuation data than are other models.

ISSN:0001-4966    

DOI:10.1121/1.391864

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Empirical and theoretical methods are used to estimate the elastic moduli of the skeletal frame in sedimentary materials. The Biot model is then used to estimate compressional wave speeds as a function of depth. These estimates are compared to laboratory data and to field measurements. Using the empirical method to estimate the frame moduli, the measured wave speeds are matched within 3% for Ottawa sand pack and within 10% for glass bead pack at pressures corresponding to depths of about 500 m or less. A new method for estimating the frame moduli of partially consolidated materials is used to quantify the effects of grain packing and cementation. Velocity gradients are estimated for shear and compressional waves in terrigenous sand and calcareous clay. Predicted gradients for compressional waves, when corrected for the effect of temperature, lie within the range of published values. Predicted gradients for shear waves fall within a range of shear‐wave gradients determined frominsitumeasurements of saturated terrestrial and marine materials. Using a constant porosity of 0.40 to simulate conditions in pure sands, predicted compressional wave gradients agree with laboratory results.

ISSN:0001-4966    

DOI:10.1121/1.391865

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Fluctuations in acoustic intensity have been studied for two locations in the Arctic—the Chukchi Sea (1974) and the Kane Basin (1979)—using the same measurement and analysis techniques. A five‐frequency transducer covering the range 10–75 kHz was moved continuously in the vertical direction from 10–70 m. The results were used to determine the vertical correlation length and the coefficient of variation (rms variance) for the intensity at the five frequencies simultaneously. Conductivity and temperature versus depth were measured continuously before and after each set of acoustic runs. These profiles were used to construct sound ray diagrams and to compute the refractive index variance. For direct‐path propagation in both locations, it was found that when the acoustic intensity variance at low spatial wavenumbers is filtered out, remaining variance depends on the first power of the frequency and approximately the square of the range. This internal‐wavelike behavior is supported by additional evidence. The vertical correlation lengths observed for the direct‐path intensity indicate that the scattering features have lifetimes longer than a few seconds and less than a few minutes. The study suggests that the scattering structures are related to anisotropic eddies that tend toward isotropy as they cascade to smaller sizes. Plots of a strength parameter versus a diffraction parameter show that after deterministic variations are removed from the measurements, the remaining variations lie in the unsaturated direct‐path region.

ISSN:0001-4966    

DOI:10.1121/1.391866

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Calculation of the energy scattered out of an advancing wave front allows one to derive an attenuation coefficient δ for the low‐frequency boundary mode carried by a rough interface between two media. For a point source of sound on or near the interface this leads to a farfield boundary wave pressurepB∝r−1/2f3/2e−δrwith δ=Af6, whereris the range,fis the frequency, andAis a parameter which depends upon the form and size of roughness (for close packing it is proportional to the fifth power of the roughness height). For givenr, then,pBmust exhibit a maximum in the frequency domain atf=(4Ar)−1/6and falls off sharply for higher frequencies. This paper gives a simple procedure for calculatingAfor bossy roughness models of two fluid interfaces. In the particular case of a hard rough boundary the theory predicts results in reasonable agreement with reported experimental results, at least insofar as the magnitude and shape of thepB(f) curve is concerned.

ISSN:0001-4966    

DOI:10.1121/1.391867

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

We present a resonance theory for the acoustic transmission and reflection coefficients of an elastic plate imbedded in a fluid medium, which includes the effects of plate viscosity. This formulation provides a direct means for determining the material parameters of the plate from the measured acoustic resonances of the Rayleigh and Lamb waves in the plate (i.e., their positions in frequency or angle, their widths, and their heights) which are given in our formalism by explicit analytic expressions that depend on the material parameters. Viscosity is seen to manifest itself in a decrease of the resonance peaks and in a broadening and frequency dependence of the resonance widths, which may be used to determine the frequency‐dependent loss factor of the plate.

ISSN:0001-4966    

DOI:10.1121/1.391868

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

A model for the plane‐wave reflection coefficient from a layered elastic solid bounded on either side by a fluid half‐space is developed and applied to study environmental factors affecting the reflectivity of smooth arctic ice. Experimental measurements of the internal friction in ice and snow are reviewed and applied to compute realistic attenuation profiles. An examination of the effect of ice layers conforming with measured temperature profiles in floe ice shows that the use of average values for sound speed and attenuation is an acceptable approximation for modeling purposes. A study of the reflectivity due to the absorption of shear and compressional waves demonstrates that shear wave attenuation is the most important loss mechanism from 20° to 60° incidence. The effect of an additional snow layer is to produce more attenuation without shifting the pattern of reflection nulls. Major results are presented for a frequency of 2 kHz. Data comparisons are performed from 0.5–3 kHz that show a limited qualitative agreement with the model.

ISSN:0001-4966    

DOI:10.1121/1.391869

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

This paper is a summary of observations of a biological chorus in deep waters northwest of Australia. The data were collected from underwater noise recordings made in the course of sonar performance trials at sites in the eastern Indian Ocean. Measurements are made for frequencies between 20 and 800 Hz. Chorus noise at 500 Hz, consisting of continual drumming sounds, was evident for 9–10 h in the evening, with the peak noise level occurring soon after sunset. The noise spectrum level at this peak frequency rose to 72 dBre: 1 μPa2/Hz, approximately 12 dB above the background noise level. Typical spectra and time waveforms for individual noise bursts are presented. The source of the noise is believed to be fish of the family Sciaenidae, commonly known as croakers.

ISSN:0001-4966    

DOI:10.1121/1.392363

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP