摘要:

This paper reports on a continuing study of the mass physical properties of surficial, shallow‐water marine sediments off San Diego, California. Sound velocity measurementsin situat 100 kc were made by pulsing between small transducers inserted into the bottom by diver. Density, porosity, and size analyses were determined on relatively undisturbed samples taken by diver. The following averaged representative values have been obtained:Velocity insediment at ImpedanceDensity Porosity Med. diam 60°F (105g/Sediment type (g/cc) (%) (mm) (ft/sec) cm2sec)Fine sand 1.93 46.2 0.19 5520 3.25Very fine sand 1.92 47.7 0.12 5435 3.18Silty very fine sand 1.68 61.3 0.05 5075 2.60Medium silt 1.69 60.9 0.03 4825 2.49Clayey fine silt 1.60 65.6 0.02 4800 2.34Laboratory measurements of velocity and attenuation 25 to 35 kc were made by a resonant‐chamber method using diver‐taken samples; average attenuation values of about 0.5 db/ft (silt) to about 5 db/ft (fine sand) were obtained. At three stations the sediment sound velocity was less than the velocity in the bottom water.

ISSN:0001-4966    

DOI:10.1121/1.1908210

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Recentin situand laboratory determinations of density and velocity of sound in fine‐grained, high‐porosity sediments of the sea floor off San Diego, California, reveal several stations at which the velocity of sound in the sediment was 2% to 3% less than the velocity of sound in the water just above the bottom. Comparison of the compressibility of the sediment computed in two ways and of the ratio: velocity in sediment/velocity in water computed and actually measured indicates that these high porosity sediments are approximately described acoustically by the velocity formula which applies to a suspension. The theoretical explanation for this phenomena was apparently made by R. J. Urick, [J. Appl. Phys.18, 983 (1947); J. Acoust. Soc. Am.20, 283 (1948)] and R. J. Urick and W. S. Ament [J. Acoust. Soc. Am.21, 115 (1949)].

ISSN:0001-4966    

DOI:10.1121/1.1908208

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Gas bubbles, when entrained in water or other liquid, can generate high sound pressures in the liquid. Significant sound pressures are associated only with volume pulsations of the bubble, whereas oscillations in the shape of the bubble do not result in appreciable sound. Calculations have been made of the sound pressures resulting from excitation of volume pulsations by the following mechanisms: by bubble formation, coalescence, or division; by the motion of a free stream of liquid containing entrained bubbles past an obstacle; and by the flow of liquid containing entrained bubbles through a pipe past a constriction. The calculation of the sound pressure generated by bubble formation has been verified by measurements with bubbles formed at a nozzle.

ISSN:0001-4966    

DOI:10.1121/1.1908212

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

An optical method for the quantitative study of ultrasonic wave fields at frequencies below 1 Mc/sec has been developed and applied to stationary waves. The method is based on the effect of mirage. A detailed theoretical analysis shows the possibility of determining wave forms and sound pressure amplitudes. Some experimental results of sound velocity and pressure amplitude determinations are given. The records of wave forms in several liquids indicate the distortion of waves during propagation.

ISSN:0001-4966    

DOI:10.1121/1.1908214

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

This report is a condensed presentation of currently available data on the velocity and absorption of high‐frequency sound in mammalian tissues.

ISSN:0001-4966    

DOI:10.1121/1.1908216

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

An optical interference technique employing illuminated multiple beam Fizeau fringes has been used to study the surface motion of barium titanate disks. In a properly polarized, accurately shaped cylindrical disk only normal modes having symmetry with respect to the axis and to the central plane are observed. A particular disk having radius/semithickness ratio (a/l) of 3.86 has been studied in some detail, and the displacement patterns for three important modes in the thickness resonance region have been accurately measured. Stress distributions for these three modes have been calculated from theory and these show that the wave motion is of a complex character in all three cases; this question is discussed in the light of elementary conceptions of thickness resonance. A more comprehensive experimental survey covering 25 different values ofa/lwithin the range 1.14 to 6.63 has now been completed, and vibration patterns of 12 modes are given together with graphs of resonance frequency and values of electromechanical coupling coefficient. At relatively low frequencies the observed modes are obviously of the radial type but as the frequency approaches a value such that2.5l = Λswhere Λsis the wavelength of Rayleigh waves, take the form of a surface wave resonance with maximum motion occurring at the edge of the disk. There is no single mode which can be uniquely identified as the fundamental dilatational thickness resonance Rather, asa/lchanges, each mode in turn passes through a maximum or minimum of electromechanical coupling the thickness resonance region. In general, for any given value ofa/ltwo or three modes have high coupling this region, and the vibration patterns have certain well‐defined forms but none approaches uniform piston‐like motion. Nevertheless, there is some evidence suggesting an optimum value ofa/lin transducer design.

ISSN:0001-4966    

DOI:10.1121/1.1908218

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The theory of radial vibrations in short, hollow cylinders of barium titanate has been developed. This development results in an expression which relates the radial coupling coefficient to the measurement of the resonant and antiresonant frequencies of the first harmonic of the radial mode of vibration. The important parameter in this development was found to be the ratio of outside diameter to inside diameter, and once this ratio was given, the expression relating coupling coefficient to resonance measurement took a particularly simple form. An interesting result of theory was that for any value of the ratio of diameters, many of the higher harmonics are forbidden in this mode of vibration.Experiments were devised to test some of the theoretical conclusions and were found to be in excellent agreement with the theory.

ISSN:0001-4966    

DOI:10.1121/1.1908220

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Two systems of equations of motion, designated as (I) and (II), for thin elastic cylindrical shells are derived which include the effects of both transverse shear deformation and rotatory inertia. The character of the two systems of equations is such that, upon the neglect of transverse shear deformation and rotatory inertia, Eqs. (I) will reduce to those known as Love's first approximation, while (II), which enjoys a considerable mathematical simplicity as compared to (I), will correspond to those given by Donnell. Both systems of Eqs. (I) and (II) are employed in a study for propagation of axisymmetric waves in an infinite cylindrical shell. The agreement between the predictions of the two systems of equations, in all modes of motion, for phase velocities of propagated waves in the complete range of wavelengths is found to be excellent. The results, with reference to the nature of the modes of motion according to both (I) and (II), are further examined and the relative merit of the present paper to the work of other authors is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1908222

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Integral expressions are derived for the mean‐square fluctuation pressure, pressure correlation, and certain moments of the pressure correlation within general anisotropic, homogeneous turbulence. Application is made to idealized flow models exhibiting certain anisotropy characteristics similar to those observed in boundary layer turbulence. Pressure fluctuations arising from the turbulence itself and from interaction of the turbulence with a mean flow exhibiting constant shear are compared with the isotropic case. It is found that, in contrast to the completely isotropic case, the anisotropic pressure correlation is negative for some difference coordinate values and exhibits a “tail” which falls off with distancexasx−3at separations for which the velocity correlations have fallen essentially to zero. It is concluded that in general the principal normalized moments of the pressure correlation will tend to be less than the corresponding velocity correlation moments. For isotropic turbulence this implies that the pressure correlation must fall off with distance faster than the velocity correlation. For the models of anisotropic turbulence treated it is found that departure from isotropy results in lower mean‐square pressure fluctuations for a given mean kinetic energy of turbulence.

ISSN:0001-4966    

DOI:10.1121/1.1908224

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A method of measuring the mechanical impedance of the earth is described, and some experimentally measured impedances as functions of water content, soil character, and source diameter are given. A comparison of the measured impedance with some previous theoretical work is also included.

ISSN:0001-4966    

DOI:10.1121/1.1908226

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP