摘要:

The reflection of an elastic wave by a rough stress‐free surface with a periodic profile has been investigated rigorously. The problem is formulated in terms of an integral equation for the particle displacement at a single period of the boundary surface. Numerical results pertaining to the reflection of either an incident P wave or an incident SV wave for a sinusoidal profile are presented.

ISSN:0001-4966    

DOI:10.1121/1.381642

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The wave equation is solved to determine the transmission and reflection coefficients for plane waves at oblique incidence on a system ofnlayers of plane parallel plates. Both shear‐ and longitudinal‐wave properties of the materials are included in the derivation. Equations are presented in a form which will facilitate adaptation to a digital computer. Data measured in the frequency range 100–700 kHz for one, two, and three solid layers immersed in water compare favorable with computer results.

ISSN:0001-4966    

DOI:10.1121/1.381643

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Diffraction of surface waves at a discontinuity of a surface impedance under oblique incidence is analyzed by means of singular integral equations. A closed form for the reflection coefficient is derived. The phenomena of nonradiation and total reflection of the surface wave are discussed. The results are used for the analysis of guided modes on a strip surface waveguide.

ISSN:0001-4966    

DOI:10.1121/1.381644

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A model is proposed to explain the means by which an edgetone transforms the energy of a fully developed plane jet into energy which is radiated as sound. The edgetone configuration considered consists of a flat plate located in the medial plane of a fully developed two‐dimensional jet. The flow is modeled as follows. A periodic disturbance at the jet origin leads to the formation of an asymmetric vortex street which propagates downstream with a fixed convection velocity and wavelength. The vortex strength, convection velocity, and wavelength are determined as functions of the Strouhal number by applying conservation laws and kinematic relationships. A potential flow analysis of the interaction of the vortices with the edge is used to estimate the nearfield oscillating flow at the jet exit which, in turn, is used to calculate the phase of the feedback mechanism. The phase then determines the operating frequency as a function of jet velocity and edge stand‐off distance. It is shown that the proposed model is capable of predicting the major observed features of edgetone operation. The frequency predictions of the theory are compared with experiments for a wide range of jet parameters in both air and water. The comparison indicates that the frequency predictions are as good or better than previous empirical or semiempirical formulas.

ISSN:0001-4966    

DOI:10.1121/1.381645

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The speed of sound in standard seawater (diluted with pure water and evaporated) have been measured relative to pure water with a Nusonics single‐transducer sound velocimeter as a function of salinity (5–40°/00), temperature 0°–40°C, and applied pressure (0–1000 bars). The effect of pressure on the relative speeds of sound, (UP−UPH2O) ‐UO−UOH2O), have been fitted to an equation of the form (with a standard deviation of 0.19 msec−1) (UP−UPH2O) ‐ (UO−UOH2O) =AS(°/oo)+BS(°/oo)3/2+CS(°/oo)2, whereUandUH20are the speeds of sound in seawater and pure water, respectively; superscriptsPandOare used to denote applied pressurePandO(1 atm);A,B, andCare temperature‐ and pressure‐dependent parameters;S(o/oo) is the salinity in parts per thousand. This equation has been combined with the refitted high‐pressure pure‐water sound‐speed equation of Wilson [Naval Ordnance Lab. Rep.(1959)], Chen and Millero [J. Acoust. Soc. Am. 60, 1270–1273 (1976)], and the 1‐atm seawater sound‐speed data of Millero and Kubinski [J. Acoust. Soc. Am. 57, 312–319 (1975)] to calculate the speeds of sound for seawater at various salinities, temperatures, and pressures. Our results agree with the work of Wilson on the average to 0.36 msec−1over the range of 5 to 40o/oo salinity, 0° to 30°C, and 0 to 1000 bars. Over the oceanic range our results agree on the average with the work of Wilson to 0.3 msec−1(maximum deviation 0.6 msec−1), and with the work of Del Grosso to 0.5 msec−1(maximum deviation 0.9 msec−1). The better agreement of our results with those of Wilson may be fortuitous since our measurements were made relative to his pure‐water data.

ISSN:0001-4966    

DOI:10.1121/1.381646

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The response of an optical fiber in water to low‐frequency acoustic waves was investigated experimentally and compared with analytical results. A single‐mode optical fiber was used to pass a laser beam through a tank in which an approximately plane acoustic wave was produced. A change in the optical index of refraction of the fiber creates an effective path‐length change for the optical beam which results in a phase shift of the optical beam with respect to a reference beam unaltered by the acoustic field. By mixing the phase‐shifted beam with a reference beam of constant phase in a photodetector the phase variation at the acoustic frequency is detected. Theoretically, the sensitivity of a fiber‐optic interferometer should be independent of frequency. Experimental results confirm this.

ISSN:0001-4966    

DOI:10.1121/1.381647

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Air‐filled spherical shells in water have been insonified by a pulsed sinusoidal beam with a carrier frequency of 2 MHz. Experimentalkavalues ranged from 47 to 550. The bulk of the investigation was directed toward the spheres with the largerkavalues; and for these, experimental results are compared with computations made for the intensity distribution in reflection from a perfectly reflecting spherical surface. It is found that the agreement is good if the thickness of the shell is less than 1/10 wavelength, but that marked departures occur for shells of appreciable thickness (of the order of a sound wavelength in the shell material).

ISSN:0001-4966    

DOI:10.1121/1.381648

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Careful developments of a number of approximate solutions of the problem of point source acoustic scattering from the ocean surface are presented. The regime of interest is the small‐waveheight regime, where the rms waveheight of the ocean surface is small compared to the acoustic wavelength and the correlation length of the ocean surface. The approximate solutions fall into two categories: those derived by utilizing the Kirchhoff approximation and those based on a small‐waveheight perturbation expansion. It is shown that within the small‐waveheight regime the small‐perturbation solution is superior to any solution based on the Kirchhoff approximation, the former being uniformly valid in the ratio of acoustic wavelength to surface‐wave wavelength. In that portion of the small‐waveheight regime where the ratio of acoustic wavelength to surface‐wave wavelength is small, all approximate solutions are shown to be in agreement. Pitfalls which can and have occurred in the misapplication of the Kirchhoff approximation are pointed out.

ISSN:0001-4966    

DOI:10.1121/1.381649

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A low‐frequency, resonant, longitudinally vibrating piston‐type rare earth iron underwater sound transducer using rods of 27% terbium – 73% dysprosium iron (Tb0.27Dy0.73Fe1.95) is described. The performance of the rare earth iron transducer is compared with the performance of the same transducer with identical ceramic active elements. Data on transmitting current response, transmitting voltage response, free‐field voltage sensitivity, coupling coefficient, efficiency, and linearity are presented. An equivalent circuit is presented which predicts the performance of the transducer in the presence of eddy currents and demagnetization. The predicted performance of a laminated transducer is compared with that of an unlaminated transducer. Advantages and disadvantages of the rare earth iron material are discussed.

ISSN:0001-4966    

DOI:10.1121/1.381650

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The effects of a random current on the fluctuations of underwater cw sound transmissions are considered for a horizontal isospeed channel. A statistical ensemble of currents is employed, whose members are depth dependent only, and current influence on ray geometry is investigated. Approximations to the total acoustic field at a receiving point are obtained, and it is shown that a current ensemble member has a significant effect on phase. A mean current is taken, on which are superimposed small depth‐dependent current changes in speed and direction. These changes are members of statistical ensembles, which lead to an ensemble of phase functions. Expressions for the mean and standard deviation of the phase, in terms of statistics of the depth‐averaged current fluctuations, are determined and analyzed. The inverse problem of determining second‐order moments of the random current, given the standard deviation of phase, is examined also. If the mean current is known, phase information at three receivers is sufficient to specify the second moments of the current fluctuations.

ISSN:0001-4966    

DOI:10.1121/1.381630

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP