摘要:

The radiation from a spherical source vibrating with an arbitrary, axisymmetric, time‐harmonic velocity distribution while positioned at an arbitrary point wholly outside a fluid sphere while both are embedded in another infinite fluid medium, is computed. The translational addition theorem for spherical wave functions is used to express series of wave modes centered at one sphere in terms of modes centered at the other, thereby facilitating the task of satisfying the boundary conditions. By letting the fluid sphere become either infinitely dense or infinitely compliant, the special cases of a spherical source radiating in the presence of a perfectly reflecting spherical scatterer are obtained. The source output and farfield directional response pattern are computed as a function of source and fluid sphere separation for some representative values of relative fluid density and sound speed. Numerous results are presented showing the modification of the radiation load on monopole and dipole sources of various wavelength sizes due to a nearby rigid or pressure release, spherical scatterer of the same size. The effect of the perfect scatterer is only important when the source and scatterer are very close and the pressure‐release scatterer has considerably more effect than the rigid one.Subject Classification: [43]20.30, [43]20.55.

ISSN:0001-4966    

DOI:10.1121/1.381158

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

We present a theory of attenuation of sound by turbulence. The mechanism underlying this theory is the turbulence‐induced broadening of finite beams of sound. It is thus conjectured that attenuation of sound by turbulence is not an intrinsic property of the medium, nor even of its dynamic state, but depends on the particular details of the experiment, such as beamwidth, beam orientation, etc. This point of view is at odds with that of some other theories, in which attenuation by turbulence is regarded primarily as a scattering process. Some conceptual flaws in these other theories are pointed out. It is shown that the present theory yields results which are in qualitative agreement with observations.Subject Classification: [43]28.40, [43]28.60; [43]20.35.

ISSN:0001-4966    

DOI:10.1121/1.381159

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Acoustic‐phase fluctuations induced by internal waves in the ocean are calculated in the geometric approximation. The results compare favorably with available experimental data.Subject Classification: [43]30; [43]28.60.

ISSN:0001-4966    

DOI:10.1121/1.381160

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The phase integral approximation is modified to describe wave propagation in three dimensions without any singularities at classical turning points. For stratified media a rigorous ray tracing scheme is derived. Stratified media are shown in general to induce dispersion. The connections to both the normal mode and filter theory methods are discussed. The effects of oceanic surface thermoclines upon rigorous ray tracing are shown to be frequency dependent.Subject Classification: [43]30.20; [43]20.15.

ISSN:0001-4966    

DOI:10.1121/1.381161

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Normal‐mode calculations are made of wave propagation in a bilinear medium with a free surface (the surface duct). The WKB approximation is used. In the usual way, the integral expression for the field is transformed into an infinite series of the residues (normal modes) of the integrand at its poles (eigenvalues). Approximations for the eigenvalues of the trapped normal modes are obtained from WKB formulas. The eigenvalues of the untrapped modes are obtained by quadratic extrapolation of the eigenvalues of the trapped modes. The accuracy of the real part of the eigenvalues of all modes is improved by taking into account the imaginary part when solving the characteristic equation. On comparing a number of WKB calculations of transmission loss with exact calculations, it is found that when there is little fine structure in the transmission loss curve, the WKB result is a good representation of the exact result. When there is significant fine structure, however, the WKB results are often in error by several decibels, and occasionally by up to 20 dB.Subject Classification: [43]30.20; [43]20.15; [43]30.50.

ISSN:0001-4966    

DOI:10.1121/1.381162

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

A treatment of the effects of arbitrary motion of a cw source and depth‐dependent sound speed on the total acoustic field at a fixed receiving point is considered for an ocean with horizontal boundaries. Application of our general method is made to a constant sound‐speed channel in which the range‐to‐depth ratio is large, when the source follows a short straight‐line path with constant velocity. Total‐field phase is investigated as a function of receiver time for various source trajectories and phase rate is examined in terms of an arbitrary, but fixed, acoustic frequency. It is shown that source motion may be accounted for by assuming the sound source to be stationary, and by replacing its frequency by approximate Doppler frequency. For long source trajectories, cumulative phase can be approximated as a hyperbolic function of time. The outputs of two uniform colinear arrays, together with power spectra there, are employed to illustrate one method for determing source speed, location, bearing, and frequency.Subject Classification: [43]30.20; [43]20.20..

ISSN:0001-4966    

DOI:10.1121/1.381163

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The acoustic pressure versus time signature of an underwater explosive source is a sensitive function of the charge weight and the depth of the explosion. If those parameters are known, then the amplitude of the primary shock pulse and the amplitudes and spacings of the following bubble pulses may be accurately predicted. The power spectrum of the signal is characterized by a scalloped form, which also is determined by the charge weight and depth. Even though the signal observed at long range is distorted due to propagation effects, the scalloped spectral structure is preserved. By using power cepstrum techniques, it is possible to determine the characteristic period of the spectrum. From the relation between the spectral period and the bubble pulse period, the exact detonation depth may be determined from a received shot signal if the charge weight is known. An example of such a measurement is presented in this paper. A series of signals from 1.8 lb Mk 61 SUS charges detonated at nominal depths of 60 ft was examined. The bubble pulse period of each source was determined from recordings made onboard the ship from which the shots were deployed. Shots were received at ranges of 250–310 NM at one location and at ranges of 625–700 NM at another location. The depths, as estimated at the remote receiver, were distributed about the onboard measurements with standard deviations of 0.49 ft at the shorter ranges and 0.52 ft at the longer ranges.Subject Classification: [43]30.75.

ISSN:0001-4966    

DOI:10.1121/1.381164

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Theoretical predictions, as well as observations at relatively short ranges and steep grazing angles, show that a sound wave which is forward scattered from the ocean surface has its frequency components smeared by surface‐wave motion [M. V. Brown and G. V. Frisk, J. Acoust. Soc. Am. 55, 744–749 (1974)]. The subject of this paper is the presence of observable sidebands in cw signals which are generated by a moving source received at ranges of up to 200 NM in the deep ocean. The sidebands are approximately 0.1 Hz from the source center frequency and are as strong as 20 dB below the level of the signal received at the source frequency.Subject Classification: [43]30.20, [43]30.30, [43]30.40.

ISSN:0001-4966    

DOI:10.1121/1.381165

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The title problem is studied using a single‐scatter theory. General expressions are obtained for the distribution of scattered acoustic intensity among the waveguide modes and for a measure of azimuthal beam pattern of the intensity in a specified waveguide mode. Detailed calculations are carried out for a specified waveguide and for specified statistics of a fluctuating sound speed, which, while not being representative of actual ocean conditions allow our drawing conclusions that are applicable to ocean acoustic experiments. The importance, previously noted by Beran and McCoy, of the highly anisotropic nature of the fluctuations caused by internal waves on the scattering process is demonstrated. Several conclusions are drawn of the effects that this anisotropy can be expected to play in the multiple‐scatter region.Subject Classification: [43]30.40, [43]30.50; [43]60.20.

ISSN:0001-4966    

DOI:10.1121/1.381153

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

This paper deals with scattering channels involving signal paths that are reflected several times from the boundary on their way from the transmitter to the receiver. The transmitted signal is a single‐frequency sine wave, and the surfaces from which it is reflected are regarded as being statistically independent. Therefore the autocorrelation function of the received signal has a very simple form consisting mainly of the product of the characteristic functions of the various reflecting surfaces.Subject Classification: [43]30.20; [43]30.40.

ISSN:0001-4966    

DOI:10.1121/1.381154

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP