摘要:

Experimental measurements are presented for the target strength and directivity patterns of the reflections from stainless steel spherical shells filled with a mixture of carbon tetrachloride and freon (F113) in the frequency range 30–130 kHz. Five spheres were tested having nominal outside diameters of 6, 7, 10, 12, and 18 in. with varying wall thicknesses. Target strength measurements were made separately on echo components arising from reflections from the front and rear surfaces of the sphere; the focused rear‐surface reflections showed target strengths up to 21 dB higher than those corresponding to the front surface, controlled by the sphere wall material and thickness, and by the index of refraction of the fluid.Subject Classification: [43]30.30.

ISSN:0001-4966    

DOI:10.1121/1.380932

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

We have derived expressions for the mean‐square phase and intensity fluctuations and their spectra for cw sound propagating through a channeled fluctuating ocean. The ’’supereikonal’’ approximation reduces to the geometric optics (eikonal) limit for short acoustic wavelengths: λ≪2πL2H/Rand λ≪L2V/(R tan2ϑ), whereLHandLVare horizontal and vertical correlation lengths of the fluctuations,Ris range, and tanϑ is the ray slope, replacing the traditional (and much more severe) Fresnel condition λ≪2πL2/Rfor a homogeneous isotropic ocean. The results can be expressed in closed form for an exponentially stratified ocean model and associated ’’canonical sound channel,’’ with superimposed fluctuations from an internal wave model spectrum based on oceanographic observations. The parameters are the stratification scaleB, the inertial and buoyancy frequencies ωinandn(z), the scalej*of internal wave mode numbers, and the internal wave energy per unit area. The results are in reasonable agreement with numerical experiments based on the parabolic wave equation. For the ’’singlepath’’ 4‐kHz transmission over Cobb Seamount the observed and computed rms fluctuations in phase are 1.6 and 2.5 cycles, respectively; in intensity these are 5.5 and 2.2 dB, respectively, with anomalous intensities measured at high frequencies (’’sporadic’’ multipathing?). For the multipath 406‐Hz MIMI transmission, we obtain 4×10−3and 5×10−3sec−1, respectively, for the experimentally determined and the computed rms phase rates.Subject Classification: [43]30.20, [43]30.40; [43]20.15.

ISSN:0001-4966    

DOI:10.1121/1.380933

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The influence of the sea bottom on shallow‐water sound propagation can be especially pronounced for the sound field near the boundaries. Comparison of the near‐surface sound field with the mid‐depth field, for example, can serve as a useful diagnostic tool for understanding the frequency‐dependent influence of the sea bottom on sound propagation in shallow water. Broad‐band shallow‐water sound‐propagation data analyzed in one‐third octave bands are compared for a very shallow receiver (2 m) and a mid‐depth receiver (50 m). The data are also compared with results from modal calculations. The interplay between the behavior of the modal depth functions and modal attenuations, as frequency is varied, provides a convenient model for interpreting the results.Subject Classification: [43]30.20, [43]30.30.

ISSN:0001-4966    

DOI:10.1121/1.380934

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Classical wave theoretical treatments can be used to predict the general characteristics of the acoustic field scattered from a roughened time‐varying sea surface. Various approximations can then be invoked to handle the so‐called slightly rough and very rough surface cases. In this paper an expression for the spectrum of the scattered sound is derived for the very rough case in terms of specific surface‐wave parameters. This expression is then evaluated for several surface spectra, including the fully aroused Neuman–Pierson and Pierson–Moskowitz surface wave spectra. Finally, these results for special cases of the Neuman–Pierson spectra are compared with those obtained by numerically integrating the general form for the same spectra, a technique that does not involve the very rough case approximation.Subject Classification: [43]30.40; [43]20.15.

ISSN:0001-4966    

DOI:10.1121/1.380935

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Results of a previous hydrodynamical study of a uniform, deep‐ocean flow are used to develop simple approximations to the sound‐speed and current distributions in the flow. The behavior of sound speed with depth, surface current, and source and receiver locations is examined. The effects of the flow on ray geometry, travel time, and spreading loss are investigated for a surfaced cw sound source and bottomed receiver. Total‐field amplitude and phase are determined and are found to be highly sensitive to surface‐current variations and to source and receiver locations. A simple method is presented for accurately estimating amplitude and phase. Then, an approximate phase formula is developed that is proportional to surface current, linear in source location, and sinusoidal in the orientation angle of the source–receiver range.Subject Classification: [43]30.20; [43]28.60.

ISSN:0001-4966    

DOI:10.1121/1.380936

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

A solution is given for the problem of the forced longitudinal vibration of an elastic circular rod, one end of which is attached to the surface of an elastic half‐space and to another end of which a periodic disturbing force is applied. Resonance curves for the motions of rods are derived using specific boundary conditions. Attention is directed to the effective damping of the motion of the rod due to dissipation of waves to infinity.Subject Classification: [43]40.20; [43]20.22.

ISSN:0001-4966    

DOI:10.1121/1.380945

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Electroelastic equations containing terms up to cubic in the small mechanical displacement field, but no higher than linear in the electric variables, are applied in the analysis of nonlinear resonance in rotated Y‐cut quartz oscillators. Both pure thickness‐shear vibrators and essentially thickness‐shear trapped‐energy resonators are treated. This is a natural continuation of earlier work on intermodulation in the same resonators. Since in each equation each nonlinear term is negligible compared to an associated linear term, the solutions are obtained by employing an asymptotic iterative procedure and expanding in the eigensolutions of the associated linear problem and, in the vicinity of a resonance, retaining only that nonlinear term correcting the dominant eigensolution. Lumped parameter representations of the solutions, which are valid in the vicinity of a resonance and relate the amplitude of the dominant mode nonlinearly to the voltage across the crystal, are presented for both the pure thickness‐shear and trapped energy thickness‐shear problems. In each instance the expression for the current through the crystal is determined, the influence of the external circuitry is included in the analysis and, ultimately, an expression cubic in the mode amplitude and linear in the driving voltage is obtained. The analyses hold for the fundamental and odd overtone thickness‐shear modes. Nonlinear resonance curves are presented for AT‐cut quartz using the nonlinear coefficient γ determined in earlier work on intermodulation.Subject Classification: [43]40.24, [43]40.30; [43]85.52.

ISSN:0001-4966    

DOI:10.1121/1.380946

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The equations of three‐dimensional linear piezoelectricity are applied in the analysis of trapped‐energy resonators with rectangular electrodes vibrating in coupled thickness shear and thickness twist in the vicinity of the fundmantal and odd overtone thickness‐shear frequencies. Closed form asymptotic expressions for the frequency wave‐number dispersion relations for the fundamental and odd overtone coupled thickness‐shear and thickness‐twist waves near cutoff are obtained for both the electroded and unelectroded regions of the trapped‐energy resonator. The influence of piezoelectric stiffening, electrode mass loading, and electrical shorting is included in the analysis. Simple approximate boundary conditions at a junction between an electroded and unelectroded region of the plate are obtained in a manner exhibiting the natural limitations inherent in the approximation. In order that these boundary conditions can be satisfied at each such junction, in the adjacent regions the wave numbers in the direction of the junction line are assumed to be the same. The boundary conditions to be satisfied at the junctions between the unelectroded corner region and the unelectroded regions adjacent to the electroded region are obtained from an extended version of the variational principle of linear piezoelectricity. These latter conditions result in the form of the solution in the corner region. One result of the foregoing analysis is the determination of a two‐dimensional condition which is a generalization of Bechmann’s number in one dimension. The above‐mentioned dispersion relations and edge conditions are applied in the analysis of the steady‐state vibrations of a trapped‐energy resonator and a lumped parameter representation of the admittance, which is valid in the vicinity of a resonance, is obtained.Subject Classification: [43]40.24; [43]85.52, [43]85.32.

ISSN:0001-4966    

DOI:10.1121/1.380947

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The perceived pitch mixture of two tones of a dichotically presented chord was studied as a function of the difference between the intensities of the right and left ear tones (ΔI). Previous experiments have shown that, within a wide range of ΔI, the pitch mixture is independent of ΔI. This intensity independence of the pitch mixture of dichotic chords is not seen with monaural chords. Within the range of ΔIover which intensity independence is seen, the pitch mixture of the dichotic chord is determined by another property of the central pitch processor—the ear dominance function. In previous experiments the intensity independent function could only be detected in those subjects with a weak ear dominance function. In the present experiments subjects adjusted the relative intensities of the two tones of a binaural chord to match the pitch mixture of a dichotic chord. Using this method, the intensity independent function was measured directly in all subjects. In addition, the present method provides a direct measure of the magnitude of the suject’s ear dominance function and clarifies the relationship between the effects of the two functions.Subject Classification: [43]65.75, [43]65.54, [43]65.62.

ISSN:0001-4966    

DOI:10.1121/1.380948

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Mechanical impedances of the mastoid portion of the temporal bone and of the forehead are presented for 60 human subjects of both sexes and of ages between 9 and 71 years. Measurements were carried out using a plane circular surface of 1.75 cm2and a static force of 5.4 N (ISO/IEC conditions). Impedance is found to vary with age and to a lesser extent with sex. Results are consistent with earlier measurements carried out under somewhat different conditions, but deviate rather substantially at most frequencies from the recommended ISO/IEC mechanical impedance for an artificial headbone. A study of the influence of variations in the mechanical headbone impedance upon bone vibrator performance by means of an analogous electrical network is reported.Subject Classification: [43]65.64; [43]85.20.

ISSN:0001-4966    

DOI:10.1121/1.380949

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP