摘要:

Edge‐mode radiation is determined for an infinite membrane with a discontinuous fluid loading condition. The upper half of the membrane is exposed to a heavy fluid which accounts for a fluid–structure interaction. The lower half of the membrane is exposed to very light fluid which imposes no fluid loading on the structure. A very soft compliant layer is attached to half of the membrane surface. The compliant layer lessens the local coupling between the fluid and the structure, thus creating the fluid loading discontinuity. The effect of this fluid loading discontinuity upon the radiated farfield is evaluated.

ISSN:0001-4966    

DOI:10.1121/1.381965

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Subharmonic vibrations of order 1/3 in stretched strings driven by a single‐mode planar simple harmonic force are investigated. It is shown that both planar and nonplanar subharmonic resonances can occur. Subharmonic vibrations are possible only if the amplitude of the force exceeds a certain critical value which depends upon the magnitude of the damping coefficient. The stability of the solution is analyzed, and it is shown that the region of stable nonplanar vibrations is wider than that of stable planar vibrations. It is also observed in the case of nonplanar vibrations that the amplitude of the subharmonic in the plane normal to the plane of the driving force is larger than that in the plane of the driving force.

ISSN:0001-4966    

DOI:10.1121/1.381966

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

When a radiofrequency potential is applied to an electrode such as gold in an electrolyte, ultrasound is generated at the interface. This effect is attributed to changes in the volume of the solution adjacent to the metal and can be used to study the structure of the interface. Preliminary measurements are reported as a function of the dc electrode potential.

ISSN:0001-4966    

DOI:10.1121/1.381967

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Conventional ultrasonic transducers transform acoustic waves into electrical signals preserving phase and amplitude information. When the acoustic wavelength is significantly smaller than the transducer diameter, severe phase modulation of the electrical signal can occur. This results in anomalous attenuation measurements, background noise in Non‐Destructive Evaluation (NDE), and in general complicates data interpretation. In this article, we describe and evaluate a phase insensitive transducer based on the acoustoelectric effect. Theory of operation of the Acousto‐Electric Transducer (AET) is discussed and some optimization procedures outlined for its use. Directivity data for for the AET is contrated with a conventional piezoelectric transducer. In addition, transmission scanning data of phantom flaws in metal plates is presented for both transducers and demonstrates a significant improvement in resolution with the AET.

ISSN:0001-4966    

DOI:10.1121/1.381968

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Investigations have been made of the effect of diffraction on the propagation of acoustic impulses in water. Gaussian shape pressure pulses were obtained by applying 0.2‐μs‐wide voltage pulses to thick piezoelectric plates that act as piston sources. Acoustic probe techniques were used to examine in detail the resulting pressure profiles. These are strongly affected by diffraction phenomena, and because of the transient nature of the process, special care must be taken in interpreting the observed data. Comparisons between experimental and theoretical time and space pressure profiles are presented.

ISSN:0001-4966    

DOI:10.1121/1.381969

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A statistical analysis of the intensity of acoustic signals received from three sources (9.8, 110, and 262 Hz) towed at long ranges (100–3000 km) in the ocean is presented. The experimental probability density functions for the linear intensity are tested against the following density functions using the Kolmogorov–Smironov test at the 5% significance level: exponential, Gamma, log‐normal, and log‐normal with a standard deviation of 5.57 dB. It is found that no single function adequately represents the experimental density functions at all three frequencies, and none of the functions is appropriate at 262 Hz. At 9.8 Hz, three distributions (Gamma, log‐normal, and log‐normal with a 5.57 dB sigma) give excellent results. At 110 Hz, only the log‐normal (with 5.57 dB sigma) theory yields good results. The ability of all the functions to describe the experimental results decreases with increasing frequency.

ISSN:0001-4966    

DOI:10.1121/1.381970

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Theory for the impulse response of a spherical wave backscattered from a plane strip has been used with a computer model of a randomly rough long‐crested ocean surface to reveal the relative contributions of diffraction, facet reflection, and interference at near‐grazing and near‐normal incidence and to incorporate acoustical shadowing in a natural way. The major findings for near‐grazing incidence are that backscatter is due to diffraction at troughs and crests; the backscattering strength is −54 dB at 5 m/s and only 2 dB more at 20 m/s, both flat for grazing angles 1° to 10°; and it decreases about 3 dB for an octave increase in frequency, independent of wind speed. At normal incidence the decreasing value of the backscattered coherent intensity with increasing roughness is due to interference. It is related to the transform of the probability density function of the surface height until the roughness parameterg(=4k2σ2) reaches approximately 5, where there is a deep minimum due primarily to interference of the highly coherent diffracted contributions. At normal incidence the backscatter is dominated either by diffraction or reflection, depending on the sphericity of the wave front.

ISSN:0001-4966    

DOI:10.1121/1.381971

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Statistics of fluctuations of low‐frequency sound in the ocean are analyzed for an arbitrary number of paths. Covariances are derived for the intensity, phase rate (time derivative of the phase), and related parameters. Power spectra are derived from the covariances. The multipath results are based on weakly fluctuating single paths whose phase is perturbed by the internal‐wave field. The theory is illustrated by deriving some results for a single internal wave. We specialize to a large number of equal energy paths by appealing to the central‐limit theorem which states that the Cartesian components for the multipath field are Gaussian distributed. Some results available in the literature are shown to be valid for the special case of a large number of paths. Power spectra for data obtained in a recent experiment are shown to follow the predictions of this analysis.

ISSN:0001-4966    

DOI:10.1121/1.381972

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The scattering of interaction‐frequency components from two sound waves interacting at a nonzero angle has been the subject of controversy for the last two decades. This paper attempts to provide better understanding of the problem by discussing the relationship found between the scattering of sound by sound and the parametric receiving array. First, the solution for a high‐frequency plane wave interacting with a low‐frequency plane wave over a half space is discussed. The high‐frequency sound wave is assumed to originate at a planar boundary and to propagate away from it. Then the interaction‐frequency components at some distance from this planar boundary are found. When this solution is related to a solution for a parametric receiving array with a low‐frequency plane signal wave and a high‐frequency narrowbeam pump wave, the two solutions are found to have very similar properties. Some experiments, as well as solutions, for various configurations of the parametric receiving array are discussed in light of the problem of scattering of sound by sound. Finally, some of the foibles associated with measurements of two interacting waves are described with the aid of the theoretical model for the parametric receiving array. In this paper interaction components are found to exist even when the two sound waves do not propagate in the same direction. It will also be shown that points exist along the nulls of the pump beam patterns where the one primary sound wave is zero and the interaction components are nonzero.

ISSN:0001-4966    

DOI:10.1121/1.381973

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The interior boundary‐value scalar (acoustic) problem in the region between two spheres of radiiR1,R2and distancedbetween their centers is considered for both Dirichlet and Neumann boundary conditions. Surface singular integral equations are used to formulate the problem. Their solution is obtained in terms of spherical wave functions in combination with related addition theorems. It is then specialized to the case of small values forkd=2πd/λ to yield exact, closed‐form expressions for the coefficientsgnsin the resulting relations ωns(kd) =ωns(0) [1+gns(kd)2+⋅⋅⋅] for the resonant (natural) frequencies of the cavity. Numerical results, comparisons, and possible generalizations are also included.

ISSN:0001-4966    

DOI:10.1121/1.381974

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP