摘要:

Second harmonic and fundamental standing‐wave amplitudes have been measured to see if nonlinearity parameters (combinations of third‐order elastic constants) can be determined from measurements made on samples driven at resonance. A model for the resonance is formulated by considering the process of overlap for a sample‐applied pulse whose length is extended to many overlap orders. Attenuation is included in the model, and the nonlinearity parameters obtained from the application of the model to experimental data are compared with values from other experiments.

ISSN:0001-4966    

DOI:10.1121/1.1913517

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The coherent component of specularly scattered underwater sound is sensitive to the probability density function (PDF) of displacements of the rough surface. For the specular reflection of diverging waves, the coherent component and the PDF are shown to be related by the Fourier transformation. Laboratory measurements of sound scattered at a partially shadowed nearly Gaussian model sea surface show the coherent component is much larger than would be expected for a Gaussian PDF. Fourier transformations of the measured PDF, on inclusion of a shadowing correction, gave the coherent component. Fourier transformation of the coherent component yields a surface PDF similar to the measured PDF with shadowing correction.

ISSN:0001-4966    

DOI:10.1121/1.1913518

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

It is shown that the Helmholtz equation is not exactly correct for a medium with a time‐dependent boundary. The equation can be used with very good approximation when the time‐derivative of the surface elevation is much smaller than the speed of the waves through the medium. For underwater sound waves, reflected and scattered by an ocean surface that can be described by the Pierson‐Moskowitz spectrum, this means that the wind speed has to be much less than the sound speed.

ISSN:0001-4966    

DOI:10.1121/1.1913519

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Transmission loss over the range of the direct arrival is examined for a receiver lying on a deep, sedimentary ocean bottom and is found to exhibit interference structure not explained by water‐borne paths alone. It is suggested that this structure can be understood in terms of energy refracted through the sediments back to the receiver. The velocity structure in the sediments required to account for the interference is quite consistent with the velocity structure inferred from seismic profiling the vicinity of the receivers.

ISSN:0001-4966    

DOI:10.1121/1.1913520

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A system consisting of three bottom‐moored 12 000‐Hz CW beacons, each separated in frequency by 40 Hz, and separated in space by about 8 km, has been used to track the motion of ship‐suspended, ship‐mounted, sonobuoy‐deployed, and bottom‐moored hydrophones to an accuracy of 4 cm. The system uses Doppler tracking of the beacon signals to provide real‐time estimation of hydrophone velocity and displacement. Factors that might compromise system performance, such as surface, bottom or forward volume scattering, or multipath effects, were found to be negligible. Random phase fluctuations in beacon signals due to these phenomena are small compared with those due to hydrophone motion. Two tests of the system, near Eleuthera Island and near Bermuda, were made in September–October 1972. [This work was performed under U.S. Office of Naval Research Contract No. N00014‐72‐C‐0205.].

ISSN:0001-4966    

DOI:10.1121/1.1913521

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Null geodesics of the metric tensor formed from the coefficients of the second‐order terms in the partial differential equation for sound are interpreted as the space‐time path histories of sound pulses in a geometric ray trace theory for sound propagation in moving inhomogeneous inviscid fluids.

ISSN:0001-4966    

DOI:10.1121/1.1913522

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Temperature‐jump measurements in sea water over the time domain 10−5to 10−2sec reveal a single relaxation of 1.5×10−4sec at 9.7°C, which appears to correspond to the ∼ 1 kHz relaxation found from long‐range sound propagation. Laboratory measurements indicate the relaxation to originate from boron with theB(OH)3‐B(OH)4−equilibrium the likely relaxation process.

ISSN:0001-4966    

DOI:10.1121/1.1913523

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Sound‐pressure levelLpat a depthd, in water, due to a point source in air at a distancehabove the water surface, may be calculated fromLp = [Ls −7 +20 log(cosθ)]−20 log(r/rs), whereLsthe source level is the sound‐pressure level in air at distancersfrom the source,ris the straight‐line distance to the receiving hydrophone from a virtual sound source situated under the actual source at heighth′ = (c1/c2) habove the surface;c1andc2are the respective speeds of sound in air and water; θ is the angle between the vertical and the line of lengthr. Comparisons with various published results obtained by more sophisticated ray‐theory show agreement within 1 dB, except at shallow depths and far sidewise from the sound source; agreement within 2 dB is found for new experimental data here presented for sound bursts of frequency 500, 1000, and 2000 Hz, andh= 3.5 m. For sound originating in water at depthdbelow the surface, the sound‐pressure level received in air is to be calculated fromLp = Ls − 52 + 40 log(cosθ) − 20 log(r/rs), whereLsis the source level, atrs, in the water. Experimental data obtained with a sound source in the water at depthd= 5.6 m, and frequencies of 500, 1000, or 2000 Hz, are in agreement with this equation, mostly within 2 dB, for receiving positions in air 1 or 2 m above the water and offsets as great as 3 m.

ISSN:0001-4966    

DOI:10.1121/1.1913524

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The evolution of finite‐amplitude plane waves as they propagate through monodisperse aerosols of spherical particulate matter is investigated theoretically. Attenuation, dispersion, and the growth of higher harmonics are considered in detail. It is shown that, except for the case of very low dust‐loading, the particulate matter dominates the gas self‐viscosity in determining acoustic processes. Using a criterion based upon harmonic ratios, regimes of allowed and precluded shock‐formation are tentatively identified and, in the case of the former, shock‐formation distances are given. The shock‐formation distance in an aerosol is shown to always be greater than that of the corresponding clean‐gas case. Finally, the theory is extended to polydisperse systems. The results reduce to those of existing theories for the limiting cases of (i) infinitesimal‐amplitude acoustics of dusty gases and (ii) finite‐amplitude acoustics of clean gases.

ISSN:0001-4966    

DOI:10.1121/1.1913525

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A technique for measuring thein vivoaverage velocity of ultrasound in the human female breast was developed and applied to determine the range of such values in the breast of normal subjects in the approximate age ranges 20 to 80 years and in subjects with selected breast pathologies. Reasonable correlation of the velocity values with breast tissue type, as determined by x ray (mammography), was obtained, indicating that ultrasonic velocity data provide useful information on the main tissue constituents in the breast and that this technique should allow safe, long‐term study of changes that may occur in the composition of such tissues.

ISSN:0001-4966    

DOI:10.1121/1.1913526

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP