摘要:

The impact of a tool against a sonic transmission line is a subprocess of the impact coupling method of sonic power transfer. This process is modeled and the nonlinear governing equation developed in this paper. A probability density function is derived that enables the average rebound velocity of the impacting tool to be established. Numerical results are obtained, for selected material‐geometry parameters, on the stress pulses resulting from several conditions of impact, for the rebound velocity as a function of phase angle of impact and for the average rebound velocity. Future work will consider the entire impact coupling process and tools of more complex shape.

ISSN:0001-4966    

DOI:10.1121/1.1913087

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The problem of transient axisymmetric vibrations of thin circular elastic plates due to sonic boom excitation is investigated. The equation of motion for a solid circular plate is solved by applying the modified finite Hankel transform and the Laplace transform, and the numerical results are obtained with the help of the digital computer. From the analysis of the data, obtained for the dynamic deflections of the plates for the boom duration, it is concluded that for a normal flight the boom duration has a significant effect on the vibrations of plates as compared to the overpressure of the boom.

ISSN:0001-4966    

DOI:10.1121/1.1913088

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

An approximateZ‐transform approach is presented to compute at discrete time intervals the time responses of lumped or distributed parameter systems which exhibit wave propagation or time delay effects. The approach was previously developed by Boxer and Thaler [R. Boxer and S. Thaler, Proc. IRE44, 89–101 (1956)] as a numerical method of solving linear and nonlinear equations and is an extension of the more familiar Laplace transform technique which is used for the analysis of continuous linear systems. Rather than directly utilizing the inverse Laplace transformation to obtain the time function, a mapping of the Laplace transform of the function from thesdomain to thezdomain is performed via the transformationz=esT, whereTis the desired sampling interval of the time function. Unlike the inverse Laplace transformation, which requires the pole‐zero structure of the transform to obtain the continuous time function, the sampled time function is then obtained from itszdomain representation without using the theory of residues. Numerical solutions to several problems are presented to illustrate the advantages of the approximateZ‐transform approach.

ISSN:0001-4966    

DOI:10.1121/1.1913089

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

To calculate the ray intensity field at a point (a receiver point) in range and depth, all significant ray paths from the source to the receiver must be found. When there are a large number of receiver points, it is desirable to use a method in which all receiver points are considered as the rays are tested to find those that travel from the source to a receiver. This paper describes a simple method for finding all ray arrivals during a single sweep out of the source beam pattern and at the same time calculating the total ray intensity field at the receiver points.

ISSN:0001-4966    

DOI:10.1121/1.1913090

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The angular plane‐wave spectrum representation of the acoustic field due to a source of arbitrary directivity is used to formulate the problem of scattering by a rough sea surface. An approximate solution is obtained by applying Kirchhoff‐type boundary condition at the surface. The solution suggests a straightforward modification of current ray‐tracing techniques in order to estimate the coherent part of the reflected field.

ISSN:0001-4966    

DOI:10.1121/1.1913091

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

This paper concerns the high‐speed motion of transient cavities generated in an acoustic stationary wave in a cylinder filled with water. Time‐exposure photographs are presented of the cavities illuminated by a high‐speed stroboscope showing multiple exposures of an individual cavity as it was propelled outward from a region of large acoustic pressure amplitude. The photographs show several interesting details of the cavitation event. Velocities obtained by the cavities were on the order of 1 m/sec, pressure amplitudes on the order of 5 bars, and cavity lifetimes on the order of 10 msec. A theoretical analysis of the cavity motion is obtained by considering the cavity as a spherical inhomogeneity in an acoustic stationary wave. Comparison of theory and experiment show good agreement provided that a velocity‐squared drag law is used with a drag coefficient of 0.77.

ISSN:0001-4966    

DOI:10.1121/1.1913092

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

When underwater sound waves propagate from a transmitter to a receiver, part of the energy reaches the receiver after reflection and scattering from the sea surface. This boundary effect can be called theimpulse responseof the sea surface if the incident sound field is caused by a delta pulse. In this paper the Helmholtz diffraction integral is used together with a perturbation technique for the derivation of a formula for the corresponding transfer function. The result is a random function that depends on the frequency of the incident wave, on time, and on the source‐receiver configuration. Its validity is limited by three assumptions: (1) the medium is ideal (constant velocity, no subsurface layer), (2) source and receiver depth are many times larger than the surface elevation, and (3) the bottom is infinitely far away. For very high frequencies the formula indicates specular reflection from each surface “highlight.” In the Fraunhofer domain, the transfer function reduces to specular reflection with phase fluctuations. Some results of a statistical analysis are included for that frequency domain.

ISSN:0001-4966    

DOI:10.1121/1.1913093

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Ray geometry, travel time, and spreading loss are examined for a moving medium. The sound speed and current are both depth‐variable, and the current direction is fixed in space. For a linear sound speed and current, ray geometry is investigated and an approximate solution is obtained which leads to helical paths. For a bottom‐mounted source and receiver in the vertical plane of the current, the linear model is used to investigate ray geometry, travel time, spreading loss, and the acoustic field associated with refracted/bottom‐reflected (RBR) transmissions. It is shown that the effects of current gradients and bottom currents on the phase and amplitude of the acoustic field are important and cannot be ignored. Further, long‐term time variations in the current gradient are shown to cause much shorter‐term variations in phase and amplitude.

ISSN:0001-4966    

DOI:10.1121/1.1913094

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The pressure field of nonuniform, slender, free‐free beams of circular cross section is constructed by modeling the beam as a dipole array. Using the orthogonality relation of normal modes, the farfield pressure in a plane normal to the beam axis is shown to be associated with rigid‐body translation and, under highly restrictive conditions, viz. local deviations of the effective beam density from the beam's mean density, on elastic, particularly resonant modes.

ISSN:0001-4966    

DOI:10.1121/1.1913095

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Observations of acoustic cavitation have been in heliumIandIIusing an extensional‐mode vibrator capable of very high intensities at 10 kHz. Remote monitoring of the drive oscillatory velocity was achieved. In helium I clouds of small vapor bubbles were visible, as well as larger bubbles near the expected radial resonance size. For comparison, observations were also made using two other normal liquids—nitrogen and water—at temperatures near their boiling points. In helium II observation of acoustic streaming with emission of white noise suggested the presence of even smaller vapor bubbles. A strong subharmonic signal with low threshold excitation has not been fully explained.

ISSN:0001-4966    

DOI:10.1121/1.1913096

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP