Volume 106, Issue 6, December 1999
Index of content:
- NONLINEAR ACOUSTICS 
106(1999); http://dx.doi.org/10.1121/1.428167View Description Hide Description
Nonlinear propagation of finite-amplitude acoustic pulse in water and through a sample of water-saturated granular medium is considered. To generate high-intensity acoustic pulses laser generation of sound was used. The region of fluid perturbed by the laser acts as a volume-distributed source. In a fluid with weak light attenuation, a cylindrical source could be formed by a narrow laser beam. The nonlinear distortion of the cylindrical finite-amplitude wave in water is investigated. The measured rate of distortion corresponds to that calculated in the approximation of nonlinear acoustics. In a strongly light-absorbing medium, a wide (compared to the typical sound wavelength) laser beam produces a circular planar source. Such a source produces acoustical pulses of amplitude up to 3 MPa and duration about 1 μs in different fluids. This source was used to investigate the propagation of high-intensity wide frequency band sound signals in a sample of water-saturated cobalt–manganese crust (CMC). Specific acoustical features of the crust such as nonlinear sound pulse distortion and the frequency dependance of attenuation, varying with the amplitude, are considered. Theoretical interpretation of the results is given.
106(1999); http://dx.doi.org/10.1121/1.428168View Description Hide Description
The quasi one-dimensional problem of nonlinear longitudinal wave propagation in the elastic medium undergoing inhomogeneous plane prestrain is investigated theoretically. The analytical solution to describe the propagation of the wave with an arbitrary smooth initial profile is derived. The influence of the magnitude of the prestrain intensity on the distortion of the wave profile is studied. The sine-wave propagation in the medium subjected to the distributed static load is considered in more detail. The dependence of the sine-wave characteristics on the physical and geometrical properties of the medium and on the parameters of the predeformed state is clarified. The possibility to enhance the efficiency of ultrasonicnondestructive testing making use of the nonlinear effects of wave propagation is discussed. The algorithm to evaluation of the parameters of plane strain on the basis of wave profile evolution data is proposed.
106(1999); http://dx.doi.org/10.1121/1.428169View Description Hide Description
A solution for multifrequency plane waves propagating through a dissipative and nonlinear medium is presented. It originates from the well-known Bessel function series ratio for a pure sinusiodal wave, introduced by Cole and Mendousse. The solution is exact. The only limitation, inherited from the single-frequency solution, is the slow convergence of the series when the nonlinearity is very large compared to the dissipation. Otherwise any frequencies, amplitudes and phases can be introduced in the original wave and the solution is valid for any propagated distance.
106(1999); http://dx.doi.org/10.1121/1.428170View Description Hide Description
Radial motion of a spherical air bubble in acoustic fields is observed experimentally. The radius-time curves and frequency responses are obtained from the experiment for comparison with a numerical calculation. The calculation is based on a mathematical model in which the thermo-fluid mechanics of the gas in the bubble is precisely described. An oscillatory pressure field is generated in a cylindrical cell, which consists of two piezoceramic transducers and a glass cylinder. A new bubble generator is developed. It is able to generate a bubble filled with an arbitrary kind of gas. The bubble motion is observed by high-speed photography. The time history of the bubble radius is measured from the pictures. The pressure field has a frequency of 19.2 kHz and its amplitude is up to 40 kPa. The bubble has an initial radius within the range from 0.1 mm to 0.25 mm. A highly viscous silicone oil, whose kinematicviscosity is 100 mm2/s, is used for the liquid to keep the spherical shape of the bubble. A quantitatively good agreement between the experimental and numerical results is obtained. The difference between experiment and theory based on the polytropic approximation for the gas is briefly discussed.