Index of content:
Volume 104, Issue 2, August 1998
- NONLINEAR ACOUSTICS, MACROSONICS 
Numerical and experimental study of finite-amplitude standing waves in a tube at high sonic frequencies104(1998); http://dx.doi.org/10.1121/1.423346View Description Hide Description
Finite-amplitude standing waves in an air-filled tube are studied numerically and experimentally. The standing wave is excited at one end of the rigid-walled tube and a rigid cap is assumed at the other end. The one-dimensional nonlinear second order wave equation is solved numerically using a finite element algorithm based on the Bubnov–Galerkin method. Viscous and thermal losses at the walls of the tube are taken into account. An experimental setup is developed for the study of standing waves at high sonic frequencies. The acoustic field is measured along the tube axis with a fine calibrated probe. Experimental data of pressure distributions for the fundamental frequency (9.5 kHz) and the second harmonic (19 kHz) are compared with the numerical results, as a function of the tube length.
104(1998); http://dx.doi.org/10.1121/1.423347View Description Hide Description
It has been proved experimentally that a boundary has the “mirror effect” on a parametrically excited soliton. The numerical simulation with the parametrically driven and damped nonlinear Schrödinger equation reproduces the observed interesting phenomena, in particular, the periodical collisions and reflections of the boundary soliton. The dynamical behaviors of the soliton are further concluded as a stability diagram in the space of control parameters. In addition, the internal dynamics including the collision-reflection mechanism of the boundary soliton is also explored tentatively.
104(1998); http://dx.doi.org/10.1121/1.423308View Description Hide Description
The difference-frequency sound generation as a result of interaction of two high-frequency harmonic waves in a bubble layer in water is investigated both theoretically and experimentally. Because the sound speed in the layer is less than that outside, the layer has resonanceproperties. As was shown before, this can considerably increase the efficiency of the nonlinear frequency transformation. However, unlike the cases considered before, the layer resonance is practically achievable only at the low (difference) frequency, whereas the high-frequency signal (pump) resonates at individual bubbles and then it strongly dissipates. Here the results of an experiment with a bubble layer with a thickness of about 10 cm in an anechoic tank are presented. One of the incident (primary) wave frequencies was 60 kHz, whereas the other could be varied, thus providing the low-frequency signal in the range of 0.8–14.8 kHz. Due to the first-mode layer resonance, this secondary signal had a pronounced maximum at a frequency of 2.4 kHz. The high attenuation of pump waves was due to resonantbubbles. A theory which agrees with the experimental results reasonably well, is developed for this type of interaction.