Research in nonlinear acoustics

Research in nonlinear acoustics was carried out during the period 1 April 1975 - 31 August 1986. The general goal was to understand the behavior of sound waves of finite amplitude. Progress toward this goal was made by attacking specific problems in the following areas: (1) Theoretical work on periodic waves, including Burgers' equation and sound beams, (2) Tones, noise, and interaction--mainly experimental, including outdoor propagation of tones and noise, suppression of sound by sound, interaction of noise with a tone, and noncollinear interaction of two tones in a rectangular waveguide; (3) N waves and other transients, including development of a schlieren system, diffraction by a slit, propagation in a cylindrical tube, shock rise time, and propagation of a weak shock having a tail of arbitrary waveform; (4) Propagation in inhomgenous fluids, including values of B/A for sea water and nonlinear geometrical acoustics with applications to long range underwater propagation; (5) Nonlinear effects in air-filled porous materials; (6) Parametric receiving array; (7) Focused beam parametric transmitter; and (8) Miscellaneous topics. Work was also done on selected topics in linear acoustics, such as thermoacoustics and water-to-air sound transmission.