MODEL EQUATIONS OF NONLINEAR ACOUSTICS

Over the past twenty-five years , nonlinear acoustics has developed into a vigorous and distinctive branch of science. The subject covers a wide range of topics, including steady finite-amplitude waves in supersonic aerodynamics, weak-shock theory, unsteady finite-amplitude waves in gases, liquids, and solids, bubble dynamics and cavitation in liquids, and phonon interactions and the quantum acoustics of solids. Practical applications are on the increase: the steady wave systems of supersonic projectiles; the nonlinear parametric sonar array devised by Westervelt (1963) for the production of a highly directional low-frequency beam in water or air; the damaging effects of cavitation and bubble implosion on ship structures in water and on nuclear reactors cooled by liquid sodium; and the use of ultrasonics in biomedical and engineering non­ destructive testing. These are all well-known examples, though they hardly exhaust the possibilities . A series of eight (as of 1978) international symposia in the USA, Europe, and the USSR has greatly stimulated work in many aspects of nonlinear acoustics