NONLINEAR AND THERMOVISCOUS PHENOMENA IN ACOUSTICS .2.

The present paper is intended as a review (over 300 Refs.) of some bas ic concepts and modern investigations of nonlinear and thermoviscous p henomena in acoustic fields in fluids. The focus is on theoretical mod els of nonlinear acoustics for acoustic time-averages, sound beams, an d nonlinear standing waves. The well-known topics of general use are c onsidered and the facts which are essential to implementation are also given. Special attention is paid to the combined analysis of the effe cts of nonlinearity and absorption, to secondary processes in intense sound fields, and to numerical simulation of nonlinear waves. The cont ent includes: Section 1. Equations of state. Fluid state. Section 2: E nergy and momentum transfer in the sound field. Section 3: Non-linear wave equation. Section 4: Evolution equations and their solutions. Sec tion 5: Standing waves. Part II of the paper includes sections 3 and 4 . In section 3, we present a derivation of the nonlinear wave equation in a thermoviscous fluid, its connection with Lighthill's equation, a nd outline the effect of acoustic streaming and heating on the nonline ar wave propagation. In section 4, frequently used model equations of nonlinear acoustics are reviewed starting with the familiar simple wav e equation. Computer codes and some experimental results are discussed for the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation and for more g eneral problem statements including the nonlinear wave equation.