Nonlinear acoustic waves in channels with variable cross sections

The point symmetry group is studied for the generalized Webster-type equation describing non-linear acoustic waves in lossy channels with variable cross sections. It is shown that, for certain types of cross section profiles, the admitted symmetry group is extended and the invariant solutions corresponding to these profiles are obtained. Approximate analytic solutions to the generalized Webster equation are derived for channels with smoothly varying cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic corrections introduced mainly in the Introduction and References. Several typos were also correcte

Group-invariant solutions of a nonlinear acoustics model

Based on a recent classification of subalgebras of the symmetry algebra of the Zabolotskaya-Khokhlov equation, all similarity reductions of this equation into ordinary differential equations are obtained. Large classes of group-invariant solutions of the equation are also determined, and some properties of the reduced equations and exact solutions are discussed.Comment: 14 page

Sound beams with shockwave pulses

The beam equation for a sound beam in a diffusive medium, called the KZK (Khokhlov-Zabolotskaya-Kuznetsov) equation, has a class of solutions, which are power series in the transverse variable with the terms given by a solution of a generalized Burgers' equation. A free parameter in this generalized Burgers' equation can be chosen so that the equation describes an N-wave which does not decay. If the beam source has the form of a spherical cap, then a beam with a preserved shock can be prepared. This is done by satisfying an inequality containing the spherical radius, the N-wave pulse duration, the N-wave pulse amplitude and the sound velocity in the fluid

Old-Age Behaviour of Cylindrical and Spherical Nonlinear Waves: Numerical and Asymptotic Results

Asymptotic and numerical analyses are presented for the nonlinear evolution of cylindrical and spherical acoustic waves subject to thermoviscous dissipation. Old-age asymptotic solutions of generalized Burgers equations are obtained for initially discontinuous profiles. These solutions and the underlying asymptotic structure are completely validated by the numerical results. For cylindrical geometry the numerical analysis supplements the asymptotic analysis by providing numerical amplitude coefficients that were previously undetermined

Nonlinear propagation of the sonic boom wave through the atmosphere turbulent layer

A new analytical approach to the statistical theory of sonic boom propagation through randomly inhomogeneous media is developed on the base of nonlinear evolution equations. The turbulent atmosphere layer is modelled by a random phase screen. A new Burqers' type equation is derived for arbitrary speeds of supersonic aircrafts using nonlinear geometrical acoustics approximation. The average peak pressure, squared pressure and dispersion of fluctuations are calculated, as well as statistical distributions for peak pressure and its outbursts. It is shown that in spite of decrease in the main characteristics of the N-wave, the fluctuations can increase and lead to the appearance of undesirable outbursts

Nonlinear Standing Waves in a Layer Excited by the Periodic Motion of its Boundary

Abstract. Simplified nonlinear evolution equations describing nonsteady-state forced vibrations in an acoustic resonator having one closed end and the other end periodically oscillating are derived. An approach is used based on a nonlinear functional equation. This approach is shown to be equivalent to the version of the successive approximation method developed in 1964 by Chester. It is explained how the acoustic field in the cavity is described as a sum of counterpropagating waves with no cross-interaction. The nonlinear Q-factor and the nonlinear frequency response of the resonator are calculated for steady-state oscillations of both inviscid and dissipative media. The general expression for the mean intensity of the acoustic wave in terms of the characteristic value of a Mathieu function is derived. The process of development of a standing wave is described analytically for three different types of periodic motion of the wall: harmonic excitation, sawtooth-shaped motion and "inverse saw motion"