A new formalism for time-dependent wave scattering from a bounded obstacle

A time-dependent three-dimensional acoustic scattering problem is considere d, An incoming wave packet is scattered by a bounded, simply connected obst acle with locally Lipschitz boundary. The obstacle is assumed to have a con stant boundary acoustic impedance. The limit cases of acoustically soft and acoustically hard obstacles are considered. The scattered acoustic field i s the solution of an exterior problem for the wave equation. A new numerica l method to compute the scattered acoustic field is proposed. This numerica l method obtains the time-dependent scattered field as a superposition of t ime-harmonic acoustic waves and computes the time-harmonic acoustic waves b y a new "operator expansion method." That is, the time-harmonic acoustic wa ves are solutions of an exterior boundary value problem for the Helmholtz e quation. The method used to compute the time-harmonic waves improves on the method proposed by Misici, Pacelli, and Zirilli [J. Acoust, Sec. Am. 103, 106-113 (1998)] and is based on a "perturbative series" of the type of the one proposed in the operator expansion method by Milder [J. Acoust. Sec. Am . 89, 529-541 (1991)]. Computationally, the method is highly parallelizable with respect to time and space variables. Some numerical experiments on te st problems obtained with a parallel implementation of the numerical method proposed are shown and discussed from the numerical and the physical point of view. The website: http://www.econ.unian.it/recchioni/w1 shows four ani mations relative to the numerical experiments. (C) 2000 Acoustical Society of America. [S0001-4966(00)05603-4].