ASA 124th Meeting New Orleans 1992 October

3pUW6. On the benchmarking of the extended wedge assemblage method: Scattering from a thin disk.

Richard S. Keiffer

NRL-SSC, Code 7181

Jorge C. Novarini

Planning Systems, Inc.

Guy V. Norton

NRL-SSC, Code 7181

The so-called wedge assemblage (WA) method was originally benchmarked for 1-D gratings [Novarini et al., J. Acoust. Soc. Am. 77, 1754--1759 (1985)], and later extended to 2-D surfaces [R. Keiffer et al., Computational Acoustics, Vol. 1, IMACS (1990)]. For either case, the exact time domain solution by Biot and Tolstoy for an infinite wedge is the starting point for the modeling of scattering from more complex surfaces. The main hypothesis involved in the extension of the WA method to surfaces that are not corrugated or long-crested is based on experimental observations [H. Medwin, J. Acoust. Soc. Am. 69, 1060--1064 (1981)] that the diffracted response of a truncated wedge is equal to the appropriately time-windowed response of equivalent infinite wedge. In this paper this hypothesis is tested for a scattering surface (the thin disk) for which the implementation of the extended WA method is conceptually simple yet, particularly for monostatic scattering at normal incidence is very demanding. As a benchmark, a T-matrix approach is adopted and Fourier transformed to the time domain for comparisons with the WA results. Both Dirichlet and Neumann boundary conditions are examined.