### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 4pPAb7. Approximate diffraction coefficients.

**Paul E. Barbone
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*Dept. of Aerospace and Mech. Eng., 110 Cummington St., Boston Univ.,
Boston, MA 02215
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Expressions for diffraction coefficients for canonical shapes, joints, and
discontinuities are necessary in applications of the geometrical theory of
diffraction to scattering from submerged structures. In many cases of practical
interest, however, the diffraction coefficients are either not available or are
very difficult to evaluate. The use of perturbation theory and matched
asymptotic expansions in obtaining suitable approximations of diffraction
coefficients is described. These two methods can yield approximations that are
simple to compute, easy to apply, and are valid in complementary parametric
ranges. The perturbation method assumes that the properties of the solid or its
geometry are nearly homogeneous. Matched asymptotics, on the other hand, is a
useful tool when the solid is nearly hard, or the fluid is light. The accuracy
of these methods is demonstrated by comparing them to the exact solution for
diffraction by an impedance discontinuity. When the effort is made to obtain
uniformly valid asymptotic expressions, the results prove to be remarkably
accurate even at values of (epsilon)=1 (here, (epsilon) is a ``small''
parameter).