ASA 127th Meeting M.I.T. 1994 June 6-10

2aNSb2. Scale model experiments on the diffraction and scattering of sound by a curved rough surface.

James Chambers

Yves Berthelot

School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405

Scale model experiments have been conducted to study the propagation of sound over a curved rough surface with curvature much greater than the wavelength and roughness smaller than the wavelength. The MAE model [J. Acoust. Soc. Am. 92, 605--608 (1993)] is used to determine the sound field in the vicinity of the curved surface. The Tolstoy--Medwin roughness model [J. Acoust. Soc. Am. 79, 657--665 (1986)] is used to model the rough surface. The two models are combined to qualitatively describe the sound field. Experiments indicate that: (1) just above the surface, the roughness causes a boundary wave that is generated by the direct waves in the bright zone and by the creeping waves in the shadow zone; (2) there are two frequency regimes with the transition determined by the curvature and the roughness; (3) along the surface, more sound (compared with diffraction by the curved smooth surface) is tunneled into the shadow zone at low frequencies and less sound is tunneled at higher frequencies. Along the line of sight, the trend is similar but more complicated. [This work is supported by a Fannie and John Hertz Fellowship.]