Angela K. Karali
Sabih I. Hayek
Dept. of Eng. Sci. and Mech., Penn State Univ., University Park, PA 16802
In a previous paper [A. K. Karali and S. I. Hayek, J. Acoust. Soc. Am. 95, 2805 (1994)] the analytic model for the prediction of the acoustic scattered field by infinite elastic plates reinforced with periodic arrays of line discontinuities was presented. In this paper the analysis is extended to infinite elastic plates reinforced with periodic arrays of ribs. If actual ribs are attached to a plate, instead of line discontinuities, their impedances are frequency dependent. The ribs are modeled as Timoshenko beams attached to an elastic plate, whose flexural vibrations are modeled using Mindlin's plate theory. Analytic expressions for the rib impedances are obtained and plotted against the normalized frequency of an incoming plane acoustic wave. The rib impedances show resonances and antiresonances in the frequency range of 1 to 15 times the classical coincidence frequency of the plate. The influence of the rib impedance resonances and antiresonances on the nonspecularly reflected field is demonstrated by direct calculation of the acoustic scattered field at several critical frequencies of the ribs.