Abstract:
The measured scattering of sound from a submerged, framed shell was considered in whose interior have been attached hundreds of precisely tuned and pseudorandomly distributed mechanical ``dumbell'' oscillators. The dumbells are attached to the frames at the formers' beam midpoints, with the beams canted at 45 deg to the frame web direction. It is assumed that, for the most part, the motion of the frames couples directly to beam-bending motion of the dumbell oscillators, the degree of freedom considered in the design of the oscillator resonant frequencies. The observed scattering---both in frequency and aspect---is quite different from that observed from the framed shell without any such oscillators. These differences are discussed in the context of membrane and flexural shell waves, the coupled frame--oscillator systems, and related mechanisms that might account for the observed scattering features. [Work supported in part by ONR Code 334.]