STRUCTURAL INTENSITY IN THIN CYLINDRICAL-SHELLS

A rigorous derivation of the structural intensity vector for a thin cylindrical shell is provided based on Flugge's equations of motion and expressions for the total energy density in the shell. The shell is assumed driven by normal forces, loaded externally by a fluid, and to have no internal loss. It is confirmed that the structural intensity vector is composed of five terms, and simple physical interpretations of these terms are provided. The relationship between the structural intensity and the normal acoustic intensity is derived. The five structural intensity terms are investigated in some detail using results from a numerical experiment. The numerical model was a simply supported, point-driven cylindrical shell with external fluid loading, assumed to exist in an infinite rigid baffle. A sum over in vacuo modes was used to solve the equations of motion. The results show, in the frequency range below the ring resonance of a steel shell with h/a = 0.01, that the divergence of the extensional power flow term dominates over the other four terms in the transfer of power to the fluid and, equivalently, into the far field.