THE SOUND RADIATION EFFICIENCY OF FINITE LENGTH CIRCULAR CYLINDRICAL SHELLS UNDER MECHANICAL EXCITATION II: LIMITATIONS OF THE INFINITE LENGTH MODEL

The acoustic radiation from circular cylindrical shells is of fundamental and applied interest. However, in previous studies, in order to obtain an analytical solution for practical applications, the cylindrical shell is normally assumed infinite in length. Obviously, this assumption would cause error in the analysis for a finite length circular cylindrical shell, especially as the length of the shell becomes comparable to the radius. In this study, the end effects of the length and the boundary conditions on the acoustic behavior of a circular cylindrical shell is discussed. It is found that the boundary conditions would affect the modal radiation efficiencies very much in the subsonic region. However, it has been shown that there exists a condition under which the end effects could be neglected for modal radiation efficiencies so that the infinite model could be used with fair accuracy. Also, it is found that if the length (l) of a circular cylindrical shell with radius a and thickness h is much greater than2πaa/h, beam-bending modes would dominate the vibration response below the cut-off frequency of the second circumferential mode and the cylindrical shell can be treated as a beam with reasonable accuracy.