Nonaxisymmetric vibration and acoustic radiation of a submerged cylindrical shell of finite length containing internal substructures

A modal-based method is developed to analyze the acoustic radiation of axisymmetric submerged shells of finite length with internal substructures, subjected to nonaxisymmetric time-harmonic loads. In this method, a variational principle is used to determine the relationship between the surface pressure and displacement of the shell, and Lagrange multipliers are used to account for the connections between the shell and the substructures. Fourier series expansions are used to represent the circumferential dependence of the surface pressure and displacement. The method is demonstrated by an extended analysis of a cylindrical shell with hemispherical elastic endcaps containing circular bulkheads. The dominant flexural wave numbers are identified from helical wave spectra. It is shown that the wave numbers of the dominant flexural waves are the same as those found in an infinite, fluid-loaded cylindrical shell. The locus of wave numbers of the dominant flexural waves lies outside of the sonic cone for low to mid frequencies. However, it is shown that bulkheads can create amplification of the flexural waves with wave numbers within the sonic cone. This is confirmed by a computation of the net power radiated by the shell: The shell with bulkheads radiates more energy than the empty shell for ka>0.5, where k is the acoustic wave number and a is the radius of the cylindrical shell.