Modal contributions to the acoustic responses of fluid-loaded shells

This work compares results from analytical and numerical techniques to predict the modal contributions to the radiated sound power and far-field sound pressure for structures submerged in a heavy fluid medium. A fluid-loaded cylindrical shell with hemispherical end caps is examined. The cylinder is excited by either axial or transverse forces acting at one end, to predominantly excite the lowest order cylinder circumferential modes. A modified variational method combined with a spectral boundary element method is used to develop an analytical model of the coupled hemispherical and cylindrical shells under heavy fluid loading conditions. The displacement components and the sound pressure are expanded in the form of a double mixed series using Fourier series and Chebyshev orthogonal polynomials. A fully coupled finite element/boundary element model of the same coupled hemispherical-cylindrical shell is also developed. A numerical technique for modal decomposition of the acoustic responses of the structure using the fluid-loaded structural modes is implemented. The individual contributions of the cylinder circumferential modes to the sound power and directivity of the radiated sound pressure are observed. The techniques presented here provide greater physical insight into structure-borne radiated noise from fluid-loaded shells.