Publication: Evaluation of modal density, radiation efficiency and acoustic response of longitudinally stiffened cylindrical shell
Abstract
An analytical method has been developed for predicting the modal density and the radiation efficiency of longitudinally stiffened cylinder to use in statistical energy analysis (SEA). In the present analysis, the stiffeners are treated as discrete elements and the natural frequencies and the mode shapes are calculated using the energy method. The modal density and the radiation efficiency are predicted from the derived natural frequencies and the mode shapes. The predicted values are compared with experimental measurements over a wide frequency range up to 10 kHz and the results are found to have good agreement except at low frequencies, where the individual global modes dominate the response. A correction factor is introduced in the estimation of radiation efficiency in the low-frequency range for unbaffled finite length cylinder. A statistical process has been evolved by considering an ensemble of 32 similar structural models with material and geometrical properties varying by ±5% over the nominal values to account for the uncertainties in the structure. For the assumed stiffened cylinder, the effect of the shapes of the stiffeners is found to have a small influence on the modal density and the radiation efficiency. As the number of stiffeners is increased beyond 32, a single term solution by neglecting the cross-coupling of various circumferential modes yields moderately accurate results and resulting in considerable saving of computation time. The acoustic responses of unstiffened and stiffened cylinders are predicted using SEA and validated by experiments. The presented analytical method can be easily extended to non-periodically stiffened cylinders with different types, shapes and orientations of the stiffeners etc. © 2007 Elsevier Ltd. All rights reserved.