Elastodynamic Modeling of Fluid-Loaded Cylindrical Shells with Multiple Layers and Internal Attachments.

First, a technique is developed to model the dynamics of cylindrical shells that can have multiple viscoelastic layers and external compliant coatings. The technique is based on well-known wavenumber transform properties, with the novel feature here being the development of a Direct Global Matrix formulation (DGM) to obtain numerically stable solutions over a wide range of axial wavenumbers and circumferential orders. The resulting computer program can model any combination of solid, fluid, and vacuum layers, arranged in any order. Fluid-loaded shells are modeled by letting the outermost layer be a fluid that radiates to infinity. The excitations used here are time-harmonic ring forces that can push on any solid layer in the radial, circumferential, or axial directions. The ring forces can have a linear phase shift around the circumference of the shell, so helical waves can be excited and studied for any circumferential order. Analytically, the order can be complex, although the software is presently implemented for real orders. Second, the method is used as a reference model to check the accuracy of three different thin shell theories. Cases of agreement and disagreement are shown and interpreted. Third, a technique is developed to attach a thin elastic plate inside the DGM shell model. To make the problem more tractable, the plate is described with a thin plate theory, while the DGM shell model is based on the full 3D elastic theory. The approximate nature of the plate theory introduces a slight incompatibility at the interface between the two theories, so a technique is developed to connect the two theories. Newton's third law is satisfied in an integral sense by matching the resultant forces and moments, and structural continuity is satisfied in an integral sense by matching the instantaneous power transferred between the plate and the shell. Finally, it is shown how these techniques can be used to model the scattering of acoustic waves from multi-layered shells. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).