Abstract:
The doubly asymptotic approximation is widely employed to model the transient (time domain) response of structures that are partially or fully immersed in water. It replaces the field equations for the fluid with an ad hoc surface interaction law that was identified from analytical solutions for spheres and infinitely long cylinders. Previously, the validity of the method for slender hemi-capped cylindrical shells was investigated by comparing DAA in the frequency domain to the surface variational principle, and then using FFT theory to obtain alternative transient responses. That study was limited by its use of Ritz series for displacement. The present work describes how SARA-2D, which is a frequency domain structural acoustics computer code, may be employed to assess the validity of DAA. SARA-2D uses finite elements for the structure, while finite and infinite elements model the fluid. Because of the narrow bandwidth of its matrices, it is more efficient than boundary elements for a frequency sweep. However, internalization of the wet surface nodes within the finite element mesh, the nonlocal nature of DAA, and the need to construct an added mass matrix for DAA lead to interesting issues in deriving an equivalent DAA model. [Work supported by ONR, Code 1222.]