Sweeps-Stags Fluid Element Grid Requirements for Accurate Representation of Fluid Loading Effects on Submerged Vibrating Structures

摘要

The second order Doubly Asymptotic Approximation (DAA2) method, has been implemented in the SWEEPS-STAGS code to provide a steady-state vibration analysis capability for submerged structures. This paper extends the previous work in determining the convergence behavior of DAA2-predicted wet surface variables. The convergence rates of fluid boundary eigenvalues and convergence behaviors of modal acoustic impedance functions are calculated for increasingly dense fluid element grids on a spherical surface. Within mode-dependent frequency ranges in which DAA2 is valid, dense grids on the order of five elements per half-wave are needed for five percent accuracy in modal acoustic impedance. This is a consequence of the low order (constant source strength) interpolation used for establishing fluid variables. There are mode-dependent frequency ranges for which DAA2 acoustic impedance predictions are inaccurate, even for very dense developing SWEEPS-STAGS idealizations for vibrations analysis of complex submerged structures.