3aSAa6. Wave-number-based assessment of the doubly asymptotic approximation.

Session: Wednesday Morning, May 15

Time: 9:15

Author: Jerry H. Ginsberg
Author: Kuangchung Wu
Location: G. W. Woodruff School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405


The most widely implemented technique for modeling fluid--structure interaction effects associated with shock response is the doubly asymptotic approximation (DAA), which has been developed in a variety of versions. Because of a lack of analytical solutions for realistic geometries, prior validation efforts have not provided definitive guidelines regarding the accuracy of the method. The present work uses Nicholas--Vuillierme's derivation [Numerical Techniques in Acoustic Radiation, edited by R. J. Bernhard and R. F. Keltie (American Society of Mechanical Engineers, New York, 1989), Vol. 6, pp. 7--13] of the frequency-domain version of DAA as the basis for examining the accuracy and limitations of DAA for a slender hemi-capped cylindrical shell. The development computes the wet surface impedance matrix relating surface pressure and velocity variables over a broad frequency band according to two DAA versions and the surface variational principle. The alternative wet surface impedances are used to predict the frequency-domain structural response of the shell to a point force, after which alternative time-domain responses are obtained from the FFT algorithm. Results for wave-number amplitudes (azimuthal and meridional) are reported for moderate and large aspect ratios. An overview indicates that a higher-order DAA version occasionally works extremely well, but that there is no consistent high/low trend as a function of wave number. [Work supported by the Office of Naval Research, Code 1222.]

from ASA 131st Meeting, Indianapolis, May 1996