ASA 127th Meeting M.I.T. 1994 June 6-10

2pSA6. Two-dimensional wave-number distributions of flexural vibration in ribbed plates.

Richard N. Brown

Sci. and Technol. Div., Bolt Beranek and Newman, Inc., 70 Fawcett St., Cambridge, MA 02138

Regularly ribbed plate constructions are common in marine, aircraft, and other applications. Since vibration of these structures can be responsible for unwanted acoustic emissions, the response of ribbed plates has been a subject of many theoretical and a few experimental studies over the years. In determining radiation and near-field acoustic levels it is important to have a knowledge of the distribution of surface velocity in wave-number space. In this paper, the elegant solution of Berkman et al. [``Radiation from Periodically Supported Fluid-Loaded Plates,'' BBN Rep. 3999 (1979)] to the ribbed plate equation of motion is used to estimate the distribution in wave number of the surface velocity. In particular, the two-dimensional solution to excitation by a point force is used. The results of the study show several distinctive features: a high level, broad-(spatial) band in the bays near the excitation force; Bragg scattering of flexural energy by the periodically spaced ribs (which is accompanied by acoustic radiation due to aliasing), an alignment of flexural traveling waves to the direction normal to the ribs, and the relative inconsequence of stop/pass band behavior. Experimental data are presented showing the existence of these features.