ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

4aSA2. The response and radiation of ribbed panels.

J. Dickey

G. Maidanik

David Taylor Res. Ctr., Annapolis, MD 21402

The dynamic response of a panel with an infinite number of regularly spaced line impedances (i.e., regularly ribbed), or a finite number which may be irregularly spaced and nonidentical, is a system which can be solved ``exactly.'' Exact, that is, to within the approximations employed in developing the equations of motion for the panel and the ribs. Even though these approximations may preclude realistic modeling in some (usually high) frequency ranges, or with some configurations (e.g., wide ribs), these canonical models exhibit many characteristics of experimental and numerical data obtained on real and more complete structures. This makes them very useful and cost effective in identifying observed characteristics and evaluating noise control measures. Models which describe flexural or longitudinal waves on membranes or thin plates have been developed by the authors. These models are reviewed and used to describe the response and radiation of a panel into an adjacent fluid. The panel is driven either by a line drive parallel with the ribs or an incident plane wave. There are a host of phenomena which manifest themselves; some of which are: (1) pass and stop bands, (2) localization and de-localization, (3) aliasing, (4) free wave dispersion and the splitting of the dispersion curves due to fluid loading, (5) Bragg diffraction, and (6) radiation efficiency. Also presented is the effect on these phenomena of: (1) altering the strict periodicity or identity of the ribs, (2) the loss factor in the panel, and (3) the degree of fluid loading.