ASA 124th Meeting New Orleans 1992 October

1pPAb5. On the convergence behavior of the exterior acoustic modes of structures.

Noelle Curry

Kenneth A. Cunefare

The George W. Woodruff School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405

The use of a modal-style approach for the analysis of the exterior radiation characteristics of structures has recently received increasing attention. This approach generally seeks to find a set of orthogonal functions, or acoustic modes, that diagonalize a radiation operator. These acoustic modes are found through an eigenfunction or singular value decomposition analysis of the radiation operator. The eigenvalue or singular value associated with a given mode is directly proportional to the radiation efficiency of that mode. One advantage of this acoustic modal approach is that the total radiated power can be found by simply summing the contributions from individual acoustic modes, since they are completely decoupled. It is shown that the accuracy of the acoustic modal representation depends on the number of degrees of freedom permitted in the derivation of the radiation operator. The most efficient acoustic modes are least sensitive to increasing degrees of freedom. The least efficient acoustic modes are most sensitive to changes in degrees of freedom. Further, it is shown that this convergence behavior of the acoustic modes can be related to the familiar convergence behavior of structural modes, through the Rayleigh quotient.