Noelle Currey
Kenneth A. Cunefare
The George W. Woodruff School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405
The modal-style approach for representing the exterior radiation characteristics of structures generally seeks to find a set of orthogonal functions, or acoustic modes, that diagonalize a radiation operator in the exterior domain of the structure. The choice of basis functions for the modal representation is arbitrary, though use of the natural modes of structural vibration tends to provide some physical insight. The acoustic modes are found through an eigen analysis 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. The dependency of the radiation efficiencies and mode shapes on the number of degrees of freedom permitted in the derivation of the radiation operator is investigated for a baffled finite rectangular plate. The accuracy of the acoustic modal representation depends on the number of degrees of freedom permitted in the derivation of the radiation operator, with the least efficient modes converging slowest. Further, the rate of convergence is dependent on the particular basis function selection. The convergence behavior has significant impact on those applications of the exterior acoustic modal approach that seek to exploit the least efficient modes. [Work supported by NASA GSRP program.]