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 continues to receive increasing attention. This approach generally seeks to find a set of orthogonal functions, or acoustic modes, that diagonalize a radiation operator in the exterior domain of an extended radiator. These acoustic modes are found through an eigenfunction/eigenvector 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. Here, the frequency dependency of the acoustic modes of a baffled beam is examined. Further, 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. It is demonstrated 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. This behavior has significant impact on applications of the exterior acoustic modal approach that seek to exploit the least efficient modes.