### 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.