A Study of the Frequency and Shape Dependency of Acoustic Radiation Modes

Acoustic radiation modes (ARMs) are a set of orthogonal velocity distributions which radiate sound power independently. Because of this characteristic, ARMs has been successfully used in active structural acoustics control. More recently, ARMs have been used to guide structural modification targeting sound power reduction, and have also been used as basis functions in acoustical holography. However, it is usually a time-consuming process to compute the ARMs of a radiating structure since they are frequency dependent. This characteristic often limits the use of ARMs in the applications mentioned above. Here, the possibility of obtaining a set of ARMs that vary slowly with frequency by performing ARM calculations on a smoothed radiating surface was investigated. Specifically, in the current work, the surface smoothing effect on the frequency dependence of the radiation mode shapes was studied. An understanding of this property will be beneficial, for example, by improving the accuracy of ARM-based acoustic holography, by facilitating more effective structural modification to reduce or improve sound radiation over a broader frequency range, and by reducing the computation effort required in active noise control applications.