Kenneth A. Cunefare
George W. Woodruff School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405
The use of the acoustic boundary element method is gaining widespread acceptance. As the BEM matures, new uses for it are being developed, including its incorporation into design optimization and active noise control algorithms. The use of quadratic shape functions in the BEM formulation provides certain benefits with regard to modeling and surface representation. However, these popular elements do pose challenges when acoustic sensitivity information is desired of the formulation, such as is used in optimization and active noise control. The difficulty arises from the implications of a positive change in a nodal value (e.g., surface normal velocity), and the net change over the balance of the element. Corner nodes will yield a net negative change, while mid-side nodes will yield a net positive change, both for positive nodal change. This presentation demonstrates that the use of quadratic elements requires careful treatment as a consequence of this behavior, and that element-based, rather than node-based, sensitivities are most appropriate with this element.