Sound Radiation Control Using Multiple Adaptive Vibration Neutralizers and Hierarchical Control Schemes

Adaptable vibration neutralizers (AVNs) have become common in the literature as solutions to controlling a single but variable frequency disturbance, such as the interior sound field in a turboprop aircraft. This paper presents a study of the feedback control of five AVNs to minimize tonal sound radiation from a rectangular plate with a response controlled by many modes. It is shown that the five AVNs with local feedback loops can be managed by a simple global algorithm to minimize the sound radiation from a plate. As an adaptive passive approach is used, each individual AVN can be constrained to be stable and the resulting global system is also stable. The contributions of this paper are an experimental demonstration of nongradient based control of individual AVNs, a simple hierarchical control of multiple AVNs to reduce a single global error and experimental confirmation of the physical mechanisms by which vibration neutralizers can be used to minimize noise radiation. Spatially averaged single frequency reductions of up to 22 dB are experimentally demonstrated in the radiated field.