Adaptive positive position feedback for energy absorption in acoustic cavities

摘要

A method for adaptive energy absorption in the low frequency region of acoustic cavities is presented. The method is based on an adaptive scheme consisting of a self-tuning regulator (STR) that has the ability to target multiple modes with a single actuator. The inner control loop of the STR uses positive position feedback (PPF) in series with a high- and low-pass Butterworth filters for each controlled mode. The outer loop consists of an algorithm that locates the zero frequencies of the collocated signal and uses these values to update the resonance frequency of the PPF filter and the cut-off and cut-on frequencies of the Butterworth filters. Experimental results of a duct are provided that show how less than a 10 percent change in the frequencies of the acoustic modes of the duct will cause a non-adaptive controller to go unstable, but the STR will maintain stability and continue absorbing energy through a 20 percent change in the frequencies of the acoustic modes of the duct. Additional experimental results of a fairing replica are provided that show internal temperature variations can change the frequencies of the acoustic modes of this larger cavity and that the STR can adapt to these changes and absorb acoustic energy.