Active Control of Flexural Vibration: An Adaptive Anechoic Termination
This paper describes an approach to the real-time, feedforward, adaptive broadband control of flexural vibrations of a beam. A wave interpretation is used: disturbance and control forces inject waves into the structure and the waves then propagate through it. The general aim is to implement an anechoic boundary to the structure which absorbs any energy incident upon it. Digital filters are implemented to estimate, in real-time, the amplitudes of the propagating waves incident on and reflected from the boundary by filtering the outputs of an array of sensors. The reflected wave is used as the cost function in a filtered-X LMS adaptive control. The feedforward reference signal used is either the primary disturbance or the incident wave — the former is rarely available outside the laboratory. Furthermore, for a finite, resonant structure, with potentially many modes in the frequency range of interest, the performance using the primary as a reference signal gives very poor performance due to the difficulty of approximating the resonant cancellation path. Control using the incident wave as a reference does not suffer from this problem. Experimental results are presented. Broadband attenuation of around 20 dB in the ratio of the reflected and incident powers is demonstrated experimentally. The effect on the input frequency response of the structure is that substantial damping is added to all the modes of vibration that lie within the broad frequency range of control: a reverberant structure becomes anechoic. The high frequency limit is caused by the delays in both the computational time and filtering phase lags. The adaptive system achieves significant attenuation for broadband incident disturbances.
KeywordsAttenuation Propa Convolution
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- 1.Fuller, C.R., Elliott, S.J., and Nelson, P.A., Active Control of Vibration. Academic Press, San Diego, 1997.Google Scholar