ASA 127th Meeting M.I.T. 1994 June 6-10

5aNS10. Linear time-invariant approaches to feedforward, multifrequency control.

Jeffrey S. Vipperman

Robert L. Clark

Dept. of Mech. Eng. and Mater. Sci., Duke Univ., Box 90302, Durham, NC 24078-0302

There are many applications where the unwanted noise or vibration response of a system is composed of multiple harmonics. Unless care is taken in selecting the size of the adaptive control filter and the sampling rate, the LMS algorithm will converge to a time-varying solution, which oscillates about the optimal control solution for the system. Further, the response due to each harmonic can vary in magnitude by more than an order of magnitude, causing a much higher signal-to-noise ratio for the weaker frequencies. In such a case, it is best to implement a separate independent reference signal and corresponding independent adaptive filter for each frequency contained in the system. The resulting filters have a stationary optimal solution and the dynamic range of the control system is improved. Experiments were performed on a simply supported steel beam to demonstrate the effects of sampling rate, filter size, and signal-to-noise ratio for multifrequency and higher harmonic control applications. [Work supported by the Structural Acoustics Branch of NASA-Langley.]