### 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.]