### ASA 125th Meeting Ottawa 1993 May

## 1pNS6. Wavelet analysis of blade--vortex interaction noise.

**Wm. Constantine
**

**
C. Pezeshki
**

**
M. Mosher
**

**
**
*Dept. of Mech. and Mater. Eng., Washington State Univ., Pullman, WA
99164-2920
*

*
*
Fourier analysis techniques for analyzing helicopter noise signals have
been shown to be an adequate, yet inefficient tool for the design of helicopter
noise control systems. Impulsive sources of noise, such as blade--vortex
interaction (BVI) noise cannot be localized in time without collecting
relatively large amounts of data at high sampling rates. Attempts to minimize
the BVI phenomenon through helicopter blade control schemes in the Fourier
domain are inherently inefficient since the control matrices must account for
the large number of Fourier components needed to represent the signal.
Time-frequency representations, such as the wavelet representation, offer an
efficient alternative to these Fourier domain methods. Wavelet analysis has
been performed on an ensemble of helicopter noise signals. An interactive
wavelet program was designed using quadrature mirror filters developed by S.
Mallat. Using the bandpass representations of the signal, BVI noise was
isolated and extracted from the overall helicopter noise signature. Future
research will integrate the wavelet decomposition into an adaptive frequency
domain controller for BVI noise minimization.[sup a)]With NASA Ames Res. Ctr.,
MS T-42, Moffett Field, CA 94035.