Project Title:

Real-Time Modification of Structural Modes

03.07-4674
Real-Time Modification of Structural Modes
Systems Technology, Inc.
2672 Bayshore Parkway #505
Mountain View, CA 94043
Wayne F. Jewell  (415-961-4674)
ARC -- NAS2-12726

Abstract:

	 The goal of this project was to improve a method of estimating, in a near-real-time
manner, modal frequencies and damping ratios of randomly excited aeroelastic vibrations
from flight test measurements. The estimation method operates without knowledge of
the random excitation, as well as with knowledge of a deterministic forcing function
applied to the aircraft through an excitation system. It is an adaptation of the
real-time non-intrusive parameter identification procedure developed by the firm
for the NASA Ames Research Center's Dryden Flight Research Facility.
	 The performance of the estimation method was documented by identifying the modal
frequencies and damping ratios of the modelled system both with and without knowledge
of the forcing function or input. With knowledge of the input, the method could accurately
identify both the frequency and damping ratio of the simulated modes as long as the
sampling frequency was properly chosen with respect to the modal frequency. The results
of applying the method without knowledge of the input show that it is possible to
identify accurately the frequency but the damping ratios were underestimated. The
model was applied to a limited amount of flight test data collected by NASA for the
F-18 aircraft.

Potential Commercial Application:

Potential Commercial Application: Real-time analysis of vibration and flutter tests
and real-time parameter identification, in general, would find applications in the
aerospace industry.