This work examines the application of sensor arrays to structures. The wave equation solution of Euler-Bernoulli beam theory provides the structural model for this study. A review of basic array theories for the enhancement of signal-to-noise ratio (SNR) and determination of angle of arrival (AOA) leading to source localization is given. Array techniques are considered with applications to dispersive flexural waves where the propagation velocity is not constant but dependent on frequency.
The theory is validated through experiments with harmonic and broad band applications. The test apparatus consisted of a long thin beam with anechoic terminations to emulate an infinite beam for frequencies above 300 Hz and a finite beam below 200 Hz. The beam was excited by a shaker (with a force transducer) mounted on one end of the beam. Measurements were taken with accelerometers and a laser velicometer at the other end of the beam. The infinite beam case was used to isolate the travelling wave response to single harmonic excitation. The finite case was used to consider transient response of the beam to an impulse.
The harmonic response experiments on the infinite beam is used to demonstrate two things. First they show that the SNR increases by the square root of the number of sensors. Secondly they show that AOA can be determined explicitly from the phase between sensors for single frequency applications. The measured values of AOA were within ±3 degrees for these experiments. This technique applies to harmonic signals in a highly damped medium.
The technique developed for transient applications uses the magnitude and the variance of the correlation coefficient of a densely populated array to determine AOA. This technique is based on correlation between measurements along a wave front. It does not assume a phase relationship between sensors but instead exploits the spread of the signal as it travels. The spread is characteristic of a dispersive medium. This resolution of this technique is directly linked to the population of the array and the angular relationship between elements. The experiments verified that this technique measures the AOA for within the resolution of the array. For arrays from 3x4 to 7x10 resolution of ± 6 to 9 degrees was possible.
This work has developed array theory for application to dispersive waves in structures. It highlights the differences in the phase relationship between elements for dispersive versus non dispersive media. It shows improvement of SNR using structural arrays. The potential for AOA determination on highly damped structures using harmonic signals was demonstrated. AOA determination was also shown for finite structures using impact excitation. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/40189 |
| Date | 26 October 2005 |
| Creators | Wynn, Carol Jaeger |
| Contributors | Mechanical Engineering, Wicks, Alfred L., Robertshaw, Harry H., Leonard, Robert G., Baumann, William T., Saunders, William R., Cudney, Harley H. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xiv, 163 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 29700071, LD5655.V856_1993.W966.pdf |
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