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Diagnosing Vibration in Rotating Cantilever Beams with Digital Image Correlation

6/15/2017

Measuring the vibration of rotating cantilever beams such as helicopter blades can be challenging because traditional sensors must pass signals through electrically noisy slip rings. There’s also a limit to how many sensors you can attach to rotating structures without the sensors themselves changing how the structure moves.

That’s why researchers from the University of Texas at Austin turned to Digital Image Correlation (DIC), a technique that uses high-speed cameras and specialized software to optically measure deformation, displacement and strain. They showed that DIC makes it possible to collect vibration data from a rotating blade using high-speed cameras and then use that visual data to perform an accurate modal analysis.

Here’s how they did it.

DIC Equipment

To capture images, the researchers used two Vision Research Phantom Miro M310 high-speed digital cameras, which can record 3,200 images per second at full 1280 x 800 resolution. They paired the camera with LaVision DaVis analysis software, which provides time domain measurements of vibration frequency.

Experiment and Results

The researchers tested their approach on a 2-meter helicopter rotor excited by a jet of compressed air, capturing images at 1,000 fps with the blade rotating at 900 RPM. They measured the rotor’s out-of-plane deformation with an accuracy of 60 microns and a spatial resolution of 7.2 mm. The results suggest that combining DIC with high-speed cameras proved to be an effective way for determining the modal parameters of rotating systems—without the need to measure excitation using sensors.

To learn more about Digital Image Correlation, download our latest white paper.

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