Abstract
This paper deals with an improved methodology to measure three-dimensional dynamic displacements of a structure by digital close-range photogrammetry. A series of stereo images of a vibrating structure installed with targets are taken at specified intervals by using two daily-use cameras. A new methodology is proposed to accurately trace the spatial displacement of each target in three-dimensional space. This method combines the correlation and the least-square image matching so that the sub-pixel targeting can be obtained to increase the measurement accuracy. Collinearity and space resection theory are used to determine the interior and exterior orientation parameters. To verify the proposed method, experiments have been performed to measure displacements of a cantilevered beam excited by an electrodynamic shaker, which is vibrating in a complex configuration with mixed bending and torsional motions simultaneously with multiple frequencies. The results by the present method showed good agreement with the measurement by two laser displacement sensors. The proposed methodology only requires inexpensive daily-use cameras, and can remotely detect the dynamic displacement of a structure vibrating in a complex three-dimensional defection shape up to sub-pixel accuracy. It has abundant potential applications to various fields, e.g., remote vibration monitoring of an inaccessible or dangerous facility.
Highlights
Measurement of structural vibration is a very important subject in various science and engineering fields
We introduce a new methodology to improve the measurement accuracy by applying the least-square image matching for sub-pixel targeting
An electronic synchronization would be more accurate, but this research focuses on the improvement by adding the least square matching procedure for sub-pixel targeting while other conditions are kept as same as possible
Summary
Measurement of structural vibration is a very important subject in various science and engineering fields. Belen Ferrer et al [12] developed a method to measure the vibration using an image processing to detect a sub-pixel movement of a structure. This method is limited to measure only the frequency from a 2-D image sequence, and cannot be applied to measure the 3-D dynamic displacement of a structure. The collinearity and space intersection were applied to trace the spatial position of each target They performed an experiment to show that the theory can capture the dynamic 3-D displacements of a beam vibrating in a pure sinusoidal pattern with its fundamental natural frequency.
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