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UBC Theses and Dissertations

Vibration analysis of singly curved surfaces by holographic interferometry. Blasko, James Alexander


Time-average and stroboscopic real-time holography have become established as the prominent tools of holographic vibration analysis. Both are able to provide a quantitative determination of the amplitudes of standing waves of a vibrating flat surface, but have to date been limited to qualitative examination of curved surfaces. The purpose of this thesis has been to investigate the problems of extending the holographic technique to the analysis of surfaces of single curvature. The presence of several component motions in curved surface vibration prompted an examination of the fringe behaviour of the individual components of motion. This was performed by studying pure rigid body step displacements using double exposure holography. The experimental work of previous investigators was duplicated and the results tabulated according to the sensitivities of the fringe period density to a change in displacement magnitude. This was then related to the rotations and translations occurring in the motion of a vibrating surface. A fully clamped curved panel was studied using the time-average method with the assumption that all points on the surface were displaced normal to it. Good agreement was obtained between the amplitudes calculated from the fringes and the measured amplitudes, by accounting for the variation in displacement direction across the surface. A fixed-free cylinder was examined simultaneously from two overlapping views using both the time-average and stroboscopic real-time methods. Comparison of the calculated and measured amplitudes of the time-average indicated that the interference fringes were not localized upon or very near the cylinder's surface. The real-time results had reinforced these findings. However, the inherent presence of residual fringes in this method caused difficulties in obtaining an accurate quantitative evaluation of the vibration amplitudes. The real-time fringes were analyzed with attention paid to the effects of the initial residual fringes upon the resultant fringes.

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