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13 June 2005 Specification of vibrational modes and amplitudes in large-scale structure by time averaging moire technique
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Specification of vibrational modes and amplitudes of structures are crucial issues in civil and mechanical engineering. Several techniques have been used for this kind of studies, including holographic interferometry, speckle interferometry and moire technique. But, for large-scale structures modal analysis technique is usually used. In this work we have used time averaging moire technique to study in plane vibrations of large structures. The study includes specification of vibrating modes and amplitudes of structures. The technique is applied by painting a suitable size linear sinusoidal reflectance pattern on the lateral surface of the structure. As the structure is put into vibration, using a wide-angle high-resolution digital camera, the image of vibrating pattern is recorded in an exposure time much larger than the vibration period. The visibilities of the image along a line parallel to the painted pattern line are derived by processing the reflectance distribution. By dividing the resulted visibilities by the visibility of the image of the static pattern we get the normalized visibility curve. The number of normalized visibilities equal to 1 provides the number of vibrational modes and the magnitudes of the visibility minima or the locations of the zero visibility give the amplitudes of vibration.
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Saifollah Rasouli and Mohammad Taghi Tavassoly "Specification of vibrational modes and amplitudes in large-scale structure by time averaging moire technique", Proc. SPIE 5856, Optical Measurement Systems for Industrial Inspection IV, (13 June 2005);

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