Abstract
Non-contact measurement of the response of vibrating structures may be achieved using several different methods including the use of video cameras that offer flexibility in use and advantage in terms of cost. Videos can provide valuable qualitative information to an informed person, but quantitative measurements obtained using computer vision techniques are essential for structural assessment. Motion Magnification in videos refers to a collection of techniques that amplify small motions in videos in specified bands of frequencies for visualization, which can also be used to determine displacements of distinct edges of structures being measured. We will present recent developments in motion magnification for the modal identification of structures. A new algorithm based on the Riesz transform has been developed allowing for real-time application of motion magnification to normal-speed videos with similar quality to the previous computationally intensive phase-based algorithm. Displacement signals are extracted from strong edges in the video as a basis for the data necessary for modal identification. Methodologies for output-only modal analysis applicable to the large number of signals and short length signals are demonstrated on example videos of vibrating structures.
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Acknowledgements
The authors acknowledge the support provided by Royal Dutch Shell through the MIT Energy Initiative, and thank chief scientists Dr. Dirk Smit, Dr. Sergio Kapusta, project managers Dr. Keng Yap and Dr. Yile Li, and Shell-MIT liaison Dr. Jonathan Kane for their oversight of this work. We also acknowledge Dr. Michael Feng and Draper Laboratory for providing experimental equipment. At the time of this work, Neal Wadhwa was supported by the MIT Department of Mathematics and the NSF Graduate Research Fellowship Program under Grant No. 1122374. Special thanks are due to Reza Mohammadi Ghazi, James Long, and Young-Jin Cha for their help with experimental collection of the data.
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Chen, J.G., Wadhwa, N., Durand, F., Freeman, W.T., Buyukozturk, O. (2015). Developments with Motion Magnification for Structural Modal Identification Through Camera Video. In: Caicedo, J., Pakzad, S. (eds) Dynamics of Civil Structures, Volume 2. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, Cham. https://doi.org/10.1007/978-3-319-15248-6_5
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DOI: https://doi.org/10.1007/978-3-319-15248-6_5
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