Live monitoring of the distributed strain field in impulsive events through fiber Bragg gratings |
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| Institution: | 1. Niccolò Cusano University, Rome, Italy;2. Unesco Chair “Water Resources Management and Culture”, University for Foreigners of Perugia, Italy;3. University of Naples “Parthenope”, Naples, Italy;4. DEIM - Engineering School, University Of Tuscia, Viterbo, Italy;1. DEIM - School of Engineering - University of Tuscia Largo dell’Universitá, 01100 Viterbo, Italy;2. Dept. of Enterprise Engineering “Mario Lucertini” - University of Rome “Tor Vergata”, Via del Politecnico 1, 00133 Rome, Italy;3. John A. Paulson School of Engineering and Applied Sciences - Harvard University 33 Oxford St., 02138 Cambridge (MA), USA;1. Department of Aeronautical Structural Engineering Northwestern Polytechnical University, Xi?an, PR China;2. School of Mathematical Sciences Monash University, Vic 3800, Australia;1. DICAM, University of Bologna, Bologna 40136, Italy;2. Department of Technologies, University of Naples “Parthenope”, Naples 80143, Italy;3. Department of Mechanical and Aerospace Engineering, Polytechnic School of Engineering, New York University, Brooklyn, NY 11201, USA;4. DEIM – Industrial Engineering School, University of Tuscia, Viterbo 01100, Italy;1. Centre for Autonomous Marine Operations and Systems (AMOS), Norwegian University of Science and Technology, N-7491 Trondheim, Norway;2. CNR-INSEAN: Italian Research Council – Institute for Marine Technology, Roma, Italy;1. CNR-INSEAN, Natl. Research Council - Marine Tech. Research Inst., Rome, Italy;2. Hyundai Heavy Industries Co. Ltd., South Korea |
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| Abstract: | In this paper, we propose a measurement technique based on local strain measurements to perform real-time reconstruction of the overall structural deformation and the distributed stress field produced by the impact of a body on a water free surface. In particular, we seek establishing a measurement chain capable of acquiring and elaborating the signals at high frequency, so that it can be utilized to study rapidly varying strain fields, such as those occurring in impulsive events. Fiber Bragg gratings are utilized to sense the local structural deformation. Experiments are conducted on flexible plastic wedges with variable deadrise angles impacting on a quiescent fluid surface. The experimental tests are performed in free fall and we explore variations of the entry velocity by varying the drop height. The structural deformation is reconstructed from point-wise strain measurements utilizing a modal reconstruction methodology. The impact dynamics are analysed through accelerometers and linear position sensors. Results show that the impact behaviour of the flexible body is characterized by a main overall deformation where the structure is distorted in the direction of the loading, whereby marked vibrations, whose amplitude increase with the entry velocity, dominate the dynamic response. The influence of the mode shapes considered in the present analysis on the accuracy of the results is also observed. The proposed methodology allows for a fairly high acquisition frequency, which translates into a real-time structural reconstruction technique. Results show that the proposed methodology can be a valuable tool for the live monitoring of structures undergoing impact events. |
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| Keywords: | FBG SHM High speed imaging Modal decomposition Hydroelasticity Water entry |
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