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21 July 2004 Structural boundary effects and their applications to health monitoring
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A signal decomposition method for extracting boundary effects from an Operational Deflection Shape (ODS) of a structure under harmonic excitation is presented here. It decomposes an ODS into central and boundary solutions using a sliding-window least-squares curve-fitting technique. The obtained boundary solutions can be used to reveal damage locations, and the central solutions can be used to identify boundary conditions. Except an experimental ODS the method requires no model or historical data for comparison. For numerical simulations, exact mode shapes and ODSs of beams with damage are obtained by spectral element analysis. Boundary and central solutions caused by different boundary conditions, different loading conditions, and different damage with or without noise are simulated and characterized. Numerical results show that Gibbs' phenomenon caused by the use of continuous functions to fit ODSs with discontinuous first-, second-, and/or third-order derivatives actually makes boundary solutions excellent damage indicators. Several experiments are performed using a scanning laser vibrometer for sensing and a PZT patch for actuation. The experimental results confirm the feasibility and accuracy of this Boundary Effect Evaluation Method (BEEM) in detecting multiple defects and identifying boundary conditions of beams.
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Perngjin Frank Pai, Lu Huang, Sharath H. Gopalakrishnamurthy, and Jaycee H. Chung "Structural boundary effects and their applications to health monitoring", Proc. SPIE 5394, Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems III, (21 July 2004);

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