Iranian Journal of  Manufacturing Engineering

Iranian Journal of Manufacturing Engineering

Operational modal analysis of thin plates using non-contact excitation and uncertainty quantification of extracted parameters

Document Type : Original Article

Authors
Faculty of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran
Abstract
Operational modal analysis is utilized in structures subjected to unmeasurable dynamic loads to optimize design and prevent premature failure under resonant conditions. Operational modal analysis using non-contact excitation is usually used to estimate modal parameters of vulnerable and sensitive impact structures. The innovation of this research lies in the use of diverse non-contact excitations and the precise comparison of the results obtained from various Operational Modal Analysis (OMA) methods. This study demonstrates that non-contact excitation can be a suitable alternative to contact excitation for sensitive structures, providing reliable results. In this study, the modal parameters of a thin cantilever rectangular plate are identified using air excitation and electromagnetic force caused by the current in a coil with an iron core. These parameters, including natural frequencies, damping ratios, and mode shapes, are initially extracted and subsequently compared with each other for contact and non-contact excitations. Then, the uncertainty of the modal parameters, is quantified by the delta method, and the results are compared. The results of validating the implemented methods show that stochastic subspace identification is the most accurate method, with the percentage difference of parameters identified by this method remaining below 1%. Also, the value of the standard deviation of natural frequencies for contact excitation is below 0.2 Hz, for electromagnetic excitation up to 0.3 Hz, and for air excitation is 1 Hz. In the other words, electromagnetic excitation is the non-contact excitation that has a lower level of uncertainty in the extraction of modal parameters of thin structures.
Keywords

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