Abstract
In this research, we have proposed a methodology for experimental identification of modal parameters based on measurement of the frequency responses of structures with complex geometries and performed an overall investigation of structural behavior on a funnel-shaped inlet of magnetic resonance tomograph. Several identification methods are implemented and compared: complex exponential, least-squares complex exponential, and polyreference least-squares complex exponential. We have implemented the modal parameter identification methodology within our own graphical user interface supported by MATLAB to create an independent tool for modal analysis. The estimation methods are compared and the comparison results are summarized showing based on tabular representation and stabilization diagrams significant advantage of the proposed methodology for determining eigenfrequencies, damping coefficients, mode shapes, and residues for complex structures investigated in broad band of frequencies. Runtime for the execution of algorithms vary depending on the applied method, assumed order of the model used for estimation, and the number of measurements, that is, inputs and outputs.
Highlights
Despite powerful simulation tools, modal analysis still remains an indispensable method for reliable investigation of the structural behavior
Modal analysis can contribute to finite element (FE) model improvement in such cases and it brings a number of other advantages such as machine diagnosis, troubleshooting problems, health monitoring, or other fields
An algorithm based on the polyreference least-squares estimator in the frequency domain has been proposed by Guillaume et al.[4] and Peeters et al.[5]
Summary
Modal analysis still remains an indispensable method for reliable investigation of the structural behavior. The funnel-shaped MRT inlet investigated in this article is characterized by complex geometry, and the characterization of the modal parameters requires a careful investigation under implementation of the identification methods in order to produce reliable statements about the eigenfrequencies, mode shapes, and damping coefficients. Experimental modal analysis is based on estimation of the frequency response functions (FRF) the transfer functions between measured outputs and inputs of a structure, that is, on identification of modal parameters from the FRF. In order to identify the modal parameters of the funnel, a detailed analysis and comparison of several estimation methods presented in Appendix 1 has been performed. Main results of these investigations are presented subsequently.
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