Mode-shape recognition and finite element model updating using the Zernike moment descriptor

In structural finite element model (FEM) updating an important step is the comparison/correlation between the FEM and experimental data. Currently the most widely used method is the modal assurance criterion (MAC), which can be interpreted as the cosine of the angle between numerical (FE model) and measured eigenvectors. However, the eigenvectors only contain the displacement of discrete coordinates, so that the MAC index carries no explicit information on shape features. A new technique, based upon the well-developed philosophies of image processing (IP) and pattern recognition (PR) are considered in this paper. The Zernike moment descriptor (ZMD) is a region-based shape descriptor having outstanding properties in IP including rotational invariance, expression and computing efficiency, ease of reconstruction and robustness to noise. In this paper the ZMD is applied to the problem of mode-shape recognition for simple plate structures. Result shows that the ZMD has considerable advantages over the traditional MAC index when identifying the cyclically symmetric mode shapes that occur in axisymmetric structures at identical frequencies.