Application Of Moment Function In Structural Dynamic Model Validation

The objective of model validation is to refine the mathematical model of a critical structure by using reference data obtained from experimental tests in order that the refined mathematical model can be capable of representing the physical behavior of the actual structure within a required accuracy, and can thus be used for design optimization.Correlation and model updating are two major steps and both play important roles in the process of FE model validation for structural dynamic analysis. The currently used correlation method, modal assurance criterion(MAC), sometimes cannot reliably compare the measurements and FE analysis in the case of complicated industrial systems and axisymmetric structures. In addition, with the development of modern full-field measurement techniques such as the Laser Doppler Velocity (LDV) method, there is no limit to obtain the number of measurement points. Such feature propose a new challenge for model correlation and model updating in the model validation process. In this thesis, based on the new vision of mode shape description, a novel technique to describe the vibration mode shape using image moment function is explored and the correlation and updating techniques based on the image moment for model validation are also developedFirstly, the description of mode shapes in moment function is studied. The mode shape of an axisymmetric structure are described in Zernike orthogonal moment, giving excellent differentiation between double-modes and their rotated angles. Secondly, a new correlation analysis method based on moment function is put forward and applied to the FEM/Test correlation analysis using two practical aero engine structures---an aeroengine pressor disc and a casing. Results show that the new correlation method can successfully identify the influences of double-modes in the structures, and accurately find the paring modes. The method also shows greater advantange than the traditional MAC assessment when dealing with mode shape correlations of axisymmetric structures. Furthermore, the model updating method based on the Zernike orthogonal moment function is also explored. Taking a disk structure as an example, a simulation is carried out, taking into account the influences of noise in the mode shape ’measurement’. Results also demonstrate the greater advantage using the proposed updating method than the traditional updating method. Finally, Zernike Orthogonal moment is further applied to the model updating of an aero-engine disc and the successful result has been obtained with its feasibility and superiority.The paper has demonstrates significant values in model validation of axisymmetric strctures and great potentials in practical application.