Research On Model Validation Based On Moment Function In Structural Dynamics

The process of demonstrating or attaining the condition that the coefficients in a model aresufficiently accurate to enable the model to provide an acceptably correct description of the subjectstructure’s behavior is called model validation. It can be used to confirm the validity of the designmodel, this is a complex process which includes steps such as finite element modeling, modal testing,model varification, correlation analysis and model updating.The advanced modal test technology such as the three-dimensional laser scanning vibrometersystem provides effective displacement data. Then, the traditional correlation analysis and modelupdating in model validation process which requires handling of large volumes of often highlyredundant data has faced a great challenge. In this thesis, a novel technique based on the new vision ofmode shape description to describe the vibration mode shape using image moment function wasexplored and the correlation and updating techniques based on the image moment for modelvalidation were also developed.Two image moment function were studied in this paper: Tchebichef moment and RadialTchebichef moment. Firstly, the description of mode shapes in moment function was studied. Thecharacteristics of the three moment functions-Tchebichef moment, Radial Tchebichef moment,Zernike moment were compared and summarized in different shapes of the image description. Then,the characteristics of Tchebichef moments and Radial Tchebichef moments in mode shape descriptionand correlation analysis process were respectively studied. Results show that the new mode shapesdescription method can effectively compress the full-field data while retaining the most importantinformation in the form of ‘shape features. And the new correlation method can not only accuratelyfind the paring modes, but also reveal the difference between analytical mode and design mode. Morefor circular symmetrical structure, the correlation analysis based on moment function can successfullyidentify the influences of double-modes due to the rotation invariance of Radial Tchebichef moment.Furthermore, taking a simulated flat and disc as examples, the mode updating method based onmoment functions is also explored. Finally, a modal testing through the laser scanning vibrationsystem on a plate was carried out and Tchebichef moment is further applied to the model updatingprocess. Research shows that the most improved model was obtained when both natural frequenciesand shape features are both included in updating process. This has important implications for thedevelopment of the model updating and model validation techniques.