Modal Parameter Identification Based On Wavelet Trasform And Research For The Display Technology Of Modal Animation

Experimental modal analysis has important application value in structural healthmonitoring, damage identification and dynamics analysis, with the increased demands onimproving the accuracy of the overall vibration characteristics of mechanicalcomponents,such as large-scale machine tools, precision medical equipment, aerospacevehicles, ect., which makes the demand of modal parameter identification accuracybecoming higher and higher. The traditional method of the frequency response functionmodal parameter identification bases on Fourier transform algorithm, since the wavelettransform has the unique time-frequency characteristics of local transformation, and canrefine the signal multiscale analysis, it has the potential research value on improving theaccuracy of modal parameter identification and the identification of modal parameters onnonlinear structural system.The paper analyzes the frequency response function modal parameter identificationmethod which based on Fourier transform (FFT), according to the relationship betweenthe frequency response function and modal parameters, utilizing the Matlab/Simulink tosimulate and programming with the script files implements the algorithm of solving themodal parameter by the method of the frequency response. It has researched theidentification of the modal frequency and damping ratio on the simulation model by usingthe instance of three degrees of freedom linear vibration system, and proved thecorrectness of the algorithm.Bases on the comparison of the wavelet transform theoretical analysis and Fouriertransform analysis, drawing support from time domain convolution theorem, it has beenderived the algorithm to solve the wavelet coefficients, and dealt with the key issues in theprogramming process. It has adopted the wavelet of Morlet which has the time-frequencycharacteristics of local transformation, and introduced two adjustment factors of thewavelet,center frequency and bandwidth, utilized the wavelet coefficients ridge lineextraction method to carry on modal parameter identification, the results showed the highaccuracy of modal parameters identification by wavelet transform.For the problem of nonlinear modal parameter identification, it has been validated the characteristics of the three degrees of freedom nonlinear stiffness Duffing equation usingthe equivalent linearization method. It uses wavelet transform algorithm to identify themodal frequencies of Duffing equation with a single degree of freedom, and to verify thatwavelet algorithm can identified the nonlinear element of the modal parameters to acertain extent.The paper has researched the implementation method with the3D animation displayby Visual Basic6.0and OpenGL, developed a display platform of the experimental modalanalysis system. By establishing the geometry node, automatically generate the structureof wireframe mode by connecting the nodes, and achieved the function of enlargement andreduction, translation and rotation of the structure, therefore it can check the localvariation information of the structure modal shape.