Research On Working Modal Analysis Techniques And System

Modal parameters are important parameters to describe the dynamic characteristics of mechanical structures.Modal analysis is one of the important means to obtain modal parameters.Using working modal analysis techniques,by measuring and analyzing the response signals of mechanical equipments in working or running state,the modal parameters such as natural frequency,damping ratio and vibration modal shape of the system are obtained,which is very important engineering application significance on structural optimization design,dynamic characteristic analysis,vibration control,early warning of potential vibration faults,safe and stable operation of a mechanical system.In this paper,the working modal analysis methods based on the features of frequency domain and time domain of signals are studied,the modal parameters of machines are identified and extracted,the working modal analysis system is designed and developped.The main research contents are as follows:(1)The principle of modal parameter identification by Frequency Domain Decomposition method is studied,and the modal identification algorithm program is written for it.By calculating the Cross-power Spectral Density of the response signal,and performing singular value decomposition on the cross-power spectral density,the modal parameters of the system are obtained according to the singular values and singular vectors.The modal parameter identification based on frequency domain signal is realized.(2)The principle and algorithm of modal parameter identification by Covariance-based Subspace Stochastic Identification method is studied.First,arranging the response data to its Hankel matrix,and then calculating the covariance matrix of the response data,the obtained covariance matrix is organized into a Toeplitz matrix,then it is made singular value decomposition,the state matrix and output matrix of the system are obtained after calculation,finally the modal parameters of the system is got according to the state matrix and output matrix.The modal parameter identification based on time domain signal is realized.(3)The modaling principles of wireframe modal,surface modal and solid modal are studied.The structure modaling methods are formed.Some founctions related to structure modaling are realized,such as wireframe modaling and surface modaling,modal imported,model editing,modal shape animation display,modal moving,ratating,zoom,and so on.(4)Using C#computer language,a working modal parameter analysis system is developped.There are several founctions in the system,including structure modeling,date aquisition,data analysis and processing,modal parameter identification,modal shape animation display,and so on.The identification of working modal parameters based on FDD and SSI-COV is realized.(5)Using the measured data of the test bench,the identification results of the modal parameter identification module including Frequency Domain Decomposition method and Stochastic Subspace Identification method in the working modal analysis system are verified.The results show that the modal parameter identification of the system are correct and effective.