Operational Modal Parameter Identification Of Linear Structures Based On Blind Source Separation

Operation modal analysis(OMA)is always a key research object at domestic and abroad.In this thesis,a series of methods are proposed to linear time invariant structure,complex three-dimensional structure and linear time-varying structure modal parameter identification by using second-order blind identification(SOBI)and independent component analysis(ICA).The main research contents include:(1)Operation modal identification method of linear time invariant structure based on SOBI and ICA is studied.Firstly,this thesis analyzes the similarity between the operation modal analysis and the blind source separation in theory,and obtain the one-to-one correspondence relationship between the mixing matrix and the modal model as well as between the separation signal and the modal coordinates response,then point out the root reasons why order of modal is uncertain and the energy of the mode is uncertain as well as the modality is missing based on the identification method of blind source separation.From the objective function and the optimization method,the advantages and disadvantages of different ICA methods in the field of time-invariant structural modal analysis are compared.Finally,since the independent component analysis method uses high-order statistics,this thesis also studies SOBI method based on second-order statistics.The results of numerical simulation verification are in the linear time-invariant structure on discrete 3-DOF and simply supported beam.This thesis compares and analyzes the advantages and disadvantages of SOBI method and various ICA methods of operation modal analysis.(2)This thesis studies the modal parameter identification of the three-dimensional structure based on SOBI.In this thesis,three modal coordinate responses to the three-dimensional structure are the same in the Cartesian coordinate system.SOBI method is used to identify the modal coordinate matrix to the direction in which the response is greatest,and then the modal coordinate matrix is used to identify themodal shape in the other two directions by using the least squares generalized inverse method,and finally complete the three-dimensional mode shape assembly.The simulation results show that the modal parameters on the three-dimensional cylindrical shell can be effectively identified based on SOBI and least squares generalized inverse.(3)The on-line identification method of linear time-varying structure operation modal parameters based on moving window second-order blind identification is studied.This method uses the "short time-invariant" theory,assuming that in a very small time window,the structure is invariant.Then second-order blind identification can be used to identify the structural modal parameters of the structure at the middle time.The window is also constantly moving forward,each time the modal parameters are identified.Finally,the modal parameters of each moment are connected together to form the modal parameters of linear time-varying structure.At the same time,this thesis puts forward the scope of this method.The simulation results of time-varying three-degree-of-freedom system and time-varying cantilever beam show that the moving window SOBI method can effectively identify the modal parameters of time-varying structure when the size of moving window is appropriate selected,and the effect is better than moving window ICA method.