Parameter Identification Of Dynamic System Based On Subspace And Transient Response

Structural parameter identification is widely used in health detection,model modification,fault diagnosis and dynamic response prediction.Actual structures often have linear or nonlinear dynamic characteristics,so it is necessary to identify structural system parameters by studying modal testing methods and linear or nonlinear parameter identification algorithms.How to accurately obtain the dynamic characteristics of structures and identify the system parameters with appropriate identification algorithms become the key of structural dynamics research.The main research work of this paper is as follows:Aiming at the problem of modal parameter identification under periodic excitation,a subspace modal parameter identification method called Periodic PO-MOESP based on transient output response was used.In this method,the dynamic response signals of a linear time-periodic system under periodic excitation are adopted,and the modal frequency,damping ratio and modal shapes of the structure are identified from the time-history data.Singular value step method and stability diagram method are used to determine the order of the system.Taking the fan tower as the research object,the identification accuracy of the algorithm under sinusoidal and harmonic excitation and the robustness of the algorithm under noise interference are studied.A flexible beam was taken as the test object,and periodic excitation was applied by a shaker.The results of modal parameters identified by this method were compared with those identified by Donghua test system to verify the accuracy and feasibility of the algorithm.In order to solve the problem of modal omission and false modes caused by artificial order determination of traditional linear subspace algorithm,an automatic modal identification algorithm based on similarity filtering and fuzzy clustering was proposed.Firstly,the singular value decomposition of the Toeplitz matrix constructed by the transient response signal was used to obtain the calculation range of modal order.The SSI-COV was used to calculate the modal triangle matrix,and the real order of the system was obtained by similarity distance function.Then,the FCM clustering algorithm was used to determine the frequency and damping ratio.The simulation of thin-walled beam and triangular truss model and the modal test of 2m flexible beam were carried out to realize automatic order determination of the structures.The robustness of the method is verified by adding noise to the response data.The accuracy of automatic order determination is verified by comparing the traditional stable diagram with the order determination of this method,and the limitation of order determination through singular value step property of subspace algorithm and stable diagram is avoided.A non-contact digital image correlation modal measurement system based on camera array is proposed to solve the problem that sensors and other contact modal measurement methods may have additional quality.The multi-group binocular vision system was used to collect the transient displacement response of the target as the measuring point of the structure.The 3D-DIC system was calibrated using Zhang Zheng You algorithm,and the 3D coordinates of the target at each sampling point were constructed after the feature matching by IC-GN sub-pixel searching algorithm.The modal identification algorithm is used to calculate the displacement response of each target point,and the modal parameters of the structure are obtained.The accuracy of the modal test of the optical measurement system is verified by the displacement pylon test,crescent structure test and telescopic arm structure test.The feasibility of the modal automatic identification system based on non-contact measurement is verified by combining the non-contact measurement and modal automatic identification algorithm of a 3m flexible suspended beam.Develop multi-camera non-contact measurement software based on Silicon Software development kit,including image acquisition,camera calibration,modal identification and postprocessing modules,and build a modal non-contact measurement system for operating modal analysis.To solve the problem that the internal parameters of structures are changed due to the influence of temperature,mass and environmental excitation,an output only measurable recursive subspace time-varying modal identification algorithm based on automatic order determination was proposed.The generalized Hankel matrix was constructed by using transient response signals,and the order of the system was determined by using the initial data instead of singular value decomposition by automatic order determination algorithm.Then,the subspace tracking is transformed into objective function by project approximation subspace tracking algorithm,and the system matrix is solved by least square method and the modal parameters are obtained.The validity of the proposed time-varying algorithm is verified by taking the 5 DOF spring vibration subsystem as the research object.In order to solve the complex problem of model selection and parameter estimation in the process of local nonlinear identification,a local nonlinear identification algorithm based on transient response is used,which is called characteristic nonlinear system identification algorithm.Different from the traditional nonlinear identification which requires vibrator excitation,this algorithm saves the test cost on the basis of pulse excitation.This method does not require prior knowledge or models governing the dynamics of linear parent structures or attachments and relies only on the transient responses of attachments and connection points.Nonlinear stiffness and damping can be identified through two stages of data processing and parameter identification.The accuracy of nonlinear parameter identification is verified by a simulation example of two degrees of freedom spring oscillator system.