Research On Health Monitorining Methods Based On The Working Vibration Response Of The Mechanical Structure

At present,the structural health monitoring methods based on structural vibration response has been focused by the scientific research institutions at home and abroad,and the operational modal analysis methods are most valuable among them.Due to the operational modal analysis methods using only the structural vibration response data which is obtained in operating conditions for on-line analysis,and it does not require artificial motive equipment to incentive the structure,so the analyzed results of such methods more in line with the operating boundary conditions of the structure.Therefore,such analysis methods have been widely used in the aerospace,bridges and mechanical manufacturing engineering applications.For these reasons,the stochastic subspace identification method relying on environmental excitation has been exploringly studied on this paper.During the research process,we have mainly done the following works:⑴On the paper,we have studied cantilever by the finite element analysis method to conduct their theoretical modal analysis,and obtained their modal frequencies and modal shape.Thus it provides a theoretical frame of reference for the experimental analysis,and comparatively analysis the experimental modal analysis results by the stochastic subspace identification method and the theoretical results,and it shows that the two modal identification results are in good agreement.⑵on the basis of previous studies,the stochastic subspace identification method which is inspired by the environment has been studied deeply on this paper.The stochastic subspace identification method mainly consists of two kinds of algorithms—the covariance-driven stochastic subspace identification method and data-driven stochastic subspace identification method,and the specific identification process of the two algorithms has been respectively discussed in detail on this paper.The former mainly uses the output covariance sequence to compose Toeplitz matrix blocks,by the singular value decomposition (SVD) to obtain the system matrix and control matrix,then it uses them to identify the modal parameters of vibrating system (modal frequencies,modal damping ratio and the modal shape); while the latter mainly uses Hankel matrix composed of the time-domain vibration response data,reduces the amount of the matrix calculations by QR decomposition,and eliminates the effect of noise by the singular value decomposition of the projection matrix,then it uses the matrix operations such as least-squares method to identify the system matrix and output matrix.Finally,it uses the system matrix and output matrix to identify the modal parameters of vibrating system (modal frequencies,modal damping ratio and modal shape).⑶Because of researching less on the system-order determination method based on the stochastic subspace identification method,we conducted an exploratory study.On this paper,we mainly studied the system order determination method by the steady-state diagram or singular entropy increment,which are both based on the stochastic subspace identification method.The former has been on-line completed by LMS Test.lab modal analysis software,but the latter has been completed by the matlab application.The results show that the results of two order determination methods are in good agreement,and they are more reliable and effective than the traditional system fixed-order method which uses the singular value decomposition.⑷After comparing with the theoretical results obtained by the finite element analysis method, we still take the cantilever structure as researched objects and incentive it by a random white noise signal to mimic its working state in the environmental conditions, with the random subspace identification method and Polymax (Least-Squares Complex Frequency-domain method) conducting on-line modal analysis for them.The results further proves the validity and reliability of the stochastic subspace identification method.In summary, the finite element modal analysis and Polymax modal analysis method are adopted,and they respectively proved the validity and reliability of the stochastic subspace identification method.In addition,on the system order determination methods,we studied two kinds of system order determination methods based on the stochastic subspace identification method—the system steady-state diagram fixed-order method and system singular entropy increment order determination method,the results showed that the fixed-order results of two system order determination method are in good agreement.In short,because the stochastic subspace identification method is a kind of modal identification method based on the structure vibration response,and the identified results is stable and reliable,and currently the system fixed-order method based on the stochastic subspace identification method has been less studied,so it plays an important role in the mechanical On-line health monitoring studies.