Cyclostationarity And Cepstrum For Operational Modal Analysis Research

Modal analysis is the basis of the mechanical dynamics analysis, which has been applied widely in the aviation, aerospace, machinery, architecture, civil engineering and shipbuilding domain. Modal analysis can be divided into the experimental modal analysis (EMA) and the operational modal analysis (OMA), which has its own shortcomings. Experimental modal analysis need exert exciting force for structure, it is difficult to achieve for large complex mechanical system. But when operational modal analysis that need not exert exciting force identifies the structural modal parameter,it only need the response signal of mechanical structure.The operational modal analysis (OMA) of mechanical systems can identify the characteristics of system in the work. In recent years, the operational modal analysis includes random subspace method (SSI), PolyMAX method and frequency domain decomposition method (FDD), etc. In order to regain scale coefficient of the relative or global among lost modal vibration, This paper presents an application of a new technique for OMA which employs two powerful signal processing tools——cyclostationarity and the cepstrum. Main research works are as follows:(1) Briefly elaborated the purpose and significance of this topic research, systematically discusses the modal parameter identification methods, applications and research status.(2) The basic principle and application of modal analysis are introduced and discussed, and the frequency domain and time domain modal parameter identification method of operational modal analysis (OMA) are discussed mainly.(3) Presented cyclostationarity and the cepstrum for operational modal analysis method, which can be applied to the general input/output system, but the system must have cyclostationarity characteristics of specific cycle frequency.This method relaxes the traditional assumption that the inputs are both frequentially and spatially white. The cyclic autocorrelation function and the cyclic spectral density have been deduced, and the cyclic spectral density has been estimated.In operational modal analysis, cyclic response signal is fit cyclic spectra and extracted resonance frequency by cepstrum analysis. And using the finite element model corrected can obtain the frequency response function, and generate the equivalent curve, so as to obtain accurate scale vibration modal.(4) The frequency and vibration mode of the good beam and the damaged beam are analyzed by using free beam model that finite element analysis software (ANSYS) established, and finite element model of the damage beam is updated to obtain the frequency response function, then generate the equivalent curve.Finally obtain accurate scale vibration modal.(5) Through modal experiment of the good damage free beam and damage beam, the modal parameters of the free beam were identified by cyclostationarity and the cepstrum for operational modal analysis method, And finite element model of the damage beam is updated to obtain the frequency response function, then generate the equivalent curve.Finally obtain accurate scale modal shapes.