Study On Modal Identification Of Plate Frame Based On Operational Modal Analysis

Traditional experimental modal analysis measures both response and excitation of structure and then establishes frequency response function in order to extract modal parameters,in which structure is tested in non-work state under artificial excitation.With the large-scale development of ship,it is more difficult to design and manufacture the excitation device,which can excite vibration of the whole ship.In addition,the excitation of ship in the working state,which can excite vibration of the whole ship,cannot be measured accurately.Operational modal analysis can solve the problem by extracting modal parameters only from response data,in which structure can be tested in the working state.In this paper,research work is as follows:According to natural excitation technique(NExT),there is a similar expression between correlation function and impulse response function when the structure is under white noise excitation.Then NExT-ERA modal identification theory can be established,and the identification process of NExT-ERA is given.Traditional experimental modal analysis theory is derived in brief,and then the identification process of peak picking method that utilizes frequency response function is given.According as the power spectral density function has a similar expression to frequency response function when the structure is under white noise excitation,OMA-PP modal identification theory can be established.In addition,the identification process of OMA-PP is given.A modal experiment of plate frame with the method of multipoint force hammer is performed.Then modal parameters can be extracted using modal software.In addition,the simulation analysis of plate frame is carried out.The simulation model,in which the weld is simulated by rigid domain,is created in Ansys in order to get more accurate simulation modal analysis result.Compared the result of experiment modal analysis and simulation analysis,there are some differences in modal frequency and then the reasons of these differences are discussed.At last,the result of traditional modal experiment is considered as the accurate solution in subsequent operational modal analysis.Taking the impulse excitation operational modal experiment for example,it is given that the identification process and the extraction of modal parameters of NExT-ERA and OMA-PP in detail.Compared with the result of traditional modal experiment,it shows that NExT-ERA and OMA-PP both have a good precision on modal parameter identification,especially in modal frequency and modal shape.Then the result of white noise excitation and swept excitation are given.Compared with the result of traditional modal experiment,it shows that operational modal analysis has a good identification accuracy on modal parameters.