Research On Modal Identification Of Cylindrical Shell Structure Based On Operational Modal Analysis

For the traditional modal test analysis of the structure,the general method is to apply external excitation to the structure,causing structural vibration,collect the response signal of the structural measurement point,and then use the response signal of the measurement point and the applied external excitation force signal to calculate the structure.Frequency response function,because the frequency response function contains the modal parameters of the structure,so the modal identification of the structure can be completed.However,in this process,the incentives received by the structure are actually artificially applied external stimuli,not the excitation signals generated by the structure itself.Nowadays,the tonnage and structure of ships are becoming larger and larger.It is difficult for engineers to design and manufacture equipment that can generate vibrations for the entire hull.Although the external excitations received by the ship during operation can cause vibrations for the entire hull,But we can’t get the external incentive signal accurately.In response to this dilemma,a method of running modal analysis has been developed.The biggest advantage of this method is that it only needs to use the vibration response signal of the collected structure without additional measurement of the external excitation force signal,so even if the structure is working,it can also be used Run a modal analysis method to extract its modal parameters.The main contents of this article are as follows:By deriving the natural excitation method,it can be seen that when the external signal used as the structure is white noise,the function expression of the cross-correlation function between the structural measurement points is similar to the structural impulse response function;the characteristic system implementation method also proves that the impulse response of the structure can be used The function performs modal identification on the structure,so by combining these two theoretical methods,the modal identification method of natural excitation-characteristic system implementation method can be obtained,referred to as NEx T-ERA method for short,and its modal identification process is given.By deriving the theory of peak picking method for operational modal analysis,when the external excitation used for the structure is white noise,the expression of the cross power spectral density function of the response between the structural measurement points is similar to the frequency response function,so the operational mode can be established The modal identification method of modal peak extraction method,referred to as the OMA-PP method,its basic idea is to use the mutual power spectral density function between structural measurement points to replace the structural frequency response function for modal identification of the structure,and the method is also given Modal recognition process.The peak extraction method of the traditional modal test,that is,the EMA-PP method theory is briefly derived.The traditional hammering method is used for modal identification of the cylindrical shell structure,the excitation and response data are imported into Donghua modal testing software,and the peak extraction method is used to identify the frequency response function,and the structural modal parameters are obtained.The finite element software Ansys was used to simulate the cylindrical shell structure,and the modal results of the simulation calculation were obtained.The simulation calculation modal results are compared with the traditional hammer shell test results of the cylindrical shell,and the causes of the errors are analyzed.In the sixth chapter of the modal analysis of cylindrical shells,the traditional hammering test results are used as the basis and the modal analysis results are compared.When the external excitation signal is pulse excitation,the process of using the OMA-PP method and the NEx T-ERA method to analyze the modal parameters of a simple structure fixed beam to obtain the structural modal parameters is first introduced,and the results are compared with the test results.,The reliability of the compiled program is verified,and the recognition effect of the two methods is proved to be good,and the error is not much different from the traditional modal test results.Then,the two methods are used to select the cylindrical shells at the near and far end of the tapping point.#21 conducted operational modal analysis,and compared the results with the traditional hammering test results.The results show that these two methods also have better recognition effect and accuracy on the cylindrical shell structure.