Research On Structural Modal Parameter Identification And Modal Shape Transformation

Compared with the traditional displacement modal analysis,the strain modal parameters are more sensitive to the structural damage,and the strain gauge structure is simple and easy to arrange,so it has been paid more and more attention in the engineering application.In this thesis,based on the practical application of aerospace structure,the theoretical and experimental research on the identification of strain modal parameters is carried out,and the transformation relationship between the strain mode and displacement mode of the structure is discussed,which has important engineering significance and theoretical value.The main work of this paper includes:(1)According to the theory of strain modal analysis,the relationship between the structural strain mode,displacement mode and the expression of force-strain transfer function matrix is studied.And several common methods of operational modal analysis are introduced,which provide the theoretical basis for the subsequent operational modal analysis based on strain response test.(2)Establishing a finite element model of the strain mode of the cantilever thin plate,and the random basic excitation experiment of the vibration table is designed.The acceleration signal and the strain signal are used as the test signals respectively to finish the operational modal analysis of the cantilever thin plate,and the finite element model is corrected according to the experimental results.(3)The optimal arrangement of sensors in strain mode test is proposed.In view of the particularity of strain measurement,the optimal arrangement of the sensor is carried out by considering the strain projection component of the measured surface,the energy of strain measurement signal and the linear independence of modal shape.The experimental results show that the optimized scheme can effectively improve the signal-to-noise ratio of strain test signals,and improve the linear independence between different modes.Finally,based on the scheme,the sensor arrangement for strain modal test of a rudder structure is completed.(4)Using the mode vector obtained from the finite element model to construct the modal shape transformation matrix,a method of obtaining the displacement modal shape of the structure from the strain mode test is proposed.At the same time,the applicability of the method in different working environments is verified by the characteristic sensitivity analysis of the structure.Finally,comparing the displacement modal shape obtained from the transformation with the displacement modal shape obtained from the modal experiment to verify the effectiveness of this method.