Structural Dynamic Analysis Based On Continuous Monitoring Of Strain Under Operational Conditions

In this paper,mainly study the real dynamic behavior of the structure under normal operating conditions based on the continuous monitoring of strain response.Based on the theoretical deduction,numerical simulation,experiment based on dynamic strain,modal parameter tracking in actual engineering,reveal the dynamic characteristics and mechanism of the structure under operation,and verify the feasibility and effectiveness of long-term monitoring with dynamic strain.The finite element method is used to derive the theory of stra in modal identification of linear elastic structure,and the relationship between the strain mode and the displacement mode is also introduced.By using the relationship between strain and displacement,the strain state equation is obtained by discretization.The Covariance-driven Stochastic Subspace method is used to obtain the system matrix and the observation matrix about the strain,and then the modal parameters of the structure are obtained.The correctness of the dynamic strain modal identification is verified by the simulation signal.In this paper,the modal parameters of the structure are obtained by using the steady-state graph,setting the criterion and effectively isolate stable points and noise points.Based on the test of dynamic strain acquisition about the Binzhou Yellow River Bridge scale model and the laboratory wind turbine model,the results show that the error of the modal modal parameters is better than that of the acceleration test in the case of ambient noise interference,and the er ror of the frequency identification is not more than 5%,the MAC value of stain mode between measurement results and numerical simulation results is higher than 0.6.Based on the continuous dynamic strain monitoring data,the vibration characteristics of the wind tower and the change of the structural modal parameters of a pedestrian bridge during the construction stage and operational stage are studied in detail.In order to accurately identify the real structural behavior of the large wind turbine in the operating state,this paper uses the dynamic strain monitoring data of the wind tower from a 5 MW wind turbine for two years.Through the automatic operation modal analysis method,the dynamic response of the wind turbine is analyzed continuously,and the dynamic parameters of the wind tower are automatically identified.By plotting Campbell diagram by the frequencies and the rotation speed of the wind turbine,the excitation frequency 1 P caused by the imbalance of blade quality in the operating state and the excitation frequency 3 P and the harmonic frequency 3k P,are obtained.When the excitation frequency 3 P matches with the structural fundamental frequency,resonance occurs,The amplitude of the strain change is obviously improved,and it is found that the existence of the Sommerfeld phenomenon causes the structure to stick in the state of 23.9% in the operating state,which seriously affects the normal operation of the wind turbine.In this paper,through the six months dynamic strain monitoring of th e Pedestrian bridge,from the structural construction stage to the bridge put into use,the automatic operation mode analysis technology is used to deal with the large amount of collected data.The modal parameters are obtained.The relationship between the strain and the modal parameters of the structure is studied in detail.The correlation of the frequencies and temperatures is affected by the bearing adjustment,the overall fluctuation of the frequency is about ± 4%.