| Photoelectric theodolite is widely used to capture and track the orientation, trajectory and the other objective characteristic of moving objects in the distance automatically. Because the photoelectric theodolites needs the capability of rapid search of high moving objects with high precision, the natural vibration frequencies of the support structure of the tracking system are required not fall into the servo bandwidth range or close to the servo systems frequency so as to avoid resonance due to the servo system or the external excitation. Therefore, it is important in the design stage to simulate the dynamic characteristic of optical and mechanical support structure accurately.The structural connection of theodolite is mainly implemented by the bolt connection. During the simulation analysis of the contact state, nonlinear contact boundary condition needs to be considered. Because of the contact area, location of contact region are changed with the structural deformation, the contact stiffness, contact area, damping characteristic of contact interface and the contact force normal to the deformation area are also changed. Therefore, the method used in the linear mode simulation cannot be directly used in structure with bold connection. And results are quite different between simulation and experiment.In this thesis, a new numerical method is proposed by combining time-domain and frequency-domain analysis to calculate the vibration characteristic of structure with bolt connection. According to method of the mode experiment, pulse and step sine sweep loading excitation of specified frequency range are constructed and time-displacement response are calculated by applying constructed excitation to the structure. The frequency characteristic about calculated time-displacement response curve are obtained by using Fast Fourier Analysis(FFT) method. Finally, the resonant frequency of structural are obtained via signal filtering method. The method that combined time-domain and frequency-domain is proved to be an effective method to model with contact effect. The time intervals and calculating time are analyzed according to the sampling theorem during calculating the time-displacement curve of consolidated structure. The beam model connected by a single bolt which pre-tightening force and contact nonlinearity is simulated through new algorithm using implicit integration method and nonlinear finite element analysis. By comparing the experimental model results and simulation results of proposed numerical method, the calculations error is less than 7%.By calculating the time-domain response of structure of single bolt, the nonlinearity vibration characteristic and secondary frequency response characteristic of beam model are pointed out. The results are compared between the model with large and small contact area. Numerical results illustrate that the smaller contact between two beams, the harmonics response characteristics are less and the difference are much less between the response frequency simulated through linear model analysis and experiment. The forced vibration of beam model with block is calculated and the result noting that under such strongly nonlinear conditions the vibration theory based on linear vibration modes cannot applied to analyze forced vibrations. In order to decrease the computational cost of time-domain analysis of structural vibration with nonlinear bolt connection, the substructure method is reseated for the cantilever beam with single bolt connection.At last, the potential improvement of the proposed numerical method are discussed for the further research on multiple-bolt connection. |
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