| The theoretical relationship between base-excited acceleration transmissibility and modal parameters is derived in this thesis. On the basis of base-excited acceleration transmissibility, modal identification method in thermal environment is investigated simultaneously. The effectiveness of this method is validated with a modal test on a cantilever in thermal environment. It provides a feasible way for modal parameter identification. The main work is as follows:Firstly, the analysis focuses on a base-excited multi-freedom system, both absolute and relative acceleration transmissibility are derived according to differential equation of vibration. The theoretical relationship between transmissibility function and structural mode is studied. After, the validation of modal analysis based on transmissibility is done on a cantilever.Secondly, based on the short time invariant hypothesis, structural modal identification with application of ordinary power polynomial fitting and time sequence analysis are studied in thermal environment. Numerical example was used to analyze the two identification methods in noise resistance research. The results suggest that the time-series analysis method has a better noise resistance ability.Finally, modal experiment on base-excited cantilever is done in thermal environment. The experiment includes normal and high temperature tests. The beam is excited with a vibrator and it’s measured with laser non-contact vibration meter. The acceleration signals of the beam at room temperature, which is 100 degree, 150 degree and 200 degree, are measured respectively. Then the acceleration transmissibility functions of different points on the beam are obtained. Therefore, modal parameters of this base-excited cantilever are identified under different temperature. The experimental results verify the feasibility of applying base excitation in modal experiments in thermal environment. |
