Operational Modal Analysis In The Change In The Structure Of The Spacecraft

In the designing period for an airplane, missile and rocket, the dynamic characteristic of the structure should be estimated first in order to avoid flutter and instability in working condition. As an mature and effective method, modal analysis has been used to identify the dynamic parameters for a long time. The operating aero structures are usually under complicated environmental excitation, which is hard to be measured. Meanwhile, it's also difficult to conduct artificial excitation to the structure. So the traditional modal analysis method based on both the input and output is not available any more.Operational modal analysis (OMA) is a newly developed method for modal identification. When the environmental excitation can be seen as white noise, we can use OMA to build identified model on the basis of pure response signal and the identified parameter can represent the real operating condition. However, in a lot of engineering applications like missile firing, the structure suffers impact as well as other non-random excitation. Therefore, the traditional OMA is not applicable. When the aero craft is working, the aerodynamic heating will make the dynamic parameter changed slowly. This also brings difficulties to the modal identifying work. Considering the real difficulty, this paper expands the applying field of OMA; propose a modal identifying method to time-varying structure on the basis of revised OMA and Short-term time-invariant assumption. This paper also verifies the new theory by two experiments. The main work of this paper includes:Firstly, this paper reviews the history of both experimental modal analysis operational modal analyses. Then the paper proves that OMA is also applicable under compound excitation which contains white noise and impact excitation. An aluminum plate experiment is designed and the modal characteristic is identified with the revised OMA theory. The identified results validate the correctness of the new method.Secondly, considering the time-varying process in aero filed, this paper proposes a modal identify method to time-varying structures, based on revised OMA theory and Short-term time-invariant assumption. Meanwhile, a moving mass-cantilever beam system is designed. The centralized mass moved from the fixed point to the unstrained point, which represents the time mass distribution varying process. The dynamic parameters of the system are identified with the new method. The identified results validate the effectiveness of the method. At last, a heated experiment to a missile empennage model is designed and the parameters are identified with the newly developed method. The time-varying modal parameter principle is also analyzed, which is meaningful to the design of real missiles and similar experiments.