Damping Characterization & Flight Identification
- Paper number
IAC-06-C2.3.04
- Author
Mr. Vincent Le Gallo, EADS Astrium, France
- Coauthor
Mr. Maurice Goursat, INRIA, France
- Coauthor
Mr. Luc Gonidou, Centre National d'Etudes Spatiales (CNES), France
- Year
2006
- Abstract
Modal analyses of data in operation by the subspace method has been succesfully applied in the industry to stationnary structures. This method permit to restitute the modal characteristics of a stationnary structure (natural frequencies and damping) excited by non stationnary perturbations, by the analysis of the responses measurements only, without knowing this excitation. Namely, the evaluation of modal damping in flight is a very interesting purpose for dynamic studies of launchers. The application to launchers will permit to increase the knowledge concerning modal damping, which could have a significant impact on several System studies (mechanical design, control …). Nevertheless, it is not easy to adapt the subspace method to launchers because of the great level of non stationnarity of their behaviour induced by the mass ejection. The success of this approach will lead to optimize the logics of launchers development and also to increase the reliability of system studies. This method has been successfully applied to the launcher ARIANE 5. To obtain good results, it has been pointed out the necessity to establish an adaptated methodology, namely to manage the instationnarity features. To deal with this problem, we developed a simple pre-treatment of the responses in order to ensure artificially constant frequency modal responses, which is a necessary condition of success of the subspace method (stability of eigen values belong time). Also, it has been identified acceptance criteria concerning the lack of precision of flight measurements as the number of quanta. Finally, one of the most important key success factors has been the idea to minimize the number of fictive modes generated by the sub-space method in order to facilitate the sure identification of real physical modes. This methodology has been previously validated on synthetic modal responses to shocks or random excitations, representative of flight measurements and for which we perfectly know the modal damping. It remains from these validation tests that the subspace method, adaptated to launchers, is efficient to identifiy precisely the damping for unstationnary excitations like shocks (lift-off, booster’s separation) or random excitations (buffeting, engine noises), if measurements are sufficiently precise. First industrial applications have been succesfully performed like exploitation of booster tests and some measurements from ARIANE 5 flights, with a first identification of dampings on the main modes of the launcher.
- Abstract document
- Manuscript document
IAC-06-C2.3.04.pdf (🔒 authorized access only).
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