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The launch vehicles are subject to severe dynamic loads at lift-off and during flight ascent. Moreover, a major part of European launch vehicles are of composite construction. A robust design requires a proper consideration of uncertainties in excitations and materials.
Thus, the mechanical dynamic qualification is closely associated with the development of a launcher Finite Element Model (FEM) that will be used to predict flight load cases and release relevant specifications addressable to the stack components of the launcher.
Such specifications must take into account the coverage:
- of all flight events,
- of a large spectrum of payload to be launched,
- of the stack FEM uncertainties.
Conversely, specifications should not result to the overdimensioning of structures that would be detrimental to the launcher performance. The mastering of uncertainties application on the launcher FEM is therefore an issue that we address in this paper.
A trade-off between the different ways to introduce uncertainties into dynamic computations oriented us towards non-parametric model of random uncertainties that is addressing uncertainties on the different sub-components of the launcher by maintaining the physical conditioning of the dynamic system to be solved.
The non-parametric methodology is applied on the condensed parts of the launcher FEM which allow introducing different level of uncertainties on parts of the launcher depending on the complexity of elements and their impact on the dynamic phenomenon targeted.
The article details the methodology implementation already achieved on ARIANE 5 on of the solid rocket booster pressure oscillation load case which is on the driving load case regarding low frequency vibrations on the launcher.
Criteria on the level of coverage to be achieved by simulations regarding flight measurement are defined and applied on the time and frequency domain simulations backed by flight measurements. First set of uncertainties applicable on the launcher condensed parts are then derived that allow covering the flight measurement with sufficient margin.
In order to mitigate the computation time a factorial design based methodology is introduced and detailed.
Confrontation of the uncertainties set to other flight load case will allow to set-up a generic uncertainties treatment that could be used to release justified and less dimensioning specifications.
- Presentation
