Launcher Structures excited by Shock in the Absence and the Presence of Fluid Loaded Vessels
- Paper number
IAC-06-C2.3.05
- Author
Mr. Bernhard Kotzias, EADS Astrium, Germany
- Year
2006
- Abstract
Part one of this paper comprises the principles of shock in launcher primary structures dedicated to the simulation of fluid-structure interaction. It is supported by part two, which is related to numerical simulation, results and the technical aspect of simulation. Shock induced vibrations in launchers are generated from engine ignition, stage or payload separation. They are to be kept as low as possible in order to improve the quality of payload and equipment environment. As in general fluid loaded vessels are present, they have an impact to the launcher environment. It is one task of the development to assess this impact related shock levels. If necessary, the assessment is supported by analysis and test. Different impedances in the propagation path, among others generated by interfaces, branches, etc, will cause a shock wave to be split into a transmission and a refection part. All multiple reflections between two interfaces will cause standing waves or so called vibrations. The composition of propagating and standing waves are a manifest of the excitation in terms of introduced impulse and energy. Both are distributed over the structure. The vibrations are in addition moderated by the first significant impedance jumps next to the shock source. Further impedance jumps/interfaces are less important for the distribution of shock wave energy, but govern the modal response of the structure. In this domain all empirical shock attenuations laws looses validity. More sophisticated analysis based on numerical algorithms has to be applied in order to get reliable predictions. This paper introduces to the consequences of above and - in addition - to the fluid loading aspect. Three aspects of fluid loading to the shock induced response can be exhibited: • Reduced shock levels due to energy removed from the structure by fluid oscillations. • Reduced or increased shock levels due to the modification of reflection or transmission in the presents of fluid. • Increased shock levels in the structure from oscillation of fluid interacting to the structure. The simulation presented is focused on the third, probably most common situation in launcher structures: In comparison to a dry structure, fluid-structure interaction modes in the relevant shock domain exist. Ones exited, these modes are shown to modify the shock levels, relevant to equipment and interface locations.
- Abstract document