A new methodology for assessing the global dynamic response of large shell structures under impact loading

Abstract : The determination of the vibration induced by an aircraft impact on an industrial structure requires dynamic studies. The determination of the response by using classical finite element method associated with explicit numerical schemes requires significant calculation time, especially during the transient stage. This kind of calculation requires several load cases to be analyzed in order to consider a wide range of scenarios. Moreover, a large frequency range has to be appropriately considered and therefore the mesh has to be very fine, resulting in a refined time discretization. The purpose of our study is to develop new ways for calculating the shaking of reinforced concrete structures following a commercial aircraft impact. The cutoff frequency for this type of loading is typically within the 50 to 100 Hz range, which would be referred to as the medium frequency range. Taking into account this type of problem and assuming that the structure is appropriately sized to withstand an aircraft impact, the vibrations induced by the shock bring about shaking of the structure. Then these vibrations can travel along the containment building, as directly linked with the impact zone, but also in the inner part of the structure due to the connection with the containment building by the raft. So the excited frequency range, due to the impact of a commercial aircraft, contains two frequency ranges: low frequencies (less than 10 wavelengths in the structure) and medium frequencies (between 10 and 100 wavelengths). In this context the use of finite elements method for the resolution of the shaking implies a spatial discretization in correlation with the number of wavelengths to represent, and thus a long computation time especially for medium frequencies. That's why in the case of a coarse mesh the medium frequency range is ignored. For example, a concrete structure with a characteristic dimension of about 30 m and 1 m of thickness, may not represent frequencies higher than 16 Hz with a mesh size of 1 m (assuming 10 elements per wavelength). So the medium frequencies can therefore induce significant displacements and stresses at the level of equipment and thus the causes damage if the structure is not dimensioning to this frequency range. Our strategy, which is presented in this paper, is inscribed in the context of the verification of inner equipment under this kind of shaking. \com{The non-linear impact zone is assumed to have been delimited with classical finite element simulations. So this shock phenomenon which induces a damaged and localized area around the impact zone, might be considered as dynamic analysis by a concentrated load. In this paper we only focus on the response of the undamaged part of the structure.} This paper shows the gain of our strategy using appropriate method to medium frequencies compared to conventional method such as finite elements.
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Submitted on : Wednesday, December 9, 2015 - 11:47:15 AM
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Christophe Rouzaud, Fabrice Gatuingt, Olivier Dorival, Hervé Guillaume, Louis Kovalevsky. A new methodology for assessing the global dynamic response of large shell structures under impact loading. Engineering Computations, Emerald, 2015, 32 (8), pp.2343-2382. ⟨10.1108/EC-06-2014-0124⟩. ⟨hal-01240476⟩

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