Estimation of Dynamic Load Factors for elastic cylinders under dynamic internal pressure
Résumé
This paper discusses the design of a cylindrical test section subjected to a dynamic internal pressure for severe accident experiments performed at CEA. A commonly used method consists in computing the static equivalent response of the structure and then applying DLF coefficients. In this paper, Dynamic Load Factor (DLF) coefficients are obtained for cylinders.
Based on a cylinder subjected to a stepped internal pressure, a set of dynamic equations is set up using the membrane theory with a modal approach (bending moments are neglected with this theory). As already commonly established, it is found that radial and axial displacements are coupled, resulting in a Multi-Degree Of Freedom (MDOF) model with coupling. The maximum DLF of the cylinder is therefore determined for both radial and axial displacements. It is found that the axial DLF reaches a maximum value when there is a specific ratio between the radius and the length (parameter (π R)⁄L equal to 1.0), while the radial DLF does not depend on the geometry.
Results are compared to Finite Elements dynamic simulations. On the whole, the dynamic results are validated for long cylinders (i.e. (π R)⁄L≤0.1). However, differences in the axial displacement tend to increase with an increase in the ratio R/L (shorter cylinders).
The regular value of 2.0 established for the Single Degree Of Freedom model and for both axial and radial directions is exceeded when the radial and axial modes are coupled. The difference can be significantly higher (DLF≥ 3.9).
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