Across the world, radioactive sources are used for a variety of applications. From X-rays and radiotherapy in hospitals, to generation of heat in a nuclear power station. All these sources, however small or large, need to be transported to the point of use and away from there for eventual disposal or recycling. It is more often the case that when the sources are transported to the site, before use, they are not particularly radioactive, but after use they can pose a serious health hazard if not handled correctly. Special, specifically designed transport packages are manufactured and tested to ensure they meet the regulatory requirements for the transport of radioactive materials [1]. Part of the regulatory requirements is that the package withstands a 9m drop on to an unyielding target without loss of containment. The external shock absorbers of a transport package are designed to absorb the energy from this impact, as well as provide other functions not covered in this paper. This paper looks at methods to assist in the designing of these shock absorbers and how LSDYNA can be instrumental in the design and testing phase.
The paper presents CNES’ and Dynas+ partnership recent activities to improve shock events simulation and predict shock propagation in structures and equipment. The last activities presented here have been focused on shock test prediction by numerical analysis (i.e. virtual shock testing). The simulations were performed using LS-DYNA®, whereas the use of explicit non-linear computation codes is not common in the space industry to deal with spacecraft mechanical environments. Especially, the activities aimed at modelling physically the shock event generated by one of CNES’ pyrotechnic test device and to predict the acceleration levels generated by this source on the structural model of a microsatellite. To do so, multiple intermediate steps had to be studied, beginning by the modelling of a simple sphere impacting a plate. The model complexity increased progressively to reach the modelling of a satellite vibrations induced by shock sources. In order to assess model predictability, all the tests were performed at various shock energies and compared to experimental results. This paper will present the results and comparisons with experimental SRS (Shock Response Spectrum) obtained starting with “simple” cases up to cases integrating complex structures and shock sources.
One way of capturing a moving object is by using a hanged cage-like net. The process is to be reliable under various impact velocities and orientations of the captured body. Thus, accurately modeling its dynamics is vital due to the need to account for multiple probable outcomes while including the complex net structure. The focus of the present work is on the modeling, characterization and calibration of the net and its motion. To best represent the geometric properties of the net, its initial state, motion, and body capturing procedure, the following stages were carried out. First, a beam-element-based model of the net was constructed in MATLAB® using a generative function, that allows simple generation of a multiple-parameter dependent net structure. This was due to the need for flexibility in dimensions, geometric properties, part allocation and base unit cell shape. Second, mechanical properties of the hyper-elastic unique net structure were characterized by a series of tensile experiments followed by properly choosing LS-DYNA elements and material formulations. Finally, two sets of finite element analyses (FEA) were conducted, where the first included folding the net to determine its initial state for the successive impact simulation. Both folding and impact procedures required careful consideration and examination of different aspects, such as contact types and formulations, mechanical forces and damping.
Designing Shock Absorbers for Nuclear Transport Packages