Why use the sub-modelling technique in a Finite Element Analysis of a nuclear transport package?

A nuclear transport package has been analysed using Finite Element Analysis (FEA) under regulatory impact conditions. Embarking on impact analyses can involve large assembled FE models comprising many individual components and the more complicated a model becomes the longer it is likely to take to complete the analysis solution. It is known, that generally, in order to achieve a sufficient level of accuracy in the analysis results, of a particular Region of Interest (ROI), typically means a refinement in the mesh density is required. Furthermore, in some instances the level of fidelity in the FE model falls short of the degree of refinement that is needed to capture the small details in the geometry. Modelling and simulating the impact of a structure involves calculating large deformations over many small time steps dynamically and the use of sophisticated explicit analysis tools. However, as a consequence, simulation of large structures in explicit analyses can be very time consuming and costly - the analysis time step is directly influenced by the smallest element size in the mesh. It is also the size of the smallest element that limits the stable time step. Using the sub-modelling technique allows a refined analysis of a ROI of a local part of a larger model in much greater detail than that directly obtained from the original full (global) model, but without the additional time and cost implications of refining the entire structure. The process of performing a sub model analysis is described with the use of the explicit FEA tool, LS-Dyna. (author)