The Application of Fluid Structure Interaction Techniques Within Finite Element Analyses Of Water-filled Transport Flasks

Abstract Historically, finite-element (FE) analyses of water-filled transport flasks and their payloads have been carried out assuming a dry environment, mainly due to lack of robust fluid structure interaction (FSI) modelling techniques. Recent years have seen significant improvements in FSI techniques. These FSI techniques have been used to investigate the effects of assuming a wet environment for the regulatory drop test within a recent Rolls-Royce Naval Marine licence renewal application. This paper will present the FSI capabilities available within various FE codes. The required structural aspects of the FE codes will also be discussed, in particular material models, as these also influence the final code selection. Two explicit dynamic FE codes were finally identified, LS-DYNA, which was used in the extant dry analyses, and RADIOSS, which was used to provide additional confidence in the FSI calculations. Fluid flow and pressure vary significantly during an impact and the effects on the contents become complex when water is incorporated into the flask analyses. Therefore, a verification and validation (V&V) exercise was undertaken to underpin the FSI techniques eventually used. Modelling a fluid environment within the entire flask to capture the explicit effects of fluid on a complex structure is impractical. A good understanding of the FSI techniques and assumptions regarding the fluid boundaries is therefore required for a representative FSI model. A number of V&V problems are presented which test key features required for analysing the payload in a water environment. In conclusion the paper will discuss FSI technology, lessons learnt, limitations of FSI techniques and further possible applications.