Initialisation of volume fraction in fluid / structure interaction problem

In this paper, an algorithm that generates volume fraction initialisation for fluid-structure interaction problems is presented and implemented in an Arbitrary Lagrangian Eulerian (ALE) code. This algorithm improves the flexibility and efficiency of multi-material ALE formulations, enabling fluid-structure coupling problems to be dealt with, in which complex-shaped structures are embedded in a Cartesian fluid mesh, and where several fluid materials are involved. When implemented in a finite element code the algorithm will be extremely useful in the modelling of highly transient problems involving fluid-structure interactions and complex structural topologies. In such problems the volume fraction of each cell must be accurately initialised in order for the fluid-structure coupling algorithm to be effective. In many fluid-structure coupling problems if the volume fraction initialisation is not processed properly, the coupling algorithm leads to numerical fluid leakage through the structure involving an erroneous solution. In this paper the volume fraction initialisation method is described in detail and applied to the modelling of a cylindrical shock tube problem and to a crash problem involving a fuel tank of complex geometry under braking conditions.