Fluid Structure Interaction with *MAT_SOFT_TISSUE and EFG Elements

This paper presents LS-DYNA 970.5434a transient simulations for the fluid- structure interaction (FSI) in a prototype biomedical duct. Standard and element free Galerkin (EFG) elements are compared for the nearly incompressible membrane out of *MAT_SOFT_TISSUE, which is a composite reinforced hyperelastic material. The coupling of a multi-fluid arbitrary Lagrangian Eulerian (ALE) solid domain to an EFG solid domain is possible and its LS-DYNA implementation keeps developing. The paper describes particularities of this coupling. The EFG simulation for nearly incompressible materials necessitates a non-default support of 1.4x1.4x1.4 or even higher for accurate results. The EFG simulation demands higher computation times than the standard formulation with reduced integration and type 6 hourglass control. An example is shown, in which the high ratio of the elastic moduli chosen for the fibers and the bulk of the soft tissue material generates a severe hourglass problem that only the EFG method can cope with. The standard formulation, however, is remarkably robust and it proves difficult generating an extreme situation where only EFG works and the solver run would abort otherwise. So the potential of the EFG method lies in the accurate prediction without introducing non-physical energy in the system for hourglass stabilization, in situations, where selective reduced or full integration show a too stiff behavior and reduced integration has a hourglass problem. Although LS-DYNA 5434a is already much faster than 5434, a more computational efficient implementation of EFG for solid elements is required. Therefore, the features of the LS-DYNA 971 beta version, which address this lack of performance, are assessed as well. The paper features an abstracted input deck.