Strong and Weak Forms of a Fully Non-Conforming Fsi Algorithm in Fast Transient Dynamics for Blast Loading of Structures

Abstract eng:
The simulation of blast loading effects on structures undergoing very large deformations, possibly up to complete failure and fragmentation, requires robust and specific Fluid-Structure Interaction (FSI) algorithms. The FLSR algorithm uses fully non-conforming fluid and structure meshes (the structure is “embedded” within the fluid), that are “strongly” coupled by suitable constraints on velocities near the F-S interface, enforced by Lagrange multipliers. This technique allows using a regular (or even a structured, typically Eulerian) fluid mesh, while the structure is Lagrangian and can undergo failure and fragmentation without the mesh entanglement difficulties that would arise with more traditional (conforming) FSI algorithms. However, the localization of coupled F-S nodes is more expensive than in the conforming case and must be continuously updated, by means of fast search algorithms, as the structure moves and deforms. The strong form of the algorithm (FLSR) is suitable for a Finite Element (FE) description of the fluid domain and has been used with success in large realistic simulations. Application to Node-Centered Finite Volumes (NCFV) requires an additional treatment of numerical fluxes, presented in the paper. Recently a “weak” variant of the algorithm (FLSW) has been developed for use with Cell-Centered Finite Volumes (CCFV) in the fluid domain. Suitable pressure (interaction) forces are used for the coupling, rather than strong conditions on velocities. Like for NCFV, appropriate treatment of numerical fluxes is required. The rationale and implications of this choice are discussed in the paper.

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