Multiphase Fluid-Structure Interaction Software Infrastructure to Enable Applications in Medicine, Biology, and Engineering Boyce E. Grifﬁth1, Amneet P. S. Bhalla2, M. Gregory Forest1, Matthew G. Knepley3, and Neelesh A. Patankar4 1University of North Carolina at Chapel Hill, 2San Diego State University, 3University at Buffalo, and 4Northwestern University NSF Awards OAC 1931516 (UNC-Chapel Hill), OAC 1931372 (Northwestern), OAC 1931368 (SDSU), and OAC 1931524 (UB) ibamr.github.io OVERVIEW Coupled ﬂuid-structure systems are ubiquitous in biology, physiology, and medicine, and these systems occur across a broad range of spatial scales: • writhing and coiling of DNA; • beating and pumping motions of cilia and ﬂagella; • ﬂow of blood in the heart and throughout the circulation; • swimming bacteria and ﬁsh, and ﬂying birds and insects; • ﬂuttering of leaves and dispersal of seeds and pollen by the wind. Fluid-structure interaction is also common in engineering applications. The immersed boundary (IB) method is an approach to to ﬂuid-structure inter- action (FSI) that uses: • an Eulerian description of the momentum and incompressibility of the ﬂuid-structure system; and • a Lagrangian description of the structural stresses, forces, and deformations. The IB approach to FSI: • facilitates the use of fast Cartesian grid solvers; • reduces or eliminates the need for dynamic regridding; and thereby • enables simulations with very large deformations/displacements. IBAMR is a C++ framework for FSI models based on the IB method. IBAMR provides support for Cartesian grid (structured) adaptive mesh reﬁne- ment (AMR). Support for Lagrangian (unstructured) AMR is planned. Cartesian grid AMR allows high spa- tial resolution to be deployed only where needed (e.g. near the immersed bodies): IBAMR also enables numerical methods research, including work on Lagrangian- Eulerian coupling schemes, time-stepping algorithms, and fast solvers. IBAMR IBAMR provides modular structural de- scriptions to enable a range of models: • systems of springs and beams; • nonlinear elasticity; • peridynamics; • elastic rods; and • rigid structures and bodies with prescribed kinematics. This project is extending IBAMR’s multiphase ﬂuids capabilities and en- hancing its Lagrangian-Eulerian coupling schemes, geometrical model representa- tions, and parallel performance. Recent methodological enhancements include: • efﬁcient Brinkman penalization-based coupling; • polymeric ﬂuid models; • one-sided IB coupling operators; • immersed interface method (IIM) coupling; • IIM-based schemes for rigid-body and ﬂexible-body FSI; and • cut cell-based methods for advection-reaction-diffusion models in moving domains. IBAMR project milestones include: • six-month release cycle since 2018; • ≥460 unit and integration tests; • new CMake-based build system; • improved support for CI to automatically run tests on multiple platforms; • autoibamr: automatically compile and install IBAMR and its dependencies; • new algorithms for parallel IB data partitioning and load balancing; and • used in ≥130 peer-reviewed publications, ≥30 graduate and undergraduate theses. 2018 2019 2020 2021 2022 2023 0 100 200 300 400 500 600 700 800 900 1000 Total Execution Time, s libMesh deal.II Benchmark performance of IBAMR’s IBFE nonlinear elasticity FSI scheme with different ﬁnite element libraries. MAJOR ENHANCEMENTS Advection and diffusion of chemical species in moving subdomains with Robin boundary conditions that convert from one concentration to the other along the moving interface. Melting and solidiﬁcation of an aluminum block with trapped gas. Porosity defect in metal 3D printing. Colors: yellow (solid Al), blue (molten Al), white (gas). Light rigid sphere rising in a water column via a new IIM-based sharp-interface FSI methodology. Contours: Q-criterion. Contact between rigid and elastic bodies via a new IIM-based sharp-interface FSI methodology. Colors: ﬂow speed (red=fast, blue=slow). APPLICATION