OpenFSI: An Efficient and Portable Fluid-Structure Interaction Package

We have developed a highly efficient and portable fluid-structure interaction (FSI) simulation package, so-called OpenFSI. Within this package, the structure dynamics is accounted by a lattice model (LM) implemented in the framework of Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS), demonstrating the same accuracy as finite element analysis. The fluid flow is resolved by Palabos, which adopts the Lattice Boltzmann method (LBM) to efficiently solve the Boltzmann equation that can recover the Navier-Stokes equation in mesoscale. Additionally, the immersed boundary method (IBM) is employed to couple LM and LBM together, therefore endowing the flexibility to choose alternative solid and fluid solvers. The whole simulation is fulfilled within the framework of Palabos, and the LAMMPS framework is called in Palabos as an external library and coupled through IBM. After validation of the package using a variety of benchmarks, it is used to investigate some classical FSI problems, including the free-falling of spheres; flapping of a deformable plate in cross-flow; spheres passing a dam; and swimming of microswimmers. To enlarge the application of OpenFSI, the transport of micro- and nano-particles in blood flow is studied, mimicking the drug vehicles circulation in the drug delivery system. The individual and synthetic effects of the so-called "4s" (size, shape, stiffness, and surface functionality) parameters of the particles are investigated through systematic modeling, including the anomalous vascular dynamics of nanoworms within blood flow; shear rate dependent margination of sphere-like, oblate-like and prolatelike micro-particles within blood flow; adhesion behavior of single cell on endothelial wall; localization of soft particle: margination and adhesion; and shape dependent transport of micro-particles in blood flow: from margination to adhesion. Lastly, the efficiency of this simulation package is explored by examining an extremely large system with thousands of red blood cells in blood flow. The OpenFSI package is found to have excellent linear scalability up to 8192 processors, due to the particle-based LM and LBM for structure and fluid flow respectively, as well as advanced cyberinfrastructure of LAMMPS package. Therefore, OpenFSI presents an alternative option to efficiently solve large scale FSI problems, hence to facilitate the unveiling of underlying physical mechanisms.