An enhanced coupled ISPH-TLSPH FSI solver with a Riemann fluid-structure acceleration scheme

In order to achieve the accurate and stable simulation of fluid-structure interactions (FSI), the development of an entirely Lagrangian meshfree FSI solver is desirable, as this method can accurately impose fluid-structure interface boundary conditions. However, the existing methods are prone to numerical noise in the results without an additional artificial stabilisation, leading to unphysical or unstable pressure fields around the interface. In this study, a Riemann-based fluid-structure acceleration scheme is proposed for discretising the fluid-to-structure acceleration term, in the framework of Incompressible SPH (ISPH)-Total Lagrangian SPH (TLSPH) FSI solvers. This scheme improves the momentum transfer from the fluid to the structure, resulting in more accurate structural kinematics and enhanced kinematic boundary conditions for the fluid solver. Thus, the proposed scheme is designed to mitigate the instabilities at the fluid-structure interface induced by the kinematic discontinuities and to enhance a physically consistent transfer of momentum between fluid and structure. Three FSI benchmark tests are considered to validate the proposed scheme. These three tests include a hydrostatic water column on an elastic base plate, rotational sloshing with an elastic baffle, and dam break flow impacting an elastic plate. Through these typical and challenging FSI simulations involving 2-D inviscid single-phase fluid, the implementation of the proposed interaction scheme demonstrates that a more accurate fluid-structure interface motion is ensured, bringing a smooth and stable pressure field around the interface. Therefore, this study has established a foundation for an accurate and stable fully particle-based FSI solver.