Multi-purpose interfaces for coupling SPH with other solvers

An algorithm for coupling SPH with an external solution is presented. The external solution can be either another SPH solution (possibly with different discretization) or a different numerical solver or an analytical solution. The interaction between the SPH solver and the external solution is achieved through an interface region. The interface region is defined as a fixed portion of the computational domain that provides a boundary condition for the SPH solver. A ghost fluid, composed by fully lagrangian particles (i.e. ghost particles) covering the interface region, is used to impose the boundary condition. The ghost particle evolution, including its position, is integrated in time according to the field of the external solution. The physical quantities of the ghost particles needed in the integration scheme are obtained through an MLS interpolation on the field of the external solution. When a ghost particle crosses the boundary of the interface region, entering in the SPH domain, it evolves according to the SPH governing equation. The spatial distribution of the ghost particles can become largely non-uniform due to the forcing by the external solution. Thus, a packing algorithm is applied on the ghost particles in the interface region, to guarantee a particle distribution suitable for SPH operators. Since the ghost particles can exit from the interface region, a seeding algorithm is needed to introduce new ghost-particles. The algorithm is tested on several benchmarks and with the external solutions given by other SPH solvers with different discretizations and by analytical solutions. The technique is deeply investigated in terms of accuracy, efficiency and possible applications. Finally a coupled simulation involving a finite volume solver is presented.