Coupling of rigid body dynamics and moving particle semi-implicit method for simulating isothermal multi-phase fluid interactions

The moving particle semi-implicit (MPS) method does not require grids for simulating fluid motions. Therefore, the MPS method can easily handle a large deformation of fluid. However, the MPS method has some difficulties in simulating transfer of momentum caused by a physical collision between different fluids because fluid particles have no mass or volume and only have weights for interacting with other particles. To overcome this inherent defect of the MPS method, rigid body dynamics is explicitly coupled with the MPS method in this study. In the first step, the MPS calculation is performed with particles which are considered to have no mass or volume. In the second step, rigid body dynamics comes into the calculation and considers the particles to have a slightly lesser diameter than the initial distance between particles. Then, physical contacts between particles are simulated with the dynamic energy conserved while the incompressibility of fluids is effectively maintained. In the single fluid region, the coupled method deals with the behavior of the particles. For the interface of the different fluids, only rigid body dynamics is used to simulate the transfer of the momentum caused by physical collisions of fluids. Through this coupling of rigid body dynamics and the MPS method, the overall stability related with the incompressibility of a fluid is comparatively increased in the single-phase fluid simulation. For the calculation of the multi-phase fluids behavior, fluids interactions can be easily treated with improving stability of the MPS calculation. In this study, collapse of water column and the isothermal fuel–coolant interaction (FCI), in which a water jet is directed into a denser fluid pool, were simulated to validate the coupling method of the MPS method and rigid body dynamics.