Improvement of boundary conditions for non-planar boundaries represented by polygons with an initial particle arrangement technique

The boundary conditions represented by polygons in moving particle semi-implicit (MPS) method (Koshizuka and Oka, Nuclear Science and Engineering, 1996 Koshizuka, S., and Y. Oka. 1996. “Moving-Particle Semi-Implicit Method for Fragmentation of Incompressible Fluid.” Nuclear Science and Engineering 123: 421–434.Taylor &; Francis Online], Web of Science ®] , Google Scholar]) have been widely used in the industry simulations since it can simply simulate complex geometry with high efficiency. However, the inaccurate particle number density near non-planar wall boundaries dramatically affects the accuracy of simulations. In this paper, we propose an initial boundary particle arrangement technique coupled with the wall weight function method (Zhang et al. Transaction of JSCES, 2015 Zhang, T.G., S. Koshizuka, K. Shibata, K. Murotani, and E. Ishii. 2015. “Improved Wall Weight Function With Polygon Boundary in Moving Particle Semi-Implicit Method.” Transaction of JSCES. No. 20150012. Google Scholar]) to improve the particle number density near slopes and curved surfaces with boundary conditions represented by polygons in three dimensions. Two uniform grids are utilized in the proposed technique. The grid points in the first uniform grid are used to construct boundary particles, and the second uniform grid stores the same information as in the work by Zhang et al. The wall weight functions of the grid points in the second uniform grid are calculated by newly constructed boundary particles. The wall weight functions of the fluid particles are interpolated from the values stored on the grid points in the second uniform grid. Because boundary particles are located on the polygons, complex geometries can be accurately represented. The proposed method can dramatically improve the particle number density and maintain the high efficiency. The performance of the previously proposed wall weight function (Zhang et al.) with the boundary particle arrangement technique is verified in comparison with the wall weight function without boundary particle arrangement by investigating two example geometries. The simulations of a water tank with a wedge and a complex geometry show the general applicability of the boundary particle arrangement technique to complex geometries and demonstrate its improvement of the wall weight function near the slopes and curved surfaces.