ABSTRACT
A Coupled method of CFD (CFD-OHMUGA, Huang, 2013) and overset grid solver (Overset-OHMUGA, Huang, 2016) is suggested to simulate ship hydrodynamics with the conditions of complicated geometry and relative motions. In this method, CFD solver is designed to couple with overset grid solver either by files (static grids) or MPI communication (dynamic grids). In the former, CFD solver gathers DCI (Domain Connectivity Information) and surface area weight coefficients from output files in parallel way, but in the later, CFD solver and overset grid solver run in different MPI parallel processors and communicate necessary information between processors directly. Arbitrary level number of fringe nodes is permitted to set in theory for the high precision CFD scheme if the grids are overlapped enough, and shape function method is used for interpolation for fringe nodes by donor elements. Diffusion method is used for hole-filling in case of special discretization stencil, but donor interpolation method is provided for those nodes at previous time who become active at current time. In addition, different domain decomposition methods are suggested either for CFD or overset grid solver to keep the simulation flexible for operation, and MPI parallel method and data structure methods, such as ADT and KD-tree methods, are used in order to make computation speed efficient. With the help of overset grid solver, CFD solver can efficiently simulate fluid-body (or wave-body) interaction problems of multi-body 6dof motions, and their multi-controllers with independent motions. Validations and demonstrations for the results of coupled CFD or overset grid solver are shown finally, by performing the cases of such as pitch and heave, zigzag, and course keeping.
Overset grid technique (Benek et al. 1983) has attracted increasing interest due to its application in CFD solvers to compute problems involving relative body motions, complicated geometries, and grid refinements. Some typical overset solvers introduced to the public are such as follows, PEGASUS5 (Suhs et al. 2002), SUGGAR++ (Noack, 2009), PUNDIT (Sitaraman et al. 2010), OVERTURE (Henshaw, 1998), X-ray hole-cutting (Chan et al. 2012), Overset-OHMUGA (Huang, 2016), and so on. Overset grid techniques also have increasing applications in CFD solvers specifically used for simulating ship hydrodynamics, for example, CFDSHIP-Iowa (Huang et al. 2008, Stern et al. 2013), UNCLE (Mulvihill and Yang, 2007), USM3D (Power et al. 2009), STAR-CCM+ (PINAEV et al. 2014), OpenFOAM (Shen et al. 2015, Chen et al. 2019), etc.
