Geometry pretreatment method for the 3D modular characteristic method based on AutoCAD

•A geometry pretreatment method is proposed for the 3D modular MOC.•The method enables the 3D MOC faithfully represent the 3D complicated geometry.•The typical modules and their characteristic rays can be automatically generated with this method.•Numerical results show the capability and accuracy.

The method of characteristics (MOC) is a competitive and widely implemented method for the 2D and 2D/1D transport calculations. However, it does not play significant of a role for the 3D transport calculations as it does in the 2D cases because of three reasons: the difficulty of pretreatment of 3D complicated geometries, tremendous amount of ray tracing data, and a comparably long running time. The focus of this work is on the geometry pretreatment based on the AutoCAD software for the 3D modular characteristic method, which was previously proposed to reduce the ray tracing data. The proposed geometry pretreatment consists of four steps: (1) the problem to be solved is modeled within AutoCAD, (2) the modeled geometry is then automatically dissected into modules, and this process is referred to as modularization, (3) during the modularization, all typical modules (unique modules) and their arrangement will be calculated, (4) characteristic segment information is generated for all typical modules. Finally the output information is used by the 3D modular characteristic code to perform the transport calculations. Numerical results demonstrate the faithful representation capability of the proposed geometry pretreatment method, which enables the MOC method have the real capability of dealing with the 3D complicated problems.