Abstract: The modeling for Monte Carlo N Particle Transport Code Program (MCNP) is a difficult problem.To solve the problem,a novel algorithm was presented to transform the BRep model to the half space Constructive Solid Geometry (CSG) model.The concept of the half space transition element was defined,and the feature recognition method for BRep model was presented based on this concept.According to the feature recognition method,the decomposition surfaces were constructed to decompose BRep model into the several half space transition elements.In addition,the assistant surfaces were added to avoid the half space description ambiguity.The ability and the efficiency of the algorithm was tested by several model transition tasks,and the result proved that the efficiency of MCNP input file production had been improved.

Key words: half-space constructive solid geometry model, model conversion, model decomposition, Monte Carlo N particle transport code program

摘要： 为了解决大型通用粒子输运计算程序MCNP建模困难的问题,提出一种基于特征分解的BRep模型到MCNP半空间构造实体几何(CSG)模型转换算法。该算法定义了半空间转换元的概念,并以此概念为基础,提出以几何特征和拓扑结构为依据的BRep模型识别方式;根据不同的特征,算法构造了合适的分解面,将Brep模型分解为半空间转换元组合,并为存在半空间描述歧义的转换元添加了合适的辅助面。通过多个模型的算法测试展示了算法的模型转换能力,通过效率测试验证了算法的计算效率,结果证明所提算法大幅提高了MCNP输入文件的制作效率。

关键词: 半空间构造实体几何(CSG)模型, 模型转换, 模型分解, MCNP程序