【作者】 高翔；

【导师】 周建新； 殷亚军；

【作者基本信息】 华中科技大学 ， 材料工程， 2019， 硕士

【摘要】 铸造充型过程是铸造生产中的关键环节,对铸件的质量有着重要影响。铸造充型过程气液两相流动数值模拟研究的一个突出问题是计算速度慢,这主要是因为两相流模拟中既要计算液态金属网格,又要计算型腔中的空气网格,计算网格数多,计算量大。为此,本文研究了基于MPI(Message Passing Interface,消息传递接口)的铸件网格并行分区建模与实现,对铸造充型过程气液两相流动算法实现并行化,最终达到提高充型过程两相流动模拟计算速度的目的。首先,根据铸件网格分布特点建立了并行分区模型。提出了基于子域中铸件网格数的标准差来评判铸件网格区域划分是否均匀的标准,设计了基于动态规划法的铸件网格分区算法,建立了基于MPI并行技术的铸件网格并行分区模型,将铸件网格信息平均分配给计算子进程,是并行算法实现的模型基础。其次,将并行分区模型应用在铸造充型过程气液两相流算法中,设计并开发了气液两相流数值模拟的并行程序。研究了典型的铸造充型过程气液两相流的SOLALevel Set算法的数学模型和离散方法,分析了铸件网格分布的特点,制定了并行程序的通信策略,提出了映射数组法来降低子域间的通信开销,设计了依赖关系复杂的流动场求解过程中子域间的通信步骤,开发了气液两相流数值模拟的并行程序。最后,将本文并行算法应用到环形、板类、箱体等铸件的充型过程气液两相流动数值模拟中,测试和分析了算法的并行效果。通过与已验证的两相流串行程序的计算结果进行数值对比,表明了本文并行算法的数值可靠性,并提出了简化版的数值准确性验证方法。测试结果表明本并行算法具有良好的加速效果,8个处理核心时最大加速比为4.6。对同一铸件,加速比随铸件网格数增加而增大。和环形、箱体铸件相比,本文算法在板类铸件上的并行拓展性最好。本文提出的气液两相流并行算法对铸造流动场数值模拟技术的发展有重要意义。更多还原

【Abstract】 The casting filling process is a key part in foundry and has an important impact on the quality of castings.A prominent problem in the numerical simulation study of casting filling two-phase flow is the slow calculation speed,which is mainly because the flow of liquid metal and air is both calculated so the mesh count to calculate is more.One of the primary means of solving this problem is to use the increasingly developing parallel technique to speed up the solution.In this study,the MPI-based parallel programming technique is used to parallelize the gas-liquid two-phase flow algorithm in the mold filling process,and finally achieve the purpose of improving the filling simulation speed.The main work of this paper are as follows:Firstly,a method of partitioning complex casting is proposed.A improved standard deviation is used as the criterion for judging how evenly the casting mesh area is divided.It is found that the dynamic programming method has better complexity in time than the enumeration method and the backtracking method.Based on the MPI parallel technology,a parallel partition model of the casting process was established.The complex casting partition method is used to evenly distribute the casting mesh information to the calculation sub-process.Secondly,the mathematical model and discrete method of SOLA-Level Set algorithm for a typical gas-liquid two-phase flow in mold filling process are studied.Combined with the characteristics of complex casting mesh distribution,the communication strategy of parallel program is designed.A mapping array method is proposed to reduce the communication overhead between sub-domains.The communication steps between subdomains are designed for the complex finite difference solution of fluid flow process.The parallel partition model is applied to the SOLA-Level Set algorithm.Finally,the parallel algorithm of this paper is applied to the numerical simulation of gas-liquid two-phase flow in the filling process of castings such as rings,plates and boxes.Through numerical comparison with the calculation results of the serial program,the numerical reliability of the parallel algorithm is shown,and a simplified version of the numerical accuracy verification method is proposed.The advantages of the complex mold partitioning method proposed in this paper are proved by comparison with the method of area division by uniform partitioning by coordinates.The results show that the parallel algorithm has a good acceleration effect,and the maximum speedup ratio is 4.6 for 8 processing cores.For the same casting,the speedup increases as the number of casting grids increases.Compared with the ring and box castings,the algorithm works best on the plate castings,and the parallel efficiency of the plate castings is about 0.6 in 1.76 million grids.The gas-liquid two-phase parallel algorithm proposed in this paper is of great significance to the development of numerical simulation technology for casting flow field.更多还原