The Auto-Importance Sampling（AIS） method is a Monte Carlo variance reduction technique proposed for deep penetration problems, which can significantly improve computational efficiency without pre-calculations for im...The Auto-Importance Sampling（AIS） method is a Monte Carlo variance reduction technique proposed for deep penetration problems, which can significantly improve computational efficiency without pre-calculations for importance distribution. However, the AIS method is only validated with several simple examples, and cannot be used for coupled neutron-photon transport. This paper presents improved algorithms for the AIS method, including particle transport, fictitious particle creation and adjustment, fictitious surface geometry, random number allocation and calculation of the estimated relative error. These improvements allow the AIS method to be applied to complicated deep penetration problems with complex geometry and multiple materials. A Completely coupled Neutron-Photon Auto-Importance Sampling（CNP-AIS） method is proposed to solve the deep penetration problems of coupled neutron-photon transport using the improved algorithms. The NUREG/CR-6115 PWR benchmark was calculated by using the methods of CNP-AIS, geometry splitting with Russian roulette and analog Monte Carlo, respectively. The calculation results of CNP-AIS are in good agreement with those of geometry splitting with Russian roulette and the benchmark solutions. The computational efficiency of CNP-AIS for both neutron and photon is much better than that of geometry splitting with Russian roulette in most cases, and increased by several orders of magnitude compared with that of the analog Monte Carlo.展开更多
压力容器在放射性等复杂的载荷下工作,容易引起工程结构的疲劳裂纹扩展,进而导致灾难性的破坏。我们利用自主开发的一体化结构有限元分析软件ATLAS对防断裂问题进行分析。该软件根据结构有限元分析的应用特点,在特殊的数据结构基础上充...压力容器在放射性等复杂的载荷下工作,容易引起工程结构的疲劳裂纹扩展,进而导致灾难性的破坏。我们利用自主开发的一体化结构有限元分析软件ATLAS对防断裂问题进行分析。该软件根据结构有限元分析的应用特点,在特殊的数据结构基础上充分利用GPU的三维渲染能力,并做了大量的优化工作,能让CAE工程师在高度交互及可视化的环境下进行仿真分析工作。我们首先分析微观孔洞大小及位置对应力分布的影响,然后以压力容器为例,针对其结构及受力状况建立模型及载荷约束,对其各部位受力及变形情况进行分析。在完成有限元求解后,我们对计算结果进行应力线性化,得到应力强度因子。我们依照ASME BPVC III D1附录G的标准进行防断裂分析校核,通过计算数值的比较得出是否满足防断裂要求的结论。基于ATLAS软件提出的压力容器防断裂一体化有限元分析方法可用于压力容器延寿等工程实践中。展开更多
基金Supported by the subject of National Science and Technology Major Project of China(2013ZX06002001-007,2011ZX06004-007)National Natural Science Foundation of China(11275110,11375103)
文摘The Auto-Importance Sampling（AIS） method is a Monte Carlo variance reduction technique proposed for deep penetration problems, which can significantly improve computational efficiency without pre-calculations for importance distribution. However, the AIS method is only validated with several simple examples, and cannot be used for coupled neutron-photon transport. This paper presents improved algorithms for the AIS method, including particle transport, fictitious particle creation and adjustment, fictitious surface geometry, random number allocation and calculation of the estimated relative error. These improvements allow the AIS method to be applied to complicated deep penetration problems with complex geometry and multiple materials. A Completely coupled Neutron-Photon Auto-Importance Sampling（CNP-AIS） method is proposed to solve the deep penetration problems of coupled neutron-photon transport using the improved algorithms. The NUREG/CR-6115 PWR benchmark was calculated by using the methods of CNP-AIS, geometry splitting with Russian roulette and analog Monte Carlo, respectively. The calculation results of CNP-AIS are in good agreement with those of geometry splitting with Russian roulette and the benchmark solutions. The computational efficiency of CNP-AIS for both neutron and photon is much better than that of geometry splitting with Russian roulette in most cases, and increased by several orders of magnitude compared with that of the analog Monte Carlo.
文摘压力容器在放射性等复杂的载荷下工作,容易引起工程结构的疲劳裂纹扩展,进而导致灾难性的破坏。我们利用自主开发的一体化结构有限元分析软件ATLAS对防断裂问题进行分析。该软件根据结构有限元分析的应用特点,在特殊的数据结构基础上充分利用GPU的三维渲染能力,并做了大量的优化工作,能让CAE工程师在高度交互及可视化的环境下进行仿真分析工作。我们首先分析微观孔洞大小及位置对应力分布的影响,然后以压力容器为例,针对其结构及受力状况建立模型及载荷约束,对其各部位受力及变形情况进行分析。在完成有限元求解后,我们对计算结果进行应力线性化,得到应力强度因子。我们依照ASME BPVC III D1附录G的标准进行防断裂分析校核,通过计算数值的比较得出是否满足防断裂要求的结论。基于ATLAS软件提出的压力容器防断裂一体化有限元分析方法可用于压力容器延寿等工程实践中。
