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从二阶自共轭角注量率(SAAF: Self-Adjoint Angular Flux)中子输运方程出发,在二维圆柱坐标系下利用球谐函数对角度变量进行展开,推导出了一组关于空间变量的偏微分方程组,然后采用有限元方法进行了空间离散,编写了二维圆柱坐标系下的球谐函数输运计算程序.对一系列例题进行校验的数值结果表明,该方法具有较高的计算精度,克服了射线效应. 相似文献
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中子输运方程是核反应堆物理分析计算的基本方程,针对深度学习技术求解输运方程因定积分项带来的困难,本文提出了微分变阶理论:将输运方程定积分项变换为对应的原函数,其他部分的角通量密度项表示为原函数高阶微分形式,从而将具有微积分形式的输运方程转换为纯粹的高阶微分方程;给出了变换后的原函数定解约束条件,以及对应的边界条件形式;构造了由原函数方程、边界条件、原函数定解、特征值约束共同形成的加权损失函数,利用深度学习使得神经网络逼近原函数;通过将原函数求导进行微分降阶,最终得到原输运方程角通量密度的数值解。针对多个平板、球几何例题进行了数值验证,获得了具有连续性特点的计算结果,证明了本文理论及相关方法的正确性,从而为中子输运方程的数值求解方法探索新的技术途径。 相似文献
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球谐函数有限元方法采用非结构网格求解中子输运方程,具备处理复杂几何的能力;同时又可避免离散纵标方法所造成的射线效应。本文从一阶中子输运方程出发,通过方程的弱形式推导了球谐函数多尺度有限元方法,并基于此方法开发了中子学分析程序NECP-FISH。通过在前后处理平台SALOME中开发接口程序,实现了程序的建模可视化和计算结果可视化。应用此程序计算了氦冷陶瓷包层,数值结果表明NECP-FISH对中子通量密度、氚增殖比和中子释热的计算结果与蒙特卡罗程序NECP-MCX吻合良好。氚增殖比相对偏差为0.56%,所有区域的中子释热偏差均在6%以内。 相似文献
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二维/一维耦合输运方法较好地平衡了效率与精度,因此被广泛应用于一步法全堆芯输运计算。二维/一维耦合输运方法中,由于泄漏项在方程右端,导致二维特征线法(MOC)计算时方程右端总源项在迭代过程中可能成为负值,造成迭代发散。本文针对二维/一维耦合输运计算中的负源项问题,提出了一种改进的泄漏项分割方法。新的泄漏项分割方法可在不造成计算精度损失和仅增加有限内存的条件下,显著提高二维/一维耦合输运方法的稳定性。通过强泄漏算例、C5G7基准题、VERA-3A基准题等进行测试,表明该方法对提高二维/一维耦合输运方法稳定性具有显著的效果。 相似文献
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本文将变分方法用于研究中子迁移问题,导出了严格渐近输运解所满足的、多群形式的扩散方程。该方程具有不同于P_1近似的扩散系数D_g,外推长度λ_g和连续性条件。扩散系数和外推距离是宏观输运截面∑_?~(tr),中子与核每次碰撞所产生的次级中子数C_g的函数。数值计算的结果表明,该方程在描述各种类型核系统的中子学问题时,其精度高于P_1近似,而计算工作量与P_1近似相近。 相似文献
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An ingenious method has been discussed to provide a brief way for the derivation of the streaming term expression in the spherical geometry coordinate system. Instead of finding the differential relationship between the dihedral angle and the neutron transport distance, finding the geometry relationship between the dihedral angle and other plane angles is much easier. And then the differential relationship (easy to be derived) between the other plane angles and the neutron transport distance can be used to derive the expression of the streaming term in the spherical geometry coordinate system indirectly but easily. This method makes the derivation process easy and intuitive, with clear physical picture. 相似文献
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非结构网格中子输运方程的球谐函数解法研究 总被引:4,自引:2,他引:2
从新的二阶自共扼角通量密度(SAAF:Self-Adjoint Angular Flux)中子输运方程出发.利用球谐函数对角度变量进行展开,导出了一组关于空间变量的偏微分方程组,中子通量密度的各个分量相互耦合,应用一定的迭代策略进行迭代求解。针对每一个方程,应用有限元方法对非结构网格进行离散求解。据此编写了二维球谐函数方法输运计算程序,对一系列基准题进行校算的数值结果表明,该方法具有较高的计算精度,克服了射线效应,并能用于非结构网格。 相似文献
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Spherical harmonics method for neutron transport equation based on unstructured-meshes 总被引:6,自引:0,他引:6
CAOLiang-Zhi WU-Hong-Chun 《核技术(英文版)》2004,15(6):335-339
Based on a new second-order neutron transport equation, self-adjoint angular flux (SAAF) equation, the spherical harmonics (PN) method for neutron transport equation on unstructured-meshes is derived. The spherical harmonics function is used to expand the angular flux. A set of differential equations about the spatial variable, which are coupled with each other, can be obtained. They are solved iteratively by using the finite element method on unstructured-meshes. A two-dimension transport calculation program is coded according to the model. The numerical results of some benchmark problems demonstrate that this method can give high precision results and avoid the ray effect very well. 相似文献
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In this paper,a novel model is proposed to investigate the neutron transport in scattering and absorbing medium.This solution to the linear Boltzmann equation is expanded from the idea of lattice Boltzmann method (LBM) with the collision and streaming process.The theoretical derivation of lattice Boltzmann model for transient neutron transport problem is proposed for the first time.The fully implicit backward difference scheme is used to ensure the numerical stability,and relaxation time and equilibrium particle distribution function are obtained.To validate the new lattice Boltzmann model,the LBM formulation is tested for a homogenous media with different sources,and both transient and steady-state LBM results get a good agreement with the benchmark solutions. 相似文献
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In this paper,a novel model is proposed to investigate the neutron transport in scattering and absorbing medium.This solution to the linear Boltzmann equation is expanded from the idea of lattice Boltzmann method (LBM) with the collision and streaming process.The theoretical derivation of lattice Boltzmann model for transient neutron transport problem is proposed for the first time.The fully implicit backward difference scheme is used to ensure the numerical stability,and relaxation time and equilibrium particle distribution function are obtained.To validate the new lattice Boltzmann model,the LBM formulation is tested for a homogenous media with different sources,and both transient and steady-state LBM results get a good agreement with the benchmark solutions. 相似文献
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Forward and adjoint Monte Carlo coupling technique has been developed for analyzing neutron streaming in a system with large geometry. Particles (neutron and adjoint particle) are scored by surface type estimators such as the next event surface crossing estimators and the boundary crossing estimators. The detector response is calculated by folding the calculated neutron and adjoint angular fluxes. The reliability and efficiency for this method were studied by solving a sample problem of neutron streaming through narrow sodium pipe embedded in an iron shield. This method turned out to give a figure of merit several times better than the conventional method. The applicability of the method to detector system design has been demonstrated by calculating the signal to noise ratio for the fuel failure detector with delayed neutron detection method, which is located behind the reactor shield of concrete. This method gives an advantage in clarifying the spatial channels for neutron streaming. 相似文献
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《Annals of Nuclear Energy》2005,32(11):1167-1190
Starting from the basic expression for the neutron flux due to a point source in an infinite homogeneous scattering and absorbing medium, the first few fundamental expansion functions corresponding to successive collisions are identified, and their analytic properties are presented, in spherical and plane geometry. Various representations of the functions are obtained in the form of power series, an expansion in a series of exponential integrals, and other integrals. The adequacy of traditional asymptotic forms is considered. 相似文献
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Hai-Tao Ju Hong-Chun Wu Yong-Qiang Zhou Liang-Zhi Cao Dong Yao Chun-Yu Xian 《Nuclear Engineering and Design》2007,237(8):823-829
A discrete ordinates finite-element method for solving the two-dimensional first-order neutron transport equation is derived using the least-squares variation. It avoids the singularity in void regions of the method derived from the second-order equation which contains the inversion of the cross-section. Different from using the standard Galerkin variation to the first-order equation, the least-squares variation results in a symmetric matrix, which can be solved easily and effectively. To eliminate the discontinuity of the angular flux on the vacuum boundary in the spherical harmonics method, the angle variable is discretized by the discrete ordinates method. A two-dimensional transport simulation code is developed and applied to some benchmark problems with unstructured geometry. The numerical results verified the validity of this method. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(11):937-948
An efficient albedo Monte Carlo method newly developed has been studied by analyzing two types of experiments on neutron streaming. The method is characterized by employing the energy-angle dependent doubly differential albedos for slab, which can be calculated in a short computer time with a one-dimensional transport theory, such as the Sn method and more efficient invariant imbedding method. This paper describes the features of the present albedo Monte Carlo method, including fundamental formulas. In the analyses of the neutron streaming experiments, the calculated results agreed with the measured data within a factor of 2 for a benchmark experiment at the YAYOI reactor and within a factor of 3 for an SNR sodium duct mock-up experiment. It is concluded that the present albedo Monte Carlo method is practical and applicable to the reactor shielding analysis concerning radiation streaming. 相似文献