共查询到19条相似文献,搜索用时 140 毫秒
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采用目前工业上成熟的非线性迭代计算策略,基于两群粗网有限差分方法和多群UNM节块方法,开发了针对压水堆工况的三维瞬态扩散计算程序。UNM方法采用解析基函数作为基函数,通过方程变换解决了解析节块法在临界节块计算不稳定的问题,提高了计算精度。热工计算采用单通道模型和燃料棒一维导热模型,相比目前堆芯在用的经验关系式方法,该模型可以更加准确地计算燃料棒温度分布。采用基于横向积分方程的三节块方法,可以有效减轻控制棒尖齿效应对瞬态计算的影响。为测试程序性能,采用NEACRP等基准算例对程序进行了校验。数值结果表明,开发的程序计算结果正确,适用于压水堆堆芯瞬态过程的模拟。 相似文献
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介绍节块内嵌离散纵标(SN)方法求解三维堆芯中子输运/扩散方程的算法框架.在基于扩散理论的三维粗网节块展开方法(NEM)的算法体系中,用基于输运理论的径向二维细网节块离散纵标方法(NDOM)的内迭代过程,替代节块展开方法(NEM)内迭代的径向求解过程.该算法充分考虑了核电厂反应堆堆芯的三维结构特点,另一方面,也充分利用了已经成熟的三维粗网节块展开方法(NEM)和二维离散纵标方法(SN)的研究成果,同时有效避免了利用离散纵标方法(SN)求解三维中子输运方程所面临的计算内存和计算时间的瓶颈问题.编制开发二维多群节块离散纵标方法(NDOM)模块程序NSNM和三维多群节块展开方法(NEM)模块程序MGNEM,并以此为基础编制开发节块内嵌SN方法的模块程序HANWIND;其中,NSNM为HANWIND求解两维问题的功能模块.针对OECD/NEA-2D C5G7MOX基准问题以及两环路核电厂三维堆芯的数值验算结果表明,节块内嵌SN方法的算法开发及程序编制有效、切实可行. 相似文献
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针对声学有限元分析中四节点等参单元计算精度低,对网格质量敏感的问题,将光滑有限元法引入到多流体域耦合声场的数值分析中,提出了二维多流体域耦合声场的光滑有限元解法。该方法在Helmholtz控制方程与多流体域耦合界面的声压/质点法向速度连续条件的基础上,得到二维多流体耦合声场的离散控制方程,并采用光滑有限元的分区光滑技术将声学梯度矩阵形函数导数的域内积分转换形函数的域边界积分,避免了雅克比矩阵的计算。以管道二维多流体域耦合内声场为数值分析算例,研究结果表明,与标准有限元相比,对单元尺寸较大或扭曲严重的四边形网格模型,光滑有限元的计算精度更高。因此光滑有限元能很好地应用于大尺寸单元或扭曲严重的网格模型下二维多流体域耦合声场的预测,具有良好的工程应用前景。 相似文献
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目前, 轻水堆堆芯计算广泛采用基于横向积分技术的中子扩散方程节块展开法, 该方法需要对横向泄漏进行多项式近似而不严格, 而且堆芯设计还需要额外的精细功率重构模块用于获得组件内各栅元的功率分布。本文提出两维广义横向积分方法, 直接采用源展开以及表面流耦合方法, 可以避免上述两个不足。由于反应堆堆芯不均匀性更多发生在径向, 因此采用径向基于广义横向积分方法结合轴向常规节块法的综合方法进行三维中子扩散计算。通过基准问题的数值计算, 验证了该方法对于堆芯扩散计算的正确性和可行性。 相似文献
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采用节块方法中有效的半解析方法求解中子扩散方程,在径向采用pin by pin的计算方式且中子通量基于两阶展开,在轴向采用基于4阶展开中子通量的节块法,并且进行全堆粗网有限差分(CMFD)加速,以达到计算精度与计算效率的平衡.通过IAEA 2D/3D基准问题和自定义3D pin by pin参考问题的数值计算,验证所提出的方法能够达到预期的精度,同时CMFD能够取得很好的加速效果. 相似文献
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燃烧室部件传热空间非均匀性对缸内燃烧的影响 总被引:1,自引:0,他引:1
将所有燃烧室部件(气缸盖-气缸套-活塞组-润滑油膜)作为一个耦合体,在对耦合体进行三维传热数值模拟的基础上,利用分区求解、边界耦合法建立缸内工作过程与燃烧室部件的三维耦合计算模型,从而实现缸内工作过程与燃烧室部件的耦合三维仿真模拟,以此考察燃烧室部件传热空间非均匀性对缸内燃烧的影响。研究结果表明,燃烧室部件传热空间非均匀性在喷雾过程几乎对燃烧没有任何影响,可以忽略不计;燃烧过程后期,这种传热空间非均匀性才越来越明显,由此可以推断,燃烧室部件传热空间非均匀性的影响在排气过程将进一步加剧。 相似文献
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Time-Domain Numerical Solutions of Maxwell Interface Problems with Discontinuous Electromagnetic Waves
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Ya Zhang Duc Duy Nguyen Kewei Du Jin Xu & Shan Zhao 《advances in applied mathematics and mechanics.》2016,8(3):353-385
This paper is devoted to time domain numerical solutions of two-dimensional
(2D) material interface problems governed by the transverse magnetic
(TM) and transverse electric (TE) Maxwell's equations with discontinuous electromagnetic
solutions. Due to the discontinuity in wave solutions across the interface, the
usual numerical methods will converge slowly or even fail to converge. This calls for
the development of advanced interface treatments for popular Maxwell solvers. We
will investigate such interface treatments by considering two typical Maxwell solvers
– one based on collocation formulation and the other based on Galerkin formulation. To
restore the accuracy reduction of the collocation finite-difference time-domain (FDTD)
algorithm near an interface, the physical jump conditions relating discontinuous wave
solutions on both sides of the interface must be rigorously enforced. For this purpose,
a novel matched interface and boundary (MIB) scheme is proposed in this work, in
which new jump conditions are derived so that the discontinuous and staggered features
of electric and magnetic field components can be accommodated. The resulting
MIB time-domain (MIBTD) scheme satisfies the jump conditions locally and suppresses
the staircase approximation errors completely over the Yee lattices. In the discontinuous
Galerkin time-domain (DGTD) algorithm – a popular Galerkin Maxwell solver, a
proper numerical flux can be designed to accurately capture the jumps in the electromagnetic
waves across the interface and automatically preserves the discontinuity in
the explicit time integration. The DGTD solution to Maxwell interface problems is explored
in this work, by considering a nodal based high order discontinuous Galerkin
method. In benchmark TM and TE tests with analytical solutions, both MIBTD and
DGTD schemes achieve the second order of accuracy in solving circular interfaces. In
comparison, the numerical convergence of the MIBTD method is slightly more uniform,
while the DGTD method is more flexible and robust. 相似文献
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Generation of Turbulent Inflow Data for Spatially-Developing Boundary Layer Simulations 总被引:4,自引:0,他引:4
A method for generating three-dimensional, time-dependent turbulent inflow data for simulations of complex spatially developing boundary layers is described. The approach is to extract instantaneous planes of velocity data from an auxiliary simulation of a zero pressure gradient boundary layer. The auxiliary simulation is also spatially developing, but generates its own inflow conditions through a sequence of operations where the velocity field at a downstream station is rescaled and re-introduced at the inlet. This procedure is essentially a variant of the Spalart method, optimized so that an existing inflow–outflow code can be converted to an inflow-generation device through the addition of one simple subroutine. The proposed method is shown to produce a realistic turbulent boundary layer which yields statistics that are in good agreement with both experimental data and results from direct simulations. The method is used to provide inflow conditions for a large eddy simulation (LES) of a spatially evolving boundary layer spanning a momentum thickness Reynolds number interval of 1530–2150. The results from the LES calculation are compared with those from other simulations that make use of more approximate inflow conditions. When compared with the approximate inflow generation techniques, the proposed method is shown to be highly accurate, with little or no adjustment of the solution near the inlet boundary. In contrast, the other methods surveyed produce a transient near the inlet that persists several boundary layer thicknesses downstream. Lack of a transient when using the proposed method is significant since the adverse effects of inflow errors are typically minimized through a costly upstream elongation of the mesh. Extension of the method for non-zero pressure gradients is also discussed. 相似文献
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N. Chatzidai A. Giannousakis Y. Dimakopoulos J. Tsamopoulos 《Journal of computational physics》2009,228(6):1980-2011
We present an improved method to generate a sequence of structured meshes even when the physical domain contains deforming inclusions. This method belongs to the class of Arbitrary Lagrangian–Eulerian (ALE) methods for solving moving boundary problems. Its tools are either (a) separate mappings of the domain boundaries and enforcing the node distribution on lines emanating from singular points or (b) domain decomposition and separate mappings of each subdomain using suitable coordinate systems. The latter is shown to be more versatile and general. In both cases a set of elliptic equations is used to generate the grid extending in this way the method advanced by Dimakopoulos and Tsamopoulos [Y. Dimakopoulos, J.A. Tsamopoulos, A quasi-elliptic transformation for moving boundary problems with large anisotropic deformations, J. Comput. Phys. 192 (2003) 494–522]. We shall present examples where this earlier method and all other mesh generating methods which are based on a conformal mapping or solving a quasi-elliptic set of PDEs fail to produce an acceptable mesh and accurate solutions in such geometries. Furthermore, in contrast to other methods, appropriate boundary conditions and constraints such as, orthogonality of specific mesh lines and prespecified node distributions on them, can be easily implemented along a specific part of the domain or its boundary. Hence, no attractive terms at specific corners or singular points are needed. To increase the mesh resolution around the moving interfaces while keeping low the memory requirements and the computational time, a local mesh refinement technique has been incorporated as well. The method is demonstrated in two challenging examples where no remeshing is required in spite of the large domain deformations. In the first one, the transient growth of two bubbles embedded in a viscoelastic filament undergoing stretching in the axial direction is examined, while in the second one the linear and non-linear dynamics of two bubbles in a viscous medium are determined in an acoustic field. The large elasticity of the filament in the first case or the large inertia in the second case coupled with the externally induced large deformations of the liquid domain requires the accurate calculation which is achieved by the method we propose herein. The governing equations are solved using the finite element/Galerkin method with appropriate modifications to solve the hyperbolic constitutive equation of a viscoelastic fluid. These are coupled with an implicit Euler method for time integration or with Arnoldi’s algorithm for normal mode analysis. 相似文献
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含冷却水管大体积混凝土温度场计算的一种新方法 总被引:2,自引:0,他引:2
水管冷却是混凝土坝施工期的主要温度控制措施,提出一种新的水管冷却数值模拟理论和计算方法.该方法将水管置于常规混凝土单元内部,在单元中把混凝土与水管的接触面作为散热面纳入控制方程的边界条件,把混凝土通过冷却水管壁面耗散的能量叠加到常规泛函中,根据此复合泛函由变分原理建立含冷却水管混凝土的有限元支配方程.编制相应的三维计算程序,在程序中水管网格的拓扑信息由程序自动完成,冷却水管可以从混凝土单元任意位置穿过,因此不增加网格剖分的难度,算例表明该方法能准确模拟混凝土的冷却效应. 相似文献
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针对先进核反应堆中结构复杂的燃料组件,中国核动力研究设计院开发了先进中子学栅格中子学程序KYLIN-2,该程序采用子群方法进行共振处理,采用特征线方法(MOC)进行复杂几何中子输运计算,并利用采用广义粗网格有限差分加速方法(GCMFD)来加速中子输运求解流程,采用基于改进预估校正临界-燃耗迭代方法(PPC)的切比雪夫方法求解复杂燃耗链,同时,为了方便用户使用,开发形成了支持复杂组件图形化建模工具和后处理显示工具。通过初步的数值检验,针对典型压水堆燃料组件,KYLIN-2具有较高的计算精度,满足工程使用需求。 相似文献