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Hybrid Lattice Boltzmann Simulation of Three-Dimensional Natural Convection 三维自然对流的混合晶格玻尔兹曼模拟
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-06-07 DOI: 10.1080/23324309.2021.1942061
A. Nee
Abstract The capability of hybrid lattice Boltzmann–finite difference model in simulation of laminar and turbulent three-dimensional (3D) natural convection was examined. Fluid dynamics was computed by means of the lattice Boltzmann method and the finite difference solver was used for advection-diffusion equation. It was found that both two-dimensional and 3D models reproduced the same thermal fields. The Nusselt numbers were in a good agreement with benchmark data with the Rayleigh number up to Computation speed of developed hybrid model was more than two times higher in comparison with conventional computational fluid dynamics (CFD) vorticity–vector potential formulation.
摘要研究了混合晶格玻尔兹曼-有限差分模型在层流和湍流三维自然对流模拟中的性能。采用点阵玻尔兹曼法计算流体力学,采用有限差分法求解平流扩散方程。研究发现,二维模型和三维模型再现了相同的热场。Nusselt数和Rayleigh数与基准数据吻合较好,所建立的混合模型的计算速度比传统计算流体力学(CFD)涡度-矢量势公式提高了2倍以上。
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引用次数: 7
Density Transform Method for Particle Transport Problems in Spherical Geometry with Linearly Anisotropic Scattering 具有线性各向异性散射的球几何粒子输运问题的密度变换方法
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-06-07 DOI: 10.1080/23324309.2021.1938610
D. Sahni
Abstract We develop the density transform method for treating particle transport problems in spherical geometry with linearly anisotropic scattering. We consider both, the interior and exterior problems of a homogeneous sphere and show that the transform satisfies an equation that resembles particle transport equation in slab geometry. The boundary conditions for these two problems are different. We also work out the density transform method for linearly anisotropic scattering for a region of arbitrary shape.
摘要:本文提出了处理具有线性各向异性散射的球几何粒子输运问题的密度变换方法。我们同时考虑了齐次球的内外问题,并证明了该变换满足一个类似于平板几何中粒子输运方程的方程。这两个问题的边界条件是不同的。给出了任意形状区域线性各向异性散射的密度变换方法。
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引用次数: 3
A Response Matrix Method for Slab-Geometry Discrete Ordinates Adjoint Calculations in Energy-Dependent Neutral Particle Transport 能量相关中性粒子输运中板几何离散坐标伴随计算的响应矩阵方法
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-04-16 DOI: 10.1080/23324309.2021.1914661
L.R.C. Moraes, R. S. Mansur, C. A. Moura, J. P. Curbelo, H. A. Filho, R. Barros
Abstract Presented here is an application of the Response Matrix (RM ) method for adjoint discrete ordinates (S ) problems in slab-geometry applied to energy-dependent neutral particle transport problems. The RM method is free from spatial truncation errors, as it generates numerical results for the adjoint angular fluxes in multilayer slabs that agree with the numerical values obtained from the analytical solution of the energy multigroup adjoint S equations. The main contribution of this work is to analyze the application of the RM method to problems where it is required to solve the energy multigroup adjoint S equations multiple times. This is the case of two classes of problems that can be taken care of through the adjoint technique: (i) source-detector problems; and (ii) the estimation of interior neutron source distributions that drive a subcritical system at a prescribed power density level. The efficiency (speed and accuracy) of the RM code is compared to the conventional Diamond Difference code.
摘要本文介绍了响应矩阵(RM)方法在板几何中伴随离散坐标(S)问题中的应用,并应用于能量依赖的中性粒子输运问题。RM法得到的多层板的伴随角通量数值结果与能量多群伴随S方程解析解得到的数值吻合,不存在空间截断误差。本工作的主要贡献是分析了RM方法在需要多次求解能量多群伴随S方程的问题中的应用。这是可以通过伴随技术处理的两类问题的情况:(i)源检测器问题;(ii)在规定功率密度水平下驱动亚临界系统的内部中子源分布的估计。将RM码的效率(速度和精度)与传统的钻石差码进行了比较。
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引用次数: 2
Three-Dimensional Numerical Study of a Fluid-Kinetic Model for Respiratory Aerosols with Variable Size and Temperature 变粒径变温度呼吸性气溶胶流体动力学模型的三维数值研究
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-04-05 DOI: 10.1080/23324309.2021.1906705
L. Boudin, D. Michel
Abstract In this paper, we extend to the three-dimensional case the numerical study previously performed in a two-dimensional framework for a complex coupled fluid-kinetic model describing respiratory aerosols. The specificity of this model lies in the fact that it takes into account the airway humidity and the resulting hygroscopic effects on the aerosol droplets, namely their size variation. The air is described through a system of partial differential equations: the incompressible Navier–Stokes equations for the air velocity, convection-diffusion equations on its temperature, and water vapor mass fraction. The aerosol distribution function obeys a Vlasov-type equation and depends on the standard kinetic variables, but also on radius and temperature variables. After discussing again the implementation strategy, we perform numerical experiments, mainly in a branched structure looking like the trachea and the first lung generation. This allows the presentation of various statistics on the aerosol behavior in terms of particle deposition, temperature, and size variation of the droplets. We observe that the outcome appears coherent with the two-dimensional case. Finally, we discuss several assumptions which may lead to model simplifications, such as the fact that the water vapor mass fraction in the air may be considered to be constant throughout the branched structure in standard breathing conditions.
摘要在本文中,我们将先前在二维框架中对描述呼吸气溶胶的复杂耦合流体动力学模型进行的数值研究扩展到三维情况。该模型的特殊性在于,它考虑了气道湿度和由此产生的气溶胶液滴吸湿效应,即其大小变化。空气是通过一个偏微分方程系统来描述的:空气速度的不可压缩Navier-Stokes方程、温度的对流-扩散方程和水蒸气质量分数。气溶胶分布函数服从Vlasov型方程,取决于标准动力学变量,也取决于半径和温度变量。在再次讨论了实现策略后,我们进行了数值实验,主要是在看起来像气管和第一代肺的分支结构中。这使得能够在颗粒沉积、温度和液滴尺寸变化方面呈现关于气溶胶行为的各种统计数据。我们观察到,结果似乎与二维情况一致。最后,我们讨论了可能导致模型简化的几个假设,例如在标准呼吸条件下,空气中的水蒸气质量分数可以被认为在整个分支结构中是恒定的。
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引用次数: 0
Gray Phonon Transport Prediction of Thermal Conductivity in Lithium Aluminate with Higher-Order Finite Elements on Meshes with Curved Surfaces 曲面网格上铝酸锂热导率的高阶有限元灰色声子输运预测
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-03-18 DOI: 10.1080/23324309.2021.1900258
N. Whitman, T. Palmer, P. Greaney, S. Hosseini, D. Burkes, D. Senor
Abstract We present a method for predicting thermal conductivity by deterministically solving the Boltzmann transport equation for gray phonons by utilizing arbitrary higher-order continuous finite elements on meshes which may also be unstructured and utilize curved surfaces. The self-adjoint angular flux (SAAF) formulation of the gray, steady-state, single relaxation time, phonon radiative transport (PRT) equation was spatially discretized using the continuous finite element method and angularly discretized using the discrete ordinates method. The solution discretization methodology was verified using a method of manufactured solution (MMS) spatial convergence test case and compared favorably to previous work. The angular phonon radiances, heat flux, and temperatures computed in this work compare favorably to previous literature in silicon thin films. Using local values of the temperature gradient and heat flux, the thermal conductivity as a function of position in a one-dimensional perfect crystal was evaluated using a Fourier’s Law representation and compared to kinetic theory. Our results show that in the interior of the simulation domain, our transport-based prediction of thermal conductivity converged on the kinetic theory estimation. We also find that near isothermal boundaries, the transport solution deviated from kinetic theory, implying non-equilibrium behavior in the thin-film limit and agreed with previous studies.
摘要本文提出了一种利用任意高阶连续有限元在非结构化网格和曲面上确定性地求解灰色声子的玻尔兹曼输运方程来预测热导率的方法。用连续有限元法对灰色、稳态、单松弛时间声子辐射输运(PRT)方程的自伴随角通量(SAAF)公式进行空间离散,用离散坐标法对其进行角离散。通过制造解(MMS)空间收敛测试案例验证了解离散化方法,并与以往的工作进行了比较。在这项工作中计算的角声子辐射,热流和温度与以前的硅薄膜文献相比是有利的。利用温度梯度和热通量的局域值,利用傅里叶定律的表示对一维完美晶体中的导热系数作为位置的函数进行了评估,并与动力学理论进行了比较。我们的结果表明,在模拟域的内部,我们基于输运的热导率预测收敛于动力学估计。我们还发现,在等温边界附近,输运解偏离了动力学理论,表明在薄膜极限下存在非平衡行为,这与前人的研究结果一致。
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引用次数: 2
Optimal Control of the Keilson-Storer Master Equation in a Monte Carlo Framework 蒙特卡罗框架下Keilson-Storer主方程的最优控制
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-03-14 DOI: 10.1080/23324309.2021.1896552
Jan Bartsch, G. Nastasi, A. Borzì
Abstract This paper is devoted to the formulation and numerical solution by Monte Carlo (MC) methods of an optimal control problem governed by the linear space-homogeneous Keilson-Storer (KS) master equation. The KS master equation is a representative model of the class of linear Boltzmann equations with many applications ranging from spectroscopy to transport theory. The purpose of the optimal control in the collision kernel of this model is to drive an ensemble of particles to acquire a desired mean velocity and to achieve a desired final velocity configuration. For this purpose, a KS optimality system characterizing the solution of the proposed optimal control problem is derived and used to construct a gradient-based optimization strategy in the framework of MC methods. This task requires to accommodate the resulting adjoint KS model in a form that is consistent with the kinetic formulation. Results of numerical experiments successfully validate the proposed control framework.
摘要本文致力于线性空间齐次Keilson-Storer(KS)主方程控制的最优控制问题的蒙特卡罗(MC)方法的公式化和数值求解。KS主方程是一类线性玻尔兹曼方程的代表性模型,具有从光谱学到输运理论的许多应用。该模型的碰撞核中的最优控制的目的是驱动粒子系综以获得期望的平均速度并实现期望的最终速度配置。为此,导出了表征所提出的最优控制问题解的KS最优性系统,并将其用于在MC方法的框架下构造基于梯度的优化策略。这项任务需要以与动力学公式一致的形式来适应由此产生的伴随KS模型。数值实验结果成功地验证了所提出的控制框架。
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引用次数: 4
Numerical Solution of the Azimuth-Dependent Fokker-Planck Equation in 1D Slab Geometry 一维平板几何中方位相关Fokker-Planck方程的数值解
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-03-01 DOI: 10.1080/23324309.2021.1896554
Ó. López Pouso, N. Jumaniyazov
Abstract This paper is devoted to solve the steady monoenergetic Fokker-Planck equation in the 1D slab when the incoming fluxes and the source term are allowed to depend on the azimuth θ. The problem is split into a collection of θ-independent problems for the Fourier coefficients of the full solution. The main difficulty is that, except for the zeroth Fourier coefficient, each of these problems contains an artificial absorption coefficient which is singular at the poles. Two numerical schemes capable of dealing with the singularities are proposed: one that is considered as the main scheme, and a second ‘security’ scheme which is used to verify that the results obtained by means of the first one are reliable. Numerical experiments showing second order of convergence are conducted and discussed.
摘要本文致力于在允许入射通量和源项取决于方位角θ的情况下,求解一维平板中的稳定单能Fokker-Planck方程。该问题被分解为一组与θ无关的问题,这些问题的傅立叶系数为全解。主要的困难在于,除了第零傅立叶系数外,这些问题中的每一个都包含一个在极点奇异的人工吸收系数。提出了两种能够处理奇异性的数值格式:一种被认为是主格式,另一种“安全”格式用于验证通过第一种方法获得的结果是可靠的。进行了显示二阶收敛性的数值实验,并对其进行了讨论。
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引用次数: 1
The Homogeneous B 1 Model as Polynomial Eigenvalue Problem 多项式特征值问题的齐次B1模型
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-02-23 DOI: 10.1080/23324309.2021.1885446
D. Tomatis, Johan Cufe
Abstract The homogeneous version of the B 1 leakage model is a non-linear eigenvalue problem which is generally solved iteratively by a root-finding algorithm, combined to the supplementary eigenvalue problem of the multiplication factor. This problem is widely used for ordinary cross section preparation in reactor analysis. Our work approximates this problem with a polynomial eigenvalue problem, which can be easily transformed into an ordinary linear generalized eigenproblem of size equal to the initial one multiplied by the polynomial degree used for the approximation of a transcendental function. This procedure avoids recurring to numerical root-finding methods supported by extra eigenvalue problems. The solution of the fundamental buckling with increasing approximation order is compared to the reference value obtained by inverse iterations.
摘要B1泄漏模型的齐次版本是一个非线性特征值问题,通常通过寻根算法迭代求解,并结合乘法因子的补充特征值问题。该问题广泛用于反应器分析中的普通截面制备。我们的工作用多项式特征值问题来近似这个问题,该问题可以很容易地转化为一个普通的线性广义特征值问题,其大小等于初始值乘以用于近似超越函数的多项式次数。该过程避免了重复使用由额外特征值问题支持的数值寻根方法。将近似阶数增加的基本屈曲的解与通过逆迭代获得的参考值进行比较。
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引用次数: 0
Entropy Generation Rate for Stationary Ballistic-Diffusive Heat Conduction in a Rectangular Flake 矩形片状静止弹道扩散热传导的熵产率
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-02-23 DOI: 10.1080/23324309.2021.1896553
S. Mansoor, B. Yilbas
Abstract Thermodynamic irreversibility in low dimensional flake is considered and entropy generation rate in two-dimensional thin film is examined, Equation of phonon radiative transfer is solved for two-dimensional and rectangular diamond flake. Volumetric and total entropy generation rate are evaluated incorporating the formulation of thermal radiation heat transfer. The influence of flake aspect ratio (width to height) on the entropy generation rate is explored while keeping the Diamond flake area constant for all aspect ratios considered. The findings reveal that the entropy generation rate increases with increasing aspect ratio for fixed boundary conditions.
摘要考虑了低维薄片的热力学不可逆性,考察了二维薄膜的熵产生率,求解了二维和矩形金刚石薄片的声子辐射传输方程。结合热辐射传热公式,对体积和总熵产生率进行了评估。在保持金刚石薄片面积不变的情况下,探讨了薄片纵横比(宽高比)对熵产生率的影响。研究结果表明,在固定边界条件下,熵产生率随纵横比的增加而增加。
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引用次数: 1
On Global Existence and Regularity of Solutions for a Transport Problem Related to Charged Particles 一类带电粒子输运问题解的整体存在性和正则性
IF 0.7 4区 工程技术 Q3 MATHEMATICS, APPLIED Pub Date : 2021-01-17 DOI: 10.1080/23324309.2020.1851722
J. Tervo
Abstract The paper considers a class of linear Boltzmann transport equations which models charged particle transport, for example in dose calculation of radiation therapy. The equation is an approximation of the exact transport equation containing hyper-singular integrals in its collision terms. The paper confines to the global case where the spatial domain G is the whole space Existence results of solutions for the due initial value problem are formulated by applying variational methods. In addition, some regularity results of solutions are verified in scales of relevant anisotropic mixed-norm Sobolev spaces.
摘要本文考虑了一类模拟带电粒子输运的线性玻尔兹曼输运方程,并以放射治疗剂量计算为例。该方程是精确输运方程的近似,在其碰撞项中包含超奇异积分。本文讨论了空间域G为整个空间的全局情况,利用变分方法给出了该问题解的存在性结果。此外,在相关的各向异性混合范数Sobolev空间尺度上验证了解的一些正则性结果。
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引用次数: 2
期刊
Journal of Computational and Theoretical Transport
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