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25 November 2016, Volume 33 Issue 6 Previous Issue    Next Issue

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Key Technologies of Coupling for Multiphysics in Numerical Reactor DENG Li, SHI Dunfu, LI Gang 2016, 33(6): 631-638.  Abstract ( )   HTML ( )   PDF (1623KB) ( )   With rapid development of computer and super computation, coupling for multi-physics,multi-scale and multi-process has become possible. Some lone process are integrated together. Some approximates from experience will be removed after all of the processes to be considered. This work is based on a virtual reactor. The goal is to improve precision by improvement of modeling and high fidelity computation. At present, study measures are changed from experiment and engineer dependent to theory analysis and numerical simulation. Numerical simulation will become more and more important. In this paper, CASL and NURESAFE are introduced. Then, several challenges, which include key technologies of software, are put forward in development of nuclear energy. Finally, suggestions are given for numerical reactor. It is only for reference and discussion.

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Particle-Flag Based Source Bias Algorithm for Simulating Time-Dependent Particle Transport SHANGGUAN Danhua, XU Haiyan 2016, 33(6): 639-644.  Abstract ( )   HTML ( )   PDF (1044KB) ( )   In multi-step Monte Carlo simulation of time-dependent particle transport problems, particle-flag based physical quantity can be calculated by appropriate classification of diverse particle's attributes. Some particle-flag based physical quantities' fluctuation are strong since only very small fraction of total histories can make non-zero contribution and it is inefficient to deal with this problem by increasing purely total history number. A source bias algorithm is proposed to decrease stochastic error of target quantity by increasing number of source particle with a specific type only. Meanwhile, precision of non-target quantities are hardly decreased. A one-dimensional multi-layer model is utilized to display effect of the method.

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Simulations of Mode-Mode Coupling Between Drive Asymmetry and Outer Surface Roughness in Ignition Capsule Implosion GU Jianfa, DAI Zhensheng, GU Peijun, YE Wenhua, ZHENG Wudi, ZOU Shiyang 2016, 33(6): 645-651.  Abstract ( )   HTML ( )   PDF (2915KB) ( )   We perform 2D ignition capsule implosion simulation by a 2D multi-group radiation diffusion hydrodynamic code LARED-S which simultaneously simulates radiation drive asymmetry and outer surface roughness. Implosion flow field shows large-amplitude spikes and bubbles as well as a significant low-mode shell areal density asymmetry. Amplitudes of modes generated by mode coupling are in good agreement with analytic mode coupling equation until perturbation amplitude of fundamental mode L24 is greater than nonlinear saturation amplitude. In deceleration phase, perturbation growth is in strong nonlinear phase, and strong mode coupling effects broaden mode distribution. High-density spikes are bent by vortex flow. Mode coupling degrades greatly implosion performance, leading to ignition failure. Further simulations of mode coupling between low-mode drive asymmetry and capsule surface roughness is critical for understanding influences of hydrodynamic instabilities on ignition capsule implosion.

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Crank-Nicolson E-H Time-Domain Finite-Element Method Based on Curvilinear Tetrahedral Elements YE Zhenbao, ZHU Jian, ZHOU Haijing 2016, 33(6): 652-660.  Abstract ( )   HTML ( )   PDF (1565KB) ( )   Based on E-H TDFEM method derived directly from Maxwell's curl equations, Crank-Nicolson difference scheme is implemented for time-partial differential equation to obtain an unconditionally stable algorithm. Curvilinear tetrahedral elements are applied to discretize computational domain and electric and magnetic fields are expanded with same hierarchical vector basis functions. A sphere cavity and a cylindrical cavity partially filled with dielectric rod are simulated. It shows that curvilinear tetrahedral elements can reach higher accuracy with same mesh numbers, compared with tetrahedral elements. Better results can be obtained by curvilinear tetrahedral elements combined with 1.0 order hierarchical basis functions with fewer unknowns than that combined with 0.5 order hierarchical basis functions.

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QMU Decision Based on Modeling & Simulation MA Zhibo, SUN Yutao, YIN Jianwei, WANG Qiuju, LV Guixia 2016, 33(6): 661-670.  Abstract ( )   HTML ( )   PDF (1357KB) ( )   With margins and their uncertainties, QMU (Quantification of Margin and Uncertainty) method can be used to make decisions on whether performances of a product reach demands or not. Recur to new methods of UQ (Uncertainty Quantification) for M&S (Modeling & Simulation), QMU is actualized with input information directly from M&S and its uncertainties. With reliability assessment for a stockpiled product, main ideas and executing details of QMU decision are demonstrated.

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Design Principles of Ghost Fluid Method XU Liang, FENG Chengliang, LIU Tiegang 2016, 33(6): 671-680.  Abstract ( )   HTML ( )   PDF (3574KB) ( )   By analyzing ghost fluid method for compressible multi-medium flows, fundamentals for defining ghost fluid state with a general equation of state are described. All possible definitions of ghost fluid states are derived according to wave patterns and free variables in ghost fluid region. Following these treatments, it reveals that solution of multi-medium Riemann problem can be obtained exactly in theory. Several simple but effective definitions independent with wave patterns in ghost fluid region, are further summarized. One of these ways is similar to reflective boundary condition. An essential prerequisite is that interfacial velocity must be predicted exactly. Numerical results show that this methodology indeed works reasonably for multi-medium flows.

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Decoupling Method for Transient Thermal Status of Low Supersonic Aircrafts LI Zhenhuan, SUN Haifeng, XIA Xinlin, LI Yang 2016, 33(6): 681-690.  Abstract ( )   HTML ( )   PDF (4122KB) ( )   Considering complexity of coupled fluid-solid calculation of low supersonic aircraft under unsteady flight condition, real time aerodynamic heat by outer fluid field is converted into floated third type boundary conditions for decoupled calculation. Take three-dimensional head cone experiencing accelerating diving as example, floated temperature and radiation equilibrium methods are adopted to extract surface heat transfer coefficients for decoupling calculation. Results are compared with coupled results to validate reliability of decoupling methods. It shows that with dispersed state points representing unsteady process, temperature distributions of cone surface at different state points by decoupling methods agree well with coupling ones. Calculating efficiency of decoupling methods is superior to coupling ones. Maximum relative errors of decoupling methods are both within 2%, even as external aerodynamic environment changes dramatically.

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Large Eddy Simulation of Atmospheric Boundary-Layer Flows Under Time-Varying Upstream Inflows LI Weijun, ZHANG Yunwei, GU Zhaolin, DUAN Cuie, ZHANG Liyuan, LU Weizhen Jane 2016, 33(6): 691-697.  Abstract ( )   HTML ( )   PDF (2731KB) ( )   In large eddy simulations (LES), a flat ground model and rough wedge ground models with different wedge heights were adopted to investigate near-surface wind field characteristics under condition of time-varying upstream inflows. In both flat ground model and rough wedge ground models, simulated results show that there is downdraft in peak period of gusty wind and updraft in valley period, respectively. Intensity of downdraft/updraft flows are related to ground roughness in upwind areas and amplitude of inflows. It follows that wind velocity and direction in atmospheric boundary layer always change over time in time-varying upstream inflows, which enhances transportation of mass and energy in actual atmospheric boundary layer.

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Lattice Boltzmann Simulation on Motion Characteristics of Indoor Respirable Particles YAN Renqiao, CHEN Liping, ZHOU Bin 2016, 33(6): 698-706.  Abstract ( )   HTML ( )   PDF (3588KB) ( )   To explore motion characteristics of indoor respirable particles, Brownian force on particles is considered in motion probability model. Motion characteristics of 0.01 μm, 0.1 μm and 1 μm particles under conditions of up supply with up return and up supply with side return air forms were simulated with lattice Boltzmann method taking Re as 400, 1 000 and 2 000, respectively. It shows that range of particle spacial distribution increases with Re, and smaller particles affected more obvious by air turbulence and diffusion effect. Mean square displacement (MSD) of particles is inversely proportional to Re and diameter of particles. At same Re, MSD of particles is greater under up supply with side return air form, thus lower suspended particles and higher indoor air quality appears in up supply with side return air form.

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Non-Darcy Flow Simulation of Oil-Water Phase in Low Permeability Reservoirs Based on Mimetic Finite Difference Method HUANG Tao, HUANG Zhaoqin, ZHANG Jianguang, YAO Jun 2016, 33(6): 707-716.  Abstract ( )   HTML ( )   PDF (3910KB) ( )   Mimetic finite difference (MFD) method was applied to numerical simulation of non-Darcy flow in low permeability reservoirs. Principle of MFD method was described in details. And corresponding numerical formula of the non-Darcy flow model was developed. An IMPES scheme was used for solution of two-phase flow simulation. Several numerical examples are presented to demonstrate efficiency and applicability of the scheme.

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Characteristics of Boundary Layer in Micro and Nano Throats of Tight Sandstone Oil Reservoirs TIAN Xiaofeng, CHENG Linsong, CAO Renyi, AN Na, ZHANG Miaoyi, WANG Yimin 2016, 33(6): 717-725.  Abstract ( )   HTML ( )   PDF (4217KB) ( )   Dissipative particle dynamics (DPD) is modified by introducing attractive force. Attractive interaction of liquid and solid and micro-scale flow in nano throats is simulated to discuss mechanism of boundary layer. It is found that thermal motion affects velocity significantly in molecular scale while pressure gradient is leading function as greater than molecular scale. However, thermal motion cannot change integral moving direction. As throat radius becomes larger, parabola shape of velocity distribution becomes more and more obvious. Boundary layer thickness is affected by pressure gradient, throat radius and fluid viscosity. As pressure gradient increases and fluid viscosity decreases, boundary layer thickness decreases. As throat radius decreases, boundary layer thickness increases first and then decreases. Boundary layer is essential reason of nonlinear flow behavior and thickness of boundary layer increasing makes nonlinear flow behavior more obvious.

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Electronic, Magnetic and Elastic Properties of Mn-Doped Mo2FeB2: First-Principles Calculations WANG Bin, LIU Ying, YE Jinwen 2016, 33(6): 726-736.  Abstract ( )   HTML ( )   PDF (1506KB) ( )   Structure stability, magnetism, electronic structure and elastic properties of (Mo,Fe,Mn)3B2 are determined with first-principles calculations. Density functional theory and ultrasoft pseudopotentials are used. Antiferromagnetic case has the lowest energy, indicating that it is ground state. DOS and population of (Mo,Mn,Fe)B2 are similar to those of Mo2FeB2. From density of states and overlap populations, it is found that B-B and B-Mo are covalent bonding and they give positive contribution to shear modulus. According to analysis of magnetism, Fe and Mn atoms play the key point. However, Mn doping has weak effect on bonding and elastic properties of hard phase Mo2FeB2.

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First-Principles Study of Carbon Monoxide Adsorption Liability on Graphite(001) HE Manchao, HU Xiangxing, ZHAO Jian 2016, 33(6): 737-742.  Abstract ( )   HTML ( )   PDF (1889KB) ( )   Adsorption mechanism of coal seam and carbon monoxide gas is studied in microscopic view by using first-principles calculation methods based on quantum mechanics. Due to complexity of coal structure, graphite is used to take place of coal seam for simulation. A model of adsorption of carbon monoxide on graphite is established. Three typical sites with high symmetry on graphite surface are considered. They are top, bridge, and hollow adsorption sites. It shows that bridge site has the highest adsorption energy as carbon monoxide molecule is perpendicular to graphite(001) surface with carbon atom near graphite film.

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Effect of Co Content on Magnetic Properties of Fe3Si Alloy HE Xiaojin, ZHANG Jinmin, HUANG Jin, LU Shunshun, HE Fan, WU Hongxian, SHAO Peng, XIE Quan 2016, 33(6): 743-748.  Abstract ( )   HTML ( )   PDF (4522KB) ( )   Magnetic properties of transition metal Co doped Fe3Si alloy are studied with first-principles pseudo-potential plane wave method based on density functional theory (DFT). It shows that magnetism of Fe3-xCoxSi mainly results from transition metal elements Fe and Co. Strong-magnetism of FeB atom is revealed compared with weak-magnetism of A- and C-site atom. Total magnetic of Fe3-xCoxSi decreases slowly in 0≤x≤0.75, but increases rapidly in 0.75≤x≤1.5. FeA,C moment shows similar trend. Magnetic moment of Co atoms increases slowly as Co content increases. Change of atomic magnetic moment is related to charge transfer of spin up and down direction.

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Analytical Potential Energy Function and Spectra of Li2S Molecule XU Yongqiang, PENG Weicheng, CAI Yuqing 2016, 33(6): 749-756.  Abstract ( )   HTML ( )   PDF (1343KB) ( )   Structures of ground states of Li2, LiS and Li2S molecules are investigated using density function theory B3LYP method and 6-311++g(d,p) basis set. It shows that their electronic states are X1Σg+, X2Πg and X1Σg+. Murrell-Sorbie potential functions with 4 parameters for LiS and Li2 molecules are obtained with nonlinear curve fitting method. Spectral parameters and force constants are studied with Murrel-Sobie potential functions. Analytical potential surface of singlet Li2S is obtained with many-body expansion theory. Rotary contour map, stretching contour map and rotary stretching contour map are reconstructed with analytical potential surface. Static characters of ground singlet Li2S are repeated exactly through these maps. They are equilibrium geometric structure, lowest energy and reasonable chemical reaction channels, respectively. Stretching vibrational contours of potential energy surface show that reaction Li+S+Li→Li2S is a no barrier reaction channel. Reaction channel of S atom attacking Li2 molecule has a transition state. Channel of Li atom attacking LiS molecule has a transition state.