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25 May 2019, Volume 36 Issue 3 Previous Issue    Next Issue

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Quantum Molecular Dynamics Simulations of Transport Properties of Liquid Plutonium WANG Shuaichuang, ZHANG Gongmu, SUN Bo, SONG Haifeng, TIAN Mingfeng, FANG Jun, LIU Haifeng 2019, 36(3): 253-258.  DOI: 10.19596/j.cnki.1001-246x.7852 Abstract ( )   HTML ( )   PDF (3036KB) ( )   We studied transport properties of liquid Pu with quantum molecular dynamics (QMD) simulations. We focused on calculating viscosity and diffusion properties from autocorrelation function. Our results are in good agreement with experiment in the range of measurement. There is obvious difference between our results and reference at lower temperatures and they show good agreement at relatively higher temperatures. Structures of autocorrelation function of off-diagonal components of stress tensor (STACF) and velocity autocorrelation function (VACF) at lower temperatures are observed and they exhibit correlated liquid-like behavior. Extrapolating autocorrelation function in t→∞ limit leads to larger error for viscosity and diffusion coefficient of correlated liquid. We obtain accurate viscosity and diffusion coefficient of liquid Pu from long simulation trajectories.

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Application of Simulated Annealing Method in Chemical Free Energy Model LI Qiong, LIU Haifeng, ZHANG Gongmu, ZHANG Qili 2019, 36(3): 259-264.  DOI: 10.19596/j.cnki.1001-246x.7853 Abstract ( )   HTML ( )   PDF (3984KB) ( )   Application of simulated annealing method in chemical free energy model to search for chemical composition of equilibrium state is proposed. Due to the random "thermal" fluctuations introduced by simulated annealing method, the difficulty associated with sensitivity of result to initial values is removed. Moreover, in the regime of first order phase transition where stable state and meta-stable state coexist, the stable state can always be obtained. As an example, chemical free energy model improved by simulated annealing method is applied to the equation of state for fluid helium, which demonstrates the plasma phase transition induced by pressure ionization.

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ISSDE: First-principles Implicit Simulations Based on Stratonovich SDE Approach of Coulumb Collision ZHENG Yifeng, WANG Yulei, LIU Jian, QIN Hong 2019, 36(3): 265-279.  DOI: 10.19596/j.cnki.1001-246x.7843 Abstract ( )   HTML ( )   PDF (12500KB) ( )   A first-principles implicit simulation program, Implicit Stratonovich Stochastic Differential Equations (ISSDE), is constructed for stochastic differential equations which describes plasmas with Coulomb collision. Basic idea of the program is stochastic equivalence between Fokker-Planck equation and Stratonovich SDE. Implicit discrete method guarantees numerical stability and conservation of kinetic energy. ISSDE is built with C++ language, and is designed to possess standard interfaces and extendible modules. Slowing-down processes of electron beams in both unmagnetized and magnetized plasmas are studied, which shows correctness of ISSDE. It provides a powerful tool for collisional plasmas studies.

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A Higher Order Regularization Approach for Object Reconstruction with Mixed Laplace-Gaussian Likelihood KONG Linghai, KONG Lingbo, XU Haibo, JIA Qinggang 2019, 36(3): 280-290.  DOI: 10.19596/j.cnki.1001-246x.7831 Abstract ( )   HTML ( )   PDF (5280KB) ( )   A combined first and second order variational model is proposed for reconstructing images corrupted by mixed Laplace-Gaussian noise. The model is constructed by joint maximum a posteriori estimation and expectation maximization. Numerical algorithm is studied by integrating splitting technique into augmented Lagrangian method with modification, such as introduction of adaptively selective functions for preserving details of original images. An adaptive soft-shrinking formulation is advanced for mixed noise removal, in which an alternating minimization algorithm is established. Numerical experiments show validation in tomography reconstruction and image restoration.

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A Fictitious Domain Method Based on Finite Volume Scheme for Particulate Flows ZHANG Longhui, YOU Changfu 2019, 36(3): 291-297.  DOI: 10.19596/j.cnki.1001-246x.7849 Abstract ( )   HTML ( )   PDF (3346KB) ( )   This research aims to develop a fictitious domain method based on finite volume discretization. The main idea is to add a source term in the momentum equation, which can apply rigid body constraint on domains covered by particles. The source term includes both particle and fluid information inside. It shows that by refreshing fluid information after each iteration, rigidity of solid can be preserved. This finite volume method is then verified by simulations of several cases and comparing results with literatures, which proves accuracy of the method.

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Effect of Mesoscopic Flow on Elastic Wave Propagation in Heterogeneous Double Porosity Media SHI Jiancheng, ZHENG Pei, GAO Zhe 2019, 36(3): 298-304.  DOI: 10.19596/j.cnki.1001-246x.7847 Abstract ( )   HTML ( )   PDF (2062KB) ( )   Based on mesoscopic heterogeneity theory model of Pride and Berryman, coupled dynamical equations were deduced with a group of displacements, and a group with displacement and pore pressure. With double-porosity model, elastic wave expression of phase velocity and inverse quality factor are deduced. Influence of mesoscopic flow on propagation of elastic waves was discussed. Numerical examples show that velocity of fast wave increases rapidly with increase of frequency, and mesoscopic flow loss is at least higher one order of magnitude than Biot loss. Besides, mesoscopic flow has different influence on slow wave. It is proved that mesoscopic flow is the main factor of wave energy loss and velocity dispersion.

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Fast Directional Boundary Element Method for Large Scale Wideband Elastodynamic Analysis CAO Yanchuang, XIAO Jinyou, WEN Lihua, WANG Zheng 2019, 36(3): 305-316.  DOI: 10.19596/j.cnki.1001-246x.7866 Abstract ( )   HTML ( )   PDF (13227KB) ( )   A fast directional boundary element method for large scale wideband elastodynamic analysis is developed. Directional low rank property of elastodynamic kernels is shown which serves as the theoretical basis of its fast directional algorithm. By only considering S-wave number, interactions of different nodes are divided into low-frequency interactions and high-frequency interactions, and the latter is further divided into interactions with directional wedges on which the directional low rank property is applied. Low-frequency interactions are computed in same manner with that in kernel independent fast multipole BEM for elastodynamics, and translation matrices for different directional wedges are calculated efficiently by coordinate frame rotations. Thus harmonic responses for any frequencies can be computed efficiently. Numerical examples show that the computational complexity for wideband elastodynamic problems are successfully brought down to O(N logαN). It can also be applied to transient elastodynamic analysis combined with convolution quadrature method.

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Full Core Pin by Pin Neutron Diffusion Nodal Method Based on CMFD Acceleration LI Zhiyong 2019, 36(3): 317-322.  DOI: 10.19596/j.cnki.1001-246x.7867 Abstract ( )   HTML ( )   PDF (2271KB) ( )   A classical semi-analytical nodal method for neutron diffusion equation with second order neutron flux expansion in radial pin by pin level and 4th order expansion for axial neutron flux is used. A full core coarse mesh finite difference (CMFD) acceleration is adopted in order to achieve good calculation accuracy and efficiency. With IAEA 2D/3D benchmark problem and self-define 3D pin by pin reference problem numerical calculation, it is demonstrated that the proposed methodology achieve anticipated accuracy and with very good CMFD acceleration.

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A Numerical Study of Frost Layer Growth with Improved Lattice Boltzmann Enthalpy Method CUI Jing, YANG Tinghao, YANG Fan, LI Hulin, YANG Guangfeng 2019, 36(3): 323-334.  DOI: 10.19596/j.cnki.1001-246x.7856 Abstract ( )   HTML ( )   PDF (15284KB) ( )   Influence of wall surface on growth of frost layer is studied by using mesoscale lattice Boltzmann method. Nucleation probability model is coupled with improved enthalpy model. A lattice Boltzmann model of frost layer growth process based on nucleation probability theory is established. It simulates thickening of frost layer growth on macro scale, and dynamic change of frost layer structure caused by growth of ice branches in microscale as well. Average thickness, average density and frosting amount of frost layer are obtained. Formation and growth of frost layer on cold wall surface are studied. Temporal and spatial evolution of topological structure of frost layer are obtained. Average thickness, average density and average solid volume fraction of frost at different time were calculated and effects of cold wall surface temperature, relative humidity and cold surface infiltration on frost were discussed.

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Dipolar Interaction in Magnetic Nanoparticle Systems: A Monte Carlo Study MO Kangxin, SU Jiajia 2019, 36(3): 335-341.  DOI: 10.19596/j.cnki.1001-246x.7845 Abstract ( )   HTML ( )   PDF (3939KB) ( )   Dipolar interactions of monodispersed single-domain Fe nanoparticles distributed in simple cubic lattice with different distribution of easy axes are studied with Monte Carlo method. Characteristic parameters of hysteresis loops and zero field cooled(ZFC)/field cooled(FC) magnetization curves are obtained. It is found that blocking temperature (TB) increases and peaks of ZFC curves are broaden with increasing strength of dipolar interaction. It means that dipolar interactions increase height of effective energy barrier and broaden distribution of effective energy barrier of systems. Reciprocals of FC magnetizations as function of temperature shown that the curves follow Curie-Weiss law well above TB. Curie-Weiss temperature (T0) is zero for non-interacting system while it is negative for dipolar interacting system. Negative T0 indicates that there is antiferromagnetic order in the interacting systems. Furthermore, with increasing strength of dipolar interaction, absolute value of T0 for interacting system increases. Below blocking temperature, Hysteresis loops show that coercivity and remanence depend strongly on dipolar interaction. It is revealed that strong dipolar interactions suppress both coercivity and remanence of densely packed nanoparticles. Magnetization curves of superparamagnetic systems show that they are depressed with increasing particle packing density. Magnetization curves do not follow Langevin function and exhibit predominantly demagnetizing interacting effect. For interacting systems with 45° angle of applied field with easy axes, height of effective energy barrier are higher than those of random distribution systems, and distribution of effective energy barrier is wider than those of random distribution systems.

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Lattice Green Function of Nickel LIU Fenghua, LIU Wanguo, LI Wei 2019, 36(3): 342-348.  DOI: 10.19596/j.cnki.1001-246x.7879 Abstract ( )   HTML ( )   PDF (1580KB) ( )   As an important multi-scale coupling method, lattice Green function (LGF) bridges gap between density functional theory (DFT) calculations on atomic scale and large-scale continuum medium elasticity theory, especially for material containing dislocation-doping complex. With LGF equilibrium dislocation core structure can be obtained. It provides basis for DFT calculations of interaction between dislocation and doping atoms. Based on lattice dynamics and force-constant matrix, LGF of perfect nickle lattice is obtained with special k-points sampling and Fourier transform, which can be applied in multi-scales calculation of nickle-base superalloy.

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Simulation of Large Vertically Polarized EMP Radiating Wave Simulator with Discrete Resistors Using Parallel FDTD Method ZHU Xiangqin, CHEN Zaigao, WU Wei, MA Liang, CHENG Yinhui, JIA Wei 2019, 36(3): 349-356.  DOI: 10.19596/j.cnki.1001-246x.7846 Abstract ( )   HTML ( )   PDF (15489KB) ( )   Parallel FDTD method, by setting resistors as lossy media across grids, is used in time-domain simulation of large vertically polarized electromagnetic pulse(EMP) radiating-wave simulator with discrete resistors. Radiation fields in time-domain with different load-type of discrete resistors are given. Effect of different resistor load is shown. Electric fields in time domain of simulator with discrete resistors and a cylinder effector are presented. It shows that loading discrete resistors improve effectively waveform of radiated electric fields by reducing reflection from simulator's top. However, radiation performance may be weaken as simulators with resistors load. Energy entering into the effector through a square hole is much as the side with hole is near to simulator and parallel with polarized orientation of simulator. The method has general application, and can be used in simulation of time-domain fields of other large vertically polarized EMP radiating-wave simulators with discrete resistors, including simulation of coupling fields as the ground and effectors existing.

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Numerical Study of Circular Dichroism Generated by Bilayered Split Rings WEN Xiaojing, QU Yu, CHEN Chengzhao 2019, 36(3): 357-362.  DOI: 10.19596/j.cnki.1001-246x.7870 Abstract ( )   HTML ( )   PDF (7210KB) ( )   Based on Jones matrix, we propose a metal nanostructure consisting of double-layer split rings, in which the opening direction between up and down split rings is twisted to break symmetry. CD effect of the nanostructure and mechanism is studied with finite element method. It shows that under excitation of left-handed circularly polarized light and right-handed circularly polarized light the structure shows different transmission. Its CD value reaches 0.34. Current density distributions show that at short resonant wavelengths equivalent dipoles of upper and bottom split-rings form antibonding mode, and at long resonant wavelengths equivalent dipoles of upper and bottom split-rings form bonding mode. These results facilitates understanding of physical mechanism of CD. It provides a way to design chiral nanostructure.

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First Principles Study of HCHO Adsorption on Hydroxylated TiO2-B(100) Surfaces LIU Huazhong, LUO Chunxia 2019, 36(3): 363-378.  DOI: 10.19596/j.cnki.1001-246x.7841 Abstract ( )   HTML ( )   PDF (21111KB) ( )   Co-adsorption of formaldehyde (HCHO) with hydroxyl groups on both clean and hydroxylated TiO2-B(100) surfaces with terminal and bridging hydroxyl groups is investigated by using first-principles method. The hydroxyl groups was found to affect chemisorption configurations of HCHO on both clean and hydroxylated TiO2-B(100) surfaces. It indicates that bridging hydroxyl on most adsorption sites near to HCHO weakens adsorption of HCHO, while terminal hydroxyl on most adsorption sites facilitates it. Investigation of hydroxyls on HCHO in different periodicities shows that terminal hydroxyl usually has significantly facilitated on adsorption of H2O in larger periodicity, while bridging hydroxyl does not have this trend. This unique mechanism provides a novel angle to understand interaction of HCHO with hydroxylated TiO2 surface.