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25 May 2017, Volume 34 Issue 3 Previous Issue    Next Issue

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Efficient Algorithm for Stiff Source Terms in Strongly Coupling Radiative Transfer and Electron Energy Equations LI Ruo, LI Weiming, SONG Peng 2017, 34(3): 253-260.  Abstract ( )   HTML ( )   PDF (1111KB) ( )   We study numerical methods for coupled radiative transfer and electron energy equations. In highly opaque materials, strong coupling between them results in stiff source terms, making design of efficient and stable algorithms a challenging task. In this paper, we develop an efficient algorithm for multi-group radiative transfer equations coupled with electron energy equations. It is an integration method based on an ansatz of electron temperature. It poses no constraint on time step, and gives physically relevent solutions under reasonable assumptions. Numerical results show that the method is highly efficient and accurate.

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Physics Evoked Cloud Method: A Versatile Systematic Method for Numerical Simulations MA Zhibo 2017, 34(3): 261-272.  Abstract ( )   HTML ( )   PDF (3573KB) ( )   In mesh free methods, discrete equations are built according to physics information of micro-bodies arbitrarily spread in vicinal space. As requirements about topology of micro-bodies are reduced, simulations with Lagrangian approach may be easier even with large distortions. Owing to insufficiency of topological information, there is a challenge for mesh-free method to reflect physics especially as discontinuities exist. In this paper a new mesh free systematic method PECM (Physics Evoked Cloud Method) based on physical laws and developing trend of numerical simulation is shown, which has excellent applicability. High fidelity to physics of the method is demonstrated through several 1-dimentional problems in which strong discontinuities exist.

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An Open Void Method of Slide Line on Unstructured N-polygon Grids LIN Wenzhou, LI Zhong, LIU Quan 2017, 34(3): 273-282.  Abstract ( )   HTML ( )   PDF (4028KB) ( )   We develop an open void method of slide line, based on unstructured arbitrary N-polygon grids managed system and tied slide technology, for simulation of large deformation problem of frequently multi-medium loading and unloading. Validity verification was done with metal hit and leave model. Method of distinguishing point and grid's open or closed void state and calculating velocity of point on slide line is given. This slide technology extends open void method of traditional structured grid to unstructured arbitrary N-polygon grids, and keeps merit of no void connectivity and simulating interface well. It has capability of simulating open and closed interface in practical problem. We did test in metal hit and leave model with conditions of many grids, different velocity and multi-medium, which proves validity of the method.

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Conservative Positivity-Preserving Algorithm for Kershaw Scheme of Anisotropic Diffusion Problems CAO Fujun, YAO Yanzhong 2017, 34(3): 283-293.  Abstract ( )   HTML ( )   PDF (6211KB) ( )   Kershaw scheme is not positivity-preserving. Negative values emerge in numerical simulation for anisotropic diffusion equations on both orthogonal and distorted meshes. A conservative enforcing negative value to zero(CENZ) algorithm is proposed, which is an improvement of traditional method. It not only repairs numerical solution nonnegative, but also keeps local conservation of energy fluxes. Numerical examples demonstrate that the method is not limited by anisotropic ratio of diffusion coefficients. The algorithm can be used for numerical solution of finite volume schemes which violate monotony or positivity-preserving.

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A Discontinuous Petrov-Galerkin Method for Two-dimensional Compressible Gas Dynamic Equations in Lagrangian Coordinates ZHAO Guozhong, YU Xijun, GUO Huaimin 2017, 34(3): 294-308.  Abstract ( )   HTML ( )   PDF (8435KB) ( )   A cell-centered scheme is constructed for two-dimensional gas dynamics equations in Lagrangian coordinates on rectangular grids. Spacial discretizations are accomplished by control volume discontinuous Petrov-Galerkin method and temporal discretization is accomplished by second order total variation diminishing Runge-Kutta method. A limiter is used to maintain stability and non-oscillatory property of Runge-Kutta control volume (RKCV) method. The method preserves local conservation of physical variables. Compared with Runge-Kutta discontinuous Galerkin (RKDG) method, computational formula of RKCV method is simpler since it contains no volume quadrature in RKDG method. Numerical examples are given to demonstrate reliability and efficiency of the algorithm.

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High-order Compact Difference Schemes and Adaptive Method for Singular Degenerate Diffusion-Reaction Equations GE Yongbin, CAI Zhiquan 2017, 34(3): 309-319.  Abstract ( )   HTML ( )   PDF (3366KB) ( )   We established a high-order compact scheme on nonuniform grids for singular degenerate diffusion reaction equation. The scheme is second order accuracy in time and third to fourth order accuracy in space. A grid adaptive method is established by using equidistribution principle. Finally,a numerical example with exact solution validates reliability and accuracy of the method. One-dimentional blow up problem was solved with the method.

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Performance Optimization of LARED-Integration Code in Radiative Transfer Calculations LI Shuanggui, HANG Xudeng, YANG Rong, SONG Peng, ZHAI Chuanlei, QI Jin 2017, 34(3): 320-326.  Abstract ( )   HTML ( )   PDF (1154KB) ( )   Take use of characteristics of inertial confinement fusion(ICF) models and associated numerical discrete schemes, we proposed multiple techniques for promoting computational efficiency of two-dimensional radiation-hydrodynamic code LARED-integration. Numerical results show that with unchanged parallel resources it is two times faster in downstream spatial sweeping of solving transport equations. Half of total running time is saved for integrated simulation of laser fusion experimental hohlraums.

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FDTD Study on Wide-Band Composite Scattering from Soil Surface Covered with Snow and a Partially Buried Column REN Xincheng, ZHU Xiaomin, LIU Peng 2017, 34(3): 327-334.  Abstract ( )   HTML ( )   PDF (3006KB) ( )   To meet requirement for measurement and detection of target buried partially beneath a rough surface, rough snow surface and soil surface is simulated in model of exponential type distribution rough surface with Monte Carlo method. Wide-band composite scattering from rough soil surface covered with snow and a column with rectangular cross-section buried partially is studied using finite difference time domain(FDTD). Frequency responses of wide-band composite scattering coefficient is obtained. Wide-band composite scattering coefficients varying with root-mean-square and correlation length of rough snow surface and soil surface, type of snow, thickness of snow layer, moisture capacity of soil, geometric parameter, tilt angle and buried depth of column and incident angle of electromagnetic wave are calculated. It shows that influences of root-mean-square and correlation length of rough snow surface on wide-band composite scattering coefficient are unobvious, but influences of other parameters on wide-band composite scattering coefficient are remarkable and complex.

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Diffusing Loss Effects of Inner Radiation Belt Energetic Electrons Based on AKEBONO Whistler Wave Parameters LUO Xudong, NIU Shengli, ZUO Yinghong, TAO Yinglong 2017, 34(3): 335-343.  Abstract ( )   HTML ( )   PDF (2725KB) ( )   With inner radiation belt AKEBONO whistle wave parameter statistics model and background cold electron density model changed with altitude, as 1.4 ≤ L ≤ 2.0 electron bounce-averaged equator pitch angle diffusion coefficients due to Coulomb collision and wave-particle resonance interaction are calculated by using quasi-linear diffusion theory. Influences of interaction mechanisms, whistle wave types such as hiss, lightning-generated whistlers (LG), artificial very low frequency(VLF), energies and magnet shell parameter(L) on inner radiation belt energetic electrons diffusing loss are analyzed. It shows that Coulomb collision caused by atmosphere plays a dominant role in energetic electrons diffusion around equator loss cone angle, while hiss and LG are main diffusion factors near 90° of equator pitch angle. Wave-particle resonance diffusion caused by VLF plays a dominant role in inner radiation belt. Diffusion coefficients is sensitive to energetic electron energy and L. Usually, the greater the L or electron energy, the more significant the electron resonance diffusion coefficient is.

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An Improved Particle Swarm Optimization Based on Diversity Monitor and Real-time Updating Strategy LI Shuailong, CUI Guomin, CHEN Jiaxing, XIAO Yuan 2017, 34(3): 344-354.  Abstract ( )   HTML ( )   PDF (2772KB) ( )   Particle swarm optimization (PSO) algorithm has strong ability to explore global optimal region for heat exchanger networks synthesis. However, particles may trap into local optima and converge prematurely in late evolution. Therefore, an improved particle swarm optimization algorithm based on diversity feedback and real-time updating strategy is proposed. Firstly, index of population health degree is established to evaluate population diversity during evolution. Secondly, a random perturbation strategy and a centrifugal strategy are combined respectively with PSO algorithm to enrich population diversity and enhance global search ability. Furthermore, gradient search strategy is applied to search efficiently local optima and improve computational efficiency of PSO algorithm. Finally, a feedback mechanism of population health degree is proposed to real-time monitor health status of population and further to adopt different update strategies for keeping particles healthy during evolution. The method was applied to several cases taken from literature and results are encouraging. They are better than those of other improvements for PSO.

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A Hydraulic Calculation Approach in District Heating Network with 3D Topology Structure ZHOU Haijian, WANG Hai, ZHU Tong 2017, 34(3): 355-364.  Abstract ( )   HTML ( )   PDF (2322KB) ( )   To develop a methodology to fulfill hydraulic analysis on asymmetry and irregular topology structure networks, we proposed a method that can fully adapt on 3D asymmetric and irregular topology structure of networks. The modeling approach is illustrated in detail and compared with traditional methods using a district heating scenario. It provides instructions for other researches.

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First-Principles Simulation on Structure-Property of Ti-Al Intermetallic Compounds TAN Junhua, ZHU Kaijin, PENG Junhui 2017, 34(3): 365-373.  Abstract ( )   HTML ( )   PDF (2403KB) ( )   Crystal structure, mechanical and electronic properties of Ti-Al intermetallic compounds were studied using first-principles implemented in CASTEP. At 0 K, 0 GPa, thermodynamically stable structures are TiAl3, TiAl2, TiAl, Ti3Al. Unit cells of TiAl3, TiAl2, TiAl are evolutions of face-centered cubic Al. Structure of Ti3Al is similar to Ti, which is hexagonal close packing structure. Mechanical properties were calculated. It was found that with increasing of Ti molar fraction, their bulk modulus are approximate equivalent. But shear modulus and Vickers hardness decrease, and so did Pugh ratios. It shows that toughness became better. At last, density of state and Mulliken population analysis were simulated. Bonding nature of Ti-Al is a combination of metallic, covalent and weak ionic.

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Primary Resonance of Strong Nonlinear Torsional Vibration System of Diesel Shafting YANG Zhian, BIAN Yayuan 2017, 34(3): 374-378.  Abstract ( )   HTML ( )   PDF (1230KB) ( )   Strong nonlinear torsional vibration system of diesel shafting is studied. A dynamic model of torsional vibration system is established based on Lagrangian equation. Modified Lindstedt-Poincaré method is used to deal with primary resonance of diesel shafting torsional vibration of strong nonlinear system. Amplitude frequency response equation is obtained and influence of parameters on amplitude frequency response is analyzed. It shows that system frequency response exists jump phenomenon. As amplitude of harmonic torque decreases and damping increases, nonlinear jump of the system weakens, amplitude of the system reduces, and regions of primary resonance of the system decreases. With change of tuning parameter, amplitude excitation response has two kinds of topological structure. The result of MLP analysis is consistent with Runge Kutta numerical solutions.