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25 November 2019, Volume 36 Issue 6 Previous Issue    Next Issue

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Numerical Simulation on Collision Characteristics of Micro-sized Particles SUN Shaowei, DENG Xiaoliang, ZHAO Meicheng, LI Peng, XU Rui, YU Guofeng, CHEN Benliang, REN Bo, JIANG Bingyou, LU Wei, QI Fugang, ZHU Wenjun, CAO Liangzhi, OUYANG Xiaoping, YUAN Liang 2019, 36(6): 631-640.  DOI: 10.19596/j.cnki.1001-246x.8103 Abstract ( )   HTML ( )   PDF (7402KB) ( )   We investigate collision characteristics of micro-sized particles (diameter less than 100 microns) via numerical simulations and experiments. Discrete element method (DEM) simulations, based on improved hard-sphere model, are performed to explore effect of initial velocity, surface energy, size, mass concentration, and wind speed on cohesive collisions and non-cohesive collisions between micro-sized particles. Aggregation and settlement process are considered as well. It is found that simulated cohesive collision rate agrees with experimental results of self-settlement of micro-sized particles.

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Multiple-resolution Parallel Direct Method of DNS for Turbulence Thermal Convection BAO Yun, HE Jianchao, FANG Mingwei 2019, 36(6): 641-647.  DOI: 10.19596/j.cnki.1001-246x.7974 Abstract ( )   HTML ( )   PDF (4637KB) ( )   Spatial and time resolution of thermal scalar field and velocity fields are different in turbulence thermal convection. A multiple-resolution parallel direct method for DNS with two different girds is presented to solve the problem of huge computational cost in simulation of turbulence thermal convection with very high Rayleigh numbers. A constant translation interpolation method of speed was designed to meet continuous equations at each finer gird in data transformation between coarser gird and finer gird. Simulations of 2D turbulence thermal convection with very high Rayleigh numbers show that computational cost is reduced an order of magnitude by using this method. Small-scale eddy-like plumes, that move rapidly in thermal convection, are well performed in instantaneous temperature fields. It is consistent with results with a single gird. Difference of Nusselt number obtained by two methods is below 1%.

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Lattice Boltzmann Study on Displacement Process of Thermal Miscible Fluids in Porous Media JU Long, ZHANG Chunhua, CHEN Songze, GUO Zhaoli 2019, 36(6): 648-658.  DOI: 10.19596/j.cnki.1001-246x.7963 Abstract ( )   HTML ( )   PDF (17718KB) ( )   With lattice Boltzmann method, thermal miscible displacement process in porous media was investigated numerically in pore scale. Influence of thermal viscous diffusion coefficient (βT) and Lewis number (Le) on interface shape and sweep efficiency are quantitatively analyzed. It shows that with the increase of βT, the instability of interface increases and the sweep efficiency decreases. As βT>0, with increase of Le, interface instability decreases; Interface between displacement fluid and displaced fluid tends to be flat; Fingertip residual rate decreases and sweep efficiency increases. As βT<0, effects of Le on sweep efficiency are opposite.

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Three-dimensional Numerical Simulation of Vapor Bubble Rising in Superheated Liquid by Lattice Boltzmann Method SUN Tao, LIU Zhibin, FAN Wei, QIN Haijie 2019, 36(6): 659-664.  DOI: 10.19596/j.cnki.1001-246x.7925 Abstract ( )   HTML ( )   PDF (11594KB) ( )   Dynamics behavior of a vapor bubble such as rising, growth and deformation in superheated liquid was simulated with three-dimensional lattice Boltzmann phase-change model. To study effect of heat and mass transfer on vapor bubble, process of bubble rising in isothermal system was simulated. It shows that deformation extent of vapor bubble is small in superheated liquid. It is suggested that the effect of phase-change on vapor bubble is similar to surface tension force, which makes vapor bubble tend to keep its initial shape. Rising velocity of vapor bubble in superheated liquid was smaller. It implied that the effect of drag force on vapor bubble was dominant in superheated situation. In addition, growth rate of vapor bubble reaches the maximum at initial stage; Then it tended to nearly a constant. As vapor bubble volume and velocity increase, influence of disturbance on flow field is more and more intense. Meanwhile, growth of vapor bubble and convection induced by bubble rising have great impact on evolution of temperature field.

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A Multiscale Deep Learning Model for Fractured Porous Media ZHANG Qingfu, YAO Jun, HUANG Zhaoqin, LI Yang, WANG Yueying 2019, 36(6): 665-672.  DOI: 10.19596/j.cnki.1001-246x.7962 Abstract ( )   HTML ( )   PDF (10318KB) ( )   A multiscale deep learning model is proposed for fluid flow in porous media. The method is formulated on hierarchical grid system, that is, a coarse grid and a fine grid. Deep learning network is used to train data on the coarse gird. Source term and permeability field is treated as input parameter and coarse-scale solution is treated as output parameter. We construct multiscale basis functions by solving local flow problems within coarse gridcells. Heterogeneity and interactions between matrix and fracture are captured by basis functions. Oversampling technique is applied to get more accurate small-scale details. Numerical experiments show that the multiscale deep learning model is promising for flow simulation in heterogeneous and fractured porous media.

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Weighted Bayesian Inversion Method in Multi-angle Dynamic Light Scattering Measurements LIU Ling, CHEN Miao, QIU Jian, PENG Li, LUO Kaiqing, HAN Peng 2019, 36(6): 673-681.  DOI: 10.19596/j.cnki.1001-246x.7954 Abstract ( )   HTML ( )   PDF (12350KB) ( )   A weighted Bayesian inversion method is proposed for estimation of unimodal particle size distribution in multi-angle dynamic light scattering measurements. Particle size informiation distribution in autocorrelation function is used as base and adjustment parameters as exponent in the weight coefficient. Traditional Bayesian inversion method is recovered. Simulation and experimental data at different noise levels show that weighted Bayesian inversion method obtains inversion results with smaller distribution error. It weakens effectively influence of data noise and improves accuracy of particle size distribution.

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Shock Waves in Magnetized Dusty Plasma and Their Dynamical Stability Under Transverse Perturbations PANG Jungang, SONG Lin, TANG Na, YANG Xueying, LI Xiaolin, XI Zhonghong, SHI Yuren 2019, 36(6): 682-690.  DOI: 10.19596/j.cnki.1001-246x.7941 Abstract ( )   HTML ( )   PDF (7819KB) ( )   A class of shock wave solutions of Zakharov-Kuznetsov-Burgers (ZKB) equation is obtained with hyperbolic-function-expansion method. Dynamical stability property of shock waves under transverse perturbations is investigated. Firstly, we made linear stability analysis on shock waves. A finite difference scheme with high accuracy is presented to solve numerically the eigenvalue problem. It shows that the shock waves are linearly stable with positive dissipation, while they are linearly unstable with negative dissipation. Secondly, a finite difference scheme is constructed to make long-time nonlinear dynamical evolution of shock waves. The results show that shock waves of ZKB equation are dynamically stable in the case of positive dissipation.

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Parallel Simulation and Analysis of Large EMP Bounded Wave Simulator with Horizontal Polarization ZHU Xiangqin, WU Wei, ZHANG Guowei, CAI Libing 2019, 36(6): 691-698.  DOI: 10.19596/j.cnki.1001-246x.7939 Abstract ( )   HTML ( )   PDF (13052KB) ( )   Parallel FDTD method is used in time-domain simulation of large horizontally polarized electromagnetic pulse(EMP) bounded wave simulator with discrete resistors, in which the earth is set as lossy media truncated by uniaxial perfectly matched layer (UPML) absorbing boundary. Simulator's radiation fields in time-domain with different earth conductivity, earth relative dielectric constant and cone's radius are given. And electric field with a 10 m-length cylinder effector in simulator is also presented. The number of total cells in parallelized FDTD computing is about 1.8 billion. It shows that reflection from the earth becomes great as the earth's dielectric constant or conductivity increasing; The cone's radius has great effect on peak value of E-field in simulator, and fields at same horizontal plane becomes uneven as the radius becomes large; Reflection and loss from the earth have great effect on peak value and pulse width of E-fields in a horizontal plan above the ground 1 m, while they have little effect on E-fields in a horizontal plan above the ground 5 m. Energy entering into effector through a square hole is great as the hole is at the same side of simulator fields' leak.

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An Algorithm for Synthesizing Excitable Gas Pressure Based on Sound Relaxation Frequency ZHANG Kesheng, ZHANG Shigong, ZHANG Xiangqun, ZHOU Zhengda 2019, 36(6): 699-706.  DOI: 10.19596/j.cnki.1001-246x.7948 Abstract ( )   HTML ( )   PDF (2687KB) ( )   Sound relaxation frequency is frequency of peak point in sound absorption spectrum, which contains information of gas composition, ambient temperature, and pressure in excitable gases. With characteristics of sound relaxation frequency is linearly in proportion to gas pressure, we propose an algorithm for synthesizing gas pressure by acoustic relaxation frequency calculated with absorption coefficients and sound speeds at two frequencies. Measurement error of sound relaxation frequency is proportional to acoustic measurement error. Specially, as sound absorption measurement errors at the two frequencies are equal, error of synthesized pressure is zero. For methane and its mixtures at a certain temperature, simulation results demonstrate effectiveness of the algorithm and its robustness to acoustic measurement errors. Thus, a novel acoustic method, which is simple, robust, and capable of on-line to detect pressure of excitable gas vessel, is provided.

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Heat Exchanger Network Optimization Based on Inner Utility Placement Strategy BAO Zhongkai, CUI Guomin, CAO Chong, REN Jie, LI Menghong 2019, 36(6): 707-718.  DOI: 10.19596/j.cnki.1001-246x.7957 Abstract ( )   HTML ( )   PDF (6517KB) ( )   Traditional stage-wised superstructure (SWS) of heat exchanger network allowes that utilities are placed at ends of process streams, which restricts flexible development of network structures. Hence, a novel inner utility placement strategy is proposed, in which utilities could be placed at each stream branch in intermediate stages. An improved random walk algorithm with compulsive evolution with structure-protection strategy (SP-RWCE) is employed, in which a pseudo optimum generation strategy is presented to modify SP-RWCE, where pseudo optimums with evolution potentialities could be promoted and generated to accept protection and exploitation by expanding optimal total annual cost of individuals in long-term evolution stagnation. Optimization results of three benchmark cases are superior to reported values, all of them include inner utilities. It indicates that the modified SWS enlarges solution space, the improved SP-RWCE has stronger search ability, and the placement of inner utility could effectively reduce heat exchange areas.

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Remote Chaotic Synchronous Control of Inductive Load in Distributed Power Generation System ZHONG Guoxiang, WEI Duqu, ZHANG Bo 2019, 36(6): 719-725.  DOI: 10.19596/j.cnki.1001-246x.7931 Abstract ( )   HTML ( )   PDF (6135KB) ( )   A remote synchronous control method of large-scale inductive loads in distributed generation (DG) systems is proposed. Firstly, a mathematical model with networked coupling effect is established, in which permanent magnet synchronous generator (PMSG) is regarded as a node of power generation and permanent magnet synchronous motor (PMSM) is considered as a practical inductive load. Then, numerical simulations were made to analyze characteristic of remote synchronization of large-scale inductive loads in DG systems with different topology network structures that including star network, multilayer networks, random network and actual power system of IEEE39. It shows unexpectedly that a practical inductive load, through relaying action of generator unit, implements remote synchronous controlling, which is important for stability of synchronization of DG systems.

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A Model of Lunar Crater Section Topography Based on Smooth Factor and Legendre Polynomials ZHONG Zhen, ZHANG Teng, LEI Liangjian 2019, 36(6): 726-732.  DOI: 10.19596/j.cnki.1001-246x.7946 Abstract ( )   HTML ( )   PDF (5912KB) ( )   We propose a theoretical model of lunar crater to suppress Gibbs phenomenon by introducing a smooth-factor. The model makes crater close to its real morphology of a bowl. Considering revolving symmetry, we model merely its section topography and expand it in Legendre polynomials for simplification. It shows that the smooth-factor smoothes crater's boundary and avoids generation of oscillations in Gibbs phenomenon. For estimation of expansion coefficients, ASY shows advantage of stability than REC, particularly at super-high degrees. It provides a reference for selenophysical parameters estimation, especially for effective elastic thickness over craters.

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Acceptor and Donor Impurity States in Group V and VII Atom-doped Two-dimensional GeSe Monolayer XIONG Zonggang, DU Juan, ZHANG Xianzhou 2019, 36(6): 733-741.  DOI: 10.19596/j.cnki.1001-246x.7961 Abstract ( )   HTML ( )   PDF (9373KB) ( )   With first-principles calculations, we investigate characteristics of n-and p-type impurities by means of group V and VII atoms substituting selenide atoms in GeSe monolayer. It shows that formation energy increases with increasing impurity atomic size. For group V atom-doped GeSe monolayer systems, calculated transition levels indicate that F, Cl, Br or I dopant provides n-type deeper donor impurity states. However, for group VII atom-doped cases, N, P or As dopant provides n-type shallow acceptor impurity states. It provides theoretical reference for related experimental research.

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Electronic Structure and Magnetic Properties of Carbon-doped Mn3Ge ZHANG Xueying, FENG Lin 2019, 36(6): 742-748.  DOI: 10.19596/j.cnki.1001-246x.7968 Abstract ( )   HTML ( )   PDF (7791KB) ( )   Carbon doping in Mn3Ge was studied with first-principles calculations. Firstly, geometry optimization was performed on crystal structure of Mn3-xGeCx. It was found that the most stable doping position of carbon is at the center of regular octahedron. We studied total magnetic moment of Mn3-xGeCx. The total magnetic moment decreases firstly and then increases as carbon concentration increasing. We found that the total magnetic moment of Mn3GeC0.4 is almost zero, in which complete magnetic compensation can be realized. In addition, magnetic properties of Mn3GeC0.4 multilayers were investigated. Crystal structure of Mn3GeC0.4 multilayers with total magnetic moment close to zero is shown. It provides references for practical application of Mn3Ge.

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Theoretical Study on Hydrogen Storage Properties of Carbon Aerogels REN Juan, ZHANG Ningchao, LIU Pingping 2019, 36(6): 749-756.  DOI: 10.19596/j.cnki.1001-246x.7938 Abstract ( )   HTML ( )   PDF (27611KB) ( )   A model of microporous carbon is made with hybrid reverse Monte Carlo method based on Metropolis and Reverse Monte Carlo. We design shape and size of mesoporous model. Hydrogen storage capacities are studied with the method of grand canonical Monte Carlo. At 77K, hydrogen storage capacity of designed carbon aerogels is almost four times than that at room temperature. The highest hydrogen storage capacities of designed carbon aerogels are 11.12 wt% and 45.68 g·L-1 at 77K and 100 bar, respectively.