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25 July 2021, Volume 38 Issue 4 Previous Issue    Next Issue
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My story with the Chinese Journal of Computational Physics Qiang WANG 2021, 38(4): 379-380.  Abstract ( )   HTML ( )   PDF (554KB) ( )

Research Reports

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Application of JFNK Method in SN Transport Calculations Kaibo ZHU, Longfei XU, Liujun PAN, Huayun SHEN 2021, 38(4): 381-392.  DOI: 10.19596/j.cnki.1001-246x.8282 Abstract ( )   HTML ( )   PDF (2909KB) ( )   JFNK method is an efficient method for nonlinear problems. We consider two nonlinearities of neutron transport equation, the negative flux correction and the k-eigenvalue problem. The nonlinear problems are transformed into nonlinear residual equation form. And then we use JFNK method to solve them. We analyze impact of different constraints on the performance of JFNK, and compare JFNK method with NK method. LGMRES is used instead of restarting GMRES(m) method. Numerical results show that: ① Compared with SI method, JFNK has higher computational efficiency, even in the case of high scattering ratio; ② Difference approximation of Jacobian matrix-vector multiplication has no effect on the result, and the physics-based constraints are more efficient than standard mathematical constraints; ③ In addition, as an alternative to GMRES(m), LGMRES makes JFNK more efficient.

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A Monte-Carlo Simulation Method for Neutron Yield and Spectrum in (α, n) Reaction Bo YANG, Bin ZHONG, Qi XU, Li CHENG, Liujun PAN, Huayun SHEN 2021, 38(4): 393-400.  DOI: 10.19596/j.cnki.1001-246x.8287 Abstract ( )   HTML ( )   PDF (4818KB) ( )   A direct Monte-Carlo simulation method was developed to calculate neutron yield and spectrum in (α, n) reaction. It is based on continuous collision method, using stopping power computed by the program SRIM to simulate the moderation of α-particle and the ACE format of the nuclear data library JENDL/AN-2005 to calculate the neutron yield and spectrum in (α, n) reaction. Moreover, a (α, n)-simulator was developed based on the program NPTS. (α, n) neutron yields of light nuclides obtained in our simulations are consistent with experiments. In terms of (α, n) neutron spectrum, our results are in good agreement with experiments in the cases of B, F and O targets, while deviations are present in the cases of C, Al and Si.

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An IMEX Method for 2-D Radiation Hydrodynamics Yaoli FANG, Yi WANG 2021, 38(4): 401-417.  DOI: 10.19596/j.cnki.1001-246x.8312 Abstract ( )   HTML ( )   PDF (5872KB) ( )   We study a finite volume solver for radiation hydrodynamical models in two space dimensions. For nonlinearity of radiation pressure and radiation energy, it is not a trivial task to develop a numerical scheme for radiation hydrodynamics compared to Euler equations. The current strategy is that the convective part is solved by MUSCL-Hancock schemes, while the diffusive part is handled through an alternative form of TR/BDF2 (trapezoidal rule with second order backward difference formula) method. An asymptotic analysis for the grey nonequilibrium diffusion model in time is presented. Numerical experiments are given to show performance of the IMEX scheme.

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An Efficient Subspace Hybrid Algorithm Based on Direct Inversion in Iterative Subspace Algorithm Yonglong DING, Linping HU, Ruiqin ZHANG 2021, 38(4): 418-422.  DOI: 10.19596/j.cnki.1001-246x.8301 Abstract ( )   HTML ( )   PDF (633KB) ( )   A hybrid algorithm based on Direct Inversion in Iterative Subspace (DIIS) algorithm is developed for rapid solution of atomic and molecular Hartree-Fock equations. The improved algorithm uses mixing of subspaces with different sizes to increase the weight of Fock matrix closer to convergence, and the mixed Fock matrix is used as a starting point of new iteration. This algorithm reduces effectively the number of iterations in SCF process. Compared with DIIS algorithm before mixing, it is found that this algorithm is superior to the DIIS algorithm with two different subspaces, and the computational cost is effectively reduced.

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Prediction of Energy Confinement Time in Tokamak Based on Neural Networks Shuyu ZHENG, Jiazhen PENG, Xianmei ZHANG, Erbing XUE, Limin YU 2021, 38(4): 423-430.  DOI: 10.19596/j.cnki.1001-246x.8277 Abstract ( )   HTML ( )   PDF (4324KB) ( )   A neural network method in machine learning theory is used to approximate complex function of energy confinement time in tokamak according to the general approximation principle. A combined structure neural network is designed based on typical experimental data of domestic tokamak. Though a series of parameter adjustment tests, a set of parameters with best performance is obtained. Energy confinement times calculated with neural network model are compared with those by power exponential multiple linear regression. It shows that the neural network model has better accuracy and prediction performance. Noise resistance experiments show that the neural network model has certain anti-noise ability. Therefore, neural network is a favorable candidate for calibration or prediction of energy confinement time.

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Goos-Hanchen Shift of Electrons Based on Wigner Equation Shouguang CHENG, Yunqian YIN, Julian ZHONG, Kunyuan XU 2021, 38(4): 431-440.  DOI: 10.19596/j.cnki.1001-246x.8310 Abstract ( )   HTML ( )   PDF (6568KB) ( )   We studied transport properties of electrons in two-dimensional electron gas with Wigner equation. It was found that as electrons enter the barrier interface obliquely and are reflected, Goos-Hanchen shift similar to light waves presents. With Wigner equation we get transient evolution of electrons, with which we can calculate Goos-Hanchen shift and study trajectory of electrons inside the potential barrier as well. Compared with Goos-Hanchen shift obtained with the stable phase method, it is found that the interface reflection considering Goos-Hanchen shift has a certain retardation in time compared with geometric optical reflection, which is independent of incident angle, but increases with the increase of width. However, Goos-Hanchen shift of electrons is independent of barrier width and increases with the incident angle or incident energy. According to this, we propose an electron beam splitter model in which Gaussian wave packets with different initial kinetic energies inject into the input. As electron energy is below 0. 01 eV, about 85% of the electrons move to the second output, while as electron energy is above 0. 07 eV, about 85% of the electrons move to the first output.

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Experimental and Simulation Studies on Relation Between Graphene Thickness and Its Force-distance Curve Yong FANG, Yongzhong JIN, Jian CHEN, Hongxiang ZONG, Liying ZHANG 2021, 38(4): 441-446.  DOI: 10.19596/j.cnki.1001-246x.8270 Abstract ( )   HTML ( )   PDF (3862KB) ( )   Relation between graphene thickness and its force-distance curve is studied with atomic force microscope and first-principles calculations. Firstly, we located relatively smooth graphene sheets with atomic force microscope line-profile, and got three graphene samples with thickness of 0.57 nm, 0.90 nm and 1.30 nm. Then, we tested force-distance curves of the samples with multiple measurements. It shows that average value of adsorption forces of the samples are 0.30 nN, 0.32 nN and 0.34 nN, and the average value of desorption forces are 5.33 nN, 5.66 nN and 7.24 nN, respectively. It shows that both adsorption and desorption forces are increased with the increasing of graphene thickness, which implies that it could be an alternative method to measure thickness of graphene with force-distance curves provided by AFM. In order to explain the experimental result, we built platinum-graphene coherent interface models by combining Pt with one, two and three graphene layers, and calculated interface separation work with first-principles calculation. Simulation results showed that the interface separation work for the models are 10.0 eV·nm-2, 10.4 eV·nm-2 and 10.8 eV·nm-2, respectively. It is consistent with the trend of adsorption forces in experiment.

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First-principles Study of Electronic Structure and Optical Properties of ZnNb2O6 with Interstitial Atoms Yuxing YAN, Juexuan ZHANG, Shuai ZHENG, Fan WANG, Linqiang XIONG 2021, 38(4): 447-455.  DOI: 10.19596/j.cnki.1001-246x.8263 Abstract ( )   HTML ( )   PDF (10510KB) ( )   With first-principles calculation of density functional theory, we investigate influence of interstitial atoms Zn, Nb and O on photoelectric characteristics of ZnNb2O6 system. It shows that lattice distortion of the defect structure is related to atomic size. However, as defect structure is formed due to electronegative differences of the interstitial atoms, length of bonds in the system changes. Systems containing interstitial atoms Zn and Nb show characteristics of a degenerate n-type semiconductor. Nb interstitial atom system shows a strong dielectric effect. By contrast, the O interstitial atom system, which is characterised by a degenerate p-type semiconductor, barely contributes to photoelectricity. It shows that the Nb interstitial atom system has potential in practical application.

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Influence of Temperature, Enclosure and Ventilation on Radon Concentration Distribution in a Blind Roadway Zhankang YANG, Yi NIU 2021, 38(4): 456-464.  DOI: 10.19596/j.cnki.1001-246x.8295 Abstract ( )   HTML ( )   PDF (8658KB) ( )   With computational fluid dynamics and physical properties of radon, a three-dimensional steady-state transport model of radon in a blind roadway with a chamber is established. The control equation is calculated with software Fluent. Radon exhalation and decay in the inner wall of the roadway are realized with UDF. Wind field structure and radon concentration distribution in roadway are obtained. It shows that when the ventilation rate is constant, temperature has a significant effect on radon concentration. The higher the temperature in the roadway, the higher the radon concentration in the roadway. Radon concentration of the chamber is the greatest in the whole roadway. Compared with radon prevention enclosure, local ventilation is better for reducing radon. As pressure ventilation is adopted, radon concentration in the roadway increases from inside to outside.Improving ventilation rate of the tunnel reduces effectively radon concentration at the entrance of the tunnel, while it has little effect on radon concentration in the chamber.

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Stability Mechanism of Adsorbed Gas in Gas-Liquid Mixed Layer Qingqun LUO, Jiansu LI 2021, 38(4): 465-469.  DOI: 10.19596/j.cnki.1001-246x.8293 Abstract ( )   HTML ( )   PDF (6228KB) ( )   Experimental results show that gas dissolved in water can be adsorbed and accumulated on hydrophobic surface. There are two formations of adsorbed gas, nanobubbles and micro pancakes. Classical theory can't explain their stable existence. In this paper, molecular dynamics simulation was used to study the adsorption and agglomeration of gas. It is found that there exist a gas-liquid mixed layer coated on the adsorbed gas. The shape and characteristics of the mixed layer were studied and analyzed. It was found that the viscosity of gas-liquid mixture was greater than that of water and it inhibits gas diffusion.

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Robustness of Power Grids Structure and Braess Paradox Phenomenon: A Complex Network Theory Study Haoqian LI, Yanli ZOU, Shaoze ZHANG, Xinyan LIU, Shuyi TAN 2021, 38(4): 470-478.  DOI: 10.19596/j.cnki.1001-246x.8279 Abstract ( )   HTML ( )   PDF (4178KB) ( )   Based on complex network theory, a modified admittance model of a power system is constructed. Cascading failures of power grids are studied with topological and electrical characteristics of power grids. Cascading failures are made by removing transmission lines randomly. Effects of the number of nodes, average degree, number of power stations and distribution of power stations on system robustness are studied. Braess paradox phenomenon in the cascading failures of small world power grids is studied. It shows that robustness of a power grid is closely related to its topological structure. As the average degree is great, there exist several bifurcation points in the robustness curve of the nearest-neighbor coupled network and the small world network. In small world structure power grids, generally, the greater the average degree and the number of nodes, the more power stations, the better robustness of the power grid. Robustness of a power grid with distributed power stations is better than that with centralized distribution. In addition, the Braess phenomenon, which leads to the decrease of robustness due to the increase of network capacity, is explained.

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Structural Diversity Analysis and Improved Optimization Strategy of Heat Exchanger Networks Based on NW-NSM Model Zhengheng HAN, Guomin CUI, Weijie ZHANG, Qianqian ZHAO, Yuan XIAO, Guanhua ZHANG 2021, 38(4): 479-488.  DOI: 10.19596/j.cnki.1001-246x.8276 Abstract ( )   HTML ( )   PDF (2576KB) ( )   In optimizing heat exchanger networks by random walk algorithm with compulsive evolution (RWCE), individual structures become similar, which leads to a decline in population diversity and algorithmic global search capability. It becames difficult to optimize the structure of heat exchanger networks further. To explore similarity of individual structures, two evaluation indexes were established to measure similarity level of individual structures.It was found that the number of similar heat units in individual structure increases gradually and the difference of heat load between similar heat units decreases during the optimization process which resulting the evolution of individual structures in the same direction. Therefore, taking the improvement of population diversity as guiding direction, a repulsive-evolution strategy for heat units was proposed. It changes the direction of structure evolution and reduces the scale of similar structure through increasing the heat load gap of similar heat exchange units and promoting differential evolution of similar heat exchange units.Finally, 20SP and 15SP were used to verify effectiveness of the strategy. Total annual cost of the structure saved 12 105 ＄·a-1 and 52 535 ＄·a-1, respectively, compared with the optimal result in literature, which indicating that the strategy enhances the algorithmic global search capability effectively.

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An RWCE Algorithm for Heat Exchanger Network Optimization with Selective Acceptance of Imperfect Networks Strategy Qianqian ZHAO, Guomin CUI, Zhengheng HAN, Yuan XIAO, Yue XU 2021, 38(4): 489-497.  DOI: 10.19596/j.cnki.1001-246x.8300 Abstract ( )   HTML ( )   PDF (2370KB) ( )   As random walk algorithm with compulsive evolution is used to optimize heat exchanger networks, it promotes effectively structural evolution by accepting difference solution with certain probability. Non-greedy difference solution search mechanism is the key for the target function to jump out of local extremum. We analyze accept imperfect networks mechanism, explore different sources of imperfect networks of the optimization phase structure, and show the next year comprehensive cost change. We found that most acceptable solution return to the original structure in the subsequent optimization. There exist a lot of invalid parameter passing process. In this paper we present a selective acceptance of imperfect networks strategy, in which only difference solutions with new individuals are accpted based on an exponential increasing probability formula. Structure of new individual is protected to enhance its survival rate in structure. Finally, 9SP2 and 20SP examples were used for verification. The optimal results are better than those in literature, which shows feasibility of the strategy.

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Optimal Identification of Variable Resistance Coefficient of Heat Supply Network Based on Flow Measurement Points Lijuan TU, Enze ZHOU, Xuefei WU, Qi YANG, Xuefeng DING 2021, 38(4): 498-504.  DOI: 10.19596/j.cnki.1001-246x.8280 Abstract ( )   HTML ( )   PDF (1047KB) ( )   With popularity of heating metering system, system can be adjusted according to the change of load, and the resistance coefficient of pipe network change. Optimal identification of variable resistance coefficient is an effective means to understand the real-time operation of heating network. We present an optimal identification method for variable resistance coefficient of heat supply network based on flow observation data. Genetic algorithm is used to solve the problem. Relative error of the identification results is less than 5% in practical verification example. It shows that the method can obtain variable resistance coefficient of heating network with high accuracy when only flow observation data is available. It can provide guidance for the operation and regulation of heating systems.