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25 September 2018, Volume 35 Issue 5 Previous Issue    Next Issue

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Theoretical Ejecta Model for Elastic-Plastic Solids Based on Richtmyer-Meshkov Instability HE Anmin, LIU Jun, SHAO Jianli, LIU Chao, WANG Pei 2018, 35(5): 505-514.  DOI: 10.19596/j.cnki.1001-246x.7721 Abstract ( )   HTML ( )   PDF (4321KB) ( )   Hydrodynamic simulations are performed to study Richtmyer-Meshkov instability (RMI) and material ejection at a metal-vacuum interface using a 2D multi-component elastic-plastic hydrodynamic Eulerian code. Effect of material strength on instability development of roughened surface is analyzed, and relationship between amount of ejected material and saturated bubble amplitude is revealed. Finally, based on RMI theory for elastic-plastic solids, theoretical models to describe critical condition of ejecta formation, total amount and maximum velocity of ejecta from unmelted metals are established.

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Reduced Basis Finite Element Method for Fast Solution of Parameterized Partial Differential Equations CHEN Gong, WANG Yizheng, WANG Ye, ZHANG Chunyu 2018, 35(5): 515-524.  DOI: 10.19596/j.cnki.1001-246x.7712 Abstract ( )   HTML ( )   PDF (6451KB) ( )   For problems that can be described by parameterized partial differential equations, reduced basis finite element constructs basis functions on top of typical high-fidelity solutions and thus greatly reduces number of unknowns. Principles of the method is introduced and favorable features are demonstrated through heat conduction problem and neutron diffusion problem. It shows speedup of three orders of magnitude during online stage.

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Weighted Essentially Non-oscillatory Schemes on Unstructured Quadrilateral Meshes ZHAO Fengxiang, PAN Liang, WANG Shuanghu 2018, 35(5): 525-534.  DOI: 10.19596/j.cnki.1001-246x.7811 Abstract ( )   HTML ( )   PDF (5262KB) ( )   A third-order weighted essentially non-oscillatory (WENO) scheme is developed for hyperbolic conservation laws on unstructured quadrilateral meshes. As starting point of WENO reconstruction, a general stencil is proposed for any local topology on quadrilateral meshes. With selected stencil, a unified linear scheme was constructed. However, very large weights and non-negative may appear, which leads the scheme unstable even for smooth flows. An optimization approach is given to deal with very large linear weights on unstructured meshes. Splitting technique is considered to deal with negative weights obtained by optimization approach. Non-linear weight with a new smooth indicator is proposed as well. With optimization approach for very large weights and splitting technique for negative weights, the current scheme becomes more robust. Numerical tests are presented to validate accuracy. Expected convergence rate of accuracy is obtained. And absolute value of error is not affected by mesh quality. Numerical results for flow with strong discontinuities are presented to validate robustness of the WENO scheme.

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Application of SN Adjoint Function on Automated Variance Reduction for Monte Carlo Particle Transport Calculation LIU Cong, ZHANG Bin, ZHANG Liang, ZHENG Junxiao, CHEN Yixue 2018, 35(5): 535-544.  DOI: 10.19596/j.cnki.1001-246x.7735 Abstract ( )   HTML ( )   PDF (2911KB) ( )   Three-dimensional adjoint transport calculation module was integrated into SN transport code ARES in which automated variance reduction parameters are generated based on consistent adjoint driven importance sampling method to accelerate calculation of MCNP5. It shows that automated variance reduction parameters are effective to improve MC calculational efficiency and to produce unbiased statistical results. Automated variance reduction technique with SN function estimates particle importance more economically and accurately. It avoids obstacles of manual estimation and could be applied for MC simulation of large-scale, complicated shielding problems.

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Low Dissipation Multidimensional Limiter for Unstructured Mesh AI Bangcheng, ZHANG Liang, CHEN Zhi 2018, 35(5): 545-553.  DOI: 10.19596/j.cnki.1001-246x.7734 Abstract ( )   HTML ( )   PDF (7088KB) ( )   Based on maximum principle analysis together with definitions of restriction position and restriction stencil, a unification of multidimensional limiter construction process for unstructured mesh was presented. To enhance flow resolution, a new type of multidimensional limiter was developed. It was compared with several conventional limiters. It shows that due to less restriction in gradient reconstruction process, the new limiter is less dissipative and has better resolution for complex flow with shock and contact discontinuity interaction.

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Performance Optimization of 3D Pseudopotential Multi-Relaxation-Time Lattice Boltzmann Model on GPU PENG Hao, SHAN Minglei, ZHU Changping, YAO Cheng 2018, 35(5): 554-562.  DOI: 10.19596/j.cnki.1001-246x.7698 Abstract ( )   HTML ( )   PDF (3508KB) ( )   Pseudopotential model of lattice Boltzmann method is partially non-local for pseudopotential calculation with coupling of lattices, which leads to synchronization of threads in parallel implementation process. Besides, it uses a large number of registers and much time of data access operations when access global memory in calculation process. They lead to low computational efficiency. In this paper, a multi-relaxation-time(MRT) 3D pseudopotential model with D3Q15 lattice is adopted as an example to investigate performance of parallel computing based on GPU. To address limitation of parallel computing of pseudo-potential model, efficiency of reading and writing of global memory is improved by using merge access method. To improve efficiency of grids retrieving data which are in boundary of lattice, a "Directional Transfer" algorithm is proposed. The role of computing resource configuration is investigated with different sizes of block, and optimal resource configuration scheme is obtained.

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Numerical Investigation of Dynamic Derivative for Airframe/Propulsion Integrative Vehicles CHEN Qi, XIE Yufei, YUAN Xianxu, CHEN Jianqiang 2018, 35(5): 563-570.  DOI: 10.19596/j.cnki.1001-246x.7733 Abstract ( )   HTML ( )   PDF (4997KB) ( )   Applicability of numerical prediction method of dynamic derivatives is studied with forced oscillation method and free oscillation method on the airframe/propulsion integrative vehicle with and without fairing. Effect of parameters on dynamic derivative prediction in forced oscillation method such as time step and oscillation frequency is analyzed in detail. It shows that forced oscillation method is well applied in dynamic derivative prediction of integrative vehicle with internal and external flow, while parameters select of time step, computational time and oscillation frequency are quite different from external-flow-only vehicle. Dynamic derivatives by free oscillation method are in agreement with results with forced oscillation method on external-flow-only vehicle. There is a difference about 50% on integrative vehicle with internal and external flow. Origin and mechanism of differences in two methods need to be deeply studied.

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Lattice Boltzmann Simulation of Flow and Mass Transfer in Membrane Bioreactor YANG Yanxia, LI Jing 2018, 35(5): 571-576.  DOI: 10.19596/j.cnki.1001-246x.7732 Abstract ( )   HTML ( )   PDF (4894KB) ( )   Effect of biofilm structure on bioreaction as well as flow and mass transfer are investigated with lattice Boltzmann method (LBM) on meso-scale. Porous construction of biofilm is regenerated by Quartet Structure Generation Set (QSGS) method, and LB method is coupled with multi-block model to obtain detail information and save computational cost. It indicates that properly increasing porosity benefits mass transportation between main region and biofilm, and hence improve substrate consumption efficiency under condition of stable biofilm structure. At given porosity of biofilm, changing growth construction of biofilm can also promote mass transfer between inner and outer of biofilm, leading to higher substrate consumption efficiency.

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Effect of Surfactant Concentration Distribution on Film Drainage YANG Shaodong, YE Xuemin, LI Chunxi 2018, 35(5): 577-586.  DOI: 10.19596/j.cnki.1001-246x.7705 Abstract ( )   HTML ( )   PDF (1197KB) ( )   Drainage of vertical foam film containing insoluble surfactant is investigated with consideration of combined effect of disjoining pressure and surface viscosity. Lubrication theory is applied to establish evolution equations of film thickness, surface concentration of insoluble surfactant and surface velocity. Film evolution under different initial surfactant concentration and gradient are simulated numerically. It shows that in the absence of initial surfactant concentration, film drainage process is very short and tends to break quickly, whereas lifetime of foam film is prolonged by adding surfactant to film surface. Under relatively low surfactant concentration, Marangoni effect is not enough to defeat gravity drainage, and "black film" cannot exist stably. Increasing concentration of initial surfactant reduces surface velocity of film and strengthens rigidity of film surface, and film stability is enhanced. Influence of concentration gradient of surfactant on drainage process is highlighted with evident reduction of surface velocity in initial stage of film drainage.

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Application of POD Reduced-order Model in Heat Transfer Performance of Flat Tube Bank Fin Heat Exchanger WANG Ye, WANG Yi, HU Wenting, WANG Liangbi 2018, 35(5): 587-596.  DOI: 10.19596/j.cnki.1001-246x.7746 Abstract ( )   HTML ( )   PDF (9842KB) ( )   Reduced-order model of proper orthogonal decomposition method (POD) was established to analyzed performance of fluid flow and heat transfer in flat tube bank fin heat exchanger. Numerical results of POD were compared with those of FVM. It indicates that average relative error between POD results and FVM results is no more than 5.7% while computational speed is improved 164.78-2021 times. Conclusion is of theoretical meaning for optimizing heat exchanger structure and running mode in engineering.

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Numerical Simulation of Magnetohydrodynamic Duct Flow with Sudden Expansion MAO Jie, XIANG Kai, WANG Yanli, WANG Hao 2018, 35(5): 597-605.  DOI: 10.19596/j.cnki.1001-246x.7711 Abstract ( )   HTML ( )   PDF (2062KB) ( )   Liquid metal flow subject to a uniform magnetic field vertical to streamwise direction confined in a rectangular duct with 45° and 90° sudden expansion, and electrically conducting walls is numerically studied using magnetohydrodynamic (MHD) flow solver developed in OpenFOAM environment. Velocity distribution, induced electric current, pressure gradient and three-dimensional MHD effect are analyzed in detail. It shows that as external magnetic field is parallel to direction of duct expansion, velocity distribution is better in 45° sudden expansion duct than that in 90° expansion duct since there is no vortex at the expansion. With Hartmann number increasing, high velocity jets and intensive induced electric current cause a strong instability at the expansion. Instability grows to upstream of the expansion through induced electric current. As external magnetic field is vertical to expansion direction, induced electric current along streamwise direction is significant. With Hartmann number increasing, MHD pressure drop increases remarkably. Dimensionless pressure drop in fully developed duct is almost the same in different expansion duct as direction of applied magnetic field and Hartmann number are the same.

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Topological Chern Numbers in a Two-dimensional Triangular-Lattice YU Hualing, GAO Yu, ZHAI Zhangyin 2018, 35(5): 606-612.  DOI: 10.19596/j.cnki.1001-246x.7696 Abstract ( )   HTML ( )   PDF (7847KB) ( )   We investigate numerically topological Chern number in a two-dimensional triangular-lattice with three bands, considering tight-binding Hamiltonian. Energy spectrum is obtained with Fourier transform and Hall conductance is calculated using Kubo formula. It is found that Chern number of energy band is modulated by next nearest neighbor hopping integral t'.Three bands own Chern numbers in sequence, {-4, 5,-1} at t'=1/2, {2,-4, 2} at t'=-1/2 and {2,-1,-1} at t'=±1/4, which leads to Hall plateaus in sequence, {-4, 1}e2/h, {2,-2}e2/h and {2, 1}e2/h, respectively. Peaks of density of states (DOS) are located at jumps of Hall conductance. Energy gap (DOS=0) gives width of corresponding Hall plateau. If energy band becomes more flat, corresponding peak of DOS becomes higher and sharper, and jump of Hall conductance becomes steeper.

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First-Principles Study on Structure and Properties of Graphite Intercalation Compound HfC2 TAN Junhua, PENG Junhui 2018, 35(5): 613-618.  DOI: 10.19596/j.cnki.1001-246x.7718 Abstract ( )   HTML ( )   PDF (4767KB) ( )   At high pressures, a new graphite intercalation compound (GIC) HfC2 was predicted. We calculate structure and properties of HfC2 at 0 GPa using first-principles method. Lattice parameters of HfC2 with geometrical optimization based on GGA-PBESOL, GGA-PW91 and LDA are almost the same. With phonon dispersion curve and elastic constant, dynamical and mechanical stability of structure were verified, respectively, which meant that HfC2 could exist stability at 0 GPa. Calculated bulk modulus and shear modulus of HfC2 are 265 GPa and 118 GPa, respectively, and Pugh ratio k<0.57. With analysis of electron density and density of states, Hf-C and C-C bond showed covalent, metallically. That is reason why it has high bulk modulus and ductility. At last, we calculated bond length, bulk modulus, shear modulus and Pugh ratios of HfC2 in pressures ranging from 0 GPa to 500 GPa.

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Spectrum and Dissociation Characteristics of Methyl Bromide in External Electric Field WANG Xiaoqing, LIU Yuzhu, YIN Wenyi, LI Jinhua 2018, 35(5): 619-625.  DOI: 10.19596/j.cnki.1001-246x.7736 Abstract ( )   HTML ( )   PDF (2892KB) ( )   B3LYP/6-311++g(d,p) method is adopted to optimize ground state structure of CH3Br molecule. Bond length, energy gap and dissociation potential energy surface of CH3Br molecule in external electric field (0-0.05 a.u.) are studied. It shows that direction and magnitude of applied electric field is of great significance to molecular structure and potential energy surface. With negative electric field (C-Br bond direction) increases from 0 to 0.05 a.u., bond length of C-Br bond decreases first and then increases. Bond length of C-H bond increases gradually. Molecular energy gap EG decreases gradually. Vibrational frequency of C-Br bond increases while IR vibration frequency decreases. It is found that potential energy of methyl bromide molecule decreases and dissociation barrier decreases, which indicating that CH3Br molecule is easy to be excited and dissociated in external electric field.

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Collision Dynamics of CO(X1∑+) Molecule with Be Atom at Cold and Ultracold Temperatures HAN Yulong, SUN Hui, SUN Jinfang, CHENG Jun, FENG Eryin 2018, 35(5): 626-630.  DOI: 10.19596/j.cnki.1001-246x.7717 Abstract ( )   HTML ( )   PDF (2698KB) ( )   With accurate interaction potential surface, Be-CO Hamiltonian equation is solved by numerical methods. Cold collision dynamics for Be atom and CO molecule is investigated by quantum scattering calculations. Influence of applying electric field on elastic and inelastic collisional cross-sections of low-field-seeking state at cold and ultracold temperatures are explored. It provides theoretical support for experimental sample molecules.