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25 January 2021, Volume 38 Issue 1 Previous Issue    Next Issue
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Numerical Simulation on Nonlinear Evolution of Magneto-Rayleigh-Taylor Instability CAO Qiwei, XIAO Delong, YANG Xianjun, WANG Jianguo 2021, 38(1): 5-15.  DOI: 10. 19596/ j. cnki. 1001-246x. 8237 Abstract ( )   HTML ( )   PDF (10495KB) ( )   A 2D numerical simulation program is developed for nonlinear evolution of magneto-Rayleigh-Taylor instability(MRTI). Based on an ideal magnetohydrodynamic model, a 5th WENO scheme is employed to calculate MHD equations and a projection scheme is used to clean spurious magnetic field divergence. The method is validated with MRTI compared with theory of linear stability. It is shown that the vertical magnetic field suppresses evidently MRTI in both linear and nonlinear stages. The parallel magnetic field has weak effect on MRTI in linear stage. However, it reduces remarkably Kelvin-Helmholtz instability and overall instability in nonlinear regime. High order harmonic occurs in the nonlinear evolution of single mode, and many modes except fundamental modes and harmonic occur in the evolution of double modes. In MRT evolution of multi-mode seeds inverse cascade occur, which means that perturbations evolve from short wavelength to long wavelength in the nonlinear stage.

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Regular Domain Iterative Collocation Method in Space-Time Region for Moving Boundary Problems WANG Zhaoqing, QIAN Hang, LI Jin 2021, 38(1): 16-24.  DOI: 10.19596/j.cnki.1001-246x.8177 Abstract ( )   HTML ( )   PDF (2787KB) ( )   The governing equation of moving boundary problem is heat conductive equation. Its definite solution domain varies with time. Highly precision numerical algorithms on space-time domain were presented to solve 1+1 dimensional moving boundary problems. An initial moving boundary was given to form an irregular physical domain, and a regular region (a rectangular in Cartesian coordinate system) was chosen to cover the irregular physical domain. The heat equation was numerically computed with a barycentric interpolation collocation method (BICM) on space-time regular region with fixed and moving boundary conditions and initial condition to obtain numerical data in regular region. The data on moving boundary of physical domain were computed with barycentric interpolation. Then, the governing equation of moving boundary was solved with BICM to recover a new moving boundary. Repeat the process, numerical data of temperature and final moving boundary position were given. Numerical examples illustrate effectiveness and accuracy of the method.

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Bayesian Sparse Identification of Time-varying Partial Differential Equations HU Jun, LIU Quan, NI Guoxi 2021, 38(1): 25-34.  DOI: 10.19596/j.cnki.1001-246x.8189 Abstract ( )   HTML ( )   PDF (2804KB) ( )   In data-driven modeling, Bayesian sparse identification method with Laplace priors was found and confirmed to recover sparse coefficients of governing partial differential equations(PDEs) by spatiotemporal data from measurement or simulation. Verification results of Bayesian sparse identification method for various canonical models (KdV equation, Burgers equation, Kuramoto-Sivashinsky equation, reaction-diffusion equations, nonlinear Schr dinger equation and Navier-Stokes equations) are compared with those of Rudy's PDE-FIND algorithm. Very well agreement between these two methods shows Bayesian sparse method has strong identification capability of PDE. However, it is also found that the Bayesian sparse method is much more sensitive to noise, which may identify more extra terms. In addition, relatively small error variances of Bayesian sparse solutions are obtained and exhibit clearly the successful identification of PDE.

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Algorithm for Three-dimensional Free-surface Green Function in Frequency Domain at Finite Water Depth and Its Derivatives XU Qianlong, LI Ye 2021, 38(1): 35-46.  DOI: 10.19596/j.cnki.1001-246x.8187 Abstract ( )   HTML ( )   PDF (3155KB) ( )   Numerical evaluation of three-dimensional free-surface Green function in frequency domain and its partial derivatives is a main difficulty in hydrodynamic analyses of marine structures. We proposed two improvements in traditional algorithms of Green function and its partial derivatives. Firstly, we transformed series expressions of Green function and its partial derivatives into expressions that were applicable in numerical evaluation. The improved algorithm is able to prevent series solutions from numerical distortion. Secondly, we improved Gauss-Laguerre algorithm to make sure it is effective at high frequencies and in large water depths. Numerical results indicate that the algorithms improved effectively numerical accuracy of Green function and its partial derivatives. It is significant for heave radiation problems of floating or submerged bodies with large draft at high frequencies.

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Numerical Simulation of Detonation Wave Motion Based on Mie-Grüneisen Equation of State WU Zongduo, YAN Jin, ZONG Zhi, PANG Jianhua, GAO Yun 2021, 38(1): 47-56.  DOI: 10.19596/j.cnki.1001-246x.8190 Abstract ( )   HTML ( )   PDF (5995KB) ( )   Based on C-J (Chapman-Jouguet) theory different reference states of gaseous detonation products and unreacted explosives in detonation problem are considered. According to these reference states, specific Mie-Grüneisen EOS (equation of states) is selected. As chemical reaction process is neglected, a zero-thickness section of guided shock wave exists as an interface in front of the detonation wave. In numerical simulation, evolution of detonation wave includes two parts:Propagation of wave section, as well as interaction with unreacted medium. In the propagation process, speed is defined as the constant detonation speed, and detonation products forms instantly. In the interaction process, Mie-Grüneisen mixture model is employed to simulate continuous impact of detonation wave. With Mie-Grüneisen EOS, as well as the Mie-Grüneisen mixture model, motion of detonation wave is simulated well. Comparing with related theoretical data and numerical results good performance was found.

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Natural Convection in Triangular Cavity Filled with Nanofluid: Lattice Boltzmann Simulation YUAN Junjie, YE Xin, SHAN Yanguang 2021, 38(1): 57-68.  DOI: 10.19596/j.cnki.1001-246x.8170 Abstract ( )   HTML ( )   PDF (14587KB) ( )   Lattice Boltzmann method was used to study natural convection in an isosceles right-angled triangular cavity filled with water-alumina nanofluids. Effects of Rayleigh number, particle volume fraction, heat source location and other factors on convective heat transfer are discussed, as well as effects of nanofluid models on simulation results. It shows that at low Rayleigh numbers, as the heat source moves upward on the left wall, the heat transfer efficiency gradually increases. At high Rayleigh number (Ra=106), the opposite phenomenon was observed. In a single-phase nanofluid model, simulation results show that the average Nusselt number ratio of the hot wall surface increases approximately linearly with the increase of volume fraction. An improved nanofluid model results show that the average Nusselt number ratio increases with the increase of volume fraction, but the slope of the average Nusselt number ratio decreases gradually. The heat transfer efficiency simulated with the improved model is higher than that of the single-phase model. This is because the improved model considers force between particles and heat transfer, which exists in actual situation.

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Lattice Boltzmann Simulation of Formaldehyde Adsorption by Activated Carbon FENG Lingling, XU Hongtao, WANG Di, LUO Zhuqing 2021, 38(1): 69-78.  DOI: 10.19596/j.cnki.1001-246x.8185 Abstract ( )   HTML ( )   PDF (23161KB) ( )   We adopted LBGK model of heat-mass coupling in lattice Boltzmann method to simulate double diffusion mixed convection, fluid-solid conjugate heat transfer and adsorption process in an enclosure filled with spherical activated carbon with real physical parameters at pore scale. D2Q9 model was used to describe velocity and temperature fields, and D2Q5 for concentration fields, respectively. Impact of activated carbon particle size, porosity and particle arrangement on entire dynamic adsorption performance was investigated. It shows that with increased activated carbon particle size the time to approach steady is increased and the adsorption rate is moderated at porosity 0.85. At particle diameter 0.43 mm, the adsorption rate is the highest and the adsorption time is the shortest. Transient adsorption capability and time consumption to equilibrium were independent of filling rate. Compared with those of line and dislocation arrangement of activated carbon particles, transient adsorption capability of random and non-adherent arrangement is better.

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Weighted Differential Evolution Algorithm for Heat Exchanger Network Synthesis QU Yuecheng, CHEN Jiaxing, CUI Guomin 2021, 38(1): 79-88.  DOI: 10.19596/j.cnki.1001-246x.8182 Abstract ( )   HTML ( )   PDF (1167KB) ( )   Considering that differential evolution algorithm (DE) is sensitive to the selection of control parameters and population diversity's decrease leads to the loss of power as DE is applied in heat exchanger network (HEN), a weighted differential evolution algorithm (WDE) is applied in this study. Effectiveness of the algorithm has been proved in continuous variable optimization. This study applies it in mixed integer nonlinear programming problems of HEN without controlling parameters. Three cases ranging from small to medium testify the effectiveness of WDE. By setting up equal mutation factor and analyzing its distribution, we explore WDE's optimization mechanism which provides reference for algorithm improvements.

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Improved RWCE Algorithm with Integer/Continuous Variable Separation Optimization Strategy to Protect Efficient Structure ZHANG Dingtai, CUI Guomin, LI Wanzong, XU Yue 2021, 38(1): 89-98.  DOI: 10.19596/j.cnki.1001-246x.8188 Abstract ( )   HTML ( )   PDF (3710KB) ( )   As random walk algorithm with compulsive evolution is used to optimize heat exchange network, the structure with lower annual cost in continuous variable evolution stage is destroyed by integer variable evolution operation. As a result, the structure formed after the evolution of continuous variables can not play its full advantages, which restricts the evolution of continuous variables. We propose an optimization strategy of separating continuous variables and integers to protect the effective structure, thereby, protecting structures with development potential and reducing the combined annual cost further. In example study our result is better than that in literature. Precision of the algorithm is improved, and validity of the strategy is verified.

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Numerical Simulation of Heat Transfer of Synthetic Oil-based Nanofluids in a Parabolic Trough Solar Receiver ZHOU Lu, MA Honghe 2021, 38(1): 99-105.  DOI: 10.19596/j.cnki.1001-246x.8183 Abstract ( )   HTML ( )   PDF (5049KB) ( )   A computational fluid dynamics numerical simulation was performed on Al2O3-synthetic oil nanofluids to study heat transfer in a trough solar receiver. Different nanofluid thermal conductivity models were tried. Calculated Nusselt numbers were compared with results of semiempirical model models. It was found that the thermal conductivity model based on Brownian motion predicted heat transfer characteristics well. The relative motion between nanoparticles and base fluid was found important in enhancing heat transfer. Further volume fraction analysis shows that the nanoparticles improved significantly average heat transfer coefficient, which indicates that nanofluids have great potential in solar collector applications.

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Structural, Electronic and Thermodynamic Properties of Heavy-fermion Superconductivity PuMGa5 (M=Co,Rh): First Principles Study LIU Tao, YANG Ziyi, CHEN Yuqing, GAO Tao 2021, 38(1): 106-112.  DOI: 10.19596/j.cnki.1001-246x.8178 Abstract ( )   HTML ( )   PDF (3588KB) ( )   Crystal structure, elasticity, electronic properties, phonon spectra and thermodynamic properties of PuCoGa5 and PuRhGa5 were studied with first-principles PBEsol+U method. PBEsol+U method is used to account for strong on-site Coulomb repulsion among localized Pu 5f electrons. Our results shown that the ground state properties, including lattice parameters and atomic sites, are agree well with experimental data. Mechanical properties and phonon dispersion indicated that the ground state structures (at zero temperature and pressure conditions) of PuCoGa5 and PuRhGa5 are stable. In particular, 5f electrons of PuCoGa5 and PuRhGa5 have obvious localization near Fermi level, and the localization of 5f electrons of PuRhGa5 is obviously stronger than that of PuCoGa5, which may be the reason that the superconducting critical transition temperature Tc of PuCoGa5 is higher than that of PuRhGa5. In addition, thermodynamic properties of PuCoGa5 and PuRhGa5 include Helmholtz free energy, entropy, internal energy and isovolume molar heat capacity have similar dependence on temperature.

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Giant Vortex States of Bose-Einstein Condensate in a Harmonic Plus Gaussian Trap WANG Shusong, ZHANG Suying 2021, 38(1): 113-119.  DOI: 10.19596/j.cnki.1001-246x.8174 Abstract ( )   HTML ( )   PDF (5530KB) ( )   We study ground states of a Bose-Einstein condensate in a harmonic plus Gaussian trap. It is found that as the condensate forms a giant vortex the number of vortices is equal to the average angular momentum and the density distribution of the ground state is the same as that of angular momentum. We draw a conclusion that the ground state with giant vortex is the eigen state of angular momentum. As the potential well changes from an isotropy toroidal trap to an anisotropic toroidal trap,the ratio of the average angular momentum of the condensates to the number of vortices decreases slowly from 1, and then drops rapidly and stays near 0.5. Characteristics of density distribution of condensate and angular momentum distribution are given and explanation is shown.

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Influence of Dipolar Interaction on Domain Distribution in a Spin-Orbit Coupled f=1 Spinor Condensate LI Yushan 2021, 38(1): 120-126.  DOI: 10.19596/j.cnki.1001-246x.8203 Abstract ( )   HTML ( )   PDF (1848KB) ( )   A spin-1 dipolar Bose-Einstein condensate with spin-orbit coupling (SOC) in a quasi-one-dimensional harmonic trap is studied. We focus on ground state domain distribution calculated numerically with spinor Gross-Pitaevskii equation. It was found that the domain structures are greatly affected by dipole-dipole interactions (DDIs). Spatial symmetry is broken and transition behaviors of distribution pattern are shown as SOC strength and magnetization are increased.