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25 September 2022, Volume 39 Issue 5 Previous Issue    Next Issue
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A Diffused Interface Type Mass Fraction Model with Time Steps Saving Mixture Rules Zongduo WU, Jin YAN, Zhi ZONG, Jianhua PANG 2022, 39(5): 510-520.  DOI: 10.19596/j.cnki.1001-246x.8453 Abstract ( )   HTML ( )   PDF (2128KB) ( )   We focused on effects of treatment of mixture model as the interface is in a diffused style. In order to seek a convenient way to treat the interface and keep strong adaptability, Mie-Grüneisen mixture model is used. The original Mie-Grüneisen mixture model in terms of volume fraction is modified. In the model, the mass fraction is employed as color function, and the optimization of sound speed is achieved with the help of the density of fluid components. The optimized sound speed reduces time steps under the convergence mechanism and promotes efficiency of the calculation. Meanwhile, the introduction of limiter make the pressure curves stable. Numerical tests show that the modified mass fraction model reduces the number of time steps under different numerical schemes. Effects of this reduction depend on physical conditions of case.

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Numerical Simulation of Debris Motion from a Near-space Nuclear Detonation Li LIU, Shengli NIU, Jinhui ZHU, Yinghong ZUO, Honggang XIE, Peng SHANG 2022, 39(5): 521-528.  DOI: 10.19596/j.cnki.1001-246x.8492 Abstract ( )   HTML ( )   PDF (3546KB) ( )   Based on conservation of mass and momentum, a fluid dynamics model of debris motion from a near-space nuclear detonation is established. Many influence factors are considered, such as energy dissipation, air density as a function of height, gravity, increasing air temperature caused by X-ray deposition and radiation cooling. A computation program is developed. The expansion and upward motion of debris in TEAK and ORANGE tests are calculated. Evolution of typical parameters such as central height, maximum horizontal radius, ascending velocity, and shape of debris are given. They are in accordance with experimental data. The model provides delayed radiation source parameters for ionospheric effect and artificial radiation band effect.

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Stability Analysis of Compressible Viscous Circular Jet Hua ZHANG, Minghui YANG 2022, 39(5): 529-536.  DOI: 10.19596/j.cnki.1001-246x.8479 Abstract ( )   HTML ( )   PDF (1051KB) ( )   Mechanism of splitting and atomization of compressible viscous 。ular jet was studied with linear stability theory. The dispersion equation for disturbance development of liquid jet surface in space mode was obtained and verified. It shows that the influence of liquid compressibility on instability of liquid jet is very small. With the increase of Mach number of liquid, the maximum growth rate of disturbance wave is basically unchanged. Effect of gas compressibility on jet stability increases with the increase of gas Mach number. With the increase of Reynolds number and Weber number, the effect of viscous force and surface tension on jet stability decreases gradually. With the increase of gas-liquid density ratio, the effect of aerodynamic force on jet stability is basically unchanged.

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Single Bubble Dynamics in Pool Boiling Under Uniform Electric Field: LBM Simulation Liubin ZHANG, Yanguang SHAN, Zhicheng RONG 2022, 39(5): 537-548.  DOI: 10.19596/j.cnki.1001-246x.8475 Abstract ( )   HTML ( )   PDF (6906KB) ( )   Lattice Boltzmann method (LBM) is used in a coupled perfect dielectric model and liquid-vapor phase-change model to simulate nucleation, growth, and separation process of a single bubble in pool boiling under uniform electric field. Effects of gravitational acceleration and electric field on bubble dynamics are studied in detail. It shows that under same gravitational acceleration, with the increase of electric field intensity, the bubble departure diameter decreases and the bubble release frequency increases, and the averaged wall heat flux increases. With the decrease of gravitational acceleration, the averaged wall heat flux decreases as well, and the electric field has significant influence on the bubble release frequency. In addition, the bubble deforms in a uniform electric field, and it stretches along the direction of electric field to become slender. The electric field intensity is linearly related to the aspect ratio and height of the bubble.

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Entropy Generation in Double-diffusive Natural Convection in a Square Porous Enclosure: Lattice Boltzmann Method Jiaxin LIU, Lin ZHENG, Beihao ZHANG 2022, 39(5): 549-563.  DOI: 10.19596/j.cnki.1001-246x.8484 Abstract ( )   HTML ( )   PDF (31310KB) ( )   A Darcy-Brinkman-Forchheimer model based lattice Boltzmann method is conducted to the simnlation of double-diffusive natural convection in an inclined square porous enclosure. Effects of porosity (0.2≤ε≤0.9), Rayleigh number (103≤Ra≤106), buoyancy ratio (-4≤Br≤2) and inclination angle (0°≤γ≤80°) on the local and total entropy generation are systematically investigated. It shows that as ε and Ra increased, peaks of local entropy generation due to heat transfer, fluid friction and mass transfer grow higher and the contribution of fluid friction to total entropy generation increased prominently. In addition, the clear fluid term has more influence on fluid friction entropy generation. Br=-1 is a critical value for the change of local entropy generation distribution. At the same time, the total entropy generation tends to zero. With the increase of inclination angle, the high entropy generation region of local fluid friction entropy generation moves clockwise. The maximum entropy caused by clear fluid term and Darcy dissipation term appears at 40° and 60°, respectively.

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Model-reduced Autoregressive Neural Network for Parameter Inversion Cong XIAO, Shicheng ZHANG, Xinfang MA, Tong ZHOU, Tengfei HOU 2022, 39(5): 564-578.  DOI: 10.19596/j.cnki.1001-246x.8473 Abstract ( )   HTML ( )   PDF (12763KB) ( )   We present an architecture of projection-based autoregressive neural network (aNN) where model-reduced adjoint is efficiently produced with the help of an easy-to-use auto-differentiation (AD) tool in deep-learning frameworks. Analogy to reduced-order tangent linear model, a projection-based aNN (POD-aNN) structure is proposed to accelerate the construction of adjoint model based on reduced subspace. The POD-aNN consists of a dimensionality reduction and an intermediate non-linear transition unit which is used to project a state system to a low-dimensional subspace and approximate time-varying evolution of system states in low dimension, respectively. The adjoint model is run in reduced space with negligible computational cost and memory requirement. Once the gradient is obtained in reduced space it is projected back in full space and then the inversion modeling is conducted. Characteristics and performance of the method are illustrated with two sets of inverse modeling experiments in a synthetic 2D fluid flow model with random spatially dependent parameters. It shows that the proposed POD-aNN obtains satisfactory results with significantly reduced computational cost and, therefore, demonstrates promising applicability to practical reservoir models.

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Coupling Strength Allocation Strategy in Power Grids Based on Complex Network Theory Zheng GAO, Yanli ZOU, Junwan HU, Gaohua YAO, Tanghuimei LIU 2022, 39(5): 579-588.  DOI: 10.19596/j.cnki.1001-246x.8500 Abstract ( )   HTML ( )   PDF (10062KB) ( )   To explore allocation strategy of network coupling strength for improving performance of power grids, we analyze synchronizability of power grids by using critical synchronization coupling strength, and compare robustness of power grids by imposing disturbance power on network nodes. It is found that local topological structure and power of nodes in power grids restrict the local synchronizability of nodes. In general, the greater the power and the smaller the degree value of the node, the weaker its local synchronizability is. And it is more difficult for the node to reach a local synchronization state with its neighbors. Based on this, a non-uniform distribution strategy of network coupling strength is proposed. Keep the total coupling strength the same, we increase the coupling strength between nodes with weak local synchronizability, and reduce the coupling strength between nodes with strong local synchronizability. It shows that this method optimizes synchronizability of the network and enhance robust performance of power grids to a certain extent.

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Magnetic Induction HR Neuron with Hidden Extreme Multistability and Its Circuit Implementation Lihong TANG, Zongmei HE, Yanli YAO 2022, 39(5): 589-597.  DOI: 10.19596/j.cnki.1001-246x.8476 Abstract ( )   HTML ( )   PDF (10450KB) ( )   With a magnetically controlled memristor to describe the coupling between membrane potential and magnetic flux, a magnetic induction HR neuron model is established. Its complex dynamical behavior is revealed with dynamic analysis methods including bifurcation diagrams, Lyapunov exponent spectrum, time sequences, and phase plots. It shows that the magnetic induction HR neuron has no equilibrium points while it can generate infinite hidden chaotic attractors with same topologies and different positions. Namely, the neuron model has the characteristic of hidden extreme multistability. Moreover, an analog equivalent circuit of the magnetic induction HR neuron is designed. Numerical simulations is verified with PSIM circuit simulations.

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Computer Simulation of Photomask-induced Self-assembly of Polymer/Nanoparticle Blends Wenting WANG, Huijin YIN, Junxing PAN, Jinjun ZHANG 2022, 39(5): 598-608.  DOI: 10.19596/j.cnki.1001-246x.8467 Abstract ( )   HTML ( )   PDF (18148KB) ( )   Self-assembly behavior of photomask-induced polymer/nanoparticle mixing systems was studied with cell dynamic system method based on Ginzburg-Landau theory. Effects of reaction rate, number of masks, composition ratio, concentration of nanoparticles and compatibility with polymer on morphology and structure of the system were discussed in detail. A two-dimensional phase diagram of the system structure and related parameters was constructed. Interaction mechanism and rules of components in the blend system and photomask regulation were obtained.A simple method was obtained to control pattern structure formation and transformation of the composite system. It provides references for the preparation of novel high-performance micro/nano materials.

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First-Principles Calculations of Electronic and Optical Properties of Ge Doped AlN Qiang LUO, Zhiwei MA, Guanzhen JIANG, Jiangfeng ZOU, Yi QIU 2022, 39(5): 609-616.  DOI: 10.19596/j.cnki.1001-246x.8483 Abstract ( )   HTML ( )   PDF (6728KB) ( )   With the first-principles method of density functional theory (DFT), the structure, electronic and optical properties of wurtzite AlN supercells were obtained by substituting Ge atoms for Al and N atoms, respectively. It shows that the structure changes obviously with doping. The lattice constants, volume and bond length along c-axis of AlN increase in both doping methods, and the lattice constants change satisfies Vegard's theorem. Forming energy of Ge atom substituted for Al atom is 5.41 eV, and that of Ge atom substituted for N atom is 5.58 eV. Stability of the doped systems is lower than that of pure AlN. Magnetism is not introduced in both doping methods, but the former introduces donor impurity band and an impurity band enters valence band, which makes it becomes negative energy gap metal. The latter introduces acceptant impurity band with a band gap of 0.910 eV. Both gaps are much smaller than intrinsic AlN band gap of 4.040 eV. Conductivity of the former is significantly improved, while conductivity of the latter may be improved. It is found that imaginary part of the complex refractive index function after doping in two ways is approximately no longer to 0 in the low energy region, indicating that the absorption ability of AlN materials to low frequency electromagnetic wave is enhanced in both doping ways. Imaginary part of dielectric function of the former has a new peak in low energy region, while the latter has no obvious peak in that region. The former has a stronger absorption capacity of long wave. The energy loss is reduced in both.

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Ground State of Bose-Einstein Condensates in a Spin-dependent Optical Lattice Liyuan WU, Suying ZHANG 2022, 39(5): 617-623.  DOI: 10.19596/j.cnki.1001-246x.8478 Abstract ( )   HTML ( )   PDF (8174KB) ( )   Based on Gross-Pitaevskii equation, we studied numerically ground-state density distribution of Bose-Einstein condensates trapped in a combined potential of a spin-dependent optical lattice potential and an infinite deep potential. We discuss specifically the influence of propagation directions and the ratio of wave numbers (l) of the two lasers, which produce the spin-dependent optical lattice on the ground-state of the Bose-Einstein condensate. As the wave number is small, two beams of light spread forward to each other. The two components exhibit continuous stripes with l < 2. And with l≥2 both components show discontinuous stripes. As the two beams of light propagate vertically, with the increase of l, component 1 changes gradually from continuous to discontinuous stripes, and component 2 behaves oppositely. The number of ground state density fringes increases with the increase of wave number, while the number of vortices remains unchanged.

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Spectrum and Dissociation Characteristics of CHBr3 Molecule Under External Electric Fields Wumaierjiang NAIPISAI, Haokui YAN, Abulimiti BUMALIYA, Danqi WANG, Mei XIANG, Huan AN 2022, 39(5): 624-630.  DOI: 10.19596/j.cnki.1001-246x.8502 Abstract ( )   HTML ( )   PDF (1379KB) ( )   Ground-state configurations of bromomethane molecules under external electric fields were optimized on B3LYP/6-311G++(d, p) basis set using density functional theory. Molecular structure, total energy, dipole moment, bond length, charge distribution, orbital energy level, infrared spectroscopy, Raman spectroscopy and dissociation potential energy curve were analyzed computationally. It shows that with the increase of external electric field (0 a.u. -0.02 a.u.) along Y axis (parallel to the 1C-4Br line), the total molecular energy decreases, the 1C-4Br bond length increases, and the molecular dipole moment increases, the molecular energy gap decreases gradually, and the molecular infrared spectrum exhibits a blue shift. The dissociation potential energy curve shows that an external electric field with a strength of 0.02 a.u. makes the 1C-4Br bond broken and the molecule degraded.