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25 November 2023, Volume 40 Issue 6 Previous Issue    Next Issue

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Numerical Simulation of Oscillating Heat Transfer of Rarefied Binary Gas Between Two Plates Qikun WAN, Yue ZHANG, Zhaoli GUO 2023, 40(6): 653-665.  DOI: 10.19596/j.cnki.1001-246x.8671 Abstract ( )   HTML ( )   PDF (9835KB) ( )   In this paper, the discrete unified gas kinetic scheme (DUGKS) is used to solve the McCormack model of binary gas, simulate the flow and heat transfer of rarefied binary gas between two plates excited by the periodic fluctuation of lower plate temperature, and analyze the effects of system rarefied parameters, temperature change frequency and component molar concentration on the flow and heat transfer between plates. The numerical results show that the gas flow and heat transfer between the two plates change periodically, and we find that the minimum local temperature exists between the plates, and its position is inversely proportional to the degree of system thinning. In addition, it is found that the thermal penetration depth decreases with the increase of the rarefaction parameter. The heat penetration depth first increases with the increase of light component concentration, reaches the highest value when the light component concentration is about 0.6, and finally decreases and is consistent with the result of single component gas.

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Improved Fifth-order WENO-Z+ Schemes Based on Modified Stencil Cheng GUO, Pengdan CHENG, Yahui WANG 2023, 40(6): 666-676.  DOI: 10.19596/j.cnki.1001-246x.8654 Abstract ( )   HTML ( )   PDF (4093KB) ( )   First, a modified stencil approximation method is introduced, which improves the second-order polynomial approximation of the numerical flux on each candidate sub-stencil in the classical fifth-order WENO-JS scheme. The stencil approximation reaches the fourth-order accuracy by adding a cubic correction term, and it has ENO property by introducing an adjustable function.Then the modified stencil approximation method is applied to WENO-Z+and WENO-Z+M schemes, and the modified WENO-Z+schemes based on the modified stencil type (WENO-MS-Z+, WENO-MS-Z+M) are developed.A series of numerical examples are used to test the new schemes. The results show that the new schemes have a strong ability to capture shock waves and high resolution for small-scale wave structures, which is significantly improved compared with the original WENO-Z+and WENO-Z+M schemes.

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Discrete Alfvén Eigenmodes in ITER with the Internal Transport Barrier Scenario Sijie OUYANG, Shuanghui HU, Xuefeng OUYANG, Wanpo ZHU, Yuandan LAN, Xuange HUANG 2023, 40(6): 677-688.  DOI: 10.19596/j.cnki.1001-246x.8672 Abstract ( )   HTML ( )   PDF (9541KB) ( )   The physical features of discrete Alfvén eigenmodes (αTAEs) bounded by the α-induced potential wells are investigated in ITER (International Thermonuclear Experimental Reactor) with the ITB (internal transport barrier) scenario, where α denotes a measure of the pressure gradient. The use of the negative-ion-based neutral beam injection (NNBI) heating and current driving can obtain a large and strong ITB for higher performance, and the instability of αTAE in this scheme is discussed. The αTAEs during sustaining, shrinking and erosion of ITB are discussed upon the pure radio frequency scenario. It is found that αTAEs exist in the ITB region due to the steep pressure gradient. More αTAEs exist in scenarios with strong ITB and the frequencies of these eigenmodes are higher. Multiple αTAEs are readily destabilized in the presence of energetic particles. The frequency of the excited αTAEs increases with increasing beam energy. The high βp scenario with ITB on DIII-D has many of the desired properties of ITER steady-state. The αTAEs in high βp scenarios are also studied.

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Non-isothermal Polymer Filling Process via Phase Field Method in Three Dimensions Puyang GAO 2023, 40(6): 689-698.  DOI: 10.19596/j.cnki.1001-246x.8659 Abstract ( )   HTML ( )   PDF (6299KB) ( )   We investigate the non-isothermal non-Newtonian filling process according to the phase field method in three dimensions. The moving interface between the Newtonian and non-Newtonian fluid is captured by the Cahn-Hilliard equation. Based on phase field parameters, the governing equations of the flow field could be written in a unified form. After that, the Navier-Stokes equations are split into several sub-equations and the FEM and SUPG will be used to handle the appropriate equations. The variation of the viscosity of the polymer melt is described via the Cross-WLF model. The thin wall rectangular cavities with and without obstacles are considered to illustrate the convergence, robustness and accuracy of the numerical algorithm. The influences of the inlet velocity and the size of the injection gate on the filling process are analyzed. The numerical results agree well with the experimental data and also exhibit good mass conservation properties.

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First-principles Study on the Influence of Alloying Elements on Galvanic Corrosion of Ternary L12-Al-Zr-X Aluminum Alloys Surface Qingzhou ZHANG, Dawei FAN, Linghong LIU 2023, 40(6): 699-711.  DOI: 10.19596/j.cnki.1001-246x.8678 Abstract ( )   HTML ( )   PDF (13390KB) ( )   The galvanic corrosion of aluminum alloy mainly depends on the potential difference between the second phase and matrix. The greater the potential difference, the stronger the corrosion driving force. Based on AlZr binary alloy, we calculated the work functions of the (100), (110) and (111) planes of 19 ternary precipitates L12-AlxZryXz(X=Pd, Pt, Au, K, Rb, Sr, Ba, Ca, Yb, La, Ce, Y, Er, Sc, Zr, Ti, Cd, Hf, In) comprehensively by using the first principle calculations. The relationship between the work functions and the electronegativity of doped atoms was analyzed, and the fundamental reason for the influence of doped atoms on the surface galvanic corrosion performance of L12 type Al-Zr-X ternary aluminum alloy is clarified from the electronic level. Through calculation, we find that when different doped crystal surfaces are exposed to the surface, the potential difference between the phase and the matrix is also different due to the varying work functions. The doped atoms Hg, Cd, Zr, Ti, Hf can increase the work functions of the (100) surface of L12-AlxZryXz ternary precipitates, Hg, Cd, In, Ti, Hf can increase the work function of the (110) surface, and Pd, Pt, Au, In, Sc, Rb, Sr, Yb, Y, Er, K, Ba, La, Ce and Ca could decrease the work function of the (111) surface. These will lead to the further reduction of the potential difference between the phase and matrix. In addition, the linear positive correlation between the electronegativity of doped atoms and the work function of the compound is revealed. In contrast, In, Cd, Hg atoms whose electronegativity is close to Al and doping the site of Al, and Ti, Hf atoms whose electronegativity is close to Zr and doping the site of Zr have less influence on the work function of the phase, and the potential difference between their compounds and aluminum matrix is small, which is beneficial to improving the corrosion resistance of materials. Other doped atoms have greater influence on the work function of the phase. Research results have explained some of the experimental results of corrosion resistance studies, which provided a theoretical reference for optimizing the design of alloy composition and improving the corrosion resistance of aluminum alloy materials.

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Study on Dissociation Properties of Chloroethane Under External Electric Field Jing TANG, Xinyang ZHANG, Yihang JIANG, Xin JIN, Yuzhu LIU 2023, 40(6): 712-717.  DOI: 10.19596/j.cnki.1001-246x.8686 Abstract ( )   HTML ( )   PDF (5409KB) ( )   Using B3LYP calculations on the 6-311G ++ (d, p) group, the structural characteristics and dissociation properties of the chloroethane molecule are discussed from the perspective of molecular structure under an external electric field (0~10.28 V·nm-1). The calculation results show that with the increase of external electric field, the total energy of the molecule increases, the bond length of the C—C single bond decreases, the bond length of the C—Cl bond increases, the dipole moment increases, the size of the energy gap bond increases and then decreases. At different frequencies, the infrared absorption peaks respectively have red shift and blue shift phenomena, and the intensity of the Raman peaks changes. In addition, with the increase of the external electric field, the dissociation energy gradually decreases, and it can be seen that the potential energy barrier almost no longer exists when the external electric field reaches 18.00 V·nm-1, representing that the degradation of the chloroethane has been achieved.

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Well Test Analysis Method for Composite Reservoir with Dynamic Non-Darcy Flow Effect Yongchuan LIU, Kang CHENG, Sheng JIANG, Jie YU, Xianlin ZHENG 2023, 40(6): 718-726.  DOI: 10.19596/j.cnki.1001-246x.8674 Abstract ( )   HTML ( )   PDF (4282KB) ( )   In order to accurately describe the change law and influencing factors of reservoir seepage flow near injection wells in low permeability reservoirs, a well test analysis method for composite reservoir with dynamic non-Darcy effect outside injection wells was constructed. Firstly, Darcy flow is considered as the inner seepage mode, and non-Darcy flow as the outer seepage mode composed of starting pressure gradient effect and dynamic permeability effect. Secondly, numerical method is used for discrete solution to calculate the bottom-hole pressure of the injection well, and then the typical curve of bottom-hole pressure response is drawn. Typical curves are divided into 5 flow sections: wellbore storage section, transition section, inner radial flow section, outer low seepage flow section and boundary reflection section. Finally, sensitivity analysis of starting pressure gradient and dynamic permeability parameters is carried out, and pressure response of different seepage laws is compared. Taking an injection well in Changqing Oilfield as an example, the well test results show that the permeability around the injection well is larger, and the outer zone is affected by the combination of starting pressure gradient and dynamic permeability, and there is a starting pressure gradient in the outer area, and the permeability is smaller, which is consistent with the field practice. This method is a relatively general numerical pressure calculation method, among which the conventional injection well composite well test analysis method and low permeability reservoir single zone test analysis method are special cases of this method.

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Embedded Discrete Fracture Model Pre-processing Algorithm Based on Collision Detection Yilin LIU, Guozhong GAO 2023, 40(6): 727-734.  DOI: 10.19596/j.cnki.1001-246x.8664 Abstract ( )   HTML ( )   PDF (2986KB) ( )   Based on the embedded discrete fracture model, an algorithm is implemented and optimized for the key problem of the intersection calculation of the fracture surface and the matrix grid in the preprocessing algorithm. Firstly, the collision detection between the fracture bounding box and the matrix grid is used to quickly determine whether the fracture surface and the matrix grid intersect. Secondly, after determining the intersection, calculate the intersection point to see if the matrix contains fractures. Finally, classify the intersection of the matrix and the grid. Experiments have demonstrated the effectiveness of the method.

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Numerical Fracture Diagnosis Method for Horizontal Well Fracturing Based on Water Hammer Zhaoying ZHU, Dengjin DAI, Wuzhi LU, Shaochun WANG, Wei LIU, Jianfeng XIAO 2023, 40(6): 735-741.  DOI: 10.19596/j.cnki.1001-246x.8668 Abstract ( )   HTML ( )   PDF (9815KB) ( )   Aiming at the diagnosis technology of the horizontal well fracturing effect, a numerical fracture diagnosis method based on the water hammer effect is proposed. Because of the energy dissipation caused by the fracture to the pump shutdown pressure, the traditional water hammer mathematical model is difficultly to apply to the fracture diagnosis of horizontal Wells. In this paper, considering the influence of fracture on the water hammer effect, a mathematical model of water hammer in a horizontal well is established based on the equivalent circuit method, and the model is solved by the characteristics method line. The fracture parameters are deduced based on the characteristics of the water hammer pressure curve, and the variation characteristics of the water hammer pressure curve with different influencing factors are analyzed. The results show that the characteristics of water hammer pressure wave are affected by fracture morphology and construction parameters. and the amplitude and period of hydraulic pressure are changed by fracture volume, displacement and fracturing stage length. The water percussion model is used to carry out historical fitting to the field data, and the coincidence rate of the obtained fracture half-length and height with the microseismic monitoring data is more than 80%, which verifies the accuracy of the model and provideds on idea and method for the fracture parameter evaluation of horizontal wells.

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Fault Identification of Post Stack Seismic Data by Improved Unet Network Guixin LIU, Zhonghua MA 2023, 40(6): 742-751.  DOI: 10.19596/j.cnki.1001-246x.8684 Abstract ( )   HTML ( )   PDF (18716KB) ( )   In order to improve the accuracy of fault identification, an improved Unet model is proposed. A multi-branch parallel structure M-block (Multi-branch block) is designed for the encoder part. It can capture multi-scale context information, and multi branch parallel structure will bring high performance benefits. Self-Attention block and attention gating mechanism are added to the decoder. Self-Attention not only enables the attention module to flexibly focus on different areas of the image, but also makes up for the shortcomings of the local CNN (Convolutional Neural Network) and brings more possibilities to the neural network through the weighted average operation of the input feature context. It is verified by synthetic data and actual data that the model combines the advantages of weight sharing in traditional convolution with the advantages of Self Attention's dynamic calculation of Attention weight to improve the accuracy of fault identification. Compared with Unet, the test loss is reduced by 33.68%. The model not only identifies fault features accurately, but also is more accurate than the current popular depth learning method.

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Dynamic Analysis of Neurons by Josephson Junction Tongtong XIAO, Xinying LI, Yuqing QIAN 2023, 40(6): 752-760.  DOI: 10.19596/j.cnki.1001-246x.8667 Abstract ( )   HTML ( )   PDF (12538KB) ( )   A four-dimensional neuron model with Josephson junction is constructed by introducing Josephson junction into HR neuron. Firstly, the dissipative property of the system and the stability of the equilibrium point are obtained through theoretical analysis. By adjusting the Josephson junction parameters to observe the bifurcation of the electric-coupled system, it is found that the system shows rich dynamic characteristics such as period-doubling bifurcation and addition-period bifurcation including chaos within the appropriate parameter range. A global coupled neural network is constructed under the action of chemical synapses. Synchronization factors are used to describe the synchronization degree of the system under different parameters. It is found that coupling strength and Josephson junction parameters can affect the discharge synchronization state of the system.

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Neural Network Models of Compressible Multi-Medium Flows Embedded with Physical Constraints Ziyan LIU, Liang XU 2023, 40(6): 761-769.  DOI: 10.19596/j.cnki.1001-246x.8670 Abstract ( )   HTML ( )   PDF (7913KB) ( )   A machine learning method for simulating compressible multi-medium flows is studied. The regression prediction of multi-medium Riemann solution is realized by using neural network. In order to make the training results more consistent with the physical flow, an additional physical constraint layer is constructed according to the discontinuity relationship of the flow field. A neural network model is established and applied to practical ghost fluid method (PGFM). Through a variety of typical one-dimensional and two-dimensional multi-medium flow problems, the surrogates trained by neural networks of different sizes are verified numerically. It is found that the results of neural network model are more consistent with the real situation after embedding physical constraints. In addition, the relatively simple neural network model can meet the computing requirements. Machine learning method has high computational accuracy and efficiency, and has potential development.

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Study on Braess Paradox of Power Grid Based on Complex Network Topology Beibei SHAO, Yanli ZOU, Shaoyan HONG, Chanjuan LIANG 2023, 40(6): 770-778.  DOI: 10.19596/j.cnki.1001-246x.8653 Abstract ( )   HTML ( )   PDF (9456KB) ( )   To explore a better power grid structure and reduce the probability of Braess paradox. In this paper, the second order Kuramoto-like phase oscillator model is used to reasonably model the power grid, and several networks are generated by ER random model in which the number of network nodes and links is the same as IEEE14, IEEE30, and IEEE39, respectively. By increasing the number of generator nodes and changing the position of generators in the random network, the occurrence probability of Braess paradox caused by a new adding transmission lines in the different power grid is studied. Study shows that appropriately increasing the number of generator nodes in the power grid can reduce the probability of the Braess paradox in the power grid, and taking large-degree nodes as generator nodes is beneficial to improve the power grid synchronizability and reduce the probability of Braess paradox. This study has certain guiding significance for the topology design and optimization of the power grid.