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25 September 2023, Volume 40 Issue 5 Previous Issue    Next Issue

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A Algebraic Multigrid Algorithm Based on Hybrid Coarsening for Pressure Poisson Equation Shaoliang HU, Kailong XU, Ran XU, Zaigang LIU, Xiaowen XU, Hengbin AN, Ronghong FAN, Zhenyu WANG, Wei WANG 2023, 40(5): 527-534.  DOI: 10.19596/j.cnki.1001-246x.8662 Abstract ( )   HTML ( )   PDF (4455KB) ( )   An algebraic multigrid (AMG) algorithm based on hybrid coarsening is proposed for the linear systems of the discrete pressure Poisson which is derived from the SIMPLE algorithm for the Navier-Stokes equations in complex flows. This algorithm combines a class of non-smoothed aggregation coarsening with classical C/F coarsening to construct grid hierarchy, hoping to reduce the cost in the setup phase of the AMG algorithm without affecting convergence. The high performance of the proposed algorithm is verified by numerical simulation of complex flow in the combustion chamber of aero-engine. The results show that the proposed algorithm can achieve 78% acceleration compared with the classical AMG algorithm.

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Parallel Finite Element Algorithms Based on Two-grid Discretizations for the Steady Navier-Stokes Equations with Damping Term Guoliang WANG, Bo ZHENG, Yueqiang SHANG 2023, 40(5): 535-547.  DOI: 10.19596/j.cnki.1001-246x.8646 Abstract ( )   HTML ( )   PDF (10112KB) ( )   Based on two-grid discretizations and domain decomposition techniques, this paper presents three parallel finite element algorithms for numerically solving the steady Navier-Stokes equations with damping term. The basic idea of the present algorithms is to first solve a fully nonlinear problem on a coarse grid to get a coarse grid solution, then solve Stokes, Oseen, and Newton linearized residual problems in parallel in overlapping local fine grid subdomains, and finally update the approximate solution in non-overlapping fine grid subdomains. The effectiveness of the proposed algorithms is demonstrated by some numerical examples.

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Efficient and High Precision Nearly Singular Domain Integrals Calculation Based on Adaptive Element Subdivision Method Fushun WANG, Baotao CHI, Zhichao JIA, Qianjian GUO, Wei YUAN 2023, 40(5): 548-555.  DOI: 10.19596/j.cnki.1001-246x.8634 Abstract ( )   HTML ( )   PDF (7403KB) ( )   An adaptive and efficient element subdivision method for accurate evaluation of nearly singular domain integrals is presented, which is mainly applied to address the difficulties involved with thin-structure mechanics, crack propagation, etc, in the boundary integral formulations. Based on the binary-tree data structure, the reasonable integration result of different types of volume elements can be achieved by the adaptive subdivision algorithm. Combined with the cavity construction and projection algorithms, high-quality regenerated patches around the source point can be obtained for evaluation of nearly singular integrals with discontinuous kernels. Compared to other methods, the proposed element subdivision method can obtain the accurate results with fewer integration nodes. Numerical results have been given to verify the effectiveness, feasibility and robustness of the illustrated integration schemes. For the stress analysis on arbitrary thin structures, accurate evaluation of the nearly singular integrals is restricted by the difficulties, such as the singularity of the integrals in the boundary integral formulations. An adaptive and efficient volume element subdivision method for evaluation of nearly singular domain integrals with continuous or discontinuous kernels is presented. For nearly singular domain integrals with continuous kernel, a reasonable result can be achieved by the binary-tree subdivision algorithm for different types of elements. By using the techniques of the binary-tree subdivision scheme, construction of the projection cavities and the cavity projection algorithm, well-shaped patches can be obtained for nearly singular domain integrals with discontinuous kernels. Numerical results for volume elements of arbitrary type with various relative locations of the source point demonstrate robustness and accuracy of the proposed method.

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Applications of Three-component Mie-GrüNeisen Mixture Model in Underwater Explosion Mitigation Problem Zongduo WU, Qingyang MAN, Jin YAN, Jianhua PANG, Yifang SUN 2023, 40(5): 556-569.  DOI: 10.19596/j.cnki.1001-246x.8658 Abstract ( )   HTML ( )   PDF (7130KB) ( )   In this paper, our main concern is the effects of the mitigation layer in the underwater explosion problem. As the explosive gaseous products, water, mitigation layer, and so on constitute a fluid mixture, the physical states of these components are covered by a uniform Mie-Grüneisen equation of states(EOS). Then the Mie-Grüneisen mixture model is applied to simulate the complicated interaction among gaseous product, water and solid layer. In the calculation, the particular parameters of EOS are used to make a distinction among the physical properties of fluid components and the volume fractions are used to identify the interfaces. In addition, the inlet and outlet boundary conditions are implemented here. During the calculation process, the effect of the mitigation layer is investigated here. According to the investigation, it is found that the effect of the layer is decided by the shock impedance of layer material. The pressure of the shock wave will decrease when it penetrates a new medium with lower impedance. On the other side, the penetrated shock wave in the layer is reflected by the structure and produces a second shock wave. During this process, the affection of layer thickness and distance is also studied here. But both two factors are unimportant under the mitigation mechanism.

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Algorithms for Solving Electronic Continuity Equation in Numerical Simulation of Semiconductor Devices Yi HU, Hengbin AN 2023, 40(5): 570-582.  DOI: 10.19596/j.cnki.1001-246x.8656 Abstract ( )   HTML ( )   PDF (1063KB) ( )   For solving the discretized electronic continuity equation, two aspects of work are carried out. Firstly, the matrix of the discretized linear system is analyzed, and three types of characteristics of the matrix are obtained. Secondly, based on the characteristics of the matrix, the discretized electronic continuity equation is solved by preconditioned Krylov subspace methods, and the effectiveness of several types of preconditioned methods is compared and analyzed. The results show that the algebraic multigrid (AMG) preconditioned Krylov subspace method is very effective for solving discretized electronic continuity equations. A large-scale parallel scalability test of the AMG preconditioned Krylov subspace method for solving discretized electronic continuity equations is carried out, and the selection of three key algorithm parameters in the AMG method is compared and analyzed.

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Adsorption Behavior of Heavy Oil on Montmorillonite Surface by Typical Surfactant: Molecular Dynamics Simulation Yu LI, Huiqing LIU, Yabin FENG, Xiaohu DONG, Qing WANG, Bo ZHANG 2023, 40(5): 583-596.  DOI: 10.19596/j.cnki.1001-246x.8647 Abstract ( )   HTML ( )   PDF (21728KB) ( )   To investigate the adsorption mechanism of heavy oil on clay mineral surface during surfactant flooding, the microscopic mechanism of heavy oil and surfactant on montmorillonite surface under different temperatures can be explained by molecular dynamics simulation. Based on the four components (SARA) of heavy oil and sodium montmorillonite, the molecular dynamics simulation of the adsorption process is carried out after the water phase adsorbent containing surfactant molecules is added into the adsorption system. It shows that cationic surfactant tends to adsorb on the surface of montmorillonite and occupy more adsorption area, which makes the heavy oil molecules tend to separate from the surface of montmorillonite. The non-ionic surfactant does not show a tendency to adsorb towards the surface of montmorillonite during the relaxation process. Non-ionic surfactant has a high self-diffusion coefficient and thus diffuses in the adsorbent environment. High temperature disperses asphaltene aggregation nuclei in heavy oil, which facilitates heavy oil to flow away from the montmorillonite surface. However, high temperatures can also cause some surfactants more adhesion to the montmorillonite surface, resulting in surfactant loss. This study provides theoretical support for adjusting temperature and surfactant types during surfactant development and enhancing oil recovery of sensitive heavy oil reservoirs.

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Numerical Simulation of Water-flooding Reservoirs Considering Permeability Time Variation Based on Mimetic Finite Difference Method Shaochun WANG, Shuoran FU, Lingkong GUO, Zhihao TANG, Na ZHANG, Qian SUN 2023, 40(5): 597-605.  DOI: 10.19596/j.cnki.1001-246x.8628 Abstract ( )   HTML ( )   PDF (6512KB) ( )   Since physical properties time variation influences the remaining oil distribution and reservoir development effect, a new method to simulate permeability time variation properties based on mimetic finite difference method is put forward. Firstly, well test permeability is fitted, and a water flooding mathematical model considering the variation of permeability based on scouring time of injected water is proposed. The model is discretized using mimetic finite difference method, which is described in details. Finally, an IMPES scheme is used for the solution of the model and the influence of different permeability multiples on distribution of residual oil, pressure, and streamline is analyzed. The results show that, when the permeability changes with time, more water channeling can occur, inducing a negative effect on oil production. Compared to traditional reservoir characterization methods, this technology reflects real condition of the block and can provide useful guidelines for further production optimization.

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Effect of Micro Pore-throat on Porosity and Permeability of Dual Media Digital Rock Chenchen WANG, Yongfei YANG, Xin NIE, Denglin HAN 2023, 40(5): 606-613.  DOI: 10.19596/j.cnki.1001-246x.8651 Abstract ( )   HTML ( )   PDF (7062KB) ( )   In this paper, the representative sandstone matrix and fracture sample are selected for CT scanning to build the corresponding matrix and fracture digital rock respectively. Then, based on the matrix and fracture digital rock with the same physical size and resolution, the Boolean superposition algorithm is introduced to construct matrix-fracture dual media digital rock; meanwhile, an image opening algorithm is used to eliminate pore voxel, and matrix digital rock with different micropore size is reconstructed, also, the superposition algorithm is conducted to reconstruct matrix-fracture dual digital rock with different micropore sizes. Finally, based on the matrix digital rock and matrix-fracture digital rock with different micropore sizs, the total porosity, connected porosity and absolute permeability are calculated. It can be found that, the micro pore-throat has lower contribution to the total porosity of matrix and dual media; the micropore-throat contributes more to the connected porosity of the matrix, but less to the connected porosity of dual media; the micropore-throat makes important contribution to the permeability of matrix, but less to the permeability of dual media. This paper provides an important platform to study the porosity and permeability characteristics of matrix-fracture dual media, which is of great significance to the development of dual-media reservoirs.

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Low-dose X-ray CT Image Reconstruction Method Based on Adaptive Total Variation Zhaoyan QU, Ximing YAN, Xiaojing XI 2023, 40(5): 614-621.  DOI: 10.19596/j.cnki.1001-246x.8639 Abstract ( )   HTML ( )   PDF (10613KB) ( )   The radiation dose of X-ray CT is closely related to the abnormal metabolism of the living body and the induction of diseases such as cancer. At this stage, how to reduce the radiation dose of CT scans and ensure the quality of image reconstruction is a huge challenge for CT image reconstruction technology. The traditional total variation regularization method is not sensitive to the direction of the image. This paper introduces directional gradient information and establishes an adaptive directional total variation sparse angle CT image reconstruction model, which aims to better preserve image edges and improve image reconstruction quality. To adaptively estimate the direction information of the image gradient, based on the geometric moment of the image, an ellipse steerable kernel is used to estimate the main direction of the image edge block. Simulation and actual data results show that the proposed algorithm has good performance in image detail preservation, artifact reduction, and noise suppression.

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Stochastic Boundary-induced Spatiotemporal Pattern Transformation in Izhikevich Neuronal Networks Guowei WANG, Yan FU 2023, 40(5): 622-632.  DOI: 10.19596/j.cnki.1001-246x.8632 Abstract ( )   HTML ( )   PDF (11540KB) ( )   Izhikevich neuronal model is based on the modeling of cortical and thalamic neurons. This model has the characteristics of being closer to the discharge properties of real biological neurons and it is convenient for large-scale simulation. A square neural network composed of 200 × 200 Izhikevich neurons is constructed under random boundary conditions in this paper, the computer simulation method is used to calculate the spatiotemporal characteristics and synchronization factor of the square network, and the firing patterns and bifurcation phenomena of neurons, as well as the spatiotemporal patterns and synchronization properties of the square network are studied. The results show that in the square neural network constructed by Izhikevich neurons with different discharge modes under the same current stimulation and coupling intensity, the emergence and disappearance of spiral wave seeds can be observed in the neural network only when the neurons are in the Regular Spiking discharge mode. On the other hand, spiral wave seeds cannot be observed in the square neural network constructed by Izhikevich neurons with other discharge modes (e.g. Fast Spiking, Chattering, Internally Bursting). When the external current stimulation is constant, only the medium-sized coupling strength between neurons can induce the emergence and extinction of spiral wave seeds in the square neural network, and smaller or larger coupling strength cannot induce spiral wave seeds in the neural network. In addition, the synchronization factor in square neural networks has been investigated.

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Research on Cascading Faults of Hybrid Point-to-Point Power Information Network Based on Blockchain Fengping HOU, Yanli ZOU, Tanghuimei LIU, Zhiwei WANG, Shuyi TAN 2023, 40(5): 633-642.  DOI: 10.19596/j.cnki.1001-246x.8637 Abstract ( )   HTML ( )   PDF (8456KB) ( )   By dividing the community of the power grid, the information network community is divided according to the current situation and the actual coupling relationship of the corresponding hierarchical partition construction of the power grid and the information network, and the node with the largest betweenness and the node with the largest degree of each community in the information network is selected for full connection. The power information interdependence network model based on the hybrid point-to-point structure of the blockchain, combined with the consensus mechanism of the blockchain, analyzes the advantages of the model, and uses the two attack strategies of high number attack and high betweenness attack to study the proposed interdependence The robustness of the network is compared with the traditional centralized control power information network and the fully decentralized point-to-point power information network. The research results show that the hybrid point-to-point power information interdependence network model can effectively reduce the communication overhead and consensus delay of the practical Byzantine fault-tolerant algorithm on the basis of improving the robustness of the network. In the hybrid peer-to-peer power information network, the system shows stronger vulnerability under the high-number attack mode.

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Modified Function Projective Synchronization of the Ring Network with Time-delay Disturbance and Its Simulation Dekui LI, Beixing MAO 2023, 40(5): 643-652.  DOI: 10.19596/j.cnki.1001-246x.8648 Abstract ( )   HTML ( )   PDF (1195KB) ( )   To improve the security of secret communication in ring networks, we analyze the effect of time delay interference on a ring network synchronization. Firstly, according to the topology of the ring network, the mathematical model of the ring network disturbed by time-varying delay is constructed. Then, based on the Lyapunov stability method, an adaptive controller is designed to control the ring network, and realize the modified function projection synchronization of the ring network with no time-delay, constant-delay and time-varying-delay, which shows that the adaptive controller is universal. At last, the correctness of the theoretical analysis is verified by numerical simulation, and it is found that the synchronization ability of the ring network is reduced by time-delay interference, the greater the delay, the worse the synchronization ability and the longer the time needed to achieve synchronization.