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    25 July 2022, Volume 39 Issue 4 Previous Issue    Next Issue

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    A Finite Volume Scheme Based on Magnetic Flux and Electromagnetic Energy Flow for Magnetic Field Diffusion Problems
    Chun-hui YAN, Bo XIAO, Gang-hua WANG, Yu LU, Ping LI
    2022, 39(4): 379-385.  DOI: 10.19596/j.cnki.1001-246x.8430
    Abstract ( )   HTML ( )   PDF (1768KB) ( )  

    An explicit finite volume discrete scheme is designed for one-dimensional magnetic field diffusion problems. The first characteristic of the scheme is that, the diffusion process of magnetic field is described as magnetic flux and the ohmic heating in energy equation is presented as electromagnetic energy flow at the element boundary as well, which guarantees the conservation of the sum of electromagnetic energy and internal energy well. The second characteristic of the scheme is that it truncates magnetic flux and electromagnetic energy flux on boundary of the element. Combined with time step amplification, the truncation could break through the limitation of stability condition on explicit scheme time step to some extent in magnetic diffusion problems with extreme resistivity.

    Robust Loss Functions for Signal Modulation Recognition with Noise Labels
    Xiao-bo WANG, Jun-ping YIN, Yan XU
    2022, 39(4): 386-394.  DOI: 10.19596/j.cnki.1001-246x.8437
    Abstract ( )   HTML ( )   PDF (3675KB) ( )  

    In view of the fact that the labeling of signal modulation type is prone to errors in applications, that is, the underlying training data set has label noise, we propose l1 norm based loss function and its extended form as robust loss function of deep convolutional neural network, which is recognized as one of the most excellent feature extraction network, to classify signal modulation types with label noisy. The algorithm achieves high accuracy even if the label noise level of training data set is up to 50%. By contrast, it is unable to predict the type of signal modulation by using usual cross entropy as the loss function of the deep convolutional neural network. Robustness of the algorithm is verified with numerical examples on public available benchmark data sets.

    A Multi-time-step Discrete Element Method for Bar Structures
    Tong LI, Qian WANG, Xian-long JIN
    2022, 39(4): 395-402.  DOI: 10.19596/j.cnki.1001-246x.8427
    Abstract ( )   HTML ( )   PDF (4780KB) ( )  

    To improve computational efficiency of discrete element method(DEM), referring to domain decomposition method and sub-cycle method in finite element method, a discrete element partition asynchronous time step computing method based on overlapping particles was proposed to deal with continuous medium problems. In the method, the continuum is divided into sub-domains. The velocity-Verlet integral scheme is used to solve the motion equation in sub-domains. Local action regions are formed with overlapping particles in adjacent sub-domains. Interpolation and truncation are not involved in transfer process of boundary data. Numerical examples show that accuracy of the method is high and the computation time is reduced effectively. In practical application, continuous media could be divided into several sub-domains with different particles size, and different time steps are adopted according to particle size characteristics of the sub-domains, with which storage space could be saved and computing efficiency improved greatly.

    Morphological Evolution and Growth Kinetics in Primary Crystallization of Amorphous: Phase Field Method
    Jin WANG, Wen-jing MA, Yu-zhou LIU, Mei-ni LÜ, Kai-jing ZHANG
    2022, 39(4): 403-410.  DOI: 10.19596/j.cnki.1001-246x.8461
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    Influence of diffusion coefficient on crystallization process is considered in a crystallization physical model. A phase field method is employed to study influence of random nucleation rates and nucleation radii on microstructure and growth kinetics in primary crystallization process. It shows that the number of grain crystal of primary crystallization increases with the increase of initial nucleation rate, and the crystal size of primary crystallization decreases with the increase of initial nucleation rate. The crystallization fraction increases with evolution time and initial nucleation rate. The greater the initial nucleation rate, the higher the crystallization fraction. With different initial nucleation radii, the quantity and size of grains in the primary crystallization process remains basically unchanged with the increase of evolutionary time. The crystallization fraction increases with the increase of evolutionary time. The growth index corresponding to different initial nucleation rates and initial nucleation radii is less than 1, which means random nucleation rate and random nucleation radius have no significant effect on the crystallization mode. The crystallization modes are primary crystallization. Control of random nucleation rate and initial nucleation radius changes effectively microstructure of the primary crystallization. The grain size and crystallization fraction affect properties of the alloy directly.

    Synthesizing Gas Pressure Based on Acoustic Relaxation Frequency of Sound Speed Dispersion Measured at Three-frequency Point
    Xiang-qun ZHANG, Gen-yuan DU, Ting-ting LIU
    2022, 39(4): 411-417.  DOI: 10.19596/j.cnki.1001-246x.8459
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    We present a method of synthesizing gas pressure based on acoustic velocity at three-frequency point with high accuracy and simple measurement. Firstly, acoustic velocity at three frequency points is measured. Then, relaxation frequency of acoustic velocity dispersion is calculated. Finally, gas pressure is obtained according to the linear proportional relation between relaxational frequency and gas pressure. Simulation results verify feasibility of the algorithm. The method is simple and of high precision for ultrasonic online real-time pressure detection of gas chambers.

    Analysis of Flow Field Around a Cylinder with Porous Media Layer
    Pin-liang LIN, Huan-huan FENG, Yu-hong DONG
    2022, 39(4): 418-426.  DOI: 10.19596/j.cnki.1001-246x.8441
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    Flow around a square cylinder with porous media is numerically simulated by means of the lattice Boltzmann equation in Darcy-Brinkman-Forchheimer force model, and influence of porous media on flow field characteristics of bluff body is studied. It shows that: Compared with a impermeable cylinder, the flow structure is modulated by the porous media layer under certain parameters. Evolution of the shear layer tends to be more symmetrical and stable, which reduces the interaction of vortex motions in the wake region and makes the vortex shedding more periodic, thus reducing effectively the amplitude of lift fluctuation, but increasing the drag in some extent. At the same time, we study surface porous media effect on square column under high Reynolds number. It shows that the porous medium wall makes wake region of the shear layer farther apart, reduces the wake turbulence kinetic energy, and moves the Reynolds stress peak of the mobile to wake region, suppresses the momentum exchange on either side of the square column, makes the momentum exchange occurred in wake region and the vortex street of the wake more regular.

    Flow Patterns in Three-dimensional Lid-driven Cavities with Curved Boundary: MRT-LBM Study
    Qiao-ling ZHANG, He-fang JING
    2022, 39(4): 427-439.  DOI: 10.19596/j.cnki.1001-246x.8447
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    D3Q15 model of multi-relaxation time lattice Boltzmann method(MRT-LBM) is applied to simulate flow in three-dimensional lid-drive cavities with different curved boundaries, including rectangular cavity, cylindrical cavity, semi-cylinder cavity, rotating hyperboloid cavity, ellipsoid cavity, hemisphere cavity and two combined cavities. Streamlines, velocity contours and vortex positions of these cavities are analyzed. Flow characteristics of typical cavities with various Reynolds numbers are compared. It shows that under same Reynolds numbers the curved boundary eliminates the second and third vortices caused by the boundary. It leads to the separation of the main vortex in the cavity and increases the vertical reflux velocity of the central profile. Streamlines of the combined cavity with cuboid up semi-cylinder are fit most with the boundary. As the Reynolds number is increasing, the main vortex in the semi-cylindrical cavity separates gradually into two homodromous vortices, and the basic flow characteristics of the cylindrical cavity and the hemispheric cavity are always maintained in the cavity with cylinder up hemisphere; While the main vortex center in the cuboid cavity remains at the same height, the secondary vortex is gradually enhanced, and the flow in the cavity becomes more and more regular in the combined cavity with cuboid up semi-cylinder, the main vortex gradually sinks, and the flow velocity is smaller at the center and is greater near the boundary in the combined cavity with cuboid up semi-cylinder.

    A VOF-LPT Coupling Method for Simulating Jet Atomization
    Zi-feng LI, Ning YANG
    2022, 39(4): 440-452.  DOI: 10.19596/j.cnki.1001-246x.8460
    Abstract ( )   HTML ( )   PDF (13729KB) ( )  

    We evaluate several VOF(Volume of Fluid) methods for interfacial reconstruction. A VOF-LPT(Lagrangian Particle Tracking) coupling method is applied in OpenFOAM, an open source CFD package, to achieve both simulation accuracy and computational efficiency. This method simulates accurately from continuous liquid to discrete small droplets for jet atomization. It provides a feasible and efficient simulation scheme for simulation of jet atomization process on large scales.

    Numerical Simulation of 3D Discrete Fracture Networks Considering Dynamic Closure of Hydraulic Fractures and Natural Fractures
    Xu-lin DU, Lin-song CHENG, Lang-yu NIU, Yu-ming CHEN, Ren-yi CAO, Yong-hong XIE
    2022, 39(4): 453-464.  DOI: 10.19596/j.cnki.1001-246x.8435
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    A characterization method for fracture dynamic closure considering influence of stress state in three-dimensional space is proposed based on an embedded discrete fracture model. Aperture and permeability of fractures in any direction are considered as functions of normal effective stress acting on the fracture surface. Meanwhile, the change of fracture conductivity is used to characterize dynamic closing behavior of proppant-filled hydraulic fractures and opened natural fractures due to the decrease of formation fluid pressure during reservoir development. It shows that the development of tight oil reservoirs is dominated by "fracture-controlled reserves". In evaluating productivity of fractured horizontal wells, the dynamic closure of fractures lead to a partial loss of production, and its influence can not be ignored. Proppant material properties of hydraulic fractures, and stiffness of natural fractures are the main controlling factors. To minimize adverse impact of fracture closure on production it is necessary to increase the concentration and particle size of proppant and improve proppant properties.

    A Single Well Production Forecasting Model of Reservoir Based on Conditional Generative Adversarial Net
    Can HUANG, Leng TIAN, Heng-li WANG, Jia-xin WANG, Li-li JIANG
    2022, 39(4): 465-478.  DOI: 10.19596/j.cnki.1001-246x.8480
    Abstract ( )   HTML ( )   PDF (11595KB) ( )  

    To address overfitting problem of production forecast model in machine learning and improve accuracy of production forecast in actual oil field, a model for single well production forecasting of reservoir based on Conditional Generative Adversarial Net(CGAN) was proposed. The model hybridizes two types of basic neural network structures, i.e., long short-term memory network and fully connected network, to construct a generative model and a discriminant model. The generative model takes production influencing factors as conditions to generate the forecasting production data. It defines a logarithmic loss function as a residual between predicted and real data, to improve comprehensively the generalization ability of the model. Bayesian hyperparameter optimization algorithm was used to optimize the model structure through game training of CGAN. With numerical simulation software Eclipse, single well production database with same well pattern under different geological and production conditions was established to train CGAN, which can be used to predict rapidly single well production of reservoir by taking geological and production factors as condition input of the model. Experimental results show that compared with prediction results of models FCNN, RF, and LSTM, mean absolute percentage error of CGAN model on the test set is increased by 2.59%, 0.81%, and 1.72%. The overfitting ratio is the smallest(1.027). It indicates that CGAN reduces overfitting degree of the machine-learning-based production forecast model, and improves generalization ability and accuracy of the model as well. This verifies superiority of the algorithm, which is of great significance to guide efficient development of oilfields and ensures security of national energy strategy.

    Mass Exchanger Network Synthesis Based on Random Walk Algorithm with Compulsive Evolution
    Xiu-bao MA, Zhao-liang GAI, Guo-min CUI, Zhi-qiang ZHOU, Xin-yu HAN, Qi-guo YANG
    2022, 39(4): 479-490.  DOI: 10.19596/j.cnki.1001-246x.8465
    Abstract ( )   HTML ( )   PDF (1461KB) ( )  

    Aiming at shortcomings of existing mass exchanger network optimization methods, a random walk algorithm with compulsive evolution for mass exchanger network synthesis is proposed, in which the mass transfer load, split ratio and the flow of lean streams of mass exchanger are increased or reduced randomly. A minimum threshold is set to realize synchronous optimization of network continuity and integer variables. A small probability is retained to accept the difference solution. It enhances mutation ability of the structure, and makes the algorithm taking into account global search and local search of mass exchanger network. Application in two mass exchanger network examples show that the optimization results are better than those in current literatures. The algorithm maintains independent evolution between individuals and has good global and local search ability.

    Differential Chaos Shift Keying Secure Communication System Based on Repeated Chaotic Spreading Sequence
    Ya-qiong JIA, Bin YU
    2022, 39(4): 491-497.  DOI: 10.19596/j.cnki.1001-246x.8431
    Abstract ( )   HTML ( )   PDF (3261KB) ( )  

    A kind of differential chaos keying communication system was presented based on repeated chaotic spreading sequence(RCSS). Bit error rate(BER) performance is theortically analyzed and then verified with numerical simulations. In the system, a repeated chaotic spreading sequence is produced by copying the reference sequence of the DCSK-modulated signal, and part of the parallel bit streams are multipled with this RSS. The resulting signals are then conveyed into the channel. Theoretical analysis and simulation results show that BER performance of the system is better than DCSK, CDSK and CD-DCSK. The system performs better as the spreading factor reduces. BER performance over an AWGN channel is better than aht over a Rayleigh channel.

    Chaos Prediction of Motor System Based on WOA-ESN
    Kai-ge LIU, Du-qu WEI
    2022, 39(4): 498-504.  DOI: 10.19596/j.cnki.1001-246x.8442
    Abstract ( )   HTML ( )   PDF (2463KB) ( )  

    We propose a WOA-ESN model, which combines Whale Optimization Algorithm(WOA) with Echo State Network(ESN) and applie to the prediction chaos of Permanent Magnet Synchronous Motor(PMSM). WOA-ESN model was compared with ESN and PSO-ESN. It shows that the method has better prediction performance.

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