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25 November 2013, Volume 30 Issue 6 Previous Issue    Next Issue

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Adaptive Discontinuous Galerkin Method with Lax-Wendroff Type Time Discretization and Three-dimensional Nonconforming Tetrahedral Mesh for Euler Equations FENG Tao, YU Xijun, AN Hengbin, CUI Xia, WU Di, LI Zhenzhen 2013, 30(6): 791-798.  Abstract ( )   PDF (1377KB) ( )   We present a Lax-Wendroff discontinuous Galerkin (LWDG) method combining with adaptive mesh refinement (AMR) to solve three-dimensional hyperbolic conservation laws. Compared with Runge-Kutta discontinuous finite element method (RKDG) the method has higher efficiency. We give an effective adaptive strategie. Equidistribution strategy is easily implemented on nonconforming tetrahedral mesh. Error indicator is introduced to solve three-dimensional Euler equations. Numerical experiments demonstrate that the method has satisfied numerical efficiency.

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Moment-based Cosh-Hilbert Inversion and Applications in Single Photon Emission Computed Tomography LUO Shousheng, YANG Jiansheng, ZHOU Tie 2013, 30(6): 799-807.  Abstract ( )   PDF (1859KB) ( )   Based on Tricomi formula for Hilbert transform and Taylor expansion of cosh-function, a numerical inversion algorithm for cosh-Hilbert transform (CHT) is proposed and applied to single photon emission computed tomography imaging. CHT of a function is represented as its Hilbert transform and a correction term including all of its moments by using Taylor expansion of cosh-function. A linear system about all moments of the function is obtained via Tricomi formula. Finite numbers of moments can be solved by truncating the infinite linear system, and the function can be reconstructed approximately. Numerical simulations are performed to verify the algorithm by comparing with analytical inversion formula.

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Lattice Boltzmann Method for Simulating Propagating Acoustic Waves DENG Yiqiu, TANG Zheng, DONG Yuhong 2013, 30(6): 808-814.  Abstract ( )   PDF (2318KB) ( )   For application of lattice Bohzmann method (LBM) in aeroacoustics field, four fundamental acoustic cases are simulated. Sound waves propagating with planar source and single point source are used to investigate reliability of LBM in aeroacoustics. Capability for reflecting waves is then investigated with diffraction and interference. Doppler effect is simulated to illustrate coupled acoustics and flows. In all cases, simulated acoustics is found in good agreement with analytic solutions. It shows that LBM has good performance in computational aeroacoustics field.

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LB-DF/FD Simulation of a Drop-shaped Particle in Two Dimensions Settling in a Vertical Channel NIE Deming, ZHENG Mengjiao, ZHANG Kai 2013, 30(6): 815-824.  Abstract ( )   PDF (2963KB) ( )   We investigate numerically sedimentation of a drop-shaped particle in an infinitely vertical channel with a LB-DF/FD method. In the method, Navier-Stokes equations are solved by lattice Bohzmann method and fluid-solid interactions are handled by fictitious domain scheme. This work focuses on effects of particle shape factor on friction coefficient and drag coefficient of drop-shaped particle in Reynolds numbers ranging from 10-2 to 102. Comparison with results of a circular particle is presented. It shows that particle friction coefficient keeps constant as Reynolds number is below 1. It increases as Reynolds number increasing as Reynolds number is greater than 1. Furthermore, it shows that both friction coefficient and drag coefficient of a circular particle are smaller than those of a drop-shaped one as Reynolds number is below 30 while it is greater as Reynolds number is greater than 30. To clarify this issue a detail investigation of pressure distribution around particle is presented.

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Analysis on Thermal Environment of Interaction Region Around Protuberance in High Speed Flows PAN Honglu, LI Junhong, ZHANG Xuejun 2013, 30(6): 825-832.  Abstract ( )   PDF (3822KB) ( )   In hypersonic/supersonic flow conditions, numerical simulations, experience relations and experiment analysis are made to study thermal-environment distribution characteristic around local-parts imposed by protuberance interacting body. Comparing flow characteristic structures in different shape, height, breadth ere, we found that interaction-zone size induced by high protuberance depend sensitively on effective breadth and short protuberance interaction-zone size depend on protuberance height. On the other hand, interaction-zone size is imposed by shade of lead edge, whether laminar or turbulence. Square-lead-surface and arc lead surface separation length ratio is 1.414. Sweepback affects separation length. A correlative line is built for size of separation imposed by sweepback.

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An Improved Particle Level Set Method and Its Application TIAN Hui, LI Guojun 2013, 30(6): 833-842.  Abstract ( )   PDF (3000KB) ( )   An improved particle level set method is proposed for simulation of incompressible two-phase flows. In this method, an improved particle correction method is developed to deal with relative positions between escaped particles and grid corner, which reduces disturbance arising in distance function correction due to non-normal direction movement of escaped particles. The method is validated with capturing accurately moving interface in single vortex flow problem. A projection method is used to solve control equations of incompressible two-phase flows with high density ratio (nearly 103) and viscosity ratio (nearly 102). Six typical bubble shapes are successfully captured in simulation of rising bubbles. Finally, time-dependent evolution of Rayleigh-Taylor instability (RTI) interface is numerically investigated. Numerical results are in good agreement with published results. Effects of control parameters on evolution of RTI are well examined.

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Dual Elastic Wave Wavefield Separating Simulation Method and Related Theory Derivation CHEN Keyang, WU Qingling, FAN Xingcai, CHEN Shumin, LI Lailin, LIU Zhenkuan, WANG Jianmin, GUAN Xin 2013, 30(6): 843-854.  Abstract ( )   PDF (3094KB) ( )   We present an equivalent dual elastic wave separation equation, which simulates particle-velocity, pressure, divergence and curl fields in pure P- and S- modes. The method is used in full elastic wave numerical simulations. We give complete derivations of explicit high-order staggered-grid finite difference discrete equations, together with stability condition, dispersion relation and perfectly matched layer (PML) absorbing boundary condition. Theoretical analysis and numerical simulations show that pare P-waves and S-waves in final numerical results are completely separated in the method. Effect of absorbing boundary is perfect. Storage and computing time requirements are greatly reduced compared with previous works.

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Multi-scale Decomposition and Reconstruction Based on Diffusion Filtering and Preliminary Application CHEN Keyang, FAN Xingcai, WU Qingling, CHEN Shumin, LI Lailin, LIU Zhenkuan, WANG Jianmin, GUAN Xin 2013, 30(6): 855-861.  Abstract ( )   PDF (1869KB) ( )   From PM equation we derive muhi-dimensionay diffusion filtering equation discrete formula and its stable condition. We construct multi-scale decomposition and reconstruction method based on diffusion filtering, and provide two specific implementation plans. Application in practical seismic data shows that the method is reasonable and reliable. In the first plan 2D Fourier wave-number spectrum main energy is away from spectrum center with increase of scale, and residual signal acts at high wave numbers, which shows perfect application in random noise suppression. In the second plan 2D Fourier wave-number spectrum energy is close to spectrum center with increase of scale, and residual signal acts at low wave numbers, which shows perfect application in low-frequency reverse time migration noise suppression. The method computation is simple and easy to implement. It provides a multi-scale decomposition and reconstruction method for signal processing. It may has great application in seismic signal processing.

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Thermal Compensation of Rocks Encircling Heat Reservoir in Heat Extraction of Enhanced Geothermal System CHEN Jiliang, LUO Liang, JIANG Fangming 2013, 30(6): 862-870.  Abstract ( )   PDF (3385KB) ( )   With a self-developed numerical model, we simulate long-time operation processes of an imaginary doublet enhanced geothermal system (EGS) with different geological conditions and analyze effects of thermal compensation on evolution of production temperature and fluid and rock temperature in the heat reservoir. The model treats heat reservoir as an equivalent porous media while considers thermal non-equilibrium between rock matrix and fluid. It uses two energy equations to describe temperature field of rock and circulating fluid, respectively, enabling thorough investigations on local heat exchange processes of rock and fluid. It reveals that influence of thermal compensation from rocks encircling heat reservoir is strongly correlated with flow pattern in the reservoir, and it does not always have positive effect on EGS production temperature. If there appears an obvious preferential flow in depth direction of the reservoir, thermal compensation can even lower production temperature during early period of EGS operation. With advance of EGS operation, rock temperature in reservoir decreases and thermal compensation gradually brings a pronounced positive effect on production temperature.

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Numerical Simulation of Down-hole Seepage Flow in Enhanced Geothermal System CHEN Jiliang, JIANG Fangming, LUO Liang 2013, 30(6): 871-878.  Abstract ( )   PDF (2414KB) ( )   With a self-developed numerical model, we simulate seepage flows in reservoir of an imaginary doublet EGS and perform a systemic investigation on flow pattern correlating with the reservoir hydraulic permeability. It reveals that the flow pattern in reservoir is mainly decided by relative magnitude of "basic pressure difference" caused by gravity and hydrodynamic-hydrostatic pressure transformation to fluid flow resistance through fractured rock mass. Circulation flow rate exhibits a limited effect on the flow pattern. Based on this we bring forward two strategies, horizontal well and multiple well layouts, to restrain the down-hole flow circuit in EGS reservoir, which acts as theoretical guidelines for practical construction of EGSs.

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Numerical Inversion for Permeability Parameters of Formation LIU Fuping, WANG Anhng, YANG Changchun 2013, 30(6): 879-885.  Abstract ( )   PDF (890KB) ( )   With relation of well-bore and grid-block pressure with any grid permeability parameters of formation (sensitivity coefficients of permeability field), we derived derivatives with respect to permeability for well indices. Numerical derivatives of well-bore pressure with respect to permeability of any grid with numerical solution of 3D fluid equation in porous media are given. Numerical calculation of sensitivity coefficients of permeability field for multi-well system is realized. Based on sensitivity coefficients, an inverse iterative equation is constructed by conjugate method. Numerical calculation for permeability parameters of formation is realized. It shows that:If permeability is uniform or block uniform, relative error of inverse permeability is less than one hundredth as inversely iterating 10 times. It is significant for dynamic simulation and examination of reservoir.

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Wavelet Element Method for Band Structures of Phononic Crystals LIU Zhangyi, WU Jiuhui, SHEN Li 2013, 30(6): 886-894.  Abstract ( )   PDF (2884KB) ( )   A wavelet element method is developed to compute band structures of phononic crystals. It is based on combining biorthogonal wavelet systems with philosophy Of spectral element method. Biorthogonal spline wavelets on interval with boundary adaption are constructed. Boundary adaption of wavelet element is extended to first-order derivatives, due to which construction of basis functions that satisfy boundary conditions exactly is possible. The method takes advantage of structural features of phononic crystals and boundary conditions are satisfied exactly. Better accuracy and higher efficiency are obtained.

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3D Modified Novel PML Absorbing Boundary Condition for Truncating Magnetized Plasma ZHENG Zhaowen, YANG Lixia 2013, 30(6): 895-901.  Abstract ( )   PDF (1275KB) ( )   We study absorbing boundary conditions (ABC) of novel perfectly matched layer (NPML) of three-dimensional truncated magnetized plasma. A modified NPML (M-NPML) method is presented. According to electromagnetic scattering theory of magnetized plasma, we stretch space variables of partial derivatives in Maxwell partial differential equations. In the stretched-scheme complex field splitting form is avoided as truncating ordinary media by PML method. Moreover, the scheme is much easier than uniaxial anisotropy perfectly matched layer (UPML) in programming. Simulation results fit analytical solutions, which shows validity of the M-NPML ABC algorithm.

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Numerical Study on Effect of Equilibrium Current Profile on Resistive Wall Mode Stability CHEN Longxi, LEI Wenqing, WU Bin 2013, 30(6): 902-908.  Abstract ( )   PDF (2334KB) ( )   Effect of equilibrium current profile on resistive wall mode stability are numerically studied. The most unstable mode with different equilibrium current profiles under fixed safety factor at plasma surface has same poloidal number and toroidal number. At same wall location, linear growth rate of (3,1) mode of non-uniform current profile is greater than that of uniform current profile. Effect of plasma flow on resistive wall mode stability is different with different current profiles. After linear evolution, RWM saturates at nonlinear phase. Saturation can be attributed to flux piling up on resistive wall. Saturation level of non-uniform current profile is lower than that of uniform current profile.

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Comparison Study of 3 mm Wave RCS of Expanded Graphite and Chaff ZHOU Mingshan, YANG Chunyan, XU Ming 2013, 30(6): 909-914.  Abstract ( )   PDF (1807KB) ( )   To investigate scattering characteristics of expanded graphite in 3 millimeter waves, with method of moment formule of radar cross section (RCS) are established based on electromagnetic scattering of finite length and conductivity cylinder. Average RCS of expanded graphite and its jamming decoy are calcutated. RCS of graphite and chaff jamming decoy are measured through field experiment. It shows that expanded graphite have some scattering ability in 3 millimeter wave. Average RCS of single expanded graphite particle is 0.867 6 mm2 as its radius and length are 0.12 mm and 1.5 ram, respectively. RCS of chaff is 7.4 times of expanded graphite as interfering material mass are same. Expanded graphite is difficult to implement in the style of chaff decoy deception jamming on guided weapons.

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Steady Oscillations of Magnetic Vortex Driven by a Spin-Polarized Current in a Confined Point-Contact Structure LIU Yan, LI Huanan, HU Yong, DU An 2013, 30(6): 915-920.  Abstract ( )   PDF (2312KB) ( )   We choose a confined point-contact geometry as research model. Steady-state oscillations of magnetic vortex driven by a spin-polarized current are calculated with analytical calculations based on Thiele's equation. It indicates that magnetic vortex can maintain steady oscillations in a specific current range. Current density range depends on nanocontact dimensions and dot aspect ratios. Both orbital radius and frequency of steady oscillations increases with current density. Adjustable range of oscillation frequency decreases dramatically with increasing nanoeontaet size.

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Theoretical Study of Nickel Doping in Copper Clusters FENG Cuiju, MI Binzhou 2013, 30(6): 921-930.  Abstract ( )   PDF (1530KB) ( )   Configurations and electronic properties of Cun-lNi and pure Cun(n=3-14) clusters are calculated in the framework of all-electron density-function theory. It demonstrates that structure of Cun(n=3-14) clusters does not grow in a compact pattern but tends to a platelet-like configuration. CunNi(n=2-13) clusters grow in an icosahedral pattern and doping of one Ni atom increases stability of pure Cun clusters. Ni atom prefers maximum numbers of neighboring Cu atoms and gradually falls into interior of the Cu framework as number of Cu atom increases. It shows that even-atom clusters have relatively higher stability. Especially, Cu3Ni, Cu7Ni and Cu9Ni are more stable. In Ni-doped copper clusters, impurity atom exhibits positive charge and donates electron to copper atoms. The presence of a doping atom like Ni atom affects chemical activity of copper clusters including corrosion-resistant properties.

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First-principles Calculation of Thermodynamic Functions of Li-Ga-S System MA Tianhui, MA Tianfang, SUN Liang, ZHU Chongqiang 2013, 30(6): 931-935.  Abstract ( )   PDF (1255KB) ( )   First-principles study of LiGa Li2S, GaS, Ga2S3 and LiGaS2 thermodynamic functions in Li-Ga-S system was performed by using plane-wave pseudopotential method. All possible chemical reactions were analyzed. It was found that the goal product LiGaS2 comes from four chemical reactions. Free energy change of direct synthesis from elements is high. Free energy change of synthesis from Li2S and Ga2S3 decreases with increasing temperature, but Ga2S3 is difficult to be obtained. These two reactions can not occur in this system. The remaining reactions by LiGa and S method and Li2S and GaS method can occur due to their low free energy changes. Free energy changes generating Li2S, GaS and LiGa are low.

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Influence of Electric Field on 1,4-Phenylene Diisocyanide Molecular Electronic Transport LIU Ruijin, SUN Yuping 2013, 30(6): 936-942.  Abstract ( )   PDF (2764KB) ( )   With ab initio theory and elastic scattering Green's function method, electronic structure, conductance and current of 1,4-phenylene diisocyanide molecule are investigated. It shows that charge of system is transferred and redistributed by electric field. Electron gathering area and dissipation area are formed near interface between molecule and electrodes. Additional electric dipoles are formed, which restrain conductance and current of molecule. Moreover, molecular orbit energy and coupling coefficients between molecule and electrodes are influenced obviously by electric field, which make differences in molecular voltage current characteristic.

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Electron Transport in Silicon Nanoscale Junctions LIU Futi, CHENG Yan, YANG Fubin, CHENG Xiaohong, CHEN Xlangrong 2013, 30(6): 943-948.  Abstract ( )   PDF (1812KB) ( )   Electron transport in a linear atomic chain composed of 3 silicon atoms and sandwiched between gold electrodes is investigated with combination of density functional theory and non-equilibrium Green's function method. Relationship of conductance with distance is calculated. It shows that:At a distance of 1.584 nm, binding energy of junctions is minimum, structure is the most stable, Si-Si bond length is 0.216 nm, Si-Au bond length is 0.227 nm, conductance is 0.729 G0(G0=2e2/h), electron transport channels mainly consist of px, py orbital electrons of Si atoms. With increase of voltage conductance decreases and I-V curve of nanoscale junctions at equilibrium position shows linear feature.