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25 November 2009, Volume 26 Issue 6 Previous Issue    Next Issue

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Conservative Remapping Algorithm in Multiscale Dynamic Simulation XU Yun, YU Xijun, CHEN Jun 2009, 26(6): 791-798.  Abstract ( )   PDF (499KB) ( )   A conservative remapping algorithm based on donor-cell method for multiscale dynamic simulation is proposed which couples micro molecular dynamics (MD) simulation with macro finite element (FE) method. Since physical quantities are obtained with integral reconstruction from information of FE nodes and their underlying MD atoms, the algorithm can be applied to both structured and unstructured meshes. An auxiliary mesh is introduced for vertex-centered unknowns. Accuracy and efficiency of the method are validated with numerical experiments.

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A Second-order Hybrid Rotated Riemann Solver for Multi-dimensional Euler Equations on Unstructured Meshes LEI Guodong, REN Yuxin 2009, 26(6): 799-805.  Abstract ( )   PDF (568KB) ( )   A second-order rotational upwind transport scheme for multidimensionul compressible Euler equations on unstructured meshes is presented. Cell-centered FVM is employed in which gradient calculation is node-based with more neighbor cells. Slope limiter schemes are constructed for unstructured meshes. Numerical fluxes are evaluated by solving two Riemann problems in two upwind directions, including velocity-difference vector and perpendicular direction. The scheme eliminate shock instabilities or carbuncle phenomena in flux-difference splitting type schemes completely. A hybrid rotated Riemann solver is employed to form an economical numeric flux function and base Riemann solvers employ HLL and Roe FDS.

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An Iterative Method For Unstructured Dynamic-grid Using Springs Based on LU-SGS WU Qing, ZHONG Yicheng, YU Shaozhi, HU Jun 2009, 26(6): 806-812.  Abstract ( )   PDF (471KB) ( )   An iterative method for unstructured dynamic-grid using springs based on LU-SGS (lower-upper symmetric Gauss-Seidel) is presented to reduce time of iterative in dynamic discontinuities simulation. Dynamic grid iterative time is as much as time of field itemtive as shock and flex-wall are numerical fitting by time-dependent Euler equations, because dynamic boundary is moving and whole unstructured grids are updated in every step of field iterative. A sparse matrix mapping grid topology based on spring strategy is presented. LU-SGS strategy is used in numerical simulation and dynamic grid is managed in order to solve the time choke point. Numerical results show that LU-SGS iterative method can be used to dynamic discontinuities fitting by implicit scheme. The presented method decreases more than 20% iterative time than classical SOR method.

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Node Placement Method with Bubble Simulation and Parallelism LIU Ying, NIE Yufeng 2009, 26(6): 813-820.  Abstract ( )   PDF (522KB) ( )   In the light of molecular dynamics simulation and bubble meshing a node placement method, called node placement method with bubble simulation, is presented. In the method nodes are bubbles and bubbles are moved by interacting forces. With dynamic simulation centers of bubbles form a good-quality node set in the domain. And this process doesn't need updating mesh connection constantly. Examples show that uniform point sets and non-uniform point sets generated by this method have good construction and gradualness. And this method is adaptable to complex regions. These placed nodes can be used in meshless method. And triangular meshes can also be generated from these placed nodes in finite element method. Furthermore, for locality of interacting forces, this method is similar to short-range molecular dynamics simulation, and is easy to parallelization. Experimental result shows that the parallelization of this method is feasible.

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A Monotonicity- and Conservation-Preserving Interpolation Operator MA Libin, HU Xiaoyan, MO Zeyao 2009, 26(6): 821-830.  Abstract ( )   PDF (394KB) ( )   We propose a monotonicity- and conservation-preserving interpolation operator, named PQIM. Its order of convergence, conservation-preserving and monotonicity-preserving properties are demonstrated. The interpolation operator is proved to restrain oscillation caused by interpolation effectively.

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An Approach for Scientific Dataset Stream Reduction Based on Information Measures WU Guoqing, MO Zeyao, CHEN Hong 2009, 26(6): 831-836.  Abstract ( )   PDF (387KB) ( )   We propose a data reduction approach based on information theory. It comprises sampling of datssets based on mutual entropy and truncation based on offline Marginal Utility. The approach is a universal method for multi-dimensional scientific dataset streams. To show applicability, results obtained with plasma simulation data are presented, It reduces relationship and redundancy between datesets.

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Numerical Simulation of Active Stall Control on High-lift Airfoil HAN Zhonghua, SONG Wenping, QIAO Zhide 2009, 26(6): 837-841.  Abstract ( )   PDF (345KB) ( )   Interaction of synthetic jet and low-speed high-lift flow past a YISG 107 airfoil is simulated and stall control of high-lift airfoil is investigated. A cell-centered finite-volume scheme is used to discrete unsteady Reynolds-Averaged Navier-Stokes equations in integral form. An AUSM± up upwind scheme and a fully implicit dual-time step method are utilized for spatial discretization and time stepping, respectively. Implicit preconditioning method and geometric multigrid method are employed to remove stiffness encountered in simulation of low-speed flows and to accelerate convergence of computation. Influence of synthetic jet on main flow is modeled with a generalized unsteady blowing/suction boundary condition. Computational results with a synthetic jet located at 17.5% c from leading edge agree weU with low-speed wind tunnel experiment. With a momentum coefficient of 0.005, nondimensional frequency of 2.75 and jet angle of 20°, critical stall angle is delayed by 2°, and the maximum lift is increased by 8.7%. Influence of momentum coefficient and jet angle on stall performance is studied. It is shown that two key reasons lead to small improvement in previous wind tunnel experiments: One is due to low momentum coefficient. Only as momentum coefficient is larger than 0.001 can relatively evident improvement of stall characteristic be obtained. Another is due to unsuitable normal jet in tall control of a high-lift thick airfoil. Near tangent jet is better than normal jet.

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Numerical Simulation of Two-dimensional Vortexes with Adaptive Wavelet Method ZONG Zhi, ZHAO Yong, ZOU Wennan, GAO Yun 2009, 26(6): 842-848.  Abstract ( )   PDF (437KB) ( )   Taking vorticity equation as a controlling equation, we simulate three vortexes developing progress with initial condition of Gaussian probability vorticity distribution. The wavelet expression of vorticity contains scaling coefficient term and wavelet coefficient tenn. The latter can be divided into a significant wavelet coefficient term and a trivial wavelet coefficient term reference to a given critical value. The critical value contains practical flow information. The vorticity is reconstructed only with scaling coefficients and significant wavelet coefficients. It saves computing time and capture most part of entrophy. Numerical results show that scaling coefficients together with significant wavelet coefficients is less than 10% of total wavelet coefficients, but they contains more than 99% of total enstrophy.

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Multiscale Simulation of Nanofluid Multiphase Flows ZHOU Lujun, XUAN Yimin, LI Qiang 2009, 26(6): 849-856.  Abstract ( )   PDF (540KB) ( )   A hybrid method is proposed to study microcosmic characteristics of nanofluid mulfiphase flows in a lattice Boltzmann approach. Multicomponent lattice Boltzmann model on fine mesh is used in regions where physical parameters, such as density and velocity change tempestuously, otherwise a single component one on coarse mesh is used. In order to keep continuity of physical information (physical parameters) in overlapping regions, principle of mass and momentum conservation is used. It shows that in the model microcosmic characteristics of nanofluid flow can be obtained. Computational efficiency is improved observably compared with a multicomponent method.

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Perturbation Finite Volume Method and Application in Two-phase Flows DONG Hefei, ZHANG Deliang, YANG Guowei 2009, 26(6): 857-864.  Abstract ( )   PDF (555KB) ( )   Droplets in liquid-liquid two-phese flow are simulated by a perturbation finite volume (PFV) method and Level Set technique. Numerical results show that the PFV scheme has advantages in fewer nodes, high accuracy and efficiency, h facilitates programming. PFV scheme successfully simulates liquid-liquid two-phase flows.

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Dynamic Characteristics of Nonsteady Flows with Phase Redistribution in Double Porous Media and Fractal Reservoir HOU Yingmin, TONG Dengke, ZHANG Huaqing 2009, 26(6): 865-871.  Abstract ( )   PDF (286KB) ( )   A fractal theory for double porous media reservoir is introduced. An effective well radius mathematical model is used to calculate pressure of non-stesdy flow in a complex intluent system considering wellbore storage, skin factor and phase redistribution. With Douglus-Jones predictor-correcter method we obtain numerical solution of infinitely large system with constant rate production. Entire drawdown curve of the complex influent system includes 4 periods. Effects of phase redistribution parameters, double porous media parameters and fractal parameters on drawdown are shown in typical pressure curves.

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A Mathematical Model of Polymer Enhanced Foam Flooding DU Qingjun, HOU Jian, LI Zhenquan, WANG Yudou, CHEN Yueming 2009, 26(6): 872-878.  Abstract ( )   PDF (387KB) ( )   A muhi-component mathematical model characterizing polymer enhanced foam flooding filtration is established with mass conservation principle of foam components. Considering combination of foam generation, coalescence and migration phenomena, the model effectively reflects mechanism of oil phase foam coalescence and polymer foam stabilizing. Differential numerical solution is conducted with adaptive implicit method. Validity of the mathematical model is verified with experiment. Meanwhile, taken foam flooding pilot region of a oilfield, a numerical simulator is employed to study filtration characteristics of enhanced foam flooding. It is indicated that the foam system could exist stably in the formation and gradually advance to production wells to improve oil recovery.

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Numerical Simulation of 3D Orthogonal Woven Composite Impacted by a Spherical Bullet YU Yumiao, WANG Xiaojun, LI Yongchi, WANG Zhihai 2009, 26(6): 879-886.  Abstract ( )   PDF (636KB) ( )   We present numerical simulation of Kevlar/Vinyl 3D orthogonal woven composite impacted by a spherical bullet with LS-Dyna software. Orthogonal constitutive equation with damage tensor and Hashin failure criteria are adopted for the Kevlar/Vinyl target. Time history of penetration velocity and loading of bullet show that steady penetration process and residual velocity agree well with experimental date. The damage modes basically reflect experimental results. Penetration process and damage modes are studied in details by analyzing damage evolution along the x fiber and interface matrix. It shows that the simulations are in good agreement with experiments.

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Numerical Study On Penetration of Shaped Charge Jets into Concrete Targets ZHANG Fenguo, FENG Qijing, HAO Pengcheng, LIANG Longhe 2009, 26(6): 887-891.  Abstract ( )   PDF (405KB) ( )   A Eulerian code MEPH2Y is combined with a Lagrangian code LTZ-2D to analyze perforation of jet and projectile on a concrete plate. The hybrid code advantages in calculation the formation of jet and projectile. High resolution on penetration and damage of concrete target are obtained. Jet penetration and damage of the concrete target are simulated and compared with experimental results. Jet penetration and damage of concrete target simulated agree well with test data.

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Fast Implementation of Forward Modeling of 3-D Geoelectric Field with Precondition Lanczos Method WAN Xinlin, XI Daoying 2009, 26(6): 892-896.  Abstract ( )   PDF (270KB) ( )   An incomplete Cholesky factorization is used to preconditioning large sparse coefficient matrix in 3-D geoelectric field forward modelling. Coefficient matrix of the new system is an approximate unit matrix. Preconditioned Lanczos algorithm improves stability and convergence of iterative procedures. In the algorithm, as iterative numbers are smaller than dimensions of coefficient matrix, approximation of the exact solution is obtained. Preconditioned Lanczos algorithm is effective in 3-D geoelectric field forward modeling. It makes a foundaiton for 3-D geoelectric inversion.

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Thermographic Identification Algorithm of Two-dimensional Irregular-shaped Self-heating Subsurface Defects FAN Chunli, SUN Fengrui, YANG Li 2009, 26(6): 897-902.  Abstract ( )   PDF (408KB) ( )   A two-dimensional heat transfer model is built and solved with finite element method to study temperature distribution on outer surface of a test piece with a self-heating subsurface defect. Based on conjugate gradient method, an algorithm is proposed for identification of subsurface defect with temperature on the outer surface of the teat piece measured with an infrared imager. Effectiveness of the method is validated by numerical experiments. It is concluded that the method identifies serf-heating defects with high precision for test pieces with small thermal conductivity. Effect of temperature measurement error, number of temperature measurement point and initial defect boundary guess on defect identification can be neglected. The greater the maximum temperature difference on outer test piece surface is, the higher precision of identification is.

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Convective Heat Transfer in Blood Vessels XIE Haiwei, ZHANG Yan, ZHU Kai 2009, 26(6): 903-910.  Abstract ( )   PDF (540KB) ( )   Convective-type boundary conditions at interface of vessel walls are used in simulating convective heat transfer in blood vessels. To study feasibility of the method, convective heat transfer between blood and tissue in a simple furcated vessel system is computed with finite element analysis. Mean Nusselt number on cross-section along the vessel is obtained at various flow velocities or vessel radii. It shows that the mean Nueselt number in the branching vessel varies within a narrow range, and shows fast convergence rate. A tongue with a simple vascular tree is simulated as an example. Conjugated numerical method, and a approximate method are used to calculate 3-D velocity and temperature of the tongue. Distributions of temperature calculated are similar and quantitative difference between temperatures obtained by two methods is less than 0.2℃.

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Core Neutron Space-time Kinetics of High Temperature Gas Cooled Reactor SONG Yingming, MA Yuanle, SHAN Wenzhi, ZHOU Zhiwei, JING Xingqing 2009, 26(6): 911-916.  Abstract ( )   PDF (293KB) ( )   3D-cylinder reactor core neutron space-time kinetics is simulated with an improved quasi-static method. The program is developed. In a supposable 250 MW modular HTGR model, the core neutron space-time kinetics is simulated. Calculated results obtained from this program and CITATION code agree well with each other at initiatory state. Variance of the core reactivity, average neutron flux of each group, and relative power with time is computed.

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Self-assembling of Amphiphilic Macromolecules: Self-consistent Field Theory YIN Haifeng, ZHU Yuejin, ZENG Chunhua 2009, 26(6): 917-924.  Abstract ( )   PDF (465KB) ( )   Complex microstructures assembled with ABC amphiphilic nanoperticle-coil macromolecules are investigated with an extending serfconsistent field theory (SCFT) and density functional theory (DFT). The tail of macromolecule is an AB dibiock copolymer, and the attached "head" is a nanoparticle in dilute solution. Serf-assembly morphologies of ABC "tadpole" are different from aggregate morphologies of linear ABC triblock copolymers. As nanoparticle is hydrophilic, spherelike micelles are observed in a weak segregation state. While interaction between different species of "tadpole" increases to a strong segregation state, aggregate morphologies of tadpole transform from spherelike micelles to quadrangle or triangle micelles with increasing of hydrophobic property of blocks A and B. In this case, block B is distributed in corners of quadrangle or triangle micelles. As block A is hydrophilic, hydrophobic nanoparticle assembles into parallel rods or squares in spherelike micelles.

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Gaussian Fluctuation-driven Ordered Structures of Binary Mixtures with Particles FENG Wenqiang, ZHU Yuejin 2009, 26(6): 925-930.  Abstract ( )   PDF (558KB) ( )   We study orderd structures of binary mixtures with mobile particles under Gaussian noise with Monte Carlo method. It shows that interaction between particle and component decides position of particles and motion of particle can break up isotropy of the system. As this interaction is large, tilted strip pattern formation is observed with a particular external C, aussian noise and particle concentration. Furthermore, an optimal noise frequency region(p=0.005~0.02)exists, in which the system quickly forms high-oriented tilted strip pattern.

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Dynamic Scaling in Growth of Holes in Ballistic Deposition Model LI Yifan, XIA Hui 2009, 26(6): 931-936.  Abstract ( )   PDF (333KB) ( )   To study scaling behavior of holes in surface and interface rough growth, simulated growth of holes in a Ballistic Deposition (BD) model is simulated and analysed. It shows that relation between number of holes and growth time exceeds linearity at initial stage and approachs to linearity. The rule is analyzed theoritieally.

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Monte Carlo Simulation of 3-dimensional Ising Model HUANG Chunqing, DENG Shaojun 2009, 26(6): 937-941.  Abstract ( )   PDF (275KB) ( )   A 3-dimensional Ising model is simulated with Monte Carlo importance sampling method. Statistical values of energy, strength of magnetization, specific heat and rate of magnetization of spin links as well as their standard errors (uncertainties) are measured. 3-dimensional Ising model shows spontaneous magnetization with no exterior magnetic field. Critical point of phase transformation is at J/(kBTc)=0.222 0 or Tc=4.500 0. Phase transformation at high temperature disappears with exterior magnetic field. Relationship between physical quantities, temperature and exterior magnetic field is investigated and analyzed.

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Ground State of Bose-Einstein Condensation in F-G-H Method WU Dapeng, MEN Fudian, LIU Hui 2009, 26(6): 942-948.  Abstract ( )   PDF (366KB) ( )   We study distribution of particles in Bose-Einstein condensation and ground state energy of condensate by solving a G-P equation with Fourier-Grid-Hamiltonian(F-G-H) method. It is shown that particle density in condensate center increases and radius of condensate decreases as intensity of power-law potential or frequency of harmonic potential is increased or repulsive interaction between particles is decreased. The ground state energy of BEG increases with increasing of total particle number, repulsive interaction between particles, frequency of harmonic potential or intensity of power-law potential. Thomas-Fermi approximation results approximate to numerical results as particle number increases. It is shown that Thomas-Fermi approximation is a good method with large particle numbers. For less particle numbers, numerical method should be used.