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25 July 2006, Volume 23 Issue 4 Previous Issue    Next Issue

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Numerical Simulation of Correlated Scattering by Very Dense Randomly Distributed Spherical Particles YANG Qing, JIN Ya-Qiu 2006, 23(4): 379-386.  Abstract ( )   PDF (400KB) ( )   Correlated scattering of very dense(fractional volume more than 0.4) randomly distributed spherical particles is studied. A Monte Carlo method and a random shuffling process are employed to generate the very dense and randomly distributed particles. With solution of the volumetric integral equation of the electric fields, the scattering, absorption and extinction coefficients, as well as effective permittivity of the very dense and randomly distributed spherical particles are numerically calculated. For a validation purpose, they are compared with other approaches such as QCA, QCA-CP and Maxwell-Garnett mixing formula at lower fractions. It shows that very dense particles demonstrate particles clustering and enhance the scattering of bigger or clustered particles.

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Calculation of the Beam Centroid in a Linear Induction Accelerator LI Xian-wen, WANG Wen-dou, FENG Li, WANG Qiang, LI Ping, DENG Jian-jun 2006, 23(4): 387-390.  Abstract ( )   PDF (230KB) ( )   A model of the beam centroid motion in a linear induction accelerator(LIA) was developed. It calculates the track of the beam centroid under the condition of cell magnet misalignment. The 3D magnetic field distribution is calculated with a coordinate transform. The track of the beam centroid is given by a coupled solution of the beam centroid and envelope equations. Quantitative relation between the transverse displacement of beam centroid and the misalignment of magnets is useful in the installation of magnets and the adjustment of steering coils.

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Numerical Simulation of Fluid Interfaces with the Adaptive Mesh Refinement Method,the Ghost Fluid Method and the Level Set Method GONG Xiang-fei, ZHANG Shu-dao, JIANG Song 2006, 23(4): 391-395.  Abstract ( )   PDF (305KB) ( )   An AMR(adaptive mesh refinement) method is presented with different time steps in the cells at inequable levels. In order to get high accuracy in the cells on the interlace, the AMR method is adopted together with the level set method and the ghost fluid method. Euler equations is solved by a WENO algorithm which is easily realized while getting a high resolution. Compared with the method without considering AMR or the level set method, our method shows an advantage in achieving high resolution on the interface. The result indicates that these methods work well together in the numerical simulation.

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On the Sonic Point Glitch of the Burgers' Equation WU Hao, SHEN Zhi-jun 2006, 23(4): 396-404,440.  Abstract ( )   PDF (417KB) ( )   We study the sonic point glitch of the Burgers' equation, which is formed in a sonic rarefaction fan. The reason of a sonic point glitch and the relation between the sonic point glitch and the entropy condition are discussed. According to these relations, several well-known schemes are classified into two and analyzed. In fact, the sonic point glitch appears only in the case of a transonic rarefaction wave. If the problem to be solved does not include transonic rarefaction waves, the difficulty in computation vanishes. Based on this idea, a new two-step splitting method eliminating the sonic point glitch is proposed. Numerical tests of applying the method to different schemes show that it is good in eliminating the sonic point glitch.

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Curved Boundary Treatment in the Lattice Boltzmann Method DU Rui, SHI Bao-chang 2006, 23(4): 405-411.  Abstract ( )   PDF (335KB) ( )   Three curved boundary treatments in the lattice Boltzmann method are studied. Numerical accuracy and stability are analyzed and compared. In simulating a two-dimensional Poiseuille flow and a driven cavity flow on an equilateral triangle, numerical accuracy and stability of the schemes are discussed.

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A Parallel Adaptive Finite Element Algorithm for Numerical Simulation of Flows ZHOU Chun-hua 2006, 23(4): 412-418.  Abstract ( )   PDF (508KB) ( )   We present a parallel mesh adaptive finite element algorithm for numerical simulation of flows based on error estimation. The Navier-Stokes equations are solved on an initial coarse mesh to produce a posteriori error estimation. Through a recursive spectral bisection weighted by error estimation, an initial mesh is partitioned to achieve the equal error approximately in each subdomain for load balance in parallel computing. Then mesh adaptations are performed independently in each subdomain using error estimation as a criterion, Finally, by a domain decomposition method based on mortar elements, the entire problem is solved on a non-matching global mesh. The error estimation for finite element solution of Navier-Stokes equations is an extension of formulation for a generalized Stokes problem. Numerical experiments are presented to validate this algorithm.

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Adaptive Distribution of Particles in a Meshfree Method NI Guo-xi, WANG Rui-li, LIN Zhong 2006, 23(4): 419-424.  Abstract ( )   PDF (361KB) ( )   A new method to generate a quasi-equal distribution of particles on arbitrary domains is provided. Based on an advancing front mesh generation method, triangles are formed at the boundary. These triangle center-points are used for the boundary condition of the Delaunay mesh generation method which generates inward triangles. All vertices of triangles are the particles in meshfree methods. An adaptive method is given to readjust distribution of particles, according to the gradient of fluid density.

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Sensitivity of Testing Parameters of a Two Phase Well with Polymer Flooding ZHANG De-zhi, YAO Jun 2006, 23(4): 425-430.  Abstract ( )   PDF (321KB) ( )   Considering factors as two-phase of oil and water, production history, areal heterogeneity of the reservoir, well-bore storativity and skin, we establish a mathematical well testing model with polymer flooding in producing period and a streamline model for unsteady well testing. Numerical solutions are gained by a stream-tube method. It shows that the pressure derivative curve moves upward with the increase of the ratio of oil/water viscosity. The effective permeability of formation decreases with an increase of production time. The effect of water-oil front cannot been reflected from the derivative curve in the water well drawdown log-log plot when a high permeable zone is distributed along the main streamline. The concave in derivative curve appears earlier with the increase of concentration of polymer injected.

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Parallel Computation of Three-Dimensional Smoothed Particle Hydrodynamics WANG Pei, HONG Tao 2006, 23(4): 431-435.  Abstract ( )   PDF (347KB) ( )   A parallel three-dimensional smoothed particle hydrodynamics cede CSPH3D based on MPI is introduced, including computational scheme, parallel method, data structure, flow chart, and skills in programming. A simulation of three-dimensional ejection and penetration model shows that the CSPH3D code preferably simulates these phenomenon and the parallel efficiency is high. The parallel efficiency of a 1527402 particles micro-ejection model and a 1454225 particles penetration model achieves 80% with 100 processors.

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Numerical Method for a Kind of Singular Complex Eigenequations LONG Yong-xing, MU Zong-ze, WANG Ai-ke, Dong Jia-qi 2006, 23(4): 436-440.  Abstract ( )   PDF (227KB) ( )   A numerical method and a code for seeking complex eigenvalues are given with the fundamental matrix method.The treatment of singularity,complex eigenvalue and numerical instability are discussed. The method is used to simulate the instability driven by a temperature gradient [ηi].Numerical results agree well with theoretical analyses.

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An Ejected Particle Cluster Detection Algorithm and Its Application ZHANG Ying, CHEN Qi-feng, CAO Xiao-lin, CAI Ling-cang, CHEN Dong-quan, LU Tie-cheng 2006, 23(4): 441-446.  Abstract ( )   PDF (396KB) ( )   Based on the cluster multiple labeling technique,a novel cluster detection algorithm is presented as an analysis subroutine in two-and three-dimensional molecular dynamic simulations of ejecta that take place as a planar shock wave encounters a free metal surface.The algorithm is described,tested,and used to detect cluster distribution of ejecta from copper and aluminum under a shock loading.The information obtained about the size,distribution,evolution of the cluster is helpful in the understanding of ejection.

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Buckling of a Spatial Elastic Thin Rod Under Torque TAN Mei-lan, WANG Xin-wei, GAN Li-fei 2006, 23(4): 447-450.  Abstract ( )   PDF (235KB) ( )   The flexural buckling of a spatial elastic thin rod under torque is discussed with FEM(finite element method).In a natural coordinate system,an energy equation is given,which considers nonlinear terms of the tortuosity about an initially curved and twisted thin rod with circular cross-section.An eigenvalue analysis is proposed to study the buckling of spatial elastic thin rods with simultaneous effect of axial force and torque.The method is clearly demonstrated by examples.Numerical results are in good agreement with theoretical solutions.

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Solving Convective Heat Transferwith a Self-adaptive Precise Algorithm in the Time Domain ZHAO Xiao, YANG Hai-tian, GAO Qiang 2006, 23(4): 451-456.  Abstract ( )   PDF (267KB) ( )   A self-adaptive precise algorithm in the time domain is presented for convective heat transfer problems.By expanding variables at a discretized time interval,a time and space coupled problem is converted into a series of boundary value problems.Based on a finite element method,a recursive and self-adaptive computation is conducted without the requirement of additional assumption and iteration for non-linear analysis.A couple of examples with high accuracy are shown.

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Determination of Emissive Direction from a Diffusing Surface in Monte Carlo Simulations LI Peng, XIAO Ze-juan, CHENG Hui-er 2006, 23(4): 457-460.  Abstract ( )   PDF (235KB) ( )   We introduce an effective method to determine the emissive direction of energy bundles from a diffusing surface,which is called a tangent sphere method.The principle and implement process of the conventional method,and the tangent sphere method are analysed.It shows that the tangent sphere method is more convenient.A Monte Carlo simulation is applied to a simple model.A comparison of numerical results and integral results shows that the tangent sphere method is feasible and its precision meets engineering requirment.A comparison of computing time shows that the computational speed of the tangent sphere method is superior to that of the conventional method.

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Thermal Characteristic Simulation of Metal Constructions with Phase Change Materials YE Hong, JIANG Li-feng, WANG Xi-yao, ZHUANG Shuang-yong 2006, 23(4): 461-469.  Abstract ( )   PDF (1091KB) ( )   The feasibility of simulating thermal characteristics of metal constructions with phase change materials(PCM) is investigated theoretically and numerically.Detailed calculations are shown to evaluate the simulation of a serial of metal boards with different thickness,such as 20 mm,30 mm,50 mm and 100 mm.It is found that the low thermal conductivity of the PCM is a significant disadvantage in simulating thicker metal boards.Based on that,the PCM with reinforced thermal conductivity is used to simulate the metal board with a thickness of more than 100 mm.Good simulation results are obtained.Furthermore,PCM simulations for two common metal constructions,a steel wheel and a pipe,are studied.

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Two Dimensional Charged Particle Wigner Crystal Lattices:the Boundary Effect ZHANG Zhen-zhong, JIANG Chang-zhong, CHANG Kai 2006, 23(4): 470-476.  Abstract ( )   PDF (390KB) ( )   A nonlinear optimizing method is applied to study the ground state configurations of a two-dimensional charged particle system in a hard-wall confining potential.We find that the circular shell configurations in a circular hard wall confinement are similar to that in a parabolic confining potential.With a hard-wall square boundary,the Wigner crystal lattice is square as the number of particles N<66,but becomes a hexagon as N≥66 since the boundary effect is weak for inner particles.The influence of the elliptic and rectangular boundary on the wigner crystal lattice is analyzed.

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A Band Structure Based Nonuniform Brillouin Zone Tetrahedron Approach CHEN Yong, RAVAIOLI Umberto 2006, 23(4): 477-482.  Abstract ( )   PDF (325KB) ( )   We propose a "state of art"tetrahedron sampling scheme based on a nonlocal pseudopotential bandstructure calculation and linear energy interpolation in each tetrahedron cell.In this approach,a relatively small amount of tetrahedrons are produced automatically and the Brillouin integration is calculated with higher precision and efficiency.In an application to diamond materials of Si and Ge,optimized nonuniform meshes are obtained automatically in the 1/48 irreducible wedge of the brillouin zone.A complement is given for the integrality of the present tetrahedron DOS expression and the DOS's for the first and second conductance band of Si and Ge are obtained with this grid and the supplemented expression.

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Dynamic Study for Numerical Solutions ofthe Gross-Pitaevskii Equation HUA Wei, LIU Xue-shen, DING Pei-zhu 2006, 23(4): 483-488.  Abstract ( )   PDF (262KB) ( )   The ground state wavefunctions of dilute Bose-condensed atoms in a harmonic trap at T=0 are evaluated by a symplectic shooting method.Stability of the wavefunctions is tested,and a stable wavefunction is used as the initial input of the time-dependent Gross-Pitaevskii equation. The dynamic property of stable wavefunctions is numerically examined in two phase spaces when the harmonic potential is altered suddenly.The figures in the two phase spaces are regular even after a long time of interations.For negative nonlinear coefficients,two eigenvalues related to the same negative nonlinear coefficient are calculated,and the stability of the corresponding two wavefunctions is tested.

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Classical Dissociation of a Diatomic Molecule with Chirped Pulses CHI Yu-hua, LIU Xue-shen, DING Pei-zhu 2006, 23(4): 489-493.  Abstract ( )   PDF (271KB) ( )   A classical trajectory method is used to study a diatomic molecule(HF) interacting with chirped intense laser pulses.In the model,the motion of nuclei is described with classical Hamiltonian canonical equations.The Hamiltonian equation is solved numerically by a symplectic method,and the initial conditions are chosen by a single trajectory in the field-free case at random.The classical dissociation of HF by chirped pulses is evaluated.The dissociation probabilities with different laser intensities are discussed.Dissociation probabilities at different initial states are also investigated.The dissociation process is illustrated by classical phase trajectories and energy versus nuclei separation.

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Effect of Pressure Gradient on the Prompt Explosion Energy of a Supernova Progenitor Ws12M⊙ LIU Men-quan, LUO Zhi-quan, PENG Qiu-he, XIE Zuo-heng 2006, 23(4): 494-498.  Abstract ( )   PDF (303KB) ( )   The supernova prompt explosion of a progenitor model Ws12M⊙ is simulated.The effect of pressure gradient on the prompt explosion energy of supernova is discussed.Numerical analysis indicates that the explosion energy is sensitive to the increasing of pressure gradient which has minor influence on the pressure. At collapse,bounce or propagation stage,the increasing of pressure gradient can improve the explosion energy obviously.

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Monte Carlo Simulation of Dendritic Growth of Metal Electrodeposition in an Invariable Magnetic Field WU Li-li, LU Hang-jun, WU Feng-min 2006, 23(4): 499-504.  Abstract ( )   PDF (433KB) ( )   Considering the influences of a magnetic field B,the concentration of the electrolytic solution and the probability of reaction Ps,a series of interesting patterns that are in good agreement with experiments', are observed.It is found that the pattern of clusters and their fractal dimensions depend strongly on the magnetic field which is presented by a rotation velocity of the diffusing particles ω in the model.Our simulation shows that the growing cluster transits from fractal to non-fractal with an increasing of magnetic field intensity.A relative high magnetic field and a greater n or f result in a non-fractal cluster.With an increasing intensity of magnetic field,the decreasing of Ps accelerates the growing cluster from fractal to non-fractal pattern.