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25 January 2007, Volume 24 Issue 1 Previous Issue    Next Issue

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Grid Strategy for Distorted Meshes in a Hohlraum YONG Heng, YUAN Guoxing, PEI Wenbing, GU Peijun 2007, 24(1): 1-6.  Abstract ( )   PDF (462KB) ( )   In order to untangle serious distortion in a hohlraum for ICF (Inertial Confinement Fusion),a nine-point rezone strategy is developed.The scheme is approximate to an elliptic or a parabolic equation,and preserves spherical symmetry.The scheme includes several forms of the nine-point rezone scheme according to different requirement in practical problems.The ALE (Arbitrary Lagrangian-Eulerian) method is used in code LARED-H. Suitable results for a hohlraum is illustrated.

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High Order Spectral Element Method and Application in Hydrodynamic Stability MA Dongjun, SUN Dejun, YIN Xieyuan 2007, 24(1): 7-12.  Abstract ( )   PDF (396KB) ( )   A high order spectral element method with a domain decomposition Stokes solver is presented for hydrodynamic stability analysis.A Jacobian-free Inexact-Newton Krylov algorithm with a Stokes time-stepping preconditioning technique is introduced to the calculation of steady state of incompressible flows.An Anoldi method is used to calculate the leading eigenvalues and corresponding eigenvectors,which are responsible for the hydrodynamic instability.The method deals with steady and unsteady simulations in a similar way without time-splitting divergence error and does not need Jacobian matrix.As a result,it reduces memory allocation and computation cost,and speeds up the convergence.(Numerical) result for Kovasznay flows with an analytic solution shows spectral accuracy with exponentially spacial convergence and superlinear convergence for inexact Newton method.An antisymmetric sinusoidal velocity driven cavity problem is considered at Re=800.The stable and unstable patterns are analyzed with leading eigenvalues of steady states.The symmetric-breaking Hopf bifurcations are considered in the wake of a circular cylinder limitlessly or between two parallel walls.The onset of instabilities agrees well with experimental and numerical results.

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A New Unstructured Quadrilateral Mesh Generation Scheme and Applications WANG Ruili, YAO Yanzhong, LIN Zhong, GE Quanwen 2007, 24(1): 13-18.  Abstract ( )   PDF (410KB) ( )   A scheme for unstructured quadrilateral mesh generation based on Delaunay triangulation is presented.With a front edge definition we mark a triangle mesh in the front edge.According to triangle mesh shape and directionality two triangular meshes are merged into a quadrilateral mesh. A 100% quadrilateral mesh obtained converts a quad-dominant to an allquad mesh with mesh conversion templates.Numerical results are shown.

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A Mesh Adaptive Method for Two-Dimensional Three-Tempeature Heat Conduction Equations JIANG Jun, SHU Shi, HUANG Yunqing, CHEN Long 2007, 24(1): 19-28.  Abstract ( )   PDF (626KB) ( )   A mesh adaptation approach based on Hessian matrix is proposed to solve two-dimensional heat conductione equations with coupled electron,iron and photon temperatures.Three kinds of adaptive mesh and two adaptation methods based on gradient and flux of the photon finite element solution are used. It is shown that the energy conservation error and computation efficiency of the approach are improved.

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Numerical Simulation of Mixed Convections CHEN Xiaochun, LIN Guanjing, ZHOU Xiang, ZHU Yingxin, WANG Yuan 2007, 24(1): 29-34.  Abstract ( )   PDF (402KB) ( )   A v'2-f model,a k-ε model and an indoor zero equation model are adopted respectively to simulate mixed convections which are typical in ventilation and air conditioning systems.It indicates that there is a separated vortex near the ventilation inlet,and the accuracy for predicting this vortex is a critical factor in the simulation.The separated vortex dimension obtained by experiments is between the values calculated by the v'2-f model and the indoor zero equation model,while the dimension predicted by the k-ε model is a bit smaller.The results predicted by the indoor zero equation fit experimental results best.However,it is not in general from the view of model structure.For calculating temperature field the v'2-f model is better than the indoor zero equation model,and the k-ε model is the worst among the three.

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An Improved Element Free Galerkin Method ZENG Yishan, ZENG Qinghong 2007, 24(1): 35-41.  Abstract ( )   PDF (314KB) ( )   The element-free Galerkin method (EFGM) is improved with partition of unity quadrature (PUQ).Partition of unity quadrature is shown strictly with finite covering and partition of unity.Using Shepard functions as partition of unity functions,we obtain good results.The EFGM with PUQ is a true meshless method. Computational results of EFGM with partition of unity quadrature are more accurate than those of the traditional EFGM with background quadrature.

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Influence of Coupling Time Accuracy on the Simulation of Aircraft Free Movement YANG Yunjun, ZHOU Weijiang, CUI Erjie 2007, 24(1): 42-48.  Abstract ( )   PDF (513KB) ( )   With a sub-iterative technique for fluid dynamic equations and rigid-body dynamic equations,a coupling numerical method is proposed to explore the unsteady movement characteristics of aero-crafts and the effect of coupling time accuracy.It is shown that the motion finally becomes a self-maintained stable limit cycle oscillation.The amplitude with an increasing incidence angle shows a jump,which is quite close to the experimental result.The coupled numerical result with the second-order time accuracy depends hardly on the physical time step for this multi-system coupling.On the contrary,the uncoupled numerical result with one step time lag depends obviously on the physical time step selected.A longer time step results in unreal numerical results.

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Simulation of an Inverse Zimmerman Wing at Low Reynolds Numbers LI Jianhua, LI Feng 2007, 24(1): 49-53.  Abstract ( )   PDF (415KB) ( )   Unsteady incompressible Navier-Stokes equations are solved with a pressure correction method.A series of numerical calculations are conducted for Low-Reynolds-Number aerodynamics of an inverse Zimmerman wing.It shows that a pair of strong leading-edge vortex exist beyond the wing.They have strong effect on the inverse Zimmerman wing aerodynamics and offer high nonlinear lift and large stall attack angle.Interaction between the leading-edge vortexes results in unsteady and asymmetry phenomenon of the wing.The inverse Zimmerman wing shows a better longitudinal stability and flow-field stability.

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A Wavelet Precise Integration Method for Burgers Equations Based on Homotopy Technique MEI Shuli, ZHANG Senwen, LU Qishao 2007, 24(1): 54-58.  Abstract ( )   PDF (211KB) ( )   Taking the Burgers equation as an example,an interval wavelet precise integration method (PIM) for nonlinear PDEs is proposed.The homotopy perturbation method (HPM) for nonlinear problems is adopted.It extends the application of HPM from one dimension to multi-dimensions.As an asymptotic analytical method,it is not sensitive to the time step and is suitable for nonlinear equations.

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Analytical Integrals in the Linear Interpolation BEM for 3-D Electrostatic Fields LI Yasha, WANG Zezhong, LU Binxian 2007, 24(1): 59-64.  Abstract ( )   PDF (288KB) ( )   3-D electrostatic fields are calculated by the linear interpolation triangular boundary element method (BEM) with analytical integrals.For integrals with 1/R and 1/R2,shape functions are disintegrated into constant,x linear and y linear terms.The boundary element integral is simplified to 6 basic integral assemblies.Analytical integral formulas for them are introduced.Repeat calculations resulting from different shape functions are avoid.The method calculates exactly integrals far from singularity, 1 and 2 order nearly singular integrals and 1 order singular integrals as well.It shows that for problems with nearly integrals and singular integrals the analytical integral method gives correct results while the numerical integral method with the same boundary meshes can not.The precision in linear interpolation BEM for 3-D electrostatic fields is improved.

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Data Assimilation for the Air Flow Around Daya Bay Nuclear Power Station PAN Meng, ZHANG Chunlin, ZHANG Jie 2007, 24(1): 65-70.  Abstract ( )   PDF (257KB) ( )   In numerical simulation of the air flow around Daya Bay nuclear power station (NPS),a simplified data assimilation method is used to restrain forecasting errors that are caused by the uneven distribution of observation data in time and space.The effect of data assimilation on the initialization field model is analyzed.It shows that the method restrains errors in initialization field and in model significantly.

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Characteristic Time of Direct Charge Tunneling in a Silicon Nanocrystal Based Memory YANG Hongguan, LI Xiaoyang, LIU Quanhui 2007, 24(1): 71-77.  Abstract ( )   PDF (399KB) ( )   Considering potential configuration of a silicon nanocrystal based memory and the mixing effect of valence bands,we calculate direct tunneling time of electron and hole with sequential tunnel theory and in the Bardeen's transfer Hamiltonian formalism.The programming and retention times of a silicon nanocrystal based memory are calculated.Influences of structure and bias on the performance of device are discussed.It is shown that new devices are expected in order to improve the retention property of silicon nanocrystal based memories.

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Exchange Bias and Coercivity in Nonmagnetic Doped Ferromagnetic/Antiferromagnetic (FM/AFM) Systems MA Mei, WANG Xingfu, CAI Lei, HU Jingguo 2007, 24(1): 78-82.  Abstract ( )   PDF (328KB) ( )   The exchange bias and coercivity of FM/AFM bilayers and FM/AFM mixed monolayers with nonmagnetic dilution are studied in a Monte Carlo model.It shows that the exchange bias increases and then decreases with the increasing of dilution concentration while the coercivity decreases and then increases. With the same dilution concentration, both the exchange bias and the coercivity of the regular dilution are stonger than those of random dilution in FM/AFM bilayers.But in the mixed monolayer,the exchange bias of regular dilution is weaker than that of random dilution while the coercivity becomes stronger.Regular dilution results asymmetry in the hysteresis loops distinctly.It shows that the asymmetry of hysteresis loops in FM/AFM systems depends on the interface microstructure.

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Simulation on Percolation of Fractal Aggregations CHENG Jinrong, DING Rui, LIU Yao 2007, 24(1): 83-89.  Abstract ( )   PDF (359KB) ( )   We present a randomsuccessive nucleation growth model,a two-and a three-dimensional aggregation generation-by-generation model to investigate percolation properties of fractal aggregations with various neighbor conditions and lattice size.Itshows that the percolationthreshold of fractal aggregationisindependent of the lattice size.It dependents onspatial dimension andneighbor conditions,andis aninherent property of the fractal system.The fractal aggregate grows infinitely withthe same fractaldimension whenthe growth probabilityis equal tothe percolationthreshold.The fractal dimension is just a linear function of thespatial dimension.

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A Nonlinear Seepage Flow Model for Deformable Double Media Fractal Gas Reservoirs ZHANG Liehui, ZHANG Jinliang, XU Bingqing 2007, 24(1): 90-94.  Abstract ( )   PDF (229KB) ( )   Based on the Warren-Root model,introducing fractal parameter and deformable coefficient and considering the effect of pressure on permeability and porosity,we construct a seepage flow model for pressure-sensitive deformable double media fractal gas reservoirs.A finite element method which has advantages in numerical solution of partial differences equations is used.The effect of parameters on pressure and importance in pressure-sensitive deformable double media fractal gas reservoirs are analyzed in detail.

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Simulated Annealing Study of Microphase Separation and Crystallization in Asymmetric Semicrystalline Diblock Copolymers YIN Yuhua, SUN Pingchuan, LI Baohui, JIN Qinghua, DING Datong 2007, 24(1): 95-98.  Abstract ( )   PDF (359KB) ( )   A simulated annealing method is used to study the microphase separation and crystallization in cylinder-forming semicrystalline diblock copolymers.The final structure depends on the relative strength of the microphase separation and the crystallization of one block copolymers.As the interblock segregation strength is relatively weak,crystallization disrupts cylindrical microphase.As the interblock segregation strength is sufficiently strong,crystallization is effectively confined within cylindrical domains formed by microphase separation in the melt.A range of intermediate segregation strength exists between the two cases,in which the crystallization is templated but not wholly confined within the nanoscale domains prescribed by microphase separation.The melt morphology is mostly retained in cooling,and the local distortions and connections between cylinders occur due to crystallization.The simulation is consistent with recently reported experimental results.In addition,as the interblock segregation strength is very strong,the crystallization is restrained which results in amorphous structures.

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FD-BPM Analysis of Er3+-Yb3+ Co-Doped Phosphate Glass Waveguides XING Zibin, ZHANG Xiaoxia 2007, 24(1): 99-104.  Abstract ( )   PDF (360KB) ( )   We introduce FD-BPM to three-dimensional waveguides and calculate the refractive index of Er3+-Yb3+ co-doped phosphate glass waveguides.The simulation for a signal light (1.54 μm) and a pump light (0.98 μm) is performed in a Er3+-Yb3+ co-doped phosphate glass waveguide with FD-BPM.It shows that the scatter loss can be neglected and the optical field is symmetric in a buried waveguide.A buried Er3+-Yb3+ co-doped phosphate glass waveguide is demonostrated the best to make Er3+-Yb3+ co-doped phosphate glass waveguide lasers and amplifiers.

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One-dimensional Sandpile Model with Avalanche Probability ZHOU Haiping, CAI Shaohong, LIU Xiaochun 2007, 24(1): 105-108.  Abstract ( )   PDF (187KB) ( )   We propose a one-dimensional sandpile model with avalanche probability.The simulation is performed with the cellular automata method.As the local slope closes to the critical slope sands avalanche with a probability.The avalanche size and the average local slope are studied at different avalanche probabilities. The self-organized critical (SOC) behavior is studied at critical exponent α=1.50±0.02 as the avalanche probability is between 0.05 and 0.98.The average local slope descends with the increase of collapse probability.A sharp transition occurs between the trival behavior and SOC behavior in this model.The SOC phenomenon in one-demensional rice-pile experiment is well explained.

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Simulation of MOS Devices in Radiation and Post-irradiation HE Baoping, ZHANG Fengqi, YAO Zhibin 2007, 24(1): 109-115.  Abstract ( )   PDF (334KB) ( )   The radiation response and long term recovery in MOS due to a pulse radiation are studied.It is assumed that electron tunneling from silicon into oxide and buildup of interface states are the post-irradiation recovery.The model uses convolution theory and considers the bias change in the recovery period.It shows that the bias in the post-irradiation recovery period and the ratio of the interface state to the electron tunneling influence the recovery rate.

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Control Period-doubling Bifurcation and Chaos in a Discrete Nonlinear System by Translation YU Jinjiang, LIU Xuejun, HAN Wanqiang, XU Haibo 2007, 24(1): 116-120.  Abstract ( )   PDF (250KB) ( )   The control of period-doubling bifurcations and chaotic attractor periodic orbits in a discrete nonlinear dynamical system is realized by translation.Appropriately adjusting the translation parameter and system place,any periodical orbit can be reached in a chaotic system.This method is applied successfully to the Logistic map and the Henon map.

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Sliding Mode Control of Lorenz Systemes with Multiple Inputs Containing Sector Nonlinearity and Deadzones WANG Xingyuan, Liu Ming 2007, 24(1): 121-126.  Abstract ( )   PDF (281KB) ( )   We design a controller for uncertain Lorenz systemes with multiple inputs containing sector nonlinearity and deadzones,and demonstrate its effectiveness theoretically.With this controller the controlled Lorenz system drives system orbits asymptotically to arbitrarily objective trajectories evenif there exist uncertainties,deadzones and sector nonlinearities in the inputs.Finally,by emulation studies of controlled Lorenz systems,effectiveness of the controller is demonstrated.