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25 November 2008, Volume 25 Issue 6 Previous Issue    Next Issue

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Algorithm and Code Development of NEM Embedded with NDOM for 3D Core Transport/Diffusion Equations SI Shengyi 2008, 25(6): 631-640.  Abstract ( )   PDF (673KB) ( )   An algorithm of 3D coarse mesh nodal expansion method (NEM) embedded with 2D fine mesh nodal discrete ordinate method (NDOM) is described. The main idea is to substitute radial part of NEM inner iteration, which is based on coarse mesh diffusion theory, with inner iteration of NDOM, which is based on fine mesh transport theory. Taking advantages of NEM and NDOM, the algorithm models efficiently heterogeneous features in radial planes of an NPP reactor core and takes less computer memory and computation time. Two prototype codes, NSNM and MGNEM, for the algorithm based on 2D multi-group NDOM and 3D multi-group NEM are developed. A computer code named HANWIND is integrated based on former codes. Numerical experiments on benchmark problem OECD/NEA-2D C5GTMOX and a self-estab-lished benchmark problem based on 3D core of 2-loop NPP reactor are shown.

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Conservative Interpolation (Remapping) Algorithm Based on ENO Interpolation and Application in Computational Fluid Dynamics WANG Yongjian, ZHAO Ning, WANG Chunwu, WANG Donghong 2008, 25(6): 641-648.  Abstract ( )   PDF (410KB) ( )   We summarize conservative remapping algorithms based on ENO (essentially non-oscillatory) interpolation. Three numerical techniques in computational fluid dynamics are discussed:overlapping mesh method, adaptive refinement mesh method and moving mesh method. Physical quantities transfer between meshes. Conservativeness is important, especially in computing shock and contact discontinuity. We propose a remapping algorithm based on ENO which is conservative and accurate in transferring physical quantities between meshes and give numerical examples. It shows that the algorithm has ability of resolving conservative problems with above mesh techniques in computational fluid dynamics.

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A Variant Restricted Additive Schwarz Preconditioner and Application in Two-dimensional Three-temperature Energy Equations CAO Yanhua, Liu Xingping, GU Tongxiang 2008, 25(6): 649-658.  Abstract ( )   PDF (480KB) ( )   We present a variant restricted Additive Schwarz preconditioner and apply Partial-Newton-Krylov-Schwarz algorithm to solve nonlinear algebraic equations of two-dimensional three-temperature systems. Iteration and CPU time for convergence are decreased. Numerical results show efficiency of the method.

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Combined Compact Upwind Difference Schemes for Navier-Stokes Equations LIANG Xian, TIAN Zhenfu 2008, 25(6): 659-667.  Abstract ( )   PDF (428KB) ( )   A fourth-order combined compact upwind (CCU) finite difference scheme with high resolving efficiency is proposed. A high-order compact difference algorithm for Navier-Stokes (NS) equations based on projection method is developed with CCU scheme on staggered grids. Convection terms are discretized by CCU scheme. Viscous terms, pressure gradient terms and pressure Poisson equations are discretized with fourth-order compact symmetric finite difference schemes. Numerical examples validate capability of the proposed approach. It is shown that the method is accurate and robust, and is applicable to complex fluid flows.

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Curvature and Front Evolution LIU Xuezhe, SHEN Zhijun, YUE Jingyan 2008, 25(6): 668-672.  Abstract ( )   PDF (245KB) ( )   Evolution of front with speed dependent on curvature is considered. The speed includes both normal and tangent components. Change of total variation of propagating front depends only on derivative of normal speed about curvature where curvature is zero. The tangent speed has no influence on change of total variation.

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Parallelization of Incomplete Factorization Preconditioning of Block Tridiagonal Linear Systems with 1-D Domain Decomposition WU Jianping, SONG Junqiang, LI Xiaomei 2008, 25(6): 673-682.  Abstract ( )   PDF (479KB) ( )   Based on one-dimensional domain decomposition with small overlapping, we approximate local lower and upper triangular incomplete factors and combine these factors into an effective approximation for global incomplete factorization preconditioner of coefficient matrix. Two implementations are considered. One is based on exchange of total boundary values of overlapped domain. The other is based on carefully arranged computation process to reduce communication of whole overlapped domain in one line of grid points. The parallelization method can be used to any incomplete factorization preconditioner. Experiments show that it is more efficient than widely-used additive Schwarz technique.

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Simulation of Vortex in Separated Flows with DES DENG Feng, WU Yizhao, LIU Xueqiang 2008, 25(6): 683-688.  Abstract ( )   PDF (456KB) ( )   Navier-Stokes equations are solved numerically to simulate vortex motion in separated flows using detached-eddy simulation (DES) method in Saplart-Allmaras one equation model. A finite volume scheme is employed. Spatial discretization is performed with Jameson central scheme. Time integration is implemented by a dual time-stepping approach. Vortex structures of flow over a circular cylinder or a stall airfoil simulated agree well with physical analyses and experimental data.

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Airfoil Leading Edge Separation Flows Under Control of Plasma Actuator XUE Bangmeng, YANG Yong 2008, 25(6): 689-693.  Abstract ( )   PDF (362KB) ( )   Plasma actuator is modeled as body force vectors resulting from external electric field and net charge distribution in plasma. Leading edge separation flows around NACA0015 airfoil under control of plasma actuator is simulated by Navier-Stokes equations with body force source which are solved by detached eddy simulation (DES) and delayed-detached eddy simulation (DDES). With actuator on, the separation flow reattached through an asymptotic progress in DDES simulation. An unsteady response occurs in DES due to grid induced separation.

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Simulation of Transonic Viscous Flows Around RAE2822 Airfoil in GAO-YONG Compressible Turbulence Model YAN Wenhui, YAN Wei, GAO Ge 2008, 25(6): 694-700.  Abstract ( )   PDF (413KB) ( )   Numerical simulation of transonic viscous flows around RAE2822 2-D airfoil in Gao-Yong compressible turbulence model is presented. Convection terms and diffusion terms are calculated with ROE (flux difference splitting) scheme and CD (center difference) scheme, respectively. Runge-Kutta time marching method is employed to solve space discrete control equations. It predicts accurately pressure coefficients on airfoil surface, mean velocity, location of shock wave and Macb number contours. Shock-wave/boundary layer interaction and translation from laminar flow to turbulence flow on airfoil surface are analyzed. Numerical results agree well with experimental data. It is demonstrated that Gao-Yong compressible turbulence model can be used to simulate transonic viscous flow around an airfoil. A method for location of translation based on theory of orthotropic turbulence viscosity in Gao-Yong compressible turbulence model is presented.

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High-order Finite Difference Method for Simulation of Ablative Rayleigh-Taylor Instability FAN Zhengfeng, LUO Jisheng 2008, 25(6): 701-704.  Abstract ( )   PDF (327KB) ( )   Steady state flow field around ablation front is solved and taken as a basic flow in the simulation of ablative Rayleigh-Taylor instability with a high-order WENO scheme. Linear growth rate simulated agrees with Lindl formula and linear stability analysis. It indicates validity and accuracy of the method. The method shows good ability in capturing interface deformation.

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Discontinuous Finite Element Method for Supersonic Flow of a Missile Propulsive Jet CHEN Eryun, MA Dawei, LE Guigao, LI Zhigang, ZHAO Jiyong 2008, 25(6): 705-710.  Abstract ( )   PDF (347KB) ( )   Supersonic inviscid flows in missile propulsive jet are simulated numerically with discontinuous finite element method based on twodimensional conservation laws, which is developed to solve axlsymmetric Euler equations. Computational results show good agreement with experimental data. The method shows higher resolution at discontinuous points compared with TVD schemes. It exhibits high capability in capturing shocks without numerical oscillation and artificial viscosity near discontinuous points.

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Molecular Behavior of Flow Around a Nano Circular Cylinder LI Yinshi, SUN Jie, HE Yaling 2008, 25(6): 711-717.  Abstract ( )   PDF (480KB) ( )   Molecular dynamics simulations are carried out to study flow of Ar around a nanoscale (Pt(FCC (100))) circular cylinder at a low Reynolds number (Re=20) with standard Lennard-Janes potential. Appearance, periodic shedding and oscillation of vortices are shown with streamlines and velocity vectors. Periodic time is about 0.3 ns and Strouhal number is about 0.2. Length of time-average vortices is 1.4 times larger than diameter of the cylinder. Velocity distribution in characteristic regions and recirculation region are obtained.

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Parallel Smoothed Molecular Dynamics Method and Coupling with Molecular Dynamics WANG Hankui, ZHANG Xiong, LIU Yan 2008, 25(6): 718-724.  Abstract ( )   PDF (428KB) ( )   A parallel smoothed molecular dynamies (SMD) method is proposed. Parallel programs with SMD and SMD-MD coupling are developed for loading problems of a plate with a crack and a nano single crystal copper beam subjected to remote tensile. With traditional molecular dynamics, smoothed molecular dynamics method introduces fixed background mesh and solves motion equations. Critical time step in SMD is controlled by background grid size and could be enlarged to save simulation time. Results are in agreement with those of traditional molecular dynamics. Compared with traditional MD simulation, SMD and SMD-MD coupling methods save computing time.

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A Sea Surface Aerodynamic Roughness Scheme SHA Wenyu, PAN Yuping, ZHU Shouxian, WANG Juhua, GE Sufang, CAI Meiqiong 2008, 25(6): 725-732.  Abstract ( )   PDF (466KB) ( )   We investigate dependence of Charnock parameters and nondimensional roughness length (zo/Ha) on wave age. A roughness scheme is developed which reflects sea state. Effects of wind fetch, duration and water depth on sea roughness are studied. Sensitivity of roughness to friction velocity and wave age is discussed. The scheme is applied to the latest COARE algorithm. With data of FPN platform in North Sea in December 1985, applicability of the new scheme is tested. It is shown that TY01 and 002 schemes overestimate u. and YT96 scheme underestimates it. Results of the new scheme are the closest to observed data.

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PDF Simulation of Bluff-body Stabilized Turbulent Non-premixed Flame HUANG Qing, ZHU Minming, YE Taohong, LIU Minghou, CHEN Yiliang, DONG Gang 2008, 25(6): 733-743.  Abstract ( )   PDF (600KB) ( )   A joint-scalar probability density function (PDF) model is used to simulate bluff-body stabilized turbulent non-premixed Sydney flames HM1. In Situ Adaptive Tabulation (ISAT) algorithm is used to accelerate chemistry calculations. A modified LRR-IP Reynolds stress model is applied to obtain mean flow and turbulent mixing fields. We consider three chemical kinetical schemes for methane chemistry. Simulation results are compared with experimental data. It shows that the model and mechanisms predict flow field, scalar field and local extinction well. C2 chemistry has minor effect on flame HM1.

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Neutron Yields, Energy Spectrum and Angular Distribution of D (d, n)3 He Reaction in a Thick Target Neutron Source YAO Zeen, DU Hongxin, TAN Xinjian, ZHANG Yu, Tooru Kobayashi, Gerard Bengua 2008, 25(6): 744-748.  Abstract ( )   PDF (245KB) ( )   A mathematical model and a program are developed to calculate neutron yields, energy spectrum and angular distribution of D (d, n)3He reaction in a thick deuterium-titanium (TiDx) target as incident deuteron energy lower than 1.0 MeV. D(d, n)3He reaction cross section from nuclear data tables and stopping power derived with SRIM-2003 code are adopted in the calculatoin of neutron production of an accelerator-based D(d, n)3He reaction neutron source. Integrated neutron yields, neutron energy spectrums and angular distribution are obtained.

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Cryptography Based on Chaos with Delayed Feedback Loop XU Shujiang, WANG Jizhi, YANG Suxiang 2008, 25(6): 749-755.  Abstract ( )   PDF (417KB) ( )   An encryption approach based on chaos in semiconductor lasers with electro-optical delayed feedback loop is proposed. To mask plaintext, we use chaotic map of semiconductor lasers subject to electro-optical feedback modeled by Ikeda equations to generate binary sequences. The plaintext block is permuted by a key-dependent shift approach and then encrypted by a classical chaotic masking technique. In each encryption turn, feedback is perturbed by a random number which depends on chaotic map, plaintext and ciphertext. State transfer function depends not only on the secret key, but also on the input plaintext of the turn and output ciphertext of the last turn to avoid chosen plaintext/ciphertext attack. Simulations show that the proposed cryptographic scheme is feasible and effective.