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25 July 2001, Volume 18 Issue 4 Previous Issue    Next Issue

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HAMILTONIAN ALGORITHM FOR SOLVING THE DYNAMIC EQUATIONS OF ATMOSPHERE WANG Bin, JI Zhong-zhen, XIAO Qing-nong 2001, 18(4): 289-297.  Abstract ( )   PDF (334KB) ( )   The Hamiltonian nature of the dynamic equations of atmosphere is studied further, based on its regular form and its infinitely many first integrals equipped with a given Poisson bracket. Without the friction and forcing processes, the dynamic equation system of atmosphere is proved to be a Hamiltonian system. A symplectic scheme to solve the system is proposed, whose good performance is shown in a numerical experiment.

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THE APPLICATION OF VERIFIED CLEAR SKY TBB DATA IN THE SOIL TEMPERATURE STUDY OF TIBETAN PLATEAU BAI Jing-yu, XU Xiang-de, LIU Rui-yun 2001, 18(4): 298-302.  Abstract ( )   PDF (242KB) ( )   It is known that there are sparse weather stations on the Tibetan Plateau,and the lack of real soil temperature data affects the understanding of surface thermodynamic structure over the Plateau.Clear sky TBB data are employed,and the verified clear sky TBB data in 1998 from May to August through variational techniques by real soil temperature can capture the distribution features of mean soil temperature of the Plateau.It turns out to be a kind of important data source to the central and western Plateau,and plays an important role in the Plateau underlying thermodynamic structure study.

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NUMERICAL SIMULATIONS OF SPATIALLY-DEVELOPING COMPRESSIBLE VORTEX ROLLUP USING A UPWIND COMPACT DIFFERENCE METHOD WANG Qiang, FU De-xun, MA Yan-wen 2001, 18(4): 303-307.  Abstract ( )   PDF (228KB) ( )   The temporal spatial discrete Fourier transformation is employed to analyze the dissipation and dispersion errors of the numerical algorithm used here. Based on directly solving the two dimensional time dependent compressible Navier Stokes equations, the spatial evolution of primary vortex generated in forced compressible plane free shear layers is simulated numerically by using a new fifth order upwind compact difference scheme. The phenomena, including the primary vortex saturating, the first pairing, and the second pairing, are shown with the passively conserved scalar method and so on. The initial value effect related to subharmonic disturbances in incoming flows is studied. The results show that the spatial evolution type of large scale compressible vortices is associated with the disturbance modes.

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INVESTIGATIONS INTO THE VISCOUS RESOLUTION OF CFD SCHEMES FOR VORTICAL FLOW SIMULATIONS YAN Chao, HUANG Xian-lu, LI Ting-he, GUI Yong-feng 2001, 18(4): 308-312.  Abstract ( )   PDF (495KB) ( )   The viscous resolution of different CFD schemes for vortical flows over delta wings has been investigated both numerically and theoretically, which include Jameson's center scheme, Roe's FDS scheme, Van Leer's FVS scheme and upwind TVD scheme. It has been concluded that Jameson's center scheme and Roe's FDS scheme have the best viscous resolutions, while Van Leer's FVS scheme and upwind TVD scheme are not suitable for vortical flow simulations.

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A MULTI-STAGGERED GRID METHOD FOR SWIRLING RECIRCULATION FLOW LIU Ying-zeng, CHEN Han-ping 2001, 18(4): 313-317.  Abstract ( )   PDF (228KB) ( )   There are rich vortex phenomena presented in swirling circulation flow, such as secondary flow and vortex breakdown. For numerical simulation of such complicated recirculating flow, higher requirements are needed for grid density and calculation precision. With the increase of grid points, both convergence rate and calculation precision of traditional iterative numerical methods decrease. On the basis of finite control volume scheme and pressure correction method, the FAS multi staggered grid scheme is presented here for Navier Stokes equation in cylinder coordination. The axisymmetric swirling flow confined in cylindrical container is used as test problem. The results indicate that both convergence rate and calculation precision are highly improved.

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APPLICATION OF MULTI-BLOCK GRID TECHNOLOGY IN NUMERICAL SIMULATION OF FLOW FIELD ABOUT AERODYNAMICS CONTROL SURFACE CHEN Hai-xin, LI Feng-wei, E Qin, SHEN Meng-yu 2001, 18(4): 318-324.  Abstract ( )   PDF (640KB) ( )   Because of the complexities in both configurations and flow phenomena,there are great difficulties in the numerical simulation of flow about wing with lift-enhancing devices and control surfaces.By using cell-centered finite volume method,it deals with Renolds-averaged Navier-Stokes equations on multi-block structural grids generated by elliptic method.Two kinds of patching schemes,point-to-point and patch-on-common-surface,are employed to establish the information exchange among blocks.In the later one,the overlap cell area weighted interpolation is used to guarantee the conservation.Ramshaw algorithm is also used to pre-determine the overlap areas.Flow fields about multi-element airfoils and delta wing with deflected flap are computed with the present method.Numerical results are all in good agreement with experiment data.Flow field visualization shows the present method has good resolution in flow details.

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A MULTI-BLOCK STRUCTURED GRID GENERATION TECHNIQUE ZHANG Li-dong, LEE Chun-hian 2001, 18(4): 325-328.  Abstract ( )   PDF (212KB) ( )   A grid generation technique adaptable for flows with complex geometrical characteristics is developed. The procedure is developed in such a way that the surface grids are first constructed and/or reconstructed in multi-block manner according to the data given at typical section of the body, utilizing the nonuniformed rational B spline (NURBS) surface representation commonly employed in CAD technique. The blocks consisting of the flow field are decomposed in accordance with the geometrical and flow characteristics of the specified problem, and the boundaries of the blocks can thus be constructed accordingly. Based on the surface grids generated, a multi-block grid system for the entire flow field can then be built up by using numerical, algebraic or mixed methods. As an illustration, the grids generated by the developed technique for several space transport systems are presented.

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FINITE ELEMENT ANALYSIS ON TRAFFIC FLOW PROBLEM Ⅰ ZHANG Peng, LIU Ru-xun 2001, 18(4): 329-333.  Abstract ( )   PDF (230KB) ( )   It proposes a viewpoint that the finite element method (FEM) might be well used in traffic flow models, among which a newly developed dynamics model is elaborated. In the discussion, it is foreseen that the new model is fundamentally sound and has much advantage over some well known traditional ones. In the FEM solution, the weak form of the model is properly constructed by means of weight residual method and equations for weak solution are given. Finally, it achieves some favorable results in the numerical simulation and this, in a degree, makes the argument convincing.

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MATHEMATICAL AND PHYSICAL MODEL AND NUMERICAL SIMULATION OF DROPWISE CONDENSATION HEAT TRANSFER WU Yu-ting, YANG Chun-xin, YUAN Xiu-gan, MA Chong-fang 2001, 18(4): 334-340.  Abstract ( )   PDF (359KB) ( )   A random fractal model of the drop size and space distribution in dropwise condensation is presented.The boundary conditions of heat conduction through the condensate wall are defined by use of the heat transfer model through a single drop proposed by Rose.Thus,the mathematical model of dropwise condensation heat transfer is established.A numerical simulation of dropwise condensation heat transfer of water on the copper wall has been performed.The results agree well with the bulk of existing experimental data and the precision is higher than that of the model proposed by Rose.

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NUMERICAL STUDY ON PULSE TUBE REFRIGERATOR WITH GAP REGENERATOR HE Ya-ling, XU Ming-yao, GAO Cheng-ming, LI Jing-gao, CHEN Zhong-qi 2001, 18(4): 341-345.  Abstract ( )   PDF (217KB) ( )   A new concept of pulse tube refrigerator using gap regenerator as its regenerator is suggested.The physical model of this pulse tube refrigerator is established.The influences of frequency,gap width,opening of orifice and double inlet valves on the refrigerator performance have been analyzed by numerical calculation based on the finite difference method.It shows that in the pulse tube refrigerator with a gap regenerator, the optimum frequency,optimum openings of orifice and double inlet valves are less than those of the pulse tube refrigerator with screen-matrix regenerator.

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ANALYSIS ON EDDY CURRENTS AND ELECTRO-MAGNETIC FORCES AT THE LOWER HYBRID WAVE LAUNCHING ANTENNA ON THE SUPERCONDUCTING TOKAMAK HT-7 YU Jia-wen, KUANG Guang-li, DING Bo-jiang, LIN Jian-an 2001, 18(4): 346-350.  Abstract ( )   PDF (234KB) ( )   It analyzes the eddy current,the distribution of the induced magnetic field and the electromagnetic force on the lower hybrid wave launching antenna on the superconducting tokamak HT 7 by using finite element circuit method.A new iterative algorithm is developed to analyze the coupled magnetic field.The method and results obtained are helpful to study the eddy current and electro magnetic force on metal plate placed in rather complicated electro magnetic environment.

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THE GROUP-CONTRIBUTION METHOD FOR SATURATED VAPOR DENSITY'S CALCULATION OF FREON OF ETHANE CLASS ZHANG Zhi, LIU Zhi-gang, LIANG De-qing 2001, 18(4): 351-355.  Abstract ( )   PDF (206KB) ( )   To meet the demands of the study of CFCs alternatives and the engineering application,a group contribution method is proposed to calculate the saturated liquid's density of freon in ethane class based on the equation of saturated liquid density of Перелъщтейн.On condition that the critical temperature and critical density or critical specific volume are known,the density of saturated liquid can be calculated with high accuracy.The obtained mean deviation and the maximum one are less than 1% and 15% separately,which can meet the demands of alternatives' studies and application.

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MOLECULAR DYNAMICS SIMULATIONS OF THE CRYSTALLIZATION OF LIQUID Au AND Ag GUAN Li, WU Ai-ling, ZHANG Xiao-ru 2001, 18(4): 356-359.  Abstract ( )   PDF (307KB) ( )   Based on many body potential model,the crystallizing processes of Au and Ag are investigated by means of molecular dynamics simulation technique.The pairs analysis method is applied to compare the difference of the local symmetry of molecular cluster between both atoms.In the process of crystallization, the rebuild of the local cluster and the transformation of pairs is found to be from 1661、1441 to 1421、1422.The other important information given is about the microstructure of Au,Ag.

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A PARALLEL SOLVER FOR CIRCULANT BLOCK-TRIDIAGONAL SYSTEMS ON DISTRIBUTED-MEMORY MULTICOMPUTERS LUO Zhi-Gang, LI Xiao-Mei, WANG Zheng-Hua 2001, 18(4): 360-365.  Abstract ( )   PDF (241KB) ( )   A parallel solver for circulant block tridiagonal systems on distributed memory multicomputers is developed.The algorithm is based on matrix block operations.The implementation of this algorithm invokes BLAS3 subroutines.The complexity of the algorithm is analyzed.A sufficient condition guaranteeing the processes not to break down is given.The numerical experiments on a distributed memory multicomputer YH3E show that this algorithm has a high parallel efficiency.

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SCALABILITY ANALYSIS OF THE 2-D ELECTROMAGNETIC PLASMA PARALLEL PROGRAM USING PARTICLE-IN-CELL METHOD CHEN Jun, MO Ze-yao, YUAN Guo-xing, LI Xiao-mei 2001, 18(4): 366-371.  Abstract ( )   PDF (269KB) ( )   With the development of massively parallel processing, it is necessary that the parallel applications would be capable of good scalability. It is described how to use the near optimal scalability analysis method with the two dimensional electromagnetic plasma parallel program using particle in cell method as an example. Having known the performance of small parallel systems, one can obtain the information about how many processors which the larger systems are running on can obtain the more"reasonable" performance when using the near optimal scalability analysis. A suit of practical scalability evaluation method is also proposed to find the reason why the practical scalability is bad, and help to optimize the application programs.

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EULER AND N-S SOLUTIONS OF A WING-BODY COMBINATION WITH AILERON CHEN Ze-min, LI Jin, ZHU Zi-qiang, WU Zong-chen 2001, 18(4): 372-376.  Abstract ( )   PDF (218KB) ( )   In terms of the combination of patched grid and domain decomposition techniques, the N S equation of the complex flow around a wing body combination with deflection of control surface (aileron) is solved. In the computation Van Leer's scheme is employed to discretize the inviscid flux terms and the viscous flux terms are discretized by adopting central difference scheme. An internal coupling condition satisfying the conservation of flux is used on the interface of neighboring regions. Numerical results show that the present method is effective one for solving the flow around a wing body combination with control surface deflection.

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COMPARATIVE STUDY OF FINITE DIFFERENCE METHODS FOR UNSTEADY FREE JET MA Hand-dong, YUANG Hong-sheng 2001, 18(4): 377-380.  Abstract ( )   PDF (209KB) ( )   Under the frame of Euler equations and Beam Warming TVD scheme,three time derivative discretion methods,i.e.Beam Warming implicit approximative factorization algorithm,implicit subiteration algorithm and simplified Runge Kutta five stage scheme,are numerically tested for the early evolution of underexpanded free jet flow.The results show that (i)Beam Warming implicit approximative factorization algorithm can give reasonable patterns of flowfield in whole.Some detailed features should be further studied;(ii)Implicit subiteration scheme with first-order accuracy in time would result in some abnormal phenomena so that the accuracy may not be enough for the unsteady flow;(iii)The results computed by implicit subiteration scheme with second order accuracy in time are well in agreement with that by simplified Runge Kutta five stage scheme, so we can regard these two difference methods as feasible algorithms for unsteady flow computation.

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CONSTRUCTION AND NUMERICAL SIMULATION OF HIGH ACCURACY WEIGHTED ENO SCHEMES WANG Chun-wu, QIU Jian-xian, DAI Jia-zun 2001, 18(4): 381-384.  Abstract ( )   PDF (142KB) ( )   According to the ENO scheme on structured grids, a class of weighted ENO finite volume scheme on unstructured mesh is developed. On every control volume, it constructs a new weighted quadratic reconstruction polynomial which can save computational costs. It also uses a method which can resolve the overdetermined systems and do not affect the accuracy of the schemes. Besides, the selection of interpolation points and the construction of weight are presented, Third order TVD Runge Kutta time discretization is used. In order to accelerate the convergence, local time step is introduced. The numerical experiments show the scheme effective.