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Numerical exploration of new features on three-dimensional transition of a cylinder wake

science china Mathematics 2004年第z1期47卷 69-80页

作者： LING Guocan, XIONG Jun & ZHU KeqinState Key Laboratory of Nonlinear mechanics, Institute of mechanics, Chinese Academy of {2.s, beijing 100080, china department of engineering mechanics, Tsinghua university, beijing 100084, china Chinese Acad Sci Inst Mech State Key Lab Nonlinear Mech Beijing 100080 Peoples R China Tsing Hua Univ Dept Engn Mech Beijing 100084 Peoples R China

The three-dimensional transition of the wake flow behind a circular cylinder is studied in detail by direct numerical simulations using 3D incompressible N-S equations for Reynolds number ranging from 2.0 to 300. New features and vortex dynamics of the 3D transition of the wake are found and investigated. At Re = 2.0, the flow pattern is characterized by mode A instability. However, the spanwise characteristic length of the cylinder determines the transition features. Particularly for the specific spanwise characteristic length linear stable mode may dominate the wake in place of mode A and determine the spanwise phase difference of the primary vortices shedding. At Re = 2.0 and 300 it is found that the streamwise vortices evolve into a new type of mode "dual vortex pair mode" downstream. The streamwise vortex structures switch among mode A, mode B and dual vortex pair mode from near wake to downstream wake. At Re = 2.0, an independent low frequency fm in addition to the vortex shedding frequency fs is identified. Frequency coupling between fm and fs occurs. These result in the irregularity of the temporal signals and become a key feature in the transition of the wake. Based on the formation analysis of the streamwise vorticity in the vicinity of cylinder, it is suggested that mode A is caused by the emergence of the spanwise velocity due to three dimensionality of the incoming flow past the cylinder. Energy distribution on various wave numbers and the frequency variation in the wake are also described.

关键词： cylinder, wake, 3D transition, Fourier-spectral-spectral-element method, direct numerical simulation (DNS).

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Ultralight X-type lattice sandwich structure (Ⅱ):Micromechanics modeling and finite element analysis

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science china(Technological sciences) 2009年第9期52卷 2670-2680页

作者： ZHANG QianCheng1,CHEN AiPing 2.CHEN ChangQing2.3 & LU TianJian2.1 State Key Laboratory for Mechanical Behavior of Materials,School of Material science and engineering,Xi’an Jiaotong {2.,Xi’an 710049,china 2.MOE Key Laboratory for Strength and Vibration,School of Aerospace,Xi’an Jiaotong {2.,Xi’an 710049,china 3 department of engineering mechanics,AML,Tsinghua {2.,beijing 100084,china State Key Laboratory for Mechanical Behavior of Materials School of Material Science and Engineering Xi’an Jiaotong University Xi’an China MOE Key Laboratory for Strength and Vibration School of Aerospace Xi’an Jiaotong University Xi’an China department of engineering {2. AML Tsinghua University Beijing China

The methods of homogenization and finite elements are employed to predict the effective elastic constants and stress-strain responses of a new type of lattice structure,the X-structure proposed by the authors in a companion paper. It is shown that in most cases the predictions by the equivalent homogenization theory agree well with the experimental and 3-dimensional finite element calculated results. The theoretical and numerical study supports the argument that the X-structure is superior to the pyramid lattice structure in terms of mechanical strength.

关键词： sandwich panel lattice structure equivalent homogenization finite element model

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SURFACE MODIFICATION OF CaCO_3 WITH DENDRITIC CARBOXYLIC ACIDS

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Chinese Journal of Polymer science 2002年第3期20卷 231-235页

作者： Zhao-xia Guo Jian Yu Institute of Polymer science and engineering {2. of Chemical engineering Tsinghua university beijing 100084 china Tsing Hua Univ Dept Chem Engn Inst Polymer Sci & Engn Beijing 100084 Peoples R China

Nanometer calcium carbonate was modified with Frechet type polyether dendrons bearing a COOH group at thefocal point by a wet-coating technique in dichloromethane at room temperature. The interaction between CaCO;and thedendritic modifier was proven by IR and mass spectroscopy of the modified CaCO;after thorough extraction withdichloromethane. The amount of tightly bonded organic modifier was estimated by TGA. It was shown that the amount ofbonded molecules decreased with increasing generation number due to the larger number of branches. Compared tounmodified CaCO;, the modified CaCO;possess different dispersibility in water and in organic solvents.

关键词： calcium carbonate surface modification polyether dendrimer dendritic carboxylic acid

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CO_2.Mitigation in Coal Gasification Cogeneration Systems with Integration of the Shift Reaction, CO_2.Absorption and Methanol Production

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Journal of Thermal science 2004年第3期13卷 193-198页

作者： Yuanyuan DUAN Jin ZHANG Key Laboratory of Thermal science and Power engineering, {2. of Thermal engineering, Tsinghua university, beijing 100084, china Key Laboratory of Thermal science and Power engineering Department of Thermal Engineering Tsinghua University Beijing China

Cogeneration of electricity and liquid fuel can achieve higher efficiencies than electricity generation alone in Integrated Gasification Combined Cycle (IGCC), and cogeneration systems are also expected to mitigate CO2.emissions. A proposed methanol-electricity cogeneration system was analyzed in this paper using exergy method to evaluate the specified system. A simple cogeneration scheme and a complicated scheme including the shift reaction and CO2.removal were compared. The results show that the complicated scheme consumes more energy, but has a higher methanol synthesis ratio with partial capture of *** those methanol and electricity cogeneration systems, the CO2.mitigation is not merely an additional process that consumes energy and reduces the overall efficiency, but is integrated into the methanol production.

关键词： cogeneration system methanol synthesis CO2 mitigation exergy analysis

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Performance Modeling and Approximate Analysis of Multiserver Multiqueue Systems with Poisson and Self-similar Arrivals

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Journal of university of science and Technology {2. 2001年第2期8卷 145-151页

作者： Zhiguang Shan, Chuang Lin, Yang Yang, Yan Wang (Information engineering School, university of {2. and Technology beijing, beijing 100083, china) (department of Computer {2. and Technology, Tsinghua university, beijing 100084, china) Univ Sci & Technol beijing Informat Engn Sch Beijing 100083 Peoples R China Tsinghua Univ Dept Comp Sci & Technol Beijing 100084 Peoples R China

The problem of state space explosion is still ran outstanding challenge in Markovian performance analysis for multiserver multiqueue (MSMQ) systems. The system behavior of a MSMQ system is described using stochastic high-level Petri net (SHLPN) models, and an approximate performance analysis technique is proposed based on decomposition and refinement methods as well as iteration technique. A real MSMQ system, Web-server cluster, is investigated. The performance of an integrated scheme of request dispatching and scheduling is analyzed with both Poisson and self-similar request arrivals. The study shows that the approximate analysis technique significantly reduces the complexity of the model solution and is also efficient for accuracy of numerical results.

关键词： multiserver multiqueue (MSMQ) system Web-server cluster performance analysis stochastic high-level Petri net (SHLPN) request dispatching request scheduling

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Crystallization Kinetics of NiTi Films with Different Ni Contents

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Journal of Materials science & Technology 2001年第4期17卷 421-424页

作者： Xunyong JIANG, Huibin XU and Shengkai GONG department of Materials science and {2., beijing university of Aeronautics and Astronautics, beijing 100083, china beijing Univ Aeronaut & Astronaut Dept Mat Sci & Engn Beijing 100083 Peoples R China

Three kinds of NiTi films with different Ni contents were prepared by DC magnetron sputtering. The crystallization kinetics of amorphous films was determined by using non-isothermal single- scan techniques. The results show that the activation energy of crystallization of Ni-rich NiTi film(Ni 51.10 at. pct, Ti 48.90 at. pct) is 715 kJ/mol; while that of Ti-rich films are similar: one is 445 kJ/mol (Ni 46.74 at. pct. Ti 53.2. at. pct), the other is 418 kJ/mol (Ni 43.2. at. pct, Ti 56.7g at. pct), which i5 lower than Ni-rich film. The Avrami parameter n of different films are 0.92.and 0.74 for Ni-rich film and Ti-rich films, respectively. The difference of kinetic parameters for NiTi films with various Ni contents implies that the crystallization behaviors of these films are distinct, which is confirmed by the calculated isothermal kinetics at different temperatures. The thorough research on this phenomenon is in progress.

关键词： NiTi Crystallization Kinetics of NiTi Films with Different Ni Contents

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Solvation effects on brain uptakes of isomers of ^(99m)Tc brain imaging agents

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Chinese science Bulletin 2002年第21期47卷 1786-1791页

作者： JIA Hongmei, MA Xiaohui, WANG Cunxin & LIU Boli1. department of Chemistry, beijing Normal {2., beijing 100875, china 2. Center for Biomedical engineering, beijing Polytechnic {2., beijing 10002., china 1. department of Chemistry Beijing Normal University Beijing 100875 China 2. Center for Biomedical engineering Beijing Polytechnic University Beijing 100022 China

Analysis of electrostatic hydration free energies of the isomers of the 99mTc-BAT and 99mTc-DADT complexes is carried out using the computer simulation technique. The results show that not only a correlation exists between the logarithm of the brain uptake and the electrostatic hydration free energy for the isomers of 99mTc-brain radiopharmaceu-ticals, but also a linear relationship exists between the logarithm of the ratio of the brain uptake of the syn isomer to that of the anti one and the difference between the electrostatic hydration free energy of the syn-isomer and that of the anti one. Furthermore, the investigation on the important factors influencing the brain uptakes of 99mTc-radiophar-maceuticals and the reasons of the different biodistribution of the isomers of the 99mTc-complexes is explored at the molecular level. The results may provide a reference for the rational drug design of brain imaging agents.

关键词： 99mTc-brain imaging agent isomer brain uptake electro-static hydration free energy.

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New direction of computational fluid dynamics and its applications in industry

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science china(Technological sciences) 2007年第5期50卷 521-533页

作者： CHEN YaoSong1, SHAN XiaoWen2.& CHEN HuDong2.1 department of mechanics,{2., beijing 1.0871. china 2.Exa Corporation, Burlington, MA 01803 USA 1. department of mechanics Peking University Beijing 100871 China 2. Exa Corporation Burlington MA 01803 USA

For the past ten years there has been much progress in computational fluid dy- namics (CFD), among which the formation and development of the lattice Boltz- mann method (LBM) are an important new direction. We give a review on the main aspect and the latest development of this method in this article, and at the same time we also discuss the related development of scientific software and its impact on the real-world applications in industry.

关键词： lattice method, Boltzmann equation, CFD

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A complex variable meshless method for fracture problems

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science china(Physics,{2. & Astronomy) 2006年第1期49卷 46-59页

作者： CHENG Yumin1 & LI Jiuhong2.1. Shanghai Institute of Applied Mathematics and mechanics, Shanghai university, Shanghai 2.0072. {2. 2. department of Building engineering, Xi’an university of Technology, Xi’an 710048, {2. Shanghai Institute of Applied Mathematics mechanics Shanghai University Shanghai 200072 China department of Building engineering Xi’an University of Technology Xi’an 710048 China

Based on the moving least-square (MLS) approximation, the complex variable moving least-square approximation (CVMLS) is discussed in this paper. The complex variable moving least-square approximation cannot form ill-conditioned equations, and has greater precision and computational efficiency. Using the analytical solution near the tip of a crack, the trial functions in the complex variable moving least-square approxi- mation are extended, and the corresponding approximation function is obtained. And from the minimum potential energy principle, a complex variable meshless method for fracture problems is presented, and the formulae of the complex variable meshless method are obtained. The complex variable meshless method in this paper has greater precision and computational efficiency than the conventional meshless method. Some examples are given.

关键词： moving least-square approximation, complex variable moving least-square approximation, meshless method, complex variable meshless method, fracture.

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Two-dimensional thermoelasticity solution for functionally graded thick beams

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science china(Physics,{2. & Astronomy) 2006年第4期49卷 451-460页

作者： Lü Chaofeng1, CHEN Weiqiu1 & ZHONG Zheng2.1. department of Civil engineering, Zhejiang {2., Hangzhou 31002., china 2. Key Laboratory of Solid mechanics of Ministry of Education, School of Aerospace engineering and Ap- plied mechanics, Tongji {2., Shanghai 2.0092. china department of Civil engineering Zhejiang University Hangzhou 310027 China Key Laboratory of Solid mechanics of Ministry of Education School of Aerospace Engineering Applied mechanics Tongji University Shanghai 200092 China

Two-dimensional thermoelasticity analysis of functionally graded thick beams is presented using the state space method coupled with the technique of differential quadrature. Material properties vary continuously and smoothly through the beam thickness, leading to variable coefficients in the state equation derived from the elasticity equations. Approximate laminate model is employed to translate the state equation into the one with constant coefficients in each layer. To avoid numerical instability, joint coupling matrices are introduced according to the continuity conditions at interfaces in the approximate model. The differential quadrature procedure is applied to discretizing the beam in the axial direction to make easy the treatment of arbitrary end conditions. A simply-supported beam with exponentially varying material properties is considered to validate the present method. Numerical examples are performed to investigate the influences of relative parameters.

关键词： state equation differential quadrature approximate laminate model joint coupling matrices thermal stresses.

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