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Journal of Materials Science & Technology 2001年第6期17卷 610-614页

作者： Wenzhen LI and Baicheng LIU department of mechanical engineering, Tsinghua University, Beijing 100084, china.Jiarong LI Beijing Institute of Aeronautical Materials, Beijing 100095, china.[Manuscri Dept. of Mech. Eng. Tsinghua Univ. Beijing 100084 China

The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus, mold type (green or dry) and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroids graphite cast iron castings were discussed. Finally, two regression equations relating these variables to the formation of shrinkage porosity were derived based upon the orthogonal experiments conducted.

关键词： Shrinkage Behaviour of Spheroidal Graphite Cast Iron in Green and Dry Sand Molds for the Benchmarking of Solidification Simulation Graphite Simulation Cast

Effect of Process Factors on Microstructure of Semisolid Continuous Casting Billets

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International Journal of Minerals,Metallurgy and Materials 2000年第4期14卷 242-245页

作者： Shuming Xing, Qijie Zhai, Hanqi Hu ( department of mechanical engineering, Tsinghua University, Beijing 100084, china.School of Material Science and engineering, Shanghai University, Shanghai 200072, china.Material Science and engineering School, Univer department of mechanical engineering Tsinghua University Beijing 100084 China School of Material Science and engineering Shanghai University Shanghai 200072 China Material Science and engineering School University of Science and Technology Beijing Beijing 100083 China

Semisolid continuous casting (SSCC) is a new technology to produce billets for semisolid metal forming (SSMF). The effect of process factors, such as pouring temperature, stirring rate, preheating temperature and thermal conductivity of stirring chamber, on the microstructure of SSCC billets was studied by means of the factorial experimental method. The results show that the microstructure of SSCC billets can be controlled by the above-mentioned four process factors. In order to obtain fine and rounded granular grains in an SSCC billet, the pouring temperature, preheating temperature and stirring rate should be kept in a moderate range, and the thermal conductivity of stirring chamber should be high. The regression equations with the process factors connecting the microstructure was also set up based on experimental data.

关键词： semisolid metal continuous casting process factors microstructure Metallurgy

A MICROMECHANICS CONSTITUTIVE THEORY FOR FORWARD TRANSFORMATION PLASTICITY WITH SHEAR AND DILATATION EFFECT:I,NONPROPORTIONAL LOADING HISTORY

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Acta Mechanica Sinica 1990年第4期6卷 324-332页

作者： Hwang Kehchih Sun Qingping Yu Shouwen (department of engineering Mechanics,Tsinghua University,Beijing,china.) department of engineering Mechanics Tsinghua University Beijing China

A micromechanics constitutive theory which takes into account both the dilatation and shear ef- fects of the transformation is proposed to describe the macroscopic plastic behavior of structure ceramics during forward transformation under different *** some basic assumptions,the analytic expressions of the Helmholtz and complementary free energy of the constitutive element are derived in a self-consistent manner by using the Mori-Tanaka's method which takes into account the interaction between the transformed *** the framework of Hill-Rice's internal variable constitutive theory,the forward transformation yield function and incremental stress strain relations,in analogy to the theory of metal plasticity,for non-proportional loading histories are obtained.

关键词： shear effect internal variables constitutive element

Catalysts for decomposing ozone tail gas

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Journal of Environmental Sciences 2003年第6期15卷 779-782页

作者： LIU Chang-an, SUN De-zhi, WANG Hui, LI Wei (department of Environmental Science and engineering, Harbin Institute of Technology, Harbin 150001,china. department of Environmental Science and engineering Harbin Institute of Technology Harbin 150001

The preparation of immobilizing-catalysts for decomposing ozone by using dipping method was studied. XRD, XPS and TEM were used to characterize the catalysts. The three kinds of catalysts were selected preferentially, and their catalytic activities were investigated. The results showed that the catalyst with activated carbon dipping acetate(active components are Mn:Cu=3:2, active component proportion in catalyst is 15%, calcination temperature is 200℃) has the best catalytic activity for ozone decomposing. One gram of catalyst can decompose 17.6 g ozone at initial ozone concentration of 2.5 g/m 3 and the residence time in reactor of 0.1 s. The experimental results also indicated that humidity of reaction system had negative effect on catalytic activity.

关键词： ozone tail gas catalytic decomposition immobilizing-catalyst MnO 2 CuO

Optimization of a serpentine flow field with variable channel heights and widths for PEM fuel cells

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Science china.Technological Sciences) 2010年第2期53卷 453-460页

作者： LIN Lin, ZHANG XinXin, FENG HuTing & WANG XiaoDong department of Thermal engineering, School of mechanical engineering, University of Science and Technology Beijing, Bejing 100083, china department of Thermal engineering School of Mechanical Engineering University of Science and Technology Beijing

The present study proposes a modified serpentine flow field design in which the channel heights vary along each straight flow path to enhance reactant transport and liquid water removal. An optimization approach, combining a simplified conjugate-gradient method (inverse solver) and a three-dimensional, two-phase, non-isothermal fuel cell model (direct solver), has been developed to optimize the key geometric parameters. The optimal design has tapered channels for channels 1, 3 and 4 and increasing heights for channels 2 and 5 with the flow widths first increasing and then decreasing. The optimal channel heights and widths enhance the efficiency by 22.51% compared with the basic design having all heights and widths of 1 mm. The diverging channels have a greater impact on cell performance than fine adjustments of the channel widths for the present simulation conditions. The channel heights have more effect on the sub-rib convection, while the channel widths affect the uniformity of the fuel delivery more. The reduced channel heights of channels 2–4 significantly enhance the sub-rib convection to effectively transport oxygen to and liquid water out of the diffusion layer. The final diverging channel prevents significant leakage of fuel to the outlet via sub-rib convection.

关键词： PEM fuel cell simplified conjugate-gradient method optimization sub-rib convection

MICROSTRUCTURES OF A NOVEL HIGH STRENGTH AND WEAR-RESISTING ZINC ALLOY

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中国有色金属学会会刊：英文版 1995年第4期5卷 84-88,132页

作者： Li Yuanyuan Xia Wei Ngai Tungwai Leo Luo Junming Zheng Lingyi(department of mechanical engineering,South china.University of Technology, Guangzhou 51064) South china.Univ of Technology Guangzhou China

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关键词： zinc alloy microstructure strength wear-resistance

A Study on Numerical Simulation of Core-Shooting Process

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Journal of Materials Science & Technology 2001年第6期17卷 625-628页

作者： Junjiao WU, Yi GUI and Wenzhen LI department of mechanical engineering, Tsinghua University, Beijing 100084, china.[Manuscript received July 18, 2000, in revised form August 25, 2000] Dept. of Mech. Eng. Tsinghua Univ. Beijing 100084 China

In order to evaluate the main factors influencing the core-shooting process and to optimize the design of core boxes, the fluid-particle (air-sand) model has been built based on the two-phase flow theory. The fluid phase, air, and the particulate phase, sand granules, have been treated as a continuum. By using this model, it is possible to simulate the flow and compaction behavior of sand particles during the core-shooting process. To benchmark the calculated results, the shooting process has been recorded with a digital high speed camera, and the inlet condition of sand particles has also been achieved by using the camera. The preliminary results have showed that the calculation is in agreement with the testing results.

关键词： A Study on Numerical Simulation of Core-Shooting Process Core Simulation

TWO KINDS OF HARMONIC PROBLEMS IN CONTROL SYSTEMS

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Journal of Systems Science & Complexity 2009年第4期22卷 587-596页

作者： Zhisheng DUAN Lin HUANG State Key Lab for Turbulence and Complex Systems and department of Mechanics and Aerospace engineering,College of engineering,Peking University,Beijing 100871,china. State Key Lab for Turbulence and Complex Systems and department of Mechanics and Aerospace engineering College of Engineering Peking University Beijing China

This paper discusses the harmonic problems in control systems from two aspects:Oneis the harmonic control among different subsystems,and the other is the harmonic control amongmultiple *** intrinsic problems in such systems are *** is pointed out that somesubsystems must be unstable to stabilize the whole interconnected system by an *** discrete-time multi-input systems,a necessary and sufficient condition is presented for the strictdecrease of the quadratic optimal performance index with the control input *** showsan essential difference between single-input and multi-input control ***,some futureresearch directions are discussed in harmonic control of interconnected systems,allocation of multi-control inputs,fault-tolerant control,and fault-diagnosis.

关键词： Interconnected system quadratic optimal control redundant inputs Riccati equation simplectic matrix.

STAGED PROGRESSION MODEL FOR EPIDEMIC SPREAD ON HOMOGENEOUS AND HETEROGENEOUS NETWORKS

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Journal of Systems Science & Complexity 2011年第4期24卷 619-630页

作者： Haifeng ZHANG Michael SMALL Xinchu FU School of Mathematical Sciences Anhui University Hefei 230039 China. department of Electronic and Information engineering Hong Kong Polytechnic University Hung HornKowloon Hong Kong China. department of Mathematics Shanghai University Shanghai 200444 China.

In this paper, epidemic spread with the staged progression model on homogeneous and heterogeneous networks is studied. First, the epidemic threshold of the simple staged progression model is given. Then the staged progression model with birth and death is also considered. The case where infectivity is a nonlinear function of the nodes＇ degree is discussed, too. Finally, the analytical results are verified by numerical simulations.

关键词： Complex network epidemic heterogenous homogeneous the staged progression model.

FORCE REDUCTION OF FLOW AROUND A SINUSOIDAL WAVY CYLINDER

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Journal of Hydrodynamics 2009年第3期21卷 308-315页

作者： ZOU Lin LIN Yu-feng School of mechanical and Electronic engineering Wuhan University of Technology Wuhan 430070 China department of mechanical engineering The Hong Kong Polytechnic University Hong Kong China

A large eddy simulation of cross-flow around a sinusoidal wavy cylinder at Re = 3000 was performed and the load cell measurement was introduced for the validation test. The mean flow field and the near wake flow structures were presented and compared with those for a circular cylinder at the same Reynolds number. The mean drag coefficient for the wavy cylinder is smaller than that for a corresponding circular cylinder due to the formation of a longer wake vortex generated by the wavy cylinder. The fluctuating lift coefficient of the wavy cylinder is also greatly reduced. This kind of wavy surface leads to the formation of 3-D free shear layers which are more stable than purely 2-D free shear layers. Such free shear layers only roll up into mature vortices at further downstream position and significantly modify the near wake structures and the pressure distributions around the wavy cylinder. Moreover, the simulations in laminar flow condition were also performed to investigate the effect of Reynolds number on force reduction control.

关键词： wavy cylinder force reduction Large Eddy Simulation (LES) Reynolds number effect