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Modeling Study of Planar Flexible Manipulator Undergoing Large Deformation

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Journal of Shanghai Jiaotong university(science) 2007年第6期12卷 824-830页

作者：尤超蓝洪嘉振蔡国平 dept. of eng. Mechanics Shanghai Jiaotong Univ.

The planar flexible manipulator undergoing large deformation is investigated by using finite element method (FEM). Three kinds of reference frames are employed to describe the deformation of arbitrary point in the flexible manipulator, which are global frame, body-fixed frame and co-rotational frame. The rigid-flexible coupling dynamic equation of the planar flexible manipulator is derived using the Hamilton’s principle. Numerical simulations are carried out in the end of this paper to demonstrate the effectiveness of the proposed model. The simulation results indicate that the proposed model is efficient not only for small deformation but also for large deformation.

关键词： planar flexible manipulator large deformation overall motion coupling dynamics co-rotational frame

3D Stochastic Modeling of Grain Structure for Aluminum Alloy Casting

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Journal of Materials science & Technology 2003年第5期19卷 391-394页

作者： Qingyan XU, Weiming Feng.and Baicheng.LIUDepartment of Mechanical eng.neering, Tsinghua University, Beijing 100084, China dept. of Mech. eng. Tsinghua Univ. Beijing 100084 China

A 3D stochastic modeling was carried out to simulate the dendritic grains during solidification of aluminum alloys, including time-dependent calculations for temperature field, solute redistribution in liquid, curvature of the dendritic tip, and growth anisotropy. The nucleation process was treated by continuous nucleation. A 3D simplified grain shape model was established to represent the equiaxed dendritic grain. Based on the Cellular Automaton method, a grain growth model was proposed to capture the neighbor cells of the nucleated cell. During growing, each grain continues to capture the nearest neighbor cells to form the final shape. When a neighbor cell was captured by other grains, the grain growth along this direction would be stopped. Three-dimensional calculations were performed to simulate the evolution of dendritic grain. In order to verify the modeling results, the predictions were compared with the observation on samples cast in the sand mold and the metal mold.

关键词： 3D stochastic modeling Nucleation Grain growth

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

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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 eng.neering, 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

NUMERICAL ANALYSIS OF SATURATED-UNSATURATED SEEPAGE FLOW IN FRACTURED ROCK MASS DUE TO SURFACE INFILTRATION

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Journal of Hydrodynamics 2001年第4期13卷 28-33页

作者： Hu, Yun-Jin Su, Bao-Yu Zhan, Mei-Li dept. of Hydraulic eng. Tsinghua Univ. Beijing 100084 China

Seepage flow in fractured rock mass due to surface infiltration is a saturated-unsaturated seepage process. Aimed at rock mass with large fracture density, which can be equivalent to continuum, a mathematical model for saturated-unsaturated seepage flow in fractured rock mass due to surface infiltration was established in this paper. The Galerkin finite element method was used in numerical simulation and a finite element program used to calculate saturated-unsaturated seepage flow due to surface infiltration was worked out. A model experiment was used to examine the reasonableness of the program. The results show that the proposed model and program are reasonable. The application of the analysis method in an eng.neering project shows that the method is reliable and feasible.

关键词： computer simulation Mathematical models Seepage

Electrostatic Suspension System Nonlinear Character Analysis and Its Internal Model Control

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Journal of Shanghai Jiaotong university(science) 2007年第3期12卷 377-382页

作者：糜长军郭晋峰金志华田蔚风 Inst. of Navigation and Control Dept. of Instrument Science and Eng. Shanghai Jiaotong Univ.

Nonlinearity is an important characteristic in electrostatic suspension system (ESS). This paper concludes the nonlinear parts in ESS, which generally result from the relationships between rotor displacement and capacitance, rotor displacement and electrostatic force, and control voltage and electrostatic force. In terms of the nonlinearities, a new control method with modified internal model control (IMC) was proposed to analyze the ESS, deduce the transfer function of the modified IMC controller in ESS, and simulate this new application in ESS. Comparing with proportional integral derivative (PID) control, IMC has only a parameter, and has better performance. As a result, IMC solves nonlinearity error well in ESS with only one uncertain parameter, and performs well when the rotor has large displacement.

关键词： electrostatic suspension system (ESS) internal model control (IMC) nonlinearity

ON THE PLANE PIEZOELECTRIC PROBLEM OF A LOADED CRACK TERMINATING AT A MATERIAL INTERFACE

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Acta Mechanica Solida Sinica 1996年第2期9卷 151-158页

作者： Qin Qinghua Yu Shouwen, dept. of eng. Mechanics, Tsinghua University, Beijing 100084 dept. of eng. Mechanics Tsinghua University Beijing 100084

The plane problem of a crack terminating at the interface of a bimaterial piezoelectric, and loaded on its faces, is treated. The emphasis is placed on how to transform this problem into a non-homogeneous Hilbert problem. To make the derivation tractable, the concept of the axial conjugate is introduced and related to the complex conjugate. The angle between the crack line and the interface may be arbitrary. Numerical results are given to illustrate the stress singularity at crack tip.

关键词： piezoelectricity crack axial conjugate interface singular integral equation

Modeling of Mold Filling and Solidification in Lost Foam Casting

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Journal of Materials science & Technology 2003年第5期19卷 395-397页

作者： Feng.un LI, Houfa SHEN and Baicheng.LIUDepartment of Mechanical eng.neering, Tsinghua University, Beijing 100084, China dept. of Mech. eng. Tsinghua Univ. Beijing 100084 China

Based on the characteristics of the lost foam casting (LFC) and the artificial neural network technique, a mathematical model for the simulation of the melt-pattern interface movement during the mold filling of LFC has been proposed and experimentally verified. The simulation results are consistent with the experiments in both the shapes of melt front and filling sequences. According to the calculated interface locations, the fluid flow and the temperature distributions during the mold filling and solidification processes were calculated, and the shrinkage defect of a lost foam ductile iron casting was predicted by considering the mold wall movement in LFC. The simulation method was applied to optimize the casting design of lost foam ductile iron castings. It is shown that the model can be used for the defects prediction and for casting design optimization in the practical LFC production.

关键词： Lost foam casting Numerical simulation Artificial neural network

Numerical Simulation of Microporosity Evolution of Aluminum Alloy Castings

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Journal of Materials science & Technology 2004年第1期20卷 23-26页

作者： Shuyong DONG, Shoumei XIONG and Baicheng.LIUDepartment of Mechanical eng.neering, Tsinghua University, Beijing 100084, China dept. of Mech. eng. Tsinghua Univ. Beijing 100084 China

A mathematical model to calculate the size and distribution of microporosities was studied and coupled with a stochastic microstructure evolution model. The model incorporates various solidification phenomena such as grain structure evolution, solidification shrinkage, interdendritic fluid flow and formation and growth of pores during solidification processes. The nucleation and growth of grains were modeled with a cellular automaton method that utilizes the results from a macro scale modeling of the solidification process. Experiments were made to validate the proposed models. The calculated results of aluminum alloy castings agreed with the experimental measurements.

关键词： Numerical simulation Microporosity evolution Aluminum alloy castings

Nitriding of Hard Fe Electrodepositionand Its Effects on Wear Resistance

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Journal of Materials science & Technology 2001年第2期17卷 271-274页

作者： Cheng.ui GAO, Dajian CHEN and Baiyang ZHOU Department of Mechanical eng.neering, Fuzhou University, Fujian, Fuzhou 350002, China dept. of Mech. eng. Fuzhou Univ. Fuzhou 350002 China

Nitriding is employed for the hard Fe electrodeposition to produce a hard-facing and antiwear coating. It only takes 1 h for the hard Fe coating, which is much shorter than nitriding the Fe and steel. The results showed that the nitriding can increase the microhardness, wear resistance of the coating, as well as the bonding streng.h of the coating with the substrate. Additionally it can eliminate the brittleness, turn the internal stress of the coating from tension to compression. The wear resistance of the nitrided Fe coating is 4.6 times as high as that of Cr coating. It is simple and economic to combine hard Fe electroplating and nitriding, which is a good technology of the tribological surface modification.

关键词： Fe Nitriding of Hard Fe Electrodepositionand Its Effects on Wear Resistance