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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

A Novel Practical Cooperative Diversity Method for the Power-Limited Wireless Sensor Network

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Journal of Shanghai Jiaotong university(Science) 2007年第4期12卷 458-463页

作者：周亮郑宝玉 dept.of Electrical eng. Shanghai Jiaotong Univ.

A novel practical cooperative diversity method for power-limited wireless sensor network system was proposed. At first, the system model was presented and the cooperation problem is formulated under the minimum outage probability criterion, then the focus was put on the power efficiency of system, such as the relay selection, cooperation strategy and power allocation etc. At last the uniform procedure of the proposed method was given. The results of the simulation clearly demonstrate that our method not only has the properties of simple operation and wide applying scope, but also outperforms those of current classical methods on the aspect of outage probability under the basis of the same power limitation.

关键词： cooperative diversity wireless sensor network power-limited

MOTIONS OF ALLOYING ADDITIONS IN GAS STIRRED LADLES

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Acta Metallurgica Sinica(eng.ish Letters) 2001年第5期14卷 359-367页

作者： S.C. Fan, B.K. Li and J.C. He Department of Thermal eng.neering, Northeastern University, Shenyang 110004, China dept. of Thermal eng. Northeastern Univ. Shenyang 110004 China

A mathematical model has been developed to analyze the flow patterns and subsurface trajectories of spherical shaped particles (alloy additions) in gas stirring ladles. First, a numerical method to solve fluid flow problems in conjunction with a curvilinear coordinate system is proposed. The internal boundary in flow field, which must be designated in the cylindrical polar coordinate system, can be avoided by using body- fitted coordinate system (BFC). Consequently, computed flow of molten steel and paths of alloying additions are able to cross smoothly the geometric centerline of cylindrical vessel. Second, motion of particles is calculated in the three-dimensional coordinate system, the modification of parameters, such as the drag coefficient and density in the gas plume region, is examined. When the density of sphere is closer and closer to that of fluid, the path of motion is longer and longer. If the plug is moved off-centered to the half of radius, the path of sphere is prolonged, and the sphere may go through the geometric centerline of vessel, reach the deeper region. The immersed depths increase with increasing entry velocities.

关键词： alloying addition gas stirring ladle motion

Geometric Nonlinear Formulation for a Rectangular Plate with Large Deformation

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Journal of Shanghai Jiaotong university(Science) 2007年第6期12卷 831-837,844页

作者：刘锦阳马易志洪嘉振 dept. of eng. Mechanics Shanghai Jiaotong Univ.

Absolute nodal coordinate formulation for a rectangular plate with large deformation was improved. Based on nonlinear elastic theory, a precise strain expression is used to derive the equations of motion. Both shear strain and transverse normal strain are taken into account. Different from the previous absolute nodal coordinate formulation, the absolute nodal coordinates, which describe the displacement and slope of the element nodes, are separated into three parts: the absolute nodal coordinates in X, Y and Z directions, respectively, so that the dimension of the mass, stiffness and force matrices is reduced. Furthermore, by using constant matrices, which can be calculated and saved before simulation, the nonlinear stiffness matrices can be calculated by matrix multiplication for each time step, so that the computational efficiency can be improved. Finally, simulation example of a rectangular plate with large deformation was used to verify the accuracy and efficiency of the present formulation.

关键词： rectangular plate absolute nodal coordinate formulation large deformation

Influence of Slot Defect Leng.h on Magnetic Flux Leakage

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Journal of Materials Science & Technology 2004年第2期20卷 231-232页

作者： Songling HUANG, Luming LI, Haiqing YANG and Keren SHIDepartment of Electrical eng.neering, Tsinghua University, Beijing 100084, China dept. of Elec. eng. Tsinghua Univ. Beijing 100084 China

A key issue, which influences the applications of magnetic flux leakage testing, is defect quantification. There have been many research on the relationship between width, depth and magnetic flux leakage of slot defect. However, the leng.h factor is often ignored. The relationship between characteristics of defect leakage field and defect leng.h was investigated. The magnetic flux leakages of a series of plate specimens with the same width, same depth and different leng.h slot defects were tested under the same magnetizing conditions. Testing results show that defect leng.h is an important parameter needed to consider in quantifying defects.

关键词： Magnetic flux leakage (MFL) testing Defect quantification Slot leng.h

A NEW HIGH ORDER SCHEME FOR CONVECTION EQUATION AND ITS APPLICATION

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Journal of Hydrodynamics 2002年第1期14卷 81-86页

作者： Zhang Xiao-feng.(Department of River eng.neering, Wuhan University, Wuhan 430072, China) Zhang Hong-wu (Department of Hydraulic eng.neering, Tsinghua University, Beijing 100084, China) Tamotsu Takahashi, Hajime Nakagawa (Disaster Prevention Research dept. of River eng. Wuhan Univ. Wuhan 430072 China

With the undetermined coefficient method, a new high order scheme for convection equation named as HAUC was worke d out. The accuracy of the new scheme was analyzed by comparing the computed res ults with the exact solutions of 1-D pure convection equation and nonlinear con vection equation. The effectiveness of the HAUC was also examined by comparing w ith the results obtained by other schemes. Finally, it was applied to simulate 1 -D dam break flow with differenct ratios of initial upstream water depth to do wnstream one. The results show that the scheme has the ability to simulate both undular bores and moving hydraulic jumps.

关键词： higher order scheme undetermined co efficient method dam break flow undular bore moving hydraulic jump

Efficient Accurate Context-Sensitive Anomaly Detection

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Journal of Shanghai Jiaotong university(Science) 2007年第5期12卷 639-644,650页

作者：李红娇李建华 dept.of Electronic eng. Shanghai Jiaotong Univ.

For program behavior-based anomaly detection, the only way to ensure accurate monitoring is to construct an efficient and precise program behavior model. A new program behavior-based anomaly detection model, called combined pushdown automaton (CPDA) model was proposed, which is based on static binary executable analysis. The CPDA model incorporates the optimized call stack walk and code instrumentation technique to gain complete context information. Thereby the proposed method can detect more attacks, while retaining good performance.

关键词： program behavior-based anomaly detection system call combined pushdown automaton (CPDA) model

Performance Analysis of Two Frequency Reuse Schemes in Fixed Relay systems

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Journal of Shanghai Jiaotong university(Science) 2007年第2期12卷 216-222页

作者：黄磊戎蒙恬 dept.of Electronic eng. Shanghai Jiaotong Univ.

An upsurge of interest in relay-augmented infrastructure-based networks has appeared in recent *** resource management in such relay systems has great influence on the system *** to utilize the limited frequency resources efficiently in the system is a hot research *** this paper,performance of frequency reuse schemes has been studied in fixed relay systems.A novel scheme is achieved by modifying an existing *** model is proposed for the performance analysis of two *** the theoretical analysis and simulation results show that the modified scheme outperforms the existing one not only in power consumption of mobile stations but also in cell carrier-to-interference ratio coverage.

关键词： frequency reuse fixed relay system power consumption carrier-to-interference ratio

NUMERICAL SIMULATION OF TURBULENT FLOW CHARACTERISTICS IN A CURVED PIPE WITH A BAFFLE

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Journal of Hydrodynamics 2002年第2期14卷 45-50页

作者： Zhang Xin-yu, Xia Zhen-hai, Fan Jian-ren, Cen Ke-fa Department of Energy eng.neering, Zhejiang University, Hangzhou 310027, China (Received March 23, 2000) dept. of Energy eng. Zhejiang Univ. Hangzhou 310027 China

A numerical study on the characteristics of developing turbulent flow in a curved pipe with a baffle was carried out in body-fitted coordinates with the k-ε model turbulence. A curved duct of square cross-section was examined first, and the results agree very well with the experimental data. Then two kinds of pipes, a normal curved pipe and that with a baffle were studied. The computational results are presented and compared with each other to illustrate the changes of the flow after adding the baffle. The longitudinal velocity in the pipe with a baffle was characterized by outer velocity bigger than the inner one. The secondary flow was characterized by four-vortex structure with the intensity reduced, which results in the equability of the flow field of the cross-section compared with that without a baffle, and has much more significant meaning in eng.neering.

关键词： numerical simulation curved pipe with a baffle secondary flow