检索结果-南通市图书馆

Numerical Simulation of Microporosity Evolution of Aluminum Alloy Castings

在线全文

学校读者我要写书评

暂无评论

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 engineering, 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

Simulation study and function analysis of the dynamic aortic valve

在线全文

学校读者我要写书评

暂无评论

Progress in Natural science:Materials International 2006年第5期16卷 512-517页

作者： XIA Dongdong and BAI Jing (Department of Biomedical engineering, tsinghua university, beijing 100084. china) Department of Biomedical engineering Tsinghua University Beijing 100084 China

The dynamic aortic valve (DAV) is a new left ventricular assist device, a micro-axial blood pump implemented at the position of the aortic valve, pumping blood from the left ventricle into the aortic artery. The present dynamic aortic valve operates at 7 different rotation speeds, ranging from 3000 r/min (speed 1) to 9000 r/min (speed 7). Because in vivo experiments need a lot of live animals and take a long period of time, modeling and simulation have been widely used to simulate and analyze hydra-dynamic property of the DAV and its assisting effects. With the measurements from the mock circulatory loop, a mathematic model of the DAV is established and embedded into the previously developed canine circulatory system. Using this model, the effect of the DAV on the failing heart at each rotation speed level is investigated. The vital cardiac variables are computed and compared with in vivo experimental results, which are in good agreement with an acceptable difference mostly 15%. The establishment of the DAV model and its simulation are useful for further improvement of the DAV device.

关键词： dynamic aortic valve mathematic model computer simulation.

Computational fluid dynamics modeling and hemolysis analysis of axial blood pumps with various impeller structures

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Progress in Natural science:Materials International 2006年第9期16卷 993-997页

作者： XIA Dongdong, ZHAO Chunzhang, ZHANG Xiwen and BAI Jing ( Department of Biomedical engineering, tsinghua university, beijing 100084. china Department of engineering Mechanics, tsinghua university, beijing 100084. china) [a]Department of Biomedical engineering Tsinghua University Beijing China [b]Department of engineering Mechanics Tsinghua University Beijing China

The flow fields in the blood pump were analyzed three- dimensionally using computational fluid dynamics (CFD). Hemolysis of the pump was calculated based on the changes in shear stress and related exposure times along the particle trace lines using a forward Euler approach. In this "way, how different impeller structures and rotational speeds affect the hemolysis was particularly acquired. As a result, impeller with long-short alternant vanes behaved best in hemolysis property and can be utilized to axial blood pumps development and design.

关键词： axial blood pump computational fluid dynamics hemolysis.

Effective elastic moduli of polymer-layered silicate nanocomposites

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Chinese science Bulletin 2001年第13期46卷 1130-1133页

作者： FENG XiqiaoDepartment of engineering Mechanics, tsinghua university, beijing 100084. china Department of engineering Mechanics Tsinghua University Beijing China

Polymer-layered silicate (PLS) nanocomposites exhibit some mechanical properties that are much better than conventional polymer filled composites. A relatively low content of layered silicate yields a significant enhancement of material performance. After the volume fraction of clay reaches a relatively low 'critical value'; however, further increasing does not show a greater stiffening effect. This phenomenon is contrary to previous micromechanical predictions and is not understood well. Based on the analysis on the microstructures of PLS nanocomposites, the present note provides an insight into the physical micromechanisms of the above unexpected phenomenon. The Mori-Tanaka scheme and a numerical method are employed to estimate the effective elastic moduli of such a composite.

关键词： nanocomposites effective moduli microstructure Mori-Tanaka method.

Mechanism and control of convective heat transfer——Coordination of velocity and heat flow fields

在线全文

学校读者我要写书评

暂无评论

Chinese science Bulletin 2001年第7期46卷 596-599页

作者： QUO ZengyuanDepartment of engineering Mechanics, tsinghua university, beijing 100084. china Department of engineering Mechanics Tsinghua University Beijing 100084 China

A second look has been given at the mechanism of convective heat transfer based on the analogy between convection and conduction with heat sources. The strength of convective heat transfer depends not only on the fluid velocity and fluid properties, but also on the coordination of fluid velocity and heat flow fields. Hence, based on the included angle of velocity and temperature gradient vectors, the presence of fluid motion may enhance or reduce heat transfer. With this concept, the known heat transfer phenomena may be understood in a deeper way. More important is that some novel approaches of heat transfer control can be developed.

关键词： convective heat transfer coordination heat transfer enhancement.

Application and Comparison of Two SGS Models in Large Eddy Simulation of FreeTurbulent Jet Flow

在线全文

学校读者我要写书评

暂无评论

Communications in Nonlinear science and Numerical Simulation 1999年第1期4卷 12-19页

作者： Hong YAN and Mingde SU (Department of engineering Mechanics, tsinghua university, beijing 100084. china) Department of engineering Mechanics Tsinghua University Beijing 100084 China

Large eddy simulations of spatially evolved turbulent round jets were presented. The two SGS models called the standard Smagorinsky’s eddy viscosity model and the non-eddy viscosity stimulated small scale(SSS) model developed by Shah & Ferziger were applied. The Reynolds number of the flow was taken as 10000 based on the orifice diameter and the axial velocity in the orifice. The comparison between these two models showed that the standard Smagorinsky’s viscosity model with Smagorinsky’s constant of 0.1 underestimated the turbulent intensity, while the SSS model showed a better agreement with the experiment. Also the SSS model was used to investigate the development of vortex. The convective boundary condition at the outflow boundary was adopted to ensure less effect of noise on the upstream.

关键词： stimulated small scale model smagorinsky’s eddy viscosity model Round jet, Large eddy simulation

INTERFACIAL REACTIONS OF METAL FILMS WITH AlN SUBSTRATE

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

中国有色金属学会会刊：英文版 1996年第2期6卷 81-85页

作者： He Xiangjun Tao Kun Fan Yudian (Department of Materials science and engineering, tsinghua university, beijing 100084. Department of Materials science and engineering Tsinghua University Beijing 100084 China

ＩＮＴＥＲＦＡＣＩＡＬＲＥＡＣＴＩＯＮＳＯＦＭＥＴＡＬＦＩＬＭＳＷＩＴＨＡｌＮＳＵＢＳＴＲＡＴＥＨｅＸｉａｎｇｊｕｎ；ＴａｏＫｕｎ；ＦａｎＹｕｄｉａｎ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅａｎｄＥ... 详细信息

ＩＮＴＥＲＦＡＣＩＡＬＲＥＡＣＴＩＯＮＳＯＦＭＥＴＡＬＦＩＬＭＳＷＩＴＨＡｌＮＳＵＢＳＴＲＡＴＥＨｅＸｉａｎｇｊｕｎ；ＴａｏＫｕｎ；ＦａｎＹｕｄｉａｎ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅａｎｄＥｎｇｉｎｅｅｒｉｎｇ，Ｔｓｉｎｇｈ...

关键词： thin films interfacial reactions AlN substrate

Coacervate Structures of CdI_2 Thin Film Grown during Phase Transformation

在线全文

学校读者我要写书评

暂无评论

Journal of Materials science & Technology 1997年第4期13卷 296-298页

作者： Xiaoyan YE and Lili CAO(Dept. of Chemistry, tsinghua university, beijing 100084. china)Jizhong ZHANG and Hengde LI(Dept. of Materials Scieuce & engineering, tsinghua university, beijing 100084. china) Dept. of Chemistry Tsinghua University Beijing 100084 China Dept. of Materials science and engineering Tsinghua University Beijing 100084 China

The microstructure of CdI2 thin film grown during vapor-phase deposition was investigated by scanning electron microscopy (SEM). The thin film deposited on Si crystal consists of numerous sunflower-like aggregates. These aggregates display well self-assembly characteristics. The size of Sunflower-like aggregates is between 12 and 44 μm. Each sunflower-like aggregate is surrounded with many adjacent wings-'petals'. The structure of central region of the 'sunflower' is obviously difFerent from that of the 'petal'. Electron spectroscopy for chemical analysis (ESCA) was employed in determining the chemical valence of the thin film. Self-organization efFect is used to explain the coring growth process of CdI2 thin film

关键词： Thin Coacervate Structures of CdI2 Thin Film Grown during Phase Transformation

Explicit Classification for Torsion Subgroups of Rational Points of Elliptic Curves

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2002年第3期18卷 539-548页

作者： De Rong QIU Center for Advanced Study, tsinghua university, beijing 100084. P. R. china Xian Ke ZHANG Department of Mathematical sciences, tsinghua university, beijing 100084. P. R. china Center for Advanced Study Tsinghua University Beijing P. R. China Department of Mathematical sciences Tsinghua University Beijing P. R. China

We study the classification of elliptic curves E over the rationals Q according to the torsion subgroups E_(tors)(Q). More precisely, we classify those elliptic curves with E_(tors)(Q) being cyclic with even orders. We also give explicit formulas for generators of E_(tors)(Q). These results, together with the recent results of K. Ono for the non-cyclic E_(tors)(Q), completely solve the problem of the explicit classification and parameterization when E has a rational point of order 2.

关键词： Elliptic curve Rational point Torsion group Mordell group Parameterization