检索结果-南通市图书馆

AN ITERATIVE METHOD FOR THE DISCRETE PROBLEMS OF A CLASS OF ELLIPTICAL VARIATIONAL INEQUALITIES

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and mech.nics(English Edition) 1995年第4期16卷 351-358页

作者：郑铁生李立许庆余 dept. of engr. mech. Xi’an Jiaotong University Xian P.R. China

Based on the nonlinear characiers of the discrete problems of some ellipticalvariational inequalities, this paper presents a numerical iterative method, the schemesof which are pithy and converge rapidly The new method possesses a high efficiency. insolving such applied engineering problems as obstacle problems and .free *** arising in fluid lubrications.

关键词： variational inequalities iterative method. fluid lubrications

EFFECT OF THE OPEN CRACK ON THE PULL-IN INSTABILITY OF AN ELECTROSTATICALLY ACTUATED MICRO-BEAM

在线全文

学校读者我要写书评

暂无评论

Acta mech.nica Solida Sinica 2012年第6期25卷 627-637页

作者： Asadollah Motallebi Mohammad Fathalilou Ghader Rezazadeh mech. Eng. dept. Islamic Azad University mech. Eng. dept. Urmia University

In this paper, the effects of the open crack on the static and dynamic pull-in volt- ages of an electrostatically actuated fixed-fixed and cantilever micro-beam are investigated. By presenting a mathematical modeling, the governing static and dynamic equations are solved by SSLM and Galerkin-based Reduced Order Model, respectively. Then, each single-side open crack in the micro-beam is modeled by a massless rotational spring and the cracked mode shapes and corresponding natural frequencies are calculated by considering the boundary and patching con- ditions and using transfer matrix methods. Finally, the effects of the crack dept. ratio, crack position and crack number on the pull-in voltage of the micro-beams are studied. It is shown that beside the residual stresses created in the machining process, the crack（s） can be initiated, growth and consequently change the pull-in voltage of the system by decreasing the natural frequencies. The results show that the crack position is effective beside the crack dept. ratio in decreasing the pull-in voltage. Also it is shown that in the fixed-fixed micro-beam there are several points for the crack location in which, the pull-in voltage is extremum.

关键词： MEMS open crack electrostatic pull-in instability

AN INVESTIGATION OF TURBULENT HEAT TRANSFER IN CHANNEL FLOWS BY LARGE EDDY SIMULATION

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2002年第2期14卷 29-35页

作者： Dong Yu-hong, Zhong Feng-quan, Lu Xi-yun, Zhuang Li-xian Department of mech.nics and mech.nical Engineering, University of Science and Technology of China, Hefei 230026, China dept. of mech. and mech. and Eng. Univ. of Sci. and Technol. of China Hefei 230026 China

Large Eddy Simulation (LES) of fully developed turbulent channel flow with heat transfer was performed to investigate the effects of the Reynolds number on the turbulence behavior. In the present study, the bottom wall of the channel was cooled and the top wall was heated. The Reynolds numbers, based on the central mean-velocity and the half-width of the channel, were chosen as 4000, 6000, 10 4 and 2×10 4, and the Prandtl number as 1.0. To validate our calculations, the present results were compared with available data obtained by Direct Numerical Simulation (DNS), which proves to be in good agreement with each other. To reveal the effects of the Reynolds number, some typical quantities, including the velocity fluctuations, temperature fluctuation, heat fluxes and turbulent Prandtl number, were studied.

关键词： Large Eddy Simulation (LES) turbulent channel flow Subgrid Scale (SGS) model heat transfer stratified turbulence

FLUID FLOW IN ROTATING HELICAL SQUARE DUCTS

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2003年第3期15卷 49-56页

作者： Chen Hua-jun, Zhang Ben-zhao, Zhang Jin-suo Department of mech.nics, Zhejiang University, Hangzhou 310027, China, dept. of mech. Zhejiang Univ. Hangzhou 310027 China

A numerical study is made for a fully developed laminar flow in rotatinghelical pipes. Due to the rotation, the Coriolis force can also contribute to the secondary *** interaction between rotation, torsion, and curvature complicates the flow characteristics. Theeffects of rotation and torsion on the flow transitions are studied in details. The results showthat there are obvious differences between the flow in rotating ducts and in helical ducts withoutrotation. Certain hitherto unknown flow patterns are found. The effects of rotation and torsion onthe friction factor are also examined. Present results show the characteristics of the fluid flow inrotating helical square ducts.

关键词： secondary flow rotating ducts helical ducts

Effects of Plastic Deformation and Stresses on Dilatation duringthe Martensitic Transformation in a B-bearing Steel

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2001年第2期17卷 203-206页

作者： M. C.Somani and L.P.Karjalainen dept. of mech.nical Engineering, University of Oulu, Oulu, Finland M. Oldenburg and M.Eriksson dept. of mech.nical Engineering, Lulea University of Technology, Lulea, Sweden dept. of mech. Eng. Univ. of Oulu Oulu Finland

To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280'C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and strength than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression.

关键词： Effects of Plastic Deformation and Stresses on Dilatation duringthe Martensitic Transformation in a B-bearing Steel

PROPULSIVE PERFORMANCE AND VORTEX SHEDDING OF A FOIL IN FLAPPING MOTION

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2003年第5期15卷 7-12页

作者： Yang Yan, Lu Xi yun, Yin Xie zhen Department of mech.nics and mech.nical Engineering, University of Science and Technology of China, Hefei 230026, China, dept. of mech. and mech. Eng. Univ. of Sci. and Technol. of China Hefei 230026 China

The propulsive performance and vortex shedding of oscillating foil, whichmimics biological locomotion, were numerically investigated. The objectives of this study were todeal with unsteady force, in particular thrust force, exerted on the foil in pitching and plungingmotions, and to explore the relation of the propulsive performance with vortex structures near thefoil and vortex shedding in the near wake. The two-dimensional incompressible Navier-Stokesequations in the vorticity and stream-function formulation were solved by fourth-order essentiallycompact finite difference schemes for the space derivatives and a fourth-order Runge-Kutta schemefor the time advancement. To reveal the mech.nism of the propulsive performance, the unsteady forceand the shedding of the trailing- and leading-edge vortices of the foil were analyzed. The effectsof some typical factors, such as the frequency and amplitude of the oscillation, the phasedifference between the pitching and plunging motions, and the thickness ratio of the foil, on thevortex shedding and unsteady force were discussed.

关键词： vortex dynamics vortex shedding thrust force unsteady flow flappingmotion

BLOCK ITERATIVE METHODS FOR LINEAR ALGEBRAIC EQUATION AND DOMAIN DECOMPOSITION METHOD FOR INCOMPRESSIBLE VISCOUS FLOW

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2002年第4期14卷 73-80页

作者： Ren, An-Lu Zou, Jian-Feng Zhou, Yong-Xia Li, Guang-Wang dept. of mech. Zhejiang Univ. Hangzhou 310027 China

It was proved numerically that the Domain Decomposition Method CDDM) with one layer overlapping grids is identical to the block iterative method of linear algebra equations. The results obtained by using DDM could be in reasonable agreement with the results of full-domain simulation. With the three dimensional solver developed by the authors, the flow field in a pipe was simulated by using the full-domain DDM with one layer overlapping grids and with patched grids respectively. Both of the two cases led to the convergent solution. Further research shows the superiority of the DDM with one layer overlapping grids to the DDM with patched grids. A comparison between the numerical results obtained by the authors and the experimental results given by Enayet[3] shows that the numerical results are reasonable.

关键词： Computational fluid dynamics Computer simulation Iterative methods Linear equations Viscous flow

RESEARCH ON DISTRIBUTION FUNCTION AND ORIENTATION TENSORS OF FIBER SUSPENSIONS IN WEDGE-SHAPED FLOW FIELD

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2002年第1期14卷 38-44页

作者： Lin, Jian-Zhong Zhang, Ling-Xin Wang, Ye-Long dept. of mech. Zhejiang Univ. Hangzhou 310027 China

The distribution function and orientation tensor of fiber suspensions in wedge shaped flow field were computed . The results indicate that with time increasing, the fiber orient themselves to flow direction gradually. At the locations with same pole radii, the angle between fiber orientation and centerline, which occurs with the most probability, decreases with the pole angle increasing . At the locations with same pole angle, the angle between fiber orientation and centerline increases with the pole radii decreasing. The second order tensors get steady more quickly at the points where the velocity g radients are larger. At the locations with same pole angle, the steady values of orientation tensors are identical. At the locations with same pole radii is, streamline becomes flatter as the pole angle decreases.

关键词： fiber suspensions wedge shaped flow distribution function orientation tensors numerical simulation

Study of Manufacturing Technology and Properties of AVGCI with Rare Earths

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2001年第1期19卷 44-48页

作者：盛达颜丙祥 dept. of mech. Eng. Tsinghua Univ. Beijing 100084 China

By vermicularizing agent containing RE (REFeSi), austempered vermicular graphite cast iron (AVGCI) with RE can be produced with austempered treatment. The process of austenitization of vermicular graphite cast iron (VGCI) with RE and the transformation of AVGCI with RE with temperature increasing were studied by SEM with heating device. Properties of AVGCI with RE, such as tensile strength, elongation, impact toughness, hardness, thermal fatigue resistance, thermal expansive coefficient and weight increasing by oxidation were measured by electron universal testing machine with heating device. Experimental results indicate that AVGCI with RE possesses good comprehensive properties at room and elevated temperatures.

关键词： rare earths austenite-bainite vermicular graphite cast iron manufacturing technology room temperature property high temperature property