检索结果-南通市图书馆

Science china(Technological Sciences) 2008年第8期51卷 1073-1086页

作者： ZHOU LiXing department of engineering mechanics, tsinghua university, beijing 100084. china department of engineering mechanics Tsinghua University Beijing China

The derivation and closure methods of the second-order moment (SOM) combus- tion model are proposed. The application of this model to Reynolds averaged (RANS) and large-eddy simulation (LES) of turbulent swirling diffusion combustion, jet diffusion combustion, and bluff-body stabilized premixed combustion is sum- marized. It is indicated that the SOM model is much better than the eddy-beak-up (EBU) and presumed PDF models widely used in commercial software and engi- neering. The SOM modeling results are close to those obtained using the most accurate but much more complex PDF equation model. Moreover, it can save much more computation time than the PDF equation model. Finally, the SOM model is validated by the direct numerical simulation (DNS) of turbulent reacting channel flows.

关键词： turbulent combustion second-order moment model Reynolds averaged simulation large-eddy simulation

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

LARGE DEFLECTION THEORY OF NANOBEAMS

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2010年第5期23卷 394-399页

作者： Dujuan Zeng Quanshui Zheng 1(department of engineering mechanics,tsinghua university,beijing 100084.china) department of engineering mechanics Tsinghua University Beijing China

One-dimensional nanostructured materials are often used as beams in many applications such as ultrahigh-frequency resonators and ultrasensitive sensors. Compared with usual macroscopic beams, nanobeams have much higher surface/volume ratios so that their surface energies may play a significant role. Besides, they often bear large deflections due to their typically large slenderness ratios and larger elastic ranges. There is, however, lack of a theory that takes into account of both the above two features owned by nanobeams. In this paper, we present such a theory and give applied examples to show that surface energy and large deflection may individually or jointly have notable effects.

关键词： nanobeam surface energy large deflection

CONSERVATION OF THREE-POINT COMPACT SCHEMES ON SINGLE AND MULTIBLOCK PATCHED GRIDS FOR HYPERBOLIC PROBLEMS

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2003年第3期21卷 383-400页

作者： Zi-niu Wu (department of engineering mechanics, tsinghua university, beijing 100084. china) department of engineering mechanics Tsinghua University 北京 100084

For nonlinear hyperbolic problems, conservation of the numerical scheme is important for convergence to the correct weak solutions. In this paper the conservation of the well-known compact scheme up to fourth order of accuracy on a single and uniform grid is studied, and a conservative interface treatment is derived for compact schemes on patched grids. For a pure initial value problem, the compact scheme is shown to be equivalent to a scheme in the usual conservative form. For the case of a mixed initial boundary value problem, the compact scheme is conservative only if the rounding errors are small enough. For a patched grid interface, a conservative interface condition useful for mesh refinement and for parallel computation is derived and its order of local accuracy is analyzed.

关键词： Conservation Compact scheme Uniform grid Multiblock patched grid.

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

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) department of Biomedical engineering Tsinghua University Beijing 100084 China department of engineering mechanics Tsinghua University Beijing 100084 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.

NUMERICAL DISSIPATION FOR THREE-POINT DIFFERENCE SCHEMES TO HYPERBOLIC EQUATIONS WITH UNEVEN MESHES

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2003年第4期21卷 519-534页

作者： Zi-niu Wu(department of engineering mechanics, tsinghua university, beijing 100084. china) department of engineering mechanics Tsinghua University 北京 100084

The widely used locally adaptive Cartesian grid methods involve a series of abruptly refined interfaces. The numerical dissipation due to these interfaces is studied here for three-point difference approximations of a hyperbolic equation. It will be shown that if the wave moves in the fine-to-coarse direction then the dissipation is positive (stabilizing), and if the wave moves in the coarse-to-fine direction then the dissipation is negative (destabilizing).

关键词： Refined interfaces Numerical dissipation Three-point difference approxima-tion Hyperbolic equation.

Multiple time step molecular dynamics simulation for interaction between dislocations and grain boundaries

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2005年第4期21卷 371-379页

作者： X.Y.Li W.Yang department of engineering mechanics,tsinghua university,beijing 100084.china department of engineering mechanics Tsinghua University Beijing China

A multiple time step algorithm, called reversible reference system propagator algorithm, is introduced for the long time molecular dynamics simulation. In contrast to the conventional algorithms, the multiple time method has better convergence, stability and efficiency. The method is validated by simulating free relaxation and the hypervelocity impact of nano-clusters. The time efficiency of the multiple time step method enables us to investigate the long time interaction between lattice dislocations and low-angle grain boundaries.

关键词： Multiple time step Molecular dynamics ,Dislocation Grain boundary

Stability of core-annular flow of power-law fluids in the presence of interfacial surfactant

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,mechanics & Astronomy) 2010年第5期53卷 933-943页

作者： SUN XueWei,PENG Jie & ZHU KeQin department of engineering mechanics,tsinghua university,beijing 100084.china department of engineering mechanics Tsinghua University Beijing China

The shear-thinning influence on the core-annular flow stability of two immiscible power-law fluids is considered by making a linear stability *** flow is driven by an axial pressure gradient in a straight pipe with the interface between the two fluids occupied by an insoluble *** the basic flow for this core-annular arrangement,the analytical solution is obtained with respect to the power-law fluid *** linearized equations for the evolution of infinitesimal disturbances are derived and the stability problem is formulated as a generalized matrix eigenvalue problem,which is solved by using the software package Matlab based on the QZ *** shear-thinning property is found to have marked influence on the power-law fluid core-annular flow stability,which is reflected in various ***,the capillary instability is magnified by the shear-thinning property,which may lead to an essential difference between power-law and Newtonian fluid *** when the interface is close to the pipe wall,the power-law fluid flow may be unstable while the Newtonian fluid flow is ***,under disturbances to the interface a velocity discontinuity at the interface appears which is destabilizing to the *** magnitude of this velocity discontinuity is affected by the power-law index and the flow stability is influenced ***,the shear-thinning property may induce new stability modes which do not appear in the Newtonian fluid *** flow stability shows much dependence on the interface location,the role of which was neglected in most previous *** shear-thinning fluid flow is more unstable to long wave disturbances when the interface is close to the pipe wall,while the Newtonian fluid flow is more unstable when the interface is close to the pipe *** this trend is changed by the addition of interfacial surfactant,for which the power-law fluid flow is more stable no matter where the interface is loca

关键词： core-annular flow power-law fluid interfacial surfactant linear stability analysis

Self-Organizing Tunnel Peers

在线全文

学校读者我要写书评

暂无评论

计算机工程 2002年第S1期28卷 7-12页

作者： CHEN Maoke , LI Xing (department of Electronic engineering, tsinghua university, beijing 100084.china ) department of Electronic engineering Tsinghua University Beijing 100084China

Tunneling is an important approach in IPv6 transition techniques. The tunnel broker model provides a way to build virtual IPv6 networks without manual ***, neither it adapts performance variation on the IPv4 infrastructure, norit is a scalable solution for a wide-area IPv6 networking environment. In this paper, a self-organizing tunnel peer (SOTP) model is *** peers are clustered in the SOTP system so that optimization is scalable. Four primitive operations related to --cluster constructionarrest,release,division and deathendow the system with the nature of self-organization. Occurrence and behavior of the operations are decided by criteria on the IPv4 end-to-end performance; hence measurement is an indispensable component of the system. The metabolism of cluster relaxes the requirement to accuracy of measurement and optimization.

关键词： S elf-organizationTunnelingEnd-to-end measurementIPv6

A MESSAGE-DRIVING FORMALISM FOR MODELING AND SIMULATION OF MULTI-AGENT SUPPLY CHAIN SYSTEMS

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Systems Science and Systems engineering 2011年第4期20卷 385-399页

作者： Wenzhe TAN1 Yueting CHAI2 Yi LIU3 1department of Automation, tsinghua university, beijing, 100084. china 2department of Automation, tsinghua university, beijing, 100084. china 3department of Automation, tsinghua university, beijing, 100084. china department of Automation Tsinghua University Beijing China

To acquire a competitive advantage in the expanding market, manufacturing enterprises should be able to manage their supply chains as effectively as possible. It is now becoming popular to model supply chains as multi-agent systems and use discrete event simulation to learn more about their behaviors or investigate the implications of alternative configurations. In order to enhance the computational efficiency and keep the simulation credibility, this paper proposes a message-driving formalism for the simulation of multi-agent supply chain systems. Through the message-driving formalism, the problem of shared variables is addressed and the parallel operation of agents is implemented. Simulation experiments with a prototype implementation show that the message-driving formalism is able to provide credible results in significantly less simulation time.

关键词： Supply chain multi-agent system modeling and simulation parallel discrete event simulation message-driving formalism