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On the dynamics in a transitional boundary layer

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Communications in Nonlinear Science and Numerical Simulation 2001年第3期6卷 111-171页

作者： C. B. LEE and R. LEE Department of Mechanics and engineering Science/state key laboratory for Studies of Turbulence and Complex Systems, Peking university, beijing 100871, china Department of engineering Mechanics, tsinghua university, beijing 100084, Chi Department of Mechanics and engineering Science / state key laboratory for Studies of Turbulence and Complex Systems Peking University Beijing 100871 China Department of engineering Mechanics Tsinghua University Beijing 100084 China

A model is presented to describe the dynamic physical processes that occur in a transitional boundary layer flow. The CS-solitons, the closed vortex, the secondary closed vortex and the chain of ring-like vortices are postulated to be the basic flow structures of the transitional boundary layer as well as the turbulent boundary layer. It is argued that the central features of transitional and developed turbulent boundary layer flows can be explained in terms of how the series vortices interact with each other, and with the CS-solitons. The physical process that leads to the regeneration of the new closed vortex along the border of the CS-soliton, as well as the processes of evolution of the vortices to high frequency vortices, is described. The model is supported by the important developments in a number of "kernel" experiments, which illustrate both transitional and developed turbulent boundary layer. An important aspect of the model is that it has been formulated to be consistent with accepted rational mechanics concepts that are known to provide a proper physical description of other flows.

关键词： boundary layer transition dynamic processes onset of turbulence

A COUPLED 1-D AND 2-D CHANNEL NETWORK MATHEMATICAL MODEL USED FOR FLOW CALCULATIONS IN THE MIDDLE REACHES OF THE YANGTZE RIVER

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Journal of Hydrodynamics 2011年第4期23卷 521-526页

作者： HAN Dong FANG Hong-wei BAIJing HE Guo-jian Department of Hydraulic engineering and state key laboratory of hydroscience and engineering Tsinghua University Beijing 100084 China

A coupled one-dimensional （1-D） and two-dimensional （2-D） channel network mathematical model is proposed for flow calculations at nodes in a channel network system in this article. For the 1-D model, the finite difference method is used to discretize the Saint-Venant equations in all channels of a looped network. The Alternating Direction Implicit （ADI） method is adopted for the 2-D model at the nodes. In the coupled model, the 1-D model provides a good approximation with small computational effort, while the 2-D model is applied for complex topography to achieve a high accuracy. An Artificial Neural Network （ANN.） method is used for the data exchange and the connectivity between the 1-D and 2-D models. The coupled model is applied to the Jingjiang-Dongting Lake region, to simulate the tremendous looped channel network system, and the results are compared with field data. The good agreement shows that the coupled hydraulic model is more effective than the conventional 1-D model.

关键词： Coupled 1-D and 2-D model looped channel network system Alternating Driection Implicit (ADI) Jingjiang-Dongting Lake region

InGaAs/InGaAlAs Strain-compensated Multiple-quantum-well Lasers with Improved Temperature Characteristic

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Chinese Journal of Lasers 1999年第5期8卷 3-5页

作者： SUN Ke WANG Jianhu ZHOU Dan PENG Jihu(state key Lab. on Integrated Optoelectronics, Electronic engineering Dept,tsinghua university, beijing 100084, china) 清华大学集成光电子学联合国家重点实验室北京 100084

It is reported on realization of pulsed operation of InGaAs/InGaAlAs straincompensated multiple-quantum-well lasers at room temperatures. The working wavelength is 1. 56μm; the threshold current density for the stripe waveguide lasers is less than 1. 85kA/cm2； for the ridge waveguide lasers, the threshold current is 35 mA. The incorporation of compensated strain, which makes the multiple-quantum-well design applicable, leads to an obvious improvement on device temperature characteristic.

关键词： strain-compensation quantum well laser diode InGaAlAs/InP

Competent predicate abstraction in model checking

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Science china(Information Sciences) 2011年第2期54卷 258-267页

作者： LI Li1,2,3, SONG XiaoYu4, GU Ming2,3 & LUO XiangYu2,3 1Department of Computer Science & Technology, tsinghua university, beijing 100084, china 2key laboratory for Information System Security, Ministry of Education of china, beijing 100084, china 3School of Software, tsinghua university, beijing 100084, china 4Department of ECE, Portland state university, Portland, Oregon 97207, USA 1. Department of Computer Science & Technology Tsinghua University Beijing 100084 China2. Key Laboratory for Information System Security Ministry of Education of China Beijing 100084 China3. School of Software Tsinghua University Beijing 100084 China4. Department of ECE Portland State University Portland Oregon 97207 USA

The paper presents a new approach to computing the abstract state and a maximum weight heuristic method for finding the shortest counter-example in verification of imperative programs. The strategy is incorporated in a verification system based on the counterexample-guided abstraction refinement method. The proposed method slashes both the size of the abstract state space and the number of invokes of a decision procedure. A number of benchmarks are employed to evaluate the effectiveness of the approach.

关键词： program model checking predicate abstraction weight heuristic

An　Experimental　Study　on　the　Motion　of　Droplets　in　Flue　Gas　Humidification　Activator　with　Pulse　Laser　Sheet　Photography

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Journal of Thermal Science 1994年第2期3卷 142-146页

作者： Ke Jiang Xuchang Xu Xuegui Shi(state key laboratory of Efficient and Clean Combustion of Coal, Department of Thermal engineering,tsinghua university, beijing 100084, china) 1. state key laboratory of Efficient and Clean Combustion of Coal Department of Thermal Engineering Tsinghua University 100084 Beijing China

In this paper a technique is introduced on visualization of emulsified droplets in gas stream by pulse laser sheet photography. By this technique fairly clear photographs of the concentration and velocity profiles of water droplets in an activation reactor were obtained. The results of the study show that with a venturi tube installed in the activator, the distribution of the droplets is more uniform than without it; the uniformity of the distribution of the droplets can improve the efficiency of the activation of the sorbent particles in the reactor. The picture of the collision of the droplets was obtained in the experiment, which could be used as basis for the study of the mechanism of humidified activation process. The results of the experimental study of the deposition of the droplets on the reactor walls is also described and discussed.

关键词： humidifier activator pulse laser sheet photography distribution of droplets deposition.

Study on internal quantum efficiency of blue InGaN multiple-quantum-well with an InGaN underneath layer

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Science china(Technological Sciences) 2010年第2期53卷 306-308页

作者： WANG JiaXing, WANG Lai, ZHAO Wei, ZOU Xiang & LUO Yi National laboratory for Information Science and Technology/state key laboratory on Integrated Optoelectronics, Department of Electronic engineering, tsinghua university, beijing 100084, china 1. National laboratory for Information Science and Technology/state key laboratory on Integrated Optoelectronics Department of Electronic Engineering Tsinghua University Beijing 100084 China

Blue InGaN multiple-quantum-well (MQW) samples with different InxGa1-xN (x=0.01–0.04) underneath layers (ULs) were grown by metal organic vapor phase epitaxy (MOVPE). Temperature dependent photoluminescence showed that the InGaN UL can improve the internal quantum efficiency (IQE) of MQW effectively due to strain release. And a maximum IQE of 50% was obtained when the thickness and In content of the InGaN UL were 60 nm and 0.01, respectively. Furthermore, the larger In content or thickness of the InGaN UL makes the IQE lower. Arrhenius fit to the experiment data showed that the IQE fall was mainly caused by the quantity increase of the nonradiative recombination centers, which was believed related to the accumulated stress in InGaN ULs.

关键词： InGaN underneath layer (UL) multiple-quantum-well (MQW) internal quantum efficiency (IQE) Arrhenius formula

Depth profiling of SBS/PET layered materials using step-scan phase modulation Fourier transform infrared photoacoustic spectroscopy and two-dimensional correlation analysis

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Science china Chemistry 2010年第5期53卷 1189-1193页

作者： LI BoBin & ZHANG PuDun state key laboratory of Chemical Resource engineering beijing university of Chemical Technology,beijing 100029,china 1. state key laboratory of Chemical Resource engineering Beijing University of Chemical Technology Beijing 100029 China

This paper demonstrates the application of step-scan phase modulation Fourier transform infrared photoacoustic spectroscopy(FTIR-PAS) in non-destructively depth profiling of styrene-butadiene-styrene block copolymer/polyethylene terephthalate(SBS/PET) layered *** surface thicknesses of three layered samples were determined to be 1.2,4.3 and 9.4μm by using phase difference analysis,overcoming the spatial detection limits of *** with generalized two-dimensional(G2D) FTIR correlation analysis,the spatial origins of peaks in the SBS/PET spectrum are identified with those having overlapping peaks between different layers are resolved.

关键词： depth profiling FTIR photoacoustic step-scan two-dimensional correlation analysis layered materials

The refined theory of deep rectangular beams for symmetrical deformation

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Science china(Physics,Mechanics & Astronomy) 2009年第6期52卷 919-925页

作者： GAO Yang1 & WANG MinZhong2 1 College of Science, china Agricultural university, beijing 100083, china 2 state key laboratory for Turbulence and Complex Systems and Department of Mechanics and Aerospace engineering, Peking university, beijing 100871, china College of Science China Agricultural University Beijing 100083 China state key laboratory for Turbulence and Complex Systems and Department of Mechanics and Aerospace engineering Peking University Beijing 100871 China

Based on elasticity theory, various one-dimensional equations for symmetrical deformation have been deduced systematically and directly from the two-dimensional theory of deep rectangular beams by using the Papkovich-Neuber solution and the Lur'e method without ad hoc assumptions, and they construct the refined theory of beams for symmetrical deformation. It is shown that the displacements and stresses of the beam can be represented by the transverse normal strain and displacement of the mid-plane. In the case of homogeneous boundary conditions, the exact solutions for the beam are derived, and the exact equations consist of two governing differential equations: the second-order equation and the transcendental equation. In the case of non-homogeneous boundary conditions, the approximate governing differential equations and solutions for the beam under normal loadings only and shear loadings only are derived directly from the refined beam theory, respectively, and the correctness of the stress assumptions in classic extension or compression problems is revised. Meanwhile, as an example, explicit expressions of analytical solutions are obtained for beams subjected to an exponentially distributed load along the length of beams.

关键词： deep rectangular beams the refined theory symmetrical deformation the Papkovich-Neuber solution the Lur’e method

Universal hierarchical symmetry for turbulence and general multi-scale fluctuation systems

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Acta Mechanica Sinica 2009年第3期25卷 279-294页

作者： Zhen-Su She Zhi-Xiong Zhang state key laboratory for Turbulence and Complex Systems, College of engineering, Peking university, 100871 beijing, china state key laboratory for Turbulence and Complex Systems College of Engineering Peking University 100871 Beijing China

Scaling is an important measure of multi-scale fluctuation systems. Turbulence as the most remarkable multi-scale system possesses scaling over a wide range of scales. She-Leveque （SL） hierarchical symmetry, since its publication in 1994, has received wide attention. A number of experimental, numerical and theoretical work have been devoted to its verification, extension, and modification. Application to the understanding of magnetohydrodynamic turbulence, motions of cosmic baryon fluids, cosmological supersonic turbulence, natural image, spiral turbulent patterns, DNA anomalous composition, human heart variability are just a few among the most successful examples. A number of modified scaling laws have been derived in the framework of the hierarchical symmetry, and the SL model parameters are found to reveal both the organizational order of the whole system and the properties of the most significant fluctuation structures. A partial set of work related to these studies are reviewed. Particular emphasis is placed on the nature of the hierarchical symmetry. It is suggested that the SL hierarchical symmetry is a new form of the self-organization principle for multi-scale fluctuation systems, and can be employed as a standard analysis tool in the general multi-scale methodology. It is further suggested that the SL hierarchical symmetry implies the existence of a turbulence ensemble. It is speculated that the search for defining the turbulence ensemble might open a new way for deriving statistical closure equations for turbulence and other multi-scale fluctuation systems.

关键词： Turbulence. Scaling law. She-Leveque modelHierarchical symmetry Self-organization - Turbulenceensemble