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Deformation reinforcement theory and its application to high arch dams

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Science China(Technological Sciences) 2008年第S2期51卷 32-47页

作者： YANG Qiang,LIU YaoRu,CHEN YingRu & ZHOU WeiYuan state key {2. of Hydroscience and {2. engineering,tsinghua university,beijing 100084,China 1. state key {2. of Hydroscience and {2. engineering Tsinghua University Beijing 100084 China

In this paper,the deformation reinforcement theory(DRT) proposed by the authors is elaborated with a new definition of instability that an elasto-plastic structure is not stable if it cannot satisfy simultaneously equilibrium condition,kinematical admissibility and constitutive equations under the prescribed *** from the definition,a proof is established to the principle of minimum plastic complementary energy for failured *** is revealed that the principle of mini-mum plastic complementary energy results in relaxed constitutive equations,especially,yield *** is demonstrated with case studies that many key issues in arch dam design,e.g.,global stability,dam-toe reinforcement,dam-toe cracking,dam-abut-ment reinforcement,can be well solved within the framework of the deformation reinforcement *** structural global stability can be described by the curve of the plastic complementary energy vs overloading *** unbalanced-forces obtained by elasto-plastic FEM can be used as the basis of analysis of global stability,dam-heel cracking,dam-toe anchorage and reinforcement of faults of high arch dams and their foundations.

关键词： high arch dams global stability reinforcement unbalanced force plastic complementary energy

Sediment transport capacity of hyperconcentrated flow

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Science China(Physics,Mechanics & Astronomy) 2008年第8期51卷 961-975页

作者： SHU AnPing1,2.& FEI XiangJun2.1 School of Environment & key laboratory of Water and Sediment Sciences,Ministry of Education,{2. Normal {2.,{2. 100875,China 2.state key laboratory of Hydroscience and engineering,tsinghua university,beijing 100084,China School of Environment & key laboratory of Water and Sediment Sciences Ministry of Education Beijing Normal University Beijing 100875 China state key {2. of Hydroscience and {2. Tsinghua University Beijing 100084 China

As one of the most important components of river mechanics,sediment transport capacity of sediment-laden flows has attracted much attention from many researchers working on river mechanics and hydraulic engineering. Based on the time-averaged equation for a turbulent energy equilibrium in solid and liquid two-phase flow,an expression for the efficiency coefficient of suspended load movement was derived for the two-dimensional,steady,uniform,fully-developed turbulent flow. A new structural expression of sediment transport capacity was achieved. Using 115 runs of flume experimental data,which were obtained through two kinds of sediment transport experiments in the {2. of equilibrium,in combination with the basic rheological and sediment transporting characteristics of hyperconcentrated flow,the main parameters in the structural expression of sediment transport capacity were calibrated,and a new formula of sediment transport capacity for hyperconcentrated flow was developed. A large amount of field data from the Yellow River,Wuding River,and Yangtze River,etc. were adopted to verify the new formula and good agreement was obtained. These results above contribute to an improved theoretical system of river mechanics and a reliable tool for management of rivers carrying high concentration of sediments.

关键词： hyperconcentrated flow turbulent energy equilibrium efficiency coefficient sediment transport capacity

Multi-dimensional project management models for mega-construction companies and their applications

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Science China(Technological Sciences) 2011年第S1期54卷 118-124页

作者： LIN ZhengHang 1,2.QIANG MaoShan 1,2.TANG WenZhe 1,2.FAN QiXiang 3 &LIU Qiang 4 1 Institute of Project Management and Construction Technology,tsinghua university,beijing 100084,China {2.,tsinghua university,beijing 100084,China 3 China Three Gorges Corporation,Yichang 443002.China 4 School of Software,tsinghua university,beijing 100084,China 1. Institute of Project Management and Construction Technology Tsinghua University Beijing 100084 China2. State Key Laboratory of Hydraulic and Engineering Tsinghua University Beijing 100084 China3. China Three Gorges Corporation Yichang 443002 China4. School of Software Tsinghua University Beijing 100084 China

China is undertaking an increasing number of mega-infrastructure projects along with its rapid economic *** participants in these projects,understand how to adapt the proper and efficient management strategies is *** this paper,we propose three distinct models for companies under various background and management requirements,based on sophisticated data analysis and model ***,we successfully committed these models with hydropower development projects and achieved a great progress in enhancing management efficiency.

关键词： project management models mega-construction companies applications hydropower development companies

Analysis on ignition and extinction of n-heptane in homogeneous systems

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Science China(Technological Sciences) 2005年第5期48卷 556-569页

作者： LIU Yongfeng1 & PEI Pucheng2.1. Mechanical and Electrical engineering Department, beijing Institute of Civil engineering and Architec-ture, beijing 100044, China 2. state key laboratory of Automotive Safety and Energy, tsinghua university, beijing 100084, China 1. Mechanical and Electrical engineering Department Beijing Institute of Civil Engineering and Architecture 100044 Beijing China 2. state key {2. of Automotive Safety and Energy Tsinghua University 100084 Beijing China

To calculate ignition delay times, the governing equations about species and temperature, which are in a closed volume based on the theory of thermal explosion and in a continuously stirred flow reactor, are deducted. The method referred to steady state assumptions is based on the observation that due to very fast chemical processes in combustion problems many chemical species and reactions are in a quasi-steady state or partial equilibrium. When a species is assumed to be in the steady state, the corresponding differential equation can be replaced by an algebraic relation, which reduces the computational costs. The steady state solution of the reactor equations describes the three ignition temperature regimes and get “S-shaped curve”. The reduced simplified 4-step mechanism for n-heptane from 1011 elementary reactions leads with the steady state assumptions to linear differential equations, which is solved. The simulation results of the 4-step reduced mechanism for n-heptane are fitted well with the experiment data. At last, two important parameters are discussed thoroughly and the temperature perturbation is given. It reduces the computational efforts considerably without losing too much accuracy and further supplies numerical methods for turbulent combustion in the diesel engine.

关键词： ignition delay times, thermal runaway, steady state assumptions, continuously stirred flow reactor.

Preparation of MWNTs/Al_2._3 composites and their mechanical and electrical properties

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Science China(Technological Sciences) 2005年第6期48卷 622-631页

作者： FAN Jinpeng1,2. ZHAO Daqing1,2. XU Zening1,2.& WU Minsheng1,2.1. Department of Mechanical engineering, tsinghua university, {2., China 2. key laboratory for Advanced Manufacturing by Materials Processing Technology, tsinghua university, {2., China 1. Department of Mechanical engineering Tsinghua University 100084 Beijing China 2. key laboratory for Advanced Manufacturing by Materials Processing Technology Tsinghua University 100084 Beijing China

The mechanical and electrical properties of MWNTs/Al2.3 composite prepared fabricated by hot pressing are investigated. The relation between properties and microstructure of composites is also discussed. With 4wt% MWNTs as reinforcement, the fracture toughness of composite obtained reaches 5.55 MPa·m1/2. which is 80% higher than that of pure Al2.3 obtained in the same conditions. The main toughening mechanism is CNTs’ pinning alumina grain boundaries, and the pullout of CNTs takes effect also. Through adding 2.t% MWNTs and altering the mix method, the fracture toughness of the composite obtained is 3.97 MPa·m1/2. Furthermore, the electrical resistivity is as low as 8.4×10?3 ?·m, decreasing by 14 orders of magnitude compared with pure alumina ceramics. The function of CNTs in composite is related to the distribution state of CNTs in composite, and the distribution state of CNTs in matrix is dependent on preparation procedures.

关键词： MWNTs, alumina, composite, fracture toughness, electrical properties.

Sediment pollution and its effect on fish through food chain in the Yangtze River

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International Journal of Sediment Research 2008年第4期23卷 338-347页

Suspended sediment adsorbs pollutants from flowing water in rivers and deposits onto the bed. However, the pollutants accumulated in the river bed sediment may affect the bio-community through food chain for a long period of time. To study the problem the concentration of heavy metals (Cr, Cd, Hg, Cu, Fe, Zn, Pb and As) in water, sediment, and fish/invertebrate were investigated in the middle and lower reaches of the Yangtze River during 2.06-2.07. The concentrations of heavy metals were 100-10,000 times higher in the sediment than in the water. Benthic invertebrates had relatively high concentrations of heavy metals in their tissues due to their proximity to contaminated sediments. Benthic invertivore fish had moderately high concentrations of heavy metals whereas phytoplanktivore fish, such as the silver carp, accumulated the lowest concentration of heavy metals. The concentrations of Cu, Zn, and Fe were higher than Hg, Pb, Cd, Cr, and As in the tissue samples. The concentration of heavy metals was lower in the river sediments than in the lake sediments. Conversely, the concentration of heavy metals was higher in river water than in lake water. While a pollution event into a water body is often transitory, the effects of the pollutants may be long-lived due to their tendency to be absorbed in the sediments and then released into the food chain. The heavy metals were concentrated in the following order: bottom material > demersal fish and benthic fauna > middle-lower layer fish > upper-middle layer fish > water.

关键词： Sediment pollution Heavy metal Fish Invertebrate Yangtze River

Experimental study on three dimensional movements of particles Ⅱ Effects of particle diameter on turbulence characteristics

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International Journal of Sediment Research 2009年第2期24卷 169-176页

作者： Limo TANG1 and Xingkui WANG2.1state key {2. of Hydrology-Water Resources and {2. engineering,Hohai university, Nanjing 2.0098,China 2.Prof.,state key {2. of Hydroscience and engineering,tsinghua university,beijing 100084,China state key {2. of Hydrology-Water Resources and {2. engineering Hohai University Nanjing 210098 China state key {2. of Hydroscience and {2. Tsinghua University Beijing 100084 China

Based on the 3D PTV(Particle Tracking Velocimetry) measuring system,the 3D movement characteristics of particles with four different diameters were investigated. Under specific flow conditions,the impact of particle diameters on 3D motion of particles was studied,and the turbulence characteristics were analyzed by different statistical methods. The results showed that the turbulence intensity of coarse particle decreased as the diameter increased. In near wall region,the probability density distributions of longitudinal and vertical fluctuation velocities both deviated from the normal distribution;while in the outer region,the probability density distribution of vertical fluctuation velocity approximately agreed with the normal distribution.

关键词： Particle diameter Turbulence Probability density distribution

Microstructures and characteristics of deep trap levels in ZnO varistors doped with Y_2._3

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Science China(Technological Sciences) 2009年第12期52卷 3668-3673页

作者： LIU Jun 1 ,HU Jun 1 ,HE JinLiang 1 ,LIN YuanHua 2.&LONG WangCheng 1 1state key {2. of Power Systems,Department of Electrical {2.,tsinghua university,beijing 100084,China 2.0} key {2. of New Ceramics and Fine Processing,Department of Material Science and {2.,tsinghua university, beijing 100084,China 1. state key {2. of Power Systems Department of Electrical Engineering Tsinghua University Beijing 100084 China 2. state key {2. of New Ceramics and Fine Processing Department of Material Science and Engineering Tsinghua University Beijing 100084 China

In this paper discussions on ZnO based varistor ceramics doped with different ratios of Y2.3 are *** on the phase and microstructures of the samples indicates that an additional phase is detected in the samples doped with Y2.3,and the average grain size of the specimens decreases from about 9.2.m to 4.5μm,with an increase in the addition of Y2.3 from 0 mol%to 3 mol%.The corresponding varistor’s voltage gradient markedly increases from 462.V/mm to 2.40 V/mm,while the nonlinear coefficient decreases from 2..3 to 11.5,***,the characteristics of deep trap levels in these ZnO samples are investigated by measuring their dielectric *** trap energy level and capture cross section evaluated by relaxation peak of the Cole-Cole plot vary slightly as the addition of Y2.3 *** traps may be ascribed to the intrinsic defects of ZnO lattice.

关键词： ZnO varistors Y2.3 electrical properties deep trap levels

Effect of streambed sediment on benthic ecology

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International Journal of Sediment Research 2009年第3期24卷 325-338页

作者： Xuehua DUAN1, Zhao-Yin WANG2. Mengzhen XU3, and Kang ZHANG41 Ph.D., Jiangyin Environmental Monitoring Station, Jiangyin 2.4431, China, Dept. of hydraulic engineering, {2.,2.Prof., state key laboratory of Hydroscience and engineering, {2., beijing 100084, China, 3 Doctoral candidate, state key laboratory of Hydroscience and engineering, {2., beijing 100084, China,4 Doctoral candidate, state key laboratory of Hydroscience and engineering, {2., beijing 100084, China [a] Ph.D. Jiangyin Environmental Monitoring Station Jiangyin 2.4431 China Dept. of hydraulic engineering tsinghua university [b] Prof. state key {2. of Hydroscience and {2. tsinghua university beijing 100084 China Tel: 86-10-62.73448(O) [c] Doctoral candidate state key {2. of Hydroscience and {2. tsinghua university beijing 100084 China [d] Doctoral candidate state key {2. of Hydroscience and {2. tsinghua university beijing 100084 China

Benthic macroinvertebrates have been commonly used as indicator species for assessment of aquatic ecology. Streambed sediment, or substrate, plays an important role in habitat conditions for macroinvertebrate communities. Field investigations were done to study the benthic diversity and macroinvertebrate compositions in various stream substrata. Sampling sites with different bed sediment, latitude, and climate were selected along the Yangtze River, the Yellow River, the East River, and the Juma River, in China. The results show that benthic community structures found in different substrata clearly differ, while those found in substrata of similar composition and flow conditions but in different macroclimates are similar. The study, thus, demonstrates that the benthic macroinvertebrate community is mainly affected by substrate composition and flow conditions, but is generally unaffected by latitudinal position and macroclimate. Taxa richness of the macroinvertebrate community was found to be the highest on hydrophyte-covered cobbles, high on moss-covered bedrock, and low on clay beds and cobble beds devoid of plant biomass. Sandy beds are compact and unstable, thus, no benthic macroinvertebrates were found colonizing such substrata. Aquatic insects account for most of the macroinvertebrates collected in these rivers. Different insects dominate in different types of substrata: mainly EPT species (Ephemeroptera, Plecoptera, Trichoptera) in cobble, gravel, and moss-covered bedrock; and Chironomidae larvae in clay beds. The relation between the number of species in the samples and the size of the sampling area fits a power function of the species area. One square meter (1m2. is suggested as the minimum sampling area. A substrate suitability index is proposed by integrating the suitability of sediment, periphyton, and benthic organic materials for macroinvertebrates. The biodiversity of macroinvertebrates increases linearly with the substrate suitability index. Benthic ta

关键词： Streambed sediment Macroinvertebrates Benthic ecology Substrate suitability Biodiversity