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THE GLOBAL ARTIFICIAL BOUNDARY CONDITIONS FOR NUMERICAL SIMULATIONS OF THE 3D FLOW AROUND A SUBMERGED BODY

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Journal of Computational Mathematics 2003年第4期21卷 435-450页

作者： Hou-de Han Xin Wen (Department of Mathematical Sciences, tsinghua university, beijing 100084, china) Department of Mathematical Sciences Tsinghua University Beijing 100084 China

We consider the numerical approximations of the three-dimensional steady potential flow around a body moving in a liquid of finite constant depth at constant speed and distance below a free surface in a channel. One vertical side is introduced as the upstream artificial boundary and two vertical sides are introduced as the downstream artificial boundaries. On the artificial boundaries, a sequence of high-order global artificial boundary conditions are given. Then the original problem is reduced to a problem defined on a finite computational domain, which is equivalent to a variational problem. After solving the variational problem by the finite element method, we obtain the numerical approximation of the original problem. The numerical examples show that the artificial boundary conditions given in this paper are very effective.

关键词： Ship wave Potential flow Global artificial boundary condition Finite element method.

EXACT NONREFLECTING BOUNDARY CONDITIONS FOR AN ACOUSTIC PROBLEM IN THREE DIMENSIONS

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Journal of Computational Mathematics 2003年第1期21卷 15-24页

作者： Houde Han Chunxiong Zheng (Department of Mathematical Sciences, tsinghua university, beijing 100084, china) Department of Mathematical Sciences Tsinghua University 北京 100084

In this paper, nonreflecting artificial boundary conditions are considered for an acoustic problem in three dimensions. With the technique of Fourier decomposition under the orthogonal basis of spherical harmonics, three kinds of equivalent exact artificial boundary conditions are obtained on a spherical artificial boundary. A numerical test is presented to show the performance of the method.

关键词： Exterior problem Nonreflecting artificial boundary condition Acoustic equa-tion Three-dimensions.

Effect of Coarse Aggregate Size on Relationship between Stress and Crack Opening in Normal and High Strength Concretes

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Journal of Materials Science & Technology 2005年第5期21卷 85-94页

作者： Jun ZHANG Qian LIU and Lin WANGDepaxtment of Civil Engineering, tsinghua university, beijing 100084, china Department of Civil Engineering Tsinghua University Beijing 100084 China

Fine and coarse aggregates play an important role in the fracture of concrete. However, quantitative informationavailable on the effect of the coarse aggregate size on the fracture properties of concrete is still limited. In the presentpaper, the effect of coarse aggregate size (single grade of 5~10, 10~16, 16~20 and 20~25 mm) on stress-crackopening (σ-ω) relation in normal and high strength concretes (compressive strength of 40 and 80 MPa, respectively)was studied. The investigation was based on three-point bending tests implemented by fictitious crack analysis. Theresult shows that coarse aggregate size and cement matrix strength significantly influence the shape of σ-ω *** a given total aggregate content, in normal strength concrete, smaller size of aggregate leads to a high tensilestrength and a sharp stress drop after the peak stress. The smaller the coarse aggregate, the steeper the σ-ω *** contrast, in high strength concrete, the effect of aggregate size on σ-ω relation almost vanishes. A similar σ-ωrelation is obtained for the concrete except for the case of 20~25 mm coarse aggregate size. The stress drop afterthe peak stress is more significant for high strength concrete than that for normal strength concrete. Meanwhile, thesmaller the coarse aggregate size, the higher the flexural strength. Fracture energy and characteristic length increasewith increasing coarse aggregate size in both normal and high strength concretes.

关键词： Aggregate size Stress-crack opening relation Fracture energy Bending test

Coacervate Structures of CdI_2 Thin Film Grown during Phase Transformation

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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

Maximal regularity of second order delay equations in Banach spaces

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Science china Mathematics 2010年第1期53卷 51-62页

作者： BU ShangQuan ? & FANG Yi Department of Mathematical Sciences, tsinghua university, beijing 100084, china Department of Mathematical Sciences, tsinghua university, beijing 100084, china Department of Mathematical Sciences Tsinghua University

We give necessary and sufficient conditions of Lp-maximal regularity(resp.B sp ,q-maximal regularity or F sp ,q-maximal regularity) for the second order delay equations:u″(t)=Au(t) + Gu't + F u t + f(t), t ∈ [0, 2π] with periodic boundary conditions u(0)=u(2π), u′(0)=u′(2π), where A is a closed operator in a Banach space X,F and G are delay operators on Lp([-2π, 0];X)(*** ,q([2π, 0];X) or Fsp,q([-2π, 0;X])).

关键词： maximal regularity second order delay equations Lebesgue-Bochner spaces Besov spaces Triebel-Lizorkin spaces

Dark output characteristic of γ-ray irradiated CMOS digital image sensors

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Rare Metals 2002年第1期21卷 79-84页

作者： MENG Xiangti and KANG A iguo Institute of Nuclear Energy Technology, tsinghua university, beijing 100084, china Institute of Nuclear Energy Technology Tsinghua University 北京 100084

The quality of dark output images from the CMOS (complementarymetal oxide semiconductor) black and white (B & W) digital imagesensors captured before and after γ-ray irradiation was studied. Thecharacteristic parameters of the dark output images captured atdifferent radiation dose, e.g. average brightness and itsnon-uniformity of dark out- put images, were analyzed by our testsoftware. The primary explanation for the change of the parameterswith the radi- ation dose was given.

关键词： CMOS digital image sensor gamma radiation dark output characteristic Si

TOUGHNESS INCREMENT BY CRACK GROWTH IN TOUGHENED STRUCTURAL MATERIALS

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Acta Mechanica Sinica 1991年第2期7卷 131-139页

作者： Yang Wei (tsinghua university,beijing 100084,china) tsinghua university Beijing China

Material toughening could be furnished by the energy dissipating wakes and bridging segments during crack *** to their contributions to the energy integral applicable to a growing crack,the toughening mechanisms are categorized as: dilatational plasticity and induced shear yielding in the crack wakes,bridging due to second inclusion phases,and the matrix bridging caused by wavy crack *** toughening analysis is pursued for structural polymers and composite materials reinforced by short aligned fibers.

关键词： material toughening crack growth bridging dilatational plasticity

REDUCTIONS OF ADJOINT REPRESENTATIONS TO LAX REPRESENTATIONS FOR CONSTRAINED FLOWS

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Chinese Annals of Mathematics,Series B 1996年第2期17卷 187-198页

作者： ZENG YUNBO Department of Applied Mathematics, tsinghua university, beijing 100084, china. 清华大学应用数学系北京

Within framework of zero-curvature representation theory, the Lax representations for x- andtn-constrained flows of soliton hierarchy are obtained from reductions of adjoint representationsof the auxiliary linear problems. This method is applied to the third order spectral problem bytaking modified Boussinesq hierarchy as an illustrative example.

关键词： Constrained flow Lax representation Adjoint representation Soliton hierarchy

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 State Key Laboratory of Hydraulic and Engineering,tsinghua university,beijing 100084,china 3 china Three Gorges Corporation,Yichang 443002,china 4 School of Software,tsinghua university,beijing 100084,china Institute of Project Management and Construction Technology Tsinghua University State Key Laboratory of Hydraulic and Engineering Tsinghua University

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