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Study on near-wall turbulence structures with local Reynolds stress

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Communications in Nonlinear Science and Numerical Simulation 2000年第3期5卷 105-117页

作者： Li LI Chunxiao XU Guixiang CUI and Zhaoshun ZHANG(department of engineering Mechanics,{2., beijing 100084, china) department of engineering Mechanics Tsinghua University Beijing 100084 China

The direct- numerical- simulated ch annel turbulence is analyzed with two-dimensional wavelet transform. Considering the relation between turbulence coherent structure and Reynolds stress in near wall region, the local Reynolds stress (LRS) is defined.A new method for extracting coherent signals from turbulence based on the LRS is developed. Velocity fiuctuations are decomposed to coherent signals and background signals. It is found that the scaling exponents of coherent signals have a considerable deviation from the Kolmogorov scaling law q/3 (K41 theory), while that of background signals is very close to q/3. It is confirmed that coherent signals are mainly responsible for the anomalous *** characterized by the positive peaks of LRS, the typical structures in near wall region are obtained by conditional statistical averaging. It is shown that the local character of near-wall turbulence structures can be effectively described with LRS.

关键词： wavelet channel turbulence the local Reynolds stress

Study on Bonding of Steel-mushy Al-7graphite

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Journal of university of Science and Technology beijing 2001年第4期8卷 283-285页

作者： Peng Zhang, Yunhui Du, Daben Zeng department of Mechanical engineering{2.. beijing 100084, china Tsing Hua Univ Dept Mech Engn Beijing 100084 Peoples R China

The bonding of steel-mushy Al-7graphite was studied. The relationship between interfacial shear strength of bonding plate and solid fraction of Al-7graphite mushy was obtained, and the interfacial structure of bonding plate was determined. The results showed that: under the condition of 500 degreesC for preheat temperature of steel plate and 10 mm/s for rolling speed, the largest interfacial shear strength of bonding plate was 70.1 MPa when solid fraction of Al-7graphite mushy was 34.6%.

关键词： interfacial shear strength solid fraction interfacial structure

THE APPROXIMATIONS OF THE EXACT BOUNDARY CONDITION AT AN ARTIFICIAL BOUNDARY FOR LINEARIZED INCOMPRESSIBLE VISCOUS FLOWS

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Journal of Computational Mathematics 1998年第3期16卷 239-256页

作者： Wei-zhu Bao (department of Applied Mathematics, tsinghua university,{2., P.R. china) 清华大学应用数学系北京

We consider the linearized incompressible Navier-Stokes (Oseen) equations in a flat channel. A sequence of approximations to the exact boundary condition at an artificial boundary is derived. Then the original problem is reduced to a boundary value problem in a bounded domain, which is well-posed. A finite element approximation on the bounded domain is given, furthermore the error estimate of the finite element approximation is obtained. Numerical example shows that our artificial boundary conditions are very effective.

关键词： Oseen equations artificial boundary artificial boundary condition finite element approximation error estimate

REGULARIZATION OF SINGULAR SYSTEMS BY OUTPUTFEEDBACK

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Journal of Computational Mathematics 2000年第1期18卷 43-60页

作者： De-lin Chu Da-yong Cai(department of Mathematical Sciences, tsinghua university,{2., china) 清华大学北京 100084

Presents a study which examined problem of regularization of a singular linear time-invariant system by derivative and proportional output feedback. Reduced form for the system that can be computed using orthogonal tr... 详细信息

关键词： regularization singular systems output feedback

AR quivers,exceptional sequences and algorithms in derived Hall algebras

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Science china Mathematics 2010年第6期53卷 1609-1624页

作者： SHENG Jie department of Mathematical Sciences,tsinghua {2.,beijing 100084,china 1. department of Mathematical Sciences Tsinghua University Beijing 100084 China

Consider the canonical isomorphism between the positive part U+ of the quantum group Uq(g) and the Hall algebra H(Λ),where the semisimple Lie algebra g and the finite-dimensional hereditary algebra Λ share a Dynkin *** and Xiao have given two algorithms to decompose the root vectors into linear combinations of monomials of Chevalley generators of U+,respectively induced by the braid group action on the exceptional sequences of Λ-modules and the structure of the Auslander-Reiten quiver of Λ.In this paper,we obtain the corresponding algorithms for the derived Hall algebra DH(Λ),which was introduced by *** show that both algorithms are applicable to the lattice algebra and Heisenberg double in the sense of *** the new recursive formulae have the same flavor with the quantum Serre relations.

关键词： derived Hall algebra exceptional sequence AR quiver

A SOLUTION PROCEDURE FOR LOWER BOUND LIMIT AND SHAKEDOWN ANALYSIS BY SGBEM

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Acta Mechanica Solida Sinica 2001年第2期14卷 118-129页

作者： Zhang Xiaofeng Liu Yinghua Cen Zhangzhi (department of engineering Mechanics,{2. university,beijing 100084,china) ***

The symmetric Galerkin boundary element method (SGBEM) instead ofthe finite element method is used t perform lower bound limit andshakedown analysis of structures. The self-equilibrium stress fieldsare constructed by a linear combination of several basicself-equilibrium stress fields with parameters to be *** basic self-equilibrium stress fields are expressed as elasticresponses of the body to im- posed permanent strains and obtainedthrough elastic-plastic incremental analysis.

关键词： limit and shakedown analysis SGBEM self-equilibrium stress

ELASTO-PLASTICITY ANALYSIS BASED ON COLLOCATION WITH THE MOVING LEAST SQUARE METHOD

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Acta Mechanica Solida Sinica 2003年第2期16卷 162-170页

作者： Song Kangzu Zhang Xiong Lu Mingwan (department of engineering Mechanics,{2. university,beijing 100084,china) departmentofengineeringMechanics TsinghuaUniversityBeijing100084China

A meshless approach based on the moving least square method is developed for elasto-plasticity analysis,in which the incremental formulation is *** this approach,the dis- placement shape functions are constructed by using the moving least square approximation,and the discrete governing equations for elasto-plastic material are constructed with the direct collo- cation *** boundary conditions are also imposed by *** method established is a truly meshless one,as it does not need any mesh,either for the purpose of interpolation of the solution variables,or for the purpose of construction of the discrete *** is simply formu- lated and very efficient,and no post-processing procedure is required to compute the derivatives of the unknown variables,since the solution from this method based on the moving least square approximation is already smooth *** examples are given to verify the accuracy of the meshless method proposed for elasto-plasticity analysis.

关键词： meshless method elasto-plasticity collocation method moving least square incremental formulation

Study on the hardening mechanism of cement asphalt binder

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Science china(Technological Sciences) 2010年第5期53卷 1406-1412页

作者： YANG JinBo,YAN PeiYu,KONG XiangMing & LI Xiang Key Laboratory of Structural engineering and Vibration of Education Ministry of china,{2. of civil engineering,tsinghua university,beijing 100084,china 1. Key Laboratory of Structural engineering and Vibration of Education Ministry of china Department of Civil Engineering Tsinghua University Beijing 100084 China

The hydration and hardening mechanism of cement asphalt binder(CAB) was *** early hydration process,hydration products and paste microstructure of CAB made by Portland cement and anionic asphalt emulsion were investigated by calorimetry,X-ray diffraction,and environmental scanning electron *** early hydration process of CAB can be characterized as 5 stages similar to those of Portland *** is no chemical reaction detected between cement and asphalt,hence no new hydration products other than those of Portland cement are *** hardening of CAB begins with the hydration of *** the hydration of cement comes into the acceleration period and its exothermic rate comes to the maximum,the coalescence of asphalt particles in asphalt emulsion is *** the hardened system of CAB,it was found that the hydration products of cement form the skeleton and are covered by the continuous asphalt *** formed an interpenetrating network *** emulsifiers in the asphalt emulsion may retard the hydration process of cement.

关键词： cement asphalt binder asphalt emulsion Portland cement hydration coalescence

Compressive Strength Development and Microstructure of Cement-asphalt Mortar

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Journal of Wuhan university of Technology(Materials Science) 2011年第5期26卷 998-1003页

作者：王强阎培渝 department of civil {2. Tsinghua University

The compressive strength developing process and the microstructure of cement-asphalt mortar （CA mortar） were *** fluidity of CA mortar has a great influence on its *** optimum value of spread diameter of slump flow test is in the range of 300 to 400 *** compressive strength of CA mortar keeps a relatively high growth rate in 56 days and grows slowly *** residual water of hydration in CA mortar freezes under minus environmental temperature which can lead to a significant reduction of the strength of CA *** A/C retards asphalt emulsion splitting and thus prolongs the setting process of CA *** hydration products of cement form the major structural framework of hardened CA mortar and asphalt is a weak phase in the framework but improves the viscoelastic behavior of CA ***,asphalt emulsion should be used as much as possible on the condition that essential performance criterions of CA mortar are satisfied.

关键词： asphalt emulsion compressive strength CA mortar microstructure