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Studies of the unsteady supersonic base flows around three afterbodies

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Acta Mechanica Sinica 2009年第4期25卷 471-479页

作者： Zhixiang Xiao Song Fu School of Aerospace Engineering,tsinghua university, 100084 beijing, china School of Aerospace Engineering Tsinghua University 100084 Beijing China

Unsteady supersonic base flows around three afterbodies, cylindrical （Cy）, boattailed （BT） and three-step （MS）, are investigated in this paper. Reynolds-averaged Navier-Stokes （RANS） and two RANS/LES （large-eddy simulation） hybrid methods, detached eddy simulation （DES） and delayed-DES （DDES）, are used to predict the base flow characteristics around the baseline Cy afterbody. All the RANS and hybrid methods are based on the two-equation SST （shear-stress transport） model with compressible corrections （CC）. According to the comparison of measurements, both DES and DDES can produce more satisfactory results than RANS. RANS can only present the ＂stable＂ flow pat- terns, while the hybrid methods can demonstrate unsteady flow structures. DDES and DES results are little different from one another although the latter exhibits better agreement with the experiment. DES is taken to investigate the 5° BT and three-step afterbodies. The mean flow data and the instantaneous turbulent coherent structures are compared against available measurements.

关键词： Cylindrical Boattailed and three-stepafterbodies DES and DDES Unsteady flow

EXTRACTION KINETICS,SYNERGISTIC EFFECTS AND INTERFACIAL chemistry FOR D_2 EHPA MPA-Fe^(3+) MIXED EXTRACTION SYSTEM

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Acta Metallurgica Sinica(English Letters) 1993年第12期6卷 405-410页

作者： YU Jingfen LIU Difei tsinghua university,beijing,china professor,Dept.of Chemical Engineering,tsinghua university,beijing 100084,china tsinghua Univ Beijing China

The thermodynamics of micella formation,interfacial characteristics,synergistic effects and interfacial kinetics for synergistic extraction system D_2 EHPA-MPA-Fe^(3+) have been *** was found that D_2EHPA in the mixed system strongly exhibits the effect on the micella formation thermodynamics and interracial characteristics of *** ther- modynamic parameters for constants of micelles formation(K_m).free energies of micelles formation(ΔG_m)and critical micella concentrations(CMC)were *** inter- facial adsorption behaviour of D_2EHPA is opposite to that of *** emulsification for single MPA and the mixed system was *** synergistic effects were found in this mixed extraction *** is proved that the process of the Fe^(3+) extraction for non-mixed extraction system is controlled by chemical reaction and the controlling reaction occurs at the interface.

关键词： interfacial chemistry synergistic effect Fe^(3+) extraction kinetics

Median cross-validation criterion

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Chinese Science Bulletin 1997年第23期42卷 1956-1959页

作者： YANG YingDepartment of Applied Mathematics, tsinghua university, beijing 100084, china Department of Applied Mathematics Tsinghua University Beijing China

CONSIDER the nonparametric median regression model Yni = g (xni) + εni, 1≤i≤n （1）where g: [0, 1]|→R is an unknown function of interest; {xni, 1≤i≤n} is the fixed design pointsin the interval [0, 1]; {εni, 1≤i≤n} is a triangular array of row iid random variables having medi-an zero, and {Yni, 1≤i≤n} is the observation. For each x∈[0, 1], n≥1, let Dnj（x） denotethe jth nearest neighber of x, j=1, 2,…, n, i. e. {Dn1（x）, Dn2（x）,…, Dnn（x）} is a trans-position of {xn1, xn2,…, xnn} satisfying |Dn1（x）-x|≤|Dn2（x）-x|≤…≤|Dnn（x）-x|.The tie is broken by the chronological order. The

关键词： median cross validation Bahadur’s representation asymptotic oplimality.

Moran sets and Moran classes

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Chinese Science Bulletin 2001年第22期46卷 1849-1856页

作者： WEN ZhiyingDepartment of Mathematics, tsinghua university, beijing 100084, china Department of Mathematics Tsinghua University Beijing China

The purpose of this survey is to present Moran sets and Moran classes which generalize the classical self-similar sets from the following points: (i) The placements of the basic sets at each step of the constructions can be arbitrary; (ii) the contraction ratios may be different at each step; and (iii) the lower limit of the contraction ratios permits zero. In this discussion we will present geometrical properties and results of dimensions of these sets and classes, and discuss conformal Moran sets and random Moran sets as well.

关键词： Moran set Moran classes dimension.

Self-Organizing Tunnel Peers

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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

DIMENSIONS OF SELF-AFFINE SETS WITH OVERLAPS

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Chinese Annals of Mathematics,Series B 2003年第3期24卷 275-284页

作者： HUA Su Department of Mathematics, tsinghua university, beijing 100084, china. Tsing Hua Univ Dept Math Beijing 100084 Peoples R China

The authora develop an algorithm to show that a class of self-affine sets with overlaps can be viewed as sofic affine-invariant sets without overlaps,thus by using the results of [11] and [10],the hausdorff and minkow... 详细信息

关键词： self-affine set overlap hausdorff dimension minkowski dimension

Development of SOM combustion model for Reynolds-averaged and large-eddy simulation of turbulent combustion and its validation by DNS

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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 100084 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

MULTISTEP DISCRETIZATION OF INDEX 3 DAES

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Journal of Computational Mathematics 2000年第3期18卷 325-336页

作者： Yang Cao Qing-yang Li (Department of Mathematics, tsinghua university, beijing 100084, china) 清华大学北京 100084

Studies the different types of multistep discretization of index 3 differential-algebraic equations in Hessenberg form. Existense, uniqueness and influence of perturbations; Local convergence of multistep discretizati... 详细信息

关键词： multistep methods Adams method BDF DAEs Index 3

Dimensions of a class of high-dimensional homogeneous Moran sets and Moran classes

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Progress in Natural Science:Materials International 2002年第9期12卷 17-22页

作者： YAN Ping(Department of Mathematical Sciences, tsinghua university, beijing 100084, china) Tsing Hua Univ Dept Math Sci Beijing 100084 Peoples R China

A class of high-dimensional homogeneous Moran sets and Moran classes are introduced and some dimensional properties are studied. The Hausdorff dimension, modified lower box-counting dimension, lower and upper box-counting dimension, and packing dimension of high-dimensional homogeneous and partial homogeneous Cantor sets are determined. Moreover, a kind of fractal E is obtained, which is not regular but with the property Dimw(Ed) = dDimw(E), where w denotes any of the dimensions mentioned above.

关键词： Moran set Moran class homogeneous Cantor set partial homogeneous Cantor set dimension.