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Direct numerical simulation of a supersonic turbulent boundary layer on a flat plate and its analysis

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Science China(Physics,Mechanics & Astronomy) 2005年第5期48卷 626-640页

作者： HUANG Zhangfeng1. ZHOU Heng1.2 & LUO Jisheng1.2 1. Department of Mechanics, Tianjin university, Tianjin 300072, China 2. Liu-Hui Center of Applied Mathematics, Nankai university and Tianjin university, Tianjin 300072, China Department of Mechanics Tianjin University Tianjin China Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University Tianjin China

Temporal mode direct numerical simulation (DNS) has been done for a supersonic turbulent boundary layer on a flat plate with Mach number 4.5. It was found that the mean flow profile, the normal-wise distribution of turbulent Mach number and the root mean square (RMS) of the fluctuations of various variables, as well as the Reynolds stresses, bore similarity in nature, when the turbulence reached a fully developed state. But the compressibility effect was strong and must be considered. The strong Reynolds analogy (SRA) and the Morkovin hypothesis were no longer valid. From the end of transition to the fully developed state of turbulence, it was in the transient period, for which the similarity did not hold.

关键词： turbulence, similarity, compressibility effect, supersonic boundary layer, direct numerical simulation.

Ord.R RESULTS FOR ALGEBRAICALLY STABLEMONO-IMPLICIT RUNGE-KUTTA METHODS

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Journal of Computational Mathematics 1999年第6期17卷 639-644页

作者： Ai-guo Xiao(1. Department of Mathematics, Xiangtan university, Xiangtan 41.1.5, China2. ICMSEC, Chinese Academy of Sciences, Beijing 1.080, China) 湘潭大学数学系湖南湘潭 411105

It is well known that mono-implicit Runge-Kutta methods have been applied in the efficient numerical solution of initial or boundary value problems of ord.nary differential equations. Burrage (1.94) has shown that the ord.r of an s-stage monoimplicit Runge-Kutta method is at most s+1.and the stage ord.r is at most 3. In this paper, it is shown that the ord.r of an s-stage mono-implicit Runge-Kutta method being algebraically stable is at most min((s) over tilde, 4), and the stage ord.r together with the optimal B-convergence ord.r is at most min(s, 2), where [GRAPHICS]

关键词： ord.nary differential equations mono-implicit Runge-Kutta methods ord.r algebraical stability

Pioneer organisms after F-F mass extinction in Dushan region,Guizhou Province,and their significance in establishing new ecosystem

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Science China Earth Sciences 2006年第5期49卷 449-460页

作者： WANG Yue1. 2, WANG Xunlian1.& SHI Xiaoying1.1. School of Earth Sciences and Resources, China university of Geosciences, Beijing 1.0083, China 2. School of Resources and Environment, Guizhou university, Guiyang 550003, China School of Earth Sciences and Resources China University of Geosciences Beijing China School of Resources and Environment Guizhou University Guiyang China

After mass extinctions, most areas became “ecologically barren areas” lacking or even without ecosystem over an extensive region. Studying the pioneer organisms and the reconstruction process of a new ecosystem in the “ecologically barren area” is very important for revealing the evo- lution after bio-mass extinctions. In the Dushan region, Guizhou Province, China, the trace fossils appeared and flourished evidently earlier than body fossils after Frasnian-Famennian (F-F) mass extinction. The pioneer organisms and pathfinders in the “ecologically barren areas” are the trace-makers that are deposit-feeders with relatively simple structure and conformation on or near the deposit surface. The trace-makers have undergone an evolutionary process that their trace structures changed from simple to complex, and their living and moving areas and spaces enlarged from linear to planar and then to three-dimension spaces. Those characters show that the ability of the trace-makers to deposits and their efficiency of looking for food have been enhanced gradually and that those trace-makers constructed gradually a base for the new ecosystem. This process is similar to that of the trace fossils near the Precambrian-Cambrian boundary. In the Dushan area, only the recovery intervals have been identified for the Famennian body fossils, with no eminent radiation interval recognizable due to the Devonian-Carboniferous (C-D) mass ex- tinction. However, both the recovery and radiation intervals may be clearly recognized in the Famen- nian trace fossils based on their conformation and diversity. The evolution and diversification of the trace fossils in the “ecologically barren area” is considered to have played a role of necessary foun- dation for the recovery of body fossils in the ecological chain. With the gradual disappearance of the unfavourable environment factors resulting in the F-F mass extinction, a new ecosystem was reconstructed in the “ecologically barren area” through a three-

关键词： pioneer organisms, reconstruction of ecosystem, trace fossils, F-F mass extinction, Later Devonian, Dushan region, Guizhou Province, China.

Research on nonlinear constitutive relationship of permanent deformation in asphalt pavements

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Science China(Physics,Mechanics & Astronomy) 2006年第6期49卷 671-682页

作者： PENG Miaojuan1.& XU Zhihong2 1. Department of Civil Engineering,Shanghai university,Shanghai 200072,China 2. School of Transportation Engineering,Tongji university,Shanghai 200092,China Department of Civil Engineering Shanghai University Shanghai China School of Transportation Engineering Tongji University Shanghai China

To predict correctly the rut depths in asphalt pavements,a new nonlinear viscoelastic-elastoplastic constitutive model of permanent deformation in asphalt pave-ments is presented. The model combines a generalized Maxwell model with an elasto-plastic one. Then from the creep theory,the linear and nonlinear constitutive equations of the generalized Maxwell model are obtained. From the nonlinear finite element method for the rutting of the asphalt pavement,the rut depths of 4 asphalt-aggregate mixtures are obtained. And the results are compared with the ones from the finite element method by SHRP and the experiments by SWK/UN. The results in this paper are better than the ones by SHRP,and agree with the ones of the experiment by SWK/UN. This shows that the nonlinear viscoelastic-elastoplastic constitutive model,which is presented in this paper for the rutting of the asphalt pavement,is effective. The properties,such as nonlinear elastic-ity,plasticity,viscoelasticity and nonlinear viscoelasticity,which affect the rutting of an asphalt pavement,can be shown in the model. And the characteristics of the permanent deformation of the asphalt pavement can be presented entirely in the model.

关键词： asphalt pavement,permanent deformation,nonlinear viscoelastic-elastoplastic constitutive relationship,generalized Maxwell model,creep compliance.

Pole assignment in descriptor periodic systems

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Science China Mathematics 2005年第10期48卷 1309-1332页

作者： FAN Hung-Yuan~1.LIN Wen-Wei~1.& XU Shufang~2 1. Department of Mathematics,Tsing Hua university,Hsinchu 30043,China 2. LMAM,School of Mathematical Sciences,Peking university,Beijing 1.0871.China Department of Mathematics Tsing Hua University Hsinchu China LMAM School of Mathematical Sciences Peking University Beijing China

In this paper a pole assignment problem is considered for the descriptor linear discrete-time periodic systems, which is using the periodic proportional-derivative feedback to modify a given system such that the closed loop system has a specified selfconjugate set of eigenvalues. It is shown that the complete reachability of an open loop periodic system is equivalent to the possibility of assigning an arbitrary set of the eigenvalues to the system by choosing the suitable periodic proportional-derivative feedback.A computational approach is also proposed to solve the problem, which uses the reliable numerical techniques based on the orthogonal transformations. Numerical examples are presented to illustrate the effectiveness of the proposed approach.

关键词： descriptor linear periodic system, pole assignment, proportional and derivative feedback, numerical method, periodic Schur decomposition.

Fracture analysis of a functionally graded interfacial zone between two dissimilar homogeneous materials

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Science China(Physics,Mechanics & Astronomy) 2006年第5期49卷 540-552页

作者： CHENG Zhanqi1.2 & ZHONG Zheng1.1. School of Aerospace Engineering and Applied mechanics, Tongji university, Shanghai 200092, China 2. College of Civil Engineering, Zhengzhou university, Zhengzhou 450002, China School of Aerospace Engineering and Applied mechanics Tongji University Shanghai China College of Civil Engineering Zhengzhou University Zhengzhou China

In this paper the plane elasticity problem for a functionally graded interfacial zone containing a crack between two dissimilar homogeneous materials has been considered. It is assumed that in the interfacial zone the reciprocal of the shear modulus is a linear function of the coord.nate, while Possion’s ratio keeps constant. By utilizing the Fourier transformation technique and the transfer matrix method, the mixed boundary problem is reduced to a system of singular integral equations that are solved numerically. The influences of the geometric parameters and the graded parameter on the stress intensity factors are investigated. The numerical results show that the graded parameters, the thickness of interfacial zone, the crack size and location have significant effects on the stress intensity factors.

关键词： functionally graded material interfacial zone fracture stress intensity factor

Numerical research on the 3D fiber orientation distribution in arbitrary planar flows

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Progress in Natural Science:Materials International 2007年第11期17卷 1357-1362页

作者： Zhou Kun1.and Lin Jianzhong1.2(1. State Key Laboratory of Fluid Power Transmission and Control, Zhejiang university, Hangzhou 31.027, China 2. China Jiliang university, Hangzhou 31.01., China) 1. State Key Laboratory of Fluid Power Transmission and Control Zhejiang University Hangzhou 310027 China

The fiber orientation distribution in a fiber suspension flow was investigated by a finite difference scheme in spherical coord.nates. The diffusivity was transformed between Cartesian and spherical coord.nates through tensor analysis to obtain efficiency. It is found that under simple shear flow condition the diffusivity in the azimuthal direction, Dr, has greater effect on the orientation distribution than that in the colatitude direction, Drθθ.

关键词： fiber suspension flow orientation distribution diffusivity

Electro-mechanical response of functionally graded beams with imperfectly integrated surface piezoelectric layers

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Science China(Physics,Mechanics & Astronomy) 2006年第5期49卷 513-525页

作者： YAN Wei1.& CHEN Weiqiu1.2 1. Department of Civil Engineering, Zhejiang university, Hangzhou 31.027, China 2. State Key Lab of CAD & CG, Zhejiang university, Hangzhou 31.027, China Department of Civil Engineering Zhejiang University Hangzhou China State Key Lab of CAD & CG Zhejiang University Hangzhou China

The time-dependent behavior of a simply-supported functionally graded beam bonded with piezoelectric sensors and actuators is studied using the state-space method. The creep behavior of bonding adhesives between piezoelectric layers and beam is characterized by a Kelvin-Voigt viscoelastic model, which is practical in a high temperature circumstance. Both the host elastic functionally graded beam and the piezoelectric layers are orthotropic and in a state of plane stress, with the former being inhomogeneous along the thickness direction. A laminate model is employed to approximate the host beam. Moreover, the coupling effect between the elastic deformation and electric field in piezoelectric layers is considered. Results indicate that the viscoelastic property of interfacial adhesives has a significant effect on the function of bonded actuators and sensors with time elapsing.

关键词： functionally graded beam piezoelectric layers Kelvin-Voigt model state-space method

Ability of Agrogyron elongatum to accumulate the single metal of cadmium, copper, nickel and lead and root exudation of organic acids

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Journal of Environmental Sciences 2001年第3期13卷 368-375页

作者： YANG Hong 1. Jongathan W.C.Wong 2, YANG Zhi min\+1. ZHOU Li xiang 1.1. College of Science, Nanjing Agricultural university, Nanjing\ 21.095, China. 2. Department of Biology, Hong Kong Baptist university, China) College of Science Nanjing Agricultural University Nanjing 210095 China

Agrogyron elongatum were grown in nutrient solution containing moderate to high amounts of separate heavy metal of Cd, Cu, Ni and Ph in a greenhouse for a 9 - day. Cd, Cu, Ni and Ph generally led to decrease in the elongation of roots although the length of seedlings exposed to Cd and Ph at 0.05 and 0.5 mg/L showed to be slightly greater than that of controls. Of the four metals in the experiment, Ph was absorbed and accumulated to the highest level, with the concentrations of 92754 mg/kg dry weight (DW) in roots and 1.683 mg/kg DW in shoots. Cd was moderately accumulated in Agrogyron elongatum, but the maximum bioaccumulation coefficients (BCs) for roots and shoots were observed. The patterns for Cu and Ni uptake and distribution in plants differed from those of Ph and Cd, as it was showed that the shoot accumulation of Cu and Ni was significantly higher than in roots. A. elongation had the highest Ni concentration in shoots (30261.mg/kg DW) at the external concentration of 250 mg/L. Cu ranked second, with a shoot concentration of 1.230 mg/kg DW when 50 mg/L Cu in solution was applied. For the four trace elements tested, the highest concentrations in shoots decreased by the ord.r of Ni > Cu > Ph > Cd (mg/kg DW), and those in roots were Ph > Cd > Ni > Cu (mg/kg DW). Malic, oxalic and citric acids exuded by roots exposed to 1.and 50 mg/L of the metals were detected. Release of organic acids from plants significantly differed among the metal treatments. Cu was most effectively in inducing root exudation of the three types of organic acids. Cd, and Ni were also the inducers of secretion of malic and oxalic acids. With reference of Pb, a small amounts of malic and oxalic acids were detected in the root exudates, but few quantities, of citric acid were. found. However, no correlation between alternations in root exudation of organic acids and metal accumulation could be established.

关键词： heavy metal organic acid Agrogyron elongation hyperaccumulation