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Science China(Physics,Mechanics & Astronomy) 2005年第5期48卷 614-625页

作者： HUANG Zhangfeng 1, CAO Wei 1,2 & ZHOU Heng 1,2 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 direction numerical simulation has been done for the transition of a supersonic boundary layer on a flat plate with Mach number 4.5. Analysis of the result showed that during the breakdown process in laminar-turbulent transition, the mechanism causing the mean flow profile to evolve swiftly from laminar to turbulent was that the modification of mean flow profile by the disturbances,when they became larger,led to a remarkable change of its stability characteristics. Though the most unstable T-S wave was of second mode for laminar flow, the first mode waves played the key role in the breakdown process in laminar-turbulent transition.

关键词： supersonic boundary layer, transition, breakdown.

Numerical exploration of new features on three-dimensional transition of a cylinder wake

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Science China Mathematics 2004年第z1期47卷 69-80页

作者： LING Guocan, XIONG Jun & ZHU KeqinState Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080, China Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing China Department of Engineering Mechanics Tsinghua University Beijing China

The three-dimensional transition of the wake flow behind a circular cylinder is studied in detail by direct numerical simulations using 3D incompressible N-S equations for Reynolds number ranging from 200 to 300. New features and vortex dynamics of the 3D transition of the wake are found and investigated. At Re = 200, the flow pattern is characterized by mode A instability. However, the spanwise characteristic length of the cylinder determines the transition features. Particularly for the specific spanwise characteristic length linear stable mode may dominate the wake in place of mode A and determine the spanwise phase difference of the primary vortices shedding. At Re = 250 and 300 it is found that the streamwise vortices evolve into a new type of mode "dual vortex pair mode" downstream. The streamwise vortex structures switch among mode A, mode B and dual vortex pair mode from near wake to downstream wake. At Re = 250, an independent low frequency fm in addition to the vortex shedding frequency fs is identified. Frequency coupling between fm and fs occurs. These result in the irregularity of the temporal signals and become a key feature in the transition of the wake. Based on the formation analysis of the streamwise vorticity in the vicinity of cylinder, it is suggested that mode A is caused by the emergence of the spanwise velocity due to three dimensionality of the incoming flow past the cylinder. Energy distribution on various wave numbers and the frequency variation in the wake are also described.

关键词： cylinder, wake, 3D transition, Fourier-spectral-spectral-element method, direct numerical simulation (DNS).

Mesozoic-Cenozoic tectonic transition in Kuqa Depression-Tianshan,Northwest China:Evidence from sandstone detrital and geochemical records

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Science China Earth Sciences 2005年第9期48卷 1387-1402页

作者： LI Zhong1, GUO Hong2, WANG Daoxuan3 & LIN Wei1 1. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 2. Tarim Oilfield Branch, CNPC, Korla 841000, China 3. Hefei University of Industry, Tunxilu 193, Hefei 230009, China Institute of Geology and Geophysics Chinese Academy of Sciences Beijing Chin Tarim Oilfield Branch CNPC Korla China Hefei University of Industry Hefei Chin

Similar to compositional evolution of sandstone modes and detrital heavy minerals from different profiles in the Kuqa Depression, Northwest China, major element analysis of whole sandstones from the same profiles shows four discontinuous depositional interfaces or periods, respectively corresponding to Lower Triassic\Middle Triassic, Upper Jurassic\Lower Cretaceous, Lower Cretaceous\Paleogene and Miocene\Pliocene, and indicates five-phase evolution during Mesozoic-Cenozoic: (1) From the first to fifth phase, a depositional suite changes from maroon and coarse clastic, through grey-dark grey and fine, red and coarse, red-mottled, interlayered by gypsum, to brown and coarse clastic assemblages, accompanying detrital component evolution in unstable-stable-unstable-very unstable-very unstable assem- blages. It is indicated that carbonate and complex detritus gradually dominate in sandstones in post-Late Jurassic, with rapid reduction of compositional maturity. (2) For major element geo- chemical parameters of whole sandstones, CaO and Fe2 O * 3+MgO contents show a change sequence in high-low-high-higher-highest values, with rapid increasing in post-Late Jurassic. (3) Contra some aggregative indicators for weathering indexes of sandstone detrital component, Al2O3/(CaO+Na2O) and ln(Q/(L+CE)), show a change sequence in low-high-low-lower-lowest ratios, with rapid decreasing in post-Late Jurassic. It is found that sandstone samples of the first, second and later three phases may be distinguished from the A-CN-K and A-CNK-FM diagrams respectively. Therefore, in the Kuqa Depression-Tianshan, the most important discontinuous depositional interface recording paleotectonic and paleoclimatic transition occurred in Early Triassic\Middle Triassic and Late Jurassic\Early Cretaceous, respectively, and, however, tec- tonic differentiations of basin-range system finally result in distinct depositional systems but similar detrital weathering indexes across the Lower Cretaceous\Paleogene

关键词： Tianshan, Kuqa Depression, basin-range, depositional record, tectonic transition, Mesozoic-Cenozoic.

Columnar to equiaxed transition during alloy solidification

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Science China(Technological Sciences) 2003年第5期46卷 475-489页

作者：林鑫李延民王猛冯莉萍陈静黄卫东 State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi'an 710072 China School of Materials Science and Engineering Shanghai Jiaotong University Shanghai 200030 China

Considering the local linear superposition of the species and combining the calculation of phase diagram, the columnar and equiaxed growth behaviours are investigated systematically during solidification of multicomponent alloys. A theoretical model is developed to describe the columnar to equiaxed transition during multicomponent alloy solidification by taking account of the competition between nucleation and growth ahead of a dendrite array, which shows a good agreement with the experimental results.

关键词： columnar-to-equiaxed transition, multicomponent alloy, solidification.

Phase transition in Pd_(40)Ni_(10)Cu_(30)P_(20) bulk metallic glass under HP & HT

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Science China(Physics,Mechanics & Astronomy) 2005年第6期48卷 716-722页

作者： Utsumi Wataru Okada Taku Synchrotron Radiation Research Center Japan Atomic Energy Research Institute 1-1-1 Kout Mikasuki Sayo Hyogo 679-5148 Japan

The phase transitions in Pd40Ni10Cu30P20 bulk metallic glass (BMG) have been studied under high pressure and high temperature (HP & HT) by X-ray diffraction measurements with synchrotron radiation source. We found that the BMG underwent a phase transitions of amorphous-crystalline-amorphous at 10 GPa upon heating. The parallel experiments were carried out at 7 GPa, while we did not observe the amorphous-crystalline-amorphous transitions by increasing temperature. Quenching the melted BMG at 7 GPa, it was found that the phase crystallized from the melt differed from the primary phase crystallized from the starting amorphous solid upon heating, suggesting there existed a distinct mechanism in two cases.

关键词： phase transition, Pd40Ni10Cu30P20, high pressure and high temperature.

Inherent mechanism of breakdown in laminar-turbulent transition of plane channel flows

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Science China(Physics,Mechanics & Astronomy) 2005年第2期48卷 228-236页

作者： LUO Jisheng, WANG Xinjun & ZHOU Heng Department of Mechanics, Tianjin University Liu-Hui Center of Mathematics, Nankai and Tianjin University, Tianjin 300071, China Department of Mechanics Tianjin University Tianjin China Liu-Hui Center of Mathematics Nankai and Tianjin University Tianjin China

Laminar-turbulent transition is an old yet unsolved problem. Notwithstanding the great effort made, there is an important question that seems not to have been addressed yet, that is, what is the inherent mechanism of breakdown that eventually leads to transition? The conventional idea is that the transition starts from the amplification of disturbances, and when the disturbances become larger, higher harmonics will be generated due to nonlinear effect, making the flow more and more complicated, and finally turbulent. Though the scenario seems clear, yet there is a missing link, that is, what happens in the breakdown process. Here we show by analyzing the results from direct numerical simulations that the change of stability characteristics of the mean flow profile plays a key role in the breakdown process.

关键词： laminar-turbulent transition, breakdown, plane channel flow.

Heterogeneous transition dynamic equations and the self-organized origin of the nesting rhythmic beddings in Panzhihua lithosomes

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Science China Earth Sciences 2005年第1期48卷 13-20页

作者： WU Jingping, LI Caiwei, BAO Zhengyu, YANG Wenhua, ZHOU Chenggang, SANG Zunan, LI Fanglin & QU Songsheng College of Chemistry and Molecular, Wuhan University, Wuhan 430071, China Faculty of Material Science and Chemical Engineering, China University of Geosciences, Wuhan 430074, China Information Department, Zhongshan University, Guangzhou 510000, China Faculty of Earth Science, China University of Geosciences, Wuhan 430074, China College of Chemistry and Molecular Wuhan University Wuhan 430071 China Faculty of Material Science and Chemical Engineering China University of Geosciences Wuhan 430074 China Information Department Zhongshan UniversityGuangzhou 510000China Faculty of Earth Science China University of GeosciencesWuhan 430074China Faculty of Material Science and Chemical Engineering China University of GeosciencesWuhan 430074China College of Chemistry and Molecular Wuhan UniversityWuhan 430071China

Dynamic equations were developed for heterogeneous phase-transition in a system of coupled nucleation, growth and ripening. Based on these equations, a self-organized origin of small-scale nesting rhythmic beddings in Pahzhihua lithosomes was investigated and the results showed that the beddings could be formed by the cross supersaturated nucleation-crystallization of augite and feldspar successively. This process could be implemented by coupling with supersaturated nucleation, Ostwald ripening, component diffusion and the primary grain diffusion under a proper temperature gradient. The slightly intensive supersaturated nucleation and Ostwald ripening occurring in Panzhihua lithosomes may relate closely to the mineral components such as V-Ti-Maanetite.

关键词： heterogeneous transition, nesting rhythmic bedding, self-organized, Panzhihua.

Micro-and submicrostructural evidence for high-temperature brittle-ductile transition deformation of hornblende: Case study of high-grade mylonites from Diancangshan, western Yunnan

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Science China Earth Sciences 2007年第10期50卷 1459-1470页

作者： CAO ShuYun, LIU JunLai? & HU Ling State Key Laboratory of Geological Processes and Mineral Resources (GPMR), China University of Geosciences, Beijing 100083, China Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education, China University of Geo- sciences, Beijing 100083, China State Key Laboratory of Geological Processes and Mineral Resources (GPMR) China University of Geosciences Beijing 100083 China Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education China University of Geosciences Beijing 100083 China

OM (optical microscope)/TEM (transmission electron microscope) micro- and submicrostructural analysis of hornblende rocks sheared at high temperatures from the Diancangshan area, western Yunnan reveals evidence for deformation in the brittle-ductile transition of hornblende at middle crustal level (about 637℃ and 0.653 GPa) and mechanisms of deformation in the transitional regime are further discussed. Sheared hornblende rocks at middle crustal level have typical mylonitic microstructures, shown by coarse porphyroclasts and fine matrix grains. Different mineral phases in the rocks show distinct deformation characteristics. Hornblende and feldspar grains are intensely deformed with ob- vious grainsize reduction, but quartz grains are recrystallized dominantly by grain growth. Hornblende grains show typical brittle-ductile transition nature. Initial crystallographic orientations of porphyro- clasts have strong effects on the behavior of grains during deformation. There are mainly two types of porphyroclasts, type I "hard" porphyroclasts and type II "soft" porphyroclasts, with [001] perpendicular and parallel to external shear stresses respectively. "Hard" porphyroclasts generally occur as compe- tent grains that are rarely deformed or sometimes deformed by fracturing and dislocation tangling. "Soft" porphyroclasts are highly deformed primarily by dislocation tangling (as shown in the cores of the porphyroclasts), but twinning, dislocation glide and climb probably due to hydrolytic weakening also contribute to dynamic recrystallization of the porphyroclasts into fine grains in the matrix. The micro- and submicrostructures of the two types of porphyroclasts and fine-grained matrix provide powerful evidence for the behavior of brittle-ductile transition of hornblende grains. It is concluded that twinning nucleation is one of the most important processes that operate during dynamic recrystalliza- tion of hornblende crystals at the brittle-ductile transition. (100) [001] t

关键词： hornblende, brittle-ductile transition, micro-and submicrostructures, twinning nucleation recrystallization, Diancangshan

Ab-initio molecular dynamics simulation on nano-system under external pressure

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Science China Mathematics 2004年第z1期47卷 92-100页

作者： Jl Min, SUN Deyan & GONG XingaoSurface Physics Laboratory and Department of Physics, Fudan University, Shanghai 200433, China Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China Interdisciplary Center for Theoretical studies, Chinese Academy of Sciences, Beijing 100080, China Surface Physics Laboratory and Department of Physics Fudan University Shanghai China Institute of Solid State Physics Chinese Academy of Sciences Hefei China Interdisciplary Center for Theoretical studies Chinese Academy of Sciences Beijing China

A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube (SWCNT) under external pressure is found, which is in agreement with the experiments.

关键词： phase transition, simulation, nano-particles

DNS of compressible turbulent boundary layer over a blunt wedge

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Science China(Physics,Mechanics & Astronomy) 2005年第2期48卷 129-141页

作者： LI Xinliang FU Dexun MA Yanwan LNM Institute of Mechanics Chinese Academy of Sciences Beijing 100080 China LNM Institute of Mechanics Chinese Academy of Sciences Beijing 100080 China LNM Institute of Mechanics Chinese Academy of Sciences Beijing 100080 China

Direct numerical simulation of spatially evolving compressible boundary layer over a blunt wedge is performed in this paper. The free-stream Mach number is 6 and the disturbance source produced by wall blowing and suction is located downstream of the sound-speed point. Statistics are studied and compared with the results in incompressible flat-plate boundary layer. The mean pressure gradient effects on the vortex structure are studied.

关键词： boundary layer, transition, direct numerical simulation, compressible turbulence.