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Large-eddy simulation of flows past a flapping airfoil using immersed boundary method

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Science china(Physics,mechanics & Astronomy) 2010年第6期53卷 1101-1108页

作者： YANG xiaolei,HE GuoWei & ZHANG Xing The state key {3. of Nonlinear mechanics,institute of mechanics,chinese academy of sciences,beijing 100190,china 1. The state key laboratory of Nonlinear {3. Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

The numerical simulation of flows past flapping foils at moderate Reynolds numbers presents two challenges to computational fluid dynamics: turbulent flows and moving boundaries. The direct forcing immersed boundary(IB) method has been developed to simulate laminar flows. However,its performance in simulating turbulent flows and transitional flows with moving boundaries has not been fully evaluated. In the present work,we use the IB method to simulate fully developed turbulent channel flows and transitional flows past a stationary/plunging SD7003.airfoil. To suppress the non-physical force oscillations in the plunging case,we use the smoothed discrete delta function for interpolation in the IB method. The results of the present work demonstrate that the IB method can be used to simulate turbulent flows and transitional flows with moving boundaries.

关键词： transitional flows moving boundary immersed boundary method smoothed discrete delta function

NONLINEAR FLUID DAMPING IN STRUCTURE-WAKE OSCILLATORS IN MODELING VORTEX-INDUCED VIBRATIONS

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Journal of Hydrodynamics 2009年第1期21卷 1-11页

作者： LIN Li-ming LING Guo-can wu Ying-xiang ZENG Xiao-hui Division of Engineering sciences Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China The state key laboratory of Nonlinear {3. Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

A Nonlinear Fluid Damping （NFD） in the form of the square-velocity is applied in the response analysis of Vortex-Induced Vibrations （VIV）. Its nonlinear hydrodynamic effects on the coupled wake and structure oscillators are investigated. A comparison between the coupled systems with the linear and nonlinear fluid dampings and experiments shows that the NFD model can well describe response characteristics, such as the amplification of body displacement at lock-in and frequency lock-in, both at high and low mass ratios. Particularly, the predicted peak amplitude of the body in the Griffin plot is in good agreement with experimental data and empirical equation, indicating the significant effect of the NFD on the structure motion.

关键词： Vortex-Induced Vibration (VIV) Nonlinear Fluid Damping (NFD) wake oscillator

Influence mechanism of government subsidy on the green transformation of coal company in china

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International Journal of Mining Science and Technology 2024年第7期34卷 1033-1040页

作者： xiaolei Li Changsong wu School of Management China University of Mining and Technology-BeijingBeijing 100083China School of Economics and Management China University of Mining and TechnologyXuzhou 221116China

The optimization of government subsidies to enhance the efficiency of coal companies’green transformation constitutes a critical component in the pursuit of global *** investigate the influence mechanism of government subsidies on the green transformation using data from the listed coal companies in china from 2007 to *** to our findings and hypothesis testing,previous government subsidies did not have a significant direct impact on coal companies’green ***,government subsidies can help coal companies transition to greener practices by promoting innovative green ***,we confirmed an indirect route:that government subsidies enable the adoption of low-carbon initiatives,which in turn could facilitate the transition of coal companies towards green *** addition,we discovered that the coal company’s digitization will improve this indirect ***,we propose increasing the effectiveness of government subsidies in facilitating coal companies’transition to green practices by focusing on technological advancements and enhancing company digitalization.

关键词： Government subsidy Green transformation Coal company Digitalization Innovation

Observation of the Turbulent Burst near ASheared Air-Water Interface

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Communications in Nonlinear Science and Numerical Simulation 1999年第2期4卷 94-99页

作者： Shuangfeng WANG Fu JIA Zhennan NIU Zhangzhi wu(institute of mechanics,{3., beijing 100080, china)(state key laboratory for Turbulence Research, Peking University, beijing 100871,china) institute of mechanics Chinese Academy of Sciences Beijing 100080 China

The turbulent burst under a sheared air-water interface was experimentally investigated using hydrogen bubble visualization technique. The surface shear wasimposed by an airflow over the water flow which was kept free from surface waves. Resultsshow that the wind shear has the main influence on the bursting events. At relativelyhigh shear rates, the flow near the interface is dominated primarily by intermittent bursting events. The general features of bursting processes are described in some detail. Theobserved bursting events show qualitative similarities with those occurring in near-wallturbulence. However, a few distinctive phenomena were also observed, including the existence of vertical vortices and thickening process of the boundary layer, which appear tobe associated with the Characteristics of air-water interface.

关键词： air-water interface turbulent burst flow-visualization

Annealing and strain rate effects on the mechanical behavior of ultrafine-grained iron produced by SPD

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Theoretical & Applied mechanics Letters 2011年第2期1卷 12-14页

作者： Fuping Yuan,~(a) Ping Jiang,~(b) and xiaolei wu~(c) state {3. laboratory of Nonlinear mechanics,institute of mechanics chinese academy of Science, beijing 100190,china state key laboratory of Nonlinear {3. Institute of Mechanics Chinese Academy of Science Beijing 100190 China

Thermal stability and strain rate sensitivity of ultrafine-grained(UFG)Fe produced by severe plastic deformation(SPD)were *** UFG Fe was processed by equal-channel angular pressing(ECAP)via route *** 6 passes,the grain size of UFG Fe reaches 600 nm, as confirmed by means of electron back scatter diffraction(EBSD).Examination of micro-hardness and grain size of UFG Fe as a function of post-ECAP annealing temperature shows a transition from recovery to *** critical transition temperature is approximately 500℃,and the material has a bimodal structure after annealing at this *** behaviors of ECAP Fe and ECAP + annealing Fe were studied under both quasi-static and dynamic compressive *** UFG iron shows increased strength and reduced strain rate sensitivity compared with its coarse-grained *** appropriate post-ECAP annealing can increase strain hardening ability and cancel out thermal softening effect with only a small loss of strength under dynamic loading.

关键词： UFG/NC Fe ECAP EBSD thermal stability strain rate sensitivity

Influence of processing temperature on microstructure and microhardness of copper subjected to high-pressure torsion

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Science china(Technological sciences) 2010年第6期53卷 1534-1539页

作者： XIE ZiLing1,2,XIE JiJia2,HONG YouShi2 & wu xiaolei2 1 College of Architecture and Civil Engineering,University of Wenzhou,Wenzhou 3.503.,china 2 {3. key laboratory of Nonlinear mechanics,institute of mechanics,chinese academy of sciences,beijing {13.,china 1. College of Architecture and Civil Engineering University of Wenzhou Wenzhou 325035 China2. State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

Cu samples were subjected to high-pressure torsion (HPT) with up to 6 turns at room temperature (RT) and liquid nitrogen temperature (LNT),*** effects of temperature on grain refinement and microhardness variation were *** the samples after HPT processing at RT,the grain size reduced from 43.μm to 265 nm,and the Vickers microhardness increased from HV52 to ***,for the samples after HPT processing at LNT,the value of microhardness reached its maximum of HV150 near the center of the sample and it decreased to HV80 at the periphery *** observations revealed that HPT straining at LNT induced lamellar structures with thickness less than 100 nm appearing near the central region of the sample,but further deformation induced an inhomogeneous distribution of grain sizes,with submicrometer-sized grains embedded inside micrometer-sized *** submicrometer-sized grains with high dislocation density indicated their nonequilibrium *** the contrary,the micrometer-sized grains were nearly free of dislocation,without obvious deformation trace remaining in *** images demonstrated that the appearance of micrometer-sized grains is the result of abnormal grain growth of the deformed fine grains.

关键词： copper high pressure torsion (HPT) microstructure grain size microhardness cryogenic temperature

The theoretical research of basic function method in incompressible viscous flow and its simulations in three-dimensional aneurysms

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Science china(Physics,mechanics & Astronomy) 2009年第6期52卷 909-918页

作者： SHEN Fang1 & wu WangYi2 1 state key {3. for Space Weather, Center for Space Science and Applied Research, chinese academy of sciences, beijing 100190, china 2 state key {3. of Turbulence and Complex Systems & Department of mechanics and Engineering Science, Peking University, beijing 100871, china 1. state key laboratory for Space Weather Center for Space Science and Applied Research Chinese Academy of Sciences Beijing 100190 China 2. state key laboratory of Turbulence and Complex Systems & Department of {3. and Engineering Science Peking University Beijing 100871 China

Basic function method is developed to treat the incompressible viscous flow. Artificial compressibility coefficient, the technique of flux splitting method and the combination of central and upwind schemes are applied to construct the basic function scheme of trigonometric function type for solving three-dimensional incompressible Navier-Stokes equations numerically. To prove the method, flows in finite-length-pipe are calculated, the velocity and pressure distribution of which solved by our method quite coincide with the exact solutions of Poiseuille flow except in the areas of entrance and exit. After the method is proved elementary, the hemodynamics in two-and three-dimensional aneurysms is researched numerically by using the basic function method of trigonometric function type and unstructured grids generation technique. The distributions of velocity, pressure and shear force in steady flow of aneurysms are calculated, and the influence of the shape of the aneurysms on the hemodynamics is studied.

关键词： basic function unstructured grid aneurysm viscous incompressible flow artificial compressibility flux splitting

CMQV+:An authenticated key exchange protocol from CMQV

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Science china(Information sciences) 2012年第7期55卷 1666-1674页

作者： LI Hui 1,2 & wu ChuanKun 1 1 state key {3. of Information Security,institute of Software,chinese academy of sciences,beijing 100190,china 2 Graduate University of chinese academy of sciences,beijing 100049,china 1. state key laboratory of Information Security Institute of Software Chinese Academy of Sciences Beijing 100190 China2. Graduate University of Chinese Academy of Sciences Beijing 100049 China

Ustaoglu presents a secure and efficient key exchange protocol named CMQV,based on the design rationales of HMQV and *** with the latter two protocols,on one hand,CMQV achieves high performance of HMQV,and on the other,it is proven secure in eCK model as NAXOS ***,CMQV enjoys the security proof under gap Diffie-Hellman assumption as indicated by its *** this paper,we propose a variant of CMQV,called CMQV+,which is proven secure under a weaker assumption (*** Diffie-Hellman assumption) in eCK model with random oracles while maintaining the high-performance feature of CMQV as much as possible.

关键词： key exchange eCK model trapdoor-test technique provable security CDH assumption

Synthetic aperture radar tomography sampling criteria and three-dimensional range migration algorithm with elevation digital spotlighting

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Science in china(Series F) 2009年第1期52卷 100-114页

作者： TAN WeiXian1,2,3., HONG Wen1,2, WANG YanPing1,2, LIN Yun1,2,3.& wu YiRong1,2 1 state key {3. of Microwave Imaging Technology, beijing 100190, china 2 institute of Electronics, chinese academy of sciences, beijing 100190, china 3.Graduate School, chinese academy of sciences, beijing 100190, china state key laboratory of Microwave Imaging Technology Beijing 100190 China institute of Electronics Chinese Academy of Sciences Beijing 100190 China Graduate School Chinese Academy of Sciences Beijing 100190 China

Based on the general geometric model of multi-baseline Synthetic Aperture Radar Tomography （TomoSAR）, the three-dimensional （3.D） sampling criteria, the analytic expression of the 3.D Point Spread Function （PSF） and the 3.D resolution are derived in the 3.D wavenumber domain in this paper. Considering the relationship between the observation geometry and the size of illuminated scenario, a 3.D Range Migration Algorithm with Elevation Digital Spotlighting （RMA-EDS） is proposed. With this algorithm 3.D images of the area of interest can be directly and accurately reconstructed in the 3.D space avoiding the complex operations of 3.D geometric correction. Finally, theoretical analyses and simulation results are presented to demonstrate the shift-varying property of the 3.D PSF and the spatialvarying property of the 3.D resolution and to demonstrate the validity of the 3.D RMA-EDS.

关键词： synthetic aperture radar tomography (TomoSAR) three-dimensional (3.D) SAR imaging 3.D sampling criteria 3.D resolution,3.D range migration algorithm with elevation digital spotlighting (RMA-EDS)