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Large eddies induced by local impulse at wall of boundary layer with pressure gradients

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Progress in Natural science:Materials International 2008年第7期18卷 873-878页

作者： Changgen Lu a,b,*, Weidong Caob, Yanmei Zhang b, Jintao Pengb a College of Atmospheric science, nanjing university of information science & technology, nanjing 210044, china b College of Environmental science and Engineering, Hohai university, nanjing 210098, china College of Atmospheric science Nanjing University of Information Science & Technology Nanjing 210044 China College of Environmental science and Engineering Hohai University Nanjing 210098 China

Large eddies induced by local impulse at the wall with pressure gradients in the boundary layer was studied by direct numerical sim- ulations. The results show that the amplitude evolution, the high and low speed stripes, the formation of streamwise vortices, the ejection and sweeping, inflexions and distortion at the mean velocity profiles, as well as other characteristics, are consistent with the experimental and other numerical results. It is also found that large eddies are easy to be excited with adverse pressure gradient in the boundary layer, and the growth of amplitudes, formation of streamwise vortices and the influencing area etc., are much larger than those with favorable pressure gradient in the boundary layer. In contrast, large eddies are hardly to be induced through local impulse disturbance at the wall with favorable pressure gradients in the boundary layer.

关键词： Boundary layer Pressure gradients Impulse Large eddies

Sufficient and necessary conditions for Lyapunov stability of Lorenz system and their application

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science china(information sciences) 2010年第8期53卷 1574-1583页

作者： LUO Qi 1 , LIAO XiaoXin 2 & ZENG ZhiGang 2 1 College of information and Control, nanjing university of information science and technology, nanjing 210044, china 2 Department of Control science and Engineering, Huazhong university of science and technology, Image Processing and Intelligent Control Key Laboratory of Education Ministry of china, Wuhan 430074, china 1. College of information and Control Nanjing University of Information Science and Technology Nanjing 210044 China2. Department of Control Science and Engineering Huazhong University of Science and Technology Image Processing and Intelligent Control Key Laboratory of Education Ministry of China Wuhan 430074 China

The sufficient and necessary conditions for Lyapunov stability of the zero equilibrium point of Lorenz system are discussed, and some brief criteria are presented for globally exponential stability, globally asymptotical stability and instability. Furthermore, the behavior of the non-zero equilibrium point of Lorenz system is also investigated, and several sufficient and necessary conditions are provided for locally exponential stability and instability. The established theorems in this paper develop and extend the existing achievements on Lyapunov stability of Lorenz system. In conclusion, by applying the obtained results, some less conservative feedback-control laws are derived to guarantee the globally exponential stability of the chaos control of Chen system, Lu¨ system, Yang-Chen system and Yu-Xia Li system.

关键词： Lorenz system Lyapunov stability sufficient and necessary condition bifurcation values globally exponential synchronization

A new smoothing scheme for mathematical programs with complementarity constraints

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science china mathematics 2010年第7期53卷 1881-1890页

作者： YAN TaoDepartment of information and Computational sciences, College of science, nanjing university of science and technology, nanjing 210094, china 1. Department of information and Computational sciences College of Science Nanjing University of Science and Technology Nanjing 210094 China

In this paper, we consider a mathematical program with complementarity constraints (MPCC). We present a new smoothing scheme for this problem, which makes the primal structure of the complementarity part unchanged mostly. For the new smoothing problem, we show that the linear independence constraint qualification (LICQ) holds under some conditions. We also analyze the convergence behavior of the smoothing problem, and get some sufficient conditions such that an accumulation point of stationary points of the smoothing problems is C (M, B)-stationarity respectively. Based on the smoothing problem, we establish an algorithm to solve the primal MPCC problem. Some numerical experiments are given in the paper.

关键词： mathematical program with complementarity constrains MPEC-LICQ B-stationarity C-stationarity M-stationarity

Seasonal variation of global stratosphere-troposphere mass exchange

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Progress in Natural science:Materials International 2007年第12期17卷 1466-1475页

作者： Guo Dong1,2, Lu Daren2 and Sun Zhaobo1(1. Institute of Atmospheric sciences, nanjing university of information science and technology, nanjing 210044, china 2. LAGEO, Institute of Atmospheric physics, Chinese Academy of sciences, Beijing 100029, china) Institute of Atmospheric sciences Nanjing University of Information Science and Technology Nanjing 210044 China LAGEO Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China

By Wei formula in pressure coordinate, the stratosphere-troposphere mass exchange (STME) is diagnosed globally for 44 years from 1958 to 2001 using the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis datasets. Regions of mass flux into the stratosphere are found over Indonesia, bay of Bangladesh and the mid-west coast of South Africa. Compensating mass outflow from the stratosphere appears mainly over mid-latitudes near large-scale troughs. Upward and downward transport of mass at the middle and high latitudes accompany with each other. Mass flux into troposphere is stronger in autumn and winter than in spring and summer. Strong downward mass flux into the troposphere occurs in eastern Asia the whole year with nearly stable sites. Although the area of eastern Asia accounts for only 5.6% of that of the northern hemisphere (NH), its net mass exchange reaches 15.83% of that of the NH, which means that research on STME of eastern Asia is greatly important to that of the NH and even the global areas. Air across the tropopause enters more from stratosphere to troposphere than that from troposphere to stratosphere, which is possibly related with systematic bias of the assimilated datasets and with persistent rise of the tropopause height. Contributions of the mass exchange and the mass flux exchange in the NH and southern hemisphere (SH) on their latitudes increase from equator to pole, with larger contributions in the NH. Mass exchange and mass flux exchange per areas at high latitudes are larger than that at low latitudes, which means greater mass exchange efficiency at high latitudes.

关键词： stratosphere troposphere mass exchange seasonal variation.

Two possible mechanisms for vortex self-organization

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science china Earth sciences 2006年第2期49卷 202-211页

作者： LUO Zhexian2, ZHOU Xiuji1 & GAO Shouting3 1. Chinese Academy of Meteorological sciences, Beijing 100081, china 2. Department of Space information science, nanjing university of information science and technology, nanjing 210044, china 3. Institute of Atmospheric physics, Chinese Academy of sciences, Beijing 100029, china 2. Department of Environmental science Nanjing University of Information Science and Technology Nanjing 210044 China 1. Chinese Academy of Meteorological sciences Beijing 100081 China 3. Institute of Atmospheric physics Chinese Academy of Sciences Beijing 100029 China

The vortex self-organization is investigated in this paper by four groups of numerical experiments within the framework of quasi-geostrophic model, and based on the experimental results two types of possible mechanisms for vortex self-organization are suggested. The meso-scale to-pography may enable separated vortices to merge into a larger scale vortex; and the interaction of meso-γ and meso-β scale systems may make separated vortices to self organize a typhoon-like vor-tex circulation.

关键词： vortex, self-organization, meso-scale topography, interaction of different scales.

Influences of Lorentz force on the hydrofoil lift

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Acta Mechanica Sinica 2009年第5期25卷 589-595页

作者： Yaohui Chen Baochun Fan Zhihua Chen Hongzhi Li Laboratory of Transient physics,nanjing university of science and technology,210094 nanjing, china Laboratory of Transient physics Nanjing University of Science and Technology 210094 Nanjing China

In this paper, Lorentz forces are proved to be able to suppress separation in flows over hydrofoils. Furthermore, a differential equation of pressure distributions on the hydrofoil surface is derived, from which it is found that BVF （boundary vortex flux） σ is a suitable criterion for describing the lift coefficient variations during the electromagnetic control process. According to our numerical results, the periodic variations of lift for a hydrofoil at an attack angle of 17 ° are analyzed and its inherent mechanism is discussed in detail with the concept of BVE On the other hand, the effects of Lorentz force on the hydrofoil＇s lift are investigated both experimentally and numerically for different magnitudes and locations.

关键词： Lorentz force Lift coefficient Hydrofoil

On the interannual variation in spring atmospheric inter-hemispheric oscillation linked to synchronous climate in china

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Progress in Natural science:Materials International 2009年第9期19卷 1125-1131页

作者： Chuhan Lu, Zhaoyong Guan * Key Laboratory of Meteorological Disaster of Ministry of Education and College of Atmospheric sciences, nanjing university of information science and technology, nanjing 210044, china [a]Key Laboratory of Meteorological Disaster of Ministry of Education and College of Atmospheric sciences Nanjing University of Information Science and Technology Nanjing 210044 China

Based on NCEP/NCAR monthly mean reanalysis data and surface observations of Chinese stations, inter-hemispheric oscillations (IHO) of spring atmospheric mass on an interannual basis in conjunction with the linkage to the synchronous climate over china are studied. Results suggest that the spring IHO exhibits a significant seesaw pattern for air mass at bi-hemispheric mid-high latitudes, with a consistent vertical circulation structure. The EOF decomposition of zonally mean surface pressures without signals of Arctic Oscillation (AO) and Antarctic Oscillation (AAO) indicates that the EOF1 IHO feature is remarkable, with the corresponding time coeficients correlated with the spring IHO index (IIHO) at 0.93; the spring IHO bears a close relation to the synchronous climate in china, showing the surface pressure, temperature and relative humidity over the country to be in good correlation with IIHO; the spring duststorms in Qinghai, Gansu, Shaanxi and Inner Mongolia have bearing on IHO. Positive-phase IIHO promotes the strengthening of the Siberian high, during which zonal winds between 60°E and 150°W show a longitudinal teleconnection structure extending from the Arctic to Antarctica, leading to positive westerly wind anomalies over Asia, affecting the spring climate of china.

关键词： Air mass Inter-hemispheric oscillation (IHO) Spring climate china

A LAW OF ITERATED LOGARITHM FOR THE MLE IN A RANDOM CENSORING MODEL WITH INCOMPLETE information

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Acta Mathematica Scientia 2008年第3期28卷 501-512页

作者：宋凤丽刘禄勤 school of mathematics and Statistics Wuhan University

In this article, a law of iterated logarithm for the maximum likelihood estimator in a random censoring model with incomplete information under certain regular conditions is obtained.

关键词： Random censoring model maximum likelihood estimator law of iterated logarithm

Investigation of fine and complex vortex circulation structures

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science china Earth sciences 2010年第10期53卷 1552-1558页

作者： LUO ZheXian1,MA GeLan1 & PING Fan2 1 Remote Sensing College,nanjing university of information science and technology,nanjing 210044,china 2 Laboratory of Cloud-Precipitation physics and Severe Storms(LACS),Institute of Atmospheric physics,Chinese Academy of sciences,Beijing 100029,china 1. Remote Sensing College Nanjing University of Information Science and Technology Nanjing 210044 China2. Laboratory of Cloud-Precipitation Physics and Severe Storms (LACS) Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China

The formation and evolution of fine and complicated vortex circulation structures were investigated using a two-dimensional quasi-geostrophic barotropic model *** find that the highly localized asymmetric and complex configuration of energy transfer flux between large-and small-scale components is caused by the nonlinear interaction between a large-scale vortex with an initial axi-symmetric flow and four beta meso-scale *** complex structure is characterized by a fine pattern,which contains seven closed systems with spatial scales of less than 100 km,embedded in a positive flux wave train and a negative wave train,*** average wind speed decreased with time in the positive flux region,but was nearly unchanged in the negative flux *** pattern reveals the evolutionary asymmetry and localization of wind speed of the major *** track of the major vortex center has a trend toward the center of the negative flux center,indicating that there is a certain relation between the complex structure of the energy transfer flux and the motion of the major vortex *** results imply that the formation and evolution of the fine and complex structure should be attributed to the nonlinear interaction between the vortices at different spatial scales.

关键词： vortex complex structure non-linear interaction energy cascade