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Partial discharge-induced crack growth in dielectric materials

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science China(Physics,Mechanics & Astronomy) 2010年第5期53卷 886-891页

作者： LUO JiaCheng,GAO CunFa & DAI XiangHua college of aerospace engineering,Nanjing University of Aeronautics & Astronautics,Nanjing 210016,China 1. college of aerospace engineering Nanjing University of Aeronautics & Astronautics Nanjing 210016 China

Partial discharge(PD) of an air-filled semi-permeable crack in a dielectric material is studied based on the streamer-type discharge mechanism to explore the effects of applied mechanical-electric fields on crack *** the frame of two-dimensional deformation,the electric field inside the crack is first derived by taking the crack deformation into ***,the effects of electric field before PD are discussed through considering the contribution of the induced electric field inside the deformed crack space to the total energy release ***,PD and its effects on crack growth are *** is found that:(1) before PD,the applied electric field always retards crack growth;(2) during PD,the applied electric field can induce crack growth in dielectric materials.

关键词： crack dielectric materials partial discharge electric field effects

structural ensemble dynamics based closure model for wall-bounded turbulent flow

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Acta Mechanica sinica 2009年第5期25卷 731-736页

作者： Zhen-su she Ning Hu You Wu state Key Laboratory for Turbulence and Complex systems and Dept Mechanical and aerospace engineering,college of engineering, Peking University,100871 Beijing, China state Key Laboratory for Turbulence and Complex systems and Dept Mechanical and aerospace engineering College of Engineering Peking University 100871 Beijing China

Wall-bounded turbulent flow involves the development of multi-scale turbulent eddies, as well as a sharply varying boundary layer. Its theoretical descriptions are yet phenomenological. We present here a new framework called structural ensemble dynamics （sED）, which aims at using systematically all relevant statistical properties of turbulent structures for a quantitative description of ensemble means. A new set of closure equations based on the sED approach for a turbulent channel flow is presented. sED order functions are defined, and numerically determined from data of direct numerical simulations （DNs）. Computational results show that the new closure model reproduces accurately the solution of the original Navier-stokes simulation, including the mean velocity profile, the kinetic energy of the streamwise velocity component, and every term in the energy budget equation. It is suggested that the sED-based studies of turbulent structure builds a bridge between the studies of physical mechanisms of turbulence and the development of accurate model equations for engineering predictions.

关键词： Turbulence Closure equation Channel flow structural ensemble dynamics

Review on abort trajectory for manned lunar landing mission

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science China(Technological sciences) 2010年第10期53卷 2691-2698页

作者： XI XiaoNing1, HUANG WenDe2 & WANG Wei2,3 1 college of Mechatronics engineering and Automation, National University of Defense Technology, Changsha 410073, China 2 college of aerospace and Material engineering, National University of Defense Technology, Changsha 410073, China 3 school of surveying and spatial Information system, University of New south Wales, sydney, NsW 2052, Australia 1. college of Mechatronics engineering and Automation National University of Defense Technology Changsha 410073 China2. College of Aerospace and Material Engineering National University of Defense Technology Changsha 410073 China3. School of Surveying and Spatial Information System University of New South Wales Sydney NSW 2052 Australia

Abort trajectory is a passage that ensures the astronauts to return safely to the earth when an emergency occurs. Firstly,the essential elements of mission abort are analyzed entirely based on summarizing the existing studies. Then,abort trajectory requirement and rational selection for different flight phases of typical manned lunar mission are discussed specifically. Considering a trade-off between the two primary constrains of an abort,the return time of flight and energy requirement,a general optimizing method for mission abort is proposed. Finally,some suggestions are given for China’s future manned lunar landing mission.

关键词： manned lunar landing mission abort trajectory design free return trajectory

synthetically adaptive robust filtering for satellite orbit determination

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science China Earth sciences 2004年第7期47卷 585-592页

作者： YANG Yuanxi1 & WEN Yuanlan2 1. Xi’an Research Institute of surveying and Mapping, Xi抋’an 710054, China 2. college of aerospace and Material engineering, National University of Defense Technology, Changsha 410073, China 1. Xi’an Research Institute of surveying and Mapping 710054 Xi’an China 2. college of aerospace and Material engineering National University of Defense Technology 410073 Changsha China

The quality of the satellite orbit determination is rested on the knowledge of per-turbing forces acting on the satellite and stochastic properties of the observations, and the ability of controlling various kinds of errors. After a brief discussion on the dynamic and geometric orbit determinations, sage adaptive filtering and robust filtering are reviewed. A new synthetically adaptive robust filtering based on a combination of robust filtering and sage filtering is *** is shown, by derivations and calculations, that the synthetically adaptive robust filtering for orbit determination is not only robust but also simple in calculation. It controls the effects of the outliers of tracking observations and the satellite dynamical disturbance on the parameter esti-mates of the satellite orbit.

关键词： satellite orbit, sage filtering, adaptive orbit determination, robust estimation.

The refined theory of deep rectangular beams for symmetrical deformation

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science China(Physics,Mechanics & Astronomy) 2009年第6期52卷 919-925页

作者： GAO Yang1 & WANG MinZhong2 1 college of science, China Agricultural University, Beijing 100083, China 2.state Key Laboratory for Turbulence and Complex systems and Department of Mechanics and aerospace engineering, Peking University, Beijing 100871, China college of science China Agricultural University Beijing 100083 China state Key Laboratory for Turbulence and Complex systems and Department of Mechanics and aerospace engineering Peking University Beijing 100871 China

Based on elasticity theory, various one-dimensional equations for symmetrical deformation have been deduced systematically and directly from the two-dimensional theory of deep rectangular beams by using the Papkovich-Neuber solution and the Lur'e method without ad hoc assumptions, and they construct the refined theory of beams for symmetrical deformation. It is shown that the displacements and stresses of the beam can be represented by the transverse normal strain and displacement of the mid-plane. In the case of homogeneous boundary conditions, the exact solutions for the beam are derived, and the exact equations consist of two governing differential equations: the second-order equation and the transcendental equation. In the case of non-homogeneous boundary conditions, the approximate governing differential equations and solutions for the beam under normal loadings only and shear loadings only are derived directly from the refined beam theory, respectively, and the correctness of the stress assumptions in classic extension or compression problems is revised. Meanwhile, as an example, explicit expressions of analytical solutions are obtained for beams subjected to an exponentially distributed load along the length of beams.

关键词： deep rectangular beams the refined theory symmetrical deformation the Papkovich-Neuber solution the Lur’e method

solution space analysis of Double Lunar-swingby periodic trajectory

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science China(Technological sciences) 2010年第8期53卷 2081-2088页

作者： LUO ZongFu ,MENG YunHe&TANG GuoJian college of aerospace and Material engineering,National University of Defense Technology,Changsha 410073,China 1. college of aerospace and Material engineering National University of Defense Technology Changsha 410073 China

The Double Lunar-swingby(DLs)periodic trajectory is a type of large-scale trajectory in Restricted Three-Body Problem ***,the principium of the DLs periodic trajectory is studied,and a preliminary design of the DLs trajectory is developed by the Patched Conic ***,the solution space of the DLs periodic trajectory is discussed in detail and in combination with numerical simulation,a distribution about orbital parameter relationship in the solution space is ***,the variations of the orbital elements with different rotation angular velocities of geocentric apsidal line are found,and two typical orbits are given according to three reference *** is shown that Patched Conic method is feasible for the DLs periodic trajectory solution space analysis,and the conclusions will be valuable to the deep-space exploration orbit design in future.

关键词： Double Lunar-swingby patched conics solution space analysis orbit design periodic orbit

Microstructure and formation mechanism of twins of laths of austenite with high nitrogen

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science China(Technological sciences) 2007年第6期50卷 755-764页

作者： WU CuiLan1,2 & LUO ChengPing2 1 Center for High Resolution Electron Microscopy, college of Materials science and engineering, Hunan University, Changsha 410082, China 2 college of Mechanical engineering, south China University of Technology, Guangzhou 510641, China 1. Center for High Resolution Electron Microscopy College of Materials Science and Engineering Hunan University Changsha 410082 China 2. college of Mechanical engineering South China University of Technology Guangzhou 510641 China

The microstructure of composite diffusion layer of the nitrided and chromized 0.2% carbon steel is investigated using TEM and EDs. It is found that laths of austenite with high nitrogen (γ N) precipitate from α-ferrite matrix in the deeper zone of the diffusion layer. These γ N laths are all twins, with their {111} twinning planes parallel to the lath axis, thus forming a characteristic "back-to-back" morphology. There are two types of γN lath. The first is a genuinely {111} twin, and γ N and α keep the accurate K-s relationship, and each γ N and α form a sharp and smooth γ N/α inter- face of {335}γN//{341}α, namely habit plane {335}fcc. The second is a pseudo-twin, with micro-twins {111} or faults formed within the two twin components. Localized lattice deformation (relaxation) seems to have occurred at the interfaces of the second type of γ N due to the formation of micro-twins or faults within the twin components. These micro-twins or faults make the orientation relationship (OR) between each of the γN and the α-matrix deviate from the accurate K-s OR, and the OR between two γ N twin components deviate from the genuine {111} twin relation- ship. In addition, the γ N/α interface of the second type of γ N is not as sharp or smooth as that of the first one.

关键词： austenite containing nitrogen, twins, steel 20, nitriding, composite chromizing

TWO KINDs OF HARMONIC PROBLEMs IN CONTROL sYsTEMs

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Journal of systems science & Complexity 2009年第4期22卷 587-596页

作者： Zhisheng DUAN Lin HUANG state Key Lab for Turbulence and Complex systems and Department of Mechanics and aerospace engineering,college of engineering,Peking University,Beijing 100871,China. state Key Lab for Turbulence and Complex systems and Department of Mechanics and aerospace engineering College of Engineering Peking University Beijing 100871 China

This paper discusses the harmonic problems in control systems from two aspects:Oneis the harmonic control among different subsystems,and the other is the harmonic control amongmultiple *** intrinsic problems in such systems are *** is pointed out that somesubsystems must be unstable to stabilize the whole interconnected system by an *** discrete-time multi-input systems,a necessary and sufficient condition is presented for the strictdecrease of the quadratic optimal performance index with the control input *** showsan essential difference between single-input and multi-input control ***,some futureresearch directions are discussed in harmonic control of interconnected systems,allocation of multi-control inputs,fault-tolerant control,and fault-diagnosis.

关键词： Interconnected system quadratic optimal control redundant inputs Riccati equation simplectic matrix.

A geometrical and physical nonlinear finite element model for spatial thin-walled beams with arbitrary section

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science China(Technological sciences) 2010年第3期53卷 829-838页

作者： YANG Qingshan 1 &WANG XiaoFeng 2 1 school of Civil engineering,Beijing Jiaotong University,Beijing 100044,China 2 college of Civil engineering,Tongji University,shanghai 200092,China 1. school of Civil engineering Beijing Jiaotong University Beijing 100044 China2. College of Civil Engineering Tongji University Shanghai 200092 China

Based on the theories of Bernoulli-Euler beams and Vlasov's thin-walled members,a new geometrical and physical nonlinear beam element model is developed by applying an interior node in the element and independent interpolations on bending angles and warp,in which factors such as traverse shear deformation,torsional shear deformation and their coupling,coupling of flexure and torsion,and second shear stress are all ***,geometrical nonlinear strain in total Lagarange(TL) and the corresponding stiffness matrix are *** plastic model is applied to physical nonlinearity to comply with the yield rule of Von Mises and incremental relationship of *** stiffness matrix is derived by numerical integration on the basis of the finite segment *** show that the developed model is feasible in analysis of thin-walled structures with high accuracy.

关键词： spatial beams thin-walled structures geometrical and physical nonlinearity finite element arbitrary section