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Preconditioned pseudo-compressibility methods for incompressible Navier-Stokes equations

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中国科学：物理学、力学、天文学英文版 2010年第11期53卷 2090-2102页

作者： QIAN ZhanSen ,ZHANG JingBai & LI ChunXuan school of aeronautics science and Engineering,Beihang university,beijing 100191,china school of aeronautics science and Engineering Beihang University Beijing China

This paper investigates the pseudo-compressibility method for the incompressible Navier-Stokes equations and the preconditioning technique for accelerating the time marching for stiff hyperbolic equations,and derives and presents the eigenvalues and eigenvectors of the Jacobian matrix of the preconditioned pseudo-compressible Navier-Stokes equations in generally cur-vilinear *** on the finite difference discretization the cored for efficiently solving incompressible flows numerically is *** reliability of the procedures is demonstrated by the application to the inviscid flow past a circular cylinder,the laminar flow over a flat plate,and steady low Reynolds number viscous incompressible flows past a circular *** is found that the solutions to the present algorithm are in good agreement with the exact solutions or experimental *** effects of the pseudo-compressibility factor and the parameter brought by preconditioning in convergence characteristics of the solution are investigated *** results show that the upwind Roe’s scheme is superior to the second order central scheme,that the convergence rate of the pseudo-compressibility method can be effectively improved by preconditioning and that the self-adaptive pseudo-compressibility factor can modify the numerical convergence rate significantly compared to the constant form,without doing artificial tuning depending on the specific flow *** validation is also performed by numerical simulations of unsteady low Reynolds number viscous incompressible flows past a circular *** results are also found in good agreement with the existing numerical results or experimental data.

关键词： pseudo-compressibility method preconditioning upwind scheme incompressible flow Navier-Stokes equations

Unmanned air/ground vehicles heterogeneous cooperative techniques:Current status and prospects

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science china(Technological sciences) 2010年第5期53卷 1349-1355页

作者： DUAN HaiBin & LIU SenQi National Key Laboratory of science and Technology on Holistic Flight Control,school of Automation science and Electrical Engineering,beijing university of aeronautics and astronautics,beijing 100191,china National Key Laboratory of science and Technology on Holistic Flight Control School of Automation Science and Electrical Engineering Beijing University of Aeronautics and Astronautics Beijing China

Multiple unmanned air/ground vehicles heterogeneous cooperation is a novel and challenging *** cooperative techniques can widen the application fields of unmanned air or ground vehicles,and enhance the effectiveness of implementing detection,search and rescue *** paper mainly focused on the key issues in multiple unmanned air/ground vehicles heterogeneous cooperation,including heterogeneous flocking,formation control,formation stability,network control,and actual *** main problems and future directions in this field were also analyzed in *** innovative technologies can significantly enhance the effectiveness of implementing complicated tasks,which definitely provide a series of novel breakthroughs for the intelligence,integration and advancement of future robot systems.

关键词： unmanned air vehicle(UAV) unmanned ground vehicle(UGV) heterogeneous cooperation

Formation control for networked spacecraft in deep space:with or without communication delays and with switching topology

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science china(Information sciences) 2011年第3期54卷 469-481页

作者： WANG Nan 1,2, ZHANG TianWu 2 & XU JieQiong 1 1 school of Aeronautic science and Engineering, beijing university of aeronautics and astronautics, beijing 100191, china 2 Department of Computer science and Engineering, Henan Institute of Engineering, Zhengzhou 451191, china school of Aeronautic science and Engineering Beijing University of Aeronautics and Astronautics Beijing China Department of Computer science and Engineering Henan Institute of Engineering Zhengzhou China

In this paper, several formation controllers are developed with constant and variable connected communication topology for six-degree-of-freedom (6-DOF) networked spacecraft flying in deep space with constant and time-varying communication delays considered. In the control algorithm, any explicit leader does not exist in the formation team and it is required that each spacecraft communicate only with its neighbors and therefore the required communication loads of the whole formation is greatly reduced. The proposed control strategies allow that each spacecraft can track its desired position and attitude and simultaneously the whole group moves to the desired formation and obtain its desired relative attitudes with its neighbors. Simulation results demonstrate the effectiveness of the proposed controllers.

关键词： deep space graph theory formation control communication topology delays

Single rub-impacting periodic motions of a rigid constrained rotor system

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Communications in Nonlinear science and Numerical Simulation 2000年第4期5卷 158-161页

作者： Qunhong LI and Qishao LU (school of science, beijing university of aeronautics and astronautics, beijing 100082, china) (Received September 25, 2000) school of science Beijing University of Aeronautics and Astronautics Beijing 100083 China

This paper discusses the existence of single rub-impacting period-n motions for a kind of rotor systems with rigid constraints. The ranges of parameters for period-2 motions are also given. An example of this method i... 详细信息

关键词： rotor system rod constraint rub-impacting mapping periodic motion\

New discrimination method for ablative control mechanism in solid-propellant rocket nozzle

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science china(Technological sciences) 2010年第10期53卷 2718-2724页

作者： ZHANG Bin, LIU Yu, WANG ChangHui & REN JunXue school of astronautics, beijing university of aeronautics and astronautics, beijing 100083, china school of astronautics Beijing University of Aeronautics and Astronautics Beijing China

A reasonable discrimination method for ablative control mechanism in solid-propellant rocket nozzle can improve the calculation accuracy of ablation rate. Based on the different rate constants for reactions of C with H2O and CO2,a new discrimination method for ablative control mechanism,which comprehensively considers the influence of nozzle surface temperature and gas component concentration,is presented. Using this new discrimination method,calculations were performed to simulate the nozzle throat insert ablation. The numerical results showed that the calculated ablation rate,which was more close to the measured values,was less than the value calculated by diffusion control mechanisms or by double control mechanisms. And H2O was proved to be the most detrimental oxidizing species in nozzle ablation.

关键词： nozzle Ablation diffusion control mechanism chemical kinetics control mechanism discrimination method

STATISTICAL MODEL FOR FRACTURE TOUGHNESS OF A MODIFIED Al-7Si-0.45Mg CAST ALLOY

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Acta Metallurgica Sinica(English Letters) 1990年第4期3卷 262-267页

作者： ZHANG Guobin CHEN Changqi beijing university of aeronautics and astronautics,beijing,china Dept.of Materials science and Engineering,beijing university of aeronautics and astronautics,beijing 100083,china

The statistical model for the fracture toughness of a modified Al-7Si-0.45Mg cast alloy has been proposed on the basis of analysis of the correlation between the size distribution of crack nuclei and Si particles and of the micromechanism of *** suitable criterion of frac- ture toughness according to the model has been *** model has found a good explana- tion for the fracture feature,fracture toughness and microstructure,and agreed with the ex- periments very well.

关键词： cast Al alloy fracture toughness statistical model

An improved constrained steering law for SGCMGs with DPC

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Acta Mechanica Sinica 2009年第5期25卷 713-720页

作者： Lei Jin Shijie Xu Department of Guidance, Navigation and Control,school of astronautics, Beihang university, 100191 beijing, china Department of Guidance Navigation and Control School of Astronautics Beihang University Beijing China

An improved constrained （IC） steering law for single gimbal control moment gyros （SGCMGs） with deformed pyramid configuration （DPC） is proposed, First of all, the original system with five pyramid configuration （FPC） whose two adjacent gyros are in failure state is reconfigured as a degraded system with DPC. Then, the singular angular momentum hypersurfaces of the original and the degraded systems are plotted via the singular angular momentum equa- tion of SGCMGs. Based on singular surfaces, the differences between FPC and DPC in singularity and momentum envelope are obtained directly, which provide an important reference for steering law design of DPC. Finally, an IC steering law is designed and applied to DPC. The simulation results demonstrate that the IC steering law has advantages in simplicity of calculation, avoidance of singularity and exactness of output torque, which endow the degraded system with fine controllability in a restricted workspace.

关键词： Single gimbal control moment gyros (SGCMGs) - Deformed pyramid configuration (DPC) Failure Singularity - Steering law

ELASTIC-PLASTIC DYNAMIC RESPONSE OF FULLY BACKED SANDWICH PLATES UNDER LOCALIZED IMPULSIVE LOADING

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Acta Mechanica Solida Sinica 2010年第4期23卷 324-335页

作者： Hua Liu Wuchao Chen Jialing Yang (The Solid Mechanics Research Center, beijing university of aeronautics and astronautics, beijing 100191, china) The Solid Mechanics Research Center Beijing University of Aeronautics and Astronautics Beijing China

An analytical model is developed to assess the elastic-plastic dynamic response of fully backed sandwich plates under localized impulse *** core is modeled as an elastic-perfectly plastic *** top face sheet is treated as an individual plate resting on the *** elastic-plastic analysis for the top face sheet is based on a minimum principle in dynamic plasticity associated with the finite difference *** effects of spatial and temporal distributions of the impulsive loading on the dynamic response of sandwich plates are *** model can be used to predict the impulse-induced local effect on fully backed sandwich plates.

关键词： sandwich plate elastic plastic localized impulse plastic dissipation

High Resolution Electron Microscopy Observations of Structural Changes in Iron Nitride Films Annealed in Vacuum

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Journal of Materials science & Technology 1997年第2期13卷 123-126页

作者： Shengkai GONG Huibin XU (Dept. of Materials science and Engineering, beijing university of aeronautics and astronautics, beijing 100083, china) Dept. of Materials science and Engineering Beijing University of Aeronautics and Astronautics Beijing 100083 China

Iron-nitride films were prepared by reactive sputtering, and the effect of annealing treatment on the structures was investigated by means of in-situ electron microscopy and high resolution electron microscopy (HREM). As-deposited films were observed to be a mixed structure of a few ultrafine epsilon-Fe2-3N particles existing in the amorphous matrix. it was found that the structure-relaxation in the amorphous occurred at 473 K, and the ultrafine grains began to grow at the higher annealing temperatures. The transition of the amorphous to epsilon-Fe2-3N was almost completed at 673 K. It is considered that the formation of the ideal epsilon-Fe3N is originated from the ordering of the nitrogen atoms during the annealing in vacuum. On the other hand, gamma'-phase (Fe4N) was seen to precipitation of epsilon-phase at 723 K. Two possible modes are proposed in the precipitation of gamma'-phase, depending on the heating rate and crystallographic orientation relationships, i.e. [121](epsilon)//[001](gamma), (2(1) over bar0$)(epsilon)//(110)(gamma) and [100](epsilon)//[110](gamma), (001)(epsilon)//(111)(gamma). In addition, alpha-Fe particles were observed to form from the gamma'-phase at high temperatures. We assumed that these structural changes are due to the diffusion of nitrogen and iron atoms during the annealing, except for the case of the precipitation of the gamma'-phase as depicted above. The results obtained in this work are in a good agreement with the assumption.

关键词： Figure High Resolution Electron Microscopy Observations of Structural Changes in Iron Nitride Films Annealed in Vacuum