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Unsteady aerodynamic modeling based on POD-observer method

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Science China(Technological Sciences) 2010年第8期53卷 2032-2037页

作者： YANG Chao,LIU XiaoYan &WU ZhiGang beijing University of Aeronautics and Astronautics,beijing 100191,China beijing University of Aeronautics and Astronautics Beijing China

A new hybrid approach to constructing reduced-order models(ROM)of unsteady aerodynamics applicable to aeroelastic analysis is presented by using proper orthogonal decomposition(POD)in combination with observer *** modes are generated through POD by sampling observations of solutions derived from the full-order *** response in the POD training is projected onto the fluid modes to determine the time history of the modal *** resulting data are used to extract the Markov parameters of the low-dimensional model for modal amplitudes using a related deadbeat *** state-space realization is synthesized from the system's Markov parameters that are processed with the eigensystem realization *** POD-observer method is applied to a two-dimensional airfoil system in subsonic flow *** results predicted by the ROM are in general agreement with those from the full-order *** ROM obtained by the hybrid approach captures the essence of a fluid system and produces vast reduction in both degrees of freedom and computational time relative to the full-order model.

关键词： aeroelasticity aerodynamic modeling proper orthogonal decomposition observer eigensystem realization algorithm

Adaptive control for autonomous rendezvous of spacecraft on elliptical orbit

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Acta Mechanica Sinica 2009年第4期25卷 539-545页

作者： Shan Lu Shijie Xu School of Astronautics, Beihang University,100191 beijing, China School of Astronautics Beihang University Beijing China

A strategy for spacecraft autonomous rendezvous on an elliptical orbit in situation of no orbit information is developed. Lawden equation is used to describe relative motion of two spacecraft. Then an adaptive gain factor is introduced, and an adaptive control law for auton- omous rendezvous on the elliptical orbit is designed using Lyapunov approach. The relative motion is proved to be ultimately bounded under this control law, and the final relative position error can achieve the expected magnitude. Simulation results indicate that the adaptive control law can realize autonomous rendezvous on the elliptical orbit with relative state information only.

关键词： Autonomous rendezvous Elliptical orbit Lyapunov approach Adaptive control Gain factor

Key Parameters and Conceptual Configuration of Unmanned Combat Aerial Vehicle Concept

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Chinese Journal of Aeronautics 2009年第4期22卷 393-400页

作者： Wang Ganglin Faculty 513,School of Aeronautic Science and Engineering,beijing University of Aeronautics and Astronautics,beijing 100191,China Faculty 513 School of Aeronautic Science and Engineering Beijing University of Aeronautics and Astronautics Beijing 100191 China

The nature and characteristics of attack unmanned combat aerial vehicle （UCAV） are analyzed. The principles of selecting takeoff thrust-weight ratio and takeoff weight of attack UCAV are presented by analyzing the statistical data of weights for various main combat aircraft. The UCAV airborne weapons are analyzed, followed by the preliminary estimation of the payload weight. Various typical engines are analyzed and one of them is selected. Then the takeoff weight of the UCAV is determined. Based on some basic parameters and assumptions, the qualitative decomposition calculation for takeoff weight is completed. The key factors for obtaining longer endurance of aircraft with small aspect ratio configuration are found to be high lift-drag ratio and internal space. On the basis of the conclusions mentioned above, a highly blended flying-wing plus lifting body concept is proposed. According to this concept, the UCAV configuration is designed and optimized. Finally, the UCAV configuration with small aspect ratio, high lift-drag ratio, and high stealth characteristic is obtained.

关键词： aircraft design unmanned aerial vehicles unmanned combat aerial vehicles conceptual design aerodynamicsstealth

Nonlinear Aeroelastic Response of High-aspect-ratio Flexible Wings

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Chinese Journal of Aeronautics 2009年第4期22卷 355-363页

作者： Zhang Jian,Xiang Jinwu School of Aeronautic Science and Engineering,beijing University of Aeronautics and Astronautics,beijing 100191,China School of Aeronautic Science and Engineering Beijing University of Aeronautics and Astronautics Beijing 100191 China

The aeroelastic analysis of high-altitude, long-endurance （HALE） aircraft that features high-aspect-ratio flexible wings needs take into account structural geometrical nonlinearities and dynamic stall. For a generic nonlinear aeroelastic system, besides the stability boundary, the characteristics of the limit-cycle oscillation （LCO） should also be accurately predicted. In order to conduct nonlinear aeroelastic analysis of high-aspect-ratio flexible wings, a first-order, state-space model is developed by combining a geometrically exact, nonlinear anisotropic beam model with nonlinear ONERA （Edlin） dynamic stall model. The present investigations focus on the initiation and sustaining mechanism of the LCO and the effects of flight speed and drag on aeroelastic behaviors. Numerical results indicate that structural geometrical nonlinearities could lead to the LCO without stall occurring. As flight speed increases, dynamic stall becomes dominant and the LCO increasingly complicated. Drag could be negligible for LCO type, but should be considered to exactly predict the onset speed of flutter or LCO of high-aspect-ratio flexible wings.

关键词： nonlinear aeroelasticity limit-cycle oscillation Galerkin methods geometrical nonlinearities dynamic stall HALEaircraft

Application of Tandem Cascade to Design of Fan Stator with Supersonic Inflow

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Chinese Journal of Aeronautics 2010年第1期23卷 9-14页

作者： Li Qiushi,Wu Hong,Zhou Sheng School of Jet Propulsion,beijing University of Aeronautics and Astronautics,beijing 100191,China School of Jet Propulsion Beijing University of Aeronautics and Astronautics Beijing 100191 China

This article proposes a tandem cascade constructed to tackle the thorny problem of designing the high-loaded stator with a supersonic inflow and a large turning angle. The front cascade adopts a supersonic profile to reduce the shock wave intensity turning the flow into subsonic,while the rear cascade adopts a subsonic profile with a large camber offering the flow a large turning angle. It is disclosed that the losses would be minimized if the leading edge of the rear cas- cade lies close to the pressure side of the front cascade at a distance of 20% pitch in pitch-wise direction without either axial spacing or overlapping in axial direction. The 2D numerical test results show that,with the inflow Mach number of 1.25 and the turning angle of 52° ,the total pressure loss coefficient of the tandem cascade reaches 0. 106 ,and the diffusion factor 0. 745. Finally,this article has designed and simulated a high-loaded fan stage with the proposed tandem stator,which has the pressure ratio of 3.15 and the efficiency of 86.32% at the rotor tip speed of 495.32 m/s.

关键词： fan/compressor tandem cascade stator supersonic inflow

Effects of surface modification on thermal cycling lifetime of thermal barrier coatings with HVOF NiCrAlY bond coat

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Progress in Natural Science:Materials International 2012年第3期22卷 237-243页

作者： Liyong Ni, Chungen Zhou Department of Materials Science and Engineering, beijing University of Aeronautics and Astronautics, beijing 100191, China Department of Materials Science and Engineering Beijing University of Aeronautics and Astronautics Beijing 100191 China

NiCrAlY bond coat was prepared by HVOF (high-velocity oxygen fuel) spray on nickel-based superalloy. Surface treatments like grit-blasting, shot-peening and vacuum treatment methods were carried out in order to study the effects of surface modification on thermal cycling lifetime of TBCs. The surface-modified TBCs exhibited better thermal shock resistance. Failure of TBCs with the as-sprayed bond coat occurred within the top coat and at the interface between spinels and the top coat, while that of after shot-peening, grit-blasting and vacuum treatment occurred mainly within the top coat. TGO (thermally grown oxide) formed on as-sprayed bond coat was composed of a Ni(Al,Cr)2O4 spinels outer layer and a Al2O3 inner layer. But, a continuous and uniform Al2O3 formed after surface modification. Formation of the mixed oxides (spinels) on the as-sprayed bond coat accelerated the failure of TBCs.

关键词： Thermal barrier coatings NiCrAlY HVOF Thermally grown oxide (TGO)

Closed form solutions for free vibrations of rectangular Mindlin plates

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Acta Mechanica Sinica 2009年第5期25卷 689-698页

作者： Yufeng Xing Bo Liu The Solid Mechanics Research Center, Beihang University,100191 beijing, China The Solid Mechanics Research Center Beihang University Beijing China

A new two-eigenfunctions theory, using the amplitude deflection and the generalized curvature as two fundamental eigenfunctions, is proposed for the free vibration solutions of a rectangular Mindlin plate. The three classical eigenvalue differential equations of a Mindlin plate are reformulated to arrive at two new eigenvalue differential equations for the proposed theory. The closed form eigensolutions, which are solved from the two differential equations by means of the method of separation of variables are identical with those via Kirchhoff plate theory for thin plate, and can be employed to predict frequencies for any combinations of simply supported and clamped edge conditions. The free edges can also be dealt with if the other pair of opposite edges are simply supported. Some of the solutions were not available before. The frequency parameters agree closely with the available ones through pb-2 Rayleigh-Ritz method for different aspect ratios and relative thickness of plate.

关键词： Mindlin plate Free vibration Closed form solution Separation of variable

Conditions for Parallel Realizable Configurations in Synthesis of Constraint-based Flexure Mechanisms

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Chinese Journal of Mechanical Engineering 2012年第6期25卷 1086-1095页

作者： LI Shouzhong, YU Jingjun*, and ZONG Guanghua Robotics Institute, Beihang University, beijing 100191, China Robotics Institute Beihang University Beijing China

In synthesis of flexure mechanism, parallel arrangement is paid more attention due to its advantages, such as compact structure and higher stiffness. Researchers have derived many parallel flexure mechanisms, but seldom discuss which kind of flexure mechanism can be realized via fully parallel arrangement. The realizable conditions proposed in current work are complicated to engineering applications. To solve two problems on how to judge whether a flexure mechanism can be realized via fully parallel arrangement and how to realize those flexure mechanisms which cannot be realized via fully parallel arrangement, the algebraic condition is derived to judge whether a freedom space is parallel realizable after introducing the definition of parallel realizable and some propositions, and the condition is there exist 6-n independent line constraints in constraint space reciprocal to dimensional freedom space. Then the realizable constraint spaces reciprocal to freedom spaces with 1-3 dimensions are provided. As a result, not all freedom spaces are parallel realizable. For freedom spaces that are not parallel realizable, the criterion of decomposing DOF is proposed to achieve all motion patterns via parallel or hybrid arrangement, that is a high dimensional freedom space can be realized via combining several low dimensional freedom spaces which are parallel realizable. Specific decomposing strategies for 4 and 5 DOF are provided and a complete flowchart is presented to guide designing flexure mechanisms, particularly those which are not parallel realizable. As case studies, synthesis processes of two helical and 3T1R motions are provided to illustrate the proposed approach. The proposed method provides a feasible approach to realize all motion patterns.

关键词： flexure mechanism type synthesis screw theory line geometry constraint design

Adaptive neuro fuzzy inference system for classification of water quality status

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Journal of Environmental Sciences 2010年第12期22卷 1891-1896页

作者： Han Yan,Zhihong Zou,Huiwen Wang School of Economics and Management,Beihang University,beijing 100191,China School of Economics and Management Beihang University Beijing 100191 China

An adaptive neuro fuzzy inference system was used for classifying water quality status of river. It applied several physical and inorganic chemical indicators including dissolved oxygen, chemical oxygen demand, and ammonia-nitrogen. A data set （nine weeks, total 845 observations） was collected from 100 monitoring stations in all major river basins in China and used for training and validating the model. Up to 89.59% of the data could be correctly classified using this model. Such performance was more competitive when compared with artificial neural networks. It is applicable in evaluation and classification of water quality status.

关键词： adaptive neuro fuzzy inference system artificial neural networks water quality status classification