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Investigation of non-premixed flame combustion characters in GO_2/GH_2 shear coaxial injectors using non-intrusive optical diagnostics

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Science China(Physics,Mechanics & Astronomy) 2015年第12期58卷 167-179页

作者： DAI Jian YU NanJia CAI GuoBiao Beijing university of aeronautics and astronautics

Single-element combustor experiments are conducted for three shear coaxial geometry configuration injectors by using gaseous oxygen and gaseous hydrogen(GO2/GH2) as propellants. During the combustion process, several spatially and time- resolved non-intrusive optical techniques, such as OH planar laser induced fluorescence(PLIF), high speed imaging, and infrared imaging, are simultaneously employed to observe the OH radical concentration distribution, flame fluctuations, and temperature fields. The results demonstrate that the turbulent flow phenomenon of non-premixed flame exhibits a remarkable periodicity, and the mixing ratio becomes a crucial factor to influence the combustion flame length. The high speed and infrared images have a consistent temperature field trend. As for the OH-PLIF images, an intuitionistic local flame structure is revealed by single-shot instantaneous images. Furthermore, the means and standard deviations of OH radical intensity are acquired to provide statistical information regarding the flame, which may be helpful for validation of numerical simulations in future. Parameters of structure configurations, such as impinging angle and oxygen post thickness, play an important role in the reaction zone distribution. Based on a successful flame contour extraction method assembled with non-linear anisotropic diffusive filtering and variational level-set, it is possible to implement a fractal analysis to describe the fractal characteristics of the non-premixed flame contour. As a result, the flame front cannot be regarded as a fractal object. However, this turbulent process presents a self-similarity characteristic.

关键词： liquid rocket engine shear coaxial injector non-intrusive optical techniques image segmentation fractal analysis

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Design of Fault Detection Observer Based on Hyper Basis Function

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Tsinghua Science and Technology 2015年第2期20卷 200-204页

作者： Xin Wen Xingwang Zhang Yaping Zhu Faculty of Aerospace Engineering Shenyang Aerospace University College astronautics Nanjing University of Aeronautics and Astronautics College astronautics Nanjing University of Aeronautics and Astronautics

In this paper, we propose the Hyper Basis Function （HBF） neural network on the basis of Radial Basis Function （RBF） neural network. Compared with RBF, HBF neural networks have a more generalized ability with different activation functions. A decision tree algorithm is used to determine the network center. Subsequently, we design an adaptive observer based on HBF neural networks and propose a fault detection and diagnosis method based on the observer for the nonlinear modeling ability of the neural network. Finally, we apply this method to nonlinear systems. The sensitivity and stability of the observer for the failure of the nonlinear systems are proved by simulation, which is beneficial for real-time online fault detection and diagnosis.

关键词： observer fault detection hyper basis function neural networks

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Tradeoff Analysis of Factors Affecting Longitudinal Carrier Landing Performance for Small UAV Based on Backstepping Controller

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Transactions of Nanjing university of aeronautics and astronautics 2015年第1期32卷 97-109页

作者：郑峰婴龚华军甄子洋 College of astronautics Nanjing University of Aeronautics and Astronautics College of Automation Engineering Nanjing University of Aeronautics and Astronautics

Tradeoff analysis of the factors,including external environment and unmanned aerial vehicle(UAV)aerodynamic attributes,which affect longitudinal carrier landing performance,is important for small ***,small UAV longitudinal carrier landing system is established,as well as the nonlinear dynamics and kinematics model,and then the longitudinal flight control system using backstepping technology with minimum information about the aerodynamic is *** assess the landing performance,a variety of influencing factors are considered,resulting in the constraints of aerodynamic attributes of carrier *** simulation results show that the severe sea condition has the greatest influence on landing dispersion,while air wake is the primary factor on impact *** the longitudinal aerodynamic parameters,the lift curve slope is the most important factor affecting the landing performance,and increasing lift curve slope can improve the landing performance significantly.A better system performance will be achieved when the lift curve slope is larger than 2per radian.

关键词： unmanned aerial vehicle(UAV) backstepping control aerodynamic attributes landing performance

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A Sequence Image Matching Method Based on Improved High-Dimensional Combined Features

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Transactions of Nanjing university of aeronautics and astronautics 2018年第5期35卷 820-828页

作者： Leng Xuefei Gong Zhe Fu Runzhe Liu Yang College of astronautics Nanjing University of Aeronautics and Astronautics

Image matching technology is theoretically significant and practically promising in the field of autonomous *** shortcomings of existing image matching navigation technologies,the concept of high-dimensional combined feature is presented based on sequence image matching *** balance between the distribution of high-dimensional combined features and the shortcomings of the only use of geometric relations,we propose a method based on Delaunay triangulation to improve the feature,and add the regional characteristics of the features together with their geometric ***,k-nearest neighbor(KNN)algorithm is adopted to optimize searching *** results show that the matching can be realized at the rotation angle of-8°to 8°and the scale factor of 0.9 to 1.1,and when the image size is 160 pixel×160 pixel,the matching time is less than 0.5 ***,the proposed algorithm can substantially reduce computational complexity,improve the matching speed,and exhibit robustness to the rotation and scale changes.

关键词： sequence image matching navigation Delaunay triangulation high-dimensional combined feature k-nearest neighbor

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Adaptive Backstepping Control for Hypersonic Vehicles with Actuator Amplitude and Rate Saturation

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Transactions of Nanjing university of aeronautics and astronautics 2019年第2期36卷 242-252页

作者： XIANG Kai DU Yanli ZHANG Peng LIN Haibing College of astronautics Nanjing University of Aeronautics and Astronautics

This paper presents a constrained control strategy for the hypersonic vehicle with actuator amplitude,rate constraints and aerodynamic ***,a vehicle-actuator control model is derived in consideration of actuator dynamics properties ***,a nonlinear disturbance observer is designed to estimate the aerodynamic uncertainties,and then an adaptive backstepping control technique is adopted with a modified first-order-filter to eliminate the“explosion of terms”***,for handling the actuator amplitude and rate constraints,a novel auxiliary compensation system is constructed to generate quickly compensating signals to ensure tracking performance of command *** the Lyapunov stability proof,the proposed control scheme can enssure that the tracking errors converge to an arbitrarily small neighborhood around zero when the actuator constraints and aerodynamic uncertainties ***,numerical simulations are implemented to illustrate the effectiveness of the proposed control method.

关键词： hypersonic vehicle amplitude and rate saturation adaptive backstepping aerodynamic uncertainty

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Accuracy Analysis on Bundle Adjustment of Remote Sensing Images Based on Dual Quaternion

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Transactions of Nanjing university of aeronautics and astronautics 2015年第5期32卷 523-529页

作者：盛庆红费利佳柳建锋陈姝文王惠南 College of astronautics Nanjing University of Aeronautics and Astronautics

A bundle adjustment method of remote sensing images based on dual quaternion is presented,which conducted the uniform disposal corresponding location and attitude of sequence images by the dual *** constraint relationship of image itself and sequence images is constructed to compensate the systematic *** feasibility of this method used in bundle adjustment is theoretically tested by the analysis of the structural characteristics of error equation and normal equation based on dual *** distributions of control points and stepwise regression analysis are introduced into the experiment for RC30 *** results show that the adjustment accuracy can achieve 0.2min plane and 1min *** a result,this method provides a new technique for geometric location problem of remote sensing images.

关键词： photogrammetry bundle adjustment geometric correction dual quaternion geometric imaging model

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Experimental and numerical analyses of electrohydrodynamic force according to air pressure

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Chinese Physics B 2023年第6期32卷 378-383页

作者：全荣辉王博姚韵佳 Nanjing university of aeronautics and astronautics College of Astronautics College of AstronauticsNanjing 211106China

Electrohydrodynamic(EHD) force produced by corona discharge is considered as a new thrust for solar-powered aircraft and stratosphere balloons in near space. However, its performance at low air pressures remains to be *** experiment of measuring the EHD force at 0.02 atm–1.0 atm(1 atm = 1.01325×10^(5)Pa) is carried out with the wireto-cylinder geometric structure. The ion distribution is analyzed by using the drift-diffusion model with two-dimensional numerical simulation. The experimental result shows that the EHD force is not linearly related to the corona discharge current at low air pressures. Numerical simulation finds that the proportion of ions in the counter-direction electric field increases from approximately 0.36% to 30% when the pressure drops from 1.0 atm to 0.2 atm. As a result, the EHD force with a constant power supply drops faster than the previous theoretical prediction in the ground experiment, suggesting that the consideration of counter-direction EHD force is necessary to improve the ionic wind propulsion efficiency in near-space applications.

关键词： electrohydrodynamic force ionic wind corona discharge

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Improved semi-analytical computation of center manifolds near collinear libration points

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Research in Astronomy and Astrophysics 2018年第11期18卷 75-88页

作者： Han-Qing Zhang Shuang Li College of astronautics Nanjing University of Aeronautics and Astronautics Advanced Space Technology Laboratory Nanjing University of Aeronautics and Astronautics

In the framework of the circular restricted three-body problem, the center manifolds associated with collinear libration points contain all the bounded orbits moving around these points. Semianalytical computation of the center manifolds and the associated canonical transformation are valuable tools for exploring the design space of libration point missions. This paper deals with the refinement of reduction to the center manifold procedure. In order to reduce the amount of calculation needed and avoid repetitive computation of the Poisson bracket, a modified method is presented. By using a polynomial optimization technique, the coordinate transformation is conducted more efficiently. In addition, an alternative way to do the canonical coordinate transformation is discussed, which complements the classical approach. Numerical simulation confirms that more accurate and efficient numerical exploration of the center manifold is made possible by using the refined method.

关键词： celestial mechanics circular restricted three-body problem center manifold collinear libration point

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A Sequential Adaptive Method for Enhancing DOA Tracking Performance

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Transactions of Nanjing university of aeronautics and astronautics 2016年第6期33卷 -页

作者： Youssef Fayad Wang Caiyun Cao Qunsheng College of Electronic and Information Engineering Nanjing University of Aeronautics and Astronautics College of astronautics Nanjing University of Aeronautics and Astronautics

A sequential processing is presented aiming at optimizing the direction of arrival(DOA)tracking ***,current positions and Doppler frequency are estimated and a mathematical model is derived in order to clarify the effect of Doppler frequency on the *** Doppler effect is employed within subspace concept in order to refine the estimation of the target ***,a renewed weight factor that depends on target maneuver is employed in order to realize more accurate association and smoothing *** results show that the presented method has high accuracy in DOA tracking.

关键词： tracking maneuver direction of arrival(DOA) Doppler effect

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Singularity analysis for single gimbal control moment gyroscope system using space expansion method

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Chinese Journal of aeronautics 2018年第4期31卷 782-794页

作者： Yunhua WU Feng HAN Bing HUA Zhiming CHEN Feng YU School of astronautics Nanjing University of Aeronautics and Astronautics School of astronautics Harbin Institute of Technology

Control Moment Gyroscope（CMG） is an effective candidate for agile satellites and large spacecraft attitude control because of its powerful torque amplification capability. The most serious situation, however, in using CMG is the inherent geometric singularity problem, where there＇s no torque output along a particular direction. Space expansion method has been proposed in this work for the singularity analysis. Based on inverse mapping transformation, an expanded Jacobian matrix which is a full rank square matrix is obtained. The singular angle sets of the 3-parallel cluster and pyramid cluster are distinguished using space expansion method. An effective hybrid steering strategy, able to deal with the elliptic singularity, is further proposed. Simulation results demonstrate the excellent performance of the proposed steering logic compared to the generalized singular robust logic and pseudo inverse logic in terms of energy consumption and torque error.

关键词： Agile spacecraft Control moment gyro Singularity analysis Space expansion method Steering strategy

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