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Experimental investigation of influence of strake wings on self-induced roll motion at high angles of attack

Chinese Journal of Aeronautics 2016年第6期29卷 1591-1601页

作者： Geng Xi shi zhiwei Cheng Keming College of Aerospace Engineering Nanjing University of Aeronautics and Astronautics

The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the selfinduced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at a = 60°. The free-to-roll results show that the model with whole strake wings(baseline), the model assembled with three strake wings(Case A)and the model assembled with two opposite strake wings(Case C) experience the spinning, while the model assembled with two adjacent strake wings(Case B), the model assembled with one strake wing(Case D) and the model with no strake wing(Case E) trim or slightly vibrate at a certain "×"rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at a = 60°.

关键词： Cruciform fins High angle of attack PIV Roll motion Strake wing

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Flight trajectory optimization of sun-tracking solar aircraft under the constraint of mission region

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Chinese Journal of Aeronautics 2021年第11期34卷 140-153页

作者： Mingjian WU zhiwei shi Tianhang XIAO Haisong ANG School of Mechanical Engineering Nanjing University of Science and TechnologyNanjing 210094China School of Aerospace Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016China

The optimal yawing angle of sun-tracking solar aircraft is tightly related to the solar azimuth angle,which results in a large arc flight path to dynamically track the sun ***,the limited detection range of payload usually requires solar aircraft to loiter over areas of interest for persistent surveillance *** large arc sun-tracking flight may cause the target area on the ground to be outside the maximum coverage area of *** present study therefore develops an optimal flight control approach for planning the flight path of sun-tracking solar aircraft within a mission *** proposed method enables sun-tracking solar aircraft to maintain the optimal yawing angle most of the time during daylight flight,except when the aircraft reverses its direction by turning *** a circular region with a mission radius of 50km,the optimal flight trajectory and controls of an example K-shaped sun-tracking solar aircraft are investigated *** demonstrate the effectiveness of the proposed approach to optimize the flight path of the sun-tracking aircraft under the given circular region while maximizing the battery input ***,the effects of varying the mission radius on energy performance are explored *** has been proved that both net energy and energy balance remain nearly constant as the radius constraint varies,which enables the solar aircraft to achieve perpetual flight at almost the same latitude as the large arc *** method and results presented in this paper can provide reference for the persistent operation of sun-tracking solar aircraft within specific mission areas.

关键词： Energy performance Mission region Optimal yawing angle Perpetual operation Sun-tracking solar aircraft Trajectory optimization

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Synthesis of polycrystalline γ-AlON powders by novel wet chemical processing

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Science China(Technological Sciences) 2012年第12期55卷 3405-3410页

作者： LEI JingXuan MA FeiZhong shi Ying XIE JianJun HU Wei shi zhiwei Department of Electronics and Information Materials School of Material Science and EngineeringShanghai UniversityShanghai 200072China Ceramic Department Shanghai FRP Research Institute Co.Ltd.Shanghai 201404China

The synthesis of polycrystalline aluminum oxynitride （AlON） powders was investigated by the carbothermal reduction and ni- tridation （CRN） of amorphous precursor obtained by wet chemical processing. Co-precipitation processing was employed to achieve amorphous precursor from AI（NO3）3 solution dispersed by nanosized carbon particles, which was composed of AI（OH）3 and C particles homogeneously. The effects of the content of carbon black, pH value, and calcination temperature on formation of A1ON phase were investigated by means of XRD, SEM and TEM, respectively. It was found that single phase AION powder could be synthesized when the resultant precursors were calcined at 1750℃ for 2 hours under flowing N2. Un- der optimal additional content of C （5.6wt%）, the resultant A1ON powders exhibited the primary particle size of about 1-3 μm with a specific surface area of 3.2 m2/g, which were superior to that of carbothermal reduction of immediate mixture of γ-A1203/C powders.

关键词： aluminum oxynitride (AION) co-precipitation processing the content of carbon black pH value calcination temperature

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Molecular diffusion in ternary poly(vinyl alcohol)solutions

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Frontiers of Chemical Science and Engineering 2022年第6期16卷 1003-1016页

作者： Katarzyna Majerczak Ophelie Squillace zhiwei shi Zhanping Zhang Zhenyu J.Zhang School of Chemical Engineering University of BirminghamBirmingham B152TTUK The Procter and Gamble Company CincinnatiOH 45040USA

The diffusion kinetics of a molecular probe-rhodamine B-in ternary aqueous solutions containing poly(vinyl alcohol),glycerol,and surfactants was investigated using fluorescence correlation spectroscopy and dynamic light *** show that the diffusion characteristics of rhodamine B in such complex systems is determined by a synergistic effect of molecular crowding and intermolecular interactions between chemical *** presence of glycerol has no noticeable impact on rhodamine B diffusion at low concentration,but significantly slows down the diffiision of rhodamine B above 3.9%(w/v)due to a dominating steric inhibition ***,introducing surfactants(cationic/nonionic/anionic)to the system results in a decreased diffusion coefficient of the molecular *** solutions containing nonionic surfactant,this can be explained by an increased crowding *** ternary poly(vinyl alcohol)solutions containing cationic or anionic surfactant,surfactant-polymer and surfactant-rhodamine B interactions alongside the crowding effect of the molecules slow down the overall diffiisivity of rhodamine *** results advance our insight of molecular migration in a broad range of industrial complex formulations that incorporate multiple compounds,and highlight the importance of selecting the appropriate additives and surfactants in formulated products.

关键词： fluorescence correlation spectroscopy poly(vinyl alcohol) anomalous diffusion crowding effects dynamic light scattering binding effects rhodamine B

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Backdoor Attacks on Image Classification Models in Deep Neural Networks

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Chinese Journal of Electronics 2022年第2期31卷 199-212页

作者： ZHANG Quanxin MA Wencong WANG Yajie ZHANG Yaoyuan shi zhiwei LI Yuanzhang Beijing Institute of Technology China Information Technology Security Evaluation Center

Deep neural network(DNN) is applied widely in many applications and achieves state-of-the-art performance. However, DNN lacks transparency and interpretability for users in structure. Attackers can use this feature to embed trojan horses in the DNN structure,such as inserting a backdoor into the DNN, so that DNN can learn both the normal main task and additional malicious tasks at the same time. Besides, DNN relies on data set for training. Attackers can tamper with training data to interfere with DNN training process, such as attaching a trigger on input data. Because of defects in DNN structure and data, the backdoor attack can be a serious threat to the security of DNN. The DNN attacked by backdoor performs well on benign inputs while it outputs an attacker-specified label on trigger attached inputs. Backdoor attack can be conducted in almost every stage of the machine learning pipeline. Although there are a few researches in the backdoor attack on image classification, a systematic review is still rare in this field. This paper is a comprehensive review of backdoor attacks. According to whether attackers have access to the training data, we divide various backdoor attacks into two types: poisoning-based attacks and non-poisoning-based attacks. We go through the details of each work in the timeline, discussing its contribution and deficiencies. We propose a detailed mathematical backdoor model to summary all kinds of backdoor attacks. In the end, we provide some insights about future studies.

关键词： nonpoisoning-based attacks image classification mathematical backdoor model machine learning pipeline backdoor attack deep learning (artificial intelligence) DNN training process image classification models trojan horses deep neural network invasive software computer network security

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WCM-WTrA: A Cross-Project Defect Prediction Method Based on Feature Selection and Distance-Weight Transfer Learning

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Chinese Journal of Electronics 2022年第2期31卷 354-366页

作者： LEI Tianwei XUE Jingfeng WANG Yong NIU Zequn shi zhiwei ZHANG Yu School of Computer Science and Technology Beijing Institute of Technology China Information Technology Security Evaluation Center School of Electrical and Information Engineering Beijing University of Civil Engineering and Architecture

Cross-project defect prediction is a hot topic in the field of defect prediction. How to reduce the difference between projects and make the model have better accuracy is the core problem. This paper starts from two perspectives: feature selection and distance-weight instance transfer. We reduce the differences between projects from the perspective of feature engineering and introduce the transfer learning technology to construct a cross-project defect prediction model WCM-WTrA and multi-source model Multi-WCM-WTrA. We have tested on AEEEM and ReLink datasets, and the results show that our method has an average improvement of 23%compared with TCA+ algorithm on AEEEM datasets,and an average improvement of 5% on ReLink datasets.

关键词： feature engineering cross-project defect prediction software defect prediction project management feature selection learning (artificial intelligence) software maintenance WCM-WTrA distance-weight transfer learning software quality distance-weight instance transfer multisource model MultiWCM-WTrA

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Virtual flight test techniques to predict a blended-wing-body aircraft in-flight departure characteristics

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Chinese Journal of Aeronautics 2022年第1期35卷 215-225页

作者： Junquan FU zhiwei shi Zheng GONG Mark HLOWENBERG Dawei WU Lijun PAN Nanjing University of Aeronautics and Astronautics Nanjing 210016China University of Bristol Bristol BS81TRUnited Kingdom CO MAC Shanghai Aircraft Design and Research Institute Shanghai 201210China

As one of the promising configurations of the next generation of commercial aircraft,research on departure characteristics of the Blended-Wing-Body(BWB)is of great signification to safe flight limits.A three-degree-of-freedom(3-DOF)virtual flight test in a wind tunnel has been implemented for a candidate configuration to predict the departure *** support mechanism,the test model and the control law of the virtual flight test are *** order to show the relationship between virtual flight test and actual flight test,the similarity criterion is also *** open loop,the model has mild oscillations in the longitudinal and lateral directions,which are stable in *** effect of flight control has been verified in virtual flight and actual subscale flight *** analysis of system identification results indicate that the model has a good response to the excitation signal,and the response is in reasonable agreement with the flight ***,the virtual flight departure test results are compared with the flight *** shows that there is a good correspondence between the angle of attack and the elevator deflection at *** gives promising evidence of the practicability of virtual flight testing to predict departure of a BWB.

关键词： Blended-wing-body Departure Flight test Similarity criterion Virtual flight test

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Vortex dynamics over an airfoil controlled by a nanosecond pulse discharge plasma actuator at low wind speed

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Plasma Science and Technology 2019年第12期21卷 85-96页

作者： Hai DU LeiWANG Wenjie KONG zhiwei shi Keming CHENG Zheng LI School of Energy and Power Engineering Xihua UniversityChengdu 610039People's Republic of China Key Laboratory of Fluid and Power Machinery Ministry of EducationXihua UniversityChengdu 610039People's Republic of China College of Aerospace Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016People's Republic of China

The vortex dynamics of flow over an airfoil controlled by a nanosecond pulse dielectric-barrierdischarge(NS-DBD) actuator is studied at a Reynolds number of 1?×?10~5 through wind tunnel experiments and numerical simulation. The numerical method is validated through comparison of the simulated and measured results regarding the effect of the discharge of an NS-DBD actuator placed on a flat plate. The simulated results show that vorticity is mainly induced by the baroclinic torque after plasma discharge, i.e. the term(■) in the equation of vorticity evolution. Both experimental and simulated results demonstrate that after the discharge of the NS-DBD actuator a series of vortices are developed in the shear layer and pull the high-moment fluid down to the wall, enhancing the mixing of internal and external flows.

关键词： plasma actuator flow control Joule heating vortex

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Analysis of flow separation control using nanosecond-pulse discharge plasma actuators on a flying wing

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Plasma Science and Technology 2018年第11期20卷 116-125页

作者： Zheng LI zhiwei shi Hai DU Qijie SUN Chenyao WEI Xi GENG College of Aerospace Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016 People＇s Republic of China The Key Laboratory of Fluid and Power Machinery Xihua UniversityChengdu 610039People＇s Republic of China

Dielectric barrier discharge （DBD） plasma is one of most promising flow control method for its several advantages. The present work investigates the control authority of nanosecond pulse DBD plasma actuators on a flying wing model＇s aerodynamic characteristics. The aerodynamic forces and moments are studied by means of experiment and numerical simulation. The numerical simulation results are in good agreement with experiment results. Both results indicate that the NS-DBD plasma actuators have negligible effect on aerodynamic forces and moment at the angles of attack smaller than 16-. However, significant changes can be achieved with actuation when the model＇s angle of attack is larger than 16° where the flow separation occurs. The spatial flow field structure results from numerical simulation suggest that the volumetric heat produced by NS-DBD plasma actuator changes the local temperature and density and induces several vortex structures, which strengthen the mixing of the shear layer with the main flow and delay separation or even reattach the separated flow.

关键词： nanosecond dielectric barrier discharge flying wing aircraft flow separation control

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A computational model for feature binding

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Science China(Life Sciences) 2008年第5期51卷 470-478页

作者： shi zhiwei1,2, shi ZhongZhi1, LIU Xi1,2 & shi ZhiPing1 1 Key Laboratory of Intelligent Information Processing, Institute of Computing Technology, Chinese Academy of Sciences, Beijing 100190, China 2 Graduate University of Chinese Academy of Sciences, Beijing 100049, China Key Laboratory of Intelligent Information Processing Institute of Computing Technology Chinese Academy of Sciences Beijing China Graduate University of Chinese Academy of Sciences Beijing China

The "Binding Problem" is an important problem across many disciplines, including psychology, neuroscience, computational modeling, and even philosophy. In this work, we proposed a novel computational model, Bayesian Linking Field Model, for feature binding in visual perception, by combining the idea of noisy neuron model, Bayesian method, Linking Field Network and competitive mechanism. Simulation Experiments demonstrated that our model perfectly fulfilled the task of feature binding in visual perception and provided us some enlightening idea for future research.

关键词： Binding Problem computational model Bayesian Linking Field Model

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