检索结果-南通市图书馆

Journal of Wuhan University of Technology(Materials Science) 2014年第5期29卷 1036-1038页

作者：龙文元 YAO Junping FU Zhengyi college of aeronautical Manufacuring Engineering Nanchang Hangkong University State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of Technology

Dense Nb/Nb5Si3 composites were fabricated via spark plasma sintering technology using Nb, Si, and Al elemental powders as raw materials. The microstructttres of the synthesised composites were analyzed through scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. The results show that the composites consisted of residual Nb particle phase and Nb5Si3 phase. The microstructure of the Nb/ Nb5Si3 in situ composites was evidently affected by Al addition, which prompted the formation of the Al3Nb10Si3 phase. In addition, the Rockwell hardness of the composites decreased with the increase in AI additions. The Rockwell hardness of Nb-20Si is 60HRC, which decreased to approximately 52.7 HRC when the Al content increased to 15 at%. The oxidation resistance of the Nb/NbsSi3 in situ composites significantly improved with the increase in Al addition.

关键词： spark plasma sintering Nb/Nb5Si3 composites oxidation resistance microstructure

Constrained docking control for shipborne UAV SideArm recovery

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2024年第5期37卷 39-59页

作者： Zikang SU Zhuolin XING Xuebing LI Chuntao LI Xinwei WANG Honglun WANG college of Automation Engineering Nanjing University of Aeronautics and AstronauticsNanjing 211106China School of Engineering and Materials Science Queen Mary University of LondonLondon E14NSUK School of Automation Science and Electrical Engineering Beihang UniversityBeijing 100191China

In this work,we sought to investigate constrained docking control during shipborne SideArm recovery of an Unmanned Aerial Vehicle(UAV)under preassigned safe docking constraints,rough ocean environments,and different initial *** aim was to solve the UAV tracking-lag problem that manifests when attempting to dock with a rapidly moving SideArm and to improve the accuracy and rapidity of ***,together with the formulations of the shipborne SideArm system and environmental airflows,the affine nonlinear dynamics of the hook was established to reduce tracking ***,echo state network approximators with good approximation capacity and low computational consumption were designed to accurately approximate the UAV’s unknown nonlinear *** feedforward compensation provided by these approximators,a nonlinear-mapping-based constrained docking control law was developed for shipborne SideArm recovery of *** approach to controlling the docking trajectory and the forward docking speed of the UAV can achieve rapid and exact docking with a moving SideArm,without violating the preassigned safe docking-constraint *** under different docking scenarios were used to validate the effectiveness and advantages of the proposed docking-control algorithm.

关键词： SideArm recovery Unmanned aerial vehicle Docking control Nonlinear mapping Echo state network

Nonlinear characteristic investigation of magnetorheological damper-rotor system with local nonlinearity

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2023年第2期36卷 111-126页

作者： Jun WANG Yunfei LIU Zhaoye QIN Liang MA Fulei CHU State Key Laboratory of Tribology Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China college of aeronautical Engineering Civil Aviation University of ChinaTianjin 300300China

Magnetorheological(MR)dampers show superior performance in reducing rotor vibration,but their high nonlinearity will cause nonsynchronous response,resulting in fatigue and instability of ***,we are devoted to the investigation of the nonlinear characteristics of MR damper mounted on a flexible ***,Reynolds equations with bilinear constitutive equations of MR fluid are employed to derive nonlinear oil film ***,the Finite Element(FE)model of rotor system is developed,where the local nonlinear support forces produced by MR damper and its coupling effects with the rotor are considered.A hybrid numerical method is proposed to solve the nonlinear FE motion equations of the MR damper-rotor *** validate the proposed model,a rotor test bench with two dual-coil MR dampers is constructed,upon which experimental studies on the dynamic characteristics of MR damper-rotor system are carried *** effects of different system parameters,including rotational speed,excitation current and amount of unbalance,on nonlinear dynamic behaviors of MR damper-rotor system are *** results show that the system may appear chaos,jumping,and other complex nonlinear phenomena,and the level of the nonlinearity can be effectively alleviated by applying suitable excitation current and oil supply pressure.

关键词： Hybrid numerical method Local nonlinearity Magnetorheological damper Nonlinear vibration Rotor system

Quasinormal modes of charged black holes in Einstein-Maxwell-Weyl gravity

在线全文

学校读者我要写书评

暂无评论

Chinese Physics C 2020年第5期44卷 124-132页

作者： De-Cheng Zou Chao Wu Ming Zhang Ruihong Yue Center for Gravitation and Cosmology and college of Physical Science and Technology Yangzhou UniversityYangzhou 225009China Faculty of Science Xi’an Aeronautical UniversityXi’an 710077 China

We study quasinormal modes(QNMs)of charged black holes in the Einstein-Maxwell-Weyl(EMW)gravity by adopting the test scalar field *** find that the imaginary part of QNM frequencies is consistently negative for different angular parameters l,indicating that these modes always decay and are therefore *** do not observe a linear relationship between the QNM frequencyωand parameter p for these black holes,as their charge Q causes a nonlinear *** evaluate the massive scalar field perturbation in charged black holes and find that random long lived modes(i.e.,quasiresonances)could exist in this spectrum.

关键词： quasinormal modes black hole stability

Agent-based Simulation Systems for Emergency Management

在线全文

学校读者我要写书评

暂无评论

International Journal of Automation and computing 2016年第2期13卷 89-98页

作者： Zhi-Chao Song Yuan-Zheng Ge Hong Duan Xiao-Gang Qiu college of Information System and Management National University of Defense Technology Hunan 410073 China aeronautical University of China People Liberation Airforce Jilin 130012 China

Emergencies, which are very difficult to be forecasted, would always bring about huge harm to people. Therefore, to find ways to reduce such devastating effects, researches on emergency management have turned to be paramount. Nowadays, the rapid development of computer technology has supplied a new and effective idea for the researches of emergency management, namely that the researches can be done in computers by performing simulation experiments according to the artificial societies, computational experiments, parallel execution （ACP） approach. Guided by this approach, this paper has proposed one agent-based prototype simulation system to research emergency management. Firstly, structure of the simulation system oriented to emergency management was analyzed and designed. Then a simulation system oriented to public health emergency management was constructed to study the transmission of infectious diseases. Finally, several experiments were carried out based on the system, with several significant conclusions having also been obtained.

关键词： Agent-based simulation emergency management artificial societies computational experiments parallel execution (ACP) simulation system public health transmission of infectious diseases.

Registration Method for CT-MR Image Based on Mutual Information

在线全文

学校读者我要写书评

暂无评论

Transactions of Tianjin University 2007年第3期13卷 226-230页

作者：张红颖张加万孙济洲 School of Computer Science and Technology Tianjin University college of aeronautical Automation Civil Aviation University of China Tianjin 300300 China

Medical image registration is important in many medical applications. Registration method based on maximization of mutual information of voxel intensities is one of the most popular methods for 3-D multi-modality medical image registration. Generally, the optimization process is easily trapped in local maximum, resulting in wrong registration results. In order to find the correct optimum, a new multi-resolution approach for brain image registration based on normalized mutual information is proposed. In this method, to eliminate the effect of local optima, multi-scale wavelet transformation is adopted to extract the image edge features. Then the feature images are registered, and the result at this level is taken as the initial estimate for the registration of the original images. Three-dimensional volumes are used to test the algorithm. Experimental results show that the registration strategy proposed is a robust and efficient method which can reach sub-voxel accuracy and improve the optimization speed.

关键词： image registration edge detection mutual information wavelet transformation

Metal magnetic memory signals from surface of low-carbon steel and low-carbon alloyed steel

在线全文

学校读者我要写书评

暂无评论

Journal of Central South University of Technology 2007年第1期14卷 24-27页

作者：董丽虹徐滨士董世运叶明慧陈群志王丹尹大伟 National Key Laboratory for Remanufacturing Armored Force Engineering Institute Department of Basic Course Ordnance Engineering College Beijing aeronautical Technology Research Center

In order to investigate the regularity of metal magnetic signals of ferromagnetic materials under the effect of applied load, the static tensile test of Q235 steel and 18CrNiWA steel plate specimens were conducted and metal magnetic memory signals of specimens were measured during the test process. The influencing factors of metal magnetic memory signals and the relationship between axial applied load and signals were analyzed. The fracture and microstructure of the specimens were observed. The results show that the magnetic signals corresponding to the measured points change linearly approximately with increasing axial load. The microstructure of Q235 steel is ferrite and perlite, whereas that of 18CrNiWA steel is bainite and low-carbon martensite. The fracture of these two kinds of specimens is ductile rupture; carbon content of specimen materials and dislocation glide give much contribution to the characteristics of magnetic curves.

关键词： metal magnetic memory low-carbon steel low-carbon alloyed steel applied load magnetic signals curve fracture microstructure

Phase transition and quasinormal modes for charged black holes in 4D Einstein-Gauss-Bonnet gravity

在线全文

学校读者我要写书评

暂无评论

Chinese Physics C 2021年第4期45卷 462-469页

作者： Ming Zhang Chao-Ming Zhang De-Cheng Zou Rui-Hong Yue Faculty of Science Xi'an Aeronautical UniversityXi'an 710077China Center for Gravitation and Cosmology College of Physical Science and TechnologyYangzhou UniversityY angzhou 225009China

In four-dimensional Einstein-Gauss-Bonnet(EGB)gravity,we consider the thermodynamic and phase transitions of(charged)AdS black *** the negative GB coefficientα2√-α.For arbitraryα>0,the system always leads to a van der Waals phase *** then study the quasinormal modes(QNMs)of massless scalar perturbations to probe the van der Waals-like phase transition between small and large black holes(SBH/LBH)for(charged)AdS black *** find that the signature of this SBH/LBH phase transition in the isobaric process can be detected since the slopes of the QNM frequencies change dramatically in small and large black holes near the critical *** obtained results further support that QNMs can be a dynamic probe of ther-modynamic properties in black holes.

关键词： Gauss-Bonnet quasinormal modes phase transition black hole physics

First-principle investigation of bismuth segregation atΣ5 (012) grain-boundaries in nickel

在线全文

学校读者我要写书评

暂无评论

中国有色金属学会会刊：英文版 2006年第B2期16卷 813-819页

作者：陈律彭平庄厚龙周惦武 Department of aeronautical Equip EngineeringChangsha aeronautical Vocational and Technical college Changsha 410124China School of Materials Science and Engineering Hunan UniversityChangsha 410082China School of Materials Science and EngineeringHunan University Changsha 410082China School of Materials Science and Engineering Hunan University Changsha 410082China

As an aid in establishing an understanding on the electronic level, the influence of bismuth on the cohesion of nickelΣ5 (012) grain boundary was determined using the plane wave pseudopotential (PWPP) method with the generalized gradient approximation. Based on the Rice-Wang model, the total energy calculations show that Bi behaves as an embrittler of the Ni grain-boundary, which predicts the experimentally known behavior. The total charge density, and difference charge density of the grain boundary also demonstrats that the Bi atom forms weaker bonds with neighboring Ni atoms in the grain boundary region. Total density of states (DOS) show that there exists significant covalent bonding for the grain boundary system with Bi segregated which help to embrittle the grain boundary and the change that Ni local d-DOS is narrowed due to segregation of Bi is also beneficial for the decohesion.

关键词：铋偏析系数镍晶界表面能材料性质

New actuator disk model for propeller-aircraft computation

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2016年第8期59卷 1201-1207页

作者： JIANG Zhe CHEN YaoSong AN YiRan WANG QiFeng Department of Mechanics and Engineering Science College of Engineering Peking University Beijing 100871 China Beijing aeronautical Science & Technology Research Institute of Commercial Aircraft of China Ltd Beijing 102211 China

There is a growing interest in propellers for transport aircraft as well as regional airliners from the viewpoint of energy saving. An important consideration for utilizing a propeller propulsion system on aircraft is the aerodynamic interaction between the propeller slipstream and other aerodynamic surfaces. It is therefore necessary to use a simplified but relatively accurate tool for propeller modeling, with the widely used actuator disk model. The advantage of this model is that it is easy to use and inex- pensive in terms of computation time required. In addition, it also produces acceptable results. In this study, a new regionalized actuator disk model was utilized in the analysis of propeller slipstream interference effects on a real four-propeller aircraft. The results are compared with the cases of inactive actuator disks, which shows that the propeller slipstream causes an increase in the lift and drag coefficients. An evident yawing effect caused by the rotating slipstream was noticed, which should be taken into account in the design phase. The regionalized actuator disk model is evaluated as a fast and relatively accurate model for propeller preliminary design.

关键词： four-propeller aircraft propeller slipstream regionalized actuator disk model