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Influence of aircraft surface distribution on electromagnetic scattering characteristics

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Chinese Journal of Aeronautics 2017年第2期30卷 759-765页

作者： Liu dawei Huang Jun Song Lei Ji Jinzu School of Aeronautic Science and Engineering Beihang University Beijing 100083 China

In this paper,two typical stealth aircraft concepts（wing fuselage blended and flyingwing） were *** three gradually changed surface distribution models with the same planform for each concept were *** on the multilevel fast multipole algorithm（MLFMA）,the vertical polarization transmitting/vertical polarization receiving（VV） and horizontal polarization transmitting/horizontal polarization receiving（HH） radar cross section（RCS） characteristics were simulated with five frequencies between 0.1 and 1.0 *** influences and mechanisms of aircraft surface distribution on electromagnetic scattering characteristics were *** results show that for the wing fuselage blended concept,the W RCS of this frequency range is higher than the HH RCS in most cases,while it is just the opposite for the flying-wing *** for the two aircraft concepts,the RCS levels of HH and W both decrease with the frequency increasing,but the HH RCS has a faster downward *** surface distribution has little influence on HH RCS *** the contrary,it has a significant impact on W RCS characteristics,and the amplitude of the VV RCS increases with the surface thickness.

关键词： Aircraft concept Electromagnetic scattering characteristic Horizontal polarization MLFMA Stealth Surface distribution Vertical polarization

Design of an Automatic Autonomous Mini Prone-cone Microsatellite Docking Mechanism

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Chinese Journal of Mechanical Engineering 2010年第3期23卷 353-360页

作者： LAI Yinan DAI Ye TIAN Hao ZHANG dawei School of Mechanical and Power Engineering Harbin University of Science and Technology Harbin 150080 China Department of Astronautics andMechanics Harbin Institute of Technology Harbin 150001 China

The capability of docking, refueling, repairing, and updating microsatellites using automatic autonomous vehicles will be of significance critical value for design and operation of several space systems in the near feature. Automatic docking capability was successfully tested by many institutions such as National Space Development Agency in Japan, European Space Agency, National Aeronautics and Space Administration in USA, etc. However, there is still much more space for improvement of degree of automation during the process of docking with large deviations of the initial attitude. A novel automatic autonomous probe-cone docking mechanism used for microsatellite docking is proposed. This docking mechanism is designed according to the design indices such as miniaturization, degree of automation and automatic capture capability within large deviation of the initial attitude. On the basis of the virtual work principle, the dynamics modeling of the docking process is presented. The position of the contact point is then analyzed. Comprehensive system level simulation is conducted in the 13 kinds of typical operating conditions with the initial deviations. Capture performance is analyzed. The simulation results show that the docking mechanism can be smoothly captured within 2 s in all cases of large attitude deviation between the active and passive spacecrafts. A virtual prototype model of the docking mechanism is established through ADAMS for further verifying the correctness of the buffer parameter model and the autonomous docking capability. A laboratory platform is designed for on-the-ground experimental validation of the property of mini probe-cone docking mechanism. Repeated docking tests prove the proposed design of the mini probe-cone docking mechanism system for its high reliability, and automatic capture capability within large attitude range. The kinetic model of the docking capture process and the mechanism structure could provide some references for similar m

关键词： docking mechanism numerical simulation virtual prototype capture buffer parameter

Supervised Feature Learning for Offline Writer Identification Using VLAD and Double Power Normalization

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Computers, Materials & Continua 2023年第7期76卷 279-293页

作者： dawei Liang Meng Wu Yan Hu College of Computer Nanjing University of Posts and TelecommunicationsNanjing210023China Department of Computer Information and Cyber Security Jiangsu Police InstituteNanjing210031China JinCheng College Nanjing University of Aeronautics and AstronauticsNanjing211156China Engineering Research Center of Electronic Data Forensics Analysis Nanjing210031Jiangsu ProvinceChina

As an indispensable part of identity authentication,offline writer identification plays a notable role in biology,forensics,and historical document ***,identifying handwriting efficiently,stably,and quickly is still challenging due to the method of extracting and processing handwriting *** this paper,we propose an efficient system to identify writers through handwritten images,which integrates local and global features from similar handwritten *** local features are modeled by effective aggregate processing,and global features are extracted through transfer ***,the proposed system employs a pre-trained Residual Network to mine the relationship between large image sets and specific handwritten images,while the vector of locally aggregated descriptors with double power normalization is employed in aggregating local and global ***,handwritten image segmentation,preprocessing,enhancement,optimization of neural network architecture,and normalization for local and global features are exploited,significantly improving system *** proposed system is evaluated on Computer Vision Lab(CVL)datasets and the International Conference on Document Analysis and Recognition(ICDAR)2013 *** results show that it represents good generalizability and achieves state-of-the-art ***,the system performs better when training complete handwriting patches with the normalization *** experimental result indicates that it’s significant to segment handwriting reasonably while dealing with handwriting overlap,which reduces visual burstiness.

关键词： Writer identification power normalization vector of locally aggregated descriptors feature extraction

STUDY ON THE CUTTING TEMPERATURE IN GEAR HOBBING

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Chinese Journal of Mechanical Engineering 1999年第2期12卷 63-68页

作者： Liu, dawei Bai, Zhimin Guo, Hongqi Qingdao Univ China

According to work tool thermocouple principle,the equipment for measuring hobbing temperature is *** changing character of cutting temperature in gear hobbing,the relation between cutting conditions and hobbing temperature,and the influence of cutting conditions on hobbing temperature are discussed by means of *** these have provided the reference standards for the equitably selecting cutting conditions and geometrical parameter of hob,prolonging the life of gear hobs,and predicting processes of gear hobbing.

关键词： Gear hobbing Cutting temperature Cutting conditions

Application of semi-analytical finite element method to analyze the bearing capacity of asphalt pavements under moving loads

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Frontiers of Structural and Civil Engineering 2018年第2期12卷 215-221页

作者： Pengfei LIU dawei WANG Frederic OTTO Markus OESER Institute of Highway Engineering RWTH Aachen University Aachen D52074 Germany

To facilitate long term infrastructure asset management systems, it is necessary to determine the bearing capacity of pavements. Currently it is common to conduct such measurements in a stationary manner, however the evaluation with stationary loading does not correspond to reality a tendency towards continuous and high speed measurements in recent years can be observed. The computational program SAFEM was developed with the objective of evaluating the dynamic response of asphalt under moving loads and is based on a semi-analytic element method. In this research project SAFEM is compared to commercial finite element software ABAQUS and field measurements to verify the computational accuracy. The computational accuracy of SAFEM was found to be high enough to be viable whilst boasting a computational time far shorter than ABAQUS. Thus, SAFEM appears to be a feasible approach to determine the dynamic response of pavements under dynamic loads and is a useful tool for infrastructure administrations to analyze the pavement bearing capacity.

关键词： semi-analytical finite element method bearing capacity asphalt pavements moving loads dynamic response

A Simulation for the Piston Effect in Supercritical Carbon Dioxide with the Non-flow Model

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Journal of Thermal Science 2013年第5期22卷 472-477页

作者： Lingjiao Wei Dazhong Yuan Bangxian Wu dawei Tang Institute of Engineering Thermophysics Chinese Academy of Sciences University of Chinese Academy of Sciences

A simulation for piston effect in supercritical carbon dioxide by employing a simple model is conducted. In the first place, the thermal properties of carbon dioxide near its liquid-vapor critical point are discussed. It is calcu- lated that the heat capacity ratio and isobaric expansion coefficient of supercritical fluids are extremely high. Furthermore, the simulation for piston effect in supereritical carbon dioxide between two infinite vertical walls is presented. The numerical results prove that piston effect has a much faster speed of heat transfer than thermal conduction under mierogravity conditions. Moreover, the piston effect turns out to be stronger when closer to the critical point.

关键词： Piston effect Carbon dioxide Supercritical Thermal properties

Contribution to sample failure probability plot and its solution by Kriging method

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Science China(Technological Sciences) 2013年第4期56卷 866-877页

作者： LI dawei Lü ZhenZhou ZHOU ChangCong School of Aeronautics Northwestern Ploytechnical University

To analyze the effect of the region of the model inputs on the model output,a novel concept about contribution to the sample failure probability plot(CSFP) is proposed based on the contribution to the sample mean plot(CSM) and the contribution to the sample variance plot(CSV).The CSFP can be used to analyze the effect of the region of the model inputs on the failure *** the definition of CSFP,its property and the differences between CSFP and CSV/CSM are *** proposed CSFP can not only provide the information about which input affects the failure probability mostly,but also identify the contribution of the regions of the input to the failure probability *** employing the Kriging model method on optimized sample points,a solution for CSFP is *** computational cost for solving CSFP is greatly decreased because of the efficiency of Kriging surrogate *** examples are used to illustrate the validity of the proposed CSFP and the applicability and feasibility of the Kriging surrogate method based solution for CSFP.

关键词： sample failure probability plot sensitivity analysis optimization sample points Kriging model region of the inputs

Effect of high magnetic fields on the solidification microstructure of an Al-Mn alloy

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Rare Metals 2009年第3期28卷 302-308页

作者： LUO dawei GUO Jin YAN Zhiming LI Tingju School of Materials Science and Engineering Dalian University of Technology Dalian 116023 China State Key Laboratory of Materials Modification by Laser Ion and Electron Beams Dalian 116023 China

The effect of high magnetic fields on the morphology of Al-Mn phases was investigated. It is found that the tropism and the alignment of Al6Mn precipitated phases become regular under high magnetic fields. The stronger the high magnetic fields, the more regular the alignment of Al6Mn precipitated phases. Al6Mn precipitated phases can generate oriented alignment and aggregation under high magnetic fields through the observation of the quenched microstructure of the Al-Mn alloy at different temperatures. Meanwhile, the number of Al6Mn phases increases continuously along with the increasing function time of high magnetic fields. X-ray diffraction also indicates that Al6Mn phases generate obvious tropism under high magnetic fields. The process of aggregation and growth of Al6Mn precipitated phases under the function of high magnetic fields after orientation were analyzed and discussed.

关键词： high magnetic fields Al-Mn alloy Al-Mn phase orientation

Sol-gel Derived TiO_2-Bioactive glass-Hydroxyapatite Bioactive Coating on Titanium Alloy Substrate

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Chinese Journal of Mechanical Engineering 2010年第2期23卷 263-268页

作者： ZHAO Kang LUO Defu TANG Yufei ZHANG dawei School of Materials Science and Engineering Xi＇ an University of Technology Xi＇ an 710048 China School of Materials Science and Engineering Xihua University Chengdu 610039 China Library of Xi＇ an Polytechnic University Xi＇ an 710049 China

Coating the hydroxyapatite （HA） on the titanium alloy surface can obtain a bioactive implant with high mechanical properties However, the bonding force between the titanium alloy and the HA was low due to their different coefficient of thermal expansion （CET）. Preparing the multi-layer coating with alleviated thermal stress on titanium alloy substrate is few reported. Fabrication of a TiO2-bioactive glass （BG）-HA bioactive coating was proposed to solve this problem. A particular TiO2 surface was prepared on the titanium alloy substrate by micro-arc oxidation treatment. The BG and HA coating were coated onto the TiO2 surface in turn by using a sol-gel method. The microstructure, surface morphology and phase composition of the coatings were analyzed. The bonding force of coatings was investigated by the nick apparatus. In vitro dissolution was performed by soaking the TiO2-BG-HA coated samples into the simulated body fluid for various periods. Micro-structural observations indicated that no delamination and crack occurred at the interface of HA/BG and BG/TiO2. The bonding between the substrate and coating consists of the mechanical interaction and the chemical bonding. The bonding force could reach about 45 N. The TiO2-BG-HA coating displayed the excellent forming ability of bone-like apatite when it was soaked into the simulated body fluid. This work suggests an innovative way to reduce the internal stress among coatings through varying BG composition to adjust its CTE, so as to enhance the bonding force.

关键词： bioactive coating sol-gel coefficient of thermal expansion TiO2-BG-HA simulated body fluid