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Novel antenna selection algorithm based on Tanimoto similarity

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Journal of Systems Engineering and Electronics 2008年第3期19卷 624-627页

作者： Yang Haifen li guangjun Dept. of Communication & Information Engineering Univ. of Electronic Science and Technology of China Chengdu 610054 P. R. China

A new antenna selection algorithm for multiple input multiple output （MIMO） wireless systems is proposed. The modified Tanimoto coefficient is used to compare the similarity of the rows/columns of the channel matrix. Based on the calculated similarity, the proposed algorithm chooses the antenna subset, which has the maximum product of dissimilarity and Frobenius norm. The proposed algorithm requires low computational complexity as to the optimal selection but with comparative outage capacity and average signal to noise ratio （SNR） performance. It can improve both the outage capacity and the average SNR as compared to random selection. The simulation results are shown to validate our algorithm.

关键词： MIMO system antenna selection Tanimoto similarity outage capacity.

Tribological evaluation of surface modified H13 tool steel in warm forming of Ti–6Al–4V titanium alloy sheet

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Chinese Journal of Aeronautics 2014年第4期27卷 1002-1009页

作者： Wang Dan li Heng Yang He Ma Jun li guangjun State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical University AVIC Cheng Du Aircraft Industry (Group) Co. Ltd

The H13 hot-working tool steel is widely used as die material in the warm forming of Ti–6Al–4V titanium alloy sheet. However, under the heating condition, severe friction and lubricating conditions between the H13 tools and Ti–6Al–4V titanium alloy sheet would cause difficulty in guaranteeing forming quality. Surface modification may be used to control the level of friction force, reduce the friction wear and extend the service life of dies. In this paper, four surface modification methods（chromium plating, TiAlN coating, surface polishing and nitriding treatment）were applied to the H13 surfaces. Taking the coefficient of friction（CoF） and the wear degree as evaluation indicators, the high-temperature tribological behavior of the surface modified H13 steel was experimentally investigated under different tribological conditions. The results of this study indicate that the tribological properties of the TiAlN coating under dry friction condition are better than the others for a wide range of temperature（from room temperature to 500 C）, while there is little difference of tribological properties between different surface modifications under graphite lubricated condition, and the variation law of CoF with temperature under graphite lubricated is opposite to that under the dry friction.

关键词： Coefficient of friction H13 Surface modification Ti-6Al-4V Tools Warm forming Wear

Springback prediction of thick-walled high-strength titanium tube bending

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Chinese Journal of Aeronautics 2013年第5期26卷 1336-1345页

作者： Song Feifei Yang He li Heng Zhan Mei li guangjun State Key Laboratory of Solidifcation Processing School of Materials Science and EngineeringNorthwestern Polytechnical University Chengdu Aircraft Industry (Group) Corporation Ltd.

Significant springback occurs after tube rotary-draw-bending （RDB）, especially for a high-strength Ti-3A1-2.5V tube （HSTT） due to its high ratio of yield strength to Young＇s modulus. The combination scheme of explicit and implicit is preferred to predict the springback. This simulation strategy includes several numerical parameters, such as element type, number of elements through thickness （NEL）, element size, etc. However, the influences of these parameters on spring- back prediction accuracy are not fully understood. Thus, taking the geometrical specification 9.525 mm × 0.508 mm ofa HSTT as the objective, the effects of numerical parameters on prediction accuracy and computation efficiency of springback simulation of HSTT RDB are investigated. The simulated springback results are compared with experimental ones. The main results are：（1） solid and continuum-shell elements predict the experimental results well; （2） for C3DSR elements, NEL of at least 3 is required to obtain reliable results and a relative error of 29% can occur as NEL is varied in the range of 1-3; （3） specifying damping factor typically works well in Abaqus/Emplicit simulation of springback and the springback results are sensitive to the magnitude of damping factor. In addition, the explanations of the effect rules are given and a guideline is added.

关键词： Bending Finite element method High strength Numerical parameters Solid elements Springback Titanium alloys Tube

Microstructure and properties of in situ synthesized TiB_2+WC reinforced composite coatings

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Rare Metals 2008年第5期27卷 451-456页

作者： li Jun ZHANG Huiying li Wenge ZHANG guangjun School of Materials Engineering Shanghai University of Engineering Science Shanghai 201620 China

Nickel-based composite coatings reinforced by in situ synthesized TiB2 and WC particles were deposited on stainless steel by laser cladding, and their microstmcture and mechanical properties were investigated. The results show that the coatings are mainly composed of 7-Ni cellular dendrites and dispersed spherical/strip/network shaped TiB2 and equiaxial WC particles. The initial WC particles are dissolved to become fine and mostly dispersed within Y-Ni cellular dendrites. The coating prepared at a special laser energy of 0.225 kJ@mm^-2 is uniform, continuous, and free of pores and cracks. With the decrease in special energy density, TiB2 phase changes from fine spherical particles which cluster together to strip shape with different morphologies and further crystallizes to form network structure, and the dispersion zone also gradually changes from intragranular to intergranular phase. The coating possesses a higher microhardness compared with the substrate, and it has a good metallurgical bond with the substrate and excellent cracking resistance.

关键词： laser cladding in situ synthesis composite coating microstructure

Performance and EXIT analysis of parallel concatenated space time trellis codes

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Journal of Systems Engineering and Electronics 2009年第6期20卷 1193-1197页

作者： Yang Haifen li guangjun Guo Zhiyong Xiong Yong Dept. of Communication gc Information Engineering Univ. of Electronic Science and Technology of China Chengdu 010054 P. R. China Shanghai Research Center for Wireless Communlcations Shanghai 200050 P. R. China

Space time trellis coding （STTC） techniques have been proposed to achieve both diversity and coding gains in multiple input multiple output （MIMO） fading channels. But with more transmit antennas STTCs suffer from the design dificulty and complexity increasing. This paper proposes a scheme, named parallel concatenated space time trellis codes （PC-STTC）, to achieve the tradeoff between the performances and complexity of STTCs for a large number of transmit antennas. Simulation results and complexity comparison are provided to demonstrate the performance and superiority of the proposed scheme over conventional schemes in fast fading channels in low signal-to-noise ratio （SNR） regions. And an EXIT （extrinsic information transform） chart is given to analyze the iterative convergence of the proposed scheme. It shows that PC-STTC has better iterative convergence in low SNR regions.

关键词： space time trellis coding EXIT chart Log-MAP decoder convergence.

Deformation Behavior of Medium-strength TA18 High-pressure Tubes During NC Bending with Different Bending Radii

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Chinese Journal of Aeronautics 2011年第5期24卷 657-664页

作者： JIANG Zhiqiang ZHAN Mei YANG He XU Xudong li guangjun School of Materials Science and Engineering State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi ＇an 710072 China Chengdu Aircraft Industry （Group） Corporation Ltd. Chengdu 610092 China

To improve the forming quality and forming limit of the numerical control （NC） bending of high-pressure titanium alloy tubes, in this study, using three-dimensional （3D） finite element method, deformation behavior of medium-strength TA 18 high-pressure tubes during NC bending with different bending radii is investigated. The results show that the cross-sectional deformation and the wall thickness variation during NC bending of TA18 tubes using a small bending radius （less than 2 times of tube outside diameter） are clearly different from that using a normal bending radius （between 2 and 4 times of tube outside diameter）. For bending with a normal bending radius, with or without a mandrel, the distribution of the flattening in the bending area resembles a platform and an asymmetric parabola, respectively. For bending with a small bending radius, with or without a mandrel, the flattening both distributes like a parabola, but the former has a stable peak which deflects toward the initial bending section, and the latter has a more pronounced peak with a bending angle and deflects slightly toward the bending section. The wall thickness variations with a normal bending radius, with and without a mandrel, both resemble a platform when the bending angle exceeds a certain angle. For the bending with a small radius, the distribution of the wall thickness variation without a mandrel follows an approximate parabola which increases in value as the bending angle increases. If a mandrel is used, the thickening ratio increases from the initial bending section to the bending section.

关键词： titanium alloy tubes deformation behaviors numerical control bending finite element method normal bending radius small bending radius

Geometry-dependent springback behaviors of thin-walled tube upon cold bending

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Science China(Technological Sciences) 2012年第12期55卷 3469-3482页

作者： li Heng YANG He TIAN Yuli li guangjun WANG ZhengHua State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi'an 710072China Chengdu Aircraft Industry(Group)Corporation Ltd Chengdu 610092China Shanghai Aircraaft Manufacturing Corporation Ltd Shanghai 200120China

As one kind of key lightweight components with enormous quantities and diversities, the bent tubular parts have attracted in- creasing applications in aerospace, automobile, etc. Thus, how the inevitable springback behaves under different bending specifications should be fully addressed to efficiently achieve the precision forming of various bent tubes. Taking the medium strength thin-walled 6061-T4 Al-alloy tube as the objective, via the deformation theory of plasticity, explicit/implicit FE method and experimental approaches, we explored and clarified the nonlinear springback rules of the tubes and corresponding mechanisms in universal rotary draw bending regarding angular springback and radius growth by deliberately changing the tube diameter D and wall thickness t. The geometry dependent springback behaviors of thin-walled tube upon cold bending are thus revealed: 1) With the increasing of D, the tangent tensile strain increases and the proportional coefficient decreases, which causes the angular springback to decrease, while the radius springback increases due to the larger bending radius. 2) With the increasing of t, the tangent tensile strain decreases and the proportional coefficient increases, resulting in the increase of both angular springback and radius springback. 3) Under the same D/t, the angular springback varies little, while the radius springback increases with the larger diameter D. 4) The D/t can be used as a reasonable nondimensional index to evaluate the springback angle; as to the radius growth, the individual effects of the D and t should be considered. 5) The verification of the above results was conducted by experiments and analytical analysis.

关键词： springback geometry dependence thin-walled tube bending aluminum alloy

Towards intelligent design optimization: Progress and challenge of design optimization theories and technologies for plastic forming

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Chinese Journal of Aeronautics 2021年第2期34卷 104-123页

作者： Heng li Jingchao YANG Guangyao CHEN Xin liU Zhao ZHANG guangjun li Wenhui liU State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Poly technical UniversityXi'an 710072China Chengdu Aircraft Industry(Group)Corporation Ltd. Chengdu 610092China High Temperature Wear Resistant Materials and Preparation Technology of Hunan Province National Defence Science and Technology Laboratory Hunan Provincial Key Laboratory of Advanced Materials for New Energy Storage and ConversionSchool of Materials Science and EngineeringHunan University of Science and TechnologyXiangtan 411201China

Plastic forming is one of enabling and fundamental technologies in advanced manufacturing chains. Design optimization is a critical way to improve the performance of the forming system, exploit the advantages of high productivity, high product quality, low production cost and short time to market and develop precise, accurate, green, and intelligent(smart) plastic forming technology. However, plastic forming is quite complicated, relating to multi-physics field coupling,multi-factor influence, multi-defect constraint, and triple nonlinear, etc., and the design optimization for plastic forming involves multi-objective, multi-parameter, multi-constraint, nonlinear,high-dimensionality, non-continuity, time-varying, and uncertainty, etc. Therefore, how to achieve accurate and efficient design optimization of products, equipment, tools/dies, and processing as well as materials characterization has always been the research frontier and focus in the field of engineering and manufacturing. In recent years, with the rapid development of computing science, data science and internet of things(Io T), the theories and technologies of design optimization have attracted more and more attention, and developed rapidly in forming process. Accordingly, this paper first introduced the framework of design optimization for plastic forming. Then, focusing on the key problems of design optimization, such as numerical model and optimization algorithm,this paper summarized the research progress on the development and application of the theories and technologies about design optimization in forming process, including deterministic and uncertain optimization. Moreover, the applicability of various modeling methods and optimization algorithms was elaborated in solving the design optimization problems of plastic forming. Finally, considering the development trends of forming technology, this paper discusses some challenges of design optimization that may need to be solved and faced in forming pr

关键词： Advanced manufacturing Design optimization Deterministic optimization(DOP) Intelligent design optimization(IDO) Plastic forming Uncertain optimization(UOP)

Collaborative beamforming based on directional perturbation using one bit feedback

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Journal of Systems Engineering and Electronics 2016年第3期27卷 549-554页

作者： Haifen Yang Ning Ding Zhi Zheng Shuisheng lin Zhongpei Zhang guangjun li School of Communication & Information Engineering University of Electronic Science and Technology of China

A novel collaborative beamforming algorithm is proposed in a wireless communication system with multiple transmitters and one receiver. All transmitters take part in the collaboration and the weighted message is transmitted simultaneously. In order to maximize the beamforming gain, the transmitters use one bit feedback information to adjust the phase offset. It tracks the direction in which the signal strength at the receiver can increase. The directional search and perturbation theory is used to achieve the phase alignment. The feasibility of the proposed algorithm is proved both experimentally and theoretically. Simulation results show that the proposed algorithm can improve the convergent speed of the phase alignment.

关键词： collaborative beamforming one-bit feedback directional perturbation convergent speed