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A fast and high-accurate commutation failure identification method for LCC-HVDC system

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HIGH VOLTAGE 2024年第3期9卷 721-732页

作者： Feng, Jing liu, Zhijie li, Kejun li, Bingkun li, Jiachen li, liangzi Shandong Univ Sch Elect Engn Jinan Shandong Peoples R China

Commutation failure (CF) is one of the most common issues in line-commuted converter-based high voltage direct current systems (LCC-HVDC), leading to critical power system security and stability problems. Accurate and rapid identification of CF is crucial to prevent subsequent CF in HVDC systems. However, the existing CF identification methods are lack of the required accuracy and speed. The relationship between bridge arm current, commutation voltage, and trigger pulse based on the commutation progress mechanism after the AC fault is analysed in this paper. A novel CF identification method is presented, which utilises the CF identification factor, enabling fast and high-accurate identification without relying on the value of the extinction angle. The proposed method offers a simpler and more efficient implementation in engineering practice. Finally, the effectiveness of the proposed method is verified in both the standard International Council on Large Electric systems HVDC model and the Hardware in Loop test using practical project parameters. The results demonstrate that the proposed method can accurately and fast identify CF.

关键词： STABIliTY ANALYSIS VOLTAGE STRATEGY

An internal ballistic model of electromagnetic railgun based on PFN coupled with multi-physical field and experimental validation

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Defence Technology（防务技术） 2024年第2期32卷 254-261页

作者： Benfeng Gu Haiyuan li Baoming li National Key Laboratory of Transient Physics Nanjing University of Science and TechnologyNanjing 210094China

To accelerate the practicality of electromagnetic railguns,it is necessary to use a combination of threedimensional numerical simulation and experiments to study the mechanism of bore *** this paper,a three-dimensional numerical model of the augmented railgun with four parallel unconventional rails is introduced to simulate the internal ballistic process and realize the multi-physics field coupling calculation of the rail gun,and a test experiment of a medium-caliber electromagnetic launcher powered by pulse formation network(PFN)is carried *** test methods such as spectrometer,fiber grating and high-speed camera are used to test several parameters such as muzzle initial velocity,transient magnetic field strength and stress-strain of *** the simulation results and experimental data,the damage condition of the contact surface is analyzed.

关键词： Internal ballistic modeling Electromagnetic rail gun Multi-physics field coupling Experimental validation PFN

An efficient approach for the equivalent linearization of frame structures with plastic hinges under nonstationary seismic excitations

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Earthquake Engineering and Engineering Vibration 2024年第3期23卷 677-690页

作者： Huang Huan li Yingxiong li Yuyu College of Water Conservancy and Civil Engineering South China Agricultural UniversityGuangzhou 510642China Institute of Smart City and Intelligent Transportation Southwest Jiaotong UniversityChengdu 611756China

An efficient approach is proposed for the equivalent linearization of frame structures with plastic hinges under nonstationary seismic *** concentrated plastic hinges,described by the Bouc-Wen model,are assumed to occur at the two ends of a linear-elastic beam *** auxiliary differential equations governing the plastic rotational displacements and their corresponding hysteretic displacements are replaced with linearized differential ***,the two sets of equations of motion for the original nonlinear system can be reduced to an expanded-order equivalent linearized equation of motion for equivalent linear *** solve the equation of motion for equivalent linear systems,the nonstationary random vibration analysis is carried out based on the explicit time-domain method with high ***,the proposed treatment method for initial values of equivalent parameters is investigated in conjunction with parallel computing technology,which provides a new way of obtaining the equivalent linear systems at different time *** on the explicit time-domain method,the key responses of interest of the converged equivalent linear system can be calculated through dimension reduction analysis with high *** examples indicate that the proposed approach has high computational efficiency,and shows good applicability to weak nonlinear and medium-intensity nonlinear systems.

关键词： nonstationary random vibration plastic hinge equivalent linearization method explicit time-domain method parallel computation

Study on the effective elastic performance of composites containing decagonal symmetric two-dimensional quasicrystal coatings

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Applied Mathematics and Mechanics(English Edition) 2024年第9期45卷 1655-1664页

作者： Yurun WU Lu li lianhe li School of Mathematics and Science Inner Mongolia Normal UniversityHohhot 010022China Inner Mongolia Applied mathematics Center Hohhot 010022China Key Laboratory of Infinite Dimensional Hamiltonian System and Its Algorithm Application Ministry of EducationHohhot 010022China

On account of the Mori-Tanaka approach,the effective elastic performance of composites containing decagonal symmetric two-dimensional(2D)quasicrystal(QC)coatings is *** expressions for the effective elastic constants of rare-earth QC reinforced magnesium-based composites are *** discussion is presented on the effects of the volume fraction of the inclusions,the aspect ratio of the inclusions,the coating thickness,and the coating material parameters on the effective elastic constants of the *** results indicate that considering the coating increases the effective elastic constants of the composites to some extent.

关键词： Mori-Tanaka approach coated inclusion decagonal symmetric twodimensional(2D)quasicrystal(QC)

Al/Hf ratio-dependent mechanisms of microstructure and mechanical property of nearly fully dense Al—Hf reactive material

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Defence Technology（防务技术） 2024年第1期31卷 230-241页

作者： Junbao li Weibing li Xiaoming Wang ZNDY of Ministerial Key Laboratory Nanjing University of Science and TechnologyNanjing 210094China

This study proposed three types of Al—Hf reactive materials with particle size ratios(a),which were almost completely dense(porosity of<5.40%)owing to their preparation using hot-pressing *** characteristics and phas... 详细信息

This study proposed three types of Al—Hf reactive materials with particle size ratios(a),which were almost completely dense(porosity oflinearly with increasing strain rate.ε.It is found that the plastic deformation of the material increased with increasing strain *** a increased from 0.1 to 1,the flow stress gradually *** failure of the material was dominated by ductile fracture with a large Al phase plastic deformation band for lower a,while brittle fracture with crushed Hf particles occurred at higher ***,a constitutive model based on BP neural network was proposed to describe the stress-strain relationships of the materials,with an average relative error of 2.22%.

关键词： Reactive material Particle size Split Hopkinson pressure bar test Stressestrain relationship Impact failure BP neural network

Gravitational waves and primordial black hole productions from gluodynamics by holography

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Science China(Physics,Mechanics & Astronomy) 2024年第4期67卷 31-42页

作者： Song He li li Zhibin li Shao-Jiang Wang Center for Theoretical Physics and College of Physics Jilin UniversityChangchun 130012China Max Planck Institute for Gravitational Physics(Albert Einstein Institute) Golm 14476Germany CAS Key Laboratory of Theoretical Physics Institute of Theoretical PhysicsChinese Academy of SciencesBeijing 100190China School of Fundamental Physics and Mathematical Sciences Hangzhou Institute for Advanced StudyUniversity of Chinese Academy of SciencesHangzhou 310024China Peng Huanwu Collaborative Center for Research and Education Beihang UniversityBeijing 100191China School of Physics and Microelectronics Zhengzhou UniversityZhengzhou 450001China

Understanding the nature of quantum chromodynamics(QCD)matter is important but challenging due to the presence of nonperturbative dynamics under extreme *** construct a holographic model describing the gluon sector of QCD at finite temperatures in the non-perturbative *** equation of state as a function of temperature is in good accordance with the lattice QCD ***,the Polyakov loop and the gluon condensation,which are proper order parameters to capture the deconfinement phase transition,also agree quantitatively well with the lattice QCD *** obtain a strong first-order confinement/deconfinement phase transition at Tc=276.5 Me V that is consistent with the lattice QCD *** on our model for a pure gluon hidden sector,we compute the stochastic gravitational waves and primordial black hole(PBH)productions from this confinement/deconfinement phase transition in the early *** resulting stochastic gravitational-wave backgrounds are found to be within detectability in the International Pulsar Timing Array and Square Kilometre Array in the near future when the associated productions of PBHs saturate the current observational bounds on the PBH abundances from the liGO-Virgo-Collaboration O3 data.

关键词： AdS/QCD confinement/deconfinement phase transition gravitational wave primordial black hole

Topology Optimization Method for Microscale Structures Described with Integral Nonlocal Theory

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Acta Mechanica Solida Sinica 2024年第1期37卷 63-71页

作者： Jiayu li Quhao li Shutian liu State Key Laboratory of Structural Analysis Optimization and CAE Software for Industrial EquipmentDalian University of TechnologyDalian 116024China

The integration of additive manufacturing and topology optimization makes it possible to fabricate complex configurations,especially for microscale structures,which can guarantee the realization of high-performance structural ***,topology results often contain microstructures(several multicellular scales)similar to the characteristic length of local macrostructures,leading to errors in structural performance analysis based on classical ***,it is necessary to consider the size effect in topology *** this paper,we establish a novel topology optimization model utilizing the integral nonlocal theory to account for the size *** approach consists of an integral constitutive model that incorporates a kernel function,enabling the description of stress at a specific point in relation to strain in a distant *** optimization structures based on nonlocal theory are presented for some benchmark examples,and the results are compared with those based on classical medium *** material layout exhibits significant differences between the two approaches,highlighting the necessity of topology optimization based on nonlocal theory and the effectiveness of the proposed method.

关键词： Topology optimization Microstructures Integral nonlocal theory Size effect

Guidance strategy of motion camouflage for spacecraft pursuit-evasion game

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Chinese Journal of Aeronautics 2024年第3期37卷 312-319页

作者： Jianqing li Chaoyong li Yonghe ZHANG Space Information Research Institute Hangzhou Dianzi UniversityHangzhou 310018China College of Electrical Engineering Zhejiang UniversityHangzhou 310027China Key Lab of Microsatellites Chinese Academy of SciencesShanghai 201210China

This work is inspired by a stealth pursuit behavior called motion camouflage whereby a pursuer approaches an evader while the pursuer camouflages itself against a predetermined *** formulate the spacecraft pursuit-evasion problem as a stealth pursuit strategy of motion camouflage,in which the pursuer tries to minimize a motion camouflage index defined in this *** Euler-Hill reference frame whose origin is set on the circular reference orbit is used to describe the *** on the rule of motion camouflage,a guidance strategy in open-loop form to achieve motion camouflage index is derived in which the pursuer lies on the camouflage constraint line connecting the central spacecraft and *** order to dispose of the dependence on the evader acceleration in the open-loop guidance strategy,we further consider the motion camouflage pursuit problem within an infinite-horizon nonlinear quadratic differential *** saddle point solution to the game is derived by using the state-dependent Riccati equation method,and the resulting closed-loop guidance strategy is effective in achieving motion *** are performed to demonstrate the capabilities of the proposed guidance strategies for the pursuit–evasion game scenario.

关键词： Pursuit-evasion problem Motion camouflage Differential game Guidance strategy Orbit control

Nonlinear encoding in diffractive information processing using linear optical materials

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light(Science & Applications) 2024年第8期13卷 1675-1688页

作者： Yuhang li Jingxi li Aydogan Ozcan Electrical&Computer Engineering Department University of CaliforniaLos AngelesCA 90095USA Bioengineering Department University of CaliforniaLos AngelesCA 90095USA California NanoSystems Institute(CNSI) University of CaliforniaLos AngelesCA 90095USA

Nonlinear encoding of optical information can be achieved using various forms of data ***,we analyze the performances of different nonlinear information encoding strategies that can be employed in diffractive optical processors based on linear materials and shed light on their utility and performance gaps compared to the state-of-the-art digital deep neural *** a comprehensive evaluation,we used different datasets to compare the statistical inference performance of simpler-to-implement nonlinear encoding strategies that involve,e.g.,phase encoding,against data repetition-based nonlinear encoding *** show that data repetition within a diffractive volume(e.g.,through an optical cavity or cascaded introduction of the input data)causes the loss of the universal linear transformation capability of a diffractive optical ***,data repetition-based diffractive blocks cannot provide optical analogs to fully connected or convolutional layers commonly employed in digital neural ***,they can still be effectively trained for specific inference tasks and achieve enhanced accuracy,benefiting from the nonlinear encoding of the input *** results also reveal that phase encoding of input information without data repetition provides a simpler nonlinear encoding strategy with comparable statistical inference accuracy to data repetition-based diffractive *** analyses and conclusions would be of broad interest to explore the push-pull relationship between linear material-based diffractive optical systems and nonlinear encoding strategies in visual information processors.

关键词： nonlinear simpler Nonlinear