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2017 International Conference on Radar Systems, Radar 2017

作者： Chen, Shuyuan Liu, Jiaqi Gao, Lu Bai, Jinliang Jiang, Zhiye Xu, Feng Qin, Peng Liu, Hongyan Liu, Xin Li, Hu Gao, Jingpeng National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing100076 China

ISBN: (纸本)9781785615153

Sheet beam Extended Interaction Klystron (EIK) is an attractive Millimeter Waves (MMW) amplifier because of its high gain per unit length and compact configuration, which can be used in radar transmission system. In this paper, RF structure and beam wave interaction system of W band sheet beam EIK has been designed. A new and effective method of designing and studying the beam wave interaction system is presented in this *** whole tube consists of one single-gap cavity, six tri-gaps cavities and one five-gaps cavity. By optimizing the position of cavities, the output power can achieve 30 kW and high gain of 50 dB, which is calculated by three dimensional particle in cell (3D-PIC)*** provides a powerful basis for the subsequent study of sheet beam EIK. © 2017 Institution of Engineering and technology. All rights reserved.

关键词： Millimeter waves

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Effects of reflection distance on Richtmyer–Meshkov instability in the reshock process: A discrete Boltzmann study

arXiv

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arXiv 2025年

作者： Lai, Huilin Lin, Chuandong Li, Demei Yang, Tao Gan, Yanbiao Lian, Lingyan Xu, Aiguo Fujian Normal University Fuzhou350117 China Sino-French Institute of Nuclear Engineering and Technology Sun Yat-sen University Zhuhai519082 China Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energy and Power Engineering Tsinghua University Beijing100084 China Hebei Key Laboratory of Trans-Media Aerial Underwater Vehicle School of Liberal Arts and Sciences North China Institute of Aerospace Engineering Langfang065000 China National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009-26 Beijing100088 China National Key Laboratory of Shock Wave and Detonation Physics Mianyang621999 China HEDPS Center for Applied Physics and Technology College of Engineering Peking University Beijing100871 China State Key Laboratory of Explosion Science and Safety Protection Beijing Institute of Technology Beijing100081 China

The Richtmyer–Meshkov (RM) instability occurs when a perturbed interface between two fluids undergoes impulsive acceleration due to a shock wave. In this paper, a numerical investigation of the RM instability during the reshock process is conducted using the two-component discrete Boltzmann method. The influence of reflection distance on the RM instability, including both hydrodynamic and thermodynamic non-equilibrium effects, is explored in detail. The interaction time between the reflected shock wave and the material interface varies with different reflection distances. Larger reflection distances lead to a longer evolution time of the material interface before reshock, resulting in more complex effects on the interface deformation, the mixing extent of the fluid system, and non-equilibrium behaviors after reshock. Additionally, while the reflection distance has a minimal impact on mixing entropy before the secondary impact, a significant difference emerges after the secondary impact. This suggests that the secondary impact enhances the evolution of the RM instability. Furthermore, non-equilibrium behaviors or quantities exhibit complex dynamics due to the influence of the transmitted shock wave, transverse waves, rarefaction waves, material interfaces, and dissipation/diffusion processes. Copyright © 2025, The Authors. All rights reserved.

关键词： Shock waves

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Supersonic flow kinetics: Mesoscale structures, thermodynamic nonequilibrium effects and entropy production mechanisms

arXiv

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arXiv 2025年

作者： Gan, Yanbiao Zhuang, Zhaowen Yang, Bin Xu, Aiguo Zhang, Dejia Chen, Feng Song, Jiahui Wu, Yanhong Hebei Key Laboratory of Trans-Media Aerial Underwater Vehicle North China Institute of Aerospace Engineering Langfang065000 China School of Energy and Safety Engineering Tianjin Chengjian University Tianjin300384 China National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009-26 Beijing100088 China National Key Laboratory of Shock Wave and Detonation Physics Mianyang621999 China HEDPS Center for Applied Physics and Technology College of Engineering Peking University Beijing100871 China State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology Beijing100081 China School of Physical Science and Technology Guangxi University Nanning530004 China School of Aeronautics Shan Dong Jiaotong University Jinan250357 China School of Aerospace Engineering Beijing Institute of Technology Beijing100081 China

Supersonic flow is a typical nonlinear, nonequilibrium, multiscale, and complex phenomenon. Compared to scenarios described by Navier-Stokes (NS) theory, mesoscale behavior in supersonic flow exhibits greater discreteness and a higher degree of nonequilibrium. Meanwhile, the entropy production mechanism, which involves compression efficiency and the ability to perform external work, is a significant focus in supersonic flow fields. As the degree of discrete/nonequilibrium effects increases, the study of entropy production based on NS theory may need reevaluation and appropriate revision. To address these issues, this paper develops and applies the discrete Boltzmann modeling and analysis method/model (DBM), based on kinetic and mean-field theories, to simulate, and analyze these phenomena. The study provides the following results: A Burnett-level DBM suitable for supersonic flow is constructed based on the Shakhov-BGK model. Higher-order analytical expressions for typical thermodynamic nonequilibrium effects are derived, providing a constitutive basis for improving traditional macroscopic hydrodynamics modeling. Criteria for evaluating the validity of DBM are established by comparing numerical and analytical solutions of nonequilibrium effects. The multiscale DBM is used to investigate discrete/nonequilibrium characteristics and entropy production mechanisms in shock regular reflection. The findings include: (a) Compared to the NS-level DBM, the Burnett-level DBM offers more accurate representations of viscous stress and heat flux, i.e., more precise dissipative mechanisms, ensures non-negativity of entropy production in accordance with the second law of thermodynamics, and exhibits better numerical stability. (b) Near the interfaces of incident and reflected shock waves, strong nonequilibrium driving forces lead to prominent nonequilibrium effects. By monitoring the timing and location of peak nonequilibrium quantities, the evolution characteristics of incident and

关键词： Supersonic flow

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Experimental Studies of Low-Pressure Plasma Jet by Means of Langmuir Probes and Emission Spectra

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Plasma science and technology 2009年第3期11卷 307-313页

作者：刘磊曹金祥牛田野王亮孟刚刘鑫袁雷邬润辉张生俊任爱民 Key Laboratory of Basic Plasma Physics Chinese Academy of Sciencesand Department of Modern PhysicsUniversity of Science and Technology of China China Academy of Space Technology Test Physics & Numerical Mathematics Laboratory

An investigation was made into the argon plasma jet that expanded in a low-pressure vacuum chamber. The spatial distributions of the parameters of the plasma jet with different supplied powers were measured using a ten-channel Langmuir probe array. The chemical species in the plasma jet were identified by emission spectroscopy. The electron excitation temperatures at two positions, 10 cm and 50 cm downstream from the nozzle exit were calculated, respectively, by the Boltzmann plot method.

关键词： plasma jet spatial distribution probe array emission spectrum

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Dynamic failure of aramid paper honeycomb under intermediate strain rate loading

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Thin-Walled Structures 2025年 215卷

作者： Meiduo Chen Xianglin Zhang Songlin Xu Hao Ma Liangzhu Yuan Yushan Xie Xiaoman Zhang Pengfei Wang University of Science and Technology of China Department of Modern Mechanics CAS Key Laboratory for Mechanical Behavior and Design of Materials Hefei Anhui 230027 China Beijing Institute of Space Long March Vehicle Beijing 100076 China National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing 100076 China

Investigation of the transformation process of failure mechanism for materials and structures under intermediate strain rate loading is of great significance. To achieve intermediate strain rate loading, a novel experimental technique is proposed using a high-speed-rotating eccentric cam to compress the specimen. The particle velocities and the stresses at both ends of the specimen are measured by the velocity interferometer system for any reflector (VISAR) and by the semiconductor strain gauges, respectively. The paper honeycomb specimens with four thicknesses (i.e. 2 mm, 3 mm, 5 mm, and 10 mm) are tested under strain rates ranging from 0.1 to 15 s -1 . Local deformation evolution in the specimen is captured based on high-speed photography and analyzed by the digital image correlation method (DIC). The deformation under intermediate strain rate loading is distinguished by higher particle velocity and lower particle acceleration, which is different from those under the static compression (at lower strain rates) and the Split Hopkinson Pressure bar (SHPB) impacting (at higher lower strain rates). Based on the DIC results, the abnormal size effect of specimen 2 mm is due to the competition between in-plane shear failure and out-of-plane buckling. The theoretical model is then established by introducing two main parameters, i.e. the lateral weakening factor ξ and the dynamic parameter k , to describe respectively the effects of in-plane shearing and strain rate on the out-of-plane wall buckling, and the critical stress for specimen buckling is obtained. The results show that the buckling deformation and the half-wave number for buckling are sensitive to the two parameters. This work provides theoretical and experimental references for the study of thin-walled structures under intermediate strain rate.

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Research on dual-polarisation printed dipole antenna for spherical near-field measurements

Research on dual-polarisation printed dipole antenna for sph...

引用

IET International Radar Conference 2018, IRC 2018

作者： Zheng, Pei Liu, JiaQi Wang, ShangYue Zhang, Ran Fan, Hu National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing China

Here a dual-polarisation printed dipole antenna for spherical near-field measurements is proposed. The printed dipole employs double-layered structure to obtain low cross-polarisation and uses irregular patch to get wide bandwidth. Two such dipoles are cross arranged to form a dual-polarisation dipole antenna. Simulated results show that the bandwidth is over 72% when VSWR is less than 3, the cross-polarisation ratio is better than 30 dB, the port isolation between two dipoles is better than −26 dB, while good radiation performance is also obtained. All the results above prove that the crossed arrangement structure will not affect the performance of the printed dipole, and the strength of mutual coupling between probes can be neglected. © 2019 Institution of Engineering and technology. All rights reserved.

关键词： Dipole antennas

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Research on near-field focusing algorithm of reconfigurable reflect-array

Research on near-field focusing algorithm of reconfigurable ...

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IET International Radar Conference 2018, IRC 2018

作者： Liu, Hong Yan Zheng, Pei Wang, Chao Guo, Lei Zhang, Xin Yu National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics Beijing China

In this study, the near-field beam focusing algorithm of reconfigurable reflect array for security imaging application is proposed. The proposed near-field focusing algorithm is based on classic array method, which is usually adopted for far-field pattern calculation. In order to satisfy the near-field imaging application, the imaging distance is added to array method, and the improved formula can calculate the shifting phase of every array element precisely. In addition, due to discrete phase characteristic of reconfigurable reflect array, a phase choice method based on trigonometric function is used in authors' design. Based on the proposed algorithm, the shifting phase of every element is calculated and obtained the simulated beam focusing patterns. Meanwhile, the calculated shifting phase is written to whole array by field-programmable gate array, the near-field beam scanning patterns is measured and the measured results are in good agreement with the simulated ones. © 2019 Institution of Engineering and technology. All rights reserved.

关键词： Field programmable gate arrays (FPGA)

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Dispersive FDTD scheme with conformal technology for analyzing electromagnetic scattering of inhomogeneous plasma array

Dispersive FDTD scheme with conformal technology for analyzi...

引用

IET International Radar Conference 2015

作者： Ai, Xia Liu, Shendong Zhang, Shengjun Wang, Mingliang Liu, Jiaqi Meng, Gang Zhou, Hongchao National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematical China

ISBN: (纸本)9781849199940

In this paper, a dispersive conformal FDTD method have been proposed to accurate model the interface between two adjacent dispersive mediums. The method is based on the technology of area average between two adjacent dispersive interfaces, which is different from existing dispersive conformal FDTD schemes which involve with the interface between free space and dispersive medium. numerical results show the proposed method would enhance the accurate level compared to the staircasing FDTD scheme involved in the inhomogeneous plasma.

关键词： numerical methods

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Higher order shift operater FDTD scheme for scattering of cloaking structure

Higher order shift operater FDTD scheme for scattering of cl...

引用

IET International Radar Conference 2015

作者： Ai, Xia Zhang, Shengjun Wang, Mingliang Wang, Weidong Liu, Jiaqi Liu, Chengguo Liu, Xuemei National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematical China

ISBN: (纸本)9781849199940

In this paper, a higher-order shift operater (SO) FDTD scheme with second-order accuracy in time and fourth-order in space has been proposed to accurately model scattering of perfect electronic conductor coated with cloaking structures. Several different electromagnetic parameters of the cloaks are taken into account using SO-FDTD method. numerical results indicate that the proposed method is more accuracy than the traditioinal method maintaining the same grid size. Scattering of different kinds of simplified cylindrical cloaks including thickness and loss are presented and could be served as further study on this subject.

关键词： Finite difference time domain method

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The research on the effects of an active FSS with circle element on the characteristics of Radar Absorbing Materials

The research on the effects of an active FSS with circle ele...

引用

IET International Radar Conference 2015

作者： Wang, Ming-Liang Zhang, Sheng-Jun Liu, Jia-Qi Wang, Wei-Dong Ai, Xia Liu, Shengdong Liang, Wei National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematical Beijing China

ISBN: (纸本)9781849199940

An active frequency selective surface (FSS) is designed, and is combined with Radar Absorbing Materials to form a composite absorbing structure. Based on the equivalent theory that the PIN diode can be regarded as resistance, the voltage-loading resistance of active FSS element is researched for RAM containing FSS, and the electromagnetic wave reflectivity performance is analyzed. The influence of active FSS design parameters on the reflectivity of RAM is researched, and the FSS design parameters include the voltage-loading manner, the resistance parameter, and the position in the RAM. The research result shows that the resonance frequency of RAM containing FSS can be dynamically adjusted from 3GHz to 4GHz by changing voltage-loading resistance of active FSS, and the reflectivity can be reduced from -13dB to -35dB.

关键词： Reflection

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