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Wideband radar cross-section reduction by a double-layer-plasma-based metasurface

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Plasma Science and technology 2024年第6期26卷 159-168页

作者：赵智明李小平董果香刘旭牟相超 School of aerospace Science and technology Xidian UniversityXi’an 710126People’s Republic of China

Reduction of the radar cross-section(RCS) is the key to stealth technology. To improve the RCS reduction effect of the designed checkerboard metasurface and overcome the limitation of thinlayer plasma in RCS reduction technology, a double-layer-plasma-based metasurface—composed of a checkerboard metasurface, a double-layer plasma and an air gap between them—was investigated. Based on the principle of backscattering cancellation, we designed a checkerboard metasurface composed of different artificial magnetic conductor units;the checkerboard metasurface can reflect vertically incident electromagnetic(EM) waves in four different inclined directions to reduce the RCS. Full-wave simulations confirm that the doublelayer-plasma-based metasurface can improve the RCS reduction effect of the metasurface and the plasma. This is because in a band lower than the working band of the metasurface, the RCS reduction effect is mainly improved by the plasma layer. In the working band of the metasurface,impedance mismatching between the air gap and first plasma layer and between first and second plasma layers cause the scattered waves to become more dispersed, so the propagation path of the EM waves in the plasma becomes longer, increasing the absorption of the EM waves by the plasma. Thus, the RCS reduction effect is enhanced. The double-layer-plasma-based metasurface can be insensitive to the polarization of the incoming EM waves, and can also maintain a satisfactory RCS reduction band when the incident waves are oblique.

关键词： stealth technology radar cross-section(RCS)reduction backscattering cancellation double-layer-plasma-based metasurface

Drag reduction characteristics of recirculation flow at rocket base in an RBCC engine under ramjet/scramjet mode

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Chinese Journal of Aeronautics 2024年第3期37卷 104-115页

作者： Menglei LI Mingbo SUN Peibo LI Daoning YANG Bin AN Yizhi YAO Jikai CHEN Taiyu WANG Jiaoru WANG Hypersonic technology Laboratory National University of Defense TechnologyChangsha 410073China Department of aerospace Science and technology Space Engineering UniversityBeijing 101416China

To reduce the drag generated by the recirculation flow at the rocket base in a RocketBased Combined Cycle(RBCC)engine operating in the ramjet/scramjet mode,a novel annular rocket RBCC engine based on a central plug cone was *** performance loss mechanism caused by the recirculation flow at the rocket base and the influence of the plug cone configuration on the thrust performance were *** indicated that the recirculation flow at the rocket base extended through the entire combustor,which creates an extensive range of the"low-kineticenergy zone"at the center and leads to an engine thrust *** plug cone serving as a surface structure had a restrictive effect on the internal flow of the engine,making it smoothly transit at the position of the large separation *** model RBCC engine could achieve a maximum thrust augmentation of 37.6%with a long plug cone that was twice diameter of the inner ***,a shorter plug cone that was half diameter of the inner isolator proved less effective at reducing the recirculation flow for a supersonic flow and induced an undesirable flow fraction that diminished the thrust ***,the effectiveness of the plug cone increased with the flight Mach number,indicating that it could further broaden the operating speed range of the scramjet mode.

关键词： Rocket-based combined cycle Ramjet/scramjet mode Plug cone Drag reduction k-x SST turbulent model

Characterization of Gauss–Markov stochastic sequences for mission analysis

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Astrodynamics 2024年第1期8卷 135-148页

作者： Carmine Giordano Department of aerospace Science and technology Politecnico di MilanoMilano20156Italy

In real scenarios,the spacecraft deviates from the intended paths owing to uncertainties in dynamics,navigation,and command *** quantifying these uncertainties is crucial for assessing the observability,collision risks,and mission *** issue is further magnified for CubeSats because they have limited control authority and thus require accurate dispersion estimates to avoid rejecting viable trajectories or selecting unviable *** uncertainties arise from random variables(e.g.,measurement errors and drag coefficients)and processes(e.g.,solar radiation pressure and low-thrust acceleration).Although random variables generally present minimal computational complexity,handling stochastic processes can be challenging because of their noisy ***,accurately modeling these processes is essential,as they significantly influence the uncertain propagation of space trajectories,and an inadequate representation can result in either underestimation or overestimation of the stochastic characteristics associated with a given *** study addresses the gap in characterizing process uncertainties,represented as Gauss–Markov processes in mission analysis,by presenting models,evaluating derived quantities,and providing results on the impact of spacecraft *** study emphasizes the importance of accurately modeling random processes to properly characterize stochastic spacecraft paths.

关键词： Gauss-Markov process uncertainty quantification stochastic dynamics Monte Carlo simulation

Fine-Grained Ship Recognition Based on Visible and Near-Infrared Multimodal Remote Sensing Images: Dataset,Methodology and Evaluation

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Computers, Materials & Continua 2024年第6期79卷 5243-5271页

作者： Shiwen Song Rui Zhang Min Hu Feiyao Huang Department of aerospace Science and technology Space Engineering UniversityBeijing101416China

Fine-grained recognition of ships based on remote sensing images is crucial to safeguarding maritime rights and interests and maintaining national ***,with the emergence of massive high-resolution multi-modality images,the use of multi-modality images for fine-grained recognition has become a promising ***-grained recognition of multi-modality images imposes higher requirements on the dataset *** key to the problem is how to extract and fuse the complementary features of multi-modality images to obtain more discriminative fusion *** attention mechanism helps the model to pinpoint the key information in the image,resulting in a significant improvement in the model’s *** this paper,a dataset for fine-grained recognition of ships based on visible and near-infrared multi-modality remote sensing images has been proposed first,named Dataset for Multimodal Fine-grained Recognition of Ships(DMFGRS).It includes 1,635 pairs of visible and near-infrared remote sensing images divided into 20 categories,collated from digital orthophotos model provided by commercial remote sensing *** provides two types of annotation format files,as well as segmentation mask images corresponding to the ship ***,a Multimodal Information Cross-Enhancement Network(MICE-Net)fusing features of visible and near-infrared remote sensing images,has been *** the network,a dual-branch feature extraction and fusion module has been designed to obtain more expressive *** Feature Cross Enhancement Module(FCEM)achieves the fusion enhancement of the two modal features by making the channel attention and spatial attention work cross-functionally on the feature map.A benchmark is established by evaluating state-of-the-art object recognition algorithms on ***-Net conducted experiments on DMFGRS,and the precision,recall,mAP0.5 and mAP0.5:0.95 reached 87%,77.1%,83.8%and 63.9%,*** experiments demons

关键词： Multi-modality dataset ship recognition fine-grained recognition attention mechanism

Efficient unequal error protection for online fountain codes

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Journal of Systems Engineering and Electronics 2024年第2期35卷 286-293页

作者： SHI Pengcheng WANG Zhenyong LI Dezhi LYU Haibo School of Electronics and Information Engineering Harbin Institute of TechnologyHarbin 150001China Shenzhen Academy of aerospace technology Shenzhen 518057China

In this paper,an efficient unequal error protection(UEP)scheme for online fountain codes is *** the buildup phase,the traversing-selection strategy is proposed to select the most important symbols(MIS).Then,in the completion phase,the weighted-selection strategy is applied to provide low *** performance of the proposed scheme is analyzed and compared with the existing UEP online fountain *** results show that in terms of MIS and the least important symbols(LIS),when the bit error ratio is 10-4,the proposed scheme can achieve 85%and 31.58%overhead reduction,respectively.

关键词： online fountain code random graph unequal error protection(UEP) rateless code

Distributed Predefined-Time Control for Cooperative Tracking of Multiple Quadrotor UAVs

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IEEE/CAA Journal of Automatica Sinica 2024年第10期11卷 2179-2181页

作者： Kewei Xia Xinyi Li Kaidan Li Yao Zou advanced Research Institute of Multidisciplinary Sciences Beijing Institute of TechnologyBeijing 100081China School of aerospace Engineering and also with the Advanced Research Institute of Multidisciplinary SciencesBeijing Institute of TechnologyBeijing 100081China the School of Automation Beijing Institute of TechnologyBeijing 100081China the School of Intelligence Science and technology and also with the Key Laboratory of Intelligent Bionic Unmanned SystemsMinistry of EducationUniversity of Science and Technology BeijingBeijing 100083China

Dear Editor,This letter addresses the predefined-time control for cooperative tracking of multiple quadrotor unmanned aerial vehicles(UAVs)under a directed communication network.A predefined-time distributed estimator... 详细信息

关键词： acceleration letter estimator

Optimization of ferroelectricity and endurance of hafnium zirconium oxide thin films by controlling element inhomogeneity

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Journal of advanced Ceramics 2024年第7期13卷 1023-1031页

作者： Fei Yan Ke Cao Yang Chen Jiajia Liao Min Liao Yichun Zhou Shaanxi Key Laboratory of High-Orbits-Electron Materials and Protection technology for aerospace School of Advanced Materials and NanotechnologyXidian UniversityXi’an 710126China Xi’an Key Laboratory of Reconfigurable Chip and Materials School of Advanced Materials and NanotechnologyXidian UniversityXi’an 710126China Frontier Research Center of Thin Films and Coatings for Device Applications Academy of Advanced Interdisciplinary ResearchXidian UniversityXi’an 710126China

Ferroelectric thin films based on HfO2 have garnered increasing attention worldwide,primarily due to their remarkable compatibility with silicon and scalability,in contrast to traditional perovskite-structured ferroelectric ***,significant challenges remain in their widespread commercial utilization,particularly concerning their notable wake-up effect and limited *** address these challenges,we propose a novel strategy involving the inhomogeneous distribution of Hf/Zr elements within thin films and explore its effects on the ferroelectricity and endurance of Hf_(0.5)Zr_(0.5)O_(2) thin *** techniques such as grazing incidence X-ray diffraction,transmission electron microscopy,and piezoresponse force microscopy,we investigated the structural characteristics and domain switching behaviors of these *** experimental results indicate that the inhomogeneous distribution of Hf/Zr contributes to improving the frequency stability and endurance while maintaining a large remnant polarization in Hf_(0.5)Zr_(0.5)O_(2) ferroelectric thin *** adjusting the distribution of Zr/Hf within the Hf_(0.5)Zr_(0.5)O_(2) thin films,significant enhancements in the remnant polarization(2Pr>35μC/cm2)and endurance(>109)along with a reduced coercive voltage can be ***,the fabricated ferroelectric thin films also exhibit high dielectric tunability(≥26%)under a low operating voltage of 2.5 V,whether in the wake-up state or *** study offers a promising approach to optimize both the ferroelectricity and endurance of HfO_(2)-based thin films.

关键词： ferroelectric capacitors thin films ferroelectricity hafnium zirconium oxide

Investigation of high rate mechanical flow followed by ignition for high-energy propellant under dynamic extrusion loading

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Defence technology（防务技术） 2024年第2期32卷 336-347页

作者： Liying Dong Yanqing Wu Kun Yang Xiao Hou State Key Laboratory of Explosion Science and technology Beijing Institute of TechnologyBeijing 100081China School of aerospace Engineering Beijing Institute of TechnologyBeijing 100081China

Investigating the ignition response of nitrate ester plasticized polyether(NEPE) propellant under dynamic extrusion loading is of great significant at least for two cases. Firstly, it helps to understand the mechanism and conditions of unwanted ignition inside charged propellant under accident ***, evaluates the risk of a shell crevice in a solid rocket motor(SRM) under a falling or overturning scene. In the present study, an innovative visual crevice extrusion experiment is designed using a dropweight apparatus. The dynamic responses of NEPE propellant during extrusion loading, including compaction and compression, rapid shear flow into the crevice, stress concentration, and ignition reaction, have been firstly observed using a high-performance high-speed camera. The ignition reaction is observed in the triangular region of the NEPE propellant sample above the crevice when the drop weight velocity was 1.90 m/s. Based on the user material subroutine interface UMAT provided by finite element software LS-DYNA, a viscoelastic-plastic model and dual ignition criterion related to plastic shear dissipation are developed and applied to the local ignition response analysis under crevice extrusion conditions. The stress concentration occurs in the crevice location of the propellant sample, the shear stress is relatively large, the effective plastic work is relatively large, and the ignition reaction is easy to occur. When the sample thickness decreases from 5 mm to 2.5 mm, the shear stress increases from 22.3 MPa to 28.6 MPa, the critical value of effective plastic work required for ignition is shortened from 1280 μs to 730 μs, and the triangular area is easily triggering an ignition reaction. The propellant sample with a small thickness is more likely to stress concentration, resulting in large shear stress and effective work, triggering an ignition reaction.

关键词： NEPE propellant Crevice extrusion Shear flow Sample thickness Ignition reaction

Aero-structural design of joined-wing aircraft based on high-fidelity model

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Chinese Journal of Aeronautics 2024年第4期37卷 363-377页

作者： Cheng HE Fengjiang ZHAN Luchuang MA Gang CHEN Jianying MA Unmanned Air Vehicle Research Institute Nanjing University of Aeronautics and AstronauticsNanjing 210016China Key Laboratory of advanced technology for Small and Medium-sized UAV Ministry of Industry and Information TechnologyNanjing University of Aeronautics and AstronauticsNanjing 210016China aerospace System Engineering Shanghai Shanghai 201108China

The joined-wing configuration reduces induced drag and structural weight by connecting the rear wing to the front *** addition,the rear wing can replace the role of the horizontal tail of a conventional aircraft,thus eliminating the aerodynamic drag and weight associated with the horizontal *** particular shape creates a highly coupled relationship between aerodynamics and structure,which must be fully considered during the overall design process to enhance aircraft *** this research,an aero-structural design model of the joined-wing aircraft is constructed based on high-fidelity computational fluid dynamics and structural finite element *** model is able to obtain accurate aerodynamic loads for the non-planar wing and to simulate the statically indeterminate structure of the closed wing *** influence of the joined-wing shape parameters on the aerodynamic and structural disciplines,as well as the influence of geometric nonlinear characteristics,deformation constraints and buckling constraints on the structural weight are all taken into *** model is applied to complete the aero-structural design optimization of a high-altitude long-endurance joined-wing aircraft,and wind tunnel tests are *** test results verify the credibility of the design model proposed and the validity of the design environment.

关键词： Joined-wing configuration Aircraft design Aero-structural design Finite element Wind tunnel test