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Journal of Modern Power Systems and Clean Energy 2023年第4期11卷 1041-1052页

作者： Jiawei zhang Zhichao Chen Ning zhang xianfeng zhang State Key Lab of Power Systems Department of Electrical EngineeringTsinghua UniversityBeijing 100084China Science and Technology Research Institute ChinaThreeGorgesCorporationBeijing100038China

Heavy renewable penetrations and high-voltage cross-regional transmission systems reduce the inertia and critical frequency stability of power systems after ***,the power system operators should ensure the frequency nadirs after possible disturbances are within the set restriction,e.g.,0.20 *** methods utilize linearized and simplified control models to quantify the frequency nadirs and achieve frequency-constrained unit commitments(FCUCs).However,the simplified models are hard to depict the frequency responses of practical units after ***,they usually neglect the regulations from battery *** paper achieves FCUCs with linear rules extracted from massive simulation *** simulate the frequency responses on typical thermal-hydro-storage systems under diverse unit online ***,we extract the rules of frequency nadirs after disturbances merely with linear support vector machine to evaluate the frequency stability of power *** algorithm holds a high accuracy in a wide range of frequency ***,we apply the rules to three typical cases to show the influences of frequency constraints on unit commitments.

关键词： Frequency regulation unit commitment machine learning rule extraction primary frequency regulation energy storage support vector machine

Study on micronozzle flow and propulsion performance using DSMC and continuum methods

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Acta Mechanica Sinica 2006年第5期22卷 409-416页

作者： Minghou Liu xianfeng zhang Genxuan zhang Yiliang Chen Department of Thermal Science and Energy Engineering University of Science and Technology of China Hefei 230027 China

In this paper, both DSMC and Navier-Stokes computational approaches were applied to study micronozzle flow. The effects of inlet condition, wall boundary condition, Reynolds number, micronozzle geometry and Knudsen number on the micronozzle flow field and propulsion performance were studied in detail. It is found that within the Knudsen number range under consideration, both the methods work to predict flow characteristics inside micronozzles. The continuum method with slip boundary conditions has shown good performance in simulating the formation of a boundary layer inside the nozzle. However, in the nozzle exit lip region, the DSMC method is better due to gas rapid expansion. It is found that with decreasing the inlet pressure, the difference between the continuum model and DSMC results increases due to the enhanced rarefaction effect. The coefficient of discharge and the thrust efficiency increase with increasing the Reynolds number. Thrust is almost proportional to the nozzle width. With dimension enlarged, the nozzle performance becomes better while the rarefaction effects would be somewhat weakened.

关键词： Micronozzle DSMC Continuum model Slip boundary condition Thrust efficiency

Extension of Flow Behaviour and Damage Models for Cast Iron Alloys with Strain Rate Effect

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Chinese Journal of Mechanical Engineering 2024年第3期37卷 297-310页

作者： Chuang Liu Dongzhi Sun xianfeng zhang Florence Andrieux Tobias Gersterc School of Mechanical Engineering Nanjing University of Science and TechnologyNanjing 210094China Fraunhofer Institute for Mechanics of Materials(IWM) 79108 FreiburgGermany Fraunhofer Institute for High Speed Dynamics Ernst-Mach-Institute(EMI)79104 FreiburgGermany

Cast iron alloys with low production cost and quite good mechanical properties are widely used in the automotive *** study the mechanical behavior of a typical ductile cast iron(GJS-450)with nodular graphite,uni-axial quasi-static and dynamic tensile tests at strain rates of 10^(-4),1,10,100,and 250 s^(-1)were carried *** order to investigate the influence of stress state on the deformation and fracture parameters,specimens with various geometries were used in the *** strain curves and fracture strains of the GJS-450 alloy in the strain rate range of 10^(-4)to 250 s^(-1)were obtained.A strain rate-dependent plastic flow model was proposed to describe the mechanical behavior in the corresponding strain-rate *** available damage model was extended to take the strain rate into account and calibrated based on the analysis of local fracture *** with the proposed plastic flow model and the damage model were conducted to observe the deformation and fracture *** results show that the strain rate has obviously nonlinear effects on the yield stress and fracture strain of GJS-450 *** predictions with the proposed plastic flow and damage models at various strain rates agree well with the experimental results,which illustrates that the rate-dependent plastic flow and damage models can be used to describe the mechanical behavior of cast iron alloys at elevated strain *** proposed plastic flow and damage models can be used to describe the deformation and fracture analysis of materials with similar properties.

关键词： Dynamic behavior of materials Strain rate dependency Damage model Voce model Cast iron

The stability analysis of rolling motion of hypersonic vehicles and its validations

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Science China(Physics,Mechanics & Astronomy) 2014年第12期57卷 2194-2204页

作者： YE YouDa ZHAO ZhongLiang TIAN Hao zhang xianfeng State Key Laboratory of Aerodynamics China Aerodynamic Research and Development Center National Laboratory for Computational Fluid Dynamics High Speed Institute of China Aerodynamic Research and Development Center

The stability of the rolling motion of near space hypersonic vehicles with rudder control is studied using method of qualitative analysis of nonlinear differential equations, and the stability criteria of the deflected rolling motions are improved. The out- comes can serve as the basis for further study regarding the influence of pitching and lateral motion on the stability of rolling motion. To validate the theoretical results, numerical simulations were do^e for the rolling motion of two hypersonic vehicles with typical configurations. Also, wind tunnel experiments for four aircraft models with typical configurations have been done. The results show that： 1） there exist two dynamic patterns of the rolling motion under statically stable condition. The first one is point attractor, for which the motion of aircraft returns to the original state. The second is periodic attractor, for which the aircraft rolls periodically. 2） Under statically unstable condition, there exist three dynamic patterns of rolling motion, namely, the point attractor, periodic attractor around deflected state of rolling motion, and double periodic attractors or chaotic attrac- tors.

关键词： rolling motion stability criterion numerical simulation wind tunnel experiment

Exploiting oleic acid to prepare two-dimensional assembly of Si@graphitic carbon yolk-shell nanoparticles for lithium-ion battery anodes

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Nano Research 2019年第3期12卷 631-636页

作者： Xiao Chen Chen Chen Yu zhang xianfeng zhang Dong Yang Angang Dong State Key Laboratory of Molecular Engineering of Polymer and Department of Macromolecular Science Fudan University Shanghai 200433 China Chem Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials and Department of Chemistry Fudan University Shanghai 200433 China

Carbon coati ng has bee n a routi ne strategy for improvi ng the performa nee of Si-based anode materials for lithium-ion batteries. The ability to tailor the thick ness, homoge neity and graph itizati on degree of carb on-coati ng layers is esse ntial for addressi ng issues that hamper the real applicatio ns of Si anodes. Herein, we report the con structio n of two-dime nsional (2D) assemblies of intercon nected Si @ graphitic carb on yolk-shell nano particles (2D-Si@gC) from commercial Si powders by exploiting oleic acid (OA). The OA molecules act as both the surface-coati ng liga nds for facilitating 2D nano particle assembly and the precursor for forming uniform and conformal graphitic shells as thin as 4 nm. The as-prepared 2D-Si@gC with rationally designed void space exhibits excellent rate capability and cycling stability when used as anode materials for lithium-ion batteries, delivering a capacity of 1,150 mAh·g^-1 at an ultrahigh current density of 10 A·g^-1 and maintaining a stabilized capacity of 1,275 mAh·g^-1 after 200 cycles at 4 A·g^-1 The formatio n of yolk-shell nano particles 8nfines the depositi on of solid electrolyte in terphase (SEI) onto the outer carb on shell, while simulta neously providing sufficie nt space for volumetric expa nsion of Si nano particles. These attributes effectively mitigate the thickness variations of the entire electrode during repeated lithiation and delithiation, which combined with the unique 2D architecture and interc onn ected graphitic carbon shells of 2D-Si@gC contributes to its superior rate capability and cycling performa nee.

关键词： oleic acid self-assembly graphitic carbon yolk-shell nanoparticles Sianodes

Carbon Nanotube-Textured Sand for Controlling Bioavailability of Contaminated Sediments

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Nano Research 2010年第6期3卷 412-422页

作者： Xingmao Ma Deepti Anand xianfeng zhang Mesfin Tsige Saikat Talapatra Department of Civil and Environmental Engineering Southern Illinois University CarbondaleIL 62901USA Department of Physics Southern Illinois University CarbondaleIL 62901USA

Sand particles textured with multi-walled carbon nanotubes (MWCNTs) can efficiently control the mobility and bioavailability of contaminants found in aquatic sediments. Adsorption measurements for a wide variety of aquatic contaminants (chlorinated hydrocarbons) on MWCNT-textured sand showed orders of magnitude increase in their sorption coefficients compared to traditional materials (sand) when used for physically separating contaminated sediments from overlying water. Molecular dynamics simulations performed on model experimental systems emphasize that the hydrophobic interactions of the MWCNT surfaces play a crucial role in driving the water molecules away, promoting such enhanced contaminant uptake. The MWCNT-textured sand significantly reduced the migration of contaminants from sediments to overlying water and possesses suitable parameters needed for contaminant sequestration and sediment remediation technologies. The single step and scalable procedure described here for synthesizing robust MWCNT-textured sand surfaces will provide important improvements in the field of remediation/aquatic environment restoration technologies.

关键词： Multi-walled carbon nanotube(MWCNT)-textured sand in situ capping capping amendments chlorinated compounds

HyperRefiner:a refined hyperspectral pansharpening network based on the autoencoder and self-attention

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International Journal of Digital Earth 2023年第1期16卷 3268-3294页

作者： Bo Zhou xianfeng zhang Xiao Chen Miao Ren Ziyuan Feng Institute of Remote Sensing and Geographic Information System Peking UniversityBeiigPeople's Republic of China

Deep learning has been developed to generate promising super resolution hyperspectral imagery by fusing hyperspectral imagery with the panchromatic ***,it is still challenging to maintain edge spectral information in the necessary upsampling processes of these approaches,and diffcult to guarantee effective feature *** study proposes a pansharpening network denoted as HyperRefiner that consists of,(1)a well performing upsampling network SRNet,in which the dual attention block and refined attention block are cascaded to accomplish the extraction and fusion of features;(2)a spectral autoencoder that is embedded to perform dimensionality reduction under constrained feature extraction;and(3)the optimization module which performs self-attention at the pixel and feature levels.A comparisonwithseveral state-of-the-art models reveals that HyperRefiner can improve the quality of the fused ***,compared to the single-head HyperTransformer and with the Chikusei dataset,our network improved the Peak Signal-to-Noise Ratio,Erreur Relative Globale Adimensionnelle de Synthese and Spectral Angle Mapper by 0.86%,3.62%,and 2.09%,and reduce the total memory,floating point operations,model parameters and computation time by 41%,75%,86%and 46%,*** experimental results show that HyperRefiner outperforms several networks and demonstrates its usefulness in hyperspectral image *** code is publicly available athttps://***/zsspo/Fusion_HyperRefiner.

关键词： Image fusion hyperspectral self-attention autoencoder edge spectrum

An IconMap-based exploratory analytical approach for multivariate geospatial data

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Science China(Information Sciences) 2013年第1期56卷 198-207页

作者： zhang xianfeng LIAO ChunHua LIU Yu LI Jonathan Institute of Remote Sensing and GIS Peking University Department of Geography and Environmental Management University of Waterloo

This paper discusses an iconmap-based visualization technique that enables multiple geospatial variables to be illustrated in a single GIS raster *** is achieved by extending the conventional pixelbased data structure to an iconic *** this way,spatial patterns generated by the interaction of geographic variables can be disclosed,and geospatial information mining can be readily *** a case study,a visual analysis of soil organic matter and soil nutrients for Shuangliu County in the city of Chengdu,China,was undertaken using the prototype IconMapper software,developed by the *** results show that the static IconMap can accurately exhibit trends in the distribution of organic matter and nutrients in *** dynamic iconmap can both reflect interaction patterns between organic matter and the nutrient variables,and display soil fertility levels in a comprehensive ***,the iconmap-based visualization approach is shown to be a non-fused,exploratory analytical approach for multivariate data analysis and as a result is a valuable method for visually analyzing soil fertility conditions.

关键词： iconmap soil fertility visualization icon blocks multivariate geospatial data

Theoretical analysis for self-sharpening penetration of tungsten high-entropy alloy into steel target with elevated impact velocities

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Acta Mechanica Sinica 2021年第6期37卷 970-982,I0002页

作者： Haihua Chen xianfeng zhang Chuang Liu Wei Xiong Mengting Tan Lan-Hong Dai School of Mechanical Engineering Nanjing University of Science&TechnologyXiaolingwei 200Nanjing210094China State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing100190China School of Engineering Science University of Chinese Academy of SciencesBeijing101408China

The“self-sharpening”effect has been observed experimentally in the penetration of tungsten high-entropy alloy(WHEA)into steel targets in previous *** the microscopic observation of the residual WHEA long-rod projectile(LRP),the multiphase structure at micro-scale of WHEA is the key effects on self-sharpening penetration *** order to describe the distinctive penetration behavior,the interaction between micro phases is introduced to modify the hydrodynamic penetration *** yield strengths of WHEA phases are determined based on the solid solution strengthening *** with the elbow-streamline model,the self-sharpening mechanism is revealed in view of the multi-phase flow dynamics and the flow field in the deformation area of the LRP nose is characterized to depict the shear layer evolution and the shape of the LRP’s nose as well as the determination of the penetration *** self-sharpening coefficient considering the reduction of nose radius is proposed and introduced into the penetration model to calculate the depth of penetration and the penetration *** show that the multi-phase interaction at the microscopic level contributes to the inhomogeneous distribution of the WHEA *** shear layer evolution separates part of the LRP material from the nose and makes the nose radius decrease more *** is also the reason that WHEA LRPs have a pointed nose compared with the mushroom nose of WHA heavy alloy(WHA)*** calculated results agree well with the corresponding experimental data of WHA and WHEA LRPs penetrating into semi-infinite medium carbon steel targets with elevated impact velocities.

关键词： Impact dynamics Long-rod projectile Tungsten high-entropy alloy(WHEA) Self-sharpening penetration Solid solution strengthening

High-quality graphene grown directly on stainless steel meshes through CVD process for enhanced current collectors of supercapacitors

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Science China(Technological Sciences) 2014年第2期57卷 259-263页

作者： NING Jing HAO Long zhang xianfeng LIANG MingHui ZHI LinJie National Center for Nanoscience and Technology University of Chinese Academy of Sciences School of Materials Science and Engineering University of Shanghai for Science and Technology

High-quality graphene coating was directly grown on stainless steel meshes via chemical vapor deposition process,during which the morphology of the stainless steel was transformed *** the graphene-coated stainless steel meshes were applied as current collectors of supercapacitors,the changes of the appearance and the graphene coating improved the contact between stainless steel meshes and the active materials,thus benefiting the performance of the ***,this simple method can be used to prepare the enhanced current collectors for other energy storage devices.

关键词： graphene current collector supercapacitor chemical vapor deposition (CVD)