检索结果-南通市图书馆

Acta Mechanica Solida Sinica 2018年第3期31卷 369-382页

作者： yunfei li Xiangguo Zeng Institute of Systems Engineering China Academy of Engineering PhysicsMianyang 621999China College of Architecture and Environment Sichuan UniversityChengdu 610065China

In this paper, a new physically based constitutive model is developed for hexagonal close-packed metals, especially the Ti-6Al-4V alloy, subjected to high strain rate and different temperatures based on the microscopic mechanism of plastic deformation and the theory of thermally activated dislocation motion. A global analysis of constitutive parameters based on the Latin Hypercube Sampling method and the Spearman＇s rank correlation method is adopted in order to improve the identification efficiency of parameters. Then, an optimal solution of constitutive parameters as a whole is obtained by using a global genetic algorithm composed of an improved niche genetic algorithm, a global peak determination strategy and the local accurate search techniques. It is concluded that the proposed constitutive modal can accurately describe the Ti-6Al-4V alloy＇s dynamic behavior because the prediction results of the model are in good agreement with the experimental data.

关键词： Hexagonal close-packed metals Physically based constitutive model Dislocationmotion High strain rate Ti-6Al-4V

Two-maneuver indirect contingency return from a low lunar orbit

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2023年第8期36卷 115-127页

作者： yunfei li Xiaosheng XIN Xiyun HOU School of Astronomy and Space Science Nanjing UniversityNanjing 210023China Key Laboratory of Modern Astronomy and Astrophysics(Nanjing University) Ministry of EducationNanjing 210023China Beijing Institute of Tracking and Telecommunication Technology Beijing 100094China

The problem of contingency return from the low lunar orbit is studied.A novel twomaneuver indirect return strategy is *** effectively using the Earth’s gravity to change the orbital plane of the transfer orbit,the second maneuver in the well-known three-maneuver return strategy can be removed,so the total delta-v is *** with the singlemaneuver direct return,our strategy has the advantage in that the re-entry epoch for the minimum delta-v cost can be advanced in time,with a minimum delta-v value similar to that of the direct *** most obvious difference between our strategy and the traditional single-or multiplemaneuver strategies is that the complete transfer orbit is a patch between a two-body conic orbit and a three-body orbit instead of two conic *** strategy can serve as a useful option for contingency return from a low lunar orbit,especially when the delta-v constraint is stringent for a direct return and the contingency epoch is far away from the return window.

关键词： Moon Lowlunarorbit Contingencyreturn Third-body maneuver Gravityassist

A Three-Dimensional Dynamic Constitutive Model and Its Finite Element Implementation for NiTi Alloy Based on Irreversible Thermodynamics

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2019年第3期32卷 356-366页

作者： yunfei li Xiangguo Zeng Huayan Chen Institute of Systems Engineering China Academy of Engineering Physics Mianyang 621999 China College of Architecture and Environment Sichuan University Chengdu 610065 China

In the present work, the governing equations based on theory of irreversible thermodynamics is deduced by introducing two internal variables to characterize the phase transformation and finite plastic deformation evolution for NiTi shape memory alloy. Thus a three-dimensional dynamic constitutive model is established by summarizing the governing equations for phase transformation and plastic deformation under high strain rate loading conditions. By adopting a stress compensation algorithm to update the stress tensor, the phenomenologicalbased constitutive model is embedded into ABAQUS finite element software as user material subroutine with FORTRAN code. Thus the numerical simulation of dynamic responses of NiTi alloy is successfully implemented. The numerical simulation results are in good agreement with the experimental data, validating the feasibility of this proposed model. Comparison between the simulation results and the experimental data indicates that the proposed model can well describe not only the different deformation stages of NiTi alloy but also its constitutive behavior subjected to different high strain rates.

关键词： NiTi alloy Irreversible thermodynamics Constitutive model User material (UMAT) subroutine Dynamic response

The nitrogen transformation behavior based on the pyrolysis products of wheat straw

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Chemical Engineering 2024年第7期71卷 58-65页

作者： Shun Guo yunfei li Shengwei Tang Tao Zhang School of Chemical Engineering Sichuan UniversityChengdu 610065China

In order to provide basic design parameters for the industrial pyrolysis process,the transformation behavior of nitrogen was investigated using wheat straw as raw *** distributions of nitrogen in pyrolysis char,oil,and gas were obtained and the nitrogenous components in the products were analyzed systematically by X-ray photoelectron spectroscopy(XPS),pyrolysis-gas chromatography/mass spectrometry(Py-GC/MS)and thermogravimetric-Fourier transform infrared spectrometry(TG-FTIR).The nitrogen distribution ranges of the pyrolysis char,oil,and gas were 37.34%–54.82%,32.87%–40.94%and 10.20%–28.83%,*** nitrogen was retained in char at lower pyrolysis temperature and the nitrogen distribution of oil was from rise to decline with increasing *** most abundant N-containing compounds in three-phase products were pyrrole-N,amines,and HCN,*** addition,the transformation mechanism of nitrogen from wheat straw to pyrolysis products was concluded.

关键词： Pyrolysis Nitrogen transformation Wheat straw Py-GC/MS TG-FTIR

Recent progress of machine learning in flow modeling and active flow control

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2022年第4期35卷 14-44页

作者： yunfei li Juntao Chang Chen Kong Wen Bao School of Energy Science and Engineering Harbin Institute of TechnologyHarbin 150001China

In terms of multiple temporal and spatial scales, massive data from experiments, flow field measurements, and high-fidelity numerical simulations have greatly promoted the rapid development of fluid mechanics. Machine Learning(ML) provides a wealth of analysis methods to extract potential information from a large amount of data for in-depth understanding of the underlying flow mechanism or for further applications. Furthermore, machine learning algorithms can enhance flow information and automatically perform tasks that involve active flow control and optimization. This article provides an overview of the past history, current development, and promising prospects of machine learning in the field of fluid mechanics. In addition, to facilitate understanding, this article outlines the basic principles of machine learning methods and their applications in engineering practice, turbulence models, flow field representation problems, and active flow control. In short, machine learning provides a powerful and more intelligent data processing architecture, and may greatly enrich the existing research methods and industrial applications of fluid mechanics.

关键词： Data-driven modeling Flow control Flow field kinematics Machine learning Neural networks-applications

Operational Characteristics of Loop Heat Pipe in Microgravity and Normal Gravity Environments

在线全文

学校读者我要写书评

暂无评论

Journal of Thermal Science 2024年第4期33卷 1394-1408页

作者： ZHONG Siyuan XIE Rongjian li yunfei SUN Xiaojin Shanghai Institution of Technology and Physics Shanghai200083China University of Chinese Academy of Sciences Beijing100049China Shanghai Institute of Satellite Engineering Shanghai200240China

The loop heat pipe(LHP)is an advanced,efficient two-phase heat transfer unit,whose operational performance may be affected by microgravity conditions in contrast to ground-based *** performance of on-orbit temperature data and ground test of a copper-propylene LHP with a condenser temperature range of 243.15 K to 303.15 K were employed to compared and *** LHP has successfully started up for more than 193 times with a good heat transfer performance and a stable start-up stabilization on-orbit under a complex orbital heating environment for more than eight *** a small heat load(10.0W),the average start-up time is 110.0 s while the start-up temperature ranges from 5.71 K-12.78 *** start-up time at large temperature differences in the high temperature zone will be higher than the time required for start-up at smaller temperature differences in the low *** the condenser temperature is 250.0 K,the stable temperature difference on orbit is 3.83 K,which is generally consistent in heat transfer compared to 2.20 K in the ground *** this paper,we can conclude that the on-orbit flight data up to now can provide a reference to the design of subsequent LHP space applications.

关键词： Loop Heat Pipe(LHP) start up microgravity on-orbit experiment

Spatio-temporal fusion for remote sensing data:an overview and new benchmark

在线全文

学校读者我要写书评

暂无评论

Science China(Information Sciences) 2020年第4期63卷 7-23页

作者： Jun li yunfei li lin HE Jin CHEN Antonio PLAZA Guangdong Provincial Key Laboratory of Urbanization and Geo-simulation School of Geography and Planning Sun Yat-sen University School of Automation Science and Engineering South China University of Technology State Key Laboratory of Earth Surface Processes and Resource Ecology Institute of Remote Sensing Science and Engineering Faculty of Geographical ScienceBeijing Normal University Hyperspectral Computing Laboratory Department of Technology of Computers and CommunicationsEscuela Politécnica University of Extremadura

Spatio-temporal fusion(STF) aims at fusing(temporally dense) coarse resolution images and(temporally sparse) fine resolution images to generate image series with adequate temporal and spatial resolution. In the last decade, STF has drawn a lot of attention and many STF methods have been ***, to date the STF domain still lacks benchmark datasets, which is a pressing issue that needs to be addressed in order to foster the development of this field. In this review, we provide(for the first time in the literature) a robust benchmark STF dataset that includes three important characteristics:(1) diversity of regions,(2) long timespan, and(3) challenging scenarios. We also provide a survey of highly representative STF techniques, along with a detailed quantitative and qualitative comparison of their performance with our newly presented benchmark dataset. The proposed dataset is public and available online.

关键词： spatio-temporal fusion(STF) multi-temporal remote sensing data benchmark data experimental validation

A deep learning approach for velocity field prediction in a scramjet isolator from Schlieren images

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2023年第11期36卷 58-70页

作者： Chen KONG Ziao WANG yunfei li Juntao CHANG School of Energy Science and Engineering Harbin Institute of TechnologyHarbin 150001China

Accurate measurements of physical parameters in a scramjet isolator are very important to promote the design and optimization of the isolator and even the *** a ground experiment,limited by the inherent characteristics of measurement technology and equipment,it is a big challenge to obtain the velocity field inside an *** this study,a deep learning approach was introduced to combine data obtained from ground experiments and numerical simulations,and a velocity field prediction model was developed for obtaining the velocity field inside an isolator based on experimental Schlieren *** velocity field prediction model was designed with convolutional neural networks as the main *** experiments of a scramjet isolator under continuous Mach number variation were carried out,and Schlieren images of the flow field inside the isolator were *** simulations of the isolator were also carried out,and the velocity fields inside the isolator under various Mach numbers were *** velocity field prediction model was trained using flow field datasets containing experimental Schlieren images and velocity field,and the mapping relationship between the experimental Schlieren images and the predicted velocity field was successfully established.

关键词： Data-driven model Deep learning Neural networks Scramjet isolator Velocity field prediction

Design of Novel and Low Cost Triple-node Upset Self-recoverable Latch

在线全文

学校读者我要写书评

暂无评论

原子能科学技术 2023年第12期57卷 2326-2336页

作者： BAI Na MING Tianbo XU Yaohua WANG Yi li yunfei li li Information Materials and Intelligent Sensing Laboratory of Anhui Province Anhui UniversityHefei 230601China Shanxi Key Laboratory of Advanced Semiconductor Optoelectronic Devices and Integrated Systems Jincheng 048000China Jincheng Research Institute of Opo-mechatronics Industry Jincheng 048000China

With the development of semiconductor technology,the size of transistors continues to *** complex radiation environments in aerospace and other fields,small-sized circuits are more prone to soft error(SE).Currently,single-node upset(SNU),double-node upset(DNU)and triple-node upset(TNU)caused by SE are relatively ***’s solution is not yet fully mature.A novel and low-cost TNU self-recoverable latch(named NLCTNURL)was designed which is resistant to harsh radiation *** analyzing circuit resiliency,a double-exponential current source is used to simulate the flipping behavior of a node’s stored value when an error *** results show that the latch has full TNU self-recovery.A comparative analysis was conducted on seven latches related to ***,a comprehensive index combining delay,power,area and self-recovery—DPAN index was proposed,and all eight types of latches from the perspectives of delay,power,area,and DPAN index were analyzed and *** simulation results show that compared with the latches LCTNURL and TNURL which can also achieve TNU self-recoverable,NLCTNURL is reduced by 68.23%and 57.46%respectively from the perspective of *** the perspective of power,NLCTNURL is reduced by 72.84%and 74.19%,*** the area perspective,NLCTNURL is reduced by about 28.57%and 53.13%,*** the DPAN index perspective,NLCTNURL is reduced by about 93.12%and 97.31%.The simulation results show that the delay and power stability of the circuit are very high no matter in different temperatures or operating voltages.

关键词： circuit reliability latch design self-recoverability soft error radiation hardening triple-node upset

Dynamic Tensile Behavior and Constitutive Modeling of TC21 Titanium Alloy

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2019年第3期34卷 707-716页

作者： li yunfei ZENG Xiangguo Institute of Systems Engineering China Academy of Engineering PhysicsMianyang 621999China College of Architecture and Environment Sichuan UniversityChengdu 610065China

The dynamic tensile behaviors of a newly developed Ti-6 Al-2 Sn-2 Zr-3 Mo-1 Cr-2 Nb-Si alloy（referred as TC21 in China） over a wide range of strain rates from quasi-static to dynamic regimes(0.001-1 200 s-1) at different temperatures were experimentally investigated. A split Hopkinson tension bar apparatus and a static material testing system were utilized to study the stress-strain responses under uniaxial tension loading condition. The experimental results indicate that the tensile behavior of TC21 titanium alloy is dependent on the strain rate and temperature. The values of initial yield stress increase with increasing strain rate and decreasing temperature. The effects of strain rate and temperature on the initial yield behavior are estimated by introducing two sensitivity parameters. The phenomenological-based constitutive model, Johnson-Cook model, is suitably modified to describe the rate-temperature dependent constitutive behavior of TC21 titanium alloy. It is observed that the modified model is in good agreement with the experimental data subjected to the investigated range of strain rates and temperatures.

关键词： two-phase titanium alloy dynamic tensile behavior rate-temperature sensitivity constitutive modeling