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Partial discharge-induced crack growth in dielectric materials

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Science China(Physics,Mechanics & Astronomy) 2010年第5期53卷 886-891页

作者： LUO JiaCheng,gao cunfa & DAI XiangHua college of aerospace engineering,nanjing university of aeronautics & astronautics,Nanjing 210016,China college of aerospace engineering Nanjing University of Aeronautics & Astronautics Nanjing China

Partial discharge(PD) of an air-filled semi-permeable crack in a dielectric material is studied based on the streamer-type discharge mechanism to explore the effects of applied mechanical-electric fields on crack growth.Within the frame of two-dimensional deformation,the electric field inside the crack is first derived by taking the crack deformation into account.Then,the effects of electric field before PD are discussed through considering the contribution of the induced electric field inside the deformed crack space to the total energy release rate.Finally,PD and its effects on crack growth are investigated.It is found that:(1) before PD,the applied electric field always retards crack growth;(2) during PD,the applied electric field can induce crack growth in dielectric materials.

关键词： crack dielectric materials partial discharge electric field effects

GENERAL SOLUTION OF STRESS FIELDS IN AN ELECTROSTRICTIVE MATERIAL WITH POINT CHARGE

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GENERAL SOLUTION OF STRESS FIELDS IN AN ELECTROSTRICTIVE MAT...

Closed-Form Solution for a Circular Nanohole with Surface Effects Under Uniform Heat Flux

第三届全国压电和声波理论及器件技术研讨会

作者： quan jiang college of aerospace engineering,Nanjing University of Aeronautics and Astronautics, Nanjing 210016,P.R.China college of Civil engineering,Nantong university,Nantong 226007,China Cun-fa gao college of aerospace engineering,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China

In this paper,the electroelastic stress fields in an electrostrictive material with point charge are studied.Firstly,the general solutions for the potential functions of electric fields and stresses are derived for the case of point charge based on analytical continuation method.The explicit results are given for the case of whole infinite plane.Finally the effect of interaction for the point charge and the perturbation or extra electric fields is discussed.It is found that the stress functions are different from the ones of piezoelectric materials.Moreover.the nonlinear effects for the coupling of electric and stress fields should be considered.

关键词： Electrostriction point charge stress field

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Acta Mechanica Solida Sinica 2024年第1期37卷 43-52页

作者： Jieyao Tang Jieyan Zhao Haibing Yang cunfa gao State Key Laboratory of Mechanics and Control for aerospace Structures Nanjing University of Aeronautics and AstronauticsNanjing 210016China School of Civil engineering and Transportation South China University of TechnologyGuangzhou 510641China college of Mechanics and Materials Hohai UniversityNanjing 211100China

This paper investigates the steady-state thermoelastic problem of a circular nanohole embedded in an infinitely large elastic plane subjected to a uniform far-field heat flux.A lowly conductive surface model is used to account for the effects of surface phonon scattering,while the complete Gurtin–Murdoch model is utilized to characterize the effects of surface tension and surface elasticity.The closed-form solution to the temperature and stress field surrounding the hole is derived in the context of complex variable methods.Several numerical examples are presented to analyze the influence of surface effects on thermal stress fields.It is shown that surface effects induce notable increases in normal and shear stresses around the hole.Specifically,all three stress components(hoop,normal,and shear)in the vicinity of the hole exhibit substantial augmentation with increasing surface tension and surface modulus.In particular,it is found that the presence of surface effects amplifies the variation in stress gradients and intensifies stress concentration around the hole.

关键词： Circular nanohole Surface effect Thermal stress Heat flux

Effects of electric/magnetic impact on the transient fracture of interface crack in piezoelectric-piezomagnetic sandwich structure: anti-plane case

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Applied Mathematics and Mechanics(English Edition) 2020年第1期41卷 139-156页

作者： Xing ZHAO Zhenghua QIAN Jinxi LIU cunfa gao Department of engineering Mechanics Shijiazhuang Tiedao UniversityShijiazhuang 050043China State Key Laboratory of Mechanics and Control of Mechanical Structures College of Aerospace EngineeringNanjing University of Aeronautics and AstronauticsNanjing 210016China

Due to the incompatibility of the interlaminar deformations,the interface debonding or cracking usually happens in a layered magnetoelectric(ME)structure under an applied load.In this paper,the transient responses of the anti-plane interface cracks in piezoelectric(PE)-piezomagnetic(PM)sandwich structures are studied by the standard methods of the integral transform and singular integral equation.Discussion on the numerical examples indicates that the PE-PM-PE structure under electric impact is more likely to fracture than the PM-PE-PM structure under a magnetic impact.The dynamic stress intensity factors(DSIFs)are more sensitive to the variation of the active layer thickness.The effects of the material constants on the DSIFs are dependent on the roles played by PE and PM media during the deformation process.

关键词： piezoelectric(PE)-piezomagnetic(PM) sandwich structure interface crack transient response dynamic stress intensity factor(DSIF)

Qualitative analysis for state/event fault trees using formal model checking

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Journal of Systems engineering and Electronics 2019年第5期30卷 959-973页

作者： jiang quan ZHU Chunling WANG Siqi college of aerospace engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016China China Academy of Electronics and Information Technology Beijing 100083China

A state/event fault tree(SEFT)is a modeling technique for describing the causal chains of events leading to failure in software-controlled complex systems.Such systems are ubiquitous in all areas of everyday life,and safety and reliability analyses are increasingly required for these systems.SEFTs combine elements from the traditional fault tree with elements from state-based techniques.In the context of the real-time safety-critical systems,SEFTs do not describe the time properties and important timedependent system behaviors that can lead to system failures.Further,SEFTs lack the precise semantics required for formally modeling time behaviors.In this paper,we present a qualitative analysis method for SEFTs based on transformation from SEFT to timed automata(TA),and use the model checker UPPAAL to verify system requirements’properties.The combination of SEFT and TA is an important step towards an integrated design and verification process for real-time safety-critical systems.Finally,we present a case study of a powerboat autopilot system to confirm our method is viable and valid after achieving the verification goal step by step.

关键词： state/event fault tree (SEFT) timed automata (TA) model transformation safety analysis

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基于负载均衡的并行FP-Growth算法

计算机工程 2019年第3期45卷 32-35,40页

作者：高权万晓冬南京航空航天大学自动化学院南京211106

针对FP-Growth算法查找操作时间复杂度较高的问题,提出一种新的算法LBPFP。在PFP算法基础上,将哈希表加入链头表以实现项地址的快速访问,并设计基于前缀长度的计算量模型,优化并行流程,提升算法的执行效率。在webdocs.dat数据库上进行... 详细信息

针对FP-Growth算法查找操作时间复杂度较高的问题,提出一种新的算法LBPFP。在PFP算法基础上,将哈希表加入链头表以实现项地址的快速访问,并设计基于前缀长度的计算量模型,优化并行流程,提升算法的执行效率。在webdocs.dat数据库上进行对比实验,结果表明,LBPFP算法比PFP、HPFP、DPFP算法具有更高的频繁项集挖掘效率。

关键词： Spark平台频繁模式增长并行负载均衡链头表计算量模型

Multi–physical-field characteristics modeling and structure optimization for kW-level ultra-high-speed PM motors with integrated support system

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Chinese Journal of aeronautics 2023年第4期36卷 455-467页

作者： Qixing gao Xiaolin WANG Yan ZHANG college of Automation engineering Nanjing University of Aeronautics and AstronauticsNanjing 211106China School of Intelligence Science and Control engineering Jinling Institute of TechnologyNanjing 211169China

In the aerospace industry,the low-mass ultra-high-speed flywheel system play a critical role.In this paper,a kW-level Ultra-High Speed Permanent Magnet Synchronous Motor(UHSPMSM)as the core component of flywheel system is proposed and analyzed with consideration of multiple physical fields,including electromagnetic characteristics,mechanical strength and rotor dynamics.The integrated support structure is put forward to improve rotation accuracy and operation stability of the UHSPMSM.Further,influence of the integrated support structure on critical speed is explored,and the key parameters such as support position and support stiffness are designed.Moreover,the rotor strength is analyzed by analytical model developed of rotor stress that can deal with multiple boundary types.Material and thickness of the sleeve are optimized,and range of interference value is accurately limited based on four extreme operating conditions.The 3-D Finite Element Model(FEM)is used to validate the strength characteristics and stress distribu-tion of rotor.A 1.5 kW-150000 r/min UHSPMSM with integrated support system is manufactured and tested.The feasibility of UHSPMSM proposed and the accuracy of analysis method are verified through electromagnetic,temperature rise and vibration characteristics test.The machine prototype realizes the load operation at rated speed and the multi-physical-field characteristics achieve the design specification.

关键词： Flywheel energy storage Integrated support system Multi–physical-field charac-teristics Mechanical strength Rotor dynamics Ultra-high-speed motor

Acoustic Bilayer Gradient Metasurfaces for Perfect and Asymmetric Beam Splitting

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Chinese Physics Letters 2024年第1期41卷 39-50页

作者：权家琪孙宝印伏洋洋高雷徐亚东 Institute of Theoretical and Applied Physics School of Physical Science and TechnologySoochow UniversitySuzhou 215006China college of Physics Nanjing University of Aeronautics and Astronautics&Key Laboratory of Aerospace Information Materials and Physics(NUAA)MIITNanjing 211106China School of Optical and Electronic Information Suzhou City UniversitySuzhou 215104China

We experimentally and theoretically present a paradigm for the accurate bilayer design of gradient metasurfaces for wave beam manipulation,producing an extremely asymmetric splitting effect by simply tailoring the interlayer size.This concept arises from anomalous diffraction in phase gradient metasurfaces and the precise combination of the phase gradient in bilayer metasurfaces.Ensured by different diffraction routes in momentum space for incident beams from opposite directions,extremely asymmetric acoustic beam splitting can be generated in a robust way,as demonstrated in experiments through a designed bilayer system.Our work provides a novel approach and feasible platform for designing tunable devices to control wave propagation.

关键词： surfaces splitting asymmetric

Liutex based new fluid kinematics

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Journal of Hydrodynamics 2022年第3期34卷 355-371页

作者： Chaoqun Liu Yifei Yu Yi-sheng gao Department of Mathematics University of Texas at ArlingtonArlingtonTexas76019USA college of aerospace engineering Nanjing University of Aeronautics and AstronauticsNanjing210016China

The traditional Cauchy-Stokes(C-S)decomposition states that the velocity gradient tensor can be decomposed into a symmetric tensor and an anti-symmetric tensor,namely the strain-rate tensor and the vorticity tensor.However,there are two problems with the C-S decomposition.One is that the anti-symmetric(vorticity)tensor cannot represent the fluid rotation or vortex.Another is that the symmetric(strain-rate)tensor cannot distinguish the stretching/compression and shear.Since vorticity cannot distinguish between the non-rotational shear and the rigid rotation,vorticity has been decomposed into a rigid rotation part called“Liutex”and an anti-symmetric shear in our previous work.A Liutex-based principal coordinate system has been proposed,and the corresponding velocity gradient tensor decomposition,called the principal decomposition,is presented in this principal coordinate system,which results in:(1)a Liutex tensor that represents rigid rotation,(2)a tensor that represents pure shear and(3)a tensor that represents stretching/compression.However,each point has its own principal coordinate system,which implies that the principal decomposition is performed in different principal coordinate systems,not the original(global)coordinate system.To address this issue,the principal decomposition in the original coordinate system is derived in this paper,and,therefore,provides a new kinematic approach to study the local rigid rotation,pure shear,and stretching/compression.The principal decomposition is unique,Galilean invariant and has clear physical meaning.The new velocity gradient tensor decomposition could become a foundation for new fluid kinematics.

关键词： Liutex principal coordinates principal decomposition Helmholtz Cauchy-Stokes(C-S)