Parametric study on supersonic flutter of angle-ply laminated plates using shear deformable finite element method

The influence of fiber orientation,flow yaw angle and length-to-thickness ratio on flutter characteristics of angle-ply laminated plates in supersonic flow is studied by finite element approach.The structural model is established using the Reissner-Mindlin theory in which the transverse shear deformation is considered.The aerodynamic pressure is evaluated by the quasi-steady first-order piston theory.The equations of motion are formulated based on the principle of virtual work.With the harmonic motion assumption,the flutter boundary is determined by solving a series of complex eigenvalue problems.Numerical study shows that （1） The flutter dynamic pressure and the coalescence of flutter modes depend on fiber orientation,flow yaw angle and length-to-thickness ratio;（2） The laminated plate with all fibers aligned with the flow direction gives the highest flutter dynamic pressure,but a slight yawing of the flow from the fiber orientation results in a sharp decrease of the flutter dynamic pressure;（3） The angle-ply laminated plate with fiber orientation angle equal to flow yaw angle gives high flutter dynamic pressure,but not the maximum flutter dynamic pressure;（4） With the decrease of length-to-thickness ratio,an adverse effect due to mode transition on the flutter dynamic pressure is found.

基于配电网自动化系统的10 kV线路继电保护整定计算

配电网自动化线路涉及3个及以上开关的保护整定,若每个开关设置一级保护,将存在保护时限紧张无法配合的问题。由于常规10kV线路两段式过流保护0s/0.3s时限不能满足配电网自动化线路多级开关保护时限配合的要求,因此提出分级整定的方案,将配电网多个开关按保护安装位置及接带负荷性质划分为三级进行整定。最后结合工程实例进行分析计算,验证了该方案的准确性与有效性,可保证继电保护动作的选择性,进一步提高供电可靠性。

分布式光伏短路特性对配电网保护的影响研究

分布式光伏电源使配电网从单电源辐射型网络变为双向的多电源网络,电网潮流、系统故障时的短路电流均发生变化,传统的继电保护整定方案已经不能满足新型运行方式下的要求。建立光伏电站的等值模型并对其短路故障特性进行仿真分析。然后结合具体工程实例,研究不同的光伏接入容量对地区电网短路水平的影响。在上述仿真研究的基础上,进一步分析分布式光伏接入对配电网继电保护配置、整定计算方面的影响并提出改进措施。

New insight into the stability and dynamics of fluid-conveying supported pipes with small geometric imperfections

In several previous studies,it was reported that a supported pipe with small geometric imperfections would lose stability when the internal flow velocity became sufficiently high.Recently,however,it has become clear that this conclusion may be at best incomplete.A reevaluation of the problem is undertaken here by essentially considering the flow-induced static deformation of a pipe.With the aid of the absolute nodal coordinate formulation(ANCF)and the extended Lagrange equations for dynamical systems containing non-material volumes,the nonlinear governing equations of a pipe with three different geometric imperfections are introduced and formulated.Based on extensive numerical calculations,the static equilibrium configuration,the stability,and the nonlinear dynamics of the considered pipe system are determined and analyzed.The results show that for a supported pipe with the geometric imperfection of a half sinusoidal wave,the dynamical system could not lose stability even if the flow velocity reaches an extremely high value of 40.However,for a supported pipe with the geometric imperfection of one or one and a half sinusoidal waves,the first-mode buckling instability would take place at high flow velocity.Moreover,based on a further parametric analysis,the effects of the amplitude of the geometric imperfection and the aspect ratio of the pipe on the static deformation,the critical flow velocity for buckling instability,and the nonlinear responses of the supported pipes with geometric imperfections are analyzed.

Dynamical Stability of Cantilevered Pipe Conveying Fluid with Inerter-Based Dynamic Vibration Absorber

Cantilevered pipe conveying fluid may become unstable and flutter instability would occur when the velocity of the fluid flow in the pipe exceeds a critical value.In the present study,the theoretical model of a cantilevered fluid-conveying pipe attached by an inerter-based dynamic vibration absorber(IDVA)is proposed and the stability of this dynamical system is explored.Based on linear governing equations of the pipe and the IDVA,the effects of damping coefficient,weight,inerter,location and spring stiffness of the IDVAon the critical flow velocities of the pipe system is examined.It is shown that the stability of the pipe may be significantly affected by the IDVA.In many cases,the stability of the cantilevered pipe can be enhanced by designing the parameter values of the IDVA.By solving nonlinear governing equations of the dynamical system,the nonlinear oscillations of the pipe with IDVA for sufficiently high flow velocity beyond the critical value are determined,showing that the oscillation amplitudes of the pipe can also be suppressed to some extent with a suitable design of the IDVA.

Dynamic analysis and regulation of the flexible pipe conveying fluid with a hard-magnetic soft segment

The recently developed hard-magnetic soft(HMS)materials can play a significant role in the actuation and control of medical devices,soft robots,flexible electronics,etc.To regulate the mechanical behaviors of the cantilevered pipe conveying fluid,the present work introduces a segment made of the HMS material located somewhere along the pipe length.Based on the absolute node coordinate formulation(ANCF),the governing equations of the pipe conveying fluid with an HMS segment are derived by the generalized Lagrange equation.By solving the derived equations with numerical methods,the static deformation,linear vibration characteristic,and nonlinear dynamic response of the pipe are analyzed.The result of the static deformation of the pipe shows that when the HMS segment is located in the middle of the pipe,the downstream portion of the pipe centerline will keep a straight shape,providing that the pipe is stable with a relatively low flow velocity.Therefore,it is possible to precisely regulate the ejection direction of the fluid flow by changing the magnetic and fluid parameters.It is also found that the intensity and direction of the external magnetic field greatly affect the stability and dynamic response of the pipe with an HMS segment.In most cases,the magnetic actuation increases the critical flow velocity for the flutter instability of the pipe system and suppresses the vibration amplitude of the pipe.

城市黑臭水体的综合治理措施及应用实践

文章结合城市黑臭水体案例,从黑臭水体的判断标准、形成原因和治理措施等方面,对黑臭水体的治理进行探讨。结果显示:治理工程完成后,河道内整体水质基本达到地表IV类水体,改变了河水黑臭的现状,实现了美化环境和净化环境相统一。

Natural Frequency and Stability Tuning of Cantilevered CNTs Conveying Fluid in Magnetic Field

This paper investigates the dynamics of cantilevered CNTs conveying fluid in lon- gitudinal magnetic field and presents the possibility of controlling/tuning the stability of the CNT system with the aid of magnetic field. The slender CNT is treated as an Euler-Bernoulli beam. Based on nonlocal elasticity theory, the equation of motion with consideration of magnetic field effect is developed. This partial differential equation is then discretized using the differen- tial quadrature method （DQM）. Numerical results show that the nonlocal small-scale parameter makes the fluid-conveying CNT more flexible and can shift the unstable mode in which flutter instability occurs first at sufficiently high flow velocity from one to another. More importantly, the addition of a longitudinal magnetic field leads to much richer dynamical behaviors of the CNT system. Indeed, the presence of longitudinal magnetic field can significantly affect the evolution of natural frequency of the dynamical system when the flow velocity is successively increased. With increasing magnetic field parameter, it is shown that the CNT system behaves stiffer and hence the critical flow velocity becomes higher. It is of particular interest that when the mag- netic field parameter is equal to or larger than the flow velocity, the cantilevered CNT conveying fluid becomes unconditionally stable, indicating that the dynamic stability of the system can be controlled due to the presence of a longitudinal magnetic field.

NONLINEAR DYNAMICS AND SYNCHRONIZATION OF TWO COUPLED PIPES CONVEYING PULSATING FLUID

In this paper, the nonlinear dynamical behavior of two coupled pipes conveying pulsating fluid is studied. The connection between the two pipes is considered as a distributed linear spring. Based on this consideration, the equations of motion of the coupled two-pipe system are obtained. The two coupled nonlinear partial differential equations, discretized using the fourth- order Galerkin method, are solved by a fourth-order Runge-Kutta integration algorithm. Results show that the connection stiffness has a significant effect on the dynamical behavior of the coupled system. It is found that for some parameter values the motion types of the two pipes might be synchronous.

TRANSFER MATRIX METHOD FOR ANALYZING VIBRATION AND DAMPING CHARACTERISTICS OF ROTATIONAL SHELL WITH PASSIVE CONSTRAINED LAYER DAMPING TREATMENT

The first order differential matrix equations of the host shell and constrained layer for a sandwich rotational shell are derived based on the thin shell theory.Employing the layer wise principle and first order shear deformation theory, only considering the shearing deformation of the viscoelastic layer, the integrated first order differential matrix equation of a passive constrained layer damping rotational shell is established by combining with the normal equilibrium equation of the viscoelastic layer.A highly precise transfer matrix method is developed by extended homogeneous capacity precision integration technology.The numerical results show that present method is accurate and effective.

MODELING AND DYNAMICS ANALYSIS OF SHELLS OF REVOLUTION BY PARTIALLY ACTIVE CONSTRAINED LAYER DAMPING TREATMENT

A new model for a smart shell of revolution treated with active constrained layer damping （ACLD） is developed, and the damping effects of the ACLD treatment are discussed. The motion and electric analytical formulation of the piezoelectric constrained layer are presented first. Based on the authors~ recent research on shells of revolution treated with passive constrained layer damping （PCLD）, the integrated first-order differential matrix equation of a shell of revolution partially treated with ring ACLD blocks is derived in the frequency domain. By virtue of the extended homogeneous capacity precision integration technology, a stable and simple numerical method is further proposed to solve the above equation. Then, the vibration responses of an ACLD shell of revolution are measured by using the present model and method. The results show that the control performance of the ACLD treatment is complicated and frequency-dependent. In a certain frequency range, the ACLD treatment can achieve better damping characteristics compared with the conventional PCLD treatment.

Tailoring Defects in Hard Carbon Anode towards Enhanced Na Storage Performance

Hard carbon(HC)anodes show conspicuously commercialized potential for sodium-ion batteries(SIBs)due to their costeffectiveness and satisfactory performance.However,the development of hard carbon anodes in SIBs is still hindered by low initial Coulombic efficiency(ICE)and insufficient cyclic stability,which are induced by inappropriate defects in the structure.Herein,we introduce a simple but effective method to tailor the defects in HC by the chemically preadsorbed K^(+).The soft Xray absorption spectroscopy at the C K-edges reveals that K^(+)can anchor on the hard carbon via C-O-K bonds,occupying the irreversible reactive sites of Na^(+).Therefore,the irreversible capacity caused by some C-O bonds can be reduced.Moreover,the preadsorbed K^(+)can induce the rearrangement of carbon layers and lead to a high graphitization structure with fewer defects and large interlayer spacing,which not only improves the structural stability and electrical conductivity of the HC anode but also facilitates fast Na^(+)diffusion.Therefore,the as-obtained optimized anode demonstrates a higher ICE with better cyclic stability and superior rate capacities compared with the anode without preadsorbed K^(+).This work indicates that K^(+)preadsorbed into hard carbon is a practicable alternative to enhance the Na storage performances of HC anodes for SIBs.

Mesoporous TiO2 microparticles formed by the oriented attachment of nanocrystals： A super-durable anode material for sodium-ion batteries

Spindle-shaped anatase TiO2 secondary particles were successfully fabricated via the oriented attachment of primary nanocrystals. By adjusting the concentration of tetrabutyl titanate, the size of the TiO2 nanocrystals and particles could be controlled, resulting in pore evolution. Pores for the random aggregation of secondary particles gradually transformed to nanopores originating from the oriented attachment of the primary nanocrystals, resulting in an excellent micro/nanostructure that increased the performance of a sodium-ion battery. The mesoporous TiO2 microparticle anode, with its unique combination of nanocrystals and uniform nanopores, displays super durability （95 mAh/g after 11,000 cycles at I C）, high initial efficiency （61.4%）, and excellent rate performance （265 and 77 mAh/g at 0.1 and 20 C, respectively）. In particular, at slow discharge （0.1 C） and fast charge （5, 50, and 100 C） rates, the anatase TiO2 shows remarkable initial charge capacities of 200, 119, and 56 mAh/g, corresponding to 172, 127, and 56 mAh/g, after 150 cycles, respectively, thus meeting the requirements for fast energy storage. This excellent performance can be attributed to the stability of the material and its high ionic conductivity, resulting from the stable architecture with a mesoporous microstructure and without the random aggregation of secondary particles. A fundamental understanding of the pore structure and controllable pore construction has been proven to be effective in increasing the rate capability and durability of nanostructured electrode materials.

Nonlinear Vibration of A Loosely Supported Curved Pipe Conveying Pulsating Fluid under Principal Parametric Resonance

In this paper,the nonlinear dynamics of a curved pipe is investigated in the case of principal parametric resonance due to pulsating flow and impact with loose supports.The coupled in-plane and out-of-plane governing equations with the consideration of von Karman geometric nonUnearity are presented and discretized via the differential quadrature method（DQM）.The nonlinear dynamic responses are calculated numerically to demonstrate the influence of pulsating frequency.Finally,the impact is taken into consideration.The influence of clearance on frettingwear damage,such as normal work rate,contact ratio and impact force level,is demonstrated.

Stability analysis of a hybrid flexible-rigid pipe conveying fluid

The stability and dynamical behavior of flexible and articulated rigid pipes conveying fluid have attracted the attention of many researchers in the field of fluid-structure interactions.The system of an articulated pipe composed of a flexible pipe and a rigid pipe is a class of hybrid flexible-rigid dynamical problems involving flow-induced vibrations.This paper establishes the governing equations of motion of a hybrid flexible-rigid pipe system based on Hamilton's principle,with the rigid pipe being hinged to the lower end of a flexible cantilevered pipe via a rotational spring.The coupling equations of motion are discretized via a Galerkin's approach.The mathematical model is validated by comparing the eigenvalue branches of a degenerated system by choosing extreme values of the parameters of the hybrid pipe with previous results.In the theoretical analysis,the critical flow velocities are calculated as a function of the stiffness of the rotational spring,mass ratio and length ratio of the rigid and flexible pipes.The unstable modes are detected from the eigenvalue branches and compared with those of a flexible cantilevered pipe.Numerical results show that the critical flow velocity is greatly influenced by several structural parameters.It is found that a small stiffness of the rotational spring tends to predict higher-mode instability,whereas a large rotational spring stiffness would generate a second-mode instability in most cases.In several system parameter spaces,the hybrid pipe may experience a transference of unstable modes with the increase of flow velocity.It is also shown that the hybrid pipe system may lose stability first in the fourth mode in some cases.Some of the fresh results obtained for the hybrid pipe system are expected to be helpful in understanding and controlling the dynamical responses of hybrid flexible-rigid fluid-conveying pipes.