Numerical simulation of the initial plasma formation and current transfer in single-wire electrical explosion in vacuum

In this paper, a computational model is constructed to investigate the phenomenon of the initial plasma formation and current transfer in the single-wire electrical explosion in a vacuum. The process of the single-wire electrical explosion is divided into four stages. Stage Ⅰ： the wire is in solid state. Stage Ⅱ： the melting stage. Stage Ⅲ： the wire melts completely and the initial plasma forms. Stage IV： the core and corona expand separately. The thermodynamic calculation is applied before the wire melts completely in stages Ⅰ and Ⅱ. In stage Ⅲ, a one-dimensional magnetohydrodynamics model comes into play until the instant when the voltage collapse occurs. The temperature, density, and velocity, which are derived from the magnetohydrodynamics calculation, are averaged over the distribution area. The averaged parameters are taken as the initial conditions for stage Ⅳ in which a simplified magnetohydrodynamics model is applied. A wide-range semi-empirical equation of state, which is established based on the Thomas-Fermi-Kirzhnits model, is constructed to describe the phase transition from solid state to plasma state. The initial plasma formation and the phenomenon of current transfer in the electrical explosion of aluminum wire are investigated using the computational model. Experiments of electrical explosion of aluminum wires are carried out to verify this model. Simulation results are also compared with experimental results of the electrical explosion of copper wire.

Significant effect of electron transfer between current collector and active material on high rate performance of Li_4Ti_5O_(12)

The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very important to effectively improve the electrochemical performances of the electrode materials. Li4Ti5O12, as a zero-strain material, has been considered as a promising anode material for long life Li-ion batteries. In this study, our results show that the Li4Ti5O12 pasted on Cu or graphite felt current collector exhibits unexpectedly higher rate performance than on A1 current collector. For Li4Ti5O12, the electron transfer between current collector and active material is the critical factor that affects its rate and cycling performances.

Study on arc characteristics and behavior of metal transfer in pulse current flux-cored arc welding of mild steel

The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative study of similar nature has also been carried out during flux-cored arc weld deposition in globular and spray transfer modes.The effect of pulse parameters has been studied by considering their mean current and arc voltage.The arc characteristics studied by its root diameter,projected diameter and length,and the behavior of metal transfer noted by the metal transfer model and the droplet diameter have been found to vary significantly with the pulse parameters.The observation may help in understanding the arc characteristics with respect to the variation in pulse parameters which may be beneficial in using pulse current FCAW to produce desired weld quality.

Modeling transient fluid flow and heat transfer phenothena in stationary pulsed current TIG weld pool

A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for weld pool convection, i,e. buoyancyforce, electromagnetic force and surface tension force. furthermore. the effect of vaporization heat flux at the free surface of weld pool and the temperature coefficient of surface tenston which is a function of temperatuer and composition are considered in the model In order to accelerate the convergence of iteration the AST(additive source term)method which concerns with the thermal energv boundary conditions is extended successfully to deal with the momentum boundary conditions by which the transient momentum equation and energy equation are mutually coupled. At the same time. ADI (Alternating direction implicit) method and DBC (double blocks correction) technque are employed to solve the finite difference equations. The results of numerical simulation demonstrate the transient behavior of PC-TIG weld pool, as well as the periodic variation of fluid flow and heat transfer with the periodic variation of welding current in stationary PC-TIG weld pool. The theoretical predictions based on this model are, shown to be in good accordance with the experimental measurements.

Charge transfer on porous silicon membranes studied by current-sensing atomic force microscopy

A visible rectification effect on the current-voltage curves of metal/porous silicon/p-silicon has been observed by current-sensing atomic force microscopy. The current-voltage curves of porous silicon membranes with different porosities, prepared through variation of etching current density for a constant time, indicate that a higher porosity results in a higher resistance and thus a lower rectification, until the current reaches a threshold at a porosity 〉55%. We propose that the conductance mode in the porous silicon membrane with porosities 〉55% is mainly a hopping mechanism between nano-crystallites and an inverse static electric field between the porous silicon and p-Si interface blocks the electron injection from porous silicon to p-Si, but with porosities ≤55%, electron flows through a direct continuous channel between nano-crystallites.

Finite element solution of heat and mass transfer flow with Hall current,heat source,and viscous dissipation

The aim of the paper is to investigate the effect of heat and mass transfer on the unsteady magnetohydrodynamic free convective flow with Hall current, heat source, and viscous dissipation. The problem is governed by the system of coupled non-linear partial differential equations whose exact solution is difficult to obtain. Therefore, the problem is solved by using the Galerkin finite element method. The effects of the various parameters like Hall current, Eckert number, heat source parameter, Prandtl number, and Schmidt number on the velocity components, the temperature, and the concentration are also examined through graphs.

Simulation of droplet transfer process and current waveform control of CO_2 arc welding

A simulation system used in the arc welding short circuit transfer process and current waveform control process was developed in this paper. The simulation results are basically consistent with welding technical experiments. The simulation system can be used to simulate and test the current waveform control parameters with welding variables. By this simulation system, the influence regularities of the current waveform control parameters in the CO 2 arc welding droplet short circuit transfer process can be got. Moreover, the basic mode of real time current waveform control can be also established by the simulation testing.

Analysis on the Transfer Characteristics of Rogowski-coil Current Transformer and Its Influence on Protective Relaying

This paper systematically analyzes the transfer characteristics of the Rogowski-coil Current Transformer and its effect on protective relaying through theoretical analysis, experiments and simulations. The frequency characteristics and transient characteristics of Rogowski transducer and Rogowski-coil Current Transformer are deeply analyzed based on the physical structure of the transformer.?It is revealed that broad bandwidth of the transformer can improve the performance of protective relaying, and the bandwidth is determined mainly by the parameters of the Rogowski transducer and signal processing circuits. It is also discovered that the measurement errors of transient current mainly depend on the abilities for the current transformer to reproduce an accurate replica of the decaying dc components, which is mainly decided by the decay time constant of the aperiodic component of transient current and the parameters of the integral unit. Finally, some measures are proposed for the performance improvement of Rogowski-coil Current Transformer to meet the requirements of protective relaying system in terms of structural design and testing standards.

Arc Characteristic and Metal Transfer of Pulse Current Horizontal Flux-Cored Arc Welding

In this work, we utilized high-speed video photography to investigate the arc characteristics, metal transfer behavior, and welding spatter of the pulse-current flux-cored arc welding(P-FCAW) process in the horizontal position. The results indicate the presence of a stable ‘‘flux pole'' during both the pulse-on and pulse-off periods when the mean current ranged from 140 to 170 A. The existence of this ‘‘flux pole'' was beneficial for droplet transfer in the‘‘axial droplet transfer'' mode. With respect to welding spatter, with an increase in the welding current, we observed three kinds of spatter—explosive spatter,rebounded droplet spatter, and scattering spatter. With an increase in the pulse current from 310.6 to 345.6 A, the deflection of the arc reduced from 30.4° to 16.6°, which positively influenced the arc rigidity, particularly in the horizontal position.

Numerical Solution of MHD Convection and Mass Transfer Flow of Viscous Incompressible Fluid about an Inclined Plate with Hall Current and Constant Heat Flux

The present numerically study investigates the influence of the Hall current and constant heat flux on the Magneto hydrodynamic (MHD) natural convection boundary layer viscous incompressible fluid flow in the manifestation of transverse magnetic field near an inclined vertical permeable flat plate. It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field. The governing boundary layer equations have been transferred into non-similar model by implementing similarity approaches. The physical dimensionless parameter has been set up into the model as Prandtl number, Eckert number, Magnetic parameter, Schmidt number, local Grashof number and local modified Grashof number. The numerical method of Nactsheim-Swigert shooting iteration technique together with Runge-Kutta six order iteration scheme has been used to solve the system of governing non-similar equations. The physical effects of the various parameters on dimensionless primary velocity profile, secondary velocity profile, and temperature and concentration profile are discussed graphically. Moreover, the local skin friction coefficient, the local Nusselt number and Sherwood number are shown in tabular form for various values of the parameters.

An Investigation into the Influence of the Airflow Path on the Convective Heat Transfer for an Eddy Current Retarder Turntable

In order to improve the convective heat transfer relating to an eddy current retarder,the finite element model has been used to assess the performances of different possible designs.In particular,assuming the steady running state of retarder as the working condition,flow and temperature fields have been obtained for the rotor.The influence of airflow path on heat dissipation has been analysed,and the influence of the temperature field distribution on the performance of retarder has been discussed accordingly.The results show that when the steady running state of the turntable is considered,the maximum temperature is lower,the level of turbulence flow is mitigated,and the temperature distribution becomes more regular.These factors contribute to improve the heat dissipation ability of the retarder.

Effects of Hall Current on MHD Boundary Layer Second-Order Viscoelastic Fluid Flow Induced by a Continuous Surface with Heat Transfer

Effects of Hall current on heat transfer and magnetohydrodynamic (MHD) boundary layer flow induced by a continuous surface in a parallel free stream of a second-order viscoelastic fluid are studied for uniform suction/injection by taking viscous dissipation into account. Complex nonsimilar solutions to the stream function and temperature are developed by means of an elegant technique, known as homotopy analysis method (HAM). Convergence of the solutions is ensured with the help of -curves. Graphical and tabular results for the effects of Hall current reveal that it has a significant influence on: complex velocity, complex temperature, magnitude of the shear stress at the surface, magnitude of the rate of heat transfer at the surface and on boundary layer thickness.

Observation of a Current Plateau in the Transfer Characteristics of InGaN/AlGaN/AlN/GaN Heterojunction Field Effect Transistors

Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is present in the transfer characteristics of InGaN/AIGaN/AIN/GaN HFETs. The theoretical calculation shows the coexistence of two-dimensional electron gas （2DEG） and two-dimensional hole gas （2DHG） in InGaN/AIGaN/A1N/GaN heterostructures, and the screening effect of 2DHG to the 2DEG in the conduction channel can explain this current plateau. Moreover, the current plateau shows the time-dependent behavior when IDs Vcs scans repeated are conducted. The obtained insight provides indication for the design in the fabrication of GaN-based super HFETs.

Study on the formation of arc plasma on the resistive wall liquid metal current limiter

Due to its significant attributes,the liquid metal current limiter(LMCL)is considered a new strategy for limiting short-circuit current in the power grid.A resistive wall liquid metal current limiter(RWLMCL)is designed to advance the starting current-limiting time.Experiments are performed to investigate the dynamic behaviors of liquid metal,and the influence of different currents on the liquid metal self-shrinkage effect is compared and analyzed.Furthermore,the liquid metal self-shrinkage effect is mathematically modeled,and the reason for the formation of arc plasma is obtained by simulation.The laws of arc plasma formation and the current transfer in the cavity are revealed,and the motion mechanisms are explained by physical principles.The simulations are in accordance with the test data.It is demonstrated that the sudden change of the current density at both ends of the wall causes the liquid metal to shrink and depress under the electromagnetic force,and the current starts to transfer from the liquid metal path to the wall resistance path.The RWLMCL can effectively advance the starting current-limiting time.

Hydrophobic ionic liquids/water interfacial phase transfer induced by direct current electric field

To investigate the affect of direct current electric field (DCEF) on the interfacial phase,in this paper,a hydrophobic ionic liquid (HIL)/water as liquid-liquid two-phase binary system is established by using the deioned water and l-butyl-3-methyl imidazolium hexafluorophosphate,and the topographies of the HIL nanodroplets and nanolayers in ambient water are observed by atomic force microscope (AFM).The results show the AFM exerting the DCEF can enhance the intersolubility of the HIL/water binary system and induce their interfacial phase transfer.

The Current Situation and Future Expectationsof China's Pilot Boatsl

Pilots need to board the ship for pilotage,but there are risks or potential dangers in the transfer of pilot.The author reviewed the history of the development of pilot boats,analyzed the potential risks or dangers of transferring pilot,proposed that pilot boat shall have the function of ensuring the safety of pilot when embarking or disembarking the ships,some suggestions on the future design and manufacture of Chinese pilot boats are also given according to the advantages and disadvantages of domestic and foreign pilot boats.

永磁同步电机交直轴电流解耦控制方法综述

该文归纳整理永磁同步电机交直轴电流解耦控制方法,分析各种解耦方法的思想来源、脉络体系和演变过程,论证不同解耦方法的解耦本质和内在联系。从整体和局部视角出发,建立解耦问题的思维架构,概括出对角化解耦、抗干扰解耦和逆系统解耦3类方法。3类方法依次体现出模型依赖性降低、鲁棒性增强、算法复杂度提高的趋势,呈现出从“模型论”向“控制论”过渡的技术发展路线。讨论参数不确定条件下各种解耦控制方法的鲁棒性,指出将解耦方法与先进控制算法、扰动观测技术、系统辨识方法以及人工智能方法相结合,并充分利用已知的模型信息,有利于提升交直轴电流解耦效果,增强系统鲁棒性,减弱单一观测器、控制器、滤波器等的设计难度与参数整定要求,有助于实现系统全局最优。最后,对永磁同步电机交直轴电流解耦问题的关键技术、应用与发展做出展望。

实验室模拟连续电流与通道光强度关系研究

雷电连续电流是云载荷源向大地转移电荷的一种重要形式,这一过程产生的热效应可能对自然以及人居环境造成严重损害,这种热效应与连续电流波形和转移电荷量有关。在高压实验室电弧放电通道间隙产生了峰值范围为233.8~633.3A的模拟雷电连续电流,利用红光敏感型(探测波长范围200~1000nm,峰值响应600nm)和近红外敏感型(探测波长范围400~1000nm,峰值响应800nm)两种光电探测器同步测量了通道光强度。结果发现,正常通道下测量得到的光强度波形能较好地跟随电流波形的变化,而电弧通道扭曲会导致测量得到的通道光强度波形产生畸变,这种畸变具体表现为光强度波形在持续阶段的凹陷,在所有光强度波形中发生畸变的概率为19.8%。进一步探究了正常通道情况下模拟连续电流与通道光强度的关系,发现在不同光谱响应下,光强度峰值与电流峰值以及光强度-时间积分与电流电荷转移量之间均存在强烈的线性相关性。结果为使用电流与相关光强度关系进行连续电流波形与转移电荷量的准确反演提供了新思路。

基于改进型ZVT Buck电路的IPT充电系统设计

为了避免在感应式无线电能传输系统的耦合机构中增加多余的开关器件以及额外的无源元件,同时减小系统工作在高频率、大功率时全控型开关器件存在的开关损耗,提出基于改进型ZVT Buck电路闭环控制的方法实现对电池的恒流、恒压充电,通过分析改进型ZVT Buck电路的工作模态以及对电路参数的设计,确保在整个充电过程中DC-DC变换器均工作在软开关状态,最后搭建充电电流为35 A、充电电压为370 V的实验平台验证该方法的可行性。结果表明:该方法控制简单,并且降低了系统电路结构的复杂度,传输效率相对较高,能够满足恒流恒压充电需求。