Numerical simulation of interaction between arc discharge and transverse magnetic field

An unsteady-state three-dimensional numerical model of radiation magnetogasdynamics is used to calculate the structure of an arc discharge which interacts with an external transverse magnetic field and transverse gas flow. The velocity field and the distribution of gas temperature obtained as a result of calculations agree with experimental data. The difference between the calculated and measured values of temperature in the discharge column is approximately 5%.     

Numerical simulation of point-to-plane corona discharge using a Monte Carlo method

Monte Carlo simulation techniques are used to study the dynamical properties of charged particles in point-to-plane corona discharge. The numerical model includes the release of electron-ion pairs by photoionization and secondary electron emission from cathode as well as the first Townsend ionization. The simulation results of negative corona discharge in nitrogen show that electron avalanche takes place in the region of high electric field near pin electrode and the photoionization is the essential mechanism to sustain the discharge as well as electron impact ionization.     

Numerical simulation of rarefied dusty plasma in a normal glow discharge

A self-consistent model of a glow discharge, burning in a normal current density mode, with dust particles placed in it is presented. The model of a normal glow discharge is based on a diffusion-drift approximation. Within the framework of this model, the regions of a spatial charge are taken into account. The motion of dust particles in the glow discharge region is calculated using the method of molecular dynamics. The particle charge is estimated based on qualitative conceptions on the process of charging of solid particles. The proposed model is studied numerically, and the corresponding results are presented.     

Spectral properties of a diffuse-constricted arc discharge

An extensive high-current electric discharge under atmospheric pressure is characterized by considerable instability, unless special measures for its stabilization are assumed (e.g., by the walls, electrodes, rotational twist, etc.). For the experimental investigation of such a discharge, both the complex diagnostics of electrical and spectral properties have been applied, supplemented with synchronous video filming of the discharge gap. The information on the spectral composition of the radiation of different discharge sections can be obtained by measuring with a system of optical fibers. Spectral measurements at the selected point of space at various moments of time make it possible to determine the alteration dynamics of plasma composition near the reference spots, as well as far from them.     

Numerical simulation of variable polarity vertical-up plasma arc welding process

Three-dimensional transient governing equations were developed based on conservation laws of energy, momentum and mass. These equations described physical phenomena of convection in weld pool and heat transfer in workpiece during variable polarity vertical-up plasma arc welding process. Boundary conditions for the developed governing equations were given. Welding energy input for variable polarity vertical-up plasma arc welding process was quantitatively expressed. Free surface deformation of the keyhole molten pool was coupled into calculation. Effect of wire filling on the geometry of molten pool and weld reinforcement was considered in the simulation. Correlations of temperature and thermophysical properties for aluminum alloy 2219 were quantitatively established. A control volume based finite difference method was used to solve the discrete governing equations. Moreover, dynamic evolutions of geometrical profile, dimension and fluid flow for the molten pool and keyhole were simulated through the developed computational routines, which achieved transient solution of fluid flow field coupling with thermophysical properties, temperature field and weld pool free surface deformation. Besides, the effect of the workpiece thickness on the moments of keyhole formation and stable keyhole establishment was analyzed, and thermal cycles for the main welding stage were calculated. In addition, experiments via variable polarity vertical-up plasma arc welding technique were conducted, and the established models were experimentally verified through weld cross-section profiles.     

Numerical simulation of stationary processes in glow discharge plasma

The problem of determining the parameters of a low-pressure stationary glow discharge is considered in application to the simulation and optimization of the process of modification of the surface of structural materials. A coupled system of nonlinear equations is formulated, which includes the equations for charged particle fluxes (with allowance for the drift and diffusion components) and the Poisson equation for the electrostatic potential. In order to study the influence of geometric factors on the physical characteristics of discharge, the problem is considered in the spherical and planar cases. The nonlinear boundary-value problem has been solved by a modified method of continuation with respect to a parameter. The influence of diffusion processes and the gas discharge geometry region on the physical characteristics of discharge is analyzed.     

Numerical simulation of surface glow discharge in molecular nitrogen

The DC surface glow discharge in molecular nitrogen at a pressure p = 10 Torr and voltages V ₀ = 600, 700, and 1000 V is considered based on the diffusion-drift model. The local maxima of the electric field strength and the current density on electrodes are determined. The temperature fields induced by Joule heating in the near-electrode regions are analyzed.     

三维空间曲面结构风荷载的数值模拟

本文运用计算流体动力学技术,基于FLUENT 流体动力学数值模拟平台,采用雷诺平均法和大涡模拟技术,对球壳、柱面、悬链面、菱形马鞍面及椭圆双曲抛物面五类结构进行了定常、非定常流场的模拟计算。使用自回归模型的线性滤波法生成了脉动风速的时间序列,该脉动风速的时间序列很好地满足了预先设定的脉动风速谱和空间相关性要求,进而将其代入到实际计算的边界条件当中。将五类空间曲面结构表面风压的模拟计算结果与风洞试验结果定量比较：稳态计算得到的平均风压数据与风洞试验结果吻合理想,非稳态计算得到的脉动风压数据与试验结果差别稍大,其中正高斯曲面模拟精度高于负高斯曲面。     

Grain structure in cathode spot trail of low vacuum arc discharge

Low vacuum arc discharge treatment in 10 Pa is applied to cleaning of a stainless steel plate, the surface of which is covered with an oxide layer. During the discharge, several luminous cathode spots move continuously in random directions on the surface of the stainless steel plate. They remove the oxide layer owing to their high energy density and leave their trail on the sample surface. Microscopic observation reveals a chain structure of metallic grains along the center of the cathode spot trail. Some chemical agents put on the oxide layer before cleaning affect on the size and the number density of the grain, which leads to the different surface roughness after treatment.     

Numerical simulation of microscopic flow in a fiber bundle using the moving particle semi-implicit method

This paper simulated the microscopic flow in a fiber bundle using the moving particle semi-implicit (MPS) method. Two phases (resin and air) were directly modeled to clarify the detailed mechanism of air entrapments in a fiber bundle. An external force was then introduced into the Navier–Stokes equation using a quasi-potential term to express the wettability between fiber and resin. To validate the MPS method for application to resin flow, we simulated a droplet of resin and the capillary flow of resin between the fibers. To validate the present approach, we simulated water-and-air two-phase flow and compared the simulation results with experiment results. The simulated results for water flow agreed well with the experiment results. Based on these validations, resin-and-air two-phase flow in a fiber bundle was simulated to analyze void formation in a fiber bundle. The simulation indicates that void formation depends on fiber arrangement as well as wettability.     

Measurement of the temperature of a pulsating electric arc discharge

A simple method for determining the temperature on the axis of an oscillating arc column is proposed.Campinas University, Gleb Vatagin Institute of Physics, Brazil. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 6, pp. 707–709, June, 1994.     

Physical investigations of a high-current vacuum arc discharge

The experimental data on the processes at the electrodes and in the interelectrode gap of a high-current vacuum arc discharge that were accumulated by different researchers are systematized. A critical analysis is conducted on the essentially static discharge models proposed earlier. A dynamic model of a two-component plasma is described and substantiated, which, in the opinion of the authors, better explains the current results of experimental studies into this type of electric discharge than the static models.Translated from Inzhernerno-Fizicheskii Zhurnal, Vol. 62, No. 5, pp. 733–738, May, 1992.     

Numerical simulation of growth pattern of a fluid-filled subsurface crack under moving hertzian loading

Cracking of a fluid-filled subsurface crack is studied by means of the distributed dislocation technique within the framework of two-dimensional linear elastic fracture mechanics. The Griffith crack was initially opened by the application of hydrostatic pressure of an incompressible fluid within the crack. A moving Hertz line contact load distribution is applied at the surface of the half-plane in the presence of friction. The stress intensity factors at the tips of the fluid-filled crack are analyzed with the restriction that due to the fluid incompressibility there is no change of the crack-opening volume. When the crack starts to propagate/kink, numerical results show that the internal fluid pressure will be relieved, and as the ratio of the branched crack length to main crack length increases, the elastic strain energy release rate decreases. The crack growth is assumed to be arrested when the energy release rate is below a certain value. Based on the energy criterion, predictions are attempted for determining the load position where the crack propagation/kink commences as well as the growth increment of the branch crack before it is arrested. A step-by-step crack path is constructed to simulate the growth pattern of the fluid-filled crack under moving Hertzian loading.     

Velocity of the electric arc in a plasmatron discharge chamber

An experimental investigation of the velocity of a high-current arc with air injection in the discharge chamber of a coaxial sectioned plasmatron is described. The experiments showed that the velocity of the cathode spot on the electrode surface depends on the arc current and on the external magnetic field strength. The air flow rate in the plasmatron chamber was 7.1 g/sec.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 3, pp. 570–574, September, 1969.     

双弧脉冲MIG焊耦合电弧特性的数值模拟研究

针对双弧脉冲MIG焊热源稳定性差的问题,本文对双弧脉冲MIG焊耦合电弧进行瞬态数值模拟,分析了不同脉冲电流参数下耦合电弧形态、温度和压力的分布及变化规律。研究表明：耦合电弧呈驼峰状,脉冲电流发生跳变时,耦合电弧伸展或收缩,并逐渐稳定,峰值电流越小,越快达到稳定;增大脉冲电流,耦合电弧温度和电弧压力随之升高;保持总电流不变,减小主弧电流,增大旁弧电流,主弧温度和电弧压力减小,旁弧温度和电弧压力增大,当旁弧电流足够大时,耦合电弧温度和电弧压力呈双峰分布。数值模拟结果与双弧脉冲MIG焊工艺实验结果吻合良好,模拟结果对调控双弧脉冲MIG焊脉冲电流参数,改善其耦合电弧稳定性及工艺性能具有重要意义。     

Determination of the spatial position of a moving object

The solution of the problem of determining the spatial position of a moving object from measured projections of the acceleration vectors of three-components accelerometers is considered. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 22–25, May, 2007.     

Numerical simulation on interaction between TIG welding arc and weld pool

The interface deformation between welding arc and weld pool is important in dynamic coupling numerical simulation on arc and pool. To reveal the interaction between welding arc and weld pool, unified mathematic model of TIG welding arc and pool was established in this paper. The moving interface was solved by updating the calculation region of arc and weld pool continually. Fluid flow and heat transfer of TIG welding arc and weld pool were analyzed basing on this model. The weld pool shape calculated by dynamic coupling welding arc and pool is more close to the experiment than that of non coupling calculation.     

Plasmachemical synthesis of coatings using a vacuum arc discharge

In this paper we discuss the issues of applying protective coatings on the copper anodes of powerful generator tubes. As a synthesized material due to its high operational properties was chosen titanium carbide obtained by sputtering a titanium cathode in benzene vapors. Scheme of a vacuum arc device used in this work and also the technological processes for the plasmachemical synthesis of coatings on complex shape anodes are described. For a correct choice of the technological parameters it was considered a model of penetration of the plasma flux into the hollow copper anode that was verified by experiments using a setup with a variable cavity diameter. On the emission spectrum of the discharge in the process of coating deposition shown in this work were recorded spectral lines corresponding to the atoms and ions of titanium and carbon ions. We investigated the distribution of elements across the thickness of the formed coating immediately after deposition and after annealing in vacuum, also the X‐ray diffraction pattern and a microsection for the obtained titanium carbide coating are presented. As a result of the work it can be noted that the described sequence of technological processes, subject to the control of plasma flux parameters, allows obtaining a high quality protective coating on parts of complex shape.     

Generation of a metal porous film by arc discharge

The copper wire vaporization method is applied to obtain porous copper film on a silicon surface. We determine the distribution of the surface clusters over the sizes and the density. The average size of the clusters under optimal conditions (at a distance of 2 mm from the discharge) is about 0.5 μm, and the deposition density is 3–5 clusters per squared μm.     

Numerical simulation of humping phenomenon in high speed gas metal arc welding

It is of great significance to obtain a thorough understanding of the physical mechanisms responsible for humping bead phenomenon in high speed gas metal arc welding (GMAW) in order to raise welding efficiency. Experiments were conducted to observe the weld pool behaviors in high speed GMAW, and it was found that both the severely deformed weld pool surface and strong backward flowing play a dominant role in humping bead formation. In this study, a mathematical model is developed to quantitatively analyze the forming mechanism of humping beads for high speed GMAW through considering both the momentum and heat content distribution of the backward flowing molten metal inside the weld pool. The transient development of temperature profiles in the weld pool with severe deformation demonstrates the humping bead forming process under some welding conditions. The predicted and measured humping bead dimensions are in agreement.