焊接电弧的等离子流力研究

以实验为基础，分析了直流ＴＩＧ电弧阳极热斑表面等离子流力的径向分布、数学表达式、电弧长度及电流的影响，阐述了该力在整个电弧机械作用力中的地位。

脉冲等离子-MIG复合焊熔滴过渡行为研究

将脉冲等离子电弧与MIG电弧同轴复合,期望利用等离子弧脉冲峰值电流产生的高速等离子射流冲击熔滴和熔池,促进熔滴过渡,同时增加焊缝熔深。开发了一套高速视觉与电信号精确同步的焊接数据采集系统,对脉冲等离子-MIG复合焊熔滴过渡行为进行研究。研究发现将等离子电流调制成脉冲波形,等离子弧对工件总体热输入下降,等离子峰值电流产生的等离子流力可以有效促进熔滴过渡。在此基础上深入分析了等离子脉冲峰值电流、脉冲宽度及熔滴在等离子弧过渡位置等参数对熔滴过渡的影响,获得了脉冲等离子-MIG复合焊一脉一滴过渡的工艺参数窗口。

外加纵向磁场对TIG电弧的影响

试验研究表明外加纵向磁场对电弧的电流密度、等离子流力有很大影响。本文对其变化规律及原因进行了分析和研究。

Analysis on the Application of Electrical New Technology of in Electromechanical Integration

The electrical new technology is a new frontier science.This kind of technology, with the development and progress of society, makes the continuous development and innovation.It is the future development trend of electrical engineering system,which plays a very important role in technological innovation.The principle and theoretical support for the development of electrical new technology includes Bio- electro magnetics, plasma physics, electromagnetic fluid mechanics and gas discharge physics etc.In addition, under the application of permanent magnetic materials and other new materials, the electrical new technology and obtained further development also promote the development and application of electronic power supply, strong magnetic field technology, solar photovoltaic power generation, and superconducting power technology.This paper mainly analyzes the application of electrical new technology in electromechanical integration.

Base Pressure Plays an Important Role for Production of Plasma Blob in Argon Plasma

Magnetic confinement of fusion plasma has a wide range of issues to be addressed. Convective transport of plasma in the scrape-off layer of magnetic confinement devices is an interesting research topic for scientists and engineers. The interest in scrape-off layer convective transport has grown in last two decades because of its effect on plasma interaction with the first wall and divertor. By increasing the particle flux into the far scrape-off layer, blobs negatively affect limiters, radio frequency antennas and the first wall. Increased convective heat transport influences core plasma confinement, at least in L-mode plasmas. Here we have reported blob formation in the absent of external magnetic field. It is observed that at low pressure -0.01 rob, transport seems to be dominated by diffusive process. At pressure 〉 1 mb, we observe convective transport in high speed imaging experiments. The role of background neutrals outside plasma boundary has the befitting answer for this phenomenon. Plasma temperature is the other key player. Another interesting observation is that at diffusive transport regime plasma life time is of the order of voltage pulse duration fed to plasma source, where as at convective transport regime plasma life time is increased appreciably.

Effect of pressure on the performance of plasma synthetic jet actuator

The effects of the ambient air pressure level on the performance of plasma synthetic jet actuator have been investigated through electrical and optical diagnostics.Pressures from 1 atm down to 0.1 atm were tested with a 10 Hz excitation.The discharge measurement demonstrates that there is a voltage range to make the actuator work reliably.Higher pressure level needs a higher breakdown voltage,and a higher discharge current and energy deposition are produced.But when the actuator works with the maximum breakdown voltage,the fraction of the initial capacitor energy delivered to the arc is almost invariable.This preliminary study also confirms the effectiveness of the plasma synthetic jet at low pressure.Indeed,the maximum velocities of the precursor shock and the plasma jet induced by the actuator with maximum breakdown voltage are independent of the ambient pressure level;reach about 530 and 460 m/s respectively.The mass flux of the plasma jet increases with ambient pressure increasing,but the strength of the precursor shock presents a local maximum at 0.6 atm.

MHD and kinetic analysis of flow bursts in the Earth's plasma sheet

In an attempt to study the flow bursts in the Earth＇s plasma sheet we select an event that took place on August 7, 2004 in the expansion phase of a substorm, using data from the geomagnetic index, solar wind data, plasma and magnetic field observa- tions from C1 Cluster satellite （the Cluster mission has 4 satellites） and from Double Star TC-1 satellite. In MHD approach, TC-1 firstly observed the tailward flow, then the earthward, and finally the flow altemated in two directions. C1 firstly ob- served the earthward plasma flow, and then the tailward plasma flow. Before flow bursts are observed by TC-1 and C1, there are disturbances in local entropy with their tailward local entropy larger than those of the earthward. The kinetic features of the plasma flow observed by C1 are similar to those in MHD. However, kinetic characteristics of the plasma flow observed by TC-1 are far more than the description in MHD. The inadequacy mainly exists in two cases： （i） the firstly enhanced tailward flows given in MHD are found without significant increase of the energetic tailward flux; （ii） the almost stagnant flow in MHD is composed of the enhanced energetic ion flux in both earthward and tailward directions. The earthward flow burst observed by TC-1 might be multiple overshoots and rebounds. The earthward flow burst observed by C1 might be simply rebounded in the near-Earth. The pulsation observed by C1 is earlier than that observed by TC-1 with the former intensity less than that of the latter. After the energetic ion flux in the tailward direction is significantly enhanced, the power spectrum intensity of the ULF wave commences to increase obviously, which may suggest that the stream instability is closely correlated with ULF pulsations.

An Experimental Study of the Drag Force on a Cylinder Exposed to an Argon Thermal Plasma Cross Flow

Experimental data are presented concerning the drag force on a cylinder exposed to an argon plasma cross flow with temperatures about 10~4 K and velocities about 10~2m/s. Using a method of sweeping a cylindrical probe across an argon plasma jet, the total drag force on the cylinder can be measured as a function of the lateral distance of cylindrical probe with respect to the plasma-jet axis. Through the Abel inversion, the drag force for per unit of cylinder length and thus the drag coefficient of cylinder have been measured under plasma conditions and compared with the values obtained from the standard drag curve of the cylinder in an isothermal flow. Experimental results show that the measured drag forces are always less than their counterparts read from the standard drag curve with the same Reynolds numbers based on the oncoming plasma properties. The drag force on the cylinder exoposed to a thermal plasma flow is shown to be approximately proportional to the square root of cylinder diameter in the present experiment and it increases slightly with increasing surface temperature of the cylinder. It is also shown that applying a voltage between the drag probe and the anode of the plasma jet generator has little effect on the drag force of cylinder under the experimental conditions. The drag force on a cylinder with finite length exposed to an argon plasma with the axis parallel to the plasma jet is independent of ratio of cylinder length to its dismeter L/d for the cases when L/d≤1.

Dielectric barrier plasma dynamics for active aerodynamic flow control

The paper investigates the dynamics of a new multiple bipolar multiple Dielectric Barrier Discharges(DBD)actuator using in large-scale flow control.Particle image velocimetry experiments are performed to characteristic the effectiveness of the multiple bipolar DBD plasma actuator.The results show that the mutual interaction between the electrodes,one major disadvantage of traditional DBD characterized by reverse discharge can be entirely avoided,and a constantly accelerating electric wind velocity can be obtained by using the new multiple bipolar DBD plasma actuator.

ASYMPTOTIC LIMITS OF ONE-DIMENSIONAL HYDRODYNAMIC MODELS FOR PLASMAS AND SEMICONDUCTORS

This paper studies the zero-electron-mass limit, the quasi-neutral limit and the zero-relaxation-time limit in one-dimensional hydrodynamic models of Euler-Poisson system for plasmas and semiconductors. For each limit in the steady-state models, the author proves the strong convergence of the sequence of solutions and gives the corresponding convergence rate. In the time-dependent models, the author shows some useful estimates for the quasi-neutral limit and the zero-electron-mass limit. This study completes the analysis made in [11,12,13,14,19].