Diagnosing ratio of electron density to collision frequency of plasma surrounding scaled model in a shock tube using low-frequency alternating magnetic field phase shift

A non-contact low-frequency(LF)method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed.This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic field through the plasma to directly measure the ratio of the plasma loop average electron density to collision frequency.An equivalent circuit model is used to analyze the relationship of the phase shift of the magnetic field component of LF electromagnetic waves with the plasma electron density and collision frequency.The applicable range of the LF method on a given plasma scale is analyzed.The upper diagnostic limit for the ratio of the electron density(unit:m^(-3))to collision frequency(unit:Hz)exceeds 1×10^(11),enabling an electron density to exceed 1×10^(20)m^(-3)and a collision frequency to be less than 1 GHz.In this work,the feasibility of using the LF phase shift to implement the plasma diagnosis is also assessed.Diagnosis experiments on shock tube equipment are conducted by using both the electrostatic probe method and LF method.By comparing the diagnostic results of the two methods,the inversion results are relatively consistent with each other,thereby preliminarily verifying the feasibility of the LF method.The ratio of the electron density to the collision frequency has a relatively uniform distribution during the plasma stabilization.The LF diagnostic path is a loop around the model,which is suitable for diagnosing the plasma that surrounds the model.Finally,the causes of diagnostic discrepancy between the two methods are analyzed.The proposed method provides a new avenue for diagnosing high-density enveloping plasma.

THE INFLUENCE OF LOW-FREQUENCY VARYING MAGNETIC FIELDON THE PULSATILE FLOW IN A RIGID ROUND TUBE

In this paper, the analytic solution of the dynamical equation of the pulsatile flow in a rigid round tube under the low-frequency varying magnetic field is obtained. The velocity distribution and the flow impedance are calculated. The results of e valuable for understanding the influence of low-frequency varying magnetic field on hemodynamics and its clinical application.

Experiment on low-frequency electromagnetic waves propagating in shock-tube-generated magnetized cylindrical enveloping plasma

We propose a method of applying a static magnetic field to reduce the attenuation of the magnetic field component(SH) of low-frequency electromagnetic(LF EM) waves in dense plasma. The principle of this method is to apply a static magnetic field to limit electron movement, thereby increasing the equivalent resistance and thus reducing the induced current and SH. We consider the static magnetic field acting on the plasma of the entire induced current loop rather than on the local plasma, where the induced current is excited by the magnetic field component of LF EM waves. Analytical expressions of SH suitable for magnetized cylindrical enveloping plasma are derived by adopting an equivalent circuit approach, by which SHis calculated with respect to various plasma parameter settings. The results show that SH can be reduced under a static magnetic field and the maximum magnetic field strength that mitigates blackout is less than 0.1 T. Experiments in which LF EM waves propagate in a shock-tubegenerated magnetized cylindrical enveloping plasma are also conducted. SH measured under the magnetic field(the magnetic field strength B0 acting on the magnetic field probe was about0.06 T) reduces at f=10 MHz and f=30 MHz when ne≈1.9×1013 cm-3, which is consistent with theoretical results. The verification of the theory thus suggests that applying a static magnetic field with a weak magnetic field has the potential to improve the transmission capacity of LF EM waves in dense plasma.

Development of a low-frequency magnetic lightning mapping system(LFM-LMS)in North China:validation and preliminary results

A low-frequency magnetic lightning mapping system(LFM-LMS)was built during the SHAndong Triggered Lightning Experiment(SHATLE),based on continuous measurements of magnetic field radiation from lightning.The hardware and source-mapping techniques used by the LFM-LMS were introduced;both Monte Carlo simulations and the observation of rocket-triggered lightning examples were employed to examine the location accuracy and detection effectiveness of the LFM-LMS.We estimated that the system’s location accuracy about 100−200 m horizontally and~200 m vertically.A natural intra-cloud lightning flash and a rocket-triggered lightning flash,both with intricate structures and discharging processes,were examined using the three-dimensional mapping results.The progressing path of negative lightning leaders is usually well-defined,and its propagation speed is estimated to be(0.5−1.4)×10^(6)m/s.In summary,the LFM-LMS can reconstruct the three-dimensional morphology of lightning flashes;this technology provides a efficient method for investigating the characteristics of lightning development,as well as the overall electrical strucuture of thunderstorms.

Macro-physical field of large diameter magnesium alloy billet electromagnetic direct-chill casting:A comparative study

A comprehensive two-dimensional axisymmetric mathematical model that couples transient electromagnetic force with fluid flow,heat transfer,and solidification was established to describe the interaction of multiphysics field during DC casting.The melt flow,heat transfer,and solidification characteristics under differential phase pulse magnetic field and differential phase low-frequency electromagnetic field(DP-PMF and DP-LFEF)were numerically investigated by means of numerical simulation during electromagnetic direct-chill(DC)casting of AZ31 alloy at the same casting conditions.The effects of differential phase electromagnetic fields on Lorentz forces distributions,melt flow,heat transfer,and liquid sump shape were discussed systematically.Based on measured current waveform,the results were compared with those obtained without magnetic field(MF)and under conventional pulse magnetic field(PMF)and low-frequency electromagnetic field(LFEF)under the same conditions.The results show that the application of magnetic fields can significantly change the solidification process of DC casting.Differential phase magnetic fields(DP-LFEF and DP-PMF)can effectively reduce the temperature of the melt in the liquid sump,and the shallower liquid sump depth can be obtained under the differential phase magnetic fields.A large velocity vibration amplitude and a lower temperature are available simultaneously under DP-PMF,resulting in more uniform temperature distribution.

Parametric instability of a liquid metal sessile drop under the action of low-frequency alternating magnetic fields

A 2-D mathematical model is developed in order to simulate a parametric electromagnetic instability oscillation process of a liquid metal droplet under the action of low frequency magnetic field. The Arbitrary Lagrangian-Eulerian （ALE） method and weak form constraint boundary condition are introduced in this model for implementation of the surface tension and electromagnetic force on liquid droplet free surface. The results of the numerical calculations indicate the appearance of various regimes of oscillation. It is found that according to the magnetic field frequency various types of oscillation modes may be found. The oscillation is originated from an instability phenomenon. The stability diagram of liquid metal droplet in the parameter space of magnetic frequency and magnetic flux density is determined numerically. The diagram is very similar to that found in the so-called parametric instability.

旋转电弧焊接技术研究进展

熔焊焊接时会不可避免地出现侧壁不熔、咬边、晶粒粗大等问题,导致接头性能较低。为更好地解决焊接中存在的问题,提出旋转电弧焊接技术。相对于普通焊接,旋转电弧中的旋转电弧耦合力在焊接时对熔池的搅拌破碎效应能加速焊缝中的传质传热,并细化晶粒减小焊缝残余应力,能解决焊接中常见问题,获得优质焊缝并提高焊接接头的使用寿命。主要综述了基于外加磁场、非对称钨极旋转电弧、缆式焊丝熔化极旋转电弧的研究现状,指出目前旋转电弧焊接技术还存在的问题,并对相关技术的应用前景进行展望。

双磁路旋转音圈电机电枢反应的抑制方法

旋转音圈电机具有体积小、精度高等优点,一直广泛运用于精密指向机构中。通电线圈引发电枢反应扰乱电机磁场分布,进而影响电机控制性能。本文研究旋转音圈电机电枢反应及其抑制方法,在电机控制模型中引入电枢反应影响系数,边磁轭开矩形口截断电枢反应干扰磁路,分析电机控制系统动态特性和稳态特性,确定最优开口参数,设计并制造样机。实验结果表明:该方法可将电机控制系统稳态误差降低近50%,有效抑制电枢反应,提高系统稳态性能。

基于旋转磁偶极子的钻井轨迹高精度导向定位方法

传统随钻测量无法满足水平对接连通井、蒸汽辅助重力驱油中的成对平行井钻井等复杂结构井高精度导向定位技术需求。为直接测量钻头与目标靶点的距离及方位信息,提出了一种基于旋转磁偶极子模型的高精度导向定位方法。通过对动态旋转磁偶极子的磁信号空间传播规律的研究发现,旋转磁偶极子可以等效为正交磁偶极子的叠加,并且存在能够对旋转磁偶极子进行导向定位的特征磁场信号,该特征信号可以通过希尔伯特变换对三轴可测磁信号进行相位解调和幅度解调获得。仿真结果表明,钻头越接近目标靶点,定位误差越小,定位精度越高。基于旋转磁偶极子的钻井轨迹高精度导向定位方法对SAGD成对平行井、煤层气开发水平对接连通井及可溶性盐卤矿井高精度钻井轨迹导向定位具有重要应用价值。

煤层气水平井组远距离连通机理模型研究

基于我国煤层气低压、低渗和低含水的特殊性,煤层气水平井通常需额外打一口直井,并将该井与多分支井连通,以便于下入有杆泵等排水采气。为了提高水平井与洞穴井连通的成功率,在水平井与洞穴直井的连通过程中引入了旋转磁场定位方法,通过磁场实时测量修正钻头与洞穴的相对位置,并引导两井连通。对旋转磁场测量模型、远距离连通工艺进行了深入探讨,建立了基于钻头与洞穴距离和方位偏差测量算法,经过计算机仿真模拟,证明连通工艺理论上是可行的。

轴向磁场控制的旋转电弧开关的研制

开关在脉冲功率技术中极其重要,其已成为制约脉冲功率技术发展的主要技术瓶颈。为了满足高电压、大电流、高电荷转移量、电极烧蚀小、寿命长的要求,文中设计了一个由轴向磁场控制的旋转电弧间隙开关,研究了其电磁场分布及轴向磁场下电弧的运动机制,并进行了初步实验。结果表明此开关中的电弧确实在轴向磁场控制下做旋转运动,且运动速度很快,不需要对触发脉冲进行陡化就能得到纳秒级脉冲。实验放电波形比较稳定,分散性为2ns;开关电极表面的烧蚀小,有利于延长开关的寿命;开关工作参数为:电压23kV,单脉冲能量0.314MJ,峰值电流100kA,电荷转移量27.3C/脉冲。

旋转恒定强磁治疗运动后肌痛机理研究

阐明旋转恒定强磁场(RCSMF)治疗运动后局部肌肉疼痛的机理.取SD大鼠在段氏电动可调大鼠多道跑台进行强迫运动,RCSMF处理2h,分别在0h、6h、12h、24h和48h后采大鼠双侧股四头肌,均浆后测量其中的乳酸和肌糖元含量变化.结果发现,RCSMF处理组的肌肉均浆内乳酸含量下降显著加快,但肌糖元正常含量的恢复时间未受影响.表明RCSMF治疗运动后局部疼痛主要在于改善局部微循环,加速代谢产物运输,与肌组织内供能物质含量的恢复无关.

永磁同步电机矢量控制系统研究

无论电机的转速高低和电机参数的大小,都可以通过计算交叉项得到准确的d、q轴电压给定值,从而准确地控制d、q轴电流,提高d、q轴电压控制精度.为此,根据永磁同步电机转子磁场定向的矢量控制理论,在分析传统控制方法存在问题的基础上,提出了一种在d、q轴电压控制方程式中引入交叉耦合项的改进的矢量控制方法,使控制系统在较宽的速度范围内能满足较高的速度控制精度要求,使永磁同步电机伺服系统可实现准确的位置、速度及转矩控制.利用所提出的控制方法,进行系统仿真研究,表明了所提出的控制策略的有效性.

基于旋转编码器的转速控制系统的实现

利用旋转编码器使用寿命长、运行稳定、对工作环境要求低等优点,设计了基于旋转编码器的转速测量模块.采用仪表通用协议——MODBUSRTU,实现了与上位监控系统的串行通信.该模块已被成功应用于永磁可变磁场控制系统中用于磁环转速的调节,结果表明设计的转速控制模块可准确地实现转速控制.

数控旋转磁场仪的研制及应用

目的:为了更方便、准确地研究旋转磁场的生物效应,研制一种以单片机为核心的高精度数控旋转磁场仪。方法:采用高性能单片机实现精确地控制进电机的转速,从而达到控制旋转磁场的频率,并利用其内带的10位A/D转换实现对磁场强度的测量,同时利用LCD显示旋转的频率、磁场强度、定时时间等信息。另外,各按钮均采用触摸式按钮,使得其操作简单、方便。结果:该数控旋转磁场仪工作稳定可靠、磁场频率精度高、操作简便,在"旋磁场对大鼠前列腺的影响"研究中使用,具有明显的生物效应。结论:该仪器可广泛用于研究旋转磁场的生物效应。

旋转磁场治疗印^(60)CO辐射造血损伤小鼠生存分析的实验研究

目的:初步探讨旋转恒定磁场治疗急性骨髓型放射病的效果。方法:BALB/C小鼠按体重随机分为磁疗组和对照组,每组再各分为4组,分别接受0Gy、6.0Gy、8.0Gy、10.0Gy^(60)COγ射线全身辐射,照后,对照组不作任何处理,磁疗组接受磁场处理30d,每天2次,每次1.5h,旋转磁场强度为0.6T,比较两组小鼠30d的存活率和存活期。结果:单纯磁场处理对正常小鼠生存状态及存活率无明显影响;10.0Gy组和8.0Gy组小鼠生存率磁疗组与对照组之间比较均无统计学差异(P>0.05);6.0Gy组生存率磁疗组和对照组之间比较有统计学差异(P<0.05),其磁疗组30d平均存活率为71.43%,平均存活期为(24.93±8.43)d,对照组30d平均存活率21.41%,平均存活期为(17.07±7.70)d。结论:旋转恒定磁场不能提高10.0Gy及8.0Gy剂量所致极重度急性骨髓型放射病小鼠的生存率,但对6.0Gy所致重度急性骨髓型放射病有明显的保护作用,从而为旋转恒定磁场应用于临床治疗重度急性骨髓型放射损伤提供了实验依据。

交变磁场控制的高效MAG焊接试验

为进一步提高MAG焊接效率,测试了在焊接电流为400～600A,焊丝干伸长为20～40mm内焊接的焊丝熔化速率,得出焊丝熔化速率最高可达到24kg/h,相比于常规MAG焊接的10kg/h,将焊接效率提高了一倍以上,通过统计回归分析得到高效焊接焊丝熔化速率的定量计算公式,并对高效焊接参数下出现熔滴旋转射流过渡的原因进行了分析,采用外加交变磁场解决了旋转射流过渡时熔滴过渡不稳定和飞溅大的问题.通过试验发现外加300Hz的交变磁场改善了熔滴过渡稳定性,焊接飞溅显著减小,同时焊缝熔深增大,熔宽减小,消除了旋转射流过渡焊缝漫溢现象,从而实现了高效MAG焊接.

磁场中导电旋转圆板的磁弹性非线性共振

研究旋转运动圆形薄板在磁场中受到机械载荷作用时的磁弹性非线性共振问题。根据哈密顿原理推导出旋转运动圆板在磁场中的磁弹性非线性振动方程,基于电磁理论给出了旋转板所受电磁力的表达式;通过位移函数的设定并应用伽辽金积分法,得到横向磁场中旋转导电圆板的磁弹性轴对称振动微分方程。应用平均法对系统非线性主共振问题进行求解,得到稳态运动下的幅频响应方程。通过数值计算,得到固支边界条件下圆板的幅频特性曲线以及振幅随磁感应强度、转速、激励力等参数的变化规律曲线图,分析了不同参数对旋转板共振幅值及非线性特性的影响。

半固态铸造的磁场与搅拌力分析

通过磁路半集总参数分析，提出了用旋转永磁体法制备非枝晶组织半固态浆料的磁路设计原则。并根据磁荷模型对工作区内的磁场及搅拌力进行了计算和讨论，其结果与实测吻合较好。

强恒磁场对孕鼠子代生化指标的影响

[目的]为明确磁场对大鼠重要脏器生理功能的影响,为今后制定我国磁疗康复装置剂量限值标准提供一些毒理学参考依据。[方法]用恒定磁场(0.4T)每日0.5、1、2 h暴磁处理SD受孕母鼠至仔鼠出生,仔鼠继续饲养至10周, 检测仔鼠的肝功能、肾功能以及糖类、脂类、蛋白质、核酸代谢的相关生化指标,据此分析磁场对大鼠生理有无影响,判断磁场是否对大鼠有害。[结果]各剂量组的各项生化指标分别与对照组相比,P值均大干0.05,组间差异也无显著性。[结论]在目前暴磁剂量下旋转恒定磁场对实验SD大鼠肝肾功能及相关生化指标无有害影响。