Thrust estimate method of an on-orbit Hall thruster using Hall drift current

In order to realize the thrust estimation of the Hall thruster during its flight mission,this study establishes an estimation method based on measurement of the Hall drift current.In this method,the Hall drift current is calculated from an inverse magnetostatic problem,which is formulated according to its induced magnetic flux density detected by sensors,and then the thrust is estimated by multiplying the Hall drift current with the characteristic magnetic flux density of the thruster itself.In addition,a three-wire torsion pendulum micro-thrust measurement system is utilized to verify the estimate values obtained from the proposed method.The errors were found to be less than 8%when the discharge voltage ranged from 250 V to 350 V and the anode flow rate ranged from 30 sccm to 50 sccm,indicating the possibility that the proposed thrust estimate method could be practically applied.Moreover,the measurement accuracy of the magnetic flux density is suggested to be lower than 0.015 mT and improvement on the inverse problem solution is required in the future.

Numerical calculation of drift current in wind waves

-Drift current induced by wind and waves is investigated with phase-averaged Navier-Stokes equation in which the Reynolds stress is closed by k-ε model. The governing equations are solved by the finite volume method in a system of nonorthogonal coordinates which is fitted to the phase-averaged wave surface. The predicted drift current is fairly reasonable and the drag coefficient of sea-surface predicted with the newly developed interface conditions shows good agreement with previous measurements when breaking waves do not exist.

Lower-Hybrid Drift Instability in Modified Harris Current Sheet

Lower-hybrid drift instability （LHDI） in a Harris current sheet including a uniform background distribution is investigated in linear local kinetic theory. It is found that the introduction of a uniform background distribution reduces the growth rate and real frequency of LHDI at all wavelengths. Some physical explanations about the effects of the background distribution are provided.

The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic（FM/OSC/FM） system

From experimental results of spin polarized injection and transport in organic semiconductors（OSCs）,we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic（FM/OSC/FM） sandwich structure according to the spin drift-diffusion theory and Ohm＇s law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.

Interactions of nonlinear gravity waves and uniform current in Lagrangian system

The particle trajectory on a weakly nonlinear progressive surface wave obliquely interacting with a uniform current is studied by using an Euler-Lagrange transformation.The third-order asymptotic solution is a periodic bounded function of Lagrangian labels and time,which imply that the entire solution is uniformly-valid.The explicit parametric solution highlights the trajectory of a water particle and mass transport associated with a particle displacement can now be obtained directly in Lagrangian form.The angular frequency and Lagrangian mean level of the particle motion in Lagrangian form differ from those of the Eulerian.The variations in the water particle orbits resulting from the oblique interaction with a steady uniform current of different magnitudes are also investigated.

Shear Flow Dispersion Under Wave and Current

The longitudinal dispersion of solute in open channel flow with short period progressive waves is investigated. The waves induce second order drift velocity in the direction of propagation and enhance the mixing process in concurrent direction. The 1-D wave-period-averaged dispersion equation is derived and an expression for the wave-current induced longitudinal dispersion coefficient （WCLDC） is propased based on Fiscber＇ s expression （1979） for dispersion in unidirectional flow. The result shows that the effect of waves on dispersion is mainly due to the cross-sectional variation of the drift velocity. Furthermore, to obtain a more practical expression of the WCLDC, the longitudinal dispersion coefficient due to Seo and Cheong （1998） is modified to incluee the effect of drift velocity. Laboratory experiments have been conducted to verify the propased expression. The experimental results, together with dimensional analysis, show that tbe wave effect can be reflected by the ratio between the wave amplitude and wave period. A comparative study between the cases with and without waves demonstrates that the magnitude of the longitudinal dispersion coefficient is increased nnder the presence of waves.

A numerical model with Stokes drift for pollutant transport within the surf zone on a plane beach

This study examines the effects of Stokes drift on pollutant transport within the surf zone on a plane beach both numerically and experimentally. Firstly, the numerical model is described. The wave-induced current is modeled using the concept of the radiation stress. The wave propagation model is based on the wave energy conservation equation. And the advective diffusion model including the Stokes drift is used to describe the pollutant transport in the surf zone. Model validation was achieved in this case versus an analytical solution for an instantaneous point source in a uniform horizontal flow. This study also describes a laboratory experiment on dye release in the surf zone over a plane beach. We examined the final inclination angle required by a continuously released pollutant plume to reach the shoreline under both cases, and transport velocities in the alongshore and cross- shore directions were estimated by linearly fitting the location of a dye-patch front at different time. Results show that this dye patch moved shoreward with an approximate speed of 0.05 m/s (0.017 m/s) between 10 s and 40 s and 0.001 m/s (0.011 m/s) after 40 s for Case 1 (2). This model was then used to simulate pollutant transport in the surf zone on a plane beach as reproduced in the current experiment. Comparisons between our dye transport experiment and numerical results were then also conducted;the data showed that the numerical results including Stokes drift agreed more closely with experimental results than those without it. The data showed that the pollutant was generally transported obviously shoreward in addition to its expected drift along the shore. We also suggest that Stokes drift plays an important role in pollutant movement in the surf zone, especially shoreward.

The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic(FM/OSC/FM) system

From experimental results of spin polarized injection and transport in organic semiconductors(OSCs),we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic(FM/OSC/FM) sandwich structure according to the spin drift-diffusion theory and Ohm’s law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.

一种超低失调集成运算放大器的设计与实现

基于双极型工艺设计了一种超低失调集成运算放大器。通过在差分输入级的有源负载处设计电阻修调网络来调整失调电压,并针对基极电流补偿不可控的问题设计了可修调的基极电流补偿结构来降低偏置电流,利用激光修调技术减小基极补偿结构引入的随机失调,有效改善了输入级失调。增益级采用结型场效应晶体管(JFET)差分对管以获得高增益,输出级采用全npn晶体管的乙类输出结构可满足大功率输出需求。芯片实测数据表明:在全温度范围内,失调电压最大为-25.3μV,失调电压温漂为0.025μV/℃,输入偏置电流为-3.535 nA,输入失调电流为-0.825 nA。实现了超低的失调电压、电流和温漂。

新型电子电气架构下的汽车车身接地点串流分析及优化

对汽车接地点基础原理和类型进行简要介绍,同时对接地电流分布、串流原理及串流路径进行深入研究分析。结合实际实验,在某新型2.0架构平台下的汽车电气系统模拟接地闭合和断开的环境,通过IPE的数据采集设备对电流进行精确监控,提出了一种线束安全的判定方法。根据电流的串流路径分析发现有风险的线束,判断功能是否符合设计要求,针对串流导致的潜在风险提出了优化方案并进行整改。整改方法包括改变和拆分接地点、加粗串流接地线等。整改后再次模拟接地点断开环境进行实验,结果表明整改后该接地点能稳定、安全、有效地保证2.0架构平台正常运行。

高压线路断路器开断故障电流零点漂移问题分析

高压交流输电线路需要准确预测电流零点时刻,从而有效确定断路器开断动作时刻,使断路器在接近于过零点时刻开断故障电流。导致开断相故障电流零点相对于预期的稳态短路电流发生漂移有以下两个因素:一是当发生短路故障时,首次开断故障电流相后,后开断相的故障电流的衰减直流分量在瞬态过程中将叠加在交流分量上从而导致其零点漂移;另一个是三相电流具有不同的零点时刻,当断路器中的一相断开电弧熄灭时,整个三相电路的拓扑结构将发生变化,从而导致其他两相的零点漂移。研究结果表明,针对中性点接地系统及非接地系统,在各种短路故障条件下,首开断相断开后,次开断相的电流零点会向前移动,而末开断相的电流过零点会向后移动。

电阻焊电流信号积分漂移软件补偿方法

为满足电阻焊电流长时间检测的需求并简化检测电路,针对罗氏线圈信号调理的积分漂移问题,探讨了基于软件补偿的漂移补偿方法。采用多款国产运算放大器构建积分器,在恒电流控制模式下检测积分器输出信号的漂移率,在数据处理过程中叠加漂移率的平均值以实现软件补偿。将积分漂移电压视为电流检测的误差,以相对误差分析了恒电流输出2 s过程中软件补偿的准确性。结果表明,基于软件补偿的漂移补偿方法在信号检测后进行数据修正,减少了对硬件补偿的依赖,在1~4 kA的被测电流范围内相对误差的平均值不超过1.0%,能够满足电阻焊电流长时间检测需求。该补偿方法丰富了基于罗氏线圈的电流信号处理手段,具有较好的工程适用性。

一种实用的组合式光伏并网系统孤岛效应检测方法

在分析传统的主动频率偏移(AFD)法基础上,提出一种适时施加脉冲式电流幅值干扰的组合式改进方法,重点讨论幅值干扰施加的方式,特别是施加时间的选取。采用该方法,并结合被动检测法中的过/欠压保护、过/欠频保护进行孤岛检测的仿真计算,结果表明,所提出的方法可克服传统AFD法或电流幅值干扰法单独使用时存在的缺点,能快速准确检测出孤岛效应的发生,实现在高速自动重合闸动作之前停止逆变器的并网运行,具有对电网谐波影响小、检测盲区小的优点。

广东海域模拟人和无动力渔船海上漂移试验研究

为探讨海上搜救目标无动力渔船和落水人员在海水中的漂移规律,对现有海上搜救目标漂移轨迹预测模型进行评估与改进,国家海洋局南海海洋工程勘察中心于2011年2月和4月在广东近岸海域开展了3组模拟人和2组无动力船海上漂移试验。试验发现模拟人与无动力船大部分时刻的漂移轨迹位于下风向的右侧,80%以上的时刻漂移轨迹位于海流流向和下风向的矢量合成区间内。以漂移速度为应变量,流速和风速为自变量进行二元回归分析发现,广东海域的模拟人和无动力渔船的流致漂移参数约为1.0,风致漂移参数分别为0.019和0.038。

等深流沉积研究进展

等深流沉积研究已有约50年的历史,其研究成果极为丰富。近10余年,随着科学技术的发展和海洋意识的提高,等深流沉积研究工作开展迅速,涌现出了大量的新成果。简要回顾了等深流沉积研究的历程,结合最新研究成果,对其进展及认识进行了总结。等深流沉积以细粒沉积为主,沉积构造及生物扰动发育,多呈细—粗—细沉积序列。其类型可分为长条形丘状漂积体、水道型漂积体、补丁型漂积体等7类。沉积模式根据地形、水动力、路径等可分为简单路径模式、复杂路径模式以及等深流与重力流交互作用模式。等深流与重力流交互作用是深水沉积研究热点之一。等深流沉积研究面临的问题及发展方向主要有三方面,即,1)完善识别标志,推广研究成果;2)综合运用多种手段和理论,探讨沉积过程与构造演化、古海洋及气候变化的耦合关系;3)加大油气勘探潜力研究力度。

南海北部珠江口盆地重力流与等深流交互作用沉积特征、过程及沉积模式

通过地震及钻孔资料对南海北部珠江口盆地重力流及等深流沉积进行了研究。南海北部重力流及等深流沉积类型多样，包括峡谷、单向迁移水道、堤岸、朵叶及漂积体。单向迁移水道迁移方向分别为北东向和南西西向，为重力流与等深流交互作用形成。漂积体有大型长条状漂积体、限制型漂积体和陆坡席状漂积体，岩性为粘土、泥质粉沙。南海北部陆坡水深200-1200m范围内发育北东向迁移水道及小规模的漂积体，而水深约1200～3000m内则以朵叶及大规模的漂积体为主，见少量南西西向迁移水道。其中，漂积体多分布于峡谷、水道及朵叶的两侧，为等深流改造堤岸、朵叶等“细粒”沉积物而成。

根据漂流浮标资料对黑潮15m层流路及流轴特征的分析

利用1979-02-2012-03共33 a的水帆位于15m层的Argos漂流浮标资料,绘制黑潮流系15m层的多年年平均和月平均流场,运用特征线方法计算得到黑潮流轴,定义黑潮流动路径的边界为流速大小20～30 cm/s的过渡性区域.结果显示：黑潮多年年平均流路大致是一个以（13°30′N,142°00′E）为圆心、2 235 km为半径的直角弧段,其在吕宋海峡、台湾东北、九州西南及伊豆海岭附近海区发生气旋式弯曲前先进行反气旋式弯曲调整,弯曲处出现的路径开口主要是支流的并入或分支的流出;黑潮流轴整体性偏向黑潮左边界,其中在吕宋岛东北至台湾以东海域最为显著,在本州岛以南海域次之,而在东海段基本居中;黑潮流路上的流速在总体上由南向北呈增大趋势,但并非沿流路持续性逐渐增加,而是呈现出较平直流段的大流速区和弯曲调整流段的低流速区相互交错的状况,其中四国岛以南至伊豆诸岛以西流段的流速为最大.多年月平均流场显示,2月,5月,8月和11月这4个月份是黑潮流路和流轴发生变化的重要转折期,而1月,4月,7月和10月这4个月份则是各季节的代表月份.其中,冬季月份的黑潮流路和流轴最为曲折,向边缘海发生显著入侵;夏季月份的黑潮流路和流轴最为平直,左侧伴随有北向流动;春、秋两季的过渡性特征则比较明显.

两种鲟鱼卵在均匀流场中的漂移特性研究

鱼卵的漂移是鱼类早期发育时期响应水文过程的一个重要阶段。鱼卵的漂移有利于其在河流生态系统中的分布扩散、孵化和躲避敌害等。鱼卵的漂移过程受到多方面的影响，包括鱼卵本身的质量、大小、形状和水的特征如流速、流态以及泥沙含量等。

顶燃式热风炉陶瓷燃烧器模型的数值模拟

运用CFD软件对顶燃式热风炉陶瓷燃烧器内气体流动进行了数值模拟,比较了煤气环道有无导流砖时燃烧室至蓄热室间流场特性,得到了模型内气体速度分布。模拟结果表明:煤气环道有导流砖时较好的解决了蓄热室的偏流问题,且模型的配气均匀度达到了95.98%。现场使用情况表明,本陶瓷燃烧器在单烧高炉煤气的情况下,风温可稳定在1200℃的水平。

线性霍尔元件的互补组合及其差分式应用

为改善线性霍尔元件的输出特性,提出了一种基于霍尔互补组合的差分式应用方法。在阐述霍尔差分式测量方法的原理和实际应用的基础上,分别给出了霍尔互补组合体的实现方法和实验结果。结果证明,霍尔元件的差分式应用方法具有增大输出电压幅度、抑制共模干扰和降低温度漂移的优点,有利于提高线性霍尔元件的稳定性和测量精度。