Hydrodynamics during melting of an electroconductive sample in microgravity conditions under contactless positioning by electromagnetic forces

MHD-flow during melting of a spherical metal sample under contactless positioning by alternating magnetic field produced by two circular turns with currents, is investigated. It is shown that when the currents supplying the turns are opposite in direction, electromagnetic forces, originating from the interaction of the Foucault currents with alternating magnetic field, induce two torus-like eddies in the interior of the molten metal drop.     

The electromagnetic rocket gun

A novel propulsion concept is proposed which has the potential of accelerating large masses to velocities substantially higher than what is possible with chemical rockets. The novel concept is an electromagnetic gun, where the projectile is a rocket. The proposed concept solves the old problem of magnetic propulsion, which is the resistive dissipation of the induced electric currents into heat which will vaporize the projectile long before it can reach a high velocity. As in a rocket, where the propellant cools and thereby prevents the rocket from burning up, the same happens in the proposed concept where the propellent also cools the projectile and prevents its vaporization. The propellant, however, not only cools the projectile but in addition is resistively heated by the magnetic field and ejected from the projectile with high velocity. The resulting recoil produces an additional thrust which is approximately as large as the thrust exerted by the magnetic field alone. The energy to drive the jet is externally supplied, making the specific impulse much larger than for chemical rockets.     

在地面上用磁性液体制造流体的超重、失重和微重力环境

磁力和重力均为非接触的力，当作用于磁性液体上的磁力和重力方向相同时，磁性液体处于超重状态；当作用于磁性液体上的磁力和重力方向相反时，磁性液体处于失重状态；当作用于磁性液体上磁力和重力相互抵消，磁性液体呈饱和磁化状态且处在均匀梯度磁场区域中时，磁性液体被表面张力约束成球体，磁性液体处于微重力状态。这一发现使我们在地面上能经济的、方便的、长时间的制造流体的小区域微重力环境，为研究微重力状态下的流体科学、生命科学，材料加工和器件开发等提供了新的方法。     

Heat transfer of thermocapillary convection in a two-layered fluid system under the influence of magnetic field

Heat transfer of a two-layer fluid system has been of great importance in a variety of industrial applications. For example, the phenomena of immiscible fluids can be found in materials processing and heat exchangers. Typically in solidification from a melt, the convective motion is the dominant factor that affects the uniformity of material properties. In the layered flow, thermocapillary forces can come into an important play, which was first emphasized by a previous investigator in 1958. Under extraterrestrial environments without gravity, thermocapillary effects can be a more dominant factor, which alters material properties in processing. Control and optimization of heat transfer in an immiscible fluid system need complete understanding of the flow phenomena that can be induced by surface tension at a fluid interface. The present work is focused on understanding of the magnetic field effects on thermocapillary convection, in order to optimize material processing. That is, it involves the study of the complicated phenomena to alter the flow motion in crystal growth. In this effort, the Marangoni convection in a cavity with differentially heated sidewalls is investigated with and without the influence of a magnetic field. As a first step, numerical analyzes are performed, by thoroughly investigating influences of all pertinent physical parameters. Experiments are then conducted, with preliminary results, for comparison with the numerical analyzes.     

One method of gravitational attitude control of a rotating satellite

The mode of spinning up a low-orbit satellite in the plane of its orbit is studied. In this mode, the satellite rotates around its longitudinal axis (principal central axis of the minimum moment of inertia), which executes small oscillations with respect to the normal to the orbit plane; the angular velocity of the rotation around the longitudinal axis is several tenths of a degree per second. Gravitational and restoring aerodynamic moments were taken into account in the equations of satellite’s motion, as well as a dissipative moment from eddy currents induced in the shell of the satellite by the Earth’s magnetic field. A small parameter characterizing deviation of the satellite from a dynamically symmetric shape and nongravitational external moments are introduced into the equations. A two-dimensional integral surface of the equations of motion, describing quasistationary rotations of the satellite close to cylindrical precession of the corresponding symmetrical satellite in a gravitational field, has been studied by the method of small parameter and numerically. We propose to consider such quasistationary rotations as unperturbed motions of the satellite in the spin-up mode.     

Alternating magnetic field forces for satellite formation flying

Selected future space missions, such as large aperture telescopes and multi-component interferometers, will require the precise positioning of a number of isolated satellites, yet many of the suggested approaches for providing satellite positioning forces have serious limitations. In this paper we propose a new approach, capable of providing both position and orientation forces, that resolves or alleviates many of these problems. We show that by using alternating fields and currents that finely-controlled forces can be induced on the satellites, which can be individually selected through frequency allocation. We also show, through analysis and experiment, that near field operation is feasible and can provide sufficient force and the necessary degrees of freedom to accurately position and orient small satellites relative to one another. In particular, the case of a telescope with a large number of free mirrors is developed to provide an example of the concept. We also discuss the far field extension of this concept.     

Optimal satellite formation reconfiguration actuated by inter-satellite electromagnetic forces

The inter-satellite electromagnetic forces generated by the magnetic dipoles on neighboring satellites provide an attractive control actuation alternative for satellite formation flight due to the prominent advantages of no propellant consumption or plume contamination. However, the internal force nature as well as the inherent high nonlinearity and coupling of electromagnetic forces bring unique dynamic characteristics and challenges. This paper investigates the nonlinear translational dynamics, trajectory planning and control of formation reconfiguration actuated by inter-satellite electromagnetic forces. The nonlinear translational dynamic model is derived by utilizing analytical mechanics theory; and analysis on the dynamic characteristics is put forward. Optimal reconfiguration trajectories of electromagnetic force actuated formation are studied by applying optimal control theory and the Gauss pseudospectral method. Considering the high nonlinearity and uncertainty in the dynamic model, an inner-and-outer loop combined control strategy based on feedback linearization theory and adaptive terminal sliding mode control is proposed with finite-time convergence capability and good robust performance. Theoretical analysis and numerical simulation results are presented to validate the feasibility of the proposed translational model, reconfiguration trajectory optimization approach and control strategy.     

Excitation and propagation of an electromagnetic pulse in magnetized plasma in the low-hybrid frequency range

We analyze specific features of slow quasi-static waves excited in the low-hybrid frequency band by a source whose dimensions are much smaller than electromagnetic wavelength. Main attention in this paper is given to an analysis of emission of harmonic signals by a dipole source in pulsed mode. First, the issue of influence of electromagnetic, thermal, and collision corrections in the dispersion equation on the field structure has been studied. Second, the structure of electric and magnetic fields near the resonant cone has been analyzed: in particular, effects of group delay and anomalous spreading of signals are considered. Thus constructed theory explains results of the OEDIPUS-C experiment, in which, for example, already at distances of order of ten wavelengths a signal delay of approximately 10^?4 s was observed. Finally, we have studied some aspects of the inverse problem of electrodynamics: the role played in field formation by smoothness of charge distribution over antenna is demonstrated, and a class of smooth distributions of charge on antenna is found that form a preset field structure.     

Estimation of the current density and analysis of the geometry of the current system surrounding the Earth

The results of an investigation of the distribution of plasma pressure, pressure gradients, and magnetic field near the equatorial plane in the plasma ring surrounding the Earth under magneto-quiet conditions are presented. Observational data obtained during the international THEMIS mission are used. The picture of the distribution of transverse-current density near the equatorial plane was obtained under assumption of observing the magnetostatic balance condition at geocentric distances from 6 to 12R _E. In estimating the integral transverse current it was accepted that in daytime sector the magnetic-field minima on magnetic field lines are not localized in the equatorial plane. Estimates of the integral transverse current were obtained, which demonstrate the possibility of closing nighttime transverse currents at geocentric distances of up to ～12R _E inside the magnetosphere, which form a high-latitudinal continuation of the ring current.     

High-acceleration mass drivers

After testing an early, simplified mass-driver (35 gravity acceleration) a second, designated MD2, was designed and is now operating. MD2 is of axial geometry, with individually powered drive coils of 13.1 cm diameter. Timing is derived through the interruption of light beams by the moving armature (bucket). Electric power is provided by the resonant discharge of sector capacitor banks through silicon-controlled rectifiers in a two-phase, quadrature circuit. The bucket flies in vacuum, guided by passive dynamic eddy-current magnetic forces, those currents flowing in strip conductors lining the inside of a nonconducting vacuum pipe. The initial length of MD2 is 2.5 m, divided equally into acceleration and deceleration. Nominal acceleration is 5000 m/sec². For routine testing an ohmic bucket is used. Quantitative measurements are obtained with a solid bucket carrying two superconducting coils with a current density of 25 kA/cm². A cryogenic station for cooling the bucket to liquid helium temperature is connected to the vacuum pipe. The test program, now begun, will concentrate on guidance and acceleration forces, measurement of drive shielding losses, and possible couplings of drive forces into modes of oscillation.     

Features of coronal mass ejections of minimum size

The coronal mass ejections (CME) with small angular dimensions (d ≤ 10°) have the simplest form, much simpler than large CME. This fact simplifies the problem of analyzing the CME structure and studying their origin. On the basis of the analysis of the LASCO C2 (SOHO) data, we show in this paper that the motion of a CME having small dimensions proceeds within a magnetic tube (a ray with increased brightness) of the streamer belt and leads to an “explosion-like” increase in the angular dimensions (rapid expansion) of the tube. A hypothesis is put forward that a small CME represents a “plasmoid” (a plasma bunch bounded in space, with its own magnetic field) thrown into the base of the magnetic tube and moving along it away from the Sun.     

某型号卫星内部磁场分析计算

文章对某型号卫星的磁力矩器在星体内部产生的磁场进行了逐点计算,并提供了大量卫星内部磁场分布图。计算结果表明,卫星内部一些关键磁敏感部件,例如铷钟、行波管等处磁场值较大,尤其是铷钟位置影响更大一些。文中对计算结果进行分析,并给出建议。     

MIC - a self deploying magnetically inflated cable system for large scale space structures

A new approach, termed MIC (Magnetically Inflated Cable) that enables large, lightweight very strong and rigid space structures is described. MIC would be launched as a compact package of coiled superconducting (SC) cables. After reaching orbit, the cables would be cryogenically cooled and electrically energized by a small power source. The resultant repulsion magnetic forces between the DC currents in the SC cables automatically cause the coiled launch package to self deploy into the final large space structure. The SC cables are held in place by a distributed network of high tensile strength tethers (e.g., Spectra material), creating a very stiff, rigid truss structure that strongly resists bending and torsional, etc. movements, without the need for gravity gradient stabilization. A linear quadrupole (LQ) MIC configuration is described that is suitable for large solar power satellites, space stations, space hotels, propellant tanks, manned Mars spacecraft, etc. The LQ has 2 long SC dipole loops, of horizontal width W, length L, and opposite magnetic polarity, which are vertically separated by distance W, producing a long truss structure of square cross-section (width W) with the 4 SC cables at the corners of the square. The SC currents are opposite in adjacent cables, yielding an outwardly directed net radial force on each cable. The ends of each SC loop experience outwards longitudinal forces. The magnetic forces are very strong, even for modest supercurrents. For example, a 4 meter square truss with I = 250 kiloamp has an outwards radial force of 220 kg per meter of cable. and 5250 kg outwards longitudinal force at the ends of each SC loop. The network of restraining tensile lines can support lightweight structures, including solar panels, propellant tankage, habitat modules, power transmission lines, etc. The design of a 1 kilometer long, 4 meter square cross section MIC truss for solar power satellites is described. The MIC launch package fits within the length/weight constraints of the shuttle bay, and includes all of the helium coolant lines, thermal insulation, and refrigeration equipment required.     

基于有限元法的水下绝缘体小目标电磁场探测方法仿真研究

开展具有自主知识产权的水下绝缘体小目标探测方法研究,可为我国海域勘探开发提供技术支撑。文章将基于有限元的电磁场探测方法应用到水下绝缘体小目标的检测:首先利用ANSYS Maxwell软件进行建模仿真;然后对不同电流及不同水面高度/水下深度有无绝缘体小目标的磁感应强度进行模拟并计算其差值。结果表明,当水下导线直流电流为200 A时,磁感应强度模拟差值大于0.3 nT,可在350 m×350 m×35 m的海域内有效探测有无绝缘体小目标通过。     

基于磁场映像的印制电路板故障诊断方法研究

简要分析了印制电路板的电磁场，提出了用电磁感应法测量磁场的电咱故障诊断新方法，并给出了测试系统组成方案。最后通过验证实验证明了该方法是确实可行的。     

一种不借助零磁线圈的星载磁强计校准方法

文章介绍一种星载磁强计校准装置及方法.首先,将高精度地面磁强计的三分量磁传感器置于标准磁场发生装置形成的磁场环境内,通过后端数据处理装置采集得到第一磁场数据,并进行不同量程下螺线管线圈常数Ci的标定;然后,将星载磁强计置于上述标准磁场环境内,并以高精度地面磁强计不同量程下获得的Ci作为基准,通过后端数据处理装置采集得到...     

双极型磁选态单束铯束管内铯原子运动轨迹的算法改进

针对简化算法得到的铯原子运动轨迹精度不高的结果,通过分析磁选态单束铯束管内双极型选态磁铁的磁场分布,提出了不简化磁场梯度和有效磁矩,用布利厄施-施多厄方法求解铯原子运动方程的算法。用此算法得到的铯原子运动轨迹与通常采用的简化算法得到的轨迹相比,最大差异约为10 mm。此计算结果影响管内机械组件的安装对中位置,可用于束光学模拟计算,提高短期稳定度指标。     

圆柱形Hall推力器磁场的设计与数值模拟

霍尔(Hall)推力器的磁场设计是提高其性能的关键技术之一。针对传统环形Hall推力器小型化带来的缺点,提出了圆柱形的Hall推力器。简要对比了环形和圆柱形两种推力器,对圆柱形推力器的工作原理、磁场设计的要求以及利用ANSYS有限元软件进行的电磁场数值模拟的结果进行了详细分析。结果表明,圆柱形推力器磁路设计是合理的,另外也证明了用ANSYS有限元软件进行电磁场模拟的可靠性。     

磁窗的一种理论模型

本文简要地回顾了“磁窗”减轻再入通讯中断的机理。推导出线极化波,园极化波穿透磁等离子体薄层时,场量的传输矩阵。给出了功率反射系数及透射系数表达式。通过这种磁窗理论模型,模拟算出了为减轻或消除再入通讯中断所需要的磁场强度。并通过激波管上进行的磁窗模拟试验,证实了这一结论。     

一种组合磁钢叠加磁场洛伦兹力磁轴承设计方法

针对现有洛伦兹力磁轴承功耗较高、工作气隙磁场非均匀性问题,提出一种基于组合磁钢叠加磁场的新型洛伦兹力磁轴承设计方法。首先建立了传统洛伦兹力磁轴承电磁力矩模型,揭示了洛伦兹力磁轴承功耗和控制精度与其磁场性能之间的对应关系。在此基础上,引入了磁场强度均值和磁场均匀度的概念,并以此为依据设计出一种轴向整环充磁磁钢与径向分块充磁磁钢组合工作的新型方案。其中轴向充磁磁钢产生主磁场,保证工作气隙周向均匀性,辅助以径向充磁磁钢,使磁场主要聚集在工作气隙处。相比现有洛伦兹力磁轴承,在相同尺寸约束条件下,新型洛伦兹力磁轴承径向磁场均匀度提升了8.7%,磁场强度提升了51.8%,周向磁场连续性显著提高。仿真结果表明,新型洛伦兹力磁轴承可以有效降低功耗、提升控制精度,研究成果可为研制超高精度磁悬浮惯性机构提供一条新的技术途径。