异步电机的无冲击起动

从系统结构和工作原理简要介绍了高压异步电机的无冲击起动方式。其具有无冲击电流、可紧急重复起动等优点。

慎用断电按钮熄火

磁电机断电按钮的作用是断电,使起动机熄火,但起动机高速运转时不宜使用。其原因是起动机高速运转时用断电按钮熄火,不仅会引起磁铁转子退磁,而且还会导致燃烧室和火花塞积炭,

Singularity-free expression of magnetic field of cuboid under undulating terrain

Most of the current computing methods used to determine the magnetic field of a uniformly magnetized cuboid assume that the observation point is located in the upper half space without a source. However, such methods may generate analytical singularities for conditions of undulating terrain. Based on basic geomagnetic field theories, in this study an improved magnetic field expression is derived using an integration method of variable substitution, and all singularity problems for the entire space without a source are discussed and solved. This integration process is simpler than that of previous methods, and final integral results with a more uniform form. AT at all points in the source-flee space can be calculated without requiring coordinate transformation; thus forward modeling is also simplified. Corresponding model tests indicate that the new magnetic field expression is more correct because there is no analytical singularity and can be used with undulating terrain.

Modeling a magneto-rheological soft starter for use with belt conveyors

The theory of magnetic circuit design, the constitutive equations of a magneto-theological fluid, and the load properties of belt conveyors were used to design a magneto-rheological soft starter test-bed. The magnetic field distribution in the working gap was analyzed and the current-speed relationship was investigated. A mathematical model for the time response was deduced. The results show that a linear relationship between current and magnetic field is seen when the magnetic materials are not saturated and the magnetic field is uniform in the working section. The rotation speed of the driven shaft changes linearly with increasing time. The response is rapid and can be as short as milliseconds. This meets the starting requirements of belt conveyors.

Numerical simulations on origin of Galilean moons' magnetic anomalies

Galileo mission detected the magnetic anomalies originated from Galilean moons.These anomalies are likely generated in the moons' interiors,under the influence of a strong ambient Jovian field.Among various possible generation mechanisms of the anomalies,we focus on magneto-convection and dynamos in the interiors via numerical simulation.To mimic the electromagnetic environment of the moons,we introduce in our numerical model an external uniform magnetic field B0 with a fixed orientation but varying field strength.Our results show that a finite B0 can substantially alter the dynamo processes inside the core.When the ambient field strength B0 increases to approximately 40% of the field generated by the pure dynamo action,the convective state in the core changes significantly:the convective flow decreases by 80% in magnitude,but the differential rotation becomes stronger in much of the fluid layer,leading to a stronger field generated in the core.The field morphologies inside the core tend to align with the ambient field,while the flow patterns show the symmetry-breaking effect under the influence of B0.Furthermore,the generated field tends to be temporally more stable.

Origin and structures of solar eruptions Ⅰ: Magnetic flux rope

Coronal mass ejections(CMEs) and solar flares are the large-scale and most energetic eruptive phenomena in our solar system and able to release a large quantity of plasma and magnetic flux from the solar atmosphere into the solar wind. When these high-speed magnetized plasmas along with the energetic particles arrive at the Earth, they may interact with the magnetosphere and ionosphere, and seriously affect the safety of human high-tech activities in outer space. The travel time of a CME to 1 AU is about 1–3 days, while energetic particles from the eruptions arrive even earlier. An efficient forecast of these phenomena therefore requires a clear detection of CMEs/flares at the stage as early as possible. To estimate the possibility of an eruption leading to a CME/flare, we need to elucidate some fundamental but elusive processes including in particular the origin and structures of CMEs/flares. Understanding these processes can not only improve the prediction of the occurrence of CMEs/flares and their effects on geospace and the heliosphere but also help understand the mass ejections and flares on other solar-type stars. The main purpose of this review is to address the origin and early structures of CMEs/flares, from multi-wavelength observational perspective. First of all, we start with the ongoing debate of whether the pre-eruptive configuration, i.e., a helical magnetic flux rope(MFR), of CMEs/flares exists before the eruption and then emphatically introduce observational manifestations of the MFR. Secondly, we elaborate on the possible formation mechanisms of the MFR through distinct ways. Thirdly, we discuss the initiation of the MFR and associated dynamics during its evolution toward the CME/flare. Finally, we come to some conclusions and put forward some prospects in the future.

Origin and structures of solar eruptions Ⅱ: Magnetic modeling

The topology and dynamics of the three-dimensional magnetic field in the solar atmosphere govern various solar eruptive phenomena and activities, such as flares, coronal mass ejections, and filaments/prominences. We have to observe and model the vector magnetic field to understand the structures and physical mechanisms of these solar activities. Vector magnetic fields on the photosphere are routinely observed via the polarized light, and inferred with the inversion of Stokes profiles. To analyze these vector magnetic fields, we need first to remove the 180° ambiguity of the transverse components and correct the projection effect. Then, the vector magnetic field can be served as the boundary conditions for a force-free field modeling after a proper preprocessing. The photospheric velocity field can also be derived from a time sequence of vector magnetic fields.Three-dimensional magnetic field could be derived and studied with theoretical force-free field models, numerical nonlinear force-free field models, magnetohydrostatic models, and magnetohydrodynamic models. Magnetic energy can be computed with three-dimensional magnetic field models or a time series of vector magnetic field. The magnetic topology is analyzed by pinpointing the positions of magnetic null points, bald patches, and quasi-separatrix layers. As a well conserved physical quantity,magnetic helicity can be computed with various methods, such as the finite volume method, discrete flux tube method, and helicity flux integration method. This quantity serves as a promising parameter characterizing the activity level of solar active regions.