电磁-热-流弱耦合的变压器绕组温升研究

绕组热问题的研究涉及到电磁学、流体动力学和数值传热学等学科,当前国内外学者未考虑变压器整体油流分布对绕组温升的影响。基于电磁-热-流弱耦合分析法,通过对变压器整体油路三维有限体积分析和绕组杂散损耗有限元数值分析,确定绕组温升数值分析的边界条件,计算绕组区域的温度场,研究绕组区域的铜—油温升和油流分布,考虑分析了不均匀油流分布下绕组区域的散热情况。以提高测温点数量与减小光纤对油路影响为前提,设计进行了高压绕组光纤测温实验,对比实验值与数值分析值,所得误差均在±3.5%以内,证明了耦合方法可直接应用于电力变压器绕组冷却系统的设计与优化。

基于电磁-热-流耦合场的多回路排管敷设电缆载流量数值计算

多回路电缆以集群方式敷设时,各回路之间的电磁耦合和热耦合都将加强,对电缆导体线芯和金属外护套的交流电阻及涡流损耗的影响均不可忽略。为准确计算四回路电缆在4×4孔排管敷设方式下的载流量,借助于Comsol和MATLAB软件建立电磁-热-流耦合物理场有限元模型,将电磁场、温度场及排管内空气流速场耦合求解。首先通过求解电磁场计算电磁热损耗,然后作为载荷施加于传热模型进行温度场分布计算。该模型对电缆复杂的邻近效应、趋肤效应进行直接仿真计算,考虑了金属材料电阻率随温度的变化关系,且传热模型中耦合了空气自然对流、热辐射和固体热传导3种导热方式。利用所提模型对6种排列方式下的电磁热损耗和温度场分布进行计算;并利用二分法计算相应的载流量。结果表明,排列方式对电缆间的邻近效应有较为显著的影响,优化排列方式可降低电缆损耗、提升载流量。

基于电磁-热-流耦合场的非开挖敷设方案的海底电缆载流量计算

海底电缆在登陆处采用非开挖敷设方式时,由于埋深较大、管道内散热较差,该敷设段成为整个海底电缆载流量的瓶颈点,为此搭建基于电磁场、流体场和热场3物理场的耦合模型,计算对比不同敷设方式下海底电缆载流量的受影响情况。首先借助于Comsol软件建立了电磁-热-流耦合物理场的有限元模型,将电磁场、温度场及管道内的空气流速场耦合求解,得到给定负荷电流下的温度分布和管内空气流速分布特性;继而以广东某地2个回路220 kV 3芯交联聚乙烯(polyethlene,PE)绝缘3×500 mm^2海底电缆为例,分析计算海底电缆在水泥顶管和定向钻PE排管2种情况下的载流量。结果表明:采用水泥顶管敷设方案时能满足工程输送容量的要求,而采用PE排管敷设方案的载流量略低于额定值;另外可通过改变管道材质、管道内充水达到提升非开挖敷设方式下海底电缆载流量的效果。

综合考虑“电磁-热-流”多场耦合的直驱式进给轴热误差建模方法

直线电机驱动的进给轴具有速度快、加速度大和响应时间短等优点,但其初级线圈发热量大易引起外部组件热变形,从而影响进给轴的定位精度。为解决这一问题,提出一种综合考虑“电磁-热-流”多物理场耦合下直驱进给轴的热误差建模方法。通过分析直驱进给轴工作时的电磁场、热场和流场,建立了多物理场耦合下温度场的控制方程。提出了一种简化的控制方程求解法,将方程分离为产热、稳态热对流和热传导3个阶段再重新耦合,可求得温度场与变形场的显式解析模型。实验结果表明,本模型揭示了直驱进给轴热误差的形成机理,其可准确预测热误差,并能自动调整线性和非线性区间,对于提高直驱机床的运动精度具有重要意义。

Directional growth behavior of a(Al) dendrites during concentration-gradientcontrolled solidification process in static magnetic field

The large and small sized Cu（solid）/Al（liquid） couples were prepared to investigate the directional growth behavior of primary a（Al） phase during a concentration-gradient-controlled solidification process under various static magnetic fields（SMFs）.The results show that in the large couples,the α（Al） dendrites reveal a directional growth character whether without or with the SMF.However,the 12 T magnetic field induces regular growth,consistent deflection and the decrease of secondary arm spacing of the dendrites.In the small couples,the α（Al） dendrites still reveal a directional growth character to some extent with a SMF of ≤5 T.However,an 8.8 T SMF destroys the directional growth and induces severe random deflections of the dendrites.When the SMF increases to 12 T,the a（Al） dendrites become quite regular despite of the consistent deflection.The directional growth arises from the continuous long-range concentration gradient field built in the melt.The morphological modification is mainly related to the suppression of natural convections and the induction of thermoelectric magnetic convection by the SMF.

脉动微波循环注热开采煤层气数值模拟

为获取脉动微波循环加热条件下低渗透储层煤层气运移采出规律,文中综合运用多孔介质传热学、电磁学、渗流力学、岩石力学等相关理论,建立低渗透储层煤层气微波注热开采过程渗流电磁-热-流-固多物理场耦合数学模型,结合COMSOL Multiphysics有限元分析软件进行了脉动微波循环加热过程煤层气运移采出规律的数值模拟,获取了不同功率脉动微波循环加热条件下煤层温度场、渗流场的变化规律,并对煤层气产量进行了预测。数值模拟结果表明:脉动微波循环加热煤储层热效应显著,煤层能快速且不断地处于高温状态,气体在高温条件下大量解吸并运移产出。采用脉动循环加热,将继续增加煤层渗透率和煤层中游离煤层气含量,相对于常规开采,煤层含气量大幅度降低,煤层气产量显著提高,增产与稳产交替变换使产量在长时期内处于增产状态。模拟方法与结果可为低渗透储层煤层气脉动微波加热开采技术方案提供理论依据。

Nonadiabatic Phase and Persistent Currents for System of Spin-1／2 Particles in Presenceof Electromagnetic Fields and Spin-Orbit Interaction

We present a comprehensive view and details of calculations on Aharonov-Anandan phase for the charged particles in the external electric and magnetic fields for a nonadiabatic process.We derive,with consideration of a spin-orbit interaction and Zeemann Splitting,the persistent currents as a response to an Aharonov-Casher topological interference effect in one-dimensional mesoscopic ring.We also establish a connection to Berry adiabatic phase with deduced dynamical-nature dependence in the nonadiabatic process.The second quantization representation has also been employed in exhibition of persistent currents in the many-body case.

Thermo-Magneto-Electric Currents with Dynamical Magnetization Inhomogeneities

We study the effect of potential and thermal gradient induced non-equilibrium magnetization in quasi1-d itinerant magnets.A semi-phenomenological theory is employed in conjunction with the drift-diffusion model forthis study.Using the methods of non-equilibrium thermodynamics,we derive the transport currents correspondingto charge,heat,and magnetization flows in the presence of non-equilibrium magnetization textures.It is shown howtime-dependent magnetic textures give rise to charge and thermal currents even in the absence of external potential andthermal gradients through spin pumping.The presence of dynamical textures also affect the thermodynamic parametersof the system.As an application,we consider the case of a helimagnet.

Design of High-Speed PM Synchronous Motor Thermal and Mechanical Analyzes Study for Aerospace Retraction Wheel Motor Application

A 3-D modeling of FEA （finite element analysis） design provides for high-speed synchronous with PMs （permanent magnets） applied in aerospace application will be examined under design considerations ofn = 12,000 rpm, short-duty operation, and etc. for an ARWM （aerospace retraction wheel motor）. First, lumped-elements will be fine-tuned following numerical method results is reported steady-state and transient solutions. Besides, the equations of thermal modeling such as Re, N,,, G,. and Pr numbers in order to calculate heat-transfer coefficient of convection on the rotor and stator surfaces in the air-gap have calculated. This section illustrates the temperature distribution of each point in a clear view. By CFD （fluid dynamic analysis） analysis, the fluid dynamics were modeled, pressure and velocity streamlines of cooling-flow have analyzed. An optimization algorithm was derived in order to have optimized number of water-channels as well. Second, calculation of nodal and tangential forces which deal with mechanical stresses of the ARWM have represented. The paper discusses an accurate magnetic-field analysis that addresses equivalent stress distribution in the magnetic core through using the transient FEA to estimate motor characteristics. The whole model shear and normal mechanical stresses and total deformation oftbe ARWM has been investigated by transient FEA. The end-winding effects were included by the authors.

典型微波频率下煤层瓦斯运移规律对比分析

为了比较915MHz和2450MHz两种典型微波频率下煤层瓦斯运移特征,本文建立了微波注热的电磁-热-流-固耦合模型,用于模拟两种典型微波频率下煤层瓦斯的运移规律。

Targeted inductive heating of nanomagnets by a com- bination of alternating current （AC） and static magnetic fields

The conversion of electromagnetic energy into heat by nanomagnets has the potential to be a powerful, non-invasive technique for cancer therapy by hyperthermia and hyperthermia-based drug release, while temperature controllability and targeted heating are challenges to developing applications of such magnetic inductive hyperthermia. This study was designed to control the hyperthermia position and area using a combination of alternating current （AC） and a static magnetic field. MnZn ferrite （MZF） nanoparticles which exhibited excellent hyperthermia properties were first prepared and characterized as an inductive heating mediator. We built model static magnetic fields simply using a pair of permanent magnets and studied the static magnetic field distributions by measurements and numerical simulations. The influence of the transverse static magnetic fields on hyperthermia properties was then investigated on MZF magnetic fluid, gel phantoms and SMMC-7721 cells in vitro. The results showed a static magnetic field can inhibit the temperature rise of MZF nanoparticles in an AC magnetic field. But in the uneven static magnetic field formed by a magnet pair with repelling poles face-to-face, the heating area can be restricted in a central low static field; meanwhile the side effects of hyperthermia can be reduced by a surrounding high static field. As a result we can position the hyperthermia area, protect the non-therapeutic area, and reduce the side effects lust by using a well-designed combination of AC and static field.

换流变阀侧套管温度分布的计算及其影响因素分析

换流变压器套管作为直流输电系统中的重要设备,不仅要求其有优异的绝缘性能,能够承受一定的机械载荷,还要求其正常运行时的温度不能超过绝缘材料的最高允许工作温度。针对500 kV换流变阀侧套管,应用三维有限元分析软件COMSOL以及ANSYS CFX对套管的温度分布进行了电-磁-热-流耦合计算。分析了环境温度、变压器油温、环氧芯子的热导率以及护套的热导率对温度分布的影响。结果表明:套管的最高温度出现在导电管与环氧芯子的界面处;环境温度、变压器油温与环氧芯子的热导率将会不同程度的影响套管的温度分布;在进行套管的热设计时需要考虑不同材料之间传热参数的配合,以获得最大的散热效率。

基于微波注热的煤层瓦斯抽采数值模拟研究

为研究微波注热下煤层瓦斯运移采出规律,基于瓦斯微波注热抽采电磁-热-流-固耦合模型,进行了微波注热下瓦斯抽采数值模拟研究,分析了不同微波频率、微波功率和初始渗透率下煤层温度和产气演化规律。数值模拟结果表明:微波注热时,注热处煤层温度快速升高,热量通过热传递和热对流作用向低温区域传递,高温范围不断由注热处向气井扩展;对比0.915 GHz和2.45 GHz两种不同微波频率,低频微波更有利于增强微波热效应;对比0, 500, 1000, 1500 W四种不同微波功率,相对于常规开采,微波注热能极大促进瓦斯解吸和运移,瓦斯含量大幅度降低,增大微波功率对提高瓦斯产量有积极作用;采用增渗措施提高初始渗透率并配合微波注热,可以进一步提高瓦斯抽采率。