恒磁场对刚性圆直管中脉动流的影响*

本文研究了恒磁场对于刚性圆直管中脉动流的影响,并根据现有的实验资料考虑了磁场对于血液粘度的影响,给出了恒磁场作用下刚性圆直管脉动流的分析解以及恒磁场对刚性圆直管中的流速分布、流量以及阻抗的影响的计算结果.这些结果对于深入研究磁场对于血液动力学的影响具有一定参考价值.     

强磁场对吸积中子星壳层中电子俘获反应的影响

本文通过考虑强磁场中电子的量子效应,讨论了强磁场对电子气体的Fermi能的影响,推导了在强磁场下吸积中子星壳层中的电子俘获反应率,并与无磁场情形进行了比较.作为例子,本文计算和分析了~3He在强磁场中的电子俘获反应.对于满足能量条件的电子俘获,在足够强的磁场和低密度的情形下(只有一个Landau能级),由于磁场的存在,反应会显著变慢;当磁场不太强或者密度较大时,磁场对反应几乎没有影响.     

矩形铁磁板的磁弹性弯曲与稳定性

本文对于在外加磁场中的矩形软铁磁弹性板的磁弹性弯曲现象进行了定量模拟;建立了能反映磁弹性相互耦合作用的数值计算程序;揭示了铁磁板弯曲变形与磁(场)力的非线性特征关系,并据此讨论了磁弹性失稳临界磁场随倾斜角变化的规律.     

强场中电子的经典行为

研究了圆偏振强激光在等离子体中产生的自生磁场及注入电子在由激光场和自生磁场构成的混合场中的经典行为.圆偏振强激光在等离子体中传播时,因逆Faraday效应,方向平行于传播方向的准静态磁场被激发.推出相对论情况下的自生磁场方程,并以此研究了自生磁场的特性.当电子或电子束注入激光脉冲,则电子将受到激光场和自生磁场的作用,满足共振条件的电子能得到加速.得出电子能量方程并计算了能量随时间的变化,就一种特殊情况计算了电子在混合场中的动力学行     

铁磁性设备补偿磁场的数学模型及其应用

研究用永磁体对铁磁性设备进行磁场补偿的问题,建立了补偿磁场的数学模型.将设备划分成若干个小长方体后,基于磁矩量法建立了数学模型,并对补偿磁场进行拟合.在计算模型中的耦合系数矩阵时,用多个点的平均值作为耦合系数的有效值,提高了计算结果的可靠性和稳定性.并且,针对永磁体距离设备很近时,设备呈现出的非线性磁化特性,通过优化方法求解各个单元的等效磁化率,这种方法不需要知道铁磁材料的磁化曲线和设备结构,便于计算和实际应用.最后,通过实验设计与数值计算,得到了永磁体对设备进行补偿的磁场分布,模型计算结果与实际测量数据误差11%以内,这说明该模型能够满足工业要求,具有实际应用价值.     

铁磁性设备补偿磁场的数学模型及其应用

研究用永磁体对铁磁性设备进行磁场补偿的问题,建立了补偿磁场的数学模型.将设备划分成若干个小长方体后,基于磁矩量法建立了数学模型,并对补偿磁场进行拟合.在计算模型中的耦合系数矩阵时,用多个点的平均值作为耦合系数的有效值,提高了计算结果的可靠性和稳定性.并且,针对永磁体距离设备很近时,设备呈现出的非线性磁化特性,通过优化方法求解各个单元的等效磁化率,这种方法不需要知道铁磁材料的磁化曲线和设备结构,便于计算和实际应用.最后,通过实验设计与数值计算,得到了永磁体对设备进行补偿的磁场分布,模型计算结果与实际测量数据误差在11%以内,这说明该模型能够满足工业要求,具有实际应用价值.     

数论网格法在磁场计算中的应用

让我们来讨论空芯线圈产生的磁场,如果介质是均匀的,而且它的磁导率μ=常数。那么磁场的计算是一个线性问题。 根据比奥-沙瓦定律,当面积dS上有一电流通过,且其电流密度为j时,它在空间一     

太阳23周活动上升期磁场剪切角的统计分布

利用国家天文台怀柔太阳观测站太阳活动区矢量磁场资料, 计算了太阳23周活动上升期(1996~2000年)活动区的磁场剪切角. 结果表明, 磁场剪切角的统计分布近似为Gauss分布, 在北半球负的剪切角占优势, 南半球正的剪切角占优势, 存在与磁场无力因子α 和电流螺度相似的南北半球符号的反对称性.     

关于无磁阻抗和无热耗散的MHD-Boussinesq系统的Prodi-Serrin型爆破准则

由速度的Prodi-Serrin条件推导出无磁阻抗,无热耗散的MHD-Boussinesq系统解的正则性.对磁场或温度变化没有作出先验假设.     

太阳风中的大尺度涡旋波

本文中提出,行星际磁场的扇形结构可能是由赤道面上的大尺度涡旋波引起的.对于太阳偶极子基本磁场来说,行星际空间中赤道面为一中性片,但当有波动形式的扰动时,就可能在赤道面上出现磁场,而在相邻区域磁场呈相反极性,文中证明了存在一种涡旋状的波动,它刚性地随同太阳一起共旋.在不考虑粘滞性和热传导的简单模型下,这种波不衰减,可以稳定地维持.按这种理论,扇形结构不是一种物质流,而是一密度波.本文还定量地估算了这种大尺度涡旋波的波长和倾角,并与人造卫星和飞船的观测资料作了比较,结果表明,两者是比较接近的。     

MHD turbulence in a channel with spanwise field

We study turbulent channel flow of an electrically conducting liquid with a homogeneous magnetic field imposed in the spanwise direction. The Lorentz force is modelled using the quasistatic approximation. Direct and large–eddy simulations are performed for hydrodynamic Reynolds numbers Re=10000 and Re=20000 and the Hartmann number varying in a wide range. The main effect of the magnetic field is the suppression of turbulent velocity fluctuations and momentum transfer in the wall–normal direction. Comparing the results from direct and large–edddy simulations we show that the dynamic Smagorinsky model accurately reproduces the flow transformation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of particle dynamics in a rapidly varying viscous flow

A method for the numerical simulation of the dynamics of particles in a rapidly varying viscous flow has been developed and implemented as a software package. The frequency of variations in the fluid velocity is assumed to be such that the nonlinear terms in the equations of motion can be neglected in comparison with the nonstationary terms. The hydrodynamic interaction of the particles is taken into account. The velocities of the particles and their trajectories are computed. It is found that the trajectories of the particles depend substantially on the ratio of their radii. In the case of dipole particles in a rapidly varying external magnetic field, the hydrodynamic interaction is shown to prevent the particles from approaching each other under the influence of dipole-dipole interaction forces.     

Numerical and asymptotic study of non‐axisymmetric magnetohydrodynamic boundary layer stagnation‐point flows

Both numerical and asymptotic analyses are performed to study the similarity solutions of three‐dimensional boundary‐layer viscous stagnation point flow in the presence of a uniform magnetic field. The three‐dimensional boundary‐layer is analyzed in a non‐axisymmetric stagnation point flow, in which the flow is developed because of influence of both applied magnetic field and external mainstream flow. Two approaches for the governing equations are employed: the Keller‐box numerical simulations solving full nonlinear coupled system and a corresponding linearized system that is obtained under a far‐field behavior and in the limit of large shear‐to‐strain‐rate parameter (λ). From these two approaches, the flow phenomena reveals a rich structure of new family of solutions for various values of the magnetic number and λ. The various results for the wall stresses and the displacement thicknesses are presented along with some velocity profiles in both directions. The analysis discovered that the flow separation occurs in the secondary flow direction in the absence of magnetic field, and the flow separation disappears when the applied magnetic field is increased. The flow field is divided into a near‐field (due to viscous forces) and far‐field (due to mainstream flows), and the velocity profiles form because of an interaction between two regions. The magnetic field plays an important role in reducing the thickness of the boundary‐layer. A physical explanation for all observed phenomena is discussed. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of the chemical reaction and radiation absorption on the unsteady MHD free convection flow past a semi infinite vertical permeable moving plate with heat source and suction

Analytical solutions for heat and mass transfer by laminar flow of a Newtonian, viscous, electrically conducting and heat generation/absorbing fluid on a continuously vertical permeable surface in the presence of a radiation, a first-order homogeneous chemical reaction and the mass flux are reported. The plate is assumed to move with a constant velocity in the direction of fluid flow. A uniform magnetic field acts perpendicular to the porous surface, which absorbs the fluid with a suction velocity varying with time. The dimensionless governing equations for this investigation are solved analytically using two-term harmonic and non-harmonic functions. Graphical results for velocity, temperature and concentration profiles of both phases based on the analytical solutions are presented and discussed.     

Laminar magnetohydrodynamic duct flow in the presence of a magnetic dipole

We study magnetohydrodynamic flow of a liquid metal in a straight duct. The magnetic field is produced by an exterior magnetic dipole. This basic configuration is of fundamental interest for Lorentz force velocimetry (LFV), where the Lorentz force opposing the relative motion of conducting medium and magnetic field is measured to determine the flow velocity. The Lorentz force acts in equal strength but opposite direction on the flow as well as on the dipole. We are interested in the dependence of the velocity on the flow rate and on strength of the magnetic field as well as on geometric parameters such as distance and position of the dipole relative to the duct. To this end, we perform numerical simulations with an accurate finite-difference method in the limit of small magnetic Reynolds number, whereby the induced magnetic field is assumed to be small compared with the external applied field. The hydrodynamic Reynolds number is also assumed to be small so that the flow remains laminar. The simulations allow us to quantify the magnetic obstacle effect as a potential complication for local flow measurement with LFV. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Locomotion based on the control of the shape of magnetic fluid surfaces and of magnetizable media

The realization of locomotion based on the deformation of a free surface of a magnetic fluid layer in a traveling magnetic field is studied. A plane flow of an incompressible viscous magnetic fluid layer on a horizontal surface in a nonuniform magnetic field and a plane two-layers flow of incompressible viscous magnetic fluids between two parallel solid planes in a magnetic field is considered. Also the flow of an incompressible viscous magnetic fluid layer on a cylinder in a nonuniform magnetic field is an object of investigation. The deformation and the motion of a body made by a magnetizable polymer in an alternating magnetic field are experimentally studied. The cylindrical body (worm) which is located in a cylindrical tube is analyzed. These effects can be used in designing autonomous mobile robots without a hard cover. Such robots can be employed in clinical practice and biological investigations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of induced magnetic field on peristaltic transport of a Carreau fluid

Magnetohydrodynamic (MHD) peristaltic flow of a Carreau fluid in a channel with different wave forms are analyzed in this investigation. The flow analysis is conducted in the presence of an induced magnetic field. Long wavelength approach is adopted. Mathematical expressions of stream function, magnetic force function and an axial induced magnetic field are constructed. Pressure rise and pumping phenomena are described.     

Unsteady couette flow of a conducting fluid between two parallel plates under a transverse magnetic field—II

The effect of a sudden change in magnetic field and pressure gradient on a steady Couette flow of a viscous incompressible fluid between two parallel plates in the presence of a transverse magnetic field is considered. Expressions for the velocity of the fluid in the disturbed flow, the intensities of the electrical and magnetic fields are obtained in two cases when the plates are non-conducting and when they are perfectly conducting.     

Aligned magnetic effects through varying permeable bed

The aligned magnetic effects on a steady laminar, viscous, incompressible, conducting fluid down an open inclined channel bounded below by a bed of varying permeability has been studied when the free surface is exposed to atmospheric pressure. Beavers and Joseph slip condition at the interface of the free flow region and the fluid flow in the porous bed and the Darcy’s law in the porous medium have been used. The expressions for velocity, magnetic strength and the mass flow across the cross-section of the channel are obtained.