Contactless induction acceleration of conductors up to hypersonic speeds

The results of an experimental investigation of the induction acceleration of ring conductors having a mass of 0.5–3 g in the pulsed magnetic field of a single-turn inductor are presented. It is shown that low-inductive capacitive energy stores in conjunction with single-turn single-shot inductors are very efficient. A speed of 3.7 km/sec was obtained experimentally with an aluminum conductor of mass 0.77 g. Methods of measuring the very high speeds of projected objects are described. The interaction of the accelerated conductor with thick and thin barriers was investigated, and the possibility of controlling the area of the damaged surface is pointed out. The results of the experiment agree well with calculations carried out on a computer which indicate the possibility of a further increase in the speed of projection.     

Flux losses during compression of a magnetic field by flat strips

The compression of a magnetic field by a moving conductor — magnetic cumulation — is used to obtain powerful magnetic fields and large pulsed currents [1, 2]. The potentialities of magnetic cumulation are determined mainly by the flux losses due to diffusion of the magnetic field into the conductor and its capture in short-circuited cavities formed upon the joining of uneven conductor surfaces. Experiments on the compression of a magnetic field by flat strips of copper and Durai are described in the report, and a comparison is made with the calculation of diffusional flux losses. The possible role of a gutter instability of the copper conductors is evaluated for the explanation of the increase in flux losses when a critical linear current density, whose value in the experiments presented was 180–210 kA/cm, is exceeded in the strips.     

Limiting currents in the compression of magnetic flux between flat and coaxial conductors

Experiments are described on magnetic flux compression by flat and coaxial conductors. As the initial current I₀ is increased the final current I₁ obtained as a result of flux compression at first increases proportionally to I₀ and then reaches a maximum and remains constant for further increases in I₀. Analysis of the experiments shows that in coaxial structures when a small explosive charge accelerates the conductors the limiting current is determined by the maximum work which a conductor can perform in compressing the magnetic field. In experiments with flat busbars and large explosive charges the limiting currents appear to be determined by the flux losses in short-circuited voids formed in the linking of irregular surfaces of the busbars. This assumption is shown to be in qualitative agreement with experiment.     

Acceleration of conductors to supersonic speeds in a pulsed magnetic field

The effect of the shape of the current-density curve and the initial angle of acceleration on the velocity of projection of current-carrying conductors in a pulsed magnetic field produced in the discharge of a capacitive energy accumulator is investigated. A variational problem is solved to determine the optimum current-density function in the projected body for a given magnetic-induction function. It is shown that the relation j =KB, where K is a constant, gives the maximum velocity. For a uniform magnetic field varying as a damped sinusoid, expressions are obtained for the current density in the accelerated body, the velocity of projection, and the acceleration path. It is shown that there is an optimum initial angle of acceleration depending on the amplitude and frequency of the accelerating force and the acceleration path. A procedure is presented for the approximate design of a hypersonic electromagnetic accelerator. In accord with the conclusions of the theory an experimental arrangement is set up and a study is made of the projection of conductors in a pulsed magnetic field. A maximum velocity of 10.5 km/sec is obtained for 0.16-mm diameter aluminum wires.Translated from Zhurnal Prikladnoi Mekhanika i Tekhnicheskoi Fiziki, No. 3, pp. 44–53, May–June, 1974.     

A novel analytic solution of MHD flow for two classes of visco-elastic fluid over a sheet stretched with non-linearly (quadratic) velocity

The laminar boundary layer flow induced in a quiescent visco-elastic fluid by a permeable stretched flat surface with non-linearly (quadratic) velocity and appropriate wall transpiration under the influence of a magnetic field is investigated. It is shown that the problem permits a complete analytic exponentially decaying solution for the set of continuity and momentum equations with both magnetic field and visco-elasticity influences for two classes of visco-elastic fluid, namely, the second grade and Walters’ liquid B fluids. The effects on both the skin friction parameter α and velocity profiles of various physical parameters such as visco-elasticity, suction/blowing parameter and magnetic parameter are studied. The results for the velocity field are presented through graphs and discussed in detail.     

Effect of Hall current on MHD mixed convection boundary layer flow over a stretched vertical flat plate

In this paper, the steady magnetohydrodynamic (MHD) mixed convection boundary layer flow of an incompressible, viscous and electrically conducting fluid over a stretching vertical flat plate is theoretically investigated with Hall effects taken into account. The governing equations are solved numerically using an implicit finite-difference scheme known as the Keller-box method. The effects of the magnetic parameter, the Hall parameter and the buoyancy parameter on the velocity profiles, the cross flow velocity profiles and the temperature profiles are presented graphically and discussed. Investigated results indicate that the Hall effect on the temperature is small, and the magnetic field and Hall currents produce opposite effects on the shear stress and the heat transfer at the stretching surface.     

Calculation of magnetic fields and currents in axisymmetric systems of inductively coupled moving conductors

An algorithm for calculating magnetic fields and currents in axisymmetric systems of inductively coupled moving and stationary conductors is developed using a hybrid method which combines the finite and boundary element methods. The finite element method is used to approximate the unsteady diffusion equation for the θ-component of the magnetic vector potential in the conductors, and the boundary-element method is employed to eliminate the space around the conductors. The proposed method takes into account the connections of the conductors with each other or with external energy sources by means of ideal electrical circuits with lumped parameters R, L, and C. An effective method is developed to take into account the external circuits by an appropriate modification of the mass matrix and the source vector of the obtained system of ordinary differential equations. Examples of using the method to calculate the fields of single- and multi-turn solenoids, magnetic flux concentrators, and induction accelerators with various methods of delivering external electromagnetic energy are considered. The high computational efficiency of the method is shown, in particular, for the case of constant electrothermal properties and sizes of the conductors. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 22–29, January–February, 2009.     

A microstructure continuum approach to electromagneto-elastic conductors

A micromorphic continuum model of a deformable electromagnetic conductor is established introducing microdensities of bound and free charges. The conductive part of electric current consists of contributions due to free charges and microdeformation. Beside the conservation of charge, we derive suitable evolution equations for electric multipoles which are exploited to obtain the macroscopic form of Maxwell’s equations. A constitutive model for electromagneto-elastic conductors is considered which allows for a natural characterization of perfect conductors independently on the form of the constitutive equation for the conduction current. A generalized Ohm’s law is also derived for not ideal conductors which accounts for relaxation effects. The consequences of the linearized Ohm’s law on the classic magnetic transport equation are shown.     

Similarity analysis in magnetohydrodynamics: Hall effects on free convection flow and mass transfer past a semi-infinite vertical flat plate

Heat and mass transfer along a semi-infinite vertical flat plate under the combined buoyancy force effects of thermal and species diffusion is investigated in the presence of a strong non-uniform magnetic field and the Hall currents are taken into account. The induced magnetic field due to the motion of the electrically conducting fluid is negligible. This assumption is valid for a small magnetic Reynolds number. The similarity solutions are obtained using the scale group of transformations. These are the only symmetry transformations admitted by the field equations. The non-linear boundary layer equations with the boundary conditions are transferred to a system of non-linear ordinary differential equations with the appropriate boundary conditions. Furthermore, the similarity equations are solved numerically by using a fourth order Runge-Kutta scheme with the shooting method. Numerical results for the velocity profiles, the temperature profiles and the concentration profiles are presented graphically for various values of the magnetic parameter M in the range of 0-1 with the Hall parameter m taking the values 0.5, 1, 2, and 3.     

区域地磁测量实验及水下载体对周围磁场的影响分析

水下载体和磁力仪的匹配是水下地磁导航的关键技术之一.为了完成匹配实验,首先要选择地磁场平缓的局部区域,基于这一目的进行了局域地磁场的测量,并通过克里金插值法构建地磁图,给出基于克里金插值的局部二维和三维地磁图.从地磁图上可以找到磁异常区域和地磁平缓区域,并在地磁平缓区域进行有无水下载体的地磁空间测量.由于载体主要由铁磁物质组成,安装在载体上的传感器所测量的磁场除了地磁场以外,还有载体硬磁材料产生的固有磁场以及载体内机电设备产生的磁场.因此,如何从复杂的磁场环境中提取地磁场信息是实时测量的一大难题.基于载体的空间磁测,利用传感器测量值构建载体磁场的数学模型,分析了水下载体对周围磁场的影响,为水下载体与磁力仪的匹配和水下磁测提供了理论和实验依据.     

Structure of the interface between magnetic and conventional fluids: Model of immiscible phases

The structure of the flat interface between a two-component magnetic suspension and a conventional nonmagnetizable fluid immiscible with it is investigated with account for the dependence of the free energy of the system on the magnetization gradients, the concentration of magnetic particles, and the bearing phase density. It is shown that at certain values of the problem parameters the volume concentration of magnetic particles strongly increases near the interface, that is, the particles are substantially adsorbed at this surface. The dependence of the surface tension tensor components on the magnetic field stress is determined.     

The experimental study on flat plate heat pipe of magnetic working fluid

An effective thermal spreader can achieve uniform heat flux distribution and thus enhance heat dissipation of heat sinks. Flat plate heat pipe is one of the highly effective thermal spreaders. Magnetic fluid is liquid and can be moved by the force of magnetic field. Therefore, the magnetic fluid is suitable to be used as the working fluid of flat plate heat pipes which have a very small gap between evaporation and condensation surfaces. We prepared a disk-shaped wickless flat plate heat pipe, and the distance between evaporation and condensation surfaces is only 1 mm. From experimental study, the effect of heat flux and working fluid ratio on the performance of flat plate heat pipe is presented. Also we compared the experimental results between the performance of water and magnetic fluid as working fluids.     

GALLOPING BEHAVIORS OF SECTOR-SHAPE ICED EIGHT BUNDLE CONDUCTORS1)

考虑到重冰区的特高压输电线路更容易形成接近扇形的覆冰,结合风洞实验及数值模拟方法研究了扇形覆冰八分裂导线的舞动特征。通过扇形覆冰八分裂输电线的节段模型风洞实验,获得各覆冰子导线随风攻角变化的气动参数。在ABAQUS软件中建立单档扇形覆冰八分裂输电线路的有限元模型,通过程序UEL输入各覆冰子导线的气动参数,根据数值模拟结果可获得舞动轨迹及振幅等舞动特征,最后讨论了风速、档距和初始风攻角对八分裂导线舞动特征的影响。     

Influence of hall effect and ion slip on velocity and temperature fields in an MHD channel

The combined influence of viscosity, Hall effect and ion slip on hydrodynamic fields and on heat transfer is investigated. The exact solutions for velocity, induced magnetic field and temperature are derived for the laminar MHD flow in a flat channel assuming a small magnetic Reynolds number, finely segmented electrodes, fully developed flow and uniform heat flux at channel walls. The internal generation of heat is not considered. The Kantorowitsch method of variational calculus is employed to approximate the complicated velocity distribution.     

Structure of the fluid interface in an external magnetic field in the presence of a magnetizable surfactant

The structure of the flat interface between two conventional fluids in an external magnetic field in the presence of a magnetizable surfactant is investigated with account for the dependence of the free energy of the system on the surfactant concentration gradients and the bearing phase density. The dependence of the surface tension tensor components on the magnetic field strength is determined.     

MHD forced convection boundary layer flow with a flat plate and porous substrate

The flow and heat transfer for an electrically conducting fluid with a porous substrate and a flat plate under the influence of magnetic field is considered. The magnetic field is assumed to be uniform and also along normal to the surface. The momentum and energy equations are transformed to ordinary differential equations by using suitable similarity transformation and are solved by standard techniques. But the energy equation is solved by considering two boundary layers, one in the porous substrate and the other above the porous substrate. Numerical results are presented through graphs with various values of magnetic parameter for both velocity and thermal boundary layers along with Nusselt number and for various values of Prandtl number and Eckert number in thermal boundary layer.     

An unsteady MHD duct flow

An exact solution is presented for unsteady laminar flow of a viscous, incompressible, electrically conducting fluid between nonconducting, parallel, flat plates. A constant magnetic field is suddenly applied perpendicular to the plates and the motion is modified by the induced current. Numerical results are given which show how the velocity profile changes from the parabolic profile of hydrodynamics to the Hartmann profile of magnetohydrodynamics.     

An unsteady MHD duct flow

An exact solution is presented for unsteady laminar flow of a viscous, incompressible, electrically conducting fluid between nonconducting, parallel, flat plates. A constant magnetic field is suddenly applied perpendicular to the plates and the motion is modified by the induced current. Numerical results are given which show how the velocity profile changes from the parabolic profile of hydrodynamics to the Hartmann profile of magnetohydrodynamics.     

Effect of magnetic field on thermal instability in mixed convection flow over a rotating boundary layer

Effect of magnetic field on the formation of longitudinal vortices in mixed convection flow over a rotating heated flat plate is presented. The onset position is characterized by the Grashof number, the rotational number, the Prandtl number, the Eckert number, the magnetic field parameter, and the wave number. Negative rotation (clockwise) and external magnetic field stabilize the boundary layer flow. On the contrary, positive rotation (anti-clockwise), the Eckert number, and the Prandtl number destabilize the flow. The numerical data show agreement with the experimental data with the case of zero Hartmann number in the literature.     

Structure and stability of the interface between magnetic and conventional fluids. Model of a three-component medium

The structure of a flat interphase boundary between a magnetic suspension and a conventional immiscible fluid is investigated within the framework of the model of a three-component medium taking the dependence of the free energy of the system on the concentration gradients into account. It is shown that for certain values of the constitutive parameters the bulk magnetic particle concentration increases significantly inside the interfacial layer, i.e., the particles are significantly adsorbed on the interface. The dependence of the surface tension on the magnetic field strength is determined. It is shown that for certain problem parameters this dependence qualitatively corresponds to that obtained experimentally and described in the phenomenological theory developed by Golubyatnikov and Subkhankulov in 1986. In the case of strong particle adsorption the dependence of the surface tension on the magnetic particle concentration on the phase interface is significantly nonlinear. A refined model of the interface as a two-dimensional continuum with surface magnetization is constructed. Constitutive equations, conditions on the interface, and necessary stability conditions are obtained.