Finite element method for solving mhd flow in a rectangular duct

A finite element method is given to obtain the solution in terms of velocity and induced magnetic field for the steady MHD (magnetohydrodynamic) flow through a rectangular pipe having arbitrarily conducting walls. Linear and then quadratic approximations have been taken for both velocity and magnetic field for comparison and it is found that with the quadratic approximation it is possible to increase the conductivity and Hartmann number M (M ≤ 100). A special solution procedure has been used for the resulting block tridiagonal system of equations. Computations have been carried out for several values of Hartmann number (5 ≤ M ≤ 100) and wall conductivity. It is also found that, if the wall conductivity increases, the flux decreases. The same is the effect of increasing the Hartmann number. Selected graphs are given showing the behaviour of the velocity field and induced magnetic field.     

A Permeability-Measuring Magnetic Flux Leakage Method for Inner Surface Crack in Thick-Walled Steel Pipe

It is difficult for traditional magnetic flux leakage (MFL) methods to detect inner surface cracks of thick-walled steel pipe or plate due to magnetic shielding of the wall and strong magnetic background noise, and for eddy current testing (ECT) as well due to its skin effect. On the basis of the nonlinear magnetic permeability of ferromagnetic materials, a new non-destructive testing method (NDT) permeability-measuring magnetic flux leakage (P-MFL) is proposed, in which the magnetization is perpendicular to the inner surface crack, and the surface layer permeability distortion caused by magnetic field distortion is measured by differential pick-up coils. Afterwards, its detection mechanism is presented and analyzed, and its feasibility is verified by simulations and experiments. Finally, some application cases for steel pipe are also realized effectively. Meanwhile, its testing characteristics for cracks are given and effects of crack size, specimen thickness, scanning paths to testing signal amplitude are briefly analyzed. Finally, the proposed P-MFL method compared to traditional MFL method is discussed in detail.     

Pseudospectral method for MHD pipe flow

The paper deals with MHD flow in pipes with arbitrary wall conductivity under the influence of a transverse magnetic field. We employ the pseudospectral collocation method for obtaining a numerical solution of the problem. The numerical results are compared with analytical ones in the case of pipe with insulating walls. We notice that the magnetic field is slowing the motion. Copyright © 2006 John Wiley & Sons, Ltd.     

Stress induced magnetization changes of steel pipes--Laboratory tests

Magnetometer surveys above gas pipelines show stress induced magnetic anomalies at pipe bends. This suggests a potential technique for the noninvasive monitoring of stress in buried pipelines, etc. Laboratory measurements of the magnetic field changes due to the elastic bending of 110 mm diameter pipe are presented. The effects of orientation with respect to the earths field and of internal pressure are reported. Hysteretic effects are found to be important.     

稳态等离子体发动机磁场设计的发展及其展望

论述了稳态等离子体发动机对于我国空间发展战略的重要意义和作用，指出磁场设计是提高稳态等离子体发动机性能的关键技术之一；分析了稳态等离子体发动机通道内磁场设计的发展过程，在此基础上提出了用于稳态等离子发动机磁场设计的体系化构想，并且指出了其中存在的一些关键问题和拟采取的解决措施以及磁场体系化设计对稳态等离子体发动机带来的预期效益和影响；最后展望了稳态等离子体发动机磁场设计体系的进一步发展和应用。     

Continuous Separation of Inclusions from Aluminum Melt Flowing in a Circular Pipe using a High Frequency Magnetic Field

The continuous separation of inclusions from aluminum melt flowing in a circular pipe using a high frequency magneticfield was investigated both theoretically and experimentally The separation efficiency was calculated based on thetrajectory method and compared with experimental results. It is found that the separation efficiency is a functilnondimensional parameters t_i·d_p~2B_e~2/μ_fμ_eα~2 and α/δ.The effective way to improve the separation efficiency is to increasethe effective magnetic flux density and decrease the pipe radius. and the value of α/δ should be kept about 2 in orderto obtain the optimum separation efficiency.     

Determination of the position of an underground pipeline using the results of measurements of its magnetic field strength

The results of an experiment to determine the position of an underground pipeline using its magnetic field strength when there are other underground systems (cables and pipelines) present, situated side by side, are presented. It is shown that the excitation of a current in the pipe by a current in a wire, grounded at the ends, occurs as a result of magnetic coupling between the wire and the pipe. At a frequency of the exciting current higher than 1 kHz, currents occur in the other nearby pipelines lines which lead to ambiguity and errors in determining the route of the pipeline.     

管道焊缝裂纹扩展的流固磁耦合表征

本工作利用虚拟裂纹闭合技术(Virtual crack closure technique,VCCT)提出一种单裂纹和多裂纹扩展通用的流固磁耦合方法,研究了流体压力的动态施加、流体-管道焊缝结构-磁场耦合作用下管道焊缝裂纹的扩展问题。该流固磁耦合方法每递增一次流体压力载荷,则完成一次裂纹增量扩展,更新裂纹几何形状,并重构网格,循环进行裂纹扩展计算和磁场分析,实现铁磁性管道焊缝裂纹扩展的流固磁耦合。以管道焊缝不同环向位置分布的单裂纹、多裂纹等六种工况为数值模拟算例,根据扩展结果中描述裂纹扩展的裂纹张开距离、裂纹扩展长度、磁感应强度水平分量峰值、磁感应强度垂直分量峰值等特征值,衡量裂纹所在位置的危险等级,判断管道焊缝损伤部位与损伤程度,识别多裂纹与单裂纹。该方法的实现可为在役管道焊缝裂纹的漏磁检测与评价、管道再制造修复等提供理论基础。     

Pulsed Eddy Current Testing of Carbon Steel Pipes’ Wall-thinning Through Insulation and Cladding

Pulsed eddy current testing of wall-thinning through cladding and insulation was studied from both theoretical and experimental aspects. The analytical solution was derived for a simplified four-layered structure and was used to conduct simulations to ascertain the feasibility of this method. A pulsed eddy current testing probe consisting of a circular excitation coil and an AMR-sensor-embedded differential detector was fabricated to measure the time-varying magnetic field signals on the axisymmetric excitation coil??s axis. The measurement system was able to measure magnetic field down to a few hundred micro-Gausses in an unshielded environment. Simulation and test results showed that over a certain time after turning off the excitation current the magnetic field signal??s decay behavior is almost merely relevant to the pipe??s wall thickness. Future development of a carbon steel pipe??s wall-thinning can be evaluated by using decay coefficients estimated from previously obtained test data.     

Hydromagnetic convection flow through a porous medium in axially varying pipe

The hydromagnetic mixed convection flow through a porous medium in a pipe of varying radius in a uniform axial magnetic field is analyzed. The pipe wall is maintained at a prescribed nonuniform temperature. The governing equations are solved analytically to obtain the velocity, temperature, and induced magnetic field. Their behaviors are evaluated for different variations in the governing parameters. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 96–104, July–August, 2006.     

焊接钢管端面分层的磁粉检测工艺

采用常规的磁粉检测工艺检测焊接钢管端面分层存在着局限性,通过对焊接钢管端面分层特点以及对钢管端面磁粉检测特殊性的分析,研究设计了一套采用窄磁极间距并结合单侧斜向分段磁化的磁轭法检测工艺,该工艺为焊接钢管端面分层磁粉检测提供了一套有效的工艺方法。     

多传感器热式气体流量计的研制

针对大中型管道以及不规则流场中气体流量测量存在的问题, 研制了一种多传感器结构的气体流量计。在测量管道中按照对数线性法选取测量特征点,采用4个热式气体流量传感器获取特征点的流量信号,利用正交多项式拟合建立特性曲线的函数关系式。在不规则流场条件下对200mm口径样机进行实验。实验结果表明,多传感器测量方法能够明显改善单传感器的测量精度不高的问题。     

Simulation of a seawater MHD power generation system

MHD (magnetohydrodynamics) power generation systems are expected to become popular with the development of superconducting technology because of their low cost and high efficiency. MHD power generation directly utilizes electromotive force, which arises when seawater crosses a magnetic field. The helical-type MHD generator is composed mainly of a helical partition board and electrodes, which include a cathode pipe on the exterior of the generator and an anode rod in the interior. Elementary research on a helical-type MHD power generation system has started at Kobe University, and a numerical simulation of the system has been carried out by FEM (Finite Element Method) at the National Institute for Materials Science. By comparing the simulation results with the theoretical and experimental results, we found that the proposed method is valid for simulating the MHD power generation system.     

Effect of bias field and stress on Barkhausen noise in pipeline steels

Surface Barkhausen noise (SBN) and encircle Barkhausen noise (EBN) measurements have been made on pipeline steel under different positive and negative DC bias field conditions. The effects of bias field on both SBN and EBN are found to be similar. With increasing positive and negative bias the Barkhausen noise (BN) is found to decrease, and at higher bias fields the BN disappears. The results confirm that magnetization in the low-field region (below 0.5 T) takes place by 180° wall motion which gives rise to magnetic BN. Tensile and compressive stresses have been applied in a section of the pipe and SBN measurements made. The SBN voltage is found to increase with tension and to decrease with compression.     

A pulsed dipole magnet made from a hollow composite superconductor with a circulatory refrigeration system

When a superconducting dipole magnetic field is limited by a value of about 2.5 T using a ‘window frame’ type dipole, the design of such a magnet can be essentially simplified, and the superconducting winding volume can be decreased. If the winding is made of hollow composite superconductor, the cryostat construction is simplified and it is easy to handle with superconducting magnets.In order to estimate the prospects of using ‘window frame’ type dipole magnets with a circulatory refrigeration system for the Nuclotron Accelerator project, a dipole magnet with a length of about 0.4 m, a 5.5 cm aperture and a magnetic field of up to 2.5 T has been constructed and tested at the High Energy Laboratory, JINR. The superconducting cable of the magnet consists of a cupro-nickel pipe with an outer diameter of 5 mm and a wall thickness of 0.5 mm on which multifilament superconductors are cabled. The magnet construction with a two-phase helium circulating refrigeration system is described. The dependences are presented of the critical current degradation and of ac losses on the magnetic field inhomogeneity and hydraulic resistance.     

Magnetomigration in granular cobalt-copper films deposited by the ion-plasma method

We have studied the effect of a constant magnetic field on the structure and composition of cobalt-copper (Co-Cu) granular alloy films deposited by the ion-plasma method. The phenomenon of magnetomigration of the main components and impurities has been observed. A necessary condition for this effect is a high mobility of adatoms, which has been achieved by ion-plasma deposition onto hot (200°C) substrates at high energies of incident metal ions. Under the action of an external magnetic field with strength above 300 Oe, both diamagnetic and paramagnetic adatoms migrate in opposite directions perpendicular to the field lines. Using this effect, it is possible to obtain thin magnetic films possessing high diamagnetic susceptibility and having a low content of undesired impurities (chlorine, hydrogen, carbon, argon, etc.).     

Superconducting cylinder in a static longitudinal magnetic field

A study of the calculation of the magnetic field forces acting on a superconducting cylinder in a longitudinal magnetic field is reported. A computation algorithm and the results of field calculation by means of the boundary integral method, taking account of the cylinder edge singularity, are presented. The method makes it possible to compute the forces pressing the cylinder with a relative error below 1%     

Heat transfer under conditions of turbulent pipe flow of electrically conducting liquid in longitudinal magnetic field in the region of hydrodynamic stabilization

Numerical simulation is performed of heat transfer under conditions of turbulent pipe flow in the vicinity of entry to longitudinal magnetic field. Use is made of the model of turbulence which was previously employed for performing calculations in the region of stabilized flow and heat transfer. The model describes the suppression of turbulence by the magnetic field and the laminarization of turbulent (at the pipe inlet) flow. The calculation results agree well with the experimental data on heat transfer and temperature profiles in the initial thermal region. The effect made on heat transfer by Joule heat release from electric currents caused by turbulent fluctuations is investigated.     

Stress-shadow magnetic inspection technique for far-side anomalies in steel pipe

A two-step process for obtaining strong magnetic leakage flux signals from far-side anomalies in steel pipe is described. The pipe is magnetized by a magnetic pig while it is stressed by line pressure. Anomalous local stresses on the near side of the steel caused by far-side corrosion produce anomalies in the residual magnetization. These near-side residual field anomalies due to the stress shadows from exterior corrosion are then readily detectable. Initial laboratory tests are described.     

Saturation magnetostriction measurements of magnetic thin films under high magnetic fields

Saturation magnetostriction measurements of magnetic thin films have been studied using a system equipped with a motor driven electromagnet and a laser displacement meter. A new method to reduce the errors caused by applied rotating magnetic field is proposed for high-sensitive and accurate measurements of saturation magnetostriction. It is shown that accurate measurements are possible for magnetic fields up to around 1 kOe, by extracting the 2nd harmonic output through Fourier analysis as a function of applied rotating magnetic field and then by taking the extrapolation of 2nd harmonic output to zero magnetic field. This method is applied to measure a saturation magnetostriction of single-crystal fcc-Co(111) film and the value of − 30 × 10^− 6 is obtained.