Uniformity condition for a rectangular field coil with a split winding

A generalized Helmholtz condition for field uniformity is derived from the closed form solution of the magnetic field in a multilayer rectangular coil pair as a function of coil dimensions and pair separation. The relation among the dimensions satisfying this condition is found and plotted in parametric form for single layer coils and for a multilayer coil with a specific winding thickness. For square coils of cross section small compared to their mean radius, the gap separation approaches half the coil radius, analogous to the classical condition for circular coils. Comparison between theoretical and measured values for tolerances within +/-5% of the field at the system center agree within a 6% maximum deviation. For the experimental coil, the area enclosed by the +/-5% contour was 58% of the area of the full coil.     

Exact solution of one problem of magnetostatics in bipolar coordinates (continued)

An exact solution for a linear problem of magnetostatics about an infinite cylinder with an infinite noncoaxial cylindrical flaw has been derived in the system of plane bipolar coordinates under the condition that external magnetizing field remains unchanged along the length axis of this model body. The solution has been tested for theoretical veracity and compared with the solution of a similar problem that was obtained by one semianalytic method [2]. For a particular problem about a halfspace with an infinite cylindrical flaw, an exact solution has been obtained and compared with results that were achieved by other methods. The mismatch between the solution of the problem about a halfspace and the solution of the problem with passage to the limit of a half-space has been considered. An algorithm is described for solving the inverse problem of separate determination of flaw depth and dimensions.     

基于ANSYS的轴向柱塞液压电机泵电磁场数值计算与分析

提出了一种新型轴向柱塞液压电机泵,简要介绍了其结构组成和工作原理。应用ANSYS/Emag模块对带有不同冷却流道的三种电机泵的定子模型对应的空载电磁场进行了数值计算。通过对计算结果进一步的分析和计算得到了电机泵电磁场的分布及油隙磁感应强度,并进行了对比分析。研究表明,带有12个条形冷却流道的定子结构的磁感应强度最大,带有24个圆形冷却流道的定子磁感应强度最低,带有8个条形冷却流道的定子结构的磁感应强度介于上述两种之间。所作研究为新型轴向柱塞液压电机泵定子的结构设计和优化提供了依据。     

Real space maps of atomic transitions

Considering the rapid technical development of transmission electron microscopes, we investigate the possibility to map electronic transitions in real space on the atomic scale. To this purpose, we analyse the information carried by the scatterer's initial and final state wave functions and the role of the different atomic transition channels for the inelastic scattering cross section. It is shown that the change in the magnetic quantum number in the transition can be mapped. Two experimental set-ups are proposed, one blocking half the diffraction plane, the other one using a cylinder lens for imaging. Both methods break the conventional circular symmetry in the electron microscope making it possible to detect the handedness of electronic transitions as an asymmetry in the image intensity. This finding is of important for atomic resolution energy-loss magnetic chiral dichroism (EMCD), allowing to obtain the magnetic moments of single atoms.     

An approximate method to build an improved stress field in local regions

An approximate procedure to enhance the accuracy of the continuous stress field in local regions has been proposed, based on Loubignac’s iterative method and the theory of conjugate approximations. The validity of the proposed method has been tested through three examples: a thick-walled cylinder under internal pressure; an infinite plate with a central circular hole subjected to uniaxial tension; and a short cantilever beam. Analysis of the examples shows that the stress field obtained for the local region model by the proposed method agrees well with that for the whole domain model. In addition, a significant reduction in computing time to obtain the improved stress field implies that the proposed method can be an efficient alternative for the detailed stress analysis in local regions.     

Diffraction of sound by a poroelastic cylindrical absorber near an impedance plane

Acoustic scattering from an infinitely long fluid-saturated porous elastic circular cylinder located near a planar boundary with locally varying surface impedance is studied. The formulation utilizes the novel features of Biot dynamic theory of poroelasticity, the appropriate wave field expansions, the classical method of images and the translational addition theorem for cylindrical wave functions along with a simple local surface reaction model involving a complex amplitude wave reflection coefficient applied to develop a closed-form solution in the form of infinite series. The analytical results are illustrated with a numerical example in which a cylindrical plastic foam absorber is located near a layer of foam material set on an impervious rigid wall. The numerical results reveal the important effects of incident wave frequency, angle of incidence, interface local surface reaction, cylinder poroelasticity and position on the acoustic field quantities. The proposed model can lead to a better understanding of acoustic scattering from two-dimensional near-interface porous absorbers or targets which are commonly encountered problems in outdoor acoustics, noise control engineering, and ocean engineering. The presented solution could eventually be used to validate those found by numerical approximation techniques.     

A procedure for the improved continuous stress field of composite media

An approximate procedure to enhance the accuracy of the continuous stress field in local regions has been proposed, based on Loubignac’s iterative method and the theory of conjugate approximations. The validity of the proposed method has been tested through three examples: a thick-walled cylinder under internal pressure; an infinite plate with a central circular hole subjected to uniaxial tension; and a short cantilever beam. Analysis of the examples shows that the stress field obtained for the local region model by the proposed method agrees well with that for the whole domain model. In addition, a significant reduction in computing time to obtain the improved stress field implies that the proposed method can be an efficient alternative for the detailed stress analysis in local regions.     

管道内地磁场特性分析及实验研究

将油气管道理想化为无限长的磁性材料圆柱腔,根据静磁场理论中的磁通连续性原理,分析了管道对地磁场不同方向分量的屏蔽系数,推导出油气管道内剩余地磁场强度与管道走向之间的关系,建立了管道内三轴磁传感器采集数据的数学模型,通过大量现场实验数据验证本模型.在管道走向检测领域具有重要意义,研究成果具有广阔的应用前景.     

Comparison between numerical computations and measurements by LDV for fluid flow in rectangular duct systems

Fluid flows in rectangular duct systems are measured by using the laser-Doppler velocity meter and computed by commercial software of Star-CD for comparisons between flows. Three rectangular systems are investigated in this study: a rectangular duct with a 90 degree bent elbow, a rectangular duct with two branches, and a rectangular duct in the middle of which a circular cylinder is located. These investigations show that the numerical solutions satisfactorily predict design factors: for example, the K -factor for an elbowed duct, the distribution ratio of flow rates into each branch from a main duct, and the Nusselt number around the circular duct. However, there are some disagreements in the velocity profile and turbulent kinetic energy at each cross section of the duct systems.     

Solution of reciprocal problem of magnetic flaw detection through calculation of multipole moments of an elliptic flaw

An algorithm has been developed for calculating parameters of an effective elliptic flaw (EEF) on the base of changes in the magnetic field intensity in the air. EEF is defined as a flaw with an elliptic cross section whose magnetic moments (dipole, quadrupole, and octupole), hence the field at a large distance, are the same as those of a given flaw with an arbitrary shape. The relation between the parameters of EEF and real flaws has been established by solving Grinberg’s integral equation for internal and surface flaws of the two-dimensional configuration in a half-space filled with a linear (μ=const) ferromagnetic material. This relation was used in drawing up the solution of the reciprocal problem of magnetic flaw detection.     

Defect inspection system for steel wire rods produced by hot rolling process

A vision-based inspection system has been investigated in order to improve the quality of products and processes found in various industries. In this paper, we propose a new defect detection algorithm for steel wire rods produced by the hot rolling process. Because the steel wire rods are long cylinder rods with a circular cross section, the brightness at the sides and center is inconsistent. Moreover, the various types of steel wire rods and the presence of scales affect the reflection properties of the rod surface. In order to resolve the abovementioned difficulties, the use of dynamic programming and a discrete wavelet transform are proposed. An adaptive local binarization method is used to further reduce the effects of scale. The effectiveness of the proposed method is shown by means of experiments conducted on images of steel wire rods that were obtained from an actual steel production line.     

基于流场动力学特性的发动机稳流数值试验研究

对化油器式四冲程汽油机最大气阀升程时的流场动力学特性进行了三维稳态数值模拟。将化油器柱塞半开和全开两种情况的内流特性进行了对比,结果表明,化油器腔体内部周围出现了低压区,柱塞全开时比半开时的低压更低,但全开时的流速比半开时大,速度最大值均发生在喷嘴两侧喉口处,进气直管入口段及缸内均呈现明显的双涡结构,但柱塞半开时的双涡结构呈现出明显不对称性,距缸盖底面两倍缸径处气流速度均存在不均匀性,压力场与速度场表现出相同的特性,稳流数值试验是对发动机台架试验的一种有益补充。     

轴向绕组磁路结构磁流变液阻尼器设计

给出轴向绕组磁路结构磁流变阻尼器的设计方法,通过判定线圈横截面积与线圈槽横截面积相等,将阻尼器结构设计与磁路设计联系起来,设计出结构合理紧凑的阻尼器。然后采用ANSYS软件对磁路结构进行电磁场有限元分析,分析表明阻尼器结构设计满足要求,轴向绕组磁路结构改善了阻尼间隙通道磁场分布。     

A three-dimensional morphometrical study of the distal human femur.

The objective of this paper is to present a method to describe the three-dimensional variations of the geometry of the three portions forming the distal part of the human femur: the medial and lateral femoral condyles and the intercondylar fossa. The contours of equally spaced sagittal slices were digitized on the distal femur to determine its surface topography. Data collection was performed using a digitizer system which utilizes low-frequency, magnetic field technology to determine the position and orientation of a magnetic field sensor in relation to a specified reference frame. The generalized reduced gradient optimization method was used to reconstruct the profile of each slice utilizing two primitives: straight-line segments and circular arcs. The profile of each slice within the medial femoral condyle was reconstructed using two circular arcs: posterior and distal. The profile of each slice within the lateral femoral condyle was reconstructed using three circular arcs: posterior, distal and anterior. Finally, the profile of each slice within the intercondylar fossa was reconstructed using two circular arcs: proximal-posterior and anterior, and a distal-posterior straight-line segment tangent to the proximal-posterior circular arc. Combining the data describing the profiles of the different slices forming the distal femur, the posterior portions of each of the medial and lateral femoral condyles were modelled using parts of spheres having an average radius of 20 mm. The anterior portion of the lateral condyle was approximated to a right cylinder having its circular base parallel to the sagittal plane with an average radius of 26 mm. The anterior portion of the intercondylar fossa was modelled using an oblique cylinder having its circular base parallel to the sagittal plane with an average radius of 22 mm. Furthermore, it is suggested that the distal portion of the lateral femoral condyle could be modelled using parts of two oblique cones while the distal portion of the medial femoral condyle could be modelled using a part of a single oblique cone, all cones having their circular bases parallel to the sagittal plane. It is also suggested that the posterior portion of the intercondylar fossa could be modelled using two oblique cones: a proximal cone having its base parallel to the sagittal plane and a distal cone having its base parallel to the frontal plane.     

Influence of axial magnetic field on shape and microstructure of stainless steel laser welding joint

The morphology and microstructure of the weld joint have significant influence on mechanical properties of welded specimens. In this paper, the mechanism on how the external magnetic field affected weld profile and microstructure was discussed by applying the longitudinal steady magnetic field to laser welding for SUS301 stainless steel. The optimal and scanning electron microscopes were used to measure the shape of the cross section and observe the microstructure after welding. The results showed that the shape of the cross section and microstructure could be significantly changed using the external magnetic field. Moreover, joint shape changed distinctly with the magnetic field intensity changing. With the increasing of magnetic flux density, the weld profile of the full penetration model changed from funnel to X type; meanwhile, the bottom weld width increased by 40%. In addition, the partial fusion zone occurred, and the weld width decreased by 20% while penetration increased by 18% when magnetic flux density turned into 380 mT. As far as microstructure of weld joint was concerned, it appeared that application of axial magnetic field led to indistinct fusion line and blocky austenite in big size rather than columnar grain in the center of the cross section. This phenomenon could be explained by numerical simulation results.     

A simple method for formation of the matching input in a helical undulator

A helical undulator is widely used in free-electron lasers with pulsed electron beams. An adiabatic input with a length of 5–10 periods is commonly used to inject the beam. A novel and simpler method for matching the undulator input is proposed, theoretically investigated, and experimentally implemented. The end field is formed with the help of wire sections in the form of straight lines and circular arcs, which permits an accurate control of geometrical dimensions. The axial length of this section is ∼1/6 of the undulator period. Experimental results obtained on the undulator with a period of 4.8 cm agree well with theoretical data.     

A model of a surface flaw of finite length under normal magnetization and calculation of the topography of its magnetostatic field

A calculated model of the magnetic field of a surface flaw with a rectangular cross section and a finite length under normal magnetization of the tested surface is proposed. Practically convenient expressions for calculating the phase angle ? between the imaginary and real magnetic components have been obtained. An algorithm for estimating the parameters of the flaw and principles of building devices for electromagnetic flaw detection and flaw measurement are proposed.     

Development of an optimised magnetic field source for flowmeter applications

Sensitivity of a magnetic flowmeter relies on many factors like magnetic field strength, gap between electrodes, material properties, magnet temperature etc. For a given measuring conditions, a strong magnetic field source can produce highest sensitivity for the flowmeter. An economic design of magnetic field source would be to produce the strongest magnetic field from a given amount of magnetic material. In this paper, various magnet configurations are analyzed using FEM and the flowmeter sensitivity using such magnet configurations are compared. It is observed that magnets arranged in a Halbach fashion produce the highest sensitivity for the flowmeter using a given amount of magnetic material. The major challenge for the development of such a magnetic field source is its fabrication from its constituent magnets, combatting their huge attractive/repulsive forces (∼2500 N for our case). Therefore, a specific mechanical tool has been designed for assembling the magnetic field source and a robust assembly technique has been devised using numerical computations. The designed magnetic field source produces a peak magnetic field of 0.78 T in the pole cross section of 50 mm × 50 mm.     

Decrease in the effect of a gap on coercimetry results when taking the properties of an attachable transducer into account

A method that allows the effect of a gap on the results of coercimetric quality control of articles to be decreased that is based on taking properties of an attachable transducer into account is proposed. The properties of a transducer are taken into account using a preliminary recorded demagnetization line of an attachable electromagnet whose magnetic circuit is not closed by an article. It is shown that the tangential component of the magnetic field of an inspected article during magnetization reversal along this line equals the coercive force of the article if its cross section does not exceed the electromagnet cross section.     

An immersed-boundary finite-volume method for simulation of heat transfer in complex geometries

An immersed boundary method for solving the Navier-Stokes and thermal energy equations is developed to compute the heat transfer over or inside the complex geometries in the Cartesian or cylindrical coordinates by introducing the momentum forcing, mass source/sink, and heat source/sink. The present method is based on the finite volume approach on a staggered mesh together with a fractional step method. The method of applying the momentum forcing and mass source/sink to satisfy the no-slip condition on the body surface is explained in detail in Kim, Kim and Choi (2001, Journal of Computational Physics). In this paper, the heat source/sink is introduced on the body surface or inside the body to satisfy the iso-thermal or iso-heat-flux condition on the immersed boundary. The present method is applied to three different problems : forced convection around a circular cylinder, mixed convection around a pair of circular cylin-ders, and forced convection around a main cylinder with a secondary small cylinder. The results show good agreements with those obtained by previous experiments and numerical simulations, verifying the accuracy of the present method.